ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.351 by root, Mon Jan 10 14:24:26 2011 UTC vs.
Revision 1.450 by root, Mon Jun 24 00:04:26 2019 UTC

		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	libev - a high performance full-featured event loop written in C	5	libev - a high performance full-featured event loop written in C
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
…		…
58	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
59		61
60	// now wait for events to arrive	62	// now wait for events to arrive
61	ev_run (loop, 0);	63	ev_run (loop, 0);
62		64
63	// unloop was called, so exit	65	// break was called, so exit
64	return 0;	66	return 0;
65	}	67	}
66		68
67	=head1 ABOUT THIS DOCUMENT	69	=head1 ABOUT THIS DOCUMENT
68		70
…		…
82		84
83	=head1 WHAT TO READ WHEN IN A HURRY	85	=head1 WHAT TO READ WHEN IN A HURRY
84		86
85	This manual tries to be very detailed, but unfortunately, this also makes	87	This manual tries to be very detailed, but unfortunately, this also makes
86	it very long. If you just want to know the basics of libev, I suggest	88	it very long. If you just want to know the basics of libev, I suggest
87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and	89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and	90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
89	C<ev_timer> sections in L<WATCHER TYPES>.	91	C<ev_timer> sections in L</WATCHER TYPES>.
90		92
91	=head1 ABOUT LIBEV	93	=head1 ABOUT LIBEV
92		94
93	Libev is an event loop: you register interest in certain events (such as a	95	Libev is an event loop: you register interest in certain events (such as a
94	file descriptor being readable or a timeout occurring), and it will manage	96	file descriptor being readable or a timeout occurring), and it will manage
…		…
103	details of the event, and then hand it over to libev by I<starting> the	105	details of the event, and then hand it over to libev by I<starting> the
104	watcher.	106	watcher.
105		107
106	=head2 FEATURES	108	=head2 FEATURES
107		109
108	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	110	Libev supports C<select>, C<poll>, the Linux-specific aio and C<epoll>
109	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port
110	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	112	mechanisms for file descriptor events (C<ev_io>), the Linux C<inotify>
111	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner	113	interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
112	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative	114	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
113	timers (C<ev_timer>), absolute timers with customised rescheduling	115	timers (C<ev_timer>), absolute timers with customised rescheduling
114	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status	116	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
115	change events (C<ev_child>), and event watchers dealing with the event	117	change events (C<ev_child>), and event watchers dealing with the event
116	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and	118	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
…		…
174	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
175		177
176	Returns the current time as libev would use it. Please note that the	178	Returns the current time as libev would use it. Please note that the
177	C<ev_now> function is usually faster and also often returns the timestamp	179	C<ev_now> function is usually faster and also often returns the timestamp
178	you actually want to know. Also interesting is the combination of	180	you actually want to know. Also interesting is the combination of
179	C<ev_update_now> and C<ev_now>.	181	C<ev_now_update> and C<ev_now>.
180		182
181	=item ev_sleep (ev_tstamp interval)	183	=item ev_sleep (ev_tstamp interval)
182		184
183	Sleep for the given interval: The current thread will be blocked until	185	Sleep for the given interval: The current thread will be blocked
184	either it is interrupted or the given time interval has passed. Basically	186	until either it is interrupted or the given time interval has
		187	passed (approximately - it might return a bit earlier even if not
		188	interrupted). Returns immediately if C<< interval <= 0 >>.
		189
185	this is a sub-second-resolution C<sleep ()>.	190	Basically this is a sub-second-resolution C<sleep ()>.
		191
		192	The range of the C<interval> is limited - libev only guarantees to work
		193	with sleep times of up to one day (C<< interval <= 86400 >>).
186		194
187	=item int ev_version_major ()	195	=item int ev_version_major ()
188		196
189	=item int ev_version_minor ()	197	=item int ev_version_minor ()
190		198
…		…
241	the current system, you would need to look at C<ev_embeddable_backends ()	249	the current system, you would need to look at C<ev_embeddable_backends ()
242	& ev_supported_backends ()>, likewise for recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
243		251
244	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
245		253
246	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
247		255
248	Sets the allocation function to use (the prototype is similar - the	256	Sets the allocation function to use (the prototype is similar - the
249	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	257	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
250	used to allocate and free memory (no surprises here). If it returns zero	258	used to allocate and free memory (no surprises here). If it returns zero
251	when memory needs to be allocated (C<size != 0>), the library might abort	259	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
257		265
258	You could override this function in high-availability programs to, say,	266	You could override this function in high-availability programs to, say,
259	free some memory if it cannot allocate memory, to use a special allocator,	267	free some memory if it cannot allocate memory, to use a special allocator,
260	or even to sleep a while and retry until some memory is available.	268	or even to sleep a while and retry until some memory is available.
261		269
		270	Example: The following is the C<realloc> function that libev itself uses
		271	which should work with C<realloc> and C<free> functions of all kinds and
		272	is probably a good basis for your own implementation.
		273
		274	static void *
		275	ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
		276	{
		277	if (size)
		278	return realloc (ptr, size);
		279
		280	free (ptr);
		281	return 0;
		282	}
		283
262	Example: Replace the libev allocator with one that waits a bit and then	284	Example: Replace the libev allocator with one that waits a bit and then
263	retries (example requires a standards-compliant C<realloc>).	285	retries.
264		286
265	static void *	287	static void *
266	persistent_realloc (void *ptr, size_t size)	288	persistent_realloc (void *ptr, size_t size)
267	{	289	{
		290	if (!size)
		291	{
		292	free (ptr);
		293	return 0;
		294	}
		295
268	for (;;)	296	for (;;)
269	{	297	{
270	void *newptr = realloc (ptr, size);	298	void *newptr = realloc (ptr, size);
271		299
272	if (newptr)	300	if (newptr)
…		…
277	}	305	}
278		306
279	...	307	...
280	ev_set_allocator (persistent_realloc);	308	ev_set_allocator (persistent_realloc);
281		309
282	=item ev_set_syserr_cb (void (*cb)(const char *msg))	310	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
283		311
284	Set the callback function to call on a retryable system call error (such	312	Set the callback function to call on a retryable system call error (such
285	as failed select, poll, epoll_wait). The message is a printable string	313	as failed select, poll, epoll_wait). The message is a printable string
286	indicating the system call or subsystem causing the problem. If this	314	indicating the system call or subsystem causing the problem. If this
287	callback is set, then libev will expect it to remedy the situation, no	315	callback is set, then libev will expect it to remedy the situation, no
…		…
390		418
391	If this flag bit is or'ed into the flag value (or the program runs setuid	419	If this flag bit is or'ed into the flag value (or the program runs setuid
392	or setgid) then libev will I<not> look at the environment variable	420	or setgid) then libev will I<not> look at the environment variable
393	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	421	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
394	override the flags completely if it is found in the environment. This is	422	override the flags completely if it is found in the environment. This is
395	useful to try out specific backends to test their performance, or to work	423	useful to try out specific backends to test their performance, to work
396	around bugs.	424	around bugs, or to make libev threadsafe (accessing environment variables
		425	cannot be done in a threadsafe way, but usually it works if no other
		426	thread modifies them).
397		427
398	=item C<EVFLAG_FORKCHECK>	428	=item C<EVFLAG_FORKCHECK>
399		429
400	Instead of calling C<ev_loop_fork> manually after a fork, you can also	430	Instead of calling C<ev_loop_fork> manually after a fork, you can also
401	make libev check for a fork in each iteration by enabling this flag.	431	make libev check for a fork in each iteration by enabling this flag.
402		432
403	This works by calling C<getpid ()> on every iteration of the loop,	433	This works by calling C<getpid ()> on every iteration of the loop,
404	and thus this might slow down your event loop if you do a lot of loop	434	and thus this might slow down your event loop if you do a lot of loop
405	iterations and little real work, but is usually not noticeable (on my	435	iterations and little real work, but is usually not noticeable (on my
406	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	436	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
407	without a system call and thus I<very> fast, but my GNU/Linux system also has	437	sequence without a system call and thus I<very> fast, but my GNU/Linux
408	C<pthread_atfork> which is even faster).	438	system also has C<pthread_atfork> which is even faster). (Update: glibc
		439	versions 2.25 apparently removed the C<getpid> optimisation again).
409		440
410	The big advantage of this flag is that you can forget about fork (and	441	The big advantage of this flag is that you can forget about fork (and
411	forget about forgetting to tell libev about forking) when you use this	442	forget about forgetting to tell libev about forking, although you still
412	flag.	443	have to ignore C<SIGPIPE>) when you use this flag.
413		444
414	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	445	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
415	environment variable.	446	environment variable.
416		447
417	=item C<EVFLAG_NOINOTIFY>	448	=item C<EVFLAG_NOINOTIFY>
…		…
435	example) that can't properly initialise their signal masks.	466	example) that can't properly initialise their signal masks.
436		467
437	=item C<EVFLAG_NOSIGMASK>	468	=item C<EVFLAG_NOSIGMASK>
438		469
439	When this flag is specified, then libev will avoid to modify the signal	470	When this flag is specified, then libev will avoid to modify the signal
440	mask. Specifically, this means you ahve to make sure signals are unblocked	471	mask. Specifically, this means you have to make sure signals are unblocked
441	when you want to receive them.	472	when you want to receive them.
442		473
443	This behaviour is useful when you want to do your own signal handling, or	474	This behaviour is useful when you want to do your own signal handling, or
444	want to handle signals only in specific threads and want to avoid libev	475	want to handle signals only in specific threads and want to avoid libev
445	unblocking the signals.	476	unblocking the signals.
		477
		478	It's also required by POSIX in a threaded program, as libev calls
		479	C<sigprocmask>, whose behaviour is officially unspecified.
446		480
447	This flag's behaviour will become the default in future versions of libev.	481	This flag's behaviour will become the default in future versions of libev.
448		482
449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	483	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
450		484
…		…
480	=item C<EVBACKEND_EPOLL> (value 4, Linux)	514	=item C<EVBACKEND_EPOLL> (value 4, Linux)
481		515
482	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	516	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
483	kernels).	517	kernels).
484		518
485	For few fds, this backend is a bit little slower than poll and select,	519	For few fds, this backend is a bit little slower than poll and select, but
486	but it scales phenomenally better. While poll and select usually scale	520	it scales phenomenally better. While poll and select usually scale like
487	like O(total_fds) where n is the total number of fds (or the highest fd),	521	O(total_fds) where total_fds is the total number of fds (or the highest
488	epoll scales either O(1) or O(active_fds).	522	fd), epoll scales either O(1) or O(active_fds).
489		523
490	The epoll mechanism deserves honorable mention as the most misdesigned	524	The epoll mechanism deserves honorable mention as the most misdesigned
491	of the more advanced event mechanisms: mere annoyances include silently	525	of the more advanced event mechanisms: mere annoyances include silently
492	dropping file descriptors, requiring a system call per change per file	526	dropping file descriptors, requiring a system call per change per file
493	descriptor (and unnecessary guessing of parameters), problems with dup,	527	descriptor (and unnecessary guessing of parameters), problems with dup,
…		…
496	0.1ms) and so on. The biggest issue is fork races, however - if a program	530	0.1ms) and so on. The biggest issue is fork races, however - if a program
497	forks then I<both> parent and child process have to recreate the epoll	531	forks then I<both> parent and child process have to recreate the epoll
498	set, which can take considerable time (one syscall per file descriptor)	532	set, which can take considerable time (one syscall per file descriptor)
499	and is of course hard to detect.	533	and is of course hard to detect.
500		534
501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	535	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
502	of course I<doesn't>, and epoll just loves to report events for totally	536	but of course I<doesn't>, and epoll just loves to report events for
503	I<different> file descriptors (even already closed ones, so one cannot	537	totally I<different> file descriptors (even already closed ones, so
504	even remove them from the set) than registered in the set (especially	538	one cannot even remove them from the set) than registered in the set
505	on SMP systems). Libev tries to counter these spurious notifications by	539	(especially on SMP systems). Libev tries to counter these spurious
506	employing an additional generation counter and comparing that against the	540	notifications by employing an additional generation counter and comparing
507	events to filter out spurious ones, recreating the set when required. Last	541	that against the events to filter out spurious ones, recreating the set
		542	when required. Epoll also erroneously rounds down timeouts, but gives you
		543	no way to know when and by how much, so sometimes you have to busy-wait
		544	because epoll returns immediately despite a nonzero timeout. And last
508	not least, it also refuses to work with some file descriptors which work	545	not least, it also refuses to work with some file descriptors which work
509	perfectly fine with C<select> (files, many character devices...).	546	perfectly fine with C<select> (files, many character devices...).
510		547
511	Epoll is truly the train wreck analog among event poll mechanisms.	548	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		549	cobbled together in a hurry, no thought to design or interaction with
		550	others. Oh, the pain, will it ever stop...
512		551
513	While stopping, setting and starting an I/O watcher in the same iteration	552	While stopping, setting and starting an I/O watcher in the same iteration
514	will result in some caching, there is still a system call per such	553	will result in some caching, there is still a system call per such
515	incident (because the same I<file descriptor> could point to a different	554	incident (because the same I<file descriptor> could point to a different
516	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	555	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
528	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or	567	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
529	faster than epoll for maybe up to a hundred file descriptors, depending on	568	faster than epoll for maybe up to a hundred file descriptors, depending on
530	the usage. So sad.	569	the usage. So sad.
531		570
532	While nominally embeddable in other event loops, this feature is broken in	571	While nominally embeddable in other event loops, this feature is broken in
533	all kernel versions tested so far.	572	a lot of kernel revisions, but probably(!) works in current versions.
		573
		574	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		575	C<EVBACKEND_POLL>.
		576
		577	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		578
		579	Use the linux-specific linux aio (I<not> C<< aio(7) >> but C<<
		580	io_submit(2) >>) event interface available in post-4.18 kernels.
		581
		582	If this backend works for you (as of this writing, it was very
		583	experimental), it is the best event interface available on linux and might
		584	be well worth enabling it - if it isn't available in your kernel this will
		585	be detected and this backend will be skipped.
		586
		587	This backend can batch oneshot requests and supports a user-space ring
		588	buffer to receive events. It also doesn't suffer from most of the design
		589	problems of epoll (such as not being able to remove event sources from
		590	the epoll set), and generally sounds too good to be true. Because, this
		591	being the linux kernel, of course it suffers from a whole new set of
		592	limitations.
		593
		594	For one, it is not easily embeddable (but probably could be done using
		595	an event fd at some extra overhead). It also is subject to a system wide
		596	limit that can be configured in F</proc/sys/fs/aio-max-nr> - each loop
		597	currently requires C<61> of this number. If no aio requests are left, this
		598	backend will be skipped during initialisation.
		599
		600	Most problematic in practise, however, is that not all file descriptors
		601	work with it. For example, in linux 5.1, tcp sockets, pipes, event fds,
		602	files, F</dev/null> and a few others are supported, but ttys do not work
		603	properly (a known bug that the kernel developers don't care about, see
		604	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		605	(yet?) a generic event polling interface.
		606
		607	To work around this latter problem, the current version of libev uses
		608	epoll as a fallback for file deescriptor types that do not work. Epoll
		609	is used in, kind of, slow mode that hopefully avoids most of its design
		610	problems and requires 1-3 extra syscalls per active fd every iteration.
534		611
535	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	612	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
536	C<EVBACKEND_POLL>.	613	C<EVBACKEND_POLL>.
537		614
538	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	615	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
…		…
553		630
554	It scales in the same way as the epoll backend, but the interface to the	631	It scales in the same way as the epoll backend, but the interface to the
555	kernel is more efficient (which says nothing about its actual speed, of	632	kernel is more efficient (which says nothing about its actual speed, of
556	course). While stopping, setting and starting an I/O watcher does never	633	course). While stopping, setting and starting an I/O watcher does never
557	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	634	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
558	two event changes per incident. Support for C<fork ()> is very bad (but	635	two event changes per incident. Support for C<fork ()> is very bad (you
559	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	636	might have to leak fd's on fork, but it's more sane than epoll) and it
560	cases	637	drops fds silently in similarly hard-to-detect cases.
561		638
562	This backend usually performs well under most conditions.	639	This backend usually performs well under most conditions.
563		640
564	While nominally embeddable in other event loops, this doesn't work	641	While nominally embeddable in other event loops, this doesn't work
565	everywhere, so you might need to test for this. And since it is broken	642	everywhere, so you might need to test for this. And since it is broken
…		…
592	On the positive side, this backend actually performed fully to	669	On the positive side, this backend actually performed fully to
593	specification in all tests and is fully embeddable, which is a rare feat	670	specification in all tests and is fully embeddable, which is a rare feat
594	among the OS-specific backends (I vastly prefer correctness over speed	671	among the OS-specific backends (I vastly prefer correctness over speed
595	hacks).	672	hacks).
596		673
597	On the negative side, the interface is I<bizarre>, with the event polling	674	On the negative side, the interface is I<bizarre> - so bizarre that
		675	even sun itself gets it wrong in their code examples: The event polling
598	function sometimes returning events to the caller even though an error	676	function sometimes returns events to the caller even though an error
599	occured, but with no indication whether it has done so or not (yes, it's	677	occurred, but with no indication whether it has done so or not (yes, it's
600	even documented that way) - deadly for edge-triggered interfaces, but	678	even documented that way) - deadly for edge-triggered interfaces where you
		679	absolutely have to know whether an event occurred or not because you have
		680	to re-arm the watcher.
		681
601	fortunately libev seems to be able to work around it.	682	Fortunately libev seems to be able to work around these idiocies.
602		683
603	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	684	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
604	C<EVBACKEND_POLL>.	685	C<EVBACKEND_POLL>.
605		686
606	=item C<EVBACKEND_ALL>	687	=item C<EVBACKEND_ALL>
…		…
634		715
635	Example: Use whatever libev has to offer, but make sure that kqueue is	716	Example: Use whatever libev has to offer, but make sure that kqueue is
636	used if available.	717	used if available.
637		718
638	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);	719	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		720
		721	Example: Similarly, on linux, you mgiht want to take advantage of the
		722	linux aio backend if possible, but fall back to something else if that
		723	isn't available.
		724
		725	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
639		726
640	=item ev_loop_destroy (loop)	727	=item ev_loop_destroy (loop)
641		728
642	Destroys an event loop object (frees all memory and kernel state	729	Destroys an event loop object (frees all memory and kernel state
643	etc.). None of the active event watchers will be stopped in the normal	730	etc.). None of the active event watchers will be stopped in the normal
…		…
660	If you need dynamically allocated loops it is better to use C<ev_loop_new>	747	If you need dynamically allocated loops it is better to use C<ev_loop_new>
661	and C<ev_loop_destroy>.	748	and C<ev_loop_destroy>.
662		749
663	=item ev_loop_fork (loop)	750	=item ev_loop_fork (loop)
664		751
665	This function sets a flag that causes subsequent C<ev_run> iterations to	752	This function sets a flag that causes subsequent C<ev_run> iterations
666	reinitialise the kernel state for backends that have one. Despite the	753	to reinitialise the kernel state for backends that have one. Despite
667	name, you can call it anytime, but it makes most sense after forking, in	754	the name, you can call it anytime you are allowed to start or stop
668	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the	755	watchers (except inside an C<ev_prepare> callback), but it makes most
		756	sense after forking, in the child process. You I<must> call it (or use
669	child before resuming or calling C<ev_run>.	757	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
670		758
		759	In addition, if you want to reuse a loop (via this function or
		760	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		761
671	Again, you I<have> to call it on I<any> loop that you want to re-use after	762	Again, you I<have> to call it on I<any> loop that you want to re-use after
672	a fork, I<even if you do not plan to use the loop in the parent>. This is	763	a fork, I<even if you do not plan to use the loop in the parent>. This is
673	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	764	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
674	during fork.	765	during fork.
675		766
676	On the other hand, you only need to call this function in the child	767	On the other hand, you only need to call this function in the child
…		…
746		837
747	This function is rarely useful, but when some event callback runs for a	838	This function is rarely useful, but when some event callback runs for a
748	very long time without entering the event loop, updating libev's idea of	839	very long time without entering the event loop, updating libev's idea of
749	the current time is a good idea.	840	the current time is a good idea.
750		841
751	See also L<The special problem of time updates> in the C<ev_timer> section.	842	See also L</The special problem of time updates> in the C<ev_timer> section.
752		843
753	=item ev_suspend (loop)	844	=item ev_suspend (loop)
754		845
755	=item ev_resume (loop)	846	=item ev_resume (loop)
756		847
…		…
774	without a previous call to C<ev_suspend>.	865	without a previous call to C<ev_suspend>.
775		866
776	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	867	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
777	event loop time (see C<ev_now_update>).	868	event loop time (see C<ev_now_update>).
778		869
779	=item ev_run (loop, int flags)	870	=item bool ev_run (loop, int flags)
780		871
781	Finally, this is it, the event handler. This function usually is called	872	Finally, this is it, the event handler. This function usually is called
782	after you have initialised all your watchers and you want to start	873	after you have initialised all your watchers and you want to start
783	handling events. It will ask the operating system for any new events, call	874	handling events. It will ask the operating system for any new events, call
784	the watcher callbacks, an then repeat the whole process indefinitely: This	875	the watcher callbacks, and then repeat the whole process indefinitely: This
785	is why event loops are called I<loops>.	876	is why event loops are called I<loops>.
786		877
787	If the flags argument is specified as C<0>, it will keep handling events	878	If the flags argument is specified as C<0>, it will keep handling events
788	until either no event watchers are active anymore or C<ev_break> was	879	until either no event watchers are active anymore or C<ev_break> was
789	called.	880	called.
		881
		882	The return value is false if there are no more active watchers (which
		883	usually means "all jobs done" or "deadlock"), and true in all other cases
		884	(which usually means " you should call C<ev_run> again").
790		885
791	Please note that an explicit C<ev_break> is usually better than	886	Please note that an explicit C<ev_break> is usually better than
792	relying on all watchers to be stopped when deciding when a program has	887	relying on all watchers to be stopped when deciding when a program has
793	finished (especially in interactive programs), but having a program	888	finished (especially in interactive programs), but having a program
794	that automatically loops as long as it has to and no longer by virtue	889	that automatically loops as long as it has to and no longer by virtue
795	of relying on its watchers stopping correctly, that is truly a thing of	890	of relying on its watchers stopping correctly, that is truly a thing of
796	beauty.	891	beauty.
797		892
798	This function is also I<mostly> exception-safe - you can break out of	893	This function is I<mostly> exception-safe - you can break out of a
799	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++	894	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
800	exception and so on. This does not decrement the C<ev_depth> value, nor	895	exception and so on. This does not decrement the C<ev_depth> value, nor
801	will it clear any outstanding C<EVBREAK_ONE> breaks.	896	will it clear any outstanding C<EVBREAK_ONE> breaks.
802		897
803	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	898	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
804	those events and any already outstanding ones, but will not wait and	899	those events and any already outstanding ones, but will not wait and
…		…
816	This is useful if you are waiting for some external event in conjunction	911	This is useful if you are waiting for some external event in conjunction
817	with something not expressible using other libev watchers (i.e. "roll your	912	with something not expressible using other libev watchers (i.e. "roll your
818	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	913	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
819	usually a better approach for this kind of thing.	914	usually a better approach for this kind of thing.
820		915
821	Here are the gory details of what C<ev_run> does:	916	Here are the gory details of what C<ev_run> does (this is for your
		917	understanding, not a guarantee that things will work exactly like this in
		918	future versions):
822		919
823	- Increment loop depth.	920	- Increment loop depth.
824	- Reset the ev_break status.	921	- Reset the ev_break status.
825	- Before the first iteration, call any pending watchers.	922	- Before the first iteration, call any pending watchers.
826	LOOP:	923	LOOP:
…		…
859	anymore.	956	anymore.
860		957
861	... queue jobs here, make sure they register event watchers as long	958	... queue jobs here, make sure they register event watchers as long
862	... as they still have work to do (even an idle watcher will do..)	959	... as they still have work to do (even an idle watcher will do..)
863	ev_run (my_loop, 0);	960	ev_run (my_loop, 0);
864	... jobs done or somebody called unloop. yeah!	961	... jobs done or somebody called break. yeah!
865		962
866	=item ev_break (loop, how)	963	=item ev_break (loop, how)
867		964
868	Can be used to make a call to C<ev_run> return early (but only after it	965	Can be used to make a call to C<ev_run> return early (but only after it
869	has processed all outstanding events). The C<how> argument must be either	966	has processed all outstanding events). The C<how> argument must be either
…		…
932	overhead for the actual polling but can deliver many events at once.	1029	overhead for the actual polling but can deliver many events at once.
933		1030
934	By setting a higher I<io collect interval> you allow libev to spend more	1031	By setting a higher I<io collect interval> you allow libev to spend more
935	time collecting I/O events, so you can handle more events per iteration,	1032	time collecting I/O events, so you can handle more events per iteration,
936	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	1033	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
937	C<ev_timer>) will be not affected. Setting this to a non-null value will	1034	C<ev_timer>) will not be affected. Setting this to a non-null value will
938	introduce an additional C<ev_sleep ()> call into most loop iterations. The	1035	introduce an additional C<ev_sleep ()> call into most loop iterations. The
939	sleep time ensures that libev will not poll for I/O events more often then	1036	sleep time ensures that libev will not poll for I/O events more often then
940	once per this interval, on average.	1037	once per this interval, on average (as long as the host time resolution is
		1038	good enough).
941		1039
942	Likewise, by setting a higher I<timeout collect interval> you allow libev	1040	Likewise, by setting a higher I<timeout collect interval> you allow libev
943	to spend more time collecting timeouts, at the expense of increased	1041	to spend more time collecting timeouts, at the expense of increased
944	latency/jitter/inexactness (the watcher callback will be called	1042	latency/jitter/inexactness (the watcher callback will be called
945	later). C<ev_io> watchers will not be affected. Setting this to a non-null	1043	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
991	invoke the actual watchers inside another context (another thread etc.).	1089	invoke the actual watchers inside another context (another thread etc.).
992		1090
993	If you want to reset the callback, use C<ev_invoke_pending> as new	1091	If you want to reset the callback, use C<ev_invoke_pending> as new
994	callback.	1092	callback.
995		1093
996	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1094	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
997		1095
998	Sometimes you want to share the same loop between multiple threads. This	1096	Sometimes you want to share the same loop between multiple threads. This
999	can be done relatively simply by putting mutex_lock/unlock calls around	1097	can be done relatively simply by putting mutex_lock/unlock calls around
1000	each call to a libev function.	1098	each call to a libev function.
1001		1099
1002	However, C<ev_run> can run an indefinite time, so it is not feasible	1100	However, C<ev_run> can run an indefinite time, so it is not feasible
1003	to wait for it to return. One way around this is to wake up the event	1101	to wait for it to return. One way around this is to wake up the event
1004	loop via C<ev_break> and C<av_async_send>, another way is to set these	1102	loop via C<ev_break> and C<ev_async_send>, another way is to set these
1005	I<release> and I<acquire> callbacks on the loop.	1103	I<release> and I<acquire> callbacks on the loop.
1006		1104
1007	When set, then C<release> will be called just before the thread is	1105	When set, then C<release> will be called just before the thread is
1008	suspended waiting for new events, and C<acquire> is called just	1106	suspended waiting for new events, and C<acquire> is called just
1009	afterwards.	1107	afterwards.
…		…
1149		1247
1150	=item C<EV_PREPARE>	1248	=item C<EV_PREPARE>
1151		1249
1152	=item C<EV_CHECK>	1250	=item C<EV_CHECK>
1153		1251
1154	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1252	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1155	to gather new events, and all C<ev_check> watchers are invoked just after	1253	gather new events, and all C<ev_check> watchers are queued (not invoked)
1156	C<ev_run> has gathered them, but before it invokes any callbacks for any	1254	just after C<ev_run> has gathered them, but before it queues any callbacks
		1255	for any received events. That means C<ev_prepare> watchers are the last
		1256	watchers invoked before the event loop sleeps or polls for new events, and
		1257	C<ev_check> watchers will be invoked before any other watchers of the same
		1258	or lower priority within an event loop iteration.
		1259
1157	received events. Callbacks of both watcher types can start and stop as	1260	Callbacks of both watcher types can start and stop as many watchers as
1158	many watchers as they want, and all of them will be taken into account	1261	they want, and all of them will be taken into account (for example, a
1159	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1262	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1160	C<ev_run> from blocking).	1263	blocking).
1161		1264
1162	=item C<EV_EMBED>	1265	=item C<EV_EMBED>
1163		1266
1164	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1267	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1165		1268
…		…
1288		1391
1289	=item callback ev_cb (ev_TYPE *watcher)	1392	=item callback ev_cb (ev_TYPE *watcher)
1290		1393
1291	Returns the callback currently set on the watcher.	1394	Returns the callback currently set on the watcher.
1292		1395
1293	=item ev_cb_set (ev_TYPE *watcher, callback)	1396	=item ev_set_cb (ev_TYPE *watcher, callback)
1294		1397
1295	Change the callback. You can change the callback at virtually any time	1398	Change the callback. You can change the callback at virtually any time
1296	(modulo threads).	1399	(modulo threads).
1297		1400
1298	=item ev_set_priority (ev_TYPE *watcher, int priority)	1401	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1316	or might not have been clamped to the valid range.	1419	or might not have been clamped to the valid range.
1317		1420
1318	The default priority used by watchers when no priority has been set is	1421	The default priority used by watchers when no priority has been set is
1319	always C<0>, which is supposed to not be too high and not be too low :).	1422	always C<0>, which is supposed to not be too high and not be too low :).
1320		1423
1321	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1424	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1322	priorities.	1425	priorities.
1323		1426
1324	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1427	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1325		1428
1326	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1429	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
…		…
1351	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1454	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1352	functions that do not need a watcher.	1455	functions that do not need a watcher.
1353		1456
1354	=back	1457	=back
1355		1458
1356	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1459	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1357		1460	OWN COMPOSITE WATCHERS> idioms.
1358	Each watcher has, by default, a member C<void *data> that you can change
1359	and read at any time: libev will completely ignore it. This can be used
1360	to associate arbitrary data with your watcher. If you need more data and
1361	don't want to allocate memory and store a pointer to it in that data
1362	member, you can also "subclass" the watcher type and provide your own
1363	data:
1364
1365	struct my_io
1366	{
1367	ev_io io;
1368	int otherfd;
1369	void *somedata;
1370	struct whatever *mostinteresting;
1371	};
1372
1373	...
1374	struct my_io w;
1375	ev_io_init (&w.io, my_cb, fd, EV_READ);
1376
1377	And since your callback will be called with a pointer to the watcher, you
1378	can cast it back to your own type:
1379
1380	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1381	{
1382	struct my_io *w = (struct my_io *)w_;
1383	...
1384	}
1385
1386	More interesting and less C-conformant ways of casting your callback type
1387	instead have been omitted.
1388
1389	Another common scenario is to use some data structure with multiple
1390	embedded watchers:
1391
1392	struct my_biggy
1393	{
1394	int some_data;
1395	ev_timer t1;
1396	ev_timer t2;
1397	}
1398
1399	In this case getting the pointer to C<my_biggy> is a bit more
1400	complicated: Either you store the address of your C<my_biggy> struct
1401	in the C<data> member of the watcher (for woozies), or you need to use
1402	some pointer arithmetic using C<offsetof> inside your watchers (for real
1403	programmers):
1404
1405	#include <stddef.h>
1406
1407	static void
1408	t1_cb (EV_P_ ev_timer *w, int revents)
1409	{
1410	struct my_biggy big = (struct my_biggy *)
1411	(((char *)w) - offsetof (struct my_biggy, t1));
1412	}
1413
1414	static void
1415	t2_cb (EV_P_ ev_timer *w, int revents)
1416	{
1417	struct my_biggy big = (struct my_biggy *)
1418	(((char *)w) - offsetof (struct my_biggy, t2));
1419	}
1420		1461
1421	=head2 WATCHER STATES	1462	=head2 WATCHER STATES
1422		1463
1423	There are various watcher states mentioned throughout this manual -	1464	There are various watcher states mentioned throughout this manual -
1424	active, pending and so on. In this section these states and the rules to	1465	active, pending and so on. In this section these states and the rules to
1425	transition between them will be described in more detail - and while these	1466	transition between them will be described in more detail - and while these
1426	rules might look complicated, they usually do "the right thing".	1467	rules might look complicated, they usually do "the right thing".
1427		1468
1428	=over 4	1469	=over 4
1429		1470
1430	=item initialiased	1471	=item initialised
1431		1472
1432	Before a watcher can be registered with the event looop it has to be	1473	Before a watcher can be registered with the event loop it has to be
1433	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1474	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1434	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1475	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1435		1476
1436	In this state it is simply some block of memory that is suitable for use	1477	In this state it is simply some block of memory that is suitable for
1437	in an event loop. It can be moved around, freed, reused etc. at will.	1478	use in an event loop. It can be moved around, freed, reused etc. at
		1479	will - as long as you either keep the memory contents intact, or call
		1480	C<ev_TYPE_init> again.
1438		1481
1439	=item started/running/active	1482	=item started/running/active
1440		1483
1441	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1484	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1442	property of the event loop, and is actively waiting for events. While in	1485	property of the event loop, and is actively waiting for events. While in
…		…
1470	latter will clear any pending state the watcher might be in, regardless	1513	latter will clear any pending state the watcher might be in, regardless
1471	of whether it was active or not, so stopping a watcher explicitly before	1514	of whether it was active or not, so stopping a watcher explicitly before
1472	freeing it is often a good idea.	1515	freeing it is often a good idea.
1473		1516
1474	While stopped (and not pending) the watcher is essentially in the	1517	While stopped (and not pending) the watcher is essentially in the
1475	initialised state, that is it can be reused, moved, modified in any way	1518	initialised state, that is, it can be reused, moved, modified in any way
1476	you wish.	1519	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1520	it again).
1477		1521
1478	=back	1522	=back
1479		1523
1480	=head2 WATCHER PRIORITY MODELS	1524	=head2 WATCHER PRIORITY MODELS
1481		1525
…		…
1610	In general you can register as many read and/or write event watchers per	1654	In general you can register as many read and/or write event watchers per
1611	fd as you want (as long as you don't confuse yourself). Setting all file	1655	fd as you want (as long as you don't confuse yourself). Setting all file
1612	descriptors to non-blocking mode is also usually a good idea (but not	1656	descriptors to non-blocking mode is also usually a good idea (but not
1613	required if you know what you are doing).	1657	required if you know what you are doing).
1614		1658
1615	If you cannot use non-blocking mode, then force the use of a
1616	known-to-be-good backend (at the time of this writing, this includes only
1617	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1618	descriptors for which non-blocking operation makes no sense (such as
1619	files) - libev doesn't guarantee any specific behaviour in that case.
1620
1621	Another thing you have to watch out for is that it is quite easy to	1659	Another thing you have to watch out for is that it is quite easy to
1622	receive "spurious" readiness notifications, that is your callback might	1660	receive "spurious" readiness notifications, that is, your callback might
1623	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1661	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1624	because there is no data. Not only are some backends known to create a	1662	because there is no data. It is very easy to get into this situation even
1625	lot of those (for example Solaris ports), it is very easy to get into	1663	with a relatively standard program structure. Thus it is best to always
1626	this situation even with a relatively standard program structure. Thus	1664	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1627	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1628	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1665	preferable to a program hanging until some data arrives.
1629		1666
1630	If you cannot run the fd in non-blocking mode (for example you should	1667	If you cannot run the fd in non-blocking mode (for example you should
1631	not play around with an Xlib connection), then you have to separately	1668	not play around with an Xlib connection), then you have to separately
1632	re-test whether a file descriptor is really ready with a known-to-be good	1669	re-test whether a file descriptor is really ready with a known-to-be good
1633	interface such as poll (fortunately in our Xlib example, Xlib already	1670	interface such as poll (fortunately in the case of Xlib, it already does
1634	does this on its own, so its quite safe to use). Some people additionally	1671	this on its own, so its quite safe to use). Some people additionally
1635	use C<SIGALRM> and an interval timer, just to be sure you won't block	1672	use C<SIGALRM> and an interval timer, just to be sure you won't block
1636	indefinitely.	1673	indefinitely.
1637		1674
1638	But really, best use non-blocking mode.	1675	But really, best use non-blocking mode.
1639		1676
1640	=head3 The special problem of disappearing file descriptors	1677	=head3 The special problem of disappearing file descriptors
1641		1678
1642	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1679	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1643	descriptor (either due to calling C<close> explicitly or any other means,	1680	a file descriptor (either due to calling C<close> explicitly or any other
1644	such as C<dup2>). The reason is that you register interest in some file	1681	means, such as C<dup2>). The reason is that you register interest in some
1645	descriptor, but when it goes away, the operating system will silently drop	1682	file descriptor, but when it goes away, the operating system will silently
1646	this interest. If another file descriptor with the same number then is	1683	drop this interest. If another file descriptor with the same number then
1647	registered with libev, there is no efficient way to see that this is, in	1684	is registered with libev, there is no efficient way to see that this is,
1648	fact, a different file descriptor.	1685	in fact, a different file descriptor.
1649		1686
1650	To avoid having to explicitly tell libev about such cases, libev follows	1687	To avoid having to explicitly tell libev about such cases, libev follows
1651	the following policy: Each time C<ev_io_set> is being called, libev	1688	the following policy: Each time C<ev_io_set> is being called, libev
1652	will assume that this is potentially a new file descriptor, otherwise	1689	will assume that this is potentially a new file descriptor, otherwise
1653	it is assumed that the file descriptor stays the same. That means that	1690	it is assumed that the file descriptor stays the same. That means that
…		…
1667		1704
1668	There is no workaround possible except not registering events	1705	There is no workaround possible except not registering events
1669	for potentially C<dup ()>'ed file descriptors, or to resort to	1706	for potentially C<dup ()>'ed file descriptors, or to resort to
1670	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1707	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1671		1708
		1709	=head3 The special problem of files
		1710
		1711	Many people try to use C<select> (or libev) on file descriptors
		1712	representing files, and expect it to become ready when their program
		1713	doesn't block on disk accesses (which can take a long time on their own).
		1714
		1715	However, this cannot ever work in the "expected" way - you get a readiness
		1716	notification as soon as the kernel knows whether and how much data is
		1717	there, and in the case of open files, that's always the case, so you
		1718	always get a readiness notification instantly, and your read (or possibly
		1719	write) will still block on the disk I/O.
		1720
		1721	Another way to view it is that in the case of sockets, pipes, character
		1722	devices and so on, there is another party (the sender) that delivers data
		1723	on its own, but in the case of files, there is no such thing: the disk
		1724	will not send data on its own, simply because it doesn't know what you
		1725	wish to read - you would first have to request some data.
		1726
		1727	Since files are typically not-so-well supported by advanced notification
		1728	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1729	to files, even though you should not use it. The reason for this is
		1730	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1731	usually a tty, often a pipe, but also sometimes files or special devices
		1732	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1733	F</dev/urandom>), and even though the file might better be served with
		1734	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1735	it "just works" instead of freezing.
		1736
		1737	So avoid file descriptors pointing to files when you know it (e.g. use
		1738	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1739	when you rarely read from a file instead of from a socket, and want to
		1740	reuse the same code path.
		1741
1672	=head3 The special problem of fork	1742	=head3 The special problem of fork
1673		1743
1674	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1744	Some backends (epoll, kqueue, probably linuxaio) do not support C<fork ()>
1675	useless behaviour. Libev fully supports fork, but needs to be told about	1745	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1676	it in the child.	1746	to be told about it in the child if you want to continue to use it in the
		1747	child.
1677		1748
1678	To support fork in your programs, you either have to call	1749	To support fork in your child processes, you have to call C<ev_loop_fork
1679	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1750	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1680	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1751	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1681	C<EVBACKEND_POLL>.
1682		1752
1683	=head3 The special problem of SIGPIPE	1753	=head3 The special problem of SIGPIPE
1684		1754
1685	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1755	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1686	when writing to a pipe whose other end has been closed, your program gets	1756	when writing to a pipe whose other end has been closed, your program gets
…		…
1784	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1854	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1785	monotonic clock option helps a lot here).	1855	monotonic clock option helps a lot here).
1786		1856
1787	The callback is guaranteed to be invoked only I<after> its timeout has	1857	The callback is guaranteed to be invoked only I<after> its timeout has
1788	passed (not I<at>, so on systems with very low-resolution clocks this	1858	passed (not I<at>, so on systems with very low-resolution clocks this
1789	might introduce a small delay). If multiple timers become ready during the	1859	might introduce a small delay, see "the special problem of being too
		1860	early", below). If multiple timers become ready during the same loop
1790	same loop iteration then the ones with earlier time-out values are invoked	1861	iteration then the ones with earlier time-out values are invoked before
1791	before ones of the same priority with later time-out values (but this is	1862	ones of the same priority with later time-out values (but this is no
1792	no longer true when a callback calls C<ev_run> recursively).	1863	longer true when a callback calls C<ev_run> recursively).
1793		1864
1794	=head3 Be smart about timeouts	1865	=head3 Be smart about timeouts
1795		1866
1796	Many real-world problems involve some kind of timeout, usually for error	1867	Many real-world problems involve some kind of timeout, usually for error
1797	recovery. A typical example is an HTTP request - if the other side hangs,	1868	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1872		1943
1873	In this case, it would be more efficient to leave the C<ev_timer> alone,	1944	In this case, it would be more efficient to leave the C<ev_timer> alone,
1874	but remember the time of last activity, and check for a real timeout only	1945	but remember the time of last activity, and check for a real timeout only
1875	within the callback:	1946	within the callback:
1876		1947
		1948	ev_tstamp timeout = 60.;
1877	ev_tstamp last_activity; // time of last activity	1949	ev_tstamp last_activity; // time of last activity
		1950	ev_timer timer;
1878		1951
1879	static void	1952	static void
1880	callback (EV_P_ ev_timer *w, int revents)	1953	callback (EV_P_ ev_timer *w, int revents)
1881	{	1954	{
1882	ev_tstamp now = ev_now (EV_A);	1955	// calculate when the timeout would happen
1883	ev_tstamp timeout = last_activity + 60.;	1956	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1884		1957
1885	// if last_activity + 60. is older than now, we did time out	1958	// if negative, it means we the timeout already occurred
1886	if (timeout < now)	1959	if (after < 0.)
1887	{	1960	{
1888	// timeout occurred, take action	1961	// timeout occurred, take action
1889	}	1962	}
1890	else	1963	else
1891	{	1964	{
1892	// callback was invoked, but there was some activity, re-arm	1965	// callback was invoked, but there was some recent
1893	// the watcher to fire in last_activity + 60, which is	1966	// activity. simply restart the timer to time out
1894	// guaranteed to be in the future, so "again" is positive:	1967	// after "after" seconds, which is the earliest time
1895	w->repeat = timeout - now;	1968	// the timeout can occur.
		1969	ev_timer_set (w, after, 0.);
1896	ev_timer_again (EV_A_ w);	1970	ev_timer_start (EV_A_ w);
1897	}	1971	}
1898	}	1972	}
1899		1973
1900	To summarise the callback: first calculate the real timeout (defined	1974	To summarise the callback: first calculate in how many seconds the
1901	as "60 seconds after the last activity"), then check if that time has	1975	timeout will occur (by calculating the absolute time when it would occur,
1902	been reached, which means something I<did>, in fact, time out. Otherwise	1976	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1903	the callback was invoked too early (C<timeout> is in the future), so	1977	(EV_A)> from that).
1904	re-schedule the timer to fire at that future time, to see if maybe we have
1905	a timeout then.
1906		1978
1907	Note how C<ev_timer_again> is used, taking advantage of the	1979	If this value is negative, then we are already past the timeout, i.e. we
1908	C<ev_timer_again> optimisation when the timer is already running.	1980	timed out, and need to do whatever is needed in this case.
		1981
		1982	Otherwise, we now the earliest time at which the timeout would trigger,
		1983	and simply start the timer with this timeout value.
		1984
		1985	In other words, each time the callback is invoked it will check whether
		1986	the timeout occurred. If not, it will simply reschedule itself to check
		1987	again at the earliest time it could time out. Rinse. Repeat.
1909		1988
1910	This scheme causes more callback invocations (about one every 60 seconds	1989	This scheme causes more callback invocations (about one every 60 seconds
1911	minus half the average time between activity), but virtually no calls to	1990	minus half the average time between activity), but virtually no calls to
1912	libev to change the timeout.	1991	libev to change the timeout.
1913		1992
1914	To start the timer, simply initialise the watcher and set C<last_activity>	1993	To start the machinery, simply initialise the watcher and set
1915	to the current time (meaning we just have some activity :), then call the	1994	C<last_activity> to the current time (meaning there was some activity just
1916	callback, which will "do the right thing" and start the timer:	1995	now), then call the callback, which will "do the right thing" and start
		1996	the timer:
1917		1997
		1998	last_activity = ev_now (EV_A);
1918	ev_init (timer, callback);	1999	ev_init (&timer, callback);
1919	last_activity = ev_now (loop);	2000	callback (EV_A_ &timer, 0);
1920	callback (loop, timer, EV_TIMER);
1921		2001
1922	And when there is some activity, simply store the current time in	2002	When there is some activity, simply store the current time in
1923	C<last_activity>, no libev calls at all:	2003	C<last_activity>, no libev calls at all:
1924		2004
		2005	if (activity detected)
1925	last_activity = ev_now (loop);	2006	last_activity = ev_now (EV_A);
		2007
		2008	When your timeout value changes, then the timeout can be changed by simply
		2009	providing a new value, stopping the timer and calling the callback, which
		2010	will again do the right thing (for example, time out immediately :).
		2011
		2012	timeout = new_value;
		2013	ev_timer_stop (EV_A_ &timer);
		2014	callback (EV_A_ &timer, 0);
1926		2015
1927	This technique is slightly more complex, but in most cases where the	2016	This technique is slightly more complex, but in most cases where the
1928	time-out is unlikely to be triggered, much more efficient.	2017	time-out is unlikely to be triggered, much more efficient.
1929
1930	Changing the timeout is trivial as well (if it isn't hard-coded in the
1931	callback :) - just change the timeout and invoke the callback, which will
1932	fix things for you.
1933		2018
1934	=item 4. Wee, just use a double-linked list for your timeouts.	2019	=item 4. Wee, just use a double-linked list for your timeouts.
1935		2020
1936	If there is not one request, but many thousands (millions...), all	2021	If there is not one request, but many thousands (millions...), all
1937	employing some kind of timeout with the same timeout value, then one can	2022	employing some kind of timeout with the same timeout value, then one can
…		…
1964	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2049	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1965	rather complicated, but extremely efficient, something that really pays	2050	rather complicated, but extremely efficient, something that really pays
1966	off after the first million or so of active timers, i.e. it's usually	2051	off after the first million or so of active timers, i.e. it's usually
1967	overkill :)	2052	overkill :)
1968		2053
		2054	=head3 The special problem of being too early
		2055
		2056	If you ask a timer to call your callback after three seconds, then
		2057	you expect it to be invoked after three seconds - but of course, this
		2058	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2059	guaranteed to any precision by libev - imagine somebody suspending the
		2060	process with a STOP signal for a few hours for example.
		2061
		2062	So, libev tries to invoke your callback as soon as possible I<after> the
		2063	delay has occurred, but cannot guarantee this.
		2064
		2065	A less obvious failure mode is calling your callback too early: many event
		2066	loops compare timestamps with a "elapsed delay >= requested delay", but
		2067	this can cause your callback to be invoked much earlier than you would
		2068	expect.
		2069
		2070	To see why, imagine a system with a clock that only offers full second
		2071	resolution (think windows if you can't come up with a broken enough OS
		2072	yourself). If you schedule a one-second timer at the time 500.9, then the
		2073	event loop will schedule your timeout to elapse at a system time of 500
		2074	(500.9 truncated to the resolution) + 1, or 501.
		2075
		2076	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2077	501" and invoke the callback 0.1s after it was started, even though a
		2078	one-second delay was requested - this is being "too early", despite best
		2079	intentions.
		2080
		2081	This is the reason why libev will never invoke the callback if the elapsed
		2082	delay equals the requested delay, but only when the elapsed delay is
		2083	larger than the requested delay. In the example above, libev would only invoke
		2084	the callback at system time 502, or 1.1s after the timer was started.
		2085
		2086	So, while libev cannot guarantee that your callback will be invoked
		2087	exactly when requested, it I<can> and I<does> guarantee that the requested
		2088	delay has actually elapsed, or in other words, it always errs on the "too
		2089	late" side of things.
		2090
1969	=head3 The special problem of time updates	2091	=head3 The special problem of time updates
1970		2092
1971	Establishing the current time is a costly operation (it usually takes at	2093	Establishing the current time is a costly operation (it usually takes
1972	least two system calls): EV therefore updates its idea of the current	2094	at least one system call): EV therefore updates its idea of the current
1973	time only before and after C<ev_run> collects new events, which causes a	2095	time only before and after C<ev_run> collects new events, which causes a
1974	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2096	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1975	lots of events in one iteration.	2097	lots of events in one iteration.
1976		2098
1977	The relative timeouts are calculated relative to the C<ev_now ()>	2099	The relative timeouts are calculated relative to the C<ev_now ()>
1978	time. This is usually the right thing as this timestamp refers to the time	2100	time. This is usually the right thing as this timestamp refers to the time
1979	of the event triggering whatever timeout you are modifying/starting. If	2101	of the event triggering whatever timeout you are modifying/starting. If
1980	you suspect event processing to be delayed and you I<need> to base the	2102	you suspect event processing to be delayed and you I<need> to base the
1981	timeout on the current time, use something like this to adjust for this:	2103	timeout on the current time, use something like the following to adjust
		2104	for it:
1982		2105
1983	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2106	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1984		2107
1985	If the event loop is suspended for a long time, you can also force an	2108	If the event loop is suspended for a long time, you can also force an
1986	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2109	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1987	()>.	2110	()>, although that will push the event time of all outstanding events
		2111	further into the future.
		2112
		2113	=head3 The special problem of unsynchronised clocks
		2114
		2115	Modern systems have a variety of clocks - libev itself uses the normal
		2116	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2117	jumps).
		2118
		2119	Neither of these clocks is synchronised with each other or any other clock
		2120	on the system, so C<ev_time ()> might return a considerably different time
		2121	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2122	a call to C<gettimeofday> might return a second count that is one higher
		2123	than a directly following call to C<time>.
		2124
		2125	The moral of this is to only compare libev-related timestamps with
		2126	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2127	a second or so.
		2128
		2129	One more problem arises due to this lack of synchronisation: if libev uses
		2130	the system monotonic clock and you compare timestamps from C<ev_time>
		2131	or C<ev_now> from when you started your timer and when your callback is
		2132	invoked, you will find that sometimes the callback is a bit "early".
		2133
		2134	This is because C<ev_timer>s work in real time, not wall clock time, so
		2135	libev makes sure your callback is not invoked before the delay happened,
		2136	I<measured according to the real time>, not the system clock.
		2137
		2138	If your timeouts are based on a physical timescale (e.g. "time out this
		2139	connection after 100 seconds") then this shouldn't bother you as it is
		2140	exactly the right behaviour.
		2141
		2142	If you want to compare wall clock/system timestamps to your timers, then
		2143	you need to use C<ev_periodic>s, as these are based on the wall clock
		2144	time, where your comparisons will always generate correct results.
1988		2145
1989	=head3 The special problems of suspended animation	2146	=head3 The special problems of suspended animation
1990		2147
1991	When you leave the server world it is quite customary to hit machines that	2148	When you leave the server world it is quite customary to hit machines that
1992	can suspend/hibernate - what happens to the clocks during such a suspend?	2149	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
2022		2179
2023	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2180	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
2024		2181
2025	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2182	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
2026		2183
2027	Configure the timer to trigger after C<after> seconds. If C<repeat>	2184	Configure the timer to trigger after C<after> seconds (fractional and
2028	is C<0.>, then it will automatically be stopped once the timeout is	2185	negative values are supported). If C<repeat> is C<0.>, then it will
2029	reached. If it is positive, then the timer will automatically be	2186	automatically be stopped once the timeout is reached. If it is positive,
2030	configured to trigger again C<repeat> seconds later, again, and again,	2187	then the timer will automatically be configured to trigger again C<repeat>
2031	until stopped manually.	2188	seconds later, again, and again, until stopped manually.
2032		2189
2033	The timer itself will do a best-effort at avoiding drift, that is, if	2190	The timer itself will do a best-effort at avoiding drift, that is, if
2034	you configure a timer to trigger every 10 seconds, then it will normally	2191	you configure a timer to trigger every 10 seconds, then it will normally
2035	trigger at exactly 10 second intervals. If, however, your program cannot	2192	trigger at exactly 10 second intervals. If, however, your program cannot
2036	keep up with the timer (because it takes longer than those 10 seconds to	2193	keep up with the timer (because it takes longer than those 10 seconds to
2037	do stuff) the timer will not fire more than once per event loop iteration.	2194	do stuff) the timer will not fire more than once per event loop iteration.
2038		2195
2039	=item ev_timer_again (loop, ev_timer *)	2196	=item ev_timer_again (loop, ev_timer *)
2040		2197
2041	This will act as if the timer timed out and restart it again if it is	2198	This will act as if the timer timed out, and restarts it again if it is
2042	repeating. The exact semantics are:	2199	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2200	timeout to the C<repeat> value and calling C<ev_timer_start>.
2043		2201
		2202	The exact semantics are as in the following rules, all of which will be
		2203	applied to the watcher:
		2204
		2205	=over 4
		2206
2044	If the timer is pending, its pending status is cleared.	2207	=item If the timer is pending, the pending status is always cleared.
2045		2208
2046	If the timer is started but non-repeating, stop it (as if it timed out).	2209	=item If the timer is started but non-repeating, stop it (as if it timed
		2210	out, without invoking it).
2047		2211
2048	If the timer is repeating, either start it if necessary (with the	2212	=item If the timer is repeating, make the C<repeat> value the new timeout
2049	C<repeat> value), or reset the running timer to the C<repeat> value.	2213	and start the timer, if necessary.
2050		2214
		2215	=back
		2216
2051	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2217	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2052	usage example.	2218	usage example.
2053		2219
2054	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2220	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2055		2221
2056	Returns the remaining time until a timer fires. If the timer is active,	2222	Returns the remaining time until a timer fires. If the timer is active,
…		…
2109	Periodic watchers are also timers of a kind, but they are very versatile	2275	Periodic watchers are also timers of a kind, but they are very versatile
2110	(and unfortunately a bit complex).	2276	(and unfortunately a bit complex).
2111		2277
2112	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2278	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2113	relative time, the physical time that passes) but on wall clock time	2279	relative time, the physical time that passes) but on wall clock time
2114	(absolute time, the thing you can read on your calender or clock). The	2280	(absolute time, the thing you can read on your calendar or clock). The
2115	difference is that wall clock time can run faster or slower than real	2281	difference is that wall clock time can run faster or slower than real
2116	time, and time jumps are not uncommon (e.g. when you adjust your	2282	time, and time jumps are not uncommon (e.g. when you adjust your
2117	wrist-watch).	2283	wrist-watch).
2118		2284
2119	You can tell a periodic watcher to trigger after some specific point	2285	You can tell a periodic watcher to trigger after some specific point
…		…
2124	C<ev_timer>, which would still trigger roughly 10 seconds after starting	2290	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2125	it, as it uses a relative timeout).	2291	it, as it uses a relative timeout).
2126		2292
2127	C<ev_periodic> watchers can also be used to implement vastly more complex	2293	C<ev_periodic> watchers can also be used to implement vastly more complex
2128	timers, such as triggering an event on each "midnight, local time", or	2294	timers, such as triggering an event on each "midnight, local time", or
2129	other complicated rules. This cannot be done with C<ev_timer> watchers, as	2295	other complicated rules. This cannot easily be done with C<ev_timer>
2130	those cannot react to time jumps.	2296	watchers, as those cannot react to time jumps.
2131		2297
2132	As with timers, the callback is guaranteed to be invoked only when the	2298	As with timers, the callback is guaranteed to be invoked only when the
2133	point in time where it is supposed to trigger has passed. If multiple	2299	point in time where it is supposed to trigger has passed. If multiple
2134	timers become ready during the same loop iteration then the ones with	2300	timers become ready during the same loop iteration then the ones with
2135	earlier time-out values are invoked before ones with later time-out values	2301	earlier time-out values are invoked before ones with later time-out values
…		…
2176		2342
2177	Another way to think about it (for the mathematically inclined) is that	2343	Another way to think about it (for the mathematically inclined) is that
2178	C<ev_periodic> will try to run the callback in this mode at the next possible	2344	C<ev_periodic> will try to run the callback in this mode at the next possible
2179	time where C<time = offset (mod interval)>, regardless of any time jumps.	2345	time where C<time = offset (mod interval)>, regardless of any time jumps.
2180		2346
2181	For numerical stability it is preferable that the C<offset> value is near	2347	The C<interval> I<MUST> be positive, and for numerical stability, the
2182	C<ev_now ()> (the current time), but there is no range requirement for	2348	interval value should be higher than C<1/8192> (which is around 100
2183	this value, and in fact is often specified as zero.	2349	microseconds) and C<offset> should be higher than C<0> and should have
		2350	at most a similar magnitude as the current time (say, within a factor of
		2351	ten). Typical values for offset are, in fact, C<0> or something between
		2352	C<0> and C<interval>, which is also the recommended range.
2184		2353
2185	Note also that there is an upper limit to how often a timer can fire (CPU	2354	Note also that there is an upper limit to how often a timer can fire (CPU
2186	speed for example), so if C<interval> is very small then timing stability	2355	speed for example), so if C<interval> is very small then timing stability
2187	will of course deteriorate. Libev itself tries to be exact to be about one	2356	will of course deteriorate. Libev itself tries to be exact to be about one
2188	millisecond (if the OS supports it and the machine is fast enough).	2357	millisecond (if the OS supports it and the machine is fast enough).
…		…
2218		2387
2219	NOTE: I<< This callback must always return a time that is higher than or	2388	NOTE: I<< This callback must always return a time that is higher than or
2220	equal to the passed C<now> value >>.	2389	equal to the passed C<now> value >>.
2221		2390
2222	This can be used to create very complex timers, such as a timer that	2391	This can be used to create very complex timers, such as a timer that
2223	triggers on "next midnight, local time". To do this, you would calculate the	2392	triggers on "next midnight, local time". To do this, you would calculate
2224	next midnight after C<now> and return the timestamp value for this. How	2393	the next midnight after C<now> and return the timestamp value for
2225	you do this is, again, up to you (but it is not trivial, which is the main	2394	this. Here is a (completely untested, no error checking) example on how to
2226	reason I omitted it as an example).	2395	do this:
		2396
		2397	#include <time.h>
		2398
		2399	static ev_tstamp
		2400	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2401	{
		2402	time_t tnow = (time_t)now;
		2403	struct tm tm;
		2404	localtime_r (&tnow, &tm);
		2405
		2406	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2407	++tm.tm_mday; // midnight next day
		2408
		2409	return mktime (&tm);
		2410	}
		2411
		2412	Note: this code might run into trouble on days that have more then two
		2413	midnights (beginning and end).
2227		2414
2228	=back	2415	=back
2229		2416
2230	=item ev_periodic_again (loop, ev_periodic *)	2417	=item ev_periodic_again (loop, ev_periodic *)
2231		2418
…		…
2296		2483
2297	ev_periodic hourly_tick;	2484	ev_periodic hourly_tick;
2298	ev_periodic_init (&hourly_tick, clock_cb,	2485	ev_periodic_init (&hourly_tick, clock_cb,
2299	fmod (ev_now (loop), 3600.), 3600., 0);	2486	fmod (ev_now (loop), 3600.), 3600., 0);
2300	ev_periodic_start (loop, &hourly_tick);	2487	ev_periodic_start (loop, &hourly_tick);
2301		2488
2302		2489
2303	=head2 C<ev_signal> - signal me when a signal gets signalled!	2490	=head2 C<ev_signal> - signal me when a signal gets signalled!
2304		2491
2305	Signal watchers will trigger an event when the process receives a specific	2492	Signal watchers will trigger an event when the process receives a specific
2306	signal one or more times. Even though signals are very asynchronous, libev	2493	signal one or more times. Even though signals are very asynchronous, libev
…		…
2316	only within the same loop, i.e. you can watch for C<SIGINT> in your	2503	only within the same loop, i.e. you can watch for C<SIGINT> in your
2317	default loop and for C<SIGIO> in another loop, but you cannot watch for	2504	default loop and for C<SIGIO> in another loop, but you cannot watch for
2318	C<SIGINT> in both the default loop and another loop at the same time. At	2505	C<SIGINT> in both the default loop and another loop at the same time. At
2319	the moment, C<SIGCHLD> is permanently tied to the default loop.	2506	the moment, C<SIGCHLD> is permanently tied to the default loop.
2320		2507
2321	When the first watcher gets started will libev actually register something	2508	Only after the first watcher for a signal is started will libev actually
2322	with the kernel (thus it coexists with your own signal handlers as long as	2509	register something with the kernel. It thus coexists with your own signal
2323	you don't register any with libev for the same signal).	2510	handlers as long as you don't register any with libev for the same signal.
2324		2511
2325	If possible and supported, libev will install its handlers with	2512	If possible and supported, libev will install its handlers with
2326	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2513	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2327	not be unduly interrupted. If you have a problem with system calls getting	2514	not be unduly interrupted. If you have a problem with system calls getting
2328	interrupted by signals you can block all signals in an C<ev_check> watcher	2515	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2331	=head3 The special problem of inheritance over fork/execve/pthread_create	2518	=head3 The special problem of inheritance over fork/execve/pthread_create
2332		2519
2333	Both the signal mask (C<sigprocmask>) and the signal disposition	2520	Both the signal mask (C<sigprocmask>) and the signal disposition
2334	(C<sigaction>) are unspecified after starting a signal watcher (and after	2521	(C<sigaction>) are unspecified after starting a signal watcher (and after
2335	stopping it again), that is, libev might or might not block the signal,	2522	stopping it again), that is, libev might or might not block the signal,
2336	and might or might not set or restore the installed signal handler.	2523	and might or might not set or restore the installed signal handler (but
		2524	see C<EVFLAG_NOSIGMASK>).
2337		2525
2338	While this does not matter for the signal disposition (libev never	2526	While this does not matter for the signal disposition (libev never
2339	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2527	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2340	C<execve>), this matters for the signal mask: many programs do not expect	2528	C<execve>), this matters for the signal mask: many programs do not expect
2341	certain signals to be blocked.	2529	certain signals to be blocked.
…		…
2512		2700
2513	=head2 C<ev_stat> - did the file attributes just change?	2701	=head2 C<ev_stat> - did the file attributes just change?
2514		2702
2515	This watches a file system path for attribute changes. That is, it calls	2703	This watches a file system path for attribute changes. That is, it calls
2516	C<stat> on that path in regular intervals (or when the OS says it changed)	2704	C<stat> on that path in regular intervals (or when the OS says it changed)
2517	and sees if it changed compared to the last time, invoking the callback if	2705	and sees if it changed compared to the last time, invoking the callback
2518	it did.	2706	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2707	happen after the watcher has been started will be reported.
2519		2708
2520	The path does not need to exist: changing from "path exists" to "path does	2709	The path does not need to exist: changing from "path exists" to "path does
2521	not exist" is a status change like any other. The condition "path does not	2710	not exist" is a status change like any other. The condition "path does not
2522	exist" (or more correctly "path cannot be stat'ed") is signified by the	2711	exist" (or more correctly "path cannot be stat'ed") is signified by the
2523	C<st_nlink> field being zero (which is otherwise always forced to be at	2712	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2753	Apart from keeping your process non-blocking (which is a useful	2942	Apart from keeping your process non-blocking (which is a useful
2754	effect on its own sometimes), idle watchers are a good place to do	2943	effect on its own sometimes), idle watchers are a good place to do
2755	"pseudo-background processing", or delay processing stuff to after the	2944	"pseudo-background processing", or delay processing stuff to after the
2756	event loop has handled all outstanding events.	2945	event loop has handled all outstanding events.
2757		2946
		2947	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2948
		2949	As long as there is at least one active idle watcher, libev will never
		2950	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2951	For this to work, the idle watcher doesn't need to be invoked at all - the
		2952	lowest priority will do.
		2953
		2954	This mode of operation can be useful together with an C<ev_check> watcher,
		2955	to do something on each event loop iteration - for example to balance load
		2956	between different connections.
		2957
		2958	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2959	example.
		2960
2758	=head3 Watcher-Specific Functions and Data Members	2961	=head3 Watcher-Specific Functions and Data Members
2759		2962
2760	=over 4	2963	=over 4
2761		2964
2762	=item ev_idle_init (ev_idle *, callback)	2965	=item ev_idle_init (ev_idle *, callback)
…		…
2773	callback, free it. Also, use no error checking, as usual.	2976	callback, free it. Also, use no error checking, as usual.
2774		2977
2775	static void	2978	static void
2776	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2979	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2777	{	2980	{
		2981	// stop the watcher
		2982	ev_idle_stop (loop, w);
		2983
		2984	// now we can free it
2778	free (w);	2985	free (w);
		2986
2779	// now do something you wanted to do when the program has	2987	// now do something you wanted to do when the program has
2780	// no longer anything immediate to do.	2988	// no longer anything immediate to do.
2781	}	2989	}
2782		2990
2783	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2991	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2785	ev_idle_start (loop, idle_watcher);	2993	ev_idle_start (loop, idle_watcher);
2786		2994
2787		2995
2788	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2996	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2789		2997
2790	Prepare and check watchers are usually (but not always) used in pairs:	2998	Prepare and check watchers are often (but not always) used in pairs:
2791	prepare watchers get invoked before the process blocks and check watchers	2999	prepare watchers get invoked before the process blocks and check watchers
2792	afterwards.	3000	afterwards.
2793		3001
2794	You I<must not> call C<ev_run> or similar functions that enter	3002	You I<must not> call C<ev_run> (or similar functions that enter the
2795	the current event loop from either C<ev_prepare> or C<ev_check>	3003	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2796	watchers. Other loops than the current one are fine, however. The	3004	C<ev_check> watchers. Other loops than the current one are fine,
2797	rationale behind this is that you do not need to check for recursion in	3005	however. The rationale behind this is that you do not need to check
2798	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3006	for recursion in those watchers, i.e. the sequence will always be
2799	C<ev_check> so if you have one watcher of each kind they will always be	3007	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2800	called in pairs bracketing the blocking call.	3008	kind they will always be called in pairs bracketing the blocking call.
2801		3009
2802	Their main purpose is to integrate other event mechanisms into libev and	3010	Their main purpose is to integrate other event mechanisms into libev and
2803	their use is somewhat advanced. They could be used, for example, to track	3011	their use is somewhat advanced. They could be used, for example, to track
2804	variable changes, implement your own watchers, integrate net-snmp or a	3012	variable changes, implement your own watchers, integrate net-snmp or a
2805	coroutine library and lots more. They are also occasionally useful if	3013	coroutine library and lots more. They are also occasionally useful if
…		…
2823	with priority higher than or equal to the event loop and one coroutine	3031	with priority higher than or equal to the event loop and one coroutine
2824	of lower priority, but only once, using idle watchers to keep the event	3032	of lower priority, but only once, using idle watchers to keep the event
2825	loop from blocking if lower-priority coroutines are active, thus mapping	3033	loop from blocking if lower-priority coroutines are active, thus mapping
2826	low-priority coroutines to idle/background tasks).	3034	low-priority coroutines to idle/background tasks).
2827		3035
2828	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3036	When used for this purpose, it is recommended to give C<ev_check> watchers
2829	priority, to ensure that they are being run before any other watchers	3037	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2830	after the poll (this doesn't matter for C<ev_prepare> watchers).	3038	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3039	watchers).
2831		3040
2832	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3041	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2833	activate ("feed") events into libev. While libev fully supports this, they	3042	activate ("feed") events into libev. While libev fully supports this, they
2834	might get executed before other C<ev_check> watchers did their job. As	3043	might get executed before other C<ev_check> watchers did their job. As
2835	C<ev_check> watchers are often used to embed other (non-libev) event	3044	C<ev_check> watchers are often used to embed other (non-libev) event
2836	loops those other event loops might be in an unusable state until their	3045	loops those other event loops might be in an unusable state until their
2837	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3046	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2838	others).	3047	others).
		3048
		3049	=head3 Abusing an C<ev_check> watcher for its side-effect
		3050
		3051	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3052	useful because they are called once per event loop iteration. For
		3053	example, if you want to handle a large number of connections fairly, you
		3054	normally only do a bit of work for each active connection, and if there
		3055	is more work to do, you wait for the next event loop iteration, so other
		3056	connections have a chance of making progress.
		3057
		3058	Using an C<ev_check> watcher is almost enough: it will be called on the
		3059	next event loop iteration. However, that isn't as soon as possible -
		3060	without external events, your C<ev_check> watcher will not be invoked.
		3061
		3062	This is where C<ev_idle> watchers come in handy - all you need is a
		3063	single global idle watcher that is active as long as you have one active
		3064	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3065	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3066	invoked. Neither watcher alone can do that.
2839		3067
2840	=head3 Watcher-Specific Functions and Data Members	3068	=head3 Watcher-Specific Functions and Data Members
2841		3069
2842	=over 4	3070	=over 4
2843		3071
…		…
3044		3272
3045	=over 4	3273	=over 4
3046		3274
3047	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3275	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
3048		3276
3049	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3277	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
3050		3278
3051	Configures the watcher to embed the given loop, which must be	3279	Configures the watcher to embed the given loop, which must be
3052	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3280	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
3053	invoked automatically, otherwise it is the responsibility of the callback	3281	invoked automatically, otherwise it is the responsibility of the callback
3054	to invoke it (it will continue to be called until the sweep has been done,	3282	to invoke it (it will continue to be called until the sweep has been done,
…		…
3075	used).	3303	used).
3076		3304
3077	struct ev_loop *loop_hi = ev_default_init (0);	3305	struct ev_loop *loop_hi = ev_default_init (0);
3078	struct ev_loop *loop_lo = 0;	3306	struct ev_loop *loop_lo = 0;
3079	ev_embed embed;	3307	ev_embed embed;
3080		3308
3081	// see if there is a chance of getting one that works	3309	// see if there is a chance of getting one that works
3082	// (remember that a flags value of 0 means autodetection)	3310	// (remember that a flags value of 0 means autodetection)
3083	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3311	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3084	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3312	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3085	: 0;	3313	: 0;
…		…
3099	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3327	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3100		3328
3101	struct ev_loop *loop = ev_default_init (0);	3329	struct ev_loop *loop = ev_default_init (0);
3102	struct ev_loop *loop_socket = 0;	3330	struct ev_loop *loop_socket = 0;
3103	ev_embed embed;	3331	ev_embed embed;
3104		3332
3105	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3333	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3106	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3334	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3107	{	3335	{
3108	ev_embed_init (&embed, 0, loop_socket);	3336	ev_embed_init (&embed, 0, loop_socket);
3109	ev_embed_start (loop, &embed);	3337	ev_embed_start (loop, &embed);
…		…
3117		3345
3118	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3346	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3119		3347
3120	Fork watchers are called when a C<fork ()> was detected (usually because	3348	Fork watchers are called when a C<fork ()> was detected (usually because
3121	whoever is a good citizen cared to tell libev about it by calling	3349	whoever is a good citizen cared to tell libev about it by calling
3122	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3350	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3123	event loop blocks next and before C<ev_check> watchers are being called,	3351	and before C<ev_check> watchers are being called, and only in the child
3124	and only in the child after the fork. If whoever good citizen calling	3352	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3125	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3353	and calls it in the wrong process, the fork handlers will be invoked, too,
3126	handlers will be invoked, too, of course.	3354	of course.
3127		3355
3128	=head3 The special problem of life after fork - how is it possible?	3356	=head3 The special problem of life after fork - how is it possible?
3129		3357
3130	Most uses of C<fork()> consist of forking, then some simple calls to set	3358	Most uses of C<fork ()> consist of forking, then some simple calls to set
3131	up/change the process environment, followed by a call to C<exec()>. This	3359	up/change the process environment, followed by a call to C<exec()>. This
3132	sequence should be handled by libev without any problems.	3360	sequence should be handled by libev without any problems.
3133		3361
3134	This changes when the application actually wants to do event handling	3362	This changes when the application actually wants to do event handling
3135	in the child, or both parent in child, in effect "continuing" after the	3363	in the child, or both parent in child, in effect "continuing" after the
…		…
3212	atexit (program_exits);	3440	atexit (program_exits);
3213		3441
3214		3442
3215	=head2 C<ev_async> - how to wake up an event loop	3443	=head2 C<ev_async> - how to wake up an event loop
3216		3444
3217	In general, you cannot use an C<ev_run> from multiple threads or other	3445	In general, you cannot use an C<ev_loop> from multiple threads or other
3218	asynchronous sources such as signal handlers (as opposed to multiple event	3446	asynchronous sources such as signal handlers (as opposed to multiple event
3219	loops - those are of course safe to use in different threads).	3447	loops - those are of course safe to use in different threads).
3220		3448
3221	Sometimes, however, you need to wake up an event loop you do not control,	3449	Sometimes, however, you need to wake up an event loop you do not control,
3222	for example because it belongs to another thread. This is what C<ev_async>	3450	for example because it belongs to another thread. This is what C<ev_async>
…		…
3224	it by calling C<ev_async_send>, which is thread- and signal safe.	3452	it by calling C<ev_async_send>, which is thread- and signal safe.
3225		3453
3226	This functionality is very similar to C<ev_signal> watchers, as signals,	3454	This functionality is very similar to C<ev_signal> watchers, as signals,
3227	too, are asynchronous in nature, and signals, too, will be compressed	3455	too, are asynchronous in nature, and signals, too, will be compressed
3228	(i.e. the number of callback invocations may be less than the number of	3456	(i.e. the number of callback invocations may be less than the number of
3229	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind	3457	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3230	of "global async watchers" by using a watcher on an otherwise unused	3458	of "global async watchers" by using a watcher on an otherwise unused
3231	signal, and C<ev_feed_signal> to signal this watcher from another thread,	3459	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3232	even without knowing which loop owns the signal.	3460	even without knowing which loop owns the signal.
3233
3234	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3235	just the default loop.
3236		3461
3237	=head3 Queueing	3462	=head3 Queueing
3238		3463
3239	C<ev_async> does not support queueing of data in any way. The reason	3464	C<ev_async> does not support queueing of data in any way. The reason
3240	is that the author does not know of a simple (or any) algorithm for a	3465	is that the author does not know of a simple (or any) algorithm for a
…		…
3332	trust me.	3557	trust me.
3333		3558
3334	=item ev_async_send (loop, ev_async *)	3559	=item ev_async_send (loop, ev_async *)
3335		3560
3336	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3561	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3337	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3562	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3563	returns.
		3564
3338	C<ev_feed_event>, this call is safe to do from other threads, signal or	3565	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3339	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3566	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3340	section below on what exactly this means).	3567	embedding section below on what exactly this means).
3341		3568
3342	Note that, as with other watchers in libev, multiple events might get	3569	Note that, as with other watchers in libev, multiple events might get
3343	compressed into a single callback invocation (another way to look at this	3570	compressed into a single callback invocation (another way to look at
3344	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3571	this is that C<ev_async> watchers are level-triggered: they are set on
3345	reset when the event loop detects that).	3572	C<ev_async_send>, reset when the event loop detects that).
3346		3573
3347	This call incurs the overhead of a system call only once per event loop	3574	This call incurs the overhead of at most one extra system call per event
3348	iteration, so while the overhead might be noticeable, it doesn't apply to	3575	loop iteration, if the event loop is blocked, and no syscall at all if
3349	repeated calls to C<ev_async_send> for the same event loop.	3576	the event loop (or your program) is processing events. That means that
		3577	repeated calls are basically free (there is no need to avoid calls for
		3578	performance reasons) and that the overhead becomes smaller (typically
		3579	zero) under load.
3350		3580
3351	=item bool = ev_async_pending (ev_async *)	3581	=item bool = ev_async_pending (ev_async *)
3352		3582
3353	Returns a non-zero value when C<ev_async_send> has been called on the	3583	Returns a non-zero value when C<ev_async_send> has been called on the
3354	watcher but the event has not yet been processed (or even noted) by the	3584	watcher but the event has not yet been processed (or even noted) by the
…		…
3371		3601
3372	There are some other functions of possible interest. Described. Here. Now.	3602	There are some other functions of possible interest. Described. Here. Now.
3373		3603
3374	=over 4	3604	=over 4
3375		3605
3376	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3606	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3377		3607
3378	This function combines a simple timer and an I/O watcher, calls your	3608	This function combines a simple timer and an I/O watcher, calls your
3379	callback on whichever event happens first and automatically stops both	3609	callback on whichever event happens first and automatically stops both
3380	watchers. This is useful if you want to wait for a single event on an fd	3610	watchers. This is useful if you want to wait for a single event on an fd
3381	or timeout without having to allocate/configure/start/stop/free one or	3611	or timeout without having to allocate/configure/start/stop/free one or
…		…
3409	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3639	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3410		3640
3411	=item ev_feed_fd_event (loop, int fd, int revents)	3641	=item ev_feed_fd_event (loop, int fd, int revents)
3412		3642
3413	Feed an event on the given fd, as if a file descriptor backend detected	3643	Feed an event on the given fd, as if a file descriptor backend detected
3414	the given events it.	3644	the given events.
3415		3645
3416	=item ev_feed_signal_event (loop, int signum)	3646	=item ev_feed_signal_event (loop, int signum)
3417		3647
3418	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,	3648	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3419	which is async-safe.	3649	which is async-safe.
…		…
3425		3655
3426	This section explains some common idioms that are not immediately	3656	This section explains some common idioms that are not immediately
3427	obvious. Note that examples are sprinkled over the whole manual, and this	3657	obvious. Note that examples are sprinkled over the whole manual, and this
3428	section only contains stuff that wouldn't fit anywhere else.	3658	section only contains stuff that wouldn't fit anywhere else.
3429		3659
3430	=over 4	3660	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3431		3661
3432	=item Model/nested event loop invocations and exit conditions.	3662	Each watcher has, by default, a C<void *data> member that you can read
		3663	or modify at any time: libev will completely ignore it. This can be used
		3664	to associate arbitrary data with your watcher. If you need more data and
		3665	don't want to allocate memory separately and store a pointer to it in that
		3666	data member, you can also "subclass" the watcher type and provide your own
		3667	data:
		3668
		3669	struct my_io
		3670	{
		3671	ev_io io;
		3672	int otherfd;
		3673	void *somedata;
		3674	struct whatever *mostinteresting;
		3675	};
		3676
		3677	...
		3678	struct my_io w;
		3679	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3680
		3681	And since your callback will be called with a pointer to the watcher, you
		3682	can cast it back to your own type:
		3683
		3684	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3685	{
		3686	struct my_io *w = (struct my_io *)w_;
		3687	...
		3688	}
		3689
		3690	More interesting and less C-conformant ways of casting your callback
		3691	function type instead have been omitted.
		3692
		3693	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3694
		3695	Another common scenario is to use some data structure with multiple
		3696	embedded watchers, in effect creating your own watcher that combines
		3697	multiple libev event sources into one "super-watcher":
		3698
		3699	struct my_biggy
		3700	{
		3701	int some_data;
		3702	ev_timer t1;
		3703	ev_timer t2;
		3704	}
		3705
		3706	In this case getting the pointer to C<my_biggy> is a bit more
		3707	complicated: Either you store the address of your C<my_biggy> struct in
		3708	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3709	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3710	real programmers):
		3711
		3712	#include <stddef.h>
		3713
		3714	static void
		3715	t1_cb (EV_P_ ev_timer *w, int revents)
		3716	{
		3717	struct my_biggy big = (struct my_biggy *)
		3718	(((char *)w) - offsetof (struct my_biggy, t1));
		3719	}
		3720
		3721	static void
		3722	t2_cb (EV_P_ ev_timer *w, int revents)
		3723	{
		3724	struct my_biggy big = (struct my_biggy *)
		3725	(((char *)w) - offsetof (struct my_biggy, t2));
		3726	}
		3727
		3728	=head2 AVOIDING FINISHING BEFORE RETURNING
		3729
		3730	Often you have structures like this in event-based programs:
		3731
		3732	callback ()
		3733	{
		3734	free (request);
		3735	}
		3736
		3737	request = start_new_request (..., callback);
		3738
		3739	The intent is to start some "lengthy" operation. The C<request> could be
		3740	used to cancel the operation, or do other things with it.
		3741
		3742	It's not uncommon to have code paths in C<start_new_request> that
		3743	immediately invoke the callback, for example, to report errors. Or you add
		3744	some caching layer that finds that it can skip the lengthy aspects of the
		3745	operation and simply invoke the callback with the result.
		3746
		3747	The problem here is that this will happen I<before> C<start_new_request>
		3748	has returned, so C<request> is not set.
		3749
		3750	Even if you pass the request by some safer means to the callback, you
		3751	might want to do something to the request after starting it, such as
		3752	canceling it, which probably isn't working so well when the callback has
		3753	already been invoked.
		3754
		3755	A common way around all these issues is to make sure that
		3756	C<start_new_request> I<always> returns before the callback is invoked. If
		3757	C<start_new_request> immediately knows the result, it can artificially
		3758	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3759	example, or more sneakily, by reusing an existing (stopped) watcher and
		3760	pushing it into the pending queue:
		3761
		3762	ev_set_cb (watcher, callback);
		3763	ev_feed_event (EV_A_ watcher, 0);
		3764
		3765	This way, C<start_new_request> can safely return before the callback is
		3766	invoked, while not delaying callback invocation too much.
		3767
		3768	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3433		3769
3434	Often (especially in GUI toolkits) there are places where you have	3770	Often (especially in GUI toolkits) there are places where you have
3435	I<modal> interaction, which is most easily implemented by recursively	3771	I<modal> interaction, which is most easily implemented by recursively
3436	invoking C<ev_run>.	3772	invoking C<ev_run>.
3437		3773
3438	This brings the problem of exiting - a callback might want to finish the	3774	This brings the problem of exiting - a callback might want to finish the
3439	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but	3775	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
3440	a modal "Are you sure?" dialog is still waiting), or just the nested one	3776	a modal "Are you sure?" dialog is still waiting), or just the nested one
3441	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some	3777	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
3442	other combination: In these cases, C<ev_break> will not work alone.	3778	other combination: In these cases, a simple C<ev_break> will not work.
3443		3779
3444	The solution is to maintain "break this loop" variable for each C<ev_run>	3780	The solution is to maintain "break this loop" variable for each C<ev_run>
3445	invocation, and use a loop around C<ev_run> until the condition is	3781	invocation, and use a loop around C<ev_run> until the condition is
3446	triggered, using C<EVRUN_ONCE>:	3782	triggered, using C<EVRUN_ONCE>:
3447		3783
…		…
3449	int exit_main_loop = 0;	3785	int exit_main_loop = 0;
3450		3786
3451	while (!exit_main_loop)	3787	while (!exit_main_loop)
3452	ev_run (EV_DEFAULT_ EVRUN_ONCE);	3788	ev_run (EV_DEFAULT_ EVRUN_ONCE);
3453		3789
3454	// in a model watcher	3790	// in a modal watcher
3455	int exit_nested_loop = 0;	3791	int exit_nested_loop = 0;
3456		3792
3457	while (!exit_nested_loop)	3793	while (!exit_nested_loop)
3458	ev_run (EV_A_ EVRUN_ONCE);	3794	ev_run (EV_A_ EVRUN_ONCE);
3459		3795
…		…
3466	exit_main_loop = 1;	3802	exit_main_loop = 1;
3467		3803
3468	// exit both	3804	// exit both
3469	exit_main_loop = exit_nested_loop = 1;	3805	exit_main_loop = exit_nested_loop = 1;
3470		3806
3471	=back	3807	=head2 THREAD LOCKING EXAMPLE
		3808
		3809	Here is a fictitious example of how to run an event loop in a different
		3810	thread from where callbacks are being invoked and watchers are
		3811	created/added/removed.
		3812
		3813	For a real-world example, see the C<EV::Loop::Async> perl module,
		3814	which uses exactly this technique (which is suited for many high-level
		3815	languages).
		3816
		3817	The example uses a pthread mutex to protect the loop data, a condition
		3818	variable to wait for callback invocations, an async watcher to notify the
		3819	event loop thread and an unspecified mechanism to wake up the main thread.
		3820
		3821	First, you need to associate some data with the event loop:
		3822
		3823	typedef struct {
		3824	mutex_t lock; /* global loop lock */
		3825	ev_async async_w;
		3826	thread_t tid;
		3827	cond_t invoke_cv;
		3828	} userdata;
		3829
		3830	void prepare_loop (EV_P)
		3831	{
		3832	// for simplicity, we use a static userdata struct.
		3833	static userdata u;
		3834
		3835	ev_async_init (&u->async_w, async_cb);
		3836	ev_async_start (EV_A_ &u->async_w);
		3837
		3838	pthread_mutex_init (&u->lock, 0);
		3839	pthread_cond_init (&u->invoke_cv, 0);
		3840
		3841	// now associate this with the loop
		3842	ev_set_userdata (EV_A_ u);
		3843	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3844	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3845
		3846	// then create the thread running ev_run
		3847	pthread_create (&u->tid, 0, l_run, EV_A);
		3848	}
		3849
		3850	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3851	solely to wake up the event loop so it takes notice of any new watchers
		3852	that might have been added:
		3853
		3854	static void
		3855	async_cb (EV_P_ ev_async *w, int revents)
		3856	{
		3857	// just used for the side effects
		3858	}
		3859
		3860	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3861	protecting the loop data, respectively.
		3862
		3863	static void
		3864	l_release (EV_P)
		3865	{
		3866	userdata *u = ev_userdata (EV_A);
		3867	pthread_mutex_unlock (&u->lock);
		3868	}
		3869
		3870	static void
		3871	l_acquire (EV_P)
		3872	{
		3873	userdata *u = ev_userdata (EV_A);
		3874	pthread_mutex_lock (&u->lock);
		3875	}
		3876
		3877	The event loop thread first acquires the mutex, and then jumps straight
		3878	into C<ev_run>:
		3879
		3880	void *
		3881	l_run (void *thr_arg)
		3882	{
		3883	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3884
		3885	l_acquire (EV_A);
		3886	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3887	ev_run (EV_A_ 0);
		3888	l_release (EV_A);
		3889
		3890	return 0;
		3891	}
		3892
		3893	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3894	signal the main thread via some unspecified mechanism (signals? pipe
		3895	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3896	have been called (in a while loop because a) spurious wakeups are possible
		3897	and b) skipping inter-thread-communication when there are no pending
		3898	watchers is very beneficial):
		3899
		3900	static void
		3901	l_invoke (EV_P)
		3902	{
		3903	userdata *u = ev_userdata (EV_A);
		3904
		3905	while (ev_pending_count (EV_A))
		3906	{
		3907	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3908	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3909	}
		3910	}
		3911
		3912	Now, whenever the main thread gets told to invoke pending watchers, it
		3913	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3914	thread to continue:
		3915
		3916	static void
		3917	real_invoke_pending (EV_P)
		3918	{
		3919	userdata *u = ev_userdata (EV_A);
		3920
		3921	pthread_mutex_lock (&u->lock);
		3922	ev_invoke_pending (EV_A);
		3923	pthread_cond_signal (&u->invoke_cv);
		3924	pthread_mutex_unlock (&u->lock);
		3925	}
		3926
		3927	Whenever you want to start/stop a watcher or do other modifications to an
		3928	event loop, you will now have to lock:
		3929
		3930	ev_timer timeout_watcher;
		3931	userdata *u = ev_userdata (EV_A);
		3932
		3933	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3934
		3935	pthread_mutex_lock (&u->lock);
		3936	ev_timer_start (EV_A_ &timeout_watcher);
		3937	ev_async_send (EV_A_ &u->async_w);
		3938	pthread_mutex_unlock (&u->lock);
		3939
		3940	Note that sending the C<ev_async> watcher is required because otherwise
		3941	an event loop currently blocking in the kernel will have no knowledge
		3942	about the newly added timer. By waking up the loop it will pick up any new
		3943	watchers in the next event loop iteration.
		3944
		3945	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3946
		3947	While the overhead of a callback that e.g. schedules a thread is small, it
		3948	is still an overhead. If you embed libev, and your main usage is with some
		3949	kind of threads or coroutines, you might want to customise libev so that
		3950	doesn't need callbacks anymore.
		3951
		3952	Imagine you have coroutines that you can switch to using a function
		3953	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3954	and that due to some magic, the currently active coroutine is stored in a
		3955	global called C<current_coro>. Then you can build your own "wait for libev
		3956	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3957	the differing C<;> conventions):
		3958
		3959	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3960	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3961
		3962	That means instead of having a C callback function, you store the
		3963	coroutine to switch to in each watcher, and instead of having libev call
		3964	your callback, you instead have it switch to that coroutine.
		3965
		3966	A coroutine might now wait for an event with a function called
		3967	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3968	matter when, or whether the watcher is active or not when this function is
		3969	called):
		3970
		3971	void
		3972	wait_for_event (ev_watcher *w)
		3973	{
		3974	ev_set_cb (w, current_coro);
		3975	switch_to (libev_coro);
		3976	}
		3977
		3978	That basically suspends the coroutine inside C<wait_for_event> and
		3979	continues the libev coroutine, which, when appropriate, switches back to
		3980	this or any other coroutine.
		3981
		3982	You can do similar tricks if you have, say, threads with an event queue -
		3983	instead of storing a coroutine, you store the queue object and instead of
		3984	switching to a coroutine, you push the watcher onto the queue and notify
		3985	any waiters.
		3986
		3987	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3988	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3989
		3990	// my_ev.h
		3991	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3992	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3993	#include "../libev/ev.h"
		3994
		3995	// my_ev.c
		3996	#define EV_H "my_ev.h"
		3997	#include "../libev/ev.c"
		3998
		3999	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4000	F<my_ev.c> into your project. When properly specifying include paths, you
		4001	can even use F<ev.h> as header file name directly.
3472		4002
3473		4003
3474	=head1 LIBEVENT EMULATION	4004	=head1 LIBEVENT EMULATION
3475		4005
3476	Libev offers a compatibility emulation layer for libevent. It cannot	4006	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3506		4036
3507	=back	4037	=back
3508		4038
3509	=head1 C++ SUPPORT	4039	=head1 C++ SUPPORT
3510		4040
		4041	=head2 C API
		4042
		4043	The normal C API should work fine when used from C++: both ev.h and the
		4044	libev sources can be compiled as C++. Therefore, code that uses the C API
		4045	will work fine.
		4046
		4047	Proper exception specifications might have to be added to callbacks passed
		4048	to libev: exceptions may be thrown only from watcher callbacks, all other
		4049	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4050	callbacks) must not throw exceptions, and might need a C<noexcept>
		4051	specification. If you have code that needs to be compiled as both C and
		4052	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4053
		4054	static void
		4055	fatal_error (const char *msg) EV_NOEXCEPT
		4056	{
		4057	perror (msg);
		4058	abort ();
		4059	}
		4060
		4061	...
		4062	ev_set_syserr_cb (fatal_error);
		4063
		4064	The only API functions that can currently throw exceptions are C<ev_run>,
		4065	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4066	because it runs cleanup watchers).
		4067
		4068	Throwing exceptions in watcher callbacks is only supported if libev itself
		4069	is compiled with a C++ compiler or your C and C++ environments allow
		4070	throwing exceptions through C libraries (most do).
		4071
		4072	=head2 C++ API
		4073
3511	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4074	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3512	you to use some convenience methods to start/stop watchers and also change	4075	you to use some convenience methods to start/stop watchers and also change
3513	the callback model to a model using method callbacks on objects.	4076	the callback model to a model using method callbacks on objects.
3514		4077
3515	To use it,	4078	To use it,
3516		4079
3517	#include <ev++.h>	4080	#include <ev++.h>
3518		4081
3519	This automatically includes F<ev.h> and puts all of its definitions (many	4082	This automatically includes F<ev.h> and puts all of its definitions (many
3520	of them macros) into the global namespace. All C++ specific things are	4083	of them macros) into the global namespace. All C++ specific things are
3521	put into the C<ev> namespace. It should support all the same embedding	4084	put into the C<ev> namespace. It should support all the same embedding
…		…
3530	with C<operator ()> can be used as callbacks. Other types should be easy	4093	with C<operator ()> can be used as callbacks. Other types should be easy
3531	to add as long as they only need one additional pointer for context. If	4094	to add as long as they only need one additional pointer for context. If
3532	you need support for other types of functors please contact the author	4095	you need support for other types of functors please contact the author
3533	(preferably after implementing it).	4096	(preferably after implementing it).
3534		4097
		4098	For all this to work, your C++ compiler either has to use the same calling
		4099	conventions as your C compiler (for static member functions), or you have
		4100	to embed libev and compile libev itself as C++.
		4101
3535	Here is a list of things available in the C<ev> namespace:	4102	Here is a list of things available in the C<ev> namespace:
3536		4103
3537	=over 4	4104	=over 4
3538		4105
3539	=item C<ev::READ>, C<ev::WRITE> etc.	4106	=item C<ev::READ>, C<ev::WRITE> etc.
…		…
3548	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4115	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3549		4116
3550	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4117	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3551	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4118	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3552	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4119	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3553	defines by many implementations.	4120	defined by many implementations.
3554		4121
3555	All of those classes have these methods:	4122	All of those classes have these methods:
3556		4123
3557	=over 4	4124	=over 4
3558		4125
…		…
3620	void operator() (ev::io &w, int revents)	4187	void operator() (ev::io &w, int revents)
3621	{	4188	{
3622	...	4189	...
3623	}	4190	}
3624	}	4191	}
3625		4192
3626	myfunctor f;	4193	myfunctor f;
3627		4194
3628	ev::io w;	4195	ev::io w;
3629	w.set (&f);	4196	w.set (&f);
3630		4197
…		…
3648	Associates a different C<struct ev_loop> with this watcher. You can only	4215	Associates a different C<struct ev_loop> with this watcher. You can only
3649	do this when the watcher is inactive (and not pending either).	4216	do this when the watcher is inactive (and not pending either).
3650		4217
3651	=item w->set ([arguments])	4218	=item w->set ([arguments])
3652		4219
3653	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4220	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3654	method or a suitable start method must be called at least once. Unlike the	4221	with the same arguments. Either this method or a suitable start method
3655	C counterpart, an active watcher gets automatically stopped and restarted	4222	must be called at least once. Unlike the C counterpart, an active watcher
3656	when reconfiguring it with this method.	4223	gets automatically stopped and restarted when reconfiguring it with this
		4224	method.
		4225
		4226	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4227	clashing with the C<set (loop)> method.
3657		4228
3658	=item w->start ()	4229	=item w->start ()
3659		4230
3660	Starts the watcher. Note that there is no C<loop> argument, as the	4231	Starts the watcher. Note that there is no C<loop> argument, as the
3661	constructor already stores the event loop.	4232	constructor already stores the event loop.
…		…
3691	watchers in the constructor.	4262	watchers in the constructor.
3692		4263
3693	class myclass	4264	class myclass
3694	{	4265	{
3695	ev::io io ; void io_cb (ev::io &w, int revents);	4266	ev::io io ; void io_cb (ev::io &w, int revents);
3696	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4267	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3697	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4268	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3698		4269
3699	myclass (int fd)	4270	myclass (int fd)
3700	{	4271	{
3701	io .set <myclass, &myclass::io_cb > (this);	4272	io .set <myclass, &myclass::io_cb > (this);
…		…
3752	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4323	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3753		4324
3754	=item D	4325	=item D
3755		4326
3756	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4327	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3757	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4328	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3758		4329
3759	=item Ocaml	4330	=item Ocaml
3760		4331
3761	Erkki Seppala has written Ocaml bindings for libev, to be found at	4332	Erkki Seppala has written Ocaml bindings for libev, to be found at
3762	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4333	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3765		4336
3766	Brian Maher has written a partial interface to libev for lua (at the	4337	Brian Maher has written a partial interface to libev for lua (at the
3767	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4338	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3768	L<http://github.com/brimworks/lua-ev>.	4339	L<http://github.com/brimworks/lua-ev>.
3769		4340
		4341	=item Javascript
		4342
		4343	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4344
		4345	=item Others
		4346
		4347	There are others, and I stopped counting.
		4348
3770	=back	4349	=back
3771		4350
3772		4351
3773	=head1 MACRO MAGIC	4352	=head1 MACRO MAGIC
3774		4353
…		…
3810	suitable for use with C<EV_A>.	4389	suitable for use with C<EV_A>.
3811		4390
3812	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4391	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3813		4392
3814	Similar to the other two macros, this gives you the value of the default	4393	Similar to the other two macros, this gives you the value of the default
3815	loop, if multiple loops are supported ("ev loop default").	4394	loop, if multiple loops are supported ("ev loop default"). The default loop
		4395	will be initialised if it isn't already initialised.
		4396
		4397	For non-multiplicity builds, these macros do nothing, so you always have
		4398	to initialise the loop somewhere.
3816		4399
3817	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4400	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3818		4401
3819	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4402	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3820	default loop has been initialised (C<UC> == unchecked). Their behaviour	4403	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3887	ev_vars.h	4470	ev_vars.h
3888	ev_wrap.h	4471	ev_wrap.h
3889		4472
3890	ev_win32.c required on win32 platforms only	4473	ev_win32.c required on win32 platforms only
3891		4474
3892	ev_select.c only when select backend is enabled (which is enabled by default)	4475	ev_select.c only when select backend is enabled
3893	ev_poll.c only when poll backend is enabled (disabled by default)	4476	ev_poll.c only when poll backend is enabled
3894	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4477	ev_epoll.c only when the epoll backend is enabled
		4478	ev_linuxaio.c only when the linux aio backend is enabled
3895	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4479	ev_kqueue.c only when the kqueue backend is enabled
3896	ev_port.c only when the solaris port backend is enabled (disabled by default)	4480	ev_port.c only when the solaris port backend is enabled
3897		4481
3898	F<ev.c> includes the backend files directly when enabled, so you only need	4482	F<ev.c> includes the backend files directly when enabled, so you only need
3899	to compile this single file.	4483	to compile this single file.
3900		4484
3901	=head3 LIBEVENT COMPATIBILITY API	4485	=head3 LIBEVENT COMPATIBILITY API
…		…
3965	supported). It will also not define any of the structs usually found in	4549	supported). It will also not define any of the structs usually found in
3966	F<event.h> that are not directly supported by the libev core alone.	4550	F<event.h> that are not directly supported by the libev core alone.
3967		4551
3968	In standalone mode, libev will still try to automatically deduce the	4552	In standalone mode, libev will still try to automatically deduce the
3969	configuration, but has to be more conservative.	4553	configuration, but has to be more conservative.
		4554
		4555	=item EV_USE_FLOOR
		4556
		4557	If defined to be C<1>, libev will use the C<floor ()> function for its
		4558	periodic reschedule calculations, otherwise libev will fall back on a
		4559	portable (slower) implementation. If you enable this, you usually have to
		4560	link against libm or something equivalent. Enabling this when the C<floor>
		4561	function is not available will fail, so the safe default is to not enable
		4562	this.
3970		4563
3971	=item EV_USE_MONOTONIC	4564	=item EV_USE_MONOTONIC
3972		4565
3973	If defined to be C<1>, libev will try to detect the availability of the	4566	If defined to be C<1>, libev will try to detect the availability of the
3974	monotonic clock option at both compile time and runtime. Otherwise no	4567	monotonic clock option at both compile time and runtime. Otherwise no
…		…
4060	If programs implement their own fd to handle mapping on win32, then this	4653	If programs implement their own fd to handle mapping on win32, then this
4061	macro can be used to override the C<close> function, useful to unregister	4654	macro can be used to override the C<close> function, useful to unregister
4062	file descriptors again. Note that the replacement function has to close	4655	file descriptors again. Note that the replacement function has to close
4063	the underlying OS handle.	4656	the underlying OS handle.
4064		4657
		4658	=item EV_USE_WSASOCKET
		4659
		4660	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4661	communication socket, which works better in some environments. Otherwise,
		4662	the normal C<socket> function will be used, which works better in other
		4663	environments.
		4664
4065	=item EV_USE_POLL	4665	=item EV_USE_POLL
4066		4666
4067	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4667	If defined to be C<1>, libev will compile in support for the C<poll>(2)
4068	backend. Otherwise it will be enabled on non-win32 platforms. It	4668	backend. Otherwise it will be enabled on non-win32 platforms. It
4069	takes precedence over select.	4669	takes precedence over select.
…		…
4073	If defined to be C<1>, libev will compile in support for the Linux	4673	If defined to be C<1>, libev will compile in support for the Linux
4074	C<epoll>(7) backend. Its availability will be detected at runtime,	4674	C<epoll>(7) backend. Its availability will be detected at runtime,
4075	otherwise another method will be used as fallback. This is the preferred	4675	otherwise another method will be used as fallback. This is the preferred
4076	backend for GNU/Linux systems. If undefined, it will be enabled if the	4676	backend for GNU/Linux systems. If undefined, it will be enabled if the
4077	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4677	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4678
		4679	=item EV_USE_LINUXAIO
		4680
		4681	If defined to be C<1>, libev will compile in support for the Linux
		4682	aio backend. Due to it's currenbt limitations it has to be requested
		4683	explicitly. If undefined, it will be enabled on linux, otherwise
		4684	disabled.
4078		4685
4079	=item EV_USE_KQUEUE	4686	=item EV_USE_KQUEUE
4080		4687
4081	If defined to be C<1>, libev will compile in support for the BSD style	4688	If defined to be C<1>, libev will compile in support for the BSD style
4082	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4689	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
4104	If defined to be C<1>, libev will compile in support for the Linux inotify	4711	If defined to be C<1>, libev will compile in support for the Linux inotify
4105	interface to speed up C<ev_stat> watchers. Its actual availability will	4712	interface to speed up C<ev_stat> watchers. Its actual availability will
4106	be detected at runtime. If undefined, it will be enabled if the headers	4713	be detected at runtime. If undefined, it will be enabled if the headers
4107	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4714	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4108		4715
		4716	=item EV_NO_SMP
		4717
		4718	If defined to be C<1>, libev will assume that memory is always coherent
		4719	between threads, that is, threads can be used, but threads never run on
		4720	different cpus (or different cpu cores). This reduces dependencies
		4721	and makes libev faster.
		4722
		4723	=item EV_NO_THREADS
		4724
		4725	If defined to be C<1>, libev will assume that it will never be called from
		4726	different threads (that includes signal handlers), which is a stronger
		4727	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4728	libev faster.
		4729
4109	=item EV_ATOMIC_T	4730	=item EV_ATOMIC_T
4110		4731
4111	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4732	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4112	access is atomic with respect to other threads or signal contexts. No such	4733	access is atomic with respect to other threads or signal contexts. No
4113	type is easily found in the C language, so you can provide your own type	4734	such type is easily found in the C language, so you can provide your own
4114	that you know is safe for your purposes. It is used both for signal handler "locking"	4735	type that you know is safe for your purposes. It is used both for signal
4115	as well as for signal and thread safety in C<ev_async> watchers.	4736	handler "locking" as well as for signal and thread safety in C<ev_async>
		4737	watchers.
4116		4738
4117	In the absence of this define, libev will use C<sig_atomic_t volatile>	4739	In the absence of this define, libev will use C<sig_atomic_t volatile>
4118	(from F<signal.h>), which is usually good enough on most platforms.	4740	(from F<signal.h>), which is usually good enough on most platforms.
4119		4741
4120	=item EV_H (h)	4742	=item EV_H (h)
…		…
4147	will have the C<struct ev_loop *> as first argument, and you can create	4769	will have the C<struct ev_loop *> as first argument, and you can create
4148	additional independent event loops. Otherwise there will be no support	4770	additional independent event loops. Otherwise there will be no support
4149	for multiple event loops and there is no first event loop pointer	4771	for multiple event loops and there is no first event loop pointer
4150	argument. Instead, all functions act on the single default loop.	4772	argument. Instead, all functions act on the single default loop.
4151		4773
		4774	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4775	default loop when multiplicity is switched off - you always have to
		4776	initialise the loop manually in this case.
		4777
4152	=item EV_MINPRI	4778	=item EV_MINPRI
4153		4779
4154	=item EV_MAXPRI	4780	=item EV_MAXPRI
4155		4781
4156	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4782	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4192	#define EV_USE_POLL 1	4818	#define EV_USE_POLL 1
4193	#define EV_CHILD_ENABLE 1	4819	#define EV_CHILD_ENABLE 1
4194	#define EV_ASYNC_ENABLE 1	4820	#define EV_ASYNC_ENABLE 1
4195		4821
4196	The actual value is a bitset, it can be a combination of the following	4822	The actual value is a bitset, it can be a combination of the following
4197	values:	4823	values (by default, all of these are enabled):
4198		4824
4199	=over 4	4825	=over 4
4200		4826
4201	=item C<1> - faster/larger code	4827	=item C<1> - faster/larger code
4202		4828
…		…
4206	code size by roughly 30% on amd64).	4832	code size by roughly 30% on amd64).
4207		4833
4208	When optimising for size, use of compiler flags such as C<-Os> with	4834	When optimising for size, use of compiler flags such as C<-Os> with
4209	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4835	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4210	assertions.	4836	assertions.
		4837
		4838	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4839	(e.g. gcc with C<-Os>).
4211		4840
4212	=item C<2> - faster/larger data structures	4841	=item C<2> - faster/larger data structures
4213		4842
4214	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4843	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4215	hash table sizes and so on. This will usually further increase code size	4844	hash table sizes and so on. This will usually further increase code size
4216	and can additionally have an effect on the size of data structures at	4845	and can additionally have an effect on the size of data structures at
4217	runtime.	4846	runtime.
4218		4847
		4848	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4849	(e.g. gcc with C<-Os>).
		4850
4219	=item C<4> - full API configuration	4851	=item C<4> - full API configuration
4220		4852
4221	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4853	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4222	enables multiplicity (C<EV_MULTIPLICITY>=1).	4854	enables multiplicity (C<EV_MULTIPLICITY>=1).
4223		4855
…		…
4253		4885
4254	With an intelligent-enough linker (gcc+binutils are intelligent enough	4886	With an intelligent-enough linker (gcc+binutils are intelligent enough
4255	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4887	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4256	your program might be left out as well - a binary starting a timer and an	4888	your program might be left out as well - a binary starting a timer and an
4257	I/O watcher then might come out at only 5Kb.	4889	I/O watcher then might come out at only 5Kb.
		4890
		4891	=item EV_API_STATIC
		4892
		4893	If this symbol is defined (by default it is not), then all identifiers
		4894	will have static linkage. This means that libev will not export any
		4895	identifiers, and you cannot link against libev anymore. This can be useful
		4896	when you embed libev, only want to use libev functions in a single file,
		4897	and do not want its identifiers to be visible.
		4898
		4899	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4900	wants to use libev.
		4901
		4902	This option only works when libev is compiled with a C compiler, as C++
		4903	doesn't support the required declaration syntax.
4258		4904
4259	=item EV_AVOID_STDIO	4905	=item EV_AVOID_STDIO
4260		4906
4261	If this is set to C<1> at compiletime, then libev will avoid using stdio	4907	If this is set to C<1> at compiletime, then libev will avoid using stdio
4262	functions (printf, scanf, perror etc.). This will increase the code size	4908	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4406	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5052	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4407		5053
4408	#include "ev_cpp.h"	5054	#include "ev_cpp.h"
4409	#include "ev.c"	5055	#include "ev.c"
4410		5056
4411	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5057	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4412		5058
4413	=head2 THREADS AND COROUTINES	5059	=head2 THREADS AND COROUTINES
4414		5060
4415	=head3 THREADS	5061	=head3 THREADS
4416		5062
…		…
4467	default loop and triggering an C<ev_async> watcher from the default loop	5113	default loop and triggering an C<ev_async> watcher from the default loop
4468	watcher callback into the event loop interested in the signal.	5114	watcher callback into the event loop interested in the signal.
4469		5115
4470	=back	5116	=back
4471		5117
4472	=head4 THREAD LOCKING EXAMPLE	5118	See also L</THREAD LOCKING EXAMPLE>.
4473
4474	Here is a fictitious example of how to run an event loop in a different
4475	thread than where callbacks are being invoked and watchers are
4476	created/added/removed.
4477
4478	For a real-world example, see the C<EV::Loop::Async> perl module,
4479	which uses exactly this technique (which is suited for many high-level
4480	languages).
4481
4482	The example uses a pthread mutex to protect the loop data, a condition
4483	variable to wait for callback invocations, an async watcher to notify the
4484	event loop thread and an unspecified mechanism to wake up the main thread.
4485
4486	First, you need to associate some data with the event loop:
4487
4488	typedef struct {
4489	mutex_t lock; /* global loop lock */
4490	ev_async async_w;
4491	thread_t tid;
4492	cond_t invoke_cv;
4493	} userdata;
4494
4495	void prepare_loop (EV_P)
4496	{
4497	// for simplicity, we use a static userdata struct.
4498	static userdata u;
4499
4500	ev_async_init (&u->async_w, async_cb);
4501	ev_async_start (EV_A_ &u->async_w);
4502
4503	pthread_mutex_init (&u->lock, 0);
4504	pthread_cond_init (&u->invoke_cv, 0);
4505
4506	// now associate this with the loop
4507	ev_set_userdata (EV_A_ u);
4508	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4509	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4510
4511	// then create the thread running ev_loop
4512	pthread_create (&u->tid, 0, l_run, EV_A);
4513	}
4514
4515	The callback for the C<ev_async> watcher does nothing: the watcher is used
4516	solely to wake up the event loop so it takes notice of any new watchers
4517	that might have been added:
4518
4519	static void
4520	async_cb (EV_P_ ev_async *w, int revents)
4521	{
4522	// just used for the side effects
4523	}
4524
4525	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4526	protecting the loop data, respectively.
4527
4528	static void
4529	l_release (EV_P)
4530	{
4531	userdata *u = ev_userdata (EV_A);
4532	pthread_mutex_unlock (&u->lock);
4533	}
4534
4535	static void
4536	l_acquire (EV_P)
4537	{
4538	userdata *u = ev_userdata (EV_A);
4539	pthread_mutex_lock (&u->lock);
4540	}
4541
4542	The event loop thread first acquires the mutex, and then jumps straight
4543	into C<ev_run>:
4544
4545	void *
4546	l_run (void *thr_arg)
4547	{
4548	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4549
4550	l_acquire (EV_A);
4551	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4552	ev_run (EV_A_ 0);
4553	l_release (EV_A);
4554
4555	return 0;
4556	}
4557
4558	Instead of invoking all pending watchers, the C<l_invoke> callback will
4559	signal the main thread via some unspecified mechanism (signals? pipe
4560	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4561	have been called (in a while loop because a) spurious wakeups are possible
4562	and b) skipping inter-thread-communication when there are no pending
4563	watchers is very beneficial):
4564
4565	static void
4566	l_invoke (EV_P)
4567	{
4568	userdata *u = ev_userdata (EV_A);
4569
4570	while (ev_pending_count (EV_A))
4571	{
4572	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4573	pthread_cond_wait (&u->invoke_cv, &u->lock);
4574	}
4575	}
4576
4577	Now, whenever the main thread gets told to invoke pending watchers, it
4578	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4579	thread to continue:
4580
4581	static void
4582	real_invoke_pending (EV_P)
4583	{
4584	userdata *u = ev_userdata (EV_A);
4585
4586	pthread_mutex_lock (&u->lock);
4587	ev_invoke_pending (EV_A);
4588	pthread_cond_signal (&u->invoke_cv);
4589	pthread_mutex_unlock (&u->lock);
4590	}
4591
4592	Whenever you want to start/stop a watcher or do other modifications to an
4593	event loop, you will now have to lock:
4594
4595	ev_timer timeout_watcher;
4596	userdata *u = ev_userdata (EV_A);
4597
4598	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4599
4600	pthread_mutex_lock (&u->lock);
4601	ev_timer_start (EV_A_ &timeout_watcher);
4602	ev_async_send (EV_A_ &u->async_w);
4603	pthread_mutex_unlock (&u->lock);
4604
4605	Note that sending the C<ev_async> watcher is required because otherwise
4606	an event loop currently blocking in the kernel will have no knowledge
4607	about the newly added timer. By waking up the loop it will pick up any new
4608	watchers in the next event loop iteration.
4609		5119
4610	=head3 COROUTINES	5120	=head3 COROUTINES
4611		5121
4612	Libev is very accommodating to coroutines ("cooperative threads"):	5122	Libev is very accommodating to coroutines ("cooperative threads"):
4613	libev fully supports nesting calls to its functions from different	5123	libev fully supports nesting calls to its functions from different
…		…
4778	requires, and its I/O model is fundamentally incompatible with the POSIX	5288	requires, and its I/O model is fundamentally incompatible with the POSIX
4779	model. Libev still offers limited functionality on this platform in	5289	model. Libev still offers limited functionality on this platform in
4780	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5290	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4781	descriptors. This only applies when using Win32 natively, not when using	5291	descriptors. This only applies when using Win32 natively, not when using
4782	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5292	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4783	as every compielr comes with a slightly differently broken/incompatible	5293	as every compiler comes with a slightly differently broken/incompatible
4784	environment.	5294	environment.
4785		5295
4786	Lifting these limitations would basically require the full	5296	Lifting these limitations would basically require the full
4787	re-implementation of the I/O system. If you are into this kind of thing,	5297	re-implementation of the I/O system. If you are into this kind of thing,
4788	then note that glib does exactly that for you in a very portable way (note	5298	then note that glib does exactly that for you in a very portable way (note
…		…
4882	structure (guaranteed by POSIX but not by ISO C for example), but it also	5392	structure (guaranteed by POSIX but not by ISO C for example), but it also
4883	assumes that the same (machine) code can be used to call any watcher	5393	assumes that the same (machine) code can be used to call any watcher
4884	callback: The watcher callbacks have different type signatures, but libev	5394	callback: The watcher callbacks have different type signatures, but libev
4885	calls them using an C<ev_watcher *> internally.	5395	calls them using an C<ev_watcher *> internally.
4886		5396
		5397	=item null pointers and integer zero are represented by 0 bytes
		5398
		5399	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5400	relies on this setting pointers and integers to null.
		5401
4887	=item pointer accesses must be thread-atomic	5402	=item pointer accesses must be thread-atomic
4888		5403
4889	Accessing a pointer value must be atomic, it must both be readable and	5404	Accessing a pointer value must be atomic, it must both be readable and
4890	writable in one piece - this is the case on all current architectures.	5405	writable in one piece - this is the case on all current architectures.
4891		5406
…		…
4904	thread" or will block signals process-wide, both behaviours would	5419	thread" or will block signals process-wide, both behaviours would
4905	be compatible with libev. Interaction between C<sigprocmask> and	5420	be compatible with libev. Interaction between C<sigprocmask> and
4906	C<pthread_sigmask> could complicate things, however.	5421	C<pthread_sigmask> could complicate things, however.
4907		5422
4908	The most portable way to handle signals is to block signals in all threads	5423	The most portable way to handle signals is to block signals in all threads
4909	except the initial one, and run the default loop in the initial thread as	5424	except the initial one, and run the signal handling loop in the initial
4910	well.	5425	thread as well.
4911		5426
4912	=item C<long> must be large enough for common memory allocation sizes	5427	=item C<long> must be large enough for common memory allocation sizes
4913		5428
4914	To improve portability and simplify its API, libev uses C<long> internally	5429	To improve portability and simplify its API, libev uses C<long> internally
4915	instead of C<size_t> when allocating its data structures. On non-POSIX	5430	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4921		5436
4922	The type C<double> is used to represent timestamps. It is required to	5437	The type C<double> is used to represent timestamps. It is required to
4923	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5438	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4924	good enough for at least into the year 4000 with millisecond accuracy	5439	good enough for at least into the year 4000 with millisecond accuracy
4925	(the design goal for libev). This requirement is overfulfilled by	5440	(the design goal for libev). This requirement is overfulfilled by
4926	implementations using IEEE 754, which is basically all existing ones. With	5441	implementations using IEEE 754, which is basically all existing ones.
		5442
4927	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5443	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5444	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5445	is either obsolete or somebody patched it to use C<long double> or
		5446	something like that, just kidding).
4928		5447
4929	=back	5448	=back
4930		5449
4931	If you know of other additional requirements drop me a note.	5450	If you know of other additional requirements drop me a note.
4932		5451
…		…
4994	=item Processing ev_async_send: O(number_of_async_watchers)	5513	=item Processing ev_async_send: O(number_of_async_watchers)
4995		5514
4996	=item Processing signals: O(max_signal_number)	5515	=item Processing signals: O(max_signal_number)
4997		5516
4998	Sending involves a system call I<iff> there were no other C<ev_async_send>	5517	Sending involves a system call I<iff> there were no other C<ev_async_send>
4999	calls in the current loop iteration. Checking for async and signal events	5518	calls in the current loop iteration and the loop is currently
		5519	blocked. Checking for async and signal events involves iterating over all
5000	involves iterating over all running async watchers or all signal numbers.	5520	running async watchers or all signal numbers.
5001		5521
5002	=back	5522	=back
5003		5523
5004		5524
5005	=head1 PORTING FROM LIBEV 3.X TO 4.X	5525	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
5014	=over 4	5534	=over 4
5015		5535
5016	=item C<EV_COMPAT3> backwards compatibility mechanism	5536	=item C<EV_COMPAT3> backwards compatibility mechanism
5017		5537
5018	The backward compatibility mechanism can be controlled by	5538	The backward compatibility mechanism can be controlled by
5019	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5539	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
5020	section.	5540	section.
5021		5541
5022	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5542	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
5023		5543
5024	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5544	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
5067	=over 4	5587	=over 4
5068		5588
5069	=item active	5589	=item active
5070		5590
5071	A watcher is active as long as it has been started and not yet stopped.	5591	A watcher is active as long as it has been started and not yet stopped.
5072	See L<WATCHER STATES> for details.	5592	See L</WATCHER STATES> for details.
5073		5593
5074	=item application	5594	=item application
5075		5595
5076	In this document, an application is whatever is using libev.	5596	In this document, an application is whatever is using libev.
5077		5597
…		…
5113	watchers and events.	5633	watchers and events.
5114		5634
5115	=item pending	5635	=item pending
5116		5636
5117	A watcher is pending as soon as the corresponding event has been	5637	A watcher is pending as soon as the corresponding event has been
5118	detected. See L<WATCHER STATES> for details.	5638	detected. See L</WATCHER STATES> for details.
5119		5639
5120	=item real time	5640	=item real time
5121		5641
5122	The physical time that is observed. It is apparently strictly monotonic :)	5642	The physical time that is observed. It is apparently strictly monotonic :)
5123		5643
5124	=item wall-clock time	5644	=item wall-clock time
5125		5645
5126	The time and date as shown on clocks. Unlike real time, it can actually	5646	The time and date as shown on clocks. Unlike real time, it can actually
5127	be wrong and jump forwards and backwards, e.g. when the you adjust your	5647	be wrong and jump forwards and backwards, e.g. when you adjust your
5128	clock.	5648	clock.
5129		5649
5130	=item watcher	5650	=item watcher
5131		5651
5132	A data structure that describes interest in certain events. Watchers need	5652	A data structure that describes interest in certain events. Watchers need
…		…
5135	=back	5655	=back
5136		5656
5137	=head1 AUTHOR	5657	=head1 AUTHOR
5138		5658
5139	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5659	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5140	Magnusson and Emanuele Giaquinta.	5660	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5141		5661

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines