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15 <h3 id="TOP">Index</h3>
17 <ul><li><a href="#NAME">NAME</a></li>
18 <li><a href="#SYNOPSIS">SYNOPSIS</a></li>
19 <li><a href="#EXAMPLE_PROGRAM">EXAMPLE PROGRAM</a></li>
20 <li><a href="#DESCRIPTION">DESCRIPTION</a></li>
21 <li><a href="#FEATURES">FEATURES</a></li>
22 <li><a href="#CONVENTIONS">CONVENTIONS</a></li>
23 <li><a href="#TIME_REPRESENTATION">TIME REPRESENTATION</a></li>
24 <li><a href="#GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</a></li>
25 <li><a href="#FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</a></li>
26 <li><a href="#ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</a>
27 <ul><li><a href="#GENERIC_WATCHER_FUNCTIONS">GENERIC WATCHER FUNCTIONS</a></li>
28 <li><a href="#ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</a></li>
31 <li><a href="#WATCHER_TYPES">WATCHER TYPES</a>
32 <ul><li><a href="#code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable?</a></li>
33 <li><a href="#code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally repeating timeouts</a></li>
34 <li><a href="#code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron?</a></li>
35 <li><a href="#code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled!</a></li>
36 <li><a href="#code_ev_child_code_watch_out_for_pro"><code>ev_child</code> - watch out for process status changes</a></li>
37 <li><a href="#code_ev_stat_code_did_the_file_attri"><code>ev_stat</code> - did the file attributes just change?</a></li>
38 <li><a href="#code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do...</a></li>
39 <li><a href="#code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop!</a></li>
40 <li><a href="#code_ev_embed_code_when_one_backend_"><code>ev_embed</code> - when one backend isn't enough...</a></li>
41 <li><a href="#code_ev_fork_code_the_audacity_to_re"><code>ev_fork</code> - the audacity to resume the event loop after a fork</a></li>
44 <li><a href="#OTHER_FUNCTIONS">OTHER FUNCTIONS</a></li>
45 <li><a href="#LIBEVENT_EMULATION">LIBEVENT EMULATION</a></li>
46 <li><a href="#C_SUPPORT">C++ SUPPORT</a></li>
47 <li><a href="#MACRO_MAGIC">MACRO MAGIC</a></li>
48 <li><a href="#EMBEDDING">EMBEDDING</a>
49 <ul><li><a href="#FILESETS">FILESETS</a>
50 <ul><li><a href="#CORE_EVENT_LOOP">CORE EVENT LOOP</a></li>
51 <li><a href="#LIBEVENT_COMPATIBILITY_API">LIBEVENT COMPATIBILITY API</a></li>
52 <li><a href="#AUTOCONF_SUPPORT">AUTOCONF SUPPORT</a></li>
55 <li><a href="#PREPROCESSOR_SYMBOLS_MACROS">PREPROCESSOR SYMBOLS/MACROS</a></li>
56 <li><a href="#EXAMPLES">EXAMPLES</a></li>
59 <li><a href="#COMPLEXITIES">COMPLEXITIES</a></li>
60 <li><a href="#AUTHOR">AUTHOR</a>
65 <h1 id="NAME">NAME</h1>
66 <div id="NAME_CONTENT">
67 <p>libev - a high performance full-featured event loop written in C</p>
70 <h1 id="SYNOPSIS">SYNOPSIS</h1>
71 <div id="SYNOPSIS_CONTENT">
72 <pre> #include <ev.h>
77 <h1 id="EXAMPLE_PROGRAM">EXAMPLE PROGRAM</h1>
78 <div id="EXAMPLE_PROGRAM_CONTENT">
79 <pre> #include <ev.h>
82 ev_timer timeout_watcher;
84 /* called when data readable on stdin */
86 stdin_cb (EV_P_ struct ev_io *w, int revents)
88 /* puts ("stdin ready"); */
89 ev_io_stop (EV_A_ w); /* just a syntax example */
90 ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */
94 timeout_cb (EV_P_ struct ev_timer *w, int revents)
96 /* puts ("timeout"); */
97 ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
103 struct ev_loop *loop = ev_default_loop (0);
105 /* initialise an io watcher, then start it */
106 ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
107 ev_io_start (loop, &stdin_watcher);
109 /* simple non-repeating 5.5 second timeout */
110 ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
111 ev_timer_start (loop, &timeout_watcher);
113 /* loop till timeout or data ready */
122 <h1 id="DESCRIPTION">DESCRIPTION</h1>
123 <div id="DESCRIPTION_CONTENT">
124 <p>Libev is an event loop: you register interest in certain events (such as a
125 file descriptor being readable or a timeout occuring), and it will manage
126 these event sources and provide your program with events.</p>
127 <p>To do this, it must take more or less complete control over your process
128 (or thread) by executing the <i>event loop</i> handler, and will then
129 communicate events via a callback mechanism.</p>
130 <p>You register interest in certain events by registering so-called <i>event
131 watchers</i>, which are relatively small C structures you initialise with the
132 details of the event, and then hand it over to libev by <i>starting</i> the
136 <h1 id="FEATURES">FEATURES</h1>
137 <div id="FEATURES_CONTENT">
138 <p>Libev supports <code>select</code>, <code>poll</code>, the Linux-specific <code>epoll</code>, the
139 BSD-specific <code>kqueue</code> and the Solaris-specific event port mechanisms
140 for file descriptor events (<code>ev_io</code>), the Linux <code>inotify</code> interface
141 (for <code>ev_stat</code>), relative timers (<code>ev_timer</code>), absolute timers
142 with customised rescheduling (<code>ev_periodic</code>), synchronous signals
143 (<code>ev_signal</code>), process status change events (<code>ev_child</code>), and event
144 watchers dealing with the event loop mechanism itself (<code>ev_idle</code>,
145 <code>ev_embed</code>, <code>ev_prepare</code> and <code>ev_check</code> watchers) as well as
146 file watchers (<code>ev_stat</code>) and even limited support for fork events
147 (<code>ev_fork</code>).</p>
148 <p>It also is quite fast (see this
149 <a href="http://libev.schmorp.de/bench.html">benchmark</a> comparing it to libevent
153 <h1 id="CONVENTIONS">CONVENTIONS</h1>
154 <div id="CONVENTIONS_CONTENT">
155 <p>Libev is very configurable. In this manual the default configuration will
156 be described, which supports multiple event loops. For more info about
157 various configuration options please have a look at <strong>EMBED</strong> section in
158 this manual. If libev was configured without support for multiple event
159 loops, then all functions taking an initial argument of name <code>loop</code>
160 (which is always of type <code>struct ev_loop *</code>) will not have this argument.</p>
163 <h1 id="TIME_REPRESENTATION">TIME REPRESENTATION</h1>
164 <div id="TIME_REPRESENTATION_CONTENT">
165 <p>Libev represents time as a single floating point number, representing the
166 (fractional) number of seconds since the (POSIX) epoch (somewhere near
167 the beginning of 1970, details are complicated, don't ask). This type is
168 called <code>ev_tstamp</code>, which is what you should use too. It usually aliases
169 to the <code>double</code> type in C, and when you need to do any calculations on
170 it, you should treat it as such.</p>
173 <h1 id="GLOBAL_FUNCTIONS">GLOBAL FUNCTIONS</h1>
174 <div id="GLOBAL_FUNCTIONS_CONTENT">
175 <p>These functions can be called anytime, even before initialising the
176 library in any way.</p>
178 <dt>ev_tstamp ev_time ()</dt>
180 <p>Returns the current time as libev would use it. Please note that the
181 <code>ev_now</code> function is usually faster and also often returns the timestamp
182 you actually want to know.</p>
184 <dt>int ev_version_major ()</dt>
185 <dt>int ev_version_minor ()</dt>
187 <p>You can find out the major and minor version numbers of the library
188 you linked against by calling the functions <code>ev_version_major</code> and
189 <code>ev_version_minor</code>. If you want, you can compare against the global
190 symbols <code>EV_VERSION_MAJOR</code> and <code>EV_VERSION_MINOR</code>, which specify the
191 version of the library your program was compiled against.</p>
192 <p>Usually, it's a good idea to terminate if the major versions mismatch,
193 as this indicates an incompatible change. Minor versions are usually
194 compatible to older versions, so a larger minor version alone is usually
196 <p>Example: Make sure we haven't accidentally been linked against the wrong
198 <pre> assert (("libev version mismatch",
199 ev_version_major () == EV_VERSION_MAJOR
200 && ev_version_minor () >= EV_VERSION_MINOR));
204 <dt>unsigned int ev_supported_backends ()</dt>
206 <p>Return the set of all backends (i.e. their corresponding <code>EV_BACKEND_*</code>
207 value) compiled into this binary of libev (independent of their
208 availability on the system you are running on). See <code>ev_default_loop</code> for
209 a description of the set values.</p>
210 <p>Example: make sure we have the epoll method, because yeah this is cool and
211 a must have and can we have a torrent of it please!!!11</p>
212 <pre> assert (("sorry, no epoll, no sex",
213 ev_supported_backends () & EVBACKEND_EPOLL));
217 <dt>unsigned int ev_recommended_backends ()</dt>
219 <p>Return the set of all backends compiled into this binary of libev and also
220 recommended for this platform. This set is often smaller than the one
221 returned by <code>ev_supported_backends</code>, as for example kqueue is broken on
222 most BSDs and will not be autodetected unless you explicitly request it
223 (assuming you know what you are doing). This is the set of backends that
224 libev will probe for if you specify no backends explicitly.</p>
226 <dt>unsigned int ev_embeddable_backends ()</dt>
228 <p>Returns the set of backends that are embeddable in other event loops. This
229 is the theoretical, all-platform, value. To find which backends
230 might be supported on the current system, you would need to look at
231 <code>ev_embeddable_backends () & ev_supported_backends ()</code>, likewise for
232 recommended ones.</p>
233 <p>See the description of <code>ev_embed</code> watchers for more info.</p>
235 <dt>ev_set_allocator (void *(*cb)(void *ptr, long size))</dt>
237 <p>Sets the allocation function to use (the prototype is similar - the
238 semantics is identical - to the realloc C function). It is used to
239 allocate and free memory (no surprises here). If it returns zero when
240 memory needs to be allocated, the library might abort or take some
241 potentially destructive action. The default is your system realloc
243 <p>You could override this function in high-availability programs to, say,
244 free some memory if it cannot allocate memory, to use a special allocator,
245 or even to sleep a while and retry until some memory is available.</p>
246 <p>Example: Replace the libev allocator with one that waits a bit and then
249 persistent_realloc (void *ptr, size_t size)
253 void *newptr = realloc (ptr, size);
263 ev_set_allocator (persistent_realloc);
267 <dt>ev_set_syserr_cb (void (*cb)(const char *msg));</dt>
269 <p>Set the callback function to call on a retryable syscall error (such
270 as failed select, poll, epoll_wait). The message is a printable string
271 indicating the system call or subsystem causing the problem. If this
272 callback is set, then libev will expect it to remedy the sitution, no
273 matter what, when it returns. That is, libev will generally retry the
274 requested operation, or, if the condition doesn't go away, do bad stuff
276 <p>Example: This is basically the same thing that libev does internally, too.</p>
278 fatal_error (const char *msg)
285 ev_set_syserr_cb (fatal_error);
292 <h1 id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP">FUNCTIONS CONTROLLING THE EVENT LOOP</h1>
293 <div id="FUNCTIONS_CONTROLLING_THE_EVENT_LOOP-2">
294 <p>An event loop is described by a <code>struct ev_loop *</code>. The library knows two
295 types of such loops, the <i>default</i> loop, which supports signals and child
296 events, and dynamically created loops which do not.</p>
297 <p>If you use threads, a common model is to run the default event loop
298 in your main thread (or in a separate thread) and for each thread you
299 create, you also create another event loop. Libev itself does no locking
300 whatsoever, so if you mix calls to the same event loop in different
301 threads, make sure you lock (this is usually a bad idea, though, even if
302 done correctly, because it's hideous and inefficient).</p>
304 <dt>struct ev_loop *ev_default_loop (unsigned int flags)</dt>
306 <p>This will initialise the default event loop if it hasn't been initialised
307 yet and return it. If the default loop could not be initialised, returns
308 false. If it already was initialised it simply returns it (and ignores the
309 flags. If that is troubling you, check <code>ev_backend ()</code> afterwards).</p>
310 <p>If you don't know what event loop to use, use the one returned from this
312 <p>The flags argument can be used to specify special behaviour or specific
313 backends to use, and is usually specified as <code>0</code> (or <code>EVFLAG_AUTO</code>).</p>
314 <p>The following flags are supported:</p>
317 <dt><code>EVFLAG_AUTO</code></dt>
319 <p>The default flags value. Use this if you have no clue (it's the right
320 thing, believe me).</p>
322 <dt><code>EVFLAG_NOENV</code></dt>
324 <p>If this flag bit is ored into the flag value (or the program runs setuid
325 or setgid) then libev will <i>not</i> look at the environment variable
326 <code>LIBEV_FLAGS</code>. Otherwise (the default), this environment variable will
327 override the flags completely if it is found in the environment. This is
328 useful to try out specific backends to test their performance, or to work
331 <dt><code>EVBACKEND_SELECT</code> (value 1, portable select backend)</dt>
333 <p>This is your standard select(2) backend. Not <i>completely</i> standard, as
334 libev tries to roll its own fd_set with no limits on the number of fds,
335 but if that fails, expect a fairly low limit on the number of fds when
336 using this backend. It doesn't scale too well (O(highest_fd)), but its usually
337 the fastest backend for a low number of fds.</p>
339 <dt><code>EVBACKEND_POLL</code> (value 2, poll backend, available everywhere except on windows)</dt>
341 <p>And this is your standard poll(2) backend. It's more complicated than
342 select, but handles sparse fds better and has no artificial limit on the
343 number of fds you can use (except it will slow down considerably with a
344 lot of inactive fds). It scales similarly to select, i.e. O(total_fds).</p>
346 <dt><code>EVBACKEND_EPOLL</code> (value 4, Linux)</dt>
348 <p>For few fds, this backend is a bit little slower than poll and select,
349 but it scales phenomenally better. While poll and select usually scale like
350 O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
351 either O(1) or O(active_fds).</p>
352 <p>While stopping and starting an I/O watcher in the same iteration will
353 result in some caching, there is still a syscall per such incident
354 (because the fd could point to a different file description now), so its
355 best to avoid that. Also, dup()ed file descriptors might not work very
356 well if you register events for both fds.</p>
357 <p>Please note that epoll sometimes generates spurious notifications, so you
358 need to use non-blocking I/O or other means to avoid blocking when no data
359 (or space) is available.</p>
361 <dt><code>EVBACKEND_KQUEUE</code> (value 8, most BSD clones)</dt>
363 <p>Kqueue deserves special mention, as at the time of this writing, it
364 was broken on all BSDs except NetBSD (usually it doesn't work with
365 anything but sockets and pipes, except on Darwin, where of course its
366 completely useless). For this reason its not being "autodetected"
367 unless you explicitly specify it explicitly in the flags (i.e. using
368 <code>EVBACKEND_KQUEUE</code>).</p>
369 <p>It scales in the same way as the epoll backend, but the interface to the
370 kernel is more efficient (which says nothing about its actual speed, of
371 course). While starting and stopping an I/O watcher does not cause an
372 extra syscall as with epoll, it still adds up to four event changes per
373 incident, so its best to avoid that.</p>
375 <dt><code>EVBACKEND_DEVPOLL</code> (value 16, Solaris 8)</dt>
377 <p>This is not implemented yet (and might never be).</p>
379 <dt><code>EVBACKEND_PORT</code> (value 32, Solaris 10)</dt>
381 <p>This uses the Solaris 10 port mechanism. As with everything on Solaris,
382 it's really slow, but it still scales very well (O(active_fds)).</p>
383 <p>Please note that solaris ports can result in a lot of spurious
384 notifications, so you need to use non-blocking I/O or other means to avoid
385 blocking when no data (or space) is available.</p>
387 <dt><code>EVBACKEND_ALL</code></dt>
389 <p>Try all backends (even potentially broken ones that wouldn't be tried
390 with <code>EVFLAG_AUTO</code>). Since this is a mask, you can do stuff such as
391 <code>EVBACKEND_ALL & ~EVBACKEND_KQUEUE</code>.</p>
395 <p>If one or more of these are ored into the flags value, then only these
396 backends will be tried (in the reverse order as given here). If none are
397 specified, most compiled-in backend will be tried, usually in reverse
398 order of their flag values :)</p>
399 <p>The most typical usage is like this:</p>
400 <pre> if (!ev_default_loop (0))
401 fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
404 <p>Restrict libev to the select and poll backends, and do not allow
405 environment settings to be taken into account:</p>
406 <pre> ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
409 <p>Use whatever libev has to offer, but make sure that kqueue is used if
410 available (warning, breaks stuff, best use only with your own private
411 event loop and only if you know the OS supports your types of fds):</p>
412 <pre> ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
416 <dt>struct ev_loop *ev_loop_new (unsigned int flags)</dt>
418 <p>Similar to <code>ev_default_loop</code>, but always creates a new event loop that is
419 always distinct from the default loop. Unlike the default loop, it cannot
420 handle signal and child watchers, and attempts to do so will be greeted by
421 undefined behaviour (or a failed assertion if assertions are enabled).</p>
422 <p>Example: Try to create a event loop that uses epoll and nothing else.</p>
423 <pre> struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
425 fatal ("no epoll found here, maybe it hides under your chair");
429 <dt>ev_default_destroy ()</dt>
431 <p>Destroys the default loop again (frees all memory and kernel state
432 etc.). None of the active event watchers will be stopped in the normal
433 sense, so e.g. <code>ev_is_active</code> might still return true. It is your
434 responsibility to either stop all watchers cleanly yoursef <i>before</i>
435 calling this function, or cope with the fact afterwards (which is usually
436 the easiest thing, youc na just ignore the watchers and/or <code>free ()</code> them
439 <dt>ev_loop_destroy (loop)</dt>
441 <p>Like <code>ev_default_destroy</code>, but destroys an event loop created by an
442 earlier call to <code>ev_loop_new</code>.</p>
444 <dt>ev_default_fork ()</dt>
446 <p>This function reinitialises the kernel state for backends that have
447 one. Despite the name, you can call it anytime, but it makes most sense
448 after forking, in either the parent or child process (or both, but that
449 again makes little sense).</p>
450 <p>You <i>must</i> call this function in the child process after forking if and
451 only if you want to use the event library in both processes. If you just
452 fork+exec, you don't have to call it.</p>
453 <p>The function itself is quite fast and it's usually not a problem to call
454 it just in case after a fork. To make this easy, the function will fit in
455 quite nicely into a call to <code>pthread_atfork</code>:</p>
456 <pre> pthread_atfork (0, 0, ev_default_fork);
459 <p>At the moment, <code>EVBACKEND_SELECT</code> and <code>EVBACKEND_POLL</code> are safe to use
460 without calling this function, so if you force one of those backends you
461 do not need to care.</p>
463 <dt>ev_loop_fork (loop)</dt>
465 <p>Like <code>ev_default_fork</code>, but acts on an event loop created by
466 <code>ev_loop_new</code>. Yes, you have to call this on every allocated event loop
467 after fork, and how you do this is entirely your own problem.</p>
469 <dt>unsigned int ev_backend (loop)</dt>
471 <p>Returns one of the <code>EVBACKEND_*</code> flags indicating the event backend in
474 <dt>ev_tstamp ev_now (loop)</dt>
476 <p>Returns the current "event loop time", which is the time the event loop
477 received events and started processing them. This timestamp does not
478 change as long as callbacks are being processed, and this is also the base
479 time used for relative timers. You can treat it as the timestamp of the
480 event occuring (or more correctly, libev finding out about it).</p>
482 <dt>ev_loop (loop, int flags)</dt>
484 <p>Finally, this is it, the event handler. This function usually is called
485 after you initialised all your watchers and you want to start handling
487 <p>If the flags argument is specified as <code>0</code>, it will not return until
488 either no event watchers are active anymore or <code>ev_unloop</code> was called.</p>
489 <p>Please note that an explicit <code>ev_unloop</code> is usually better than
490 relying on all watchers to be stopped when deciding when a program has
491 finished (especially in interactive programs), but having a program that
492 automatically loops as long as it has to and no longer by virtue of
493 relying on its watchers stopping correctly is a thing of beauty.</p>
494 <p>A flags value of <code>EVLOOP_NONBLOCK</code> will look for new events, will handle
495 those events and any outstanding ones, but will not block your process in
496 case there are no events and will return after one iteration of the loop.</p>
497 <p>A flags value of <code>EVLOOP_ONESHOT</code> will look for new events (waiting if
498 neccessary) and will handle those and any outstanding ones. It will block
499 your process until at least one new event arrives, and will return after
500 one iteration of the loop. This is useful if you are waiting for some
501 external event in conjunction with something not expressible using other
502 libev watchers. However, a pair of <code>ev_prepare</code>/<code>ev_check</code> watchers is
503 usually a better approach for this kind of thing.</p>
504 <p>Here are the gory details of what <code>ev_loop</code> does:</p>
505 <pre> * If there are no active watchers (reference count is zero), return.
506 - Queue prepare watchers and then call all outstanding watchers.
507 - If we have been forked, recreate the kernel state.
508 - Update the kernel state with all outstanding changes.
509 - Update the "event loop time".
510 - Calculate for how long to block.
511 - Block the process, waiting for any events.
512 - Queue all outstanding I/O (fd) events.
513 - Update the "event loop time" and do time jump handling.
514 - Queue all outstanding timers.
515 - Queue all outstanding periodics.
516 - If no events are pending now, queue all idle watchers.
517 - Queue all check watchers.
518 - Call all queued watchers in reverse order (i.e. check watchers first).
519 Signals and child watchers are implemented as I/O watchers, and will
520 be handled here by queueing them when their watcher gets executed.
521 - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
522 were used, return, otherwise continue with step *.
525 <p>Example: Queue some jobs and then loop until no events are outsanding
527 <pre> ... queue jobs here, make sure they register event watchers as long
528 ... as they still have work to do (even an idle watcher will do..)
529 ev_loop (my_loop, 0);
534 <dt>ev_unloop (loop, how)</dt>
536 <p>Can be used to make a call to <code>ev_loop</code> return early (but only after it
537 has processed all outstanding events). The <code>how</code> argument must be either
538 <code>EVUNLOOP_ONE</code>, which will make the innermost <code>ev_loop</code> call return, or
539 <code>EVUNLOOP_ALL</code>, which will make all nested <code>ev_loop</code> calls return.</p>
541 <dt>ev_ref (loop)</dt>
542 <dt>ev_unref (loop)</dt>
544 <p>Ref/unref can be used to add or remove a reference count on the event
545 loop: Every watcher keeps one reference, and as long as the reference
546 count is nonzero, <code>ev_loop</code> will not return on its own. If you have
547 a watcher you never unregister that should not keep <code>ev_loop</code> from
548 returning, ev_unref() after starting, and ev_ref() before stopping it. For
549 example, libev itself uses this for its internal signal pipe: It is not
550 visible to the libev user and should not keep <code>ev_loop</code> from exiting if
551 no event watchers registered by it are active. It is also an excellent
552 way to do this for generic recurring timers or from within third-party
553 libraries. Just remember to <i>unref after start</i> and <i>ref before stop</i>.</p>
554 <p>Example: Create a signal watcher, but keep it from keeping <code>ev_loop</code>
555 running when nothing else is active.</p>
556 <pre> struct ev_signal exitsig;
557 ev_signal_init (&exitsig, sig_cb, SIGINT);
558 ev_signal_start (loop, &exitsig);
562 <p>Example: For some weird reason, unregister the above signal handler again.</p>
564 ev_signal_stop (loop, &exitsig);
575 <h1 id="ANATOMY_OF_A_WATCHER">ANATOMY OF A WATCHER</h1>
576 <div id="ANATOMY_OF_A_WATCHER_CONTENT">
577 <p>A watcher is a structure that you create and register to record your
578 interest in some event. For instance, if you want to wait for STDIN to
579 become readable, you would create an <code>ev_io</code> watcher for that:</p>
580 <pre> static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
583 ev_unloop (loop, EVUNLOOP_ALL);
586 struct ev_loop *loop = ev_default_loop (0);
587 struct ev_io stdin_watcher;
588 ev_init (&stdin_watcher, my_cb);
589 ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
590 ev_io_start (loop, &stdin_watcher);
594 <p>As you can see, you are responsible for allocating the memory for your
595 watcher structures (and it is usually a bad idea to do this on the stack,
596 although this can sometimes be quite valid).</p>
597 <p>Each watcher structure must be initialised by a call to <code>ev_init
598 (watcher *, callback)</code>, which expects a callback to be provided. This
599 callback gets invoked each time the event occurs (or, in the case of io
600 watchers, each time the event loop detects that the file descriptor given
601 is readable and/or writable).</p>
602 <p>Each watcher type has its own <code>ev_<type>_set (watcher *, ...)</code> macro
603 with arguments specific to this watcher type. There is also a macro
604 to combine initialisation and setting in one call: <code>ev_<type>_init
605 (watcher *, callback, ...)</code>.</p>
606 <p>To make the watcher actually watch out for events, you have to start it
607 with a watcher-specific start function (<code>ev_<type>_start (loop, watcher
608 *)</code>), and you can stop watching for events at any time by calling the
609 corresponding stop function (<code>ev_<type>_stop (loop, watcher *)</code>.</p>
610 <p>As long as your watcher is active (has been started but not stopped) you
611 must not touch the values stored in it. Most specifically you must never
612 reinitialise it or call its <code>set</code> macro.</p>
613 <p>Each and every callback receives the event loop pointer as first, the
614 registered watcher structure as second, and a bitset of received events as
616 <p>The received events usually include a single bit per event type received
617 (you can receive multiple events at the same time). The possible bit masks
620 <dt><code>EV_READ</code></dt>
621 <dt><code>EV_WRITE</code></dt>
623 <p>The file descriptor in the <code>ev_io</code> watcher has become readable and/or
626 <dt><code>EV_TIMEOUT</code></dt>
628 <p>The <code>ev_timer</code> watcher has timed out.</p>
630 <dt><code>EV_PERIODIC</code></dt>
632 <p>The <code>ev_periodic</code> watcher has timed out.</p>
634 <dt><code>EV_SIGNAL</code></dt>
636 <p>The signal specified in the <code>ev_signal</code> watcher has been received by a thread.</p>
638 <dt><code>EV_CHILD</code></dt>
640 <p>The pid specified in the <code>ev_child</code> watcher has received a status change.</p>
642 <dt><code>EV_STAT</code></dt>
644 <p>The path specified in the <code>ev_stat</code> watcher changed its attributes somehow.</p>
646 <dt><code>EV_IDLE</code></dt>
648 <p>The <code>ev_idle</code> watcher has determined that you have nothing better to do.</p>
650 <dt><code>EV_PREPARE</code></dt>
651 <dt><code>EV_CHECK</code></dt>
653 <p>All <code>ev_prepare</code> watchers are invoked just <i>before</i> <code>ev_loop</code> starts
654 to gather new events, and all <code>ev_check</code> watchers are invoked just after
655 <code>ev_loop</code> has gathered them, but before it invokes any callbacks for any
656 received events. Callbacks of both watcher types can start and stop as
657 many watchers as they want, and all of them will be taken into account
658 (for example, a <code>ev_prepare</code> watcher might start an idle watcher to keep
659 <code>ev_loop</code> from blocking).</p>
661 <dt><code>EV_EMBED</code></dt>
663 <p>The embedded event loop specified in the <code>ev_embed</code> watcher needs attention.</p>
665 <dt><code>EV_FORK</code></dt>
667 <p>The event loop has been resumed in the child process after fork (see
668 <code>ev_fork</code>).</p>
670 <dt><code>EV_ERROR</code></dt>
672 <p>An unspecified error has occured, the watcher has been stopped. This might
673 happen because the watcher could not be properly started because libev
674 ran out of memory, a file descriptor was found to be closed or any other
675 problem. You best act on it by reporting the problem and somehow coping
676 with the watcher being stopped.</p>
677 <p>Libev will usually signal a few "dummy" events together with an error,
678 for example it might indicate that a fd is readable or writable, and if
679 your callbacks is well-written it can just attempt the operation and cope
680 with the error from read() or write(). This will not work in multithreaded
681 programs, though, so beware.</p>
686 <h2 id="GENERIC_WATCHER_FUNCTIONS">GENERIC WATCHER FUNCTIONS</h2>
687 <div id="GENERIC_WATCHER_FUNCTIONS_CONTENT">
688 <p>In the following description, <code>TYPE</code> stands for the watcher type,
689 e.g. <code>timer</code> for <code>ev_timer</code> watchers and <code>io</code> for <code>ev_io</code> watchers.</p>
691 <dt><code>ev_init</code> (ev_TYPE *watcher, callback)</dt>
693 <p>This macro initialises the generic portion of a watcher. The contents
694 of the watcher object can be arbitrary (so <code>malloc</code> will do). Only
695 the generic parts of the watcher are initialised, you <i>need</i> to call
696 the type-specific <code>ev_TYPE_set</code> macro afterwards to initialise the
697 type-specific parts. For each type there is also a <code>ev_TYPE_init</code> macro
698 which rolls both calls into one.</p>
699 <p>You can reinitialise a watcher at any time as long as it has been stopped
700 (or never started) and there are no pending events outstanding.</p>
701 <p>The callback is always of type <code>void (*)(ev_loop *loop, ev_TYPE *watcher,
702 int revents)</code>.</p>
704 <dt><code>ev_TYPE_set</code> (ev_TYPE *, [args])</dt>
706 <p>This macro initialises the type-specific parts of a watcher. You need to
707 call <code>ev_init</code> at least once before you call this macro, but you can
708 call <code>ev_TYPE_set</code> any number of times. You must not, however, call this
709 macro on a watcher that is active (it can be pending, however, which is a
710 difference to the <code>ev_init</code> macro).</p>
711 <p>Although some watcher types do not have type-specific arguments
712 (e.g. <code>ev_prepare</code>) you still need to call its <code>set</code> macro.</p>
714 <dt><code>ev_TYPE_init</code> (ev_TYPE *watcher, callback, [args])</dt>
716 <p>This convinience macro rolls both <code>ev_init</code> and <code>ev_TYPE_set</code> macro
717 calls into a single call. This is the most convinient method to initialise
718 a watcher. The same limitations apply, of course.</p>
720 <dt><code>ev_TYPE_start</code> (loop *, ev_TYPE *watcher)</dt>
722 <p>Starts (activates) the given watcher. Only active watchers will receive
723 events. If the watcher is already active nothing will happen.</p>
725 <dt><code>ev_TYPE_stop</code> (loop *, ev_TYPE *watcher)</dt>
727 <p>Stops the given watcher again (if active) and clears the pending
728 status. It is possible that stopped watchers are pending (for example,
729 non-repeating timers are being stopped when they become pending), but
730 <code>ev_TYPE_stop</code> ensures that the watcher is neither active nor pending. If
731 you want to free or reuse the memory used by the watcher it is therefore a
732 good idea to always call its <code>ev_TYPE_stop</code> function.</p>
734 <dt>bool ev_is_active (ev_TYPE *watcher)</dt>
736 <p>Returns a true value iff the watcher is active (i.e. it has been started
737 and not yet been stopped). As long as a watcher is active you must not modify
740 <dt>bool ev_is_pending (ev_TYPE *watcher)</dt>
742 <p>Returns a true value iff the watcher is pending, (i.e. it has outstanding
743 events but its callback has not yet been invoked). As long as a watcher
744 is pending (but not active) you must not call an init function on it (but
745 <code>ev_TYPE_set</code> is safe) and you must make sure the watcher is available to
746 libev (e.g. you cnanot <code>free ()</code> it).</p>
748 <dt>callback ev_cb (ev_TYPE *watcher)</dt>
750 <p>Returns the callback currently set on the watcher.</p>
752 <dt>ev_cb_set (ev_TYPE *watcher, callback)</dt>
754 <p>Change the callback. You can change the callback at virtually any time
755 (modulo threads).</p>
764 <h2 id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH">ASSOCIATING CUSTOM DATA WITH A WATCHER</h2>
765 <div id="ASSOCIATING_CUSTOM_DATA_WITH_A_WATCH-2">
766 <p>Each watcher has, by default, a member <code>void *data</code> that you can change
767 and read at any time, libev will completely ignore it. This can be used
768 to associate arbitrary data with your watcher. If you need more data and
769 don't want to allocate memory and store a pointer to it in that data
770 member, you can also "subclass" the watcher type and provide your own
777 struct whatever *mostinteresting;
781 <p>And since your callback will be called with a pointer to the watcher, you
782 can cast it back to your own type:</p>
783 <pre> static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
785 struct my_io *w = (struct my_io *)w_;
790 <p>More interesting and less C-conformant ways of casting your callback type
791 instead have been omitted.</p>
792 <p>Another common scenario is having some data structure with multiple
794 <pre> struct my_biggy
802 <p>In this case getting the pointer to <code>my_biggy</code> is a bit more complicated,
803 you need to use <code>offsetof</code>:</p>
804 <pre> #include <stddef.h>
807 t1_cb (EV_P_ struct ev_timer *w, int revents)
809 struct my_biggy big = (struct my_biggy *
810 (((char *)w) - offsetof (struct my_biggy, t1));
814 t2_cb (EV_P_ struct ev_timer *w, int revents)
816 struct my_biggy big = (struct my_biggy *
817 (((char *)w) - offsetof (struct my_biggy, t2));
826 <h1 id="WATCHER_TYPES">WATCHER TYPES</h1>
827 <div id="WATCHER_TYPES_CONTENT">
828 <p>This section describes each watcher in detail, but will not repeat
829 information given in the last section. Any initialisation/set macros,
830 functions and members specific to the watcher type are explained.</p>
831 <p>Members are additionally marked with either <i>[read-only]</i>, meaning that,
832 while the watcher is active, you can look at the member and expect some
833 sensible content, but you must not modify it (you can modify it while the
834 watcher is stopped to your hearts content), or <i>[read-write]</i>, which
835 means you can expect it to have some sensible content while the watcher
836 is active, but you can also modify it. Modifying it may not do something
837 sensible or take immediate effect (or do anything at all), but libev will
838 not crash or malfunction in any way.</p>
845 <h2 id="code_ev_io_code_is_this_file_descrip"><code>ev_io</code> - is this file descriptor readable or writable?</h2>
846 <div id="code_ev_io_code_is_this_file_descrip-2">
847 <p>I/O watchers check whether a file descriptor is readable or writable
848 in each iteration of the event loop, or, more precisely, when reading
849 would not block the process and writing would at least be able to write
850 some data. This behaviour is called level-triggering because you keep
851 receiving events as long as the condition persists. Remember you can stop
852 the watcher if you don't want to act on the event and neither want to
853 receive future events.</p>
854 <p>In general you can register as many read and/or write event watchers per
855 fd as you want (as long as you don't confuse yourself). Setting all file
856 descriptors to non-blocking mode is also usually a good idea (but not
857 required if you know what you are doing).</p>
858 <p>You have to be careful with dup'ed file descriptors, though. Some backends
859 (the linux epoll backend is a notable example) cannot handle dup'ed file
860 descriptors correctly if you register interest in two or more fds pointing
861 to the same underlying file/socket/etc. description (that is, they share
862 the same underlying "file open").</p>
863 <p>If you must do this, then force the use of a known-to-be-good backend
864 (at the time of this writing, this includes only <code>EVBACKEND_SELECT</code> and
865 <code>EVBACKEND_POLL</code>).</p>
866 <p>Another thing you have to watch out for is that it is quite easy to
867 receive "spurious" readyness notifications, that is your callback might
868 be called with <code>EV_READ</code> but a subsequent <code>read</code>(2) will actually block
869 because there is no data. Not only are some backends known to create a
870 lot of those (for example solaris ports), it is very easy to get into
871 this situation even with a relatively standard program structure. Thus
872 it is best to always use non-blocking I/O: An extra <code>read</code>(2) returning
873 <code>EAGAIN</code> is far preferable to a program hanging until some data arrives.</p>
874 <p>If you cannot run the fd in non-blocking mode (for example you should not
875 play around with an Xlib connection), then you have to seperately re-test
876 wether a file descriptor is really ready with a known-to-be good interface
877 such as poll (fortunately in our Xlib example, Xlib already does this on
878 its own, so its quite safe to use).</p>
880 <dt>ev_io_init (ev_io *, callback, int fd, int events)</dt>
881 <dt>ev_io_set (ev_io *, int fd, int events)</dt>
883 <p>Configures an <code>ev_io</code> watcher. The <code>fd</code> is the file descriptor to
884 rceeive events for and events is either <code>EV_READ</code>, <code>EV_WRITE</code> or
885 <code>EV_READ | EV_WRITE</code> to receive the given events.</p>
887 <dt>int fd [read-only]</dt>
889 <p>The file descriptor being watched.</p>
891 <dt>int events [read-only]</dt>
893 <p>The events being watched.</p>
896 <p>Example: Call <code>stdin_readable_cb</code> when STDIN_FILENO has become, well
897 readable, but only once. Since it is likely line-buffered, you could
898 attempt to read a whole line in the callback.</p>
900 stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
902 ev_io_stop (loop, w);
903 .. read from stdin here (or from w->fd) and haqndle any I/O errors
907 struct ev_loop *loop = ev_default_init (0);
908 struct ev_io stdin_readable;
909 ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
910 ev_io_start (loop, &stdin_readable);
919 <h2 id="code_ev_timer_code_relative_and_opti"><code>ev_timer</code> - relative and optionally repeating timeouts</h2>
920 <div id="code_ev_timer_code_relative_and_opti-2">
921 <p>Timer watchers are simple relative timers that generate an event after a
922 given time, and optionally repeating in regular intervals after that.</p>
923 <p>The timers are based on real time, that is, if you register an event that
924 times out after an hour and you reset your system clock to last years
925 time, it will still time out after (roughly) and hour. "Roughly" because
926 detecting time jumps is hard, and some inaccuracies are unavoidable (the
927 monotonic clock option helps a lot here).</p>
928 <p>The relative timeouts are calculated relative to the <code>ev_now ()</code>
929 time. This is usually the right thing as this timestamp refers to the time
930 of the event triggering whatever timeout you are modifying/starting. If
931 you suspect event processing to be delayed and you <i>need</i> to base the timeout
932 on the current time, use something like this to adjust for this:</p>
933 <pre> ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
936 <p>The callback is guarenteed to be invoked only when its timeout has passed,
937 but if multiple timers become ready during the same loop iteration then
938 order of execution is undefined.</p>
940 <dt>ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)</dt>
941 <dt>ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)</dt>
943 <p>Configure the timer to trigger after <code>after</code> seconds. If <code>repeat</code> is
944 <code>0.</code>, then it will automatically be stopped. If it is positive, then the
945 timer will automatically be configured to trigger again <code>repeat</code> seconds
946 later, again, and again, until stopped manually.</p>
947 <p>The timer itself will do a best-effort at avoiding drift, that is, if you
948 configure a timer to trigger every 10 seconds, then it will trigger at
949 exactly 10 second intervals. If, however, your program cannot keep up with
950 the timer (because it takes longer than those 10 seconds to do stuff) the
951 timer will not fire more than once per event loop iteration.</p>
953 <dt>ev_timer_again (loop)</dt>
955 <p>This will act as if the timer timed out and restart it again if it is
956 repeating. The exact semantics are:</p>
957 <p>If the timer is started but nonrepeating, stop it.</p>
958 <p>If the timer is repeating, either start it if necessary (with the repeat
959 value), or reset the running timer to the repeat value.</p>
960 <p>This sounds a bit complicated, but here is a useful and typical
961 example: Imagine you have a tcp connection and you want a so-called
962 idle timeout, that is, you want to be called when there have been,
963 say, 60 seconds of inactivity on the socket. The easiest way to do
964 this is to configure an <code>ev_timer</code> with <code>after</code>=<code>repeat</code>=<code>60</code> and calling
965 <code>ev_timer_again</code> each time you successfully read or write some data. If
966 you go into an idle state where you do not expect data to travel on the
967 socket, you can stop the timer, and again will automatically restart it if
969 <p>You can also ignore the <code>after</code> value and <code>ev_timer_start</code> altogether
970 and only ever use the <code>repeat</code> value:</p>
971 <pre> ev_timer_init (timer, callback, 0., 5.);
972 ev_timer_again (loop, timer);
974 timer->again = 17.;
975 ev_timer_again (loop, timer);
977 timer->again = 10.;
978 ev_timer_again (loop, timer);
981 <p>This is more efficient then stopping/starting the timer eahc time you want
982 to modify its timeout value.</p>
984 <dt>ev_tstamp repeat [read-write]</dt>
986 <p>The current <code>repeat</code> value. Will be used each time the watcher times out
987 or <code>ev_timer_again</code> is called and determines the next timeout (if any),
988 which is also when any modifications are taken into account.</p>
991 <p>Example: Create a timer that fires after 60 seconds.</p>
993 one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
995 .. one minute over, w is actually stopped right here
998 struct ev_timer mytimer;
999 ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1000 ev_timer_start (loop, &mytimer);
1003 <p>Example: Create a timeout timer that times out after 10 seconds of
1006 timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1008 .. ten seconds without any activity
1011 struct ev_timer mytimer;
1012 ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1013 ev_timer_again (&mytimer); /* start timer */
1016 // and in some piece of code that gets executed on any "activity":
1017 // reset the timeout to start ticking again at 10 seconds
1018 ev_timer_again (&mytimer);
1026 <h2 id="code_ev_periodic_code_to_cron_or_not"><code>ev_periodic</code> - to cron or not to cron?</h2>
1027 <div id="code_ev_periodic_code_to_cron_or_not-2">
1028 <p>Periodic watchers are also timers of a kind, but they are very versatile
1029 (and unfortunately a bit complex).</p>
1030 <p>Unlike <code>ev_timer</code>'s, they are not based on real time (or relative time)
1031 but on wallclock time (absolute time). You can tell a periodic watcher
1032 to trigger "at" some specific point in time. For example, if you tell a
1033 periodic watcher to trigger in 10 seconds (by specifiying e.g. <code>ev_now ()
1034 + 10.</code>) and then reset your system clock to the last year, then it will
1035 take a year to trigger the event (unlike an <code>ev_timer</code>, which would trigger
1036 roughly 10 seconds later and of course not if you reset your system time
1038 <p>They can also be used to implement vastly more complex timers, such as
1039 triggering an event on eahc midnight, local time.</p>
1040 <p>As with timers, the callback is guarenteed to be invoked only when the
1041 time (<code>at</code>) has been passed, but if multiple periodic timers become ready
1042 during the same loop iteration then order of execution is undefined.</p>
1044 <dt>ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)</dt>
1045 <dt>ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)</dt>
1047 <p>Lots of arguments, lets sort it out... There are basically three modes of
1048 operation, and we will explain them from simplest to complex:</p>
1051 <dt>* absolute timer (interval = reschedule_cb = 0)</dt>
1053 <p>In this configuration the watcher triggers an event at the wallclock time
1054 <code>at</code> and doesn't repeat. It will not adjust when a time jump occurs,
1055 that is, if it is to be run at January 1st 2011 then it will run when the
1056 system time reaches or surpasses this time.</p>
1058 <dt>* non-repeating interval timer (interval > 0, reschedule_cb = 0)</dt>
1060 <p>In this mode the watcher will always be scheduled to time out at the next
1061 <code>at + N * interval</code> time (for some integer N) and then repeat, regardless
1062 of any time jumps.</p>
1063 <p>This can be used to create timers that do not drift with respect to system
1065 <pre> ev_periodic_set (&periodic, 0., 3600., 0);
1068 <p>This doesn't mean there will always be 3600 seconds in between triggers,
1069 but only that the the callback will be called when the system time shows a
1070 full hour (UTC), or more correctly, when the system time is evenly divisible
1072 <p>Another way to think about it (for the mathematically inclined) is that
1073 <code>ev_periodic</code> will try to run the callback in this mode at the next possible
1074 time where <code>time = at (mod interval)</code>, regardless of any time jumps.</p>
1076 <dt>* manual reschedule mode (reschedule_cb = callback)</dt>
1078 <p>In this mode the values for <code>interval</code> and <code>at</code> are both being
1079 ignored. Instead, each time the periodic watcher gets scheduled, the
1080 reschedule callback will be called with the watcher as first, and the
1081 current time as second argument.</p>
1082 <p>NOTE: <i>This callback MUST NOT stop or destroy any periodic watcher,
1083 ever, or make any event loop modifications</i>. If you need to stop it,
1084 return <code>now + 1e30</code> (or so, fudge fudge) and stop it afterwards (e.g. by
1085 starting a prepare watcher).</p>
1086 <p>Its prototype is <code>ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
1087 ev_tstamp now)</code>, e.g.:</p>
1088 <pre> static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1094 <p>It must return the next time to trigger, based on the passed time value
1095 (that is, the lowest time value larger than to the second argument). It
1096 will usually be called just before the callback will be triggered, but
1097 might be called at other times, too.</p>
1098 <p>NOTE: <i>This callback must always return a time that is later than the
1099 passed <code>now</code> value</i>. Not even <code>now</code> itself will do, it <i>must</i> be larger.</p>
1100 <p>This can be used to create very complex timers, such as a timer that
1101 triggers on each midnight, local time. To do this, you would calculate the
1102 next midnight after <code>now</code> and return the timestamp value for this. How
1103 you do this is, again, up to you (but it is not trivial, which is the main
1104 reason I omitted it as an example).</p>
1109 <dt>ev_periodic_again (loop, ev_periodic *)</dt>
1111 <p>Simply stops and restarts the periodic watcher again. This is only useful
1112 when you changed some parameters or the reschedule callback would return
1113 a different time than the last time it was called (e.g. in a crond like
1114 program when the crontabs have changed).</p>
1116 <dt>ev_tstamp interval [read-write]</dt>
1118 <p>The current interval value. Can be modified any time, but changes only
1119 take effect when the periodic timer fires or <code>ev_periodic_again</code> is being
1122 <dt>ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]</dt>
1124 <p>The current reschedule callback, or <code>0</code>, if this functionality is
1125 switched off. Can be changed any time, but changes only take effect when
1126 the periodic timer fires or <code>ev_periodic_again</code> is being called.</p>
1129 <p>Example: Call a callback every hour, or, more precisely, whenever the
1130 system clock is divisible by 3600. The callback invocation times have
1131 potentially a lot of jittering, but good long-term stability.</p>
1133 clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1135 ... its now a full hour (UTC, or TAI or whatever your clock follows)
1138 struct ev_periodic hourly_tick;
1139 ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1140 ev_periodic_start (loop, &hourly_tick);
1143 <p>Example: The same as above, but use a reschedule callback to do it:</p>
1144 <pre> #include <math.h>
1147 my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
1149 return fmod (now, 3600.) + 3600.;
1152 ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1155 <p>Example: Call a callback every hour, starting now:</p>
1156 <pre> struct ev_periodic hourly_tick;
1157 ev_periodic_init (&hourly_tick, clock_cb,
1158 fmod (ev_now (loop), 3600.), 3600., 0);
1159 ev_periodic_start (loop, &hourly_tick);
1167 <h2 id="code_ev_signal_code_signal_me_when_a"><code>ev_signal</code> - signal me when a signal gets signalled!</h2>
1168 <div id="code_ev_signal_code_signal_me_when_a-2">
1169 <p>Signal watchers will trigger an event when the process receives a specific
1170 signal one or more times. Even though signals are very asynchronous, libev
1171 will try it's best to deliver signals synchronously, i.e. as part of the
1172 normal event processing, like any other event.</p>
1173 <p>You can configure as many watchers as you like per signal. Only when the
1174 first watcher gets started will libev actually register a signal watcher
1175 with the kernel (thus it coexists with your own signal handlers as long
1176 as you don't register any with libev). Similarly, when the last signal
1177 watcher for a signal is stopped libev will reset the signal handler to
1178 SIG_DFL (regardless of what it was set to before).</p>
1180 <dt>ev_signal_init (ev_signal *, callback, int signum)</dt>
1181 <dt>ev_signal_set (ev_signal *, int signum)</dt>
1183 <p>Configures the watcher to trigger on the given signal number (usually one
1184 of the <code>SIGxxx</code> constants).</p>
1186 <dt>int signum [read-only]</dt>
1188 <p>The signal the watcher watches out for.</p>
1197 <h2 id="code_ev_child_code_watch_out_for_pro"><code>ev_child</code> - watch out for process status changes</h2>
1198 <div id="code_ev_child_code_watch_out_for_pro-2">
1199 <p>Child watchers trigger when your process receives a SIGCHLD in response to
1200 some child status changes (most typically when a child of yours dies).</p>
1202 <dt>ev_child_init (ev_child *, callback, int pid)</dt>
1203 <dt>ev_child_set (ev_child *, int pid)</dt>
1205 <p>Configures the watcher to wait for status changes of process <code>pid</code> (or
1206 <i>any</i> process if <code>pid</code> is specified as <code>0</code>). The callback can look
1207 at the <code>rstatus</code> member of the <code>ev_child</code> watcher structure to see
1208 the status word (use the macros from <code>sys/wait.h</code> and see your systems
1209 <code>waitpid</code> documentation). The <code>rpid</code> member contains the pid of the
1210 process causing the status change.</p>
1212 <dt>int pid [read-only]</dt>
1214 <p>The process id this watcher watches out for, or <code>0</code>, meaning any process id.</p>
1216 <dt>int rpid [read-write]</dt>
1218 <p>The process id that detected a status change.</p>
1220 <dt>int rstatus [read-write]</dt>
1222 <p>The process exit/trace status caused by <code>rpid</code> (see your systems
1223 <code>waitpid</code> and <code>sys/wait.h</code> documentation for details).</p>
1226 <p>Example: Try to exit cleanly on SIGINT and SIGTERM.</p>
1228 sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1230 ev_unloop (loop, EVUNLOOP_ALL);
1233 struct ev_signal signal_watcher;
1234 ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1235 ev_signal_start (loop, &sigint_cb);
1243 <h2 id="code_ev_stat_code_did_the_file_attri"><code>ev_stat</code> - did the file attributes just change?</h2>
1244 <div id="code_ev_stat_code_did_the_file_attri-2">
1245 <p>This watches a filesystem path for attribute changes. That is, it calls
1246 <code>stat</code> regularly (or when the OS says it changed) and sees if it changed
1247 compared to the last time, invoking the callback if it did.</p>
1248 <p>The path does not need to exist: changing from "path exists" to "path does
1249 not exist" is a status change like any other. The condition "path does
1250 not exist" is signified by the <code>st_nlink</code> field being zero (which is
1251 otherwise always forced to be at least one) and all the other fields of
1252 the stat buffer having unspecified contents.</p>
1253 <p>Since there is no standard to do this, the portable implementation simply
1254 calls <code>stat (2)</code> regularly on the path to see if it changed somehow. You
1255 can specify a recommended polling interval for this case. If you specify
1256 a polling interval of <code>0</code> (highly recommended!) then a <i>suitable,
1257 unspecified default</i> value will be used (which you can expect to be around
1258 five seconds, although this might change dynamically). Libev will also
1259 impose a minimum interval which is currently around <code>0.1</code>, but thats
1260 usually overkill.</p>
1261 <p>This watcher type is not meant for massive numbers of stat watchers,
1262 as even with OS-supported change notifications, this can be
1263 resource-intensive.</p>
1264 <p>At the time of this writing, only the Linux inotify interface is
1265 implemented (implementing kqueue support is left as an exercise for the
1266 reader). Inotify will be used to give hints only and should not change the
1267 semantics of <code>ev_stat</code> watchers, which means that libev sometimes needs
1268 to fall back to regular polling again even with inotify, but changes are
1269 usually detected immediately, and if the file exists there will be no
1272 <dt>ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)</dt>
1273 <dt>ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)</dt>
1275 <p>Configures the watcher to wait for status changes of the given
1276 <code>path</code>. The <code>interval</code> is a hint on how quickly a change is expected to
1277 be detected and should normally be specified as <code>0</code> to let libev choose
1278 a suitable value. The memory pointed to by <code>path</code> must point to the same
1279 path for as long as the watcher is active.</p>
1280 <p>The callback will be receive <code>EV_STAT</code> when a change was detected,
1281 relative to the attributes at the time the watcher was started (or the
1282 last change was detected).</p>
1284 <dt>ev_stat_stat (ev_stat *)</dt>
1286 <p>Updates the stat buffer immediately with new values. If you change the
1287 watched path in your callback, you could call this fucntion to avoid
1288 detecting this change (while introducing a race condition). Can also be
1289 useful simply to find out the new values.</p>
1291 <dt>ev_statdata attr [read-only]</dt>
1293 <p>The most-recently detected attributes of the file. Although the type is of
1294 <code>ev_statdata</code>, this is usually the (or one of the) <code>struct stat</code> types
1295 suitable for your system. If the <code>st_nlink</code> member is <code>0</code>, then there
1296 was some error while <code>stat</code>ing the file.</p>
1298 <dt>ev_statdata prev [read-only]</dt>
1300 <p>The previous attributes of the file. The callback gets invoked whenever
1301 <code>prev</code> != <code>attr</code>.</p>
1303 <dt>ev_tstamp interval [read-only]</dt>
1305 <p>The specified interval.</p>
1307 <dt>const char *path [read-only]</dt>
1309 <p>The filesystem path that is being watched.</p>
1312 <p>Example: Watch <code>/etc/passwd</code> for attribute changes.</p>
1314 passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1316 /* /etc/passwd changed in some way */
1317 if (w->attr.st_nlink)
1319 printf ("passwd current size %ld\n", (long)w->attr.st_size);
1320 printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1321 printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1324 /* you shalt not abuse printf for puts */
1325 puts ("wow, /etc/passwd is not there, expect problems. "
1326 "if this is windows, they already arrived\n");
1332 ev_stat_init (&passwd, passwd_cb, "/etc/passwd");
1333 ev_stat_start (loop, &passwd);
1341 <h2 id="code_ev_idle_code_when_you_ve_got_no"><code>ev_idle</code> - when you've got nothing better to do...</h2>
1342 <div id="code_ev_idle_code_when_you_ve_got_no-2">
1343 <p>Idle watchers trigger events when there are no other events are pending
1344 (prepare, check and other idle watchers do not count). That is, as long
1345 as your process is busy handling sockets or timeouts (or even signals,
1346 imagine) it will not be triggered. But when your process is idle all idle
1347 watchers are being called again and again, once per event loop iteration -
1348 until stopped, that is, or your process receives more events and becomes
1350 <p>The most noteworthy effect is that as long as any idle watchers are
1351 active, the process will not block when waiting for new events.</p>
1352 <p>Apart from keeping your process non-blocking (which is a useful
1353 effect on its own sometimes), idle watchers are a good place to do
1354 "pseudo-background processing", or delay processing stuff to after the
1355 event loop has handled all outstanding events.</p>
1357 <dt>ev_idle_init (ev_signal *, callback)</dt>
1359 <p>Initialises and configures the idle watcher - it has no parameters of any
1360 kind. There is a <code>ev_idle_set</code> macro, but using it is utterly pointless,
1364 <p>Example: Dynamically allocate an <code>ev_idle</code> watcher, start it, and in the
1365 callback, free it. Also, use no error checking, as usual.</p>
1367 idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1370 // now do something you wanted to do when the program has
1371 // no longer asnything immediate to do.
1374 struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1375 ev_idle_init (idle_watcher, idle_cb);
1376 ev_idle_start (loop, idle_cb);
1384 <h2 id="code_ev_prepare_code_and_code_ev_che"><code>ev_prepare</code> and <code>ev_check</code> - customise your event loop!</h2>
1385 <div id="code_ev_prepare_code_and_code_ev_che-2">
1386 <p>Prepare and check watchers are usually (but not always) used in tandem:
1387 prepare watchers get invoked before the process blocks and check watchers
1389 <p>You <i>must not</i> call <code>ev_loop</code> or similar functions that enter
1390 the current event loop from either <code>ev_prepare</code> or <code>ev_check</code>
1391 watchers. Other loops than the current one are fine, however. The
1392 rationale behind this is that you do not need to check for recursion in
1393 those watchers, i.e. the sequence will always be <code>ev_prepare</code>, blocking,
1394 <code>ev_check</code> so if you have one watcher of each kind they will always be
1395 called in pairs bracketing the blocking call.</p>
1396 <p>Their main purpose is to integrate other event mechanisms into libev and
1397 their use is somewhat advanced. This could be used, for example, to track
1398 variable changes, implement your own watchers, integrate net-snmp or a
1399 coroutine library and lots more. They are also occasionally useful if
1400 you cache some data and want to flush it before blocking (for example,
1401 in X programs you might want to do an <code>XFlush ()</code> in an <code>ev_prepare</code>
1403 <p>This is done by examining in each prepare call which file descriptors need
1404 to be watched by the other library, registering <code>ev_io</code> watchers for
1405 them and starting an <code>ev_timer</code> watcher for any timeouts (many libraries
1406 provide just this functionality). Then, in the check watcher you check for
1407 any events that occured (by checking the pending status of all watchers
1408 and stopping them) and call back into the library. The I/O and timer
1409 callbacks will never actually be called (but must be valid nevertheless,
1410 because you never know, you know?).</p>
1411 <p>As another example, the Perl Coro module uses these hooks to integrate
1412 coroutines into libev programs, by yielding to other active coroutines
1413 during each prepare and only letting the process block if no coroutines
1414 are ready to run (it's actually more complicated: it only runs coroutines
1415 with priority higher than or equal to the event loop and one coroutine
1416 of lower priority, but only once, using idle watchers to keep the event
1417 loop from blocking if lower-priority coroutines are active, thus mapping
1418 low-priority coroutines to idle/background tasks).</p>
1420 <dt>ev_prepare_init (ev_prepare *, callback)</dt>
1421 <dt>ev_check_init (ev_check *, callback)</dt>
1423 <p>Initialises and configures the prepare or check watcher - they have no
1424 parameters of any kind. There are <code>ev_prepare_set</code> and <code>ev_check_set</code>
1425 macros, but using them is utterly, utterly and completely pointless.</p>
1428 <p>Example: To include a library such as adns, you would add IO watchers
1429 and a timeout watcher in a prepare handler, as required by libadns, and
1430 in a check watcher, destroy them and call into libadns. What follows is
1431 pseudo-code only of course:</p>
1432 <pre> static ev_io iow [nfd];
1436 io_cb (ev_loop *loop, ev_io *w, int revents)
1438 // set the relevant poll flags
1439 // could also call adns_processreadable etc. here
1440 struct pollfd *fd = (struct pollfd *)w->data;
1441 if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1442 if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1445 // create io watchers for each fd and a timer before blocking
1447 adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
1449 int timeout = 3600000;truct pollfd fds [nfd];
1450 // actual code will need to loop here and realloc etc.
1451 adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1453 /* the callback is illegal, but won't be called as we stop during check */
1454 ev_timer_init (&tw, 0, timeout * 1e-3);
1455 ev_timer_start (loop, &tw);
1457 // create on ev_io per pollfd
1458 for (int i = 0; i < nfd; ++i)
1460 ev_io_init (iow + i, io_cb, fds [i].fd,
1461 ((fds [i].events & POLLIN ? EV_READ : 0)
1462 | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1464 fds [i].revents = 0;
1465 iow [i].data = fds + i;
1466 ev_io_start (loop, iow + i);
1470 // stop all watchers after blocking
1472 adns_check_cb (ev_loop *loop, ev_check *w, int revents)
1474 ev_timer_stop (loop, &tw);
1476 for (int i = 0; i < nfd; ++i)
1477 ev_io_stop (loop, iow + i);
1479 adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1488 <h2 id="code_ev_embed_code_when_one_backend_"><code>ev_embed</code> - when one backend isn't enough...</h2>
1489 <div id="code_ev_embed_code_when_one_backend_-2">
1490 <p>This is a rather advanced watcher type that lets you embed one event loop
1491 into another (currently only <code>ev_io</code> events are supported in the embedded
1492 loop, other types of watchers might be handled in a delayed or incorrect
1493 fashion and must not be used).</p>
1494 <p>There are primarily two reasons you would want that: work around bugs and
1496 <p>As an example for a bug workaround, the kqueue backend might only support
1497 sockets on some platform, so it is unusable as generic backend, but you
1498 still want to make use of it because you have many sockets and it scales
1499 so nicely. In this case, you would create a kqueue-based loop and embed it
1500 into your default loop (which might use e.g. poll). Overall operation will
1501 be a bit slower because first libev has to poll and then call kevent, but
1502 at least you can use both at what they are best.</p>
1503 <p>As for prioritising I/O: rarely you have the case where some fds have
1504 to be watched and handled very quickly (with low latency), and even
1505 priorities and idle watchers might have too much overhead. In this case
1506 you would put all the high priority stuff in one loop and all the rest in
1507 a second one, and embed the second one in the first.</p>
1508 <p>As long as the watcher is active, the callback will be invoked every time
1509 there might be events pending in the embedded loop. The callback must then
1510 call <code>ev_embed_sweep (mainloop, watcher)</code> to make a single sweep and invoke
1511 their callbacks (you could also start an idle watcher to give the embedded
1512 loop strictly lower priority for example). You can also set the callback
1513 to <code>0</code>, in which case the embed watcher will automatically execute the
1514 embedded loop sweep.</p>
1515 <p>As long as the watcher is started it will automatically handle events. The
1516 callback will be invoked whenever some events have been handled. You can
1517 set the callback to <code>0</code> to avoid having to specify one if you are not
1518 interested in that.</p>
1519 <p>Also, there have not currently been made special provisions for forking:
1520 when you fork, you not only have to call <code>ev_loop_fork</code> on both loops,
1521 but you will also have to stop and restart any <code>ev_embed</code> watchers
1523 <p>Unfortunately, not all backends are embeddable, only the ones returned by
1524 <code>ev_embeddable_backends</code> are, which, unfortunately, does not include any
1526 <p>So when you want to use this feature you will always have to be prepared
1527 that you cannot get an embeddable loop. The recommended way to get around
1528 this is to have a separate variables for your embeddable loop, try to
1529 create it, and if that fails, use the normal loop for everything:</p>
1530 <pre> struct ev_loop *loop_hi = ev_default_init (0);
1531 struct ev_loop *loop_lo = 0;
1532 struct ev_embed embed;
1534 // see if there is a chance of getting one that works
1535 // (remember that a flags value of 0 means autodetection)
1536 loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1537 ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1540 // if we got one, then embed it, otherwise default to loop_hi
1543 ev_embed_init (&embed, 0, loop_lo);
1544 ev_embed_start (loop_hi, &embed);
1551 <dt>ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)</dt>
1552 <dt>ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)</dt>
1554 <p>Configures the watcher to embed the given loop, which must be
1555 embeddable. If the callback is <code>0</code>, then <code>ev_embed_sweep</code> will be
1556 invoked automatically, otherwise it is the responsibility of the callback
1557 to invoke it (it will continue to be called until the sweep has been done,
1558 if you do not want thta, you need to temporarily stop the embed watcher).</p>
1560 <dt>ev_embed_sweep (loop, ev_embed *)</dt>
1562 <p>Make a single, non-blocking sweep over the embedded loop. This works
1563 similarly to <code>ev_loop (embedded_loop, EVLOOP_NONBLOCK)</code>, but in the most
1564 apropriate way for embedded loops.</p>
1566 <dt>struct ev_loop *loop [read-only]</dt>
1568 <p>The embedded event loop.</p>
1577 <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>
1578 <div id="code_ev_fork_code_the_audacity_to_re-2">
1579 <p>Fork watchers are called when a <code>fork ()</code> was detected (usually because
1580 whoever is a good citizen cared to tell libev about it by calling
1581 <code>ev_default_fork</code> or <code>ev_loop_fork</code>). The invocation is done before the
1582 event loop blocks next and before <code>ev_check</code> watchers are being called,
1583 and only in the child after the fork. If whoever good citizen calling
1584 <code>ev_default_fork</code> cheats and calls it in the wrong process, the fork
1585 handlers will be invoked, too, of course.</p>
1587 <dt>ev_fork_init (ev_signal *, callback)</dt>
1589 <p>Initialises and configures the fork watcher - it has no parameters of any
1590 kind. There is a <code>ev_fork_set</code> macro, but using it is utterly pointless,
1600 <h1 id="OTHER_FUNCTIONS">OTHER FUNCTIONS</h1>
1601 <div id="OTHER_FUNCTIONS_CONTENT">
1602 <p>There are some other functions of possible interest. Described. Here. Now.</p>
1604 <dt>ev_once (loop, int fd, int events, ev_tstamp timeout, callback)</dt>
1606 <p>This function combines a simple timer and an I/O watcher, calls your
1607 callback on whichever event happens first and automatically stop both
1608 watchers. This is useful if you want to wait for a single event on an fd
1609 or timeout without having to allocate/configure/start/stop/free one or
1610 more watchers yourself.</p>
1611 <p>If <code>fd</code> is less than 0, then no I/O watcher will be started and events
1612 is being ignored. Otherwise, an <code>ev_io</code> watcher for the given <code>fd</code> and
1613 <code>events</code> set will be craeted and started.</p>
1614 <p>If <code>timeout</code> is less than 0, then no timeout watcher will be
1615 started. Otherwise an <code>ev_timer</code> watcher with after = <code>timeout</code> (and
1616 repeat = 0) will be started. While <code>0</code> is a valid timeout, it is of
1618 <p>The callback has the type <code>void (*cb)(int revents, void *arg)</code> and gets
1619 passed an <code>revents</code> set like normal event callbacks (a combination of
1620 <code>EV_ERROR</code>, <code>EV_READ</code>, <code>EV_WRITE</code> or <code>EV_TIMEOUT</code>) and the <code>arg</code>
1621 value passed to <code>ev_once</code>:</p>
1622 <pre> static void stdin_ready (int revents, void *arg)
1624 if (revents & EV_TIMEOUT)
1625 /* doh, nothing entered */;
1626 else if (revents & EV_READ)
1627 /* stdin might have data for us, joy! */;
1630 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1634 <dt>ev_feed_event (ev_loop *, watcher *, int revents)</dt>
1636 <p>Feeds the given event set into the event loop, as if the specified event
1637 had happened for the specified watcher (which must be a pointer to an
1638 initialised but not necessarily started event watcher).</p>
1640 <dt>ev_feed_fd_event (ev_loop *, int fd, int revents)</dt>
1642 <p>Feed an event on the given fd, as if a file descriptor backend detected
1643 the given events it.</p>
1645 <dt>ev_feed_signal_event (ev_loop *loop, int signum)</dt>
1647 <p>Feed an event as if the given signal occured (<code>loop</code> must be the default
1657 <h1 id="LIBEVENT_EMULATION">LIBEVENT EMULATION</h1>
1658 <div id="LIBEVENT_EMULATION_CONTENT">
1659 <p>Libev offers a compatibility emulation layer for libevent. It cannot
1660 emulate the internals of libevent, so here are some usage hints:</p>
1662 <dt>* Use it by including <event.h>, as usual.</dt>
1663 <dt>* The following members are fully supported: ev_base, ev_callback,
1664 ev_arg, ev_fd, ev_res, ev_events.</dt>
1665 <dt>* Avoid using ev_flags and the EVLIST_*-macros, while it is
1666 maintained by libev, it does not work exactly the same way as in libevent (consider
1667 it a private API).</dt>
1668 <dt>* Priorities are not currently supported. Initialising priorities
1669 will fail and all watchers will have the same priority, even though there
1670 is an ev_pri field.</dt>
1671 <dt>* Other members are not supported.</dt>
1672 <dt>* The libev emulation is <i>not</i> ABI compatible to libevent, you need
1673 to use the libev header file and library.</dt>
1677 <h1 id="C_SUPPORT">C++ SUPPORT</h1>
1678 <div id="C_SUPPORT_CONTENT">
1679 <p>Libev comes with some simplistic wrapper classes for C++ that mainly allow
1680 you to use some convinience methods to start/stop watchers and also change
1681 the callback model to a model using method callbacks on objects.</p>
1683 <pre> #include <ev++.h>
1686 <p>(it is not installed by default). This automatically includes <cite>ev.h</cite>
1687 and puts all of its definitions (many of them macros) into the global
1688 namespace. All C++ specific things are put into the <code>ev</code> namespace.</p>
1689 <p>It should support all the same embedding options as <cite>ev.h</cite>, most notably
1690 <code>EV_MULTIPLICITY</code>.</p>
1691 <p>Here is a list of things available in the <code>ev</code> namespace:</p>
1693 <dt><code>ev::READ</code>, <code>ev::WRITE</code> etc.</dt>
1695 <p>These are just enum values with the same values as the <code>EV_READ</code> etc.
1696 macros from <cite>ev.h</cite>.</p>
1698 <dt><code>ev::tstamp</code>, <code>ev::now</code></dt>
1700 <p>Aliases to the same types/functions as with the <code>ev_</code> prefix.</p>
1702 <dt><code>ev::io</code>, <code>ev::timer</code>, <code>ev::periodic</code>, <code>ev::idle</code>, <code>ev::sig</code> etc.</dt>
1704 <p>For each <code>ev_TYPE</code> watcher in <cite>ev.h</cite> there is a corresponding class of
1705 the same name in the <code>ev</code> namespace, with the exception of <code>ev_signal</code>
1706 which is called <code>ev::sig</code> to avoid clashes with the <code>signal</code> macro
1707 defines by many implementations.</p>
1708 <p>All of those classes have these methods:</p>
1711 <dt>ev::TYPE::TYPE (object *, object::method *)</dt>
1712 <dt>ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)</dt>
1713 <dt>ev::TYPE::~TYPE</dt>
1715 <p>The constructor takes a pointer to an object and a method pointer to
1716 the event handler callback to call in this class. The constructor calls
1717 <code>ev_init</code> for you, which means you have to call the <code>set</code> method
1718 before starting it. If you do not specify a loop then the constructor
1719 automatically associates the default loop with this watcher.</p>
1720 <p>The destructor automatically stops the watcher if it is active.</p>
1722 <dt>w->set (struct ev_loop *)</dt>
1724 <p>Associates a different <code>struct ev_loop</code> with this watcher. You can only
1725 do this when the watcher is inactive (and not pending either).</p>
1727 <dt>w->set ([args])</dt>
1729 <p>Basically the same as <code>ev_TYPE_set</code>, with the same args. Must be
1730 called at least once. Unlike the C counterpart, an active watcher gets
1731 automatically stopped and restarted.</p>
1733 <dt>w->start ()</dt>
1735 <p>Starts the watcher. Note that there is no <code>loop</code> argument as the
1736 constructor already takes the loop.</p>
1738 <dt>w->stop ()</dt>
1740 <p>Stops the watcher if it is active. Again, no <code>loop</code> argument.</p>
1742 <dt>w->again () <code>ev::timer</code>, <code>ev::periodic</code> only</dt>
1744 <p>For <code>ev::timer</code> and <code>ev::periodic</code>, this invokes the corresponding
1745 <code>ev_TYPE_again</code> function.</p>
1747 <dt>w->sweep () <code>ev::embed</code> only</dt>
1749 <p>Invokes <code>ev_embed_sweep</code>.</p>
1751 <dt>w->update () <code>ev::stat</code> only</dt>
1753 <p>Invokes <code>ev_stat_stat</code>.</p>
1759 <p>Example: Define a class with an IO and idle watcher, start one of them in
1760 the constructor.</p>
1763 ev_io io; void io_cb (ev::io &w, int revents);
1764 ev_idle idle void idle_cb (ev::idle &w, int revents);
1769 myclass::myclass (int fd)
1770 : io (this, &myclass::io_cb),
1771 idle (this, &myclass::idle_cb)
1773 io.start (fd, ev::READ);
1782 <h1 id="MACRO_MAGIC">MACRO MAGIC</h1>
1783 <div id="MACRO_MAGIC_CONTENT">
1784 <p>Libev can be compiled with a variety of options, the most fundemantal is
1785 <code>EV_MULTIPLICITY</code>. This option determines wether (most) functions and
1786 callbacks have an initial <code>struct ev_loop *</code> argument.</p>
1787 <p>To make it easier to write programs that cope with either variant, the
1788 following macros are defined:</p>
1790 <dt><code>EV_A</code>, <code>EV_A_</code></dt>
1792 <p>This provides the loop <i>argument</i> for functions, if one is required ("ev
1793 loop argument"). The <code>EV_A</code> form is used when this is the sole argument,
1794 <code>EV_A_</code> is used when other arguments are following. Example:</p>
1795 <pre> ev_unref (EV_A);
1796 ev_timer_add (EV_A_ watcher);
1800 <p>It assumes the variable <code>loop</code> of type <code>struct ev_loop *</code> is in scope,
1801 which is often provided by the following macro.</p>
1803 <dt><code>EV_P</code>, <code>EV_P_</code></dt>
1805 <p>This provides the loop <i>parameter</i> for functions, if one is required ("ev
1806 loop parameter"). The <code>EV_P</code> form is used when this is the sole parameter,
1807 <code>EV_P_</code> is used when other parameters are following. Example:</p>
1808 <pre> // this is how ev_unref is being declared
1809 static void ev_unref (EV_P);
1811 // this is how you can declare your typical callback
1812 static void cb (EV_P_ ev_timer *w, int revents)
1815 <p>It declares a parameter <code>loop</code> of type <code>struct ev_loop *</code>, quite
1816 suitable for use with <code>EV_A</code>.</p>
1818 <dt><code>EV_DEFAULT</code>, <code>EV_DEFAULT_</code></dt>
1820 <p>Similar to the other two macros, this gives you the value of the default
1821 loop, if multiple loops are supported ("ev loop default").</p>
1824 <p>Example: Declare and initialise a check watcher, working regardless of
1825 wether multiple loops are supported or not.</p>
1827 check_cb (EV_P_ ev_timer *w, int revents)
1829 ev_check_stop (EV_A_ w);
1833 ev_check_init (&check, check_cb);
1834 ev_check_start (EV_DEFAULT_ &check);
1835 ev_loop (EV_DEFAULT_ 0);
1843 <h1 id="EMBEDDING">EMBEDDING</h1>
1844 <div id="EMBEDDING_CONTENT">
1845 <p>Libev can (and often is) directly embedded into host
1846 applications. Examples of applications that embed it include the Deliantra
1847 Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1848 and rxvt-unicode.</p>
1849 <p>The goal is to enable you to just copy the neecssary files into your
1850 source directory without having to change even a single line in them, so
1851 you can easily upgrade by simply copying (or having a checked-out copy of
1852 libev somewhere in your source tree).</p>
1855 <h2 id="FILESETS">FILESETS</h2>
1856 <div id="FILESETS_CONTENT">
1857 <p>Depending on what features you need you need to include one or more sets of files
1861 <h3 id="CORE_EVENT_LOOP">CORE EVENT LOOP</h3>
1862 <div id="CORE_EVENT_LOOP_CONTENT">
1863 <p>To include only the libev core (all the <code>ev_*</code> functions), with manual
1864 configuration (no autoconf):</p>
1865 <pre> #define EV_STANDALONE 1
1866 #include "ev.c"
1869 <p>This will automatically include <cite>ev.h</cite>, too, and should be done in a
1870 single C source file only to provide the function implementations. To use
1871 it, do the same for <cite>ev.h</cite> in all files wishing to use this API (best
1872 done by writing a wrapper around <cite>ev.h</cite> that you can include instead and
1873 where you can put other configuration options):</p>
1874 <pre> #define EV_STANDALONE 1
1875 #include "ev.h"
1878 <p>Both header files and implementation files can be compiled with a C++
1879 compiler (at least, thats a stated goal, and breakage will be treated
1881 <p>You need the following files in your source tree, or in a directory
1882 in your include path (e.g. in libev/ when using -Ilibev):</p>
1888 ev_win32.c required on win32 platforms only
1890 ev_select.c only when select backend is enabled (which is by default)
1891 ev_poll.c only when poll backend is enabled (disabled by default)
1892 ev_epoll.c only when the epoll backend is enabled (disabled by default)
1893 ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1894 ev_port.c only when the solaris port backend is enabled (disabled by default)
1897 <p><cite>ev.c</cite> includes the backend files directly when enabled, so you only need
1898 to compile this single file.</p>
1901 <h3 id="LIBEVENT_COMPATIBILITY_API">LIBEVENT COMPATIBILITY API</h3>
1902 <div id="LIBEVENT_COMPATIBILITY_API_CONTENT">
1903 <p>To include the libevent compatibility API, also include:</p>
1904 <pre> #include "event.c"
1907 <p>in the file including <cite>ev.c</cite>, and:</p>
1908 <pre> #include "event.h"
1911 <p>in the files that want to use the libevent API. This also includes <cite>ev.h</cite>.</p>
1912 <p>You need the following additional files for this:</p>
1919 <h3 id="AUTOCONF_SUPPORT">AUTOCONF SUPPORT</h3>
1920 <div id="AUTOCONF_SUPPORT_CONTENT">
1921 <p>Instead of using <code>EV_STANDALONE=1</code> and providing your config in
1922 whatever way you want, you can also <code>m4_include([libev.m4])</code> in your
1923 <cite>configure.ac</cite> and leave <code>EV_STANDALONE</code> undefined. <cite>ev.c</cite> will then
1924 include <cite>config.h</cite> and configure itself accordingly.</p>
1925 <p>For this of course you need the m4 file:</p>
1931 <h2 id="PREPROCESSOR_SYMBOLS_MACROS">PREPROCESSOR SYMBOLS/MACROS</h2>
1932 <div id="PREPROCESSOR_SYMBOLS_MACROS_CONTENT">
1933 <p>Libev can be configured via a variety of preprocessor symbols you have to define
1934 before including any of its files. The default is not to build for multiplicity
1935 and only include the select backend.</p>
1937 <dt>EV_STANDALONE</dt>
1939 <p>Must always be <code>1</code> if you do not use autoconf configuration, which
1940 keeps libev from including <cite>config.h</cite>, and it also defines dummy
1941 implementations for some libevent functions (such as logging, which is not
1942 supported). It will also not define any of the structs usually found in
1943 <cite>event.h</cite> that are not directly supported by the libev core alone.</p>
1945 <dt>EV_USE_MONOTONIC</dt>
1947 <p>If defined to be <code>1</code>, libev will try to detect the availability of the
1948 monotonic clock option at both compiletime and runtime. Otherwise no use
1949 of the monotonic clock option will be attempted. If you enable this, you
1950 usually have to link against librt or something similar. Enabling it when
1951 the functionality isn't available is safe, though, althoguh you have
1952 to make sure you link against any libraries where the <code>clock_gettime</code>
1953 function is hiding in (often <cite>-lrt</cite>).</p>
1955 <dt>EV_USE_REALTIME</dt>
1957 <p>If defined to be <code>1</code>, libev will try to detect the availability of the
1958 realtime clock option at compiletime (and assume its availability at
1959 runtime if successful). Otherwise no use of the realtime clock option will
1960 be attempted. This effectively replaces <code>gettimeofday</code> by <code>clock_get
1961 (CLOCK_REALTIME, ...)</code> and will not normally affect correctness. See tzhe note about libraries
1962 in the description of <code>EV_USE_MONOTONIC</code>, though.</p>
1964 <dt>EV_USE_SELECT</dt>
1966 <p>If undefined or defined to be <code>1</code>, libev will compile in support for the
1967 <code>select</code>(2) backend. No attempt at autodetection will be done: if no
1968 other method takes over, select will be it. Otherwise the select backend
1969 will not be compiled in.</p>
1971 <dt>EV_SELECT_USE_FD_SET</dt>
1973 <p>If defined to <code>1</code>, then the select backend will use the system <code>fd_set</code>
1974 structure. This is useful if libev doesn't compile due to a missing
1975 <code>NFDBITS</code> or <code>fd_mask</code> definition or it misguesses the bitset layout on
1976 exotic systems. This usually limits the range of file descriptors to some
1977 low limit such as 1024 or might have other limitations (winsocket only
1978 allows 64 sockets). The <code>FD_SETSIZE</code> macro, set before compilation, might
1979 influence the size of the <code>fd_set</code> used.</p>
1981 <dt>EV_SELECT_IS_WINSOCKET</dt>
1983 <p>When defined to <code>1</code>, the select backend will assume that
1984 select/socket/connect etc. don't understand file descriptors but
1985 wants osf handles on win32 (this is the case when the select to
1986 be used is the winsock select). This means that it will call
1987 <code>_get_osfhandle</code> on the fd to convert it to an OS handle. Otherwise,
1988 it is assumed that all these functions actually work on fds, even
1989 on win32. Should not be defined on non-win32 platforms.</p>
1991 <dt>EV_USE_POLL</dt>
1993 <p>If defined to be <code>1</code>, libev will compile in support for the <code>poll</code>(2)
1994 backend. Otherwise it will be enabled on non-win32 platforms. It
1995 takes precedence over select.</p>
1997 <dt>EV_USE_EPOLL</dt>
1999 <p>If defined to be <code>1</code>, libev will compile in support for the Linux
2000 <code>epoll</code>(7) backend. Its availability will be detected at runtime,
2001 otherwise another method will be used as fallback. This is the
2002 preferred backend for GNU/Linux systems.</p>
2004 <dt>EV_USE_KQUEUE</dt>
2006 <p>If defined to be <code>1</code>, libev will compile in support for the BSD style
2007 <code>kqueue</code>(2) backend. Its actual availability will be detected at runtime,
2008 otherwise another method will be used as fallback. This is the preferred
2009 backend for BSD and BSD-like systems, although on most BSDs kqueue only
2010 supports some types of fds correctly (the only platform we found that
2011 supports ptys for example was NetBSD), so kqueue might be compiled in, but
2012 not be used unless explicitly requested. The best way to use it is to find
2013 out whether kqueue supports your type of fd properly and use an embedded
2016 <dt>EV_USE_PORT</dt>
2018 <p>If defined to be <code>1</code>, libev will compile in support for the Solaris
2019 10 port style backend. Its availability will be detected at runtime,
2020 otherwise another method will be used as fallback. This is the preferred
2021 backend for Solaris 10 systems.</p>
2023 <dt>EV_USE_DEVPOLL</dt>
2025 <p>reserved for future expansion, works like the USE symbols above.</p>
2027 <dt>EV_USE_INOTIFY</dt>
2029 <p>If defined to be <code>1</code>, libev will compile in support for the Linux inotify
2030 interface to speed up <code>ev_stat</code> watchers. Its actual availability will
2031 be detected at runtime.</p>
2035 <p>The name of the <cite>ev.h</cite> header file used to include it. The default if
2036 undefined is <code><ev.h></code> in <cite>event.h</cite> and <code>"ev.h"</code> in <cite>ev.c</cite>. This
2037 can be used to virtually rename the <cite>ev.h</cite> header file in case of conflicts.</p>
2039 <dt>EV_CONFIG_H</dt>
2041 <p>If <code>EV_STANDALONE</code> isn't <code>1</code>, this variable can be used to override
2042 <cite>ev.c</cite>'s idea of where to find the <cite>config.h</cite> file, similarly to
2043 <code>EV_H</code>, above.</p>
2047 <p>Similarly to <code>EV_H</code>, this macro can be used to override <cite>event.c</cite>'s idea
2048 of how the <cite>event.h</cite> header can be found.</p>
2050 <dt>EV_PROTOTYPES</dt>
2052 <p>If defined to be <code>0</code>, then <cite>ev.h</cite> will not define any function
2053 prototypes, but still define all the structs and other symbols. This is
2054 occasionally useful if you want to provide your own wrapper functions
2055 around libev functions.</p>
2057 <dt>EV_MULTIPLICITY</dt>
2059 <p>If undefined or defined to <code>1</code>, then all event-loop-specific functions
2060 will have the <code>struct ev_loop *</code> as first argument, and you can create
2061 additional independent event loops. Otherwise there will be no support
2062 for multiple event loops and there is no first event loop pointer
2063 argument. Instead, all functions act on the single default loop.</p>
2065 <dt>EV_PERIODIC_ENABLE</dt>
2067 <p>If undefined or defined to be <code>1</code>, then periodic timers are supported. If
2068 defined to be <code>0</code>, then they are not. Disabling them saves a few kB of
2071 <dt>EV_EMBED_ENABLE</dt>
2073 <p>If undefined or defined to be <code>1</code>, then embed watchers are supported. If
2074 defined to be <code>0</code>, then they are not.</p>
2076 <dt>EV_STAT_ENABLE</dt>
2078 <p>If undefined or defined to be <code>1</code>, then stat watchers are supported. If
2079 defined to be <code>0</code>, then they are not.</p>
2081 <dt>EV_FORK_ENABLE</dt>
2083 <p>If undefined or defined to be <code>1</code>, then fork watchers are supported. If
2084 defined to be <code>0</code>, then they are not.</p>
2088 <p>If you need to shave off some kilobytes of code at the expense of some
2089 speed, define this symbol to <code>1</code>. Currently only used for gcc to override
2090 some inlining decisions, saves roughly 30% codesize of amd64.</p>
2092 <dt>EV_PID_HASHSIZE</dt>
2094 <p><code>ev_child</code> watchers use a small hash table to distribute workload by
2095 pid. The default size is <code>16</code> (or <code>1</code> with <code>EV_MINIMAL</code>), usually more
2096 than enough. If you need to manage thousands of children you might want to
2097 increase this value (<i>must</i> be a power of two).</p>
2099 <dt>EV_INOTIFY_HASHSIZE</dt>
2101 <p><code>ev_staz</code> watchers use a small hash table to distribute workload by
2102 inotify watch id. The default size is <code>16</code> (or <code>1</code> with <code>EV_MINIMAL</code>),
2103 usually more than enough. If you need to manage thousands of <code>ev_stat</code>
2104 watchers you might want to increase this value (<i>must</i> be a power of
2109 <p>By default, all watchers have a <code>void *data</code> member. By redefining
2110 this macro to a something else you can include more and other types of
2111 members. You have to define it each time you include one of the files,
2112 though, and it must be identical each time.</p>
2113 <p>For example, the perl EV module uses something like this:</p>
2114 <pre> #define EV_COMMON \
2115 SV *self; /* contains this struct */ \
2116 SV *cb_sv, *fh /* note no trailing ";" */
2120 <dt>EV_CB_DECLARE (type)</dt>
2121 <dt>EV_CB_INVOKE (watcher, revents)</dt>
2122 <dt>ev_set_cb (ev, cb)</dt>
2124 <p>Can be used to change the callback member declaration in each watcher,
2125 and the way callbacks are invoked and set. Must expand to a struct member
2126 definition and a statement, respectively. See the <cite>ev.v</cite> header file for
2127 their default definitions. One possible use for overriding these is to
2128 avoid the <code>struct ev_loop *</code> as first argument in all cases, or to use
2129 method calls instead of plain function calls in C++.</p>
2132 <h2 id="EXAMPLES">EXAMPLES</h2>
2133 <div id="EXAMPLES_CONTENT">
2134 <p>For a real-world example of a program the includes libev
2135 verbatim, you can have a look at the EV perl module
2136 (<a href="http://software.schmorp.de/pkg/EV.html">http://software.schmorp.de/pkg/EV.html</a>). It has the libev files in
2137 the <cite>libev/</cite> subdirectory and includes them in the <cite>EV/EVAPI.h</cite> (public
2138 interface) and <cite>EV.xs</cite> (implementation) files. Only the <cite>EV.xs</cite> file
2139 will be compiled. It is pretty complex because it provides its own header
2141 <p>The usage in rxvt-unicode is simpler. It has a <cite>ev_cpp.h</cite> header file
2142 that everybody includes and which overrides some autoconf choices:</p>
2143 <pre> #define EV_USE_POLL 0
2144 #define EV_MULTIPLICITY 0
2145 #define EV_PERIODICS 0
2146 #define EV_CONFIG_H <config.h>
2148 #include "ev++.h"
2151 <p>And a <cite>ev_cpp.C</cite> implementation file that contains libev proper and is compiled:</p>
2152 <pre> #include "ev_cpp.h"
2153 #include "ev.c"
2161 <h1 id="COMPLEXITIES">COMPLEXITIES</h1>
2162 <div id="COMPLEXITIES_CONTENT">
2163 <p>In this section the complexities of (many of) the algorithms used inside
2164 libev will be explained. For complexity discussions about backends see the
2165 documentation for <code>ev_default_init</code>.</p>
2168 <dt>Starting and stopping timer/periodic watchers: O(log skipped_other_timers)</dt>
2169 <dt>Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)</dt>
2170 <dt>Starting io/check/prepare/idle/signal/child watchers: O(1)</dt>
2171 <dt>Stopping check/prepare/idle watchers: O(1)</dt>
2172 <dt>Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))</dt>
2173 <dt>Finding the next timer per loop iteration: O(1)</dt>
2174 <dt>Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)</dt>
2175 <dt>Activating one watcher: O(1)</dt>
2184 <h1 id="AUTHOR">AUTHOR</h1>
2185 <div id="AUTHOR_CONTENT">
2186 <p>Marc Lehmann <libev@schmorp.de>.</p>
projects / software / libev.git / blob