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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>The newest version of this document is also available as a html-formatted
125 web page you might find easier to navigate when reading it for the first
126 time: <a href="http://cvs.schmorp.de/libev/ev.html">http://cvs.schmorp.de/libev/ev.html</a>.</p>
127 <p>Libev is an event loop: you register interest in certain events (such as a
128 file descriptor being readable or a timeout occuring), and it will manage
129 these event sources and provide your program with events.</p>
130 <p>To do this, it must take more or less complete control over your process
131 (or thread) by executing the <i>event loop</i> handler, and will then
132 communicate events via a callback mechanism.</p>
133 <p>You register interest in certain events by registering so-called <i>event
134 watchers</i>, which are relatively small C structures you initialise with the
135 details of the event, and then hand it over to libev by <i>starting</i> the
139 <h1 id="FEATURES">FEATURES</h1>
140 <div id="FEATURES_CONTENT">
141 <p>Libev supports <code>select</code>, <code>poll</code>, the Linux-specific <code>epoll</code>, the
142 BSD-specific <code>kqueue</code> and the Solaris-specific event port mechanisms
143 for file descriptor events (<code>ev_io</code>), the Linux <code>inotify</code> interface
144 (for <code>ev_stat</code>), relative timers (<code>ev_timer</code>), absolute timers
145 with customised rescheduling (<code>ev_periodic</code>), synchronous signals
146 (<code>ev_signal</code>), process status change events (<code>ev_child</code>), and event
147 watchers dealing with the event loop mechanism itself (<code>ev_idle</code>,
148 <code>ev_embed</code>, <code>ev_prepare</code> and <code>ev_check</code> watchers) as well as
149 file watchers (<code>ev_stat</code>) and even limited support for fork events
150 (<code>ev_fork</code>).</p>
151 <p>It also is quite fast (see this
152 <a href="http://libev.schmorp.de/bench.html">benchmark</a> comparing it to libevent
156 <h1 id="CONVENTIONS">CONVENTIONS</h1>
157 <div id="CONVENTIONS_CONTENT">
158 <p>Libev is very configurable. In this manual the default configuration will
159 be described, which supports multiple event loops. For more info about
160 various configuration options please have a look at <strong>EMBED</strong> section in
161 this manual. If libev was configured without support for multiple event
162 loops, then all functions taking an initial argument of name <code>loop</code>
163 (which is always of type <code>struct ev_loop *</code>) will not have this argument.</p>
166 <h1 id="TIME_REPRESENTATION">TIME REPRESENTATION</h1>
167 <div id="TIME_REPRESENTATION_CONTENT">
168 <p>Libev represents time as a single floating point number, representing the
169 (fractional) number of seconds since the (POSIX) epoch (somewhere near
170 the beginning of 1970, details are complicated, don't ask). This type is
171 called <code>ev_tstamp</code>, which is what you should use too. It usually aliases
172 to the <code>double</code> type in C, and when you need to do any calculations on
173 it, you should treat it as such.</p>
176 <h1 id="GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</h1>
177 <div id="GLOBAL_FUNCTIONS_CONTENT">
178 <p>These functions can be called anytime, even before initialising the
179 library in any way.</p>
181 <dt>ev_tstamp ev_time ()</dt>
183 <p>Returns the current time as libev would use it. Please note that the
184 <code>ev_now</code> function is usually faster and also often returns the timestamp
185 you actually want to know.</p>
187 <dt>int ev_version_major ()</dt>
188 <dt>int ev_version_minor ()</dt>
190 <p>You can find out the major and minor version numbers of the library
191 you linked against by calling the functions <code>ev_version_major</code> and
192 <code>ev_version_minor</code>. If you want, you can compare against the global
193 symbols <code>EV_VERSION_MAJOR</code> and <code>EV_VERSION_MINOR</code>, which specify the
194 version of the library your program was compiled against.</p>
195 <p>Usually, it's a good idea to terminate if the major versions mismatch,
196 as this indicates an incompatible change. Minor versions are usually
197 compatible to older versions, so a larger minor version alone is usually
199 <p>Example: Make sure we haven't accidentally been linked against the wrong
201 <pre> assert (("libev version mismatch",
202 ev_version_major () == EV_VERSION_MAJOR
203 && ev_version_minor () >= EV_VERSION_MINOR));
207 <dt>unsigned int ev_supported_backends ()</dt>
209 <p>Return the set of all backends (i.e. their corresponding <code>EV_BACKEND_*</code>
210 value) compiled into this binary of libev (independent of their
211 availability on the system you are running on). See <code>ev_default_loop</code> for
212 a description of the set values.</p>
213 <p>Example: make sure we have the epoll method, because yeah this is cool and
214 a must have and can we have a torrent of it please!!!11</p>
215 <pre> assert (("sorry, no epoll, no sex",
216 ev_supported_backends () & EVBACKEND_EPOLL));
220 <dt>unsigned int ev_recommended_backends ()</dt>
222 <p>Return the set of all backends compiled into this binary of libev and also
223 recommended for this platform. This set is often smaller than the one
224 returned by <code>ev_supported_backends</code>, as for example kqueue is broken on
225 most BSDs and will not be autodetected unless you explicitly request it
226 (assuming you know what you are doing). This is the set of backends that
227 libev will probe for if you specify no backends explicitly.</p>
229 <dt>unsigned int ev_embeddable_backends ()</dt>
231 <p>Returns the set of backends that are embeddable in other event loops. This
232 is the theoretical, all-platform, value. To find which backends
233 might be supported on the current system, you would need to look at
234 <code>ev_embeddable_backends () & ev_supported_backends ()</code>, likewise for
235 recommended ones.</p>
236 <p>See the description of <code>ev_embed</code> watchers for more info.</p>
238 <dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt>
240 <p>Sets the allocation function to use (the prototype is similar - the
241 semantics is identical - to the realloc C function). It is used to
242 allocate and free memory (no surprises here). If it returns zero when
243 memory needs to be allocated, the library might abort or take some
244 potentially destructive action. The default is your system realloc
246 <p>You could override this function in high-availability programs to, say,
247 free some memory if it cannot allocate memory, to use a special allocator,
248 or even to sleep a while and retry until some memory is available.</p>
249 <p>Example: Replace the libev allocator with one that waits a bit and then
252 persistent_realloc (void *ptr, size_t size)
256 void *newptr = realloc (ptr, size);
266 ev_set_allocator (persistent_realloc);
270 <dt>ev_set_syserr_cb (void (*cb)(const char *msg));</dt>
272 <p>Set the callback function to call on a retryable syscall error (such
273 as failed select, poll, epoll_wait). The message is a printable string
274 indicating the system call or subsystem causing the problem. If this
275 callback is set, then libev will expect it to remedy the sitution, no
276 matter what, when it returns. That is, libev will generally retry the
277 requested operation, or, if the condition doesn't go away, do bad stuff
279 <p>Example: This is basically the same thing that libev does internally, too.</p>
281 fatal_error (const char *msg)
288 ev_set_syserr_cb (fatal_error);
295 <h1 id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</h1>
296 <div id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP-2">
297 <p>An event loop is described by a <code>struct ev_loop *</code>. The library knows two
298 types of such loops, the <i>default</i> loop, which supports signals and child
299 events, and dynamically created loops which do not.</p>
300 <p>If you use threads, a common model is to run the default event loop
301 in your main thread (or in a separate thread) and for each thread you
302 create, you also create another event loop. Libev itself does no locking
303 whatsoever, so if you mix calls to the same event loop in different
304 threads, make sure you lock (this is usually a bad idea, though, even if
305 done correctly, because it's hideous and inefficient).</p>
307 <dt>struct ev_loop *ev_default_loop (unsigned int flags)</dt>
309 <p>This will initialise the default event loop if it hasn't been initialised
310 yet and return it. If the default loop could not be initialised, returns
311 false. If it already was initialised it simply returns it (and ignores the
312 flags. If that is troubling you, check <code>ev_backend ()</code> afterwards).</p>
313 <p>If you don't know what event loop to use, use the one returned from this
315 <p>The flags argument can be used to specify special behaviour or specific
316 backends to use, and is usually specified as <code>0</code> (or <code>EVFLAG_AUTO</code>).</p>
317 <p>The following flags are supported:</p>
320 <dt><code>EVFLAG_AUTO</code></dt>
322 <p>The default flags value. Use this if you have no clue (it's the right
323 thing, believe me).</p>
325 <dt><code>EVFLAG_NOENV</code></dt>
327 <p>If this flag bit is ored into the flag value (or the program runs setuid
328 or setgid) then libev will <i>not</i> look at the environment variable
329 <code>LIBEV_FLAGS</code>. Otherwise (the default), this environment variable will
330 override the flags completely if it is found in the environment. This is
331 useful to try out specific backends to test their performance, or to work
334 <dt><code>EVFLAG_FORKCHECK</code></dt>
336 <p>Instead of calling <code>ev_default_fork</code> or <code>ev_loop_fork</code> manually after
337 a fork, you can also make libev check for a fork in each iteration by
338 enabling this flag.</p>
339 <p>This works by calling <code>getpid ()</code> on every iteration of the loop,
340 and thus this might slow down your event loop if you do a lot of loop
341 iterations and little real work, but is usually not noticeable (on my
342 Linux system for example, <code>getpid</code> is actually a simple 5-insn sequence
343 without a syscall and thus <i>very</i> fast, but my Linux system also has
344 <code>pthread_atfork</code> which is even faster).</p>
345 <p>The big advantage of this flag is that you can forget about fork (and
346 forget about forgetting to tell libev about forking) when you use this
348 <p>This flag setting cannot be overriden or specified in the <code>LIBEV_FLAGS</code>
349 environment variable.</p>
351 <dt><code>EVBACKEND_SELECT</code> (value 1, portable select backend)</dt>
353 <p>This is your standard select(2) backend. Not <i>completely</i> standard, as
354 libev tries to roll its own fd_set with no limits on the number of fds,
355 but if that fails, expect a fairly low limit on the number of fds when
356 using this backend. It doesn't scale too well (O(highest_fd)), but its usually
357 the fastest backend for a low number of fds.</p>
359 <dt><code>EVBACKEND_POLL</code> (value 2, poll backend, available everywhere except on windows)</dt>
361 <p>And this is your standard poll(2) backend. It's more complicated than
362 select, but handles sparse fds better and has no artificial limit on the
363 number of fds you can use (except it will slow down considerably with a
364 lot of inactive fds). It scales similarly to select, i.e. O(total_fds).</p>
366 <dt><code>EVBACKEND_EPOLL</code> (value 4, Linux)</dt>
368 <p>For few fds, this backend is a bit little slower than poll and select,
369 but it scales phenomenally better. While poll and select usually scale like
370 O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
371 either O(1) or O(active_fds).</p>
372 <p>While stopping and starting an I/O watcher in the same iteration will
373 result in some caching, there is still a syscall per such incident
374 (because the fd could point to a different file description now), so its
375 best to avoid that. Also, dup()ed file descriptors might not work very
376 well if you register events for both fds.</p>
377 <p>Please note that epoll sometimes generates spurious notifications, so you
378 need to use non-blocking I/O or other means to avoid blocking when no data
379 (or space) is available.</p>
381 <dt><code>EVBACKEND_KQUEUE</code> (value 8, most BSD clones)</dt>
383 <p>Kqueue deserves special mention, as at the time of this writing, it
384 was broken on all BSDs except NetBSD (usually it doesn't work with
385 anything but sockets and pipes, except on Darwin, where of course its
386 completely useless). For this reason its not being "autodetected"
387 unless you explicitly specify it explicitly in the flags (i.e. using
388 <code>EVBACKEND_KQUEUE</code>).</p>
389 <p>It scales in the same way as the epoll backend, but the interface to the
390 kernel is more efficient (which says nothing about its actual speed, of
391 course). While starting and stopping an I/O watcher does not cause an
392 extra syscall as with epoll, it still adds up to four event changes per
393 incident, so its best to avoid that.</p>
395 <dt><code>EVBACKEND_DEVPOLL</code> (value 16, Solaris 8)</dt>
397 <p>This is not implemented yet (and might never be).</p>
399 <dt><code>EVBACKEND_PORT</code> (value 32, Solaris 10)</dt>
401 <p>This uses the Solaris 10 port mechanism. As with everything on Solaris,
402 it's really slow, but it still scales very well (O(active_fds)).</p>
403 <p>Please note that solaris ports can result in a lot of spurious
404 notifications, so you need to use non-blocking I/O or other means to avoid
405 blocking when no data (or space) is available.</p>
407 <dt><code>EVBACKEND_ALL</code></dt>
409 <p>Try all backends (even potentially broken ones that wouldn't be tried
410 with <code>EVFLAG_AUTO</code>). Since this is a mask, you can do stuff such as
411 <code>EVBACKEND_ALL & ~EVBACKEND_KQUEUE</code>.</p>
415 <p>If one or more of these are ored into the flags value, then only these
416 backends will be tried (in the reverse order as given here). If none are
417 specified, most compiled-in backend will be tried, usually in reverse
418 order of their flag values :)</p>
419 <p>The most typical usage is like this:</p>
420 <pre> if (!ev_default_loop (0))
421 fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
424 <p>Restrict libev to the select and poll backends, and do not allow
425 environment settings to be taken into account:</p>
426 <pre> ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
429 <p>Use whatever libev has to offer, but make sure that kqueue is used if
430 available (warning, breaks stuff, best use only with your own private
431 event loop and only if you know the OS supports your types of fds):</p>
432 <pre> ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
436 <dt>struct ev_loop *ev_loop_new (unsigned int flags)</dt>
438 <p>Similar to <code>ev_default_loop</code>, but always creates a new event loop that is
439 always distinct from the default loop. Unlike the default loop, it cannot
440 handle signal and child watchers, and attempts to do so will be greeted by
441 undefined behaviour (or a failed assertion if assertions are enabled).</p>
442 <p>Example: Try to create a event loop that uses epoll and nothing else.</p>
443 <pre> struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
445 fatal ("no epoll found here, maybe it hides under your chair");
449 <dt>ev_default_destroy ()</dt>
451 <p>Destroys the default loop again (frees all memory and kernel state
452 etc.). None of the active event watchers will be stopped in the normal
453 sense, so e.g. <code>ev_is_active</code> might still return true. It is your
454 responsibility to either stop all watchers cleanly yoursef <i>before</i>
455 calling this function, or cope with the fact afterwards (which is usually
456 the easiest thing, youc na just ignore the watchers and/or <code>free ()</code> them
459 <dt>ev_loop_destroy (loop)</dt>
461 <p>Like <code>ev_default_destroy</code>, but destroys an event loop created by an
462 earlier call to <code>ev_loop_new</code>.</p>
464 <dt>ev_default_fork ()</dt>
466 <p>This function reinitialises the kernel state for backends that have
467 one. Despite the name, you can call it anytime, but it makes most sense
468 after forking, in either the parent or child process (or both, but that
469 again makes little sense).</p>
470 <p>You <i>must</i> call this function in the child process after forking if and
471 only if you want to use the event library in both processes. If you just
472 fork+exec, you don't have to call it.</p>
473 <p>The function itself is quite fast and it's usually not a problem to call
474 it just in case after a fork. To make this easy, the function will fit in
475 quite nicely into a call to <code>pthread_atfork</code>:</p>
476 <pre> pthread_atfork (0, 0, ev_default_fork);
479 <p>At the moment, <code>EVBACKEND_SELECT</code> and <code>EVBACKEND_POLL</code> are safe to use
480 without calling this function, so if you force one of those backends you
481 do not need to care.</p>
483 <dt>ev_loop_fork (loop)</dt>
485 <p>Like <code>ev_default_fork</code>, but acts on an event loop created by
486 <code>ev_loop_new</code>. Yes, you have to call this on every allocated event loop
487 after fork, and how you do this is entirely your own problem.</p>
489 <dt>unsigned int ev_loop_count (loop)</dt>
491 <p>Returns the count of loop iterations for the loop, which is identical to
492 the number of times libev did poll for new events. It starts at <code>0</code> and
493 happily wraps around with enough iterations.</p>
494 <p>This value can sometimes be useful as a generation counter of sorts (it
495 "ticks" the number of loop iterations), as it roughly corresponds with
496 <code>ev_prepare</code> and <code>ev_check</code> calls.</p>
498 <dt>unsigned int ev_backend (loop)</dt>
500 <p>Returns one of the <code>EVBACKEND_*</code> flags indicating the event backend in
503 <dt>ev_tstamp ev_now (loop)</dt>
505 <p>Returns the current "event loop time", which is the time the event loop
506 received events and started processing them. This timestamp does not
507 change as long as callbacks are being processed, and this is also the base
508 time used for relative timers. You can treat it as the timestamp of the
509 event occuring (or more correctly, libev finding out about it).</p>
511 <dt>ev_loop (loop, int flags)</dt>
513 <p>Finally, this is it, the event handler. This function usually is called
514 after you initialised all your watchers and you want to start handling
516 <p>If the flags argument is specified as <code>0</code>, it will not return until
517 either no event watchers are active anymore or <code>ev_unloop</code> was called.</p>
518 <p>Please note that an explicit <code>ev_unloop</code> is usually better than
519 relying on all watchers to be stopped when deciding when a program has
520 finished (especially in interactive programs), but having a program that
521 automatically loops as long as it has to and no longer by virtue of
522 relying on its watchers stopping correctly is a thing of beauty.</p>
523 <p>A flags value of <code>EVLOOP_NONBLOCK</code> will look for new events, will handle
524 those events and any outstanding ones, but will not block your process in
525 case there are no events and will return after one iteration of the loop.</p>
526 <p>A flags value of <code>EVLOOP_ONESHOT</code> will look for new events (waiting if
527 neccessary) and will handle those and any outstanding ones. It will block
528 your process until at least one new event arrives, and will return after
529 one iteration of the loop. This is useful if you are waiting for some
530 external event in conjunction with something not expressible using other
531 libev watchers. However, a pair of <code>ev_prepare</code>/<code>ev_check</code> watchers is
532 usually a better approach for this kind of thing.</p>
533 <p>Here are the gory details of what <code>ev_loop</code> does:</p>
534 <pre> - Before the first iteration, call any pending watchers.
535 * If there are no active watchers (reference count is zero), return.
536 - Queue all prepare watchers and then call all outstanding watchers.
537 - If we have been forked, recreate the kernel state.
538 - Update the kernel state with all outstanding changes.
539 - Update the "event loop time".
540 - Calculate for how long to block.
541 - Block the process, waiting for any events.
542 - Queue all outstanding I/O (fd) events.
543 - Update the "event loop time" and do time jump handling.
544 - Queue all outstanding timers.
545 - Queue all outstanding periodics.
546 - If no events are pending now, queue all idle watchers.
547 - Queue all check watchers.
548 - Call all queued watchers in reverse order (i.e. check watchers first).
549 Signals and child watchers are implemented as I/O watchers, and will
550 be handled here by queueing them when their watcher gets executed.
551 - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
552 were used, return, otherwise continue with step *.
555 <p>Example: Queue some jobs and then loop until no events are outsanding
557 <pre> ... queue jobs here, make sure they register event watchers as long
558 ... as they still have work to do (even an idle watcher will do..)
559 ev_loop (my_loop, 0);
564 <dt>ev_unloop (loop, how)</dt>
566 <p>Can be used to make a call to <code>ev_loop</code> return early (but only after it
567 has processed all outstanding events). The <code>how</code> argument must be either
568 <code>EVUNLOOP_ONE</code>, which will make the innermost <code>ev_loop</code> call return, or
569 <code>EVUNLOOP_ALL</code>, which will make all nested <code>ev_loop</code> calls return.</p>
571 <dt>ev_ref (loop)</dt>
572 <dt>ev_unref (loop)</dt>
574 <p>Ref/unref can be used to add or remove a reference count on the event
575 loop: Every watcher keeps one reference, and as long as the reference
576 count is nonzero, <code>ev_loop</code> will not return on its own. If you have
577 a watcher you never unregister that should not keep <code>ev_loop</code> from
578 returning, ev_unref() after starting, and ev_ref() before stopping it. For
579 example, libev itself uses this for its internal signal pipe: It is not
580 visible to the libev user and should not keep <code>ev_loop</code> from exiting if
581 no event watchers registered by it are active. It is also an excellent
582 way to do this for generic recurring timers or from within third-party
583 libraries. Just remember to <i>unref after start</i> and <i>ref before stop</i>.</p>
584 <p>Example: Create a signal watcher, but keep it from keeping <code>ev_loop</code>
585 running when nothing else is active.</p>
586 <pre> struct ev_signal exitsig;
587 ev_signal_init (&exitsig, sig_cb, SIGINT);
588 ev_signal_start (loop, &exitsig);
592 <p>Example: For some weird reason, unregister the above signal handler again.</p>
594 ev_signal_stop (loop, &exitsig);
605 <h1 id="ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</h1>
606 <div id="ANATOMY_OF_A_WATCHER_CONTENT">
607 <p>A watcher is a structure that you create and register to record your
608 interest in some event. For instance, if you want to wait for STDIN to
609 become readable, you would create an <code>ev_io</code> watcher for that:</p>
610 <pre> static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
613 ev_unloop (loop, EVUNLOOP_ALL);
616 struct ev_loop *loop = ev_default_loop (0);
617 struct ev_io stdin_watcher;
618 ev_init (&stdin_watcher, my_cb);
619 ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
620 ev_io_start (loop, &stdin_watcher);
624 <p>As you can see, you are responsible for allocating the memory for your
625 watcher structures (and it is usually a bad idea to do this on the stack,
626 although this can sometimes be quite valid).</p>
627 <p>Each watcher structure must be initialised by a call to <code>ev_init
628 (watcher *, callback)</code>, which expects a callback to be provided. This
629 callback gets invoked each time the event occurs (or, in the case of io
630 watchers, each time the event loop detects that the file descriptor given
631 is readable and/or writable).</p>
632 <p>Each watcher type has its own <code>ev_<type>_set (watcher *, ...)</code> macro
633 with arguments specific to this watcher type. There is also a macro
634 to combine initialisation and setting in one call: <code>ev_<type>_init
635 (watcher *, callback, ...)</code>.</p>
636 <p>To make the watcher actually watch out for events, you have to start it
637 with a watcher-specific start function (<code>ev_<type>_start (loop, watcher
638 *)</code>), and you can stop watching for events at any time by calling the
639 corresponding stop function (<code>ev_<type>_stop (loop, watcher *)</code>.</p>
640 <p>As long as your watcher is active (has been started but not stopped) you
641 must not touch the values stored in it. Most specifically you must never
642 reinitialise it or call its <code>set</code> macro.</p>
643 <p>Each and every callback receives the event loop pointer as first, the
644 registered watcher structure as second, and a bitset of received events as
646 <p>The received events usually include a single bit per event type received
647 (you can receive multiple events at the same time). The possible bit masks
650 <dt><code>EV_READ</code></dt>
651 <dt><code>EV_WRITE</code></dt>
653 <p>The file descriptor in the <code>ev_io</code> watcher has become readable and/or
656 <dt><code>EV_TIMEOUT</code></dt>
658 <p>The <code>ev_timer</code> watcher has timed out.</p>
660 <dt><code>EV_PERIODIC</code></dt>
662 <p>The <code>ev_periodic</code> watcher has timed out.</p>
664 <dt><code>EV_SIGNAL</code></dt>
666 <p>The signal specified in the <code>ev_signal</code> watcher has been received by a thread.</p>
668 <dt><code>EV_CHILD</code></dt>
670 <p>The pid specified in the <code>ev_child</code> watcher has received a status change.</p>
672 <dt><code>EV_STAT</code></dt>
674 <p>The path specified in the <code>ev_stat</code> watcher changed its attributes somehow.</p>
676 <dt><code>EV_IDLE</code></dt>
678 <p>The <code>ev_idle</code> watcher has determined that you have nothing better to do.</p>
680 <dt><code>EV_PREPARE</code></dt>
681 <dt><code>EV_CHECK</code></dt>
683 <p>All <code>ev_prepare</code> watchers are invoked just <i>before</i> <code>ev_loop</code> starts
684 to gather new events, and all <code>ev_check</code> watchers are invoked just after
685 <code>ev_loop</code> has gathered them, but before it invokes any callbacks for any
686 received events. Callbacks of both watcher types can start and stop as
687 many watchers as they want, and all of them will be taken into account
688 (for example, a <code>ev_prepare</code> watcher might start an idle watcher to keep
689 <code>ev_loop</code> from blocking).</p>
691 <dt><code>EV_EMBED</code></dt>
693 <p>The embedded event loop specified in the <code>ev_embed</code> watcher needs attention.</p>
695 <dt><code>EV_FORK</code></dt>
697 <p>The event loop has been resumed in the child process after fork (see
698 <code>ev_fork</code>).</p>
700 <dt><code>EV_ERROR</code></dt>
702 <p>An unspecified error has occured, the watcher has been stopped. This might
703 happen because the watcher could not be properly started because libev
704 ran out of memory, a file descriptor was found to be closed or any other
705 problem. You best act on it by reporting the problem and somehow coping
706 with the watcher being stopped.</p>
707 <p>Libev will usually signal a few "dummy" events together with an error,
708 for example it might indicate that a fd is readable or writable, and if
709 your callbacks is well-written it can just attempt the operation and cope
710 with the error from read() or write(). This will not work in multithreaded
711 programs, though, so beware.</p>
716 <h2 id="GENERIC_WATCHER_FUNCTIONS">GENERIC WATCHER FUNCTIONS</h2>
717 <div id="GENERIC_WATCHER_FUNCTIONS_CONTENT">
718 <p>In the following description, <code>TYPE</code> stands for the watcher type,
719 e.g. <code>timer</code> for <code>ev_timer</code> watchers and <code>io</code> for <code>ev_io</code> watchers.</p>
721 <dt><code>ev_init</code> (ev_TYPE *watcher, callback)</dt>
723 <p>This macro initialises the generic portion of a watcher. The contents
724 of the watcher object can be arbitrary (so <code>malloc</code> will do). Only
725 the generic parts of the watcher are initialised, you <i>need</i> to call
726 the type-specific <code>ev_TYPE_set</code> macro afterwards to initialise the
727 type-specific parts. For each type there is also a <code>ev_TYPE_init</code> macro
728 which rolls both calls into one.</p>
729 <p>You can reinitialise a watcher at any time as long as it has been stopped
730 (or never started) and there are no pending events outstanding.</p>
731 <p>The callback is always of type <code>void (*)(ev_loop *loop, ev_TYPE *watcher,
732 int revents)</code>.</p>
734 <dt><code>ev_TYPE_set</code> (ev_TYPE *, [args])</dt>
736 <p>This macro initialises the type-specific parts of a watcher. You need to
737 call <code>ev_init</code> at least once before you call this macro, but you can
738 call <code>ev_TYPE_set</code> any number of times. You must not, however, call this
739 macro on a watcher that is active (it can be pending, however, which is a
740 difference to the <code>ev_init</code> macro).</p>
741 <p>Although some watcher types do not have type-specific arguments
742 (e.g. <code>ev_prepare</code>) you still need to call its <code>set</code> macro.</p>
744 <dt><code>ev_TYPE_init</code> (ev_TYPE *watcher, callback, [args])</dt>
746 <p>This convinience macro rolls both <code>ev_init</code> and <code>ev_TYPE_set</code> macro
747 calls into a single call. This is the most convinient method to initialise
748 a watcher. The same limitations apply, of course.</p>
750 <dt><code>ev_TYPE_start</code> (loop *, ev_TYPE *watcher)</dt>
752 <p>Starts (activates) the given watcher. Only active watchers will receive
753 events. If the watcher is already active nothing will happen.</p>
755 <dt><code>ev_TYPE_stop</code> (loop *, ev_TYPE *watcher)</dt>
757 <p>Stops the given watcher again (if active) and clears the pending
758 status. It is possible that stopped watchers are pending (for example,
759 non-repeating timers are being stopped when they become pending), but
760 <code>ev_TYPE_stop</code> ensures that the watcher is neither active nor pending. If
761 you want to free or reuse the memory used by the watcher it is therefore a
762 good idea to always call its <code>ev_TYPE_stop</code> function.</p>
764 <dt>bool ev_is_active (ev_TYPE *watcher)</dt>
766 <p>Returns a true value iff the watcher is active (i.e. it has been started
767 and not yet been stopped). As long as a watcher is active you must not modify
770 <dt>bool ev_is_pending (ev_TYPE *watcher)</dt>
772 <p>Returns a true value iff the watcher is pending, (i.e. it has outstanding
773 events but its callback has not yet been invoked). As long as a watcher
774 is pending (but not active) you must not call an init function on it (but
775 <code>ev_TYPE_set</code> is safe), you must not change its priority, and you must
776 make sure the watcher is available to libev (e.g. you cannot <code>free ()</code>
779 <dt>callback ev_cb (ev_TYPE *watcher)</dt>
781 <p>Returns the callback currently set on the watcher.</p>
783 <dt>ev_cb_set (ev_TYPE *watcher, callback)</dt>
785 <p>Change the callback. You can change the callback at virtually any time
786 (modulo threads).</p>
788 <dt>ev_set_priority (ev_TYPE *watcher, priority)</dt>
789 <dt>int ev_priority (ev_TYPE *watcher)</dt>
791 <p>Set and query the priority of the watcher. The priority is a small
792 integer between <code>EV_MAXPRI</code> (default: <code>2</code>) and <code>EV_MINPRI</code>
793 (default: <code>-2</code>). Pending watchers with higher priority will be invoked
794 before watchers with lower priority, but priority will not keep watchers
795 from being executed (except for <code>ev_idle</code> watchers).</p>
796 <p>This means that priorities are <i>only</i> used for ordering callback
797 invocation after new events have been received. This is useful, for
798 example, to reduce latency after idling, or more often, to bind two
799 watchers on the same event and make sure one is called first.</p>
800 <p>If you need to suppress invocation when higher priority events are pending
801 you need to look at <code>ev_idle</code> watchers, which provide this functionality.</p>
802 <p>You <i>must not</i> change the priority of a watcher as long as it is active or
804 <p>The default priority used by watchers when no priority has been set is
805 always <code>0</code>, which is supposed to not be too high and not be too low :).</p>
806 <p>Setting a priority outside the range of <code>EV_MINPRI</code> to <code>EV_MAXPRI</code> is
807 fine, as long as you do not mind that the priority value you query might
808 or might not have been adjusted to be within valid range.</p>
810 <dt>ev_invoke (loop, ev_TYPE *watcher, int revents)</dt>
812 <p>Invoke the <code>watcher</code> with the given <code>loop</code> and <code>revents</code>. Neither
813 <code>loop</code> nor <code>revents</code> need to be valid as long as the watcher callback
814 can deal with that fact.</p>
816 <dt>int ev_clear_pending (loop, ev_TYPE *watcher)</dt>
818 <p>If the watcher is pending, this function returns clears its pending status
819 and returns its <code>revents</code> bitset (as if its callback was invoked). If the
820 watcher isn't pending it does nothing and returns <code>0</code>.</p>
829 <h2 id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</h2>
830 <div id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH-2">
831 <p>Each watcher has, by default, a member <code>void *data</code> that you can change
832 and read at any time, libev will completely ignore it. This can be used
833 to associate arbitrary data with your watcher. If you need more data and
834 don't want to allocate memory and store a pointer to it in that data
835 member, you can also "subclass" the watcher type and provide your own
842 struct whatever *mostinteresting;
846 <p>And since your callback will be called with a pointer to the watcher, you
847 can cast it back to your own type:</p>
848 <pre> static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
850 struct my_io *w = (struct my_io *)w_;
855 <p>More interesting and less C-conformant ways of casting your callback type
856 instead have been omitted.</p>
857 <p>Another common scenario is having some data structure with multiple
859 <pre> struct my_biggy
867 <p>In this case getting the pointer to <code>my_biggy</code> is a bit more complicated,
868 you need to use <code>offsetof</code>:</p>
869 <pre> #include <stddef.h>
872 t1_cb (EV_P_ struct ev_timer *w, int revents)
874 struct my_biggy big = (struct my_biggy *
875 (((char *)w) - offsetof (struct my_biggy, t1));
879 t2_cb (EV_P_ struct ev_timer *w, int revents)
881 struct my_biggy big = (struct my_biggy *
882 (((char *)w) - offsetof (struct my_biggy, t2));
891 <h1 id="WATCHER_TYPES">WATCHER TYPES</h1>
892 <div id="WATCHER_TYPES_CONTENT">
893 <p>This section describes each watcher in detail, but will not repeat
894 information given in the last section. Any initialisation/set macros,
895 functions and members specific to the watcher type are explained.</p>
896 <p>Members are additionally marked with either <i>[read-only]</i>, meaning that,
897 while the watcher is active, you can look at the member and expect some
898 sensible content, but you must not modify it (you can modify it while the
899 watcher is stopped to your hearts content), or <i>[read-write]</i>, which
900 means you can expect it to have some sensible content while the watcher
901 is active, but you can also modify it. Modifying it may not do something
902 sensible or take immediate effect (or do anything at all), but libev will
903 not crash or malfunction in any way.</p>
910 <h2 id="code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable?</h2>
911 <div id="code_ev_io_code_is_this_file_descrip-2">
912 <p>I/O watchers check whether a file descriptor is readable or writable
913 in each iteration of the event loop, or, more precisely, when reading
914 would not block the process and writing would at least be able to write
915 some data. This behaviour is called level-triggering because you keep
916 receiving events as long as the condition persists. Remember you can stop
917 the watcher if you don't want to act on the event and neither want to
918 receive future events.</p>
919 <p>In general you can register as many read and/or write event watchers per
920 fd as you want (as long as you don't confuse yourself). Setting all file
921 descriptors to non-blocking mode is also usually a good idea (but not
922 required if you know what you are doing).</p>
923 <p>You have to be careful with dup'ed file descriptors, though. Some backends
924 (the linux epoll backend is a notable example) cannot handle dup'ed file
925 descriptors correctly if you register interest in two or more fds pointing
926 to the same underlying file/socket/etc. description (that is, they share
927 the same underlying "file open").</p>
928 <p>If you must do this, then force the use of a known-to-be-good backend
929 (at the time of this writing, this includes only <code>EVBACKEND_SELECT</code> and
930 <code>EVBACKEND_POLL</code>).</p>
931 <p>Another thing you have to watch out for is that it is quite easy to
932 receive "spurious" readyness notifications, that is your callback might
933 be called with <code>EV_READ</code> but a subsequent <code>read</code>(2) will actually block
934 because there is no data. Not only are some backends known to create a
935 lot of those (for example solaris ports), it is very easy to get into
936 this situation even with a relatively standard program structure. Thus
937 it is best to always use non-blocking I/O: An extra <code>read</code>(2) returning
938 <code>EAGAIN</code> is far preferable to a program hanging until some data arrives.</p>
939 <p>If you cannot run the fd in non-blocking mode (for example you should not
940 play around with an Xlib connection), then you have to seperately re-test
941 whether a file descriptor is really ready with a known-to-be good interface
942 such as poll (fortunately in our Xlib example, Xlib already does this on
943 its own, so its quite safe to use).</p>
945 <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt>
946 <dt>ev_io_set (ev_io *, int fd, int events)</dt>
948 <p>Configures an <code>ev_io</code> watcher. The <code>fd</code> is the file descriptor to
949 rceeive events for and events is either <code>EV_READ</code>, <code>EV_WRITE</code> or
950 <code>EV_READ | EV_WRITE</code> to receive the given events.</p>
952 <dt>int fd [read-only]</dt>
954 <p>The file descriptor being watched.</p>
956 <dt>int events [read-only]</dt>
958 <p>The events being watched.</p>
961 <p>Example: Call <code>stdin_readable_cb</code> when STDIN_FILENO has become, well
962 readable, but only once. Since it is likely line-buffered, you could
963 attempt to read a whole line in the callback.</p>
965 stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
967 ev_io_stop (loop, w);
968 .. read from stdin here (or from w->fd) and haqndle any I/O errors
972 struct ev_loop *loop = ev_default_init (0);
973 struct ev_io stdin_readable;
974 ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
975 ev_io_start (loop, &stdin_readable);
984 <h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally repeating timeouts</h2>
985 <div id="code_ev_timer_code_relative_and_opti-2">
986 <p>Timer watchers are simple relative timers that generate an event after a
987 given time, and optionally repeating in regular intervals after that.</p>
988 <p>The timers are based on real time, that is, if you register an event that
989 times out after an hour and you reset your system clock to last years
990 time, it will still time out after (roughly) and hour. "Roughly" because
991 detecting time jumps is hard, and some inaccuracies are unavoidable (the
992 monotonic clock option helps a lot here).</p>
993 <p>The relative timeouts are calculated relative to the <code>ev_now ()</code>
994 time. This is usually the right thing as this timestamp refers to the time
995 of the event triggering whatever timeout you are modifying/starting. If
996 you suspect event processing to be delayed and you <i>need</i> to base the timeout
997 on the current time, use something like this to adjust for this:</p>
998 <pre> ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1001 <p>The callback is guarenteed to be invoked only when its timeout has passed,
1002 but if multiple timers become ready during the same loop iteration then
1003 order of execution is undefined.</p>
1005 <dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt>
1006 <dt>ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)</dt>
1008 <p>Configure the timer to trigger after <code>after</code> seconds. If <code>repeat</code> is
1009 <code>0.</code>, then it will automatically be stopped. If it is positive, then the
1010 timer will automatically be configured to trigger again <code>repeat</code> seconds
1011 later, again, and again, until stopped manually.</p>
1012 <p>The timer itself will do a best-effort at avoiding drift, that is, if you
1013 configure a timer to trigger every 10 seconds, then it will trigger at
1014 exactly 10 second intervals. If, however, your program cannot keep up with
1015 the timer (because it takes longer than those 10 seconds to do stuff) the
1016 timer will not fire more than once per event loop iteration.</p>
1018 <dt>ev_timer_again (loop)</dt>
1020 <p>This will act as if the timer timed out and restart it again if it is
1021 repeating. The exact semantics are:</p>
1022 <p>If the timer is pending, its pending status is cleared.</p>
1023 <p>If the timer is started but nonrepeating, stop it (as if it timed out).</p>
1024 <p>If the timer is repeating, either start it if necessary (with the
1025 <code>repeat</code> value), or reset the running timer to the <code>repeat</code> value.</p>
1026 <p>This sounds a bit complicated, but here is a useful and typical
1027 example: Imagine you have a tcp connection and you want a so-called idle
1028 timeout, that is, you want to be called when there have been, say, 60
1029 seconds of inactivity on the socket. The easiest way to do this is to
1030 configure an <code>ev_timer</code> with a <code>repeat</code> value of <code>60</code> and then call
1031 <code>ev_timer_again</code> each time you successfully read or write some data. If
1032 you go into an idle state where you do not expect data to travel on the
1033 socket, you can <code>ev_timer_stop</code> the timer, and <code>ev_timer_again</code> will
1034 automatically restart it if need be.</p>
1035 <p>That means you can ignore the <code>after</code> value and <code>ev_timer_start</code>
1036 altogether and only ever use the <code>repeat</code> value and <code>ev_timer_again</code>:</p>
1037 <pre> ev_timer_init (timer, callback, 0., 5.);
1038 ev_timer_again (loop, timer);
1040 timer->again = 17.;
1041 ev_timer_again (loop, timer);
1043 timer->again = 10.;
1044 ev_timer_again (loop, timer);
1047 <p>This is more slightly efficient then stopping/starting the timer each time
1048 you want to modify its timeout value.</p>
1050 <dt>ev_tstamp repeat [read-write]</dt>
1052 <p>The current <code>repeat</code> value. Will be used each time the watcher times out
1053 or <code>ev_timer_again</code> is called and determines the next timeout (if any),
1054 which is also when any modifications are taken into account.</p>
1057 <p>Example: Create a timer that fires after 60 seconds.</p>
1059 one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1061 .. one minute over, w is actually stopped right here
1064 struct ev_timer mytimer;
1065 ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1066 ev_timer_start (loop, &mytimer);
1069 <p>Example: Create a timeout timer that times out after 10 seconds of
1072 timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1074 .. ten seconds without any activity
1077 struct ev_timer mytimer;
1078 ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1079 ev_timer_again (&mytimer); /* start timer */
1082 // and in some piece of code that gets executed on any "activity":
1083 // reset the timeout to start ticking again at 10 seconds
1084 ev_timer_again (&mytimer);
1092 <h2 id="code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron?</h2>
1093 <div id="code_ev_periodic_code_to_cron_or_not-2">
1094 <p>Periodic watchers are also timers of a kind, but they are very versatile
1095 (and unfortunately a bit complex).</p>
1096 <p>Unlike <code>ev_timer</code>'s, they are not based on real time (or relative time)
1097 but on wallclock time (absolute time). You can tell a periodic watcher
1098 to trigger "at" some specific point in time. For example, if you tell a
1099 periodic watcher to trigger in 10 seconds (by specifiying e.g. <code>ev_now ()
1100 + 10.</code>) and then reset your system clock to the last year, then it will
1101 take a year to trigger the event (unlike an <code>ev_timer</code>, which would trigger
1102 roughly 10 seconds later and of course not if you reset your system time
1104 <p>They can also be used to implement vastly more complex timers, such as
1105 triggering an event on eahc midnight, local time.</p>
1106 <p>As with timers, the callback is guarenteed to be invoked only when the
1107 time (<code>at</code>) has been passed, but if multiple periodic timers become ready
1108 during the same loop iteration then order of execution is undefined.</p>
1110 <dt>ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)</dt>
1111 <dt>ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)</dt>
1113 <p>Lots of arguments, lets sort it out... There are basically three modes of
1114 operation, and we will explain them from simplest to complex:</p>
1117 <dt>* absolute timer (interval = reschedule_cb = 0)</dt>
1119 <p>In this configuration the watcher triggers an event at the wallclock time
1120 <code>at</code> and doesn't repeat. It will not adjust when a time jump occurs,
1121 that is, if it is to be run at January 1st 2011 then it will run when the
1122 system time reaches or surpasses this time.</p>
1124 <dt>* non-repeating interval timer (interval > 0, reschedule_cb = 0)</dt>
1126 <p>In this mode the watcher will always be scheduled to time out at the next
1127 <code>at + N * interval</code> time (for some integer N) and then repeat, regardless
1128 of any time jumps.</p>
1129 <p>This can be used to create timers that do not drift with respect to system
1131 <pre> ev_periodic_set (&periodic, 0., 3600., 0);
1134 <p>This doesn't mean there will always be 3600 seconds in between triggers,
1135 but only that the the callback will be called when the system time shows a
1136 full hour (UTC), or more correctly, when the system time is evenly divisible
1138 <p>Another way to think about it (for the mathematically inclined) is that
1139 <code>ev_periodic</code> will try to run the callback in this mode at the next possible
1140 time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p>
1142 <dt>* manual reschedule mode (reschedule_cb = callback)</dt>
1144 <p>In this mode the values for <code>interval</code> and <code>at</code> are both being
1145 ignored. Instead, each time the periodic watcher gets scheduled, the
1146 reschedule callback will be called with the watcher as first, and the
1147 current time as second argument.</p>
1148 <p>NOTE: <i>This callback MUST NOT stop or destroy any periodic watcher,
1149 ever, or make any event loop modifications</i>. If you need to stop it,
1150 return <code>now + 1e30</code> (or so, fudge fudge) and stop it afterwards (e.g. by
1151 starting a prepare watcher).</p>
1152 <p>Its prototype is <code>ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
1153 ev_tstamp now)</code>, e.g.:</p>
1154 <pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1160 <p>It must return the next time to trigger, based on the passed time value
1161 (that is, the lowest time value larger than to the second argument). It
1162 will usually be called just before the callback will be triggered, but
1163 might be called at other times, too.</p>
1164 <p>NOTE: <i>This callback must always return a time that is later than the
1165 passed <code>now</code> value</i>. Not even <code>now</code> itself will do, it <i>must</i> be larger.</p>
1166 <p>This can be used to create very complex timers, such as a timer that
1167 triggers on each midnight, local time. To do this, you would calculate the
1168 next midnight after <code>now</code> and return the timestamp value for this. How
1169 you do this is, again, up to you (but it is not trivial, which is the main
1170 reason I omitted it as an example).</p>
1175 <dt>ev_periodic_again (loop, ev_periodic *)</dt>
1177 <p>Simply stops and restarts the periodic watcher again. This is only useful
1178 when you changed some parameters or the reschedule callback would return
1179 a different time than the last time it was called (e.g. in a crond like
1180 program when the crontabs have changed).</p>
1182 <dt>ev_tstamp interval [read-write]</dt>
1184 <p>The current interval value. Can be modified any time, but changes only
1185 take effect when the periodic timer fires or <code>ev_periodic_again</code> is being
1188 <dt>ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]</dt>
1190 <p>The current reschedule callback, or <code>0</code>, if this functionality is
1191 switched off. Can be changed any time, but changes only take effect when
1192 the periodic timer fires or <code>ev_periodic_again</code> is being called.</p>
1195 <p>Example: Call a callback every hour, or, more precisely, whenever the
1196 system clock is divisible by 3600. The callback invocation times have
1197 potentially a lot of jittering, but good long-term stability.</p>
1199 clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1201 ... its now a full hour (UTC, or TAI or whatever your clock follows)
1204 struct ev_periodic hourly_tick;
1205 ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1206 ev_periodic_start (loop, &hourly_tick);
1209 <p>Example: The same as above, but use a reschedule callback to do it:</p>
1210 <pre> #include <math.h>
1213 my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
1215 return fmod (now, 3600.) + 3600.;
1218 ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1221 <p>Example: Call a callback every hour, starting now:</p>
1222 <pre> struct ev_periodic hourly_tick;
1223 ev_periodic_init (&hourly_tick, clock_cb,
1224 fmod (ev_now (loop), 3600.), 3600., 0);
1225 ev_periodic_start (loop, &hourly_tick);
1233 <h2 id="code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled!</h2>
1234 <div id="code_ev_signal_code_signal_me_when_a-2">
1235 <p>Signal watchers will trigger an event when the process receives a specific
1236 signal one or more times. Even though signals are very asynchronous, libev
1237 will try it's best to deliver signals synchronously, i.e. as part of the
1238 normal event processing, like any other event.</p>
1239 <p>You can configure as many watchers as you like per signal. Only when the
1240 first watcher gets started will libev actually register a signal watcher
1241 with the kernel (thus it coexists with your own signal handlers as long
1242 as you don't register any with libev). Similarly, when the last signal
1243 watcher for a signal is stopped libev will reset the signal handler to
1244 SIG_DFL (regardless of what it was set to before).</p>
1246 <dt>ev_signal_init (ev_signal *, callback, int signum)</dt>
1247 <dt>ev_signal_set (ev_signal *, int signum)</dt>
1249 <p>Configures the watcher to trigger on the given signal number (usually one
1250 of the <code>SIGxxx</code> constants).</p>
1252 <dt>int signum [read-only]</dt>
1254 <p>The signal the watcher watches out for.</p>
1263 <h2 id="code_ev_child_code_watch_out_for_pro"><code>ev_child</code> - watch out for process status changes</h2>
1264 <div id="code_ev_child_code_watch_out_for_pro-2">
1265 <p>Child watchers trigger when your process receives a SIGCHLD in response to
1266 some child status changes (most typically when a child of yours dies).</p>
1268 <dt>ev_child_init (ev_child *, callback, int pid)</dt>
1269 <dt>ev_child_set (ev_child *, int pid)</dt>
1271 <p>Configures the watcher to wait for status changes of process <code>pid</code> (or
1272 <i>any</i> process if <code>pid</code> is specified as <code>0</code>). The callback can look
1273 at the <code>rstatus</code> member of the <code>ev_child</code> watcher structure to see
1274 the status word (use the macros from <code>sys/wait.h</code> and see your systems
1275 <code>waitpid</code> documentation). The <code>rpid</code> member contains the pid of the
1276 process causing the status change.</p>
1278 <dt>int pid [read-only]</dt>
1280 <p>The process id this watcher watches out for, or <code>0</code>, meaning any process id.</p>
1282 <dt>int rpid [read-write]</dt>
1284 <p>The process id that detected a status change.</p>
1286 <dt>int rstatus [read-write]</dt>
1288 <p>The process exit/trace status caused by <code>rpid</code> (see your systems
1289 <code>waitpid</code> and <code>sys/wait.h</code> documentation for details).</p>
1292 <p>Example: Try to exit cleanly on SIGINT and SIGTERM.</p>
1294 sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1296 ev_unloop (loop, EVUNLOOP_ALL);
1299 struct ev_signal signal_watcher;
1300 ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1301 ev_signal_start (loop, &sigint_cb);
1309 <h2 id="code_ev_stat_code_did_the_file_attri"><code>ev_stat</code> - did the file attributes just change?</h2>
1310 <div id="code_ev_stat_code_did_the_file_attri-2">
1311 <p>This watches a filesystem path for attribute changes. That is, it calls
1312 <code>stat</code> regularly (or when the OS says it changed) and sees if it changed
1313 compared to the last time, invoking the callback if it did.</p>
1314 <p>The path does not need to exist: changing from "path exists" to "path does
1315 not exist" is a status change like any other. The condition "path does
1316 not exist" is signified by the <code>st_nlink</code> field being zero (which is
1317 otherwise always forced to be at least one) and all the other fields of
1318 the stat buffer having unspecified contents.</p>
1319 <p>The path <i>should</i> be absolute and <i>must not</i> end in a slash. If it is
1320 relative and your working directory changes, the behaviour is undefined.</p>
1321 <p>Since there is no standard to do this, the portable implementation simply
1322 calls <code>stat (2)</code> regularly on the path to see if it changed somehow. You
1323 can specify a recommended polling interval for this case. If you specify
1324 a polling interval of <code>0</code> (highly recommended!) then a <i>suitable,
1325 unspecified default</i> value will be used (which you can expect to be around
1326 five seconds, although this might change dynamically). Libev will also
1327 impose a minimum interval which is currently around <code>0.1</code>, but thats
1328 usually overkill.</p>
1329 <p>This watcher type is not meant for massive numbers of stat watchers,
1330 as even with OS-supported change notifications, this can be
1331 resource-intensive.</p>
1332 <p>At the time of this writing, only the Linux inotify interface is
1333 implemented (implementing kqueue support is left as an exercise for the
1334 reader). Inotify will be used to give hints only and should not change the
1335 semantics of <code>ev_stat</code> watchers, which means that libev sometimes needs
1336 to fall back to regular polling again even with inotify, but changes are
1337 usually detected immediately, and if the file exists there will be no
1340 <dt>ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)</dt>
1341 <dt>ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)</dt>
1343 <p>Configures the watcher to wait for status changes of the given
1344 <code>path</code>. The <code>interval</code> is a hint on how quickly a change is expected to
1345 be detected and should normally be specified as <code>0</code> to let libev choose
1346 a suitable value. The memory pointed to by <code>path</code> must point to the same
1347 path for as long as the watcher is active.</p>
1348 <p>The callback will be receive <code>EV_STAT</code> when a change was detected,
1349 relative to the attributes at the time the watcher was started (or the
1350 last change was detected).</p>
1352 <dt>ev_stat_stat (ev_stat *)</dt>
1354 <p>Updates the stat buffer immediately with new values. If you change the
1355 watched path in your callback, you could call this fucntion to avoid
1356 detecting this change (while introducing a race condition). Can also be
1357 useful simply to find out the new values.</p>
1359 <dt>ev_statdata attr [read-only]</dt>
1361 <p>The most-recently detected attributes of the file. Although the type is of
1362 <code>ev_statdata</code>, this is usually the (or one of the) <code>struct stat</code> types
1363 suitable for your system. If the <code>st_nlink</code> member is <code>0</code>, then there
1364 was some error while <code>stat</code>ing the file.</p>
1366 <dt>ev_statdata prev [read-only]</dt>
1368 <p>The previous attributes of the file. The callback gets invoked whenever
1369 <code>prev</code> != <code>attr</code>.</p>
1371 <dt>ev_tstamp interval [read-only]</dt>
1373 <p>The specified interval.</p>
1375 <dt>const char *path [read-only]</dt>
1377 <p>The filesystem path that is being watched.</p>
1380 <p>Example: Watch <code>/etc/passwd</code> for attribute changes.</p>
1382 passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1384 /* /etc/passwd changed in some way */
1385 if (w->attr.st_nlink)
1387 printf ("passwd current size %ld\n", (long)w->attr.st_size);
1388 printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1389 printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1392 /* you shalt not abuse printf for puts */
1393 puts ("wow, /etc/passwd is not there, expect problems. "
1394 "if this is windows, they already arrived\n");
1400 ev_stat_init (&passwd, passwd_cb, "/etc/passwd");
1401 ev_stat_start (loop, &passwd);
1409 <h2 id="code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do...</h2>
1410 <div id="code_ev_idle_code_when_you_ve_got_no-2">
1411 <p>Idle watchers trigger events when no other events of the same or higher
1412 priority are pending (prepare, check and other idle watchers do not
1414 <p>That is, as long as your process is busy handling sockets or timeouts
1415 (or even signals, imagine) of the same or higher priority it will not be
1416 triggered. But when your process is idle (or only lower-priority watchers
1417 are pending), the idle watchers are being called once per event loop
1418 iteration - until stopped, that is, or your process receives more events
1419 and becomes busy again with higher priority stuff.</p>
1420 <p>The most noteworthy effect is that as long as any idle watchers are
1421 active, the process will not block when waiting for new events.</p>
1422 <p>Apart from keeping your process non-blocking (which is a useful
1423 effect on its own sometimes), idle watchers are a good place to do
1424 "pseudo-background processing", or delay processing stuff to after the
1425 event loop has handled all outstanding events.</p>
1427 <dt>ev_idle_init (ev_signal *, callback)</dt>
1429 <p>Initialises and configures the idle watcher - it has no parameters of any
1430 kind. There is a <code>ev_idle_set</code> macro, but using it is utterly pointless,
1434 <p>Example: Dynamically allocate an <code>ev_idle</code> watcher, start it, and in the
1435 callback, free it. Also, use no error checking, as usual.</p>
1437 idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1440 // now do something you wanted to do when the program has
1441 // no longer asnything immediate to do.
1444 struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1445 ev_idle_init (idle_watcher, idle_cb);
1446 ev_idle_start (loop, idle_cb);
1454 <h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop!</h2>
1455 <div id="code_ev_prepare_code_and_code_ev_che-2">
1456 <p>Prepare and check watchers are usually (but not always) used in tandem:
1457 prepare watchers get invoked before the process blocks and check watchers
1459 <p>You <i>must not</i> call <code>ev_loop</code> or similar functions that enter
1460 the current event loop from either <code>ev_prepare</code> or <code>ev_check</code>
1461 watchers. Other loops than the current one are fine, however. The
1462 rationale behind this is that you do not need to check for recursion in
1463 those watchers, i.e. the sequence will always be <code>ev_prepare</code>, blocking,
1464 <code>ev_check</code> so if you have one watcher of each kind they will always be
1465 called in pairs bracketing the blocking call.</p>
1466 <p>Their main purpose is to integrate other event mechanisms into libev and
1467 their use is somewhat advanced. This could be used, for example, to track
1468 variable changes, implement your own watchers, integrate net-snmp or a
1469 coroutine library and lots more. They are also occasionally useful if
1470 you cache some data and want to flush it before blocking (for example,
1471 in X programs you might want to do an <code>XFlush ()</code> in an <code>ev_prepare</code>
1473 <p>This is done by examining in each prepare call which file descriptors need
1474 to be watched by the other library, registering <code>ev_io</code> watchers for
1475 them and starting an <code>ev_timer</code> watcher for any timeouts (many libraries
1476 provide just this functionality). Then, in the check watcher you check for
1477 any events that occured (by checking the pending status of all watchers
1478 and stopping them) and call back into the library. The I/O and timer
1479 callbacks will never actually be called (but must be valid nevertheless,
1480 because you never know, you know?).</p>
1481 <p>As another example, the Perl Coro module uses these hooks to integrate
1482 coroutines into libev programs, by yielding to other active coroutines
1483 during each prepare and only letting the process block if no coroutines
1484 are ready to run (it's actually more complicated: it only runs coroutines
1485 with priority higher than or equal to the event loop and one coroutine
1486 of lower priority, but only once, using idle watchers to keep the event
1487 loop from blocking if lower-priority coroutines are active, thus mapping
1488 low-priority coroutines to idle/background tasks).</p>
1489 <p>It is recommended to give <code>ev_check</code> watchers highest (<code>EV_MAXPRI</code>)
1490 priority, to ensure that they are being run before any other watchers
1491 after the poll. Also, <code>ev_check</code> watchers (and <code>ev_prepare</code> watchers,
1492 too) should not activate ("feed") events into libev. While libev fully
1493 supports this, they will be called before other <code>ev_check</code> watchers did
1494 their job. As <code>ev_check</code> watchers are often used to embed other event
1495 loops those other event loops might be in an unusable state until their
1496 <code>ev_check</code> watcher ran (always remind yourself to coexist peacefully with
1499 <dt>ev_prepare_init (ev_prepare *, callback)</dt>
1500 <dt>ev_check_init (ev_check *, callback)</dt>
1502 <p>Initialises and configures the prepare or check watcher - they have no
1503 parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check_set</code>
1504 macros, but using them is utterly, utterly and completely pointless.</p>
1507 <p>There are a number of principal ways to embed other event loops or modules
1508 into libev. Here are some ideas on how to include libadns into libev
1509 (there is a Perl module named <code>EV::ADNS</code> that does this, which you could
1510 use for an actually working example. Another Perl module named <code>EV::Glib</code>
1511 embeds a Glib main context into libev, and finally, <code>Glib::EV</code> embeds EV
1512 into the Glib event loop).</p>
1513 <p>Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1514 and in a check watcher, destroy them and call into libadns. What follows
1515 is pseudo-code only of course. This requires you to either use a low
1516 priority for the check watcher or use <code>ev_clear_pending</code> explicitly, as
1517 the callbacks for the IO/timeout watchers might not have been called yet.</p>
1518 <pre> static ev_io iow [nfd];
1522 io_cb (ev_loop *loop, ev_io *w, int revents)
1526 // create io watchers for each fd and a timer before blocking
1528 adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
1530 int timeout = 3600000;
1531 struct pollfd fds [nfd];
1532 // actual code will need to loop here and realloc etc.
1533 adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1535 /* the callback is illegal, but won't be called as we stop during check */
1536 ev_timer_init (&tw, 0, timeout * 1e-3);
1537 ev_timer_start (loop, &tw);
1539 // create one ev_io per pollfd
1540 for (int i = 0; i < nfd; ++i)
1542 ev_io_init (iow + i, io_cb, fds [i].fd,
1543 ((fds [i].events & POLLIN ? EV_READ : 0)
1544 | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1546 fds [i].revents = 0;
1547 ev_io_start (loop, iow + i);
1551 // stop all watchers after blocking
1553 adns_check_cb (ev_loop *loop, ev_check *w, int revents)
1555 ev_timer_stop (loop, &tw);
1557 for (int i = 0; i < nfd; ++i)
1559 // set the relevant poll flags
1560 // could also call adns_processreadable etc. here
1561 struct pollfd *fd = fds + i;
1562 int revents = ev_clear_pending (iow + i);
1563 if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1564 if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1566 // now stop the watcher
1567 ev_io_stop (loop, iow + i);
1570 adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1574 <p>Method 2: This would be just like method 1, but you run <code>adns_afterpoll</code>
1575 in the prepare watcher and would dispose of the check watcher.</p>
1576 <p>Method 3: If the module to be embedded supports explicit event
1577 notification (adns does), you can also make use of the actual watcher
1578 callbacks, and only destroy/create the watchers in the prepare watcher.</p>
1580 timer_cb (EV_P_ ev_timer *w, int revents)
1582 adns_state ads = (adns_state)w->data;
1585 adns_processtimeouts (ads, &tv_now);
1589 io_cb (EV_P_ ev_io *w, int revents)
1591 adns_state ads = (adns_state)w->data;
1594 if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1595 if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1598 // do not ever call adns_afterpoll
1601 <p>Method 4: Do not use a prepare or check watcher because the module you
1602 want to embed is too inflexible to support it. Instead, youc na override
1603 their poll function. The drawback with this solution is that the main
1604 loop is now no longer controllable by EV. The <code>Glib::EV</code> module does
1607 event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1611 for (n = 0; n < nfds; ++n)
1612 // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1614 if (timeout >= 0)
1615 // create/start timer
1621 if (timeout >= 0)
1622 ev_timer_stop (EV_A_ &to);
1624 // stop io watchers again - their callbacks should have set
1625 for (n = 0; n < nfds; ++n)
1626 ev_io_stop (EV_A_ iow [n]);
1637 <h2 id="code_ev_embed_code_when_one_backend_"><code>ev_embed</code> - when one backend isn't enough...</h2>
1638 <div id="code_ev_embed_code_when_one_backend_-2">
1639 <p>This is a rather advanced watcher type that lets you embed one event loop
1640 into another (currently only <code>ev_io</code> events are supported in the embedded
1641 loop, other types of watchers might be handled in a delayed or incorrect
1642 fashion and must not be used).</p>
1643 <p>There are primarily two reasons you would want that: work around bugs and
1645 <p>As an example for a bug workaround, the kqueue backend might only support
1646 sockets on some platform, so it is unusable as generic backend, but you
1647 still want to make use of it because you have many sockets and it scales
1648 so nicely. In this case, you would create a kqueue-based loop and embed it
1649 into your default loop (which might use e.g. poll). Overall operation will
1650 be a bit slower because first libev has to poll and then call kevent, but
1651 at least you can use both at what they are best.</p>
1652 <p>As for prioritising I/O: rarely you have the case where some fds have
1653 to be watched and handled very quickly (with low latency), and even
1654 priorities and idle watchers might have too much overhead. In this case
1655 you would put all the high priority stuff in one loop and all the rest in
1656 a second one, and embed the second one in the first.</p>
1657 <p>As long as the watcher is active, the callback will be invoked every time
1658 there might be events pending in the embedded loop. The callback must then
1659 call <code>ev_embed_sweep (mainloop, watcher)</code> to make a single sweep and invoke
1660 their callbacks (you could also start an idle watcher to give the embedded
1661 loop strictly lower priority for example). You can also set the callback
1662 to <code>0</code>, in which case the embed watcher will automatically execute the
1663 embedded loop sweep.</p>
1664 <p>As long as the watcher is started it will automatically handle events. The
1665 callback will be invoked whenever some events have been handled. You can
1666 set the callback to <code>0</code> to avoid having to specify one if you are not
1667 interested in that.</p>
1668 <p>Also, there have not currently been made special provisions for forking:
1669 when you fork, you not only have to call <code>ev_loop_fork</code> on both loops,
1670 but you will also have to stop and restart any <code>ev_embed</code> watchers
1672 <p>Unfortunately, not all backends are embeddable, only the ones returned by
1673 <code>ev_embeddable_backends</code> are, which, unfortunately, does not include any
1675 <p>So when you want to use this feature you will always have to be prepared
1676 that you cannot get an embeddable loop. The recommended way to get around
1677 this is to have a separate variables for your embeddable loop, try to
1678 create it, and if that fails, use the normal loop for everything:</p>
1679 <pre> struct ev_loop *loop_hi = ev_default_init (0);
1680 struct ev_loop *loop_lo = 0;
1681 struct ev_embed embed;
1683 // see if there is a chance of getting one that works
1684 // (remember that a flags value of 0 means autodetection)
1685 loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1686 ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1689 // if we got one, then embed it, otherwise default to loop_hi
1692 ev_embed_init (&embed, 0, loop_lo);
1693 ev_embed_start (loop_hi, &embed);
1700 <dt>ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)</dt>
1701 <dt>ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)</dt>
1703 <p>Configures the watcher to embed the given loop, which must be
1704 embeddable. If the callback is <code>0</code>, then <code>ev_embed_sweep</code> will be
1705 invoked automatically, otherwise it is the responsibility of the callback
1706 to invoke it (it will continue to be called until the sweep has been done,
1707 if you do not want thta, you need to temporarily stop the embed watcher).</p>
1709 <dt>ev_embed_sweep (loop, ev_embed *)</dt>
1711 <p>Make a single, non-blocking sweep over the embedded loop. This works
1712 similarly to <code>ev_loop (embedded_loop, EVLOOP_NONBLOCK)</code>, but in the most
1713 apropriate way for embedded loops.</p>
1715 <dt>struct ev_loop *loop [read-only]</dt>
1717 <p>The embedded event loop.</p>
1726 <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>
1727 <div id="code_ev_fork_code_the_audacity_to_re-2">
1728 <p>Fork watchers are called when a <code>fork ()</code> was detected (usually because
1729 whoever is a good citizen cared to tell libev about it by calling
1730 <code>ev_default_fork</code> or <code>ev_loop_fork</code>). The invocation is done before the
1731 event loop blocks next and before <code>ev_check</code> watchers are being called,
1732 and only in the child after the fork. If whoever good citizen calling
1733 <code>ev_default_fork</code> cheats and calls it in the wrong process, the fork
1734 handlers will be invoked, too, of course.</p>
1736 <dt>ev_fork_init (ev_signal *, callback)</dt>
1738 <p>Initialises and configures the fork watcher - it has no parameters of any
1739 kind. There is a <code>ev_fork_set</code> macro, but using it is utterly pointless,
1749 <h1 id="OTHER_FUNCTIONS">OTHER FUNCTIONS</h1>
1750 <div id="OTHER_FUNCTIONS_CONTENT">
1751 <p>There are some other functions of possible interest. Described. Here. Now.</p>
1753 <dt>ev_once (loop, int fd, int events, ev_tstamp timeout, callback)</dt>
1755 <p>This function combines a simple timer and an I/O watcher, calls your
1756 callback on whichever event happens first and automatically stop both
1757 watchers. This is useful if you want to wait for a single event on an fd
1758 or timeout without having to allocate/configure/start/stop/free one or
1759 more watchers yourself.</p>
1760 <p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events
1761 is being ignored. Otherwise, an <code>ev_io</code> watcher for the given <code>fd</code> and
1762 <code>events</code> set will be craeted and started.</p>
1763 <p>If <code>timeout</code> is less than 0, then no timeout watcher will be
1764 started. Otherwise an <code>ev_timer</code> watcher with after = <code>timeout</code> (and
1765 repeat = 0) will be started. While <code>0</code> is a valid timeout, it is of
1767 <p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and gets
1768 passed an <code>revents</code> set like normal event callbacks (a combination of
1769 <code>EV_ERROR</code>, <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_TIMEOUT</code>) and the <code>arg</code>
1770 value passed to <code>ev_once</code>:</p>
1771 <pre> static void stdin_ready (int revents, void *arg)
1773 if (revents & EV_TIMEOUT)
1774 /* doh, nothing entered */;
1775 else if (revents & EV_READ)
1776 /* stdin might have data for us, joy! */;
1779 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1783 <dt>ev_feed_event (ev_loop *, watcher *, int revents)</dt>
1785 <p>Feeds the given event set into the event loop, as if the specified event
1786 had happened for the specified watcher (which must be a pointer to an
1787 initialised but not necessarily started event watcher).</p>
1789 <dt>ev_feed_fd_event (ev_loop *, int fd, int revents)</dt>
1791 <p>Feed an event on the given fd, as if a file descriptor backend detected
1792 the given events it.</p>
1794 <dt>ev_feed_signal_event (ev_loop *loop, int signum)</dt>
1796 <p>Feed an event as if the given signal occured (<code>loop</code> must be the default
1806 <h1 id="LIBEVENT_EMULATION">LIBEVENT EMULATION</h1>
1807 <div id="LIBEVENT_EMULATION_CONTENT">
1808 <p>Libev offers a compatibility emulation layer for libevent. It cannot
1809 emulate the internals of libevent, so here are some usage hints:</p>
1811 <dt>* Use it by including <event.h>, as usual.</dt>
1812 <dt>* The following members are fully supported: ev_base, ev_callback,
1813 ev_arg, ev_fd, ev_res, ev_events.</dt>
1814 <dt>* Avoid using ev_flags and the EVLIST_*-macros, while it is
1815 maintained by libev, it does not work exactly the same way as in libevent (consider
1816 it a private API).</dt>
1817 <dt>* Priorities are not currently supported. Initialising priorities
1818 will fail and all watchers will have the same priority, even though there
1819 is an ev_pri field.</dt>
1820 <dt>* Other members are not supported.</dt>
1821 <dt>* The libev emulation is <i>not</i> ABI compatible to libevent, you need
1822 to use the libev header file and library.</dt>
1826 <h1 id="C_SUPPORT">C++ SUPPORT</h1>
1827 <div id="C_SUPPORT_CONTENT">
1828 <p>Libev comes with some simplistic wrapper classes for C++ that mainly allow
1829 you to use some convinience methods to start/stop watchers and also change
1830 the callback model to a model using method callbacks on objects.</p>
1832 <pre> #include <ev++.h>
1835 <p>This automatically includes <cite>ev.h</cite> and puts all of its definitions (many
1836 of them macros) into the global namespace. All C++ specific things are
1837 put into the <code>ev</code> namespace. It should support all the same embedding
1838 options as <cite>ev.h</cite>, most notably <code>EV_MULTIPLICITY</code>.</p>
1839 <p>Care has been taken to keep the overhead low. The only data member the C++
1840 classes add (compared to plain C-style watchers) is the event loop pointer
1841 that the watcher is associated with (or no additional members at all if
1842 you disable <code>EV_MULTIPLICITY</code> when embedding libev).</p>
1843 <p>Currently, functions, and static and non-static member functions can be
1844 used as callbacks. Other types should be easy to add as long as they only
1845 need one additional pointer for context. If you need support for other
1846 types of functors please contact the author (preferably after implementing
1848 <p>Here is a list of things available in the <code>ev</code> namespace:</p>
1850 <dt><code>ev::READ</code>, <code>ev::WRITE</code> etc.</dt>
1852 <p>These are just enum values with the same values as the <code>EV_READ</code> etc.
1853 macros from <cite>ev.h</cite>.</p>
1855 <dt><code>ev::tstamp</code>, <code>ev::now</code></dt>
1857 <p>Aliases to the same types/functions as with the <code>ev_</code> prefix.</p>
1859 <dt><code>ev::io</code>, <code>ev::timer</code>, <code>ev::periodic</code>, <code>ev::idle</code>, <code>ev::sig</code> etc.</dt>
1861 <p>For each <code>ev_TYPE</code> watcher in <cite>ev.h</cite> there is a corresponding class of
1862 the same name in the <code>ev</code> namespace, with the exception of <code>ev_signal</code>
1863 which is called <code>ev::sig</code> to avoid clashes with the <code>signal</code> macro
1864 defines by many implementations.</p>
1865 <p>All of those classes have these methods:</p>
1868 <dt>ev::TYPE::TYPE ()</dt>
1869 <dt>ev::TYPE::TYPE (struct ev_loop *)</dt>
1870 <dt>ev::TYPE::~TYPE</dt>
1872 <p>The constructor (optionally) takes an event loop to associate the watcher
1873 with. If it is omitted, it will use <code>EV_DEFAULT</code>.</p>
1874 <p>The constructor calls <code>ev_init</code> for you, which means you have to call the
1875 <code>set</code> method before starting it.</p>
1876 <p>It will not set a callback, however: You have to call the templated <code>set</code>
1877 method to set a callback before you can start the watcher.</p>
1878 <p>(The reason why you have to use a method is a limitation in C++ which does
1879 not allow explicit template arguments for constructors).</p>
1880 <p>The destructor automatically stops the watcher if it is active.</p>
1882 <dt>w->set<class, &class::method> (object *)</dt>
1884 <p>This method sets the callback method to call. The method has to have a
1885 signature of <code>void (*)(ev_TYPE &, int)</code>, it receives the watcher as
1886 first argument and the <code>revents</code> as second. The object must be given as
1887 parameter and is stored in the <code>data</code> member of the watcher.</p>
1888 <p>This method synthesizes efficient thunking code to call your method from
1889 the C callback that libev requires. If your compiler can inline your
1890 callback (i.e. it is visible to it at the place of the <code>set</code> call and
1891 your compiler is good :), then the method will be fully inlined into the
1892 thunking function, making it as fast as a direct C callback.</p>
1893 <p>Example: simple class declaration and watcher initialisation</p>
1894 <pre> struct myclass
1896 void io_cb (ev::io &w, int revents) { }
1901 iow.set <myclass, &myclass::io_cb> (&obj);
1905 <dt>w->set<function> (void *data = 0)</dt>
1907 <p>Also sets a callback, but uses a static method or plain function as
1908 callback. The optional <code>data</code> argument will be stored in the watcher's
1909 <code>data</code> member and is free for you to use.</p>
1910 <p>The prototype of the <code>function</code> must be <code>void (*)(ev::TYPE &w, int)</code>.</p>
1911 <p>See the method-<code>set</code> above for more details.</p>
1913 <pre> static void io_cb (ev::io &w, int revents) { }
1914 iow.set <io_cb> ();
1918 <dt>w->set (struct ev_loop *)</dt>
1920 <p>Associates a different <code>struct ev_loop</code> with this watcher. You can only
1921 do this when the watcher is inactive (and not pending either).</p>
1923 <dt>w->set ([args])</dt>
1925 <p>Basically the same as <code>ev_TYPE_set</code>, with the same args. Must be
1926 called at least once. Unlike the C counterpart, an active watcher gets
1927 automatically stopped and restarted when reconfiguring it with this
1930 <dt>w->start ()</dt>
1932 <p>Starts the watcher. Note that there is no <code>loop</code> argument, as the
1933 constructor already stores the event loop.</p>
1935 <dt>w->stop ()</dt>
1937 <p>Stops the watcher if it is active. Again, no <code>loop</code> argument.</p>
1939 <dt>w->again () <code>ev::timer</code>, <code>ev::periodic</code> only</dt>
1941 <p>For <code>ev::timer</code> and <code>ev::periodic</code>, this invokes the corresponding
1942 <code>ev_TYPE_again</code> function.</p>
1944 <dt>w->sweep () <code>ev::embed</code> only</dt>
1946 <p>Invokes <code>ev_embed_sweep</code>.</p>
1948 <dt>w->update () <code>ev::stat</code> only</dt>
1950 <p>Invokes <code>ev_stat_stat</code>.</p>
1956 <p>Example: Define a class with an IO and idle watcher, start one of them in
1957 the constructor.</p>
1960 ev_io io; void io_cb (ev::io &w, int revents);
1961 ev_idle idle void idle_cb (ev::idle &w, int revents);
1966 myclass::myclass (int fd)
1968 io .set <myclass, &myclass::io_cb > (this);
1969 idle.set <myclass, &myclass::idle_cb> (this);
1971 io.start (fd, ev::READ);
1980 <h1 id="MACRO_MAGIC">MACRO MAGIC</h1>
1981 <div id="MACRO_MAGIC_CONTENT">
1982 <p>Libev can be compiled with a variety of options, the most fundemantal is
1983 <code>EV_MULTIPLICITY</code>. This option determines whether (most) functions and
1984 callbacks have an initial <code>struct ev_loop *</code> argument.</p>
1985 <p>To make it easier to write programs that cope with either variant, the
1986 following macros are defined:</p>
1988 <dt><code>EV_A</code>, <code>EV_A_</code></dt>
1990 <p>This provides the loop <i>argument</i> for functions, if one is required ("ev
1991 loop argument"). The <code>EV_A</code> form is used when this is the sole argument,
1992 <code>EV_A_</code> is used when other arguments are following. Example:</p>
1993 <pre> ev_unref (EV_A);
1994 ev_timer_add (EV_A_ watcher);
1998 <p>It assumes the variable <code>loop</code> of type <code>struct ev_loop *</code> is in scope,
1999 which is often provided by the following macro.</p>
2001 <dt><code>EV_P</code>, <code>EV_P_</code></dt>
2003 <p>This provides the loop <i>parameter</i> for functions, if one is required ("ev
2004 loop parameter"). The <code>EV_P</code> form is used when this is the sole parameter,
2005 <code>EV_P_</code> is used when other parameters are following. Example:</p>
2006 <pre> // this is how ev_unref is being declared
2007 static void ev_unref (EV_P);
2009 // this is how you can declare your typical callback
2010 static void cb (EV_P_ ev_timer *w, int revents)
2013 <p>It declares a parameter <code>loop</code> of type <code>struct ev_loop *</code>, quite
2014 suitable for use with <code>EV_A</code>.</p>
2016 <dt><code>EV_DEFAULT</code>, <code>EV_DEFAULT_</code></dt>
2018 <p>Similar to the other two macros, this gives you the value of the default
2019 loop, if multiple loops are supported ("ev loop default").</p>
2022 <p>Example: Declare and initialise a check watcher, utilising the above
2023 macros so it will work regardless of whether multiple loops are supported
2026 check_cb (EV_P_ ev_timer *w, int revents)
2028 ev_check_stop (EV_A_ w);
2032 ev_check_init (&check, check_cb);
2033 ev_check_start (EV_DEFAULT_ &check);
2034 ev_loop (EV_DEFAULT_ 0);
2039 <h1 id="EMBEDDING">EMBEDDING</h1>
2040 <div id="EMBEDDING_CONTENT">
2041 <p>Libev can (and often is) directly embedded into host
2042 applications. Examples of applications that embed it include the Deliantra
2043 Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
2044 and rxvt-unicode.</p>
2045 <p>The goal is to enable you to just copy the neecssary files into your
2046 source directory without having to change even a single line in them, so
2047 you can easily upgrade by simply copying (or having a checked-out copy of
2048 libev somewhere in your source tree).</p>
2051 <h2 id="FILESETS">FILESETS</h2>
2052 <div id="FILESETS_CONTENT">
2053 <p>Depending on what features you need you need to include one or more sets of files
2057 <h3 id="CORE_EVENT_LOOP">CORE EVENT LOOP</h3>
2058 <div id="CORE_EVENT_LOOP_CONTENT">
2059 <p>To include only the libev core (all the <code>ev_*</code> functions), with manual
2060 configuration (no autoconf):</p>
2061 <pre> #define EV_STANDALONE 1
2062 #include "ev.c"
2065 <p>This will automatically include <cite>ev.h</cite>, too, and should be done in a
2066 single C source file only to provide the function implementations. To use
2067 it, do the same for <cite>ev.h</cite> in all files wishing to use this API (best
2068 done by writing a wrapper around <cite>ev.h</cite> that you can include instead and
2069 where you can put other configuration options):</p>
2070 <pre> #define EV_STANDALONE 1
2071 #include "ev.h"
2074 <p>Both header files and implementation files can be compiled with a C++
2075 compiler (at least, thats a stated goal, and breakage will be treated
2077 <p>You need the following files in your source tree, or in a directory
2078 in your include path (e.g. in libev/ when using -Ilibev):</p>
2084 ev_win32.c required on win32 platforms only
2086 ev_select.c only when select backend is enabled (which is enabled by default)
2087 ev_poll.c only when poll backend is enabled (disabled by default)
2088 ev_epoll.c only when the epoll backend is enabled (disabled by default)
2089 ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2090 ev_port.c only when the solaris port backend is enabled (disabled by default)
2093 <p><cite>ev.c</cite> includes the backend files directly when enabled, so you only need
2094 to compile this single file.</p>
2097 <h3 id="LIBEVENT_COMPATIBILITY_API">LIBEVENT COMPATIBILITY API</h3>
2098 <div id="LIBEVENT_COMPATIBILITY_API_CONTENT">
2099 <p>To include the libevent compatibility API, also include:</p>
2100 <pre> #include "event.c"
2103 <p>in the file including <cite>ev.c</cite>, and:</p>
2104 <pre> #include "event.h"
2107 <p>in the files that want to use the libevent API. This also includes <cite>ev.h</cite>.</p>
2108 <p>You need the following additional files for this:</p>
2115 <h3 id="AUTOCONF_SUPPORT">AUTOCONF SUPPORT</h3>
2116 <div id="AUTOCONF_SUPPORT_CONTENT">
2117 <p>Instead of using <code>EV_STANDALONE=1</code> and providing your config in
2118 whatever way you want, you can also <code>m4_include([libev.m4])</code> in your
2119 <cite>configure.ac</cite> and leave <code>EV_STANDALONE</code> undefined. <cite>ev.c</cite> will then
2120 include <cite>config.h</cite> and configure itself accordingly.</p>
2121 <p>For this of course you need the m4 file:</p>
2127 <h2 id="PREPROCESSOR_SYMBOLS_MACROS">PREPROCESSOR SYMBOLS/MACROS</h2>
2128 <div id="PREPROCESSOR_SYMBOLS_MACROS_CONTENT">
2129 <p>Libev can be configured via a variety of preprocessor symbols you have to define
2130 before including any of its files. The default is not to build for multiplicity
2131 and only include the select backend.</p>
2133 <dt>EV_STANDALONE</dt>
2135 <p>Must always be <code>1</code> if you do not use autoconf configuration, which
2136 keeps libev from including <cite>config.h</cite>, and it also defines dummy
2137 implementations for some libevent functions (such as logging, which is not
2138 supported). It will also not define any of the structs usually found in
2139 <cite>event.h</cite> that are not directly supported by the libev core alone.</p>
2141 <dt>EV_USE_MONOTONIC</dt>
2143 <p>If defined to be <code>1</code>, libev will try to detect the availability of the
2144 monotonic clock option at both compiletime and runtime. Otherwise no use
2145 of the monotonic clock option will be attempted. If you enable this, you
2146 usually have to link against librt or something similar. Enabling it when
2147 the functionality isn't available is safe, though, althoguh you have
2148 to make sure you link against any libraries where the <code>clock_gettime</code>
2149 function is hiding in (often <cite>-lrt</cite>).</p>
2151 <dt>EV_USE_REALTIME</dt>
2153 <p>If defined to be <code>1</code>, libev will try to detect the availability of the
2154 realtime clock option at compiletime (and assume its availability at
2155 runtime if successful). Otherwise no use of the realtime clock option will
2156 be attempted. This effectively replaces <code>gettimeofday</code> by <code>clock_get
2157 (CLOCK_REALTIME, ...)</code> and will not normally affect correctness. See tzhe note about libraries
2158 in the description of <code>EV_USE_MONOTONIC</code>, though.</p>
2160 <dt>EV_USE_SELECT</dt>
2162 <p>If undefined or defined to be <code>1</code>, libev will compile in support for the
2163 <code>select</code>(2) backend. No attempt at autodetection will be done: if no
2164 other method takes over, select will be it. Otherwise the select backend
2165 will not be compiled in.</p>
2167 <dt>EV_SELECT_USE_FD_SET</dt>
2169 <p>If defined to <code>1</code>, then the select backend will use the system <code>fd_set</code>
2170 structure. This is useful if libev doesn't compile due to a missing
2171 <code>NFDBITS</code> or <code>fd_mask</code> definition or it misguesses the bitset layout on
2172 exotic systems. This usually limits the range of file descriptors to some
2173 low limit such as 1024 or might have other limitations (winsocket only
2174 allows 64 sockets). The <code>FD_SETSIZE</code> macro, set before compilation, might
2175 influence the size of the <code>fd_set</code> used.</p>
2177 <dt>EV_SELECT_IS_WINSOCKET</dt>
2179 <p>When defined to <code>1</code>, the select backend will assume that
2180 select/socket/connect etc. don't understand file descriptors but
2181 wants osf handles on win32 (this is the case when the select to
2182 be used is the winsock select). This means that it will call
2183 <code>_get_osfhandle</code> on the fd to convert it to an OS handle. Otherwise,
2184 it is assumed that all these functions actually work on fds, even
2185 on win32. Should not be defined on non-win32 platforms.</p>
2187 <dt>EV_USE_POLL</dt>
2189 <p>If defined to be <code>1</code>, libev will compile in support for the <code>poll</code>(2)
2190 backend. Otherwise it will be enabled on non-win32 platforms. It
2191 takes precedence over select.</p>
2193 <dt>EV_USE_EPOLL</dt>
2195 <p>If defined to be <code>1</code>, libev will compile in support for the Linux
2196 <code>epoll</code>(7) backend. Its availability will be detected at runtime,
2197 otherwise another method will be used as fallback. This is the
2198 preferred backend for GNU/Linux systems.</p>
2200 <dt>EV_USE_KQUEUE</dt>
2202 <p>If defined to be <code>1</code>, libev will compile in support for the BSD style
2203 <code>kqueue</code>(2) backend. Its actual availability will be detected at runtime,
2204 otherwise another method will be used as fallback. This is the preferred
2205 backend for BSD and BSD-like systems, although on most BSDs kqueue only
2206 supports some types of fds correctly (the only platform we found that
2207 supports ptys for example was NetBSD), so kqueue might be compiled in, but
2208 not be used unless explicitly requested. The best way to use it is to find
2209 out whether kqueue supports your type of fd properly and use an embedded
2212 <dt>EV_USE_PORT</dt>
2214 <p>If defined to be <code>1</code>, libev will compile in support for the Solaris
2215 10 port style backend. Its availability will be detected at runtime,
2216 otherwise another method will be used as fallback. This is the preferred
2217 backend for Solaris 10 systems.</p>
2219 <dt>EV_USE_DEVPOLL</dt>
2221 <p>reserved for future expansion, works like the USE symbols above.</p>
2223 <dt>EV_USE_INOTIFY</dt>
2225 <p>If defined to be <code>1</code>, libev will compile in support for the Linux inotify
2226 interface to speed up <code>ev_stat</code> watchers. Its actual availability will
2227 be detected at runtime.</p>
2231 <p>The name of the <cite>ev.h</cite> header file used to include it. The default if
2232 undefined is <code><ev.h></code> in <cite>event.h</cite> and <code>"ev.h"</code> in <cite>ev.c</cite>. This
2233 can be used to virtually rename the <cite>ev.h</cite> header file in case of conflicts.</p>
2235 <dt>EV_CONFIG_H</dt>
2237 <p>If <code>EV_STANDALONE</code> isn't <code>1</code>, this variable can be used to override
2238 <cite>ev.c</cite>'s idea of where to find the <cite>config.h</cite> file, similarly to
2239 <code>EV_H</code>, above.</p>
2243 <p>Similarly to <code>EV_H</code>, this macro can be used to override <cite>event.c</cite>'s idea
2244 of how the <cite>event.h</cite> header can be found.</p>
2246 <dt>EV_PROTOTYPES</dt>
2248 <p>If defined to be <code>0</code>, then <cite>ev.h</cite> will not define any function
2249 prototypes, but still define all the structs and other symbols. This is
2250 occasionally useful if you want to provide your own wrapper functions
2251 around libev functions.</p>
2253 <dt>EV_MULTIPLICITY</dt>
2255 <p>If undefined or defined to <code>1</code>, then all event-loop-specific functions
2256 will have the <code>struct ev_loop *</code> as first argument, and you can create
2257 additional independent event loops. Otherwise there will be no support
2258 for multiple event loops and there is no first event loop pointer
2259 argument. Instead, all functions act on the single default loop.</p>
2264 <p>The range of allowed priorities. <code>EV_MINPRI</code> must be smaller or equal to
2265 <code>EV_MAXPRI</code>, but otherwise there are no non-obvious limitations. You can
2266 provide for more priorities by overriding those symbols (usually defined
2267 to be <code>-2</code> and <code>2</code>, respectively).</p>
2268 <p>When doing priority-based operations, libev usually has to linearly search
2269 all the priorities, so having many of them (hundreds) uses a lot of space
2270 and time, so using the defaults of five priorities (-2 .. +2) is usually
2272 <p>If your embedding app does not need any priorities, defining these both to
2273 <code>0</code> will save some memory and cpu.</p>
2275 <dt>EV_PERIODIC_ENABLE</dt>
2277 <p>If undefined or defined to be <code>1</code>, then periodic timers are supported. If
2278 defined to be <code>0</code>, then they are not. Disabling them saves a few kB of
2281 <dt>EV_IDLE_ENABLE</dt>
2283 <p>If undefined or defined to be <code>1</code>, then idle watchers are supported. If
2284 defined to be <code>0</code>, then they are not. Disabling them saves a few kB of
2287 <dt>EV_EMBED_ENABLE</dt>
2289 <p>If undefined or defined to be <code>1</code>, then embed watchers are supported. If
2290 defined to be <code>0</code>, then they are not.</p>
2292 <dt>EV_STAT_ENABLE</dt>
2294 <p>If undefined or defined to be <code>1</code>, then stat watchers are supported. If
2295 defined to be <code>0</code>, then they are not.</p>
2297 <dt>EV_FORK_ENABLE</dt>
2299 <p>If undefined or defined to be <code>1</code>, then fork watchers are supported. If
2300 defined to be <code>0</code>, then they are not.</p>
2304 <p>If you need to shave off some kilobytes of code at the expense of some
2305 speed, define this symbol to <code>1</code>. Currently only used for gcc to override
2306 some inlining decisions, saves roughly 30% codesize of amd64.</p>
2308 <dt>EV_PID_HASHSIZE</dt>
2310 <p><code>ev_child</code> watchers use a small hash table to distribute workload by
2311 pid. The default size is <code>16</code> (or <code>1</code> with <code>EV_MINIMAL</code>), usually more
2312 than enough. If you need to manage thousands of children you might want to
2313 increase this value (<i>must</i> be a power of two).</p>
2315 <dt>EV_INOTIFY_HASHSIZE</dt>
2317 <p><code>ev_staz</code> watchers use a small hash table to distribute workload by
2318 inotify watch id. The default size is <code>16</code> (or <code>1</code> with <code>EV_MINIMAL</code>),
2319 usually more than enough. If you need to manage thousands of <code>ev_stat</code>
2320 watchers you might want to increase this value (<i>must</i> be a power of
2325 <p>By default, all watchers have a <code>void *data</code> member. By redefining
2326 this macro to a something else you can include more and other types of
2327 members. You have to define it each time you include one of the files,
2328 though, and it must be identical each time.</p>
2329 <p>For example, the perl EV module uses something like this:</p>
2330 <pre> #define EV_COMMON \
2331 SV *self; /* contains this struct */ \
2332 SV *cb_sv, *fh /* note no trailing ";" */
2336 <dt>EV_CB_DECLARE (type)</dt>
2337 <dt>EV_CB_INVOKE (watcher, revents)</dt>
2338 <dt>ev_set_cb (ev, cb)</dt>
2340 <p>Can be used to change the callback member declaration in each watcher,
2341 and the way callbacks are invoked and set. Must expand to a struct member
2342 definition and a statement, respectively. See the <cite>ev.v</cite> header file for
2343 their default definitions. One possible use for overriding these is to
2344 avoid the <code>struct ev_loop *</code> as first argument in all cases, or to use
2345 method calls instead of plain function calls in C++.</p>
2348 <h2 id="EXAMPLES">EXAMPLES</h2>
2349 <div id="EXAMPLES_CONTENT">
2350 <p>For a real-world example of a program the includes libev
2351 verbatim, you can have a look at the EV perl module
2352 (<a href="http://software.schmorp.de/pkg/EV.html">http://software.schmorp.de/pkg/EV.html</a>). It has the libev files in
2353 the <cite>libev/</cite> subdirectory and includes them in the <cite>EV/EVAPI.h</cite> (public
2354 interface) and <cite>EV.xs</cite> (implementation) files. Only the <cite>EV.xs</cite> file
2355 will be compiled. It is pretty complex because it provides its own header
2357 <p>The usage in rxvt-unicode is simpler. It has a <cite>ev_cpp.h</cite> header file
2358 that everybody includes and which overrides some configure choices:</p>
2359 <pre> #define EV_MINIMAL 1
2360 #define EV_USE_POLL 0
2361 #define EV_MULTIPLICITY 0
2362 #define EV_PERIODIC_ENABLE 0
2363 #define EV_STAT_ENABLE 0
2364 #define EV_FORK_ENABLE 0
2365 #define EV_CONFIG_H <config.h>
2369 #include "ev++.h"
2372 <p>And a <cite>ev_cpp.C</cite> implementation file that contains libev proper and is compiled:</p>
2373 <pre> #include "ev_cpp.h"
2374 #include "ev.c"
2382 <h1 id="COMPLEXITIES">COMPLEXITIES</h1>
2383 <div id="COMPLEXITIES_CONTENT">
2384 <p>In this section the complexities of (many of) the algorithms used inside
2385 libev will be explained. For complexity discussions about backends see the
2386 documentation for <code>ev_default_init</code>.</p>
2387 <p>All of the following are about amortised time: If an array needs to be
2388 extended, libev needs to realloc and move the whole array, but this
2389 happens asymptotically never with higher number of elements, so O(1) might
2390 mean it might do a lengthy realloc operation in rare cases, but on average
2391 it is much faster and asymptotically approaches constant time.</p>
2394 <dt>Starting and stopping timer/periodic watchers: O(log skipped_other_timers)</dt>
2396 <p>This means that, when you have a watcher that triggers in one hour and
2397 there are 100 watchers that would trigger before that then inserting will
2398 have to skip those 100 watchers.</p>
2400 <dt>Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)</dt>
2402 <p>That means that for changing a timer costs less than removing/adding them
2403 as only the relative motion in the event queue has to be paid for.</p>
2405 <dt>Starting io/check/prepare/idle/signal/child watchers: O(1)</dt>
2407 <p>These just add the watcher into an array or at the head of a list.
2408 =item Stopping check/prepare/idle watchers: O(1)</p>
2410 <dt>Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))</dt>
2412 <p>These watchers are stored in lists then need to be walked to find the
2413 correct watcher to remove. The lists are usually short (you don't usually
2414 have many watchers waiting for the same fd or signal).</p>
2416 <dt>Finding the next timer per loop iteration: O(1)</dt>
2417 <dt>Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)</dt>
2419 <p>A change means an I/O watcher gets started or stopped, which requires
2420 libev to recalculate its status (and possibly tell the kernel).</p>
2422 <dt>Activating one watcher: O(1)</dt>
2423 <dt>Priority handling: O(number_of_priorities)</dt>
2425 <p>Priorities are implemented by allocating some space for each
2426 priority. When doing priority-based operations, libev usually has to
2427 linearly search all the priorities.</p>
2437 <h1 id="AUTHOR">AUTHOR</h1>
2438 <div id="AUTHOR_CONTENT">
2439 <p>Marc Lehmann <libev@schmorp.de>.</p>
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