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  132. .rm #[ #] #H #V #F C
  133. .\" ========================================================================
  134. .\"
  135. .IX Title "LIBEV 3"
  136. .TH LIBEV 3 "2020-01-22" "libev-4.31" "libev - high performance full featured event loop"
  137. .\" For nroff, turn off justification. Always turn off hyphenation; it makes
  138. .\" way too many mistakes in technical documents.
  139. .if n .ad l
  140. .nh
  141. .SH "NAME"
  142. libev \- a high performance full\-featured event loop written in C
  143. .SH "SYNOPSIS"
  144. .IX Header "SYNOPSIS"
  145. .Vb 1
  146. \& #include <ev.h>
  147. .Ve
  148. .SS "\s-1EXAMPLE PROGRAM\s0"
  149. .IX Subsection "EXAMPLE PROGRAM"
  150. .Vb 2
  151. \& // a single header file is required
  152. \& #include <ev.h>
  153. \&
  154. \& #include <stdio.h> // for puts
  155. \&
  156. \& // every watcher type has its own typedef\*(Aqd struct
  157. \& // with the name ev_TYPE
  158. \& ev_io stdin_watcher;
  159. \& ev_timer timeout_watcher;
  160. \&
  161. \& // all watcher callbacks have a similar signature
  162. \& // this callback is called when data is readable on stdin
  163. \& static void
  164. \& stdin_cb (EV_P_ ev_io *w, int revents)
  165. \& {
  166. \& puts ("stdin ready");
  167. \& // for one\-shot events, one must manually stop the watcher
  168. \& // with its corresponding stop function.
  169. \& ev_io_stop (EV_A_ w);
  170. \&
  171. \& // this causes all nested ev_run\*(Aqs to stop iterating
  172. \& ev_break (EV_A_ EVBREAK_ALL);
  173. \& }
  174. \&
  175. \& // another callback, this time for a time\-out
  176. \& static void
  177. \& timeout_cb (EV_P_ ev_timer *w, int revents)
  178. \& {
  179. \& puts ("timeout");
  180. \& // this causes the innermost ev_run to stop iterating
  181. \& ev_break (EV_A_ EVBREAK_ONE);
  182. \& }
  183. \&
  184. \& int
  185. \& main (void)
  186. \& {
  187. \& // use the default event loop unless you have special needs
  188. \& struct ev_loop *loop = EV_DEFAULT;
  189. \&
  190. \& // initialise an io watcher, then start it
  191. \& // this one will watch for stdin to become readable
  192. \& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
  193. \& ev_io_start (loop, &stdin_watcher);
  194. \&
  195. \& // initialise a timer watcher, then start it
  196. \& // simple non\-repeating 5.5 second timeout
  197. \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
  198. \& ev_timer_start (loop, &timeout_watcher);
  199. \&
  200. \& // now wait for events to arrive
  201. \& ev_run (loop, 0);
  202. \&
  203. \& // break was called, so exit
  204. \& return 0;
  205. \& }
  206. .Ve
  209. This document documents the libev software package.
  210. .PP
  211. The newest version of this document is also available as an html-formatted
  212. web page you might find easier to navigate when reading it for the first
  213. time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
  214. .PP
  215. While this document tries to be as complete as possible in documenting
  216. libev, its usage and the rationale behind its design, it is not a tutorial
  217. on event-based programming, nor will it introduce event-based programming
  218. with libev.
  219. .PP
  220. Familiarity with event based programming techniques in general is assumed
  221. throughout this document.
  224. This manual tries to be very detailed, but unfortunately, this also makes
  225. it very long. If you just want to know the basics of libev, I suggest
  226. reading \*(L"\s-1ANATOMY OF A WATCHER\*(R"\s0, then the \*(L"\s-1EXAMPLE PROGRAM\*(R"\s0 above and
  227. look up the missing functions in \*(L"\s-1GLOBAL FUNCTIONS\*(R"\s0 and the \f(CW\*(C`ev_io\*(C'\fR and
  228. \&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER TYPES\*(R"\s0.
  229. .SH "ABOUT LIBEV"
  230. .IX Header "ABOUT LIBEV"
  231. Libev is an event loop: you register interest in certain events (such as a
  232. file descriptor being readable or a timeout occurring), and it will manage
  233. these event sources and provide your program with events.
  234. .PP
  235. To do this, it must take more or less complete control over your process
  236. (or thread) by executing the \fIevent loop\fR handler, and will then
  237. communicate events via a callback mechanism.
  238. .PP
  239. You register interest in certain events by registering so-called \fIevent
  240. watchers\fR, which are relatively small C structures you initialise with the
  241. details of the event, and then hand it over to libev by \fIstarting\fR the
  242. watcher.
  243. .SS "\s-1FEATURES\s0"
  244. .IX Subsection "FEATURES"
  245. Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific aio and \f(CW\*(C`epoll\*(C'\fR
  246. interfaces, the BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port
  247. mechanisms for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR
  248. interface (for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
  249. inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
  250. timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
  251. (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
  252. change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
  253. loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
  254. \&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
  255. limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
  256. .PP
  257. It also is quite fast (see this
  258. benchmark <http://libev.schmorp.de/bench.html> comparing it to libevent
  259. for example).
  260. .SS "\s-1CONVENTIONS\s0"
  261. .IX Subsection "CONVENTIONS"
  262. Libev is very configurable. In this manual the default (and most common)
  263. configuration will be described, which supports multiple event loops. For
  264. more info about various configuration options please have a look at
  265. \&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
  266. for multiple event loops, then all functions taking an initial argument of
  267. name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
  268. this argument.
  270. .IX Subsection "TIME REPRESENTATION"
  271. Libev represents time as a single floating point number, representing
  272. the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice
  273. somewhere near the beginning of 1970, details are complicated, don't
  274. ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
  275. too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
  276. any calculations on it, you should treat it as some floating point value.
  277. .PP
  278. Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
  279. time differences (e.g. delays) throughout libev.
  281. .IX Header "ERROR HANDLING"
  282. Libev knows three classes of errors: operating system errors, usage errors
  283. and internal errors (bugs).
  284. .PP
  285. When libev catches an operating system error it cannot handle (for example
  286. a system call indicating a condition libev cannot fix), it calls the callback
  287. set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
  288. abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
  289. ()\*(C'\fR.
  290. .PP
  291. When libev detects a usage error such as a negative timer interval, then
  292. it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
  293. so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
  294. the libev caller and need to be fixed there.
  295. .PP
  296. Via the \f(CW\*(C`EV_FREQUENT\*(C'\fR macro you can compile in and/or enable extensive
  297. consistency checking code inside libev that can be used to check for
  298. internal inconsistencies, suually caused by application bugs.
  299. .PP
  300. Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions. These do not
  301. trigger under normal circumstances, as they indicate either a bug in libev
  302. or worse.
  304. .IX Header "GLOBAL FUNCTIONS"
  305. These functions can be called anytime, even before initialising the
  306. library in any way.
  307. .IP "ev_tstamp ev_time ()" 4
  308. .IX Item "ev_tstamp ev_time ()"
  309. Returns the current time as libev would use it. Please note that the
  310. \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
  311. you actually want to know. Also interesting is the combination of
  312. \&\f(CW\*(C`ev_now_update\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
  313. .IP "ev_sleep (ev_tstamp interval)" 4
  314. .IX Item "ev_sleep (ev_tstamp interval)"
  315. Sleep for the given interval: The current thread will be blocked
  316. until either it is interrupted or the given time interval has
  317. passed (approximately \- it might return a bit earlier even if not
  318. interrupted). Returns immediately if \f(CW\*(C`interval <= 0\*(C'\fR.
  319. .Sp
  320. Basically this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
  321. .Sp
  322. The range of the \f(CW\*(C`interval\*(C'\fR is limited \- libev only guarantees to work
  323. with sleep times of up to one day (\f(CW\*(C`interval <= 86400\*(C'\fR).
  324. .IP "int ev_version_major ()" 4
  325. .IX Item "int ev_version_major ()"
  326. .PD 0
  327. .IP "int ev_version_minor ()" 4
  328. .IX Item "int ev_version_minor ()"
  329. .PD
  330. You can find out the major and minor \s-1ABI\s0 version numbers of the library
  331. you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
  332. \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
  333. symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
  334. version of the library your program was compiled against.
  335. .Sp
  336. These version numbers refer to the \s-1ABI\s0 version of the library, not the
  337. release version.
  338. .Sp
  339. Usually, it's a good idea to terminate if the major versions mismatch,
  340. as this indicates an incompatible change. Minor versions are usually
  341. compatible to older versions, so a larger minor version alone is usually
  342. not a problem.
  343. .Sp
  344. Example: Make sure we haven't accidentally been linked against the wrong
  345. version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
  346. such as \s-1LFS\s0 or reentrancy).
  347. .Sp
  348. .Vb 3
  349. \& assert (("libev version mismatch",
  350. \& ev_version_major () == EV_VERSION_MAJOR
  351. \& && ev_version_minor () >= EV_VERSION_MINOR));
  352. .Ve
  353. .IP "unsigned int ev_supported_backends ()" 4
  354. .IX Item "unsigned int ev_supported_backends ()"
  355. Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
  356. value) compiled into this binary of libev (independent of their
  357. availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
  358. a description of the set values.
  359. .Sp
  360. Example: make sure we have the epoll method, because yeah this is cool and
  361. a must have and can we have a torrent of it please!!!11
  362. .Sp
  363. .Vb 2
  364. \& assert (("sorry, no epoll, no sex",
  365. \& ev_supported_backends () & EVBACKEND_EPOLL));
  366. .Ve
  367. .IP "unsigned int ev_recommended_backends ()" 4
  368. .IX Item "unsigned int ev_recommended_backends ()"
  369. Return the set of all backends compiled into this binary of libev and
  370. also recommended for this platform, meaning it will work for most file
  371. descriptor types. This set is often smaller than the one returned by
  372. \&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
  373. and will not be auto-detected unless you explicitly request it (assuming
  374. you know what you are doing). This is the set of backends that libev will
  375. probe for if you specify no backends explicitly.
  376. .IP "unsigned int ev_embeddable_backends ()" 4
  377. .IX Item "unsigned int ev_embeddable_backends ()"
  378. Returns the set of backends that are embeddable in other event loops. This
  379. value is platform-specific but can include backends not available on the
  380. current system. To find which embeddable backends might be supported on
  381. the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
  382. & ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
  383. .Sp
  384. See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
  385. .IP "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" 4
  386. .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())"
  387. Sets the allocation function to use (the prototype is similar \- the
  388. semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
  389. used to allocate and free memory (no surprises here). If it returns zero
  390. when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
  391. or take some potentially destructive action.
  392. .Sp
  393. Since some systems (at least OpenBSD and Darwin) fail to implement
  394. correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
  395. \&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
  396. .Sp
  397. You could override this function in high-availability programs to, say,
  398. free some memory if it cannot allocate memory, to use a special allocator,
  399. or even to sleep a while and retry until some memory is available.
  400. .Sp
  401. Example: The following is the \f(CW\*(C`realloc\*(C'\fR function that libev itself uses
  402. which should work with \f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions of all kinds and
  403. is probably a good basis for your own implementation.
  404. .Sp
  405. .Vb 5
  406. \& static void *
  407. \& ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
  408. \& {
  409. \& if (size)
  410. \& return realloc (ptr, size);
  411. \&
  412. \& free (ptr);
  413. \& return 0;
  414. \& }
  415. .Ve
  416. .Sp
  417. Example: Replace the libev allocator with one that waits a bit and then
  418. retries.
  419. .Sp
  420. .Vb 8
  421. \& static void *
  422. \& persistent_realloc (void *ptr, size_t size)
  423. \& {
  424. \& if (!size)
  425. \& {
  426. \& free (ptr);
  427. \& return 0;
  428. \& }
  429. \&
  430. \& for (;;)
  431. \& {
  432. \& void *newptr = realloc (ptr, size);
  433. \&
  434. \& if (newptr)
  435. \& return newptr;
  436. \&
  437. \& sleep (60);
  438. \& }
  439. \& }
  440. \&
  441. \& ...
  442. \& ev_set_allocator (persistent_realloc);
  443. .Ve
  444. .IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4
  445. .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())"
  446. Set the callback function to call on a retryable system call error (such
  447. as failed select, poll, epoll_wait). The message is a printable string
  448. indicating the system call or subsystem causing the problem. If this
  449. callback is set, then libev will expect it to remedy the situation, no
  450. matter what, when it returns. That is, libev will generally retry the
  451. requested operation, or, if the condition doesn't go away, do bad stuff
  452. (such as abort).
  453. .Sp
  454. Example: This is basically the same thing that libev does internally, too.
  455. .Sp
  456. .Vb 6
  457. \& static void
  458. \& fatal_error (const char *msg)
  459. \& {
  460. \& perror (msg);
  461. \& abort ();
  462. \& }
  463. \&
  464. \& ...
  465. \& ev_set_syserr_cb (fatal_error);
  466. .Ve
  467. .IP "ev_feed_signal (int signum)" 4
  468. .IX Item "ev_feed_signal (int signum)"
  469. This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
  470. safe to call this function at any time, from any context, including signal
  471. handlers or random threads.
  472. .Sp
  473. Its main use is to customise signal handling in your process, especially
  474. in the presence of threads. For example, you could block signals
  475. by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
  476. creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
  477. mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
  478. \&\f(CW\*(C`ev_feed_signal\*(C'\fR.
  481. An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
  482. \&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
  483. libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
  484. .PP
  485. The library knows two types of such loops, the \fIdefault\fR loop, which
  486. supports child process events, and dynamically created event loops which
  487. do not.
  488. .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
  489. .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
  490. This returns the \*(L"default\*(R" event loop object, which is what you should
  491. normally use when you just need \*(L"the event loop\*(R". Event loop objects and
  492. the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
  493. \&\f(CW\*(C`ev_loop_new\*(C'\fR.
  494. .Sp
  495. If the default loop is already initialised then this function simply
  496. returns it (and ignores the flags. If that is troubling you, check
  497. \&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
  498. flags, which should almost always be \f(CW0\fR, unless the caller is also the
  499. one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
  500. .Sp
  501. If you don't know what event loop to use, use the one returned from this
  502. function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
  503. .Sp
  504. Note that this function is \fInot\fR thread-safe, so if you want to use it
  505. from multiple threads, you have to employ some kind of mutex (note also
  506. that this case is unlikely, as loops cannot be shared easily between
  507. threads anyway).
  508. .Sp
  509. The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
  510. and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
  511. a problem for your application you can either create a dynamic loop with
  512. \&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
  513. \&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
  514. .Sp
  515. Example: This is the most typical usage.
  516. .Sp
  517. .Vb 2
  518. \& if (!ev_default_loop (0))
  519. \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
  520. .Ve
  521. .Sp
  522. Example: Restrict libev to the select and poll backends, and do not allow
  523. environment settings to be taken into account:
  524. .Sp
  525. .Vb 1
  527. .Ve
  528. .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
  529. .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
  530. This will create and initialise a new event loop object. If the loop
  531. could not be initialised, returns false.
  532. .Sp
  533. This function is thread-safe, and one common way to use libev with
  534. threads is indeed to create one loop per thread, and using the default
  535. loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
  536. .Sp
  537. The flags argument can be used to specify special behaviour or specific
  538. backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
  539. .Sp
  540. The following flags are supported:
  541. .RS 4
  542. .ie n .IP """EVFLAG_AUTO""" 4
  543. .el .IP "\f(CWEVFLAG_AUTO\fR" 4
  544. .IX Item "EVFLAG_AUTO"
  545. The default flags value. Use this if you have no clue (it's the right
  546. thing, believe me).
  547. .ie n .IP """EVFLAG_NOENV""" 4
  548. .el .IP "\f(CWEVFLAG_NOENV\fR" 4
  549. .IX Item "EVFLAG_NOENV"
  550. If this flag bit is or'ed into the flag value (or the program runs setuid
  551. or setgid) then libev will \fInot\fR look at the environment variable
  552. \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
  553. override the flags completely if it is found in the environment. This is
  554. useful to try out specific backends to test their performance, to work
  555. around bugs, or to make libev threadsafe (accessing environment variables
  556. cannot be done in a threadsafe way, but usually it works if no other
  557. thread modifies them).
  558. .ie n .IP """EVFLAG_FORKCHECK""" 4
  559. .el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
  561. Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
  562. make libev check for a fork in each iteration by enabling this flag.
  563. .Sp
  564. This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
  565. and thus this might slow down your event loop if you do a lot of loop
  566. iterations and little real work, but is usually not noticeable (on my
  567. GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn
  568. sequence without a system call and thus \fIvery\fR fast, but my GNU/Linux
  569. system also has \f(CW\*(C`pthread_atfork\*(C'\fR which is even faster). (Update: glibc
  570. versions 2.25 apparently removed the \f(CW\*(C`getpid\*(C'\fR optimisation again).
  571. .Sp
  572. The big advantage of this flag is that you can forget about fork (and
  573. forget about forgetting to tell libev about forking, although you still
  574. have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR) when you use this flag.
  575. .Sp
  576. This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
  577. environment variable.
  578. .ie n .IP """EVFLAG_NOINOTIFY""" 4
  579. .el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
  581. When this flag is specified, then libev will not attempt to use the
  582. \&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
  583. testing, this flag can be useful to conserve inotify file descriptors, as
  584. otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
  585. .ie n .IP """EVFLAG_SIGNALFD""" 4
  586. .el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
  588. When this flag is specified, then libev will attempt to use the
  589. \&\fIsignalfd\fR \s-1API\s0 for its \f(CW\*(C`ev_signal\*(C'\fR (and \f(CW\*(C`ev_child\*(C'\fR) watchers. This \s-1API\s0
  590. delivers signals synchronously, which makes it both faster and might make
  591. it possible to get the queued signal data. It can also simplify signal
  592. handling with threads, as long as you properly block signals in your
  593. threads that are not interested in handling them.
  594. .Sp
  595. Signalfd will not be used by default as this changes your signal mask, and
  596. there are a lot of shoddy libraries and programs (glib's threadpool for
  597. example) that can't properly initialise their signal masks.
  598. .ie n .IP """EVFLAG_NOSIGMASK""" 4
  599. .el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
  601. When this flag is specified, then libev will avoid to modify the signal
  602. mask. Specifically, this means you have to make sure signals are unblocked
  603. when you want to receive them.
  604. .Sp
  605. This behaviour is useful when you want to do your own signal handling, or
  606. want to handle signals only in specific threads and want to avoid libev
  607. unblocking the signals.
  608. .Sp
  609. It's also required by \s-1POSIX\s0 in a threaded program, as libev calls
  610. \&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified.
  611. .ie n .IP """EVFLAG_NOTIMERFD""" 4
  612. .el .IP "\f(CWEVFLAG_NOTIMERFD\fR" 4
  614. When this flag is specified, the libev will avoid using a \f(CW\*(C`timerfd\*(C'\fR to
  615. detect time jumps. It will still be able to detect time jumps, but takes
  616. longer and has a lower accuracy in doing so, but saves a file descriptor
  617. per loop.
  618. .Sp
  619. The current implementation only tries to use a \f(CW\*(C`timerfd\*(C'\fR when the first
  620. \&\f(CW\*(C`ev_periodic\*(C'\fR watcher is started and falls back on other methods if it
  621. cannot be created, but this behaviour might change in the future.
  622. .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
  623. .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
  624. .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
  625. This is your standard \fBselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
  626. libev tries to roll its own fd_set with no limits on the number of fds,
  627. but if that fails, expect a fairly low limit on the number of fds when
  628. using this backend. It doesn't scale too well (O(highest_fd)), but its
  629. usually the fastest backend for a low number of (low-numbered :) fds.
  630. .Sp
  631. To get good performance out of this backend you need a high amount of
  632. parallelism (most of the file descriptors should be busy). If you are
  633. writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
  634. connections as possible during one iteration. You might also want to have
  635. a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
  636. readiness notifications you get per iteration.
  637. .Sp
  638. This backend maps \f(CW\*(C`EV_READ\*(C'\fR to the \f(CW\*(C`readfds\*(C'\fR set and \f(CW\*(C`EV_WRITE\*(C'\fR to the
  639. \&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
  640. \&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
  641. .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
  642. .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
  643. .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
  644. And this is your standard \fBpoll\fR\|(2) backend. It's more complicated
  645. than select, but handles sparse fds better and has no artificial
  646. limit on the number of fds you can use (except it will slow down
  647. considerably with a lot of inactive fds). It scales similarly to select,
  648. i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
  649. performance tips.
  650. .Sp
  651. This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
  652. \&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
  653. .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
  654. .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
  655. .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
  656. Use the Linux-specific \fBepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
  657. kernels).
  658. .Sp
  659. For few fds, this backend is a bit little slower than poll and select, but
  660. it scales phenomenally better. While poll and select usually scale like
  661. O(total_fds) where total_fds is the total number of fds (or the highest
  662. fd), epoll scales either O(1) or O(active_fds).
  663. .Sp
  664. The epoll mechanism deserves honorable mention as the most misdesigned
  665. of the more advanced event mechanisms: mere annoyances include silently
  666. dropping file descriptors, requiring a system call per change per file
  667. descriptor (and unnecessary guessing of parameters), problems with dup,
  668. returning before the timeout value, resulting in additional iterations
  669. (and only giving 5ms accuracy while select on the same platform gives
  670. 0.1ms) and so on. The biggest issue is fork races, however \- if a program
  671. forks then \fIboth\fR parent and child process have to recreate the epoll
  672. set, which can take considerable time (one syscall per file descriptor)
  673. and is of course hard to detect.
  674. .Sp
  675. Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work,
  676. but of course \fIdoesn't\fR, and epoll just loves to report events for
  677. totally \fIdifferent\fR file descriptors (even already closed ones, so
  678. one cannot even remove them from the set) than registered in the set
  679. (especially on \s-1SMP\s0 systems). Libev tries to counter these spurious
  680. notifications by employing an additional generation counter and comparing
  681. that against the events to filter out spurious ones, recreating the set
  682. when required. Epoll also erroneously rounds down timeouts, but gives you
  683. no way to know when and by how much, so sometimes you have to busy-wait
  684. because epoll returns immediately despite a nonzero timeout. And last
  685. not least, it also refuses to work with some file descriptors which work
  686. perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
  687. .Sp
  688. Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
  689. cobbled together in a hurry, no thought to design or interaction with
  690. others. Oh, the pain, will it ever stop...
  691. .Sp
  692. While stopping, setting and starting an I/O watcher in the same iteration
  693. will result in some caching, there is still a system call per such
  694. incident (because the same \fIfile descriptor\fR could point to a different
  695. \&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
  696. file descriptors might not work very well if you register events for both
  697. file descriptors.
  698. .Sp
  699. Best performance from this backend is achieved by not unregistering all
  700. watchers for a file descriptor until it has been closed, if possible,
  701. i.e. keep at least one watcher active per fd at all times. Stopping and
  702. starting a watcher (without re-setting it) also usually doesn't cause
  703. extra overhead. A fork can both result in spurious notifications as well
  704. as in libev having to destroy and recreate the epoll object, which can
  705. take considerable time and thus should be avoided.
  706. .Sp
  707. All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
  708. faster than epoll for maybe up to a hundred file descriptors, depending on
  709. the usage. So sad.
  710. .Sp
  711. While nominally embeddable in other event loops, this feature is broken in
  712. a lot of kernel revisions, but probably(!) works in current versions.
  713. .Sp
  714. This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
  715. \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
  716. .ie n .IP """EVBACKEND_LINUXAIO"" (value 64, Linux)" 4
  717. .el .IP "\f(CWEVBACKEND_LINUXAIO\fR (value 64, Linux)" 4
  718. .IX Item "EVBACKEND_LINUXAIO (value 64, Linux)"
  719. Use the Linux-specific Linux \s-1AIO\s0 (\fInot\fR \f(CWaio(7)\fR but \f(CWio_submit(2)\fR) event interface available in post\-4.18 kernels (but libev
  720. only tries to use it in 4.19+).
  721. .Sp
  722. This is another Linux train wreck of an event interface.
  723. .Sp
  724. If this backend works for you (as of this writing, it was very
  725. experimental), it is the best event interface available on Linux and might
  726. be well worth enabling it \- if it isn't available in your kernel this will
  727. be detected and this backend will be skipped.
  728. .Sp
  729. This backend can batch oneshot requests and supports a user-space ring
  730. buffer to receive events. It also doesn't suffer from most of the design
  731. problems of epoll (such as not being able to remove event sources from
  732. the epoll set), and generally sounds too good to be true. Because, this
  733. being the Linux kernel, of course it suffers from a whole new set of
  734. limitations, forcing you to fall back to epoll, inheriting all its design
  735. issues.
  736. .Sp
  737. For one, it is not easily embeddable (but probably could be done using
  738. an event fd at some extra overhead). It also is subject to a system wide
  739. limit that can be configured in \fI/proc/sys/fs/aio\-max\-nr\fR. If no \s-1AIO\s0
  740. requests are left, this backend will be skipped during initialisation, and
  741. will switch to epoll when the loop is active.
  742. .Sp
  743. Most problematic in practice, however, is that not all file descriptors
  744. work with it. For example, in Linux 5.1, \s-1TCP\s0 sockets, pipes, event fds,
  745. files, \fI/dev/null\fR and many others are supported, but ttys do not work
  746. properly (a known bug that the kernel developers don't care about, see
  747. <https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
  748. (yet?) a generic event polling interface.
  749. .Sp
  750. Overall, it seems the Linux developers just don't want it to have a
  751. generic event handling mechanism other than \f(CW\*(C`select\*(C'\fR or \f(CW\*(C`poll\*(C'\fR.
  752. .Sp
  753. To work around all these problem, the current version of libev uses its
  754. epoll backend as a fallback for file descriptor types that do not work. Or
  755. falls back completely to epoll if the kernel acts up.
  756. .Sp
  757. This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
  758. \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
  759. .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
  760. .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
  761. .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
  762. Kqueue deserves special mention, as at the time this backend was
  763. implemented, it was broken on all BSDs except NetBSD (usually it doesn't
  764. work reliably with anything but sockets and pipes, except on Darwin,
  765. where of course it's completely useless). Unlike epoll, however, whose
  766. brokenness is by design, these kqueue bugs can be (and mostly have been)
  767. fixed without \s-1API\s0 changes to existing programs. For this reason it's not
  768. being \*(L"auto-detected\*(R" on all platforms unless you explicitly specify it
  769. in the flags (i.e. using \f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a
  770. known-to-be-good (\-enough) system like NetBSD.
  771. .Sp
  772. You still can embed kqueue into a normal poll or select backend and use it
  773. only for sockets (after having made sure that sockets work with kqueue on
  774. the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
  775. .Sp
  776. It scales in the same way as the epoll backend, but the interface to the
  777. kernel is more efficient (which says nothing about its actual speed, of
  778. course). While stopping, setting and starting an I/O watcher does never
  779. cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
  780. two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (you
  781. might have to leak fds on fork, but it's more sane than epoll) and it
  782. drops fds silently in similarly hard-to-detect cases.
  783. .Sp
  784. This backend usually performs well under most conditions.
  785. .Sp
  786. While nominally embeddable in other event loops, this doesn't work
  787. everywhere, so you might need to test for this. And since it is broken
  788. almost everywhere, you should only use it when you have a lot of sockets
  789. (for which it usually works), by embedding it into another event loop
  790. (e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR (but \f(CW\*(C`poll\*(C'\fR is of course
  791. also broken on \s-1OS X\s0)) and, did I mention it, using it only for sockets.
  792. .Sp
  793. This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
  794. \&\f(CW\*(C`NOTE_EOF\*(C'\fR, and \f(CW\*(C`EV_WRITE\*(C'\fR into an \f(CW\*(C`EVFILT_WRITE\*(C'\fR kevent with
  795. \&\f(CW\*(C`NOTE_EOF\*(C'\fR.
  796. .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
  797. .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
  798. .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
  799. This is not implemented yet (and might never be, unless you send me an
  800. implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
  801. and is not embeddable, which would limit the usefulness of this backend
  802. immensely.
  803. .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
  804. .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
  805. .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
  806. This uses the Solaris 10 event port mechanism. As with everything on Solaris,
  807. it's really slow, but it still scales very well (O(active_fds)).
  808. .Sp
  809. While this backend scales well, it requires one system call per active
  810. file descriptor per loop iteration. For small and medium numbers of file
  811. descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
  812. might perform better.
  813. .Sp
  814. On the positive side, this backend actually performed fully to
  815. specification in all tests and is fully embeddable, which is a rare feat
  816. among the OS-specific backends (I vastly prefer correctness over speed
  817. hacks).
  818. .Sp
  819. On the negative side, the interface is \fIbizarre\fR \- so bizarre that
  820. even sun itself gets it wrong in their code examples: The event polling
  821. function sometimes returns events to the caller even though an error
  822. occurred, but with no indication whether it has done so or not (yes, it's
  823. even documented that way) \- deadly for edge-triggered interfaces where you
  824. absolutely have to know whether an event occurred or not because you have
  825. to re-arm the watcher.
  826. .Sp
  827. Fortunately libev seems to be able to work around these idiocies.
  828. .Sp
  829. This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
  830. \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
  831. .ie n .IP """EVBACKEND_ALL""" 4
  832. .el .IP "\f(CWEVBACKEND_ALL\fR" 4
  833. .IX Item "EVBACKEND_ALL"
  834. Try all backends (even potentially broken ones that wouldn't be tried
  835. with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
  837. .Sp
  838. It is definitely not recommended to use this flag, use whatever
  839. \&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
  840. at all.
  841. .ie n .IP """EVBACKEND_MASK""" 4
  842. .el .IP "\f(CWEVBACKEND_MASK\fR" 4
  843. .IX Item "EVBACKEND_MASK"
  844. Not a backend at all, but a mask to select all backend bits from a
  845. \&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
  846. value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
  847. .RE
  848. .RS 4
  849. .Sp
  850. If one or more of the backend flags are or'ed into the flags value,
  851. then only these backends will be tried (in the reverse order as listed
  852. here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
  853. ()\*(C'\fR will be tried.
  854. .Sp
  855. Example: Try to create a event loop that uses epoll and nothing else.
  856. .Sp
  857. .Vb 3
  858. \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
  859. \& if (!epoller)
  860. \& fatal ("no epoll found here, maybe it hides under your chair");
  861. .Ve
  862. .Sp
  863. Example: Use whatever libev has to offer, but make sure that kqueue is
  864. used if available.
  865. .Sp
  866. .Vb 1
  867. \& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
  868. .Ve
  869. .Sp
  870. Example: Similarly, on linux, you mgiht want to take advantage of the
  871. linux aio backend if possible, but fall back to something else if that
  872. isn't available.
  873. .Sp
  874. .Vb 1
  875. \& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
  876. .Ve
  877. .RE
  878. .IP "ev_loop_destroy (loop)" 4
  879. .IX Item "ev_loop_destroy (loop)"
  880. Destroys an event loop object (frees all memory and kernel state
  881. etc.). None of the active event watchers will be stopped in the normal
  882. sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
  883. responsibility to either stop all watchers cleanly yourself \fIbefore\fR
  884. calling this function, or cope with the fact afterwards (which is usually
  885. the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
  886. for example).
  887. .Sp
  888. Note that certain global state, such as signal state (and installed signal
  889. handlers), will not be freed by this function, and related watchers (such
  890. as signal and child watchers) would need to be stopped manually.
  891. .Sp
  892. This function is normally used on loop objects allocated by
  893. \&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
  894. \&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
  895. .Sp
  896. Note that it is not advisable to call this function on the default loop
  897. except in the rare occasion where you really need to free its resources.
  898. If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
  899. and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
  900. .IP "ev_loop_fork (loop)" 4
  901. .IX Item "ev_loop_fork (loop)"
  902. This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations
  903. to reinitialise the kernel state for backends that have one. Despite
  904. the name, you can call it anytime you are allowed to start or stop
  905. watchers (except inside an \f(CW\*(C`ev_prepare\*(C'\fR callback), but it makes most
  906. sense after forking, in the child process. You \fImust\fR call it (or use
  907. \&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
  908. .Sp
  909. In addition, if you want to reuse a loop (via this function or
  910. \&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR), you \fIalso\fR have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR.
  911. .Sp
  912. Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
  913. a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
  914. because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
  915. during fork.
  916. .Sp
  917. On the other hand, you only need to call this function in the child
  918. process if and only if you want to use the event loop in the child. If
  919. you just fork+exec or create a new loop in the child, you don't have to
  920. call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
  921. difference, but libev will usually detect this case on its own and do a
  922. costly reset of the backend).
  923. .Sp
  924. The function itself is quite fast and it's usually not a problem to call
  925. it just in case after a fork.
  926. .Sp
  927. Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
  928. using pthreads.
  929. .Sp
  930. .Vb 5
  931. \& static void
  932. \& post_fork_child (void)
  933. \& {
  934. \& ev_loop_fork (EV_DEFAULT);
  935. \& }
  936. \&
  937. \& ...
  938. \& pthread_atfork (0, 0, post_fork_child);
  939. .Ve
  940. .IP "int ev_is_default_loop (loop)" 4
  941. .IX Item "int ev_is_default_loop (loop)"
  942. Returns true when the given loop is, in fact, the default loop, and false
  943. otherwise.
  944. .IP "unsigned int ev_iteration (loop)" 4
  945. .IX Item "unsigned int ev_iteration (loop)"
  946. Returns the current iteration count for the event loop, which is identical
  947. to the number of times libev did poll for new events. It starts at \f(CW0\fR
  948. and happily wraps around with enough iterations.
  949. .Sp
  950. This value can sometimes be useful as a generation counter of sorts (it
  951. \&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
  952. \&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
  953. prepare and check phases.
  954. .IP "unsigned int ev_depth (loop)" 4
  955. .IX Item "unsigned int ev_depth (loop)"
  956. Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
  957. times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
  958. .Sp
  959. Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
  960. \&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
  961. in which case it is higher.
  962. .Sp
  963. Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
  964. throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
  965. as a hint to avoid such ungentleman-like behaviour unless it's really
  966. convenient, in which case it is fully supported.
  967. .IP "unsigned int ev_backend (loop)" 4
  968. .IX Item "unsigned int ev_backend (loop)"
  969. Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
  970. use.
  971. .IP "ev_tstamp ev_now (loop)" 4
  972. .IX Item "ev_tstamp ev_now (loop)"
  973. Returns the current \*(L"event loop time\*(R", which is the time the event loop
  974. received events and started processing them. This timestamp does not
  975. change as long as callbacks are being processed, and this is also the base
  976. time used for relative timers. You can treat it as the timestamp of the
  977. event occurring (or more correctly, libev finding out about it).
  978. .IP "ev_now_update (loop)" 4
  979. .IX Item "ev_now_update (loop)"
  980. Establishes the current time by querying the kernel, updating the time
  981. returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
  982. is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
  983. .Sp
  984. This function is rarely useful, but when some event callback runs for a
  985. very long time without entering the event loop, updating libev's idea of
  986. the current time is a good idea.
  987. .Sp
  988. See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
  989. .IP "ev_suspend (loop)" 4
  990. .IX Item "ev_suspend (loop)"
  991. .PD 0
  992. .IP "ev_resume (loop)" 4
  993. .IX Item "ev_resume (loop)"
  994. .PD
  995. These two functions suspend and resume an event loop, for use when the
  996. loop is not used for a while and timeouts should not be processed.
  997. .Sp
  998. A typical use case would be an interactive program such as a game: When
  999. the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
  1000. would be best to handle timeouts as if no time had actually passed while
  1001. the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
  1002. in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
  1003. \&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
  1004. .Sp
  1005. Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
  1006. between \f(CW\*(C`ev_suspend\*(C'\fR and \f(CW\*(C`ev_resume\*(C'\fR, and all \f(CW\*(C`ev_periodic\*(C'\fR watchers
  1007. will be rescheduled (that is, they will lose any events that would have
  1008. occurred while suspended).
  1009. .Sp
  1010. After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
  1011. given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
  1012. without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
  1013. .Sp
  1014. Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
  1015. event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
  1016. .IP "bool ev_run (loop, int flags)" 4
  1017. .IX Item "bool ev_run (loop, int flags)"
  1018. Finally, this is it, the event handler. This function usually is called
  1019. after you have initialised all your watchers and you want to start
  1020. handling events. It will ask the operating system for any new events, call
  1021. the watcher callbacks, and then repeat the whole process indefinitely: This
  1022. is why event loops are called \fIloops\fR.
  1023. .Sp
  1024. If the flags argument is specified as \f(CW0\fR, it will keep handling events
  1025. until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
  1026. called.
  1027. .Sp
  1028. The return value is false if there are no more active watchers (which
  1029. usually means \*(L"all jobs done\*(R" or \*(L"deadlock\*(R"), and true in all other cases
  1030. (which usually means " you should call \f(CW\*(C`ev_run\*(C'\fR again").
  1031. .Sp
  1032. Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
  1033. relying on all watchers to be stopped when deciding when a program has
  1034. finished (especially in interactive programs), but having a program
  1035. that automatically loops as long as it has to and no longer by virtue
  1036. of relying on its watchers stopping correctly, that is truly a thing of
  1037. beauty.
  1038. .Sp
  1039. This function is \fImostly\fR exception-safe \- you can break out of a
  1040. \&\f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
  1041. exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
  1042. will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
  1043. .Sp
  1044. A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
  1045. those events and any already outstanding ones, but will not wait and
  1046. block your process in case there are no events and will return after one
  1047. iteration of the loop. This is sometimes useful to poll and handle new
  1048. events while doing lengthy calculations, to keep the program responsive.
  1049. .Sp
  1050. A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
  1051. necessary) and will handle those and any already outstanding ones. It
  1052. will block your process until at least one new event arrives (which could
  1053. be an event internal to libev itself, so there is no guarantee that a
  1054. user-registered callback will be called), and will return after one
  1055. iteration of the loop.
  1056. .Sp
  1057. This is useful if you are waiting for some external event in conjunction
  1058. with something not expressible using other libev watchers (i.e. "roll your
  1059. own \f(CW\*(C`ev_run\*(C'\fR"). However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
  1060. usually a better approach for this kind of thing.
  1061. .Sp
  1062. Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
  1063. understanding, not a guarantee that things will work exactly like this in
  1064. future versions):
  1065. .Sp
  1066. .Vb 10
  1067. \& \- Increment loop depth.
  1068. \& \- Reset the ev_break status.
  1069. \& \- Before the first iteration, call any pending watchers.
  1070. \& LOOP:
  1071. \& \- If EVFLAG_FORKCHECK was used, check for a fork.
  1072. \& \- If a fork was detected (by any means), queue and call all fork watchers.
  1073. \& \- Queue and call all prepare watchers.
  1074. \& \- If ev_break was called, goto FINISH.
  1075. \& \- If we have been forked, detach and recreate the kernel state
  1076. \& as to not disturb the other process.
  1077. \& \- Update the kernel state with all outstanding changes.
  1078. \& \- Update the "event loop time" (ev_now ()).
  1079. \& \- Calculate for how long to sleep or block, if at all
  1080. \& (active idle watchers, EVRUN_NOWAIT or not having
  1081. \& any active watchers at all will result in not sleeping).
  1082. \& \- Sleep if the I/O and timer collect interval say so.
  1083. \& \- Increment loop iteration counter.
  1084. \& \- Block the process, waiting for any events.
  1085. \& \- Queue all outstanding I/O (fd) events.
  1086. \& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
  1087. \& \- Queue all expired timers.
  1088. \& \- Queue all expired periodics.
  1089. \& \- Queue all idle watchers with priority higher than that of pending events.
  1090. \& \- Queue all check watchers.
  1091. \& \- Call all queued watchers in reverse order (i.e. check watchers first).
  1092. \& Signals and child watchers are implemented as I/O watchers, and will
  1093. \& be handled here by queueing them when their watcher gets executed.
  1094. \& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
  1095. \& were used, or there are no active watchers, goto FINISH, otherwise
  1096. \& continue with step LOOP.
  1097. \& FINISH:
  1098. \& \- Reset the ev_break status iff it was EVBREAK_ONE.
  1099. \& \- Decrement the loop depth.
  1100. \& \- Return.
  1101. .Ve
  1102. .Sp
  1103. Example: Queue some jobs and then loop until no events are outstanding
  1104. anymore.
  1105. .Sp
  1106. .Vb 4
  1107. \& ... queue jobs here, make sure they register event watchers as long
  1108. \& ... as they still have work to do (even an idle watcher will do..)
  1109. \& ev_run (my_loop, 0);
  1110. \& ... jobs done or somebody called break. yeah!
  1111. .Ve
  1112. .IP "ev_break (loop, how)" 4
  1113. .IX Item "ev_break (loop, how)"
  1114. Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
  1115. has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
  1116. \&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
  1117. \&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
  1118. .Sp
  1119. This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
  1120. .Sp
  1121. It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
  1122. which case it will have no effect.
  1123. .IP "ev_ref (loop)" 4
  1124. .IX Item "ev_ref (loop)"
  1125. .PD 0
  1126. .IP "ev_unref (loop)" 4
  1127. .IX Item "ev_unref (loop)"
  1128. .PD
  1129. Ref/unref can be used to add or remove a reference count on the event
  1130. loop: Every watcher keeps one reference, and as long as the reference
  1131. count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
  1132. .Sp
  1133. This is useful when you have a watcher that you never intend to
  1134. unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
  1135. returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
  1136. before stopping it.
  1137. .Sp
  1138. As an example, libev itself uses this for its internal signal pipe: It
  1139. is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
  1140. exiting if no event watchers registered by it are active. It is also an
  1141. excellent way to do this for generic recurring timers or from within
  1142. third-party libraries. Just remember to \fIunref after start\fR and \fIref
  1143. before stop\fR (but only if the watcher wasn't active before, or was active
  1144. before, respectively. Note also that libev might stop watchers itself
  1145. (e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
  1146. in the callback).
  1147. .Sp
  1148. Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
  1149. running when nothing else is active.
  1150. .Sp
  1151. .Vb 4
  1152. \& ev_signal exitsig;
  1153. \& ev_signal_init (&exitsig, sig_cb, SIGINT);
  1154. \& ev_signal_start (loop, &exitsig);
  1155. \& ev_unref (loop);
  1156. .Ve
  1157. .Sp
  1158. Example: For some weird reason, unregister the above signal handler again.
  1159. .Sp
  1160. .Vb 2
  1161. \& ev_ref (loop);
  1162. \& ev_signal_stop (loop, &exitsig);
  1163. .Ve
  1164. .IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
  1165. .IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
  1166. .PD 0
  1167. .IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
  1168. .IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
  1169. .PD
  1170. These advanced functions influence the time that libev will spend waiting
  1171. for events. Both time intervals are by default \f(CW0\fR, meaning that libev
  1172. will try to invoke timer/periodic callbacks and I/O callbacks with minimum
  1173. latency.
  1174. .Sp
  1175. Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
  1176. allows libev to delay invocation of I/O and timer/periodic callbacks
  1177. to increase efficiency of loop iterations (or to increase power-saving
  1178. opportunities).
  1179. .Sp
  1180. The idea is that sometimes your program runs just fast enough to handle
  1181. one (or very few) event(s) per loop iteration. While this makes the
  1182. program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
  1183. events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
  1184. overhead for the actual polling but can deliver many events at once.
  1185. .Sp
  1186. By setting a higher \fIio collect interval\fR you allow libev to spend more
  1187. time collecting I/O events, so you can handle more events per iteration,
  1188. at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
  1189. \&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
  1190. introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
  1191. sleep time ensures that libev will not poll for I/O events more often then
  1192. once per this interval, on average (as long as the host time resolution is
  1193. good enough).
  1194. .Sp
  1195. Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
  1196. to spend more time collecting timeouts, at the expense of increased
  1197. latency/jitter/inexactness (the watcher callback will be called
  1198. later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
  1199. value will not introduce any overhead in libev.
  1200. .Sp
  1201. Many (busy) programs can usually benefit by setting the I/O collect
  1202. interval to a value near \f(CW0.1\fR or so, which is often enough for
  1203. interactive servers (of course not for games), likewise for timeouts. It
  1204. usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
  1205. as this approaches the timing granularity of most systems. Note that if
  1206. you do transactions with the outside world and you can't increase the
  1207. parallelity, then this setting will limit your transaction rate (if you
  1208. need to poll once per transaction and the I/O collect interval is 0.01,
  1209. then you can't do more than 100 transactions per second).
  1210. .Sp
  1211. Setting the \fItimeout collect interval\fR can improve the opportunity for
  1212. saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
  1213. are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
  1214. times the process sleeps and wakes up again. Another useful technique to
  1215. reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
  1216. they fire on, say, one-second boundaries only.
  1217. .Sp
  1218. Example: we only need 0.1s timeout granularity, and we wish not to poll
  1219. more often than 100 times per second:
  1220. .Sp
  1221. .Vb 2
  1222. \& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
  1223. \& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
  1224. .Ve
  1225. .IP "ev_invoke_pending (loop)" 4
  1226. .IX Item "ev_invoke_pending (loop)"
  1227. This call will simply invoke all pending watchers while resetting their
  1228. pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
  1229. but when overriding the invoke callback this call comes handy. This
  1230. function can be invoked from a watcher \- this can be useful for example
  1231. when you want to do some lengthy calculation and want to pass further
  1232. event handling to another thread (you still have to make sure only one
  1233. thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
  1234. .IP "int ev_pending_count (loop)" 4
  1235. .IX Item "int ev_pending_count (loop)"
  1236. Returns the number of pending watchers \- zero indicates that no watchers
  1237. are pending.
  1238. .IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
  1239. .IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
  1240. This overrides the invoke pending functionality of the loop: Instead of
  1241. invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
  1242. this callback instead. This is useful, for example, when you want to
  1243. invoke the actual watchers inside another context (another thread etc.).
  1244. .Sp
  1245. If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
  1246. callback.
  1247. .IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0) throw (), void (*acquire)(\s-1EV_P\s0) throw ())" 4
  1248. .IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())"
  1249. Sometimes you want to share the same loop between multiple threads. This
  1250. can be done relatively simply by putting mutex_lock/unlock calls around
  1251. each call to a libev function.
  1252. .Sp
  1253. However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
  1254. to wait for it to return. One way around this is to wake up the event
  1255. loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
  1256. \&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
  1257. .Sp
  1258. When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
  1259. suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
  1260. afterwards.
  1261. .Sp
  1262. Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
  1263. \&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
  1264. .Sp
  1265. While event loop modifications are allowed between invocations of
  1266. \&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
  1267. modifications done will affect the event loop, i.e. adding watchers will
  1268. have no effect on the set of file descriptors being watched, or the time
  1269. waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
  1270. to take note of any changes you made.
  1271. .Sp
  1272. In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
  1273. invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
  1274. .Sp
  1275. See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
  1276. document.
  1277. .IP "ev_set_userdata (loop, void *data)" 4
  1278. .IX Item "ev_set_userdata (loop, void *data)"
  1279. .PD 0
  1280. .IP "void *ev_userdata (loop)" 4
  1281. .IX Item "void *ev_userdata (loop)"
  1282. .PD
  1283. Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
  1284. \&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
  1285. \&\f(CW0\fR.
  1286. .Sp
  1287. These two functions can be used to associate arbitrary data with a loop,
  1288. and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
  1289. \&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
  1290. any other purpose as well.
  1291. .IP "ev_verify (loop)" 4
  1292. .IX Item "ev_verify (loop)"
  1293. This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
  1294. compiled in, which is the default for non-minimal builds. It tries to go
  1295. through all internal structures and checks them for validity. If anything
  1296. is found to be inconsistent, it will print an error message to standard
  1297. error and call \f(CW\*(C`abort ()\*(C'\fR.
  1298. .Sp
  1299. This can be used to catch bugs inside libev itself: under normal
  1300. circumstances, this function will never abort as of course libev keeps its
  1301. data structures consistent.
  1303. .IX Header "ANATOMY OF A WATCHER"
  1304. In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
  1305. watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
  1306. watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
  1307. .PP
  1308. A watcher is an opaque structure that you allocate and register to record
  1309. your interest in some event. To make a concrete example, imagine you want
  1310. to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
  1311. for that:
  1312. .PP
  1313. .Vb 5
  1314. \& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
  1315. \& {
  1316. \& ev_io_stop (w);
  1317. \& ev_break (loop, EVBREAK_ALL);
  1318. \& }
  1319. \&
  1320. \& struct ev_loop *loop = ev_default_loop (0);
  1321. \&
  1322. \& ev_io stdin_watcher;
  1323. \&
  1324. \& ev_init (&stdin_watcher, my_cb);
  1325. \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
  1326. \& ev_io_start (loop, &stdin_watcher);
  1327. \&
  1328. \& ev_run (loop, 0);
  1329. .Ve
  1330. .PP
  1331. As you can see, you are responsible for allocating the memory for your
  1332. watcher structures (and it is \fIusually\fR a bad idea to do this on the
  1333. stack).
  1334. .PP
  1335. Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
  1336. or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
  1337. .PP
  1338. Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
  1339. *, callback)\*(C'\fR, which expects a callback to be provided. This callback is
  1340. invoked each time the event occurs (or, in the case of I/O watchers, each
  1341. time the event loop detects that the file descriptor given is readable
  1342. and/or writable).
  1343. .PP
  1344. Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
  1345. macro to configure it, with arguments specific to the watcher type. There
  1346. is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
  1347. .PP
  1348. To make the watcher actually watch out for events, you have to start it
  1349. with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
  1350. *)\*(C'\fR), and you can stop watching for events at any time by calling the
  1351. corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
  1352. .PP
  1353. As long as your watcher is active (has been started but not stopped) you
  1354. must not touch the values stored in it except when explicitly documented
  1355. otherwise. Most specifically you must never reinitialise it or call its
  1356. \&\f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
  1357. .PP
  1358. Each and every callback receives the event loop pointer as first, the
  1359. registered watcher structure as second, and a bitset of received events as
  1360. third argument.
  1361. .PP
  1362. The received events usually include a single bit per event type received
  1363. (you can receive multiple events at the same time). The possible bit masks
  1364. are:
  1365. .ie n .IP """EV_READ""" 4
  1366. .el .IP "\f(CWEV_READ\fR" 4
  1367. .IX Item "EV_READ"
  1368. .PD 0
  1369. .ie n .IP """EV_WRITE""" 4
  1370. .el .IP "\f(CWEV_WRITE\fR" 4
  1371. .IX Item "EV_WRITE"
  1372. .PD
  1373. The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
  1374. writable.
  1375. .ie n .IP """EV_TIMER""" 4
  1376. .el .IP "\f(CWEV_TIMER\fR" 4
  1377. .IX Item "EV_TIMER"
  1378. The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
  1379. .ie n .IP """EV_PERIODIC""" 4
  1380. .el .IP "\f(CWEV_PERIODIC\fR" 4
  1381. .IX Item "EV_PERIODIC"
  1382. The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
  1383. .ie n .IP """EV_SIGNAL""" 4
  1384. .el .IP "\f(CWEV_SIGNAL\fR" 4
  1385. .IX Item "EV_SIGNAL"
  1386. The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
  1387. .ie n .IP """EV_CHILD""" 4
  1388. .el .IP "\f(CWEV_CHILD\fR" 4
  1389. .IX Item "EV_CHILD"
  1390. The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
  1391. .ie n .IP """EV_STAT""" 4
  1392. .el .IP "\f(CWEV_STAT\fR" 4
  1393. .IX Item "EV_STAT"
  1394. The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
  1395. .ie n .IP """EV_IDLE""" 4
  1396. .el .IP "\f(CWEV_IDLE\fR" 4
  1397. .IX Item "EV_IDLE"
  1398. The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
  1399. .ie n .IP """EV_PREPARE""" 4
  1400. .el .IP "\f(CWEV_PREPARE\fR" 4
  1401. .IX Item "EV_PREPARE"
  1402. .PD 0
  1403. .ie n .IP """EV_CHECK""" 4
  1404. .el .IP "\f(CWEV_CHECK\fR" 4
  1405. .IX Item "EV_CHECK"
  1406. .PD
  1407. All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts to
  1408. gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are queued (not invoked)
  1409. just after \f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it queues any callbacks
  1410. for any received events. That means \f(CW\*(C`ev_prepare\*(C'\fR watchers are the last
  1411. watchers invoked before the event loop sleeps or polls for new events, and
  1412. \&\f(CW\*(C`ev_check\*(C'\fR watchers will be invoked before any other watchers of the same
  1413. or lower priority within an event loop iteration.
  1414. .Sp
  1415. Callbacks of both watcher types can start and stop as many watchers as
  1416. they want, and all of them will be taken into account (for example, a
  1417. \&\f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep \f(CW\*(C`ev_run\*(C'\fR from
  1418. blocking).
  1419. .ie n .IP """EV_EMBED""" 4
  1420. .el .IP "\f(CWEV_EMBED\fR" 4
  1421. .IX Item "EV_EMBED"
  1422. The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
  1423. .ie n .IP """EV_FORK""" 4
  1424. .el .IP "\f(CWEV_FORK\fR" 4
  1425. .IX Item "EV_FORK"
  1426. The event loop has been resumed in the child process after fork (see
  1427. \&\f(CW\*(C`ev_fork\*(C'\fR).
  1428. .ie n .IP """EV_CLEANUP""" 4
  1429. .el .IP "\f(CWEV_CLEANUP\fR" 4
  1430. .IX Item "EV_CLEANUP"
  1431. The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
  1432. .ie n .IP """EV_ASYNC""" 4
  1433. .el .IP "\f(CWEV_ASYNC\fR" 4
  1434. .IX Item "EV_ASYNC"
  1435. The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
  1436. .ie n .IP """EV_CUSTOM""" 4
  1437. .el .IP "\f(CWEV_CUSTOM\fR" 4
  1438. .IX Item "EV_CUSTOM"
  1439. Not ever sent (or otherwise used) by libev itself, but can be freely used
  1440. by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
  1441. .ie n .IP """EV_ERROR""" 4
  1442. .el .IP "\f(CWEV_ERROR\fR" 4
  1443. .IX Item "EV_ERROR"
  1444. An unspecified error has occurred, the watcher has been stopped. This might
  1445. happen because the watcher could not be properly started because libev
  1446. ran out of memory, a file descriptor was found to be closed or any other
  1447. problem. Libev considers these application bugs.
  1448. .Sp
  1449. You best act on it by reporting the problem and somehow coping with the
  1450. watcher being stopped. Note that well-written programs should not receive
  1451. an error ever, so when your watcher receives it, this usually indicates a
  1452. bug in your program.
  1453. .Sp
  1454. Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
  1455. example it might indicate that a fd is readable or writable, and if your
  1456. callbacks is well-written it can just attempt the operation and cope with
  1457. the error from \fBread()\fR or \fBwrite()\fR. This will not work in multi-threaded
  1458. programs, though, as the fd could already be closed and reused for another
  1459. thing, so beware.
  1462. .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
  1463. .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
  1464. .IX Item "ev_init (ev_TYPE *watcher, callback)"
  1465. This macro initialises the generic portion of a watcher. The contents
  1466. of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
  1467. the generic parts of the watcher are initialised, you \fIneed\fR to call
  1468. the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
  1469. type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
  1470. which rolls both calls into one.
  1471. .Sp
  1472. You can reinitialise a watcher at any time as long as it has been stopped
  1473. (or never started) and there are no pending events outstanding.
  1474. .Sp
  1475. The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
  1476. int revents)\*(C'\fR.
  1477. .Sp
  1478. Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
  1479. .Sp
  1480. .Vb 3
  1481. \& ev_io w;
  1482. \& ev_init (&w, my_cb);
  1483. \& ev_io_set (&w, STDIN_FILENO, EV_READ);
  1484. .Ve
  1485. .ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
  1486. .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
  1487. .IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
  1488. This macro initialises the type-specific parts of a watcher. You need to
  1489. call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
  1490. call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
  1491. macro on a watcher that is active (it can be pending, however, which is a
  1492. difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
  1493. .Sp
  1494. Although some watcher types do not have type-specific arguments
  1495. (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
  1496. .Sp
  1497. See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
  1498. .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
  1499. .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
  1500. .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
  1501. This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
  1502. calls into a single call. This is the most convenient method to initialise
  1503. a watcher. The same limitations apply, of course.
  1504. .Sp
  1505. Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
  1506. .Sp
  1507. .Vb 1
  1508. \& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
  1509. .Ve
  1510. .ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
  1511. .el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
  1512. .IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
  1513. Starts (activates) the given watcher. Only active watchers will receive
  1514. events. If the watcher is already active nothing will happen.
  1515. .Sp
  1516. Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
  1517. whole section.
  1518. .Sp
  1519. .Vb 1
  1520. \& ev_io_start (EV_DEFAULT_UC, &w);
  1521. .Ve
  1522. .ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
  1523. .el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
  1524. .IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
  1525. Stops the given watcher if active, and clears the pending status (whether
  1526. the watcher was active or not).
  1527. .Sp
  1528. It is possible that stopped watchers are pending \- for example,
  1529. non-repeating timers are being stopped when they become pending \- but
  1530. calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
  1531. pending. If you want to free or reuse the memory used by the watcher it is
  1532. therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
  1533. .IP "bool ev_is_active (ev_TYPE *watcher)" 4
  1534. .IX Item "bool ev_is_active (ev_TYPE *watcher)"
  1535. Returns a true value iff the watcher is active (i.e. it has been started
  1536. and not yet been stopped). As long as a watcher is active you must not modify
  1537. it.
  1538. .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
  1539. .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
  1540. Returns a true value iff the watcher is pending, (i.e. it has outstanding
  1541. events but its callback has not yet been invoked). As long as a watcher
  1542. is pending (but not active) you must not call an init function on it (but
  1543. \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
  1544. make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
  1545. it).
  1546. .IP "callback ev_cb (ev_TYPE *watcher)" 4
  1547. .IX Item "callback ev_cb (ev_TYPE *watcher)"
  1548. Returns the callback currently set on the watcher.
  1549. .IP "ev_set_cb (ev_TYPE *watcher, callback)" 4
  1550. .IX Item "ev_set_cb (ev_TYPE *watcher, callback)"
  1551. Change the callback. You can change the callback at virtually any time
  1552. (modulo threads).
  1553. .IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
  1554. .IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
  1555. .PD 0
  1556. .IP "int ev_priority (ev_TYPE *watcher)" 4
  1557. .IX Item "int ev_priority (ev_TYPE *watcher)"
  1558. .PD
  1559. Set and query the priority of the watcher. The priority is a small
  1560. integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
  1561. (default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
  1562. before watchers with lower priority, but priority will not keep watchers
  1563. from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
  1564. .Sp
  1565. If you need to suppress invocation when higher priority events are pending
  1566. you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
  1567. .Sp
  1568. You \fImust not\fR change the priority of a watcher as long as it is active or
  1569. pending.
  1570. .Sp
  1571. Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
  1572. fine, as long as you do not mind that the priority value you query might
  1573. or might not have been clamped to the valid range.
  1574. .Sp
  1575. The default priority used by watchers when no priority has been set is
  1576. always \f(CW0\fR, which is supposed to not be too high and not be too low :).
  1577. .Sp
  1578. See \*(L"\s-1WATCHER PRIORITY MODELS\*(R"\s0, below, for a more thorough treatment of
  1579. priorities.
  1580. .IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
  1581. .IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
  1582. Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
  1583. \&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
  1584. can deal with that fact, as both are simply passed through to the
  1585. callback.
  1586. .IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
  1587. .IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
  1588. If the watcher is pending, this function clears its pending status and
  1589. returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
  1590. watcher isn't pending it does nothing and returns \f(CW0\fR.
  1591. .Sp
  1592. Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
  1593. callback to be invoked, which can be accomplished with this function.
  1594. .IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
  1595. .IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
  1596. Feeds the given event set into the event loop, as if the specified event
  1597. had happened for the specified watcher (which must be a pointer to an
  1598. initialised but not necessarily started event watcher). Obviously you must
  1599. not free the watcher as long as it has pending events.
  1600. .Sp
  1601. Stopping the watcher, letting libev invoke it, or calling
  1602. \&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
  1603. not started in the first place.
  1604. .Sp
  1605. See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
  1606. functions that do not need a watcher.
  1607. .PP
  1608. See also the \*(L"\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\*(R"\s0 and \*(L"\s-1BUILDING YOUR
  1609. OWN COMPOSITE WATCHERS\*(R"\s0 idioms.
  1610. .SS "\s-1WATCHER STATES\s0"
  1611. .IX Subsection "WATCHER STATES"
  1612. There are various watcher states mentioned throughout this manual \-
  1613. active, pending and so on. In this section these states and the rules to
  1614. transition between them will be described in more detail \- and while these
  1615. rules might look complicated, they usually do \*(L"the right thing\*(R".
  1616. .IP "initialised" 4
  1617. .IX Item "initialised"
  1618. Before a watcher can be registered with the event loop it has to be
  1619. initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
  1620. \&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
  1621. .Sp
  1622. In this state it is simply some block of memory that is suitable for
  1623. use in an event loop. It can be moved around, freed, reused etc. at
  1624. will \- as long as you either keep the memory contents intact, or call
  1625. \&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
  1626. .IP "started/running/active" 4
  1627. .IX Item "started/running/active"
  1628. Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
  1629. property of the event loop, and is actively waiting for events. While in
  1630. this state it cannot be accessed (except in a few documented ways), moved,
  1631. freed or anything else \- the only legal thing is to keep a pointer to it,
  1632. and call libev functions on it that are documented to work on active watchers.
  1633. .IP "pending" 4
  1634. .IX Item "pending"
  1635. If a watcher is active and libev determines that an event it is interested
  1636. in has occurred (such as a timer expiring), it will become pending. It will
  1637. stay in this pending state until either it is stopped or its callback is
  1638. about to be invoked, so it is not normally pending inside the watcher
  1639. callback.
  1640. .Sp
  1641. The watcher might or might not be active while it is pending (for example,
  1642. an expired non-repeating timer can be pending but no longer active). If it
  1643. is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
  1644. but it is still property of the event loop at this time, so cannot be
  1645. moved, freed or reused. And if it is active the rules described in the
  1646. previous item still apply.
  1647. .Sp
  1648. It is also possible to feed an event on a watcher that is not active (e.g.
  1649. via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
  1650. active.
  1651. .IP "stopped" 4
  1652. .IX Item "stopped"
  1653. A watcher can be stopped implicitly by libev (in which case it might still
  1654. be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
  1655. latter will clear any pending state the watcher might be in, regardless
  1656. of whether it was active or not, so stopping a watcher explicitly before
  1657. freeing it is often a good idea.
  1658. .Sp
  1659. While stopped (and not pending) the watcher is essentially in the
  1660. initialised state, that is, it can be reused, moved, modified in any way
  1661. you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
  1662. it again).
  1664. .IX Subsection "WATCHER PRIORITY MODELS"
  1665. Many event loops support \fIwatcher priorities\fR, which are usually small
  1666. integers that influence the ordering of event callback invocation
  1667. between watchers in some way, all else being equal.
  1668. .PP
  1669. In libev, watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
  1670. description for the more technical details such as the actual priority
  1671. range.
  1672. .PP
  1673. There are two common ways how these these priorities are being interpreted
  1674. by event loops:
  1675. .PP
  1676. In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
  1677. of lower priority watchers, which means as long as higher priority
  1678. watchers receive events, lower priority watchers are not being invoked.
  1679. .PP
  1680. The less common only-for-ordering model uses priorities solely to order
  1681. callback invocation within a single event loop iteration: Higher priority
  1682. watchers are invoked before lower priority ones, but they all get invoked
  1683. before polling for new events.
  1684. .PP
  1685. Libev uses the second (only-for-ordering) model for all its watchers
  1686. except for idle watchers (which use the lock-out model).
  1687. .PP
  1688. The rationale behind this is that implementing the lock-out model for
  1689. watchers is not well supported by most kernel interfaces, and most event
  1690. libraries will just poll for the same events again and again as long as
  1691. their callbacks have not been executed, which is very inefficient in the
  1692. common case of one high-priority watcher locking out a mass of lower
  1693. priority ones.
  1694. .PP
  1695. Static (ordering) priorities are most useful when you have two or more
  1696. watchers handling the same resource: a typical usage example is having an
  1697. \&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
  1698. timeouts. Under load, data might be received while the program handles
  1699. other jobs, but since timers normally get invoked first, the timeout
  1700. handler will be executed before checking for data. In that case, giving
  1701. the timer a lower priority than the I/O watcher ensures that I/O will be
  1702. handled first even under adverse conditions (which is usually, but not
  1703. always, what you want).
  1704. .PP
  1705. Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
  1706. will only be executed when no same or higher priority watchers have
  1707. received events, they can be used to implement the \*(L"lock-out\*(R" model when
  1708. required.
  1709. .PP
  1710. For example, to emulate how many other event libraries handle priorities,
  1711. you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
  1712. the normal watcher callback, you just start the idle watcher. The real
  1713. processing is done in the idle watcher callback. This causes libev to
  1714. continuously poll and process kernel event data for the watcher, but when
  1715. the lock-out case is known to be rare (which in turn is rare :), this is
  1716. workable.
  1717. .PP
  1718. Usually, however, the lock-out model implemented that way will perform
  1719. miserably under the type of load it was designed to handle. In that case,
  1720. it might be preferable to stop the real watcher before starting the
  1721. idle watcher, so the kernel will not have to process the event in case
  1722. the actual processing will be delayed for considerable time.
  1723. .PP
  1724. Here is an example of an I/O watcher that should run at a strictly lower
  1725. priority than the default, and which should only process data when no
  1726. other events are pending:
  1727. .PP
  1728. .Vb 2
  1729. \& ev_idle idle; // actual processing watcher
  1730. \& ev_io io; // actual event watcher
  1731. \&
  1732. \& static void
  1733. \& io_cb (EV_P_ ev_io *w, int revents)
  1734. \& {
  1735. \& // stop the I/O watcher, we received the event, but
  1736. \& // are not yet ready to handle it.
  1737. \& ev_io_stop (EV_A_ w);
  1738. \&
  1739. \& // start the idle watcher to handle the actual event.
  1740. \& // it will not be executed as long as other watchers
  1741. \& // with the default priority are receiving events.
  1742. \& ev_idle_start (EV_A_ &idle);
  1743. \& }
  1744. \&
  1745. \& static void
  1746. \& idle_cb (EV_P_ ev_idle *w, int revents)
  1747. \& {
  1748. \& // actual processing
  1749. \& read (STDIN_FILENO, ...);
  1750. \&
  1751. \& // have to start the I/O watcher again, as
  1752. \& // we have handled the event
  1753. \& ev_io_start (EV_P_ &io);
  1754. \& }
  1755. \&
  1756. \& // initialisation
  1757. \& ev_idle_init (&idle, idle_cb);
  1758. \& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
  1759. \& ev_io_start (EV_DEFAULT_ &io);
  1760. .Ve
  1761. .PP
  1762. In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
  1763. low-priority connections can not be locked out forever under load. This
  1764. enables your program to keep a lower latency for important connections
  1765. during short periods of high load, while not completely locking out less
  1766. important ones.
  1768. .IX Header "WATCHER TYPES"
  1769. This section describes each watcher in detail, but will not repeat
  1770. information given in the last section. Any initialisation/set macros,
  1771. functions and members specific to the watcher type are explained.
  1772. .PP
  1773. Most members are additionally marked with either \fI[read\-only]\fR, meaning
  1774. that, while the watcher is active, you can look at the member and expect
  1775. some sensible content, but you must not modify it (you can modify it while
  1776. the watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
  1777. means you can expect it to have some sensible content while the watcher
  1778. is active, but you can also modify it. Modifying it may not do something
  1779. sensible or take immediate effect (or do anything at all), but libev will
  1780. not crash or malfunction in any way.
  1781. .PP
  1782. In any case, the documentation for each member will explain what the
  1783. effects are, and if there are any additional access restrictions.
  1784. .ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
  1785. .el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
  1786. .IX Subsection "ev_io - is this file descriptor readable or writable?"
  1787. I/O watchers check whether a file descriptor is readable or writable
  1788. in each iteration of the event loop, or, more precisely, when reading
  1789. would not block the process and writing would at least be able to write
  1790. some data. This behaviour is called level-triggering because you keep
  1791. receiving events as long as the condition persists. Remember you can stop
  1792. the watcher if you don't want to act on the event and neither want to
  1793. receive future events.
  1794. .PP
  1795. In general you can register as many read and/or write event watchers per
  1796. fd as you want (as long as you don't confuse yourself). Setting all file
  1797. descriptors to non-blocking mode is also usually a good idea (but not
  1798. required if you know what you are doing).
  1799. .PP
  1800. Another thing you have to watch out for is that it is quite easy to
  1801. receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
  1802. be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
  1803. because there is no data. It is very easy to get into this situation even
  1804. with a relatively standard program structure. Thus it is best to always
  1805. use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
  1806. preferable to a program hanging until some data arrives.
  1807. .PP
  1808. If you cannot run the fd in non-blocking mode (for example you should
  1809. not play around with an Xlib connection), then you have to separately
  1810. re-test whether a file descriptor is really ready with a known-to-be good
  1811. interface such as poll (fortunately in the case of Xlib, it already does
  1812. this on its own, so its quite safe to use). Some people additionally
  1813. use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
  1814. indefinitely.
  1815. .PP
  1816. But really, best use non-blocking mode.
  1817. .PP
  1818. \fIThe special problem of disappearing file descriptors\fR
  1819. .IX Subsection "The special problem of disappearing file descriptors"
  1820. .PP
  1821. Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
  1822. a file descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other
  1823. means, such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some
  1824. file descriptor, but when it goes away, the operating system will silently
  1825. drop this interest. If another file descriptor with the same number then
  1826. is registered with libev, there is no efficient way to see that this is,
  1827. in fact, a different file descriptor.
  1828. .PP
  1829. To avoid having to explicitly tell libev about such cases, libev follows
  1830. the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
  1831. will assume that this is potentially a new file descriptor, otherwise
  1832. it is assumed that the file descriptor stays the same. That means that
  1833. you \fIhave\fR to call \f(CW\*(C`ev_io_set\*(C'\fR (or \f(CW\*(C`ev_io_init\*(C'\fR) when you change the
  1834. descriptor even if the file descriptor number itself did not change.
  1835. .PP
  1836. This is how one would do it normally anyway, the important point is that
  1837. the libev application should not optimise around libev but should leave
  1838. optimisations to libev.
  1839. .PP
  1840. \fIThe special problem of dup'ed file descriptors\fR
  1841. .IX Subsection "The special problem of dup'ed file descriptors"
  1842. .PP
  1843. Some backends (e.g. epoll), cannot register events for file descriptors,
  1844. but only events for the underlying file descriptions. That means when you
  1845. have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
  1846. events for them, only one file descriptor might actually receive events.
  1847. .PP
  1848. There is no workaround possible except not registering events
  1849. for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
  1850. \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
  1851. .PP
  1852. \fIThe special problem of files\fR
  1853. .IX Subsection "The special problem of files"
  1854. .PP
  1855. Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
  1856. representing files, and expect it to become ready when their program
  1857. doesn't block on disk accesses (which can take a long time on their own).
  1858. .PP
  1859. However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
  1860. notification as soon as the kernel knows whether and how much data is
  1861. there, and in the case of open files, that's always the case, so you
  1862. always get a readiness notification instantly, and your read (or possibly
  1863. write) will still block on the disk I/O.
  1864. .PP
  1865. Another way to view it is that in the case of sockets, pipes, character
  1866. devices and so on, there is another party (the sender) that delivers data
  1867. on its own, but in the case of files, there is no such thing: the disk
  1868. will not send data on its own, simply because it doesn't know what you
  1869. wish to read \- you would first have to request some data.
  1870. .PP
  1871. Since files are typically not-so-well supported by advanced notification
  1872. mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
  1873. to files, even though you should not use it. The reason for this is
  1874. convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT,\s0 which is
  1875. usually a tty, often a pipe, but also sometimes files or special devices
  1876. (for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
  1877. \&\fI/dev/urandom\fR), and even though the file might better be served with
  1878. asynchronous I/O instead of with non-blocking I/O, it is still useful when
  1879. it \*(L"just works\*(R" instead of freezing.
  1880. .PP
  1881. So avoid file descriptors pointing to files when you know it (e.g. use
  1882. libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT,\s0 or
  1883. when you rarely read from a file instead of from a socket, and want to
  1884. reuse the same code path.
  1885. .PP
  1886. \fIThe special problem of fork\fR
  1887. .IX Subsection "The special problem of fork"
  1888. .PP
  1889. Some backends (epoll, kqueue, linuxaio, iouring) do not support \f(CW\*(C`fork ()\*(C'\fR
  1890. at all or exhibit useless behaviour. Libev fully supports fork, but needs
  1891. to be told about it in the child if you want to continue to use it in the
  1892. child.
  1893. .PP
  1894. To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
  1895. ()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
  1896. \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
  1897. .PP
  1898. \fIThe special problem of \s-1SIGPIPE\s0\fR
  1899. .IX Subsection "The special problem of SIGPIPE"
  1900. .PP
  1901. While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
  1902. when writing to a pipe whose other end has been closed, your program gets
  1903. sent a \s-1SIGPIPE,\s0 which, by default, aborts your program. For most programs
  1904. this is sensible behaviour, for daemons, this is usually undesirable.
  1905. .PP
  1906. So when you encounter spurious, unexplained daemon exits, make sure you
  1907. ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
  1908. somewhere, as that would have given you a big clue).
  1909. .PP
  1910. \fIThe special problem of \f(BIaccept()\fIing when you can't\fR
  1911. .IX Subsection "The special problem of accept()ing when you can't"
  1912. .PP
  1913. Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
  1914. found in post\-2004 Linux) have the peculiar behaviour of not removing a
  1915. connection from the pending queue in all error cases.
  1916. .PP
  1917. For example, larger servers often run out of file descriptors (because
  1918. of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
  1919. rejecting the connection, leading to libev signalling readiness on
  1920. the next iteration again (the connection still exists after all), and
  1921. typically causing the program to loop at 100% \s-1CPU\s0 usage.
  1922. .PP
  1923. Unfortunately, the set of errors that cause this issue differs between
  1924. operating systems, there is usually little the app can do to remedy the
  1925. situation, and no known thread-safe method of removing the connection to
  1926. cope with overload is known (to me).
  1927. .PP
  1928. One of the easiest ways to handle this situation is to just ignore it
  1929. \&\- when the program encounters an overload, it will just loop until the
  1930. situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
  1931. event-based way to handle this situation, so it's the best one can do.
  1932. .PP
  1933. A better way to handle the situation is to log any errors other than
  1934. \&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
  1935. messages, and continue as usual, which at least gives the user an idea of
  1936. what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
  1937. the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
  1938. usage.
  1939. .PP
  1940. If your program is single-threaded, then you could also keep a dummy file
  1941. descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
  1942. when you run into \f(CW\*(C`ENFILE\*(C'\fR or \f(CW\*(C`EMFILE\*(C'\fR, close it, run \f(CW\*(C`accept\*(C'\fR,
  1943. close that fd, and create a new dummy fd. This will gracefully refuse
  1944. clients under typical overload conditions.
  1945. .PP
  1946. The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
  1947. is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
  1948. opportunity for a DoS attack.
  1949. .PP
  1950. \fIWatcher-Specific Functions\fR
  1951. .IX Subsection "Watcher-Specific Functions"
  1952. .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
  1953. .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
  1954. .PD 0
  1955. .IP "ev_io_set (ev_io *, int fd, int events)" 4
  1956. .IX Item "ev_io_set (ev_io *, int fd, int events)"
  1957. .PD
  1958. Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
  1959. receive events for and \f(CW\*(C`events\*(C'\fR is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR, both
  1960. \&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR or \f(CW0\fR, to express the desire to receive the given
  1961. events.
  1962. .Sp
  1963. Note that setting the \f(CW\*(C`events\*(C'\fR to \f(CW0\fR and starting the watcher is
  1964. supported, but not specially optimized \- if your program sometimes happens
  1965. to generate this combination this is fine, but if it is easy to avoid
  1966. starting an io watcher watching for no events you should do so.
  1967. .IP "ev_io_modify (ev_io *, int events)" 4
  1968. .IX Item "ev_io_modify (ev_io *, int events)"
  1969. Similar to \f(CW\*(C`ev_io_set\*(C'\fR, but only changes the event mask. Using this might
  1970. be faster with some backends, as libev can assume that the \f(CW\*(C`fd\*(C'\fR still
  1971. refers to the same underlying file description, something it cannot do
  1972. when using \f(CW\*(C`ev_io_set\*(C'\fR.
  1973. .IP "int fd [no\-modify]" 4
  1974. .IX Item "int fd [no-modify]"
  1975. The file descriptor being watched. While it can be read at any time, you
  1976. must not modify this member even when the watcher is stopped \- always use
  1977. \&\f(CW\*(C`ev_io_set\*(C'\fR for that.
  1978. .IP "int events [no\-modify]" 4
  1979. .IX Item "int events [no-modify]"
  1980. The set of events the fd is being watched for, among other flags. Remember
  1981. that this is a bit set \- to test for \f(CW\*(C`EV_READ\*(C'\fR, use \f(CW\*(C`w\->events &
  1982. EV_READ\*(C'\fR, and similarly for \f(CW\*(C`EV_WRITE\*(C'\fR.
  1983. .Sp
  1984. As with \f(CW\*(C`fd\*(C'\fR, you must not modify this member even when the watcher is
  1985. stopped, always use \f(CW\*(C`ev_io_set\*(C'\fR or \f(CW\*(C`ev_io_modify\*(C'\fR for that.
  1986. .PP
  1987. \fIExamples\fR
  1988. .IX Subsection "Examples"
  1989. .PP
  1990. Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
  1991. readable, but only once. Since it is likely line-buffered, you could
  1992. attempt to read a whole line in the callback.
  1993. .PP
  1994. .Vb 6
  1995. \& static void
  1996. \& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
  1997. \& {
  1998. \& ev_io_stop (loop, w);
  1999. \& .. read from stdin here (or from w\->fd) and handle any I/O errors
  2000. \& }
  2001. \&
  2002. \& ...
  2003. \& struct ev_loop *loop = ev_default_init (0);
  2004. \& ev_io stdin_readable;
  2005. \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
  2006. \& ev_io_start (loop, &stdin_readable);
  2007. \& ev_run (loop, 0);
  2008. .Ve
  2009. .ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
  2010. .el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
  2011. .IX Subsection "ev_timer - relative and optionally repeating timeouts"
  2012. Timer watchers are simple relative timers that generate an event after a
  2013. given time, and optionally repeating in regular intervals after that.
  2014. .PP
  2015. The timers are based on real time, that is, if you register an event that
  2016. times out after an hour and you reset your system clock to January last
  2017. year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
  2018. detecting time jumps is hard, and some inaccuracies are unavoidable (the
  2019. monotonic clock option helps a lot here).
  2020. .PP
  2021. The callback is guaranteed to be invoked only \fIafter\fR its timeout has
  2022. passed (not \fIat\fR, so on systems with very low-resolution clocks this
  2023. might introduce a small delay, see \*(L"the special problem of being too
  2024. early\*(R", below). If multiple timers become ready during the same loop
  2025. iteration then the ones with earlier time-out values are invoked before
  2026. ones of the same priority with later time-out values (but this is no
  2027. longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
  2028. .PP
  2029. \fIBe smart about timeouts\fR
  2030. .IX Subsection "Be smart about timeouts"
  2031. .PP
  2032. Many real-world problems involve some kind of timeout, usually for error
  2033. recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
  2034. you want to raise some error after a while.
  2035. .PP
  2036. What follows are some ways to handle this problem, from obvious and
  2037. inefficient to smart and efficient.
  2038. .PP
  2039. In the following, a 60 second activity timeout is assumed \- a timeout that
  2040. gets reset to 60 seconds each time there is activity (e.g. each time some
  2041. data or other life sign was received).
  2042. .IP "1. Use a timer and stop, reinitialise and start it on activity." 4
  2043. .IX Item "1. Use a timer and stop, reinitialise and start it on activity."
  2044. This is the most obvious, but not the most simple way: In the beginning,
  2045. start the watcher:
  2046. .Sp
  2047. .Vb 2
  2048. \& ev_timer_init (timer, callback, 60., 0.);
  2049. \& ev_timer_start (loop, timer);
  2050. .Ve
  2051. .Sp
  2052. Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
  2053. and start it again:
  2054. .Sp
  2055. .Vb 3
  2056. \& ev_timer_stop (loop, timer);
  2057. \& ev_timer_set (timer, 60., 0.);
  2058. \& ev_timer_start (loop, timer);
  2059. .Ve
  2060. .Sp
  2061. This is relatively simple to implement, but means that each time there is
  2062. some activity, libev will first have to remove the timer from its internal
  2063. data structure and then add it again. Libev tries to be fast, but it's
  2064. still not a constant-time operation.
  2065. .ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
  2066. .el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
  2067. .IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
  2068. This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
  2069. \&\f(CW\*(C`ev_timer_start\*(C'\fR.
  2070. .Sp
  2071. To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
  2072. of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
  2073. successfully read or write some data. If you go into an idle state where
  2074. you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
  2075. the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
  2076. .Sp
  2077. That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
  2078. \&\f(CW\*(C`after\*(C'\fR argument to \f(CW\*(C`ev_timer_set\*(C'\fR, and only ever use the \f(CW\*(C`repeat\*(C'\fR
  2079. member and \f(CW\*(C`ev_timer_again\*(C'\fR.
  2080. .Sp
  2081. At start:
  2082. .Sp
  2083. .Vb 3
  2084. \& ev_init (timer, callback);
  2085. \& timer\->repeat = 60.;
  2086. \& ev_timer_again (loop, timer);
  2087. .Ve
  2088. .Sp
  2089. Each time there is some activity:
  2090. .Sp
  2091. .Vb 1
  2092. \& ev_timer_again (loop, timer);
  2093. .Ve
  2094. .Sp
  2095. It is even possible to change the time-out on the fly, regardless of
  2096. whether the watcher is active or not:
  2097. .Sp
  2098. .Vb 2
  2099. \& timer\->repeat = 30.;
  2100. \& ev_timer_again (loop, timer);
  2101. .Ve
  2102. .Sp
  2103. This is slightly more efficient then stopping/starting the timer each time
  2104. you want to modify its timeout value, as libev does not have to completely
  2105. remove and re-insert the timer from/into its internal data structure.
  2106. .Sp
  2107. It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
  2108. .IP "3. Let the timer time out, but then re-arm it as required." 4
  2109. .IX Item "3. Let the timer time out, but then re-arm it as required."
  2110. This method is more tricky, but usually most efficient: Most timeouts are
  2111. relatively long compared to the intervals between other activity \- in
  2112. our example, within 60 seconds, there are usually many I/O events with
  2113. associated activity resets.
  2114. .Sp
  2115. In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
  2116. but remember the time of last activity, and check for a real timeout only
  2117. within the callback:
  2118. .Sp
  2119. .Vb 3
  2120. \& ev_tstamp timeout = 60.;
  2121. \& ev_tstamp last_activity; // time of last activity
  2122. \& ev_timer timer;
  2123. \&
  2124. \& static void
  2125. \& callback (EV_P_ ev_timer *w, int revents)
  2126. \& {
  2127. \& // calculate when the timeout would happen
  2128. \& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
  2129. \&
  2130. \& // if negative, it means we the timeout already occurred
  2131. \& if (after < 0.)
  2132. \& {
  2133. \& // timeout occurred, take action
  2134. \& }
  2135. \& else
  2136. \& {
  2137. \& // callback was invoked, but there was some recent
  2138. \& // activity. simply restart the timer to time out
  2139. \& // after "after" seconds, which is the earliest time
  2140. \& // the timeout can occur.
  2141. \& ev_timer_set (w, after, 0.);
  2142. \& ev_timer_start (EV_A_ w);
  2143. \& }
  2144. \& }
  2145. .Ve
  2146. .Sp
  2147. To summarise the callback: first calculate in how many seconds the
  2148. timeout will occur (by calculating the absolute time when it would occur,
  2149. \&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
  2150. (EV_A)\*(C'\fR from that).
  2151. .Sp
  2152. If this value is negative, then we are already past the timeout, i.e. we
  2153. timed out, and need to do whatever is needed in this case.
  2154. .Sp
  2155. Otherwise, we now the earliest time at which the timeout would trigger,
  2156. and simply start the timer with this timeout value.
  2157. .Sp
  2158. In other words, each time the callback is invoked it will check whether
  2159. the timeout occurred. If not, it will simply reschedule itself to check
  2160. again at the earliest time it could time out. Rinse. Repeat.
  2161. .Sp
  2162. This scheme causes more callback invocations (about one every 60 seconds
  2163. minus half the average time between activity), but virtually no calls to
  2164. libev to change the timeout.
  2165. .Sp
  2166. To start the machinery, simply initialise the watcher and set
  2167. \&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
  2168. now), then call the callback, which will \*(L"do the right thing\*(R" and start
  2169. the timer:
  2170. .Sp
  2171. .Vb 3
  2172. \& last_activity = ev_now (EV_A);
  2173. \& ev_init (&timer, callback);
  2174. \& callback (EV_A_ &timer, 0);
  2175. .Ve
  2176. .Sp
  2177. When there is some activity, simply store the current time in
  2178. \&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
  2179. .Sp
  2180. .Vb 2
  2181. \& if (activity detected)
  2182. \& last_activity = ev_now (EV_A);
  2183. .Ve
  2184. .Sp
  2185. When your timeout value changes, then the timeout can be changed by simply
  2186. providing a new value, stopping the timer and calling the callback, which
  2187. will again do the right thing (for example, time out immediately :).
  2188. .Sp
  2189. .Vb 3
  2190. \& timeout = new_value;
  2191. \& ev_timer_stop (EV_A_ &timer);
  2192. \& callback (EV_A_ &timer, 0);
  2193. .Ve
  2194. .Sp
  2195. This technique is slightly more complex, but in most cases where the
  2196. time-out is unlikely to be triggered, much more efficient.
  2197. .IP "4. Wee, just use a double-linked list for your timeouts." 4
  2198. .IX Item "4. Wee, just use a double-linked list for your timeouts."
  2199. If there is not one request, but many thousands (millions...), all
  2200. employing some kind of timeout with the same timeout value, then one can
  2201. do even better:
  2202. .Sp
  2203. When starting the timeout, calculate the timeout value and put the timeout
  2204. at the \fIend\fR of the list.
  2205. .Sp
  2206. Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
  2207. the list is expected to fire (for example, using the technique #3).
  2208. .Sp
  2209. When there is some activity, remove the timer from the list, recalculate
  2210. the timeout, append it to the end of the list again, and make sure to
  2211. update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
  2212. .Sp
  2213. This way, one can manage an unlimited number of timeouts in O(1) time for
  2214. starting, stopping and updating the timers, at the expense of a major
  2215. complication, and having to use a constant timeout. The constant timeout
  2216. ensures that the list stays sorted.
  2217. .PP
  2218. So which method the best?
  2219. .PP
  2220. Method #2 is a simple no-brain-required solution that is adequate in most
  2221. situations. Method #3 requires a bit more thinking, but handles many cases
  2222. better, and isn't very complicated either. In most case, choosing either
  2223. one is fine, with #3 being better in typical situations.
  2224. .PP
  2225. Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
  2226. rather complicated, but extremely efficient, something that really pays
  2227. off after the first million or so of active timers, i.e. it's usually
  2228. overkill :)
  2229. .PP
  2230. \fIThe special problem of being too early\fR
  2231. .IX Subsection "The special problem of being too early"
  2232. .PP
  2233. If you ask a timer to call your callback after three seconds, then
  2234. you expect it to be invoked after three seconds \- but of course, this
  2235. cannot be guaranteed to infinite precision. Less obviously, it cannot be
  2236. guaranteed to any precision by libev \- imagine somebody suspending the
  2237. process with a \s-1STOP\s0 signal for a few hours for example.
  2238. .PP
  2239. So, libev tries to invoke your callback as soon as possible \fIafter\fR the
  2240. delay has occurred, but cannot guarantee this.
  2241. .PP
  2242. A less obvious failure mode is calling your callback too early: many event
  2243. loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
  2244. this can cause your callback to be invoked much earlier than you would
  2245. expect.
  2246. .PP
  2247. To see why, imagine a system with a clock that only offers full second
  2248. resolution (think windows if you can't come up with a broken enough \s-1OS\s0
  2249. yourself). If you schedule a one-second timer at the time 500.9, then the
  2250. event loop will schedule your timeout to elapse at a system time of 500
  2251. (500.9 truncated to the resolution) + 1, or 501.
  2252. .PP
  2253. If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
  2254. 501\*(R" and invoke the callback 0.1s after it was started, even though a
  2255. one-second delay was requested \- this is being \*(L"too early\*(R", despite best
  2256. intentions.
  2257. .PP
  2258. This is the reason why libev will never invoke the callback if the elapsed
  2259. delay equals the requested delay, but only when the elapsed delay is
  2260. larger than the requested delay. In the example above, libev would only invoke
  2261. the callback at system time 502, or 1.1s after the timer was started.
  2262. .PP
  2263. So, while libev cannot guarantee that your callback will be invoked
  2264. exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
  2265. delay has actually elapsed, or in other words, it always errs on the \*(L"too
  2266. late\*(R" side of things.
  2267. .PP
  2268. \fIThe special problem of time updates\fR
  2269. .IX Subsection "The special problem of time updates"
  2270. .PP
  2271. Establishing the current time is a costly operation (it usually takes
  2272. at least one system call): \s-1EV\s0 therefore updates its idea of the current
  2273. time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
  2274. growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
  2275. lots of events in one iteration.
  2276. .PP
  2277. The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
  2278. time. This is usually the right thing as this timestamp refers to the time
  2279. of the event triggering whatever timeout you are modifying/starting. If
  2280. you suspect event processing to be delayed and you \fIneed\fR to base the
  2281. timeout on the current time, use something like the following to adjust
  2282. for it:
  2283. .PP
  2284. .Vb 1
  2285. \& ev_timer_set (&timer, after + (ev_time () \- ev_now ()), 0.);
  2286. .Ve
  2287. .PP
  2288. If the event loop is suspended for a long time, you can also force an
  2289. update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
  2290. ()\*(C'\fR, although that will push the event time of all outstanding events
  2291. further into the future.
  2292. .PP
  2293. \fIThe special problem of unsynchronised clocks\fR
  2294. .IX Subsection "The special problem of unsynchronised clocks"
  2295. .PP
  2296. Modern systems have a variety of clocks \- libev itself uses the normal
  2297. \&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
  2298. jumps).
  2299. .PP
  2300. Neither of these clocks is synchronised with each other or any other clock
  2301. on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
  2302. than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
  2303. a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
  2304. than a directly following call to \f(CW\*(C`time\*(C'\fR.
  2305. .PP
  2306. The moral of this is to only compare libev-related timestamps with
  2307. \&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
  2308. a second or so.
  2309. .PP
  2310. One more problem arises due to this lack of synchronisation: if libev uses
  2311. the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
  2312. or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
  2313. invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
  2314. .PP
  2315. This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
  2316. libev makes sure your callback is not invoked before the delay happened,
  2317. \&\fImeasured according to the real time\fR, not the system clock.
  2318. .PP
  2319. If your timeouts are based on a physical timescale (e.g. \*(L"time out this
  2320. connection after 100 seconds\*(R") then this shouldn't bother you as it is
  2321. exactly the right behaviour.
  2322. .PP
  2323. If you want to compare wall clock/system timestamps to your timers, then
  2324. you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
  2325. time, where your comparisons will always generate correct results.
  2326. .PP
  2327. \fIThe special problems of suspended animation\fR
  2328. .IX Subsection "The special problems of suspended animation"
  2329. .PP
  2330. When you leave the server world it is quite customary to hit machines that
  2331. can suspend/hibernate \- what happens to the clocks during such a suspend?
  2332. .PP
  2333. Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
  2334. all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
  2335. to run until the system is suspended, but they will not advance while the
  2336. system is suspended. That means, on resume, it will be as if the program
  2337. was frozen for a few seconds, but the suspend time will not be counted
  2338. towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
  2339. clock advanced as expected, but if it is used as sole clocksource, then a
  2340. long suspend would be detected as a time jump by libev, and timers would
  2341. be adjusted accordingly.
  2342. .PP
  2343. I would not be surprised to see different behaviour in different between
  2344. operating systems, \s-1OS\s0 versions or even different hardware.
  2345. .PP
  2346. The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
  2347. time jump in the monotonic clocks and the realtime clock. If the program
  2348. is suspended for a very long time, and monotonic clock sources are in use,
  2349. then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
  2350. will be counted towards the timers. When no monotonic clock source is in
  2351. use, then libev will again assume a timejump and adjust accordingly.
  2352. .PP
  2353. It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
  2354. and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
  2355. deterministic behaviour in this case (you can do nothing against
  2356. \&\f(CW\*(C`SIGSTOP\*(C'\fR).
  2357. .PP
  2358. \fIWatcher-Specific Functions and Data Members\fR
  2359. .IX Subsection "Watcher-Specific Functions and Data Members"
  2360. .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
  2361. .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
  2362. .PD 0
  2363. .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
  2364. .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
  2365. .PD
  2366. Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds (fractional and
  2367. negative values are supported). If \f(CW\*(C`repeat\*(C'\fR is \f(CW0.\fR, then it will
  2368. automatically be stopped once the timeout is reached. If it is positive,
  2369. then the timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR
  2370. seconds later, again, and again, until stopped manually.
  2371. .Sp
  2372. The timer itself will do a best-effort at avoiding drift, that is, if
  2373. you configure a timer to trigger every 10 seconds, then it will normally
  2374. trigger at exactly 10 second intervals. If, however, your program cannot
  2375. keep up with the timer (because it takes longer than those 10 seconds to
  2376. do stuff) the timer will not fire more than once per event loop iteration.
  2377. .IP "ev_timer_again (loop, ev_timer *)" 4
  2378. .IX Item "ev_timer_again (loop, ev_timer *)"
  2379. This will act as if the timer timed out, and restarts it again if it is
  2380. repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
  2381. timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
  2382. .Sp
  2383. The exact semantics are as in the following rules, all of which will be
  2384. applied to the watcher:
  2385. .RS 4
  2386. .IP "If the timer is pending, the pending status is always cleared." 4
  2387. .IX Item "If the timer is pending, the pending status is always cleared."
  2388. .PD 0
  2389. .IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
  2390. .IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
  2391. .ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
  2392. .el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
  2393. .IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
  2394. .RE
  2395. .RS 4
  2396. .PD
  2397. .Sp
  2398. This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
  2399. usage example.
  2400. .RE
  2401. .IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
  2402. .IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
  2403. Returns the remaining time until a timer fires. If the timer is active,
  2404. then this time is relative to the current event loop time, otherwise it's
  2405. the timeout value currently configured.
  2406. .Sp
  2407. That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
  2408. \&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
  2409. will return \f(CW4\fR. When the timer expires and is restarted, it will return
  2410. roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
  2411. too), and so on.
  2412. .IP "ev_tstamp repeat [read\-write]" 4
  2413. .IX Item "ev_tstamp repeat [read-write]"
  2414. The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
  2415. or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
  2416. which is also when any modifications are taken into account.
  2417. .PP
  2418. \fIExamples\fR
  2419. .IX Subsection "Examples"
  2420. .PP
  2421. Example: Create a timer that fires after 60 seconds.
  2422. .PP
  2423. .Vb 5
  2424. \& static void
  2425. \& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
  2426. \& {
  2427. \& .. one minute over, w is actually stopped right here
  2428. \& }
  2429. \&
  2430. \& ev_timer mytimer;
  2431. \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
  2432. \& ev_timer_start (loop, &mytimer);
  2433. .Ve
  2434. .PP
  2435. Example: Create a timeout timer that times out after 10 seconds of
  2436. inactivity.
  2437. .PP
  2438. .Vb 5
  2439. \& static void
  2440. \& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
  2441. \& {
  2442. \& .. ten seconds without any activity
  2443. \& }
  2444. \&
  2445. \& ev_timer mytimer;
  2446. \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
  2447. \& ev_timer_again (&mytimer); /* start timer */
  2448. \& ev_run (loop, 0);
  2449. \&
  2450. \& // and in some piece of code that gets executed on any "activity":
  2451. \& // reset the timeout to start ticking again at 10 seconds
  2452. \& ev_timer_again (&mytimer);
  2453. .Ve
  2454. .ie n .SS """ev_periodic"" \- to cron or not to cron?"
  2455. .el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
  2456. .IX Subsection "ev_periodic - to cron or not to cron?"
  2457. Periodic watchers are also timers of a kind, but they are very versatile
  2458. (and unfortunately a bit complex).
  2459. .PP
  2460. Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
  2461. relative time, the physical time that passes) but on wall clock time
  2462. (absolute time, the thing you can read on your calendar or clock). The
  2463. difference is that wall clock time can run faster or slower than real
  2464. time, and time jumps are not uncommon (e.g. when you adjust your
  2465. wrist-watch).
  2466. .PP
  2467. You can tell a periodic watcher to trigger after some specific point
  2468. in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
  2469. seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
  2470. not a delay) and then reset your system clock to January of the previous
  2471. year, then it will take a year or more to trigger the event (unlike an
  2472. \&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
  2473. it, as it uses a relative timeout).
  2474. .PP
  2475. \&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
  2476. timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
  2477. other complicated rules. This cannot easily be done with \f(CW\*(C`ev_timer\*(C'\fR
  2478. watchers, as those cannot react to time jumps.
  2479. .PP
  2480. As with timers, the callback is guaranteed to be invoked only when the
  2481. point in time where it is supposed to trigger has passed. If multiple
  2482. timers become ready during the same loop iteration then the ones with
  2483. earlier time-out values are invoked before ones with later time-out values
  2484. (but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
  2485. .PP
  2486. \fIWatcher-Specific Functions and Data Members\fR
  2487. .IX Subsection "Watcher-Specific Functions and Data Members"
  2488. .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
  2489. .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
  2490. .PD 0
  2491. .IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
  2492. .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
  2493. .PD
  2494. Lots of arguments, let's sort it out... There are basically three modes of
  2495. operation, and we will explain them from simplest to most complex:
  2496. .RS 4
  2497. .IP "\(bu" 4
  2498. absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
  2499. .Sp
  2500. In this configuration the watcher triggers an event after the wall clock
  2501. time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
  2502. time jump occurs, that is, if it is to be run at January 1st 2011 then it
  2503. will be stopped and invoked when the system clock reaches or surpasses
  2504. this point in time.
  2505. .IP "\(bu" 4
  2506. repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
  2507. .Sp
  2508. In this mode the watcher will always be scheduled to time out at the next
  2509. \&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
  2510. negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
  2511. argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
  2512. .Sp
  2513. This can be used to create timers that do not drift with respect to the
  2514. system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
  2515. hour, on the hour (with respect to \s-1UTC\s0):
  2516. .Sp
  2517. .Vb 1
  2518. \& ev_periodic_set (&periodic, 0., 3600., 0);
  2519. .Ve
  2520. .Sp
  2521. This doesn't mean there will always be 3600 seconds in between triggers,
  2522. but only that the callback will be called when the system time shows a
  2523. full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
  2524. by 3600.
  2525. .Sp
  2526. Another way to think about it (for the mathematically inclined) is that
  2527. \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
  2528. time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
  2529. .Sp
  2530. The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
  2531. interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
  2532. microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
  2533. at most a similar magnitude as the current time (say, within a factor of
  2534. ten). Typical values for offset are, in fact, \f(CW0\fR or something between
  2535. \&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
  2536. .Sp
  2537. Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
  2538. speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
  2539. will of course deteriorate. Libev itself tries to be exact to be about one
  2540. millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
  2541. .IP "\(bu" 4
  2542. manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
  2543. .Sp
  2544. In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
  2545. ignored. Instead, each time the periodic watcher gets scheduled, the
  2546. reschedule callback will be called with the watcher as first, and the
  2547. current time as second argument.
  2548. .Sp
  2549. \&\s-1NOTE:\s0 \fIThis callback \s-1MUST NOT\s0 stop or destroy any periodic watcher, ever,
  2550. or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
  2551. allowed by documentation here\fR.
  2552. .Sp
  2553. If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
  2554. it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
  2555. only event loop modification you are allowed to do).
  2556. .Sp
  2557. The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
  2558. *w, ev_tstamp now)\*(C'\fR, e.g.:
  2559. .Sp
  2560. .Vb 5
  2561. \& static ev_tstamp
  2562. \& my_rescheduler (ev_periodic *w, ev_tstamp now)
  2563. \& {
  2564. \& return now + 60.;
  2565. \& }
  2566. .Ve
  2567. .Sp
  2568. It must return the next time to trigger, based on the passed time value
  2569. (that is, the lowest time value larger than to the second argument). It
  2570. will usually be called just before the callback will be triggered, but
  2571. might be called at other times, too.
  2572. .Sp
  2573. \&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
  2574. equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
  2575. .Sp
  2576. This can be used to create very complex timers, such as a timer that
  2577. triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate
  2578. the next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for
  2579. this. Here is a (completely untested, no error checking) example on how to
  2580. do this:
  2581. .Sp
  2582. .Vb 1
  2583. \& #include <time.h>
  2584. \&
  2585. \& static ev_tstamp
  2586. \& my_rescheduler (ev_periodic *w, ev_tstamp now)
  2587. \& {
  2588. \& time_t tnow = (time_t)now;
  2589. \& struct tm tm;
  2590. \& localtime_r (&tnow, &tm);
  2591. \&
  2592. \& tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
  2593. \& ++tm.tm_mday; // midnight next day
  2594. \&
  2595. \& return mktime (&tm);
  2596. \& }
  2597. .Ve
  2598. .Sp
  2599. Note: this code might run into trouble on days that have more then two
  2600. midnights (beginning and end).
  2601. .RE
  2602. .RS 4
  2603. .RE
  2604. .IP "ev_periodic_again (loop, ev_periodic *)" 4
  2605. .IX Item "ev_periodic_again (loop, ev_periodic *)"
  2606. Simply stops and restarts the periodic watcher again. This is only useful
  2607. when you changed some parameters or the reschedule callback would return
  2608. a different time than the last time it was called (e.g. in a crond like
  2609. program when the crontabs have changed).
  2610. .IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
  2611. .IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
  2612. When active, returns the absolute time that the watcher is supposed
  2613. to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
  2614. \&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
  2615. rescheduling modes.
  2616. .IP "ev_tstamp offset [read\-write]" 4
  2617. .IX Item "ev_tstamp offset [read-write]"
  2618. When repeating, this contains the offset value, otherwise this is the
  2619. absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
  2620. although libev might modify this value for better numerical stability).
  2621. .Sp
  2622. Can be modified any time, but changes only take effect when the periodic
  2623. timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
  2624. .IP "ev_tstamp interval [read\-write]" 4
  2625. .IX Item "ev_tstamp interval [read-write]"
  2626. The current interval value. Can be modified any time, but changes only
  2627. take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
  2628. called.
  2629. .IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
  2630. .IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
  2631. The current reschedule callback, or \f(CW0\fR, if this functionality is
  2632. switched off. Can be changed any time, but changes only take effect when
  2633. the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
  2634. .PP
  2635. \fIExamples\fR
  2636. .IX Subsection "Examples"
  2637. .PP
  2638. Example: Call a callback every hour, or, more precisely, whenever the
  2639. system time is divisible by 3600. The callback invocation times have
  2640. potentially a lot of jitter, but good long-term stability.
  2641. .PP
  2642. .Vb 5
  2643. \& static void
  2644. \& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
  2645. \& {
  2646. \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
  2647. \& }
  2648. \&
  2649. \& ev_periodic hourly_tick;
  2650. \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
  2651. \& ev_periodic_start (loop, &hourly_tick);
  2652. .Ve
  2653. .PP
  2654. Example: The same as above, but use a reschedule callback to do it:
  2655. .PP
  2656. .Vb 1
  2657. \& #include <math.h>
  2658. \&
  2659. \& static ev_tstamp
  2660. \& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
  2661. \& {
  2662. \& return now + (3600. \- fmod (now, 3600.));
  2663. \& }
  2664. \&
  2665. \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
  2666. .Ve
  2667. .PP
  2668. Example: Call a callback every hour, starting now:
  2669. .PP
  2670. .Vb 4
  2671. \& ev_periodic hourly_tick;
  2672. \& ev_periodic_init (&hourly_tick, clock_cb,
  2673. \& fmod (ev_now (loop), 3600.), 3600., 0);
  2674. \& ev_periodic_start (loop, &hourly_tick);
  2675. .Ve
  2676. .ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
  2677. .el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
  2678. .IX Subsection "ev_signal - signal me when a signal gets signalled!"
  2679. Signal watchers will trigger an event when the process receives a specific
  2680. signal one or more times. Even though signals are very asynchronous, libev
  2681. will try its best to deliver signals synchronously, i.e. as part of the
  2682. normal event processing, like any other event.
  2683. .PP
  2684. If you want signals to be delivered truly asynchronously, just use
  2685. \&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
  2686. the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
  2687. synchronously wake up an event loop.
  2688. .PP
  2689. You can configure as many watchers as you like for the same signal, but
  2690. only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
  2691. default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
  2692. \&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
  2693. the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
  2694. .PP
  2695. Only after the first watcher for a signal is started will libev actually
  2696. register something with the kernel. It thus coexists with your own signal
  2697. handlers as long as you don't register any with libev for the same signal.
  2698. .PP
  2699. If possible and supported, libev will install its handlers with
  2700. \&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
  2701. not be unduly interrupted. If you have a problem with system calls getting
  2702. interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
  2703. and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
  2704. .PP
  2705. \fIThe special problem of inheritance over fork/execve/pthread_create\fR
  2706. .IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
  2707. .PP
  2708. Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
  2709. (\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
  2710. stopping it again), that is, libev might or might not block the signal,
  2711. and might or might not set or restore the installed signal handler (but
  2712. see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
  2713. .PP
  2714. While this does not matter for the signal disposition (libev never
  2715. sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
  2716. \&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
  2717. certain signals to be blocked.
  2718. .PP
  2719. This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
  2720. the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
  2721. choice usually).
  2722. .PP
  2723. The simplest way to ensure that the signal mask is reset in the child is
  2724. to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
  2725. catch fork calls done by libraries (such as the libc) as well.
  2726. .PP
  2727. In current versions of libev, the signal will not be blocked indefinitely
  2728. unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
  2729. the window of opportunity for problems, it will not go away, as libev
  2730. \&\fIhas\fR to modify the signal mask, at least temporarily.
  2731. .PP
  2732. So I can't stress this enough: \fIIf you do not reset your signal mask when
  2733. you expect it to be empty, you have a race condition in your code\fR. This
  2734. is not a libev-specific thing, this is true for most event libraries.
  2735. .PP
  2736. \fIThe special problem of threads signal handling\fR
  2737. .IX Subsection "The special problem of threads signal handling"
  2738. .PP
  2739. \&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
  2740. a lot of functionality (sigfd, sigwait etc.) only really works if all
  2741. threads in a process block signals, which is hard to achieve.
  2742. .PP
  2743. When you want to use sigwait (or mix libev signal handling with your own
  2744. for the same signals), you can tackle this problem by globally blocking
  2745. all signals before creating any threads (or creating them with a fully set
  2746. sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
  2747. loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
  2748. these signals. You can pass on any signals that libev might be interested
  2749. in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
  2750. .PP
  2751. \fIWatcher-Specific Functions and Data Members\fR
  2752. .IX Subsection "Watcher-Specific Functions and Data Members"
  2753. .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
  2754. .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
  2755. .PD 0
  2756. .IP "ev_signal_set (ev_signal *, int signum)" 4
  2757. .IX Item "ev_signal_set (ev_signal *, int signum)"
  2758. .PD
  2759. Configures the watcher to trigger on the given signal number (usually one
  2760. of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
  2761. .IP "int signum [read\-only]" 4
  2762. .IX Item "int signum [read-only]"
  2763. The signal the watcher watches out for.
  2764. .PP
  2765. \fIExamples\fR
  2766. .IX Subsection "Examples"
  2767. .PP
  2768. Example: Try to exit cleanly on \s-1SIGINT.\s0
  2769. .PP
  2770. .Vb 5
  2771. \& static void
  2772. \& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
  2773. \& {
  2774. \& ev_break (loop, EVBREAK_ALL);
  2775. \& }
  2776. \&
  2777. \& ev_signal signal_watcher;
  2778. \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
  2779. \& ev_signal_start (loop, &signal_watcher);
  2780. .Ve
  2781. .ie n .SS """ev_child"" \- watch out for process status changes"
  2782. .el .SS "\f(CWev_child\fP \- watch out for process status changes"
  2783. .IX Subsection "ev_child - watch out for process status changes"
  2784. Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
  2785. some child status changes (most typically when a child of yours dies or
  2786. exits). It is permissible to install a child watcher \fIafter\fR the child
  2787. has been forked (which implies it might have already exited), as long
  2788. as the event loop isn't entered (or is continued from a watcher), i.e.,
  2789. forking and then immediately registering a watcher for the child is fine,
  2790. but forking and registering a watcher a few event loop iterations later or
  2791. in the next callback invocation is not.
  2792. .PP
  2793. Only the default event loop is capable of handling signals, and therefore
  2794. you can only register child watchers in the default event loop.
  2795. .PP
  2796. Due to some design glitches inside libev, child watchers will always be
  2797. handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
  2798. libev)
  2799. .PP
  2800. \fIProcess Interaction\fR
  2801. .IX Subsection "Process Interaction"
  2802. .PP
  2803. Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
  2804. initialised. This is necessary to guarantee proper behaviour even if the
  2805. first child watcher is started after the child exits. The occurrence
  2806. of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
  2807. synchronously as part of the event loop processing. Libev always reaps all
  2808. children, even ones not watched.
  2809. .PP
  2810. \fIOverriding the Built-In Processing\fR
  2811. .IX Subsection "Overriding the Built-In Processing"
  2812. .PP
  2813. Libev offers no special support for overriding the built-in child
  2814. processing, but if your application collides with libev's default child
  2815. handler, you can override it easily by installing your own handler for
  2816. \&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
  2817. default loop never gets destroyed. You are encouraged, however, to use an
  2818. event-based approach to child reaping and thus use libev's support for
  2819. that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
  2820. .PP
  2821. \fIStopping the Child Watcher\fR
  2822. .IX Subsection "Stopping the Child Watcher"
  2823. .PP
  2824. Currently, the child watcher never gets stopped, even when the
  2825. child terminates, so normally one needs to stop the watcher in the
  2826. callback. Future versions of libev might stop the watcher automatically
  2827. when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
  2828. problem).
  2829. .PP
  2830. \fIWatcher-Specific Functions and Data Members\fR
  2831. .IX Subsection "Watcher-Specific Functions and Data Members"
  2832. .IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
  2833. .IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
  2834. .PD 0
  2835. .IP "ev_child_set (ev_child *, int pid, int trace)" 4
  2836. .IX Item "ev_child_set (ev_child *, int pid, int trace)"
  2837. .PD
  2838. Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
  2839. \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
  2840. at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
  2841. the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
  2842. \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
  2843. process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
  2844. activate the watcher when the process terminates) or \f(CW1\fR (additionally
  2845. activate the watcher when the process is stopped or continued).
  2846. .IP "int pid [read\-only]" 4
  2847. .IX Item "int pid [read-only]"
  2848. The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
  2849. .IP "int rpid [read\-write]" 4
  2850. .IX Item "int rpid [read-write]"
  2851. The process id that detected a status change.
  2852. .IP "int rstatus [read\-write]" 4
  2853. .IX Item "int rstatus [read-write]"
  2854. The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
  2855. \&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
  2856. .PP
  2857. \fIExamples\fR
  2858. .IX Subsection "Examples"
  2859. .PP
  2860. Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
  2861. its completion.
  2862. .PP
  2863. .Vb 1
  2864. \& ev_child cw;
  2865. \&
  2866. \& static void
  2867. \& child_cb (EV_P_ ev_child *w, int revents)
  2868. \& {
  2869. \& ev_child_stop (EV_A_ w);
  2870. \& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
  2871. \& }
  2872. \&
  2873. \& pid_t pid = fork ();
  2874. \&
  2875. \& if (pid < 0)
  2876. \& // error
  2877. \& else if (pid == 0)
  2878. \& {
  2879. \& // the forked child executes here
  2880. \& exit (1);
  2881. \& }
  2882. \& else
  2883. \& {
  2884. \& ev_child_init (&cw, child_cb, pid, 0);
  2885. \& ev_child_start (EV_DEFAULT_ &cw);
  2886. \& }
  2887. .Ve
  2888. .ie n .SS """ev_stat"" \- did the file attributes just change?"
  2889. .el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
  2890. .IX Subsection "ev_stat - did the file attributes just change?"
  2891. This watches a file system path for attribute changes. That is, it calls
  2892. \&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
  2893. and sees if it changed compared to the last time, invoking the callback
  2894. if it did. Starting the watcher \f(CW\*(C`stat\*(C'\fR's the file, so only changes that
  2895. happen after the watcher has been started will be reported.
  2896. .PP
  2897. The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
  2898. not exist\*(R" is a status change like any other. The condition \*(L"path does not
  2899. exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
  2900. \&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
  2901. least one) and all the other fields of the stat buffer having unspecified
  2902. contents.
  2903. .PP
  2904. The path \fImust not\fR end in a slash or contain special components such as
  2905. \&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
  2906. your working directory changes, then the behaviour is undefined.
  2907. .PP
  2908. Since there is no portable change notification interface available, the
  2909. portable implementation simply calls \f(CWstat(2)\fR regularly on the path
  2910. to see if it changed somehow. You can specify a recommended polling
  2911. interval for this case. If you specify a polling interval of \f(CW0\fR (highly
  2912. recommended!) then a \fIsuitable, unspecified default\fR value will be used
  2913. (which you can expect to be around five seconds, although this might
  2914. change dynamically). Libev will also impose a minimum interval which is
  2915. currently around \f(CW0.1\fR, but that's usually overkill.
  2916. .PP
  2917. This watcher type is not meant for massive numbers of stat watchers,
  2918. as even with OS-supported change notifications, this can be
  2919. resource-intensive.
  2920. .PP
  2921. At the time of this writing, the only OS-specific interface implemented
  2922. is the Linux inotify interface (implementing kqueue support is left as an
  2923. exercise for the reader. Note, however, that the author sees no way of
  2924. implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
  2925. .PP
  2926. \fI\s-1ABI\s0 Issues (Largefile Support)\fR
  2927. .IX Subsection "ABI Issues (Largefile Support)"
  2928. .PP
  2929. Libev by default (unless the user overrides this) uses the default
  2930. compilation environment, which means that on systems with large file
  2931. support disabled by default, you get the 32 bit version of the stat
  2932. structure. When using the library from programs that change the \s-1ABI\s0 to
  2933. use 64 bit file offsets the programs will fail. In that case you have to
  2934. compile libev with the same flags to get binary compatibility. This is
  2935. obviously the case with any flags that change the \s-1ABI,\s0 but the problem is
  2936. most noticeably displayed with ev_stat and large file support.
  2937. .PP
  2938. The solution for this is to lobby your distribution maker to make large
  2939. file interfaces available by default (as e.g. FreeBSD does) and not
  2940. optional. Libev cannot simply switch on large file support because it has
  2941. to exchange stat structures with application programs compiled using the
  2942. default compilation environment.
  2943. .PP
  2944. \fIInotify and Kqueue\fR
  2945. .IX Subsection "Inotify and Kqueue"
  2946. .PP
  2947. When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
  2948. runtime, it will be used to speed up change detection where possible. The
  2949. inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
  2950. watcher is being started.
  2951. .PP
  2952. Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
  2953. except that changes might be detected earlier, and in some cases, to avoid
  2954. making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
  2955. there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
  2956. but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
  2957. many bugs), the path exists (i.e. stat succeeds), and the path resides on
  2958. a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
  2959. xfs are fully working) libev usually gets away without polling.
  2960. .PP
  2961. There is no support for kqueue, as apparently it cannot be used to
  2962. implement this functionality, due to the requirement of having a file
  2963. descriptor open on the object at all times, and detecting renames, unlinks
  2964. etc. is difficult.
  2965. .PP
  2966. \fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
  2967. .IX Subsection "stat () is a synchronous operation"
  2968. .PP
  2969. Libev doesn't normally do any kind of I/O itself, and so is not blocking
  2970. the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
  2971. ()\*(C'\fR, which is a synchronous operation.
  2972. .PP
  2973. For local paths, this usually doesn't matter: unless the system is very
  2974. busy or the intervals between stat's are large, a stat call will be fast,
  2975. as the path data is usually in memory already (except when starting the
  2976. watcher).
  2977. .PP
  2978. For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
  2979. time due to network issues, and even under good conditions, a stat call
  2980. often takes multiple milliseconds.
  2981. .PP
  2982. Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
  2983. paths, although this is fully supported by libev.
  2984. .PP
  2985. \fIThe special problem of stat time resolution\fR
  2986. .IX Subsection "The special problem of stat time resolution"
  2987. .PP
  2988. The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
  2989. and even on systems where the resolution is higher, most file systems
  2990. still only support whole seconds.
  2991. .PP
  2992. That means that, if the time is the only thing that changes, you can
  2993. easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
  2994. calls your callback, which does something. When there is another update
  2995. within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
  2996. stat data does change in other ways (e.g. file size).
  2997. .PP
  2998. The solution to this is to delay acting on a change for slightly more
  2999. than a second (or till slightly after the next full second boundary), using
  3000. a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
  3001. ev_timer_again (loop, w)\*(C'\fR).
  3002. .PP
  3003. The \f(CW.02\fR offset is added to work around small timing inconsistencies
  3004. of some operating systems (where the second counter of the current time
  3005. might be be delayed. One such system is the Linux kernel, where a call to
  3006. \&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
  3007. a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
  3008. update file times then there will be a small window where the kernel uses
  3009. the previous second to update file times but libev might already execute
  3010. the timer callback).
  3011. .PP
  3012. \fIWatcher-Specific Functions and Data Members\fR
  3013. .IX Subsection "Watcher-Specific Functions and Data Members"
  3014. .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
  3015. .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
  3016. .PD 0
  3017. .IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
  3018. .IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
  3019. .PD
  3020. Configures the watcher to wait for status changes of the given
  3021. \&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
  3022. be detected and should normally be specified as \f(CW0\fR to let libev choose
  3023. a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
  3024. path for as long as the watcher is active.
  3025. .Sp
  3026. The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
  3027. relative to the attributes at the time the watcher was started (or the
  3028. last change was detected).
  3029. .IP "ev_stat_stat (loop, ev_stat *)" 4
  3030. .IX Item "ev_stat_stat (loop, ev_stat *)"
  3031. Updates the stat buffer immediately with new values. If you change the
  3032. watched path in your callback, you could call this function to avoid
  3033. detecting this change (while introducing a race condition if you are not
  3034. the only one changing the path). Can also be useful simply to find out the
  3035. new values.
  3036. .IP "ev_statdata attr [read\-only]" 4
  3037. .IX Item "ev_statdata attr [read-only]"
  3038. The most-recently detected attributes of the file. Although the type is
  3039. \&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
  3040. suitable for your system, but you can only rely on the POSIX-standardised
  3041. members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
  3042. some error while \f(CW\*(C`stat\*(C'\fRing the file.
  3043. .IP "ev_statdata prev [read\-only]" 4
  3044. .IX Item "ev_statdata prev [read-only]"
  3045. The previous attributes of the file. The callback gets invoked whenever
  3046. \&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
  3047. differ: \f(CW\*(C`st_dev\*(C'\fR, \f(CW\*(C`st_ino\*(C'\fR, \f(CW\*(C`st_mode\*(C'\fR, \f(CW\*(C`st_nlink\*(C'\fR, \f(CW\*(C`st_uid\*(C'\fR,
  3048. \&\f(CW\*(C`st_gid\*(C'\fR, \f(CW\*(C`st_rdev\*(C'\fR, \f(CW\*(C`st_size\*(C'\fR, \f(CW\*(C`st_atime\*(C'\fR, \f(CW\*(C`st_mtime\*(C'\fR, \f(CW\*(C`st_ctime\*(C'\fR.
  3049. .IP "ev_tstamp interval [read\-only]" 4
  3050. .IX Item "ev_tstamp interval [read-only]"
  3051. The specified interval.
  3052. .IP "const char *path [read\-only]" 4
  3053. .IX Item "const char *path [read-only]"
  3054. The file system path that is being watched.
  3055. .PP
  3056. \fIExamples\fR
  3057. .IX Subsection "Examples"
  3058. .PP
  3059. Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
  3060. .PP
  3061. .Vb 10
  3062. \& static void
  3063. \& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
  3064. \& {
  3065. \& /* /etc/passwd changed in some way */
  3066. \& if (w\->attr.st_nlink)
  3067. \& {
  3068. \& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
  3069. \& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
  3070. \& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
  3071. \& }
  3072. \& else
  3073. \& /* you shalt not abuse printf for puts */
  3074. \& puts ("wow, /etc/passwd is not there, expect problems. "
  3075. \& "if this is windows, they already arrived\en");
  3076. \& }
  3077. \&
  3078. \& ...
  3079. \& ev_stat passwd;
  3080. \&
  3081. \& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
  3082. \& ev_stat_start (loop, &passwd);
  3083. .Ve
  3084. .PP
  3085. Example: Like above, but additionally use a one-second delay so we do not
  3086. miss updates (however, frequent updates will delay processing, too, so
  3087. one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
  3088. \&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
  3089. .PP
  3090. .Vb 2
  3091. \& static ev_stat passwd;
  3092. \& static ev_timer timer;
  3093. \&
  3094. \& static void
  3095. \& timer_cb (EV_P_ ev_timer *w, int revents)
  3096. \& {
  3097. \& ev_timer_stop (EV_A_ w);
  3098. \&
  3099. \& /* now it\*(Aqs one second after the most recent passwd change */
  3100. \& }
  3101. \&
  3102. \& static void
  3103. \& stat_cb (EV_P_ ev_stat *w, int revents)
  3104. \& {
  3105. \& /* reset the one\-second timer */
  3106. \& ev_timer_again (EV_A_ &timer);
  3107. \& }
  3108. \&
  3109. \& ...
  3110. \& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
  3111. \& ev_stat_start (loop, &passwd);
  3112. \& ev_timer_init (&timer, timer_cb, 0., 1.02);
  3113. .Ve
  3114. .ie n .SS """ev_idle"" \- when you've got nothing better to do..."
  3115. .el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
  3116. .IX Subsection "ev_idle - when you've got nothing better to do..."
  3117. Idle watchers trigger events when no other events of the same or higher
  3118. priority are pending (prepare, check and other idle watchers do not count
  3119. as receiving \*(L"events\*(R").
  3120. .PP
  3121. That is, as long as your process is busy handling sockets or timeouts
  3122. (or even signals, imagine) of the same or higher priority it will not be
  3123. triggered. But when your process is idle (or only lower-priority watchers
  3124. are pending), the idle watchers are being called once per event loop
  3125. iteration \- until stopped, that is, or your process receives more events
  3126. and becomes busy again with higher priority stuff.
  3127. .PP
  3128. The most noteworthy effect is that as long as any idle watchers are
  3129. active, the process will not block when waiting for new events.
  3130. .PP
  3131. Apart from keeping your process non-blocking (which is a useful
  3132. effect on its own sometimes), idle watchers are a good place to do
  3133. \&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
  3134. event loop has handled all outstanding events.
  3135. .PP
  3136. \fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR
  3137. .IX Subsection "Abusing an ev_idle watcher for its side-effect"
  3138. .PP
  3139. As long as there is at least one active idle watcher, libev will never
  3140. sleep unnecessarily. Or in other words, it will loop as fast as possible.
  3141. For this to work, the idle watcher doesn't need to be invoked at all \- the
  3142. lowest priority will do.
  3143. .PP
  3144. This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher,
  3145. to do something on each event loop iteration \- for example to balance load
  3146. between different connections.
  3147. .PP
  3148. See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer
  3149. example.
  3150. .PP
  3151. \fIWatcher-Specific Functions and Data Members\fR
  3152. .IX Subsection "Watcher-Specific Functions and Data Members"
  3153. .IP "ev_idle_init (ev_idle *, callback)" 4
  3154. .IX Item "ev_idle_init (ev_idle *, callback)"
  3155. Initialises and configures the idle watcher \- it has no parameters of any
  3156. kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
  3157. believe me.
  3158. .PP
  3159. \fIExamples\fR
  3160. .IX Subsection "Examples"
  3161. .PP
  3162. Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
  3163. callback, free it. Also, use no error checking, as usual.
  3164. .PP
  3165. .Vb 5
  3166. \& static void
  3167. \& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
  3168. \& {
  3169. \& // stop the watcher
  3170. \& ev_idle_stop (loop, w);
  3171. \&
  3172. \& // now we can free it
  3173. \& free (w);
  3174. \&
  3175. \& // now do something you wanted to do when the program has
  3176. \& // no longer anything immediate to do.
  3177. \& }
  3178. \&
  3179. \& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
  3180. \& ev_idle_init (idle_watcher, idle_cb);
  3181. \& ev_idle_start (loop, idle_watcher);
  3182. .Ve
  3183. .ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
  3184. .el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
  3185. .IX Subsection "ev_prepare and ev_check - customise your event loop!"
  3186. Prepare and check watchers are often (but not always) used in pairs:
  3187. prepare watchers get invoked before the process blocks and check watchers
  3188. afterwards.
  3189. .PP
  3190. You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR (or similar functions that enter the
  3191. current event loop) or \f(CW\*(C`ev_loop_fork\*(C'\fR from either \f(CW\*(C`ev_prepare\*(C'\fR or
  3192. \&\f(CW\*(C`ev_check\*(C'\fR watchers. Other loops than the current one are fine,
  3193. however. The rationale behind this is that you do not need to check
  3194. for recursion in those watchers, i.e. the sequence will always be
  3195. \&\f(CW\*(C`ev_prepare\*(C'\fR, blocking, \f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each
  3196. kind they will always be called in pairs bracketing the blocking call.
  3197. .PP
  3198. Their main purpose is to integrate other event mechanisms into libev and
  3199. their use is somewhat advanced. They could be used, for example, to track
  3200. variable changes, implement your own watchers, integrate net-snmp or a
  3201. coroutine library and lots more. They are also occasionally useful if
  3202. you cache some data and want to flush it before blocking (for example,
  3203. in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
  3204. watcher).
  3205. .PP
  3206. This is done by examining in each prepare call which file descriptors
  3207. need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
  3208. for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
  3209. libraries provide exactly this functionality). Then, in the check watcher,
  3210. you check for any events that occurred (by checking the pending status
  3211. of all watchers and stopping them) and call back into the library. The
  3212. I/O and timer callbacks will never actually be called (but must be valid
  3213. nevertheless, because you never know, you know?).
  3214. .PP
  3215. As another example, the Perl Coro module uses these hooks to integrate
  3216. coroutines into libev programs, by yielding to other active coroutines
  3217. during each prepare and only letting the process block if no coroutines
  3218. are ready to run (it's actually more complicated: it only runs coroutines
  3219. with priority higher than or equal to the event loop and one coroutine
  3220. of lower priority, but only once, using idle watchers to keep the event
  3221. loop from blocking if lower-priority coroutines are active, thus mapping
  3222. low-priority coroutines to idle/background tasks).
  3223. .PP
  3224. When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers
  3225. highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before
  3226. any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR
  3227. watchers).
  3228. .PP
  3229. Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
  3230. activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
  3231. might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
  3232. \&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
  3233. loops those other event loops might be in an unusable state until their
  3234. \&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
  3235. others).
  3236. .PP
  3237. \fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR
  3238. .IX Subsection "Abusing an ev_check watcher for its side-effect"
  3239. .PP
  3240. \&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be
  3241. useful because they are called once per event loop iteration. For
  3242. example, if you want to handle a large number of connections fairly, you
  3243. normally only do a bit of work for each active connection, and if there
  3244. is more work to do, you wait for the next event loop iteration, so other
  3245. connections have a chance of making progress.
  3246. .PP
  3247. Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the
  3248. next event loop iteration. However, that isn't as soon as possible \-
  3249. without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked.
  3250. .PP
  3251. This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a
  3252. single global idle watcher that is active as long as you have one active
  3253. \&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop
  3254. will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets
  3255. invoked. Neither watcher alone can do that.
  3256. .PP
  3257. \fIWatcher-Specific Functions and Data Members\fR
  3258. .IX Subsection "Watcher-Specific Functions and Data Members"
  3259. .IP "ev_prepare_init (ev_prepare *, callback)" 4
  3260. .IX Item "ev_prepare_init (ev_prepare *, callback)"
  3261. .PD 0
  3262. .IP "ev_check_init (ev_check *, callback)" 4
  3263. .IX Item "ev_check_init (ev_check *, callback)"
  3264. .PD
  3265. Initialises and configures the prepare or check watcher \- they have no
  3266. parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
  3267. macros, but using them is utterly, utterly, utterly and completely
  3268. pointless.
  3269. .PP
  3270. \fIExamples\fR
  3271. .IX Subsection "Examples"
  3272. .PP
  3273. There are a number of principal ways to embed other event loops or modules
  3274. into libev. Here are some ideas on how to include libadns into libev
  3275. (there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
  3276. use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
  3277. Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
  3278. Glib event loop).
  3279. .PP
  3280. Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
  3281. and in a check watcher, destroy them and call into libadns. What follows
  3282. is pseudo-code only of course. This requires you to either use a low
  3283. priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
  3284. the callbacks for the IO/timeout watchers might not have been called yet.
  3285. .PP
  3286. .Vb 2
  3287. \& static ev_io iow [nfd];
  3288. \& static ev_timer tw;
  3289. \&
  3290. \& static void
  3291. \& io_cb (struct ev_loop *loop, ev_io *w, int revents)
  3292. \& {
  3293. \& }
  3294. \&
  3295. \& // create io watchers for each fd and a timer before blocking
  3296. \& static void
  3297. \& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
  3298. \& {
  3299. \& int timeout = 3600000;
  3300. \& struct pollfd fds [nfd];
  3301. \& // actual code will need to loop here and realloc etc.
  3302. \& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
  3303. \&
  3304. \& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
  3305. \& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
  3306. \& ev_timer_start (loop, &tw);
  3307. \&
  3308. \& // create one ev_io per pollfd
  3309. \& for (int i = 0; i < nfd; ++i)
  3310. \& {
  3311. \& ev_io_init (iow + i, io_cb, fds [i].fd,
  3312. \& ((fds [i].events & POLLIN ? EV_READ : 0)
  3313. \& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
  3314. \&
  3315. \& fds [i].revents = 0;
  3316. \& ev_io_start (loop, iow + i);
  3317. \& }
  3318. \& }
  3319. \&
  3320. \& // stop all watchers after blocking
  3321. \& static void
  3322. \& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
  3323. \& {
  3324. \& ev_timer_stop (loop, &tw);
  3325. \&
  3326. \& for (int i = 0; i < nfd; ++i)
  3327. \& {
  3328. \& // set the relevant poll flags
  3329. \& // could also call adns_processreadable etc. here
  3330. \& struct pollfd *fd = fds + i;
  3331. \& int revents = ev_clear_pending (iow + i);
  3332. \& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
  3333. \& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
  3334. \&
  3335. \& // now stop the watcher
  3336. \& ev_io_stop (loop, iow + i);
  3337. \& }
  3338. \&
  3339. \& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
  3340. \& }
  3341. .Ve
  3342. .PP
  3343. Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
  3344. in the prepare watcher and would dispose of the check watcher.
  3345. .PP
  3346. Method 3: If the module to be embedded supports explicit event
  3347. notification (libadns does), you can also make use of the actual watcher
  3348. callbacks, and only destroy/create the watchers in the prepare watcher.
  3349. .PP
  3350. .Vb 5
  3351. \& static void
  3352. \& timer_cb (EV_P_ ev_timer *w, int revents)
  3353. \& {
  3354. \& adns_state ads = (adns_state)w\->data;
  3355. \& update_now (EV_A);
  3356. \&
  3357. \& adns_processtimeouts (ads, &tv_now);
  3358. \& }
  3359. \&
  3360. \& static void
  3361. \& io_cb (EV_P_ ev_io *w, int revents)
  3362. \& {
  3363. \& adns_state ads = (adns_state)w\->data;
  3364. \& update_now (EV_A);
  3365. \&
  3366. \& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
  3367. \& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
  3368. \& }
  3369. \&
  3370. \& // do not ever call adns_afterpoll
  3371. .Ve
  3372. .PP
  3373. Method 4: Do not use a prepare or check watcher because the module you
  3374. want to embed is not flexible enough to support it. Instead, you can
  3375. override their poll function. The drawback with this solution is that the
  3376. main loop is now no longer controllable by \s-1EV.\s0 The \f(CW\*(C`Glib::EV\*(C'\fR module uses
  3377. this approach, effectively embedding \s-1EV\s0 as a client into the horrible
  3378. libglib event loop.
  3379. .PP
  3380. .Vb 4
  3381. \& static gint
  3382. \& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
  3383. \& {
  3384. \& int got_events = 0;
  3385. \&
  3386. \& for (n = 0; n < nfds; ++n)
  3387. \& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
  3388. \&
  3389. \& if (timeout >= 0)
  3390. \& // create/start timer
  3391. \&
  3392. \& // poll
  3393. \& ev_run (EV_A_ 0);
  3394. \&
  3395. \& // stop timer again
  3396. \& if (timeout >= 0)
  3397. \& ev_timer_stop (EV_A_ &to);
  3398. \&
  3399. \& // stop io watchers again \- their callbacks should have set
  3400. \& for (n = 0; n < nfds; ++n)
  3401. \& ev_io_stop (EV_A_ iow [n]);
  3402. \&
  3403. \& return got_events;
  3404. \& }
  3405. .Ve
  3406. .ie n .SS """ev_embed"" \- when one backend isn't enough..."
  3407. .el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
  3408. .IX Subsection "ev_embed - when one backend isn't enough..."
  3409. This is a rather advanced watcher type that lets you embed one event loop
  3410. into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
  3411. loop, other types of watchers might be handled in a delayed or incorrect
  3412. fashion and must not be used).
  3413. .PP
  3414. There are primarily two reasons you would want that: work around bugs and
  3415. prioritise I/O.
  3416. .PP
  3417. As an example for a bug workaround, the kqueue backend might only support
  3418. sockets on some platform, so it is unusable as generic backend, but you
  3419. still want to make use of it because you have many sockets and it scales
  3420. so nicely. In this case, you would create a kqueue-based loop and embed
  3421. it into your default loop (which might use e.g. poll). Overall operation
  3422. will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
  3423. \&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
  3424. best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
  3425. .PP
  3426. As for prioritising I/O: under rare circumstances you have the case where
  3427. some fds have to be watched and handled very quickly (with low latency),
  3428. and even priorities and idle watchers might have too much overhead. In
  3429. this case you would put all the high priority stuff in one loop and all
  3430. the rest in a second one, and embed the second one in the first.
  3431. .PP
  3432. As long as the watcher is active, the callback will be invoked every
  3433. time there might be events pending in the embedded loop. The callback
  3434. must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
  3435. sweep and invoke their callbacks (the callback doesn't need to invoke the
  3436. \&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
  3437. to give the embedded loop strictly lower priority for example).
  3438. .PP
  3439. You can also set the callback to \f(CW0\fR, in which case the embed watcher
  3440. will automatically execute the embedded loop sweep whenever necessary.
  3441. .PP
  3442. Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
  3443. is active, i.e., the embedded loop will automatically be forked when the
  3444. embedding loop forks. In other cases, the user is responsible for calling
  3445. \&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
  3446. .PP
  3447. Unfortunately, not all backends are embeddable: only the ones returned by
  3448. \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
  3449. portable one.
  3450. .PP
  3451. So when you want to use this feature you will always have to be prepared
  3452. that you cannot get an embeddable loop. The recommended way to get around
  3453. this is to have a separate variables for your embeddable loop, try to
  3454. create it, and if that fails, use the normal loop for everything.
  3455. .PP
  3456. \fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
  3457. .IX Subsection "ev_embed and fork"
  3458. .PP
  3459. While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
  3460. automatically be applied to the embedded loop as well, so no special
  3461. fork handling is required in that case. When the watcher is not running,
  3462. however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
  3463. as applicable.
  3464. .PP
  3465. \fIWatcher-Specific Functions and Data Members\fR
  3466. .IX Subsection "Watcher-Specific Functions and Data Members"
  3467. .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
  3468. .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
  3469. .PD 0
  3470. .IP "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" 4
  3471. .IX Item "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)"
  3472. .PD
  3473. Configures the watcher to embed the given loop, which must be
  3474. embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
  3475. invoked automatically, otherwise it is the responsibility of the callback
  3476. to invoke it (it will continue to be called until the sweep has been done,
  3477. if you do not want that, you need to temporarily stop the embed watcher).
  3478. .IP "ev_embed_sweep (loop, ev_embed *)" 4
  3479. .IX Item "ev_embed_sweep (loop, ev_embed *)"
  3480. Make a single, non-blocking sweep over the embedded loop. This works
  3481. similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
  3482. appropriate way for embedded loops.
  3483. .IP "struct ev_loop *other [read\-only]" 4
  3484. .IX Item "struct ev_loop *other [read-only]"
  3485. The embedded event loop.
  3486. .PP
  3487. \fIExamples\fR
  3488. .IX Subsection "Examples"
  3489. .PP
  3490. Example: Try to get an embeddable event loop and embed it into the default
  3491. event loop. If that is not possible, use the default loop. The default
  3492. loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
  3493. \&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
  3494. used).
  3495. .PP
  3496. .Vb 3
  3497. \& struct ev_loop *loop_hi = ev_default_init (0);
  3498. \& struct ev_loop *loop_lo = 0;
  3499. \& ev_embed embed;
  3500. \&
  3501. \& // see if there is a chance of getting one that works
  3502. \& // (remember that a flags value of 0 means autodetection)
  3503. \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
  3504. \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
  3505. \& : 0;
  3506. \&
  3507. \& // if we got one, then embed it, otherwise default to loop_hi
  3508. \& if (loop_lo)
  3509. \& {
  3510. \& ev_embed_init (&embed, 0, loop_lo);
  3511. \& ev_embed_start (loop_hi, &embed);
  3512. \& }
  3513. \& else
  3514. \& loop_lo = loop_hi;
  3515. .Ve
  3516. .PP
  3517. Example: Check if kqueue is available but not recommended and create
  3518. a kqueue backend for use with sockets (which usually work with any
  3519. kqueue implementation). Store the kqueue/socket\-only event loop in
  3520. \&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
  3521. .PP
  3522. .Vb 3
  3523. \& struct ev_loop *loop = ev_default_init (0);
  3524. \& struct ev_loop *loop_socket = 0;
  3525. \& ev_embed embed;
  3526. \&
  3527. \& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
  3528. \& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
  3529. \& {
  3530. \& ev_embed_init (&embed, 0, loop_socket);
  3531. \& ev_embed_start (loop, &embed);
  3532. \& }
  3533. \&
  3534. \& if (!loop_socket)
  3535. \& loop_socket = loop;
  3536. \&
  3537. \& // now use loop_socket for all sockets, and loop for everything else
  3538. .Ve
  3539. .ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
  3540. .el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
  3541. .IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
  3542. Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
  3543. whoever is a good citizen cared to tell libev about it by calling
  3544. \&\f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the event loop blocks next
  3545. and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, and only in the child
  3546. after the fork. If whoever good citizen calling \f(CW\*(C`ev_default_fork\*(C'\fR cheats
  3547. and calls it in the wrong process, the fork handlers will be invoked, too,
  3548. of course.
  3549. .PP
  3550. \fIThe special problem of life after fork \- how is it possible?\fR
  3551. .IX Subsection "The special problem of life after fork - how is it possible?"
  3552. .PP
  3553. Most uses of \f(CW\*(C`fork ()\*(C'\fR consist of forking, then some simple calls to set
  3554. up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
  3555. sequence should be handled by libev without any problems.
  3556. .PP
  3557. This changes when the application actually wants to do event handling
  3558. in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
  3559. fork.
  3560. .PP
  3561. The default mode of operation (for libev, with application help to detect
  3562. forks) is to duplicate all the state in the child, as would be expected
  3563. when \fIeither\fR the parent \fIor\fR the child process continues.
  3564. .PP
  3565. When both processes want to continue using libev, then this is usually the
  3566. wrong result. In that case, usually one process (typically the parent) is
  3567. supposed to continue with all watchers in place as before, while the other
  3568. process typically wants to start fresh, i.e. without any active watchers.
  3569. .PP
  3570. The cleanest and most efficient way to achieve that with libev is to
  3571. simply create a new event loop, which of course will be \*(L"empty\*(R", and
  3572. use that for new watchers. This has the advantage of not touching more
  3573. memory than necessary, and thus avoiding the copy-on-write, and the
  3574. disadvantage of having to use multiple event loops (which do not support
  3575. signal watchers).
  3576. .PP
  3577. When this is not possible, or you want to use the default loop for
  3578. other reasons, then in the process that wants to start \*(L"fresh\*(R", call
  3579. \&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
  3580. Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
  3581. watchers, so you have to be careful not to execute code that modifies
  3582. those watchers. Note also that in that case, you have to re-register any
  3583. signal watchers.
  3584. .PP
  3585. \fIWatcher-Specific Functions and Data Members\fR
  3586. .IX Subsection "Watcher-Specific Functions and Data Members"
  3587. .IP "ev_fork_init (ev_fork *, callback)" 4
  3588. .IX Item "ev_fork_init (ev_fork *, callback)"
  3589. Initialises and configures the fork watcher \- it has no parameters of any
  3590. kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
  3591. really.
  3592. .ie n .SS """ev_cleanup"" \- even the best things end"
  3593. .el .SS "\f(CWev_cleanup\fP \- even the best things end"
  3594. .IX Subsection "ev_cleanup - even the best things end"
  3595. Cleanup watchers are called just before the event loop is being destroyed
  3596. by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
  3597. .PP
  3598. While there is no guarantee that the event loop gets destroyed, cleanup
  3599. watchers provide a convenient method to install cleanup hooks for your
  3600. program, worker threads and so on \- you just to make sure to destroy the
  3601. loop when you want them to be invoked.
  3602. .PP
  3603. Cleanup watchers are invoked in the same way as any other watcher. Unlike
  3604. all other watchers, they do not keep a reference to the event loop (which
  3605. makes a lot of sense if you think about it). Like all other watchers, you
  3606. can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
  3607. .PP
  3608. \fIWatcher-Specific Functions and Data Members\fR
  3609. .IX Subsection "Watcher-Specific Functions and Data Members"
  3610. .IP "ev_cleanup_init (ev_cleanup *, callback)" 4
  3611. .IX Item "ev_cleanup_init (ev_cleanup *, callback)"
  3612. Initialises and configures the cleanup watcher \- it has no parameters of
  3613. any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
  3614. pointless, I assure you.
  3615. .PP
  3616. Example: Register an atexit handler to destroy the default loop, so any
  3617. cleanup functions are called.
  3618. .PP
  3619. .Vb 5
  3620. \& static void
  3621. \& program_exits (void)
  3622. \& {
  3623. \& ev_loop_destroy (EV_DEFAULT_UC);
  3624. \& }
  3625. \&
  3626. \& ...
  3627. \& atexit (program_exits);
  3628. .Ve
  3629. .ie n .SS """ev_async"" \- how to wake up an event loop"
  3630. .el .SS "\f(CWev_async\fP \- how to wake up an event loop"
  3631. .IX Subsection "ev_async - how to wake up an event loop"
  3632. In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
  3633. asynchronous sources such as signal handlers (as opposed to multiple event
  3634. loops \- those are of course safe to use in different threads).
  3635. .PP
  3636. Sometimes, however, you need to wake up an event loop you do not control,
  3637. for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
  3638. watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
  3639. it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
  3640. .PP
  3641. This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
  3642. too, are asynchronous in nature, and signals, too, will be compressed
  3643. (i.e. the number of callback invocations may be less than the number of
  3644. \&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind
  3645. of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
  3646. signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
  3647. even without knowing which loop owns the signal.
  3648. .PP
  3649. \fIQueueing\fR
  3650. .IX Subsection "Queueing"
  3651. .PP
  3652. \&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
  3653. is that the author does not know of a simple (or any) algorithm for a
  3654. multiple-writer-single-reader queue that works in all cases and doesn't
  3655. need elaborate support such as pthreads or unportable memory access
  3656. semantics.
  3657. .PP
  3658. That means that if you want to queue data, you have to provide your own
  3659. queue. But at least I can tell you how to implement locking around your
  3660. queue:
  3661. .IP "queueing from a signal handler context" 4
  3662. .IX Item "queueing from a signal handler context"
  3663. To implement race-free queueing, you simply add to the queue in the signal
  3664. handler but you block the signal handler in the watcher callback. Here is
  3665. an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
  3666. .Sp
  3667. .Vb 1
  3668. \& static ev_async mysig;
  3669. \&
  3670. \& static void
  3671. \& sigusr1_handler (void)
  3672. \& {
  3673. \& sometype data;
  3674. \&
  3675. \& // no locking etc.
  3676. \& queue_put (data);
  3677. \& ev_async_send (EV_DEFAULT_ &mysig);
  3678. \& }
  3679. \&
  3680. \& static void
  3681. \& mysig_cb (EV_P_ ev_async *w, int revents)
  3682. \& {
  3683. \& sometype data;
  3684. \& sigset_t block, prev;
  3685. \&
  3686. \& sigemptyset (&block);
  3687. \& sigaddset (&block, SIGUSR1);
  3688. \& sigprocmask (SIG_BLOCK, &block, &prev);
  3689. \&
  3690. \& while (queue_get (&data))
  3691. \& process (data);
  3692. \&
  3693. \& if (sigismember (&prev, SIGUSR1)
  3694. \& sigprocmask (SIG_UNBLOCK, &block, 0);
  3695. \& }
  3696. .Ve
  3697. .Sp
  3698. (Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
  3699. instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
  3700. either...).
  3701. .IP "queueing from a thread context" 4
  3702. .IX Item "queueing from a thread context"
  3703. The strategy for threads is different, as you cannot (easily) block
  3704. threads but you can easily preempt them, so to queue safely you need to
  3705. employ a traditional mutex lock, such as in this pthread example:
  3706. .Sp
  3707. .Vb 2
  3708. \& static ev_async mysig;
  3709. \& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
  3710. \&
  3711. \& static void
  3712. \& otherthread (void)
  3713. \& {
  3714. \& // only need to lock the actual queueing operation
  3715. \& pthread_mutex_lock (&mymutex);
  3716. \& queue_put (data);
  3717. \& pthread_mutex_unlock (&mymutex);
  3718. \&
  3719. \& ev_async_send (EV_DEFAULT_ &mysig);
  3720. \& }
  3721. \&
  3722. \& static void
  3723. \& mysig_cb (EV_P_ ev_async *w, int revents)
  3724. \& {
  3725. \& pthread_mutex_lock (&mymutex);
  3726. \&
  3727. \& while (queue_get (&data))
  3728. \& process (data);
  3729. \&
  3730. \& pthread_mutex_unlock (&mymutex);
  3731. \& }
  3732. .Ve
  3733. .PP
  3734. \fIWatcher-Specific Functions and Data Members\fR
  3735. .IX Subsection "Watcher-Specific Functions and Data Members"
  3736. .IP "ev_async_init (ev_async *, callback)" 4
  3737. .IX Item "ev_async_init (ev_async *, callback)"
  3738. Initialises and configures the async watcher \- it has no parameters of any
  3739. kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
  3740. trust me.
  3741. .IP "ev_async_send (loop, ev_async *)" 4
  3742. .IX Item "ev_async_send (loop, ev_async *)"
  3743. Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
  3744. an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
  3745. returns.
  3746. .Sp
  3747. Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
  3748. signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
  3749. embedding section below on what exactly this means).
  3750. .Sp
  3751. Note that, as with other watchers in libev, multiple events might get
  3752. compressed into a single callback invocation (another way to look at
  3753. this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
  3754. \&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
  3755. .Sp
  3756. This call incurs the overhead of at most one extra system call per event
  3757. loop iteration, if the event loop is blocked, and no syscall at all if
  3758. the event loop (or your program) is processing events. That means that
  3759. repeated calls are basically free (there is no need to avoid calls for
  3760. performance reasons) and that the overhead becomes smaller (typically
  3761. zero) under load.
  3762. .IP "bool = ev_async_pending (ev_async *)" 4
  3763. .IX Item "bool = ev_async_pending (ev_async *)"
  3764. Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
  3765. watcher but the event has not yet been processed (or even noted) by the
  3766. event loop.
  3767. .Sp
  3768. \&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
  3769. the loop iterates next and checks for the watcher to have become active,
  3770. it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
  3771. quickly check whether invoking the loop might be a good idea.
  3772. .Sp
  3773. Not that this does \fInot\fR check whether the watcher itself is pending,
  3774. only whether it has been requested to make this watcher pending: there
  3775. is a time window between the event loop checking and resetting the async
  3776. notification, and the callback being invoked.
  3778. .IX Header "OTHER FUNCTIONS"
  3779. There are some other functions of possible interest. Described. Here. Now.
  3780. .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)" 4
  3781. .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)"
  3782. This function combines a simple timer and an I/O watcher, calls your
  3783. callback on whichever event happens first and automatically stops both
  3784. watchers. This is useful if you want to wait for a single event on an fd
  3785. or timeout without having to allocate/configure/start/stop/free one or
  3786. more watchers yourself.
  3787. .Sp
  3788. If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
  3789. \&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
  3790. the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
  3791. .Sp
  3792. If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
  3793. started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
  3794. repeat = 0) will be started. \f(CW0\fR is a valid timeout.
  3795. .Sp
  3796. The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
  3797. passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
  3798. \&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMER\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
  3799. value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
  3800. a timeout and an io event at the same time \- you probably should give io
  3801. events precedence.
  3802. .Sp
  3803. Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO.\s0
  3804. .Sp
  3805. .Vb 7
  3806. \& static void stdin_ready (int revents, void *arg)
  3807. \& {
  3808. \& if (revents & EV_READ)
  3809. \& /* stdin might have data for us, joy! */;
  3810. \& else if (revents & EV_TIMER)
  3811. \& /* doh, nothing entered */;
  3812. \& }
  3813. \&
  3814. \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
  3815. .Ve
  3816. .IP "ev_feed_fd_event (loop, int fd, int revents)" 4
  3817. .IX Item "ev_feed_fd_event (loop, int fd, int revents)"
  3818. Feed an event on the given fd, as if a file descriptor backend detected
  3819. the given events.
  3820. .IP "ev_feed_signal_event (loop, int signum)" 4
  3821. .IX Item "ev_feed_signal_event (loop, int signum)"
  3822. Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
  3823. which is async-safe.
  3826. This section explains some common idioms that are not immediately
  3827. obvious. Note that examples are sprinkled over the whole manual, and this
  3828. section only contains stuff that wouldn't fit anywhere else.
  3831. Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
  3832. or modify at any time: libev will completely ignore it. This can be used
  3833. to associate arbitrary data with your watcher. If you need more data and
  3834. don't want to allocate memory separately and store a pointer to it in that
  3835. data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
  3836. data:
  3837. .PP
  3838. .Vb 7
  3839. \& struct my_io
  3840. \& {
  3841. \& ev_io io;
  3842. \& int otherfd;
  3843. \& void *somedata;
  3844. \& struct whatever *mostinteresting;
  3845. \& };
  3846. \&
  3847. \& ...
  3848. \& struct my_io w;
  3849. \& ev_io_init (&w.io, my_cb, fd, EV_READ);
  3850. .Ve
  3851. .PP
  3852. And since your callback will be called with a pointer to the watcher, you
  3853. can cast it back to your own type:
  3854. .PP
  3855. .Vb 5
  3856. \& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
  3857. \& {
  3858. \& struct my_io *w = (struct my_io *)w_;
  3859. \& ...
  3860. \& }
  3861. .Ve
  3862. .PP
  3863. More interesting and less C\-conformant ways of casting your callback
  3864. function type instead have been omitted.
  3867. Another common scenario is to use some data structure with multiple
  3868. embedded watchers, in effect creating your own watcher that combines
  3869. multiple libev event sources into one \*(L"super-watcher\*(R":
  3870. .PP
  3871. .Vb 6
  3872. \& struct my_biggy
  3873. \& {
  3874. \& int some_data;
  3875. \& ev_timer t1;
  3876. \& ev_timer t2;
  3877. \& }
  3878. .Ve
  3879. .PP
  3880. In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
  3881. complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
  3882. the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
  3883. to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
  3884. real programmers):
  3885. .PP
  3886. .Vb 1
  3887. \& #include <stddef.h>
  3888. \&
  3889. \& static void
  3890. \& t1_cb (EV_P_ ev_timer *w, int revents)
  3891. \& {
  3892. \& struct my_biggy big = (struct my_biggy *)
  3893. \& (((char *)w) \- offsetof (struct my_biggy, t1));
  3894. \& }
  3895. \&
  3896. \& static void
  3897. \& t2_cb (EV_P_ ev_timer *w, int revents)
  3898. \& {
  3899. \& struct my_biggy big = (struct my_biggy *)
  3900. \& (((char *)w) \- offsetof (struct my_biggy, t2));
  3901. \& }
  3902. .Ve
  3905. Often you have structures like this in event-based programs:
  3906. .PP
  3907. .Vb 4
  3908. \& callback ()
  3909. \& {
  3910. \& free (request);
  3911. \& }
  3912. \&
  3913. \& request = start_new_request (..., callback);
  3914. .Ve
  3915. .PP
  3916. The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
  3917. used to cancel the operation, or do other things with it.
  3918. .PP
  3919. It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
  3920. immediately invoke the callback, for example, to report errors. Or you add
  3921. some caching layer that finds that it can skip the lengthy aspects of the
  3922. operation and simply invoke the callback with the result.
  3923. .PP
  3924. The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
  3925. has returned, so \f(CW\*(C`request\*(C'\fR is not set.
  3926. .PP
  3927. Even if you pass the request by some safer means to the callback, you
  3928. might want to do something to the request after starting it, such as
  3929. canceling it, which probably isn't working so well when the callback has
  3930. already been invoked.
  3931. .PP
  3932. A common way around all these issues is to make sure that
  3933. \&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
  3934. \&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
  3935. delay invoking the callback by using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher for
  3936. example, or more sneakily, by reusing an existing (stopped) watcher and
  3937. pushing it into the pending queue:
  3938. .PP
  3939. .Vb 2
  3940. \& ev_set_cb (watcher, callback);
  3941. \& ev_feed_event (EV_A_ watcher, 0);
  3942. .Ve
  3943. .PP
  3944. This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
  3945. invoked, while not delaying callback invocation too much.
  3948. Often (especially in \s-1GUI\s0 toolkits) there are places where you have
  3949. \&\fImodal\fR interaction, which is most easily implemented by recursively
  3950. invoking \f(CW\*(C`ev_run\*(C'\fR.
  3951. .PP
  3952. This brings the problem of exiting \- a callback might want to finish the
  3953. main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
  3954. a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
  3955. and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
  3956. other combination: In these cases, a simple \f(CW\*(C`ev_break\*(C'\fR will not work.
  3957. .PP
  3958. The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
  3959. invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
  3960. triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
  3961. .PP
  3962. .Vb 2
  3963. \& // main loop
  3964. \& int exit_main_loop = 0;
  3965. \&
  3966. \& while (!exit_main_loop)
  3967. \& ev_run (EV_DEFAULT_ EVRUN_ONCE);
  3968. \&
  3969. \& // in a modal watcher
  3970. \& int exit_nested_loop = 0;
  3971. \&
  3972. \& while (!exit_nested_loop)
  3973. \& ev_run (EV_A_ EVRUN_ONCE);
  3974. .Ve
  3975. .PP
  3976. To exit from any of these loops, just set the corresponding exit variable:
  3977. .PP
  3978. .Vb 2
  3979. \& // exit modal loop
  3980. \& exit_nested_loop = 1;
  3981. \&
  3982. \& // exit main program, after modal loop is finished
  3983. \& exit_main_loop = 1;
  3984. \&
  3985. \& // exit both
  3986. \& exit_main_loop = exit_nested_loop = 1;
  3987. .Ve
  3989. .IX Subsection "THREAD LOCKING EXAMPLE"
  3990. Here is a fictitious example of how to run an event loop in a different
  3991. thread from where callbacks are being invoked and watchers are
  3992. created/added/removed.
  3993. .PP
  3994. For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
  3995. which uses exactly this technique (which is suited for many high-level
  3996. languages).
  3997. .PP
  3998. The example uses a pthread mutex to protect the loop data, a condition
  3999. variable to wait for callback invocations, an async watcher to notify the
  4000. event loop thread and an unspecified mechanism to wake up the main thread.
  4001. .PP
  4002. First, you need to associate some data with the event loop:
  4003. .PP
  4004. .Vb 6
  4005. \& typedef struct {
  4006. \& mutex_t lock; /* global loop lock */
  4007. \& ev_async async_w;
  4008. \& thread_t tid;
  4009. \& cond_t invoke_cv;
  4010. \& } userdata;
  4011. \&
  4012. \& void prepare_loop (EV_P)
  4013. \& {
  4014. \& // for simplicity, we use a static userdata struct.
  4015. \& static userdata u;
  4016. \&
  4017. \& ev_async_init (&u\->async_w, async_cb);
  4018. \& ev_async_start (EV_A_ &u\->async_w);
  4019. \&
  4020. \& pthread_mutex_init (&u\->lock, 0);
  4021. \& pthread_cond_init (&u\->invoke_cv, 0);
  4022. \&
  4023. \& // now associate this with the loop
  4024. \& ev_set_userdata (EV_A_ u);
  4025. \& ev_set_invoke_pending_cb (EV_A_ l_invoke);
  4026. \& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
  4027. \&
  4028. \& // then create the thread running ev_run
  4029. \& pthread_create (&u\->tid, 0, l_run, EV_A);
  4030. \& }
  4031. .Ve
  4032. .PP
  4033. The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
  4034. solely to wake up the event loop so it takes notice of any new watchers
  4035. that might have been added:
  4036. .PP
  4037. .Vb 5
  4038. \& static void
  4039. \& async_cb (EV_P_ ev_async *w, int revents)
  4040. \& {
  4041. \& // just used for the side effects
  4042. \& }
  4043. .Ve
  4044. .PP
  4045. The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
  4046. protecting the loop data, respectively.
  4047. .PP
  4048. .Vb 6
  4049. \& static void
  4050. \& l_release (EV_P)
  4051. \& {
  4052. \& userdata *u = ev_userdata (EV_A);
  4053. \& pthread_mutex_unlock (&u\->lock);
  4054. \& }
  4055. \&
  4056. \& static void
  4057. \& l_acquire (EV_P)
  4058. \& {
  4059. \& userdata *u = ev_userdata (EV_A);
  4060. \& pthread_mutex_lock (&u\->lock);
  4061. \& }
  4062. .Ve
  4063. .PP
  4064. The event loop thread first acquires the mutex, and then jumps straight
  4065. into \f(CW\*(C`ev_run\*(C'\fR:
  4066. .PP
  4067. .Vb 4
  4068. \& void *
  4069. \& l_run (void *thr_arg)
  4070. \& {
  4071. \& struct ev_loop *loop = (struct ev_loop *)thr_arg;
  4072. \&
  4073. \& l_acquire (EV_A);
  4074. \& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
  4075. \& ev_run (EV_A_ 0);
  4076. \& l_release (EV_A);
  4077. \&
  4078. \& return 0;
  4079. \& }
  4080. .Ve
  4081. .PP
  4082. Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
  4083. signal the main thread via some unspecified mechanism (signals? pipe
  4084. writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
  4085. have been called (in a while loop because a) spurious wakeups are possible
  4086. and b) skipping inter-thread-communication when there are no pending
  4087. watchers is very beneficial):
  4088. .PP
  4089. .Vb 4
  4090. \& static void
  4091. \& l_invoke (EV_P)
  4092. \& {
  4093. \& userdata *u = ev_userdata (EV_A);
  4094. \&
  4095. \& while (ev_pending_count (EV_A))
  4096. \& {
  4097. \& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
  4098. \& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
  4099. \& }
  4100. \& }
  4101. .Ve
  4102. .PP
  4103. Now, whenever the main thread gets told to invoke pending watchers, it
  4104. will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
  4105. thread to continue:
  4106. .PP
  4107. .Vb 4
  4108. \& static void
  4109. \& real_invoke_pending (EV_P)
  4110. \& {
  4111. \& userdata *u = ev_userdata (EV_A);
  4112. \&
  4113. \& pthread_mutex_lock (&u\->lock);
  4114. \& ev_invoke_pending (EV_A);
  4115. \& pthread_cond_signal (&u\->invoke_cv);
  4116. \& pthread_mutex_unlock (&u\->lock);
  4117. \& }
  4118. .Ve
  4119. .PP
  4120. Whenever you want to start/stop a watcher or do other modifications to an
  4121. event loop, you will now have to lock:
  4122. .PP
  4123. .Vb 2
  4124. \& ev_timer timeout_watcher;
  4125. \& userdata *u = ev_userdata (EV_A);
  4126. \&
  4127. \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
  4128. \&
  4129. \& pthread_mutex_lock (&u\->lock);
  4130. \& ev_timer_start (EV_A_ &timeout_watcher);
  4131. \& ev_async_send (EV_A_ &u\->async_w);
  4132. \& pthread_mutex_unlock (&u\->lock);
  4133. .Ve
  4134. .PP
  4135. Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
  4136. an event loop currently blocking in the kernel will have no knowledge
  4137. about the newly added timer. By waking up the loop it will pick up any new
  4138. watchers in the next event loop iteration.
  4141. While the overhead of a callback that e.g. schedules a thread is small, it
  4142. is still an overhead. If you embed libev, and your main usage is with some
  4143. kind of threads or coroutines, you might want to customise libev so that
  4144. doesn't need callbacks anymore.
  4145. .PP
  4146. Imagine you have coroutines that you can switch to using a function
  4147. \&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
  4148. and that due to some magic, the currently active coroutine is stored in a
  4149. global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
  4150. event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
  4151. the differing \f(CW\*(C`;\*(C'\fR conventions):
  4152. .PP
  4153. .Vb 2
  4154. \& #define EV_CB_DECLARE(type) struct my_coro *cb;
  4155. \& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
  4156. .Ve
  4157. .PP
  4158. That means instead of having a C callback function, you store the
  4159. coroutine to switch to in each watcher, and instead of having libev call
  4160. your callback, you instead have it switch to that coroutine.
  4161. .PP
  4162. A coroutine might now wait for an event with a function called
  4163. \&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
  4164. matter when, or whether the watcher is active or not when this function is
  4165. called):
  4166. .PP
  4167. .Vb 6
  4168. \& void
  4169. \& wait_for_event (ev_watcher *w)
  4170. \& {
  4171. \& ev_set_cb (w, current_coro);
  4172. \& switch_to (libev_coro);
  4173. \& }
  4174. .Ve
  4175. .PP
  4176. That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
  4177. continues the libev coroutine, which, when appropriate, switches back to
  4178. this or any other coroutine.
  4179. .PP
  4180. You can do similar tricks if you have, say, threads with an event queue \-
  4181. instead of storing a coroutine, you store the queue object and instead of
  4182. switching to a coroutine, you push the watcher onto the queue and notify
  4183. any waiters.
  4184. .PP
  4185. To embed libev, see \*(L"\s-1EMBEDDING\*(R"\s0, but in short, it's easiest to create two
  4186. files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
  4187. .PP
  4188. .Vb 4
  4189. \& // my_ev.h
  4190. \& #define EV_CB_DECLARE(type) struct my_coro *cb;
  4191. \& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
  4192. \& #include "../libev/ev.h"
  4193. \&
  4194. \& // my_ev.c
  4195. \& #define EV_H "my_ev.h"
  4196. \& #include "../libev/ev.c"
  4197. .Ve
  4198. .PP
  4199. And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
  4200. \&\fImy_ev.c\fR into your project. When properly specifying include paths, you
  4201. can even use \fIev.h\fR as header file name directly.
  4204. Libev offers a compatibility emulation layer for libevent. It cannot
  4205. emulate the internals of libevent, so here are some usage hints:
  4206. .IP "\(bu" 4
  4207. Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
  4208. .Sp
  4209. This was the newest libevent version available when libev was implemented,
  4210. and is still mostly unchanged in 2010.
  4211. .IP "\(bu" 4
  4212. Use it by including <event.h>, as usual.
  4213. .IP "\(bu" 4
  4214. The following members are fully supported: ev_base, ev_callback,
  4215. ev_arg, ev_fd, ev_res, ev_events.
  4216. .IP "\(bu" 4
  4217. Avoid using ev_flags and the EVLIST_*\-macros, while it is
  4218. maintained by libev, it does not work exactly the same way as in libevent (consider
  4219. it a private \s-1API\s0).
  4220. .IP "\(bu" 4
  4221. Priorities are not currently supported. Initialising priorities
  4222. will fail and all watchers will have the same priority, even though there
  4223. is an ev_pri field.
  4224. .IP "\(bu" 4
  4225. In libevent, the last base created gets the signals, in libev, the
  4226. base that registered the signal gets the signals.
  4227. .IP "\(bu" 4
  4228. Other members are not supported.
  4229. .IP "\(bu" 4
  4230. The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
  4231. to use the libev header file and library.
  4232. .SH "\*(C+ SUPPORT"
  4233. .IX Header " SUPPORT"
  4234. .SS "C \s-1API\s0"
  4235. .IX Subsection "C API"
  4236. The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
  4237. libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
  4238. will work fine.
  4239. .PP
  4240. Proper exception specifications might have to be added to callbacks passed
  4241. to libev: exceptions may be thrown only from watcher callbacks, all other
  4242. callbacks (allocator, syserr, loop acquire/release and periodic reschedule
  4243. callbacks) must not throw exceptions, and might need a \f(CW\*(C`noexcept\*(C'\fR
  4244. specification. If you have code that needs to be compiled as both C and
  4245. \&\*(C+ you can use the \f(CW\*(C`EV_NOEXCEPT\*(C'\fR macro for this:
  4246. .PP
  4247. .Vb 6
  4248. \& static void
  4249. \& fatal_error (const char *msg) EV_NOEXCEPT
  4250. \& {
  4251. \& perror (msg);
  4252. \& abort ();
  4253. \& }
  4254. \&
  4255. \& ...
  4256. \& ev_set_syserr_cb (fatal_error);
  4257. .Ve
  4258. .PP
  4259. The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
  4260. \&\f(CW\*(C`ev_invoke\*(C'\fR, \f(CW\*(C`ev_invoke_pending\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR (the latter
  4261. because it runs cleanup watchers).
  4262. .PP
  4263. Throwing exceptions in watcher callbacks is only supported if libev itself
  4264. is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
  4265. throwing exceptions through C libraries (most do).
  4266. .SS "\*(C+ \s-1API\s0"
  4267. .IX Subsection " API"
  4268. Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
  4269. you to use some convenience methods to start/stop watchers and also change
  4270. the callback model to a model using method callbacks on objects.
  4271. .PP
  4272. To use it,
  4273. .PP
  4274. .Vb 1
  4275. \& #include <ev++.h>
  4276. .Ve
  4277. .PP
  4278. This automatically includes \fIev.h\fR and puts all of its definitions (many
  4279. of them macros) into the global namespace. All \*(C+ specific things are
  4280. put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
  4281. options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
  4282. .PP
  4283. Care has been taken to keep the overhead low. The only data member the \*(C+
  4284. classes add (compared to plain C\-style watchers) is the event loop pointer
  4285. that the watcher is associated with (or no additional members at all if
  4286. you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
  4287. .PP
  4288. Currently, functions, static and non-static member functions and classes
  4289. with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
  4290. to add as long as they only need one additional pointer for context. If
  4291. you need support for other types of functors please contact the author
  4292. (preferably after implementing it).
  4293. .PP
  4294. For all this to work, your \*(C+ compiler either has to use the same calling
  4295. conventions as your C compiler (for static member functions), or you have
  4296. to embed libev and compile libev itself as \*(C+.
  4297. .PP
  4298. Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
  4299. .ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
  4300. .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
  4301. .IX Item "ev::READ, ev::WRITE etc."
  4302. These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
  4303. macros from \fIev.h\fR.
  4304. .ie n .IP """ev::tstamp"", ""ev::now""" 4
  4305. .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
  4306. .IX Item "ev::tstamp, ev::now"
  4307. Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
  4308. .ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
  4309. .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
  4310. .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
  4311. For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
  4312. the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
  4313. which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
  4314. defined by many implementations.
  4315. .Sp
  4316. All of those classes have these methods:
  4317. .RS 4
  4318. .IP "ev::TYPE::TYPE ()" 4
  4319. .IX Item "ev::TYPE::TYPE ()"
  4320. .PD 0
  4321. .IP "ev::TYPE::TYPE (loop)" 4
  4322. .IX Item "ev::TYPE::TYPE (loop)"
  4323. .IP "ev::TYPE::~TYPE" 4
  4324. .IX Item "ev::TYPE::~TYPE"
  4325. .PD
  4326. The constructor (optionally) takes an event loop to associate the watcher
  4327. with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
  4328. .Sp
  4329. The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
  4330. \&\f(CW\*(C`set\*(C'\fR method before starting it.
  4331. .Sp
  4332. It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
  4333. method to set a callback before you can start the watcher.
  4334. .Sp
  4335. (The reason why you have to use a method is a limitation in \*(C+ which does
  4336. not allow explicit template arguments for constructors).
  4337. .Sp
  4338. The destructor automatically stops the watcher if it is active.
  4339. .IP "w\->set<class, &class::method> (object *)" 4
  4340. .IX Item "w->set<class, &class::method> (object *)"
  4341. This method sets the callback method to call. The method has to have a
  4342. signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
  4343. first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
  4344. parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
  4345. .Sp
  4346. This method synthesizes efficient thunking code to call your method from
  4347. the C callback that libev requires. If your compiler can inline your
  4348. callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
  4349. your compiler is good :), then the method will be fully inlined into the
  4350. thunking function, making it as fast as a direct C callback.
  4351. .Sp
  4352. Example: simple class declaration and watcher initialisation
  4353. .Sp
  4354. .Vb 4
  4355. \& struct myclass
  4356. \& {
  4357. \& void io_cb (ev::io &w, int revents) { }
  4358. \& }
  4359. \&
  4360. \& myclass obj;
  4361. \& ev::io iow;
  4362. \& iow.set <myclass, &myclass::io_cb> (&obj);
  4363. .Ve
  4364. .IP "w\->set (object *)" 4
  4365. .IX Item "w->set (object *)"
  4366. This is a variation of a method callback \- leaving out the method to call
  4367. will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
  4368. functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
  4369. the time. Incidentally, you can then also leave out the template argument
  4370. list.
  4371. .Sp
  4372. The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
  4373. int revents)\*(C'\fR.
  4374. .Sp
  4375. See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
  4376. .Sp
  4377. Example: use a functor object as callback.
  4378. .Sp
  4379. .Vb 7
  4380. \& struct myfunctor
  4381. \& {
  4382. \& void operator() (ev::io &w, int revents)
  4383. \& {
  4384. \& ...
  4385. \& }
  4386. \& }
  4387. \&
  4388. \& myfunctor f;
  4389. \&
  4390. \& ev::io w;
  4391. \& w.set (&f);
  4392. .Ve
  4393. .IP "w\->set<function> (void *data = 0)" 4
  4394. .IX Item "w->set<function> (void *data = 0)"
  4395. Also sets a callback, but uses a static method or plain function as
  4396. callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
  4397. \&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
  4398. .Sp
  4399. The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
  4400. .Sp
  4401. See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
  4402. .Sp
  4403. Example: Use a plain function as callback.
  4404. .Sp
  4405. .Vb 2
  4406. \& static void io_cb (ev::io &w, int revents) { }
  4407. \& iow.set <io_cb> ();
  4408. .Ve
  4409. .IP "w\->set (loop)" 4
  4410. .IX Item "w->set (loop)"
  4411. Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
  4412. do this when the watcher is inactive (and not pending either).
  4413. .IP "w\->set ([arguments])" 4
  4414. .IX Item "w->set ([arguments])"
  4415. Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR (except for \f(CW\*(C`ev::embed\*(C'\fR watchers>),
  4416. with the same arguments. Either this method or a suitable start method
  4417. must be called at least once. Unlike the C counterpart, an active watcher
  4418. gets automatically stopped and restarted when reconfiguring it with this
  4419. method.
  4420. .Sp
  4421. For \f(CW\*(C`ev::embed\*(C'\fR watchers this method is called \f(CW\*(C`set_embed\*(C'\fR, to avoid
  4422. clashing with the \f(CW\*(C`set (loop)\*(C'\fR method.
  4423. .Sp
  4424. For \f(CW\*(C`ev::io\*(C'\fR watchers there is an additional \f(CW\*(C`set\*(C'\fR method that acepts a
  4425. new event mask only, and internally calls \f(CW\*(C`ev_io_modfify\*(C'\fR.
  4426. .IP "w\->start ()" 4
  4427. .IX Item "w->start ()"
  4428. Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
  4429. constructor already stores the event loop.
  4430. .IP "w\->start ([arguments])" 4
  4431. .IX Item "w->start ([arguments])"
  4432. Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
  4433. convenient to wrap them in one call. Uses the same type of arguments as
  4434. the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
  4435. .IP "w\->stop ()" 4
  4436. .IX Item "w->stop ()"
  4437. Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
  4438. .ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
  4439. .el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
  4440. .IX Item "w->again () (ev::timer, ev::periodic only)"
  4441. For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
  4442. \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
  4443. .ie n .IP "w\->sweep () (""ev::embed"" only)" 4
  4444. .el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
  4445. .IX Item "w->sweep () (ev::embed only)"
  4446. Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
  4447. .ie n .IP "w\->update () (""ev::stat"" only)" 4
  4448. .el .IP "w\->update () (\f(CWev::stat\fR only)" 4
  4449. .IX Item "w->update () (ev::stat only)"
  4450. Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
  4451. .RE
  4452. .RS 4
  4453. .RE
  4454. .PP
  4455. Example: Define a class with two I/O and idle watchers, start the I/O
  4456. watchers in the constructor.
  4457. .PP
  4458. .Vb 5
  4459. \& class myclass
  4460. \& {
  4461. \& ev::io io ; void io_cb (ev::io &w, int revents);
  4462. \& ev::io io2 ; void io2_cb (ev::io &w, int revents);
  4463. \& ev::idle idle; void idle_cb (ev::idle &w, int revents);
  4464. \&
  4465. \& myclass (int fd)
  4466. \& {
  4467. \& io .set <myclass, &myclass::io_cb > (this);
  4468. \& io2 .set <myclass, &myclass::io2_cb > (this);
  4469. \& idle.set <myclass, &myclass::idle_cb> (this);
  4470. \&
  4471. \& io.set (fd, ev::WRITE); // configure the watcher
  4472. \& io.start (); // start it whenever convenient
  4473. \&
  4474. \& io2.start (fd, ev::READ); // set + start in one call
  4475. \& }
  4476. \& };
  4477. .Ve
  4480. Libev does not offer other language bindings itself, but bindings for a
  4481. number of languages exist in the form of third-party packages. If you know
  4482. any interesting language binding in addition to the ones listed here, drop
  4483. me a note.
  4484. .IP "Perl" 4
  4485. .IX Item "Perl"
  4486. The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
  4487. libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
  4488. there are additional modules that implement libev-compatible interfaces
  4489. to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
  4490. \&\f(CW\*(C`Net::SNMP\*(C'\fR (\f(CW\*(C`Net::SNMP::EV\*(C'\fR) and the \f(CW\*(C`libglib\*(C'\fR event core (\f(CW\*(C`Glib::EV\*(C'\fR
  4491. and \f(CW\*(C`EV::Glib\*(C'\fR).
  4492. .Sp
  4493. It can be found and installed via \s-1CPAN,\s0 its homepage is at
  4494. <http://software.schmorp.de/pkg/EV>.
  4495. .IP "Python" 4
  4496. .IX Item "Python"
  4497. Python bindings can be found at <http://code.google.com/p/pyev/>. It
  4498. seems to be quite complete and well-documented.
  4499. .IP "Ruby" 4
  4500. .IX Item "Ruby"
  4501. Tony Arcieri has written a ruby extension that offers access to a subset
  4502. of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
  4503. more on top of it. It can be found via gem servers. Its homepage is at
  4504. <http://rev.rubyforge.org/>.
  4505. .Sp
  4506. Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
  4507. makes rev work even on mingw.
  4508. .IP "Haskell" 4
  4509. .IX Item "Haskell"
  4510. A haskell binding to libev is available at
  4511. <http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
  4512. .IP "D" 4
  4513. .IX Item "D"
  4514. Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
  4515. be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
  4516. .IP "Ocaml" 4
  4517. .IX Item "Ocaml"
  4518. Erkki Seppala has written Ocaml bindings for libev, to be found at
  4519. <http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
  4520. .IP "Lua" 4
  4521. .IX Item "Lua"
  4522. Brian Maher has written a partial interface to libev for lua (at the
  4523. time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
  4524. <http://github.com/brimworks/lua\-ev>.
  4525. .IP "Javascript" 4
  4526. .IX Item "Javascript"
  4527. Node.js (<http://nodejs.org>) uses libev as the underlying event library.
  4528. .IP "Others" 4
  4529. .IX Item "Others"
  4530. There are others, and I stopped counting.
  4531. .SH "MACRO MAGIC"
  4532. .IX Header "MACRO MAGIC"
  4533. Libev can be compiled with a variety of options, the most fundamental
  4534. of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
  4535. functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
  4536. .PP
  4537. To make it easier to write programs that cope with either variant, the
  4538. following macros are defined:
  4539. .ie n .IP """EV_A"", ""EV_A_""" 4
  4540. .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
  4541. .IX Item "EV_A, EV_A_"
  4542. This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
  4543. loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
  4544. \&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
  4545. .Sp
  4546. .Vb 3
  4547. \& ev_unref (EV_A);
  4548. \& ev_timer_add (EV_A_ watcher);
  4549. \& ev_run (EV_A_ 0);
  4550. .Ve
  4551. .Sp
  4552. It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
  4553. which is often provided by the following macro.
  4554. .ie n .IP """EV_P"", ""EV_P_""" 4
  4555. .el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
  4556. .IX Item "EV_P, EV_P_"
  4557. This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
  4558. loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
  4559. \&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
  4560. .Sp
  4561. .Vb 2
  4562. \& // this is how ev_unref is being declared
  4563. \& static void ev_unref (EV_P);
  4564. \&
  4565. \& // this is how you can declare your typical callback
  4566. \& static void cb (EV_P_ ev_timer *w, int revents)
  4567. .Ve
  4568. .Sp
  4569. It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
  4570. suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
  4571. .ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
  4572. .el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
  4573. .IX Item "EV_DEFAULT, EV_DEFAULT_"
  4574. Similar to the other two macros, this gives you the value of the default
  4575. loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
  4576. will be initialised if it isn't already initialised.
  4577. .Sp
  4578. For non-multiplicity builds, these macros do nothing, so you always have
  4579. to initialise the loop somewhere.
  4580. .ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
  4581. .el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
  4583. Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
  4584. default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
  4585. is undefined when the default loop has not been initialised by a previous
  4586. execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
  4587. .Sp
  4588. It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
  4589. watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
  4590. .PP
  4591. Example: Declare and initialise a check watcher, utilising the above
  4592. macros so it will work regardless of whether multiple loops are supported
  4593. or not.
  4594. .PP
  4595. .Vb 5
  4596. \& static void
  4597. \& check_cb (EV_P_ ev_timer *w, int revents)
  4598. \& {
  4599. \& ev_check_stop (EV_A_ w);
  4600. \& }
  4601. \&
  4602. \& ev_check check;
  4603. \& ev_check_init (&check, check_cb);
  4604. \& ev_check_start (EV_DEFAULT_ &check);
  4605. \& ev_run (EV_DEFAULT_ 0);
  4606. .Ve
  4607. .SH "EMBEDDING"
  4608. .IX Header "EMBEDDING"
  4609. Libev can (and often is) directly embedded into host
  4610. applications. Examples of applications that embed it include the Deliantra
  4611. Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
  4612. and rxvt-unicode.
  4613. .PP
  4614. The goal is to enable you to just copy the necessary files into your
  4615. source directory without having to change even a single line in them, so
  4616. you can easily upgrade by simply copying (or having a checked-out copy of
  4617. libev somewhere in your source tree).
  4618. .SS "\s-1FILESETS\s0"
  4619. .IX Subsection "FILESETS"
  4620. Depending on what features you need you need to include one or more sets of files
  4621. in your application.
  4622. .PP
  4623. \fI\s-1CORE EVENT LOOP\s0\fR
  4624. .IX Subsection "CORE EVENT LOOP"
  4625. .PP
  4626. To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
  4627. configuration (no autoconf):
  4628. .PP
  4629. .Vb 2
  4630. \& #define EV_STANDALONE 1
  4631. \& #include "ev.c"
  4632. .Ve
  4633. .PP
  4634. This will automatically include \fIev.h\fR, too, and should be done in a
  4635. single C source file only to provide the function implementations. To use
  4636. it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
  4637. done by writing a wrapper around \fIev.h\fR that you can include instead and
  4638. where you can put other configuration options):
  4639. .PP
  4640. .Vb 2
  4641. \& #define EV_STANDALONE 1
  4642. \& #include "ev.h"
  4643. .Ve
  4644. .PP
  4645. Both header files and implementation files can be compiled with a \*(C+
  4646. compiler (at least, that's a stated goal, and breakage will be treated
  4647. as a bug).
  4648. .PP
  4649. You need the following files in your source tree, or in a directory
  4650. in your include path (e.g. in libev/ when using \-Ilibev):
  4651. .PP
  4652. .Vb 4
  4653. \& ev.h
  4654. \& ev.c
  4655. \& ev_vars.h
  4656. \& ev_wrap.h
  4657. \&
  4658. \& ev_win32.c required on win32 platforms only
  4659. \&
  4660. \& ev_select.c only when select backend is enabled
  4661. \& ev_poll.c only when poll backend is enabled
  4662. \& ev_epoll.c only when the epoll backend is enabled
  4663. \& ev_linuxaio.c only when the linux aio backend is enabled
  4664. \& ev_iouring.c only when the linux io_uring backend is enabled
  4665. \& ev_kqueue.c only when the kqueue backend is enabled
  4666. \& ev_port.c only when the solaris port backend is enabled
  4667. .Ve
  4668. .PP
  4669. \&\fIev.c\fR includes the backend files directly when enabled, so you only need
  4670. to compile this single file.
  4671. .PP
  4674. .PP
  4675. To include the libevent compatibility \s-1API,\s0 also include:
  4676. .PP
  4677. .Vb 1
  4678. \& #include "event.c"
  4679. .Ve
  4680. .PP
  4681. in the file including \fIev.c\fR, and:
  4682. .PP
  4683. .Vb 1
  4684. \& #include "event.h"
  4685. .Ve
  4686. .PP
  4687. in the files that want to use the libevent \s-1API.\s0 This also includes \fIev.h\fR.
  4688. .PP
  4689. You need the following additional files for this:
  4690. .PP
  4691. .Vb 2
  4692. \& event.h
  4693. \& event.c
  4694. .Ve
  4695. .PP
  4696. \fI\s-1AUTOCONF SUPPORT\s0\fR
  4697. .IX Subsection "AUTOCONF SUPPORT"
  4698. .PP
  4699. Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
  4700. whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
  4701. \&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
  4702. include \fIconfig.h\fR and configure itself accordingly.
  4703. .PP
  4704. For this of course you need the m4 file:
  4705. .PP
  4706. .Vb 1
  4707. \& libev.m4
  4708. .Ve
  4711. Libev can be configured via a variety of preprocessor symbols you have to
  4712. define before including (or compiling) any of its files. The default in
  4713. the absence of autoconf is documented for every option.
  4714. .PP
  4715. Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI,\s0 and can have different
  4716. values when compiling libev vs. including \fIev.h\fR, so it is permissible
  4717. to redefine them before including \fIev.h\fR without breaking compatibility
  4718. to a compiled library. All other symbols change the \s-1ABI,\s0 which means all
  4719. users of libev and the libev code itself must be compiled with compatible
  4720. settings.
  4721. .IP "\s-1EV_COMPAT3\s0 (h)" 4
  4722. .IX Item "EV_COMPAT3 (h)"
  4723. Backwards compatibility is a major concern for libev. This is why this
  4724. release of libev comes with wrappers for the functions and symbols that
  4725. have been renamed between libev version 3 and 4.
  4726. .Sp
  4727. You can disable these wrappers (to test compatibility with future
  4728. versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
  4729. sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
  4730. from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
  4731. typedef in that case.
  4732. .Sp
  4733. In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
  4734. and in some even more future version the compatibility code will be
  4735. removed completely.
  4736. .IP "\s-1EV_STANDALONE\s0 (h)" 4
  4737. .IX Item "EV_STANDALONE (h)"
  4738. Must always be \f(CW1\fR if you do not use autoconf configuration, which
  4739. keeps libev from including \fIconfig.h\fR, and it also defines dummy
  4740. implementations for some libevent functions (such as logging, which is not
  4741. supported). It will also not define any of the structs usually found in
  4742. \&\fIevent.h\fR that are not directly supported by the libev core alone.
  4743. .Sp
  4744. In standalone mode, libev will still try to automatically deduce the
  4745. configuration, but has to be more conservative.
  4746. .IP "\s-1EV_USE_FLOOR\s0" 4
  4747. .IX Item "EV_USE_FLOOR"
  4748. If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
  4749. periodic reschedule calculations, otherwise libev will fall back on a
  4750. portable (slower) implementation. If you enable this, you usually have to
  4751. link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
  4752. function is not available will fail, so the safe default is to not enable
  4753. this.
  4754. .IP "\s-1EV_USE_MONOTONIC\s0" 4
  4755. .IX Item "EV_USE_MONOTONIC"
  4756. If defined to be \f(CW1\fR, libev will try to detect the availability of the
  4757. monotonic clock option at both compile time and runtime. Otherwise no
  4758. use of the monotonic clock option will be attempted. If you enable this,
  4759. you usually have to link against librt or something similar. Enabling it
  4760. when the functionality isn't available is safe, though, although you have
  4761. to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
  4762. function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
  4763. .IP "\s-1EV_USE_REALTIME\s0" 4
  4764. .IX Item "EV_USE_REALTIME"
  4765. If defined to be \f(CW1\fR, libev will try to detect the availability of the
  4766. real-time clock option at compile time (and assume its availability
  4767. at runtime if successful). Otherwise no use of the real-time clock
  4768. option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
  4769. by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
  4770. correctness. See the note about libraries in the description of
  4771. \&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
  4772. \&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
  4773. .IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
  4775. If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
  4776. of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
  4777. exists because on GNU/Linux, \f(CW\*(C`clock_gettime\*(C'\fR is in \f(CW\*(C`librt\*(C'\fR, but \f(CW\*(C`librt\*(C'\fR
  4778. unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
  4779. programs needlessly. Using a direct syscall is slightly slower (in
  4780. theory), because no optimised vdso implementation can be used, but avoids
  4781. the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
  4782. higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
  4783. .IP "\s-1EV_USE_NANOSLEEP\s0" 4
  4784. .IX Item "EV_USE_NANOSLEEP"
  4785. If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
  4786. and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
  4787. .IP "\s-1EV_USE_EVENTFD\s0" 4
  4788. .IX Item "EV_USE_EVENTFD"
  4789. If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
  4790. available and will probe for kernel support at runtime. This will improve
  4791. \&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
  4792. If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
  4793. 2.7 or newer, otherwise disabled.
  4794. .IP "\s-1EV_USE_SIGNALFD\s0" 4
  4795. .IX Item "EV_USE_SIGNALFD"
  4796. If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`signalfd ()\*(C'\fR is
  4797. available and will probe for kernel support at runtime. This enables
  4798. the use of \s-1EVFLAG_SIGNALFD\s0 for faster and simpler signal handling. If
  4799. undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
  4800. 2.7 or newer, otherwise disabled.
  4801. .IP "\s-1EV_USE_TIMERFD\s0" 4
  4802. .IX Item "EV_USE_TIMERFD"
  4803. If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`timerfd ()\*(C'\fR is
  4804. available and will probe for kernel support at runtime. This allows
  4805. libev to detect time jumps accurately. If undefined, it will be enabled
  4806. if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
  4807. \&\f(CW\*(C`TFD_TIMER_CANCEL_ON_SET\*(C'\fR, otherwise disabled.
  4808. .IP "\s-1EV_USE_EVENTFD\s0" 4
  4809. .IX Item "EV_USE_EVENTFD"
  4810. If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
  4811. available and will probe for kernel support at runtime. This will improve
  4812. \&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
  4813. If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
  4814. 2.7 or newer, otherwise disabled.
  4815. .IP "\s-1EV_USE_SELECT\s0" 4
  4816. .IX Item "EV_USE_SELECT"
  4817. If undefined or defined to be \f(CW1\fR, libev will compile in support for the
  4818. \&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
  4819. other method takes over, select will be it. Otherwise the select backend
  4820. will not be compiled in.
  4821. .IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
  4822. .IX Item "EV_SELECT_USE_FD_SET"
  4823. If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
  4824. structure. This is useful if libev doesn't compile due to a missing
  4825. \&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
  4826. on exotic systems. This usually limits the range of file descriptors to
  4827. some low limit such as 1024 or might have other limitations (winsocket
  4828. only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
  4829. configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
  4830. .IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
  4832. When defined to \f(CW1\fR, the select backend will assume that
  4833. select/socket/connect etc. don't understand file descriptors but
  4834. wants osf handles on win32 (this is the case when the select to
  4835. be used is the winsock select). This means that it will call
  4836. \&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
  4837. it is assumed that all these functions actually work on fds, even
  4838. on win32. Should not be defined on non\-win32 platforms.
  4839. .IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
  4840. .IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
  4841. If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
  4842. file descriptors to socket handles. When not defining this symbol (the
  4843. default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
  4844. correct. In some cases, programs use their own file descriptor management,
  4845. in which case they can provide this function to map fds to socket handles.
  4846. .IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
  4847. .IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
  4848. If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
  4849. using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
  4850. their own fd to handle mapping, overwriting this function makes it easier
  4851. to do so. This can be done by defining this macro to an appropriate value.
  4852. .IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
  4853. .IX Item "EV_WIN32_CLOSE_FD(fd)"
  4854. If programs implement their own fd to handle mapping on win32, then this
  4855. macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
  4856. file descriptors again. Note that the replacement function has to close
  4857. the underlying \s-1OS\s0 handle.
  4858. .IP "\s-1EV_USE_WSASOCKET\s0" 4
  4859. .IX Item "EV_USE_WSASOCKET"
  4860. If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal
  4861. communication socket, which works better in some environments. Otherwise,
  4862. the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other
  4863. environments.
  4864. .IP "\s-1EV_USE_POLL\s0" 4
  4865. .IX Item "EV_USE_POLL"
  4866. If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
  4867. backend. Otherwise it will be enabled on non\-win32 platforms. It
  4868. takes precedence over select.
  4869. .IP "\s-1EV_USE_EPOLL\s0" 4
  4870. .IX Item "EV_USE_EPOLL"
  4871. If defined to be \f(CW1\fR, libev will compile in support for the Linux
  4872. \&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
  4873. otherwise another method will be used as fallback. This is the preferred
  4874. backend for GNU/Linux systems. If undefined, it will be enabled if the
  4875. headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
  4876. .IP "\s-1EV_USE_LINUXAIO\s0" 4
  4877. .IX Item "EV_USE_LINUXAIO"
  4878. If defined to be \f(CW1\fR, libev will compile in support for the Linux aio
  4879. backend (\f(CW\*(C`EV_USE_EPOLL\*(C'\fR must also be enabled). If undefined, it will be
  4880. enabled on linux, otherwise disabled.
  4881. .IP "\s-1EV_USE_IOURING\s0" 4
  4882. .IX Item "EV_USE_IOURING"
  4883. If defined to be \f(CW1\fR, libev will compile in support for the Linux
  4884. io_uring backend (\f(CW\*(C`EV_USE_EPOLL\*(C'\fR must also be enabled). Due to it's
  4885. current limitations it has to be requested explicitly. If undefined, it
  4886. will be enabled on linux, otherwise disabled.
  4887. .IP "\s-1EV_USE_KQUEUE\s0" 4
  4888. .IX Item "EV_USE_KQUEUE"
  4889. If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
  4890. \&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
  4891. otherwise another method will be used as fallback. This is the preferred
  4892. backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
  4893. supports some types of fds correctly (the only platform we found that
  4894. supports ptys for example was NetBSD), so kqueue might be compiled in, but
  4895. not be used unless explicitly requested. The best way to use it is to find
  4896. out whether kqueue supports your type of fd properly and use an embedded
  4897. kqueue loop.
  4898. .IP "\s-1EV_USE_PORT\s0" 4
  4899. .IX Item "EV_USE_PORT"
  4900. If defined to be \f(CW1\fR, libev will compile in support for the Solaris
  4901. 10 port style backend. Its availability will be detected at runtime,
  4902. otherwise another method will be used as fallback. This is the preferred
  4903. backend for Solaris 10 systems.
  4904. .IP "\s-1EV_USE_DEVPOLL\s0" 4
  4905. .IX Item "EV_USE_DEVPOLL"
  4906. Reserved for future expansion, works like the \s-1USE\s0 symbols above.
  4907. .IP "\s-1EV_USE_INOTIFY\s0" 4
  4908. .IX Item "EV_USE_INOTIFY"
  4909. If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
  4910. interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
  4911. be detected at runtime. If undefined, it will be enabled if the headers
  4912. indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
  4913. .IP "\s-1EV_NO_SMP\s0" 4
  4914. .IX Item "EV_NO_SMP"
  4915. If defined to be \f(CW1\fR, libev will assume that memory is always coherent
  4916. between threads, that is, threads can be used, but threads never run on
  4917. different cpus (or different cpu cores). This reduces dependencies
  4918. and makes libev faster.
  4919. .IP "\s-1EV_NO_THREADS\s0" 4
  4920. .IX Item "EV_NO_THREADS"
  4921. If defined to be \f(CW1\fR, libev will assume that it will never be called from
  4922. different threads (that includes signal handlers), which is a stronger
  4923. assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR, above. This reduces dependencies and makes
  4924. libev faster.
  4925. .IP "\s-1EV_ATOMIC_T\s0" 4
  4926. .IX Item "EV_ATOMIC_T"
  4927. Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
  4928. access is atomic with respect to other threads or signal contexts. No
  4929. such type is easily found in the C language, so you can provide your own
  4930. type that you know is safe for your purposes. It is used both for signal
  4931. handler \*(L"locking\*(R" as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR
  4932. watchers.
  4933. .Sp
  4934. In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
  4935. (from \fIsignal.h\fR), which is usually good enough on most platforms.
  4936. .IP "\s-1EV_H\s0 (h)" 4
  4937. .IX Item "EV_H (h)"
  4938. The name of the \fIev.h\fR header file used to include it. The default if
  4939. undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
  4940. used to virtually rename the \fIev.h\fR header file in case of conflicts.
  4941. .IP "\s-1EV_CONFIG_H\s0 (h)" 4
  4942. .IX Item "EV_CONFIG_H (h)"
  4943. If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
  4944. \&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
  4945. \&\f(CW\*(C`EV_H\*(C'\fR, above.
  4946. .IP "\s-1EV_EVENT_H\s0 (h)" 4
  4947. .IX Item "EV_EVENT_H (h)"
  4948. Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
  4949. of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
  4950. .IP "\s-1EV_PROTOTYPES\s0 (h)" 4
  4951. .IX Item "EV_PROTOTYPES (h)"
  4952. If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
  4953. prototypes, but still define all the structs and other symbols. This is
  4954. occasionally useful if you want to provide your own wrapper functions
  4955. around libev functions.
  4956. .IP "\s-1EV_MULTIPLICITY\s0" 4
  4957. .IX Item "EV_MULTIPLICITY"
  4958. If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
  4959. will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
  4960. additional independent event loops. Otherwise there will be no support
  4961. for multiple event loops and there is no first event loop pointer
  4962. argument. Instead, all functions act on the single default loop.
  4963. .Sp
  4964. Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
  4965. default loop when multiplicity is switched off \- you always have to
  4966. initialise the loop manually in this case.
  4967. .IP "\s-1EV_MINPRI\s0" 4
  4968. .IX Item "EV_MINPRI"
  4969. .PD 0
  4970. .IP "\s-1EV_MAXPRI\s0" 4
  4971. .IX Item "EV_MAXPRI"
  4972. .PD
  4973. The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
  4974. \&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
  4975. provide for more priorities by overriding those symbols (usually defined
  4976. to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
  4977. .Sp
  4978. When doing priority-based operations, libev usually has to linearly search
  4979. all the priorities, so having many of them (hundreds) uses a lot of space
  4980. and time, so using the defaults of five priorities (\-2 .. +2) is usually
  4981. fine.
  4982. .Sp
  4983. If your embedding application does not need any priorities, defining these
  4984. both to \f(CW0\fR will save some memory and \s-1CPU.\s0
  4987. If undefined or defined to be \f(CW1\fR (and the platform supports it), then
  4988. the respective watcher type is supported. If defined to be \f(CW0\fR, then it
  4989. is not. Disabling watcher types mainly saves code size.
  4990. .IP "\s-1EV_FEATURES\s0" 4
  4991. .IX Item "EV_FEATURES"
  4992. If you need to shave off some kilobytes of code at the expense of some
  4993. speed (but with the full \s-1API\s0), you can define this symbol to request
  4994. certain subsets of functionality. The default is to enable all features
  4995. that can be enabled on the platform.
  4996. .Sp
  4997. A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
  4998. with some broad features you want) and then selectively re-enable
  4999. additional parts you want, for example if you want everything minimal,
  5000. but multiple event loop support, async and child watchers and the poll
  5001. backend, use this:
  5002. .Sp
  5003. .Vb 5
  5004. \& #define EV_FEATURES 0
  5005. \& #define EV_MULTIPLICITY 1
  5006. \& #define EV_USE_POLL 1
  5007. \& #define EV_CHILD_ENABLE 1
  5008. \& #define EV_ASYNC_ENABLE 1
  5009. .Ve
  5010. .Sp
  5011. The actual value is a bitset, it can be a combination of the following
  5012. values (by default, all of these are enabled):
  5013. .RS 4
  5014. .ie n .IP "1 \- faster/larger code" 4
  5015. .el .IP "\f(CW1\fR \- faster/larger code" 4
  5016. .IX Item "1 - faster/larger code"
  5017. Use larger code to speed up some operations.
  5018. .Sp
  5019. Currently this is used to override some inlining decisions (enlarging the
  5020. code size by roughly 30% on amd64).
  5021. .Sp
  5022. When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
  5023. gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
  5024. assertions.
  5025. .Sp
  5026. The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
  5027. (e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
  5028. .ie n .IP "2 \- faster/larger data structures" 4
  5029. .el .IP "\f(CW2\fR \- faster/larger data structures" 4
  5030. .IX Item "2 - faster/larger data structures"
  5031. Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
  5032. hash table sizes and so on. This will usually further increase code size
  5033. and can additionally have an effect on the size of data structures at
  5034. runtime.
  5035. .Sp
  5036. The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
  5037. (e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
  5038. .ie n .IP "4 \- full \s-1API\s0 configuration" 4
  5039. .el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
  5040. .IX Item "4 - full API configuration"
  5041. This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
  5042. enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
  5043. .ie n .IP "8 \- full \s-1API\s0" 4
  5044. .el .IP "\f(CW8\fR \- full \s-1API\s0" 4
  5045. .IX Item "8 - full API"
  5046. This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
  5047. details on which parts of the \s-1API\s0 are still available without this
  5048. feature, and do not complain if this subset changes over time.
  5049. .ie n .IP "16 \- enable all optional watcher types" 4
  5050. .el .IP "\f(CW16\fR \- enable all optional watcher types" 4
  5051. .IX Item "16 - enable all optional watcher types"
  5052. Enables all optional watcher types. If you want to selectively enable
  5053. only some watcher types other than I/O and timers (e.g. prepare,
  5054. embed, async, child...) you can enable them manually by defining
  5055. \&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
  5056. .ie n .IP "32 \- enable all backends" 4
  5057. .el .IP "\f(CW32\fR \- enable all backends" 4
  5058. .IX Item "32 - enable all backends"
  5059. This enables all backends \- without this feature, you need to enable at
  5060. least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
  5061. .ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
  5062. .el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
  5063. .IX Item "64 - enable OS-specific helper APIs"
  5064. Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
  5065. default.
  5066. .RE
  5067. .RS 4
  5068. .Sp
  5069. Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
  5070. reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
  5071. code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
  5072. watchers, timers and monotonic clock support.
  5073. .Sp
  5074. With an intelligent-enough linker (gcc+binutils are intelligent enough
  5075. when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
  5076. your program might be left out as well \- a binary starting a timer and an
  5077. I/O watcher then might come out at only 5Kb.
  5078. .RE
  5079. .IP "\s-1EV_API_STATIC\s0" 4
  5080. .IX Item "EV_API_STATIC"
  5081. If this symbol is defined (by default it is not), then all identifiers
  5082. will have static linkage. This means that libev will not export any
  5083. identifiers, and you cannot link against libev anymore. This can be useful
  5084. when you embed libev, only want to use libev functions in a single file,
  5085. and do not want its identifiers to be visible.
  5086. .Sp
  5087. To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
  5088. wants to use libev.
  5089. .Sp
  5090. This option only works when libev is compiled with a C compiler, as \*(C+
  5091. doesn't support the required declaration syntax.
  5092. .IP "\s-1EV_AVOID_STDIO\s0" 4
  5093. .IX Item "EV_AVOID_STDIO"
  5094. If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
  5095. functions (printf, scanf, perror etc.). This will increase the code size
  5096. somewhat, but if your program doesn't otherwise depend on stdio and your
  5097. libc allows it, this avoids linking in the stdio library which is quite
  5098. big.
  5099. .Sp
  5100. Note that error messages might become less precise when this option is
  5101. enabled.
  5102. .IP "\s-1EV_NSIG\s0" 4
  5103. .IX Item "EV_NSIG"
  5104. The highest supported signal number, +1 (or, the number of
  5105. signals): Normally, libev tries to deduce the maximum number of signals
  5106. automatically, but sometimes this fails, in which case it can be
  5107. specified. Also, using a lower number than detected (\f(CW32\fR should be
  5108. good for about any system in existence) can save some memory, as libev
  5109. statically allocates some 12\-24 bytes per signal number.
  5110. .IP "\s-1EV_PID_HASHSIZE\s0" 4
  5111. .IX Item "EV_PID_HASHSIZE"
  5112. \&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
  5113. pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
  5114. usually more than enough. If you need to manage thousands of children you
  5115. might want to increase this value (\fImust\fR be a power of two).
  5116. .IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
  5118. \&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
  5119. inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
  5120. disabled), usually more than enough. If you need to manage thousands of
  5121. \&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
  5122. power of two).
  5123. .IP "\s-1EV_USE_4HEAP\s0" 4
  5124. .IX Item "EV_USE_4HEAP"
  5125. Heaps are not very cache-efficient. To improve the cache-efficiency of the
  5126. timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
  5127. to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
  5128. faster performance with many (thousands) of watchers.
  5129. .Sp
  5130. The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
  5131. will be \f(CW0\fR.
  5132. .IP "\s-1EV_HEAP_CACHE_AT\s0" 4
  5133. .IX Item "EV_HEAP_CACHE_AT"
  5134. Heaps are not very cache-efficient. To improve the cache-efficiency of the
  5135. timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
  5136. the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
  5137. which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
  5138. but avoids random read accesses on heap changes. This improves performance
  5139. noticeably with many (hundreds) of watchers.
  5140. .Sp
  5141. The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
  5142. will be \f(CW0\fR.
  5143. .IP "\s-1EV_VERIFY\s0" 4
  5144. .IX Item "EV_VERIFY"
  5145. Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
  5146. be done: If set to \f(CW0\fR, no internal verification code will be compiled
  5147. in. If set to \f(CW1\fR, then verification code will be compiled in, but not
  5148. called. If set to \f(CW2\fR, then the internal verification code will be
  5149. called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
  5150. verification code will be called very frequently, which will slow down
  5151. libev considerably.
  5152. .Sp
  5153. Verification errors are reported via C's \f(CW\*(C`assert\*(C'\fR mechanism, so if you
  5154. disable that (e.g. by defining \f(CW\*(C`NDEBUG\*(C'\fR) then no errors will be reported.
  5155. .Sp
  5156. The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
  5157. will be \f(CW0\fR.
  5158. .IP "\s-1EV_COMMON\s0" 4
  5159. .IX Item "EV_COMMON"
  5160. By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
  5161. this macro to something else you can include more and other types of
  5162. members. You have to define it each time you include one of the files,
  5163. though, and it must be identical each time.
  5164. .Sp
  5165. For example, the perl \s-1EV\s0 module uses something like this:
  5166. .Sp
  5167. .Vb 3
  5168. \& #define EV_COMMON \e
  5169. \& SV *self; /* contains this struct */ \e
  5170. \& SV *cb_sv, *fh /* note no trailing ";" */
  5171. .Ve
  5172. .IP "\s-1EV_CB_DECLARE\s0 (type)" 4
  5173. .IX Item "EV_CB_DECLARE (type)"
  5174. .PD 0
  5175. .IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
  5176. .IX Item "EV_CB_INVOKE (watcher, revents)"
  5177. .IP "ev_set_cb (ev, cb)" 4
  5178. .IX Item "ev_set_cb (ev, cb)"
  5179. .PD
  5180. Can be used to change the callback member declaration in each watcher,
  5181. and the way callbacks are invoked and set. Must expand to a struct member
  5182. definition and a statement, respectively. See the \fIev.h\fR header file for
  5183. their default definitions. One possible use for overriding these is to
  5184. avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
  5185. method calls instead of plain function calls in \*(C+.
  5186. .SS "\s-1EXPORTED API SYMBOLS\s0"
  5187. .IX Subsection "EXPORTED API SYMBOLS"
  5188. If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
  5189. exported symbols, you can use the provided \fISymbol.*\fR files which list
  5190. all public symbols, one per line:
  5191. .PP
  5192. .Vb 2
  5193. \& Symbols.ev for libev proper
  5194. \& Symbols.event for the libevent emulation
  5195. .Ve
  5196. .PP
  5197. This can also be used to rename all public symbols to avoid clashes with
  5198. multiple versions of libev linked together (which is obviously bad in
  5199. itself, but sometimes it is inconvenient to avoid this).
  5200. .PP
  5201. A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
  5202. include before including \fIev.h\fR:
  5203. .PP
  5204. .Vb 1
  5205. \& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
  5206. .Ve
  5207. .PP
  5208. This would create a file \fIwrap.h\fR which essentially looks like this:
  5209. .PP
  5210. .Vb 4
  5211. \& #define ev_backend myprefix_ev_backend
  5212. \& #define ev_check_start myprefix_ev_check_start
  5213. \& #define ev_check_stop myprefix_ev_check_stop
  5214. \& ...
  5215. .Ve
  5216. .SS "\s-1EXAMPLES\s0"
  5217. .IX Subsection "EXAMPLES"
  5218. For a real-world example of a program the includes libev
  5219. verbatim, you can have a look at the \s-1EV\s0 perl module
  5220. (<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
  5221. the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
  5222. interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
  5223. will be compiled. It is pretty complex because it provides its own header
  5224. file.
  5225. .PP
  5226. The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
  5227. that everybody includes and which overrides some configure choices:
  5228. .PP
  5229. .Vb 8
  5230. \& #define EV_FEATURES 8
  5231. \& #define EV_USE_SELECT 1
  5232. \& #define EV_PREPARE_ENABLE 1
  5233. \& #define EV_IDLE_ENABLE 1
  5234. \& #define EV_SIGNAL_ENABLE 1
  5235. \& #define EV_CHILD_ENABLE 1
  5236. \& #define EV_USE_STDEXCEPT 0
  5237. \& #define EV_CONFIG_H <config.h>
  5238. \&
  5239. \& #include "ev++.h"
  5240. .Ve
  5241. .PP
  5242. And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
  5243. .PP
  5244. .Vb 2
  5245. \& #include "ev_cpp.h"
  5246. \& #include "ev.c"
  5247. .Ve
  5251. .IX Subsection "THREADS AND COROUTINES"
  5252. \fI\s-1THREADS\s0\fR
  5253. .IX Subsection "THREADS"
  5254. .PP
  5255. All libev functions are reentrant and thread-safe unless explicitly
  5256. documented otherwise, but libev implements no locking itself. This means
  5257. that you can use as many loops as you want in parallel, as long as there
  5258. are no concurrent calls into any libev function with the same loop
  5259. parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
  5260. of course): libev guarantees that different event loops share no data
  5261. structures that need any locking.
  5262. .PP
  5263. Or to put it differently: calls with different loop parameters can be done
  5264. concurrently from multiple threads, calls with the same loop parameter
  5265. must be done serially (but can be done from different threads, as long as
  5266. only one thread ever is inside a call at any point in time, e.g. by using
  5267. a mutex per loop).
  5268. .PP
  5269. Specifically to support threads (and signal handlers), libev implements
  5270. so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
  5271. concurrency on the same event loop, namely waking it up \*(L"from the
  5272. outside\*(R".
  5273. .PP
  5274. If you want to know which design (one loop, locking, or multiple loops
  5275. without or something else still) is best for your problem, then I cannot
  5276. help you, but here is some generic advice:
  5277. .IP "\(bu" 4
  5278. most applications have a main thread: use the default libev loop
  5279. in that thread, or create a separate thread running only the default loop.
  5280. .Sp
  5281. This helps integrating other libraries or software modules that use libev
  5282. themselves and don't care/know about threading.
  5283. .IP "\(bu" 4
  5284. one loop per thread is usually a good model.
  5285. .Sp
  5286. Doing this is almost never wrong, sometimes a better-performance model
  5287. exists, but it is always a good start.
  5288. .IP "\(bu" 4
  5289. other models exist, such as the leader/follower pattern, where one
  5290. loop is handed through multiple threads in a kind of round-robin fashion.
  5291. .Sp
  5292. Choosing a model is hard \- look around, learn, know that usually you can do
  5293. better than you currently do :\-)
  5294. .IP "\(bu" 4
  5295. often you need to talk to some other thread which blocks in the
  5296. event loop.
  5297. .Sp
  5298. \&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
  5299. (or from signal contexts...).
  5300. .Sp
  5301. An example use would be to communicate signals or other events that only
  5302. work in the default loop by registering the signal watcher with the
  5303. default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
  5304. watcher callback into the event loop interested in the signal.
  5305. .PP
  5306. See also \*(L"\s-1THREAD LOCKING EXAMPLE\*(R"\s0.
  5307. .PP
  5308. \fI\s-1COROUTINES\s0\fR
  5309. .IX Subsection "COROUTINES"
  5310. .PP
  5311. Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
  5312. libev fully supports nesting calls to its functions from different
  5313. coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
  5314. different coroutines, and switch freely between both coroutines running
  5315. the loop, as long as you don't confuse yourself). The only exception is
  5316. that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
  5317. .PP
  5318. Care has been taken to ensure that libev does not keep local state inside
  5319. \&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
  5320. they do not call any callbacks.
  5321. .SS "\s-1COMPILER WARNINGS\s0"
  5322. .IX Subsection "COMPILER WARNINGS"
  5323. Depending on your compiler and compiler settings, you might get no or a
  5324. lot of warnings when compiling libev code. Some people are apparently
  5325. scared by this.
  5326. .PP
  5327. However, these are unavoidable for many reasons. For one, each compiler
  5328. has different warnings, and each user has different tastes regarding
  5329. warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
  5330. targeting a specific compiler and compiler-version.
  5331. .PP
  5332. Another reason is that some compiler warnings require elaborate
  5333. workarounds, or other changes to the code that make it less clear and less
  5334. maintainable.
  5335. .PP
  5336. And of course, some compiler warnings are just plain stupid, or simply
  5337. wrong (because they don't actually warn about the condition their message
  5338. seems to warn about). For example, certain older gcc versions had some
  5339. warnings that resulted in an extreme number of false positives. These have
  5340. been fixed, but some people still insist on making code warn-free with
  5341. such buggy versions.
  5342. .PP
  5343. While libev is written to generate as few warnings as possible,
  5344. \&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
  5345. with any compiler warnings enabled unless you are prepared to cope with
  5346. them (e.g. by ignoring them). Remember that warnings are just that:
  5347. warnings, not errors, or proof of bugs.
  5348. .SS "\s-1VALGRIND\s0"
  5349. .IX Subsection "VALGRIND"
  5350. Valgrind has a special section here because it is a popular tool that is
  5351. highly useful. Unfortunately, valgrind reports are very hard to interpret.
  5352. .PP
  5353. If you think you found a bug (memory leak, uninitialised data access etc.)
  5354. in libev, then check twice: If valgrind reports something like:
  5355. .PP
  5356. .Vb 3
  5357. \& ==2274== definitely lost: 0 bytes in 0 blocks.
  5358. \& ==2274== possibly lost: 0 bytes in 0 blocks.
  5359. \& ==2274== still reachable: 256 bytes in 1 blocks.
  5360. .Ve
  5361. .PP
  5362. Then there is no memory leak, just as memory accounted to global variables
  5363. is not a memleak \- the memory is still being referenced, and didn't leak.
  5364. .PP
  5365. Similarly, under some circumstances, valgrind might report kernel bugs
  5366. as if it were a bug in libev (e.g. in realloc or in the poll backend,
  5367. although an acceptable workaround has been found here), or it might be
  5368. confused.
  5369. .PP
  5370. Keep in mind that valgrind is a very good tool, but only a tool. Don't
  5371. make it into some kind of religion.
  5372. .PP
  5373. If you are unsure about something, feel free to contact the mailing list
  5374. with the full valgrind report and an explanation on why you think this
  5375. is a bug in libev (best check the archives, too :). However, don't be
  5376. annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
  5377. of learning how to interpret valgrind properly.
  5378. .PP
  5379. If you need, for some reason, empty reports from valgrind for your project
  5380. I suggest using suppression lists.
  5382. .IX Header "PORTABILITY NOTES"
  5383. .SS "\s-1GNU/LINUX 32 BIT LIMITATIONS\s0"
  5384. .IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
  5385. GNU/Linux is the only common platform that supports 64 bit file/large file
  5386. interfaces but \fIdisables\fR them by default.
  5387. .PP
  5388. That means that libev compiled in the default environment doesn't support
  5389. files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
  5390. .PP
  5391. Unfortunately, many programs try to work around this GNU/Linux issue
  5392. by enabling the large file \s-1API,\s0 which makes them incompatible with the
  5393. standard libev compiled for their system.
  5394. .PP
  5395. Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
  5396. suddenly make it incompatible to the default compile time environment,
  5397. i.e. all programs not using special compile switches.
  5398. .SS "\s-1OS/X AND DARWIN BUGS\s0"
  5399. .IX Subsection "OS/X AND DARWIN BUGS"
  5400. The whole thing is a bug if you ask me \- basically any system interface
  5401. you touch is broken, whether it is locales, poll, kqueue or even the
  5402. OpenGL drivers.
  5403. .PP
  5404. \fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
  5405. .IX Subsection "kqueue is buggy"
  5406. .PP
  5407. The kqueue syscall is broken in all known versions \- most versions support
  5408. only sockets, many support pipes.
  5409. .PP
  5410. Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
  5411. rotten platform, but of course you can still ask for it when creating a
  5412. loop \- embedding a socket-only kqueue loop into a select-based one is
  5413. probably going to work well.
  5414. .PP
  5415. \fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
  5416. .IX Subsection "poll is buggy"
  5417. .PP
  5418. Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
  5419. implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
  5420. release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
  5421. .PP
  5422. Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
  5423. this rotten platform, but of course you can still ask for it when creating
  5424. a loop.
  5425. .PP
  5426. \fI\f(CI\*(C`select\*(C'\fI is buggy\fR
  5427. .IX Subsection "select is buggy"
  5428. .PP
  5429. All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
  5430. one up as well: On \s-1OS/X,\s0 \f(CW\*(C`select\*(C'\fR actively limits the number of file
  5431. descriptors you can pass in to 1024 \- your program suddenly crashes when
  5432. you use more.
  5433. .PP
  5434. There is an undocumented \*(L"workaround\*(R" for this \- defining
  5435. \&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
  5436. work on \s-1OS/X.\s0
  5439. \fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
  5440. .IX Subsection "errno reentrancy"
  5441. .PP
  5442. The default compile environment on Solaris is unfortunately so
  5443. thread-unsafe that you can't even use components/libraries compiled
  5444. without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
  5445. defined by default. A valid, if stupid, implementation choice.
  5446. .PP
  5447. If you want to use libev in threaded environments you have to make sure
  5448. it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
  5449. .PP
  5450. \fIEvent port backend\fR
  5451. .IX Subsection "Event port backend"
  5452. .PP
  5453. The scalable event interface for Solaris is called \*(L"event
  5454. ports\*(R". Unfortunately, this mechanism is very buggy in all major
  5455. releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
  5456. a large number of spurious wakeups, make sure you have all the relevant
  5457. and latest kernel patches applied. No, I don't know which ones, but there
  5458. are multiple ones to apply, and afterwards, event ports actually work
  5459. great.
  5460. .PP
  5461. If you can't get it to work, you can try running the program by setting
  5462. the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
  5463. \&\f(CW\*(C`select\*(C'\fR backends.
  5464. .SS "\s-1AIX POLL BUG\s0"
  5465. .IX Subsection "AIX POLL BUG"
  5466. \&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
  5467. this by trying to avoid the poll backend altogether (i.e. it's not even
  5468. compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
  5469. with large bitsets on \s-1AIX,\s0 and \s-1AIX\s0 is dead anyway.
  5472. \fIGeneral issues\fR
  5473. .IX Subsection "General issues"
  5474. .PP
  5475. Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
  5476. requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
  5477. model. Libev still offers limited functionality on this platform in
  5478. the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
  5479. descriptors. This only applies when using Win32 natively, not when using
  5480. e.g. cygwin. Actually, it only applies to the microsofts own compilers,
  5481. as every compiler comes with a slightly differently broken/incompatible
  5482. environment.
  5483. .PP
  5484. Lifting these limitations would basically require the full
  5485. re-implementation of the I/O system. If you are into this kind of thing,
  5486. then note that glib does exactly that for you in a very portable way (note
  5487. also that glib is the slowest event library known to man).
  5488. .PP
  5489. There is no supported compilation method available on windows except
  5490. embedding it into other applications.
  5491. .PP
  5492. Sensible signal handling is officially unsupported by Microsoft \- libev
  5493. tries its best, but under most conditions, signals will simply not work.
  5494. .PP
  5495. Not a libev limitation but worth mentioning: windows apparently doesn't
  5496. accept large writes: instead of resulting in a partial write, windows will
  5497. either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
  5498. so make sure you only write small amounts into your sockets (less than a
  5499. megabyte seems safe, but this apparently depends on the amount of memory
  5500. available).
  5501. .PP
  5502. Due to the many, low, and arbitrary limits on the win32 platform and
  5503. the abysmal performance of winsockets, using a large number of sockets
  5504. is not recommended (and not reasonable). If your program needs to use
  5505. more than a hundred or so sockets, then likely it needs to use a totally
  5506. different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
  5507. notification model, which cannot be implemented efficiently on windows
  5508. (due to Microsoft monopoly games).
  5509. .PP
  5510. A typical way to use libev under windows is to embed it (see the embedding
  5511. section for details) and use the following \fIevwrap.h\fR header file instead
  5512. of \fIev.h\fR:
  5513. .PP
  5514. .Vb 2
  5515. \& #define EV_STANDALONE /* keeps ev from requiring config.h */
  5516. \& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
  5517. \&
  5518. \& #include "ev.h"
  5519. .Ve
  5520. .PP
  5521. And compile the following \fIevwrap.c\fR file into your project (make sure
  5522. you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
  5523. .PP
  5524. .Vb 2
  5525. \& #include "evwrap.h"
  5526. \& #include "ev.c"
  5527. .Ve
  5528. .PP
  5529. \fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
  5530. .IX Subsection "The winsocket select function"
  5531. .PP
  5532. The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
  5533. requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
  5534. also extremely buggy). This makes select very inefficient, and also
  5535. requires a mapping from file descriptors to socket handles (the Microsoft
  5536. C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
  5537. discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
  5538. \&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
  5539. .PP
  5540. The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
  5541. libraries and raw winsocket select is:
  5542. .PP
  5543. .Vb 2
  5544. \& #define EV_USE_SELECT 1
  5545. \& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
  5546. .Ve
  5547. .PP
  5548. Note that winsockets handling of fd sets is O(n), so you can easily get a
  5549. complexity in the O(nX) range when using win32.
  5550. .PP
  5551. \fILimited number of file descriptors\fR
  5552. .IX Subsection "Limited number of file descriptors"
  5553. .PP
  5554. Windows has numerous arbitrary (and low) limits on things.
  5555. .PP
  5556. Early versions of winsocket's select only supported waiting for a maximum
  5557. of \f(CW64\fR handles (probably owning to the fact that all windows kernels
  5558. can only wait for \f(CW64\fR things at the same time internally; Microsoft
  5559. recommends spawning a chain of threads and wait for 63 handles and the
  5560. previous thread in each. Sounds great!).
  5561. .PP
  5562. Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
  5563. to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
  5564. call (which might be in libev or elsewhere, for example, perl and many
  5565. other interpreters do their own select emulation on windows).
  5566. .PP
  5567. Another limit is the number of file descriptors in the Microsoft runtime
  5568. libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
  5569. fetish or something like this inside Microsoft). You can increase this
  5570. by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
  5571. (another arbitrary limit), but is broken in many versions of the Microsoft
  5572. runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
  5573. (depending on windows version and/or the phase of the moon). To get more,
  5574. you need to wrap all I/O functions and provide your own fd management, but
  5575. the cost of calling select (O(nX)) will likely make this unworkable.
  5578. In addition to a working ISO-C implementation and of course the
  5579. backend-specific APIs, libev relies on a few additional extensions:
  5580. .ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
  5581. .el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
  5582. .IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
  5583. Libev assumes not only that all watcher pointers have the same internal
  5584. structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO C\s0 for example), but it also
  5585. assumes that the same (machine) code can be used to call any watcher
  5586. callback: The watcher callbacks have different type signatures, but libev
  5587. calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
  5588. .IP "null pointers and integer zero are represented by 0 bytes" 4
  5589. .IX Item "null pointers and integer zero are represented by 0 bytes"
  5590. Libev uses \f(CW\*(C`memset\*(C'\fR to initialise structs and arrays to \f(CW0\fR bytes, and
  5591. relies on this setting pointers and integers to null.
  5592. .IP "pointer accesses must be thread-atomic" 4
  5593. .IX Item "pointer accesses must be thread-atomic"
  5594. Accessing a pointer value must be atomic, it must both be readable and
  5595. writable in one piece \- this is the case on all current architectures.
  5596. .ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
  5597. .el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
  5598. .IX Item "sig_atomic_t volatile must be thread-atomic as well"
  5599. The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
  5600. \&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
  5601. threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
  5602. believed to be sufficiently portable.
  5603. .ie n .IP """sigprocmask"" must work in a threaded environment" 4
  5604. .el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
  5605. .IX Item "sigprocmask must work in a threaded environment"
  5606. Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
  5607. allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
  5608. pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
  5609. thread\*(R" or will block signals process-wide, both behaviours would
  5610. be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
  5611. \&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
  5612. .Sp
  5613. The most portable way to handle signals is to block signals in all threads
  5614. except the initial one, and run the signal handling loop in the initial
  5615. thread as well.
  5616. .ie n .IP """long"" must be large enough for common memory allocation sizes" 4
  5617. .el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
  5618. .IX Item "long must be large enough for common memory allocation sizes"
  5619. To improve portability and simplify its \s-1API,\s0 libev uses \f(CW\*(C`long\*(C'\fR internally
  5620. instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
  5621. systems (Microsoft...) this might be unexpectedly low, but is still at
  5622. least 31 bits everywhere, which is enough for hundreds of millions of
  5623. watchers.
  5624. .ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
  5625. .el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
  5626. .IX Item "double must hold a time value in seconds with enough accuracy"
  5627. The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
  5628. have at least 51 bits of mantissa (and 9 bits of exponent), which is
  5629. good enough for at least into the year 4000 with millisecond accuracy
  5630. (the design goal for libev). This requirement is overfulfilled by
  5631. implementations using \s-1IEEE 754,\s0 which is basically all existing ones.
  5632. .Sp
  5633. With \s-1IEEE 754\s0 doubles, you get microsecond accuracy until at least the
  5634. year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
  5635. is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
  5636. something like that, just kidding).
  5637. .PP
  5638. If you know of other additional requirements drop me a note.
  5641. In this section the complexities of (many of) the algorithms used inside
  5642. libev will be documented. For complexity discussions about backends see
  5643. the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
  5644. .PP
  5645. All of the following are about amortised time: If an array needs to be
  5646. extended, libev needs to realloc and move the whole array, but this
  5647. happens asymptotically rarer with higher number of elements, so O(1) might
  5648. mean that libev does a lengthy realloc operation in rare cases, but on
  5649. average it is much faster and asymptotically approaches constant time.
  5650. .IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
  5651. .IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
  5652. This means that, when you have a watcher that triggers in one hour and
  5653. there are 100 watchers that would trigger before that, then inserting will
  5654. have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
  5655. .IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
  5656. .IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
  5657. That means that changing a timer costs less than removing/adding them,
  5658. as only the relative motion in the event queue has to be paid for.
  5659. .IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
  5660. .IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
  5661. These just add the watcher into an array or at the head of a list.
  5662. .IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
  5663. .IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
  5664. .PD 0
  5665. .IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
  5666. .IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
  5667. .PD
  5668. These watchers are stored in lists, so they need to be walked to find the
  5669. correct watcher to remove. The lists are usually short (you don't usually
  5670. have many watchers waiting for the same fd or signal: one is typical, two
  5671. is rare).
  5672. .IP "Finding the next timer in each loop iteration: O(1)" 4
  5673. .IX Item "Finding the next timer in each loop iteration: O(1)"
  5674. By virtue of using a binary or 4\-heap, the next timer is always found at a
  5675. fixed position in the storage array.
  5676. .IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
  5677. .IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
  5678. A change means an I/O watcher gets started or stopped, which requires
  5679. libev to recalculate its status (and possibly tell the kernel, depending
  5680. on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
  5681. .IP "Activating one watcher (putting it into the pending state): O(1)" 4
  5682. .IX Item "Activating one watcher (putting it into the pending state): O(1)"
  5683. .PD 0
  5684. .IP "Priority handling: O(number_of_priorities)" 4
  5685. .IX Item "Priority handling: O(number_of_priorities)"
  5686. .PD
  5687. Priorities are implemented by allocating some space for each
  5688. priority. When doing priority-based operations, libev usually has to
  5689. linearly search all the priorities, but starting/stopping and activating
  5690. watchers becomes O(1) with respect to priority handling.
  5691. .IP "Sending an ev_async: O(1)" 4
  5692. .IX Item "Sending an ev_async: O(1)"
  5693. .PD 0
  5694. .IP "Processing ev_async_send: O(number_of_async_watchers)" 4
  5695. .IX Item "Processing ev_async_send: O(number_of_async_watchers)"
  5696. .IP "Processing signals: O(max_signal_number)" 4
  5697. .IX Item "Processing signals: O(max_signal_number)"
  5698. .PD
  5699. Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
  5700. calls in the current loop iteration and the loop is currently
  5701. blocked. Checking for async and signal events involves iterating over all
  5702. running async watchers or all signal numbers.
  5704. .IX Header "PORTING FROM LIBEV 3.X TO 4.X"
  5705. The major version 4 introduced some incompatible changes to the \s-1API.\s0
  5706. .PP
  5707. At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
  5708. for all changes, so most programs should still compile. The compatibility
  5709. layer might be removed in later versions of libev, so better update to the
  5710. new \s-1API\s0 early than late.
  5711. .ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
  5712. .el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
  5713. .IX Item "EV_COMPAT3 backwards compatibility mechanism"
  5714. The backward compatibility mechanism can be controlled by
  5715. \&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1PREPROCESSOR SYMBOLS/MACROS\*(R"\s0 in the \*(L"\s-1EMBEDDING\*(R"\s0
  5716. section.
  5717. .ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
  5718. .el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
  5719. .IX Item "ev_default_destroy and ev_default_fork have been removed"
  5720. These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
  5721. .Sp
  5722. .Vb 2
  5723. \& ev_loop_destroy (EV_DEFAULT_UC);
  5724. \& ev_loop_fork (EV_DEFAULT);
  5725. .Ve
  5726. .IP "function/symbol renames" 4
  5727. .IX Item "function/symbol renames"
  5728. A number of functions and symbols have been renamed:
  5729. .Sp
  5730. .Vb 3
  5731. \& ev_loop => ev_run
  5734. \&
  5735. \& ev_unloop => ev_break
  5739. \&
  5740. \& EV_TIMEOUT => EV_TIMER
  5741. \&
  5742. \& ev_loop_count => ev_iteration
  5743. \& ev_loop_depth => ev_depth
  5744. \& ev_loop_verify => ev_verify
  5745. .Ve
  5746. .Sp
  5747. Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
  5748. \&\f(CW\*(C`ev_loop_\*(C'\fR prefix, so it was removed; \f(CW\*(C`ev_loop\*(C'\fR, \f(CW\*(C`ev_unloop\*(C'\fR and
  5749. associated constants have been renamed to not collide with the \f(CW\*(C`struct
  5750. ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
  5751. as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
  5752. \&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
  5753. typedef.
  5754. .ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
  5755. .el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
  5756. .IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
  5757. The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
  5758. mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
  5759. and work, but the library code will of course be larger.
  5760. .SH "GLOSSARY"
  5761. .IX Header "GLOSSARY"
  5762. .IP "active" 4
  5763. .IX Item "active"
  5764. A watcher is active as long as it has been started and not yet stopped.
  5765. See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
  5766. .IP "application" 4
  5767. .IX Item "application"
  5768. In this document, an application is whatever is using libev.
  5769. .IP "backend" 4
  5770. .IX Item "backend"
  5771. The part of the code dealing with the operating system interfaces.
  5772. .IP "callback" 4
  5773. .IX Item "callback"
  5774. The address of a function that is called when some event has been
  5775. detected. Callbacks are being passed the event loop, the watcher that
  5776. received the event, and the actual event bitset.
  5777. .IP "callback/watcher invocation" 4
  5778. .IX Item "callback/watcher invocation"
  5779. The act of calling the callback associated with a watcher.
  5780. .IP "event" 4
  5781. .IX Item "event"
  5782. A change of state of some external event, such as data now being available
  5783. for reading on a file descriptor, time having passed or simply not having
  5784. any other events happening anymore.
  5785. .Sp
  5786. In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
  5787. \&\f(CW\*(C`EV_TIMER\*(C'\fR).
  5788. .IP "event library" 4
  5789. .IX Item "event library"
  5790. A software package implementing an event model and loop.
  5791. .IP "event loop" 4
  5792. .IX Item "event loop"
  5793. An entity that handles and processes external events and converts them
  5794. into callback invocations.
  5795. .IP "event model" 4
  5796. .IX Item "event model"
  5797. The model used to describe how an event loop handles and processes
  5798. watchers and events.
  5799. .IP "pending" 4
  5800. .IX Item "pending"
  5801. A watcher is pending as soon as the corresponding event has been
  5802. detected. See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
  5803. .IP "real time" 4
  5804. .IX Item "real time"
  5805. The physical time that is observed. It is apparently strictly monotonic :)
  5806. .IP "wall-clock time" 4
  5807. .IX Item "wall-clock time"
  5808. The time and date as shown on clocks. Unlike real time, it can actually
  5809. be wrong and jump forwards and backwards, e.g. when you adjust your
  5810. clock.
  5811. .IP "watcher" 4
  5812. .IX Item "watcher"
  5813. A data structure that describes interest in certain events. Watchers need
  5814. to be started (attached to an event loop) before they can receive events.
  5815. .SH "AUTHOR"
  5816. .IX Header "AUTHOR"
  5817. Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
  5818. Magnusson and Emanuele Giaquinta, and minor corrections by many others.