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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
…		…
157	When libev detects a usage error such as a negative timer interval, then	159	When libev detects a usage error such as a negative timer interval, then
158	it will print a diagnostic message and abort (via the C<assert> mechanism,	160	it will print a diagnostic message and abort (via the C<assert> mechanism,
159	so C<NDEBUG> will disable this checking): these are programming errors in	161	so C<NDEBUG> will disable this checking): these are programming errors in
160	the libev caller and need to be fixed there.	162	the libev caller and need to be fixed there.
161		163
		164	Via the C<EV_FREQUENT> macro you can compile in and/or enable extensive
		165	consistency checking code inside libev that can be used to check for
		166	internal inconsistencies, suually caused by application bugs.
		167
162	Libev also has a few internal error-checking C<assert>ions, and also has	168	Libev also has a few internal error-checking C<assert>ions. These do not
163	extensive consistency checking code. These do not trigger under normal
164	circumstances, as they indicate either a bug in libev or worse.	169	trigger under normal circumstances, as they indicate either a bug in libev
		170	or worse.
165		171
166		172
167	=head1 GLOBAL FUNCTIONS	173	=head1 GLOBAL FUNCTIONS
168		174
169	These functions can be called anytime, even before initialising the	175	These functions can be called anytime, even before initialising the
…		…
174	=item ev_tstamp ev_time ()	180	=item ev_tstamp ev_time ()
175		181
176	Returns the current time as libev would use it. Please note that the	182	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	183	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	184	you actually want to know. Also interesting is the combination of
179	C<ev_update_now> and C<ev_now>.	185	C<ev_now_update> and C<ev_now>.
180		186
181	=item ev_sleep (ev_tstamp interval)	187	=item ev_sleep (ev_tstamp interval)
182		188
183	Sleep for the given interval: The current thread will be blocked until	189	Sleep for the given interval: The current thread will be blocked
184	either it is interrupted or the given time interval has passed. Basically	190	until either it is interrupted or the given time interval has
		191	passed (approximately - it might return a bit earlier even if not
		192	interrupted). Returns immediately if C<< interval <= 0 >>.
		193
185	this is a sub-second-resolution C<sleep ()>.	194	Basically this is a sub-second-resolution C<sleep ()>.
		195
		196	The range of the C<interval> is limited - libev only guarantees to work
		197	with sleep times of up to one day (C<< interval <= 86400 >>).
186		198
187	=item int ev_version_major ()	199	=item int ev_version_major ()
188		200
189	=item int ev_version_minor ()	201	=item int ev_version_minor ()
190		202
…		…
241	the current system, you would need to look at C<ev_embeddable_backends ()	253	the current system, you would need to look at C<ev_embeddable_backends ()
242	& ev_supported_backends ()>, likewise for recommended ones.	254	& ev_supported_backends ()>, likewise for recommended ones.
243		255
244	See the description of C<ev_embed> watchers for more info.	256	See the description of C<ev_embed> watchers for more info.
245		257
246	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	258	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
247		259
248	Sets the allocation function to use (the prototype is similar - the	260	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	261	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	262	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	263	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
257		269
258	You could override this function in high-availability programs to, say,	270	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,	271	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.	272	or even to sleep a while and retry until some memory is available.
261		273
		274	Example: The following is the C<realloc> function that libev itself uses
		275	which should work with C<realloc> and C<free> functions of all kinds and
		276	is probably a good basis for your own implementation.
		277
		278	static void *
		279	ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
		280	{
		281	if (size)
		282	return realloc (ptr, size);
		283
		284	free (ptr);
		285	return 0;
		286	}
		287
262	Example: Replace the libev allocator with one that waits a bit and then	288	Example: Replace the libev allocator with one that waits a bit and then
263	retries (example requires a standards-compliant C<realloc>).	289	retries.
264		290
265	static void *	291	static void *
266	persistent_realloc (void *ptr, size_t size)	292	persistent_realloc (void *ptr, size_t size)
267	{	293	{
		294	if (!size)
		295	{
		296	free (ptr);
		297	return 0;
		298	}
		299
268	for (;;)	300	for (;;)
269	{	301	{
270	void *newptr = realloc (ptr, size);	302	void *newptr = realloc (ptr, size);
271		303
272	if (newptr)	304	if (newptr)
…		…
277	}	309	}
278		310
279	...	311	...
280	ev_set_allocator (persistent_realloc);	312	ev_set_allocator (persistent_realloc);
281		313
282	=item ev_set_syserr_cb (void (*cb)(const char *msg))	314	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
283		315
284	Set the callback function to call on a retryable system call error (such	316	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	317	as failed select, poll, epoll_wait). The message is a printable string
286	indicating the system call or subsystem causing the problem. If this	318	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	319	callback is set, then libev will expect it to remedy the situation, no
…		…
390		422
391	If this flag bit is or'ed into the flag value (or the program runs setuid	423	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	424	or setgid) then libev will I<not> look at the environment variable
393	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	425	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
394	override the flags completely if it is found in the environment. This is	426	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	427	useful to try out specific backends to test their performance, to work
396	around bugs.	428	around bugs, or to make libev threadsafe (accessing environment variables
		429	cannot be done in a threadsafe way, but usually it works if no other
		430	thread modifies them).
397		431
398	=item C<EVFLAG_FORKCHECK>	432	=item C<EVFLAG_FORKCHECK>
399		433
400	Instead of calling C<ev_loop_fork> manually after a fork, you can also	434	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.	435	make libev check for a fork in each iteration by enabling this flag.
402		436
403	This works by calling C<getpid ()> on every iteration of the loop,	437	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	438	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	439	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	440	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	441	sequence without a system call and thus I<very> fast, but my GNU/Linux
408	C<pthread_atfork> which is even faster).	442	system also has C<pthread_atfork> which is even faster). (Update: glibc
		443	versions 2.25 apparently removed the C<getpid> optimisation again).
409		444
410	The big advantage of this flag is that you can forget about fork (and	445	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	446	forget about forgetting to tell libev about forking, although you still
412	flag.	447	have to ignore C<SIGPIPE>) when you use this flag.
413		448
414	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	449	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
415	environment variable.	450	environment variable.
416		451
417	=item C<EVFLAG_NOINOTIFY>	452	=item C<EVFLAG_NOINOTIFY>
…		…
435	example) that can't properly initialise their signal masks.	470	example) that can't properly initialise their signal masks.
436		471
437	=item C<EVFLAG_NOSIGMASK>	472	=item C<EVFLAG_NOSIGMASK>
438		473
439	When this flag is specified, then libev will avoid to modify the signal	474	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	475	mask. Specifically, this means you have to make sure signals are unblocked
441	when you want to receive them.	476	when you want to receive them.
442		477
443	This behaviour is useful when you want to do your own signal handling, or	478	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	479	want to handle signals only in specific threads and want to avoid libev
445	unblocking the signals.	480	unblocking the signals.
		481
		482	It's also required by POSIX in a threaded program, as libev calls
		483	C<sigprocmask>, whose behaviour is officially unspecified.
446		484
447	This flag's behaviour will become the default in future versions of libev.	485	This flag's behaviour will become the default in future versions of libev.
448		486
449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	487	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
450		488
…		…
477	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and	515	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
478	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	516	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
479		517
480	=item C<EVBACKEND_EPOLL> (value 4, Linux)	518	=item C<EVBACKEND_EPOLL> (value 4, Linux)
481		519
482	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	520	Use the Linux-specific epoll(7) interface (for both pre- and post-2.6.9
483	kernels).	521	kernels).
484		522
485	For few fds, this backend is a bit little slower than poll and select,	523	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	524	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),	525	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).	526	fd), epoll scales either O(1) or O(active_fds).
489		527
490	The epoll mechanism deserves honorable mention as the most misdesigned	528	The epoll mechanism deserves honorable mention as the most misdesigned
491	of the more advanced event mechanisms: mere annoyances include silently	529	of the more advanced event mechanisms: mere annoyances include silently
492	dropping file descriptors, requiring a system call per change per file	530	dropping file descriptors, requiring a system call per change per file
493	descriptor (and unnecessary guessing of parameters), problems with dup,	531	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	534	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	535	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)	536	set, which can take considerable time (one syscall per file descriptor)
499	and is of course hard to detect.	537	and is of course hard to detect.
500		538
501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	539	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	540	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	541	totally I<different> file descriptors (even already closed ones, so
504	even remove them from the set) than registered in the set (especially	542	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	543	(especially on SMP systems). Libev tries to counter these spurious
506	employing an additional generation counter and comparing that against the	544	notifications by employing an additional generation counter and comparing
507	events to filter out spurious ones, recreating the set when required. Last	545	that against the events to filter out spurious ones, recreating the set
		546	when required. Epoll also erroneously rounds down timeouts, but gives you
		547	no way to know when and by how much, so sometimes you have to busy-wait
		548	because epoll returns immediately despite a nonzero timeout. And last
508	not least, it also refuses to work with some file descriptors which work	549	not least, it also refuses to work with some file descriptors which work
509	perfectly fine with C<select> (files, many character devices...).	550	perfectly fine with C<select> (files, many character devices...).
510		551
511	Epoll is truly the train wreck analog among event poll mechanisms,	552	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
512	a frankenpoll, cobbled together in a hurry, no thought to design or	553	cobbled together in a hurry, no thought to design or interaction with
513	interaction with others.	554	others. Oh, the pain, will it ever stop...
514		555
515	While stopping, setting and starting an I/O watcher in the same iteration	556	While stopping, setting and starting an I/O watcher in the same iteration
516	will result in some caching, there is still a system call per such	557	will result in some caching, there is still a system call per such
517	incident (because the same I<file descriptor> could point to a different	558	incident (because the same I<file descriptor> could point to a different
518	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	559	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
530	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or	571	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
531	faster than epoll for maybe up to a hundred file descriptors, depending on	572	faster than epoll for maybe up to a hundred file descriptors, depending on
532	the usage. So sad.	573	the usage. So sad.
533		574
534	While nominally embeddable in other event loops, this feature is broken in	575	While nominally embeddable in other event loops, this feature is broken in
535	all kernel versions tested so far.	576	a lot of kernel revisions, but probably(!) works in current versions.
536		577
537	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	578	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
538	C<EVBACKEND_POLL>.	579	C<EVBACKEND_POLL>.
539		580
		581	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		582
		583	Use the Linux-specific Linux AIO (I<not> C<< aio(7) >> but C<<
		584	io_submit(2) >>) event interface available in post-4.18 kernels (but libev
		585	only tries to use it in 4.19+).
		586
		587	This is another Linux train wreck of an event interface.
		588
		589	If this backend works for you (as of this writing, it was very
		590	experimental), it is the best event interface available on Linux and might
		591	be well worth enabling it - if it isn't available in your kernel this will
		592	be detected and this backend will be skipped.
		593
		594	This backend can batch oneshot requests and supports a user-space ring
		595	buffer to receive events. It also doesn't suffer from most of the design
		596	problems of epoll (such as not being able to remove event sources from
		597	the epoll set), and generally sounds too good to be true. Because, this
		598	being the Linux kernel, of course it suffers from a whole new set of
		599	limitations, forcing you to fall back to epoll, inheriting all its design
		600	issues.
		601
		602	For one, it is not easily embeddable (but probably could be done using
		603	an event fd at some extra overhead). It also is subject to a system wide
		604	limit that can be configured in F</proc/sys/fs/aio-max-nr>. If no AIO
		605	requests are left, this backend will be skipped during initialisation, and
		606	will switch to epoll when the loop is active.
		607
		608	Most problematic in practice, however, is that not all file descriptors
		609	work with it. For example, in Linux 5.1, TCP sockets, pipes, event fds,
		610	files, F</dev/null> and many others are supported, but ttys do not work
		611	properly (a known bug that the kernel developers don't care about, see
		612	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		613	(yet?) a generic event polling interface.
		614
		615	Overall, it seems the Linux developers just don't want it to have a
		616	generic event handling mechanism other than C<select> or C<poll>.
		617
		618	To work around all these problem, the current version of libev uses its
		619	epoll backend as a fallback for file descriptor types that do not work. Or
		620	falls back completely to epoll if the kernel acts up.
		621
		622	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		623	C<EVBACKEND_POLL>.
		624
540	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	625	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
541		626
542	Kqueue deserves special mention, as at the time of this writing, it	627	Kqueue deserves special mention, as at the time this backend was
543	was broken on all BSDs except NetBSD (usually it doesn't work reliably	628	implemented, it was broken on all BSDs except NetBSD (usually it doesn't
544	with anything but sockets and pipes, except on Darwin, where of course	629	work reliably with anything but sockets and pipes, except on Darwin,
545	it's completely useless). Unlike epoll, however, whose brokenness	630	where of course it's completely useless). Unlike epoll, however, whose
546	is by design, these kqueue bugs can (and eventually will) be fixed	631	brokenness is by design, these kqueue bugs can be (and mostly have been)
547	without API changes to existing programs. For this reason it's not being	632	fixed without API changes to existing programs. For this reason it's not
548	"auto-detected" unless you explicitly specify it in the flags (i.e. using	633	being "auto-detected" on all platforms unless you explicitly specify it
549	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	634	in the flags (i.e. using C<EVBACKEND_KQUEUE>) or libev was compiled on a
550	system like NetBSD.	635	known-to-be-good (-enough) system like NetBSD.
551		636
552	You still can embed kqueue into a normal poll or select backend and use it	637	You still can embed kqueue into a normal poll or select backend and use it
553	only for sockets (after having made sure that sockets work with kqueue on	638	only for sockets (after having made sure that sockets work with kqueue on
554	the target platform). See C<ev_embed> watchers for more info.	639	the target platform). See C<ev_embed> watchers for more info.
555		640
556	It scales in the same way as the epoll backend, but the interface to the	641	It scales in the same way as the epoll backend, but the interface to the
557	kernel is more efficient (which says nothing about its actual speed, of	642	kernel is more efficient (which says nothing about its actual speed, of
558	course). While stopping, setting and starting an I/O watcher does never	643	course). While stopping, setting and starting an I/O watcher does never
559	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	644	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
560	two event changes per incident. Support for C<fork ()> is very bad (but	645	two event changes per incident. Support for C<fork ()> is very bad (you
561	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	646	might have to leak fds on fork, but it's more sane than epoll) and it
562	cases	647	drops fds silently in similarly hard-to-detect cases.
563		648
564	This backend usually performs well under most conditions.	649	This backend usually performs well under most conditions.
565		650
566	While nominally embeddable in other event loops, this doesn't work	651	While nominally embeddable in other event loops, this doesn't work
567	everywhere, so you might need to test for this. And since it is broken	652	everywhere, so you might need to test for this. And since it is broken
…		…
596	among the OS-specific backends (I vastly prefer correctness over speed	681	among the OS-specific backends (I vastly prefer correctness over speed
597	hacks).	682	hacks).
598		683
599	On the negative side, the interface is I<bizarre> - so bizarre that	684	On the negative side, the interface is I<bizarre> - so bizarre that
600	even sun itself gets it wrong in their code examples: The event polling	685	even sun itself gets it wrong in their code examples: The event polling
601	function sometimes returning events to the caller even though an error	686	function sometimes returns events to the caller even though an error
602	occurred, but with no indication whether it has done so or not (yes, it's	687	occurred, but with no indication whether it has done so or not (yes, it's
603	even documented that way) - deadly for edge-triggered interfaces where	688	even documented that way) - deadly for edge-triggered interfaces where you
604	you absolutely have to know whether an event occurred or not because you	689	absolutely have to know whether an event occurred or not because you have
605	have to re-arm the watcher.	690	to re-arm the watcher.
606		691
607	Fortunately libev seems to be able to work around these idiocies.	692	Fortunately libev seems to be able to work around these idiocies.
608		693
609	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	694	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
610	C<EVBACKEND_POLL>.	695	C<EVBACKEND_POLL>.
…		…
640		725
641	Example: Use whatever libev has to offer, but make sure that kqueue is	726	Example: Use whatever libev has to offer, but make sure that kqueue is
642	used if available.	727	used if available.
643		728
644	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);	729	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		730
		731	Example: Similarly, on linux, you mgiht want to take advantage of the
		732	linux aio backend if possible, but fall back to something else if that
		733	isn't available.
		734
		735	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
645		736
646	=item ev_loop_destroy (loop)	737	=item ev_loop_destroy (loop)
647		738
648	Destroys an event loop object (frees all memory and kernel state	739	Destroys an event loop object (frees all memory and kernel state
649	etc.). None of the active event watchers will be stopped in the normal	740	etc.). None of the active event watchers will be stopped in the normal
…		…
666	If you need dynamically allocated loops it is better to use C<ev_loop_new>	757	If you need dynamically allocated loops it is better to use C<ev_loop_new>
667	and C<ev_loop_destroy>.	758	and C<ev_loop_destroy>.
668		759
669	=item ev_loop_fork (loop)	760	=item ev_loop_fork (loop)
670		761
671	This function sets a flag that causes subsequent C<ev_run> iterations to	762	This function sets a flag that causes subsequent C<ev_run> iterations
672	reinitialise the kernel state for backends that have one. Despite the	763	to reinitialise the kernel state for backends that have one. Despite
673	name, you can call it anytime, but it makes most sense after forking, in	764	the name, you can call it anytime you are allowed to start or stop
674	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the	765	watchers (except inside an C<ev_prepare> callback), but it makes most
		766	sense after forking, in the child process. You I<must> call it (or use
675	child before resuming or calling C<ev_run>.	767	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
676		768
		769	In addition, if you want to reuse a loop (via this function or
		770	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		771
677	Again, you I<have> to call it on I<any> loop that you want to re-use after	772	Again, you I<have> to call it on I<any> loop that you want to re-use after
678	a fork, I<even if you do not plan to use the loop in the parent>. This is	773	a fork, I<even if you do not plan to use the loop in the parent>. This is
679	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	774	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
680	during fork.	775	during fork.
681		776
682	On the other hand, you only need to call this function in the child	777	On the other hand, you only need to call this function in the child
…		…
752		847
753	This function is rarely useful, but when some event callback runs for a	848	This function is rarely useful, but when some event callback runs for a
754	very long time without entering the event loop, updating libev's idea of	849	very long time without entering the event loop, updating libev's idea of
755	the current time is a good idea.	850	the current time is a good idea.
756		851
757	See also L<The special problem of time updates> in the C<ev_timer> section.	852	See also L</The special problem of time updates> in the C<ev_timer> section.
758		853
759	=item ev_suspend (loop)	854	=item ev_suspend (loop)
760		855
761	=item ev_resume (loop)	856	=item ev_resume (loop)
762		857
…		…
780	without a previous call to C<ev_suspend>.	875	without a previous call to C<ev_suspend>.
781		876
782	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	877	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
783	event loop time (see C<ev_now_update>).	878	event loop time (see C<ev_now_update>).
784		879
785	=item ev_run (loop, int flags)	880	=item bool ev_run (loop, int flags)
786		881
787	Finally, this is it, the event handler. This function usually is called	882	Finally, this is it, the event handler. This function usually is called
788	after you have initialised all your watchers and you want to start	883	after you have initialised all your watchers and you want to start
789	handling events. It will ask the operating system for any new events, call	884	handling events. It will ask the operating system for any new events, call
790	the watcher callbacks, an then repeat the whole process indefinitely: This	885	the watcher callbacks, and then repeat the whole process indefinitely: This
791	is why event loops are called I<loops>.	886	is why event loops are called I<loops>.
792		887
793	If the flags argument is specified as C<0>, it will keep handling events	888	If the flags argument is specified as C<0>, it will keep handling events
794	until either no event watchers are active anymore or C<ev_break> was	889	until either no event watchers are active anymore or C<ev_break> was
795	called.	890	called.
		891
		892	The return value is false if there are no more active watchers (which
		893	usually means "all jobs done" or "deadlock"), and true in all other cases
		894	(which usually means " you should call C<ev_run> again").
796		895
797	Please note that an explicit C<ev_break> is usually better than	896	Please note that an explicit C<ev_break> is usually better than
798	relying on all watchers to be stopped when deciding when a program has	897	relying on all watchers to be stopped when deciding when a program has
799	finished (especially in interactive programs), but having a program	898	finished (especially in interactive programs), but having a program
800	that automatically loops as long as it has to and no longer by virtue	899	that automatically loops as long as it has to and no longer by virtue
801	of relying on its watchers stopping correctly, that is truly a thing of	900	of relying on its watchers stopping correctly, that is truly a thing of
802	beauty.	901	beauty.
803		902
804	This function is also I<mostly> exception-safe - you can break out of	903	This function is I<mostly> exception-safe - you can break out of a
805	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++	904	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
806	exception and so on. This does not decrement the C<ev_depth> value, nor	905	exception and so on. This does not decrement the C<ev_depth> value, nor
807	will it clear any outstanding C<EVBREAK_ONE> breaks.	906	will it clear any outstanding C<EVBREAK_ONE> breaks.
808		907
809	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	908	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
810	those events and any already outstanding ones, but will not wait and	909	those events and any already outstanding ones, but will not wait and
…		…
822	This is useful if you are waiting for some external event in conjunction	921	This is useful if you are waiting for some external event in conjunction
823	with something not expressible using other libev watchers (i.e. "roll your	922	with something not expressible using other libev watchers (i.e. "roll your
824	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	923	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
825	usually a better approach for this kind of thing.	924	usually a better approach for this kind of thing.
826		925
827	Here are the gory details of what C<ev_run> does:	926	Here are the gory details of what C<ev_run> does (this is for your
		927	understanding, not a guarantee that things will work exactly like this in
		928	future versions):
828		929
829	- Increment loop depth.	930	- Increment loop depth.
830	- Reset the ev_break status.	931	- Reset the ev_break status.
831	- Before the first iteration, call any pending watchers.	932	- Before the first iteration, call any pending watchers.
832	LOOP:	933	LOOP:
…		…
865	anymore.	966	anymore.
866		967
867	... queue jobs here, make sure they register event watchers as long	968	... queue jobs here, make sure they register event watchers as long
868	... as they still have work to do (even an idle watcher will do..)	969	... as they still have work to do (even an idle watcher will do..)
869	ev_run (my_loop, 0);	970	ev_run (my_loop, 0);
870	... jobs done or somebody called unloop. yeah!	971	... jobs done or somebody called break. yeah!
871		972
872	=item ev_break (loop, how)	973	=item ev_break (loop, how)
873		974
874	Can be used to make a call to C<ev_run> return early (but only after it	975	Can be used to make a call to C<ev_run> return early (but only after it
875	has processed all outstanding events). The C<how> argument must be either	976	has processed all outstanding events). The C<how> argument must be either
…		…
938	overhead for the actual polling but can deliver many events at once.	1039	overhead for the actual polling but can deliver many events at once.
939		1040
940	By setting a higher I<io collect interval> you allow libev to spend more	1041	By setting a higher I<io collect interval> you allow libev to spend more
941	time collecting I/O events, so you can handle more events per iteration,	1042	time collecting I/O events, so you can handle more events per iteration,
942	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	1043	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
943	C<ev_timer>) will be not affected. Setting this to a non-null value will	1044	C<ev_timer>) will not be affected. Setting this to a non-null value will
944	introduce an additional C<ev_sleep ()> call into most loop iterations. The	1045	introduce an additional C<ev_sleep ()> call into most loop iterations. The
945	sleep time ensures that libev will not poll for I/O events more often then	1046	sleep time ensures that libev will not poll for I/O events more often then
946	once per this interval, on average.	1047	once per this interval, on average (as long as the host time resolution is
		1048	good enough).
947		1049
948	Likewise, by setting a higher I<timeout collect interval> you allow libev	1050	Likewise, by setting a higher I<timeout collect interval> you allow libev
949	to spend more time collecting timeouts, at the expense of increased	1051	to spend more time collecting timeouts, at the expense of increased
950	latency/jitter/inexactness (the watcher callback will be called	1052	latency/jitter/inexactness (the watcher callback will be called
951	later). C<ev_io> watchers will not be affected. Setting this to a non-null	1053	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
997	invoke the actual watchers inside another context (another thread etc.).	1099	invoke the actual watchers inside another context (another thread etc.).
998		1100
999	If you want to reset the callback, use C<ev_invoke_pending> as new	1101	If you want to reset the callback, use C<ev_invoke_pending> as new
1000	callback.	1102	callback.
1001		1103
1002	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1104	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
1003		1105
1004	Sometimes you want to share the same loop between multiple threads. This	1106	Sometimes you want to share the same loop between multiple threads. This
1005	can be done relatively simply by putting mutex_lock/unlock calls around	1107	can be done relatively simply by putting mutex_lock/unlock calls around
1006	each call to a libev function.	1108	each call to a libev function.
1007		1109
1008	However, C<ev_run> can run an indefinite time, so it is not feasible	1110	However, C<ev_run> can run an indefinite time, so it is not feasible
1009	to wait for it to return. One way around this is to wake up the event	1111	to wait for it to return. One way around this is to wake up the event
1010	loop via C<ev_break> and C<av_async_send>, another way is to set these	1112	loop via C<ev_break> and C<ev_async_send>, another way is to set these
1011	I<release> and I<acquire> callbacks on the loop.	1113	I<release> and I<acquire> callbacks on the loop.
1012		1114
1013	When set, then C<release> will be called just before the thread is	1115	When set, then C<release> will be called just before the thread is
1014	suspended waiting for new events, and C<acquire> is called just	1116	suspended waiting for new events, and C<acquire> is called just
1015	afterwards.	1117	afterwards.
…		…
1155		1257
1156	=item C<EV_PREPARE>	1258	=item C<EV_PREPARE>
1157		1259
1158	=item C<EV_CHECK>	1260	=item C<EV_CHECK>
1159		1261
1160	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1262	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1161	to gather new events, and all C<ev_check> watchers are invoked just after	1263	gather new events, and all C<ev_check> watchers are queued (not invoked)
1162	C<ev_run> has gathered them, but before it invokes any callbacks for any	1264	just after C<ev_run> has gathered them, but before it queues any callbacks
		1265	for any received events. That means C<ev_prepare> watchers are the last
		1266	watchers invoked before the event loop sleeps or polls for new events, and
		1267	C<ev_check> watchers will be invoked before any other watchers of the same
		1268	or lower priority within an event loop iteration.
		1269
1163	received events. Callbacks of both watcher types can start and stop as	1270	Callbacks of both watcher types can start and stop as many watchers as
1164	many watchers as they want, and all of them will be taken into account	1271	they want, and all of them will be taken into account (for example, a
1165	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1272	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1166	C<ev_run> from blocking).	1273	blocking).
1167		1274
1168	=item C<EV_EMBED>	1275	=item C<EV_EMBED>
1169		1276
1170	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1277	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1171		1278
…		…
1294		1401
1295	=item callback ev_cb (ev_TYPE *watcher)	1402	=item callback ev_cb (ev_TYPE *watcher)
1296		1403
1297	Returns the callback currently set on the watcher.	1404	Returns the callback currently set on the watcher.
1298		1405
1299	=item ev_cb_set (ev_TYPE *watcher, callback)	1406	=item ev_set_cb (ev_TYPE *watcher, callback)
1300		1407
1301	Change the callback. You can change the callback at virtually any time	1408	Change the callback. You can change the callback at virtually any time
1302	(modulo threads).	1409	(modulo threads).
1303		1410
1304	=item ev_set_priority (ev_TYPE *watcher, int priority)	1411	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1322	or might not have been clamped to the valid range.	1429	or might not have been clamped to the valid range.
1323		1430
1324	The default priority used by watchers when no priority has been set is	1431	The default priority used by watchers when no priority has been set is
1325	always C<0>, which is supposed to not be too high and not be too low :).	1432	always C<0>, which is supposed to not be too high and not be too low :).
1326		1433
1327	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1434	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1328	priorities.	1435	priorities.
1329		1436
1330	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1437	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1331		1438
1332	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1439	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
…		…
1357	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1464	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1358	functions that do not need a watcher.	1465	functions that do not need a watcher.
1359		1466
1360	=back	1467	=back
1361		1468
1362	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1469	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1363		1470	OWN COMPOSITE WATCHERS> idioms.
1364	Each watcher has, by default, a member C<void *data> that you can change
1365	and read at any time: libev will completely ignore it. This can be used
1366	to associate arbitrary data with your watcher. If you need more data and
1367	don't want to allocate memory and store a pointer to it in that data
1368	member, you can also "subclass" the watcher type and provide your own
1369	data:
1370
1371	struct my_io
1372	{
1373	ev_io io;
1374	int otherfd;
1375	void *somedata;
1376	struct whatever *mostinteresting;
1377	};
1378
1379	...
1380	struct my_io w;
1381	ev_io_init (&w.io, my_cb, fd, EV_READ);
1382
1383	And since your callback will be called with a pointer to the watcher, you
1384	can cast it back to your own type:
1385
1386	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1387	{
1388	struct my_io *w = (struct my_io *)w_;
1389	...
1390	}
1391
1392	More interesting and less C-conformant ways of casting your callback type
1393	instead have been omitted.
1394
1395	Another common scenario is to use some data structure with multiple
1396	embedded watchers:
1397
1398	struct my_biggy
1399	{
1400	int some_data;
1401	ev_timer t1;
1402	ev_timer t2;
1403	}
1404
1405	In this case getting the pointer to C<my_biggy> is a bit more
1406	complicated: Either you store the address of your C<my_biggy> struct
1407	in the C<data> member of the watcher (for woozies), or you need to use
1408	some pointer arithmetic using C<offsetof> inside your watchers (for real
1409	programmers):
1410
1411	#include <stddef.h>
1412
1413	static void
1414	t1_cb (EV_P_ ev_timer *w, int revents)
1415	{
1416	struct my_biggy big = (struct my_biggy *)
1417	(((char *)w) - offsetof (struct my_biggy, t1));
1418	}
1419
1420	static void
1421	t2_cb (EV_P_ ev_timer *w, int revents)
1422	{
1423	struct my_biggy big = (struct my_biggy *)
1424	(((char *)w) - offsetof (struct my_biggy, t2));
1425	}
1426		1471
1427	=head2 WATCHER STATES	1472	=head2 WATCHER STATES
1428		1473
1429	There are various watcher states mentioned throughout this manual -	1474	There are various watcher states mentioned throughout this manual -
1430	active, pending and so on. In this section these states and the rules to	1475	active, pending and so on. In this section these states and the rules to
1431	transition between them will be described in more detail - and while these	1476	transition between them will be described in more detail - and while these
1432	rules might look complicated, they usually do "the right thing".	1477	rules might look complicated, they usually do "the right thing".
1433		1478
1434	=over 4	1479	=over 4
1435		1480
1436	=item initialiased	1481	=item initialised
1437		1482
1438	Before a watcher can be registered with the event looop it has to be	1483	Before a watcher can be registered with the event loop it has to be
1439	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1484	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1440	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1485	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1441		1486
1442	In this state it is simply some block of memory that is suitable for use	1487	In this state it is simply some block of memory that is suitable for
1443	in an event loop. It can be moved around, freed, reused etc. at will.	1488	use in an event loop. It can be moved around, freed, reused etc. at
		1489	will - as long as you either keep the memory contents intact, or call
		1490	C<ev_TYPE_init> again.
1444		1491
1445	=item started/running/active	1492	=item started/running/active
1446		1493
1447	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1494	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1448	property of the event loop, and is actively waiting for events. While in	1495	property of the event loop, and is actively waiting for events. While in
…		…
1476	latter will clear any pending state the watcher might be in, regardless	1523	latter will clear any pending state the watcher might be in, regardless
1477	of whether it was active or not, so stopping a watcher explicitly before	1524	of whether it was active or not, so stopping a watcher explicitly before
1478	freeing it is often a good idea.	1525	freeing it is often a good idea.
1479		1526
1480	While stopped (and not pending) the watcher is essentially in the	1527	While stopped (and not pending) the watcher is essentially in the
1481	initialised state, that is it can be reused, moved, modified in any way	1528	initialised state, that is, it can be reused, moved, modified in any way
1482	you wish.	1529	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1530	it again).
1483		1531
1484	=back	1532	=back
1485		1533
1486	=head2 WATCHER PRIORITY MODELS	1534	=head2 WATCHER PRIORITY MODELS
1487		1535
1488	Many event loops support I<watcher priorities>, which are usually small	1536	Many event loops support I<watcher priorities>, which are usually small
1489	integers that influence the ordering of event callback invocation	1537	integers that influence the ordering of event callback invocation
1490	between watchers in some way, all else being equal.	1538	between watchers in some way, all else being equal.
1491		1539
1492	In libev, Watcher priorities can be set using C<ev_set_priority>. See its	1540	In libev, watcher priorities can be set using C<ev_set_priority>. See its
1493	description for the more technical details such as the actual priority	1541	description for the more technical details such as the actual priority
1494	range.	1542	range.
1495		1543
1496	There are two common ways how these these priorities are being interpreted	1544	There are two common ways how these these priorities are being interpreted
1497	by event loops:	1545	by event loops:
…		…
1636		1684
1637	But really, best use non-blocking mode.	1685	But really, best use non-blocking mode.
1638		1686
1639	=head3 The special problem of disappearing file descriptors	1687	=head3 The special problem of disappearing file descriptors
1640		1688
1641	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1689	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1642	descriptor (either due to calling C<close> explicitly or any other means,	1690	a file descriptor (either due to calling C<close> explicitly or any other
1643	such as C<dup2>). The reason is that you register interest in some file	1691	means, such as C<dup2>). The reason is that you register interest in some
1644	descriptor, but when it goes away, the operating system will silently drop	1692	file descriptor, but when it goes away, the operating system will silently
1645	this interest. If another file descriptor with the same number then is	1693	drop this interest. If another file descriptor with the same number then
1646	registered with libev, there is no efficient way to see that this is, in	1694	is registered with libev, there is no efficient way to see that this is,
1647	fact, a different file descriptor.	1695	in fact, a different file descriptor.
1648		1696
1649	To avoid having to explicitly tell libev about such cases, libev follows	1697	To avoid having to explicitly tell libev about such cases, libev follows
1650	the following policy: Each time C<ev_io_set> is being called, libev	1698	the following policy: Each time C<ev_io_set> is being called, libev
1651	will assume that this is potentially a new file descriptor, otherwise	1699	will assume that this is potentially a new file descriptor, otherwise
1652	it is assumed that the file descriptor stays the same. That means that	1700	it is assumed that the file descriptor stays the same. That means that
…		…
1680	always get a readiness notification instantly, and your read (or possibly	1728	always get a readiness notification instantly, and your read (or possibly
1681	write) will still block on the disk I/O.	1729	write) will still block on the disk I/O.
1682		1730
1683	Another way to view it is that in the case of sockets, pipes, character	1731	Another way to view it is that in the case of sockets, pipes, character
1684	devices and so on, there is another party (the sender) that delivers data	1732	devices and so on, there is another party (the sender) that delivers data
1685	on it's own, but in the case of files, there is no such thing: the disk	1733	on its own, but in the case of files, there is no such thing: the disk
1686	will not send data on it's own, simply because it doesn't know what you	1734	will not send data on its own, simply because it doesn't know what you
1687	wish to read - you would first have to request some data.	1735	wish to read - you would first have to request some data.
1688		1736
1689	Since files are typically not-so-well supported by advanced notification	1737	Since files are typically not-so-well supported by advanced notification
1690	mechanism, libev tries hard to emulate POSIX behaviour with respect	1738	mechanism, libev tries hard to emulate POSIX behaviour with respect
1691	to files, even though you should not use it. The reason for this is	1739	to files, even though you should not use it. The reason for this is
…		…
1701	when you rarely read from a file instead of from a socket, and want to	1749	when you rarely read from a file instead of from a socket, and want to
1702	reuse the same code path.	1750	reuse the same code path.
1703		1751
1704	=head3 The special problem of fork	1752	=head3 The special problem of fork
1705		1753
1706	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1754	Some backends (epoll, kqueue, linuxaio, iouring) do not support C<fork ()>
1707	useless behaviour. Libev fully supports fork, but needs to be told about	1755	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1708	it in the child if you want to continue to use it in the child.	1756	to be told about it in the child if you want to continue to use it in the
		1757	child.
1709		1758
1710	To support fork in your child processes, you have to call C<ev_loop_fork	1759	To support fork in your child processes, you have to call C<ev_loop_fork
1711	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to	1760	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1712	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1761	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1713		1762
…		…
1815	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1864	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1816	monotonic clock option helps a lot here).	1865	monotonic clock option helps a lot here).
1817		1866
1818	The callback is guaranteed to be invoked only I<after> its timeout has	1867	The callback is guaranteed to be invoked only I<after> its timeout has
1819	passed (not I<at>, so on systems with very low-resolution clocks this	1868	passed (not I<at>, so on systems with very low-resolution clocks this
1820	might introduce a small delay). If multiple timers become ready during the	1869	might introduce a small delay, see "the special problem of being too
		1870	early", below). If multiple timers become ready during the same loop
1821	same loop iteration then the ones with earlier time-out values are invoked	1871	iteration then the ones with earlier time-out values are invoked before
1822	before ones of the same priority with later time-out values (but this is	1872	ones of the same priority with later time-out values (but this is no
1823	no longer true when a callback calls C<ev_run> recursively).	1873	longer true when a callback calls C<ev_run> recursively).
1824		1874
1825	=head3 Be smart about timeouts	1875	=head3 Be smart about timeouts
1826		1876
1827	Many real-world problems involve some kind of timeout, usually for error	1877	Many real-world problems involve some kind of timeout, usually for error
1828	recovery. A typical example is an HTTP request - if the other side hangs,	1878	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1903		1953
1904	In this case, it would be more efficient to leave the C<ev_timer> alone,	1954	In this case, it would be more efficient to leave the C<ev_timer> alone,
1905	but remember the time of last activity, and check for a real timeout only	1955	but remember the time of last activity, and check for a real timeout only
1906	within the callback:	1956	within the callback:
1907		1957
		1958	ev_tstamp timeout = 60.;
1908	ev_tstamp last_activity; // time of last activity	1959	ev_tstamp last_activity; // time of last activity
		1960	ev_timer timer;
1909		1961
1910	static void	1962	static void
1911	callback (EV_P_ ev_timer *w, int revents)	1963	callback (EV_P_ ev_timer *w, int revents)
1912	{	1964	{
1913	ev_tstamp now = ev_now (EV_A);	1965	// calculate when the timeout would happen
1914	ev_tstamp timeout = last_activity + 60.;	1966	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1915		1967
1916	// if last_activity + 60. is older than now, we did time out	1968	// if negative, it means we the timeout already occurred
1917	if (timeout < now)	1969	if (after < 0.)
1918	{	1970	{
1919	// timeout occurred, take action	1971	// timeout occurred, take action
1920	}	1972	}
1921	else	1973	else
1922	{	1974	{
1923	// callback was invoked, but there was some activity, re-arm	1975	// callback was invoked, but there was some recent
1924	// the watcher to fire in last_activity + 60, which is	1976	// activity. simply restart the timer to time out
1925	// guaranteed to be in the future, so "again" is positive:	1977	// after "after" seconds, which is the earliest time
1926	w->repeat = timeout - now;	1978	// the timeout can occur.
		1979	ev_timer_set (w, after, 0.);
1927	ev_timer_again (EV_A_ w);	1980	ev_timer_start (EV_A_ w);
1928	}	1981	}
1929	}	1982	}
1930		1983
1931	To summarise the callback: first calculate the real timeout (defined	1984	To summarise the callback: first calculate in how many seconds the
1932	as "60 seconds after the last activity"), then check if that time has	1985	timeout will occur (by calculating the absolute time when it would occur,
1933	been reached, which means something I<did>, in fact, time out. Otherwise	1986	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1934	the callback was invoked too early (C<timeout> is in the future), so	1987	(EV_A)> from that).
1935	re-schedule the timer to fire at that future time, to see if maybe we have
1936	a timeout then.
1937		1988
1938	Note how C<ev_timer_again> is used, taking advantage of the	1989	If this value is negative, then we are already past the timeout, i.e. we
1939	C<ev_timer_again> optimisation when the timer is already running.	1990	timed out, and need to do whatever is needed in this case.
		1991
		1992	Otherwise, we now the earliest time at which the timeout would trigger,
		1993	and simply start the timer with this timeout value.
		1994
		1995	In other words, each time the callback is invoked it will check whether
		1996	the timeout occurred. If not, it will simply reschedule itself to check
		1997	again at the earliest time it could time out. Rinse. Repeat.
1940		1998
1941	This scheme causes more callback invocations (about one every 60 seconds	1999	This scheme causes more callback invocations (about one every 60 seconds
1942	minus half the average time between activity), but virtually no calls to	2000	minus half the average time between activity), but virtually no calls to
1943	libev to change the timeout.	2001	libev to change the timeout.
1944		2002
1945	To start the timer, simply initialise the watcher and set C<last_activity>	2003	To start the machinery, simply initialise the watcher and set
1946	to the current time (meaning we just have some activity :), then call the	2004	C<last_activity> to the current time (meaning there was some activity just
1947	callback, which will "do the right thing" and start the timer:	2005	now), then call the callback, which will "do the right thing" and start
		2006	the timer:
1948		2007
		2008	last_activity = ev_now (EV_A);
1949	ev_init (timer, callback);	2009	ev_init (&timer, callback);
1950	last_activity = ev_now (loop);	2010	callback (EV_A_ &timer, 0);
1951	callback (loop, timer, EV_TIMER);
1952		2011
1953	And when there is some activity, simply store the current time in	2012	When there is some activity, simply store the current time in
1954	C<last_activity>, no libev calls at all:	2013	C<last_activity>, no libev calls at all:
1955		2014
		2015	if (activity detected)
1956	last_activity = ev_now (loop);	2016	last_activity = ev_now (EV_A);
		2017
		2018	When your timeout value changes, then the timeout can be changed by simply
		2019	providing a new value, stopping the timer and calling the callback, which
		2020	will again do the right thing (for example, time out immediately :).
		2021
		2022	timeout = new_value;
		2023	ev_timer_stop (EV_A_ &timer);
		2024	callback (EV_A_ &timer, 0);
1957		2025
1958	This technique is slightly more complex, but in most cases where the	2026	This technique is slightly more complex, but in most cases where the
1959	time-out is unlikely to be triggered, much more efficient.	2027	time-out is unlikely to be triggered, much more efficient.
1960
1961	Changing the timeout is trivial as well (if it isn't hard-coded in the
1962	callback :) - just change the timeout and invoke the callback, which will
1963	fix things for you.
1964		2028
1965	=item 4. Wee, just use a double-linked list for your timeouts.	2029	=item 4. Wee, just use a double-linked list for your timeouts.
1966		2030
1967	If there is not one request, but many thousands (millions...), all	2031	If there is not one request, but many thousands (millions...), all
1968	employing some kind of timeout with the same timeout value, then one can	2032	employing some kind of timeout with the same timeout value, then one can
…		…
1995	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2059	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1996	rather complicated, but extremely efficient, something that really pays	2060	rather complicated, but extremely efficient, something that really pays
1997	off after the first million or so of active timers, i.e. it's usually	2061	off after the first million or so of active timers, i.e. it's usually
1998	overkill :)	2062	overkill :)
1999		2063
		2064	=head3 The special problem of being too early
		2065
		2066	If you ask a timer to call your callback after three seconds, then
		2067	you expect it to be invoked after three seconds - but of course, this
		2068	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2069	guaranteed to any precision by libev - imagine somebody suspending the
		2070	process with a STOP signal for a few hours for example.
		2071
		2072	So, libev tries to invoke your callback as soon as possible I<after> the
		2073	delay has occurred, but cannot guarantee this.
		2074
		2075	A less obvious failure mode is calling your callback too early: many event
		2076	loops compare timestamps with a "elapsed delay >= requested delay", but
		2077	this can cause your callback to be invoked much earlier than you would
		2078	expect.
		2079
		2080	To see why, imagine a system with a clock that only offers full second
		2081	resolution (think windows if you can't come up with a broken enough OS
		2082	yourself). If you schedule a one-second timer at the time 500.9, then the
		2083	event loop will schedule your timeout to elapse at a system time of 500
		2084	(500.9 truncated to the resolution) + 1, or 501.
		2085
		2086	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2087	501" and invoke the callback 0.1s after it was started, even though a
		2088	one-second delay was requested - this is being "too early", despite best
		2089	intentions.
		2090
		2091	This is the reason why libev will never invoke the callback if the elapsed
		2092	delay equals the requested delay, but only when the elapsed delay is
		2093	larger than the requested delay. In the example above, libev would only invoke
		2094	the callback at system time 502, or 1.1s after the timer was started.
		2095
		2096	So, while libev cannot guarantee that your callback will be invoked
		2097	exactly when requested, it I<can> and I<does> guarantee that the requested
		2098	delay has actually elapsed, or in other words, it always errs on the "too
		2099	late" side of things.
		2100
2000	=head3 The special problem of time updates	2101	=head3 The special problem of time updates
2001		2102
2002	Establishing the current time is a costly operation (it usually takes at	2103	Establishing the current time is a costly operation (it usually takes
2003	least two system calls): EV therefore updates its idea of the current	2104	at least one system call): EV therefore updates its idea of the current
2004	time only before and after C<ev_run> collects new events, which causes a	2105	time only before and after C<ev_run> collects new events, which causes a
2005	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2106	growing difference between C<ev_now ()> and C<ev_time ()> when handling
2006	lots of events in one iteration.	2107	lots of events in one iteration.
2007		2108
2008	The relative timeouts are calculated relative to the C<ev_now ()>	2109	The relative timeouts are calculated relative to the C<ev_now ()>
2009	time. This is usually the right thing as this timestamp refers to the time	2110	time. This is usually the right thing as this timestamp refers to the time
2010	of the event triggering whatever timeout you are modifying/starting. If	2111	of the event triggering whatever timeout you are modifying/starting. If
2011	you suspect event processing to be delayed and you I<need> to base the	2112	you suspect event processing to be delayed and you I<need> to base the
2012	timeout on the current time, use something like this to adjust for this:	2113	timeout on the current time, use something like the following to adjust
		2114	for it:
2013		2115
2014	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2116	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
2015		2117
2016	If the event loop is suspended for a long time, you can also force an	2118	If the event loop is suspended for a long time, you can also force an
2017	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2119	update of the time returned by C<ev_now ()> by calling C<ev_now_update
2018	()>.	2120	()>, although that will push the event time of all outstanding events
		2121	further into the future.
		2122
		2123	=head3 The special problem of unsynchronised clocks
		2124
		2125	Modern systems have a variety of clocks - libev itself uses the normal
		2126	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2127	jumps).
		2128
		2129	Neither of these clocks is synchronised with each other or any other clock
		2130	on the system, so C<ev_time ()> might return a considerably different time
		2131	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2132	a call to C<gettimeofday> might return a second count that is one higher
		2133	than a directly following call to C<time>.
		2134
		2135	The moral of this is to only compare libev-related timestamps with
		2136	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2137	a second or so.
		2138
		2139	One more problem arises due to this lack of synchronisation: if libev uses
		2140	the system monotonic clock and you compare timestamps from C<ev_time>
		2141	or C<ev_now> from when you started your timer and when your callback is
		2142	invoked, you will find that sometimes the callback is a bit "early".
		2143
		2144	This is because C<ev_timer>s work in real time, not wall clock time, so
		2145	libev makes sure your callback is not invoked before the delay happened,
		2146	I<measured according to the real time>, not the system clock.
		2147
		2148	If your timeouts are based on a physical timescale (e.g. "time out this
		2149	connection after 100 seconds") then this shouldn't bother you as it is
		2150	exactly the right behaviour.
		2151
		2152	If you want to compare wall clock/system timestamps to your timers, then
		2153	you need to use C<ev_periodic>s, as these are based on the wall clock
		2154	time, where your comparisons will always generate correct results.
2019		2155
2020	=head3 The special problems of suspended animation	2156	=head3 The special problems of suspended animation
2021		2157
2022	When you leave the server world it is quite customary to hit machines that	2158	When you leave the server world it is quite customary to hit machines that
2023	can suspend/hibernate - what happens to the clocks during such a suspend?	2159	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
2053		2189
2054	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2190	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
2055		2191
2056	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2192	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
2057		2193
2058	Configure the timer to trigger after C<after> seconds. If C<repeat>	2194	Configure the timer to trigger after C<after> seconds (fractional and
2059	is C<0.>, then it will automatically be stopped once the timeout is	2195	negative values are supported). If C<repeat> is C<0.>, then it will
2060	reached. If it is positive, then the timer will automatically be	2196	automatically be stopped once the timeout is reached. If it is positive,
2061	configured to trigger again C<repeat> seconds later, again, and again,	2197	then the timer will automatically be configured to trigger again C<repeat>
2062	until stopped manually.	2198	seconds later, again, and again, until stopped manually.
2063		2199
2064	The timer itself will do a best-effort at avoiding drift, that is, if	2200	The timer itself will do a best-effort at avoiding drift, that is, if
2065	you configure a timer to trigger every 10 seconds, then it will normally	2201	you configure a timer to trigger every 10 seconds, then it will normally
2066	trigger at exactly 10 second intervals. If, however, your program cannot	2202	trigger at exactly 10 second intervals. If, however, your program cannot
2067	keep up with the timer (because it takes longer than those 10 seconds to	2203	keep up with the timer (because it takes longer than those 10 seconds to
2068	do stuff) the timer will not fire more than once per event loop iteration.	2204	do stuff) the timer will not fire more than once per event loop iteration.
2069		2205
2070	=item ev_timer_again (loop, ev_timer *)	2206	=item ev_timer_again (loop, ev_timer *)
2071		2207
2072	This will act as if the timer timed out and restart it again if it is	2208	This will act as if the timer timed out, and restarts it again if it is
2073	repeating. The exact semantics are:	2209	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2210	timeout to the C<repeat> value and calling C<ev_timer_start>.
2074		2211
		2212	The exact semantics are as in the following rules, all of which will be
		2213	applied to the watcher:
		2214
		2215	=over 4
		2216
2075	If the timer is pending, its pending status is cleared.	2217	=item If the timer is pending, the pending status is always cleared.
2076		2218
2077	If the timer is started but non-repeating, stop it (as if it timed out).	2219	=item If the timer is started but non-repeating, stop it (as if it timed
		2220	out, without invoking it).
2078		2221
2079	If the timer is repeating, either start it if necessary (with the	2222	=item If the timer is repeating, make the C<repeat> value the new timeout
2080	C<repeat> value), or reset the running timer to the C<repeat> value.	2223	and start the timer, if necessary.
2081		2224
		2225	=back
		2226
2082	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2227	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2083	usage example.	2228	usage example.
2084		2229
2085	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2230	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2086		2231
2087	Returns the remaining time until a timer fires. If the timer is active,	2232	Returns the remaining time until a timer fires. If the timer is active,
…		…
2140	Periodic watchers are also timers of a kind, but they are very versatile	2285	Periodic watchers are also timers of a kind, but they are very versatile
2141	(and unfortunately a bit complex).	2286	(and unfortunately a bit complex).
2142		2287
2143	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2288	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2144	relative time, the physical time that passes) but on wall clock time	2289	relative time, the physical time that passes) but on wall clock time
2145	(absolute time, the thing you can read on your calender or clock). The	2290	(absolute time, the thing you can read on your calendar or clock). The
2146	difference is that wall clock time can run faster or slower than real	2291	difference is that wall clock time can run faster or slower than real
2147	time, and time jumps are not uncommon (e.g. when you adjust your	2292	time, and time jumps are not uncommon (e.g. when you adjust your
2148	wrist-watch).	2293	wrist-watch).
2149		2294
2150	You can tell a periodic watcher to trigger after some specific point	2295	You can tell a periodic watcher to trigger after some specific point
…		…
2155	C<ev_timer>, which would still trigger roughly 10 seconds after starting	2300	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2156	it, as it uses a relative timeout).	2301	it, as it uses a relative timeout).
2157		2302
2158	C<ev_periodic> watchers can also be used to implement vastly more complex	2303	C<ev_periodic> watchers can also be used to implement vastly more complex
2159	timers, such as triggering an event on each "midnight, local time", or	2304	timers, such as triggering an event on each "midnight, local time", or
2160	other complicated rules. This cannot be done with C<ev_timer> watchers, as	2305	other complicated rules. This cannot easily be done with C<ev_timer>
2161	those cannot react to time jumps.	2306	watchers, as those cannot react to time jumps.
2162		2307
2163	As with timers, the callback is guaranteed to be invoked only when the	2308	As with timers, the callback is guaranteed to be invoked only when the
2164	point in time where it is supposed to trigger has passed. If multiple	2309	point in time where it is supposed to trigger has passed. If multiple
2165	timers become ready during the same loop iteration then the ones with	2310	timers become ready during the same loop iteration then the ones with
2166	earlier time-out values are invoked before ones with later time-out values	2311	earlier time-out values are invoked before ones with later time-out values
…		…
2207		2352
2208	Another way to think about it (for the mathematically inclined) is that	2353	Another way to think about it (for the mathematically inclined) is that
2209	C<ev_periodic> will try to run the callback in this mode at the next possible	2354	C<ev_periodic> will try to run the callback in this mode at the next possible
2210	time where C<time = offset (mod interval)>, regardless of any time jumps.	2355	time where C<time = offset (mod interval)>, regardless of any time jumps.
2211		2356
2212	For numerical stability it is preferable that the C<offset> value is near	2357	The C<interval> I<MUST> be positive, and for numerical stability, the
2213	C<ev_now ()> (the current time), but there is no range requirement for	2358	interval value should be higher than C<1/8192> (which is around 100
2214	this value, and in fact is often specified as zero.	2359	microseconds) and C<offset> should be higher than C<0> and should have
		2360	at most a similar magnitude as the current time (say, within a factor of
		2361	ten). Typical values for offset are, in fact, C<0> or something between
		2362	C<0> and C<interval>, which is also the recommended range.
2215		2363
2216	Note also that there is an upper limit to how often a timer can fire (CPU	2364	Note also that there is an upper limit to how often a timer can fire (CPU
2217	speed for example), so if C<interval> is very small then timing stability	2365	speed for example), so if C<interval> is very small then timing stability
2218	will of course deteriorate. Libev itself tries to be exact to be about one	2366	will of course deteriorate. Libev itself tries to be exact to be about one
2219	millisecond (if the OS supports it and the machine is fast enough).	2367	millisecond (if the OS supports it and the machine is fast enough).
…		…
2249		2397
2250	NOTE: I<< This callback must always return a time that is higher than or	2398	NOTE: I<< This callback must always return a time that is higher than or
2251	equal to the passed C<now> value >>.	2399	equal to the passed C<now> value >>.
2252		2400
2253	This can be used to create very complex timers, such as a timer that	2401	This can be used to create very complex timers, such as a timer that
2254	triggers on "next midnight, local time". To do this, you would calculate the	2402	triggers on "next midnight, local time". To do this, you would calculate
2255	next midnight after C<now> and return the timestamp value for this. How	2403	the next midnight after C<now> and return the timestamp value for
2256	you do this is, again, up to you (but it is not trivial, which is the main	2404	this. Here is a (completely untested, no error checking) example on how to
2257	reason I omitted it as an example).	2405	do this:
		2406
		2407	#include <time.h>
		2408
		2409	static ev_tstamp
		2410	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2411	{
		2412	time_t tnow = (time_t)now;
		2413	struct tm tm;
		2414	localtime_r (&tnow, &tm);
		2415
		2416	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2417	++tm.tm_mday; // midnight next day
		2418
		2419	return mktime (&tm);
		2420	}
		2421
		2422	Note: this code might run into trouble on days that have more then two
		2423	midnights (beginning and end).
2258		2424
2259	=back	2425	=back
2260		2426
2261	=item ev_periodic_again (loop, ev_periodic *)	2427	=item ev_periodic_again (loop, ev_periodic *)
2262		2428
…		…
2327		2493
2328	ev_periodic hourly_tick;	2494	ev_periodic hourly_tick;
2329	ev_periodic_init (&hourly_tick, clock_cb,	2495	ev_periodic_init (&hourly_tick, clock_cb,
2330	fmod (ev_now (loop), 3600.), 3600., 0);	2496	fmod (ev_now (loop), 3600.), 3600., 0);
2331	ev_periodic_start (loop, &hourly_tick);	2497	ev_periodic_start (loop, &hourly_tick);
2332		2498
2333		2499
2334	=head2 C<ev_signal> - signal me when a signal gets signalled!	2500	=head2 C<ev_signal> - signal me when a signal gets signalled!
2335		2501
2336	Signal watchers will trigger an event when the process receives a specific	2502	Signal watchers will trigger an event when the process receives a specific
2337	signal one or more times. Even though signals are very asynchronous, libev	2503	signal one or more times. Even though signals are very asynchronous, libev
…		…
2347	only within the same loop, i.e. you can watch for C<SIGINT> in your	2513	only within the same loop, i.e. you can watch for C<SIGINT> in your
2348	default loop and for C<SIGIO> in another loop, but you cannot watch for	2514	default loop and for C<SIGIO> in another loop, but you cannot watch for
2349	C<SIGINT> in both the default loop and another loop at the same time. At	2515	C<SIGINT> in both the default loop and another loop at the same time. At
2350	the moment, C<SIGCHLD> is permanently tied to the default loop.	2516	the moment, C<SIGCHLD> is permanently tied to the default loop.
2351		2517
2352	When the first watcher gets started will libev actually register something	2518	Only after the first watcher for a signal is started will libev actually
2353	with the kernel (thus it coexists with your own signal handlers as long as	2519	register something with the kernel. It thus coexists with your own signal
2354	you don't register any with libev for the same signal).	2520	handlers as long as you don't register any with libev for the same signal.
2355		2521
2356	If possible and supported, libev will install its handlers with	2522	If possible and supported, libev will install its handlers with
2357	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2523	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2358	not be unduly interrupted. If you have a problem with system calls getting	2524	not be unduly interrupted. If you have a problem with system calls getting
2359	interrupted by signals you can block all signals in an C<ev_check> watcher	2525	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2362	=head3 The special problem of inheritance over fork/execve/pthread_create	2528	=head3 The special problem of inheritance over fork/execve/pthread_create
2363		2529
2364	Both the signal mask (C<sigprocmask>) and the signal disposition	2530	Both the signal mask (C<sigprocmask>) and the signal disposition
2365	(C<sigaction>) are unspecified after starting a signal watcher (and after	2531	(C<sigaction>) are unspecified after starting a signal watcher (and after
2366	stopping it again), that is, libev might or might not block the signal,	2532	stopping it again), that is, libev might or might not block the signal,
2367	and might or might not set or restore the installed signal handler.	2533	and might or might not set or restore the installed signal handler (but
		2534	see C<EVFLAG_NOSIGMASK>).
2368		2535
2369	While this does not matter for the signal disposition (libev never	2536	While this does not matter for the signal disposition (libev never
2370	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2537	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2371	C<execve>), this matters for the signal mask: many programs do not expect	2538	C<execve>), this matters for the signal mask: many programs do not expect
2372	certain signals to be blocked.	2539	certain signals to be blocked.
…		…
2543		2710
2544	=head2 C<ev_stat> - did the file attributes just change?	2711	=head2 C<ev_stat> - did the file attributes just change?
2545		2712
2546	This watches a file system path for attribute changes. That is, it calls	2713	This watches a file system path for attribute changes. That is, it calls
2547	C<stat> on that path in regular intervals (or when the OS says it changed)	2714	C<stat> on that path in regular intervals (or when the OS says it changed)
2548	and sees if it changed compared to the last time, invoking the callback if	2715	and sees if it changed compared to the last time, invoking the callback
2549	it did.	2716	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2717	happen after the watcher has been started will be reported.
2550		2718
2551	The path does not need to exist: changing from "path exists" to "path does	2719	The path does not need to exist: changing from "path exists" to "path does
2552	not exist" is a status change like any other. The condition "path does not	2720	not exist" is a status change like any other. The condition "path does not
2553	exist" (or more correctly "path cannot be stat'ed") is signified by the	2721	exist" (or more correctly "path cannot be stat'ed") is signified by the
2554	C<st_nlink> field being zero (which is otherwise always forced to be at	2722	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2784	Apart from keeping your process non-blocking (which is a useful	2952	Apart from keeping your process non-blocking (which is a useful
2785	effect on its own sometimes), idle watchers are a good place to do	2953	effect on its own sometimes), idle watchers are a good place to do
2786	"pseudo-background processing", or delay processing stuff to after the	2954	"pseudo-background processing", or delay processing stuff to after the
2787	event loop has handled all outstanding events.	2955	event loop has handled all outstanding events.
2788		2956
		2957	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2958
		2959	As long as there is at least one active idle watcher, libev will never
		2960	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2961	For this to work, the idle watcher doesn't need to be invoked at all - the
		2962	lowest priority will do.
		2963
		2964	This mode of operation can be useful together with an C<ev_check> watcher,
		2965	to do something on each event loop iteration - for example to balance load
		2966	between different connections.
		2967
		2968	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2969	example.
		2970
2789	=head3 Watcher-Specific Functions and Data Members	2971	=head3 Watcher-Specific Functions and Data Members
2790		2972
2791	=over 4	2973	=over 4
2792		2974
2793	=item ev_idle_init (ev_idle *, callback)	2975	=item ev_idle_init (ev_idle *, callback)
…		…
2804	callback, free it. Also, use no error checking, as usual.	2986	callback, free it. Also, use no error checking, as usual.
2805		2987
2806	static void	2988	static void
2807	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2989	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2808	{	2990	{
		2991	// stop the watcher
		2992	ev_idle_stop (loop, w);
		2993
		2994	// now we can free it
2809	free (w);	2995	free (w);
		2996
2810	// now do something you wanted to do when the program has	2997	// now do something you wanted to do when the program has
2811	// no longer anything immediate to do.	2998	// no longer anything immediate to do.
2812	}	2999	}
2813		3000
2814	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	3001	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2816	ev_idle_start (loop, idle_watcher);	3003	ev_idle_start (loop, idle_watcher);
2817		3004
2818		3005
2819	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3006	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2820		3007
2821	Prepare and check watchers are usually (but not always) used in pairs:	3008	Prepare and check watchers are often (but not always) used in pairs:
2822	prepare watchers get invoked before the process blocks and check watchers	3009	prepare watchers get invoked before the process blocks and check watchers
2823	afterwards.	3010	afterwards.
2824		3011
2825	You I<must not> call C<ev_run> or similar functions that enter	3012	You I<must not> call C<ev_run> (or similar functions that enter the
2826	the current event loop from either C<ev_prepare> or C<ev_check>	3013	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2827	watchers. Other loops than the current one are fine, however. The	3014	C<ev_check> watchers. Other loops than the current one are fine,
2828	rationale behind this is that you do not need to check for recursion in	3015	however. The rationale behind this is that you do not need to check
2829	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3016	for recursion in those watchers, i.e. the sequence will always be
2830	C<ev_check> so if you have one watcher of each kind they will always be	3017	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2831	called in pairs bracketing the blocking call.	3018	kind they will always be called in pairs bracketing the blocking call.
2832		3019
2833	Their main purpose is to integrate other event mechanisms into libev and	3020	Their main purpose is to integrate other event mechanisms into libev and
2834	their use is somewhat advanced. They could be used, for example, to track	3021	their use is somewhat advanced. They could be used, for example, to track
2835	variable changes, implement your own watchers, integrate net-snmp or a	3022	variable changes, implement your own watchers, integrate net-snmp or a
2836	coroutine library and lots more. They are also occasionally useful if	3023	coroutine library and lots more. They are also occasionally useful if
…		…
2854	with priority higher than or equal to the event loop and one coroutine	3041	with priority higher than or equal to the event loop and one coroutine
2855	of lower priority, but only once, using idle watchers to keep the event	3042	of lower priority, but only once, using idle watchers to keep the event
2856	loop from blocking if lower-priority coroutines are active, thus mapping	3043	loop from blocking if lower-priority coroutines are active, thus mapping
2857	low-priority coroutines to idle/background tasks).	3044	low-priority coroutines to idle/background tasks).
2858		3045
2859	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3046	When used for this purpose, it is recommended to give C<ev_check> watchers
2860	priority, to ensure that they are being run before any other watchers	3047	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2861	after the poll (this doesn't matter for C<ev_prepare> watchers).	3048	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3049	watchers).
2862		3050
2863	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3051	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2864	activate ("feed") events into libev. While libev fully supports this, they	3052	activate ("feed") events into libev. While libev fully supports this, they
2865	might get executed before other C<ev_check> watchers did their job. As	3053	might get executed before other C<ev_check> watchers did their job. As
2866	C<ev_check> watchers are often used to embed other (non-libev) event	3054	C<ev_check> watchers are often used to embed other (non-libev) event
2867	loops those other event loops might be in an unusable state until their	3055	loops those other event loops might be in an unusable state until their
2868	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3056	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2869	others).	3057	others).
		3058
		3059	=head3 Abusing an C<ev_check> watcher for its side-effect
		3060
		3061	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3062	useful because they are called once per event loop iteration. For
		3063	example, if you want to handle a large number of connections fairly, you
		3064	normally only do a bit of work for each active connection, and if there
		3065	is more work to do, you wait for the next event loop iteration, so other
		3066	connections have a chance of making progress.
		3067
		3068	Using an C<ev_check> watcher is almost enough: it will be called on the
		3069	next event loop iteration. However, that isn't as soon as possible -
		3070	without external events, your C<ev_check> watcher will not be invoked.
		3071
		3072	This is where C<ev_idle> watchers come in handy - all you need is a
		3073	single global idle watcher that is active as long as you have one active
		3074	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3075	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3076	invoked. Neither watcher alone can do that.
2870		3077
2871	=head3 Watcher-Specific Functions and Data Members	3078	=head3 Watcher-Specific Functions and Data Members
2872		3079
2873	=over 4	3080	=over 4
2874		3081
…		…
3075		3282
3076	=over 4	3283	=over 4
3077		3284
3078	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3285	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
3079		3286
3080	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3287	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
3081		3288
3082	Configures the watcher to embed the given loop, which must be	3289	Configures the watcher to embed the given loop, which must be
3083	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3290	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
3084	invoked automatically, otherwise it is the responsibility of the callback	3291	invoked automatically, otherwise it is the responsibility of the callback
3085	to invoke it (it will continue to be called until the sweep has been done,	3292	to invoke it (it will continue to be called until the sweep has been done,
…		…
3106	used).	3313	used).
3107		3314
3108	struct ev_loop *loop_hi = ev_default_init (0);	3315	struct ev_loop *loop_hi = ev_default_init (0);
3109	struct ev_loop *loop_lo = 0;	3316	struct ev_loop *loop_lo = 0;
3110	ev_embed embed;	3317	ev_embed embed;
3111		3318
3112	// see if there is a chance of getting one that works	3319	// see if there is a chance of getting one that works
3113	// (remember that a flags value of 0 means autodetection)	3320	// (remember that a flags value of 0 means autodetection)
3114	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3321	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3115	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3322	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3116	: 0;	3323	: 0;
…		…
3130	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3337	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3131		3338
3132	struct ev_loop *loop = ev_default_init (0);	3339	struct ev_loop *loop = ev_default_init (0);
3133	struct ev_loop *loop_socket = 0;	3340	struct ev_loop *loop_socket = 0;
3134	ev_embed embed;	3341	ev_embed embed;
3135		3342
3136	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3343	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3137	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3344	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3138	{	3345	{
3139	ev_embed_init (&embed, 0, loop_socket);	3346	ev_embed_init (&embed, 0, loop_socket);
3140	ev_embed_start (loop, &embed);	3347	ev_embed_start (loop, &embed);
…		…
3148		3355
3149	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3356	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3150		3357
3151	Fork watchers are called when a C<fork ()> was detected (usually because	3358	Fork watchers are called when a C<fork ()> was detected (usually because
3152	whoever is a good citizen cared to tell libev about it by calling	3359	whoever is a good citizen cared to tell libev about it by calling
3153	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3360	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3154	event loop blocks next and before C<ev_check> watchers are being called,	3361	and before C<ev_check> watchers are being called, and only in the child
3155	and only in the child after the fork. If whoever good citizen calling	3362	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3156	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3363	and calls it in the wrong process, the fork handlers will be invoked, too,
3157	handlers will be invoked, too, of course.	3364	of course.
3158		3365
3159	=head3 The special problem of life after fork - how is it possible?	3366	=head3 The special problem of life after fork - how is it possible?
3160		3367
3161	Most uses of C<fork()> consist of forking, then some simple calls to set	3368	Most uses of C<fork ()> consist of forking, then some simple calls to set
3162	up/change the process environment, followed by a call to C<exec()>. This	3369	up/change the process environment, followed by a call to C<exec()>. This
3163	sequence should be handled by libev without any problems.	3370	sequence should be handled by libev without any problems.
3164		3371
3165	This changes when the application actually wants to do event handling	3372	This changes when the application actually wants to do event handling
3166	in the child, or both parent in child, in effect "continuing" after the	3373	in the child, or both parent in child, in effect "continuing" after the
…		…
3243	atexit (program_exits);	3450	atexit (program_exits);
3244		3451
3245		3452
3246	=head2 C<ev_async> - how to wake up an event loop	3453	=head2 C<ev_async> - how to wake up an event loop
3247		3454
3248	In general, you cannot use an C<ev_run> from multiple threads or other	3455	In general, you cannot use an C<ev_loop> from multiple threads or other
3249	asynchronous sources such as signal handlers (as opposed to multiple event	3456	asynchronous sources such as signal handlers (as opposed to multiple event
3250	loops - those are of course safe to use in different threads).	3457	loops - those are of course safe to use in different threads).
3251		3458
3252	Sometimes, however, you need to wake up an event loop you do not control,	3459	Sometimes, however, you need to wake up an event loop you do not control,
3253	for example because it belongs to another thread. This is what C<ev_async>	3460	for example because it belongs to another thread. This is what C<ev_async>
…		…
3255	it by calling C<ev_async_send>, which is thread- and signal safe.	3462	it by calling C<ev_async_send>, which is thread- and signal safe.
3256		3463
3257	This functionality is very similar to C<ev_signal> watchers, as signals,	3464	This functionality is very similar to C<ev_signal> watchers, as signals,
3258	too, are asynchronous in nature, and signals, too, will be compressed	3465	too, are asynchronous in nature, and signals, too, will be compressed
3259	(i.e. the number of callback invocations may be less than the number of	3466	(i.e. the number of callback invocations may be less than the number of
3260	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind	3467	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3261	of "global async watchers" by using a watcher on an otherwise unused	3468	of "global async watchers" by using a watcher on an otherwise unused
3262	signal, and C<ev_feed_signal> to signal this watcher from another thread,	3469	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3263	even without knowing which loop owns the signal.	3470	even without knowing which loop owns the signal.
3264
3265	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3266	just the default loop.
3267		3471
3268	=head3 Queueing	3472	=head3 Queueing
3269		3473
3270	C<ev_async> does not support queueing of data in any way. The reason	3474	C<ev_async> does not support queueing of data in any way. The reason
3271	is that the author does not know of a simple (or any) algorithm for a	3475	is that the author does not know of a simple (or any) algorithm for a
…		…
3363	trust me.	3567	trust me.
3364		3568
3365	=item ev_async_send (loop, ev_async *)	3569	=item ev_async_send (loop, ev_async *)
3366		3570
3367	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3571	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3368	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3572	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3573	returns.
		3574
3369	C<ev_feed_event>, this call is safe to do from other threads, signal or	3575	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3370	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3576	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3371	section below on what exactly this means).	3577	embedding section below on what exactly this means).
3372		3578
3373	Note that, as with other watchers in libev, multiple events might get	3579	Note that, as with other watchers in libev, multiple events might get
3374	compressed into a single callback invocation (another way to look at this	3580	compressed into a single callback invocation (another way to look at
3375	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3581	this is that C<ev_async> watchers are level-triggered: they are set on
3376	reset when the event loop detects that).	3582	C<ev_async_send>, reset when the event loop detects that).
3377		3583
3378	This call incurs the overhead of a system call only once per event loop	3584	This call incurs the overhead of at most one extra system call per event
3379	iteration, so while the overhead might be noticeable, it doesn't apply to	3585	loop iteration, if the event loop is blocked, and no syscall at all if
3380	repeated calls to C<ev_async_send> for the same event loop.	3586	the event loop (or your program) is processing events. That means that
		3587	repeated calls are basically free (there is no need to avoid calls for
		3588	performance reasons) and that the overhead becomes smaller (typically
		3589	zero) under load.
3381		3590
3382	=item bool = ev_async_pending (ev_async *)	3591	=item bool = ev_async_pending (ev_async *)
3383		3592
3384	Returns a non-zero value when C<ev_async_send> has been called on the	3593	Returns a non-zero value when C<ev_async_send> has been called on the
3385	watcher but the event has not yet been processed (or even noted) by the	3594	watcher but the event has not yet been processed (or even noted) by the
…		…
3402		3611
3403	There are some other functions of possible interest. Described. Here. Now.	3612	There are some other functions of possible interest. Described. Here. Now.
3404		3613
3405	=over 4	3614	=over 4
3406		3615
3407	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3616	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3408		3617
3409	This function combines a simple timer and an I/O watcher, calls your	3618	This function combines a simple timer and an I/O watcher, calls your
3410	callback on whichever event happens first and automatically stops both	3619	callback on whichever event happens first and automatically stops both
3411	watchers. This is useful if you want to wait for a single event on an fd	3620	watchers. This is useful if you want to wait for a single event on an fd
3412	or timeout without having to allocate/configure/start/stop/free one or	3621	or timeout without having to allocate/configure/start/stop/free one or
…		…
3440	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3649	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3441		3650
3442	=item ev_feed_fd_event (loop, int fd, int revents)	3651	=item ev_feed_fd_event (loop, int fd, int revents)
3443		3652
3444	Feed an event on the given fd, as if a file descriptor backend detected	3653	Feed an event on the given fd, as if a file descriptor backend detected
3445	the given events it.	3654	the given events.
3446		3655
3447	=item ev_feed_signal_event (loop, int signum)	3656	=item ev_feed_signal_event (loop, int signum)
3448		3657
3449	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,	3658	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3450	which is async-safe.	3659	which is async-safe.
…		…
3455	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)	3664	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
3456		3665
3457	This section explains some common idioms that are not immediately	3666	This section explains some common idioms that are not immediately
3458	obvious. Note that examples are sprinkled over the whole manual, and this	3667	obvious. Note that examples are sprinkled over the whole manual, and this
3459	section only contains stuff that wouldn't fit anywhere else.	3668	section only contains stuff that wouldn't fit anywhere else.
		3669
		3670	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3671
		3672	Each watcher has, by default, a C<void *data> member that you can read
		3673	or modify at any time: libev will completely ignore it. This can be used
		3674	to associate arbitrary data with your watcher. If you need more data and
		3675	don't want to allocate memory separately and store a pointer to it in that
		3676	data member, you can also "subclass" the watcher type and provide your own
		3677	data:
		3678
		3679	struct my_io
		3680	{
		3681	ev_io io;
		3682	int otherfd;
		3683	void *somedata;
		3684	struct whatever *mostinteresting;
		3685	};
		3686
		3687	...
		3688	struct my_io w;
		3689	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3690
		3691	And since your callback will be called with a pointer to the watcher, you
		3692	can cast it back to your own type:
		3693
		3694	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3695	{
		3696	struct my_io *w = (struct my_io *)w_;
		3697	...
		3698	}
		3699
		3700	More interesting and less C-conformant ways of casting your callback
		3701	function type instead have been omitted.
		3702
		3703	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3704
		3705	Another common scenario is to use some data structure with multiple
		3706	embedded watchers, in effect creating your own watcher that combines
		3707	multiple libev event sources into one "super-watcher":
		3708
		3709	struct my_biggy
		3710	{
		3711	int some_data;
		3712	ev_timer t1;
		3713	ev_timer t2;
		3714	}
		3715
		3716	In this case getting the pointer to C<my_biggy> is a bit more
		3717	complicated: Either you store the address of your C<my_biggy> struct in
		3718	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3719	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3720	real programmers):
		3721
		3722	#include <stddef.h>
		3723
		3724	static void
		3725	t1_cb (EV_P_ ev_timer *w, int revents)
		3726	{
		3727	struct my_biggy big = (struct my_biggy *)
		3728	(((char *)w) - offsetof (struct my_biggy, t1));
		3729	}
		3730
		3731	static void
		3732	t2_cb (EV_P_ ev_timer *w, int revents)
		3733	{
		3734	struct my_biggy big = (struct my_biggy *)
		3735	(((char *)w) - offsetof (struct my_biggy, t2));
		3736	}
		3737
		3738	=head2 AVOIDING FINISHING BEFORE RETURNING
		3739
		3740	Often you have structures like this in event-based programs:
		3741
		3742	callback ()
		3743	{
		3744	free (request);
		3745	}
		3746
		3747	request = start_new_request (..., callback);
		3748
		3749	The intent is to start some "lengthy" operation. The C<request> could be
		3750	used to cancel the operation, or do other things with it.
		3751
		3752	It's not uncommon to have code paths in C<start_new_request> that
		3753	immediately invoke the callback, for example, to report errors. Or you add
		3754	some caching layer that finds that it can skip the lengthy aspects of the
		3755	operation and simply invoke the callback with the result.
		3756
		3757	The problem here is that this will happen I<before> C<start_new_request>
		3758	has returned, so C<request> is not set.
		3759
		3760	Even if you pass the request by some safer means to the callback, you
		3761	might want to do something to the request after starting it, such as
		3762	canceling it, which probably isn't working so well when the callback has
		3763	already been invoked.
		3764
		3765	A common way around all these issues is to make sure that
		3766	C<start_new_request> I<always> returns before the callback is invoked. If
		3767	C<start_new_request> immediately knows the result, it can artificially
		3768	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3769	example, or more sneakily, by reusing an existing (stopped) watcher and
		3770	pushing it into the pending queue:
		3771
		3772	ev_set_cb (watcher, callback);
		3773	ev_feed_event (EV_A_ watcher, 0);
		3774
		3775	This way, C<start_new_request> can safely return before the callback is
		3776	invoked, while not delaying callback invocation too much.
3460		3777
3461	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS	3778	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3462		3779
3463	Often (especially in GUI toolkits) there are places where you have	3780	Often (especially in GUI toolkits) there are places where you have
3464	I<modal> interaction, which is most easily implemented by recursively	3781	I<modal> interaction, which is most easily implemented by recursively
…		…
3466		3783
3467	This brings the problem of exiting - a callback might want to finish the	3784	This brings the problem of exiting - a callback might want to finish the
3468	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but	3785	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
3469	a modal "Are you sure?" dialog is still waiting), or just the nested one	3786	a modal "Are you sure?" dialog is still waiting), or just the nested one
3470	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some	3787	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
3471	other combination: In these cases, C<ev_break> will not work alone.	3788	other combination: In these cases, a simple C<ev_break> will not work.
3472		3789
3473	The solution is to maintain "break this loop" variable for each C<ev_run>	3790	The solution is to maintain "break this loop" variable for each C<ev_run>
3474	invocation, and use a loop around C<ev_run> until the condition is	3791	invocation, and use a loop around C<ev_run> until the condition is
3475	triggered, using C<EVRUN_ONCE>:	3792	triggered, using C<EVRUN_ONCE>:
3476		3793
…		…
3478	int exit_main_loop = 0;	3795	int exit_main_loop = 0;
3479		3796
3480	while (!exit_main_loop)	3797	while (!exit_main_loop)
3481	ev_run (EV_DEFAULT_ EVRUN_ONCE);	3798	ev_run (EV_DEFAULT_ EVRUN_ONCE);
3482		3799
3483	// in a model watcher	3800	// in a modal watcher
3484	int exit_nested_loop = 0;	3801	int exit_nested_loop = 0;
3485		3802
3486	while (!exit_nested_loop)	3803	while (!exit_nested_loop)
3487	ev_run (EV_A_ EVRUN_ONCE);	3804	ev_run (EV_A_ EVRUN_ONCE);
3488		3805
…		…
3498	exit_main_loop = exit_nested_loop = 1;	3815	exit_main_loop = exit_nested_loop = 1;
3499		3816
3500	=head2 THREAD LOCKING EXAMPLE	3817	=head2 THREAD LOCKING EXAMPLE
3501		3818
3502	Here is a fictitious example of how to run an event loop in a different	3819	Here is a fictitious example of how to run an event loop in a different
3503	thread than where callbacks are being invoked and watchers are	3820	thread from where callbacks are being invoked and watchers are
3504	created/added/removed.	3821	created/added/removed.
3505		3822
3506	For a real-world example, see the C<EV::Loop::Async> perl module,	3823	For a real-world example, see the C<EV::Loop::Async> perl module,
3507	which uses exactly this technique (which is suited for many high-level	3824	which uses exactly this technique (which is suited for many high-level
3508	languages).	3825	languages).
…		…
3534	// now associate this with the loop	3851	// now associate this with the loop
3535	ev_set_userdata (EV_A_ u);	3852	ev_set_userdata (EV_A_ u);
3536	ev_set_invoke_pending_cb (EV_A_ l_invoke);	3853	ev_set_invoke_pending_cb (EV_A_ l_invoke);
3537	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);	3854	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3538		3855
3539	// then create the thread running ev_loop	3856	// then create the thread running ev_run
3540	pthread_create (&u->tid, 0, l_run, EV_A);	3857	pthread_create (&u->tid, 0, l_run, EV_A);
3541	}	3858	}
3542		3859
3543	The callback for the C<ev_async> watcher does nothing: the watcher is used	3860	The callback for the C<ev_async> watcher does nothing: the watcher is used
3544	solely to wake up the event loop so it takes notice of any new watchers	3861	solely to wake up the event loop so it takes notice of any new watchers
…		…
3633	Note that sending the C<ev_async> watcher is required because otherwise	3950	Note that sending the C<ev_async> watcher is required because otherwise
3634	an event loop currently blocking in the kernel will have no knowledge	3951	an event loop currently blocking in the kernel will have no knowledge
3635	about the newly added timer. By waking up the loop it will pick up any new	3952	about the newly added timer. By waking up the loop it will pick up any new
3636	watchers in the next event loop iteration.	3953	watchers in the next event loop iteration.
3637		3954
3638	=back	3955	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3956
		3957	While the overhead of a callback that e.g. schedules a thread is small, it
		3958	is still an overhead. If you embed libev, and your main usage is with some
		3959	kind of threads or coroutines, you might want to customise libev so that
		3960	doesn't need callbacks anymore.
		3961
		3962	Imagine you have coroutines that you can switch to using a function
		3963	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3964	and that due to some magic, the currently active coroutine is stored in a
		3965	global called C<current_coro>. Then you can build your own "wait for libev
		3966	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3967	the differing C<;> conventions):
		3968
		3969	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3970	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3971
		3972	That means instead of having a C callback function, you store the
		3973	coroutine to switch to in each watcher, and instead of having libev call
		3974	your callback, you instead have it switch to that coroutine.
		3975
		3976	A coroutine might now wait for an event with a function called
		3977	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3978	matter when, or whether the watcher is active or not when this function is
		3979	called):
		3980
		3981	void
		3982	wait_for_event (ev_watcher *w)
		3983	{
		3984	ev_set_cb (w, current_coro);
		3985	switch_to (libev_coro);
		3986	}
		3987
		3988	That basically suspends the coroutine inside C<wait_for_event> and
		3989	continues the libev coroutine, which, when appropriate, switches back to
		3990	this or any other coroutine.
		3991
		3992	You can do similar tricks if you have, say, threads with an event queue -
		3993	instead of storing a coroutine, you store the queue object and instead of
		3994	switching to a coroutine, you push the watcher onto the queue and notify
		3995	any waiters.
		3996
		3997	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3998	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3999
		4000	// my_ev.h
		4001	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4002	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4003	#include "../libev/ev.h"
		4004
		4005	// my_ev.c
		4006	#define EV_H "my_ev.h"
		4007	#include "../libev/ev.c"
		4008
		4009	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4010	F<my_ev.c> into your project. When properly specifying include paths, you
		4011	can even use F<ev.h> as header file name directly.
3639		4012
3640		4013
3641	=head1 LIBEVENT EMULATION	4014	=head1 LIBEVENT EMULATION
3642		4015
3643	Libev offers a compatibility emulation layer for libevent. It cannot	4016	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3673		4046
3674	=back	4047	=back
3675		4048
3676	=head1 C++ SUPPORT	4049	=head1 C++ SUPPORT
3677		4050
		4051	=head2 C API
		4052
		4053	The normal C API should work fine when used from C++: both ev.h and the
		4054	libev sources can be compiled as C++. Therefore, code that uses the C API
		4055	will work fine.
		4056
		4057	Proper exception specifications might have to be added to callbacks passed
		4058	to libev: exceptions may be thrown only from watcher callbacks, all other
		4059	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4060	callbacks) must not throw exceptions, and might need a C<noexcept>
		4061	specification. If you have code that needs to be compiled as both C and
		4062	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4063
		4064	static void
		4065	fatal_error (const char *msg) EV_NOEXCEPT
		4066	{
		4067	perror (msg);
		4068	abort ();
		4069	}
		4070
		4071	...
		4072	ev_set_syserr_cb (fatal_error);
		4073
		4074	The only API functions that can currently throw exceptions are C<ev_run>,
		4075	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4076	because it runs cleanup watchers).
		4077
		4078	Throwing exceptions in watcher callbacks is only supported if libev itself
		4079	is compiled with a C++ compiler or your C and C++ environments allow
		4080	throwing exceptions through C libraries (most do).
		4081
		4082	=head2 C++ API
		4083
3678	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4084	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3679	you to use some convenience methods to start/stop watchers and also change	4085	you to use some convenience methods to start/stop watchers and also change
3680	the callback model to a model using method callbacks on objects.	4086	the callback model to a model using method callbacks on objects.
3681		4087
3682	To use it,	4088	To use it,
3683		4089
3684	#include <ev++.h>	4090	#include <ev++.h>
3685		4091
3686	This automatically includes F<ev.h> and puts all of its definitions (many	4092	This automatically includes F<ev.h> and puts all of its definitions (many
3687	of them macros) into the global namespace. All C++ specific things are	4093	of them macros) into the global namespace. All C++ specific things are
3688	put into the C<ev> namespace. It should support all the same embedding	4094	put into the C<ev> namespace. It should support all the same embedding
…		…
3697	with C<operator ()> can be used as callbacks. Other types should be easy	4103	with C<operator ()> can be used as callbacks. Other types should be easy
3698	to add as long as they only need one additional pointer for context. If	4104	to add as long as they only need one additional pointer for context. If
3699	you need support for other types of functors please contact the author	4105	you need support for other types of functors please contact the author
3700	(preferably after implementing it).	4106	(preferably after implementing it).
3701		4107
		4108	For all this to work, your C++ compiler either has to use the same calling
		4109	conventions as your C compiler (for static member functions), or you have
		4110	to embed libev and compile libev itself as C++.
		4111
3702	Here is a list of things available in the C<ev> namespace:	4112	Here is a list of things available in the C<ev> namespace:
3703		4113
3704	=over 4	4114	=over 4
3705		4115
3706	=item C<ev::READ>, C<ev::WRITE> etc.	4116	=item C<ev::READ>, C<ev::WRITE> etc.
…		…
3715	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4125	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3716		4126
3717	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4127	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3718	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4128	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3719	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4129	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3720	defines by many implementations.	4130	defined by many implementations.
3721		4131
3722	All of those classes have these methods:	4132	All of those classes have these methods:
3723		4133
3724	=over 4	4134	=over 4
3725		4135
…		…
3787	void operator() (ev::io &w, int revents)	4197	void operator() (ev::io &w, int revents)
3788	{	4198	{
3789	...	4199	...
3790	}	4200	}
3791	}	4201	}
3792		4202
3793	myfunctor f;	4203	myfunctor f;
3794		4204
3795	ev::io w;	4205	ev::io w;
3796	w.set (&f);	4206	w.set (&f);
3797		4207
…		…
3815	Associates a different C<struct ev_loop> with this watcher. You can only	4225	Associates a different C<struct ev_loop> with this watcher. You can only
3816	do this when the watcher is inactive (and not pending either).	4226	do this when the watcher is inactive (and not pending either).
3817		4227
3818	=item w->set ([arguments])	4228	=item w->set ([arguments])
3819		4229
3820	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4230	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3821	method or a suitable start method must be called at least once. Unlike the	4231	with the same arguments. Either this method or a suitable start method
3822	C counterpart, an active watcher gets automatically stopped and restarted	4232	must be called at least once. Unlike the C counterpart, an active watcher
3823	when reconfiguring it with this method.	4233	gets automatically stopped and restarted when reconfiguring it with this
		4234	method.
		4235
		4236	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4237	clashing with the C<set (loop)> method.
3824		4238
3825	=item w->start ()	4239	=item w->start ()
3826		4240
3827	Starts the watcher. Note that there is no C<loop> argument, as the	4241	Starts the watcher. Note that there is no C<loop> argument, as the
3828	constructor already stores the event loop.	4242	constructor already stores the event loop.
…		…
3858	watchers in the constructor.	4272	watchers in the constructor.
3859		4273
3860	class myclass	4274	class myclass
3861	{	4275	{
3862	ev::io io ; void io_cb (ev::io &w, int revents);	4276	ev::io io ; void io_cb (ev::io &w, int revents);
3863	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4277	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3864	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4278	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3865		4279
3866	myclass (int fd)	4280	myclass (int fd)
3867	{	4281	{
3868	io .set <myclass, &myclass::io_cb > (this);	4282	io .set <myclass, &myclass::io_cb > (this);
…		…
3919	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4333	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3920		4334
3921	=item D	4335	=item D
3922		4336
3923	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4337	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3924	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4338	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3925		4339
3926	=item Ocaml	4340	=item Ocaml
3927		4341
3928	Erkki Seppala has written Ocaml bindings for libev, to be found at	4342	Erkki Seppala has written Ocaml bindings for libev, to be found at
3929	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4343	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3932		4346
3933	Brian Maher has written a partial interface to libev for lua (at the	4347	Brian Maher has written a partial interface to libev for lua (at the
3934	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4348	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3935	L<http://github.com/brimworks/lua-ev>.	4349	L<http://github.com/brimworks/lua-ev>.
3936		4350
		4351	=item Javascript
		4352
		4353	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4354
		4355	=item Others
		4356
		4357	There are others, and I stopped counting.
		4358
3937	=back	4359	=back
3938		4360
3939		4361
3940	=head1 MACRO MAGIC	4362	=head1 MACRO MAGIC
3941		4363
…		…
3977	suitable for use with C<EV_A>.	4399	suitable for use with C<EV_A>.
3978		4400
3979	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4401	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3980		4402
3981	Similar to the other two macros, this gives you the value of the default	4403	Similar to the other two macros, this gives you the value of the default
3982	loop, if multiple loops are supported ("ev loop default").	4404	loop, if multiple loops are supported ("ev loop default"). The default loop
		4405	will be initialised if it isn't already initialised.
		4406
		4407	For non-multiplicity builds, these macros do nothing, so you always have
		4408	to initialise the loop somewhere.
3983		4409
3984	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4410	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3985		4411
3986	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4412	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3987	default loop has been initialised (C<UC> == unchecked). Their behaviour	4413	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
4054	ev_vars.h	4480	ev_vars.h
4055	ev_wrap.h	4481	ev_wrap.h
4056		4482
4057	ev_win32.c required on win32 platforms only	4483	ev_win32.c required on win32 platforms only
4058		4484
4059	ev_select.c only when select backend is enabled (which is enabled by default)	4485	ev_select.c only when select backend is enabled
4060	ev_poll.c only when poll backend is enabled (disabled by default)	4486	ev_poll.c only when poll backend is enabled
4061	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4487	ev_epoll.c only when the epoll backend is enabled
		4488	ev_linuxaio.c only when the linux aio backend is enabled
		4489	ev_iouring.c only when the linux io_uring backend is enabled
4062	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4490	ev_kqueue.c only when the kqueue backend is enabled
4063	ev_port.c only when the solaris port backend is enabled (disabled by default)	4491	ev_port.c only when the solaris port backend is enabled
4064		4492
4065	F<ev.c> includes the backend files directly when enabled, so you only need	4493	F<ev.c> includes the backend files directly when enabled, so you only need
4066	to compile this single file.	4494	to compile this single file.
4067		4495
4068	=head3 LIBEVENT COMPATIBILITY API	4496	=head3 LIBEVENT COMPATIBILITY API
…		…
4132	supported). It will also not define any of the structs usually found in	4560	supported). It will also not define any of the structs usually found in
4133	F<event.h> that are not directly supported by the libev core alone.	4561	F<event.h> that are not directly supported by the libev core alone.
4134		4562
4135	In standalone mode, libev will still try to automatically deduce the	4563	In standalone mode, libev will still try to automatically deduce the
4136	configuration, but has to be more conservative.	4564	configuration, but has to be more conservative.
		4565
		4566	=item EV_USE_FLOOR
		4567
		4568	If defined to be C<1>, libev will use the C<floor ()> function for its
		4569	periodic reschedule calculations, otherwise libev will fall back on a
		4570	portable (slower) implementation. If you enable this, you usually have to
		4571	link against libm or something equivalent. Enabling this when the C<floor>
		4572	function is not available will fail, so the safe default is to not enable
		4573	this.
4137		4574
4138	=item EV_USE_MONOTONIC	4575	=item EV_USE_MONOTONIC
4139		4576
4140	If defined to be C<1>, libev will try to detect the availability of the	4577	If defined to be C<1>, libev will try to detect the availability of the
4141	monotonic clock option at both compile time and runtime. Otherwise no	4578	monotonic clock option at both compile time and runtime. Otherwise no
…		…
4227	If programs implement their own fd to handle mapping on win32, then this	4664	If programs implement their own fd to handle mapping on win32, then this
4228	macro can be used to override the C<close> function, useful to unregister	4665	macro can be used to override the C<close> function, useful to unregister
4229	file descriptors again. Note that the replacement function has to close	4666	file descriptors again. Note that the replacement function has to close
4230	the underlying OS handle.	4667	the underlying OS handle.
4231		4668
		4669	=item EV_USE_WSASOCKET
		4670
		4671	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4672	communication socket, which works better in some environments. Otherwise,
		4673	the normal C<socket> function will be used, which works better in other
		4674	environments.
		4675
4232	=item EV_USE_POLL	4676	=item EV_USE_POLL
4233		4677
4234	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4678	If defined to be C<1>, libev will compile in support for the C<poll>(2)
4235	backend. Otherwise it will be enabled on non-win32 platforms. It	4679	backend. Otherwise it will be enabled on non-win32 platforms. It
4236	takes precedence over select.	4680	takes precedence over select.
…		…
4240	If defined to be C<1>, libev will compile in support for the Linux	4684	If defined to be C<1>, libev will compile in support for the Linux
4241	C<epoll>(7) backend. Its availability will be detected at runtime,	4685	C<epoll>(7) backend. Its availability will be detected at runtime,
4242	otherwise another method will be used as fallback. This is the preferred	4686	otherwise another method will be used as fallback. This is the preferred
4243	backend for GNU/Linux systems. If undefined, it will be enabled if the	4687	backend for GNU/Linux systems. If undefined, it will be enabled if the
4244	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4688	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4689
		4690	=item EV_USE_LINUXAIO
		4691
		4692	If defined to be C<1>, libev will compile in support for the Linux aio
		4693	backend (C<EV_USE_EPOLL> must also be enabled). If undefined, it will be
		4694	enabled on linux, otherwise disabled.
		4695
		4696	=item EV_USE_IOURING
		4697
		4698	If defined to be C<1>, libev will compile in support for the Linux
		4699	io_uring backend (C<EV_USE_EPOLL> must also be enabled). Due to it's
		4700	current limitations it has to be requested explicitly. If undefined, it
		4701	will be enabled on linux, otherwise disabled.
4245		4702
4246	=item EV_USE_KQUEUE	4703	=item EV_USE_KQUEUE
4247		4704
4248	If defined to be C<1>, libev will compile in support for the BSD style	4705	If defined to be C<1>, libev will compile in support for the BSD style
4249	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4706	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
4271	If defined to be C<1>, libev will compile in support for the Linux inotify	4728	If defined to be C<1>, libev will compile in support for the Linux inotify
4272	interface to speed up C<ev_stat> watchers. Its actual availability will	4729	interface to speed up C<ev_stat> watchers. Its actual availability will
4273	be detected at runtime. If undefined, it will be enabled if the headers	4730	be detected at runtime. If undefined, it will be enabled if the headers
4274	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4731	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4275		4732
		4733	=item EV_NO_SMP
		4734
		4735	If defined to be C<1>, libev will assume that memory is always coherent
		4736	between threads, that is, threads can be used, but threads never run on
		4737	different cpus (or different cpu cores). This reduces dependencies
		4738	and makes libev faster.
		4739
		4740	=item EV_NO_THREADS
		4741
		4742	If defined to be C<1>, libev will assume that it will never be called from
		4743	different threads (that includes signal handlers), which is a stronger
		4744	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4745	libev faster.
		4746
4276	=item EV_ATOMIC_T	4747	=item EV_ATOMIC_T
4277		4748
4278	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4749	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4279	access is atomic with respect to other threads or signal contexts. No such	4750	access is atomic with respect to other threads or signal contexts. No
4280	type is easily found in the C language, so you can provide your own type	4751	such type is easily found in the C language, so you can provide your own
4281	that you know is safe for your purposes. It is used both for signal handler "locking"	4752	type that you know is safe for your purposes. It is used both for signal
4282	as well as for signal and thread safety in C<ev_async> watchers.	4753	handler "locking" as well as for signal and thread safety in C<ev_async>
		4754	watchers.
4283		4755
4284	In the absence of this define, libev will use C<sig_atomic_t volatile>	4756	In the absence of this define, libev will use C<sig_atomic_t volatile>
4285	(from F<signal.h>), which is usually good enough on most platforms.	4757	(from F<signal.h>), which is usually good enough on most platforms.
4286		4758
4287	=item EV_H (h)	4759	=item EV_H (h)
…		…
4314	will have the C<struct ev_loop *> as first argument, and you can create	4786	will have the C<struct ev_loop *> as first argument, and you can create
4315	additional independent event loops. Otherwise there will be no support	4787	additional independent event loops. Otherwise there will be no support
4316	for multiple event loops and there is no first event loop pointer	4788	for multiple event loops and there is no first event loop pointer
4317	argument. Instead, all functions act on the single default loop.	4789	argument. Instead, all functions act on the single default loop.
4318		4790
		4791	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4792	default loop when multiplicity is switched off - you always have to
		4793	initialise the loop manually in this case.
		4794
4319	=item EV_MINPRI	4795	=item EV_MINPRI
4320		4796
4321	=item EV_MAXPRI	4797	=item EV_MAXPRI
4322		4798
4323	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4799	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4359	#define EV_USE_POLL 1	4835	#define EV_USE_POLL 1
4360	#define EV_CHILD_ENABLE 1	4836	#define EV_CHILD_ENABLE 1
4361	#define EV_ASYNC_ENABLE 1	4837	#define EV_ASYNC_ENABLE 1
4362		4838
4363	The actual value is a bitset, it can be a combination of the following	4839	The actual value is a bitset, it can be a combination of the following
4364	values:	4840	values (by default, all of these are enabled):
4365		4841
4366	=over 4	4842	=over 4
4367		4843
4368	=item C<1> - faster/larger code	4844	=item C<1> - faster/larger code
4369		4845
…		…
4373	code size by roughly 30% on amd64).	4849	code size by roughly 30% on amd64).
4374		4850
4375	When optimising for size, use of compiler flags such as C<-Os> with	4851	When optimising for size, use of compiler flags such as C<-Os> with
4376	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4852	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4377	assertions.	4853	assertions.
		4854
		4855	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4856	(e.g. gcc with C<-Os>).
4378		4857
4379	=item C<2> - faster/larger data structures	4858	=item C<2> - faster/larger data structures
4380		4859
4381	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4860	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4382	hash table sizes and so on. This will usually further increase code size	4861	hash table sizes and so on. This will usually further increase code size
4383	and can additionally have an effect on the size of data structures at	4862	and can additionally have an effect on the size of data structures at
4384	runtime.	4863	runtime.
4385		4864
		4865	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4866	(e.g. gcc with C<-Os>).
		4867
4386	=item C<4> - full API configuration	4868	=item C<4> - full API configuration
4387		4869
4388	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4870	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4389	enables multiplicity (C<EV_MULTIPLICITY>=1).	4871	enables multiplicity (C<EV_MULTIPLICITY>=1).
4390		4872
…		…
4420		4902
4421	With an intelligent-enough linker (gcc+binutils are intelligent enough	4903	With an intelligent-enough linker (gcc+binutils are intelligent enough
4422	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4904	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4423	your program might be left out as well - a binary starting a timer and an	4905	your program might be left out as well - a binary starting a timer and an
4424	I/O watcher then might come out at only 5Kb.	4906	I/O watcher then might come out at only 5Kb.
		4907
		4908	=item EV_API_STATIC
		4909
		4910	If this symbol is defined (by default it is not), then all identifiers
		4911	will have static linkage. This means that libev will not export any
		4912	identifiers, and you cannot link against libev anymore. This can be useful
		4913	when you embed libev, only want to use libev functions in a single file,
		4914	and do not want its identifiers to be visible.
		4915
		4916	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4917	wants to use libev.
		4918
		4919	This option only works when libev is compiled with a C compiler, as C++
		4920	doesn't support the required declaration syntax.
4425		4921
4426	=item EV_AVOID_STDIO	4922	=item EV_AVOID_STDIO
4427		4923
4428	If this is set to C<1> at compiletime, then libev will avoid using stdio	4924	If this is set to C<1> at compiletime, then libev will avoid using stdio
4429	functions (printf, scanf, perror etc.). This will increase the code size	4925	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4487	in. If set to C<1>, then verification code will be compiled in, but not	4983	in. If set to C<1>, then verification code will be compiled in, but not
4488	called. If set to C<2>, then the internal verification code will be	4984	called. If set to C<2>, then the internal verification code will be
4489	called once per loop, which can slow down libev. If set to C<3>, then the	4985	called once per loop, which can slow down libev. If set to C<3>, then the
4490	verification code will be called very frequently, which will slow down	4986	verification code will be called very frequently, which will slow down
4491	libev considerably.	4987	libev considerably.
		4988
		4989	Verification errors are reported via C's C<assert> mechanism, so if you
		4990	disable that (e.g. by defining C<NDEBUG>) then no errors will be reported.
4492		4991
4493	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it	4992	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
4494	will be C<0>.	4993	will be C<0>.
4495		4994
4496	=item EV_COMMON	4995	=item EV_COMMON
…		…
4573	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5072	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4574		5073
4575	#include "ev_cpp.h"	5074	#include "ev_cpp.h"
4576	#include "ev.c"	5075	#include "ev.c"
4577		5076
4578	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5077	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4579		5078
4580	=head2 THREADS AND COROUTINES	5079	=head2 THREADS AND COROUTINES
4581		5080
4582	=head3 THREADS	5081	=head3 THREADS
4583		5082
…		…
4634	default loop and triggering an C<ev_async> watcher from the default loop	5133	default loop and triggering an C<ev_async> watcher from the default loop
4635	watcher callback into the event loop interested in the signal.	5134	watcher callback into the event loop interested in the signal.
4636		5135
4637	=back	5136	=back
4638		5137
4639	See also L<THREAD LOCKING EXAMPLE>.	5138	See also L</THREAD LOCKING EXAMPLE>.
4640		5139
4641	=head3 COROUTINES	5140	=head3 COROUTINES
4642		5141
4643	Libev is very accommodating to coroutines ("cooperative threads"):	5142	Libev is very accommodating to coroutines ("cooperative threads"):
4644	libev fully supports nesting calls to its functions from different	5143	libev fully supports nesting calls to its functions from different
…		…
4809	requires, and its I/O model is fundamentally incompatible with the POSIX	5308	requires, and its I/O model is fundamentally incompatible with the POSIX
4810	model. Libev still offers limited functionality on this platform in	5309	model. Libev still offers limited functionality on this platform in
4811	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5310	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4812	descriptors. This only applies when using Win32 natively, not when using	5311	descriptors. This only applies when using Win32 natively, not when using
4813	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5312	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4814	as every compielr comes with a slightly differently broken/incompatible	5313	as every compiler comes with a slightly differently broken/incompatible
4815	environment.	5314	environment.
4816		5315
4817	Lifting these limitations would basically require the full	5316	Lifting these limitations would basically require the full
4818	re-implementation of the I/O system. If you are into this kind of thing,	5317	re-implementation of the I/O system. If you are into this kind of thing,
4819	then note that glib does exactly that for you in a very portable way (note	5318	then note that glib does exactly that for you in a very portable way (note
…		…
4913	structure (guaranteed by POSIX but not by ISO C for example), but it also	5412	structure (guaranteed by POSIX but not by ISO C for example), but it also
4914	assumes that the same (machine) code can be used to call any watcher	5413	assumes that the same (machine) code can be used to call any watcher
4915	callback: The watcher callbacks have different type signatures, but libev	5414	callback: The watcher callbacks have different type signatures, but libev
4916	calls them using an C<ev_watcher *> internally.	5415	calls them using an C<ev_watcher *> internally.
4917		5416
		5417	=item null pointers and integer zero are represented by 0 bytes
		5418
		5419	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5420	relies on this setting pointers and integers to null.
		5421
4918	=item pointer accesses must be thread-atomic	5422	=item pointer accesses must be thread-atomic
4919		5423
4920	Accessing a pointer value must be atomic, it must both be readable and	5424	Accessing a pointer value must be atomic, it must both be readable and
4921	writable in one piece - this is the case on all current architectures.	5425	writable in one piece - this is the case on all current architectures.
4922		5426
…		…
4935	thread" or will block signals process-wide, both behaviours would	5439	thread" or will block signals process-wide, both behaviours would
4936	be compatible with libev. Interaction between C<sigprocmask> and	5440	be compatible with libev. Interaction between C<sigprocmask> and
4937	C<pthread_sigmask> could complicate things, however.	5441	C<pthread_sigmask> could complicate things, however.
4938		5442
4939	The most portable way to handle signals is to block signals in all threads	5443	The most portable way to handle signals is to block signals in all threads
4940	except the initial one, and run the default loop in the initial thread as	5444	except the initial one, and run the signal handling loop in the initial
4941	well.	5445	thread as well.
4942		5446
4943	=item C<long> must be large enough for common memory allocation sizes	5447	=item C<long> must be large enough for common memory allocation sizes
4944		5448
4945	To improve portability and simplify its API, libev uses C<long> internally	5449	To improve portability and simplify its API, libev uses C<long> internally
4946	instead of C<size_t> when allocating its data structures. On non-POSIX	5450	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4952		5456
4953	The type C<double> is used to represent timestamps. It is required to	5457	The type C<double> is used to represent timestamps. It is required to
4954	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5458	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4955	good enough for at least into the year 4000 with millisecond accuracy	5459	good enough for at least into the year 4000 with millisecond accuracy
4956	(the design goal for libev). This requirement is overfulfilled by	5460	(the design goal for libev). This requirement is overfulfilled by
4957	implementations using IEEE 754, which is basically all existing ones. With	5461	implementations using IEEE 754, which is basically all existing ones.
		5462
4958	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5463	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5464	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5465	is either obsolete or somebody patched it to use C<long double> or
		5466	something like that, just kidding).
4959		5467
4960	=back	5468	=back
4961		5469
4962	If you know of other additional requirements drop me a note.	5470	If you know of other additional requirements drop me a note.
4963		5471
…		…
5025	=item Processing ev_async_send: O(number_of_async_watchers)	5533	=item Processing ev_async_send: O(number_of_async_watchers)
5026		5534
5027	=item Processing signals: O(max_signal_number)	5535	=item Processing signals: O(max_signal_number)
5028		5536
5029	Sending involves a system call I<iff> there were no other C<ev_async_send>	5537	Sending involves a system call I<iff> there were no other C<ev_async_send>
5030	calls in the current loop iteration. Checking for async and signal events	5538	calls in the current loop iteration and the loop is currently
		5539	blocked. Checking for async and signal events involves iterating over all
5031	involves iterating over all running async watchers or all signal numbers.	5540	running async watchers or all signal numbers.
5032		5541
5033	=back	5542	=back
5034		5543
5035		5544
5036	=head1 PORTING FROM LIBEV 3.X TO 4.X	5545	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
5045	=over 4	5554	=over 4
5046		5555
5047	=item C<EV_COMPAT3> backwards compatibility mechanism	5556	=item C<EV_COMPAT3> backwards compatibility mechanism
5048		5557
5049	The backward compatibility mechanism can be controlled by	5558	The backward compatibility mechanism can be controlled by
5050	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5559	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
5051	section.	5560	section.
5052		5561
5053	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5562	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
5054		5563
5055	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5564	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
5098	=over 4	5607	=over 4
5099		5608
5100	=item active	5609	=item active
5101		5610
5102	A watcher is active as long as it has been started and not yet stopped.	5611	A watcher is active as long as it has been started and not yet stopped.
5103	See L<WATCHER STATES> for details.	5612	See L</WATCHER STATES> for details.
5104		5613
5105	=item application	5614	=item application
5106		5615
5107	In this document, an application is whatever is using libev.	5616	In this document, an application is whatever is using libev.
5108		5617
…		…
5144	watchers and events.	5653	watchers and events.
5145		5654
5146	=item pending	5655	=item pending
5147		5656
5148	A watcher is pending as soon as the corresponding event has been	5657	A watcher is pending as soon as the corresponding event has been
5149	detected. See L<WATCHER STATES> for details.	5658	detected. See L</WATCHER STATES> for details.
5150		5659
5151	=item real time	5660	=item real time
5152		5661
5153	The physical time that is observed. It is apparently strictly monotonic :)	5662	The physical time that is observed. It is apparently strictly monotonic :)
5154		5663
5155	=item wall-clock time	5664	=item wall-clock time
5156		5665
5157	The time and date as shown on clocks. Unlike real time, it can actually	5666	The time and date as shown on clocks. Unlike real time, it can actually
5158	be wrong and jump forwards and backwards, e.g. when the you adjust your	5667	be wrong and jump forwards and backwards, e.g. when you adjust your
5159	clock.	5668	clock.
5160		5669
5161	=item watcher	5670	=item watcher
5162		5671
5163	A data structure that describes interest in certain events. Watchers need	5672	A data structure that describes interest in certain events. Watchers need
…		…
5166	=back	5675	=back
5167		5676
5168	=head1 AUTHOR	5677	=head1 AUTHOR
5169		5678
5170	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5679	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5171	Magnusson and Emanuele Giaquinta.	5680	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5172		5681

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