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15 <h3 id="TOP">Index</h3>
17 <ul><li><a href="#NAME">NAME</a></li>
18 <li><a href="#SYNOPSIS">SYNOPSIS</a></li>
19 <li><a href="#EXAMPLE_PROGRAM">EXAMPLE PROGRAM</a></li>
20 <li><a href="#DESCRIPTION">DESCRIPTION</a></li>
21 <li><a href="#FEATURES">FEATURES</a></li>
22 <li><a href="#CONVENTIONS">CONVENTIONS</a></li>
23 <li><a href="#TIME_REPRESENTATION">TIME REPRESENTATION</a></li>
24 <li><a href="#GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</a></li>
25 <li><a href="#FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</a></li>
26 <li><a href="#ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</a>
27 <ul><li><a href="#GENERIC_WATCHER_FUNCTIONS">GENERIC WATCHER FUNCTIONS</a></li>
28 <li><a href="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</a></li>
31 <li><a href="#WATCHER_TYPES">WATCHER TYPES</a>
32 <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>
33 <li><a href="#code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally repeating timeouts</a></li>
34 <li><a href="#code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron?</a></li>
35 <li><a href="#code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled!</a></li>
36 <li><a href="#code_ev_child_code_watch_out_for_pro"><code>ev_child</code> - watch out for process status changes</a></li>
37 <li><a href="#code_ev_stat_code_did_the_file_attri"><code>ev_stat</code> - did the file attributes just change?</a></li>
38 <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>
39 <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>
40 <li><a href="#code_ev_embed_code_when_one_backend_"><code>ev_embed</code> - when one backend isn't enough...</a></li>
41 <li><a href="#code_ev_fork_code_the_audacity_to_re"><code>ev_fork</code> - the audacity to resume the event loop after a fork</a></li>
44 <li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li>
45 <li><a href="#LIBEVENT_EMULATION">LIBEVENT EMULATION</a></li>
46 <li><a href="#C_SUPPORT">C++ SUPPORT</a></li>
47 <li><a href="#MACRO_MAGIC">MACRO MAGIC</a></li>
48 <li><a href="#EMBEDDING">EMBEDDING</a>
49 <ul><li><a href="#FILESETS">FILESETS</a>
50 <ul><li><a href="#CORE_EVENT_LOOP">CORE EVENT LOOP</a></li>
51 <li><a href="#LIBEVENT_COMPATIBILITY_API">LIBEVENT COMPATIBILITY API</a></li>
52 <li><a href="#AUTOCONF_SUPPORT">AUTOCONF SUPPORT</a></li>
55 <li><a href="#PREPROCESSOR_SYMBOLS_MACROS">PREPROCESSOR SYMBOLS/MACROS</a></li>
56 <li><a href="#EXAMPLES">EXAMPLES</a></li>
59 <li><a href="#COMPLEXITIES">COMPLEXITIES</a></li>
60 <li><a href="#AUTHOR">AUTHOR</a>
65 <h1 id="NAME">NAME</h1>
66 <div id="NAME_CONTENT">
67 <p>libev - a high performance full-featured event loop written in C</p>
70 <h1 id="SYNOPSIS">SYNOPSIS</h1>
71 <div id="SYNOPSIS_CONTENT">
72 <pre> #include <ev.h>
77 <h1 id="EXAMPLE_PROGRAM">EXAMPLE PROGRAM</h1>
78 <div id="EXAMPLE_PROGRAM_CONTENT">
79 <pre> #include <ev.h>
82 ev_timer timeout_watcher;
84 /* called when data readable on stdin */
86 stdin_cb (EV_P_ struct ev_io *w, int revents)
88 /* puts ("stdin ready"); */
89 ev_io_stop (EV_A_ w); /* just a syntax example */
90 ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */
94 timeout_cb (EV_P_ struct ev_timer *w, int revents)
96 /* puts ("timeout"); */
97 ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
103 struct ev_loop *loop = ev_default_loop (0);
105 /* initialise an io watcher, then start it */
106 ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
107 ev_io_start (loop, &stdin_watcher);
109 /* simple non-repeating 5.5 second timeout */
110 ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
111 ev_timer_start (loop, &timeout_watcher);
113 /* loop till timeout or data ready */
122 <h1 id="DESCRIPTION">DESCRIPTION</h1>
123 <div id="DESCRIPTION_CONTENT">
124 <p>Libev is an event loop: you register interest in certain events (such as a
125 file descriptor being readable or a timeout occuring), and it will manage
126 these event sources and provide your program with events.</p>
127 <p>To do this, it must take more or less complete control over your process
128 (or thread) by executing the <i>event loop</i> handler, and will then
129 communicate events via a callback mechanism.</p>
130 <p>You register interest in certain events by registering so-called <i>event
131 watchers</i>, which are relatively small C structures you initialise with the
132 details of the event, and then hand it over to libev by <i>starting</i> the
136 <h1 id="FEATURES">FEATURES</h1>
137 <div id="FEATURES_CONTENT">
138 <p>Libev supports <code>select</code>, <code>poll</code>, the Linux-specific <code>epoll</code>, the
139 BSD-specific <code>kqueue</code> and the Solaris-specific event port mechanisms
140 for file descriptor events (<code>ev_io</code>), the Linux <code>inotify</code> interface
141 (for <code>ev_stat</code>), relative timers (<code>ev_timer</code>), absolute timers
142 with customised rescheduling (<code>ev_periodic</code>), synchronous signals
143 (<code>ev_signal</code>), process status change events (<code>ev_child</code>), and event
144 watchers dealing with the event loop mechanism itself (<code>ev_idle</code>,
145 <code>ev_embed</code>, <code>ev_prepare</code> and <code>ev_check</code> watchers) as well as
146 file watchers (<code>ev_stat</code>) and even limited support for fork events
147 (<code>ev_fork</code>).</p>
148 <p>It also is quite fast (see this
149 <a href="http://libev.schmorp.de/bench.html">benchmark</a> comparing it to libevent
153 <h1 id="CONVENTIONS">CONVENTIONS</h1>
154 <div id="CONVENTIONS_CONTENT">
155 <p>Libev is very configurable. In this manual the default configuration will
156 be described, which supports multiple event loops. For more info about
157 various configuration options please have a look at <strong>EMBED</strong> section in
158 this manual. If libev was configured without support for multiple event
159 loops, then all functions taking an initial argument of name <code>loop</code>
160 (which is always of type <code>struct ev_loop *</code>) will not have this argument.</p>
163 <h1 id="TIME_REPRESENTATION">TIME REPRESENTATION</h1>
164 <div id="TIME_REPRESENTATION_CONTENT">
165 <p>Libev represents time as a single floating point number, representing the
166 (fractional) number of seconds since the (POSIX) epoch (somewhere near
167 the beginning of 1970, details are complicated, don't ask). This type is
168 called <code>ev_tstamp</code>, which is what you should use too. It usually aliases
169 to the <code>double</code> type in C, and when you need to do any calculations on
170 it, you should treat it as such.</p>
173 <h1 id="GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</h1>
174 <div id="GLOBAL_FUNCTIONS_CONTENT">
175 <p>These functions can be called anytime, even before initialising the
176 library in any way.</p>
178 <dt>ev_tstamp ev_time ()</dt>
180 <p>Returns the current time as libev would use it. Please note that the
181 <code>ev_now</code> function is usually faster and also often returns the timestamp
182 you actually want to know.</p>
184 <dt>int ev_version_major ()</dt>
185 <dt>int ev_version_minor ()</dt>
187 <p>You can find out the major and minor version numbers of the library
188 you linked against by calling the functions <code>ev_version_major</code> and
189 <code>ev_version_minor</code>. If you want, you can compare against the global
190 symbols <code>EV_VERSION_MAJOR</code> and <code>EV_VERSION_MINOR</code>, which specify the
191 version of the library your program was compiled against.</p>
192 <p>Usually, it's a good idea to terminate if the major versions mismatch,
193 as this indicates an incompatible change. Minor versions are usually
194 compatible to older versions, so a larger minor version alone is usually
196 <p>Example: Make sure we haven't accidentally been linked against the wrong
198 <pre> assert (("libev version mismatch",
199 ev_version_major () == EV_VERSION_MAJOR
200 && ev_version_minor () >= EV_VERSION_MINOR));
204 <dt>unsigned int ev_supported_backends ()</dt>
206 <p>Return the set of all backends (i.e. their corresponding <code>EV_BACKEND_*</code>
207 value) compiled into this binary of libev (independent of their
208 availability on the system you are running on). See <code>ev_default_loop</code> for
209 a description of the set values.</p>
210 <p>Example: make sure we have the epoll method, because yeah this is cool and
211 a must have and can we have a torrent of it please!!!11</p>
212 <pre> assert (("sorry, no epoll, no sex",
213 ev_supported_backends () & EVBACKEND_EPOLL));
217 <dt>unsigned int ev_recommended_backends ()</dt>
219 <p>Return the set of all backends compiled into this binary of libev and also
220 recommended for this platform. This set is often smaller than the one
221 returned by <code>ev_supported_backends</code>, as for example kqueue is broken on
222 most BSDs and will not be autodetected unless you explicitly request it
223 (assuming you know what you are doing). This is the set of backends that
224 libev will probe for if you specify no backends explicitly.</p>
226 <dt>unsigned int ev_embeddable_backends ()</dt>
228 <p>Returns the set of backends that are embeddable in other event loops. This
229 is the theoretical, all-platform, value. To find which backends
230 might be supported on the current system, you would need to look at
231 <code>ev_embeddable_backends () & ev_supported_backends ()</code>, likewise for
232 recommended ones.</p>
233 <p>See the description of <code>ev_embed</code> watchers for more info.</p>
235 <dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt>
237 <p>Sets the allocation function to use (the prototype is similar - the
238 semantics is identical - to the realloc C function). It is used to
239 allocate and free memory (no surprises here). If it returns zero when
240 memory needs to be allocated, the library might abort or take some
241 potentially destructive action. The default is your system realloc
243 <p>You could override this function in high-availability programs to, say,
244 free some memory if it cannot allocate memory, to use a special allocator,
245 or even to sleep a while and retry until some memory is available.</p>
246 <p>Example: Replace the libev allocator with one that waits a bit and then
249 persistent_realloc (void *ptr, size_t size)
253 void *newptr = realloc (ptr, size);
263 ev_set_allocator (persistent_realloc);
267 <dt>ev_set_syserr_cb (void (*cb)(const char *msg));</dt>
269 <p>Set the callback function to call on a retryable syscall error (such
270 as failed select, poll, epoll_wait). The message is a printable string
271 indicating the system call or subsystem causing the problem. If this
272 callback is set, then libev will expect it to remedy the sitution, no
273 matter what, when it returns. That is, libev will generally retry the
274 requested operation, or, if the condition doesn't go away, do bad stuff
276 <p>Example: This is basically the same thing that libev does internally, too.</p>
278 fatal_error (const char *msg)
285 ev_set_syserr_cb (fatal_error);
292 <h1 id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</h1>
293 <div id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP-2">
294 <p>An event loop is described by a <code>struct ev_loop *</code>. The library knows two
295 types of such loops, the <i>default</i> loop, which supports signals and child
296 events, and dynamically created loops which do not.</p>
297 <p>If you use threads, a common model is to run the default event loop
298 in your main thread (or in a separate thread) and for each thread you
299 create, you also create another event loop. Libev itself does no locking
300 whatsoever, so if you mix calls to the same event loop in different
301 threads, make sure you lock (this is usually a bad idea, though, even if
302 done correctly, because it's hideous and inefficient).</p>
304 <dt>struct ev_loop *ev_default_loop (unsigned int flags)</dt>
306 <p>This will initialise the default event loop if it hasn't been initialised
307 yet and return it. If the default loop could not be initialised, returns
308 false. If it already was initialised it simply returns it (and ignores the
309 flags. If that is troubling you, check <code>ev_backend ()</code> afterwards).</p>
310 <p>If you don't know what event loop to use, use the one returned from this
312 <p>The flags argument can be used to specify special behaviour or specific
313 backends to use, and is usually specified as <code>0</code> (or <code>EVFLAG_AUTO</code>).</p>
314 <p>The following flags are supported:</p>
317 <dt><code>EVFLAG_AUTO</code></dt>
319 <p>The default flags value. Use this if you have no clue (it's the right
320 thing, believe me).</p>
322 <dt><code>EVFLAG_NOENV</code></dt>
324 <p>If this flag bit is ored into the flag value (or the program runs setuid
325 or setgid) then libev will <i>not</i> look at the environment variable
326 <code>LIBEV_FLAGS</code>. Otherwise (the default), this environment variable will
327 override the flags completely if it is found in the environment. This is
328 useful to try out specific backends to test their performance, or to work
331 <dt><code>EVFLAG_FORKCHECK</code></dt>
333 <p>Instead of calling <code>ev_default_fork</code> or <code>ev_loop_fork</code> manually after
334 a fork, you can also make libev check for a fork in each iteration by
335 enabling this flag.</p>
336 <p>This works by calling <code>getpid ()</code> on every iteration of the loop,
337 and thus this might slow down your event loop if you do a lot of loop
338 iterations and little real work, but is usually not noticeable (on my
339 Linux system for example, <code>getpid</code> is actually a simple 5-insn sequence
340 without a syscall and thus <i>very</i> fast, but my Linux system also has
341 <code>pthread_atfork</code> which is even faster).</p>
342 <p>The big advantage of this flag is that you can forget about fork (and
343 forget about forgetting to tell libev about forking) when you use this
345 <p>This flag setting cannot be overriden or specified in the <code>LIBEV_FLAGS</code>
346 environment variable.</p>
348 <dt><code>EVBACKEND_SELECT</code> (value 1, portable select backend)</dt>
350 <p>This is your standard select(2) backend. Not <i>completely</i> standard, as
351 libev tries to roll its own fd_set with no limits on the number of fds,
352 but if that fails, expect a fairly low limit on the number of fds when
353 using this backend. It doesn't scale too well (O(highest_fd)), but its usually
354 the fastest backend for a low number of fds.</p>
356 <dt><code>EVBACKEND_POLL</code> (value 2, poll backend, available everywhere except on windows)</dt>
358 <p>And this is your standard poll(2) backend. It's more complicated than
359 select, but handles sparse fds better and has no artificial limit on the
360 number of fds you can use (except it will slow down considerably with a
361 lot of inactive fds). It scales similarly to select, i.e. O(total_fds).</p>
363 <dt><code>EVBACKEND_EPOLL</code> (value 4, Linux)</dt>
365 <p>For few fds, this backend is a bit little slower than poll and select,
366 but it scales phenomenally better. While poll and select usually scale like
367 O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
368 either O(1) or O(active_fds).</p>
369 <p>While stopping and starting an I/O watcher in the same iteration will
370 result in some caching, there is still a syscall per such incident
371 (because the fd could point to a different file description now), so its
372 best to avoid that. Also, dup()ed file descriptors might not work very
373 well if you register events for both fds.</p>
374 <p>Please note that epoll sometimes generates spurious notifications, so you
375 need to use non-blocking I/O or other means to avoid blocking when no data
376 (or space) is available.</p>
378 <dt><code>EVBACKEND_KQUEUE</code> (value 8, most BSD clones)</dt>
380 <p>Kqueue deserves special mention, as at the time of this writing, it
381 was broken on all BSDs except NetBSD (usually it doesn't work with
382 anything but sockets and pipes, except on Darwin, where of course its
383 completely useless). For this reason its not being "autodetected"
384 unless you explicitly specify it explicitly in the flags (i.e. using
385 <code>EVBACKEND_KQUEUE</code>).</p>
386 <p>It scales in the same way as the epoll backend, but the interface to the
387 kernel is more efficient (which says nothing about its actual speed, of
388 course). While starting and stopping an I/O watcher does not cause an
389 extra syscall as with epoll, it still adds up to four event changes per
390 incident, so its best to avoid that.</p>
392 <dt><code>EVBACKEND_DEVPOLL</code> (value 16, Solaris 8)</dt>
394 <p>This is not implemented yet (and might never be).</p>
396 <dt><code>EVBACKEND_PORT</code> (value 32, Solaris 10)</dt>
398 <p>This uses the Solaris 10 port mechanism. As with everything on Solaris,
399 it's really slow, but it still scales very well (O(active_fds)).</p>
400 <p>Please note that solaris ports can result in a lot of spurious
401 notifications, so you need to use non-blocking I/O or other means to avoid
402 blocking when no data (or space) is available.</p>
404 <dt><code>EVBACKEND_ALL</code></dt>
406 <p>Try all backends (even potentially broken ones that wouldn't be tried
407 with <code>EVFLAG_AUTO</code>). Since this is a mask, you can do stuff such as
408 <code>EVBACKEND_ALL & ~EVBACKEND_KQUEUE</code>.</p>
412 <p>If one or more of these are ored into the flags value, then only these
413 backends will be tried (in the reverse order as given here). If none are
414 specified, most compiled-in backend will be tried, usually in reverse
415 order of their flag values :)</p>
416 <p>The most typical usage is like this:</p>
417 <pre> if (!ev_default_loop (0))
418 fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
421 <p>Restrict libev to the select and poll backends, and do not allow
422 environment settings to be taken into account:</p>
423 <pre> ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
426 <p>Use whatever libev has to offer, but make sure that kqueue is used if
427 available (warning, breaks stuff, best use only with your own private
428 event loop and only if you know the OS supports your types of fds):</p>
429 <pre> ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
433 <dt>struct ev_loop *ev_loop_new (unsigned int flags)</dt>
435 <p>Similar to <code>ev_default_loop</code>, but always creates a new event loop that is
436 always distinct from the default loop. Unlike the default loop, it cannot
437 handle signal and child watchers, and attempts to do so will be greeted by
438 undefined behaviour (or a failed assertion if assertions are enabled).</p>
439 <p>Example: Try to create a event loop that uses epoll and nothing else.</p>
440 <pre> struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
442 fatal ("no epoll found here, maybe it hides under your chair");
446 <dt>ev_default_destroy ()</dt>
448 <p>Destroys the default loop again (frees all memory and kernel state
449 etc.). None of the active event watchers will be stopped in the normal
450 sense, so e.g. <code>ev_is_active</code> might still return true. It is your
451 responsibility to either stop all watchers cleanly yoursef <i>before</i>
452 calling this function, or cope with the fact afterwards (which is usually
453 the easiest thing, youc na just ignore the watchers and/or <code>free ()</code> them
456 <dt>ev_loop_destroy (loop)</dt>
458 <p>Like <code>ev_default_destroy</code>, but destroys an event loop created by an
459 earlier call to <code>ev_loop_new</code>.</p>
461 <dt>ev_default_fork ()</dt>
463 <p>This function reinitialises the kernel state for backends that have
464 one. Despite the name, you can call it anytime, but it makes most sense
465 after forking, in either the parent or child process (or both, but that
466 again makes little sense).</p>
467 <p>You <i>must</i> call this function in the child process after forking if and
468 only if you want to use the event library in both processes. If you just
469 fork+exec, you don't have to call it.</p>
470 <p>The function itself is quite fast and it's usually not a problem to call
471 it just in case after a fork. To make this easy, the function will fit in
472 quite nicely into a call to <code>pthread_atfork</code>:</p>
473 <pre> pthread_atfork (0, 0, ev_default_fork);
476 <p>At the moment, <code>EVBACKEND_SELECT</code> and <code>EVBACKEND_POLL</code> are safe to use
477 without calling this function, so if you force one of those backends you
478 do not need to care.</p>
480 <dt>ev_loop_fork (loop)</dt>
482 <p>Like <code>ev_default_fork</code>, but acts on an event loop created by
483 <code>ev_loop_new</code>. Yes, you have to call this on every allocated event loop
484 after fork, and how you do this is entirely your own problem.</p>
486 <dt>unsigned int ev_loop_count (loop)</dt>
488 <p>Returns the count of loop iterations for the loop, which is identical to
489 the number of times libev did poll for new events. It starts at <code>0</code> and
490 happily wraps around with enough iterations.</p>
491 <p>This value can sometimes be useful as a generation counter of sorts (it
492 "ticks" the number of loop iterations), as it roughly corresponds with
493 <code>ev_prepare</code> and <code>ev_check</code> calls.</p>
495 <dt>unsigned int ev_backend (loop)</dt>
497 <p>Returns one of the <code>EVBACKEND_*</code> flags indicating the event backend in
500 <dt>ev_tstamp ev_now (loop)</dt>
502 <p>Returns the current "event loop time", which is the time the event loop
503 received events and started processing them. This timestamp does not
504 change as long as callbacks are being processed, and this is also the base
505 time used for relative timers. You can treat it as the timestamp of the
506 event occuring (or more correctly, libev finding out about it).</p>
508 <dt>ev_loop (loop, int flags)</dt>
510 <p>Finally, this is it, the event handler. This function usually is called
511 after you initialised all your watchers and you want to start handling
513 <p>If the flags argument is specified as <code>0</code>, it will not return until
514 either no event watchers are active anymore or <code>ev_unloop</code> was called.</p>
515 <p>Please note that an explicit <code>ev_unloop</code> is usually better than
516 relying on all watchers to be stopped when deciding when a program has
517 finished (especially in interactive programs), but having a program that
518 automatically loops as long as it has to and no longer by virtue of
519 relying on its watchers stopping correctly is a thing of beauty.</p>
520 <p>A flags value of <code>EVLOOP_NONBLOCK</code> will look for new events, will handle
521 those events and any outstanding ones, but will not block your process in
522 case there are no events and will return after one iteration of the loop.</p>
523 <p>A flags value of <code>EVLOOP_ONESHOT</code> will look for new events (waiting if
524 neccessary) and will handle those and any outstanding ones. It will block
525 your process until at least one new event arrives, and will return after
526 one iteration of the loop. This is useful if you are waiting for some
527 external event in conjunction with something not expressible using other
528 libev watchers. However, a pair of <code>ev_prepare</code>/<code>ev_check</code> watchers is
529 usually a better approach for this kind of thing.</p>
530 <p>Here are the gory details of what <code>ev_loop</code> does:</p>
531 <pre> * If there are no active watchers (reference count is zero), return.
532 - Queue prepare watchers and then call all outstanding watchers.
533 - If we have been forked, recreate the kernel state.
534 - Update the kernel state with all outstanding changes.
535 - Update the "event loop time".
536 - Calculate for how long to block.
537 - Block the process, waiting for any events.
538 - Queue all outstanding I/O (fd) events.
539 - Update the "event loop time" and do time jump handling.
540 - Queue all outstanding timers.
541 - Queue all outstanding periodics.
542 - If no events are pending now, queue all idle watchers.
543 - Queue all check watchers.
544 - Call all queued watchers in reverse order (i.e. check watchers first).
545 Signals and child watchers are implemented as I/O watchers, and will
546 be handled here by queueing them when their watcher gets executed.
547 - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
548 were used, return, otherwise continue with step *.
551 <p>Example: Queue some jobs and then loop until no events are outsanding
553 <pre> ... queue jobs here, make sure they register event watchers as long
554 ... as they still have work to do (even an idle watcher will do..)
555 ev_loop (my_loop, 0);
560 <dt>ev_unloop (loop, how)</dt>
562 <p>Can be used to make a call to <code>ev_loop</code> return early (but only after it
563 has processed all outstanding events). The <code>how</code> argument must be either
564 <code>EVUNLOOP_ONE</code>, which will make the innermost <code>ev_loop</code> call return, or
565 <code>EVUNLOOP_ALL</code>, which will make all nested <code>ev_loop</code> calls return.</p>
567 <dt>ev_ref (loop)</dt>
568 <dt>ev_unref (loop)</dt>
570 <p>Ref/unref can be used to add or remove a reference count on the event
571 loop: Every watcher keeps one reference, and as long as the reference
572 count is nonzero, <code>ev_loop</code> will not return on its own. If you have
573 a watcher you never unregister that should not keep <code>ev_loop</code> from
574 returning, ev_unref() after starting, and ev_ref() before stopping it. For
575 example, libev itself uses this for its internal signal pipe: It is not
576 visible to the libev user and should not keep <code>ev_loop</code> from exiting if
577 no event watchers registered by it are active. It is also an excellent
578 way to do this for generic recurring timers or from within third-party
579 libraries. Just remember to <i>unref after start</i> and <i>ref before stop</i>.</p>
580 <p>Example: Create a signal watcher, but keep it from keeping <code>ev_loop</code>
581 running when nothing else is active.</p>
582 <pre> struct ev_signal exitsig;
583 ev_signal_init (&exitsig, sig_cb, SIGINT);
584 ev_signal_start (loop, &exitsig);
588 <p>Example: For some weird reason, unregister the above signal handler again.</p>
590 ev_signal_stop (loop, &exitsig);
601 <h1 id="ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</h1>
602 <div id="ANATOMY_OF_A_WATCHER_CONTENT">
603 <p>A watcher is a structure that you create and register to record your
604 interest in some event. For instance, if you want to wait for STDIN to
605 become readable, you would create an <code>ev_io</code> watcher for that:</p>
606 <pre> static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
609 ev_unloop (loop, EVUNLOOP_ALL);
612 struct ev_loop *loop = ev_default_loop (0);
613 struct ev_io stdin_watcher;
614 ev_init (&stdin_watcher, my_cb);
615 ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
616 ev_io_start (loop, &stdin_watcher);
620 <p>As you can see, you are responsible for allocating the memory for your
621 watcher structures (and it is usually a bad idea to do this on the stack,
622 although this can sometimes be quite valid).</p>
623 <p>Each watcher structure must be initialised by a call to <code>ev_init
624 (watcher *, callback)</code>, which expects a callback to be provided. This
625 callback gets invoked each time the event occurs (or, in the case of io
626 watchers, each time the event loop detects that the file descriptor given
627 is readable and/or writable).</p>
628 <p>Each watcher type has its own <code>ev_<type>_set (watcher *, ...)</code> macro
629 with arguments specific to this watcher type. There is also a macro
630 to combine initialisation and setting in one call: <code>ev_<type>_init
631 (watcher *, callback, ...)</code>.</p>
632 <p>To make the watcher actually watch out for events, you have to start it
633 with a watcher-specific start function (<code>ev_<type>_start (loop, watcher
634 *)</code>), and you can stop watching for events at any time by calling the
635 corresponding stop function (<code>ev_<type>_stop (loop, watcher *)</code>.</p>
636 <p>As long as your watcher is active (has been started but not stopped) you
637 must not touch the values stored in it. Most specifically you must never
638 reinitialise it or call its <code>set</code> macro.</p>
639 <p>Each and every callback receives the event loop pointer as first, the
640 registered watcher structure as second, and a bitset of received events as
642 <p>The received events usually include a single bit per event type received
643 (you can receive multiple events at the same time). The possible bit masks
646 <dt><code>EV_READ</code></dt>
647 <dt><code>EV_WRITE</code></dt>
649 <p>The file descriptor in the <code>ev_io</code> watcher has become readable and/or
652 <dt><code>EV_TIMEOUT</code></dt>
654 <p>The <code>ev_timer</code> watcher has timed out.</p>
656 <dt><code>EV_PERIODIC</code></dt>
658 <p>The <code>ev_periodic</code> watcher has timed out.</p>
660 <dt><code>EV_SIGNAL</code></dt>
662 <p>The signal specified in the <code>ev_signal</code> watcher has been received by a thread.</p>
664 <dt><code>EV_CHILD</code></dt>
666 <p>The pid specified in the <code>ev_child</code> watcher has received a status change.</p>
668 <dt><code>EV_STAT</code></dt>
670 <p>The path specified in the <code>ev_stat</code> watcher changed its attributes somehow.</p>
672 <dt><code>EV_IDLE</code></dt>
674 <p>The <code>ev_idle</code> watcher has determined that you have nothing better to do.</p>
676 <dt><code>EV_PREPARE</code></dt>
677 <dt><code>EV_CHECK</code></dt>
679 <p>All <code>ev_prepare</code> watchers are invoked just <i>before</i> <code>ev_loop</code> starts
680 to gather new events, and all <code>ev_check</code> watchers are invoked just after
681 <code>ev_loop</code> has gathered them, but before it invokes any callbacks for any
682 received events. Callbacks of both watcher types can start and stop as
683 many watchers as they want, and all of them will be taken into account
684 (for example, a <code>ev_prepare</code> watcher might start an idle watcher to keep
685 <code>ev_loop</code> from blocking).</p>
687 <dt><code>EV_EMBED</code></dt>
689 <p>The embedded event loop specified in the <code>ev_embed</code> watcher needs attention.</p>
691 <dt><code>EV_FORK</code></dt>
693 <p>The event loop has been resumed in the child process after fork (see
694 <code>ev_fork</code>).</p>
696 <dt><code>EV_ERROR</code></dt>
698 <p>An unspecified error has occured, the watcher has been stopped. This might
699 happen because the watcher could not be properly started because libev
700 ran out of memory, a file descriptor was found to be closed or any other
701 problem. You best act on it by reporting the problem and somehow coping
702 with the watcher being stopped.</p>
703 <p>Libev will usually signal a few "dummy" events together with an error,
704 for example it might indicate that a fd is readable or writable, and if
705 your callbacks is well-written it can just attempt the operation and cope
706 with the error from read() or write(). This will not work in multithreaded
707 programs, though, so beware.</p>
712 <h2 id="GENERIC_WATCHER_FUNCTIONS">GENERIC WATCHER FUNCTIONS</h2>
713 <div id="GENERIC_WATCHER_FUNCTIONS_CONTENT">
714 <p>In the following description, <code>TYPE</code> stands for the watcher type,
715 e.g. <code>timer</code> for <code>ev_timer</code> watchers and <code>io</code> for <code>ev_io</code> watchers.</p>
717 <dt><code>ev_init</code> (ev_TYPE *watcher, callback)</dt>
719 <p>This macro initialises the generic portion of a watcher. The contents
720 of the watcher object can be arbitrary (so <code>malloc</code> will do). Only
721 the generic parts of the watcher are initialised, you <i>need</i> to call
722 the type-specific <code>ev_TYPE_set</code> macro afterwards to initialise the
723 type-specific parts. For each type there is also a <code>ev_TYPE_init</code> macro
724 which rolls both calls into one.</p>
725 <p>You can reinitialise a watcher at any time as long as it has been stopped
726 (or never started) and there are no pending events outstanding.</p>
727 <p>The callback is always of type <code>void (*)(ev_loop *loop, ev_TYPE *watcher,
728 int revents)</code>.</p>
730 <dt><code>ev_TYPE_set</code> (ev_TYPE *, [args])</dt>
732 <p>This macro initialises the type-specific parts of a watcher. You need to
733 call <code>ev_init</code> at least once before you call this macro, but you can
734 call <code>ev_TYPE_set</code> any number of times. You must not, however, call this
735 macro on a watcher that is active (it can be pending, however, which is a
736 difference to the <code>ev_init</code> macro).</p>
737 <p>Although some watcher types do not have type-specific arguments
738 (e.g. <code>ev_prepare</code>) you still need to call its <code>set</code> macro.</p>
740 <dt><code>ev_TYPE_init</code> (ev_TYPE *watcher, callback, [args])</dt>
742 <p>This convinience macro rolls both <code>ev_init</code> and <code>ev_TYPE_set</code> macro
743 calls into a single call. This is the most convinient method to initialise
744 a watcher. The same limitations apply, of course.</p>
746 <dt><code>ev_TYPE_start</code> (loop *, ev_TYPE *watcher)</dt>
748 <p>Starts (activates) the given watcher. Only active watchers will receive
749 events. If the watcher is already active nothing will happen.</p>
751 <dt><code>ev_TYPE_stop</code> (loop *, ev_TYPE *watcher)</dt>
753 <p>Stops the given watcher again (if active) and clears the pending
754 status. It is possible that stopped watchers are pending (for example,
755 non-repeating timers are being stopped when they become pending), but
756 <code>ev_TYPE_stop</code> ensures that the watcher is neither active nor pending. If
757 you want to free or reuse the memory used by the watcher it is therefore a
758 good idea to always call its <code>ev_TYPE_stop</code> function.</p>
760 <dt>bool ev_is_active (ev_TYPE *watcher)</dt>
762 <p>Returns a true value iff the watcher is active (i.e. it has been started
763 and not yet been stopped). As long as a watcher is active you must not modify
766 <dt>bool ev_is_pending (ev_TYPE *watcher)</dt>
768 <p>Returns a true value iff the watcher is pending, (i.e. it has outstanding
769 events but its callback has not yet been invoked). As long as a watcher
770 is pending (but not active) you must not call an init function on it (but
771 <code>ev_TYPE_set</code> is safe) and you must make sure the watcher is available to
772 libev (e.g. you cnanot <code>free ()</code> it).</p>
774 <dt>callback ev_cb (ev_TYPE *watcher)</dt>
776 <p>Returns the callback currently set on the watcher.</p>
778 <dt>ev_cb_set (ev_TYPE *watcher, callback)</dt>
780 <p>Change the callback. You can change the callback at virtually any time
781 (modulo threads).</p>
783 <dt>ev_set_priority (ev_TYPE *watcher, priority)</dt>
784 <dt>int ev_priority (ev_TYPE *watcher)</dt>
786 <p>Set and query the priority of the watcher. The priority is a small
787 integer between <code>EV_MAXPRI</code> (default: <code>2</code>) and <code>EV_MINPRI</code>
788 (default: <code>-2</code>). Pending watchers with higher priority will be invoked
789 before watchers with lower priority, but priority will not keep watchers
790 from being executed (except for <code>ev_idle</code> watchers).</p>
791 <p>This means that priorities are <i>only</i> used for ordering callback
792 invocation after new events have been received. This is useful, for
793 example, to reduce latency after idling, or more often, to bind two
794 watchers on the same event and make sure one is called first.</p>
795 <p>If you need to suppress invocation when higher priority events are pending
796 you need to look at <code>ev_idle</code> watchers, which provide this functionality.</p>
797 <p>The default priority used by watchers when no priority has been set is
798 always <code>0</code>, which is supposed to not be too high and not be too low :).</p>
799 <p>Setting a priority outside the range of <code>EV_MINPRI</code> to <code>EV_MAXPRI</code> is
800 fine, as long as you do not mind that the priority value you query might
801 or might not have been adjusted to be within valid range.</p>
810 <h2 id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</h2>
811 <div id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH-2">
812 <p>Each watcher has, by default, a member <code>void *data</code> that you can change
813 and read at any time, libev will completely ignore it. This can be used
814 to associate arbitrary data with your watcher. If you need more data and
815 don't want to allocate memory and store a pointer to it in that data
816 member, you can also "subclass" the watcher type and provide your own
823 struct whatever *mostinteresting;
827 <p>And since your callback will be called with a pointer to the watcher, you
828 can cast it back to your own type:</p>
829 <pre> static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
831 struct my_io *w = (struct my_io *)w_;
836 <p>More interesting and less C-conformant ways of casting your callback type
837 instead have been omitted.</p>
838 <p>Another common scenario is having some data structure with multiple
840 <pre> struct my_biggy
848 <p>In this case getting the pointer to <code>my_biggy</code> is a bit more complicated,
849 you need to use <code>offsetof</code>:</p>
850 <pre> #include <stddef.h>
853 t1_cb (EV_P_ struct ev_timer *w, int revents)
855 struct my_biggy big = (struct my_biggy *
856 (((char *)w) - offsetof (struct my_biggy, t1));
860 t2_cb (EV_P_ struct ev_timer *w, int revents)
862 struct my_biggy big = (struct my_biggy *
863 (((char *)w) - offsetof (struct my_biggy, t2));
872 <h1 id="WATCHER_TYPES">WATCHER TYPES</h1>
873 <div id="WATCHER_TYPES_CONTENT">
874 <p>This section describes each watcher in detail, but will not repeat
875 information given in the last section. Any initialisation/set macros,
876 functions and members specific to the watcher type are explained.</p>
877 <p>Members are additionally marked with either <i>[read-only]</i>, meaning that,
878 while the watcher is active, you can look at the member and expect some
879 sensible content, but you must not modify it (you can modify it while the
880 watcher is stopped to your hearts content), or <i>[read-write]</i>, which
881 means you can expect it to have some sensible content while the watcher
882 is active, but you can also modify it. Modifying it may not do something
883 sensible or take immediate effect (or do anything at all), but libev will
884 not crash or malfunction in any way.</p>
891 <h2 id="code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable?</h2>
892 <div id="code_ev_io_code_is_this_file_descrip-2">
893 <p>I/O watchers check whether a file descriptor is readable or writable
894 in each iteration of the event loop, or, more precisely, when reading
895 would not block the process and writing would at least be able to write
896 some data. This behaviour is called level-triggering because you keep
897 receiving events as long as the condition persists. Remember you can stop
898 the watcher if you don't want to act on the event and neither want to
899 receive future events.</p>
900 <p>In general you can register as many read and/or write event watchers per
901 fd as you want (as long as you don't confuse yourself). Setting all file
902 descriptors to non-blocking mode is also usually a good idea (but not
903 required if you know what you are doing).</p>
904 <p>You have to be careful with dup'ed file descriptors, though. Some backends
905 (the linux epoll backend is a notable example) cannot handle dup'ed file
906 descriptors correctly if you register interest in two or more fds pointing
907 to the same underlying file/socket/etc. description (that is, they share
908 the same underlying "file open").</p>
909 <p>If you must do this, then force the use of a known-to-be-good backend
910 (at the time of this writing, this includes only <code>EVBACKEND_SELECT</code> and
911 <code>EVBACKEND_POLL</code>).</p>
912 <p>Another thing you have to watch out for is that it is quite easy to
913 receive "spurious" readyness notifications, that is your callback might
914 be called with <code>EV_READ</code> but a subsequent <code>read</code>(2) will actually block
915 because there is no data. Not only are some backends known to create a
916 lot of those (for example solaris ports), it is very easy to get into
917 this situation even with a relatively standard program structure. Thus
918 it is best to always use non-blocking I/O: An extra <code>read</code>(2) returning
919 <code>EAGAIN</code> is far preferable to a program hanging until some data arrives.</p>
920 <p>If you cannot run the fd in non-blocking mode (for example you should not
921 play around with an Xlib connection), then you have to seperately re-test
922 whether a file descriptor is really ready with a known-to-be good interface
923 such as poll (fortunately in our Xlib example, Xlib already does this on
924 its own, so its quite safe to use).</p>
926 <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt>
927 <dt>ev_io_set (ev_io *, int fd, int events)</dt>
929 <p>Configures an <code>ev_io</code> watcher. The <code>fd</code> is the file descriptor to
930 rceeive events for and events is either <code>EV_READ</code>, <code>EV_WRITE</code> or
931 <code>EV_READ | EV_WRITE</code> to receive the given events.</p>
933 <dt>int fd [read-only]</dt>
935 <p>The file descriptor being watched.</p>
937 <dt>int events [read-only]</dt>
939 <p>The events being watched.</p>
942 <p>Example: Call <code>stdin_readable_cb</code> when STDIN_FILENO has become, well
943 readable, but only once. Since it is likely line-buffered, you could
944 attempt to read a whole line in the callback.</p>
946 stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
948 ev_io_stop (loop, w);
949 .. read from stdin here (or from w->fd) and haqndle any I/O errors
953 struct ev_loop *loop = ev_default_init (0);
954 struct ev_io stdin_readable;
955 ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
956 ev_io_start (loop, &stdin_readable);
965 <h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally repeating timeouts</h2>
966 <div id="code_ev_timer_code_relative_and_opti-2">
967 <p>Timer watchers are simple relative timers that generate an event after a
968 given time, and optionally repeating in regular intervals after that.</p>
969 <p>The timers are based on real time, that is, if you register an event that
970 times out after an hour and you reset your system clock to last years
971 time, it will still time out after (roughly) and hour. "Roughly" because
972 detecting time jumps is hard, and some inaccuracies are unavoidable (the
973 monotonic clock option helps a lot here).</p>
974 <p>The relative timeouts are calculated relative to the <code>ev_now ()</code>
975 time. This is usually the right thing as this timestamp refers to the time
976 of the event triggering whatever timeout you are modifying/starting. If
977 you suspect event processing to be delayed and you <i>need</i> to base the timeout
978 on the current time, use something like this to adjust for this:</p>
979 <pre> ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
982 <p>The callback is guarenteed to be invoked only when its timeout has passed,
983 but if multiple timers become ready during the same loop iteration then
984 order of execution is undefined.</p>
986 <dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt>
987 <dt>ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)</dt>
989 <p>Configure the timer to trigger after <code>after</code> seconds. If <code>repeat</code> is
990 <code>0.</code>, then it will automatically be stopped. If it is positive, then the
991 timer will automatically be configured to trigger again <code>repeat</code> seconds
992 later, again, and again, until stopped manually.</p>
993 <p>The timer itself will do a best-effort at avoiding drift, that is, if you
994 configure a timer to trigger every 10 seconds, then it will trigger at
995 exactly 10 second intervals. If, however, your program cannot keep up with
996 the timer (because it takes longer than those 10 seconds to do stuff) the
997 timer will not fire more than once per event loop iteration.</p>
999 <dt>ev_timer_again (loop)</dt>
1001 <p>This will act as if the timer timed out and restart it again if it is
1002 repeating. The exact semantics are:</p>
1003 <p>If the timer is pending, its pending status is cleared.</p>
1004 <p>If the timer is started but nonrepeating, stop it (as if it timed out).</p>
1005 <p>If the timer is repeating, either start it if necessary (with the
1006 <code>repeat</code> value), or reset the running timer to the <code>repeat</code> value.</p>
1007 <p>This sounds a bit complicated, but here is a useful and typical
1008 example: Imagine you have a tcp connection and you want a so-called idle
1009 timeout, that is, you want to be called when there have been, say, 60
1010 seconds of inactivity on the socket. The easiest way to do this is to
1011 configure an <code>ev_timer</code> with a <code>repeat</code> value of <code>60</code> and then call
1012 <code>ev_timer_again</code> each time you successfully read or write some data. If
1013 you go into an idle state where you do not expect data to travel on the
1014 socket, you can <code>ev_timer_stop</code> the timer, and <code>ev_timer_again</code> will
1015 automatically restart it if need be.</p>
1016 <p>That means you can ignore the <code>after</code> value and <code>ev_timer_start</code>
1017 altogether and only ever use the <code>repeat</code> value and <code>ev_timer_again</code>:</p>
1018 <pre> ev_timer_init (timer, callback, 0., 5.);
1019 ev_timer_again (loop, timer);
1021 timer->again = 17.;
1022 ev_timer_again (loop, timer);
1024 timer->again = 10.;
1025 ev_timer_again (loop, timer);
1028 <p>This is more slightly efficient then stopping/starting the timer each time
1029 you want to modify its timeout value.</p>
1031 <dt>ev_tstamp repeat [read-write]</dt>
1033 <p>The current <code>repeat</code> value. Will be used each time the watcher times out
1034 or <code>ev_timer_again</code> is called and determines the next timeout (if any),
1035 which is also when any modifications are taken into account.</p>
1038 <p>Example: Create a timer that fires after 60 seconds.</p>
1040 one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1042 .. one minute over, w is actually stopped right here
1045 struct ev_timer mytimer;
1046 ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1047 ev_timer_start (loop, &mytimer);
1050 <p>Example: Create a timeout timer that times out after 10 seconds of
1053 timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1055 .. ten seconds without any activity
1058 struct ev_timer mytimer;
1059 ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1060 ev_timer_again (&mytimer); /* start timer */
1063 // and in some piece of code that gets executed on any "activity":
1064 // reset the timeout to start ticking again at 10 seconds
1065 ev_timer_again (&mytimer);
1073 <h2 id="code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron?</h2>
1074 <div id="code_ev_periodic_code_to_cron_or_not-2">
1075 <p>Periodic watchers are also timers of a kind, but they are very versatile
1076 (and unfortunately a bit complex).</p>
1077 <p>Unlike <code>ev_timer</code>'s, they are not based on real time (or relative time)
1078 but on wallclock time (absolute time). You can tell a periodic watcher
1079 to trigger "at" some specific point in time. For example, if you tell a
1080 periodic watcher to trigger in 10 seconds (by specifiying e.g. <code>ev_now ()
1081 + 10.</code>) and then reset your system clock to the last year, then it will
1082 take a year to trigger the event (unlike an <code>ev_timer</code>, which would trigger
1083 roughly 10 seconds later and of course not if you reset your system time
1085 <p>They can also be used to implement vastly more complex timers, such as
1086 triggering an event on eahc midnight, local time.</p>
1087 <p>As with timers, the callback is guarenteed to be invoked only when the
1088 time (<code>at</code>) has been passed, but if multiple periodic timers become ready
1089 during the same loop iteration then order of execution is undefined.</p>
1091 <dt>ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)</dt>
1092 <dt>ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)</dt>
1094 <p>Lots of arguments, lets sort it out... There are basically three modes of
1095 operation, and we will explain them from simplest to complex:</p>
1098 <dt>* absolute timer (interval = reschedule_cb = 0)</dt>
1100 <p>In this configuration the watcher triggers an event at the wallclock time
1101 <code>at</code> and doesn't repeat. It will not adjust when a time jump occurs,
1102 that is, if it is to be run at January 1st 2011 then it will run when the
1103 system time reaches or surpasses this time.</p>
1105 <dt>* non-repeating interval timer (interval > 0, reschedule_cb = 0)</dt>
1107 <p>In this mode the watcher will always be scheduled to time out at the next
1108 <code>at + N * interval</code> time (for some integer N) and then repeat, regardless
1109 of any time jumps.</p>
1110 <p>This can be used to create timers that do not drift with respect to system
1112 <pre> ev_periodic_set (&periodic, 0., 3600., 0);
1115 <p>This doesn't mean there will always be 3600 seconds in between triggers,
1116 but only that the the callback will be called when the system time shows a
1117 full hour (UTC), or more correctly, when the system time is evenly divisible
1119 <p>Another way to think about it (for the mathematically inclined) is that
1120 <code>ev_periodic</code> will try to run the callback in this mode at the next possible
1121 time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p>
1123 <dt>* manual reschedule mode (reschedule_cb = callback)</dt>
1125 <p>In this mode the values for <code>interval</code> and <code>at</code> are both being
1126 ignored. Instead, each time the periodic watcher gets scheduled, the
1127 reschedule callback will be called with the watcher as first, and the
1128 current time as second argument.</p>
1129 <p>NOTE: <i>This callback MUST NOT stop or destroy any periodic watcher,
1130 ever, or make any event loop modifications</i>. If you need to stop it,
1131 return <code>now + 1e30</code> (or so, fudge fudge) and stop it afterwards (e.g. by
1132 starting a prepare watcher).</p>
1133 <p>Its prototype is <code>ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
1134 ev_tstamp now)</code>, e.g.:</p>
1135 <pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1141 <p>It must return the next time to trigger, based on the passed time value
1142 (that is, the lowest time value larger than to the second argument). It
1143 will usually be called just before the callback will be triggered, but
1144 might be called at other times, too.</p>
1145 <p>NOTE: <i>This callback must always return a time that is later than the
1146 passed <code>now</code> value</i>. Not even <code>now</code> itself will do, it <i>must</i> be larger.</p>
1147 <p>This can be used to create very complex timers, such as a timer that
1148 triggers on each midnight, local time. To do this, you would calculate the
1149 next midnight after <code>now</code> and return the timestamp value for this. How
1150 you do this is, again, up to you (but it is not trivial, which is the main
1151 reason I omitted it as an example).</p>
1156 <dt>ev_periodic_again (loop, ev_periodic *)</dt>
1158 <p>Simply stops and restarts the periodic watcher again. This is only useful
1159 when you changed some parameters or the reschedule callback would return
1160 a different time than the last time it was called (e.g. in a crond like
1161 program when the crontabs have changed).</p>
1163 <dt>ev_tstamp interval [read-write]</dt>
1165 <p>The current interval value. Can be modified any time, but changes only
1166 take effect when the periodic timer fires or <code>ev_periodic_again</code> is being
1169 <dt>ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]</dt>
1171 <p>The current reschedule callback, or <code>0</code>, if this functionality is
1172 switched off. Can be changed any time, but changes only take effect when
1173 the periodic timer fires or <code>ev_periodic_again</code> is being called.</p>
1176 <p>Example: Call a callback every hour, or, more precisely, whenever the
1177 system clock is divisible by 3600. The callback invocation times have
1178 potentially a lot of jittering, but good long-term stability.</p>
1180 clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1182 ... its now a full hour (UTC, or TAI or whatever your clock follows)
1185 struct ev_periodic hourly_tick;
1186 ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1187 ev_periodic_start (loop, &hourly_tick);
1190 <p>Example: The same as above, but use a reschedule callback to do it:</p>
1191 <pre> #include <math.h>
1194 my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
1196 return fmod (now, 3600.) + 3600.;
1199 ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1202 <p>Example: Call a callback every hour, starting now:</p>
1203 <pre> struct ev_periodic hourly_tick;
1204 ev_periodic_init (&hourly_tick, clock_cb,
1205 fmod (ev_now (loop), 3600.), 3600., 0);
1206 ev_periodic_start (loop, &hourly_tick);
1214 <h2 id="code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled!</h2>
1215 <div id="code_ev_signal_code_signal_me_when_a-2">
1216 <p>Signal watchers will trigger an event when the process receives a specific
1217 signal one or more times. Even though signals are very asynchronous, libev
1218 will try it's best to deliver signals synchronously, i.e. as part of the
1219 normal event processing, like any other event.</p>
1220 <p>You can configure as many watchers as you like per signal. Only when the
1221 first watcher gets started will libev actually register a signal watcher
1222 with the kernel (thus it coexists with your own signal handlers as long
1223 as you don't register any with libev). Similarly, when the last signal
1224 watcher for a signal is stopped libev will reset the signal handler to
1225 SIG_DFL (regardless of what it was set to before).</p>
1227 <dt>ev_signal_init (ev_signal *, callback, int signum)</dt>
1228 <dt>ev_signal_set (ev_signal *, int signum)</dt>
1230 <p>Configures the watcher to trigger on the given signal number (usually one
1231 of the <code>SIGxxx</code> constants).</p>
1233 <dt>int signum [read-only]</dt>
1235 <p>The signal the watcher watches out for.</p>
1244 <h2 id="code_ev_child_code_watch_out_for_pro"><code>ev_child</code> - watch out for process status changes</h2>
1245 <div id="code_ev_child_code_watch_out_for_pro-2">
1246 <p>Child watchers trigger when your process receives a SIGCHLD in response to
1247 some child status changes (most typically when a child of yours dies).</p>
1249 <dt>ev_child_init (ev_child *, callback, int pid)</dt>
1250 <dt>ev_child_set (ev_child *, int pid)</dt>
1252 <p>Configures the watcher to wait for status changes of process <code>pid</code> (or
1253 <i>any</i> process if <code>pid</code> is specified as <code>0</code>). The callback can look
1254 at the <code>rstatus</code> member of the <code>ev_child</code> watcher structure to see
1255 the status word (use the macros from <code>sys/wait.h</code> and see your systems
1256 <code>waitpid</code> documentation). The <code>rpid</code> member contains the pid of the
1257 process causing the status change.</p>
1259 <dt>int pid [read-only]</dt>
1261 <p>The process id this watcher watches out for, or <code>0</code>, meaning any process id.</p>
1263 <dt>int rpid [read-write]</dt>
1265 <p>The process id that detected a status change.</p>
1267 <dt>int rstatus [read-write]</dt>
1269 <p>The process exit/trace status caused by <code>rpid</code> (see your systems
1270 <code>waitpid</code> and <code>sys/wait.h</code> documentation for details).</p>
1273 <p>Example: Try to exit cleanly on SIGINT and SIGTERM.</p>
1275 sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1277 ev_unloop (loop, EVUNLOOP_ALL);
1280 struct ev_signal signal_watcher;
1281 ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1282 ev_signal_start (loop, &sigint_cb);
1290 <h2 id="code_ev_stat_code_did_the_file_attri"><code>ev_stat</code> - did the file attributes just change?</h2>
1291 <div id="code_ev_stat_code_did_the_file_attri-2">
1292 <p>This watches a filesystem path for attribute changes. That is, it calls
1293 <code>stat</code> regularly (or when the OS says it changed) and sees if it changed
1294 compared to the last time, invoking the callback if it did.</p>
1295 <p>The path does not need to exist: changing from "path exists" to "path does
1296 not exist" is a status change like any other. The condition "path does
1297 not exist" is signified by the <code>st_nlink</code> field being zero (which is
1298 otherwise always forced to be at least one) and all the other fields of
1299 the stat buffer having unspecified contents.</p>
1300 <p>The path <i>should</i> be absolute and <i>must not</i> end in a slash. If it is
1301 relative and your working directory changes, the behaviour is undefined.</p>
1302 <p>Since there is no standard to do this, the portable implementation simply
1303 calls <code>stat (2)</code> regularly on the path to see if it changed somehow. You
1304 can specify a recommended polling interval for this case. If you specify
1305 a polling interval of <code>0</code> (highly recommended!) then a <i>suitable,
1306 unspecified default</i> value will be used (which you can expect to be around
1307 five seconds, although this might change dynamically). Libev will also
1308 impose a minimum interval which is currently around <code>0.1</code>, but thats
1309 usually overkill.</p>
1310 <p>This watcher type is not meant for massive numbers of stat watchers,
1311 as even with OS-supported change notifications, this can be
1312 resource-intensive.</p>
1313 <p>At the time of this writing, only the Linux inotify interface is
1314 implemented (implementing kqueue support is left as an exercise for the
1315 reader). Inotify will be used to give hints only and should not change the
1316 semantics of <code>ev_stat</code> watchers, which means that libev sometimes needs
1317 to fall back to regular polling again even with inotify, but changes are
1318 usually detected immediately, and if the file exists there will be no
1321 <dt>ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)</dt>
1322 <dt>ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)</dt>
1324 <p>Configures the watcher to wait for status changes of the given
1325 <code>path</code>. The <code>interval</code> is a hint on how quickly a change is expected to
1326 be detected and should normally be specified as <code>0</code> to let libev choose
1327 a suitable value. The memory pointed to by <code>path</code> must point to the same
1328 path for as long as the watcher is active.</p>
1329 <p>The callback will be receive <code>EV_STAT</code> when a change was detected,
1330 relative to the attributes at the time the watcher was started (or the
1331 last change was detected).</p>
1333 <dt>ev_stat_stat (ev_stat *)</dt>
1335 <p>Updates the stat buffer immediately with new values. If you change the
1336 watched path in your callback, you could call this fucntion to avoid
1337 detecting this change (while introducing a race condition). Can also be
1338 useful simply to find out the new values.</p>
1340 <dt>ev_statdata attr [read-only]</dt>
1342 <p>The most-recently detected attributes of the file. Although the type is of
1343 <code>ev_statdata</code>, this is usually the (or one of the) <code>struct stat</code> types
1344 suitable for your system. If the <code>st_nlink</code> member is <code>0</code>, then there
1345 was some error while <code>stat</code>ing the file.</p>
1347 <dt>ev_statdata prev [read-only]</dt>
1349 <p>The previous attributes of the file. The callback gets invoked whenever
1350 <code>prev</code> != <code>attr</code>.</p>
1352 <dt>ev_tstamp interval [read-only]</dt>
1354 <p>The specified interval.</p>
1356 <dt>const char *path [read-only]</dt>
1358 <p>The filesystem path that is being watched.</p>
1361 <p>Example: Watch <code>/etc/passwd</code> for attribute changes.</p>
1363 passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1365 /* /etc/passwd changed in some way */
1366 if (w->attr.st_nlink)
1368 printf ("passwd current size %ld\n", (long)w->attr.st_size);
1369 printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1370 printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1373 /* you shalt not abuse printf for puts */
1374 puts ("wow, /etc/passwd is not there, expect problems. "
1375 "if this is windows, they already arrived\n");
1381 ev_stat_init (&passwd, passwd_cb, "/etc/passwd");
1382 ev_stat_start (loop, &passwd);
1390 <h2 id="code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do...</h2>
1391 <div id="code_ev_idle_code_when_you_ve_got_no-2">
1392 <p>Idle watchers trigger events when no other events of the same or higher
1393 priority are pending (prepare, check and other idle watchers do not
1395 <p>That is, as long as your process is busy handling sockets or timeouts
1396 (or even signals, imagine) of the same or higher priority it will not be
1397 triggered. But when your process is idle (or only lower-priority watchers
1398 are pending), the idle watchers are being called once per event loop
1399 iteration - until stopped, that is, or your process receives more events
1400 and becomes busy again with higher priority stuff.</p>
1401 <p>The most noteworthy effect is that as long as any idle watchers are
1402 active, the process will not block when waiting for new events.</p>
1403 <p>Apart from keeping your process non-blocking (which is a useful
1404 effect on its own sometimes), idle watchers are a good place to do
1405 "pseudo-background processing", or delay processing stuff to after the
1406 event loop has handled all outstanding events.</p>
1408 <dt>ev_idle_init (ev_signal *, callback)</dt>
1410 <p>Initialises and configures the idle watcher - it has no parameters of any
1411 kind. There is a <code>ev_idle_set</code> macro, but using it is utterly pointless,
1415 <p>Example: Dynamically allocate an <code>ev_idle</code> watcher, start it, and in the
1416 callback, free it. Also, use no error checking, as usual.</p>
1418 idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1421 // now do something you wanted to do when the program has
1422 // no longer asnything immediate to do.
1425 struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1426 ev_idle_init (idle_watcher, idle_cb);
1427 ev_idle_start (loop, idle_cb);
1435 <h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop!</h2>
1436 <div id="code_ev_prepare_code_and_code_ev_che-2">
1437 <p>Prepare and check watchers are usually (but not always) used in tandem:
1438 prepare watchers get invoked before the process blocks and check watchers
1440 <p>You <i>must not</i> call <code>ev_loop</code> or similar functions that enter
1441 the current event loop from either <code>ev_prepare</code> or <code>ev_check</code>
1442 watchers. Other loops than the current one are fine, however. The
1443 rationale behind this is that you do not need to check for recursion in
1444 those watchers, i.e. the sequence will always be <code>ev_prepare</code>, blocking,
1445 <code>ev_check</code> so if you have one watcher of each kind they will always be
1446 called in pairs bracketing the blocking call.</p>
1447 <p>Their main purpose is to integrate other event mechanisms into libev and
1448 their use is somewhat advanced. This could be used, for example, to track
1449 variable changes, implement your own watchers, integrate net-snmp or a
1450 coroutine library and lots more. They are also occasionally useful if
1451 you cache some data and want to flush it before blocking (for example,
1452 in X programs you might want to do an <code>XFlush ()</code> in an <code>ev_prepare</code>
1454 <p>This is done by examining in each prepare call which file descriptors need
1455 to be watched by the other library, registering <code>ev_io</code> watchers for
1456 them and starting an <code>ev_timer</code> watcher for any timeouts (many libraries
1457 provide just this functionality). Then, in the check watcher you check for
1458 any events that occured (by checking the pending status of all watchers
1459 and stopping them) and call back into the library. The I/O and timer
1460 callbacks will never actually be called (but must be valid nevertheless,
1461 because you never know, you know?).</p>
1462 <p>As another example, the Perl Coro module uses these hooks to integrate
1463 coroutines into libev programs, by yielding to other active coroutines
1464 during each prepare and only letting the process block if no coroutines
1465 are ready to run (it's actually more complicated: it only runs coroutines
1466 with priority higher than or equal to the event loop and one coroutine
1467 of lower priority, but only once, using idle watchers to keep the event
1468 loop from blocking if lower-priority coroutines are active, thus mapping
1469 low-priority coroutines to idle/background tasks).</p>
1471 <dt>ev_prepare_init (ev_prepare *, callback)</dt>
1472 <dt>ev_check_init (ev_check *, callback)</dt>
1474 <p>Initialises and configures the prepare or check watcher - they have no
1475 parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check_set</code>
1476 macros, but using them is utterly, utterly and completely pointless.</p>
1479 <p>Example: To include a library such as adns, you would add IO watchers
1480 and a timeout watcher in a prepare handler, as required by libadns, and
1481 in a check watcher, destroy them and call into libadns. What follows is
1482 pseudo-code only of course:</p>
1483 <pre> static ev_io iow [nfd];
1487 io_cb (ev_loop *loop, ev_io *w, int revents)
1489 // set the relevant poll flags
1490 // could also call adns_processreadable etc. here
1491 struct pollfd *fd = (struct pollfd *)w->data;
1492 if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1493 if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1496 // create io watchers for each fd and a timer before blocking
1498 adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
1500 int timeout = 3600000;
1501 struct pollfd fds [nfd];
1502 // actual code will need to loop here and realloc etc.
1503 adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1505 /* the callback is illegal, but won't be called as we stop during check */
1506 ev_timer_init (&tw, 0, timeout * 1e-3);
1507 ev_timer_start (loop, &tw);
1509 // create on ev_io per pollfd
1510 for (int i = 0; i < nfd; ++i)
1512 ev_io_init (iow + i, io_cb, fds [i].fd,
1513 ((fds [i].events & POLLIN ? EV_READ : 0)
1514 | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1516 fds [i].revents = 0;
1517 iow [i].data = fds + i;
1518 ev_io_start (loop, iow + i);
1522 // stop all watchers after blocking
1524 adns_check_cb (ev_loop *loop, ev_check *w, int revents)
1526 ev_timer_stop (loop, &tw);
1528 for (int i = 0; i < nfd; ++i)
1529 ev_io_stop (loop, iow + i);
1531 adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1540 <h2 id="code_ev_embed_code_when_one_backend_"><code>ev_embed</code> - when one backend isn't enough...</h2>
1541 <div id="code_ev_embed_code_when_one_backend_-2">
1542 <p>This is a rather advanced watcher type that lets you embed one event loop
1543 into another (currently only <code>ev_io</code> events are supported in the embedded
1544 loop, other types of watchers might be handled in a delayed or incorrect
1545 fashion and must not be used).</p>
1546 <p>There are primarily two reasons you would want that: work around bugs and
1548 <p>As an example for a bug workaround, the kqueue backend might only support
1549 sockets on some platform, so it is unusable as generic backend, but you
1550 still want to make use of it because you have many sockets and it scales
1551 so nicely. In this case, you would create a kqueue-based loop and embed it
1552 into your default loop (which might use e.g. poll). Overall operation will
1553 be a bit slower because first libev has to poll and then call kevent, but
1554 at least you can use both at what they are best.</p>
1555 <p>As for prioritising I/O: rarely you have the case where some fds have
1556 to be watched and handled very quickly (with low latency), and even
1557 priorities and idle watchers might have too much overhead. In this case
1558 you would put all the high priority stuff in one loop and all the rest in
1559 a second one, and embed the second one in the first.</p>
1560 <p>As long as the watcher is active, the callback will be invoked every time
1561 there might be events pending in the embedded loop. The callback must then
1562 call <code>ev_embed_sweep (mainloop, watcher)</code> to make a single sweep and invoke
1563 their callbacks (you could also start an idle watcher to give the embedded
1564 loop strictly lower priority for example). You can also set the callback
1565 to <code>0</code>, in which case the embed watcher will automatically execute the
1566 embedded loop sweep.</p>
1567 <p>As long as the watcher is started it will automatically handle events. The
1568 callback will be invoked whenever some events have been handled. You can
1569 set the callback to <code>0</code> to avoid having to specify one if you are not
1570 interested in that.</p>
1571 <p>Also, there have not currently been made special provisions for forking:
1572 when you fork, you not only have to call <code>ev_loop_fork</code> on both loops,
1573 but you will also have to stop and restart any <code>ev_embed</code> watchers
1575 <p>Unfortunately, not all backends are embeddable, only the ones returned by
1576 <code>ev_embeddable_backends</code> are, which, unfortunately, does not include any
1578 <p>So when you want to use this feature you will always have to be prepared
1579 that you cannot get an embeddable loop. The recommended way to get around
1580 this is to have a separate variables for your embeddable loop, try to
1581 create it, and if that fails, use the normal loop for everything:</p>
1582 <pre> struct ev_loop *loop_hi = ev_default_init (0);
1583 struct ev_loop *loop_lo = 0;
1584 struct ev_embed embed;
1586 // see if there is a chance of getting one that works
1587 // (remember that a flags value of 0 means autodetection)
1588 loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1589 ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1592 // if we got one, then embed it, otherwise default to loop_hi
1595 ev_embed_init (&embed, 0, loop_lo);
1596 ev_embed_start (loop_hi, &embed);
1603 <dt>ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)</dt>
1604 <dt>ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)</dt>
1606 <p>Configures the watcher to embed the given loop, which must be
1607 embeddable. If the callback is <code>0</code>, then <code>ev_embed_sweep</code> will be
1608 invoked automatically, otherwise it is the responsibility of the callback
1609 to invoke it (it will continue to be called until the sweep has been done,
1610 if you do not want thta, you need to temporarily stop the embed watcher).</p>
1612 <dt>ev_embed_sweep (loop, ev_embed *)</dt>
1614 <p>Make a single, non-blocking sweep over the embedded loop. This works
1615 similarly to <code>ev_loop (embedded_loop, EVLOOP_NONBLOCK)</code>, but in the most
1616 apropriate way for embedded loops.</p>
1618 <dt>struct ev_loop *loop [read-only]</dt>
1620 <p>The embedded event loop.</p>
1629 <h2 id="code_ev_fork_code_the_audacity_to_re"><code>ev_fork</code> - the audacity to resume the event loop after a fork</h2>
1630 <div id="code_ev_fork_code_the_audacity_to_re-2">
1631 <p>Fork watchers are called when a <code>fork ()</code> was detected (usually because
1632 whoever is a good citizen cared to tell libev about it by calling
1633 <code>ev_default_fork</code> or <code>ev_loop_fork</code>). The invocation is done before the
1634 event loop blocks next and before <code>ev_check</code> watchers are being called,
1635 and only in the child after the fork. If whoever good citizen calling
1636 <code>ev_default_fork</code> cheats and calls it in the wrong process, the fork
1637 handlers will be invoked, too, of course.</p>
1639 <dt>ev_fork_init (ev_signal *, callback)</dt>
1641 <p>Initialises and configures the fork watcher - it has no parameters of any
1642 kind. There is a <code>ev_fork_set</code> macro, but using it is utterly pointless,
1652 <h1 id="OTHER_FUNCTIONS">OTHER FUNCTIONS</h1>
1653 <div id="OTHER_FUNCTIONS_CONTENT">
1654 <p>There are some other functions of possible interest. Described. Here. Now.</p>
1656 <dt>ev_once (loop, int fd, int events, ev_tstamp timeout, callback)</dt>
1658 <p>This function combines a simple timer and an I/O watcher, calls your
1659 callback on whichever event happens first and automatically stop both
1660 watchers. This is useful if you want to wait for a single event on an fd
1661 or timeout without having to allocate/configure/start/stop/free one or
1662 more watchers yourself.</p>
1663 <p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events
1664 is being ignored. Otherwise, an <code>ev_io</code> watcher for the given <code>fd</code> and
1665 <code>events</code> set will be craeted and started.</p>
1666 <p>If <code>timeout</code> is less than 0, then no timeout watcher will be
1667 started. Otherwise an <code>ev_timer</code> watcher with after = <code>timeout</code> (and
1668 repeat = 0) will be started. While <code>0</code> is a valid timeout, it is of
1670 <p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and gets
1671 passed an <code>revents</code> set like normal event callbacks (a combination of
1672 <code>EV_ERROR</code>, <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_TIMEOUT</code>) and the <code>arg</code>
1673 value passed to <code>ev_once</code>:</p>
1674 <pre> static void stdin_ready (int revents, void *arg)
1676 if (revents & EV_TIMEOUT)
1677 /* doh, nothing entered */;
1678 else if (revents & EV_READ)
1679 /* stdin might have data for us, joy! */;
1682 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1686 <dt>ev_feed_event (ev_loop *, watcher *, int revents)</dt>
1688 <p>Feeds the given event set into the event loop, as if the specified event
1689 had happened for the specified watcher (which must be a pointer to an
1690 initialised but not necessarily started event watcher).</p>
1692 <dt>ev_feed_fd_event (ev_loop *, int fd, int revents)</dt>
1694 <p>Feed an event on the given fd, as if a file descriptor backend detected
1695 the given events it.</p>
1697 <dt>ev_feed_signal_event (ev_loop *loop, int signum)</dt>
1699 <p>Feed an event as if the given signal occured (<code>loop</code> must be the default
1709 <h1 id="LIBEVENT_EMULATION">LIBEVENT EMULATION</h1>
1710 <div id="LIBEVENT_EMULATION_CONTENT">
1711 <p>Libev offers a compatibility emulation layer for libevent. It cannot
1712 emulate the internals of libevent, so here are some usage hints:</p>
1714 <dt>* Use it by including <event.h>, as usual.</dt>
1715 <dt>* The following members are fully supported: ev_base, ev_callback,
1716 ev_arg, ev_fd, ev_res, ev_events.</dt>
1717 <dt>* Avoid using ev_flags and the EVLIST_*-macros, while it is
1718 maintained by libev, it does not work exactly the same way as in libevent (consider
1719 it a private API).</dt>
1720 <dt>* Priorities are not currently supported. Initialising priorities
1721 will fail and all watchers will have the same priority, even though there
1722 is an ev_pri field.</dt>
1723 <dt>* Other members are not supported.</dt>
1724 <dt>* The libev emulation is <i>not</i> ABI compatible to libevent, you need
1725 to use the libev header file and library.</dt>
1729 <h1 id="C_SUPPORT">C++ SUPPORT</h1>
1730 <div id="C_SUPPORT_CONTENT">
1731 <p>Libev comes with some simplistic wrapper classes for C++ that mainly allow
1732 you to use some convinience methods to start/stop watchers and also change
1733 the callback model to a model using method callbacks on objects.</p>
1735 <pre> #include <ev++.h>
1738 <p>(it is not installed by default). This automatically includes <cite>ev.h</cite>
1739 and puts all of its definitions (many of them macros) into the global
1740 namespace. All C++ specific things are put into the <code>ev</code> namespace.</p>
1741 <p>It should support all the same embedding options as <cite>ev.h</cite>, most notably
1742 <code>EV_MULTIPLICITY</code>.</p>
1743 <p>Here is a list of things available in the <code>ev</code> namespace:</p>
1745 <dt><code>ev::READ</code>, <code>ev::WRITE</code> etc.</dt>
1747 <p>These are just enum values with the same values as the <code>EV_READ</code> etc.
1748 macros from <cite>ev.h</cite>.</p>
1750 <dt><code>ev::tstamp</code>, <code>ev::now</code></dt>
1752 <p>Aliases to the same types/functions as with the <code>ev_</code> prefix.</p>
1754 <dt><code>ev::io</code>, <code>ev::timer</code>, <code>ev::periodic</code>, <code>ev::idle</code>, <code>ev::sig</code> etc.</dt>
1756 <p>For each <code>ev_TYPE</code> watcher in <cite>ev.h</cite> there is a corresponding class of
1757 the same name in the <code>ev</code> namespace, with the exception of <code>ev_signal</code>
1758 which is called <code>ev::sig</code> to avoid clashes with the <code>signal</code> macro
1759 defines by many implementations.</p>
1760 <p>All of those classes have these methods:</p>
1763 <dt>ev::TYPE::TYPE (object *, object::method *)</dt>
1764 <dt>ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)</dt>
1765 <dt>ev::TYPE::~TYPE</dt>
1767 <p>The constructor takes a pointer to an object and a method pointer to
1768 the event handler callback to call in this class. The constructor calls
1769 <code>ev_init</code> for you, which means you have to call the <code>set</code> method
1770 before starting it. If you do not specify a loop then the constructor
1771 automatically associates the default loop with this watcher.</p>
1772 <p>The destructor automatically stops the watcher if it is active.</p>
1774 <dt>w->set (struct ev_loop *)</dt>
1776 <p>Associates a different <code>struct ev_loop</code> with this watcher. You can only
1777 do this when the watcher is inactive (and not pending either).</p>
1779 <dt>w->set ([args])</dt>
1781 <p>Basically the same as <code>ev_TYPE_set</code>, with the same args. Must be
1782 called at least once. Unlike the C counterpart, an active watcher gets
1783 automatically stopped and restarted.</p>
1785 <dt>w->start ()</dt>
1787 <p>Starts the watcher. Note that there is no <code>loop</code> argument as the
1788 constructor already takes the loop.</p>
1790 <dt>w->stop ()</dt>
1792 <p>Stops the watcher if it is active. Again, no <code>loop</code> argument.</p>
1794 <dt>w->again () <code>ev::timer</code>, <code>ev::periodic</code> only</dt>
1796 <p>For <code>ev::timer</code> and <code>ev::periodic</code>, this invokes the corresponding
1797 <code>ev_TYPE_again</code> function.</p>
1799 <dt>w->sweep () <code>ev::embed</code> only</dt>
1801 <p>Invokes <code>ev_embed_sweep</code>.</p>
1803 <dt>w->update () <code>ev::stat</code> only</dt>
1805 <p>Invokes <code>ev_stat_stat</code>.</p>
1811 <p>Example: Define a class with an IO and idle watcher, start one of them in
1812 the constructor.</p>
1815 ev_io io; void io_cb (ev::io &w, int revents);
1816 ev_idle idle void idle_cb (ev::idle &w, int revents);
1821 myclass::myclass (int fd)
1822 : io (this, &myclass::io_cb),
1823 idle (this, &myclass::idle_cb)
1825 io.start (fd, ev::READ);
1834 <h1 id="MACRO_MAGIC">MACRO MAGIC</h1>
1835 <div id="MACRO_MAGIC_CONTENT">
1836 <p>Libev can be compiled with a variety of options, the most fundemantal is
1837 <code>EV_MULTIPLICITY</code>. This option determines whether (most) functions and
1838 callbacks have an initial <code>struct ev_loop *</code> argument.</p>
1839 <p>To make it easier to write programs that cope with either variant, the
1840 following macros are defined:</p>
1842 <dt><code>EV_A</code>, <code>EV_A_</code></dt>
1844 <p>This provides the loop <i>argument</i> for functions, if one is required ("ev
1845 loop argument"). The <code>EV_A</code> form is used when this is the sole argument,
1846 <code>EV_A_</code> is used when other arguments are following. Example:</p>
1847 <pre> ev_unref (EV_A);
1848 ev_timer_add (EV_A_ watcher);
1852 <p>It assumes the variable <code>loop</code> of type <code>struct ev_loop *</code> is in scope,
1853 which is often provided by the following macro.</p>
1855 <dt><code>EV_P</code>, <code>EV_P_</code></dt>
1857 <p>This provides the loop <i>parameter</i> for functions, if one is required ("ev
1858 loop parameter"). The <code>EV_P</code> form is used when this is the sole parameter,
1859 <code>EV_P_</code> is used when other parameters are following. Example:</p>
1860 <pre> // this is how ev_unref is being declared
1861 static void ev_unref (EV_P);
1863 // this is how you can declare your typical callback
1864 static void cb (EV_P_ ev_timer *w, int revents)
1867 <p>It declares a parameter <code>loop</code> of type <code>struct ev_loop *</code>, quite
1868 suitable for use with <code>EV_A</code>.</p>
1870 <dt><code>EV_DEFAULT</code>, <code>EV_DEFAULT_</code></dt>
1872 <p>Similar to the other two macros, this gives you the value of the default
1873 loop, if multiple loops are supported ("ev loop default").</p>
1876 <p>Example: Declare and initialise a check watcher, utilising the above
1877 macros so it will work regardless of whether multiple loops are supported
1880 check_cb (EV_P_ ev_timer *w, int revents)
1882 ev_check_stop (EV_A_ w);
1886 ev_check_init (&check, check_cb);
1887 ev_check_start (EV_DEFAULT_ &check);
1888 ev_loop (EV_DEFAULT_ 0);
1893 <h1 id="EMBEDDING">EMBEDDING</h1>
1894 <div id="EMBEDDING_CONTENT">
1895 <p>Libev can (and often is) directly embedded into host
1896 applications. Examples of applications that embed it include the Deliantra
1897 Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1898 and rxvt-unicode.</p>
1899 <p>The goal is to enable you to just copy the neecssary files into your
1900 source directory without having to change even a single line in them, so
1901 you can easily upgrade by simply copying (or having a checked-out copy of
1902 libev somewhere in your source tree).</p>
1905 <h2 id="FILESETS">FILESETS</h2>
1906 <div id="FILESETS_CONTENT">
1907 <p>Depending on what features you need you need to include one or more sets of files
1911 <h3 id="CORE_EVENT_LOOP">CORE EVENT LOOP</h3>
1912 <div id="CORE_EVENT_LOOP_CONTENT">
1913 <p>To include only the libev core (all the <code>ev_*</code> functions), with manual
1914 configuration (no autoconf):</p>
1915 <pre> #define EV_STANDALONE 1
1916 #include "ev.c"
1919 <p>This will automatically include <cite>ev.h</cite>, too, and should be done in a
1920 single C source file only to provide the function implementations. To use
1921 it, do the same for <cite>ev.h</cite> in all files wishing to use this API (best
1922 done by writing a wrapper around <cite>ev.h</cite> that you can include instead and
1923 where you can put other configuration options):</p>
1924 <pre> #define EV_STANDALONE 1
1925 #include "ev.h"
1928 <p>Both header files and implementation files can be compiled with a C++
1929 compiler (at least, thats a stated goal, and breakage will be treated
1931 <p>You need the following files in your source tree, or in a directory
1932 in your include path (e.g. in libev/ when using -Ilibev):</p>
1938 ev_win32.c required on win32 platforms only
1940 ev_select.c only when select backend is enabled (which is enabled by default)
1941 ev_poll.c only when poll backend is enabled (disabled by default)
1942 ev_epoll.c only when the epoll backend is enabled (disabled by default)
1943 ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1944 ev_port.c only when the solaris port backend is enabled (disabled by default)
1947 <p><cite>ev.c</cite> includes the backend files directly when enabled, so you only need
1948 to compile this single file.</p>
1951 <h3 id="LIBEVENT_COMPATIBILITY_API">LIBEVENT COMPATIBILITY API</h3>
1952 <div id="LIBEVENT_COMPATIBILITY_API_CONTENT">
1953 <p>To include the libevent compatibility API, also include:</p>
1954 <pre> #include "event.c"
1957 <p>in the file including <cite>ev.c</cite>, and:</p>
1958 <pre> #include "event.h"
1961 <p>in the files that want to use the libevent API. This also includes <cite>ev.h</cite>.</p>
1962 <p>You need the following additional files for this:</p>
1969 <h3 id="AUTOCONF_SUPPORT">AUTOCONF SUPPORT</h3>
1970 <div id="AUTOCONF_SUPPORT_CONTENT">
1971 <p>Instead of using <code>EV_STANDALONE=1</code> and providing your config in
1972 whatever way you want, you can also <code>m4_include([libev.m4])</code> in your
1973 <cite>configure.ac</cite> and leave <code>EV_STANDALONE</code> undefined. <cite>ev.c</cite> will then
1974 include <cite>config.h</cite> and configure itself accordingly.</p>
1975 <p>For this of course you need the m4 file:</p>
1981 <h2 id="PREPROCESSOR_SYMBOLS_MACROS">PREPROCESSOR SYMBOLS/MACROS</h2>
1982 <div id="PREPROCESSOR_SYMBOLS_MACROS_CONTENT">
1983 <p>Libev can be configured via a variety of preprocessor symbols you have to define
1984 before including any of its files. The default is not to build for multiplicity
1985 and only include the select backend.</p>
1987 <dt>EV_STANDALONE</dt>
1989 <p>Must always be <code>1</code> if you do not use autoconf configuration, which
1990 keeps libev from including <cite>config.h</cite>, and it also defines dummy
1991 implementations for some libevent functions (such as logging, which is not
1992 supported). It will also not define any of the structs usually found in
1993 <cite>event.h</cite> that are not directly supported by the libev core alone.</p>
1995 <dt>EV_USE_MONOTONIC</dt>
1997 <p>If defined to be <code>1</code>, libev will try to detect the availability of the
1998 monotonic clock option at both compiletime and runtime. Otherwise no use
1999 of the monotonic clock option will be attempted. If you enable this, you
2000 usually have to link against librt or something similar. Enabling it when
2001 the functionality isn't available is safe, though, althoguh you have
2002 to make sure you link against any libraries where the <code>clock_gettime</code>
2003 function is hiding in (often <cite>-lrt</cite>).</p>
2005 <dt>EV_USE_REALTIME</dt>
2007 <p>If defined to be <code>1</code>, libev will try to detect the availability of the
2008 realtime clock option at compiletime (and assume its availability at
2009 runtime if successful). Otherwise no use of the realtime clock option will
2010 be attempted. This effectively replaces <code>gettimeofday</code> by <code>clock_get
2011 (CLOCK_REALTIME, ...)</code> and will not normally affect correctness. See tzhe note about libraries
2012 in the description of <code>EV_USE_MONOTONIC</code>, though.</p>
2014 <dt>EV_USE_SELECT</dt>
2016 <p>If undefined or defined to be <code>1</code>, libev will compile in support for the
2017 <code>select</code>(2) backend. No attempt at autodetection will be done: if no
2018 other method takes over, select will be it. Otherwise the select backend
2019 will not be compiled in.</p>
2021 <dt>EV_SELECT_USE_FD_SET</dt>
2023 <p>If defined to <code>1</code>, then the select backend will use the system <code>fd_set</code>
2024 structure. This is useful if libev doesn't compile due to a missing
2025 <code>NFDBITS</code> or <code>fd_mask</code> definition or it misguesses the bitset layout on
2026 exotic systems. This usually limits the range of file descriptors to some
2027 low limit such as 1024 or might have other limitations (winsocket only
2028 allows 64 sockets). The <code>FD_SETSIZE</code> macro, set before compilation, might
2029 influence the size of the <code>fd_set</code> used.</p>
2031 <dt>EV_SELECT_IS_WINSOCKET</dt>
2033 <p>When defined to <code>1</code>, the select backend will assume that
2034 select/socket/connect etc. don't understand file descriptors but
2035 wants osf handles on win32 (this is the case when the select to
2036 be used is the winsock select). This means that it will call
2037 <code>_get_osfhandle</code> on the fd to convert it to an OS handle. Otherwise,
2038 it is assumed that all these functions actually work on fds, even
2039 on win32. Should not be defined on non-win32 platforms.</p>
2041 <dt>EV_USE_POLL</dt>
2043 <p>If defined to be <code>1</code>, libev will compile in support for the <code>poll</code>(2)
2044 backend. Otherwise it will be enabled on non-win32 platforms. It
2045 takes precedence over select.</p>
2047 <dt>EV_USE_EPOLL</dt>
2049 <p>If defined to be <code>1</code>, libev will compile in support for the Linux
2050 <code>epoll</code>(7) backend. Its availability will be detected at runtime,
2051 otherwise another method will be used as fallback. This is the
2052 preferred backend for GNU/Linux systems.</p>
2054 <dt>EV_USE_KQUEUE</dt>
2056 <p>If defined to be <code>1</code>, libev will compile in support for the BSD style
2057 <code>kqueue</code>(2) backend. Its actual availability will be detected at runtime,
2058 otherwise another method will be used as fallback. This is the preferred
2059 backend for BSD and BSD-like systems, although on most BSDs kqueue only
2060 supports some types of fds correctly (the only platform we found that
2061 supports ptys for example was NetBSD), so kqueue might be compiled in, but
2062 not be used unless explicitly requested. The best way to use it is to find
2063 out whether kqueue supports your type of fd properly and use an embedded
2066 <dt>EV_USE_PORT</dt>
2068 <p>If defined to be <code>1</code>, libev will compile in support for the Solaris
2069 10 port style backend. Its availability will be detected at runtime,
2070 otherwise another method will be used as fallback. This is the preferred
2071 backend for Solaris 10 systems.</p>
2073 <dt>EV_USE_DEVPOLL</dt>
2075 <p>reserved for future expansion, works like the USE symbols above.</p>
2077 <dt>EV_USE_INOTIFY</dt>
2079 <p>If defined to be <code>1</code>, libev will compile in support for the Linux inotify
2080 interface to speed up <code>ev_stat</code> watchers. Its actual availability will
2081 be detected at runtime.</p>
2085 <p>The name of the <cite>ev.h</cite> header file used to include it. The default if
2086 undefined is <code><ev.h></code> in <cite>event.h</cite> and <code>"ev.h"</code> in <cite>ev.c</cite>. This
2087 can be used to virtually rename the <cite>ev.h</cite> header file in case of conflicts.</p>
2089 <dt>EV_CONFIG_H</dt>
2091 <p>If <code>EV_STANDALONE</code> isn't <code>1</code>, this variable can be used to override
2092 <cite>ev.c</cite>'s idea of where to find the <cite>config.h</cite> file, similarly to
2093 <code>EV_H</code>, above.</p>
2097 <p>Similarly to <code>EV_H</code>, this macro can be used to override <cite>event.c</cite>'s idea
2098 of how the <cite>event.h</cite> header can be found.</p>
2100 <dt>EV_PROTOTYPES</dt>
2102 <p>If defined to be <code>0</code>, then <cite>ev.h</cite> will not define any function
2103 prototypes, but still define all the structs and other symbols. This is
2104 occasionally useful if you want to provide your own wrapper functions
2105 around libev functions.</p>
2107 <dt>EV_MULTIPLICITY</dt>
2109 <p>If undefined or defined to <code>1</code>, then all event-loop-specific functions
2110 will have the <code>struct ev_loop *</code> as first argument, and you can create
2111 additional independent event loops. Otherwise there will be no support
2112 for multiple event loops and there is no first event loop pointer
2113 argument. Instead, all functions act on the single default loop.</p>
2115 <dt>EV_PERIODIC_ENABLE</dt>
2117 <p>If undefined or defined to be <code>1</code>, then periodic timers are supported. If
2118 defined to be <code>0</code>, then they are not. Disabling them saves a few kB of
2121 <dt>EV_IDLE_ENABLE</dt>
2123 <p>If undefined or defined to be <code>1</code>, then idle watchers are supported. If
2124 defined to be <code>0</code>, then they are not. Disabling them saves a few kB of
2127 <dt>EV_EMBED_ENABLE</dt>
2129 <p>If undefined or defined to be <code>1</code>, then embed watchers are supported. If
2130 defined to be <code>0</code>, then they are not.</p>
2132 <dt>EV_STAT_ENABLE</dt>
2134 <p>If undefined or defined to be <code>1</code>, then stat watchers are supported. If
2135 defined to be <code>0</code>, then they are not.</p>
2137 <dt>EV_FORK_ENABLE</dt>
2139 <p>If undefined or defined to be <code>1</code>, then fork watchers are supported. If
2140 defined to be <code>0</code>, then they are not.</p>
2144 <p>If you need to shave off some kilobytes of code at the expense of some
2145 speed, define this symbol to <code>1</code>. Currently only used for gcc to override
2146 some inlining decisions, saves roughly 30% codesize of amd64.</p>
2148 <dt>EV_PID_HASHSIZE</dt>
2150 <p><code>ev_child</code> watchers use a small hash table to distribute workload by
2151 pid. The default size is <code>16</code> (or <code>1</code> with <code>EV_MINIMAL</code>), usually more
2152 than enough. If you need to manage thousands of children you might want to
2153 increase this value (<i>must</i> be a power of two).</p>
2155 <dt>EV_INOTIFY_HASHSIZE</dt>
2157 <p><code>ev_staz</code> watchers use a small hash table to distribute workload by
2158 inotify watch id. The default size is <code>16</code> (or <code>1</code> with <code>EV_MINIMAL</code>),
2159 usually more than enough. If you need to manage thousands of <code>ev_stat</code>
2160 watchers you might want to increase this value (<i>must</i> be a power of
2165 <p>By default, all watchers have a <code>void *data</code> member. By redefining
2166 this macro to a something else you can include more and other types of
2167 members. You have to define it each time you include one of the files,
2168 though, and it must be identical each time.</p>
2169 <p>For example, the perl EV module uses something like this:</p>
2170 <pre> #define EV_COMMON \
2171 SV *self; /* contains this struct */ \
2172 SV *cb_sv, *fh /* note no trailing ";" */
2176 <dt>EV_CB_DECLARE (type)</dt>
2177 <dt>EV_CB_INVOKE (watcher, revents)</dt>
2178 <dt>ev_set_cb (ev, cb)</dt>
2180 <p>Can be used to change the callback member declaration in each watcher,
2181 and the way callbacks are invoked and set. Must expand to a struct member
2182 definition and a statement, respectively. See the <cite>ev.v</cite> header file for
2183 their default definitions. One possible use for overriding these is to
2184 avoid the <code>struct ev_loop *</code> as first argument in all cases, or to use
2185 method calls instead of plain function calls in C++.</p>
2188 <h2 id="EXAMPLES">EXAMPLES</h2>
2189 <div id="EXAMPLES_CONTENT">
2190 <p>For a real-world example of a program the includes libev
2191 verbatim, you can have a look at the EV perl module
2192 (<a href="http://software.schmorp.de/pkg/EV.html">http://software.schmorp.de/pkg/EV.html</a>). It has the libev files in
2193 the <cite>libev/</cite> subdirectory and includes them in the <cite>EV/EVAPI.h</cite> (public
2194 interface) and <cite>EV.xs</cite> (implementation) files. Only the <cite>EV.xs</cite> file
2195 will be compiled. It is pretty complex because it provides its own header
2197 <p>The usage in rxvt-unicode is simpler. It has a <cite>ev_cpp.h</cite> header file
2198 that everybody includes and which overrides some configure choices:</p>
2199 <pre> #define EV_MINIMAL 1
2200 #define EV_USE_POLL 0
2201 #define EV_MULTIPLICITY 0
2202 #define EV_PERIODIC_ENABLE 0
2203 #define EV_STAT_ENABLE 0
2204 #define EV_FORK_ENABLE 0
2205 #define EV_CONFIG_H <config.h>
2209 #include "ev++.h"
2212 <p>And a <cite>ev_cpp.C</cite> implementation file that contains libev proper and is compiled:</p>
2213 <pre> #include "ev_cpp.h"
2214 #include "ev.c"
2222 <h1 id="COMPLEXITIES">COMPLEXITIES</h1>
2223 <div id="COMPLEXITIES_CONTENT">
2224 <p>In this section the complexities of (many of) the algorithms used inside
2225 libev will be explained. For complexity discussions about backends see the
2226 documentation for <code>ev_default_init</code>.</p>
2229 <dt>Starting and stopping timer/periodic watchers: O(log skipped_other_timers)</dt>
2230 <dt>Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)</dt>
2231 <dt>Starting io/check/prepare/idle/signal/child watchers: O(1)</dt>
2232 <dt>Stopping check/prepare/idle watchers: O(1)</dt>
2233 <dt>Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))</dt>
2234 <dt>Finding the next timer per loop iteration: O(1)</dt>
2235 <dt>Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)</dt>
2236 <dt>Activating one watcher: O(1)</dt>
2245 <h1 id="AUTHOR">AUTHOR</h1>
2246 <div id="AUTHOR_CONTENT">
2247 <p>Marc Lehmann <libev@schmorp.de>.</p>
projects / software / libev.git / blob