@ -1,10 +1,10 @@
Revision history for libev, a high-performance and full-featured event loop
Revision history for libev, a high-performance and full-featured event loop.
3.1 Thu Mar 13 13:45:22 CET 2008
- implement ev_async watchers.
- only initialise signal pipe on demand.
- make use of sig_atomic_t configurable.
- improved ev_child documentation.
- improved documentation.
3.0 Mon Jan 28 13:14:47 CET 2008
- API/ABI bump to version 3.0.
@ -1,3 +1,6 @@
@ -1,7 +1,7 @@
@ -132,7 +132,7 @@
.IX Title "EV 1"
.TH EV 1 "2008-01-28" "perl v5.10.0" "User Contributed Perl Documentation"
.TH EV 1 "2008-03-08" "perl v5.10.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
@ -146,50 +146,64 @@ libev \- a high performance full\-featured event loop written in C
.Sh "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
.IX Subsection "EXAMPLE PROGRAM"
\& // a single header file is required
\& #include <ev.h>
\& // every watcher type has its own typedef\*(Aqd struct
\& // with the name ev_<type>
\& ev_io stdin_watcher;
\& ev_timer timeout_watcher;
\& /* called when data readable on stdin */
\& // all watcher callbacks have a similar signature
\& // this callback is called when data is readable on stdin
\& static void
\& stdin_cb (EV_P_ struct ev_io *w, int revents)
\& /* puts ("stdin ready"); */
\& ev_io_stop (EV_A_ w); /* just a syntax example */
\& ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */
\& puts ("stdin ready");
\& // for one\-shot events, one must manually stop the watcher
\& // with its corresponding stop function.
\& ev_io_stop (EV_A_ w);
\& // this causes all nested ev_loop\*(Aqs to stop iterating
\& ev_unloop (EV_A_ EVUNLOOP_ALL);
\& // another callback, this time for a time\-out
\& timeout_cb (EV_P_ struct ev_timer *w, int revents)
\& /* puts ("timeout"); */
\& ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
\& puts ("timeout");
\& // this causes the innermost ev_loop to stop iterating
\& ev_unloop (EV_A_ EVUNLOOP_ONE);
\& main (void)
\& // use the default event loop unless you have special needs
\& struct ev_loop *loop = ev_default_loop (0);
\& /* initialise an io watcher, then start it */
\& // initialise an io watcher, then start it
\& // this one will watch for stdin to become readable
\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
\& ev_io_start (loop, &stdin_watcher);
\& /* simple non\-repeating 5.5 second timeout */
\& // initialise a timer watcher, then start it
\& // simple non\-repeating 5.5 second timeout
\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
\& ev_timer_start (loop, &timeout_watcher);
\& /* loop till timeout or data ready */
\& // now wait for events to arrive
\& ev_loop (loop, 0);
\& // unloop was called, so exit
\& return 0;
.IX Header "DESCRIPTION"
The newest version of this document is also available as a html-formatted
The newest version of this document is also available as an html-formatted
web page you might find easier to navigate when reading it for the first
@ -223,12 +237,13 @@ benchmark comparing it to libevent
.IX Subsection "CONVENTIONS"
Libev is very configurable. In this manual the default configuration will
be described, which supports multiple event loops. For more info about
various configuration options please have a look at \fB\s-1EMBED\s0\fR section in
this manual. If libev was configured without support for multiple event
loops, then all functions taking an initial argument of name \f(CW\*(C`loop\*(C'\fR
(which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have this argument.
Libev is very configurable. In this manual the default (and most common)
configuration will be described, which supports multiple event loops. For
more info about various configuration options please have a look at
\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
for multiple event loops, then all functions taking an initial argument of
name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
.Sh "\s-1TIME\s0 \s-1REPRESENTATION\s0"
.IX Subsection "TIME REPRESENTATION"
Libev represents time as a single floating point number, representing the
@ -427,8 +442,8 @@ enabling this flag.
This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
and thus this might slow down your event loop if you do a lot of loop
iterations and little real work, but is usually not noticeable (on my
Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
without a syscall and thus \fIvery\fR fast, but my Linux system also has
GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
without a syscall and thus \fIvery\fR fast, but my GNU/Linux system also has
\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
The big advantage of this flag is that you can forget about fork (and
@ -641,6 +656,9 @@ quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
after fork, and how you do this is entirely your own problem.
.IP "int ev_is_default_loop (loop)" 4
.IX Item "int ev_is_default_loop (loop)"
Returns true when the given loop actually is the default loop, false otherwise.
.IP "unsigned int ev_loop_count (loop)" 4
.IX Item "unsigned int ev_loop_count (loop)"
Returns the count of loop iterations for the loop, which is identical to
@ -916,6 +934,10 @@ The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher need
.IX Item "EV_FORK"
The event loop has been resumed in the child process after fork (see
.ie n .IP """EV_ASYNC""" 4
.el .IP "\f(CWEV_ASYNC\fR" 4
.IX Item "EV_ASYNC"
The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
.ie n .IP """EV_ERROR""" 4
.el .IP "\f(CWEV_ERROR\fR" 4
.IX Item "EV_ERROR"
@ -1283,8 +1305,8 @@ 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.
.IP "ev_timer_again (loop)" 4
.IX Item "ev_timer_again (loop)"
.IP "ev_timer_again (loop, ev_timer *)" 4
.IX Item "ev_timer_again (loop, ev_timer *)"
This will act as if the timer timed out and restart it again if it is
repeating. The exact semantics are:
@ -1404,7 +1426,7 @@ In this configuration the watcher triggers an event at the wallclock time
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.
.IP "\(bu" 4
non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
In this mode the watcher will always be scheduled to time out at the next
\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N, which can also be negative)
@ -1552,6 +1574,12 @@ 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
\&\s-1SIG_DFL\s0 (regardless of what it was set to before).
If possible and supported, libev will install its handlers with
\&\f(CW\*(C`SA_RESTART\*(C'\fR behaviour enabled, so syscalls should not be unduly
interrupted. If you have a problem with syscalls getting interrupted by
signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher and unblock
them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
\fIWatcher-Specific Functions and Data Members\fR
.IX Subsection "Watcher-Specific Functions and Data Members"
.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
@ -1565,11 +1593,55 @@ of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
.IP "int signum [read\-only]" 4
.IX Item "int signum [read-only]"
The signal the watcher watches out for.
.IX Subsection "Examples"
Example: Try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0.
\& 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);
.ie n .Sh """ev_child"" \- watch out for process status changes"
.el .Sh "\f(CWev_child\fP \- watch out for process status changes"
.IX Subsection "ev_child - watch out for process status changes"
Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
some child status changes (most typically when a child of yours dies).
some child status changes (most typically when a child of yours dies). It
is permissible to install a child watcher \fIafter\fR the child has been
forked (which implies it might have already exited), as long as the event
loop isn't entered (or is continued from a watcher).
Only the default event loop is capable of handling signals, and therefore
you can only rgeister child watchers in the default event loop.
.IX Subsection "Process Interaction"
Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
initialised. This is necessary to guarantee proper behaviour even if
the first child watcher is started after the child exits. The occurance
of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
synchronously as part of the event loop processing. Libev always reaps all
children, even ones not watched.
\fIOverriding the Built-In Processing\fR
.IX Subsection "Overriding the Built-In Processing"
Libev offers no special support for overriding the built-in child
processing, but if your application collides with libev's default child
handler, you can override it easily by installing your own handler for
\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
default loop never gets destroyed. You are encouraged, however, to use an
event-based approach to child reaping and thus use libev's support for
that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
@ -1601,18 +1673,33 @@ The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
\& ev_child cw;
\& child_cb (EV_P_ struct ev_child *w, int revents)
\& ev_child_stop (EV_A_ w);
\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
\& pid_t pid = fork ();
\& if (pid < 0)
\& // error
\& else if (pid == 0)
\& // the forked child executes here
\& exit (1);
\& ev_child_init (&cw, child_cb, pid, 0);
\& ev_child_start (EV_DEFAULT_ &cw);
.ie n .Sh """ev_stat"" \- did the file attributes just change?"
.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?"
@ -1703,8 +1790,8 @@ path for as long as the watcher is active.
The callback will be receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected,
relative to the attributes at the time the watcher was started (or the
last change was detected).
.IP "ev_stat_stat (ev_stat *)" 4
.IX Item "ev_stat_stat (ev_stat *)"
.IP "ev_stat_stat (loop, ev_stat *)" 4
.IX Item "ev_stat_stat (loop, ev_stat *)"
Updates the stat buffer immediately with new values. If you change the
watched path in your callback, you could call this fucntion to avoid
detecting this change (while introducing a race condition). Can also be
@ -2175,6 +2262,129 @@ handlers will be invoked, too, of course.
Initialises and configures the fork watcher \- it has no parameters of any
kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
.ie n .Sh """ev_async"" \- how to wake up another event loop"
.el .Sh "\f(CWev_async\fP \- how to wake up another event loop"
.IX Subsection "ev_async - how to wake up another event loop"
In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
asynchronous sources such as signal handlers (as opposed to multiple event
loops \- those are of course safe to use in different threads).
Sometimes, however, you need to wake up another event loop you do not
control, for example because it belongs to another thread. This is what
\&\f(CW\*(C`ev_async\*(C'\fR watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you
can signal it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal
This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
too, are asynchronous in nature, and signals, too, will be compressed
(i.e. the number of callback invocations may be less than the number of
Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
just the default loop.
.IX Subsection "Queueing"
\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
is that the author does not know of a simple (or any) algorithm for a
multiple-writer-single-reader queue that works in all cases and doesn't
need elaborate support such as pthreads.
That means that if you want to queue data, you have to provide your own
queue. But at least I can tell you would implement locking around your
.IP "queueing from a signal handler context" 4
.IX Item "queueing from a signal handler context"
To implement race-free queueing, you simply add to the queue in the signal
handler but you block the signal handler in the watcher callback. Here is an example that does that for
some fictitiuous \s-1SIGUSR1\s0 handler:
\& static ev_async mysig;
\& static void
\& sigusr1_handler (void)
\& sometype data;
\& // no locking etc.
\& queue_put (data);
\& ev_async_send (EV_DEFAULT_ &mysig);
\& mysig_cb (EV_P_ ev_async *w, int revents)
\& sigset_t block, prev;
\& sigemptyset (&block);
\& sigaddset (&block, SIGUSR1);
\& sigprocmask (SIG_BLOCK, &block, &prev);
\& while (queue_get (&data))
\& process (data);
\& if (sigismember (&prev, SIGUSR1)
\& sigprocmask (SIG_UNBLOCK, &block, 0);
(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
.IP "queueing from a thread context" 4
.IX Item "queueing from a thread context"
The strategy for threads is different, as you cannot (easily) block
threads but you can easily preempt them, so to queue safely you need to
employ a traditional mutex lock, such as in this pthread example:
\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
\& otherthread (void)
\& // only need to lock the actual queueing operation
\& pthread_mutex_lock (&mymutex);
\& pthread_mutex_unlock (&mymutex);
.IP "ev_async_init (ev_async *, callback)" 4
.IX Item "ev_async_init (ev_async *, callback)"
Initialises and configures the async watcher \- it has no parameters of any
kind. There is a \f(CW\*(C`ev_asynd_set\*(C'\fR macro, but using it is utterly pointless,
.IP "ev_async_send (loop, ev_async *)" 4
.IX Item "ev_async_send (loop, ev_async *)"
Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
\&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do in other threads, signal or
similar contexts (see the dicusssion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
section below on what exactly this means).
This call incurs the overhead of a syscall only once per loop iteration,
so while the overhead might be noticable, it doesn't apply to repeated
calls to \f(CW\*(C`ev_async_send\*(C'\fR.
.SH "OTHER FUNCTIONS"
.IX Header "OTHER FUNCTIONS"
There are some other functions of possible interest. Described. Here. Now.
@ -2670,6 +2880,16 @@ reserved for future expansion, works like the \s-1USE\s0 symbols above.
If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
be detected at runtime.
.IP "\s-1EV_ATOMIC_T\s0" 4
.IX Item "EV_ATOMIC_T"
Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
access is atomic with respect to other threads or signal contexts. No such
type is easily found in the C language, so you can provide your own type
that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
In the absense of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
(from \fIsignal.h\fR), which is usually good enough on most platforms.
.IP "\s-1EV_H\s0" 4
.IX Item "EV_H"
The name of the \fIev.h\fR header file used to include it. The default if
@ -2737,6 +2957,10 @@ defined to be \f(CW0\fR, then they are not.
.IX Item "EV_FORK_ENABLE"
If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
defined to be \f(CW0\fR, then they are not.
.IP "\s-1EV_ASYNC_ENABLE\s0" 4
.IX Item "EV_ASYNC_ENABLE"
If undefined or defined to be \f(CW1\fR, then async watchers are supported. If
.IP "\s-1EV_MINIMAL\s0" 4
.IX Item "EV_MINIMAL"
If you need to shave off some kilobytes of code at the expense of some
@ -2866,11 +3090,11 @@ have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
That means that changing a timer costs less than removing/adding them
as only the relative motion in the event queue has to be paid for.
.IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4
.IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)"
.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
These just add the watcher into an array or at the head of a list.
.IP "Stopping check/prepare/idle watchers: O(1)" 4
.IX Item "Stopping check/prepare/idle watchers: O(1)"
.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
@ -2896,7 +3120,18 @@ on backend and wether \f(CW\*(C`ev_io_set\*(C'\fR was used).
Priorities are implemented by allocating some space for each
priority. When doing priority-based operations, libev usually has to
linearly search all the priorities, but starting/stopping and activating
watchers becomes O(1) w.r.t. prioritiy handling.
watchers becomes O(1) w.r.t. priority handling.
.IP "Sending an ev_async: O(1)" 4
.IX Item "Sending an ev_async: O(1)"
.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
.IP "Processing signals: O(max_signal_number)" 4
.IX Item "Processing signals: O(max_signal_number)"
Sending involves a syscall \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
calls in the current loop iteration. Checking for async and signal events
involves iterating over all running async watchers or all signal numbers.
.SH "Win32 platform limitations and workarounds"
.IX Header "Win32 platform limitations and workarounds"
Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
@ -2964,6 +3199,6 @@ Marc Lehmann <email@example.com>.
.SH "POD ERRORS"
.IX Header "POD ERRORS"
Hey! \fBThe above document had some coding errors, which are explained below:\fR
.IP "Around line 2686:" 4
.IX Item "Around line 2686:"
.IP "Around line 2916:" 4
.IX Item "Around line 2916:"
You forgot a '=back' before '=head2'
@ -2511,6 +2511,41 @@ the constructor.
=head1 OTHER LANGUAGE BINDINGS
Libev does not offer other language bindings itself, but bindings for a
numbe rof languages exist in the form of third-party packages. If you know
any interesting language binding in addition to the ones listed here, drop
me a note.
The EV module implements the full libev API and is actually used to test
libev. EV is developed together with libev. Apart from the EV core module,
there are additional modules that implement libev-compatible interfaces
to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
It can be found and installed via CPAN, its homepage is found at
Tony Arcieri has written a ruby extension that offers access to a subset
of the libev API and adds filehandle abstractions, asynchronous DNS and
more on top of it. It can be found via gem servers. Its homepage is at
Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.
=head1 MACRO MAGIC
Libev can be compiled with a variety of options, the most fundamantal
@ -1,6 +1,6 @@
if ! [ -e evbuffer.c ]; then
echo do not run this programm unless you know what you are doing
@ -108,7 +108,7 @@ perl -ne '