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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.
446		481
447	This flag's behaviour will become the default in future versions of libev.	482	It's also required by POSIX in a threaded program, as libev calls
		483	C<sigprocmask>, whose behaviour is officially unspecified.
		484
		485	=item C<EVFLAG_NOTIMERFD>
		486
		487	When this flag is specified, the libev will avoid using a C<timerfd> to
		488	detect time jumps. It will still be able to detect time jumps, but takes
		489	longer and has a lower accuracy in doing so, but saves a file descriptor
		490	per loop.
		491
		492	The current implementation only tries to use a C<timerfd> when the first
		493	C<ev_periodic> watcher is started and falls back on other methods if it
		494	cannot be created, but this behaviour might change in the future.
448		495
449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	496	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
450		497
451	This is your standard select(2) backend. Not I<completely> standard, as	498	This is your standard select(2) backend. Not I<completely> standard, as
452	libev tries to roll its own fd_set with no limits on the number of fds,	499	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
477	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and	524	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
478	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	525	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
479		526
480	=item C<EVBACKEND_EPOLL> (value 4, Linux)	527	=item C<EVBACKEND_EPOLL> (value 4, Linux)
481		528
482	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	529	Use the Linux-specific epoll(7) interface (for both pre- and post-2.6.9
483	kernels).	530	kernels).
484		531
485	For few fds, this backend is a bit little slower than poll and select,	532	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	533	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),	534	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).	535	fd), epoll scales either O(1) or O(active_fds).
489		536
490	The epoll mechanism deserves honorable mention as the most misdesigned	537	The epoll mechanism deserves honorable mention as the most misdesigned
491	of the more advanced event mechanisms: mere annoyances include silently	538	of the more advanced event mechanisms: mere annoyances include silently
492	dropping file descriptors, requiring a system call per change per file	539	dropping file descriptors, requiring a system call per change per file
493	descriptor (and unnecessary guessing of parameters), problems with dup,	540	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	543	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	544	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)	545	set, which can take considerable time (one syscall per file descriptor)
499	and is of course hard to detect.	546	and is of course hard to detect.
500		547
501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	548	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	549	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	550	totally I<different> file descriptors (even already closed ones, so
504	even remove them from the set) than registered in the set (especially	551	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	552	(especially on SMP systems). Libev tries to counter these spurious
506	employing an additional generation counter and comparing that against the	553	notifications by employing an additional generation counter and comparing
507	events to filter out spurious ones, recreating the set when required. Last	554	that against the events to filter out spurious ones, recreating the set
		555	when required. Epoll also erroneously rounds down timeouts, but gives you
		556	no way to know when and by how much, so sometimes you have to busy-wait
		557	because epoll returns immediately despite a nonzero timeout. And last
508	not least, it also refuses to work with some file descriptors which work	558	not least, it also refuses to work with some file descriptors which work
509	perfectly fine with C<select> (files, many character devices...).	559	perfectly fine with C<select> (files, many character devices...).
510		560
511	Epoll is truly the train wreck analog among event poll mechanisms,	561	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	562	cobbled together in a hurry, no thought to design or interaction with
513	interaction with others.	563	others. Oh, the pain, will it ever stop...
514		564
515	While stopping, setting and starting an I/O watcher in the same iteration	565	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	566	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	567	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	568	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	580	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	581	faster than epoll for maybe up to a hundred file descriptors, depending on
532	the usage. So sad.	582	the usage. So sad.
533		583
534	While nominally embeddable in other event loops, this feature is broken in	584	While nominally embeddable in other event loops, this feature is broken in
535	all kernel versions tested so far.	585	a lot of kernel revisions, but probably(!) works in current versions.
536		586
537	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	587	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
538	C<EVBACKEND_POLL>.	588	C<EVBACKEND_POLL>.
539		589
		590	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		591
		592	Use the Linux-specific Linux AIO (I<not> C<< aio(7) >> but C<<
		593	io_submit(2) >>) event interface available in post-4.18 kernels (but libev
		594	only tries to use it in 4.19+).
		595
		596	This is another Linux train wreck of an event interface.
		597
		598	If this backend works for you (as of this writing, it was very
		599	experimental), it is the best event interface available on Linux and might
		600	be well worth enabling it - if it isn't available in your kernel this will
		601	be detected and this backend will be skipped.
		602
		603	This backend can batch oneshot requests and supports a user-space ring
		604	buffer to receive events. It also doesn't suffer from most of the design
		605	problems of epoll (such as not being able to remove event sources from
		606	the epoll set), and generally sounds too good to be true. Because, this
		607	being the Linux kernel, of course it suffers from a whole new set of
		608	limitations, forcing you to fall back to epoll, inheriting all its design
		609	issues.
		610
		611	For one, it is not easily embeddable (but probably could be done using
		612	an event fd at some extra overhead). It also is subject to a system wide
		613	limit that can be configured in F</proc/sys/fs/aio-max-nr>. If no AIO
		614	requests are left, this backend will be skipped during initialisation, and
		615	will switch to epoll when the loop is active.
		616
		617	Most problematic in practice, however, is that not all file descriptors
		618	work with it. For example, in Linux 5.1, TCP sockets, pipes, event fds,
		619	files, F</dev/null> and many others are supported, but ttys do not work
		620	properly (a known bug that the kernel developers don't care about, see
		621	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		622	(yet?) a generic event polling interface.
		623
		624	Overall, it seems the Linux developers just don't want it to have a
		625	generic event handling mechanism other than C<select> or C<poll>.
		626
		627	To work around all these problem, the current version of libev uses its
		628	epoll backend as a fallback for file descriptor types that do not work. Or
		629	falls back completely to epoll if the kernel acts up.
		630
		631	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		632	C<EVBACKEND_POLL>.
		633
540	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	634	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
541		635
542	Kqueue deserves special mention, as at the time of this writing, it	636	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	637	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	638	work reliably with anything but sockets and pipes, except on Darwin,
545	it's completely useless). Unlike epoll, however, whose brokenness	639	where of course it's completely useless). Unlike epoll, however, whose
546	is by design, these kqueue bugs can (and eventually will) be fixed	640	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	641	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	642	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)	643	in the flags (i.e. using C<EVBACKEND_KQUEUE>) or libev was compiled on a
550	system like NetBSD.	644	known-to-be-good (-enough) system like NetBSD.
551		645
552	You still can embed kqueue into a normal poll or select backend and use it	646	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	647	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.	648	the target platform). See C<ev_embed> watchers for more info.
555		649
556	It scales in the same way as the epoll backend, but the interface to the	650	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	651	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	652	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	653	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	654	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	655	might have to leak fds on fork, but it's more sane than epoll) and it
562	cases	656	drops fds silently in similarly hard-to-detect cases.
563		657
564	This backend usually performs well under most conditions.	658	This backend usually performs well under most conditions.
565		659
566	While nominally embeddable in other event loops, this doesn't work	660	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	661	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	690	among the OS-specific backends (I vastly prefer correctness over speed
597	hacks).	691	hacks).
598		692
599	On the negative side, the interface is I<bizarre> - so bizarre that	693	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	694	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	695	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	696	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	697	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	698	absolutely have to know whether an event occurred or not because you have
605	have to re-arm the watcher.	699	to re-arm the watcher.
606		700
607	Fortunately libev seems to be able to work around these idiocies.	701	Fortunately libev seems to be able to work around these idiocies.
608		702
609	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	703	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
610	C<EVBACKEND_POLL>.	704	C<EVBACKEND_POLL>.
…		…
640		734
641	Example: Use whatever libev has to offer, but make sure that kqueue is	735	Example: Use whatever libev has to offer, but make sure that kqueue is
642	used if available.	736	used if available.
643		737
644	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);	738	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		739
		740	Example: Similarly, on linux, you mgiht want to take advantage of the
		741	linux aio backend if possible, but fall back to something else if that
		742	isn't available.
		743
		744	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
645		745
646	=item ev_loop_destroy (loop)	746	=item ev_loop_destroy (loop)
647		747
648	Destroys an event loop object (frees all memory and kernel state	748	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	749	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>	766	If you need dynamically allocated loops it is better to use C<ev_loop_new>
667	and C<ev_loop_destroy>.	767	and C<ev_loop_destroy>.
668		768
669	=item ev_loop_fork (loop)	769	=item ev_loop_fork (loop)
670		770
671	This function sets a flag that causes subsequent C<ev_run> iterations to	771	This function sets a flag that causes subsequent C<ev_run> iterations
672	reinitialise the kernel state for backends that have one. Despite the	772	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	773	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	774	watchers (except inside an C<ev_prepare> callback), but it makes most
		775	sense after forking, in the child process. You I<must> call it (or use
675	child before resuming or calling C<ev_run>.	776	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
676		777
		778	In addition, if you want to reuse a loop (via this function or
		779	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		780
677	Again, you I<have> to call it on I<any> loop that you want to re-use after	781	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	782	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	783	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
680	during fork.	784	during fork.
681		785
682	On the other hand, you only need to call this function in the child	786	On the other hand, you only need to call this function in the child
…		…
752		856
753	This function is rarely useful, but when some event callback runs for a	857	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	858	very long time without entering the event loop, updating libev's idea of
755	the current time is a good idea.	859	the current time is a good idea.
756		860
757	See also L<The special problem of time updates> in the C<ev_timer> section.	861	See also L</The special problem of time updates> in the C<ev_timer> section.
758		862
759	=item ev_suspend (loop)	863	=item ev_suspend (loop)
760		864
761	=item ev_resume (loop)	865	=item ev_resume (loop)
762		866
…		…
780	without a previous call to C<ev_suspend>.	884	without a previous call to C<ev_suspend>.
781		885
782	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	886	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
783	event loop time (see C<ev_now_update>).	887	event loop time (see C<ev_now_update>).
784		888
785	=item ev_run (loop, int flags)	889	=item bool ev_run (loop, int flags)
786		890
787	Finally, this is it, the event handler. This function usually is called	891	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	892	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	893	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	894	the watcher callbacks, and then repeat the whole process indefinitely: This
791	is why event loops are called I<loops>.	895	is why event loops are called I<loops>.
792		896
793	If the flags argument is specified as C<0>, it will keep handling events	897	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	898	until either no event watchers are active anymore or C<ev_break> was
795	called.	899	called.
		900
		901	The return value is false if there are no more active watchers (which
		902	usually means "all jobs done" or "deadlock"), and true in all other cases
		903	(which usually means " you should call C<ev_run> again").
796		904
797	Please note that an explicit C<ev_break> is usually better than	905	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	906	relying on all watchers to be stopped when deciding when a program has
799	finished (especially in interactive programs), but having a program	907	finished (especially in interactive programs), but having a program
800	that automatically loops as long as it has to and no longer by virtue	908	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	909	of relying on its watchers stopping correctly, that is truly a thing of
802	beauty.	910	beauty.
803		911
804	This function is also I<mostly> exception-safe - you can break out of	912	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++	913	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	914	exception and so on. This does not decrement the C<ev_depth> value, nor
807	will it clear any outstanding C<EVBREAK_ONE> breaks.	915	will it clear any outstanding C<EVBREAK_ONE> breaks.
808		916
809	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	917	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	918	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	930	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	931	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	932	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.	933	usually a better approach for this kind of thing.
826		934
827	Here are the gory details of what C<ev_run> does:	935	Here are the gory details of what C<ev_run> does (this is for your
		936	understanding, not a guarantee that things will work exactly like this in
		937	future versions):
828		938
829	- Increment loop depth.	939	- Increment loop depth.
830	- Reset the ev_break status.	940	- Reset the ev_break status.
831	- Before the first iteration, call any pending watchers.	941	- Before the first iteration, call any pending watchers.
832	LOOP:	942	LOOP:
…		…
865	anymore.	975	anymore.
866		976
867	... queue jobs here, make sure they register event watchers as long	977	... 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..)	978	... as they still have work to do (even an idle watcher will do..)
869	ev_run (my_loop, 0);	979	ev_run (my_loop, 0);
870	... jobs done or somebody called unloop. yeah!	980	... jobs done or somebody called break. yeah!
871		981
872	=item ev_break (loop, how)	982	=item ev_break (loop, how)
873		983
874	Can be used to make a call to C<ev_run> return early (but only after it	984	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	985	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.	1048	overhead for the actual polling but can deliver many events at once.
939		1049
940	By setting a higher I<io collect interval> you allow libev to spend more	1050	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,	1051	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	1052	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	1053	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	1054	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	1055	sleep time ensures that libev will not poll for I/O events more often then
946	once per this interval, on average.	1056	once per this interval, on average (as long as the host time resolution is
		1057	good enough).
947		1058
948	Likewise, by setting a higher I<timeout collect interval> you allow libev	1059	Likewise, by setting a higher I<timeout collect interval> you allow libev
949	to spend more time collecting timeouts, at the expense of increased	1060	to spend more time collecting timeouts, at the expense of increased
950	latency/jitter/inexactness (the watcher callback will be called	1061	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	1062	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.).	1108	invoke the actual watchers inside another context (another thread etc.).
998		1109
999	If you want to reset the callback, use C<ev_invoke_pending> as new	1110	If you want to reset the callback, use C<ev_invoke_pending> as new
1000	callback.	1111	callback.
1001		1112
1002	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1113	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
1003		1114
1004	Sometimes you want to share the same loop between multiple threads. This	1115	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	1116	can be done relatively simply by putting mutex_lock/unlock calls around
1006	each call to a libev function.	1117	each call to a libev function.
1007		1118
1008	However, C<ev_run> can run an indefinite time, so it is not feasible	1119	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	1120	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	1121	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.	1122	I<release> and I<acquire> callbacks on the loop.
1012		1123
1013	When set, then C<release> will be called just before the thread is	1124	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	1125	suspended waiting for new events, and C<acquire> is called just
1015	afterwards.	1126	afterwards.
…		…
1155		1266
1156	=item C<EV_PREPARE>	1267	=item C<EV_PREPARE>
1157		1268
1158	=item C<EV_CHECK>	1269	=item C<EV_CHECK>
1159		1270
1160	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1271	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	1272	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	1273	just after C<ev_run> has gathered them, but before it queues any callbacks
		1274	for any received events. That means C<ev_prepare> watchers are the last
		1275	watchers invoked before the event loop sleeps or polls for new events, and
		1276	C<ev_check> watchers will be invoked before any other watchers of the same
		1277	or lower priority within an event loop iteration.
		1278
1163	received events. Callbacks of both watcher types can start and stop as	1279	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	1280	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	1281	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1166	C<ev_run> from blocking).	1282	blocking).
1167		1283
1168	=item C<EV_EMBED>	1284	=item C<EV_EMBED>
1169		1285
1170	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1286	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1171		1287
…		…
1294		1410
1295	=item callback ev_cb (ev_TYPE *watcher)	1411	=item callback ev_cb (ev_TYPE *watcher)
1296		1412
1297	Returns the callback currently set on the watcher.	1413	Returns the callback currently set on the watcher.
1298		1414
1299	=item ev_cb_set (ev_TYPE *watcher, callback)	1415	=item ev_set_cb (ev_TYPE *watcher, callback)
1300		1416
1301	Change the callback. You can change the callback at virtually any time	1417	Change the callback. You can change the callback at virtually any time
1302	(modulo threads).	1418	(modulo threads).
1303		1419
1304	=item ev_set_priority (ev_TYPE *watcher, int priority)	1420	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1322	or might not have been clamped to the valid range.	1438	or might not have been clamped to the valid range.
1323		1439
1324	The default priority used by watchers when no priority has been set is	1440	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 :).	1441	always C<0>, which is supposed to not be too high and not be too low :).
1326		1442
1327	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1443	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1328	priorities.	1444	priorities.
1329		1445
1330	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1446	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1331		1447
1332	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1448	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	1473	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1358	functions that do not need a watcher.	1474	functions that do not need a watcher.
1359		1475
1360	=back	1476	=back
1361		1477
1362	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1478	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1363		1479	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		1480
1427	=head2 WATCHER STATES	1481	=head2 WATCHER STATES
1428		1482
1429	There are various watcher states mentioned throughout this manual -	1483	There are various watcher states mentioned throughout this manual -
1430	active, pending and so on. In this section these states and the rules to	1484	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	1485	transition between them will be described in more detail - and while these
1432	rules might look complicated, they usually do "the right thing".	1486	rules might look complicated, they usually do "the right thing".
1433		1487
1434	=over 4	1488	=over 4
1435		1489
1436	=item initialiased	1490	=item initialised
1437		1491
1438	Before a watcher can be registered with the event looop it has to be	1492	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	1493	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.	1494	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1441		1495
1442	In this state it is simply some block of memory that is suitable for use	1496	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.	1497	use in an event loop. It can be moved around, freed, reused etc. at
		1498	will - as long as you either keep the memory contents intact, or call
		1499	C<ev_TYPE_init> again.
1444		1500
1445	=item started/running/active	1501	=item started/running/active
1446		1502
1447	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1503	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	1504	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	1532	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	1533	of whether it was active or not, so stopping a watcher explicitly before
1478	freeing it is often a good idea.	1534	freeing it is often a good idea.
1479		1535
1480	While stopped (and not pending) the watcher is essentially in the	1536	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	1537	initialised state, that is, it can be reused, moved, modified in any way
1482	you wish.	1538	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1539	it again).
1483		1540
1484	=back	1541	=back
1485		1542
1486	=head2 WATCHER PRIORITY MODELS	1543	=head2 WATCHER PRIORITY MODELS
1487		1544
1488	Many event loops support I<watcher priorities>, which are usually small	1545	Many event loops support I<watcher priorities>, which are usually small
1489	integers that influence the ordering of event callback invocation	1546	integers that influence the ordering of event callback invocation
1490	between watchers in some way, all else being equal.	1547	between watchers in some way, all else being equal.
1491		1548
1492	In libev, Watcher priorities can be set using C<ev_set_priority>. See its	1549	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	1550	description for the more technical details such as the actual priority
1494	range.	1551	range.
1495		1552
1496	There are two common ways how these these priorities are being interpreted	1553	There are two common ways how these these priorities are being interpreted
1497	by event loops:	1554	by event loops:
…		…
1591		1648
1592	This section describes each watcher in detail, but will not repeat	1649	This section describes each watcher in detail, but will not repeat
1593	information given in the last section. Any initialisation/set macros,	1650	information given in the last section. Any initialisation/set macros,
1594	functions and members specific to the watcher type are explained.	1651	functions and members specific to the watcher type are explained.
1595		1652
1596	Members are additionally marked with either I<[read-only]>, meaning that,	1653	Most members are additionally marked with either I<[read-only]>, meaning
1597	while the watcher is active, you can look at the member and expect some	1654	that, while the watcher is active, you can look at the member and expect
1598	sensible content, but you must not modify it (you can modify it while the	1655	some sensible content, but you must not modify it (you can modify it while
1599	watcher is stopped to your hearts content), or I<[read-write]>, which	1656	the watcher is stopped to your hearts content), or I<[read-write]>, which
1600	means you can expect it to have some sensible content while the watcher	1657	means you can expect it to have some sensible content while the watcher
1601	is active, but you can also modify it. Modifying it may not do something	1658	is active, but you can also modify it. Modifying it may not do something
1602	sensible or take immediate effect (or do anything at all), but libev will	1659	sensible or take immediate effect (or do anything at all), but libev will
1603	not crash or malfunction in any way.	1660	not crash or malfunction in any way.
1604		1661
		1662	In any case, the documentation for each member will explain what the
		1663	effects are, and if there are any additional access restrictions.
1605		1664
1606	=head2 C<ev_io> - is this file descriptor readable or writable?	1665	=head2 C<ev_io> - is this file descriptor readable or writable?
1607		1666
1608	I/O watchers check whether a file descriptor is readable or writable	1667	I/O watchers check whether a file descriptor is readable or writable
1609	in each iteration of the event loop, or, more precisely, when reading	1668	in each iteration of the event loop, or, more precisely, when reading
…		…
1636		1695
1637	But really, best use non-blocking mode.	1696	But really, best use non-blocking mode.
1638		1697
1639	=head3 The special problem of disappearing file descriptors	1698	=head3 The special problem of disappearing file descriptors
1640		1699
1641	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1700	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,	1701	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	1702	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	1703	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	1704	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	1705	is registered with libev, there is no efficient way to see that this is,
1647	fact, a different file descriptor.	1706	in fact, a different file descriptor.
1648		1707
1649	To avoid having to explicitly tell libev about such cases, libev follows	1708	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	1709	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	1710	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	1711	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	1739	always get a readiness notification instantly, and your read (or possibly
1681	write) will still block on the disk I/O.	1740	write) will still block on the disk I/O.
1682		1741
1683	Another way to view it is that in the case of sockets, pipes, character	1742	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	1743	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	1744	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	1745	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.	1746	wish to read - you would first have to request some data.
1688		1747
1689	Since files are typically not-so-well supported by advanced notification	1748	Since files are typically not-so-well supported by advanced notification
1690	mechanism, libev tries hard to emulate POSIX behaviour with respect	1749	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	1750	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	1760	when you rarely read from a file instead of from a socket, and want to
1702	reuse the same code path.	1761	reuse the same code path.
1703		1762
1704	=head3 The special problem of fork	1763	=head3 The special problem of fork
1705		1764
1706	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1765	Some backends (epoll, kqueue, linuxaio, iouring) do not support C<fork ()>
1707	useless behaviour. Libev fully supports fork, but needs to be told about	1766	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.	1767	to be told about it in the child if you want to continue to use it in the
		1768	child.
1709		1769
1710	To support fork in your child processes, you have to call C<ev_loop_fork	1770	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	1771	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1712	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1772	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1713		1773
…		…
1771		1831
1772	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1832	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1773	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or	1833	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1774	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.	1834	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1775		1835
1776	=item int fd [read-only]	1836	=item ev_io_modify (ev_io *, int events)
1777		1837
1778	The file descriptor being watched.	1838	Similar to C<ev_io_set>, but only changes the event mask. Using this might
		1839	be faster with some backends, as libev can assume that the C<fd> still
		1840	refers to the same underlying file description, something it cannot do
		1841	when using C<ev_io_set>.
1779		1842
		1843	=item int fd [no-modify]
		1844
		1845	The file descriptor being watched. While it can be read at any time, you
		1846	must not modify this member even when the watcher is stopped - always use
		1847	C<ev_io_set> for that.
		1848
1780	=item int events [read-only]	1849	=item int events [no-modify]
1781		1850
1782	The events being watched.	1851	The set of events being watched, among other flags. This field is a
		1852	bit set - to test for C<EV_READ>, use C<< w->events & EV_READ >>, and
		1853	similarly for C<EV_WRITE>.
		1854
		1855	As with C<fd>, you must not modify this member even when the watcher is
		1856	stopped, always use C<ev_io_set> or C<ev_io_modify> for that.
1783		1857
1784	=back	1858	=back
1785		1859
1786	=head3 Examples	1860	=head3 Examples
1787		1861
…		…
1815	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1889	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1816	monotonic clock option helps a lot here).	1890	monotonic clock option helps a lot here).
1817		1891
1818	The callback is guaranteed to be invoked only I<after> its timeout has	1892	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	1893	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	1894	might introduce a small delay, see "the special problem of being too
		1895	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	1896	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	1897	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).	1898	longer true when a callback calls C<ev_run> recursively).
1824		1899
1825	=head3 Be smart about timeouts	1900	=head3 Be smart about timeouts
1826		1901
1827	Many real-world problems involve some kind of timeout, usually for error	1902	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,	1903	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1903		1978
1904	In this case, it would be more efficient to leave the C<ev_timer> alone,	1979	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	1980	but remember the time of last activity, and check for a real timeout only
1906	within the callback:	1981	within the callback:
1907		1982
		1983	ev_tstamp timeout = 60.;
1908	ev_tstamp last_activity; // time of last activity	1984	ev_tstamp last_activity; // time of last activity
		1985	ev_timer timer;
1909		1986
1910	static void	1987	static void
1911	callback (EV_P_ ev_timer *w, int revents)	1988	callback (EV_P_ ev_timer *w, int revents)
1912	{	1989	{
1913	ev_tstamp now = ev_now (EV_A);	1990	// calculate when the timeout would happen
1914	ev_tstamp timeout = last_activity + 60.;	1991	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1915		1992
1916	// if last_activity + 60. is older than now, we did time out	1993	// if negative, it means we the timeout already occurred
1917	if (timeout < now)	1994	if (after < 0.)
1918	{	1995	{
1919	// timeout occurred, take action	1996	// timeout occurred, take action
1920	}	1997	}
1921	else	1998	else
1922	{	1999	{
1923	// callback was invoked, but there was some activity, re-arm	2000	// callback was invoked, but there was some recent
1924	// the watcher to fire in last_activity + 60, which is	2001	// activity. simply restart the timer to time out
1925	// guaranteed to be in the future, so "again" is positive:	2002	// after "after" seconds, which is the earliest time
1926	w->repeat = timeout - now;	2003	// the timeout can occur.
		2004	ev_timer_set (w, after, 0.);
1927	ev_timer_again (EV_A_ w);	2005	ev_timer_start (EV_A_ w);
1928	}	2006	}
1929	}	2007	}
1930		2008
1931	To summarise the callback: first calculate the real timeout (defined	2009	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	2010	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	2011	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	2012	(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		2013
1938	Note how C<ev_timer_again> is used, taking advantage of the	2014	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.	2015	timed out, and need to do whatever is needed in this case.
		2016
		2017	Otherwise, we now the earliest time at which the timeout would trigger,
		2018	and simply start the timer with this timeout value.
		2019
		2020	In other words, each time the callback is invoked it will check whether
		2021	the timeout occurred. If not, it will simply reschedule itself to check
		2022	again at the earliest time it could time out. Rinse. Repeat.
1940		2023
1941	This scheme causes more callback invocations (about one every 60 seconds	2024	This scheme causes more callback invocations (about one every 60 seconds
1942	minus half the average time between activity), but virtually no calls to	2025	minus half the average time between activity), but virtually no calls to
1943	libev to change the timeout.	2026	libev to change the timeout.
1944		2027
1945	To start the timer, simply initialise the watcher and set C<last_activity>	2028	To start the machinery, simply initialise the watcher and set
1946	to the current time (meaning we just have some activity :), then call the	2029	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:	2030	now), then call the callback, which will "do the right thing" and start
		2031	the timer:
1948		2032
		2033	last_activity = ev_now (EV_A);
1949	ev_init (timer, callback);	2034	ev_init (&timer, callback);
1950	last_activity = ev_now (loop);	2035	callback (EV_A_ &timer, 0);
1951	callback (loop, timer, EV_TIMER);
1952		2036
1953	And when there is some activity, simply store the current time in	2037	When there is some activity, simply store the current time in
1954	C<last_activity>, no libev calls at all:	2038	C<last_activity>, no libev calls at all:
1955		2039
		2040	if (activity detected)
1956	last_activity = ev_now (loop);	2041	last_activity = ev_now (EV_A);
		2042
		2043	When your timeout value changes, then the timeout can be changed by simply
		2044	providing a new value, stopping the timer and calling the callback, which
		2045	will again do the right thing (for example, time out immediately :).
		2046
		2047	timeout = new_value;
		2048	ev_timer_stop (EV_A_ &timer);
		2049	callback (EV_A_ &timer, 0);
1957		2050
1958	This technique is slightly more complex, but in most cases where the	2051	This technique is slightly more complex, but in most cases where the
1959	time-out is unlikely to be triggered, much more efficient.	2052	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		2053
1965	=item 4. Wee, just use a double-linked list for your timeouts.	2054	=item 4. Wee, just use a double-linked list for your timeouts.
1966		2055
1967	If there is not one request, but many thousands (millions...), all	2056	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	2057	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	2084	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	2085	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	2086	off after the first million or so of active timers, i.e. it's usually
1998	overkill :)	2087	overkill :)
1999		2088
		2089	=head3 The special problem of being too early
		2090
		2091	If you ask a timer to call your callback after three seconds, then
		2092	you expect it to be invoked after three seconds - but of course, this
		2093	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2094	guaranteed to any precision by libev - imagine somebody suspending the
		2095	process with a STOP signal for a few hours for example.
		2096
		2097	So, libev tries to invoke your callback as soon as possible I<after> the
		2098	delay has occurred, but cannot guarantee this.
		2099
		2100	A less obvious failure mode is calling your callback too early: many event
		2101	loops compare timestamps with a "elapsed delay >= requested delay", but
		2102	this can cause your callback to be invoked much earlier than you would
		2103	expect.
		2104
		2105	To see why, imagine a system with a clock that only offers full second
		2106	resolution (think windows if you can't come up with a broken enough OS
		2107	yourself). If you schedule a one-second timer at the time 500.9, then the
		2108	event loop will schedule your timeout to elapse at a system time of 500
		2109	(500.9 truncated to the resolution) + 1, or 501.
		2110
		2111	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2112	501" and invoke the callback 0.1s after it was started, even though a
		2113	one-second delay was requested - this is being "too early", despite best
		2114	intentions.
		2115
		2116	This is the reason why libev will never invoke the callback if the elapsed
		2117	delay equals the requested delay, but only when the elapsed delay is
		2118	larger than the requested delay. In the example above, libev would only invoke
		2119	the callback at system time 502, or 1.1s after the timer was started.
		2120
		2121	So, while libev cannot guarantee that your callback will be invoked
		2122	exactly when requested, it I<can> and I<does> guarantee that the requested
		2123	delay has actually elapsed, or in other words, it always errs on the "too
		2124	late" side of things.
		2125
2000	=head3 The special problem of time updates	2126	=head3 The special problem of time updates
2001		2127
2002	Establishing the current time is a costly operation (it usually takes at	2128	Establishing the current time is a costly operation (it usually takes
2003	least two system calls): EV therefore updates its idea of the current	2129	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	2130	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	2131	growing difference between C<ev_now ()> and C<ev_time ()> when handling
2006	lots of events in one iteration.	2132	lots of events in one iteration.
2007		2133
2008	The relative timeouts are calculated relative to the C<ev_now ()>	2134	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	2135	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	2136	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	2137	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:	2138	timeout on the current time, use something like the following to adjust
		2139	for it:
2013		2140
2014	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2141	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
2015		2142
2016	If the event loop is suspended for a long time, you can also force an	2143	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	2144	update of the time returned by C<ev_now ()> by calling C<ev_now_update
2018	()>.	2145	()>, although that will push the event time of all outstanding events
		2146	further into the future.
		2147
		2148	=head3 The special problem of unsynchronised clocks
		2149
		2150	Modern systems have a variety of clocks - libev itself uses the normal
		2151	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2152	jumps).
		2153
		2154	Neither of these clocks is synchronised with each other or any other clock
		2155	on the system, so C<ev_time ()> might return a considerably different time
		2156	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2157	a call to C<gettimeofday> might return a second count that is one higher
		2158	than a directly following call to C<time>.
		2159
		2160	The moral of this is to only compare libev-related timestamps with
		2161	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2162	a second or so.
		2163
		2164	One more problem arises due to this lack of synchronisation: if libev uses
		2165	the system monotonic clock and you compare timestamps from C<ev_time>
		2166	or C<ev_now> from when you started your timer and when your callback is
		2167	invoked, you will find that sometimes the callback is a bit "early".
		2168
		2169	This is because C<ev_timer>s work in real time, not wall clock time, so
		2170	libev makes sure your callback is not invoked before the delay happened,
		2171	I<measured according to the real time>, not the system clock.
		2172
		2173	If your timeouts are based on a physical timescale (e.g. "time out this
		2174	connection after 100 seconds") then this shouldn't bother you as it is
		2175	exactly the right behaviour.
		2176
		2177	If you want to compare wall clock/system timestamps to your timers, then
		2178	you need to use C<ev_periodic>s, as these are based on the wall clock
		2179	time, where your comparisons will always generate correct results.
2019		2180
2020	=head3 The special problems of suspended animation	2181	=head3 The special problems of suspended animation
2021		2182
2022	When you leave the server world it is quite customary to hit machines that	2183	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?	2184	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
2053		2214
2054	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2215	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
2055		2216
2056	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2217	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
2057		2218
2058	Configure the timer to trigger after C<after> seconds. If C<repeat>	2219	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	2220	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	2221	automatically be stopped once the timeout is reached. If it is positive,
2061	configured to trigger again C<repeat> seconds later, again, and again,	2222	then the timer will automatically be configured to trigger again C<repeat>
2062	until stopped manually.	2223	seconds later, again, and again, until stopped manually.
2063		2224
2064	The timer itself will do a best-effort at avoiding drift, that is, if	2225	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	2226	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	2227	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	2228	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.	2229	do stuff) the timer will not fire more than once per event loop iteration.
2069		2230
2070	=item ev_timer_again (loop, ev_timer *)	2231	=item ev_timer_again (loop, ev_timer *)
2071		2232
2072	This will act as if the timer timed out and restart it again if it is	2233	This will act as if the timer timed out, and restarts it again if it is
2073	repeating. The exact semantics are:	2234	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2235	timeout to the C<repeat> value and calling C<ev_timer_start>.
2074		2236
		2237	The exact semantics are as in the following rules, all of which will be
		2238	applied to the watcher:
		2239
		2240	=over 4
		2241
2075	If the timer is pending, its pending status is cleared.	2242	=item If the timer is pending, the pending status is always cleared.
2076		2243
2077	If the timer is started but non-repeating, stop it (as if it timed out).	2244	=item If the timer is started but non-repeating, stop it (as if it timed
		2245	out, without invoking it).
2078		2246
2079	If the timer is repeating, either start it if necessary (with the	2247	=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.	2248	and start the timer, if necessary.
2081		2249
		2250	=back
		2251
2082	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2252	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2083	usage example.	2253	usage example.
2084		2254
2085	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2255	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2086		2256
2087	Returns the remaining time until a timer fires. If the timer is active,	2257	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	2310	Periodic watchers are also timers of a kind, but they are very versatile
2141	(and unfortunately a bit complex).	2311	(and unfortunately a bit complex).
2142		2312
2143	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2313	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	2314	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	2315	(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	2316	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	2317	time, and time jumps are not uncommon (e.g. when you adjust your
2148	wrist-watch).	2318	wrist-watch).
2149		2319
2150	You can tell a periodic watcher to trigger after some specific point	2320	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	2325	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2156	it, as it uses a relative timeout).	2326	it, as it uses a relative timeout).
2157		2327
2158	C<ev_periodic> watchers can also be used to implement vastly more complex	2328	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	2329	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	2330	other complicated rules. This cannot easily be done with C<ev_timer>
2161	those cannot react to time jumps.	2331	watchers, as those cannot react to time jumps.
2162		2332
2163	As with timers, the callback is guaranteed to be invoked only when the	2333	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	2334	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	2335	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	2336	earlier time-out values are invoked before ones with later time-out values
…		…
2207		2377
2208	Another way to think about it (for the mathematically inclined) is that	2378	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	2379	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.	2380	time where C<time = offset (mod interval)>, regardless of any time jumps.
2211		2381
2212	For numerical stability it is preferable that the C<offset> value is near	2382	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	2383	interval value should be higher than C<1/8192> (which is around 100
2214	this value, and in fact is often specified as zero.	2384	microseconds) and C<offset> should be higher than C<0> and should have
		2385	at most a similar magnitude as the current time (say, within a factor of
		2386	ten). Typical values for offset are, in fact, C<0> or something between
		2387	C<0> and C<interval>, which is also the recommended range.
2215		2388
2216	Note also that there is an upper limit to how often a timer can fire (CPU	2389	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	2390	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	2391	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).	2392	millisecond (if the OS supports it and the machine is fast enough).
…		…
2249		2422
2250	NOTE: I<< This callback must always return a time that is higher than or	2423	NOTE: I<< This callback must always return a time that is higher than or
2251	equal to the passed C<now> value >>.	2424	equal to the passed C<now> value >>.
2252		2425
2253	This can be used to create very complex timers, such as a timer that	2426	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	2427	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	2428	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	2429	this. Here is a (completely untested, no error checking) example on how to
2257	reason I omitted it as an example).	2430	do this:
		2431
		2432	#include <time.h>
		2433
		2434	static ev_tstamp
		2435	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2436	{
		2437	time_t tnow = (time_t)now;
		2438	struct tm tm;
		2439	localtime_r (&tnow, &tm);
		2440
		2441	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2442	++tm.tm_mday; // midnight next day
		2443
		2444	return mktime (&tm);
		2445	}
		2446
		2447	Note: this code might run into trouble on days that have more then two
		2448	midnights (beginning and end).
2258		2449
2259	=back	2450	=back
2260		2451
2261	=item ev_periodic_again (loop, ev_periodic *)	2452	=item ev_periodic_again (loop, ev_periodic *)
2262		2453
…		…
2327		2518
2328	ev_periodic hourly_tick;	2519	ev_periodic hourly_tick;
2329	ev_periodic_init (&hourly_tick, clock_cb,	2520	ev_periodic_init (&hourly_tick, clock_cb,
2330	fmod (ev_now (loop), 3600.), 3600., 0);	2521	fmod (ev_now (loop), 3600.), 3600., 0);
2331	ev_periodic_start (loop, &hourly_tick);	2522	ev_periodic_start (loop, &hourly_tick);
2332		2523
2333		2524
2334	=head2 C<ev_signal> - signal me when a signal gets signalled!	2525	=head2 C<ev_signal> - signal me when a signal gets signalled!
2335		2526
2336	Signal watchers will trigger an event when the process receives a specific	2527	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	2528	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	2538	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	2539	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	2540	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.	2541	the moment, C<SIGCHLD> is permanently tied to the default loop.
2351		2542
2352	When the first watcher gets started will libev actually register something	2543	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	2544	register something with the kernel. It thus coexists with your own signal
2354	you don't register any with libev for the same signal).	2545	handlers as long as you don't register any with libev for the same signal.
2355		2546
2356	If possible and supported, libev will install its handlers with	2547	If possible and supported, libev will install its handlers with
2357	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2548	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	2549	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	2550	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	2553	=head3 The special problem of inheritance over fork/execve/pthread_create
2363		2554
2364	Both the signal mask (C<sigprocmask>) and the signal disposition	2555	Both the signal mask (C<sigprocmask>) and the signal disposition
2365	(C<sigaction>) are unspecified after starting a signal watcher (and after	2556	(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,	2557	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.	2558	and might or might not set or restore the installed signal handler (but
		2559	see C<EVFLAG_NOSIGMASK>).
2368		2560
2369	While this does not matter for the signal disposition (libev never	2561	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	2562	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	2563	C<execve>), this matters for the signal mask: many programs do not expect
2372	certain signals to be blocked.	2564	certain signals to be blocked.
…		…
2543		2735
2544	=head2 C<ev_stat> - did the file attributes just change?	2736	=head2 C<ev_stat> - did the file attributes just change?
2545		2737
2546	This watches a file system path for attribute changes. That is, it calls	2738	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)	2739	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	2740	and sees if it changed compared to the last time, invoking the callback
2549	it did.	2741	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2742	happen after the watcher has been started will be reported.
2550		2743
2551	The path does not need to exist: changing from "path exists" to "path does	2744	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	2745	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	2746	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	2747	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	2977	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	2978	effect on its own sometimes), idle watchers are a good place to do
2786	"pseudo-background processing", or delay processing stuff to after the	2979	"pseudo-background processing", or delay processing stuff to after the
2787	event loop has handled all outstanding events.	2980	event loop has handled all outstanding events.
2788		2981
		2982	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2983
		2984	As long as there is at least one active idle watcher, libev will never
		2985	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2986	For this to work, the idle watcher doesn't need to be invoked at all - the
		2987	lowest priority will do.
		2988
		2989	This mode of operation can be useful together with an C<ev_check> watcher,
		2990	to do something on each event loop iteration - for example to balance load
		2991	between different connections.
		2992
		2993	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2994	example.
		2995
2789	=head3 Watcher-Specific Functions and Data Members	2996	=head3 Watcher-Specific Functions and Data Members
2790		2997
2791	=over 4	2998	=over 4
2792		2999
2793	=item ev_idle_init (ev_idle *, callback)	3000	=item ev_idle_init (ev_idle *, callback)
…		…
2804	callback, free it. Also, use no error checking, as usual.	3011	callback, free it. Also, use no error checking, as usual.
2805		3012
2806	static void	3013	static void
2807	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	3014	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2808	{	3015	{
		3016	// stop the watcher
		3017	ev_idle_stop (loop, w);
		3018
		3019	// now we can free it
2809	free (w);	3020	free (w);
		3021
2810	// now do something you wanted to do when the program has	3022	// now do something you wanted to do when the program has
2811	// no longer anything immediate to do.	3023	// no longer anything immediate to do.
2812	}	3024	}
2813		3025
2814	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	3026	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2816	ev_idle_start (loop, idle_watcher);	3028	ev_idle_start (loop, idle_watcher);
2817		3029
2818		3030
2819	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3031	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2820		3032
2821	Prepare and check watchers are usually (but not always) used in pairs:	3033	Prepare and check watchers are often (but not always) used in pairs:
2822	prepare watchers get invoked before the process blocks and check watchers	3034	prepare watchers get invoked before the process blocks and check watchers
2823	afterwards.	3035	afterwards.
2824		3036
2825	You I<must not> call C<ev_run> or similar functions that enter	3037	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>	3038	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	3039	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	3040	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,	3041	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	3042	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2831	called in pairs bracketing the blocking call.	3043	kind they will always be called in pairs bracketing the blocking call.
2832		3044
2833	Their main purpose is to integrate other event mechanisms into libev and	3045	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	3046	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	3047	variable changes, implement your own watchers, integrate net-snmp or a
2836	coroutine library and lots more. They are also occasionally useful if	3048	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	3066	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	3067	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	3068	loop from blocking if lower-priority coroutines are active, thus mapping
2857	low-priority coroutines to idle/background tasks).	3069	low-priority coroutines to idle/background tasks).
2858		3070
2859	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3071	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	3072	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).	3073	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3074	watchers).
2862		3075
2863	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3076	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	3077	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	3078	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	3079	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	3080	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	3081	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2869	others).	3082	others).
		3083
		3084	=head3 Abusing an C<ev_check> watcher for its side-effect
		3085
		3086	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3087	useful because they are called once per event loop iteration. For
		3088	example, if you want to handle a large number of connections fairly, you
		3089	normally only do a bit of work for each active connection, and if there
		3090	is more work to do, you wait for the next event loop iteration, so other
		3091	connections have a chance of making progress.
		3092
		3093	Using an C<ev_check> watcher is almost enough: it will be called on the
		3094	next event loop iteration. However, that isn't as soon as possible -
		3095	without external events, your C<ev_check> watcher will not be invoked.
		3096
		3097	This is where C<ev_idle> watchers come in handy - all you need is a
		3098	single global idle watcher that is active as long as you have one active
		3099	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3100	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3101	invoked. Neither watcher alone can do that.
2870		3102
2871	=head3 Watcher-Specific Functions and Data Members	3103	=head3 Watcher-Specific Functions and Data Members
2872		3104
2873	=over 4	3105	=over 4
2874		3106
…		…
3075		3307
3076	=over 4	3308	=over 4
3077		3309
3078	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3310	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
3079		3311
3080	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3312	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
3081		3313
3082	Configures the watcher to embed the given loop, which must be	3314	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	3315	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	3316	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,	3317	to invoke it (it will continue to be called until the sweep has been done,
…		…
3106	used).	3338	used).
3107		3339
3108	struct ev_loop *loop_hi = ev_default_init (0);	3340	struct ev_loop *loop_hi = ev_default_init (0);
3109	struct ev_loop *loop_lo = 0;	3341	struct ev_loop *loop_lo = 0;
3110	ev_embed embed;	3342	ev_embed embed;
3111		3343
3112	// see if there is a chance of getting one that works	3344	// see if there is a chance of getting one that works
3113	// (remember that a flags value of 0 means autodetection)	3345	// (remember that a flags value of 0 means autodetection)
3114	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3346	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3115	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3347	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3116	: 0;	3348	: 0;
…		…
3130	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3362	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3131		3363
3132	struct ev_loop *loop = ev_default_init (0);	3364	struct ev_loop *loop = ev_default_init (0);
3133	struct ev_loop *loop_socket = 0;	3365	struct ev_loop *loop_socket = 0;
3134	ev_embed embed;	3366	ev_embed embed;
3135		3367
3136	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3368	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3137	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3369	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3138	{	3370	{
3139	ev_embed_init (&embed, 0, loop_socket);	3371	ev_embed_init (&embed, 0, loop_socket);
3140	ev_embed_start (loop, &embed);	3372	ev_embed_start (loop, &embed);
…		…
3148		3380
3149	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3381	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3150		3382
3151	Fork watchers are called when a C<fork ()> was detected (usually because	3383	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	3384	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	3385	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,	3386	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	3387	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	3388	and calls it in the wrong process, the fork handlers will be invoked, too,
3157	handlers will be invoked, too, of course.	3389	of course.
3158		3390
3159	=head3 The special problem of life after fork - how is it possible?	3391	=head3 The special problem of life after fork - how is it possible?
3160		3392
3161	Most uses of C<fork()> consist of forking, then some simple calls to set	3393	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	3394	up/change the process environment, followed by a call to C<exec()>. This
3163	sequence should be handled by libev without any problems.	3395	sequence should be handled by libev without any problems.
3164		3396
3165	This changes when the application actually wants to do event handling	3397	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	3398	in the child, or both parent in child, in effect "continuing" after the
…		…
3243	atexit (program_exits);	3475	atexit (program_exits);
3244		3476
3245		3477
3246	=head2 C<ev_async> - how to wake up an event loop	3478	=head2 C<ev_async> - how to wake up an event loop
3247		3479
3248	In general, you cannot use an C<ev_run> from multiple threads or other	3480	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	3481	asynchronous sources such as signal handlers (as opposed to multiple event
3250	loops - those are of course safe to use in different threads).	3482	loops - those are of course safe to use in different threads).
3251		3483
3252	Sometimes, however, you need to wake up an event loop you do not control,	3484	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>	3485	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.	3487	it by calling C<ev_async_send>, which is thread- and signal safe.
3256		3488
3257	This functionality is very similar to C<ev_signal> watchers, as signals,	3489	This functionality is very similar to C<ev_signal> watchers, as signals,
3258	too, are asynchronous in nature, and signals, too, will be compressed	3490	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	3491	(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	3492	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	3493	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,	3494	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3263	even without knowing which loop owns the signal.	3495	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		3496
3268	=head3 Queueing	3497	=head3 Queueing
3269		3498
3270	C<ev_async> does not support queueing of data in any way. The reason	3499	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	3500	is that the author does not know of a simple (or any) algorithm for a
…		…
3363	trust me.	3592	trust me.
3364		3593
3365	=item ev_async_send (loop, ev_async *)	3594	=item ev_async_send (loop, ev_async *)
3366		3595
3367	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3596	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	3597	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3598	returns.
		3599
3369	C<ev_feed_event>, this call is safe to do from other threads, signal or	3600	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	3601	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3371	section below on what exactly this means).	3602	embedding section below on what exactly this means).
3372		3603
3373	Note that, as with other watchers in libev, multiple events might get	3604	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	3605	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>,	3606	this is that C<ev_async> watchers are level-triggered: they are set on
3376	reset when the event loop detects that).	3607	C<ev_async_send>, reset when the event loop detects that).
3377		3608
3378	This call incurs the overhead of a system call only once per event loop	3609	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	3610	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.	3611	the event loop (or your program) is processing events. That means that
		3612	repeated calls are basically free (there is no need to avoid calls for
		3613	performance reasons) and that the overhead becomes smaller (typically
		3614	zero) under load.
3381		3615
3382	=item bool = ev_async_pending (ev_async *)	3616	=item bool = ev_async_pending (ev_async *)
3383		3617
3384	Returns a non-zero value when C<ev_async_send> has been called on the	3618	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	3619	watcher but the event has not yet been processed (or even noted) by the
…		…
3402		3636
3403	There are some other functions of possible interest. Described. Here. Now.	3637	There are some other functions of possible interest. Described. Here. Now.
3404		3638
3405	=over 4	3639	=over 4
3406		3640
3407	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3641	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3408		3642
3409	This function combines a simple timer and an I/O watcher, calls your	3643	This function combines a simple timer and an I/O watcher, calls your
3410	callback on whichever event happens first and automatically stops both	3644	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	3645	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	3646	or timeout without having to allocate/configure/start/stop/free one or
…		…
3440	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3674	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3441		3675
3442	=item ev_feed_fd_event (loop, int fd, int revents)	3676	=item ev_feed_fd_event (loop, int fd, int revents)
3443		3677
3444	Feed an event on the given fd, as if a file descriptor backend detected	3678	Feed an event on the given fd, as if a file descriptor backend detected
3445	the given events it.	3679	the given events.
3446		3680
3447	=item ev_feed_signal_event (loop, int signum)	3681	=item ev_feed_signal_event (loop, int signum)
3448		3682
3449	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,	3683	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3450	which is async-safe.	3684	which is async-safe.
…		…
3455	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)	3689	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
3456		3690
3457	This section explains some common idioms that are not immediately	3691	This section explains some common idioms that are not immediately
3458	obvious. Note that examples are sprinkled over the whole manual, and this	3692	obvious. Note that examples are sprinkled over the whole manual, and this
3459	section only contains stuff that wouldn't fit anywhere else.	3693	section only contains stuff that wouldn't fit anywhere else.
		3694
		3695	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3696
		3697	Each watcher has, by default, a C<void *data> member that you can read
		3698	or modify at any time: libev will completely ignore it. This can be used
		3699	to associate arbitrary data with your watcher. If you need more data and
		3700	don't want to allocate memory separately and store a pointer to it in that
		3701	data member, you can also "subclass" the watcher type and provide your own
		3702	data:
		3703
		3704	struct my_io
		3705	{
		3706	ev_io io;
		3707	int otherfd;
		3708	void *somedata;
		3709	struct whatever *mostinteresting;
		3710	};
		3711
		3712	...
		3713	struct my_io w;
		3714	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3715
		3716	And since your callback will be called with a pointer to the watcher, you
		3717	can cast it back to your own type:
		3718
		3719	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3720	{
		3721	struct my_io *w = (struct my_io *)w_;
		3722	...
		3723	}
		3724
		3725	More interesting and less C-conformant ways of casting your callback
		3726	function type instead have been omitted.
		3727
		3728	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3729
		3730	Another common scenario is to use some data structure with multiple
		3731	embedded watchers, in effect creating your own watcher that combines
		3732	multiple libev event sources into one "super-watcher":
		3733
		3734	struct my_biggy
		3735	{
		3736	int some_data;
		3737	ev_timer t1;
		3738	ev_timer t2;
		3739	}
		3740
		3741	In this case getting the pointer to C<my_biggy> is a bit more
		3742	complicated: Either you store the address of your C<my_biggy> struct in
		3743	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3744	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3745	real programmers):
		3746
		3747	#include <stddef.h>
		3748
		3749	static void
		3750	t1_cb (EV_P_ ev_timer *w, int revents)
		3751	{
		3752	struct my_biggy big = (struct my_biggy *)
		3753	(((char *)w) - offsetof (struct my_biggy, t1));
		3754	}
		3755
		3756	static void
		3757	t2_cb (EV_P_ ev_timer *w, int revents)
		3758	{
		3759	struct my_biggy big = (struct my_biggy *)
		3760	(((char *)w) - offsetof (struct my_biggy, t2));
		3761	}
		3762
		3763	=head2 AVOIDING FINISHING BEFORE RETURNING
		3764
		3765	Often you have structures like this in event-based programs:
		3766
		3767	callback ()
		3768	{
		3769	free (request);
		3770	}
		3771
		3772	request = start_new_request (..., callback);
		3773
		3774	The intent is to start some "lengthy" operation. The C<request> could be
		3775	used to cancel the operation, or do other things with it.
		3776
		3777	It's not uncommon to have code paths in C<start_new_request> that
		3778	immediately invoke the callback, for example, to report errors. Or you add
		3779	some caching layer that finds that it can skip the lengthy aspects of the
		3780	operation and simply invoke the callback with the result.
		3781
		3782	The problem here is that this will happen I<before> C<start_new_request>
		3783	has returned, so C<request> is not set.
		3784
		3785	Even if you pass the request by some safer means to the callback, you
		3786	might want to do something to the request after starting it, such as
		3787	canceling it, which probably isn't working so well when the callback has
		3788	already been invoked.
		3789
		3790	A common way around all these issues is to make sure that
		3791	C<start_new_request> I<always> returns before the callback is invoked. If
		3792	C<start_new_request> immediately knows the result, it can artificially
		3793	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3794	example, or more sneakily, by reusing an existing (stopped) watcher and
		3795	pushing it into the pending queue:
		3796
		3797	ev_set_cb (watcher, callback);
		3798	ev_feed_event (EV_A_ watcher, 0);
		3799
		3800	This way, C<start_new_request> can safely return before the callback is
		3801	invoked, while not delaying callback invocation too much.
3460		3802
3461	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS	3803	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3462		3804
3463	Often (especially in GUI toolkits) there are places where you have	3805	Often (especially in GUI toolkits) there are places where you have
3464	I<modal> interaction, which is most easily implemented by recursively	3806	I<modal> interaction, which is most easily implemented by recursively
…		…
3466		3808
3467	This brings the problem of exiting - a callback might want to finish the	3809	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	3810	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	3811	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	3812	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.	3813	other combination: In these cases, a simple C<ev_break> will not work.
3472		3814
3473	The solution is to maintain "break this loop" variable for each C<ev_run>	3815	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	3816	invocation, and use a loop around C<ev_run> until the condition is
3475	triggered, using C<EVRUN_ONCE>:	3817	triggered, using C<EVRUN_ONCE>:
3476		3818
…		…
3478	int exit_main_loop = 0;	3820	int exit_main_loop = 0;
3479		3821
3480	while (!exit_main_loop)	3822	while (!exit_main_loop)
3481	ev_run (EV_DEFAULT_ EVRUN_ONCE);	3823	ev_run (EV_DEFAULT_ EVRUN_ONCE);
3482		3824
3483	// in a model watcher	3825	// in a modal watcher
3484	int exit_nested_loop = 0;	3826	int exit_nested_loop = 0;
3485		3827
3486	while (!exit_nested_loop)	3828	while (!exit_nested_loop)
3487	ev_run (EV_A_ EVRUN_ONCE);	3829	ev_run (EV_A_ EVRUN_ONCE);
3488		3830
…		…
3498	exit_main_loop = exit_nested_loop = 1;	3840	exit_main_loop = exit_nested_loop = 1;
3499		3841
3500	=head2 THREAD LOCKING EXAMPLE	3842	=head2 THREAD LOCKING EXAMPLE
3501		3843
3502	Here is a fictitious example of how to run an event loop in a different	3844	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	3845	thread from where callbacks are being invoked and watchers are
3504	created/added/removed.	3846	created/added/removed.
3505		3847
3506	For a real-world example, see the C<EV::Loop::Async> perl module,	3848	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	3849	which uses exactly this technique (which is suited for many high-level
3508	languages).	3850	languages).
…		…
3534	// now associate this with the loop	3876	// now associate this with the loop
3535	ev_set_userdata (EV_A_ u);	3877	ev_set_userdata (EV_A_ u);
3536	ev_set_invoke_pending_cb (EV_A_ l_invoke);	3878	ev_set_invoke_pending_cb (EV_A_ l_invoke);
3537	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);	3879	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3538		3880
3539	// then create the thread running ev_loop	3881	// then create the thread running ev_run
3540	pthread_create (&u->tid, 0, l_run, EV_A);	3882	pthread_create (&u->tid, 0, l_run, EV_A);
3541	}	3883	}
3542		3884
3543	The callback for the C<ev_async> watcher does nothing: the watcher is used	3885	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	3886	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	3975	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	3976	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	3977	about the newly added timer. By waking up the loop it will pick up any new
3636	watchers in the next event loop iteration.	3978	watchers in the next event loop iteration.
3637		3979
		3980	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3981
		3982	While the overhead of a callback that e.g. schedules a thread is small, it
		3983	is still an overhead. If you embed libev, and your main usage is with some
		3984	kind of threads or coroutines, you might want to customise libev so that
		3985	doesn't need callbacks anymore.
		3986
		3987	Imagine you have coroutines that you can switch to using a function
		3988	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3989	and that due to some magic, the currently active coroutine is stored in a
		3990	global called C<current_coro>. Then you can build your own "wait for libev
		3991	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3992	the differing C<;> conventions):
		3993
		3994	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3995	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3996
		3997	That means instead of having a C callback function, you store the
		3998	coroutine to switch to in each watcher, and instead of having libev call
		3999	your callback, you instead have it switch to that coroutine.
		4000
		4001	A coroutine might now wait for an event with a function called
		4002	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		4003	matter when, or whether the watcher is active or not when this function is
		4004	called):
		4005
		4006	void
		4007	wait_for_event (ev_watcher *w)
		4008	{
		4009	ev_set_cb (w, current_coro);
		4010	switch_to (libev_coro);
		4011	}
		4012
		4013	That basically suspends the coroutine inside C<wait_for_event> and
		4014	continues the libev coroutine, which, when appropriate, switches back to
		4015	this or any other coroutine.
		4016
		4017	You can do similar tricks if you have, say, threads with an event queue -
		4018	instead of storing a coroutine, you store the queue object and instead of
		4019	switching to a coroutine, you push the watcher onto the queue and notify
		4020	any waiters.
		4021
		4022	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		4023	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		4024
		4025	// my_ev.h
		4026	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4027	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4028	#include "../libev/ev.h"
		4029
		4030	// my_ev.c
		4031	#define EV_H "my_ev.h"
		4032	#include "../libev/ev.c"
		4033
		4034	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4035	F<my_ev.c> into your project. When properly specifying include paths, you
		4036	can even use F<ev.h> as header file name directly.
		4037
3638		4038
3639	=head1 LIBEVENT EMULATION	4039	=head1 LIBEVENT EMULATION
3640		4040
3641	Libev offers a compatibility emulation layer for libevent. It cannot	4041	Libev offers a compatibility emulation layer for libevent. It cannot
3642	emulate the internals of libevent, so here are some usage hints:	4042	emulate the internals of libevent, so here are some usage hints:
…		…
3671		4071
3672	=back	4072	=back
3673		4073
3674	=head1 C++ SUPPORT	4074	=head1 C++ SUPPORT
3675		4075
		4076	=head2 C API
		4077
		4078	The normal C API should work fine when used from C++: both ev.h and the
		4079	libev sources can be compiled as C++. Therefore, code that uses the C API
		4080	will work fine.
		4081
		4082	Proper exception specifications might have to be added to callbacks passed
		4083	to libev: exceptions may be thrown only from watcher callbacks, all other
		4084	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4085	callbacks) must not throw exceptions, and might need a C<noexcept>
		4086	specification. If you have code that needs to be compiled as both C and
		4087	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4088
		4089	static void
		4090	fatal_error (const char *msg) EV_NOEXCEPT
		4091	{
		4092	perror (msg);
		4093	abort ();
		4094	}
		4095
		4096	...
		4097	ev_set_syserr_cb (fatal_error);
		4098
		4099	The only API functions that can currently throw exceptions are C<ev_run>,
		4100	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4101	because it runs cleanup watchers).
		4102
		4103	Throwing exceptions in watcher callbacks is only supported if libev itself
		4104	is compiled with a C++ compiler or your C and C++ environments allow
		4105	throwing exceptions through C libraries (most do).
		4106
		4107	=head2 C++ API
		4108
3676	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4109	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3677	you to use some convenience methods to start/stop watchers and also change	4110	you to use some convenience methods to start/stop watchers and also change
3678	the callback model to a model using method callbacks on objects.	4111	the callback model to a model using method callbacks on objects.
3679		4112
3680	To use it,	4113	To use it,
3681		4114
3682	#include <ev++.h>	4115	#include <ev++.h>
3683		4116
3684	This automatically includes F<ev.h> and puts all of its definitions (many	4117	This automatically includes F<ev.h> and puts all of its definitions (many
3685	of them macros) into the global namespace. All C++ specific things are	4118	of them macros) into the global namespace. All C++ specific things are
3686	put into the C<ev> namespace. It should support all the same embedding	4119	put into the C<ev> namespace. It should support all the same embedding
…		…
3695	with C<operator ()> can be used as callbacks. Other types should be easy	4128	with C<operator ()> can be used as callbacks. Other types should be easy
3696	to add as long as they only need one additional pointer for context. If	4129	to add as long as they only need one additional pointer for context. If
3697	you need support for other types of functors please contact the author	4130	you need support for other types of functors please contact the author
3698	(preferably after implementing it).	4131	(preferably after implementing it).
3699		4132
		4133	For all this to work, your C++ compiler either has to use the same calling
		4134	conventions as your C compiler (for static member functions), or you have
		4135	to embed libev and compile libev itself as C++.
		4136
3700	Here is a list of things available in the C<ev> namespace:	4137	Here is a list of things available in the C<ev> namespace:
3701		4138
3702	=over 4	4139	=over 4
3703		4140
3704	=item C<ev::READ>, C<ev::WRITE> etc.	4141	=item C<ev::READ>, C<ev::WRITE> etc.
…		…
3713	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4150	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3714		4151
3715	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4152	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3716	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4153	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3717	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4154	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3718	defines by many implementations.	4155	defined by many implementations.
3719		4156
3720	All of those classes have these methods:	4157	All of those classes have these methods:
3721		4158
3722	=over 4	4159	=over 4
3723		4160
…		…
3785	void operator() (ev::io &w, int revents)	4222	void operator() (ev::io &w, int revents)
3786	{	4223	{
3787	...	4224	...
3788	}	4225	}
3789	}	4226	}
3790		4227
3791	myfunctor f;	4228	myfunctor f;
3792		4229
3793	ev::io w;	4230	ev::io w;
3794	w.set (&f);	4231	w.set (&f);
3795		4232
…		…
3813	Associates a different C<struct ev_loop> with this watcher. You can only	4250	Associates a different C<struct ev_loop> with this watcher. You can only
3814	do this when the watcher is inactive (and not pending either).	4251	do this when the watcher is inactive (and not pending either).
3815		4252
3816	=item w->set ([arguments])	4253	=item w->set ([arguments])
3817		4254
3818	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4255	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3819	method or a suitable start method must be called at least once. Unlike the	4256	with the same arguments. Either this method or a suitable start method
3820	C counterpart, an active watcher gets automatically stopped and restarted	4257	must be called at least once. Unlike the C counterpart, an active watcher
3821	when reconfiguring it with this method.	4258	gets automatically stopped and restarted when reconfiguring it with this
		4259	method.
		4260
		4261	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4262	clashing with the C<set (loop)> method.
3822		4263
3823	=item w->start ()	4264	=item w->start ()
3824		4265
3825	Starts the watcher. Note that there is no C<loop> argument, as the	4266	Starts the watcher. Note that there is no C<loop> argument, as the
3826	constructor already stores the event loop.	4267	constructor already stores the event loop.
…		…
3856	watchers in the constructor.	4297	watchers in the constructor.
3857		4298
3858	class myclass	4299	class myclass
3859	{	4300	{
3860	ev::io io ; void io_cb (ev::io &w, int revents);	4301	ev::io io ; void io_cb (ev::io &w, int revents);
3861	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4302	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3862	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4303	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3863		4304
3864	myclass (int fd)	4305	myclass (int fd)
3865	{	4306	{
3866	io .set <myclass, &myclass::io_cb > (this);	4307	io .set <myclass, &myclass::io_cb > (this);
…		…
3917	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4358	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3918		4359
3919	=item D	4360	=item D
3920		4361
3921	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4362	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3922	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4363	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3923		4364
3924	=item Ocaml	4365	=item Ocaml
3925		4366
3926	Erkki Seppala has written Ocaml bindings for libev, to be found at	4367	Erkki Seppala has written Ocaml bindings for libev, to be found at
3927	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4368	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3930		4371
3931	Brian Maher has written a partial interface to libev for lua (at the	4372	Brian Maher has written a partial interface to libev for lua (at the
3932	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4373	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3933	L<http://github.com/brimworks/lua-ev>.	4374	L<http://github.com/brimworks/lua-ev>.
3934		4375
		4376	=item Javascript
		4377
		4378	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4379
		4380	=item Others
		4381
		4382	There are others, and I stopped counting.
		4383
3935	=back	4384	=back
3936		4385
3937		4386
3938	=head1 MACRO MAGIC	4387	=head1 MACRO MAGIC
3939		4388
…		…
3975	suitable for use with C<EV_A>.	4424	suitable for use with C<EV_A>.
3976		4425
3977	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4426	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3978		4427
3979	Similar to the other two macros, this gives you the value of the default	4428	Similar to the other two macros, this gives you the value of the default
3980	loop, if multiple loops are supported ("ev loop default").	4429	loop, if multiple loops are supported ("ev loop default"). The default loop
		4430	will be initialised if it isn't already initialised.
		4431
		4432	For non-multiplicity builds, these macros do nothing, so you always have
		4433	to initialise the loop somewhere.
3981		4434
3982	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4435	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3983		4436
3984	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4437	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3985	default loop has been initialised (C<UC> == unchecked). Their behaviour	4438	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
4052	ev_vars.h	4505	ev_vars.h
4053	ev_wrap.h	4506	ev_wrap.h
4054		4507
4055	ev_win32.c required on win32 platforms only	4508	ev_win32.c required on win32 platforms only
4056		4509
4057	ev_select.c only when select backend is enabled (which is enabled by default)	4510	ev_select.c only when select backend is enabled
4058	ev_poll.c only when poll backend is enabled (disabled by default)	4511	ev_poll.c only when poll backend is enabled
4059	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4512	ev_epoll.c only when the epoll backend is enabled
		4513	ev_linuxaio.c only when the linux aio backend is enabled
		4514	ev_iouring.c only when the linux io_uring backend is enabled
4060	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4515	ev_kqueue.c only when the kqueue backend is enabled
4061	ev_port.c only when the solaris port backend is enabled (disabled by default)	4516	ev_port.c only when the solaris port backend is enabled
4062		4517
4063	F<ev.c> includes the backend files directly when enabled, so you only need	4518	F<ev.c> includes the backend files directly when enabled, so you only need
4064	to compile this single file.	4519	to compile this single file.
4065		4520
4066	=head3 LIBEVENT COMPATIBILITY API	4521	=head3 LIBEVENT COMPATIBILITY API
…		…
4130	supported). It will also not define any of the structs usually found in	4585	supported). It will also not define any of the structs usually found in
4131	F<event.h> that are not directly supported by the libev core alone.	4586	F<event.h> that are not directly supported by the libev core alone.
4132		4587
4133	In standalone mode, libev will still try to automatically deduce the	4588	In standalone mode, libev will still try to automatically deduce the
4134	configuration, but has to be more conservative.	4589	configuration, but has to be more conservative.
		4590
		4591	=item EV_USE_FLOOR
		4592
		4593	If defined to be C<1>, libev will use the C<floor ()> function for its
		4594	periodic reschedule calculations, otherwise libev will fall back on a
		4595	portable (slower) implementation. If you enable this, you usually have to
		4596	link against libm or something equivalent. Enabling this when the C<floor>
		4597	function is not available will fail, so the safe default is to not enable
		4598	this.
4135		4599
4136	=item EV_USE_MONOTONIC	4600	=item EV_USE_MONOTONIC
4137		4601
4138	If defined to be C<1>, libev will try to detect the availability of the	4602	If defined to be C<1>, libev will try to detect the availability of the
4139	monotonic clock option at both compile time and runtime. Otherwise no	4603	monotonic clock option at both compile time and runtime. Otherwise no
…		…
4176	available and will probe for kernel support at runtime. This will improve	4640	available and will probe for kernel support at runtime. This will improve
4177	C<ev_signal> and C<ev_async> performance and reduce resource consumption.	4641	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
4178	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc	4642	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
4179	2.7 or newer, otherwise disabled.	4643	2.7 or newer, otherwise disabled.
4180		4644
		4645	=item EV_USE_SIGNALFD
		4646
		4647	If defined to be C<1>, then libev will assume that C<signalfd ()> is
		4648	available and will probe for kernel support at runtime. This enables
		4649	the use of EVFLAG_SIGNALFD for faster and simpler signal handling. If
		4650	undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4651	2.7 or newer, otherwise disabled.
		4652
		4653	=item EV_USE_TIMERFD
		4654
		4655	If defined to be C<1>, then libev will assume that C<timerfd ()> is
		4656	available and will probe for kernel support at runtime. This allows
		4657	libev to detect time jumps accurately. If undefined, it will be enabled
		4658	if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
		4659	C<TFD_TIMER_CANCEL_ON_SET>, otherwise disabled.
		4660
		4661	=item EV_USE_EVENTFD
		4662
		4663	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4664	available and will probe for kernel support at runtime. This will improve
		4665	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4666	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4667	2.7 or newer, otherwise disabled.
		4668
4181	=item EV_USE_SELECT	4669	=item EV_USE_SELECT
4182		4670
4183	If undefined or defined to be C<1>, libev will compile in support for the	4671	If undefined or defined to be C<1>, libev will compile in support for the
4184	C<select>(2) backend. No attempt at auto-detection will be done: if no	4672	C<select>(2) backend. No attempt at auto-detection will be done: if no
4185	other method takes over, select will be it. Otherwise the select backend	4673	other method takes over, select will be it. Otherwise the select backend
…		…
4225	If programs implement their own fd to handle mapping on win32, then this	4713	If programs implement their own fd to handle mapping on win32, then this
4226	macro can be used to override the C<close> function, useful to unregister	4714	macro can be used to override the C<close> function, useful to unregister
4227	file descriptors again. Note that the replacement function has to close	4715	file descriptors again. Note that the replacement function has to close
4228	the underlying OS handle.	4716	the underlying OS handle.
4229		4717
		4718	=item EV_USE_WSASOCKET
		4719
		4720	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4721	communication socket, which works better in some environments. Otherwise,
		4722	the normal C<socket> function will be used, which works better in other
		4723	environments.
		4724
4230	=item EV_USE_POLL	4725	=item EV_USE_POLL
4231		4726
4232	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4727	If defined to be C<1>, libev will compile in support for the C<poll>(2)
4233	backend. Otherwise it will be enabled on non-win32 platforms. It	4728	backend. Otherwise it will be enabled on non-win32 platforms. It
4234	takes precedence over select.	4729	takes precedence over select.
…		…
4238	If defined to be C<1>, libev will compile in support for the Linux	4733	If defined to be C<1>, libev will compile in support for the Linux
4239	C<epoll>(7) backend. Its availability will be detected at runtime,	4734	C<epoll>(7) backend. Its availability will be detected at runtime,
4240	otherwise another method will be used as fallback. This is the preferred	4735	otherwise another method will be used as fallback. This is the preferred
4241	backend for GNU/Linux systems. If undefined, it will be enabled if the	4736	backend for GNU/Linux systems. If undefined, it will be enabled if the
4242	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4737	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4738
		4739	=item EV_USE_LINUXAIO
		4740
		4741	If defined to be C<1>, libev will compile in support for the Linux aio
		4742	backend (C<EV_USE_EPOLL> must also be enabled). If undefined, it will be
		4743	enabled on linux, otherwise disabled.
		4744
		4745	=item EV_USE_IOURING
		4746
		4747	If defined to be C<1>, libev will compile in support for the Linux
		4748	io_uring backend (C<EV_USE_EPOLL> must also be enabled). Due to it's
		4749	current limitations it has to be requested explicitly. If undefined, it
		4750	will be enabled on linux, otherwise disabled.
4243		4751
4244	=item EV_USE_KQUEUE	4752	=item EV_USE_KQUEUE
4245		4753
4246	If defined to be C<1>, libev will compile in support for the BSD style	4754	If defined to be C<1>, libev will compile in support for the BSD style
4247	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4755	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
4269	If defined to be C<1>, libev will compile in support for the Linux inotify	4777	If defined to be C<1>, libev will compile in support for the Linux inotify
4270	interface to speed up C<ev_stat> watchers. Its actual availability will	4778	interface to speed up C<ev_stat> watchers. Its actual availability will
4271	be detected at runtime. If undefined, it will be enabled if the headers	4779	be detected at runtime. If undefined, it will be enabled if the headers
4272	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4780	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4273		4781
		4782	=item EV_NO_SMP
		4783
		4784	If defined to be C<1>, libev will assume that memory is always coherent
		4785	between threads, that is, threads can be used, but threads never run on
		4786	different cpus (or different cpu cores). This reduces dependencies
		4787	and makes libev faster.
		4788
		4789	=item EV_NO_THREADS
		4790
		4791	If defined to be C<1>, libev will assume that it will never be called from
		4792	different threads (that includes signal handlers), which is a stronger
		4793	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4794	libev faster.
		4795
4274	=item EV_ATOMIC_T	4796	=item EV_ATOMIC_T
4275		4797
4276	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4798	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4277	access is atomic with respect to other threads or signal contexts. No such	4799	access is atomic with respect to other threads or signal contexts. No
4278	type is easily found in the C language, so you can provide your own type	4800	such type is easily found in the C language, so you can provide your own
4279	that you know is safe for your purposes. It is used both for signal handler "locking"	4801	type that you know is safe for your purposes. It is used both for signal
4280	as well as for signal and thread safety in C<ev_async> watchers.	4802	handler "locking" as well as for signal and thread safety in C<ev_async>
		4803	watchers.
4281		4804
4282	In the absence of this define, libev will use C<sig_atomic_t volatile>	4805	In the absence of this define, libev will use C<sig_atomic_t volatile>
4283	(from F<signal.h>), which is usually good enough on most platforms.	4806	(from F<signal.h>), which is usually good enough on most platforms.
4284		4807
4285	=item EV_H (h)	4808	=item EV_H (h)
…		…
4312	will have the C<struct ev_loop *> as first argument, and you can create	4835	will have the C<struct ev_loop *> as first argument, and you can create
4313	additional independent event loops. Otherwise there will be no support	4836	additional independent event loops. Otherwise there will be no support
4314	for multiple event loops and there is no first event loop pointer	4837	for multiple event loops and there is no first event loop pointer
4315	argument. Instead, all functions act on the single default loop.	4838	argument. Instead, all functions act on the single default loop.
4316		4839
		4840	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4841	default loop when multiplicity is switched off - you always have to
		4842	initialise the loop manually in this case.
		4843
4317	=item EV_MINPRI	4844	=item EV_MINPRI
4318		4845
4319	=item EV_MAXPRI	4846	=item EV_MAXPRI
4320		4847
4321	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4848	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4357	#define EV_USE_POLL 1	4884	#define EV_USE_POLL 1
4358	#define EV_CHILD_ENABLE 1	4885	#define EV_CHILD_ENABLE 1
4359	#define EV_ASYNC_ENABLE 1	4886	#define EV_ASYNC_ENABLE 1
4360		4887
4361	The actual value is a bitset, it can be a combination of the following	4888	The actual value is a bitset, it can be a combination of the following
4362	values:	4889	values (by default, all of these are enabled):
4363		4890
4364	=over 4	4891	=over 4
4365		4892
4366	=item C<1> - faster/larger code	4893	=item C<1> - faster/larger code
4367		4894
…		…
4371	code size by roughly 30% on amd64).	4898	code size by roughly 30% on amd64).
4372		4899
4373	When optimising for size, use of compiler flags such as C<-Os> with	4900	When optimising for size, use of compiler flags such as C<-Os> with
4374	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4901	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4375	assertions.	4902	assertions.
		4903
		4904	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4905	(e.g. gcc with C<-Os>).
4376		4906
4377	=item C<2> - faster/larger data structures	4907	=item C<2> - faster/larger data structures
4378		4908
4379	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4909	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4380	hash table sizes and so on. This will usually further increase code size	4910	hash table sizes and so on. This will usually further increase code size
4381	and can additionally have an effect on the size of data structures at	4911	and can additionally have an effect on the size of data structures at
4382	runtime.	4912	runtime.
4383		4913
		4914	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4915	(e.g. gcc with C<-Os>).
		4916
4384	=item C<4> - full API configuration	4917	=item C<4> - full API configuration
4385		4918
4386	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4919	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4387	enables multiplicity (C<EV_MULTIPLICITY>=1).	4920	enables multiplicity (C<EV_MULTIPLICITY>=1).
4388		4921
…		…
4418		4951
4419	With an intelligent-enough linker (gcc+binutils are intelligent enough	4952	With an intelligent-enough linker (gcc+binutils are intelligent enough
4420	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4953	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4421	your program might be left out as well - a binary starting a timer and an	4954	your program might be left out as well - a binary starting a timer and an
4422	I/O watcher then might come out at only 5Kb.	4955	I/O watcher then might come out at only 5Kb.
		4956
		4957	=item EV_API_STATIC
		4958
		4959	If this symbol is defined (by default it is not), then all identifiers
		4960	will have static linkage. This means that libev will not export any
		4961	identifiers, and you cannot link against libev anymore. This can be useful
		4962	when you embed libev, only want to use libev functions in a single file,
		4963	and do not want its identifiers to be visible.
		4964
		4965	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4966	wants to use libev.
		4967
		4968	This option only works when libev is compiled with a C compiler, as C++
		4969	doesn't support the required declaration syntax.
4423		4970
4424	=item EV_AVOID_STDIO	4971	=item EV_AVOID_STDIO
4425		4972
4426	If this is set to C<1> at compiletime, then libev will avoid using stdio	4973	If this is set to C<1> at compiletime, then libev will avoid using stdio
4427	functions (printf, scanf, perror etc.). This will increase the code size	4974	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4485	in. If set to C<1>, then verification code will be compiled in, but not	5032	in. If set to C<1>, then verification code will be compiled in, but not
4486	called. If set to C<2>, then the internal verification code will be	5033	called. If set to C<2>, then the internal verification code will be
4487	called once per loop, which can slow down libev. If set to C<3>, then the	5034	called once per loop, which can slow down libev. If set to C<3>, then the
4488	verification code will be called very frequently, which will slow down	5035	verification code will be called very frequently, which will slow down
4489	libev considerably.	5036	libev considerably.
		5037
		5038	Verification errors are reported via C's C<assert> mechanism, so if you
		5039	disable that (e.g. by defining C<NDEBUG>) then no errors will be reported.
4490		5040
4491	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it	5041	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
4492	will be C<0>.	5042	will be C<0>.
4493		5043
4494	=item EV_COMMON	5044	=item EV_COMMON
…		…
4632	default loop and triggering an C<ev_async> watcher from the default loop	5182	default loop and triggering an C<ev_async> watcher from the default loop
4633	watcher callback into the event loop interested in the signal.	5183	watcher callback into the event loop interested in the signal.
4634		5184
4635	=back	5185	=back
4636		5186
4637	See also L<THREAD LOCKING EXAMPLE>.	5187	See also L</THREAD LOCKING EXAMPLE>.
4638		5188
4639	=head3 COROUTINES	5189	=head3 COROUTINES
4640		5190
4641	Libev is very accommodating to coroutines ("cooperative threads"):	5191	Libev is very accommodating to coroutines ("cooperative threads"):
4642	libev fully supports nesting calls to its functions from different	5192	libev fully supports nesting calls to its functions from different
…		…
4807	requires, and its I/O model is fundamentally incompatible with the POSIX	5357	requires, and its I/O model is fundamentally incompatible with the POSIX
4808	model. Libev still offers limited functionality on this platform in	5358	model. Libev still offers limited functionality on this platform in
4809	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5359	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4810	descriptors. This only applies when using Win32 natively, not when using	5360	descriptors. This only applies when using Win32 natively, not when using
4811	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5361	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4812	as every compielr comes with a slightly differently broken/incompatible	5362	as every compiler comes with a slightly differently broken/incompatible
4813	environment.	5363	environment.
4814		5364
4815	Lifting these limitations would basically require the full	5365	Lifting these limitations would basically require the full
4816	re-implementation of the I/O system. If you are into this kind of thing,	5366	re-implementation of the I/O system. If you are into this kind of thing,
4817	then note that glib does exactly that for you in a very portable way (note	5367	then note that glib does exactly that for you in a very portable way (note
…		…
4911	structure (guaranteed by POSIX but not by ISO C for example), but it also	5461	structure (guaranteed by POSIX but not by ISO C for example), but it also
4912	assumes that the same (machine) code can be used to call any watcher	5462	assumes that the same (machine) code can be used to call any watcher
4913	callback: The watcher callbacks have different type signatures, but libev	5463	callback: The watcher callbacks have different type signatures, but libev
4914	calls them using an C<ev_watcher *> internally.	5464	calls them using an C<ev_watcher *> internally.
4915		5465
		5466	=item null pointers and integer zero are represented by 0 bytes
		5467
		5468	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5469	relies on this setting pointers and integers to null.
		5470
4916	=item pointer accesses must be thread-atomic	5471	=item pointer accesses must be thread-atomic
4917		5472
4918	Accessing a pointer value must be atomic, it must both be readable and	5473	Accessing a pointer value must be atomic, it must both be readable and
4919	writable in one piece - this is the case on all current architectures.	5474	writable in one piece - this is the case on all current architectures.
4920		5475
…		…
4933	thread" or will block signals process-wide, both behaviours would	5488	thread" or will block signals process-wide, both behaviours would
4934	be compatible with libev. Interaction between C<sigprocmask> and	5489	be compatible with libev. Interaction between C<sigprocmask> and
4935	C<pthread_sigmask> could complicate things, however.	5490	C<pthread_sigmask> could complicate things, however.
4936		5491
4937	The most portable way to handle signals is to block signals in all threads	5492	The most portable way to handle signals is to block signals in all threads
4938	except the initial one, and run the default loop in the initial thread as	5493	except the initial one, and run the signal handling loop in the initial
4939	well.	5494	thread as well.
4940		5495
4941	=item C<long> must be large enough for common memory allocation sizes	5496	=item C<long> must be large enough for common memory allocation sizes
4942		5497
4943	To improve portability and simplify its API, libev uses C<long> internally	5498	To improve portability and simplify its API, libev uses C<long> internally
4944	instead of C<size_t> when allocating its data structures. On non-POSIX	5499	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4950		5505
4951	The type C<double> is used to represent timestamps. It is required to	5506	The type C<double> is used to represent timestamps. It is required to
4952	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5507	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4953	good enough for at least into the year 4000 with millisecond accuracy	5508	good enough for at least into the year 4000 with millisecond accuracy
4954	(the design goal for libev). This requirement is overfulfilled by	5509	(the design goal for libev). This requirement is overfulfilled by
4955	implementations using IEEE 754, which is basically all existing ones. With	5510	implementations using IEEE 754, which is basically all existing ones.
		5511
4956	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5512	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5513	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5514	is either obsolete or somebody patched it to use C<long double> or
		5515	something like that, just kidding).
4957		5516
4958	=back	5517	=back
4959		5518
4960	If you know of other additional requirements drop me a note.	5519	If you know of other additional requirements drop me a note.
4961		5520
…		…
5023	=item Processing ev_async_send: O(number_of_async_watchers)	5582	=item Processing ev_async_send: O(number_of_async_watchers)
5024		5583
5025	=item Processing signals: O(max_signal_number)	5584	=item Processing signals: O(max_signal_number)
5026		5585
5027	Sending involves a system call I<iff> there were no other C<ev_async_send>	5586	Sending involves a system call I<iff> there were no other C<ev_async_send>
5028	calls in the current loop iteration. Checking for async and signal events	5587	calls in the current loop iteration and the loop is currently
		5588	blocked. Checking for async and signal events involves iterating over all
5029	involves iterating over all running async watchers or all signal numbers.	5589	running async watchers or all signal numbers.
5030		5590
5031	=back	5591	=back
5032		5592
5033		5593
5034	=head1 PORTING FROM LIBEV 3.X TO 4.X	5594	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
5043	=over 4	5603	=over 4
5044		5604
5045	=item C<EV_COMPAT3> backwards compatibility mechanism	5605	=item C<EV_COMPAT3> backwards compatibility mechanism
5046		5606
5047	The backward compatibility mechanism can be controlled by	5607	The backward compatibility mechanism can be controlled by
5048	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5608	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
5049	section.	5609	section.
5050		5610
5051	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5611	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
5052		5612
5053	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5613	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
5096	=over 4	5656	=over 4
5097		5657
5098	=item active	5658	=item active
5099		5659
5100	A watcher is active as long as it has been started and not yet stopped.	5660	A watcher is active as long as it has been started and not yet stopped.
5101	See L<WATCHER STATES> for details.	5661	See L</WATCHER STATES> for details.
5102		5662
5103	=item application	5663	=item application
5104		5664
5105	In this document, an application is whatever is using libev.	5665	In this document, an application is whatever is using libev.
5106		5666
…		…
5142	watchers and events.	5702	watchers and events.
5143		5703
5144	=item pending	5704	=item pending
5145		5705
5146	A watcher is pending as soon as the corresponding event has been	5706	A watcher is pending as soon as the corresponding event has been
5147	detected. See L<WATCHER STATES> for details.	5707	detected. See L</WATCHER STATES> for details.
5148		5708
5149	=item real time	5709	=item real time
5150		5710
5151	The physical time that is observed. It is apparently strictly monotonic :)	5711	The physical time that is observed. It is apparently strictly monotonic :)
5152		5712
5153	=item wall-clock time	5713	=item wall-clock time
5154		5714
5155	The time and date as shown on clocks. Unlike real time, it can actually	5715	The time and date as shown on clocks. Unlike real time, it can actually
5156	be wrong and jump forwards and backwards, e.g. when the you adjust your	5716	be wrong and jump forwards and backwards, e.g. when you adjust your
5157	clock.	5717	clock.
5158		5718
5159	=item watcher	5719	=item watcher
5160		5720
5161	A data structure that describes interest in certain events. Watchers need	5721	A data structure that describes interest in certain events. Watchers need
…		…
5164	=back	5724	=back
5165		5725
5166	=head1 AUTHOR	5726	=head1 AUTHOR
5167		5727
5168	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5728	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5169	Magnusson and Emanuele Giaquinta.	5729	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5170		5730

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