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51 KiB
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<head> |
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<title>libev</title> |
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<meta name="description" content="Pod documentation for libev" /> |
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<meta name="inputfile" content="<standard input>" /> |
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<meta name="outputfile" content="<standard output>" /> |
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<meta name="created" content="Fri Nov 23 17:17:04 2007" /> |
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<meta name="generator" content="Pod::Xhtml 1.57" /> |
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<link rel="stylesheet" href="http://res.tst.eu/pod.css"/></head> |
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<body> |
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<div class="pod"> |
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<!-- INDEX START --> |
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<h3 id="TOP">Index</h3> |
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<ul><li><a href="#NAME">NAME</a></li> |
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<li><a href="#SYNOPSIS">SYNOPSIS</a></li> |
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<li><a href="#DESCRIPTION">DESCRIPTION</a></li> |
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<li><a href="#FEATURES">FEATURES</a></li> |
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<li><a href="#CONVENTIONS">CONVENTIONS</a></li> |
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<li><a href="#TIME_REPRESENTATION">TIME REPRESENTATION</a></li> |
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<li><a href="#GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</a></li> |
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<li><a href="#FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</a></li> |
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<li><a href="#ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</a> |
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<ul><li><a href="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</a></li> |
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</ul> |
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</li> |
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<li><a href="#WATCHER_TYPES">WATCHER TYPES</a> |
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<ul><li><a href="#code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable</a></li> |
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<li><a href="#code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</a></li> |
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<li><a href="#code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron</a></li> |
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<li><a href="#code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled</a></li> |
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<li><a href="#code_ev_child_code_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</a></li> |
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<li><a href="#code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do</a></li> |
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<li><a href="#code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop</a></li> |
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</ul> |
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</li> |
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<li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li> |
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<li><a href="#LIBEVENT_EMULATION">LIBEVENT EMULATION</a></li> |
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<li><a href="#C_SUPPORT">C++ SUPPORT</a></li> |
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<li><a href="#AUTHOR">AUTHOR</a> |
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</li> |
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</ul><hr /> |
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<!-- INDEX END --> |
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<h1 id="NAME">NAME</h1><p><a href="#TOP" class="toplink">Top</a></p> |
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<div id="NAME_CONTENT"> |
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<p>libev - a high performance full-featured event loop written in C</p> |
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</div> |
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<h1 id="SYNOPSIS">SYNOPSIS</h1><p><a href="#TOP" class="toplink">Top</a></p> |
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<div id="SYNOPSIS_CONTENT"> |
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<pre> #include <ev.h> |
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</pre> |
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</div> |
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<h1 id="DESCRIPTION">DESCRIPTION</h1><p><a href="#TOP" class="toplink">Top</a></p> |
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<div id="DESCRIPTION_CONTENT"> |
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<p>Libev is an event loop: you register interest in certain events (such as a |
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file descriptor being readable or a timeout occuring), and it will manage |
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these event sources and provide your program with events.</p> |
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<p>To do this, it must take more or less complete control over your process |
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(or thread) by executing the <i>event loop</i> handler, and will then |
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communicate events via a callback mechanism.</p> |
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<p>You register interest in certain events by registering so-called <i>event |
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watchers</i>, which are relatively small C structures you initialise with the |
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details of the event, and then hand it over to libev by <i>starting</i> the |
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watcher.</p> |
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</div> |
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<h1 id="FEATURES">FEATURES</h1><p><a href="#TOP" class="toplink">Top</a></p> |
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<div id="FEATURES_CONTENT"> |
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<p>Libev supports select, poll, the linux-specific epoll and the bsd-specific |
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kqueue mechanisms for file descriptor events, relative timers, absolute |
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timers with customised rescheduling, signal events, process status change |
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events (related to SIGCHLD), and event watchers dealing with the event |
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loop mechanism itself (idle, prepare and check watchers). It also is quite |
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fast (see this <a href="http://libev.schmorp.de/bench.html">benchmark</a> comparing |
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it to libevent for example).</p> |
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</div> |
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<h1 id="CONVENTIONS">CONVENTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p> |
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<div id="CONVENTIONS_CONTENT"> |
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<p>Libev is very configurable. In this manual the default configuration |
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will be described, which supports multiple event loops. For more info |
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about various configuration options please have a look at the file |
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<cite>README.embed</cite> in the libev distribution. If libev was configured without |
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support for multiple event loops, then all functions taking an initial |
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argument of name <code>loop</code> (which is always of type <code>struct ev_loop *</code>) |
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will not have this argument.</p> |
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</div> |
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<h1 id="TIME_REPRESENTATION">TIME REPRESENTATION</h1><p><a href="#TOP" class="toplink">Top</a></p> |
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<div id="TIME_REPRESENTATION_CONTENT"> |
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<p>Libev represents time as a single floating point number, representing the |
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(fractional) number of seconds since the (POSIX) epoch (somewhere near |
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the beginning of 1970, details are complicated, don't ask). This type is |
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called <code>ev_tstamp</code>, which is what you should use too. It usually aliases |
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to the <code>double</code> type in C, and when you need to do any calculations on |
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it, you should treat it as such.</p> |
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</div> |
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<h1 id="GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p> |
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<div id="GLOBAL_FUNCTIONS_CONTENT"> |
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<p>These functions can be called anytime, even before initialising the |
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library in any way.</p> |
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<dl> |
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<dt>ev_tstamp ev_time ()</dt> |
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<dd> |
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<p>Returns the current time as libev would use it. Please note that the |
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<code>ev_now</code> function is usually faster and also often returns the timestamp |
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you actually want to know.</p> |
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</dd> |
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<dt>int ev_version_major ()</dt> |
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<dt>int ev_version_minor ()</dt> |
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<dd> |
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<p>You can find out the major and minor version numbers of the library |
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you linked against by calling the functions <code>ev_version_major</code> and |
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<code>ev_version_minor</code>. If you want, you can compare against the global |
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symbols <code>EV_VERSION_MAJOR</code> and <code>EV_VERSION_MINOR</code>, which specify the |
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version of the library your program was compiled against.</p> |
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<p>Usually, it's a good idea to terminate if the major versions mismatch, |
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as this indicates an incompatible change. Minor versions are usually |
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compatible to older versions, so a larger minor version alone is usually |
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not a problem.</p> |
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<p>Example: make sure we haven't accidentally been linked against the wrong |
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version:</p> |
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<pre> assert (("libev version mismatch", |
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ev_version_major () == EV_VERSION_MAJOR |
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&& ev_version_minor () >= EV_VERSION_MINOR)); |
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</pre> |
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</dd> |
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<dt>unsigned int ev_supported_backends ()</dt> |
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<dd> |
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<p>Return the set of all backends (i.e. their corresponding <code>EV_BACKEND_*</code> |
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value) compiled into this binary of libev (independent of their |
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availability on the system you are running on). See <code>ev_default_loop</code> for |
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a description of the set values.</p> |
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<p>Example: make sure we have the epoll method, because yeah this is cool and |
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a must have and can we have a torrent of it please!!!11</p> |
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<pre> assert (("sorry, no epoll, no sex", |
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ev_supported_backends () & EVBACKEND_EPOLL)); |
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</pre> |
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</dd> |
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<dt>unsigned int ev_recommended_backends ()</dt> |
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<dd> |
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<p>Return the set of all backends compiled into this binary of libev and also |
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recommended for this platform. This set is often smaller than the one |
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returned by <code>ev_supported_backends</code>, as for example kqueue is broken on |
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most BSDs and will not be autodetected unless you explicitly request it |
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(assuming you know what you are doing). This is the set of backends that |
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libev will probe for if you specify no backends explicitly.</p> |
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</dd> |
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<dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt> |
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<dd> |
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<p>Sets the allocation function to use (the prototype is similar to the |
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realloc C function, the semantics are identical). It is used to allocate |
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and free memory (no surprises here). If it returns zero when memory |
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needs to be allocated, the library might abort or take some potentially |
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destructive action. The default is your system realloc function.</p> |
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<p>You could override this function in high-availability programs to, say, |
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free some memory if it cannot allocate memory, to use a special allocator, |
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or even to sleep a while and retry until some memory is available.</p> |
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<p>Example: replace the libev allocator with one that waits a bit and then |
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retries: better than mine).</p> |
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<pre> static void * |
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persistent_realloc (void *ptr, long size) |
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{ |
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for (;;) |
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{ |
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void *newptr = realloc (ptr, size); |
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if (newptr) |
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return newptr; |
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sleep (60); |
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} |
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} |
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|
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... |
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ev_set_allocator (persistent_realloc); |
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|
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</pre> |
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</dd> |
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<dt>ev_set_syserr_cb (void (*cb)(const char *msg));</dt> |
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<dd> |
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<p>Set the callback function to call on a retryable syscall error (such |
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as failed select, poll, epoll_wait). The message is a printable string |
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indicating the system call or subsystem causing the problem. If this |
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callback is set, then libev will expect it to remedy the sitution, no |
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matter what, when it returns. That is, libev will generally retry the |
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requested operation, or, if the condition doesn't go away, do bad stuff |
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(such as abort).</p> |
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<p>Example: do the same thing as libev does internally:</p> |
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<pre> static void |
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fatal_error (const char *msg) |
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{ |
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perror (msg); |
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abort (); |
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} |
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... |
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ev_set_syserr_cb (fatal_error); |
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|
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</pre> |
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</dd> |
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</dl> |
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</div> |
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<h1 id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</h1><p><a href="#TOP" class="toplink">Top</a></p> |
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<div id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP-2"> |
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<p>An event loop is described by a <code>struct ev_loop *</code>. The library knows two |
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types of such loops, the <i>default</i> loop, which supports signals and child |
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events, and dynamically created loops which do not.</p> |
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<p>If you use threads, a common model is to run the default event loop |
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in your main thread (or in a separate thread) and for each thread you |
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create, you also create another event loop. Libev itself does no locking |
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whatsoever, so if you mix calls to the same event loop in different |
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threads, make sure you lock (this is usually a bad idea, though, even if |
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done correctly, because it's hideous and inefficient).</p> |
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<dl> |
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<dt>struct ev_loop *ev_default_loop (unsigned int flags)</dt> |
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<dd> |
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<p>This will initialise the default event loop if it hasn't been initialised |
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yet and return it. If the default loop could not be initialised, returns |
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false. If it already was initialised it simply returns it (and ignores the |
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flags. If that is troubling you, check <code>ev_backend ()</code> afterwards).</p> |
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<p>If you don't know what event loop to use, use the one returned from this |
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function.</p> |
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<p>The flags argument can be used to specify special behaviour or specific |
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backends to use, and is usually specified as <code>0</code> (or <code>EVFLAG_AUTO</code>).</p> |
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<p>The following flags are supported:</p> |
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<p> |
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<dl> |
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<dt><code>EVFLAG_AUTO</code></dt> |
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<dd> |
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<p>The default flags value. Use this if you have no clue (it's the right |
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thing, believe me).</p> |
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</dd> |
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<dt><code>EVFLAG_NOENV</code></dt> |
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<dd> |
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<p>If this flag bit is ored into the flag value (or the program runs setuid |
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or setgid) then libev will <i>not</i> look at the environment variable |
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<code>LIBEV_FLAGS</code>. Otherwise (the default), this environment variable will |
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override the flags completely if it is found in the environment. This is |
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useful to try out specific backends to test their performance, or to work |
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around bugs.</p> |
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</dd> |
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<dt><code>EVBACKEND_SELECT</code> (value 1, portable select backend)</dt> |
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<dd> |
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<p>This is your standard select(2) backend. Not <i>completely</i> standard, as |
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libev tries to roll its own fd_set with no limits on the number of fds, |
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but if that fails, expect a fairly low limit on the number of fds when |
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using this backend. It doesn't scale too well (O(highest_fd)), but its usually |
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the fastest backend for a low number of fds.</p> |
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</dd> |
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<dt><code>EVBACKEND_POLL</code> (value 2, poll backend, available everywhere except on windows)</dt> |
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<dd> |
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<p>And this is your standard poll(2) backend. It's more complicated than |
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select, but handles sparse fds better and has no artificial limit on the |
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number of fds you can use (except it will slow down considerably with a |
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lot of inactive fds). It scales similarly to select, i.e. O(total_fds).</p> |
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</dd> |
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<dt><code>EVBACKEND_EPOLL</code> (value 4, Linux)</dt> |
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<dd> |
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<p>For few fds, this backend is a bit little slower than poll and select, |
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but it scales phenomenally better. While poll and select usually scale like |
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O(total_fds) where n is the total number of fds (or the highest fd), epoll scales |
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either O(1) or O(active_fds).</p> |
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<p>While stopping and starting an I/O watcher in the same iteration will |
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result in some caching, there is still a syscall per such incident |
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(because the fd could point to a different file description now), so its |
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best to avoid that. Also, dup()ed file descriptors might not work very |
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well if you register events for both fds.</p> |
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<p>Please note that epoll sometimes generates spurious notifications, so you |
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need to use non-blocking I/O or other means to avoid blocking when no data |
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(or space) is available.</p> |
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</dd> |
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<dt><code>EVBACKEND_KQUEUE</code> (value 8, most BSD clones)</dt> |
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<dd> |
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<p>Kqueue deserves special mention, as at the time of this writing, it |
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was broken on all BSDs except NetBSD (usually it doesn't work with |
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anything but sockets and pipes, except on Darwin, where of course its |
|
completely useless). For this reason its not being "autodetected" |
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unless you explicitly specify it explicitly in the flags (i.e. using |
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<code>EVBACKEND_KQUEUE</code>).</p> |
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<p>It scales in the same way as the epoll backend, but the interface to the |
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kernel is more efficient (which says nothing about its actual speed, of |
|
course). While starting and stopping an I/O watcher does not cause an |
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extra syscall as with epoll, it still adds up to four event changes per |
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incident, so its best to avoid that.</p> |
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</dd> |
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<dt><code>EVBACKEND_DEVPOLL</code> (value 16, Solaris 8)</dt> |
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<dd> |
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<p>This is not implemented yet (and might never be).</p> |
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</dd> |
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<dt><code>EVBACKEND_PORT</code> (value 32, Solaris 10)</dt> |
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<dd> |
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<p>This uses the Solaris 10 port mechanism. As with everything on Solaris, |
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it's really slow, but it still scales very well (O(active_fds)).</p> |
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<p>Please note that solaris ports can result in a lot of spurious |
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notifications, so you need to use non-blocking I/O or other means to avoid |
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blocking when no data (or space) is available.</p> |
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</dd> |
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<dt><code>EVBACKEND_ALL</code></dt> |
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<dd> |
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<p>Try all backends (even potentially broken ones that wouldn't be tried |
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with <code>EVFLAG_AUTO</code>). Since this is a mask, you can do stuff such as |
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<code>EVBACKEND_ALL & ~EVBACKEND_KQUEUE</code>.</p> |
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</dd> |
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</dl> |
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</p> |
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<p>If one or more of these are ored into the flags value, then only these |
|
backends will be tried (in the reverse order as given here). If none are |
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specified, most compiled-in backend will be tried, usually in reverse |
|
order of their flag values :)</p> |
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<p>The most typical usage is like this:</p> |
|
<pre> if (!ev_default_loop (0)) |
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fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); |
|
|
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</pre> |
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<p>Restrict libev to the select and poll backends, and do not allow |
|
environment settings to be taken into account:</p> |
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<pre> ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); |
|
|
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</pre> |
|
<p>Use whatever libev has to offer, but make sure that kqueue is used if |
|
available (warning, breaks stuff, best use only with your own private |
|
event loop and only if you know the OS supports your types of fds):</p> |
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<pre> ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); |
|
|
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</pre> |
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</dd> |
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<dt>struct ev_loop *ev_loop_new (unsigned int flags)</dt> |
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<dd> |
|
<p>Similar to <code>ev_default_loop</code>, but always creates a new event loop that is |
|
always distinct from the default loop. Unlike the default loop, it cannot |
|
handle signal and child watchers, and attempts to do so will be greeted by |
|
undefined behaviour (or a failed assertion if assertions are enabled).</p> |
|
<p>Example: try to create a event loop that uses epoll and nothing else.</p> |
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<pre> struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV); |
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if (!epoller) |
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fatal ("no epoll found here, maybe it hides under your chair"); |
|
|
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</pre> |
|
</dd> |
|
<dt>ev_default_destroy ()</dt> |
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<dd> |
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<p>Destroys the default loop again (frees all memory and kernel state |
|
etc.). This stops all registered event watchers (by not touching them in |
|
any way whatsoever, although you cannot rely on this :).</p> |
|
</dd> |
|
<dt>ev_loop_destroy (loop)</dt> |
|
<dd> |
|
<p>Like <code>ev_default_destroy</code>, but destroys an event loop created by an |
|
earlier call to <code>ev_loop_new</code>.</p> |
|
</dd> |
|
<dt>ev_default_fork ()</dt> |
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<dd> |
|
<p>This function reinitialises the kernel state for backends that have |
|
one. Despite the name, you can call it anytime, but it makes most sense |
|
after forking, in either the parent or child process (or both, but that |
|
again makes little sense).</p> |
|
<p>You <i>must</i> call this function in the child process after forking if and |
|
only if you want to use the event library in both processes. If you just |
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fork+exec, you don't have to call it.</p> |
|
<p>The function itself is quite fast and it's usually not a problem to call |
|
it just in case after a fork. To make this easy, the function will fit in |
|
quite nicely into a call to <code>pthread_atfork</code>:</p> |
|
<pre> pthread_atfork (0, 0, ev_default_fork); |
|
|
|
</pre> |
|
<p>At the moment, <code>EVBACKEND_SELECT</code> and <code>EVBACKEND_POLL</code> are safe to use |
|
without calling this function, so if you force one of those backends you |
|
do not need to care.</p> |
|
</dd> |
|
<dt>ev_loop_fork (loop)</dt> |
|
<dd> |
|
<p>Like <code>ev_default_fork</code>, but acts on an event loop created by |
|
<code>ev_loop_new</code>. Yes, you have to call this on every allocated event loop |
|
after fork, and how you do this is entirely your own problem.</p> |
|
</dd> |
|
<dt>unsigned int ev_backend (loop)</dt> |
|
<dd> |
|
<p>Returns one of the <code>EVBACKEND_*</code> flags indicating the event backend in |
|
use.</p> |
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</dd> |
|
<dt>ev_tstamp ev_now (loop)</dt> |
|
<dd> |
|
<p>Returns the current "event loop time", which is the time the event loop |
|
received events and started processing them. This timestamp does not |
|
change as long as callbacks are being processed, and this is also the base |
|
time used for relative timers. You can treat it as the timestamp of the |
|
event occuring (or more correctly, libev finding out about it).</p> |
|
</dd> |
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<dt>ev_loop (loop, int flags)</dt> |
|
<dd> |
|
<p>Finally, this is it, the event handler. This function usually is called |
|
after you initialised all your watchers and you want to start handling |
|
events.</p> |
|
<p>If the flags argument is specified as <code>0</code>, it will not return until |
|
either no event watchers are active anymore or <code>ev_unloop</code> was called.</p> |
|
<p>Please note that an explicit <code>ev_unloop</code> is usually better than |
|
relying on all watchers to be stopped when deciding when a program has |
|
finished (especially in interactive programs), but having a program that |
|
automatically loops as long as it has to and no longer by virtue of |
|
relying on its watchers stopping correctly is a thing of beauty.</p> |
|
<p>A flags value of <code>EVLOOP_NONBLOCK</code> will look for new events, will handle |
|
those events and any outstanding ones, but will not block your process in |
|
case there are no events and will return after one iteration of the loop.</p> |
|
<p>A flags value of <code>EVLOOP_ONESHOT</code> will look for new events (waiting if |
|
neccessary) and will handle those and any outstanding ones. It will block |
|
your process until at least one new event arrives, and will return after |
|
one iteration of the loop. This is useful if you are waiting for some |
|
external event in conjunction with something not expressible using other |
|
libev watchers. However, a pair of <code>ev_prepare</code>/<code>ev_check</code> watchers is |
|
usually a better approach for this kind of thing.</p> |
|
<p>Here are the gory details of what <code>ev_loop</code> does:</p> |
|
<pre> * If there are no active watchers (reference count is zero), return. |
|
- Queue prepare watchers and then call all outstanding watchers. |
|
- If we have been forked, recreate the kernel state. |
|
- Update the kernel state with all outstanding changes. |
|
- Update the "event loop time". |
|
- Calculate for how long to block. |
|
- Block the process, waiting for any events. |
|
- Queue all outstanding I/O (fd) events. |
|
- Update the "event loop time" and do time jump handling. |
|
- Queue all outstanding timers. |
|
- Queue all outstanding periodics. |
|
- If no events are pending now, queue all idle watchers. |
|
- Queue all check watchers. |
|
- Call all queued watchers in reverse order (i.e. check watchers first). |
|
Signals and child watchers are implemented as I/O watchers, and will |
|
be handled here by queueing them when their watcher gets executed. |
|
- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK |
|
were used, return, otherwise continue with step *. |
|
|
|
</pre> |
|
<p>Example: queue some jobs and then loop until no events are outsanding |
|
anymore.</p> |
|
<pre> ... queue jobs here, make sure they register event watchers as long |
|
... as they still have work to do (even an idle watcher will do..) |
|
ev_loop (my_loop, 0); |
|
... jobs done. yeah! |
|
|
|
</pre> |
|
</dd> |
|
<dt>ev_unloop (loop, how)</dt> |
|
<dd> |
|
<p>Can be used to make a call to <code>ev_loop</code> return early (but only after it |
|
has processed all outstanding events). The <code>how</code> argument must be either |
|
<code>EVUNLOOP_ONE</code>, which will make the innermost <code>ev_loop</code> call return, or |
|
<code>EVUNLOOP_ALL</code>, which will make all nested <code>ev_loop</code> calls return.</p> |
|
</dd> |
|
<dt>ev_ref (loop)</dt> |
|
<dt>ev_unref (loop)</dt> |
|
<dd> |
|
<p>Ref/unref can be used to add or remove a reference count on the event |
|
loop: Every watcher keeps one reference, and as long as the reference |
|
count is nonzero, <code>ev_loop</code> will not return on its own. If you have |
|
a watcher you never unregister that should not keep <code>ev_loop</code> from |
|
returning, ev_unref() after starting, and ev_ref() before stopping it. For |
|
example, libev itself uses this for its internal signal pipe: It is not |
|
visible to the libev user and should not keep <code>ev_loop</code> from exiting if |
|
no event watchers registered by it are active. It is also an excellent |
|
way to do this for generic recurring timers or from within third-party |
|
libraries. Just remember to <i>unref after start</i> and <i>ref before stop</i>.</p> |
|
<p>Example: create a signal watcher, but keep it from keeping <code>ev_loop</code> |
|
running when nothing else is active.</p> |
|
<pre> struct dv_signal exitsig; |
|
ev_signal_init (&exitsig, sig_cb, SIGINT); |
|
ev_signal_start (myloop, &exitsig); |
|
evf_unref (myloop); |
|
|
|
</pre> |
|
<p>Example: for some weird reason, unregister the above signal handler again.</p> |
|
<pre> ev_ref (myloop); |
|
ev_signal_stop (myloop, &exitsig); |
|
|
|
</pre> |
|
</dd> |
|
</dl> |
|
|
|
</div> |
|
<h1 id="ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</h1><p><a href="#TOP" class="toplink">Top</a></p> |
|
<div id="ANATOMY_OF_A_WATCHER_CONTENT"> |
|
<p>A watcher is a structure that you create and register to record your |
|
interest in some event. For instance, if you want to wait for STDIN to |
|
become readable, you would create an <code>ev_io</code> watcher for that:</p> |
|
<pre> static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) |
|
{ |
|
ev_io_stop (w); |
|
ev_unloop (loop, EVUNLOOP_ALL); |
|
} |
|
|
|
struct ev_loop *loop = ev_default_loop (0); |
|
struct ev_io stdin_watcher; |
|
ev_init (&stdin_watcher, my_cb); |
|
ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); |
|
ev_io_start (loop, &stdin_watcher); |
|
ev_loop (loop, 0); |
|
|
|
</pre> |
|
<p>As you can see, you are responsible for allocating the memory for your |
|
watcher structures (and it is usually a bad idea to do this on the stack, |
|
although this can sometimes be quite valid).</p> |
|
<p>Each watcher structure must be initialised by a call to <code>ev_init |
|
(watcher *, callback)</code>, which expects a callback to be provided. This |
|
callback gets invoked each time the event occurs (or, in the case of io |
|
watchers, each time the event loop detects that the file descriptor given |
|
is readable and/or writable).</p> |
|
<p>Each watcher type has its own <code>ev_<type>_set (watcher *, ...)</code> macro |
|
with arguments specific to this watcher type. There is also a macro |
|
to combine initialisation and setting in one call: <code>ev_<type>_init |
|
(watcher *, callback, ...)</code>.</p> |
|
<p>To make the watcher actually watch out for events, you have to start it |
|
with a watcher-specific start function (<code>ev_<type>_start (loop, watcher |
|
*)</code>), and you can stop watching for events at any time by calling the |
|
corresponding stop function (<code>ev_<type>_stop (loop, watcher *)</code>.</p> |
|
<p>As long as your watcher is active (has been started but not stopped) you |
|
must not touch the values stored in it. Most specifically you must never |
|
reinitialise it or call its set macro.</p> |
|
<p>You can check whether an event is active by calling the <code>ev_is_active |
|
(watcher *)</code> macro. To see whether an event is outstanding (but the |
|
callback for it has not been called yet) you can use the <code>ev_is_pending |
|
(watcher *)</code> macro.</p> |
|
<p>Each and every callback receives the event loop pointer as first, the |
|
registered watcher structure as second, and a bitset of received events as |
|
third argument.</p> |
|
<p>The received events usually include a single bit per event type received |
|
(you can receive multiple events at the same time). The possible bit masks |
|
are:</p> |
|
<dl> |
|
<dt><code>EV_READ</code></dt> |
|
<dt><code>EV_WRITE</code></dt> |
|
<dd> |
|
<p>The file descriptor in the <code>ev_io</code> watcher has become readable and/or |
|
writable.</p> |
|
</dd> |
|
<dt><code>EV_TIMEOUT</code></dt> |
|
<dd> |
|
<p>The <code>ev_timer</code> watcher has timed out.</p> |
|
</dd> |
|
<dt><code>EV_PERIODIC</code></dt> |
|
<dd> |
|
<p>The <code>ev_periodic</code> watcher has timed out.</p> |
|
</dd> |
|
<dt><code>EV_SIGNAL</code></dt> |
|
<dd> |
|
<p>The signal specified in the <code>ev_signal</code> watcher has been received by a thread.</p> |
|
</dd> |
|
<dt><code>EV_CHILD</code></dt> |
|
<dd> |
|
<p>The pid specified in the <code>ev_child</code> watcher has received a status change.</p> |
|
</dd> |
|
<dt><code>EV_IDLE</code></dt> |
|
<dd> |
|
<p>The <code>ev_idle</code> watcher has determined that you have nothing better to do.</p> |
|
</dd> |
|
<dt><code>EV_PREPARE</code></dt> |
|
<dt><code>EV_CHECK</code></dt> |
|
<dd> |
|
<p>All <code>ev_prepare</code> watchers are invoked just <i>before</i> <code>ev_loop</code> starts |
|
to gather new events, and all <code>ev_check</code> watchers are invoked just after |
|
<code>ev_loop</code> has gathered them, but before it invokes any callbacks for any |
|
received events. Callbacks of both watcher types can start and stop as |
|
many watchers as they want, and all of them will be taken into account |
|
(for example, a <code>ev_prepare</code> watcher might start an idle watcher to keep |
|
<code>ev_loop</code> from blocking).</p> |
|
</dd> |
|
<dt><code>EV_ERROR</code></dt> |
|
<dd> |
|
<p>An unspecified error has occured, the watcher has been stopped. This might |
|
happen because the watcher could not be properly started because libev |
|
ran out of memory, a file descriptor was found to be closed or any other |
|
problem. You best act on it by reporting the problem and somehow coping |
|
with the watcher being stopped.</p> |
|
<p>Libev will usually signal a few "dummy" events together with an error, |
|
for example it might indicate that a fd is readable or writable, and if |
|
your callbacks is well-written it can just attempt the operation and cope |
|
with the error from read() or write(). This will not work in multithreaded |
|
programs, though, so beware.</p> |
|
</dd> |
|
</dl> |
|
|
|
</div> |
|
<h2 id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</h2> |
|
<div id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH-2"> |
|
<p>Each watcher has, by default, a member <code>void *data</code> that you can change |
|
and read at any time, libev will completely ignore it. This can be used |
|
to associate arbitrary data with your watcher. If you need more data and |
|
don't want to allocate memory and store a pointer to it in that data |
|
member, you can also "subclass" the watcher type and provide your own |
|
data:</p> |
|
<pre> struct my_io |
|
{ |
|
struct ev_io io; |
|
int otherfd; |
|
void *somedata; |
|
struct whatever *mostinteresting; |
|
} |
|
|
|
</pre> |
|
<p>And since your callback will be called with a pointer to the watcher, you |
|
can cast it back to your own type:</p> |
|
<pre> static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) |
|
{ |
|
struct my_io *w = (struct my_io *)w_; |
|
... |
|
} |
|
|
|
</pre> |
|
<p>More interesting and less C-conformant ways of catsing your callback type |
|
have been omitted....</p> |
|
|
|
|
|
|
|
|
|
|
|
</div> |
|
<h1 id="WATCHER_TYPES">WATCHER TYPES</h1><p><a href="#TOP" class="toplink">Top</a></p> |
|
<div id="WATCHER_TYPES_CONTENT"> |
|
<p>This section describes each watcher in detail, but will not repeat |
|
information given in the last section.</p> |
|
|
|
|
|
|
|
|
|
|
|
</div> |
|
<h2 id="code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable</h2> |
|
<div id="code_ev_io_code_is_this_file_descrip-2"> |
|
<p>I/O watchers check whether a file descriptor is readable or writable |
|
in each iteration of the event loop (This behaviour is called |
|
level-triggering because you keep receiving events as long as the |
|
condition persists. Remember you can stop the watcher if you don't want to |
|
act on the event and neither want to receive future events).</p> |
|
<p>In general you can register as many read and/or write event watchers per |
|
fd as you want (as long as you don't confuse yourself). Setting all file |
|
descriptors to non-blocking mode is also usually a good idea (but not |
|
required if you know what you are doing).</p> |
|
<p>You have to be careful with dup'ed file descriptors, though. Some backends |
|
(the linux epoll backend is a notable example) cannot handle dup'ed file |
|
descriptors correctly if you register interest in two or more fds pointing |
|
to the same underlying file/socket etc. description (that is, they share |
|
the same underlying "file open").</p> |
|
<p>If you must do this, then force the use of a known-to-be-good backend |
|
(at the time of this writing, this includes only <code>EVBACKEND_SELECT</code> and |
|
<code>EVBACKEND_POLL</code>).</p> |
|
<dl> |
|
<dt>ev_io_init (ev_io *, callback, int fd, int events)</dt> |
|
<dt>ev_io_set (ev_io *, int fd, int events)</dt> |
|
<dd> |
|
<p>Configures an <code>ev_io</code> watcher. The fd is the file descriptor to rceeive |
|
events for and events is either <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_READ | |
|
EV_WRITE</code> to receive the given events.</p> |
|
<p>Please note that most of the more scalable backend mechanisms (for example |
|
epoll and solaris ports) can result in spurious readyness notifications |
|
for file descriptors, so you practically need to use non-blocking I/O (and |
|
treat callback invocation as hint only), or retest separately with a safe |
|
interface before doing I/O (XLib can do this), or force the use of either |
|
<code>EVBACKEND_SELECT</code> or <code>EVBACKEND_POLL</code>, which don't suffer from this |
|
problem. Also note that it is quite easy to have your callback invoked |
|
when the readyness condition is no longer valid even when employing |
|
typical ways of handling events, so its a good idea to use non-blocking |
|
I/O unconditionally.</p> |
|
</dd> |
|
</dl> |
|
<p>Example: call <code>stdin_readable_cb</code> when STDIN_FILENO has become, well |
|
readable, but only once. Since it is likely line-buffered, you could |
|
attempt to read a whole line in the callback:</p> |
|
<pre> static void |
|
stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) |
|
{ |
|
ev_io_stop (loop, w); |
|
.. read from stdin here (or from w->fd) and haqndle any I/O errors |
|
} |
|
|
|
... |
|
struct ev_loop *loop = ev_default_init (0); |
|
struct ev_io stdin_readable; |
|
ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); |
|
ev_io_start (loop, &stdin_readable); |
|
ev_loop (loop, 0); |
|
|
|
|
|
|
|
|
|
</pre> |
|
|
|
</div> |
|
<h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally recurring timeouts</h2> |
|
<div id="code_ev_timer_code_relative_and_opti-2"> |
|
<p>Timer watchers are simple relative timers that generate an event after a |
|
given time, and optionally repeating in regular intervals after that.</p> |
|
<p>The timers are based on real time, that is, if you register an event that |
|
times out after an hour and you reset your system clock to last years |
|
time, it will still time out after (roughly) and hour. "Roughly" because |
|
detecting time jumps is hard, and some inaccuracies are unavoidable (the |
|
monotonic clock option helps a lot here).</p> |
|
<p>The relative timeouts are calculated relative to the <code>ev_now ()</code> |
|
time. This is usually the right thing as this timestamp refers to the time |
|
of the event triggering whatever timeout you are modifying/starting. If |
|
you suspect event processing to be delayed and you <i>need</i> to base the timeout |
|
on the current time, use something like this to adjust for this:</p> |
|
<pre> ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); |
|
|
|
</pre> |
|
<p>The callback is guarenteed to be invoked only when its timeout has passed, |
|
but if multiple timers become ready during the same loop iteration then |
|
order of execution is undefined.</p> |
|
<dl> |
|
<dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt> |
|
<dt>ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)</dt> |
|
<dd> |
|
<p>Configure the timer to trigger after <code>after</code> seconds. If <code>repeat</code> is |
|
<code>0.</code>, then it will automatically be stopped. If it is positive, then the |
|
timer will automatically be configured to trigger again <code>repeat</code> seconds |
|
later, again, and again, until stopped manually.</p> |
|
<p>The timer itself will do a best-effort at avoiding drift, that is, if you |
|
configure a timer to trigger every 10 seconds, then it will trigger at |
|
exactly 10 second intervals. If, however, your program cannot keep up with |
|
the timer (because it takes longer than those 10 seconds to do stuff) the |
|
timer will not fire more than once per event loop iteration.</p> |
|
</dd> |
|
<dt>ev_timer_again (loop)</dt> |
|
<dd> |
|
<p>This will act as if the timer timed out and restart it again if it is |
|
repeating. The exact semantics are:</p> |
|
<p>If the timer is started but nonrepeating, stop it.</p> |
|
<p>If the timer is repeating, either start it if necessary (with the repeat |
|
value), or reset the running timer to the repeat value.</p> |
|
<p>This sounds a bit complicated, but here is a useful and typical |
|
example: Imagine you have a tcp connection and you want a so-called idle |
|
timeout, that is, you want to be called when there have been, say, 60 |
|
seconds of inactivity on the socket. The easiest way to do this is to |
|
configure an <code>ev_timer</code> with after=repeat=60 and calling ev_timer_again each |
|
time you successfully read or write some data. If you go into an idle |
|
state where you do not expect data to travel on the socket, you can stop |
|
the timer, and again will automatically restart it if need be.</p> |
|
</dd> |
|
</dl> |
|
<p>Example: create a timer that fires after 60 seconds.</p> |
|
<pre> static void |
|
one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) |
|
{ |
|
.. one minute over, w is actually stopped right here |
|
} |
|
|
|
struct ev_timer mytimer; |
|
ev_timer_init (&mytimer, one_minute_cb, 60., 0.); |
|
ev_timer_start (loop, &mytimer); |
|
|
|
</pre> |
|
<p>Example: create a timeout timer that times out after 10 seconds of |
|
inactivity.</p> |
|
<pre> static void |
|
timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) |
|
{ |
|
.. ten seconds without any activity |
|
} |
|
|
|
struct ev_timer mytimer; |
|
ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ |
|
ev_timer_again (&mytimer); /* start timer */ |
|
ev_loop (loop, 0); |
|
|
|
// and in some piece of code that gets executed on any "activity": |
|
// reset the timeout to start ticking again at 10 seconds |
|
ev_timer_again (&mytimer); |
|
|
|
|
|
|
|
|
|
</pre> |
|
|
|
</div> |
|
<h2 id="code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron</h2> |
|
<div id="code_ev_periodic_code_to_cron_or_not-2"> |
|
<p>Periodic watchers are also timers of a kind, but they are very versatile |
|
(and unfortunately a bit complex).</p> |
|
<p>Unlike <code>ev_timer</code>'s, they are not based on real time (or relative time) |
|
but on wallclock time (absolute time). You can tell a periodic watcher |
|
to trigger "at" some specific point in time. For example, if you tell a |
|
periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () |
|
+ 10.>) and then reset your system clock to the last year, then it will |
|
take a year to trigger the event (unlike an <code>ev_timer</code>, which would trigger |
|
roughly 10 seconds later and of course not if you reset your system time |
|
again).</p> |
|
<p>They can also be used to implement vastly more complex timers, such as |
|
triggering an event on eahc midnight, local time.</p> |
|
<p>As with timers, the callback is guarenteed to be invoked only when the |
|
time (<code>at</code>) has been passed, but if multiple periodic timers become ready |
|
during the same loop iteration then order of execution is undefined.</p> |
|
<dl> |
|
<dt>ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)</dt> |
|
<dt>ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)</dt> |
|
<dd> |
|
<p>Lots of arguments, lets sort it out... There are basically three modes of |
|
operation, and we will explain them from simplest to complex:</p> |
|
<p> |
|
<dl> |
|
<dt>* absolute timer (interval = reschedule_cb = 0)</dt> |
|
<dd> |
|
<p>In this configuration the watcher triggers an event at the wallclock time |
|
<code>at</code> and doesn't repeat. It will not adjust when a time jump occurs, |
|
that is, if it is to be run at January 1st 2011 then it will run when the |
|
system time reaches or surpasses this time.</p> |
|
</dd> |
|
<dt>* non-repeating interval timer (interval > 0, reschedule_cb = 0)</dt> |
|
<dd> |
|
<p>In this mode the watcher will always be scheduled to time out at the next |
|
<code>at + N * interval</code> time (for some integer N) and then repeat, regardless |
|
of any time jumps.</p> |
|
<p>This can be used to create timers that do not drift with respect to system |
|
time:</p> |
|
<pre> ev_periodic_set (&periodic, 0., 3600., 0); |
|
|
|
</pre> |
|
<p>This doesn't mean there will always be 3600 seconds in between triggers, |
|
but only that the the callback will be called when the system time shows a |
|
full hour (UTC), or more correctly, when the system time is evenly divisible |
|
by 3600.</p> |
|
<p>Another way to think about it (for the mathematically inclined) is that |
|
<code>ev_periodic</code> will try to run the callback in this mode at the next possible |
|
time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p> |
|
</dd> |
|
<dt>* manual reschedule mode (reschedule_cb = callback)</dt> |
|
<dd> |
|
<p>In this mode the values for <code>interval</code> and <code>at</code> are both being |
|
ignored. Instead, each time the periodic watcher gets scheduled, the |
|
reschedule callback will be called with the watcher as first, and the |
|
current time as second argument.</p> |
|
<p>NOTE: <i>This callback MUST NOT stop or destroy any periodic watcher, |
|
ever, or make any event loop modifications</i>. If you need to stop it, |
|
return <code>now + 1e30</code> (or so, fudge fudge) and stop it afterwards (e.g. by |
|
starting a prepare watcher).</p> |
|
<p>Its prototype is <code>ev_tstamp (*reschedule_cb)(struct ev_periodic *w, |
|
ev_tstamp now)</code>, e.g.:</p> |
|
<pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) |
|
{ |
|
return now + 60.; |
|
} |
|
|
|
</pre> |
|
<p>It must return the next time to trigger, based on the passed time value |
|
(that is, the lowest time value larger than to the second argument). It |
|
will usually be called just before the callback will be triggered, but |
|
might be called at other times, too.</p> |
|
<p>NOTE: <i>This callback must always return a time that is later than the |
|
passed <code>now</code> value</i>. Not even <code>now</code> itself will do, it <i>must</i> be larger.</p> |
|
<p>This can be used to create very complex timers, such as a timer that |
|
triggers on each midnight, local time. To do this, you would calculate the |
|
next midnight after <code>now</code> and return the timestamp value for this. How |
|
you do this is, again, up to you (but it is not trivial, which is the main |
|
reason I omitted it as an example).</p> |
|
</dd> |
|
</dl> |
|
</p> |
|
</dd> |
|
<dt>ev_periodic_again (loop, ev_periodic *)</dt> |
|
<dd> |
|
<p>Simply stops and restarts the periodic watcher again. This is only useful |
|
when you changed some parameters or the reschedule callback would return |
|
a different time than the last time it was called (e.g. in a crond like |
|
program when the crontabs have changed).</p> |
|
</dd> |
|
</dl> |
|
<p>Example: call a callback every hour, or, more precisely, whenever the |
|
system clock is divisible by 3600. The callback invocation times have |
|
potentially a lot of jittering, but good long-term stability.</p> |
|
<pre> static void |
|
clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) |
|
{ |
|
... its now a full hour (UTC, or TAI or whatever your clock follows) |
|
} |
|
|
|
struct ev_periodic hourly_tick; |
|
ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); |
|
ev_periodic_start (loop, &hourly_tick); |
|
|
|
</pre> |
|
<p>Example: the same as above, but use a reschedule callback to do it:</p> |
|
<pre> #include <math.h> |
|
|
|
static ev_tstamp |
|
my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) |
|
{ |
|
return fmod (now, 3600.) + 3600.; |
|
} |
|
|
|
ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); |
|
|
|
</pre> |
|
<p>Example: call a callback every hour, starting now:</p> |
|
<pre> struct ev_periodic hourly_tick; |
|
ev_periodic_init (&hourly_tick, clock_cb, |
|
fmod (ev_now (loop), 3600.), 3600., 0); |
|
ev_periodic_start (loop, &hourly_tick); |
|
|
|
|
|
|
|
|
|
</pre> |
|
|
|
</div> |
|
<h2 id="code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled</h2> |
|
<div id="code_ev_signal_code_signal_me_when_a-2"> |
|
<p>Signal watchers will trigger an event when the process receives a specific |
|
signal one or more times. Even though signals are very asynchronous, libev |
|
will try it's best to deliver signals synchronously, i.e. as part of the |
|
normal event processing, like any other event.</p> |
|
<p>You can configure as many watchers as you like per signal. Only when the |
|
first watcher gets started will libev actually register a signal watcher |
|
with the kernel (thus it coexists with your own signal handlers as long |
|
as you don't register any with libev). Similarly, when the last signal |
|
watcher for a signal is stopped libev will reset the signal handler to |
|
SIG_DFL (regardless of what it was set to before).</p> |
|
<dl> |
|
<dt>ev_signal_init (ev_signal *, callback, int signum)</dt> |
|
<dt>ev_signal_set (ev_signal *, int signum)</dt> |
|
<dd> |
|
<p>Configures the watcher to trigger on the given signal number (usually one |
|
of the <code>SIGxxx</code> constants).</p> |
|
</dd> |
|
</dl> |
|
|
|
</div> |
|
<h2 id="code_ev_child_code_wait_for_pid_stat"><code>ev_child</code> - wait for pid status changes</h2> |
|
<div id="code_ev_child_code_wait_for_pid_stat-2"> |
|
<p>Child watchers trigger when your process receives a SIGCHLD in response to |
|
some child status changes (most typically when a child of yours dies).</p> |
|
<dl> |
|
<dt>ev_child_init (ev_child *, callback, int pid)</dt> |
|
<dt>ev_child_set (ev_child *, int pid)</dt> |
|
<dd> |
|
<p>Configures the watcher to wait for status changes of process <code>pid</code> (or |
|
<i>any</i> process if <code>pid</code> is specified as <code>0</code>). The callback can look |
|
at the <code>rstatus</code> member of the <code>ev_child</code> watcher structure to see |
|
the status word (use the macros from <code>sys/wait.h</code> and see your systems |
|
<code>waitpid</code> documentation). The <code>rpid</code> member contains the pid of the |
|
process causing the status change.</p> |
|
</dd> |
|
</dl> |
|
<p>Example: try to exit cleanly on SIGINT and SIGTERM.</p> |
|
<pre> static void |
|
sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) |
|
{ |
|
ev_unloop (loop, EVUNLOOP_ALL); |
|
} |
|
|
|
struct ev_signal signal_watcher; |
|
ev_signal_init (&signal_watcher, sigint_cb, SIGINT); |
|
ev_signal_start (loop, &sigint_cb); |
|
|
|
|
|
|
|
|
|
</pre> |
|
|
|
</div> |
|
<h2 id="code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do</h2> |
|
<div id="code_ev_idle_code_when_you_ve_got_no-2"> |
|
<p>Idle watchers trigger events when there are no other events are pending |
|
(prepare, check and other idle watchers do not count). That is, as long |
|
as your process is busy handling sockets or timeouts (or even signals, |
|
imagine) it will not be triggered. But when your process is idle all idle |
|
watchers are being called again and again, once per event loop iteration - |
|
until stopped, that is, or your process receives more events and becomes |
|
busy.</p> |
|
<p>The most noteworthy effect is that as long as any idle watchers are |
|
active, the process will not block when waiting for new events.</p> |
|
<p>Apart from keeping your process non-blocking (which is a useful |
|
effect on its own sometimes), idle watchers are a good place to do |
|
"pseudo-background processing", or delay processing stuff to after the |
|
event loop has handled all outstanding events.</p> |
|
<dl> |
|
<dt>ev_idle_init (ev_signal *, callback)</dt> |
|
<dd> |
|
<p>Initialises and configures the idle watcher - it has no parameters of any |
|
kind. There is a <code>ev_idle_set</code> macro, but using it is utterly pointless, |
|
believe me.</p> |
|
</dd> |
|
</dl> |
|
<p>Example: dynamically allocate an <code>ev_idle</code>, start it, and in the |
|
callback, free it. Alos, use no error checking, as usual.</p> |
|
<pre> static void |
|
idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) |
|
{ |
|
free (w); |
|
// now do something you wanted to do when the program has |
|
// no longer asnything immediate to do. |
|
} |
|
|
|
struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); |
|
ev_idle_init (idle_watcher, idle_cb); |
|
ev_idle_start (loop, idle_cb); |
|
|
|
|
|
|
|
|
|
</pre> |
|
|
|
</div> |
|
<h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop</h2> |
|
<div id="code_ev_prepare_code_and_code_ev_che-2"> |
|
<p>Prepare and check watchers are usually (but not always) used in tandem: |
|
prepare watchers get invoked before the process blocks and check watchers |
|
afterwards.</p> |
|
<p>Their main purpose is to integrate other event mechanisms into libev. This |
|
could be used, for example, to track variable changes, implement your own |
|
watchers, integrate net-snmp or a coroutine library and lots more.</p> |
|
<p>This is done by examining in each prepare call which file descriptors need |
|
to be watched by the other library, registering <code>ev_io</code> watchers for |
|
them and starting an <code>ev_timer</code> watcher for any timeouts (many libraries |
|
provide just this functionality). Then, in the check watcher you check for |
|
any events that occured (by checking the pending status of all watchers |
|
and stopping them) and call back into the library. The I/O and timer |
|
callbacks will never actually be called (but must be valid nevertheless, |
|
because you never know, you know?).</p> |
|
<p>As another example, the Perl Coro module uses these hooks to integrate |
|
coroutines into libev programs, by yielding to other active coroutines |
|
during each prepare and only letting the process block if no coroutines |
|
are ready to run (it's actually more complicated: it only runs coroutines |
|
with priority higher than or equal to the event loop and one coroutine |
|
of lower priority, but only once, using idle watchers to keep the event |
|
loop from blocking if lower-priority coroutines are active, thus mapping |
|
low-priority coroutines to idle/background tasks).</p> |
|
<dl> |
|
<dt>ev_prepare_init (ev_prepare *, callback)</dt> |
|
<dt>ev_check_init (ev_check *, callback)</dt> |
|
<dd> |
|
<p>Initialises and configures the prepare or check watcher - they have no |
|
parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check_set</code> |
|
macros, but using them is utterly, utterly and completely pointless.</p> |
|
</dd> |
|
</dl> |
|
<p>Example: *TODO*.</p> |
|
|
|
|
|
|
|
|
|
|
|
</div> |
|
<h1 id="OTHER_FUNCTIONS">OTHER FUNCTIONS</h1><p><a href="#TOP" class="toplink">Top</a></p> |
|
<div id="OTHER_FUNCTIONS_CONTENT"> |
|
<p>There are some other functions of possible interest. Described. Here. Now.</p> |
|
<dl> |
|
<dt>ev_once (loop, int fd, int events, ev_tstamp timeout, callback)</dt> |
|
<dd> |
|
<p>This function combines a simple timer and an I/O watcher, calls your |
|
callback on whichever event happens first and automatically stop both |
|
watchers. This is useful if you want to wait for a single event on an fd |
|
or timeout without having to allocate/configure/start/stop/free one or |
|
more watchers yourself.</p> |
|
<p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events |
|
is being ignored. Otherwise, an <code>ev_io</code> watcher for the given <code>fd</code> and |
|
<code>events</code> set will be craeted and started.</p> |
|
<p>If <code>timeout</code> is less than 0, then no timeout watcher will be |
|
started. Otherwise an <code>ev_timer</code> watcher with after = <code>timeout</code> (and |
|
repeat = 0) will be started. While <code>0</code> is a valid timeout, it is of |
|
dubious value.</p> |
|
<p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and gets |
|
passed an <code>revents</code> set like normal event callbacks (a combination of |
|
<code>EV_ERROR</code>, <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_TIMEOUT</code>) and the <code>arg</code> |
|
value passed to <code>ev_once</code>:</p> |
|
<pre> static void stdin_ready (int revents, void *arg) |
|
{ |
|
if (revents & EV_TIMEOUT) |
|
/* doh, nothing entered */; |
|
else if (revents & EV_READ) |
|
/* stdin might have data for us, joy! */; |
|
} |
|
|
|
ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); |
|
|
|
</pre> |
|
</dd> |
|
<dt>ev_feed_event (loop, watcher, int events)</dt> |
|
<dd> |
|
<p>Feeds the given event set into the event loop, as if the specified event |
|
had happened for the specified watcher (which must be a pointer to an |
|
initialised but not necessarily started event watcher).</p> |
|
</dd> |
|
<dt>ev_feed_fd_event (loop, int fd, int revents)</dt> |
|
<dd> |
|
<p>Feed an event on the given fd, as if a file descriptor backend detected |
|
the given events it.</p> |
|
</dd> |
|
<dt>ev_feed_signal_event (loop, int signum)</dt> |
|
<dd> |
|
<p>Feed an event as if the given signal occured (loop must be the default loop!).</p> |
|
</dd> |
|
</dl> |
|
|
|
|
|
|
|
|
|
|
|
</div> |
|
<h1 id="LIBEVENT_EMULATION">LIBEVENT EMULATION</h1><p><a href="#TOP" class="toplink">Top</a></p> |
|
<div id="LIBEVENT_EMULATION_CONTENT"> |
|
<p>Libev offers a compatibility emulation layer for libevent. It cannot |
|
emulate the internals of libevent, so here are some usage hints:</p> |
|
<dl> |
|
<dt>* Use it by including <event.h>, as usual.</dt> |
|
<dt>* The following members are fully supported: ev_base, ev_callback, |
|
ev_arg, ev_fd, ev_res, ev_events.</dt> |
|
<dt>* Avoid using ev_flags and the EVLIST_*-macros, while it is |
|
maintained by libev, it does not work exactly the same way as in libevent (consider |
|
it a private API).</dt> |
|
<dt>* Priorities are not currently supported. Initialising priorities |
|
will fail and all watchers will have the same priority, even though there |
|
is an ev_pri field.</dt> |
|
<dt>* Other members are not supported.</dt> |
|
<dt>* The libev emulation is <i>not</i> ABI compatible to libevent, you need |
|
to use the libev header file and library.</dt> |
|
</dl> |
|
|
|
</div> |
|
<h1 id="C_SUPPORT">C++ SUPPORT</h1><p><a href="#TOP" class="toplink">Top</a></p> |
|
<div id="C_SUPPORT_CONTENT"> |
|
<p>TBD.</p> |
|
|
|
</div> |
|
<h1 id="AUTHOR">AUTHOR</h1><p><a href="#TOP" class="toplink">Top</a></p> |
|
<div id="AUTHOR_CONTENT"> |
|
<p>Marc Lehmann <libev@schmorp.de>.</p> |
|
|
|
</div> |
|
</div></body> |
|
</html>
|
|
|