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Revision 1.449 by root, Sun Jun 23 02:02:30 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	(probably because of a bug), so this is not (yet?) a generic event polling
		604	interface.
		605
		606	To work around this latter problem, the current version of libev uses
		607	epoll as a fallback for file deescriptor types that do not work. Epoll
		608	is used in, kind of, slow mode that hopefully avoids most of its design
		609	problems and requires 1-3 extra syscalls per active fd every iteration.
534		610
535	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	611	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
536	C<EVBACKEND_POLL>.	612	C<EVBACKEND_POLL>.
537		613
538	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	614	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
…		…
553		629
554	It scales in the same way as the epoll backend, but the interface to the	630	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	631	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	632	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	633	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	634	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	635	might have to leak fd's on fork, but it's more sane than epoll) and it
560	cases	636	drops fds silently in similarly hard-to-detect cases.
561		637
562	This backend usually performs well under most conditions.	638	This backend usually performs well under most conditions.
563		639
564	While nominally embeddable in other event loops, this doesn't work	640	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	641	everywhere, so you might need to test for this. And since it is broken
…		…
582	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	658	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
583		659
584	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	660	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
585	it's really slow, but it still scales very well (O(active_fds)).	661	it's really slow, but it still scales very well (O(active_fds)).
586		662
587	Please note that Solaris event ports can deliver a lot of spurious
588	notifications, so you need to use non-blocking I/O or other means to avoid
589	blocking when no data (or space) is available.
590
591	While this backend scales well, it requires one system call per active	663	While this backend scales well, it requires one system call per active
592	file descriptor per loop iteration. For small and medium numbers of file	664	file descriptor per loop iteration. For small and medium numbers of file
593	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	665	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
594	might perform better.	666	might perform better.
595		667
596	On the positive side, with the exception of the spurious readiness	668	On the positive side, this backend actually performed fully to
597	notifications, this backend actually performed fully to specification
598	in all tests and is fully embeddable, which is a rare feat among the	669	specification in all tests and is fully embeddable, which is a rare feat
599	OS-specific backends (I vastly prefer correctness over speed hacks).	670	among the OS-specific backends (I vastly prefer correctness over speed
		671	hacks).
		672
		673	On the negative side, the interface is I<bizarre> - so bizarre that
		674	even sun itself gets it wrong in their code examples: The event polling
		675	function sometimes returns events to the caller even though an error
		676	occurred, but with no indication whether it has done so or not (yes, it's
		677	even documented that way) - deadly for edge-triggered interfaces where you
		678	absolutely have to know whether an event occurred or not because you have
		679	to re-arm the watcher.
		680
		681	Fortunately libev seems to be able to work around these idiocies.
600		682
601	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	683	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
602	C<EVBACKEND_POLL>.	684	C<EVBACKEND_POLL>.
603		685
604	=item C<EVBACKEND_ALL>	686	=item C<EVBACKEND_ALL>
…		…
632		714
633	Example: Use whatever libev has to offer, but make sure that kqueue is	715	Example: Use whatever libev has to offer, but make sure that kqueue is
634	used if available.	716	used if available.
635		717
636	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);	718	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		719
		720	Example: Similarly, on linux, you mgiht want to take advantage of the
		721	linux aio backend if possible, but fall back to something else if that
		722	isn't available.
		723
		724	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
637		725
638	=item ev_loop_destroy (loop)	726	=item ev_loop_destroy (loop)
639		727
640	Destroys an event loop object (frees all memory and kernel state	728	Destroys an event loop object (frees all memory and kernel state
641	etc.). None of the active event watchers will be stopped in the normal	729	etc.). None of the active event watchers will be stopped in the normal
…		…
658	If you need dynamically allocated loops it is better to use C<ev_loop_new>	746	If you need dynamically allocated loops it is better to use C<ev_loop_new>
659	and C<ev_loop_destroy>.	747	and C<ev_loop_destroy>.
660		748
661	=item ev_loop_fork (loop)	749	=item ev_loop_fork (loop)
662		750
663	This function sets a flag that causes subsequent C<ev_run> iterations to	751	This function sets a flag that causes subsequent C<ev_run> iterations
664	reinitialise the kernel state for backends that have one. Despite the	752	to reinitialise the kernel state for backends that have one. Despite
665	name, you can call it anytime, but it makes most sense after forking, in	753	the name, you can call it anytime you are allowed to start or stop
666	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the	754	watchers (except inside an C<ev_prepare> callback), but it makes most
		755	sense after forking, in the child process. You I<must> call it (or use
667	child before resuming or calling C<ev_run>.	756	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
668		757
		758	In addition, if you want to reuse a loop (via this function or
		759	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		760
669	Again, you I<have> to call it on I<any> loop that you want to re-use after	761	Again, you I<have> to call it on I<any> loop that you want to re-use after
670	a fork, I<even if you do not plan to use the loop in the parent>. This is	762	a fork, I<even if you do not plan to use the loop in the parent>. This is
671	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	763	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
672	during fork.	764	during fork.
673		765
674	On the other hand, you only need to call this function in the child	766	On the other hand, you only need to call this function in the child
…		…
744		836
745	This function is rarely useful, but when some event callback runs for a	837	This function is rarely useful, but when some event callback runs for a
746	very long time without entering the event loop, updating libev's idea of	838	very long time without entering the event loop, updating libev's idea of
747	the current time is a good idea.	839	the current time is a good idea.
748		840
749	See also L<The special problem of time updates> in the C<ev_timer> section.	841	See also L</The special problem of time updates> in the C<ev_timer> section.
750		842
751	=item ev_suspend (loop)	843	=item ev_suspend (loop)
752		844
753	=item ev_resume (loop)	845	=item ev_resume (loop)
754		846
…		…
772	without a previous call to C<ev_suspend>.	864	without a previous call to C<ev_suspend>.
773		865
774	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	866	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
775	event loop time (see C<ev_now_update>).	867	event loop time (see C<ev_now_update>).
776		868
777	=item ev_run (loop, int flags)	869	=item bool ev_run (loop, int flags)
778		870
779	Finally, this is it, the event handler. This function usually is called	871	Finally, this is it, the event handler. This function usually is called
780	after you have initialised all your watchers and you want to start	872	after you have initialised all your watchers and you want to start
781	handling events. It will ask the operating system for any new events, call	873	handling events. It will ask the operating system for any new events, call
782	the watcher callbacks, an then repeat the whole process indefinitely: This	874	the watcher callbacks, and then repeat the whole process indefinitely: This
783	is why event loops are called I<loops>.	875	is why event loops are called I<loops>.
784		876
785	If the flags argument is specified as C<0>, it will keep handling events	877	If the flags argument is specified as C<0>, it will keep handling events
786	until either no event watchers are active anymore or C<ev_break> was	878	until either no event watchers are active anymore or C<ev_break> was
787	called.	879	called.
		880
		881	The return value is false if there are no more active watchers (which
		882	usually means "all jobs done" or "deadlock"), and true in all other cases
		883	(which usually means " you should call C<ev_run> again").
788		884
789	Please note that an explicit C<ev_break> is usually better than	885	Please note that an explicit C<ev_break> is usually better than
790	relying on all watchers to be stopped when deciding when a program has	886	relying on all watchers to be stopped when deciding when a program has
791	finished (especially in interactive programs), but having a program	887	finished (especially in interactive programs), but having a program
792	that automatically loops as long as it has to and no longer by virtue	888	that automatically loops as long as it has to and no longer by virtue
793	of relying on its watchers stopping correctly, that is truly a thing of	889	of relying on its watchers stopping correctly, that is truly a thing of
794	beauty.	890	beauty.
795		891
796	This function is also I<mostly> exception-safe - you can break out of	892	This function is I<mostly> exception-safe - you can break out of a
797	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++	893	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
798	exception and so on. This does not decrement the C<ev_depth> value, nor	894	exception and so on. This does not decrement the C<ev_depth> value, nor
799	will it clear any outstanding C<EVBREAK_ONE> breaks.	895	will it clear any outstanding C<EVBREAK_ONE> breaks.
800		896
801	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	897	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
802	those events and any already outstanding ones, but will not wait and	898	those events and any already outstanding ones, but will not wait and
…		…
814	This is useful if you are waiting for some external event in conjunction	910	This is useful if you are waiting for some external event in conjunction
815	with something not expressible using other libev watchers (i.e. "roll your	911	with something not expressible using other libev watchers (i.e. "roll your
816	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	912	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
817	usually a better approach for this kind of thing.	913	usually a better approach for this kind of thing.
818		914
819	Here are the gory details of what C<ev_run> does:	915	Here are the gory details of what C<ev_run> does (this is for your
		916	understanding, not a guarantee that things will work exactly like this in
		917	future versions):
820		918
821	- Increment loop depth.	919	- Increment loop depth.
822	- Reset the ev_break status.	920	- Reset the ev_break status.
823	- Before the first iteration, call any pending watchers.	921	- Before the first iteration, call any pending watchers.
824	LOOP:	922	LOOP:
…		…
857	anymore.	955	anymore.
858		956
859	... queue jobs here, make sure they register event watchers as long	957	... queue jobs here, make sure they register event watchers as long
860	... as they still have work to do (even an idle watcher will do..)	958	... as they still have work to do (even an idle watcher will do..)
861	ev_run (my_loop, 0);	959	ev_run (my_loop, 0);
862	... jobs done or somebody called unloop. yeah!	960	... jobs done or somebody called break. yeah!
863		961
864	=item ev_break (loop, how)	962	=item ev_break (loop, how)
865		963
866	Can be used to make a call to C<ev_run> return early (but only after it	964	Can be used to make a call to C<ev_run> return early (but only after it
867	has processed all outstanding events). The C<how> argument must be either	965	has processed all outstanding events). The C<how> argument must be either
…		…
930	overhead for the actual polling but can deliver many events at once.	1028	overhead for the actual polling but can deliver many events at once.
931		1029
932	By setting a higher I<io collect interval> you allow libev to spend more	1030	By setting a higher I<io collect interval> you allow libev to spend more
933	time collecting I/O events, so you can handle more events per iteration,	1031	time collecting I/O events, so you can handle more events per iteration,
934	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	1032	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
935	C<ev_timer>) will be not affected. Setting this to a non-null value will	1033	C<ev_timer>) will not be affected. Setting this to a non-null value will
936	introduce an additional C<ev_sleep ()> call into most loop iterations. The	1034	introduce an additional C<ev_sleep ()> call into most loop iterations. The
937	sleep time ensures that libev will not poll for I/O events more often then	1035	sleep time ensures that libev will not poll for I/O events more often then
938	once per this interval, on average.	1036	once per this interval, on average (as long as the host time resolution is
		1037	good enough).
939		1038
940	Likewise, by setting a higher I<timeout collect interval> you allow libev	1039	Likewise, by setting a higher I<timeout collect interval> you allow libev
941	to spend more time collecting timeouts, at the expense of increased	1040	to spend more time collecting timeouts, at the expense of increased
942	latency/jitter/inexactness (the watcher callback will be called	1041	latency/jitter/inexactness (the watcher callback will be called
943	later). C<ev_io> watchers will not be affected. Setting this to a non-null	1042	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
989	invoke the actual watchers inside another context (another thread etc.).	1088	invoke the actual watchers inside another context (another thread etc.).
990		1089
991	If you want to reset the callback, use C<ev_invoke_pending> as new	1090	If you want to reset the callback, use C<ev_invoke_pending> as new
992	callback.	1091	callback.
993		1092
994	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1093	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
995		1094
996	Sometimes you want to share the same loop between multiple threads. This	1095	Sometimes you want to share the same loop between multiple threads. This
997	can be done relatively simply by putting mutex_lock/unlock calls around	1096	can be done relatively simply by putting mutex_lock/unlock calls around
998	each call to a libev function.	1097	each call to a libev function.
999		1098
1000	However, C<ev_run> can run an indefinite time, so it is not feasible	1099	However, C<ev_run> can run an indefinite time, so it is not feasible
1001	to wait for it to return. One way around this is to wake up the event	1100	to wait for it to return. One way around this is to wake up the event
1002	loop via C<ev_break> and C<av_async_send>, another way is to set these	1101	loop via C<ev_break> and C<ev_async_send>, another way is to set these
1003	I<release> and I<acquire> callbacks on the loop.	1102	I<release> and I<acquire> callbacks on the loop.
1004		1103
1005	When set, then C<release> will be called just before the thread is	1104	When set, then C<release> will be called just before the thread is
1006	suspended waiting for new events, and C<acquire> is called just	1105	suspended waiting for new events, and C<acquire> is called just
1007	afterwards.	1106	afterwards.
…		…
1147		1246
1148	=item C<EV_PREPARE>	1247	=item C<EV_PREPARE>
1149		1248
1150	=item C<EV_CHECK>	1249	=item C<EV_CHECK>
1151		1250
1152	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1251	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1153	to gather new events, and all C<ev_check> watchers are invoked just after	1252	gather new events, and all C<ev_check> watchers are queued (not invoked)
1154	C<ev_run> has gathered them, but before it invokes any callbacks for any	1253	just after C<ev_run> has gathered them, but before it queues any callbacks
		1254	for any received events. That means C<ev_prepare> watchers are the last
		1255	watchers invoked before the event loop sleeps or polls for new events, and
		1256	C<ev_check> watchers will be invoked before any other watchers of the same
		1257	or lower priority within an event loop iteration.
		1258
1155	received events. Callbacks of both watcher types can start and stop as	1259	Callbacks of both watcher types can start and stop as many watchers as
1156	many watchers as they want, and all of them will be taken into account	1260	they want, and all of them will be taken into account (for example, a
1157	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1261	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1158	C<ev_run> from blocking).	1262	blocking).
1159		1263
1160	=item C<EV_EMBED>	1264	=item C<EV_EMBED>
1161		1265
1162	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1266	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1163		1267
…		…
1286		1390
1287	=item callback ev_cb (ev_TYPE *watcher)	1391	=item callback ev_cb (ev_TYPE *watcher)
1288		1392
1289	Returns the callback currently set on the watcher.	1393	Returns the callback currently set on the watcher.
1290		1394
1291	=item ev_cb_set (ev_TYPE *watcher, callback)	1395	=item ev_set_cb (ev_TYPE *watcher, callback)
1292		1396
1293	Change the callback. You can change the callback at virtually any time	1397	Change the callback. You can change the callback at virtually any time
1294	(modulo threads).	1398	(modulo threads).
1295		1399
1296	=item ev_set_priority (ev_TYPE *watcher, int priority)	1400	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1314	or might not have been clamped to the valid range.	1418	or might not have been clamped to the valid range.
1315		1419
1316	The default priority used by watchers when no priority has been set is	1420	The default priority used by watchers when no priority has been set is
1317	always C<0>, which is supposed to not be too high and not be too low :).	1421	always C<0>, which is supposed to not be too high and not be too low :).
1318		1422
1319	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1423	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1320	priorities.	1424	priorities.
1321		1425
1322	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1426	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1323		1427
1324	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1428	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
…		…
1349	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1453	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1350	functions that do not need a watcher.	1454	functions that do not need a watcher.
1351		1455
1352	=back	1456	=back
1353		1457
1354	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1458	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1355		1459	OWN COMPOSITE WATCHERS> idioms.
1356	Each watcher has, by default, a member C<void *data> that you can change
1357	and read at any time: libev will completely ignore it. This can be used
1358	to associate arbitrary data with your watcher. If you need more data and
1359	don't want to allocate memory and store a pointer to it in that data
1360	member, you can also "subclass" the watcher type and provide your own
1361	data:
1362
1363	struct my_io
1364	{
1365	ev_io io;
1366	int otherfd;
1367	void *somedata;
1368	struct whatever *mostinteresting;
1369	};
1370
1371	...
1372	struct my_io w;
1373	ev_io_init (&w.io, my_cb, fd, EV_READ);
1374
1375	And since your callback will be called with a pointer to the watcher, you
1376	can cast it back to your own type:
1377
1378	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1379	{
1380	struct my_io *w = (struct my_io *)w_;
1381	...
1382	}
1383
1384	More interesting and less C-conformant ways of casting your callback type
1385	instead have been omitted.
1386
1387	Another common scenario is to use some data structure with multiple
1388	embedded watchers:
1389
1390	struct my_biggy
1391	{
1392	int some_data;
1393	ev_timer t1;
1394	ev_timer t2;
1395	}
1396
1397	In this case getting the pointer to C<my_biggy> is a bit more
1398	complicated: Either you store the address of your C<my_biggy> struct
1399	in the C<data> member of the watcher (for woozies), or you need to use
1400	some pointer arithmetic using C<offsetof> inside your watchers (for real
1401	programmers):
1402
1403	#include <stddef.h>
1404
1405	static void
1406	t1_cb (EV_P_ ev_timer *w, int revents)
1407	{
1408	struct my_biggy big = (struct my_biggy *)
1409	(((char *)w) - offsetof (struct my_biggy, t1));
1410	}
1411
1412	static void
1413	t2_cb (EV_P_ ev_timer *w, int revents)
1414	{
1415	struct my_biggy big = (struct my_biggy *)
1416	(((char *)w) - offsetof (struct my_biggy, t2));
1417	}
1418		1460
1419	=head2 WATCHER STATES	1461	=head2 WATCHER STATES
1420		1462
1421	There are various watcher states mentioned throughout this manual -	1463	There are various watcher states mentioned throughout this manual -
1422	active, pending and so on. In this section these states and the rules to	1464	active, pending and so on. In this section these states and the rules to
1423	transition between them will be described in more detail - and while these	1465	transition between them will be described in more detail - and while these
1424	rules might look complicated, they usually do "the right thing".	1466	rules might look complicated, they usually do "the right thing".
1425		1467
1426	=over 4	1468	=over 4
1427		1469
1428	=item initialiased	1470	=item initialised
1429		1471
1430	Before a watcher can be registered with the event looop it has to be	1472	Before a watcher can be registered with the event loop it has to be
1431	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1473	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1432	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1474	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1433		1475
1434	In this state it is simply some block of memory that is suitable for use	1476	In this state it is simply some block of memory that is suitable for
1435	in an event loop. It can be moved around, freed, reused etc. at will.	1477	use in an event loop. It can be moved around, freed, reused etc. at
		1478	will - as long as you either keep the memory contents intact, or call
		1479	C<ev_TYPE_init> again.
1436		1480
1437	=item started/running/active	1481	=item started/running/active
1438		1482
1439	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1483	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1440	property of the event loop, and is actively waiting for events. While in	1484	property of the event loop, and is actively waiting for events. While in
…		…
1468	latter will clear any pending state the watcher might be in, regardless	1512	latter will clear any pending state the watcher might be in, regardless
1469	of whether it was active or not, so stopping a watcher explicitly before	1513	of whether it was active or not, so stopping a watcher explicitly before
1470	freeing it is often a good idea.	1514	freeing it is often a good idea.
1471		1515
1472	While stopped (and not pending) the watcher is essentially in the	1516	While stopped (and not pending) the watcher is essentially in the
1473	initialised state, that is it can be reused, moved, modified in any way	1517	initialised state, that is, it can be reused, moved, modified in any way
1474	you wish.	1518	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1519	it again).
1475		1520
1476	=back	1521	=back
1477		1522
1478	=head2 WATCHER PRIORITY MODELS	1523	=head2 WATCHER PRIORITY MODELS
1479		1524
…		…
1608	In general you can register as many read and/or write event watchers per	1653	In general you can register as many read and/or write event watchers per
1609	fd as you want (as long as you don't confuse yourself). Setting all file	1654	fd as you want (as long as you don't confuse yourself). Setting all file
1610	descriptors to non-blocking mode is also usually a good idea (but not	1655	descriptors to non-blocking mode is also usually a good idea (but not
1611	required if you know what you are doing).	1656	required if you know what you are doing).
1612		1657
1613	If you cannot use non-blocking mode, then force the use of a
1614	known-to-be-good backend (at the time of this writing, this includes only
1615	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1616	descriptors for which non-blocking operation makes no sense (such as
1617	files) - libev doesn't guarantee any specific behaviour in that case.
1618
1619	Another thing you have to watch out for is that it is quite easy to	1658	Another thing you have to watch out for is that it is quite easy to
1620	receive "spurious" readiness notifications, that is your callback might	1659	receive "spurious" readiness notifications, that is, your callback might
1621	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1660	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1622	because there is no data. Not only are some backends known to create a	1661	because there is no data. It is very easy to get into this situation even
1623	lot of those (for example Solaris ports), it is very easy to get into	1662	with a relatively standard program structure. Thus it is best to always
1624	this situation even with a relatively standard program structure. Thus	1663	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1625	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1626	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1664	preferable to a program hanging until some data arrives.
1627		1665
1628	If you cannot run the fd in non-blocking mode (for example you should	1666	If you cannot run the fd in non-blocking mode (for example you should
1629	not play around with an Xlib connection), then you have to separately	1667	not play around with an Xlib connection), then you have to separately
1630	re-test whether a file descriptor is really ready with a known-to-be good	1668	re-test whether a file descriptor is really ready with a known-to-be good
1631	interface such as poll (fortunately in our Xlib example, Xlib already	1669	interface such as poll (fortunately in the case of Xlib, it already does
1632	does this on its own, so its quite safe to use). Some people additionally	1670	this on its own, so its quite safe to use). Some people additionally
1633	use C<SIGALRM> and an interval timer, just to be sure you won't block	1671	use C<SIGALRM> and an interval timer, just to be sure you won't block
1634	indefinitely.	1672	indefinitely.
1635		1673
1636	But really, best use non-blocking mode.	1674	But really, best use non-blocking mode.
1637		1675
1638	=head3 The special problem of disappearing file descriptors	1676	=head3 The special problem of disappearing file descriptors
1639		1677
1640	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1678	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1641	descriptor (either due to calling C<close> explicitly or any other means,	1679	a file descriptor (either due to calling C<close> explicitly or any other
1642	such as C<dup2>). The reason is that you register interest in some file	1680	means, such as C<dup2>). The reason is that you register interest in some
1643	descriptor, but when it goes away, the operating system will silently drop	1681	file descriptor, but when it goes away, the operating system will silently
1644	this interest. If another file descriptor with the same number then is	1682	drop this interest. If another file descriptor with the same number then
1645	registered with libev, there is no efficient way to see that this is, in	1683	is registered with libev, there is no efficient way to see that this is,
1646	fact, a different file descriptor.	1684	in fact, a different file descriptor.
1647		1685
1648	To avoid having to explicitly tell libev about such cases, libev follows	1686	To avoid having to explicitly tell libev about such cases, libev follows
1649	the following policy: Each time C<ev_io_set> is being called, libev	1687	the following policy: Each time C<ev_io_set> is being called, libev
1650	will assume that this is potentially a new file descriptor, otherwise	1688	will assume that this is potentially a new file descriptor, otherwise
1651	it is assumed that the file descriptor stays the same. That means that	1689	it is assumed that the file descriptor stays the same. That means that
…		…
1665		1703
1666	There is no workaround possible except not registering events	1704	There is no workaround possible except not registering events
1667	for potentially C<dup ()>'ed file descriptors, or to resort to	1705	for potentially C<dup ()>'ed file descriptors, or to resort to
1668	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1706	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1669		1707
		1708	=head3 The special problem of files
		1709
		1710	Many people try to use C<select> (or libev) on file descriptors
		1711	representing files, and expect it to become ready when their program
		1712	doesn't block on disk accesses (which can take a long time on their own).
		1713
		1714	However, this cannot ever work in the "expected" way - you get a readiness
		1715	notification as soon as the kernel knows whether and how much data is
		1716	there, and in the case of open files, that's always the case, so you
		1717	always get a readiness notification instantly, and your read (or possibly
		1718	write) will still block on the disk I/O.
		1719
		1720	Another way to view it is that in the case of sockets, pipes, character
		1721	devices and so on, there is another party (the sender) that delivers data
		1722	on its own, but in the case of files, there is no such thing: the disk
		1723	will not send data on its own, simply because it doesn't know what you
		1724	wish to read - you would first have to request some data.
		1725
		1726	Since files are typically not-so-well supported by advanced notification
		1727	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1728	to files, even though you should not use it. The reason for this is
		1729	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1730	usually a tty, often a pipe, but also sometimes files or special devices
		1731	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1732	F</dev/urandom>), and even though the file might better be served with
		1733	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1734	it "just works" instead of freezing.
		1735
		1736	So avoid file descriptors pointing to files when you know it (e.g. use
		1737	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1738	when you rarely read from a file instead of from a socket, and want to
		1739	reuse the same code path.
		1740
1670	=head3 The special problem of fork	1741	=head3 The special problem of fork
1671		1742
1672	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1743	Some backends (epoll, kqueue, probably linuxaio) do not support C<fork ()>
1673	useless behaviour. Libev fully supports fork, but needs to be told about	1744	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1674	it in the child.	1745	to be told about it in the child if you want to continue to use it in the
		1746	child.
1675		1747
1676	To support fork in your programs, you either have to call	1748	To support fork in your child processes, you have to call C<ev_loop_fork
1677	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1749	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1678	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1750	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1679	C<EVBACKEND_POLL>.
1680		1751
1681	=head3 The special problem of SIGPIPE	1752	=head3 The special problem of SIGPIPE
1682		1753
1683	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1754	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1684	when writing to a pipe whose other end has been closed, your program gets	1755	when writing to a pipe whose other end has been closed, your program gets
…		…
1782	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1853	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1783	monotonic clock option helps a lot here).	1854	monotonic clock option helps a lot here).
1784		1855
1785	The callback is guaranteed to be invoked only I<after> its timeout has	1856	The callback is guaranteed to be invoked only I<after> its timeout has
1786	passed (not I<at>, so on systems with very low-resolution clocks this	1857	passed (not I<at>, so on systems with very low-resolution clocks this
1787	might introduce a small delay). If multiple timers become ready during the	1858	might introduce a small delay, see "the special problem of being too
		1859	early", below). If multiple timers become ready during the same loop
1788	same loop iteration then the ones with earlier time-out values are invoked	1860	iteration then the ones with earlier time-out values are invoked before
1789	before ones of the same priority with later time-out values (but this is	1861	ones of the same priority with later time-out values (but this is no
1790	no longer true when a callback calls C<ev_run> recursively).	1862	longer true when a callback calls C<ev_run> recursively).
1791		1863
1792	=head3 Be smart about timeouts	1864	=head3 Be smart about timeouts
1793		1865
1794	Many real-world problems involve some kind of timeout, usually for error	1866	Many real-world problems involve some kind of timeout, usually for error
1795	recovery. A typical example is an HTTP request - if the other side hangs,	1867	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1870		1942
1871	In this case, it would be more efficient to leave the C<ev_timer> alone,	1943	In this case, it would be more efficient to leave the C<ev_timer> alone,
1872	but remember the time of last activity, and check for a real timeout only	1944	but remember the time of last activity, and check for a real timeout only
1873	within the callback:	1945	within the callback:
1874		1946
		1947	ev_tstamp timeout = 60.;
1875	ev_tstamp last_activity; // time of last activity	1948	ev_tstamp last_activity; // time of last activity
		1949	ev_timer timer;
1876		1950
1877	static void	1951	static void
1878	callback (EV_P_ ev_timer *w, int revents)	1952	callback (EV_P_ ev_timer *w, int revents)
1879	{	1953	{
1880	ev_tstamp now = ev_now (EV_A);	1954	// calculate when the timeout would happen
1881	ev_tstamp timeout = last_activity + 60.;	1955	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1882		1956
1883	// if last_activity + 60. is older than now, we did time out	1957	// if negative, it means we the timeout already occurred
1884	if (timeout < now)	1958	if (after < 0.)
1885	{	1959	{
1886	// timeout occurred, take action	1960	// timeout occurred, take action
1887	}	1961	}
1888	else	1962	else
1889	{	1963	{
1890	// callback was invoked, but there was some activity, re-arm	1964	// callback was invoked, but there was some recent
1891	// the watcher to fire in last_activity + 60, which is	1965	// activity. simply restart the timer to time out
1892	// guaranteed to be in the future, so "again" is positive:	1966	// after "after" seconds, which is the earliest time
1893	w->repeat = timeout - now;	1967	// the timeout can occur.
		1968	ev_timer_set (w, after, 0.);
1894	ev_timer_again (EV_A_ w);	1969	ev_timer_start (EV_A_ w);
1895	}	1970	}
1896	}	1971	}
1897		1972
1898	To summarise the callback: first calculate the real timeout (defined	1973	To summarise the callback: first calculate in how many seconds the
1899	as "60 seconds after the last activity"), then check if that time has	1974	timeout will occur (by calculating the absolute time when it would occur,
1900	been reached, which means something I<did>, in fact, time out. Otherwise	1975	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1901	the callback was invoked too early (C<timeout> is in the future), so	1976	(EV_A)> from that).
1902	re-schedule the timer to fire at that future time, to see if maybe we have
1903	a timeout then.
1904		1977
1905	Note how C<ev_timer_again> is used, taking advantage of the	1978	If this value is negative, then we are already past the timeout, i.e. we
1906	C<ev_timer_again> optimisation when the timer is already running.	1979	timed out, and need to do whatever is needed in this case.
		1980
		1981	Otherwise, we now the earliest time at which the timeout would trigger,
		1982	and simply start the timer with this timeout value.
		1983
		1984	In other words, each time the callback is invoked it will check whether
		1985	the timeout occurred. If not, it will simply reschedule itself to check
		1986	again at the earliest time it could time out. Rinse. Repeat.
1907		1987
1908	This scheme causes more callback invocations (about one every 60 seconds	1988	This scheme causes more callback invocations (about one every 60 seconds
1909	minus half the average time between activity), but virtually no calls to	1989	minus half the average time between activity), but virtually no calls to
1910	libev to change the timeout.	1990	libev to change the timeout.
1911		1991
1912	To start the timer, simply initialise the watcher and set C<last_activity>	1992	To start the machinery, simply initialise the watcher and set
1913	to the current time (meaning we just have some activity :), then call the	1993	C<last_activity> to the current time (meaning there was some activity just
1914	callback, which will "do the right thing" and start the timer:	1994	now), then call the callback, which will "do the right thing" and start
		1995	the timer:
1915		1996
		1997	last_activity = ev_now (EV_A);
1916	ev_init (timer, callback);	1998	ev_init (&timer, callback);
1917	last_activity = ev_now (loop);	1999	callback (EV_A_ &timer, 0);
1918	callback (loop, timer, EV_TIMER);
1919		2000
1920	And when there is some activity, simply store the current time in	2001	When there is some activity, simply store the current time in
1921	C<last_activity>, no libev calls at all:	2002	C<last_activity>, no libev calls at all:
1922		2003
		2004	if (activity detected)
1923	last_activity = ev_now (loop);	2005	last_activity = ev_now (EV_A);
		2006
		2007	When your timeout value changes, then the timeout can be changed by simply
		2008	providing a new value, stopping the timer and calling the callback, which
		2009	will again do the right thing (for example, time out immediately :).
		2010
		2011	timeout = new_value;
		2012	ev_timer_stop (EV_A_ &timer);
		2013	callback (EV_A_ &timer, 0);
1924		2014
1925	This technique is slightly more complex, but in most cases where the	2015	This technique is slightly more complex, but in most cases where the
1926	time-out is unlikely to be triggered, much more efficient.	2016	time-out is unlikely to be triggered, much more efficient.
1927
1928	Changing the timeout is trivial as well (if it isn't hard-coded in the
1929	callback :) - just change the timeout and invoke the callback, which will
1930	fix things for you.
1931		2017
1932	=item 4. Wee, just use a double-linked list for your timeouts.	2018	=item 4. Wee, just use a double-linked list for your timeouts.
1933		2019
1934	If there is not one request, but many thousands (millions...), all	2020	If there is not one request, but many thousands (millions...), all
1935	employing some kind of timeout with the same timeout value, then one can	2021	employing some kind of timeout with the same timeout value, then one can
…		…
1962	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2048	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1963	rather complicated, but extremely efficient, something that really pays	2049	rather complicated, but extremely efficient, something that really pays
1964	off after the first million or so of active timers, i.e. it's usually	2050	off after the first million or so of active timers, i.e. it's usually
1965	overkill :)	2051	overkill :)
1966		2052
		2053	=head3 The special problem of being too early
		2054
		2055	If you ask a timer to call your callback after three seconds, then
		2056	you expect it to be invoked after three seconds - but of course, this
		2057	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2058	guaranteed to any precision by libev - imagine somebody suspending the
		2059	process with a STOP signal for a few hours for example.
		2060
		2061	So, libev tries to invoke your callback as soon as possible I<after> the
		2062	delay has occurred, but cannot guarantee this.
		2063
		2064	A less obvious failure mode is calling your callback too early: many event
		2065	loops compare timestamps with a "elapsed delay >= requested delay", but
		2066	this can cause your callback to be invoked much earlier than you would
		2067	expect.
		2068
		2069	To see why, imagine a system with a clock that only offers full second
		2070	resolution (think windows if you can't come up with a broken enough OS
		2071	yourself). If you schedule a one-second timer at the time 500.9, then the
		2072	event loop will schedule your timeout to elapse at a system time of 500
		2073	(500.9 truncated to the resolution) + 1, or 501.
		2074
		2075	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2076	501" and invoke the callback 0.1s after it was started, even though a
		2077	one-second delay was requested - this is being "too early", despite best
		2078	intentions.
		2079
		2080	This is the reason why libev will never invoke the callback if the elapsed
		2081	delay equals the requested delay, but only when the elapsed delay is
		2082	larger than the requested delay. In the example above, libev would only invoke
		2083	the callback at system time 502, or 1.1s after the timer was started.
		2084
		2085	So, while libev cannot guarantee that your callback will be invoked
		2086	exactly when requested, it I<can> and I<does> guarantee that the requested
		2087	delay has actually elapsed, or in other words, it always errs on the "too
		2088	late" side of things.
		2089
1967	=head3 The special problem of time updates	2090	=head3 The special problem of time updates
1968		2091
1969	Establishing the current time is a costly operation (it usually takes at	2092	Establishing the current time is a costly operation (it usually takes
1970	least two system calls): EV therefore updates its idea of the current	2093	at least one system call): EV therefore updates its idea of the current
1971	time only before and after C<ev_run> collects new events, which causes a	2094	time only before and after C<ev_run> collects new events, which causes a
1972	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2095	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1973	lots of events in one iteration.	2096	lots of events in one iteration.
1974		2097
1975	The relative timeouts are calculated relative to the C<ev_now ()>	2098	The relative timeouts are calculated relative to the C<ev_now ()>
1976	time. This is usually the right thing as this timestamp refers to the time	2099	time. This is usually the right thing as this timestamp refers to the time
1977	of the event triggering whatever timeout you are modifying/starting. If	2100	of the event triggering whatever timeout you are modifying/starting. If
1978	you suspect event processing to be delayed and you I<need> to base the	2101	you suspect event processing to be delayed and you I<need> to base the
1979	timeout on the current time, use something like this to adjust for this:	2102	timeout on the current time, use something like the following to adjust
		2103	for it:
1980		2104
1981	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2105	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1982		2106
1983	If the event loop is suspended for a long time, you can also force an	2107	If the event loop is suspended for a long time, you can also force an
1984	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2108	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1985	()>.	2109	()>, although that will push the event time of all outstanding events
		2110	further into the future.
		2111
		2112	=head3 The special problem of unsynchronised clocks
		2113
		2114	Modern systems have a variety of clocks - libev itself uses the normal
		2115	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2116	jumps).
		2117
		2118	Neither of these clocks is synchronised with each other or any other clock
		2119	on the system, so C<ev_time ()> might return a considerably different time
		2120	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2121	a call to C<gettimeofday> might return a second count that is one higher
		2122	than a directly following call to C<time>.
		2123
		2124	The moral of this is to only compare libev-related timestamps with
		2125	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2126	a second or so.
		2127
		2128	One more problem arises due to this lack of synchronisation: if libev uses
		2129	the system monotonic clock and you compare timestamps from C<ev_time>
		2130	or C<ev_now> from when you started your timer and when your callback is
		2131	invoked, you will find that sometimes the callback is a bit "early".
		2132
		2133	This is because C<ev_timer>s work in real time, not wall clock time, so
		2134	libev makes sure your callback is not invoked before the delay happened,
		2135	I<measured according to the real time>, not the system clock.
		2136
		2137	If your timeouts are based on a physical timescale (e.g. "time out this
		2138	connection after 100 seconds") then this shouldn't bother you as it is
		2139	exactly the right behaviour.
		2140
		2141	If you want to compare wall clock/system timestamps to your timers, then
		2142	you need to use C<ev_periodic>s, as these are based on the wall clock
		2143	time, where your comparisons will always generate correct results.
1986		2144
1987	=head3 The special problems of suspended animation	2145	=head3 The special problems of suspended animation
1988		2146
1989	When you leave the server world it is quite customary to hit machines that	2147	When you leave the server world it is quite customary to hit machines that
1990	can suspend/hibernate - what happens to the clocks during such a suspend?	2148	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
2020		2178
2021	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2179	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
2022		2180
2023	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2181	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
2024		2182
2025	Configure the timer to trigger after C<after> seconds. If C<repeat>	2183	Configure the timer to trigger after C<after> seconds (fractional and
2026	is C<0.>, then it will automatically be stopped once the timeout is	2184	negative values are supported). If C<repeat> is C<0.>, then it will
2027	reached. If it is positive, then the timer will automatically be	2185	automatically be stopped once the timeout is reached. If it is positive,
2028	configured to trigger again C<repeat> seconds later, again, and again,	2186	then the timer will automatically be configured to trigger again C<repeat>
2029	until stopped manually.	2187	seconds later, again, and again, until stopped manually.
2030		2188
2031	The timer itself will do a best-effort at avoiding drift, that is, if	2189	The timer itself will do a best-effort at avoiding drift, that is, if
2032	you configure a timer to trigger every 10 seconds, then it will normally	2190	you configure a timer to trigger every 10 seconds, then it will normally
2033	trigger at exactly 10 second intervals. If, however, your program cannot	2191	trigger at exactly 10 second intervals. If, however, your program cannot
2034	keep up with the timer (because it takes longer than those 10 seconds to	2192	keep up with the timer (because it takes longer than those 10 seconds to
2035	do stuff) the timer will not fire more than once per event loop iteration.	2193	do stuff) the timer will not fire more than once per event loop iteration.
2036		2194
2037	=item ev_timer_again (loop, ev_timer *)	2195	=item ev_timer_again (loop, ev_timer *)
2038		2196
2039	This will act as if the timer timed out and restart it again if it is	2197	This will act as if the timer timed out, and restarts it again if it is
2040	repeating. The exact semantics are:	2198	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2199	timeout to the C<repeat> value and calling C<ev_timer_start>.
2041		2200
		2201	The exact semantics are as in the following rules, all of which will be
		2202	applied to the watcher:
		2203
		2204	=over 4
		2205
2042	If the timer is pending, its pending status is cleared.	2206	=item If the timer is pending, the pending status is always cleared.
2043		2207
2044	If the timer is started but non-repeating, stop it (as if it timed out).	2208	=item If the timer is started but non-repeating, stop it (as if it timed
		2209	out, without invoking it).
2045		2210
2046	If the timer is repeating, either start it if necessary (with the	2211	=item If the timer is repeating, make the C<repeat> value the new timeout
2047	C<repeat> value), or reset the running timer to the C<repeat> value.	2212	and start the timer, if necessary.
2048		2213
		2214	=back
		2215
2049	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2216	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2050	usage example.	2217	usage example.
2051		2218
2052	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2219	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2053		2220
2054	Returns the remaining time until a timer fires. If the timer is active,	2221	Returns the remaining time until a timer fires. If the timer is active,
…		…
2107	Periodic watchers are also timers of a kind, but they are very versatile	2274	Periodic watchers are also timers of a kind, but they are very versatile
2108	(and unfortunately a bit complex).	2275	(and unfortunately a bit complex).
2109		2276
2110	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2277	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2111	relative time, the physical time that passes) but on wall clock time	2278	relative time, the physical time that passes) but on wall clock time
2112	(absolute time, the thing you can read on your calender or clock). The	2279	(absolute time, the thing you can read on your calendar or clock). The
2113	difference is that wall clock time can run faster or slower than real	2280	difference is that wall clock time can run faster or slower than real
2114	time, and time jumps are not uncommon (e.g. when you adjust your	2281	time, and time jumps are not uncommon (e.g. when you adjust your
2115	wrist-watch).	2282	wrist-watch).
2116		2283
2117	You can tell a periodic watcher to trigger after some specific point	2284	You can tell a periodic watcher to trigger after some specific point
…		…
2122	C<ev_timer>, which would still trigger roughly 10 seconds after starting	2289	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2123	it, as it uses a relative timeout).	2290	it, as it uses a relative timeout).
2124		2291
2125	C<ev_periodic> watchers can also be used to implement vastly more complex	2292	C<ev_periodic> watchers can also be used to implement vastly more complex
2126	timers, such as triggering an event on each "midnight, local time", or	2293	timers, such as triggering an event on each "midnight, local time", or
2127	other complicated rules. This cannot be done with C<ev_timer> watchers, as	2294	other complicated rules. This cannot easily be done with C<ev_timer>
2128	those cannot react to time jumps.	2295	watchers, as those cannot react to time jumps.
2129		2296
2130	As with timers, the callback is guaranteed to be invoked only when the	2297	As with timers, the callback is guaranteed to be invoked only when the
2131	point in time where it is supposed to trigger has passed. If multiple	2298	point in time where it is supposed to trigger has passed. If multiple
2132	timers become ready during the same loop iteration then the ones with	2299	timers become ready during the same loop iteration then the ones with
2133	earlier time-out values are invoked before ones with later time-out values	2300	earlier time-out values are invoked before ones with later time-out values
…		…
2174		2341
2175	Another way to think about it (for the mathematically inclined) is that	2342	Another way to think about it (for the mathematically inclined) is that
2176	C<ev_periodic> will try to run the callback in this mode at the next possible	2343	C<ev_periodic> will try to run the callback in this mode at the next possible
2177	time where C<time = offset (mod interval)>, regardless of any time jumps.	2344	time where C<time = offset (mod interval)>, regardless of any time jumps.
2178		2345
2179	For numerical stability it is preferable that the C<offset> value is near	2346	The C<interval> I<MUST> be positive, and for numerical stability, the
2180	C<ev_now ()> (the current time), but there is no range requirement for	2347	interval value should be higher than C<1/8192> (which is around 100
2181	this value, and in fact is often specified as zero.	2348	microseconds) and C<offset> should be higher than C<0> and should have
		2349	at most a similar magnitude as the current time (say, within a factor of
		2350	ten). Typical values for offset are, in fact, C<0> or something between
		2351	C<0> and C<interval>, which is also the recommended range.
2182		2352
2183	Note also that there is an upper limit to how often a timer can fire (CPU	2353	Note also that there is an upper limit to how often a timer can fire (CPU
2184	speed for example), so if C<interval> is very small then timing stability	2354	speed for example), so if C<interval> is very small then timing stability
2185	will of course deteriorate. Libev itself tries to be exact to be about one	2355	will of course deteriorate. Libev itself tries to be exact to be about one
2186	millisecond (if the OS supports it and the machine is fast enough).	2356	millisecond (if the OS supports it and the machine is fast enough).
…		…
2216		2386
2217	NOTE: I<< This callback must always return a time that is higher than or	2387	NOTE: I<< This callback must always return a time that is higher than or
2218	equal to the passed C<now> value >>.	2388	equal to the passed C<now> value >>.
2219		2389
2220	This can be used to create very complex timers, such as a timer that	2390	This can be used to create very complex timers, such as a timer that
2221	triggers on "next midnight, local time". To do this, you would calculate the	2391	triggers on "next midnight, local time". To do this, you would calculate
2222	next midnight after C<now> and return the timestamp value for this. How	2392	the next midnight after C<now> and return the timestamp value for
2223	you do this is, again, up to you (but it is not trivial, which is the main	2393	this. Here is a (completely untested, no error checking) example on how to
2224	reason I omitted it as an example).	2394	do this:
		2395
		2396	#include <time.h>
		2397
		2398	static ev_tstamp
		2399	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2400	{
		2401	time_t tnow = (time_t)now;
		2402	struct tm tm;
		2403	localtime_r (&tnow, &tm);
		2404
		2405	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2406	++tm.tm_mday; // midnight next day
		2407
		2408	return mktime (&tm);
		2409	}
		2410
		2411	Note: this code might run into trouble on days that have more then two
		2412	midnights (beginning and end).
2225		2413
2226	=back	2414	=back
2227		2415
2228	=item ev_periodic_again (loop, ev_periodic *)	2416	=item ev_periodic_again (loop, ev_periodic *)
2229		2417
…		…
2294		2482
2295	ev_periodic hourly_tick;	2483	ev_periodic hourly_tick;
2296	ev_periodic_init (&hourly_tick, clock_cb,	2484	ev_periodic_init (&hourly_tick, clock_cb,
2297	fmod (ev_now (loop), 3600.), 3600., 0);	2485	fmod (ev_now (loop), 3600.), 3600., 0);
2298	ev_periodic_start (loop, &hourly_tick);	2486	ev_periodic_start (loop, &hourly_tick);
2299		2487
2300		2488
2301	=head2 C<ev_signal> - signal me when a signal gets signalled!	2489	=head2 C<ev_signal> - signal me when a signal gets signalled!
2302		2490
2303	Signal watchers will trigger an event when the process receives a specific	2491	Signal watchers will trigger an event when the process receives a specific
2304	signal one or more times. Even though signals are very asynchronous, libev	2492	signal one or more times. Even though signals are very asynchronous, libev
…		…
2314	only within the same loop, i.e. you can watch for C<SIGINT> in your	2502	only within the same loop, i.e. you can watch for C<SIGINT> in your
2315	default loop and for C<SIGIO> in another loop, but you cannot watch for	2503	default loop and for C<SIGIO> in another loop, but you cannot watch for
2316	C<SIGINT> in both the default loop and another loop at the same time. At	2504	C<SIGINT> in both the default loop and another loop at the same time. At
2317	the moment, C<SIGCHLD> is permanently tied to the default loop.	2505	the moment, C<SIGCHLD> is permanently tied to the default loop.
2318		2506
2319	When the first watcher gets started will libev actually register something	2507	Only after the first watcher for a signal is started will libev actually
2320	with the kernel (thus it coexists with your own signal handlers as long as	2508	register something with the kernel. It thus coexists with your own signal
2321	you don't register any with libev for the same signal).	2509	handlers as long as you don't register any with libev for the same signal.
2322		2510
2323	If possible and supported, libev will install its handlers with	2511	If possible and supported, libev will install its handlers with
2324	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2512	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2325	not be unduly interrupted. If you have a problem with system calls getting	2513	not be unduly interrupted. If you have a problem with system calls getting
2326	interrupted by signals you can block all signals in an C<ev_check> watcher	2514	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2329	=head3 The special problem of inheritance over fork/execve/pthread_create	2517	=head3 The special problem of inheritance over fork/execve/pthread_create
2330		2518
2331	Both the signal mask (C<sigprocmask>) and the signal disposition	2519	Both the signal mask (C<sigprocmask>) and the signal disposition
2332	(C<sigaction>) are unspecified after starting a signal watcher (and after	2520	(C<sigaction>) are unspecified after starting a signal watcher (and after
2333	stopping it again), that is, libev might or might not block the signal,	2521	stopping it again), that is, libev might or might not block the signal,
2334	and might or might not set or restore the installed signal handler.	2522	and might or might not set or restore the installed signal handler (but
		2523	see C<EVFLAG_NOSIGMASK>).
2335		2524
2336	While this does not matter for the signal disposition (libev never	2525	While this does not matter for the signal disposition (libev never
2337	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2526	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2338	C<execve>), this matters for the signal mask: many programs do not expect	2527	C<execve>), this matters for the signal mask: many programs do not expect
2339	certain signals to be blocked.	2528	certain signals to be blocked.
…		…
2510		2699
2511	=head2 C<ev_stat> - did the file attributes just change?	2700	=head2 C<ev_stat> - did the file attributes just change?
2512		2701
2513	This watches a file system path for attribute changes. That is, it calls	2702	This watches a file system path for attribute changes. That is, it calls
2514	C<stat> on that path in regular intervals (or when the OS says it changed)	2703	C<stat> on that path in regular intervals (or when the OS says it changed)
2515	and sees if it changed compared to the last time, invoking the callback if	2704	and sees if it changed compared to the last time, invoking the callback
2516	it did.	2705	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2706	happen after the watcher has been started will be reported.
2517		2707
2518	The path does not need to exist: changing from "path exists" to "path does	2708	The path does not need to exist: changing from "path exists" to "path does
2519	not exist" is a status change like any other. The condition "path does not	2709	not exist" is a status change like any other. The condition "path does not
2520	exist" (or more correctly "path cannot be stat'ed") is signified by the	2710	exist" (or more correctly "path cannot be stat'ed") is signified by the
2521	C<st_nlink> field being zero (which is otherwise always forced to be at	2711	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2751	Apart from keeping your process non-blocking (which is a useful	2941	Apart from keeping your process non-blocking (which is a useful
2752	effect on its own sometimes), idle watchers are a good place to do	2942	effect on its own sometimes), idle watchers are a good place to do
2753	"pseudo-background processing", or delay processing stuff to after the	2943	"pseudo-background processing", or delay processing stuff to after the
2754	event loop has handled all outstanding events.	2944	event loop has handled all outstanding events.
2755		2945
		2946	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2947
		2948	As long as there is at least one active idle watcher, libev will never
		2949	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2950	For this to work, the idle watcher doesn't need to be invoked at all - the
		2951	lowest priority will do.
		2952
		2953	This mode of operation can be useful together with an C<ev_check> watcher,
		2954	to do something on each event loop iteration - for example to balance load
		2955	between different connections.
		2956
		2957	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2958	example.
		2959
2756	=head3 Watcher-Specific Functions and Data Members	2960	=head3 Watcher-Specific Functions and Data Members
2757		2961
2758	=over 4	2962	=over 4
2759		2963
2760	=item ev_idle_init (ev_idle *, callback)	2964	=item ev_idle_init (ev_idle *, callback)
…		…
2771	callback, free it. Also, use no error checking, as usual.	2975	callback, free it. Also, use no error checking, as usual.
2772		2976
2773	static void	2977	static void
2774	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2978	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2775	{	2979	{
		2980	// stop the watcher
		2981	ev_idle_stop (loop, w);
		2982
		2983	// now we can free it
2776	free (w);	2984	free (w);
		2985
2777	// now do something you wanted to do when the program has	2986	// now do something you wanted to do when the program has
2778	// no longer anything immediate to do.	2987	// no longer anything immediate to do.
2779	}	2988	}
2780		2989
2781	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2990	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2783	ev_idle_start (loop, idle_watcher);	2992	ev_idle_start (loop, idle_watcher);
2784		2993
2785		2994
2786	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2995	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2787		2996
2788	Prepare and check watchers are usually (but not always) used in pairs:	2997	Prepare and check watchers are often (but not always) used in pairs:
2789	prepare watchers get invoked before the process blocks and check watchers	2998	prepare watchers get invoked before the process blocks and check watchers
2790	afterwards.	2999	afterwards.
2791		3000
2792	You I<must not> call C<ev_run> or similar functions that enter	3001	You I<must not> call C<ev_run> (or similar functions that enter the
2793	the current event loop from either C<ev_prepare> or C<ev_check>	3002	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2794	watchers. Other loops than the current one are fine, however. The	3003	C<ev_check> watchers. Other loops than the current one are fine,
2795	rationale behind this is that you do not need to check for recursion in	3004	however. The rationale behind this is that you do not need to check
2796	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3005	for recursion in those watchers, i.e. the sequence will always be
2797	C<ev_check> so if you have one watcher of each kind they will always be	3006	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2798	called in pairs bracketing the blocking call.	3007	kind they will always be called in pairs bracketing the blocking call.
2799		3008
2800	Their main purpose is to integrate other event mechanisms into libev and	3009	Their main purpose is to integrate other event mechanisms into libev and
2801	their use is somewhat advanced. They could be used, for example, to track	3010	their use is somewhat advanced. They could be used, for example, to track
2802	variable changes, implement your own watchers, integrate net-snmp or a	3011	variable changes, implement your own watchers, integrate net-snmp or a
2803	coroutine library and lots more. They are also occasionally useful if	3012	coroutine library and lots more. They are also occasionally useful if
…		…
2821	with priority higher than or equal to the event loop and one coroutine	3030	with priority higher than or equal to the event loop and one coroutine
2822	of lower priority, but only once, using idle watchers to keep the event	3031	of lower priority, but only once, using idle watchers to keep the event
2823	loop from blocking if lower-priority coroutines are active, thus mapping	3032	loop from blocking if lower-priority coroutines are active, thus mapping
2824	low-priority coroutines to idle/background tasks).	3033	low-priority coroutines to idle/background tasks).
2825		3034
2826	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3035	When used for this purpose, it is recommended to give C<ev_check> watchers
2827	priority, to ensure that they are being run before any other watchers	3036	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2828	after the poll (this doesn't matter for C<ev_prepare> watchers).	3037	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3038	watchers).
2829		3039
2830	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3040	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2831	activate ("feed") events into libev. While libev fully supports this, they	3041	activate ("feed") events into libev. While libev fully supports this, they
2832	might get executed before other C<ev_check> watchers did their job. As	3042	might get executed before other C<ev_check> watchers did their job. As
2833	C<ev_check> watchers are often used to embed other (non-libev) event	3043	C<ev_check> watchers are often used to embed other (non-libev) event
2834	loops those other event loops might be in an unusable state until their	3044	loops those other event loops might be in an unusable state until their
2835	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3045	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2836	others).	3046	others).
		3047
		3048	=head3 Abusing an C<ev_check> watcher for its side-effect
		3049
		3050	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3051	useful because they are called once per event loop iteration. For
		3052	example, if you want to handle a large number of connections fairly, you
		3053	normally only do a bit of work for each active connection, and if there
		3054	is more work to do, you wait for the next event loop iteration, so other
		3055	connections have a chance of making progress.
		3056
		3057	Using an C<ev_check> watcher is almost enough: it will be called on the
		3058	next event loop iteration. However, that isn't as soon as possible -
		3059	without external events, your C<ev_check> watcher will not be invoked.
		3060
		3061	This is where C<ev_idle> watchers come in handy - all you need is a
		3062	single global idle watcher that is active as long as you have one active
		3063	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3064	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3065	invoked. Neither watcher alone can do that.
2837		3066
2838	=head3 Watcher-Specific Functions and Data Members	3067	=head3 Watcher-Specific Functions and Data Members
2839		3068
2840	=over 4	3069	=over 4
2841		3070
…		…
3042		3271
3043	=over 4	3272	=over 4
3044		3273
3045	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3274	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
3046		3275
3047	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3276	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
3048		3277
3049	Configures the watcher to embed the given loop, which must be	3278	Configures the watcher to embed the given loop, which must be
3050	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3279	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
3051	invoked automatically, otherwise it is the responsibility of the callback	3280	invoked automatically, otherwise it is the responsibility of the callback
3052	to invoke it (it will continue to be called until the sweep has been done,	3281	to invoke it (it will continue to be called until the sweep has been done,
…		…
3073	used).	3302	used).
3074		3303
3075	struct ev_loop *loop_hi = ev_default_init (0);	3304	struct ev_loop *loop_hi = ev_default_init (0);
3076	struct ev_loop *loop_lo = 0;	3305	struct ev_loop *loop_lo = 0;
3077	ev_embed embed;	3306	ev_embed embed;
3078		3307
3079	// see if there is a chance of getting one that works	3308	// see if there is a chance of getting one that works
3080	// (remember that a flags value of 0 means autodetection)	3309	// (remember that a flags value of 0 means autodetection)
3081	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3310	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3082	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3311	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3083	: 0;	3312	: 0;
…		…
3097	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3326	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3098		3327
3099	struct ev_loop *loop = ev_default_init (0);	3328	struct ev_loop *loop = ev_default_init (0);
3100	struct ev_loop *loop_socket = 0;	3329	struct ev_loop *loop_socket = 0;
3101	ev_embed embed;	3330	ev_embed embed;
3102		3331
3103	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3332	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3104	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3333	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3105	{	3334	{
3106	ev_embed_init (&embed, 0, loop_socket);	3335	ev_embed_init (&embed, 0, loop_socket);
3107	ev_embed_start (loop, &embed);	3336	ev_embed_start (loop, &embed);
…		…
3115		3344
3116	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3345	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3117		3346
3118	Fork watchers are called when a C<fork ()> was detected (usually because	3347	Fork watchers are called when a C<fork ()> was detected (usually because
3119	whoever is a good citizen cared to tell libev about it by calling	3348	whoever is a good citizen cared to tell libev about it by calling
3120	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3349	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3121	event loop blocks next and before C<ev_check> watchers are being called,	3350	and before C<ev_check> watchers are being called, and only in the child
3122	and only in the child after the fork. If whoever good citizen calling	3351	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3123	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3352	and calls it in the wrong process, the fork handlers will be invoked, too,
3124	handlers will be invoked, too, of course.	3353	of course.
3125		3354
3126	=head3 The special problem of life after fork - how is it possible?	3355	=head3 The special problem of life after fork - how is it possible?
3127		3356
3128	Most uses of C<fork()> consist of forking, then some simple calls to set	3357	Most uses of C<fork ()> consist of forking, then some simple calls to set
3129	up/change the process environment, followed by a call to C<exec()>. This	3358	up/change the process environment, followed by a call to C<exec()>. This
3130	sequence should be handled by libev without any problems.	3359	sequence should be handled by libev without any problems.
3131		3360
3132	This changes when the application actually wants to do event handling	3361	This changes when the application actually wants to do event handling
3133	in the child, or both parent in child, in effect "continuing" after the	3362	in the child, or both parent in child, in effect "continuing" after the
…		…
3210	atexit (program_exits);	3439	atexit (program_exits);
3211		3440
3212		3441
3213	=head2 C<ev_async> - how to wake up an event loop	3442	=head2 C<ev_async> - how to wake up an event loop
3214		3443
3215	In general, you cannot use an C<ev_run> from multiple threads or other	3444	In general, you cannot use an C<ev_loop> from multiple threads or other
3216	asynchronous sources such as signal handlers (as opposed to multiple event	3445	asynchronous sources such as signal handlers (as opposed to multiple event
3217	loops - those are of course safe to use in different threads).	3446	loops - those are of course safe to use in different threads).
3218		3447
3219	Sometimes, however, you need to wake up an event loop you do not control,	3448	Sometimes, however, you need to wake up an event loop you do not control,
3220	for example because it belongs to another thread. This is what C<ev_async>	3449	for example because it belongs to another thread. This is what C<ev_async>
…		…
3222	it by calling C<ev_async_send>, which is thread- and signal safe.	3451	it by calling C<ev_async_send>, which is thread- and signal safe.
3223		3452
3224	This functionality is very similar to C<ev_signal> watchers, as signals,	3453	This functionality is very similar to C<ev_signal> watchers, as signals,
3225	too, are asynchronous in nature, and signals, too, will be compressed	3454	too, are asynchronous in nature, and signals, too, will be compressed
3226	(i.e. the number of callback invocations may be less than the number of	3455	(i.e. the number of callback invocations may be less than the number of
3227	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind	3456	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3228	of "global async watchers" by using a watcher on an otherwise unused	3457	of "global async watchers" by using a watcher on an otherwise unused
3229	signal, and C<ev_feed_signal> to signal this watcher from another thread,	3458	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3230	even without knowing which loop owns the signal.	3459	even without knowing which loop owns the signal.
3231
3232	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3233	just the default loop.
3234		3460
3235	=head3 Queueing	3461	=head3 Queueing
3236		3462
3237	C<ev_async> does not support queueing of data in any way. The reason	3463	C<ev_async> does not support queueing of data in any way. The reason
3238	is that the author does not know of a simple (or any) algorithm for a	3464	is that the author does not know of a simple (or any) algorithm for a
…		…
3330	trust me.	3556	trust me.
3331		3557
3332	=item ev_async_send (loop, ev_async *)	3558	=item ev_async_send (loop, ev_async *)
3333		3559
3334	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3560	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3335	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3561	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3562	returns.
		3563
3336	C<ev_feed_event>, this call is safe to do from other threads, signal or	3564	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3337	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3565	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3338	section below on what exactly this means).	3566	embedding section below on what exactly this means).
3339		3567
3340	Note that, as with other watchers in libev, multiple events might get	3568	Note that, as with other watchers in libev, multiple events might get
3341	compressed into a single callback invocation (another way to look at this	3569	compressed into a single callback invocation (another way to look at
3342	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3570	this is that C<ev_async> watchers are level-triggered: they are set on
3343	reset when the event loop detects that).	3571	C<ev_async_send>, reset when the event loop detects that).
3344		3572
3345	This call incurs the overhead of a system call only once per event loop	3573	This call incurs the overhead of at most one extra system call per event
3346	iteration, so while the overhead might be noticeable, it doesn't apply to	3574	loop iteration, if the event loop is blocked, and no syscall at all if
3347	repeated calls to C<ev_async_send> for the same event loop.	3575	the event loop (or your program) is processing events. That means that
		3576	repeated calls are basically free (there is no need to avoid calls for
		3577	performance reasons) and that the overhead becomes smaller (typically
		3578	zero) under load.
3348		3579
3349	=item bool = ev_async_pending (ev_async *)	3580	=item bool = ev_async_pending (ev_async *)
3350		3581
3351	Returns a non-zero value when C<ev_async_send> has been called on the	3582	Returns a non-zero value when C<ev_async_send> has been called on the
3352	watcher but the event has not yet been processed (or even noted) by the	3583	watcher but the event has not yet been processed (or even noted) by the
…		…
3369		3600
3370	There are some other functions of possible interest. Described. Here. Now.	3601	There are some other functions of possible interest. Described. Here. Now.
3371		3602
3372	=over 4	3603	=over 4
3373		3604
3374	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3605	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3375		3606
3376	This function combines a simple timer and an I/O watcher, calls your	3607	This function combines a simple timer and an I/O watcher, calls your
3377	callback on whichever event happens first and automatically stops both	3608	callback on whichever event happens first and automatically stops both
3378	watchers. This is useful if you want to wait for a single event on an fd	3609	watchers. This is useful if you want to wait for a single event on an fd
3379	or timeout without having to allocate/configure/start/stop/free one or	3610	or timeout without having to allocate/configure/start/stop/free one or
…		…
3407	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3638	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3408		3639
3409	=item ev_feed_fd_event (loop, int fd, int revents)	3640	=item ev_feed_fd_event (loop, int fd, int revents)
3410		3641
3411	Feed an event on the given fd, as if a file descriptor backend detected	3642	Feed an event on the given fd, as if a file descriptor backend detected
3412	the given events it.	3643	the given events.
3413		3644
3414	=item ev_feed_signal_event (loop, int signum)	3645	=item ev_feed_signal_event (loop, int signum)
3415		3646
3416	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,	3647	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3417	which is async-safe.	3648	which is async-safe.
…		…
3423		3654
3424	This section explains some common idioms that are not immediately	3655	This section explains some common idioms that are not immediately
3425	obvious. Note that examples are sprinkled over the whole manual, and this	3656	obvious. Note that examples are sprinkled over the whole manual, and this
3426	section only contains stuff that wouldn't fit anywhere else.	3657	section only contains stuff that wouldn't fit anywhere else.
3427		3658
3428	=over 4	3659	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3429		3660
3430	=item Model/nested event loop invocations and exit conditions.	3661	Each watcher has, by default, a C<void *data> member that you can read
		3662	or modify at any time: libev will completely ignore it. This can be used
		3663	to associate arbitrary data with your watcher. If you need more data and
		3664	don't want to allocate memory separately and store a pointer to it in that
		3665	data member, you can also "subclass" the watcher type and provide your own
		3666	data:
		3667
		3668	struct my_io
		3669	{
		3670	ev_io io;
		3671	int otherfd;
		3672	void *somedata;
		3673	struct whatever *mostinteresting;
		3674	};
		3675
		3676	...
		3677	struct my_io w;
		3678	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3679
		3680	And since your callback will be called with a pointer to the watcher, you
		3681	can cast it back to your own type:
		3682
		3683	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3684	{
		3685	struct my_io *w = (struct my_io *)w_;
		3686	...
		3687	}
		3688
		3689	More interesting and less C-conformant ways of casting your callback
		3690	function type instead have been omitted.
		3691
		3692	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3693
		3694	Another common scenario is to use some data structure with multiple
		3695	embedded watchers, in effect creating your own watcher that combines
		3696	multiple libev event sources into one "super-watcher":
		3697
		3698	struct my_biggy
		3699	{
		3700	int some_data;
		3701	ev_timer t1;
		3702	ev_timer t2;
		3703	}
		3704
		3705	In this case getting the pointer to C<my_biggy> is a bit more
		3706	complicated: Either you store the address of your C<my_biggy> struct in
		3707	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3708	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3709	real programmers):
		3710
		3711	#include <stddef.h>
		3712
		3713	static void
		3714	t1_cb (EV_P_ ev_timer *w, int revents)
		3715	{
		3716	struct my_biggy big = (struct my_biggy *)
		3717	(((char *)w) - offsetof (struct my_biggy, t1));
		3718	}
		3719
		3720	static void
		3721	t2_cb (EV_P_ ev_timer *w, int revents)
		3722	{
		3723	struct my_biggy big = (struct my_biggy *)
		3724	(((char *)w) - offsetof (struct my_biggy, t2));
		3725	}
		3726
		3727	=head2 AVOIDING FINISHING BEFORE RETURNING
		3728
		3729	Often you have structures like this in event-based programs:
		3730
		3731	callback ()
		3732	{
		3733	free (request);
		3734	}
		3735
		3736	request = start_new_request (..., callback);
		3737
		3738	The intent is to start some "lengthy" operation. The C<request> could be
		3739	used to cancel the operation, or do other things with it.
		3740
		3741	It's not uncommon to have code paths in C<start_new_request> that
		3742	immediately invoke the callback, for example, to report errors. Or you add
		3743	some caching layer that finds that it can skip the lengthy aspects of the
		3744	operation and simply invoke the callback with the result.
		3745
		3746	The problem here is that this will happen I<before> C<start_new_request>
		3747	has returned, so C<request> is not set.
		3748
		3749	Even if you pass the request by some safer means to the callback, you
		3750	might want to do something to the request after starting it, such as
		3751	canceling it, which probably isn't working so well when the callback has
		3752	already been invoked.
		3753
		3754	A common way around all these issues is to make sure that
		3755	C<start_new_request> I<always> returns before the callback is invoked. If
		3756	C<start_new_request> immediately knows the result, it can artificially
		3757	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3758	example, or more sneakily, by reusing an existing (stopped) watcher and
		3759	pushing it into the pending queue:
		3760
		3761	ev_set_cb (watcher, callback);
		3762	ev_feed_event (EV_A_ watcher, 0);
		3763
		3764	This way, C<start_new_request> can safely return before the callback is
		3765	invoked, while not delaying callback invocation too much.
		3766
		3767	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3431		3768
3432	Often (especially in GUI toolkits) there are places where you have	3769	Often (especially in GUI toolkits) there are places where you have
3433	I<modal> interaction, which is most easily implemented by recursively	3770	I<modal> interaction, which is most easily implemented by recursively
3434	invoking C<ev_run>.	3771	invoking C<ev_run>.
3435		3772
3436	This brings the problem of exiting - a callback might want to finish the	3773	This brings the problem of exiting - a callback might want to finish the
3437	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but	3774	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
3438	a modal "Are you sure?" dialog is still waiting), or just the nested one	3775	a modal "Are you sure?" dialog is still waiting), or just the nested one
3439	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some	3776	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
3440	other combination: In these cases, C<ev_break> will not work alone.	3777	other combination: In these cases, a simple C<ev_break> will not work.
3441		3778
3442	The solution is to maintain "break this loop" variable for each C<ev_run>	3779	The solution is to maintain "break this loop" variable for each C<ev_run>
3443	invocation, and use a loop around C<ev_run> until the condition is	3780	invocation, and use a loop around C<ev_run> until the condition is
3444	triggered, using C<EVRUN_ONCE>:	3781	triggered, using C<EVRUN_ONCE>:
3445		3782
…		…
3447	int exit_main_loop = 0;	3784	int exit_main_loop = 0;
3448		3785
3449	while (!exit_main_loop)	3786	while (!exit_main_loop)
3450	ev_run (EV_DEFAULT_ EVRUN_ONCE);	3787	ev_run (EV_DEFAULT_ EVRUN_ONCE);
3451		3788
3452	// in a model watcher	3789	// in a modal watcher
3453	int exit_nested_loop = 0;	3790	int exit_nested_loop = 0;
3454		3791
3455	while (!exit_nested_loop)	3792	while (!exit_nested_loop)
3456	ev_run (EV_A_ EVRUN_ONCE);	3793	ev_run (EV_A_ EVRUN_ONCE);
3457		3794
…		…
3464	exit_main_loop = 1;	3801	exit_main_loop = 1;
3465		3802
3466	// exit both	3803	// exit both
3467	exit_main_loop = exit_nested_loop = 1;	3804	exit_main_loop = exit_nested_loop = 1;
3468		3805
3469	=back	3806	=head2 THREAD LOCKING EXAMPLE
		3807
		3808	Here is a fictitious example of how to run an event loop in a different
		3809	thread from where callbacks are being invoked and watchers are
		3810	created/added/removed.
		3811
		3812	For a real-world example, see the C<EV::Loop::Async> perl module,
		3813	which uses exactly this technique (which is suited for many high-level
		3814	languages).
		3815
		3816	The example uses a pthread mutex to protect the loop data, a condition
		3817	variable to wait for callback invocations, an async watcher to notify the
		3818	event loop thread and an unspecified mechanism to wake up the main thread.
		3819
		3820	First, you need to associate some data with the event loop:
		3821
		3822	typedef struct {
		3823	mutex_t lock; /* global loop lock */
		3824	ev_async async_w;
		3825	thread_t tid;
		3826	cond_t invoke_cv;
		3827	} userdata;
		3828
		3829	void prepare_loop (EV_P)
		3830	{
		3831	// for simplicity, we use a static userdata struct.
		3832	static userdata u;
		3833
		3834	ev_async_init (&u->async_w, async_cb);
		3835	ev_async_start (EV_A_ &u->async_w);
		3836
		3837	pthread_mutex_init (&u->lock, 0);
		3838	pthread_cond_init (&u->invoke_cv, 0);
		3839
		3840	// now associate this with the loop
		3841	ev_set_userdata (EV_A_ u);
		3842	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3843	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3844
		3845	// then create the thread running ev_run
		3846	pthread_create (&u->tid, 0, l_run, EV_A);
		3847	}
		3848
		3849	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3850	solely to wake up the event loop so it takes notice of any new watchers
		3851	that might have been added:
		3852
		3853	static void
		3854	async_cb (EV_P_ ev_async *w, int revents)
		3855	{
		3856	// just used for the side effects
		3857	}
		3858
		3859	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3860	protecting the loop data, respectively.
		3861
		3862	static void
		3863	l_release (EV_P)
		3864	{
		3865	userdata *u = ev_userdata (EV_A);
		3866	pthread_mutex_unlock (&u->lock);
		3867	}
		3868
		3869	static void
		3870	l_acquire (EV_P)
		3871	{
		3872	userdata *u = ev_userdata (EV_A);
		3873	pthread_mutex_lock (&u->lock);
		3874	}
		3875
		3876	The event loop thread first acquires the mutex, and then jumps straight
		3877	into C<ev_run>:
		3878
		3879	void *
		3880	l_run (void *thr_arg)
		3881	{
		3882	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3883
		3884	l_acquire (EV_A);
		3885	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3886	ev_run (EV_A_ 0);
		3887	l_release (EV_A);
		3888
		3889	return 0;
		3890	}
		3891
		3892	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3893	signal the main thread via some unspecified mechanism (signals? pipe
		3894	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3895	have been called (in a while loop because a) spurious wakeups are possible
		3896	and b) skipping inter-thread-communication when there are no pending
		3897	watchers is very beneficial):
		3898
		3899	static void
		3900	l_invoke (EV_P)
		3901	{
		3902	userdata *u = ev_userdata (EV_A);
		3903
		3904	while (ev_pending_count (EV_A))
		3905	{
		3906	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3907	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3908	}
		3909	}
		3910
		3911	Now, whenever the main thread gets told to invoke pending watchers, it
		3912	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3913	thread to continue:
		3914
		3915	static void
		3916	real_invoke_pending (EV_P)
		3917	{
		3918	userdata *u = ev_userdata (EV_A);
		3919
		3920	pthread_mutex_lock (&u->lock);
		3921	ev_invoke_pending (EV_A);
		3922	pthread_cond_signal (&u->invoke_cv);
		3923	pthread_mutex_unlock (&u->lock);
		3924	}
		3925
		3926	Whenever you want to start/stop a watcher or do other modifications to an
		3927	event loop, you will now have to lock:
		3928
		3929	ev_timer timeout_watcher;
		3930	userdata *u = ev_userdata (EV_A);
		3931
		3932	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3933
		3934	pthread_mutex_lock (&u->lock);
		3935	ev_timer_start (EV_A_ &timeout_watcher);
		3936	ev_async_send (EV_A_ &u->async_w);
		3937	pthread_mutex_unlock (&u->lock);
		3938
		3939	Note that sending the C<ev_async> watcher is required because otherwise
		3940	an event loop currently blocking in the kernel will have no knowledge
		3941	about the newly added timer. By waking up the loop it will pick up any new
		3942	watchers in the next event loop iteration.
		3943
		3944	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3945
		3946	While the overhead of a callback that e.g. schedules a thread is small, it
		3947	is still an overhead. If you embed libev, and your main usage is with some
		3948	kind of threads or coroutines, you might want to customise libev so that
		3949	doesn't need callbacks anymore.
		3950
		3951	Imagine you have coroutines that you can switch to using a function
		3952	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3953	and that due to some magic, the currently active coroutine is stored in a
		3954	global called C<current_coro>. Then you can build your own "wait for libev
		3955	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3956	the differing C<;> conventions):
		3957
		3958	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3959	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3960
		3961	That means instead of having a C callback function, you store the
		3962	coroutine to switch to in each watcher, and instead of having libev call
		3963	your callback, you instead have it switch to that coroutine.
		3964
		3965	A coroutine might now wait for an event with a function called
		3966	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3967	matter when, or whether the watcher is active or not when this function is
		3968	called):
		3969
		3970	void
		3971	wait_for_event (ev_watcher *w)
		3972	{
		3973	ev_set_cb (w, current_coro);
		3974	switch_to (libev_coro);
		3975	}
		3976
		3977	That basically suspends the coroutine inside C<wait_for_event> and
		3978	continues the libev coroutine, which, when appropriate, switches back to
		3979	this or any other coroutine.
		3980
		3981	You can do similar tricks if you have, say, threads with an event queue -
		3982	instead of storing a coroutine, you store the queue object and instead of
		3983	switching to a coroutine, you push the watcher onto the queue and notify
		3984	any waiters.
		3985
		3986	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3987	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3988
		3989	// my_ev.h
		3990	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3991	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3992	#include "../libev/ev.h"
		3993
		3994	// my_ev.c
		3995	#define EV_H "my_ev.h"
		3996	#include "../libev/ev.c"
		3997
		3998	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3999	F<my_ev.c> into your project. When properly specifying include paths, you
		4000	can even use F<ev.h> as header file name directly.
3470		4001
3471		4002
3472	=head1 LIBEVENT EMULATION	4003	=head1 LIBEVENT EMULATION
3473		4004
3474	Libev offers a compatibility emulation layer for libevent. It cannot	4005	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3504		4035
3505	=back	4036	=back
3506		4037
3507	=head1 C++ SUPPORT	4038	=head1 C++ SUPPORT
3508		4039
		4040	=head2 C API
		4041
		4042	The normal C API should work fine when used from C++: both ev.h and the
		4043	libev sources can be compiled as C++. Therefore, code that uses the C API
		4044	will work fine.
		4045
		4046	Proper exception specifications might have to be added to callbacks passed
		4047	to libev: exceptions may be thrown only from watcher callbacks, all other
		4048	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4049	callbacks) must not throw exceptions, and might need a C<noexcept>
		4050	specification. If you have code that needs to be compiled as both C and
		4051	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4052
		4053	static void
		4054	fatal_error (const char *msg) EV_NOEXCEPT
		4055	{
		4056	perror (msg);
		4057	abort ();
		4058	}
		4059
		4060	...
		4061	ev_set_syserr_cb (fatal_error);
		4062
		4063	The only API functions that can currently throw exceptions are C<ev_run>,
		4064	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4065	because it runs cleanup watchers).
		4066
		4067	Throwing exceptions in watcher callbacks is only supported if libev itself
		4068	is compiled with a C++ compiler or your C and C++ environments allow
		4069	throwing exceptions through C libraries (most do).
		4070
		4071	=head2 C++ API
		4072
3509	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4073	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3510	you to use some convenience methods to start/stop watchers and also change	4074	you to use some convenience methods to start/stop watchers and also change
3511	the callback model to a model using method callbacks on objects.	4075	the callback model to a model using method callbacks on objects.
3512		4076
3513	To use it,	4077	To use it,
3514		4078
3515	#include <ev++.h>	4079	#include <ev++.h>
3516		4080
3517	This automatically includes F<ev.h> and puts all of its definitions (many	4081	This automatically includes F<ev.h> and puts all of its definitions (many
3518	of them macros) into the global namespace. All C++ specific things are	4082	of them macros) into the global namespace. All C++ specific things are
3519	put into the C<ev> namespace. It should support all the same embedding	4083	put into the C<ev> namespace. It should support all the same embedding
…		…
3528	with C<operator ()> can be used as callbacks. Other types should be easy	4092	with C<operator ()> can be used as callbacks. Other types should be easy
3529	to add as long as they only need one additional pointer for context. If	4093	to add as long as they only need one additional pointer for context. If
3530	you need support for other types of functors please contact the author	4094	you need support for other types of functors please contact the author
3531	(preferably after implementing it).	4095	(preferably after implementing it).
3532		4096
		4097	For all this to work, your C++ compiler either has to use the same calling
		4098	conventions as your C compiler (for static member functions), or you have
		4099	to embed libev and compile libev itself as C++.
		4100
3533	Here is a list of things available in the C<ev> namespace:	4101	Here is a list of things available in the C<ev> namespace:
3534		4102
3535	=over 4	4103	=over 4
3536		4104
3537	=item C<ev::READ>, C<ev::WRITE> etc.	4105	=item C<ev::READ>, C<ev::WRITE> etc.
…		…
3546	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4114	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3547		4115
3548	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4116	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3549	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4117	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3550	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4118	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3551	defines by many implementations.	4119	defined by many implementations.
3552		4120
3553	All of those classes have these methods:	4121	All of those classes have these methods:
3554		4122
3555	=over 4	4123	=over 4
3556		4124
…		…
3618	void operator() (ev::io &w, int revents)	4186	void operator() (ev::io &w, int revents)
3619	{	4187	{
3620	...	4188	...
3621	}	4189	}
3622	}	4190	}
3623		4191
3624	myfunctor f;	4192	myfunctor f;
3625		4193
3626	ev::io w;	4194	ev::io w;
3627	w.set (&f);	4195	w.set (&f);
3628		4196
…		…
3646	Associates a different C<struct ev_loop> with this watcher. You can only	4214	Associates a different C<struct ev_loop> with this watcher. You can only
3647	do this when the watcher is inactive (and not pending either).	4215	do this when the watcher is inactive (and not pending either).
3648		4216
3649	=item w->set ([arguments])	4217	=item w->set ([arguments])
3650		4218
3651	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4219	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3652	method or a suitable start method must be called at least once. Unlike the	4220	with the same arguments. Either this method or a suitable start method
3653	C counterpart, an active watcher gets automatically stopped and restarted	4221	must be called at least once. Unlike the C counterpart, an active watcher
3654	when reconfiguring it with this method.	4222	gets automatically stopped and restarted when reconfiguring it with this
		4223	method.
		4224
		4225	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4226	clashing with the C<set (loop)> method.
3655		4227
3656	=item w->start ()	4228	=item w->start ()
3657		4229
3658	Starts the watcher. Note that there is no C<loop> argument, as the	4230	Starts the watcher. Note that there is no C<loop> argument, as the
3659	constructor already stores the event loop.	4231	constructor already stores the event loop.
…		…
3689	watchers in the constructor.	4261	watchers in the constructor.
3690		4262
3691	class myclass	4263	class myclass
3692	{	4264	{
3693	ev::io io ; void io_cb (ev::io &w, int revents);	4265	ev::io io ; void io_cb (ev::io &w, int revents);
3694	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4266	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3695	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4267	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3696		4268
3697	myclass (int fd)	4269	myclass (int fd)
3698	{	4270	{
3699	io .set <myclass, &myclass::io_cb > (this);	4271	io .set <myclass, &myclass::io_cb > (this);
…		…
3750	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4322	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3751		4323
3752	=item D	4324	=item D
3753		4325
3754	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4326	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3755	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4327	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3756		4328
3757	=item Ocaml	4329	=item Ocaml
3758		4330
3759	Erkki Seppala has written Ocaml bindings for libev, to be found at	4331	Erkki Seppala has written Ocaml bindings for libev, to be found at
3760	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4332	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3763		4335
3764	Brian Maher has written a partial interface to libev for lua (at the	4336	Brian Maher has written a partial interface to libev for lua (at the
3765	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4337	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3766	L<http://github.com/brimworks/lua-ev>.	4338	L<http://github.com/brimworks/lua-ev>.
3767		4339
		4340	=item Javascript
		4341
		4342	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4343
		4344	=item Others
		4345
		4346	There are others, and I stopped counting.
		4347
3768	=back	4348	=back
3769		4349
3770		4350
3771	=head1 MACRO MAGIC	4351	=head1 MACRO MAGIC
3772		4352
…		…
3808	suitable for use with C<EV_A>.	4388	suitable for use with C<EV_A>.
3809		4389
3810	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4390	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3811		4391
3812	Similar to the other two macros, this gives you the value of the default	4392	Similar to the other two macros, this gives you the value of the default
3813	loop, if multiple loops are supported ("ev loop default").	4393	loop, if multiple loops are supported ("ev loop default"). The default loop
		4394	will be initialised if it isn't already initialised.
		4395
		4396	For non-multiplicity builds, these macros do nothing, so you always have
		4397	to initialise the loop somewhere.
3814		4398
3815	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4399	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3816		4400
3817	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4401	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3818	default loop has been initialised (C<UC> == unchecked). Their behaviour	4402	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3885	ev_vars.h	4469	ev_vars.h
3886	ev_wrap.h	4470	ev_wrap.h
3887		4471
3888	ev_win32.c required on win32 platforms only	4472	ev_win32.c required on win32 platforms only
3889		4473
3890	ev_select.c only when select backend is enabled (which is enabled by default)	4474	ev_select.c only when select backend is enabled
3891	ev_poll.c only when poll backend is enabled (disabled by default)	4475	ev_poll.c only when poll backend is enabled
3892	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4476	ev_epoll.c only when the epoll backend is enabled
		4477	ev_linuxaio.c only when the linux aio backend is enabled
3893	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4478	ev_kqueue.c only when the kqueue backend is enabled
3894	ev_port.c only when the solaris port backend is enabled (disabled by default)	4479	ev_port.c only when the solaris port backend is enabled
3895		4480
3896	F<ev.c> includes the backend files directly when enabled, so you only need	4481	F<ev.c> includes the backend files directly when enabled, so you only need
3897	to compile this single file.	4482	to compile this single file.
3898		4483
3899	=head3 LIBEVENT COMPATIBILITY API	4484	=head3 LIBEVENT COMPATIBILITY API
…		…
3963	supported). It will also not define any of the structs usually found in	4548	supported). It will also not define any of the structs usually found in
3964	F<event.h> that are not directly supported by the libev core alone.	4549	F<event.h> that are not directly supported by the libev core alone.
3965		4550
3966	In standalone mode, libev will still try to automatically deduce the	4551	In standalone mode, libev will still try to automatically deduce the
3967	configuration, but has to be more conservative.	4552	configuration, but has to be more conservative.
		4553
		4554	=item EV_USE_FLOOR
		4555
		4556	If defined to be C<1>, libev will use the C<floor ()> function for its
		4557	periodic reschedule calculations, otherwise libev will fall back on a
		4558	portable (slower) implementation. If you enable this, you usually have to
		4559	link against libm or something equivalent. Enabling this when the C<floor>
		4560	function is not available will fail, so the safe default is to not enable
		4561	this.
3968		4562
3969	=item EV_USE_MONOTONIC	4563	=item EV_USE_MONOTONIC
3970		4564
3971	If defined to be C<1>, libev will try to detect the availability of the	4565	If defined to be C<1>, libev will try to detect the availability of the
3972	monotonic clock option at both compile time and runtime. Otherwise no	4566	monotonic clock option at both compile time and runtime. Otherwise no
…		…
4058	If programs implement their own fd to handle mapping on win32, then this	4652	If programs implement their own fd to handle mapping on win32, then this
4059	macro can be used to override the C<close> function, useful to unregister	4653	macro can be used to override the C<close> function, useful to unregister
4060	file descriptors again. Note that the replacement function has to close	4654	file descriptors again. Note that the replacement function has to close
4061	the underlying OS handle.	4655	the underlying OS handle.
4062		4656
		4657	=item EV_USE_WSASOCKET
		4658
		4659	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4660	communication socket, which works better in some environments. Otherwise,
		4661	the normal C<socket> function will be used, which works better in other
		4662	environments.
		4663
4063	=item EV_USE_POLL	4664	=item EV_USE_POLL
4064		4665
4065	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4666	If defined to be C<1>, libev will compile in support for the C<poll>(2)
4066	backend. Otherwise it will be enabled on non-win32 platforms. It	4667	backend. Otherwise it will be enabled on non-win32 platforms. It
4067	takes precedence over select.	4668	takes precedence over select.
…		…
4071	If defined to be C<1>, libev will compile in support for the Linux	4672	If defined to be C<1>, libev will compile in support for the Linux
4072	C<epoll>(7) backend. Its availability will be detected at runtime,	4673	C<epoll>(7) backend. Its availability will be detected at runtime,
4073	otherwise another method will be used as fallback. This is the preferred	4674	otherwise another method will be used as fallback. This is the preferred
4074	backend for GNU/Linux systems. If undefined, it will be enabled if the	4675	backend for GNU/Linux systems. If undefined, it will be enabled if the
4075	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4676	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4677
		4678	=item EV_USE_LINUXAIO
		4679
		4680	If defined to be C<1>, libev will compile in support for the Linux
		4681	aio backend. Due to it's currenbt limitations it has to be requested
		4682	explicitly. If undefined, it will be enabled on linux, otherwise
		4683	disabled.
4076		4684
4077	=item EV_USE_KQUEUE	4685	=item EV_USE_KQUEUE
4078		4686
4079	If defined to be C<1>, libev will compile in support for the BSD style	4687	If defined to be C<1>, libev will compile in support for the BSD style
4080	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4688	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
4102	If defined to be C<1>, libev will compile in support for the Linux inotify	4710	If defined to be C<1>, libev will compile in support for the Linux inotify
4103	interface to speed up C<ev_stat> watchers. Its actual availability will	4711	interface to speed up C<ev_stat> watchers. Its actual availability will
4104	be detected at runtime. If undefined, it will be enabled if the headers	4712	be detected at runtime. If undefined, it will be enabled if the headers
4105	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4713	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4106		4714
		4715	=item EV_NO_SMP
		4716
		4717	If defined to be C<1>, libev will assume that memory is always coherent
		4718	between threads, that is, threads can be used, but threads never run on
		4719	different cpus (or different cpu cores). This reduces dependencies
		4720	and makes libev faster.
		4721
		4722	=item EV_NO_THREADS
		4723
		4724	If defined to be C<1>, libev will assume that it will never be called from
		4725	different threads (that includes signal handlers), which is a stronger
		4726	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4727	libev faster.
		4728
4107	=item EV_ATOMIC_T	4729	=item EV_ATOMIC_T
4108		4730
4109	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4731	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4110	access is atomic with respect to other threads or signal contexts. No such	4732	access is atomic with respect to other threads or signal contexts. No
4111	type is easily found in the C language, so you can provide your own type	4733	such type is easily found in the C language, so you can provide your own
4112	that you know is safe for your purposes. It is used both for signal handler "locking"	4734	type that you know is safe for your purposes. It is used both for signal
4113	as well as for signal and thread safety in C<ev_async> watchers.	4735	handler "locking" as well as for signal and thread safety in C<ev_async>
		4736	watchers.
4114		4737
4115	In the absence of this define, libev will use C<sig_atomic_t volatile>	4738	In the absence of this define, libev will use C<sig_atomic_t volatile>
4116	(from F<signal.h>), which is usually good enough on most platforms.	4739	(from F<signal.h>), which is usually good enough on most platforms.
4117		4740
4118	=item EV_H (h)	4741	=item EV_H (h)
…		…
4145	will have the C<struct ev_loop *> as first argument, and you can create	4768	will have the C<struct ev_loop *> as first argument, and you can create
4146	additional independent event loops. Otherwise there will be no support	4769	additional independent event loops. Otherwise there will be no support
4147	for multiple event loops and there is no first event loop pointer	4770	for multiple event loops and there is no first event loop pointer
4148	argument. Instead, all functions act on the single default loop.	4771	argument. Instead, all functions act on the single default loop.
4149		4772
		4773	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4774	default loop when multiplicity is switched off - you always have to
		4775	initialise the loop manually in this case.
		4776
4150	=item EV_MINPRI	4777	=item EV_MINPRI
4151		4778
4152	=item EV_MAXPRI	4779	=item EV_MAXPRI
4153		4780
4154	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4781	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4190	#define EV_USE_POLL 1	4817	#define EV_USE_POLL 1
4191	#define EV_CHILD_ENABLE 1	4818	#define EV_CHILD_ENABLE 1
4192	#define EV_ASYNC_ENABLE 1	4819	#define EV_ASYNC_ENABLE 1
4193		4820
4194	The actual value is a bitset, it can be a combination of the following	4821	The actual value is a bitset, it can be a combination of the following
4195	values:	4822	values (by default, all of these are enabled):
4196		4823
4197	=over 4	4824	=over 4
4198		4825
4199	=item C<1> - faster/larger code	4826	=item C<1> - faster/larger code
4200		4827
…		…
4204	code size by roughly 30% on amd64).	4831	code size by roughly 30% on amd64).
4205		4832
4206	When optimising for size, use of compiler flags such as C<-Os> with	4833	When optimising for size, use of compiler flags such as C<-Os> with
4207	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4834	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4208	assertions.	4835	assertions.
		4836
		4837	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4838	(e.g. gcc with C<-Os>).
4209		4839
4210	=item C<2> - faster/larger data structures	4840	=item C<2> - faster/larger data structures
4211		4841
4212	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4842	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4213	hash table sizes and so on. This will usually further increase code size	4843	hash table sizes and so on. This will usually further increase code size
4214	and can additionally have an effect on the size of data structures at	4844	and can additionally have an effect on the size of data structures at
4215	runtime.	4845	runtime.
4216		4846
		4847	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4848	(e.g. gcc with C<-Os>).
		4849
4217	=item C<4> - full API configuration	4850	=item C<4> - full API configuration
4218		4851
4219	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4852	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4220	enables multiplicity (C<EV_MULTIPLICITY>=1).	4853	enables multiplicity (C<EV_MULTIPLICITY>=1).
4221		4854
…		…
4251		4884
4252	With an intelligent-enough linker (gcc+binutils are intelligent enough	4885	With an intelligent-enough linker (gcc+binutils are intelligent enough
4253	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4886	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4254	your program might be left out as well - a binary starting a timer and an	4887	your program might be left out as well - a binary starting a timer and an
4255	I/O watcher then might come out at only 5Kb.	4888	I/O watcher then might come out at only 5Kb.
		4889
		4890	=item EV_API_STATIC
		4891
		4892	If this symbol is defined (by default it is not), then all identifiers
		4893	will have static linkage. This means that libev will not export any
		4894	identifiers, and you cannot link against libev anymore. This can be useful
		4895	when you embed libev, only want to use libev functions in a single file,
		4896	and do not want its identifiers to be visible.
		4897
		4898	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4899	wants to use libev.
		4900
		4901	This option only works when libev is compiled with a C compiler, as C++
		4902	doesn't support the required declaration syntax.
4256		4903
4257	=item EV_AVOID_STDIO	4904	=item EV_AVOID_STDIO
4258		4905
4259	If this is set to C<1> at compiletime, then libev will avoid using stdio	4906	If this is set to C<1> at compiletime, then libev will avoid using stdio
4260	functions (printf, scanf, perror etc.). This will increase the code size	4907	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4404	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5051	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4405		5052
4406	#include "ev_cpp.h"	5053	#include "ev_cpp.h"
4407	#include "ev.c"	5054	#include "ev.c"
4408		5055
4409	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5056	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4410		5057
4411	=head2 THREADS AND COROUTINES	5058	=head2 THREADS AND COROUTINES
4412		5059
4413	=head3 THREADS	5060	=head3 THREADS
4414		5061
…		…
4465	default loop and triggering an C<ev_async> watcher from the default loop	5112	default loop and triggering an C<ev_async> watcher from the default loop
4466	watcher callback into the event loop interested in the signal.	5113	watcher callback into the event loop interested in the signal.
4467		5114
4468	=back	5115	=back
4469		5116
4470	=head4 THREAD LOCKING EXAMPLE	5117	See also L</THREAD LOCKING EXAMPLE>.
4471
4472	Here is a fictitious example of how to run an event loop in a different
4473	thread than where callbacks are being invoked and watchers are
4474	created/added/removed.
4475
4476	For a real-world example, see the C<EV::Loop::Async> perl module,
4477	which uses exactly this technique (which is suited for many high-level
4478	languages).
4479
4480	The example uses a pthread mutex to protect the loop data, a condition
4481	variable to wait for callback invocations, an async watcher to notify the
4482	event loop thread and an unspecified mechanism to wake up the main thread.
4483
4484	First, you need to associate some data with the event loop:
4485
4486	typedef struct {
4487	mutex_t lock; /* global loop lock */
4488	ev_async async_w;
4489	thread_t tid;
4490	cond_t invoke_cv;
4491	} userdata;
4492
4493	void prepare_loop (EV_P)
4494	{
4495	// for simplicity, we use a static userdata struct.
4496	static userdata u;
4497
4498	ev_async_init (&u->async_w, async_cb);
4499	ev_async_start (EV_A_ &u->async_w);
4500
4501	pthread_mutex_init (&u->lock, 0);
4502	pthread_cond_init (&u->invoke_cv, 0);
4503
4504	// now associate this with the loop
4505	ev_set_userdata (EV_A_ u);
4506	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4507	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4508
4509	// then create the thread running ev_loop
4510	pthread_create (&u->tid, 0, l_run, EV_A);
4511	}
4512
4513	The callback for the C<ev_async> watcher does nothing: the watcher is used
4514	solely to wake up the event loop so it takes notice of any new watchers
4515	that might have been added:
4516
4517	static void
4518	async_cb (EV_P_ ev_async *w, int revents)
4519	{
4520	// just used for the side effects
4521	}
4522
4523	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4524	protecting the loop data, respectively.
4525
4526	static void
4527	l_release (EV_P)
4528	{
4529	userdata *u = ev_userdata (EV_A);
4530	pthread_mutex_unlock (&u->lock);
4531	}
4532
4533	static void
4534	l_acquire (EV_P)
4535	{
4536	userdata *u = ev_userdata (EV_A);
4537	pthread_mutex_lock (&u->lock);
4538	}
4539
4540	The event loop thread first acquires the mutex, and then jumps straight
4541	into C<ev_run>:
4542
4543	void *
4544	l_run (void *thr_arg)
4545	{
4546	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4547
4548	l_acquire (EV_A);
4549	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4550	ev_run (EV_A_ 0);
4551	l_release (EV_A);
4552
4553	return 0;
4554	}
4555
4556	Instead of invoking all pending watchers, the C<l_invoke> callback will
4557	signal the main thread via some unspecified mechanism (signals? pipe
4558	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4559	have been called (in a while loop because a) spurious wakeups are possible
4560	and b) skipping inter-thread-communication when there are no pending
4561	watchers is very beneficial):
4562
4563	static void
4564	l_invoke (EV_P)
4565	{
4566	userdata *u = ev_userdata (EV_A);
4567
4568	while (ev_pending_count (EV_A))
4569	{
4570	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4571	pthread_cond_wait (&u->invoke_cv, &u->lock);
4572	}
4573	}
4574
4575	Now, whenever the main thread gets told to invoke pending watchers, it
4576	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4577	thread to continue:
4578
4579	static void
4580	real_invoke_pending (EV_P)
4581	{
4582	userdata *u = ev_userdata (EV_A);
4583
4584	pthread_mutex_lock (&u->lock);
4585	ev_invoke_pending (EV_A);
4586	pthread_cond_signal (&u->invoke_cv);
4587	pthread_mutex_unlock (&u->lock);
4588	}
4589
4590	Whenever you want to start/stop a watcher or do other modifications to an
4591	event loop, you will now have to lock:
4592
4593	ev_timer timeout_watcher;
4594	userdata *u = ev_userdata (EV_A);
4595
4596	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4597
4598	pthread_mutex_lock (&u->lock);
4599	ev_timer_start (EV_A_ &timeout_watcher);
4600	ev_async_send (EV_A_ &u->async_w);
4601	pthread_mutex_unlock (&u->lock);
4602
4603	Note that sending the C<ev_async> watcher is required because otherwise
4604	an event loop currently blocking in the kernel will have no knowledge
4605	about the newly added timer. By waking up the loop it will pick up any new
4606	watchers in the next event loop iteration.
4607		5118
4608	=head3 COROUTINES	5119	=head3 COROUTINES
4609		5120
4610	Libev is very accommodating to coroutines ("cooperative threads"):	5121	Libev is very accommodating to coroutines ("cooperative threads"):
4611	libev fully supports nesting calls to its functions from different	5122	libev fully supports nesting calls to its functions from different
…		…
4776	requires, and its I/O model is fundamentally incompatible with the POSIX	5287	requires, and its I/O model is fundamentally incompatible with the POSIX
4777	model. Libev still offers limited functionality on this platform in	5288	model. Libev still offers limited functionality on this platform in
4778	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5289	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4779	descriptors. This only applies when using Win32 natively, not when using	5290	descriptors. This only applies when using Win32 natively, not when using
4780	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5291	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4781	as every compielr comes with a slightly differently broken/incompatible	5292	as every compiler comes with a slightly differently broken/incompatible
4782	environment.	5293	environment.
4783		5294
4784	Lifting these limitations would basically require the full	5295	Lifting these limitations would basically require the full
4785	re-implementation of the I/O system. If you are into this kind of thing,	5296	re-implementation of the I/O system. If you are into this kind of thing,
4786	then note that glib does exactly that for you in a very portable way (note	5297	then note that glib does exactly that for you in a very portable way (note
…		…
4880	structure (guaranteed by POSIX but not by ISO C for example), but it also	5391	structure (guaranteed by POSIX but not by ISO C for example), but it also
4881	assumes that the same (machine) code can be used to call any watcher	5392	assumes that the same (machine) code can be used to call any watcher
4882	callback: The watcher callbacks have different type signatures, but libev	5393	callback: The watcher callbacks have different type signatures, but libev
4883	calls them using an C<ev_watcher *> internally.	5394	calls them using an C<ev_watcher *> internally.
4884		5395
		5396	=item null pointers and integer zero are represented by 0 bytes
		5397
		5398	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5399	relies on this setting pointers and integers to null.
		5400
4885	=item pointer accesses must be thread-atomic	5401	=item pointer accesses must be thread-atomic
4886		5402
4887	Accessing a pointer value must be atomic, it must both be readable and	5403	Accessing a pointer value must be atomic, it must both be readable and
4888	writable in one piece - this is the case on all current architectures.	5404	writable in one piece - this is the case on all current architectures.
4889		5405
…		…
4902	thread" or will block signals process-wide, both behaviours would	5418	thread" or will block signals process-wide, both behaviours would
4903	be compatible with libev. Interaction between C<sigprocmask> and	5419	be compatible with libev. Interaction between C<sigprocmask> and
4904	C<pthread_sigmask> could complicate things, however.	5420	C<pthread_sigmask> could complicate things, however.
4905		5421
4906	The most portable way to handle signals is to block signals in all threads	5422	The most portable way to handle signals is to block signals in all threads
4907	except the initial one, and run the default loop in the initial thread as	5423	except the initial one, and run the signal handling loop in the initial
4908	well.	5424	thread as well.
4909		5425
4910	=item C<long> must be large enough for common memory allocation sizes	5426	=item C<long> must be large enough for common memory allocation sizes
4911		5427
4912	To improve portability and simplify its API, libev uses C<long> internally	5428	To improve portability and simplify its API, libev uses C<long> internally
4913	instead of C<size_t> when allocating its data structures. On non-POSIX	5429	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4919		5435
4920	The type C<double> is used to represent timestamps. It is required to	5436	The type C<double> is used to represent timestamps. It is required to
4921	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5437	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4922	good enough for at least into the year 4000 with millisecond accuracy	5438	good enough for at least into the year 4000 with millisecond accuracy
4923	(the design goal for libev). This requirement is overfulfilled by	5439	(the design goal for libev). This requirement is overfulfilled by
4924	implementations using IEEE 754, which is basically all existing ones. With	5440	implementations using IEEE 754, which is basically all existing ones.
		5441
4925	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5442	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5443	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5444	is either obsolete or somebody patched it to use C<long double> or
		5445	something like that, just kidding).
4926		5446
4927	=back	5447	=back
4928		5448
4929	If you know of other additional requirements drop me a note.	5449	If you know of other additional requirements drop me a note.
4930		5450
…		…
4992	=item Processing ev_async_send: O(number_of_async_watchers)	5512	=item Processing ev_async_send: O(number_of_async_watchers)
4993		5513
4994	=item Processing signals: O(max_signal_number)	5514	=item Processing signals: O(max_signal_number)
4995		5515
4996	Sending involves a system call I<iff> there were no other C<ev_async_send>	5516	Sending involves a system call I<iff> there were no other C<ev_async_send>
4997	calls in the current loop iteration. Checking for async and signal events	5517	calls in the current loop iteration and the loop is currently
		5518	blocked. Checking for async and signal events involves iterating over all
4998	involves iterating over all running async watchers or all signal numbers.	5519	running async watchers or all signal numbers.
4999		5520
5000	=back	5521	=back
5001		5522
5002		5523
5003	=head1 PORTING FROM LIBEV 3.X TO 4.X	5524	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
5012	=over 4	5533	=over 4
5013		5534
5014	=item C<EV_COMPAT3> backwards compatibility mechanism	5535	=item C<EV_COMPAT3> backwards compatibility mechanism
5015		5536
5016	The backward compatibility mechanism can be controlled by	5537	The backward compatibility mechanism can be controlled by
5017	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5538	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
5018	section.	5539	section.
5019		5540
5020	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5541	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
5021		5542
5022	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5543	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
5065	=over 4	5586	=over 4
5066		5587
5067	=item active	5588	=item active
5068		5589
5069	A watcher is active as long as it has been started and not yet stopped.	5590	A watcher is active as long as it has been started and not yet stopped.
5070	See L<WATCHER STATES> for details.	5591	See L</WATCHER STATES> for details.
5071		5592
5072	=item application	5593	=item application
5073		5594
5074	In this document, an application is whatever is using libev.	5595	In this document, an application is whatever is using libev.
5075		5596
…		…
5111	watchers and events.	5632	watchers and events.
5112		5633
5113	=item pending	5634	=item pending
5114		5635
5115	A watcher is pending as soon as the corresponding event has been	5636	A watcher is pending as soon as the corresponding event has been
5116	detected. See L<WATCHER STATES> for details.	5637	detected. See L</WATCHER STATES> for details.
5117		5638
5118	=item real time	5639	=item real time
5119		5640
5120	The physical time that is observed. It is apparently strictly monotonic :)	5641	The physical time that is observed. It is apparently strictly monotonic :)
5121		5642
5122	=item wall-clock time	5643	=item wall-clock time
5123		5644
5124	The time and date as shown on clocks. Unlike real time, it can actually	5645	The time and date as shown on clocks. Unlike real time, it can actually
5125	be wrong and jump forwards and backwards, e.g. when the you adjust your	5646	be wrong and jump forwards and backwards, e.g. when you adjust your
5126	clock.	5647	clock.
5127		5648
5128	=item watcher	5649	=item watcher
5129		5650
5130	A data structure that describes interest in certain events. Watchers need	5651	A data structure that describes interest in certain events. Watchers need
…		…
5133	=back	5654	=back
5134		5655
5135	=head1 AUTHOR	5656	=head1 AUTHOR
5136		5657
5137	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5658	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5138	Magnusson and Emanuele Giaquinta.	5659	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5139		5660

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