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		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 the
		590	epoll set), and generally sounds too good to be true. Because, this being
		591	the linux kernel, of course it suffers from a whole new set of limitations.
		592
		593	For one, it is not easily embeddable (but probably could be done using
		594	an event fd at some extra overhead). It also is subject to a system wide
		595	limit that can be configured in F</proc/sys/fs/aio-max-nr> - each loop
		596	currently requires C<61> of this number. If no aio requests are left, this
		597	backend will be skipped during initialisation.
		598
		599	Most problematic in practise, however, is that not all file descriptors
		600	work with it. For example, in linux 5.1, tcp sockets, pipes, event fds,
		601	files, F</dev/null> and a few others are supported, but ttys do not work
		602	properly (a known bug that the kernel developers don't care about, see
		603	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		604	(yet?) a generic event polling interface.
		605
		606	Overall, it seems the linux developers just don't want it to have a
		607	generic event handling mechanism other than C<select> or C<poll>.
		608
		609	To work around the fd type problem, the current version of libev uses
		610	epoll as a fallback for file deescriptor types that do not work. Epoll
		611	is used in, kind of, slow mode that hopefully avoids most of its design
		612	problems and requires 1-3 extra syscalls per active fd every iteration.
534		613
535	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	614	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
536	C<EVBACKEND_POLL>.	615	C<EVBACKEND_POLL>.
537		616
538	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	617	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
…		…
553		632
554	It scales in the same way as the epoll backend, but the interface to the	633	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	634	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	635	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	636	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	637	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	638	might have to leak fd's on fork, but it's more sane than epoll) and it
560	cases	639	drops fds silently in similarly hard-to-detect cases.
561		640
562	This backend usually performs well under most conditions.	641	This backend usually performs well under most conditions.
563		642
564	While nominally embeddable in other event loops, this doesn't work	643	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	644	everywhere, so you might need to test for this. And since it is broken
…		…
582	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	661	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
583		662
584	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	663	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)).	664	it's really slow, but it still scales very well (O(active_fds)).
586		665
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	666	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	667	file descriptor per loop iteration. For small and medium numbers of file
593	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	668	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
594	might perform better.	669	might perform better.
595		670
596	On the positive side, with the exception of the spurious readiness	671	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	672	specification in all tests and is fully embeddable, which is a rare feat
599	OS-specific backends (I vastly prefer correctness over speed hacks).	673	among the OS-specific backends (I vastly prefer correctness over speed
		674	hacks).
		675
		676	On the negative side, the interface is I<bizarre> - so bizarre that
		677	even sun itself gets it wrong in their code examples: The event polling
		678	function sometimes returns events to the caller even though an error
		679	occurred, but with no indication whether it has done so or not (yes, it's
		680	even documented that way) - deadly for edge-triggered interfaces where you
		681	absolutely have to know whether an event occurred or not because you have
		682	to re-arm the watcher.
		683
		684	Fortunately libev seems to be able to work around these idiocies.
600		685
601	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	686	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
602	C<EVBACKEND_POLL>.	687	C<EVBACKEND_POLL>.
603		688
604	=item C<EVBACKEND_ALL>	689	=item C<EVBACKEND_ALL>
…		…
632		717
633	Example: Use whatever libev has to offer, but make sure that kqueue is	718	Example: Use whatever libev has to offer, but make sure that kqueue is
634	used if available.	719	used if available.
635		720
636	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);	721	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		722
		723	Example: Similarly, on linux, you mgiht want to take advantage of the
		724	linux aio backend if possible, but fall back to something else if that
		725	isn't available.
		726
		727	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
637		728
638	=item ev_loop_destroy (loop)	729	=item ev_loop_destroy (loop)
639		730
640	Destroys an event loop object (frees all memory and kernel state	731	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	732	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>	749	If you need dynamically allocated loops it is better to use C<ev_loop_new>
659	and C<ev_loop_destroy>.	750	and C<ev_loop_destroy>.
660		751
661	=item ev_loop_fork (loop)	752	=item ev_loop_fork (loop)
662		753
663	This function sets a flag that causes subsequent C<ev_run> iterations to	754	This function sets a flag that causes subsequent C<ev_run> iterations
664	reinitialise the kernel state for backends that have one. Despite the	755	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	756	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	757	watchers (except inside an C<ev_prepare> callback), but it makes most
		758	sense after forking, in the child process. You I<must> call it (or use
667	child before resuming or calling C<ev_run>.	759	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
668		760
		761	In addition, if you want to reuse a loop (via this function or
		762	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		763
669	Again, you I<have> to call it on I<any> loop that you want to re-use after	764	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	765	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	766	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
672	during fork.	767	during fork.
673		768
674	On the other hand, you only need to call this function in the child	769	On the other hand, you only need to call this function in the child
…		…
744		839
745	This function is rarely useful, but when some event callback runs for a	840	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	841	very long time without entering the event loop, updating libev's idea of
747	the current time is a good idea.	842	the current time is a good idea.
748		843
749	See also L<The special problem of time updates> in the C<ev_timer> section.	844	See also L</The special problem of time updates> in the C<ev_timer> section.
750		845
751	=item ev_suspend (loop)	846	=item ev_suspend (loop)
752		847
753	=item ev_resume (loop)	848	=item ev_resume (loop)
754		849
…		…
772	without a previous call to C<ev_suspend>.	867	without a previous call to C<ev_suspend>.
773		868
774	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	869	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
775	event loop time (see C<ev_now_update>).	870	event loop time (see C<ev_now_update>).
776		871
777	=item ev_run (loop, int flags)	872	=item bool ev_run (loop, int flags)
778		873
779	Finally, this is it, the event handler. This function usually is called	874	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	875	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	876	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	877	the watcher callbacks, and then repeat the whole process indefinitely: This
783	is why event loops are called I<loops>.	878	is why event loops are called I<loops>.
784		879
785	If the flags argument is specified as C<0>, it will keep handling events	880	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	881	until either no event watchers are active anymore or C<ev_break> was
787	called.	882	called.
		883
		884	The return value is false if there are no more active watchers (which
		885	usually means "all jobs done" or "deadlock"), and true in all other cases
		886	(which usually means " you should call C<ev_run> again").
788		887
789	Please note that an explicit C<ev_break> is usually better than	888	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	889	relying on all watchers to be stopped when deciding when a program has
791	finished (especially in interactive programs), but having a program	890	finished (especially in interactive programs), but having a program
792	that automatically loops as long as it has to and no longer by virtue	891	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	892	of relying on its watchers stopping correctly, that is truly a thing of
794	beauty.	893	beauty.
795		894
796	This function is also I<mostly> exception-safe - you can break out of	895	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++	896	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	897	exception and so on. This does not decrement the C<ev_depth> value, nor
799	will it clear any outstanding C<EVBREAK_ONE> breaks.	898	will it clear any outstanding C<EVBREAK_ONE> breaks.
800		899
801	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	900	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	901	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	913	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	914	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	915	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.	916	usually a better approach for this kind of thing.
818		917
819	Here are the gory details of what C<ev_run> does:	918	Here are the gory details of what C<ev_run> does (this is for your
		919	understanding, not a guarantee that things will work exactly like this in
		920	future versions):
820		921
821	- Increment loop depth.	922	- Increment loop depth.
822	- Reset the ev_break status.	923	- Reset the ev_break status.
823	- Before the first iteration, call any pending watchers.	924	- Before the first iteration, call any pending watchers.
824	LOOP:	925	LOOP:
…		…
857	anymore.	958	anymore.
858		959
859	... queue jobs here, make sure they register event watchers as long	960	... 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..)	961	... as they still have work to do (even an idle watcher will do..)
861	ev_run (my_loop, 0);	962	ev_run (my_loop, 0);
862	... jobs done or somebody called unloop. yeah!	963	... jobs done or somebody called break. yeah!
863		964
864	=item ev_break (loop, how)	965	=item ev_break (loop, how)
865		966
866	Can be used to make a call to C<ev_run> return early (but only after it	967	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	968	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.	1031	overhead for the actual polling but can deliver many events at once.
931		1032
932	By setting a higher I<io collect interval> you allow libev to spend more	1033	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,	1034	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	1035	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	1036	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	1037	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	1038	sleep time ensures that libev will not poll for I/O events more often then
938	once per this interval, on average.	1039	once per this interval, on average (as long as the host time resolution is
		1040	good enough).
939		1041
940	Likewise, by setting a higher I<timeout collect interval> you allow libev	1042	Likewise, by setting a higher I<timeout collect interval> you allow libev
941	to spend more time collecting timeouts, at the expense of increased	1043	to spend more time collecting timeouts, at the expense of increased
942	latency/jitter/inexactness (the watcher callback will be called	1044	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	1045	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.).	1091	invoke the actual watchers inside another context (another thread etc.).
990		1092
991	If you want to reset the callback, use C<ev_invoke_pending> as new	1093	If you want to reset the callback, use C<ev_invoke_pending> as new
992	callback.	1094	callback.
993		1095
994	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1096	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
995		1097
996	Sometimes you want to share the same loop between multiple threads. This	1098	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	1099	can be done relatively simply by putting mutex_lock/unlock calls around
998	each call to a libev function.	1100	each call to a libev function.
999		1101
1000	However, C<ev_run> can run an indefinite time, so it is not feasible	1102	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	1103	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	1104	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.	1105	I<release> and I<acquire> callbacks on the loop.
1004		1106
1005	When set, then C<release> will be called just before the thread is	1107	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	1108	suspended waiting for new events, and C<acquire> is called just
1007	afterwards.	1109	afterwards.
…		…
1147		1249
1148	=item C<EV_PREPARE>	1250	=item C<EV_PREPARE>
1149		1251
1150	=item C<EV_CHECK>	1252	=item C<EV_CHECK>
1151		1253
1152	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1254	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	1255	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	1256	just after C<ev_run> has gathered them, but before it queues any callbacks
		1257	for any received events. That means C<ev_prepare> watchers are the last
		1258	watchers invoked before the event loop sleeps or polls for new events, and
		1259	C<ev_check> watchers will be invoked before any other watchers of the same
		1260	or lower priority within an event loop iteration.
		1261
1155	received events. Callbacks of both watcher types can start and stop as	1262	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	1263	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	1264	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1158	C<ev_run> from blocking).	1265	blocking).
1159		1266
1160	=item C<EV_EMBED>	1267	=item C<EV_EMBED>
1161		1268
1162	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1269	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1163		1270
…		…
1286		1393
1287	=item callback ev_cb (ev_TYPE *watcher)	1394	=item callback ev_cb (ev_TYPE *watcher)
1288		1395
1289	Returns the callback currently set on the watcher.	1396	Returns the callback currently set on the watcher.
1290		1397
1291	=item ev_cb_set (ev_TYPE *watcher, callback)	1398	=item ev_set_cb (ev_TYPE *watcher, callback)
1292		1399
1293	Change the callback. You can change the callback at virtually any time	1400	Change the callback. You can change the callback at virtually any time
1294	(modulo threads).	1401	(modulo threads).
1295		1402
1296	=item ev_set_priority (ev_TYPE *watcher, int priority)	1403	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1314	or might not have been clamped to the valid range.	1421	or might not have been clamped to the valid range.
1315		1422
1316	The default priority used by watchers when no priority has been set is	1423	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 :).	1424	always C<0>, which is supposed to not be too high and not be too low :).
1318		1425
1319	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1426	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1320	priorities.	1427	priorities.
1321		1428
1322	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1429	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1323		1430
1324	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1431	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	1456	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1350	functions that do not need a watcher.	1457	functions that do not need a watcher.
1351		1458
1352	=back	1459	=back
1353		1460
1354	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1461	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1355		1462	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		1463
1419	=head2 WATCHER STATES	1464	=head2 WATCHER STATES
1420		1465
1421	There are various watcher states mentioned throughout this manual -	1466	There are various watcher states mentioned throughout this manual -
1422	active, pending and so on. In this section these states and the rules to	1467	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	1468	transition between them will be described in more detail - and while these
1424	rules might look complicated, they usually do "the right thing".	1469	rules might look complicated, they usually do "the right thing".
1425		1470
1426	=over 4	1471	=over 4
1427		1472
1428	=item initialiased	1473	=item initialised
1429		1474
1430	Before a watcher can be registered with the event looop it has to be	1475	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	1476	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.	1477	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1433		1478
1434	In this state it is simply some block of memory that is suitable for use	1479	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.	1480	use in an event loop. It can be moved around, freed, reused etc. at
		1481	will - as long as you either keep the memory contents intact, or call
		1482	C<ev_TYPE_init> again.
1436		1483
1437	=item started/running/active	1484	=item started/running/active
1438		1485
1439	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1486	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	1487	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	1515	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	1516	of whether it was active or not, so stopping a watcher explicitly before
1470	freeing it is often a good idea.	1517	freeing it is often a good idea.
1471		1518
1472	While stopped (and not pending) the watcher is essentially in the	1519	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	1520	initialised state, that is, it can be reused, moved, modified in any way
1474	you wish.	1521	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1522	it again).
1475		1523
1476	=back	1524	=back
1477		1525
1478	=head2 WATCHER PRIORITY MODELS	1526	=head2 WATCHER PRIORITY MODELS
1479		1527
…		…
1608	In general you can register as many read and/or write event watchers per	1656	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	1657	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	1658	descriptors to non-blocking mode is also usually a good idea (but not
1611	required if you know what you are doing).	1659	required if you know what you are doing).
1612		1660
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	1661	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	1662	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	1663	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	1664	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	1665	with a relatively standard program structure. Thus it is best to always
1624	this situation even with a relatively standard program structure. Thus	1666	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.	1667	preferable to a program hanging until some data arrives.
1627		1668
1628	If you cannot run the fd in non-blocking mode (for example you should	1669	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	1670	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	1671	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	1672	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	1673	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	1674	use C<SIGALRM> and an interval timer, just to be sure you won't block
1634	indefinitely.	1675	indefinitely.
1635		1676
1636	But really, best use non-blocking mode.	1677	But really, best use non-blocking mode.
1637		1678
1638	=head3 The special problem of disappearing file descriptors	1679	=head3 The special problem of disappearing file descriptors
1639		1680
1640	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1681	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,	1682	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	1683	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	1684	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	1685	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	1686	is registered with libev, there is no efficient way to see that this is,
1646	fact, a different file descriptor.	1687	in fact, a different file descriptor.
1647		1688
1648	To avoid having to explicitly tell libev about such cases, libev follows	1689	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	1690	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	1691	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	1692	it is assumed that the file descriptor stays the same. That means that
…		…
1665		1706
1666	There is no workaround possible except not registering events	1707	There is no workaround possible except not registering events
1667	for potentially C<dup ()>'ed file descriptors, or to resort to	1708	for potentially C<dup ()>'ed file descriptors, or to resort to
1668	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1709	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1669		1710
		1711	=head3 The special problem of files
		1712
		1713	Many people try to use C<select> (or libev) on file descriptors
		1714	representing files, and expect it to become ready when their program
		1715	doesn't block on disk accesses (which can take a long time on their own).
		1716
		1717	However, this cannot ever work in the "expected" way - you get a readiness
		1718	notification as soon as the kernel knows whether and how much data is
		1719	there, and in the case of open files, that's always the case, so you
		1720	always get a readiness notification instantly, and your read (or possibly
		1721	write) will still block on the disk I/O.
		1722
		1723	Another way to view it is that in the case of sockets, pipes, character
		1724	devices and so on, there is another party (the sender) that delivers data
		1725	on its own, but in the case of files, there is no such thing: the disk
		1726	will not send data on its own, simply because it doesn't know what you
		1727	wish to read - you would first have to request some data.
		1728
		1729	Since files are typically not-so-well supported by advanced notification
		1730	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1731	to files, even though you should not use it. The reason for this is
		1732	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1733	usually a tty, often a pipe, but also sometimes files or special devices
		1734	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1735	F</dev/urandom>), and even though the file might better be served with
		1736	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1737	it "just works" instead of freezing.
		1738
		1739	So avoid file descriptors pointing to files when you know it (e.g. use
		1740	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1741	when you rarely read from a file instead of from a socket, and want to
		1742	reuse the same code path.
		1743
1670	=head3 The special problem of fork	1744	=head3 The special problem of fork
1671		1745
1672	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1746	Some backends (epoll, kqueue, probably linuxaio) do not support C<fork ()>
1673	useless behaviour. Libev fully supports fork, but needs to be told about	1747	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1674	it in the child.	1748	to be told about it in the child if you want to continue to use it in the
		1749	child.
1675		1750
1676	To support fork in your programs, you either have to call	1751	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,	1752	()> 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	1753	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1679	C<EVBACKEND_POLL>.
1680		1754
1681	=head3 The special problem of SIGPIPE	1755	=head3 The special problem of SIGPIPE
1682		1756
1683	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1757	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	1758	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	1856	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1783	monotonic clock option helps a lot here).	1857	monotonic clock option helps a lot here).
1784		1858
1785	The callback is guaranteed to be invoked only I<after> its timeout has	1859	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	1860	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	1861	might introduce a small delay, see "the special problem of being too
		1862	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	1863	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	1864	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).	1865	longer true when a callback calls C<ev_run> recursively).
1791		1866
1792	=head3 Be smart about timeouts	1867	=head3 Be smart about timeouts
1793		1868
1794	Many real-world problems involve some kind of timeout, usually for error	1869	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,	1870	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1870		1945
1871	In this case, it would be more efficient to leave the C<ev_timer> alone,	1946	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	1947	but remember the time of last activity, and check for a real timeout only
1873	within the callback:	1948	within the callback:
1874		1949
		1950	ev_tstamp timeout = 60.;
1875	ev_tstamp last_activity; // time of last activity	1951	ev_tstamp last_activity; // time of last activity
		1952	ev_timer timer;
1876		1953
1877	static void	1954	static void
1878	callback (EV_P_ ev_timer *w, int revents)	1955	callback (EV_P_ ev_timer *w, int revents)
1879	{	1956	{
1880	ev_tstamp now = ev_now (EV_A);	1957	// calculate when the timeout would happen
1881	ev_tstamp timeout = last_activity + 60.;	1958	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1882		1959
1883	// if last_activity + 60. is older than now, we did time out	1960	// if negative, it means we the timeout already occurred
1884	if (timeout < now)	1961	if (after < 0.)
1885	{	1962	{
1886	// timeout occurred, take action	1963	// timeout occurred, take action
1887	}	1964	}
1888	else	1965	else
1889	{	1966	{
1890	// callback was invoked, but there was some activity, re-arm	1967	// callback was invoked, but there was some recent
1891	// the watcher to fire in last_activity + 60, which is	1968	// activity. simply restart the timer to time out
1892	// guaranteed to be in the future, so "again" is positive:	1969	// after "after" seconds, which is the earliest time
1893	w->repeat = timeout - now;	1970	// the timeout can occur.
		1971	ev_timer_set (w, after, 0.);
1894	ev_timer_again (EV_A_ w);	1972	ev_timer_start (EV_A_ w);
1895	}	1973	}
1896	}	1974	}
1897		1975
1898	To summarise the callback: first calculate the real timeout (defined	1976	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	1977	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	1978	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	1979	(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		1980
1905	Note how C<ev_timer_again> is used, taking advantage of the	1981	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.	1982	timed out, and need to do whatever is needed in this case.
		1983
		1984	Otherwise, we now the earliest time at which the timeout would trigger,
		1985	and simply start the timer with this timeout value.
		1986
		1987	In other words, each time the callback is invoked it will check whether
		1988	the timeout occurred. If not, it will simply reschedule itself to check
		1989	again at the earliest time it could time out. Rinse. Repeat.
1907		1990
1908	This scheme causes more callback invocations (about one every 60 seconds	1991	This scheme causes more callback invocations (about one every 60 seconds
1909	minus half the average time between activity), but virtually no calls to	1992	minus half the average time between activity), but virtually no calls to
1910	libev to change the timeout.	1993	libev to change the timeout.
1911		1994
1912	To start the timer, simply initialise the watcher and set C<last_activity>	1995	To start the machinery, simply initialise the watcher and set
1913	to the current time (meaning we just have some activity :), then call the	1996	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:	1997	now), then call the callback, which will "do the right thing" and start
		1998	the timer:
1915		1999
		2000	last_activity = ev_now (EV_A);
1916	ev_init (timer, callback);	2001	ev_init (&timer, callback);
1917	last_activity = ev_now (loop);	2002	callback (EV_A_ &timer, 0);
1918	callback (loop, timer, EV_TIMER);
1919		2003
1920	And when there is some activity, simply store the current time in	2004	When there is some activity, simply store the current time in
1921	C<last_activity>, no libev calls at all:	2005	C<last_activity>, no libev calls at all:
1922		2006
		2007	if (activity detected)
1923	last_activity = ev_now (loop);	2008	last_activity = ev_now (EV_A);
		2009
		2010	When your timeout value changes, then the timeout can be changed by simply
		2011	providing a new value, stopping the timer and calling the callback, which
		2012	will again do the right thing (for example, time out immediately :).
		2013
		2014	timeout = new_value;
		2015	ev_timer_stop (EV_A_ &timer);
		2016	callback (EV_A_ &timer, 0);
1924		2017
1925	This technique is slightly more complex, but in most cases where the	2018	This technique is slightly more complex, but in most cases where the
1926	time-out is unlikely to be triggered, much more efficient.	2019	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		2020
1932	=item 4. Wee, just use a double-linked list for your timeouts.	2021	=item 4. Wee, just use a double-linked list for your timeouts.
1933		2022
1934	If there is not one request, but many thousands (millions...), all	2023	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	2024	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	2051	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	2052	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	2053	off after the first million or so of active timers, i.e. it's usually
1965	overkill :)	2054	overkill :)
1966		2055
		2056	=head3 The special problem of being too early
		2057
		2058	If you ask a timer to call your callback after three seconds, then
		2059	you expect it to be invoked after three seconds - but of course, this
		2060	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2061	guaranteed to any precision by libev - imagine somebody suspending the
		2062	process with a STOP signal for a few hours for example.
		2063
		2064	So, libev tries to invoke your callback as soon as possible I<after> the
		2065	delay has occurred, but cannot guarantee this.
		2066
		2067	A less obvious failure mode is calling your callback too early: many event
		2068	loops compare timestamps with a "elapsed delay >= requested delay", but
		2069	this can cause your callback to be invoked much earlier than you would
		2070	expect.
		2071
		2072	To see why, imagine a system with a clock that only offers full second
		2073	resolution (think windows if you can't come up with a broken enough OS
		2074	yourself). If you schedule a one-second timer at the time 500.9, then the
		2075	event loop will schedule your timeout to elapse at a system time of 500
		2076	(500.9 truncated to the resolution) + 1, or 501.
		2077
		2078	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2079	501" and invoke the callback 0.1s after it was started, even though a
		2080	one-second delay was requested - this is being "too early", despite best
		2081	intentions.
		2082
		2083	This is the reason why libev will never invoke the callback if the elapsed
		2084	delay equals the requested delay, but only when the elapsed delay is
		2085	larger than the requested delay. In the example above, libev would only invoke
		2086	the callback at system time 502, or 1.1s after the timer was started.
		2087
		2088	So, while libev cannot guarantee that your callback will be invoked
		2089	exactly when requested, it I<can> and I<does> guarantee that the requested
		2090	delay has actually elapsed, or in other words, it always errs on the "too
		2091	late" side of things.
		2092
1967	=head3 The special problem of time updates	2093	=head3 The special problem of time updates
1968		2094
1969	Establishing the current time is a costly operation (it usually takes at	2095	Establishing the current time is a costly operation (it usually takes
1970	least two system calls): EV therefore updates its idea of the current	2096	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	2097	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	2098	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1973	lots of events in one iteration.	2099	lots of events in one iteration.
1974		2100
1975	The relative timeouts are calculated relative to the C<ev_now ()>	2101	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	2102	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	2103	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	2104	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:	2105	timeout on the current time, use something like the following to adjust
		2106	for it:
1980		2107
1981	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2108	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1982		2109
1983	If the event loop is suspended for a long time, you can also force an	2110	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	2111	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1985	()>.	2112	()>, although that will push the event time of all outstanding events
		2113	further into the future.
		2114
		2115	=head3 The special problem of unsynchronised clocks
		2116
		2117	Modern systems have a variety of clocks - libev itself uses the normal
		2118	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2119	jumps).
		2120
		2121	Neither of these clocks is synchronised with each other or any other clock
		2122	on the system, so C<ev_time ()> might return a considerably different time
		2123	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2124	a call to C<gettimeofday> might return a second count that is one higher
		2125	than a directly following call to C<time>.
		2126
		2127	The moral of this is to only compare libev-related timestamps with
		2128	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2129	a second or so.
		2130
		2131	One more problem arises due to this lack of synchronisation: if libev uses
		2132	the system monotonic clock and you compare timestamps from C<ev_time>
		2133	or C<ev_now> from when you started your timer and when your callback is
		2134	invoked, you will find that sometimes the callback is a bit "early".
		2135
		2136	This is because C<ev_timer>s work in real time, not wall clock time, so
		2137	libev makes sure your callback is not invoked before the delay happened,
		2138	I<measured according to the real time>, not the system clock.
		2139
		2140	If your timeouts are based on a physical timescale (e.g. "time out this
		2141	connection after 100 seconds") then this shouldn't bother you as it is
		2142	exactly the right behaviour.
		2143
		2144	If you want to compare wall clock/system timestamps to your timers, then
		2145	you need to use C<ev_periodic>s, as these are based on the wall clock
		2146	time, where your comparisons will always generate correct results.
1986		2147
1987	=head3 The special problems of suspended animation	2148	=head3 The special problems of suspended animation
1988		2149
1989	When you leave the server world it is quite customary to hit machines that	2150	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?	2151	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
2020		2181
2021	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2182	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
2022		2183
2023	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2184	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
2024		2185
2025	Configure the timer to trigger after C<after> seconds. If C<repeat>	2186	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	2187	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	2188	automatically be stopped once the timeout is reached. If it is positive,
2028	configured to trigger again C<repeat> seconds later, again, and again,	2189	then the timer will automatically be configured to trigger again C<repeat>
2029	until stopped manually.	2190	seconds later, again, and again, until stopped manually.
2030		2191
2031	The timer itself will do a best-effort at avoiding drift, that is, if	2192	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	2193	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	2194	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	2195	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.	2196	do stuff) the timer will not fire more than once per event loop iteration.
2036		2197
2037	=item ev_timer_again (loop, ev_timer *)	2198	=item ev_timer_again (loop, ev_timer *)
2038		2199
2039	This will act as if the timer timed out and restart it again if it is	2200	This will act as if the timer timed out, and restarts it again if it is
2040	repeating. The exact semantics are:	2201	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2202	timeout to the C<repeat> value and calling C<ev_timer_start>.
2041		2203
		2204	The exact semantics are as in the following rules, all of which will be
		2205	applied to the watcher:
		2206
		2207	=over 4
		2208
2042	If the timer is pending, its pending status is cleared.	2209	=item If the timer is pending, the pending status is always cleared.
2043		2210
2044	If the timer is started but non-repeating, stop it (as if it timed out).	2211	=item If the timer is started but non-repeating, stop it (as if it timed
		2212	out, without invoking it).
2045		2213
2046	If the timer is repeating, either start it if necessary (with the	2214	=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.	2215	and start the timer, if necessary.
2048		2216
		2217	=back
		2218
2049	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2219	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2050	usage example.	2220	usage example.
2051		2221
2052	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2222	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2053		2223
2054	Returns the remaining time until a timer fires. If the timer is active,	2224	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	2277	Periodic watchers are also timers of a kind, but they are very versatile
2108	(and unfortunately a bit complex).	2278	(and unfortunately a bit complex).
2109		2279
2110	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2280	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	2281	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	2282	(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	2283	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	2284	time, and time jumps are not uncommon (e.g. when you adjust your
2115	wrist-watch).	2285	wrist-watch).
2116		2286
2117	You can tell a periodic watcher to trigger after some specific point	2287	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	2292	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2123	it, as it uses a relative timeout).	2293	it, as it uses a relative timeout).
2124		2294
2125	C<ev_periodic> watchers can also be used to implement vastly more complex	2295	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	2296	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	2297	other complicated rules. This cannot easily be done with C<ev_timer>
2128	those cannot react to time jumps.	2298	watchers, as those cannot react to time jumps.
2129		2299
2130	As with timers, the callback is guaranteed to be invoked only when the	2300	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	2301	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	2302	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	2303	earlier time-out values are invoked before ones with later time-out values
…		…
2174		2344
2175	Another way to think about it (for the mathematically inclined) is that	2345	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	2346	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.	2347	time where C<time = offset (mod interval)>, regardless of any time jumps.
2178		2348
2179	For numerical stability it is preferable that the C<offset> value is near	2349	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	2350	interval value should be higher than C<1/8192> (which is around 100
2181	this value, and in fact is often specified as zero.	2351	microseconds) and C<offset> should be higher than C<0> and should have
		2352	at most a similar magnitude as the current time (say, within a factor of
		2353	ten). Typical values for offset are, in fact, C<0> or something between
		2354	C<0> and C<interval>, which is also the recommended range.
2182		2355
2183	Note also that there is an upper limit to how often a timer can fire (CPU	2356	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	2357	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	2358	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).	2359	millisecond (if the OS supports it and the machine is fast enough).
…		…
2216		2389
2217	NOTE: I<< This callback must always return a time that is higher than or	2390	NOTE: I<< This callback must always return a time that is higher than or
2218	equal to the passed C<now> value >>.	2391	equal to the passed C<now> value >>.
2219		2392
2220	This can be used to create very complex timers, such as a timer that	2393	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	2394	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	2395	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	2396	this. Here is a (completely untested, no error checking) example on how to
2224	reason I omitted it as an example).	2397	do this:
		2398
		2399	#include <time.h>
		2400
		2401	static ev_tstamp
		2402	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2403	{
		2404	time_t tnow = (time_t)now;
		2405	struct tm tm;
		2406	localtime_r (&tnow, &tm);
		2407
		2408	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2409	++tm.tm_mday; // midnight next day
		2410
		2411	return mktime (&tm);
		2412	}
		2413
		2414	Note: this code might run into trouble on days that have more then two
		2415	midnights (beginning and end).
2225		2416
2226	=back	2417	=back
2227		2418
2228	=item ev_periodic_again (loop, ev_periodic *)	2419	=item ev_periodic_again (loop, ev_periodic *)
2229		2420
…		…
2294		2485
2295	ev_periodic hourly_tick;	2486	ev_periodic hourly_tick;
2296	ev_periodic_init (&hourly_tick, clock_cb,	2487	ev_periodic_init (&hourly_tick, clock_cb,
2297	fmod (ev_now (loop), 3600.), 3600., 0);	2488	fmod (ev_now (loop), 3600.), 3600., 0);
2298	ev_periodic_start (loop, &hourly_tick);	2489	ev_periodic_start (loop, &hourly_tick);
2299		2490
2300		2491
2301	=head2 C<ev_signal> - signal me when a signal gets signalled!	2492	=head2 C<ev_signal> - signal me when a signal gets signalled!
2302		2493
2303	Signal watchers will trigger an event when the process receives a specific	2494	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	2495	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	2505	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	2506	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	2507	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.	2508	the moment, C<SIGCHLD> is permanently tied to the default loop.
2318		2509
2319	When the first watcher gets started will libev actually register something	2510	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	2511	register something with the kernel. It thus coexists with your own signal
2321	you don't register any with libev for the same signal).	2512	handlers as long as you don't register any with libev for the same signal.
2322		2513
2323	If possible and supported, libev will install its handlers with	2514	If possible and supported, libev will install its handlers with
2324	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2515	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	2516	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	2517	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	2520	=head3 The special problem of inheritance over fork/execve/pthread_create
2330		2521
2331	Both the signal mask (C<sigprocmask>) and the signal disposition	2522	Both the signal mask (C<sigprocmask>) and the signal disposition
2332	(C<sigaction>) are unspecified after starting a signal watcher (and after	2523	(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,	2524	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.	2525	and might or might not set or restore the installed signal handler (but
		2526	see C<EVFLAG_NOSIGMASK>).
2335		2527
2336	While this does not matter for the signal disposition (libev never	2528	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	2529	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	2530	C<execve>), this matters for the signal mask: many programs do not expect
2339	certain signals to be blocked.	2531	certain signals to be blocked.
…		…
2510		2702
2511	=head2 C<ev_stat> - did the file attributes just change?	2703	=head2 C<ev_stat> - did the file attributes just change?
2512		2704
2513	This watches a file system path for attribute changes. That is, it calls	2705	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)	2706	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	2707	and sees if it changed compared to the last time, invoking the callback
2516	it did.	2708	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2709	happen after the watcher has been started will be reported.
2517		2710
2518	The path does not need to exist: changing from "path exists" to "path does	2711	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	2712	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	2713	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	2714	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	2944	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	2945	effect on its own sometimes), idle watchers are a good place to do
2753	"pseudo-background processing", or delay processing stuff to after the	2946	"pseudo-background processing", or delay processing stuff to after the
2754	event loop has handled all outstanding events.	2947	event loop has handled all outstanding events.
2755		2948
		2949	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2950
		2951	As long as there is at least one active idle watcher, libev will never
		2952	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2953	For this to work, the idle watcher doesn't need to be invoked at all - the
		2954	lowest priority will do.
		2955
		2956	This mode of operation can be useful together with an C<ev_check> watcher,
		2957	to do something on each event loop iteration - for example to balance load
		2958	between different connections.
		2959
		2960	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2961	example.
		2962
2756	=head3 Watcher-Specific Functions and Data Members	2963	=head3 Watcher-Specific Functions and Data Members
2757		2964
2758	=over 4	2965	=over 4
2759		2966
2760	=item ev_idle_init (ev_idle *, callback)	2967	=item ev_idle_init (ev_idle *, callback)
…		…
2771	callback, free it. Also, use no error checking, as usual.	2978	callback, free it. Also, use no error checking, as usual.
2772		2979
2773	static void	2980	static void
2774	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2981	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2775	{	2982	{
		2983	// stop the watcher
		2984	ev_idle_stop (loop, w);
		2985
		2986	// now we can free it
2776	free (w);	2987	free (w);
		2988
2777	// now do something you wanted to do when the program has	2989	// now do something you wanted to do when the program has
2778	// no longer anything immediate to do.	2990	// no longer anything immediate to do.
2779	}	2991	}
2780		2992
2781	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2993	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2783	ev_idle_start (loop, idle_watcher);	2995	ev_idle_start (loop, idle_watcher);
2784		2996
2785		2997
2786	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2998	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2787		2999
2788	Prepare and check watchers are usually (but not always) used in pairs:	3000	Prepare and check watchers are often (but not always) used in pairs:
2789	prepare watchers get invoked before the process blocks and check watchers	3001	prepare watchers get invoked before the process blocks and check watchers
2790	afterwards.	3002	afterwards.
2791		3003
2792	You I<must not> call C<ev_run> or similar functions that enter	3004	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>	3005	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	3006	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	3007	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,	3008	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	3009	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2798	called in pairs bracketing the blocking call.	3010	kind they will always be called in pairs bracketing the blocking call.
2799		3011
2800	Their main purpose is to integrate other event mechanisms into libev and	3012	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	3013	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	3014	variable changes, implement your own watchers, integrate net-snmp or a
2803	coroutine library and lots more. They are also occasionally useful if	3015	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	3033	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	3034	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	3035	loop from blocking if lower-priority coroutines are active, thus mapping
2824	low-priority coroutines to idle/background tasks).	3036	low-priority coroutines to idle/background tasks).
2825		3037
2826	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3038	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	3039	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).	3040	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3041	watchers).
2829		3042
2830	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3043	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	3044	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	3045	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	3046	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	3047	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	3048	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2836	others).	3049	others).
		3050
		3051	=head3 Abusing an C<ev_check> watcher for its side-effect
		3052
		3053	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3054	useful because they are called once per event loop iteration. For
		3055	example, if you want to handle a large number of connections fairly, you
		3056	normally only do a bit of work for each active connection, and if there
		3057	is more work to do, you wait for the next event loop iteration, so other
		3058	connections have a chance of making progress.
		3059
		3060	Using an C<ev_check> watcher is almost enough: it will be called on the
		3061	next event loop iteration. However, that isn't as soon as possible -
		3062	without external events, your C<ev_check> watcher will not be invoked.
		3063
		3064	This is where C<ev_idle> watchers come in handy - all you need is a
		3065	single global idle watcher that is active as long as you have one active
		3066	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3067	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3068	invoked. Neither watcher alone can do that.
2837		3069
2838	=head3 Watcher-Specific Functions and Data Members	3070	=head3 Watcher-Specific Functions and Data Members
2839		3071
2840	=over 4	3072	=over 4
2841		3073
…		…
3042		3274
3043	=over 4	3275	=over 4
3044		3276
3045	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3277	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
3046		3278
3047	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3279	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
3048		3280
3049	Configures the watcher to embed the given loop, which must be	3281	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	3282	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	3283	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,	3284	to invoke it (it will continue to be called until the sweep has been done,
…		…
3073	used).	3305	used).
3074		3306
3075	struct ev_loop *loop_hi = ev_default_init (0);	3307	struct ev_loop *loop_hi = ev_default_init (0);
3076	struct ev_loop *loop_lo = 0;	3308	struct ev_loop *loop_lo = 0;
3077	ev_embed embed;	3309	ev_embed embed;
3078		3310
3079	// see if there is a chance of getting one that works	3311	// see if there is a chance of getting one that works
3080	// (remember that a flags value of 0 means autodetection)	3312	// (remember that a flags value of 0 means autodetection)
3081	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3313	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3082	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3314	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3083	: 0;	3315	: 0;
…		…
3097	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3329	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3098		3330
3099	struct ev_loop *loop = ev_default_init (0);	3331	struct ev_loop *loop = ev_default_init (0);
3100	struct ev_loop *loop_socket = 0;	3332	struct ev_loop *loop_socket = 0;
3101	ev_embed embed;	3333	ev_embed embed;
3102		3334
3103	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3335	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3104	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3336	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3105	{	3337	{
3106	ev_embed_init (&embed, 0, loop_socket);	3338	ev_embed_init (&embed, 0, loop_socket);
3107	ev_embed_start (loop, &embed);	3339	ev_embed_start (loop, &embed);
…		…
3115		3347
3116	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3348	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3117		3349
3118	Fork watchers are called when a C<fork ()> was detected (usually because	3350	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	3351	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	3352	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,	3353	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	3354	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	3355	and calls it in the wrong process, the fork handlers will be invoked, too,
3124	handlers will be invoked, too, of course.	3356	of course.
3125		3357
3126	=head3 The special problem of life after fork - how is it possible?	3358	=head3 The special problem of life after fork - how is it possible?
3127		3359
3128	Most uses of C<fork()> consist of forking, then some simple calls to set	3360	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	3361	up/change the process environment, followed by a call to C<exec()>. This
3130	sequence should be handled by libev without any problems.	3362	sequence should be handled by libev without any problems.
3131		3363
3132	This changes when the application actually wants to do event handling	3364	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	3365	in the child, or both parent in child, in effect "continuing" after the
…		…
3210	atexit (program_exits);	3442	atexit (program_exits);
3211		3443
3212		3444
3213	=head2 C<ev_async> - how to wake up an event loop	3445	=head2 C<ev_async> - how to wake up an event loop
3214		3446
3215	In general, you cannot use an C<ev_run> from multiple threads or other	3447	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	3448	asynchronous sources such as signal handlers (as opposed to multiple event
3217	loops - those are of course safe to use in different threads).	3449	loops - those are of course safe to use in different threads).
3218		3450
3219	Sometimes, however, you need to wake up an event loop you do not control,	3451	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>	3452	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.	3454	it by calling C<ev_async_send>, which is thread- and signal safe.
3223		3455
3224	This functionality is very similar to C<ev_signal> watchers, as signals,	3456	This functionality is very similar to C<ev_signal> watchers, as signals,
3225	too, are asynchronous in nature, and signals, too, will be compressed	3457	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	3458	(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	3459	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	3460	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,	3461	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3230	even without knowing which loop owns the signal.	3462	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		3463
3235	=head3 Queueing	3464	=head3 Queueing
3236		3465
3237	C<ev_async> does not support queueing of data in any way. The reason	3466	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	3467	is that the author does not know of a simple (or any) algorithm for a
…		…
3330	trust me.	3559	trust me.
3331		3560
3332	=item ev_async_send (loop, ev_async *)	3561	=item ev_async_send (loop, ev_async *)
3333		3562
3334	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3563	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	3564	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3565	returns.
		3566
3336	C<ev_feed_event>, this call is safe to do from other threads, signal or	3567	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	3568	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3338	section below on what exactly this means).	3569	embedding section below on what exactly this means).
3339		3570
3340	Note that, as with other watchers in libev, multiple events might get	3571	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	3572	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>,	3573	this is that C<ev_async> watchers are level-triggered: they are set on
3343	reset when the event loop detects that).	3574	C<ev_async_send>, reset when the event loop detects that).
3344		3575
3345	This call incurs the overhead of a system call only once per event loop	3576	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	3577	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.	3578	the event loop (or your program) is processing events. That means that
		3579	repeated calls are basically free (there is no need to avoid calls for
		3580	performance reasons) and that the overhead becomes smaller (typically
		3581	zero) under load.
3348		3582
3349	=item bool = ev_async_pending (ev_async *)	3583	=item bool = ev_async_pending (ev_async *)
3350		3584
3351	Returns a non-zero value when C<ev_async_send> has been called on the	3585	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	3586	watcher but the event has not yet been processed (or even noted) by the
…		…
3369		3603
3370	There are some other functions of possible interest. Described. Here. Now.	3604	There are some other functions of possible interest. Described. Here. Now.
3371		3605
3372	=over 4	3606	=over 4
3373		3607
3374	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3608	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3375		3609
3376	This function combines a simple timer and an I/O watcher, calls your	3610	This function combines a simple timer and an I/O watcher, calls your
3377	callback on whichever event happens first and automatically stops both	3611	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	3612	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	3613	or timeout without having to allocate/configure/start/stop/free one or
…		…
3407	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3641	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3408		3642
3409	=item ev_feed_fd_event (loop, int fd, int revents)	3643	=item ev_feed_fd_event (loop, int fd, int revents)
3410		3644
3411	Feed an event on the given fd, as if a file descriptor backend detected	3645	Feed an event on the given fd, as if a file descriptor backend detected
3412	the given events it.	3646	the given events.
3413		3647
3414	=item ev_feed_signal_event (loop, int signum)	3648	=item ev_feed_signal_event (loop, int signum)
3415		3649
3416	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,	3650	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3417	which is async-safe.	3651	which is async-safe.
…		…
3423		3657
3424	This section explains some common idioms that are not immediately	3658	This section explains some common idioms that are not immediately
3425	obvious. Note that examples are sprinkled over the whole manual, and this	3659	obvious. Note that examples are sprinkled over the whole manual, and this
3426	section only contains stuff that wouldn't fit anywhere else.	3660	section only contains stuff that wouldn't fit anywhere else.
3427		3661
3428	=over 4	3662	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3429		3663
3430	=item Model/nested event loop invocations and exit conditions.	3664	Each watcher has, by default, a C<void *data> member that you can read
		3665	or modify at any time: libev will completely ignore it. This can be used
		3666	to associate arbitrary data with your watcher. If you need more data and
		3667	don't want to allocate memory separately and store a pointer to it in that
		3668	data member, you can also "subclass" the watcher type and provide your own
		3669	data:
		3670
		3671	struct my_io
		3672	{
		3673	ev_io io;
		3674	int otherfd;
		3675	void *somedata;
		3676	struct whatever *mostinteresting;
		3677	};
		3678
		3679	...
		3680	struct my_io w;
		3681	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3682
		3683	And since your callback will be called with a pointer to the watcher, you
		3684	can cast it back to your own type:
		3685
		3686	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3687	{
		3688	struct my_io *w = (struct my_io *)w_;
		3689	...
		3690	}
		3691
		3692	More interesting and less C-conformant ways of casting your callback
		3693	function type instead have been omitted.
		3694
		3695	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3696
		3697	Another common scenario is to use some data structure with multiple
		3698	embedded watchers, in effect creating your own watcher that combines
		3699	multiple libev event sources into one "super-watcher":
		3700
		3701	struct my_biggy
		3702	{
		3703	int some_data;
		3704	ev_timer t1;
		3705	ev_timer t2;
		3706	}
		3707
		3708	In this case getting the pointer to C<my_biggy> is a bit more
		3709	complicated: Either you store the address of your C<my_biggy> struct in
		3710	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3711	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3712	real programmers):
		3713
		3714	#include <stddef.h>
		3715
		3716	static void
		3717	t1_cb (EV_P_ ev_timer *w, int revents)
		3718	{
		3719	struct my_biggy big = (struct my_biggy *)
		3720	(((char *)w) - offsetof (struct my_biggy, t1));
		3721	}
		3722
		3723	static void
		3724	t2_cb (EV_P_ ev_timer *w, int revents)
		3725	{
		3726	struct my_biggy big = (struct my_biggy *)
		3727	(((char *)w) - offsetof (struct my_biggy, t2));
		3728	}
		3729
		3730	=head2 AVOIDING FINISHING BEFORE RETURNING
		3731
		3732	Often you have structures like this in event-based programs:
		3733
		3734	callback ()
		3735	{
		3736	free (request);
		3737	}
		3738
		3739	request = start_new_request (..., callback);
		3740
		3741	The intent is to start some "lengthy" operation. The C<request> could be
		3742	used to cancel the operation, or do other things with it.
		3743
		3744	It's not uncommon to have code paths in C<start_new_request> that
		3745	immediately invoke the callback, for example, to report errors. Or you add
		3746	some caching layer that finds that it can skip the lengthy aspects of the
		3747	operation and simply invoke the callback with the result.
		3748
		3749	The problem here is that this will happen I<before> C<start_new_request>
		3750	has returned, so C<request> is not set.
		3751
		3752	Even if you pass the request by some safer means to the callback, you
		3753	might want to do something to the request after starting it, such as
		3754	canceling it, which probably isn't working so well when the callback has
		3755	already been invoked.
		3756
		3757	A common way around all these issues is to make sure that
		3758	C<start_new_request> I<always> returns before the callback is invoked. If
		3759	C<start_new_request> immediately knows the result, it can artificially
		3760	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3761	example, or more sneakily, by reusing an existing (stopped) watcher and
		3762	pushing it into the pending queue:
		3763
		3764	ev_set_cb (watcher, callback);
		3765	ev_feed_event (EV_A_ watcher, 0);
		3766
		3767	This way, C<start_new_request> can safely return before the callback is
		3768	invoked, while not delaying callback invocation too much.
		3769
		3770	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3431		3771
3432	Often (especially in GUI toolkits) there are places where you have	3772	Often (especially in GUI toolkits) there are places where you have
3433	I<modal> interaction, which is most easily implemented by recursively	3773	I<modal> interaction, which is most easily implemented by recursively
3434	invoking C<ev_run>.	3774	invoking C<ev_run>.
3435		3775
3436	This brings the problem of exiting - a callback might want to finish the	3776	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	3777	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	3778	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	3779	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.	3780	other combination: In these cases, a simple C<ev_break> will not work.
3441		3781
3442	The solution is to maintain "break this loop" variable for each C<ev_run>	3782	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	3783	invocation, and use a loop around C<ev_run> until the condition is
3444	triggered, using C<EVRUN_ONCE>:	3784	triggered, using C<EVRUN_ONCE>:
3445		3785
…		…
3447	int exit_main_loop = 0;	3787	int exit_main_loop = 0;
3448		3788
3449	while (!exit_main_loop)	3789	while (!exit_main_loop)
3450	ev_run (EV_DEFAULT_ EVRUN_ONCE);	3790	ev_run (EV_DEFAULT_ EVRUN_ONCE);
3451		3791
3452	// in a model watcher	3792	// in a modal watcher
3453	int exit_nested_loop = 0;	3793	int exit_nested_loop = 0;
3454		3794
3455	while (!exit_nested_loop)	3795	while (!exit_nested_loop)
3456	ev_run (EV_A_ EVRUN_ONCE);	3796	ev_run (EV_A_ EVRUN_ONCE);
3457		3797
…		…
3464	exit_main_loop = 1;	3804	exit_main_loop = 1;
3465		3805
3466	// exit both	3806	// exit both
3467	exit_main_loop = exit_nested_loop = 1;	3807	exit_main_loop = exit_nested_loop = 1;
3468		3808
3469	=back	3809	=head2 THREAD LOCKING EXAMPLE
		3810
		3811	Here is a fictitious example of how to run an event loop in a different
		3812	thread from where callbacks are being invoked and watchers are
		3813	created/added/removed.
		3814
		3815	For a real-world example, see the C<EV::Loop::Async> perl module,
		3816	which uses exactly this technique (which is suited for many high-level
		3817	languages).
		3818
		3819	The example uses a pthread mutex to protect the loop data, a condition
		3820	variable to wait for callback invocations, an async watcher to notify the
		3821	event loop thread and an unspecified mechanism to wake up the main thread.
		3822
		3823	First, you need to associate some data with the event loop:
		3824
		3825	typedef struct {
		3826	mutex_t lock; /* global loop lock */
		3827	ev_async async_w;
		3828	thread_t tid;
		3829	cond_t invoke_cv;
		3830	} userdata;
		3831
		3832	void prepare_loop (EV_P)
		3833	{
		3834	// for simplicity, we use a static userdata struct.
		3835	static userdata u;
		3836
		3837	ev_async_init (&u->async_w, async_cb);
		3838	ev_async_start (EV_A_ &u->async_w);
		3839
		3840	pthread_mutex_init (&u->lock, 0);
		3841	pthread_cond_init (&u->invoke_cv, 0);
		3842
		3843	// now associate this with the loop
		3844	ev_set_userdata (EV_A_ u);
		3845	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3846	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3847
		3848	// then create the thread running ev_run
		3849	pthread_create (&u->tid, 0, l_run, EV_A);
		3850	}
		3851
		3852	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3853	solely to wake up the event loop so it takes notice of any new watchers
		3854	that might have been added:
		3855
		3856	static void
		3857	async_cb (EV_P_ ev_async *w, int revents)
		3858	{
		3859	// just used for the side effects
		3860	}
		3861
		3862	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3863	protecting the loop data, respectively.
		3864
		3865	static void
		3866	l_release (EV_P)
		3867	{
		3868	userdata *u = ev_userdata (EV_A);
		3869	pthread_mutex_unlock (&u->lock);
		3870	}
		3871
		3872	static void
		3873	l_acquire (EV_P)
		3874	{
		3875	userdata *u = ev_userdata (EV_A);
		3876	pthread_mutex_lock (&u->lock);
		3877	}
		3878
		3879	The event loop thread first acquires the mutex, and then jumps straight
		3880	into C<ev_run>:
		3881
		3882	void *
		3883	l_run (void *thr_arg)
		3884	{
		3885	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3886
		3887	l_acquire (EV_A);
		3888	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3889	ev_run (EV_A_ 0);
		3890	l_release (EV_A);
		3891
		3892	return 0;
		3893	}
		3894
		3895	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3896	signal the main thread via some unspecified mechanism (signals? pipe
		3897	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3898	have been called (in a while loop because a) spurious wakeups are possible
		3899	and b) skipping inter-thread-communication when there are no pending
		3900	watchers is very beneficial):
		3901
		3902	static void
		3903	l_invoke (EV_P)
		3904	{
		3905	userdata *u = ev_userdata (EV_A);
		3906
		3907	while (ev_pending_count (EV_A))
		3908	{
		3909	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3910	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3911	}
		3912	}
		3913
		3914	Now, whenever the main thread gets told to invoke pending watchers, it
		3915	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3916	thread to continue:
		3917
		3918	static void
		3919	real_invoke_pending (EV_P)
		3920	{
		3921	userdata *u = ev_userdata (EV_A);
		3922
		3923	pthread_mutex_lock (&u->lock);
		3924	ev_invoke_pending (EV_A);
		3925	pthread_cond_signal (&u->invoke_cv);
		3926	pthread_mutex_unlock (&u->lock);
		3927	}
		3928
		3929	Whenever you want to start/stop a watcher or do other modifications to an
		3930	event loop, you will now have to lock:
		3931
		3932	ev_timer timeout_watcher;
		3933	userdata *u = ev_userdata (EV_A);
		3934
		3935	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3936
		3937	pthread_mutex_lock (&u->lock);
		3938	ev_timer_start (EV_A_ &timeout_watcher);
		3939	ev_async_send (EV_A_ &u->async_w);
		3940	pthread_mutex_unlock (&u->lock);
		3941
		3942	Note that sending the C<ev_async> watcher is required because otherwise
		3943	an event loop currently blocking in the kernel will have no knowledge
		3944	about the newly added timer. By waking up the loop it will pick up any new
		3945	watchers in the next event loop iteration.
		3946
		3947	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3948
		3949	While the overhead of a callback that e.g. schedules a thread is small, it
		3950	is still an overhead. If you embed libev, and your main usage is with some
		3951	kind of threads or coroutines, you might want to customise libev so that
		3952	doesn't need callbacks anymore.
		3953
		3954	Imagine you have coroutines that you can switch to using a function
		3955	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3956	and that due to some magic, the currently active coroutine is stored in a
		3957	global called C<current_coro>. Then you can build your own "wait for libev
		3958	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3959	the differing C<;> conventions):
		3960
		3961	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3962	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3963
		3964	That means instead of having a C callback function, you store the
		3965	coroutine to switch to in each watcher, and instead of having libev call
		3966	your callback, you instead have it switch to that coroutine.
		3967
		3968	A coroutine might now wait for an event with a function called
		3969	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3970	matter when, or whether the watcher is active or not when this function is
		3971	called):
		3972
		3973	void
		3974	wait_for_event (ev_watcher *w)
		3975	{
		3976	ev_set_cb (w, current_coro);
		3977	switch_to (libev_coro);
		3978	}
		3979
		3980	That basically suspends the coroutine inside C<wait_for_event> and
		3981	continues the libev coroutine, which, when appropriate, switches back to
		3982	this or any other coroutine.
		3983
		3984	You can do similar tricks if you have, say, threads with an event queue -
		3985	instead of storing a coroutine, you store the queue object and instead of
		3986	switching to a coroutine, you push the watcher onto the queue and notify
		3987	any waiters.
		3988
		3989	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3990	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3991
		3992	// my_ev.h
		3993	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3994	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3995	#include "../libev/ev.h"
		3996
		3997	// my_ev.c
		3998	#define EV_H "my_ev.h"
		3999	#include "../libev/ev.c"
		4000
		4001	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4002	F<my_ev.c> into your project. When properly specifying include paths, you
		4003	can even use F<ev.h> as header file name directly.
3470		4004
3471		4005
3472	=head1 LIBEVENT EMULATION	4006	=head1 LIBEVENT EMULATION
3473		4007
3474	Libev offers a compatibility emulation layer for libevent. It cannot	4008	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3504		4038
3505	=back	4039	=back
3506		4040
3507	=head1 C++ SUPPORT	4041	=head1 C++ SUPPORT
3508		4042
		4043	=head2 C API
		4044
		4045	The normal C API should work fine when used from C++: both ev.h and the
		4046	libev sources can be compiled as C++. Therefore, code that uses the C API
		4047	will work fine.
		4048
		4049	Proper exception specifications might have to be added to callbacks passed
		4050	to libev: exceptions may be thrown only from watcher callbacks, all other
		4051	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4052	callbacks) must not throw exceptions, and might need a C<noexcept>
		4053	specification. If you have code that needs to be compiled as both C and
		4054	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4055
		4056	static void
		4057	fatal_error (const char *msg) EV_NOEXCEPT
		4058	{
		4059	perror (msg);
		4060	abort ();
		4061	}
		4062
		4063	...
		4064	ev_set_syserr_cb (fatal_error);
		4065
		4066	The only API functions that can currently throw exceptions are C<ev_run>,
		4067	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4068	because it runs cleanup watchers).
		4069
		4070	Throwing exceptions in watcher callbacks is only supported if libev itself
		4071	is compiled with a C++ compiler or your C and C++ environments allow
		4072	throwing exceptions through C libraries (most do).
		4073
		4074	=head2 C++ API
		4075
3509	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4076	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	4077	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.	4078	the callback model to a model using method callbacks on objects.
3512		4079
3513	To use it,	4080	To use it,
3514		4081
3515	#include <ev++.h>	4082	#include <ev++.h>
3516		4083
3517	This automatically includes F<ev.h> and puts all of its definitions (many	4084	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	4085	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	4086	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	4095	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	4096	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	4097	you need support for other types of functors please contact the author
3531	(preferably after implementing it).	4098	(preferably after implementing it).
3532		4099
		4100	For all this to work, your C++ compiler either has to use the same calling
		4101	conventions as your C compiler (for static member functions), or you have
		4102	to embed libev and compile libev itself as C++.
		4103
3533	Here is a list of things available in the C<ev> namespace:	4104	Here is a list of things available in the C<ev> namespace:
3534		4105
3535	=over 4	4106	=over 4
3536		4107
3537	=item C<ev::READ>, C<ev::WRITE> etc.	4108	=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.	4117	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3547		4118
3548	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4119	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>	4120	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	4121	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3551	defines by many implementations.	4122	defined by many implementations.
3552		4123
3553	All of those classes have these methods:	4124	All of those classes have these methods:
3554		4125
3555	=over 4	4126	=over 4
3556		4127
…		…
3618	void operator() (ev::io &w, int revents)	4189	void operator() (ev::io &w, int revents)
3619	{	4190	{
3620	...	4191	...
3621	}	4192	}
3622	}	4193	}
3623		4194
3624	myfunctor f;	4195	myfunctor f;
3625		4196
3626	ev::io w;	4197	ev::io w;
3627	w.set (&f);	4198	w.set (&f);
3628		4199
…		…
3646	Associates a different C<struct ev_loop> with this watcher. You can only	4217	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).	4218	do this when the watcher is inactive (and not pending either).
3648		4219
3649	=item w->set ([arguments])	4220	=item w->set ([arguments])
3650		4221
3651	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4222	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	4223	with the same arguments. Either this method or a suitable start method
3653	C counterpart, an active watcher gets automatically stopped and restarted	4224	must be called at least once. Unlike the C counterpart, an active watcher
3654	when reconfiguring it with this method.	4225	gets automatically stopped and restarted when reconfiguring it with this
		4226	method.
		4227
		4228	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4229	clashing with the C<set (loop)> method.
3655		4230
3656	=item w->start ()	4231	=item w->start ()
3657		4232
3658	Starts the watcher. Note that there is no C<loop> argument, as the	4233	Starts the watcher. Note that there is no C<loop> argument, as the
3659	constructor already stores the event loop.	4234	constructor already stores the event loop.
…		…
3689	watchers in the constructor.	4264	watchers in the constructor.
3690		4265
3691	class myclass	4266	class myclass
3692	{	4267	{
3693	ev::io io ; void io_cb (ev::io &w, int revents);	4268	ev::io io ; void io_cb (ev::io &w, int revents);
3694	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4269	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3695	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4270	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3696		4271
3697	myclass (int fd)	4272	myclass (int fd)
3698	{	4273	{
3699	io .set <myclass, &myclass::io_cb > (this);	4274	io .set <myclass, &myclass::io_cb > (this);
…		…
3750	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4325	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3751		4326
3752	=item D	4327	=item D
3753		4328
3754	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4329	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>.	4330	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3756		4331
3757	=item Ocaml	4332	=item Ocaml
3758		4333
3759	Erkki Seppala has written Ocaml bindings for libev, to be found at	4334	Erkki Seppala has written Ocaml bindings for libev, to be found at
3760	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4335	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3763		4338
3764	Brian Maher has written a partial interface to libev for lua (at the	4339	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	4340	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3766	L<http://github.com/brimworks/lua-ev>.	4341	L<http://github.com/brimworks/lua-ev>.
3767		4342
		4343	=item Javascript
		4344
		4345	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4346
		4347	=item Others
		4348
		4349	There are others, and I stopped counting.
		4350
3768	=back	4351	=back
3769		4352
3770		4353
3771	=head1 MACRO MAGIC	4354	=head1 MACRO MAGIC
3772		4355
…		…
3808	suitable for use with C<EV_A>.	4391	suitable for use with C<EV_A>.
3809		4392
3810	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4393	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3811		4394
3812	Similar to the other two macros, this gives you the value of the default	4395	Similar to the other two macros, this gives you the value of the default
3813	loop, if multiple loops are supported ("ev loop default").	4396	loop, if multiple loops are supported ("ev loop default"). The default loop
		4397	will be initialised if it isn't already initialised.
		4398
		4399	For non-multiplicity builds, these macros do nothing, so you always have
		4400	to initialise the loop somewhere.
3814		4401
3815	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4402	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3816		4403
3817	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4404	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	4405	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3885	ev_vars.h	4472	ev_vars.h
3886	ev_wrap.h	4473	ev_wrap.h
3887		4474
3888	ev_win32.c required on win32 platforms only	4475	ev_win32.c required on win32 platforms only
3889		4476
3890	ev_select.c only when select backend is enabled (which is enabled by default)	4477	ev_select.c only when select backend is enabled
3891	ev_poll.c only when poll backend is enabled (disabled by default)	4478	ev_poll.c only when poll backend is enabled
3892	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4479	ev_epoll.c only when the epoll backend is enabled
		4480	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)	4481	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)	4482	ev_port.c only when the solaris port backend is enabled
3895		4483
3896	F<ev.c> includes the backend files directly when enabled, so you only need	4484	F<ev.c> includes the backend files directly when enabled, so you only need
3897	to compile this single file.	4485	to compile this single file.
3898		4486
3899	=head3 LIBEVENT COMPATIBILITY API	4487	=head3 LIBEVENT COMPATIBILITY API
…		…
3963	supported). It will also not define any of the structs usually found in	4551	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.	4552	F<event.h> that are not directly supported by the libev core alone.
3965		4553
3966	In standalone mode, libev will still try to automatically deduce the	4554	In standalone mode, libev will still try to automatically deduce the
3967	configuration, but has to be more conservative.	4555	configuration, but has to be more conservative.
		4556
		4557	=item EV_USE_FLOOR
		4558
		4559	If defined to be C<1>, libev will use the C<floor ()> function for its
		4560	periodic reschedule calculations, otherwise libev will fall back on a
		4561	portable (slower) implementation. If you enable this, you usually have to
		4562	link against libm or something equivalent. Enabling this when the C<floor>
		4563	function is not available will fail, so the safe default is to not enable
		4564	this.
3968		4565
3969	=item EV_USE_MONOTONIC	4566	=item EV_USE_MONOTONIC
3970		4567
3971	If defined to be C<1>, libev will try to detect the availability of the	4568	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	4569	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	4655	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	4656	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	4657	file descriptors again. Note that the replacement function has to close
4061	the underlying OS handle.	4658	the underlying OS handle.
4062		4659
		4660	=item EV_USE_WSASOCKET
		4661
		4662	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4663	communication socket, which works better in some environments. Otherwise,
		4664	the normal C<socket> function will be used, which works better in other
		4665	environments.
		4666
4063	=item EV_USE_POLL	4667	=item EV_USE_POLL
4064		4668
4065	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4669	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	4670	backend. Otherwise it will be enabled on non-win32 platforms. It
4067	takes precedence over select.	4671	takes precedence over select.
…		…
4071	If defined to be C<1>, libev will compile in support for the Linux	4675	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,	4676	C<epoll>(7) backend. Its availability will be detected at runtime,
4073	otherwise another method will be used as fallback. This is the preferred	4677	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	4678	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.	4679	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4680
		4681	=item EV_USE_LINUXAIO
		4682
		4683	If defined to be C<1>, libev will compile in support for the Linux
		4684	aio backend. Due to it's currenbt limitations it has to be requested
		4685	explicitly. If undefined, it will be enabled on linux, otherwise
		4686	disabled.
4076		4687
4077	=item EV_USE_KQUEUE	4688	=item EV_USE_KQUEUE
4078		4689
4079	If defined to be C<1>, libev will compile in support for the BSD style	4690	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,	4691	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	4713	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	4714	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	4715	be detected at runtime. If undefined, it will be enabled if the headers
4105	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4716	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4106		4717
		4718	=item EV_NO_SMP
		4719
		4720	If defined to be C<1>, libev will assume that memory is always coherent
		4721	between threads, that is, threads can be used, but threads never run on
		4722	different cpus (or different cpu cores). This reduces dependencies
		4723	and makes libev faster.
		4724
		4725	=item EV_NO_THREADS
		4726
		4727	If defined to be C<1>, libev will assume that it will never be called from
		4728	different threads (that includes signal handlers), which is a stronger
		4729	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4730	libev faster.
		4731
4107	=item EV_ATOMIC_T	4732	=item EV_ATOMIC_T
4108		4733
4109	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4734	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	4735	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	4736	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"	4737	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.	4738	handler "locking" as well as for signal and thread safety in C<ev_async>
		4739	watchers.
4114		4740
4115	In the absence of this define, libev will use C<sig_atomic_t volatile>	4741	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.	4742	(from F<signal.h>), which is usually good enough on most platforms.
4117		4743
4118	=item EV_H (h)	4744	=item EV_H (h)
…		…
4145	will have the C<struct ev_loop *> as first argument, and you can create	4771	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	4772	additional independent event loops. Otherwise there will be no support
4147	for multiple event loops and there is no first event loop pointer	4773	for multiple event loops and there is no first event loop pointer
4148	argument. Instead, all functions act on the single default loop.	4774	argument. Instead, all functions act on the single default loop.
4149		4775
		4776	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4777	default loop when multiplicity is switched off - you always have to
		4778	initialise the loop manually in this case.
		4779
4150	=item EV_MINPRI	4780	=item EV_MINPRI
4151		4781
4152	=item EV_MAXPRI	4782	=item EV_MAXPRI
4153		4783
4154	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4784	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4190	#define EV_USE_POLL 1	4820	#define EV_USE_POLL 1
4191	#define EV_CHILD_ENABLE 1	4821	#define EV_CHILD_ENABLE 1
4192	#define EV_ASYNC_ENABLE 1	4822	#define EV_ASYNC_ENABLE 1
4193		4823
4194	The actual value is a bitset, it can be a combination of the following	4824	The actual value is a bitset, it can be a combination of the following
4195	values:	4825	values (by default, all of these are enabled):
4196		4826
4197	=over 4	4827	=over 4
4198		4828
4199	=item C<1> - faster/larger code	4829	=item C<1> - faster/larger code
4200		4830
…		…
4204	code size by roughly 30% on amd64).	4834	code size by roughly 30% on amd64).
4205		4835
4206	When optimising for size, use of compiler flags such as C<-Os> with	4836	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	4837	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4208	assertions.	4838	assertions.
		4839
		4840	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4841	(e.g. gcc with C<-Os>).
4209		4842
4210	=item C<2> - faster/larger data structures	4843	=item C<2> - faster/larger data structures
4211		4844
4212	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4845	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	4846	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	4847	and can additionally have an effect on the size of data structures at
4215	runtime.	4848	runtime.
4216		4849
		4850	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4851	(e.g. gcc with C<-Os>).
		4852
4217	=item C<4> - full API configuration	4853	=item C<4> - full API configuration
4218		4854
4219	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4855	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4220	enables multiplicity (C<EV_MULTIPLICITY>=1).	4856	enables multiplicity (C<EV_MULTIPLICITY>=1).
4221		4857
…		…
4251		4887
4252	With an intelligent-enough linker (gcc+binutils are intelligent enough	4888	With an intelligent-enough linker (gcc+binutils are intelligent enough
4253	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4889	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	4890	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.	4891	I/O watcher then might come out at only 5Kb.
		4892
		4893	=item EV_API_STATIC
		4894
		4895	If this symbol is defined (by default it is not), then all identifiers
		4896	will have static linkage. This means that libev will not export any
		4897	identifiers, and you cannot link against libev anymore. This can be useful
		4898	when you embed libev, only want to use libev functions in a single file,
		4899	and do not want its identifiers to be visible.
		4900
		4901	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4902	wants to use libev.
		4903
		4904	This option only works when libev is compiled with a C compiler, as C++
		4905	doesn't support the required declaration syntax.
4256		4906
4257	=item EV_AVOID_STDIO	4907	=item EV_AVOID_STDIO
4258		4908
4259	If this is set to C<1> at compiletime, then libev will avoid using stdio	4909	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	4910	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:	5054	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4405		5055
4406	#include "ev_cpp.h"	5056	#include "ev_cpp.h"
4407	#include "ev.c"	5057	#include "ev.c"
4408		5058
4409	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5059	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4410		5060
4411	=head2 THREADS AND COROUTINES	5061	=head2 THREADS AND COROUTINES
4412		5062
4413	=head3 THREADS	5063	=head3 THREADS
4414		5064
…		…
4465	default loop and triggering an C<ev_async> watcher from the default loop	5115	default loop and triggering an C<ev_async> watcher from the default loop
4466	watcher callback into the event loop interested in the signal.	5116	watcher callback into the event loop interested in the signal.
4467		5117
4468	=back	5118	=back
4469		5119
4470	=head4 THREAD LOCKING EXAMPLE	5120	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		5121
4608	=head3 COROUTINES	5122	=head3 COROUTINES
4609		5123
4610	Libev is very accommodating to coroutines ("cooperative threads"):	5124	Libev is very accommodating to coroutines ("cooperative threads"):
4611	libev fully supports nesting calls to its functions from different	5125	libev fully supports nesting calls to its functions from different
…		…
4776	requires, and its I/O model is fundamentally incompatible with the POSIX	5290	requires, and its I/O model is fundamentally incompatible with the POSIX
4777	model. Libev still offers limited functionality on this platform in	5291	model. Libev still offers limited functionality on this platform in
4778	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5292	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4779	descriptors. This only applies when using Win32 natively, not when using	5293	descriptors. This only applies when using Win32 natively, not when using
4780	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5294	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4781	as every compielr comes with a slightly differently broken/incompatible	5295	as every compiler comes with a slightly differently broken/incompatible
4782	environment.	5296	environment.
4783		5297
4784	Lifting these limitations would basically require the full	5298	Lifting these limitations would basically require the full
4785	re-implementation of the I/O system. If you are into this kind of thing,	5299	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	5300	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	5394	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	5395	assumes that the same (machine) code can be used to call any watcher
4882	callback: The watcher callbacks have different type signatures, but libev	5396	callback: The watcher callbacks have different type signatures, but libev
4883	calls them using an C<ev_watcher *> internally.	5397	calls them using an C<ev_watcher *> internally.
4884		5398
		5399	=item null pointers and integer zero are represented by 0 bytes
		5400
		5401	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5402	relies on this setting pointers and integers to null.
		5403
4885	=item pointer accesses must be thread-atomic	5404	=item pointer accesses must be thread-atomic
4886		5405
4887	Accessing a pointer value must be atomic, it must both be readable and	5406	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.	5407	writable in one piece - this is the case on all current architectures.
4889		5408
…		…
4902	thread" or will block signals process-wide, both behaviours would	5421	thread" or will block signals process-wide, both behaviours would
4903	be compatible with libev. Interaction between C<sigprocmask> and	5422	be compatible with libev. Interaction between C<sigprocmask> and
4904	C<pthread_sigmask> could complicate things, however.	5423	C<pthread_sigmask> could complicate things, however.
4905		5424
4906	The most portable way to handle signals is to block signals in all threads	5425	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	5426	except the initial one, and run the signal handling loop in the initial
4908	well.	5427	thread as well.
4909		5428
4910	=item C<long> must be large enough for common memory allocation sizes	5429	=item C<long> must be large enough for common memory allocation sizes
4911		5430
4912	To improve portability and simplify its API, libev uses C<long> internally	5431	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	5432	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4919		5438
4920	The type C<double> is used to represent timestamps. It is required to	5439	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	5440	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	5441	good enough for at least into the year 4000 with millisecond accuracy
4923	(the design goal for libev). This requirement is overfulfilled by	5442	(the design goal for libev). This requirement is overfulfilled by
4924	implementations using IEEE 754, which is basically all existing ones. With	5443	implementations using IEEE 754, which is basically all existing ones.
		5444
4925	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5445	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5446	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5447	is either obsolete or somebody patched it to use C<long double> or
		5448	something like that, just kidding).
4926		5449
4927	=back	5450	=back
4928		5451
4929	If you know of other additional requirements drop me a note.	5452	If you know of other additional requirements drop me a note.
4930		5453
…		…
4992	=item Processing ev_async_send: O(number_of_async_watchers)	5515	=item Processing ev_async_send: O(number_of_async_watchers)
4993		5516
4994	=item Processing signals: O(max_signal_number)	5517	=item Processing signals: O(max_signal_number)
4995		5518
4996	Sending involves a system call I<iff> there were no other C<ev_async_send>	5519	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	5520	calls in the current loop iteration and the loop is currently
		5521	blocked. Checking for async and signal events involves iterating over all
4998	involves iterating over all running async watchers or all signal numbers.	5522	running async watchers or all signal numbers.
4999		5523
5000	=back	5524	=back
5001		5525
5002		5526
5003	=head1 PORTING FROM LIBEV 3.X TO 4.X	5527	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
5012	=over 4	5536	=over 4
5013		5537
5014	=item C<EV_COMPAT3> backwards compatibility mechanism	5538	=item C<EV_COMPAT3> backwards compatibility mechanism
5015		5539
5016	The backward compatibility mechanism can be controlled by	5540	The backward compatibility mechanism can be controlled by
5017	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5541	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
5018	section.	5542	section.
5019		5543
5020	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5544	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
5021		5545
5022	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5546	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
5065	=over 4	5589	=over 4
5066		5590
5067	=item active	5591	=item active
5068		5592
5069	A watcher is active as long as it has been started and not yet stopped.	5593	A watcher is active as long as it has been started and not yet stopped.
5070	See L<WATCHER STATES> for details.	5594	See L</WATCHER STATES> for details.
5071		5595
5072	=item application	5596	=item application
5073		5597
5074	In this document, an application is whatever is using libev.	5598	In this document, an application is whatever is using libev.
5075		5599
…		…
5111	watchers and events.	5635	watchers and events.
5112		5636
5113	=item pending	5637	=item pending
5114		5638
5115	A watcher is pending as soon as the corresponding event has been	5639	A watcher is pending as soon as the corresponding event has been
5116	detected. See L<WATCHER STATES> for details.	5640	detected. See L</WATCHER STATES> for details.
5117		5641
5118	=item real time	5642	=item real time
5119		5643
5120	The physical time that is observed. It is apparently strictly monotonic :)	5644	The physical time that is observed. It is apparently strictly monotonic :)
5121		5645
5122	=item wall-clock time	5646	=item wall-clock time
5123		5647
5124	The time and date as shown on clocks. Unlike real time, it can actually	5648	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	5649	be wrong and jump forwards and backwards, e.g. when you adjust your
5126	clock.	5650	clock.
5127		5651
5128	=item watcher	5652	=item watcher
5129		5653
5130	A data structure that describes interest in certain events. Watchers need	5654	A data structure that describes interest in certain events. Watchers need
…		…
5133	=back	5657	=back
5134		5658
5135	=head1 AUTHOR	5659	=head1 AUTHOR
5136		5660
5137	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5661	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5138	Magnusson and Emanuele Giaquinta.	5662	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5139		5663

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