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Revision: 1.9
Committed: Fri Nov 23 16:17:12 2007 UTC (16 years, 5 months ago) by root
Branch: MAIN
Changes since 1.8: +252 -5 lines
Log Message:
add lots of theoretical examples

File Contents

# User Rev Content
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131     .IX Title ""<STANDARD INPUT>" 1"
132 root 1.5 .TH "<STANDARD INPUT>" 1 "2007-11-23" "perl v5.8.8" "User Contributed Perl Documentation"
133 root 1.1 .SH "NAME"
134     libev \- a high performance full\-featured event loop written in C
135     .SH "SYNOPSIS"
136     .IX Header "SYNOPSIS"
137     .Vb 1
138     \& #include <ev.h>
139     .Ve
140     .SH "DESCRIPTION"
141     .IX Header "DESCRIPTION"
142     Libev is an event loop: you register interest in certain events (such as a
143     file descriptor being readable or a timeout occuring), and it will manage
144     these event sources and provide your program with events.
145     .PP
146     To do this, it must take more or less complete control over your process
147     (or thread) by executing the \fIevent loop\fR handler, and will then
148     communicate events via a callback mechanism.
149     .PP
150     You register interest in certain events by registering so-called \fIevent
151     watchers\fR, which are relatively small C structures you initialise with the
152     details of the event, and then hand it over to libev by \fIstarting\fR the
153     watcher.
154     .SH "FEATURES"
155     .IX Header "FEATURES"
156     Libev supports select, poll, the linux-specific epoll and the bsd-specific
157     kqueue mechanisms for file descriptor events, relative timers, absolute
158     timers with customised rescheduling, signal events, process status change
159     events (related to \s-1SIGCHLD\s0), and event watchers dealing with the event
160     loop mechanism itself (idle, prepare and check watchers). It also is quite
161     fast (see this benchmark comparing
162     it to libevent for example).
163     .SH "CONVENTIONS"
164     .IX Header "CONVENTIONS"
165     Libev is very configurable. In this manual the default configuration
166     will be described, which supports multiple event loops. For more info
167     about various configuration options please have a look at the file
168     \&\fI\s-1README\s0.embed\fR in the libev distribution. If libev was configured without
169     support for multiple event loops, then all functions taking an initial
170     argument of name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR)
171     will not have this argument.
172     .SH "TIME REPRESENTATION"
173     .IX Header "TIME REPRESENTATION"
174     Libev represents time as a single floating point number, representing the
175     (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near
176     the beginning of 1970, details are complicated, don't ask). This type is
177     called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases
178 root 1.9 to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on
179     it, you should treat it as such.
180 root 1.1 .SH "GLOBAL FUNCTIONS"
181     .IX Header "GLOBAL FUNCTIONS"
182     These functions can be called anytime, even before initialising the
183     library in any way.
184     .IP "ev_tstamp ev_time ()" 4
185     .IX Item "ev_tstamp ev_time ()"
186 root 1.2 Returns the current time as libev would use it. Please note that the
187     \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
188     you actually want to know.
189 root 1.1 .IP "int ev_version_major ()" 4
190     .IX Item "int ev_version_major ()"
191     .PD 0
192     .IP "int ev_version_minor ()" 4
193     .IX Item "int ev_version_minor ()"
194     .PD
195     You can find out the major and minor version numbers of the library
196     you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
197     \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
198     symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
199     version of the library your program was compiled against.
200     .Sp
201     Usually, it's a good idea to terminate if the major versions mismatch,
202     as this indicates an incompatible change. Minor versions are usually
203     compatible to older versions, so a larger minor version alone is usually
204     not a problem.
205 root 1.9 .Sp
206     Example: make sure we haven't accidentally been linked against the wrong
207     version:
208     .Sp
209     .Vb 3
210     \& assert (("libev version mismatch",
211     \& ev_version_major () == EV_VERSION_MAJOR
212     \& && ev_version_minor () >= EV_VERSION_MINOR));
213     .Ve
214 root 1.6 .IP "unsigned int ev_supported_backends ()" 4
215     .IX Item "unsigned int ev_supported_backends ()"
216     Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
217     value) compiled into this binary of libev (independent of their
218     availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
219     a description of the set values.
220 root 1.9 .Sp
221     Example: make sure we have the epoll method, because yeah this is cool and
222     a must have and can we have a torrent of it please!!!11
223     .Sp
224     .Vb 2
225     \& assert (("sorry, no epoll, no sex",
226     \& ev_supported_backends () & EVBACKEND_EPOLL));
227     .Ve
228 root 1.6 .IP "unsigned int ev_recommended_backends ()" 4
229     .IX Item "unsigned int ev_recommended_backends ()"
230     Return the set of all backends compiled into this binary of libev and also
231     recommended for this platform. This set is often smaller than the one
232     returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on
233     most BSDs and will not be autodetected unless you explicitly request it
234     (assuming you know what you are doing). This is the set of backends that
235 root 1.8 libev will probe for if you specify no backends explicitly.
236 root 1.1 .IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
237     .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
238     Sets the allocation function to use (the prototype is similar to the
239     realloc C function, the semantics are identical). It is used to allocate
240     and free memory (no surprises here). If it returns zero when memory
241     needs to be allocated, the library might abort or take some potentially
242     destructive action. The default is your system realloc function.
243     .Sp
244     You could override this function in high-availability programs to, say,
245     free some memory if it cannot allocate memory, to use a special allocator,
246     or even to sleep a while and retry until some memory is available.
247 root 1.9 .Sp
248     Example: replace the libev allocator with one that waits a bit and then
249     retries: better than mine).
250     .Sp
251     .Vb 6
252     \& static void *
253     \& persistent_realloc (void *ptr, long size)
254     \& {
255     \& for (;;)
256     \& {
257     \& void *newptr = realloc (ptr, size);
258     .Ve
259     .Sp
260     .Vb 2
261     \& if (newptr)
262     \& return newptr;
263     .Ve
264     .Sp
265     .Vb 3
266     \& sleep (60);
267     \& }
268     \& }
269     .Ve
270     .Sp
271     .Vb 2
272     \& ...
273     \& ev_set_allocator (persistent_realloc);
274     .Ve
275 root 1.1 .IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4
276     .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));"
277     Set the callback function to call on a retryable syscall error (such
278     as failed select, poll, epoll_wait). The message is a printable string
279     indicating the system call or subsystem causing the problem. If this
280     callback is set, then libev will expect it to remedy the sitution, no
281     matter what, when it returns. That is, libev will generally retry the
282     requested operation, or, if the condition doesn't go away, do bad stuff
283     (such as abort).
284 root 1.9 .Sp
285     Example: do the same thing as libev does internally:
286     .Sp
287     .Vb 6
288     \& static void
289     \& fatal_error (const char *msg)
290     \& {
291     \& perror (msg);
292     \& abort ();
293     \& }
294     .Ve
295     .Sp
296     .Vb 2
297     \& ...
298     \& ev_set_syserr_cb (fatal_error);
299     .Ve
300 root 1.1 .SH "FUNCTIONS CONTROLLING THE EVENT LOOP"
301     .IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP"
302     An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two
303     types of such loops, the \fIdefault\fR loop, which supports signals and child
304     events, and dynamically created loops which do not.
305     .PP
306     If you use threads, a common model is to run the default event loop
307     in your main thread (or in a separate thread) and for each thread you
308     create, you also create another event loop. Libev itself does no locking
309     whatsoever, so if you mix calls to the same event loop in different
310     threads, make sure you lock (this is usually a bad idea, though, even if
311     done correctly, because it's hideous and inefficient).
312     .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
313     .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
314     This will initialise the default event loop if it hasn't been initialised
315     yet and return it. If the default loop could not be initialised, returns
316     false. If it already was initialised it simply returns it (and ignores the
317 root 1.6 flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
318 root 1.1 .Sp
319     If you don't know what event loop to use, use the one returned from this
320     function.
321     .Sp
322     The flags argument can be used to specify special behaviour or specific
323 root 1.8 backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
324 root 1.1 .Sp
325 root 1.8 The following flags are supported:
326 root 1.1 .RS 4
327     .ie n .IP """EVFLAG_AUTO""" 4
328     .el .IP "\f(CWEVFLAG_AUTO\fR" 4
329     .IX Item "EVFLAG_AUTO"
330     The default flags value. Use this if you have no clue (it's the right
331     thing, believe me).
332     .ie n .IP """EVFLAG_NOENV""" 4
333     .el .IP "\f(CWEVFLAG_NOENV\fR" 4
334     .IX Item "EVFLAG_NOENV"
335     If this flag bit is ored into the flag value (or the program runs setuid
336     or setgid) then libev will \fInot\fR look at the environment variable
337     \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
338     override the flags completely if it is found in the environment. This is
339     useful to try out specific backends to test their performance, or to work
340     around bugs.
341 root 1.6 .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
342     .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
343     .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
344 root 1.3 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
345     libev tries to roll its own fd_set with no limits on the number of fds,
346     but if that fails, expect a fairly low limit on the number of fds when
347     using this backend. It doesn't scale too well (O(highest_fd)), but its usually
348     the fastest backend for a low number of fds.
349 root 1.6 .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
350     .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
351     .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
352 root 1.3 And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than
353     select, but handles sparse fds better and has no artificial limit on the
354     number of fds you can use (except it will slow down considerably with a
355     lot of inactive fds). It scales similarly to select, i.e. O(total_fds).
356 root 1.6 .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
357     .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
358     .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
359 root 1.3 For few fds, this backend is a bit little slower than poll and select,
360     but it scales phenomenally better. While poll and select usually scale like
361     O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
362     either O(1) or O(active_fds).
363     .Sp
364     While stopping and starting an I/O watcher in the same iteration will
365     result in some caching, there is still a syscall per such incident
366     (because the fd could point to a different file description now), so its
367     best to avoid that. Also, \fIdup()\fRed file descriptors might not work very
368     well if you register events for both fds.
369 root 1.7 .Sp
370     Please note that epoll sometimes generates spurious notifications, so you
371     need to use non-blocking I/O or other means to avoid blocking when no data
372     (or space) is available.
373 root 1.6 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
374     .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
375     .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
376 root 1.3 Kqueue deserves special mention, as at the time of this writing, it
377     was broken on all BSDs except NetBSD (usually it doesn't work with
378     anything but sockets and pipes, except on Darwin, where of course its
379 root 1.8 completely useless). For this reason its not being \*(L"autodetected\*(R"
380     unless you explicitly specify it explicitly in the flags (i.e. using
381     \&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR).
382 root 1.3 .Sp
383     It scales in the same way as the epoll backend, but the interface to the
384     kernel is more efficient (which says nothing about its actual speed, of
385     course). While starting and stopping an I/O watcher does not cause an
386     extra syscall as with epoll, it still adds up to four event changes per
387     incident, so its best to avoid that.
388 root 1.6 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
389     .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
390     .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
391 root 1.3 This is not implemented yet (and might never be).
392 root 1.6 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
393     .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
394     .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
395 root 1.3 This uses the Solaris 10 port mechanism. As with everything on Solaris,
396     it's really slow, but it still scales very well (O(active_fds)).
397 root 1.7 .Sp
398     Please note that solaris ports can result in a lot of spurious
399     notifications, so you need to use non-blocking I/O or other means to avoid
400     blocking when no data (or space) is available.
401 root 1.6 .ie n .IP """EVBACKEND_ALL""" 4
402     .el .IP "\f(CWEVBACKEND_ALL\fR" 4
403     .IX Item "EVBACKEND_ALL"
404 root 1.4 Try all backends (even potentially broken ones that wouldn't be tried
405     with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
406 root 1.6 \&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
407 root 1.1 .RE
408     .RS 4
409 root 1.3 .Sp
410     If one or more of these are ored into the flags value, then only these
411     backends will be tried (in the reverse order as given here). If none are
412     specified, most compiled-in backend will be tried, usually in reverse
413     order of their flag values :)
414 root 1.8 .Sp
415     The most typical usage is like this:
416     .Sp
417     .Vb 2
418     \& if (!ev_default_loop (0))
419     \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
420     .Ve
421     .Sp
422     Restrict libev to the select and poll backends, and do not allow
423     environment settings to be taken into account:
424     .Sp
425     .Vb 1
426     \& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
427     .Ve
428     .Sp
429     Use whatever libev has to offer, but make sure that kqueue is used if
430     available (warning, breaks stuff, best use only with your own private
431     event loop and only if you know the \s-1OS\s0 supports your types of fds):
432     .Sp
433     .Vb 1
434     \& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
435     .Ve
436 root 1.1 .RE
437     .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
438     .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
439     Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
440     always distinct from the default loop. Unlike the default loop, it cannot
441     handle signal and child watchers, and attempts to do so will be greeted by
442     undefined behaviour (or a failed assertion if assertions are enabled).
443 root 1.9 .Sp
444     Example: try to create a event loop that uses epoll and nothing else.
445     .Sp
446     .Vb 3
447     \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
448     \& if (!epoller)
449     \& fatal ("no epoll found here, maybe it hides under your chair");
450     .Ve
451 root 1.1 .IP "ev_default_destroy ()" 4
452     .IX Item "ev_default_destroy ()"
453     Destroys the default loop again (frees all memory and kernel state
454     etc.). This stops all registered event watchers (by not touching them in
455     any way whatsoever, although you cannot rely on this :).
456     .IP "ev_loop_destroy (loop)" 4
457     .IX Item "ev_loop_destroy (loop)"
458     Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
459     earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
460     .IP "ev_default_fork ()" 4
461     .IX Item "ev_default_fork ()"
462     This function reinitialises the kernel state for backends that have
463     one. Despite the name, you can call it anytime, but it makes most sense
464     after forking, in either the parent or child process (or both, but that
465     again makes little sense).
466     .Sp
467 root 1.5 You \fImust\fR call this function in the child process after forking if and
468     only if you want to use the event library in both processes. If you just
469     fork+exec, you don't have to call it.
470 root 1.1 .Sp
471     The function itself is quite fast and it's usually not a problem to call
472     it just in case after a fork. To make this easy, the function will fit in
473     quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
474     .Sp
475     .Vb 1
476     \& pthread_atfork (0, 0, ev_default_fork);
477     .Ve
478 root 1.6 .Sp
479     At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
480     without calling this function, so if you force one of those backends you
481     do not need to care.
482 root 1.1 .IP "ev_loop_fork (loop)" 4
483     .IX Item "ev_loop_fork (loop)"
484     Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
485     \&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
486     after fork, and how you do this is entirely your own problem.
487 root 1.6 .IP "unsigned int ev_backend (loop)" 4
488     .IX Item "unsigned int ev_backend (loop)"
489     Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
490 root 1.1 use.
491     .IP "ev_tstamp ev_now (loop)" 4
492     .IX Item "ev_tstamp ev_now (loop)"
493     Returns the current \*(L"event loop time\*(R", which is the time the event loop
494 root 1.9 received events and started processing them. This timestamp does not
495     change as long as callbacks are being processed, and this is also the base
496     time used for relative timers. You can treat it as the timestamp of the
497     event occuring (or more correctly, libev finding out about it).
498 root 1.1 .IP "ev_loop (loop, int flags)" 4
499     .IX Item "ev_loop (loop, int flags)"
500     Finally, this is it, the event handler. This function usually is called
501     after you initialised all your watchers and you want to start handling
502     events.
503     .Sp
504 root 1.8 If the flags argument is specified as \f(CW0\fR, it will not return until
505     either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
506 root 1.1 .Sp
507 root 1.9 Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than
508     relying on all watchers to be stopped when deciding when a program has
509     finished (especially in interactive programs), but having a program that
510     automatically loops as long as it has to and no longer by virtue of
511     relying on its watchers stopping correctly is a thing of beauty.
512     .Sp
513 root 1.1 A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
514     those events and any outstanding ones, but will not block your process in
515     case there are no events and will return after one iteration of the loop.
516     .Sp
517     A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
518     neccessary) and will handle those and any outstanding ones. It will block
519     your process until at least one new event arrives, and will return after
520 root 1.8 one iteration of the loop. This is useful if you are waiting for some
521     external event in conjunction with something not expressible using other
522     libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
523     usually a better approach for this kind of thing.
524     .Sp
525     Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
526     .Sp
527     .Vb 18
528     \& * If there are no active watchers (reference count is zero), return.
529     \& - Queue prepare watchers and then call all outstanding watchers.
530     \& - If we have been forked, recreate the kernel state.
531     \& - Update the kernel state with all outstanding changes.
532     \& - Update the "event loop time".
533     \& - Calculate for how long to block.
534     \& - Block the process, waiting for any events.
535     \& - Queue all outstanding I/O (fd) events.
536     \& - Update the "event loop time" and do time jump handling.
537     \& - Queue all outstanding timers.
538     \& - Queue all outstanding periodics.
539     \& - If no events are pending now, queue all idle watchers.
540     \& - Queue all check watchers.
541     \& - Call all queued watchers in reverse order (i.e. check watchers first).
542     \& Signals and child watchers are implemented as I/O watchers, and will
543     \& be handled here by queueing them when their watcher gets executed.
544     \& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
545     \& were used, return, otherwise continue with step *.
546 root 1.2 .Ve
547 root 1.9 .Sp
548     Example: queue some jobs and then loop until no events are outsanding
549     anymore.
550     .Sp
551     .Vb 4
552     \& ... queue jobs here, make sure they register event watchers as long
553     \& ... as they still have work to do (even an idle watcher will do..)
554     \& ev_loop (my_loop, 0);
555     \& ... jobs done. yeah!
556     .Ve
557 root 1.1 .IP "ev_unloop (loop, how)" 4
558     .IX Item "ev_unloop (loop, how)"
559     Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
560     has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
561     \&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
562     \&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
563     .IP "ev_ref (loop)" 4
564     .IX Item "ev_ref (loop)"
565     .PD 0
566     .IP "ev_unref (loop)" 4
567     .IX Item "ev_unref (loop)"
568     .PD
569     Ref/unref can be used to add or remove a reference count on the event
570     loop: Every watcher keeps one reference, and as long as the reference
571     count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have
572     a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from
573     returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For
574     example, libev itself uses this for its internal signal pipe: It is not
575     visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if
576     no event watchers registered by it are active. It is also an excellent
577     way to do this for generic recurring timers or from within third-party
578     libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR.
579 root 1.9 .Sp
580     Example: create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
581     running when nothing else is active.
582     .Sp
583     .Vb 4
584     \& struct dv_signal exitsig;
585     \& ev_signal_init (&exitsig, sig_cb, SIGINT);
586     \& ev_signal_start (myloop, &exitsig);
587     \& evf_unref (myloop);
588     .Ve
589     .Sp
590     Example: for some weird reason, unregister the above signal handler again.
591     .Sp
592     .Vb 2
593     \& ev_ref (myloop);
594     \& ev_signal_stop (myloop, &exitsig);
595     .Ve
596 root 1.1 .SH "ANATOMY OF A WATCHER"
597     .IX Header "ANATOMY OF A WATCHER"
598     A watcher is a structure that you create and register to record your
599     interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
600     become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
601     .PP
602     .Vb 5
603     \& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
604     \& {
605     \& ev_io_stop (w);
606     \& ev_unloop (loop, EVUNLOOP_ALL);
607     \& }
608     .Ve
609     .PP
610     .Vb 6
611     \& struct ev_loop *loop = ev_default_loop (0);
612     \& struct ev_io stdin_watcher;
613     \& ev_init (&stdin_watcher, my_cb);
614     \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
615     \& ev_io_start (loop, &stdin_watcher);
616     \& ev_loop (loop, 0);
617     .Ve
618     .PP
619     As you can see, you are responsible for allocating the memory for your
620     watcher structures (and it is usually a bad idea to do this on the stack,
621     although this can sometimes be quite valid).
622     .PP
623     Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
624     (watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
625     callback gets invoked each time the event occurs (or, in the case of io
626     watchers, each time the event loop detects that the file descriptor given
627     is readable and/or writable).
628     .PP
629     Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro
630     with arguments specific to this watcher type. There is also a macro
631     to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init
632     (watcher *, callback, ...)\*(C'\fR.
633     .PP
634     To make the watcher actually watch out for events, you have to start it
635     with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher
636     *)\*(C'\fR), and you can stop watching for events at any time by calling the
637     corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR.
638     .PP
639     As long as your watcher is active (has been started but not stopped) you
640     must not touch the values stored in it. Most specifically you must never
641 root 1.6 reinitialise it or call its set macro.
642 root 1.1 .PP
643     You can check whether an event is active by calling the \f(CW\*(C`ev_is_active
644     (watcher *)\*(C'\fR macro. To see whether an event is outstanding (but the
645     callback for it has not been called yet) you can use the \f(CW\*(C`ev_is_pending
646     (watcher *)\*(C'\fR macro.
647     .PP
648     Each and every callback receives the event loop pointer as first, the
649     registered watcher structure as second, and a bitset of received events as
650     third argument.
651     .PP
652     The received events usually include a single bit per event type received
653     (you can receive multiple events at the same time). The possible bit masks
654     are:
655     .ie n .IP """EV_READ""" 4
656     .el .IP "\f(CWEV_READ\fR" 4
657     .IX Item "EV_READ"
658     .PD 0
659     .ie n .IP """EV_WRITE""" 4
660     .el .IP "\f(CWEV_WRITE\fR" 4
661     .IX Item "EV_WRITE"
662     .PD
663     The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
664     writable.
665     .ie n .IP """EV_TIMEOUT""" 4
666     .el .IP "\f(CWEV_TIMEOUT\fR" 4
667     .IX Item "EV_TIMEOUT"
668     The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
669     .ie n .IP """EV_PERIODIC""" 4
670     .el .IP "\f(CWEV_PERIODIC\fR" 4
671     .IX Item "EV_PERIODIC"
672     The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
673     .ie n .IP """EV_SIGNAL""" 4
674     .el .IP "\f(CWEV_SIGNAL\fR" 4
675     .IX Item "EV_SIGNAL"
676     The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
677     .ie n .IP """EV_CHILD""" 4
678     .el .IP "\f(CWEV_CHILD\fR" 4
679     .IX Item "EV_CHILD"
680     The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
681     .ie n .IP """EV_IDLE""" 4
682     .el .IP "\f(CWEV_IDLE\fR" 4
683     .IX Item "EV_IDLE"
684     The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
685     .ie n .IP """EV_PREPARE""" 4
686     .el .IP "\f(CWEV_PREPARE\fR" 4
687     .IX Item "EV_PREPARE"
688     .PD 0
689     .ie n .IP """EV_CHECK""" 4
690     .el .IP "\f(CWEV_CHECK\fR" 4
691     .IX Item "EV_CHECK"
692     .PD
693     All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts
694     to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
695     \&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
696     received events. Callbacks of both watcher types can start and stop as
697     many watchers as they want, and all of them will be taken into account
698     (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
699     \&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
700     .ie n .IP """EV_ERROR""" 4
701     .el .IP "\f(CWEV_ERROR\fR" 4
702     .IX Item "EV_ERROR"
703     An unspecified error has occured, the watcher has been stopped. This might
704     happen because the watcher could not be properly started because libev
705     ran out of memory, a file descriptor was found to be closed or any other
706     problem. You best act on it by reporting the problem and somehow coping
707     with the watcher being stopped.
708     .Sp
709     Libev will usually signal a few \*(L"dummy\*(R" events together with an error,
710     for example it might indicate that a fd is readable or writable, and if
711     your callbacks is well-written it can just attempt the operation and cope
712     with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded
713     programs, though, so beware.
714     .Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
715     .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
716     Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
717     and read at any time, libev will completely ignore it. This can be used
718     to associate arbitrary data with your watcher. If you need more data and
719     don't want to allocate memory and store a pointer to it in that data
720     member, you can also \*(L"subclass\*(R" the watcher type and provide your own
721     data:
722     .PP
723     .Vb 7
724     \& struct my_io
725     \& {
726     \& struct ev_io io;
727     \& int otherfd;
728     \& void *somedata;
729     \& struct whatever *mostinteresting;
730     \& }
731     .Ve
732     .PP
733     And since your callback will be called with a pointer to the watcher, you
734     can cast it back to your own type:
735     .PP
736     .Vb 5
737     \& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
738     \& {
739     \& struct my_io *w = (struct my_io *)w_;
740     \& ...
741     \& }
742     .Ve
743     .PP
744     More interesting and less C\-conformant ways of catsing your callback type
745     have been omitted....
746     .SH "WATCHER TYPES"
747     .IX Header "WATCHER TYPES"
748     This section describes each watcher in detail, but will not repeat
749     information given in the last section.
750     .ie n .Sh """ev_io"" \- is this file descriptor readable or writable"
751     .el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable"
752     .IX Subsection "ev_io - is this file descriptor readable or writable"
753     I/O watchers check whether a file descriptor is readable or writable
754     in each iteration of the event loop (This behaviour is called
755     level-triggering because you keep receiving events as long as the
756     condition persists. Remember you can stop the watcher if you don't want to
757     act on the event and neither want to receive future events).
758     .PP
759     In general you can register as many read and/or write event watchers per
760     fd as you want (as long as you don't confuse yourself). Setting all file
761     descriptors to non-blocking mode is also usually a good idea (but not
762     required if you know what you are doing).
763     .PP
764     You have to be careful with dup'ed file descriptors, though. Some backends
765     (the linux epoll backend is a notable example) cannot handle dup'ed file
766     descriptors correctly if you register interest in two or more fds pointing
767     to the same underlying file/socket etc. description (that is, they share
768     the same underlying \*(L"file open\*(R").
769     .PP
770     If you must do this, then force the use of a known-to-be-good backend
771 root 1.6 (at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
772     \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
773 root 1.1 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
774     .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
775     .PD 0
776     .IP "ev_io_set (ev_io *, int fd, int events)" 4
777     .IX Item "ev_io_set (ev_io *, int fd, int events)"
778     .PD
779     Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive
780     events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_READ |
781     EV_WRITE\*(C'\fR to receive the given events.
782 root 1.7 .Sp
783     Please note that most of the more scalable backend mechanisms (for example
784     epoll and solaris ports) can result in spurious readyness notifications
785     for file descriptors, so you practically need to use non-blocking I/O (and
786     treat callback invocation as hint only), or retest separately with a safe
787     interface before doing I/O (XLib can do this), or force the use of either
788     \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR, which don't suffer from this
789     problem. Also note that it is quite easy to have your callback invoked
790     when the readyness condition is no longer valid even when employing
791     typical ways of handling events, so its a good idea to use non-blocking
792     I/O unconditionally.
793 root 1.9 .PP
794     Example: call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
795     readable, but only once. Since it is likely line\-buffered, you could
796     attempt to read a whole line in the callback:
797     .PP
798     .Vb 6
799     \& static void
800     \& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
801     \& {
802     \& ev_io_stop (loop, w);
803     \& .. read from stdin here (or from w->fd) and haqndle any I/O errors
804     \& }
805     .Ve
806     .PP
807     .Vb 6
808     \& ...
809     \& struct ev_loop *loop = ev_default_init (0);
810     \& struct ev_io stdin_readable;
811     \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
812     \& ev_io_start (loop, &stdin_readable);
813     \& ev_loop (loop, 0);
814     .Ve
815 root 1.1 .ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts"
816     .el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts"
817     .IX Subsection "ev_timer - relative and optionally recurring timeouts"
818     Timer watchers are simple relative timers that generate an event after a
819     given time, and optionally repeating in regular intervals after that.
820     .PP
821     The timers are based on real time, that is, if you register an event that
822     times out after an hour and you reset your system clock to last years
823     time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because
824 root 1.2 detecting time jumps is hard, and some inaccuracies are unavoidable (the
825 root 1.1 monotonic clock option helps a lot here).
826     .PP
827     The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
828     time. This is usually the right thing as this timestamp refers to the time
829 root 1.2 of the event triggering whatever timeout you are modifying/starting. If
830     you suspect event processing to be delayed and you \fIneed\fR to base the timeout
831 root 1.1 on the current time, use something like this to adjust for this:
832     .PP
833     .Vb 1
834     \& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
835     .Ve
836 root 1.2 .PP
837     The callback is guarenteed to be invoked only when its timeout has passed,
838     but if multiple timers become ready during the same loop iteration then
839     order of execution is undefined.
840 root 1.1 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
841     .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
842     .PD 0
843     .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
844     .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
845     .PD
846     Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is
847     \&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the
848     timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds
849     later, again, and again, until stopped manually.
850     .Sp
851     The timer itself will do a best-effort at avoiding drift, that is, if you
852     configure a timer to trigger every 10 seconds, then it will trigger at
853     exactly 10 second intervals. If, however, your program cannot keep up with
854     the timer (because it takes longer than those 10 seconds to do stuff) the
855     timer will not fire more than once per event loop iteration.
856     .IP "ev_timer_again (loop)" 4
857     .IX Item "ev_timer_again (loop)"
858     This will act as if the timer timed out and restart it again if it is
859     repeating. The exact semantics are:
860     .Sp
861     If the timer is started but nonrepeating, stop it.
862     .Sp
863     If the timer is repeating, either start it if necessary (with the repeat
864     value), or reset the running timer to the repeat value.
865     .Sp
866     This sounds a bit complicated, but here is a useful and typical
867     example: Imagine you have a tcp connection and you want a so-called idle
868     timeout, that is, you want to be called when there have been, say, 60
869     seconds of inactivity on the socket. The easiest way to do this is to
870     configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each
871     time you successfully read or write some data. If you go into an idle
872     state where you do not expect data to travel on the socket, you can stop
873     the timer, and again will automatically restart it if need be.
874 root 1.9 .PP
875     Example: create a timer that fires after 60 seconds.
876     .PP
877     .Vb 5
878     \& static void
879     \& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
880     \& {
881     \& .. one minute over, w is actually stopped right here
882     \& }
883     .Ve
884     .PP
885     .Vb 3
886     \& struct ev_timer mytimer;
887     \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
888     \& ev_timer_start (loop, &mytimer);
889     .Ve
890     .PP
891     Example: create a timeout timer that times out after 10 seconds of
892     inactivity.
893     .PP
894     .Vb 5
895     \& static void
896     \& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
897     \& {
898     \& .. ten seconds without any activity
899     \& }
900     .Ve
901     .PP
902     .Vb 4
903     \& struct ev_timer mytimer;
904     \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
905     \& ev_timer_again (&mytimer); /* start timer */
906     \& ev_loop (loop, 0);
907     .Ve
908     .PP
909     .Vb 3
910     \& // and in some piece of code that gets executed on any "activity":
911     \& // reset the timeout to start ticking again at 10 seconds
912     \& ev_timer_again (&mytimer);
913     .Ve
914 root 1.1 .ie n .Sh """ev_periodic"" \- to cron or not to cron"
915     .el .Sh "\f(CWev_periodic\fP \- to cron or not to cron"
916     .IX Subsection "ev_periodic - to cron or not to cron"
917     Periodic watchers are also timers of a kind, but they are very versatile
918     (and unfortunately a bit complex).
919     .PP
920     Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)
921     but on wallclock time (absolute time). You can tell a periodic watcher
922     to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a
923     periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
924     + 10.>) and then reset your system clock to the last year, then it will
925     take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger
926     roughly 10 seconds later and of course not if you reset your system time
927     again).
928     .PP
929     They can also be used to implement vastly more complex timers, such as
930     triggering an event on eahc midnight, local time.
931 root 1.2 .PP
932     As with timers, the callback is guarenteed to be invoked only when the
933     time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready
934     during the same loop iteration then order of execution is undefined.
935 root 1.1 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
936     .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
937     .PD 0
938     .IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
939     .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
940     .PD
941     Lots of arguments, lets sort it out... There are basically three modes of
942     operation, and we will explain them from simplest to complex:
943     .RS 4
944     .IP "* absolute timer (interval = reschedule_cb = 0)" 4
945     .IX Item "absolute timer (interval = reschedule_cb = 0)"
946     In this configuration the watcher triggers an event at the wallclock time
947     \&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs,
948     that is, if it is to be run at January 1st 2011 then it will run when the
949     system time reaches or surpasses this time.
950     .IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4
951     .IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)"
952     In this mode the watcher will always be scheduled to time out at the next
953     \&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless
954     of any time jumps.
955     .Sp
956     This can be used to create timers that do not drift with respect to system
957     time:
958     .Sp
959     .Vb 1
960     \& ev_periodic_set (&periodic, 0., 3600., 0);
961     .Ve
962     .Sp
963     This doesn't mean there will always be 3600 seconds in between triggers,
964     but only that the the callback will be called when the system time shows a
965     full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
966     by 3600.
967     .Sp
968     Another way to think about it (for the mathematically inclined) is that
969     \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
970     time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps.
971     .IP "* manual reschedule mode (reschedule_cb = callback)" 4
972     .IX Item "manual reschedule mode (reschedule_cb = callback)"
973     In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
974     ignored. Instead, each time the periodic watcher gets scheduled, the
975     reschedule callback will be called with the watcher as first, and the
976     current time as second argument.
977     .Sp
978     \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
979     ever, or make any event loop modifications\fR. If you need to stop it,
980     return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by
981     starting a prepare watcher).
982     .Sp
983     Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
984     ev_tstamp now)\*(C'\fR, e.g.:
985     .Sp
986     .Vb 4
987     \& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
988     \& {
989     \& return now + 60.;
990     \& }
991     .Ve
992     .Sp
993     It must return the next time to trigger, based on the passed time value
994     (that is, the lowest time value larger than to the second argument). It
995     will usually be called just before the callback will be triggered, but
996     might be called at other times, too.
997     .Sp
998     \&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the
999     passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger.
1000     .Sp
1001     This can be used to create very complex timers, such as a timer that
1002     triggers on each midnight, local time. To do this, you would calculate the
1003     next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1004     you do this is, again, up to you (but it is not trivial, which is the main
1005     reason I omitted it as an example).
1006     .RE
1007     .RS 4
1008     .RE
1009     .IP "ev_periodic_again (loop, ev_periodic *)" 4
1010     .IX Item "ev_periodic_again (loop, ev_periodic *)"
1011     Simply stops and restarts the periodic watcher again. This is only useful
1012     when you changed some parameters or the reschedule callback would return
1013     a different time than the last time it was called (e.g. in a crond like
1014     program when the crontabs have changed).
1015 root 1.9 .PP
1016     Example: call a callback every hour, or, more precisely, whenever the
1017     system clock is divisible by 3600. The callback invocation times have
1018     potentially a lot of jittering, but good long-term stability.
1019     .PP
1020     .Vb 5
1021     \& static void
1022     \& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1023     \& {
1024     \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1025     \& }
1026     .Ve
1027     .PP
1028     .Vb 3
1029     \& struct ev_periodic hourly_tick;
1030     \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1031     \& ev_periodic_start (loop, &hourly_tick);
1032     .Ve
1033     .PP
1034     Example: the same as above, but use a reschedule callback to do it:
1035     .PP
1036     .Vb 1
1037     \& #include <math.h>
1038     .Ve
1039     .PP
1040     .Vb 5
1041     \& static ev_tstamp
1042     \& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
1043     \& {
1044     \& return fmod (now, 3600.) + 3600.;
1045     \& }
1046     .Ve
1047     .PP
1048     .Vb 1
1049     \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1050     .Ve
1051     .PP
1052     Example: call a callback every hour, starting now:
1053     .PP
1054     .Vb 4
1055     \& struct ev_periodic hourly_tick;
1056     \& ev_periodic_init (&hourly_tick, clock_cb,
1057     \& fmod (ev_now (loop), 3600.), 3600., 0);
1058     \& ev_periodic_start (loop, &hourly_tick);
1059     .Ve
1060 root 1.1 .ie n .Sh """ev_signal"" \- signal me when a signal gets signalled"
1061     .el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled"
1062     .IX Subsection "ev_signal - signal me when a signal gets signalled"
1063     Signal watchers will trigger an event when the process receives a specific
1064     signal one or more times. Even though signals are very asynchronous, libev
1065     will try it's best to deliver signals synchronously, i.e. as part of the
1066     normal event processing, like any other event.
1067     .PP
1068     You can configure as many watchers as you like per signal. Only when the
1069     first watcher gets started will libev actually register a signal watcher
1070     with the kernel (thus it coexists with your own signal handlers as long
1071     as you don't register any with libev). Similarly, when the last signal
1072     watcher for a signal is stopped libev will reset the signal handler to
1073     \&\s-1SIG_DFL\s0 (regardless of what it was set to before).
1074     .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1075     .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1076     .PD 0
1077     .IP "ev_signal_set (ev_signal *, int signum)" 4
1078     .IX Item "ev_signal_set (ev_signal *, int signum)"
1079     .PD
1080     Configures the watcher to trigger on the given signal number (usually one
1081     of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1082     .ie n .Sh """ev_child"" \- wait for pid status changes"
1083     .el .Sh "\f(CWev_child\fP \- wait for pid status changes"
1084     .IX Subsection "ev_child - wait for pid status changes"
1085     Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1086     some child status changes (most typically when a child of yours dies).
1087     .IP "ev_child_init (ev_child *, callback, int pid)" 4
1088     .IX Item "ev_child_init (ev_child *, callback, int pid)"
1089     .PD 0
1090     .IP "ev_child_set (ev_child *, int pid)" 4
1091     .IX Item "ev_child_set (ev_child *, int pid)"
1092     .PD
1093     Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1094     \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1095     at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1096     the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1097     \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1098     process causing the status change.
1099 root 1.9 .PP
1100     Example: try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0.
1101     .PP
1102     .Vb 5
1103     \& static void
1104     \& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1105     \& {
1106     \& ev_unloop (loop, EVUNLOOP_ALL);
1107     \& }
1108     .Ve
1109     .PP
1110     .Vb 3
1111     \& struct ev_signal signal_watcher;
1112     \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1113     \& ev_signal_start (loop, &sigint_cb);
1114     .Ve
1115 root 1.1 .ie n .Sh """ev_idle"" \- when you've got nothing better to do"
1116     .el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do"
1117     .IX Subsection "ev_idle - when you've got nothing better to do"
1118     Idle watchers trigger events when there are no other events are pending
1119     (prepare, check and other idle watchers do not count). That is, as long
1120     as your process is busy handling sockets or timeouts (or even signals,
1121     imagine) it will not be triggered. But when your process is idle all idle
1122     watchers are being called again and again, once per event loop iteration \-
1123     until stopped, that is, or your process receives more events and becomes
1124     busy.
1125     .PP
1126     The most noteworthy effect is that as long as any idle watchers are
1127     active, the process will not block when waiting for new events.
1128     .PP
1129     Apart from keeping your process non-blocking (which is a useful
1130     effect on its own sometimes), idle watchers are a good place to do
1131     \&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the
1132     event loop has handled all outstanding events.
1133     .IP "ev_idle_init (ev_signal *, callback)" 4
1134     .IX Item "ev_idle_init (ev_signal *, callback)"
1135     Initialises and configures the idle watcher \- it has no parameters of any
1136     kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1137     believe me.
1138 root 1.9 .PP
1139     Example: dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR, start it, and in the
1140     callback, free it. Alos, use no error checking, as usual.
1141     .PP
1142     .Vb 7
1143     \& static void
1144     \& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1145     \& {
1146     \& free (w);
1147     \& // now do something you wanted to do when the program has
1148     \& // no longer asnything immediate to do.
1149     \& }
1150     .Ve
1151     .PP
1152     .Vb 3
1153     \& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1154     \& ev_idle_init (idle_watcher, idle_cb);
1155     \& ev_idle_start (loop, idle_cb);
1156     .Ve
1157 root 1.1 .ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop"
1158     .el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop"
1159     .IX Subsection "ev_prepare and ev_check - customise your event loop"
1160     Prepare and check watchers are usually (but not always) used in tandem:
1161     prepare watchers get invoked before the process blocks and check watchers
1162     afterwards.
1163     .PP
1164     Their main purpose is to integrate other event mechanisms into libev. This
1165     could be used, for example, to track variable changes, implement your own
1166     watchers, integrate net-snmp or a coroutine library and lots more.
1167     .PP
1168     This is done by examining in each prepare call which file descriptors need
1169     to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for
1170     them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries
1171     provide just this functionality). Then, in the check watcher you check for
1172     any events that occured (by checking the pending status of all watchers
1173     and stopping them) and call back into the library. The I/O and timer
1174     callbacks will never actually be called (but must be valid nevertheless,
1175     because you never know, you know?).
1176     .PP
1177     As another example, the Perl Coro module uses these hooks to integrate
1178     coroutines into libev programs, by yielding to other active coroutines
1179     during each prepare and only letting the process block if no coroutines
1180     are ready to run (it's actually more complicated: it only runs coroutines
1181     with priority higher than or equal to the event loop and one coroutine
1182     of lower priority, but only once, using idle watchers to keep the event
1183     loop from blocking if lower-priority coroutines are active, thus mapping
1184     low-priority coroutines to idle/background tasks).
1185     .IP "ev_prepare_init (ev_prepare *, callback)" 4
1186     .IX Item "ev_prepare_init (ev_prepare *, callback)"
1187     .PD 0
1188     .IP "ev_check_init (ev_check *, callback)" 4
1189     .IX Item "ev_check_init (ev_check *, callback)"
1190     .PD
1191     Initialises and configures the prepare or check watcher \- they have no
1192     parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1193     macros, but using them is utterly, utterly and completely pointless.
1194 root 1.9 .PP
1195     Example: *TODO*.
1196 root 1.1 .SH "OTHER FUNCTIONS"
1197     .IX Header "OTHER FUNCTIONS"
1198     There are some other functions of possible interest. Described. Here. Now.
1199     .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
1200     .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
1201     This function combines a simple timer and an I/O watcher, calls your
1202     callback on whichever event happens first and automatically stop both
1203     watchers. This is useful if you want to wait for a single event on an fd
1204     or timeout without having to allocate/configure/start/stop/free one or
1205     more watchers yourself.
1206     .Sp
1207     If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events
1208     is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and
1209     \&\f(CW\*(C`events\*(C'\fR set will be craeted and started.
1210     .Sp
1211     If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1212     started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1213     repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of
1214     dubious value.
1215     .Sp
1216     The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
1217     passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1218     \&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMEOUT\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
1219     value passed to \f(CW\*(C`ev_once\*(C'\fR:
1220     .Sp
1221     .Vb 7
1222     \& static void stdin_ready (int revents, void *arg)
1223     \& {
1224     \& if (revents & EV_TIMEOUT)
1225     \& /* doh, nothing entered */;
1226     \& else if (revents & EV_READ)
1227     \& /* stdin might have data for us, joy! */;
1228     \& }
1229     .Ve
1230     .Sp
1231     .Vb 1
1232     \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1233     .Ve
1234     .IP "ev_feed_event (loop, watcher, int events)" 4
1235     .IX Item "ev_feed_event (loop, watcher, int events)"
1236     Feeds the given event set into the event loop, as if the specified event
1237     had happened for the specified watcher (which must be a pointer to an
1238     initialised but not necessarily started event watcher).
1239     .IP "ev_feed_fd_event (loop, int fd, int revents)" 4
1240     .IX Item "ev_feed_fd_event (loop, int fd, int revents)"
1241     Feed an event on the given fd, as if a file descriptor backend detected
1242     the given events it.
1243     .IP "ev_feed_signal_event (loop, int signum)" 4
1244     .IX Item "ev_feed_signal_event (loop, int signum)"
1245     Feed an event as if the given signal occured (loop must be the default loop!).
1246     .SH "LIBEVENT EMULATION"
1247     .IX Header "LIBEVENT EMULATION"
1248     Libev offers a compatibility emulation layer for libevent. It cannot
1249     emulate the internals of libevent, so here are some usage hints:
1250     .IP "* Use it by including <event.h>, as usual." 4
1251     .IX Item "Use it by including <event.h>, as usual."
1252     .PD 0
1253     .IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4
1254     .IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events."
1255     .IP "* Avoid using ev_flags and the EVLIST_*\-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private \s-1API\s0)." 4
1256     .IX Item "Avoid using ev_flags and the EVLIST_*-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private API)."
1257     .IP "* Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 4
1258     .IX Item "Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field."
1259     .IP "* Other members are not supported." 4
1260     .IX Item "Other members are not supported."
1261     .IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4
1262     .IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library."
1263     .PD
1264     .SH "\*(C+ SUPPORT"
1265     .IX Header " SUPPORT"
1266     \&\s-1TBD\s0.
1267     .SH "AUTHOR"
1268     .IX Header "AUTHOR"
1269     Marc Lehmann <libev@schmorp.de>.