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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
…		…
299	}	331	}
300		332
301	...	333	...
302	ev_set_syserr_cb (fatal_error);	334	ev_set_syserr_cb (fatal_error);
303		335
		336	=item ev_feed_signal (int signum)
		337
		338	This function can be used to "simulate" a signal receive. It is completely
		339	safe to call this function at any time, from any context, including signal
		340	handlers or random threads.
		341
		342	Its main use is to customise signal handling in your process, especially
		343	in the presence of threads. For example, you could block signals
		344	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		345	creating any loops), and in one thread, use C<sigwait> or any other
		346	mechanism to wait for signals, then "deliver" them to libev by calling
		347	C<ev_feed_signal>.
		348
304	=back	349	=back
305		350
306	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	351	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
307		352
308	An event loop is described by a C<struct ev_loop *> (the C<struct> is	353	An event loop is described by a C<struct ev_loop *> (the C<struct> is
…		…
377		422
378	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
379	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
380	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	425	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
381	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
382	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
383	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).
384		431
385	=item C<EVFLAG_FORKCHECK>	432	=item C<EVFLAG_FORKCHECK>
386		433
387	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
388	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.
389		436
390	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,
391	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
392	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
393	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
394	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
395	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).
396		444
397	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
398	forget about forgetting to tell libev about forking) when you use this	446	forget about forgetting to tell libev about forking, although you still
399	flag.	447	have to ignore C<SIGPIPE>) when you use this flag.
400		448
401	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>
402	environment variable.	450	environment variable.
403		451
404	=item C<EVFLAG_NOINOTIFY>	452	=item C<EVFLAG_NOINOTIFY>
…		…
419		467
420	Signalfd will not be used by default as this changes your signal mask, and	468	Signalfd will not be used by default as this changes your signal mask, and
421	there are a lot of shoddy libraries and programs (glib's threadpool for	469	there are a lot of shoddy libraries and programs (glib's threadpool for
422	example) that can't properly initialise their signal masks.	470	example) that can't properly initialise their signal masks.
423		471
		472	=item C<EVFLAG_NOSIGMASK>
		473
		474	When this flag is specified, then libev will avoid to modify the signal
		475	mask. Specifically, this means you have to make sure signals are unblocked
		476	when you want to receive them.
		477
		478	This behaviour is useful when you want to do your own signal handling, or
		479	want to handle signals only in specific threads and want to avoid libev
		480	unblocking the signals.
		481
		482	It's also required by POSIX in a threaded program, as libev calls
		483	C<sigprocmask>, whose behaviour is officially unspecified.
		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.
		495
424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	496	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
425		497
426	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
427	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,
428	but if that fails, expect a fairly low limit on the number of fds when	500	but if that fails, expect a fairly low limit on the number of fds when
…		…
452	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
453	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	525	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
454		526
455	=item C<EVBACKEND_EPOLL> (value 4, Linux)	527	=item C<EVBACKEND_EPOLL> (value 4, Linux)
456		528
457	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
458	kernels).	530	kernels).
459		531
460	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
461	but it scales phenomenally better. While poll and select usually scale	533	it scales phenomenally better. While poll and select usually scale like
462	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
463	epoll scales either O(1) or O(active_fds).	535	fd), epoll scales either O(1) or O(active_fds).
464		536
465	The epoll mechanism deserves honorable mention as the most misdesigned	537	The epoll mechanism deserves honorable mention as the most misdesigned
466	of the more advanced event mechanisms: mere annoyances include silently	538	of the more advanced event mechanisms: mere annoyances include silently
467	dropping file descriptors, requiring a system call per change per file	539	dropping file descriptors, requiring a system call per change per file
468	descriptor (and unnecessary guessing of parameters), problems with dup,	540	descriptor (and unnecessary guessing of parameters), problems with dup,
…		…
471	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
472	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
473	set, which can take considerable time (one syscall per file descriptor)	545	set, which can take considerable time (one syscall per file descriptor)
474	and is of course hard to detect.	546	and is of course hard to detect.
475		547
476	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	548	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
477	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
478	I<different> file descriptors (even already closed ones, so one cannot	550	totally I<different> file descriptors (even already closed ones, so
479	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
480	on SMP systems). Libev tries to counter these spurious notifications by	552	(especially on SMP systems). Libev tries to counter these spurious
481	employing an additional generation counter and comparing that against the	553	notifications by employing an additional generation counter and comparing
482	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
483	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
484	perfectly fine with C<select> (files, many character devices...).	559	perfectly fine with C<select> (files, many character devices...).
485		560
486	Epoll is truly the train wreck analog among event poll mechanisms.	561	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		562	cobbled together in a hurry, no thought to design or interaction with
		563	others. Oh, the pain, will it ever stop...
487		564
488	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
489	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
490	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
491	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
…		…
503	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
504	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
505	the usage. So sad.	582	the usage. So sad.
506		583
507	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
508	all kernel versions tested so far.	585	a lot of kernel revisions, but probably(!) works in current versions.
509		586
510	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
511	C<EVBACKEND_POLL>.	588	C<EVBACKEND_POLL>.
512		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
513	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	634	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
514		635
515	Kqueue deserves special mention, as at the time of this writing, it	636	Kqueue deserves special mention, as at the time this backend was
516	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
517	with anything but sockets and pipes, except on Darwin, where of course	638	work reliably with anything but sockets and pipes, except on Darwin,
518	it's completely useless). Unlike epoll, however, whose brokenness	639	where of course it's completely useless). Unlike epoll, however, whose
519	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)
520	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
521	"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
522	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
523	system like NetBSD.	644	known-to-be-good (-enough) system like NetBSD.
524		645
525	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
526	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
527	the target platform). See C<ev_embed> watchers for more info.	648	the target platform). See C<ev_embed> watchers for more info.
528		649
529	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
530	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
531	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
532	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
533	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
534	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
535	cases	656	drops fds silently in similarly hard-to-detect cases.
536		657
537	This backend usually performs well under most conditions.	658	This backend usually performs well under most conditions.
538		659
539	While nominally embeddable in other event loops, this doesn't work	660	While nominally embeddable in other event loops, this doesn't work
540	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
…		…
557	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	678	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
558		679
559	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	680	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
560	it's really slow, but it still scales very well (O(active_fds)).	681	it's really slow, but it still scales very well (O(active_fds)).
561		682
562	Please note that Solaris event ports can deliver a lot of spurious
563	notifications, so you need to use non-blocking I/O or other means to avoid
564	blocking when no data (or space) is available.
565
566	While this backend scales well, it requires one system call per active	683	While this backend scales well, it requires one system call per active
567	file descriptor per loop iteration. For small and medium numbers of file	684	file descriptor per loop iteration. For small and medium numbers of file
568	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	685	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
569	might perform better.	686	might perform better.
570		687
571	On the positive side, with the exception of the spurious readiness	688	On the positive side, this backend actually performed fully to
572	notifications, this backend actually performed fully to specification
573	in all tests and is fully embeddable, which is a rare feat among the	689	specification in all tests and is fully embeddable, which is a rare feat
574	OS-specific backends (I vastly prefer correctness over speed hacks).	690	among the OS-specific backends (I vastly prefer correctness over speed
		691	hacks).
		692
		693	On the negative side, the interface is I<bizarre> - so bizarre that
		694	even sun itself gets it wrong in their code examples: The event polling
		695	function sometimes returns events to the caller even though an error
		696	occurred, but with no indication whether it has done so or not (yes, it's
		697	even documented that way) - deadly for edge-triggered interfaces where you
		698	absolutely have to know whether an event occurred or not because you have
		699	to re-arm the watcher.
		700
		701	Fortunately libev seems to be able to work around these idiocies.
575		702
576	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
577	C<EVBACKEND_POLL>.	704	C<EVBACKEND_POLL>.
578		705
579	=item C<EVBACKEND_ALL>	706	=item C<EVBACKEND_ALL>
580		707
581	Try all backends (even potentially broken ones that wouldn't be tried	708	Try all backends (even potentially broken ones that wouldn't be tried
582	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	709	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
583	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	710	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
584		711
585	It is definitely not recommended to use this flag.	712	It is definitely not recommended to use this flag, use whatever
		713	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		714	at all.
		715
		716	=item C<EVBACKEND_MASK>
		717
		718	Not a backend at all, but a mask to select all backend bits from a
		719	C<flags> value, in case you want to mask out any backends from a flags
		720	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
586		721
587	=back	722	=back
588		723
589	If one or more of the backend flags are or'ed into the flags value,	724	If one or more of the backend flags are or'ed into the flags value,
590	then only these backends will be tried (in the reverse order as listed	725	then only these backends will be tried (in the reverse order as listed
…		…
599		734
600	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
601	used if available.	736	used if available.
602		737
603	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);
604		745
605	=item ev_loop_destroy (loop)	746	=item ev_loop_destroy (loop)
606		747
607	Destroys an event loop object (frees all memory and kernel state	748	Destroys an event loop object (frees all memory and kernel state
608	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
…		…
625	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>
626	and C<ev_loop_destroy>.	767	and C<ev_loop_destroy>.
627		768
628	=item ev_loop_fork (loop)	769	=item ev_loop_fork (loop)
629		770
630	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
631	reinitialise the kernel state for backends that have one. Despite the	772	to reinitialise the kernel state for backends that have one. Despite
632	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
633	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
634	child before resuming or calling C<ev_run>.	776	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
635		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
636	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
637	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
638	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	783	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
639	during fork.	784	during fork.
640		785
641	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
…		…
711		856
712	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
713	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
714	the current time is a good idea.	859	the current time is a good idea.
715		860
716	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.
717		862
718	=item ev_suspend (loop)	863	=item ev_suspend (loop)
719		864
720	=item ev_resume (loop)	865	=item ev_resume (loop)
721		866
…		…
739	without a previous call to C<ev_suspend>.	884	without a previous call to C<ev_suspend>.
740		885
741	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
742	event loop time (see C<ev_now_update>).	887	event loop time (see C<ev_now_update>).
743		888
744	=item ev_run (loop, int flags)	889	=item bool ev_run (loop, int flags)
745		890
746	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
747	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
748	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
749	the watcher callbacks, an then repeat the whole process indefinitely: This	894	the watcher callbacks, and then repeat the whole process indefinitely: This
750	is why event loops are called I<loops>.	895	is why event loops are called I<loops>.
751		896
752	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
753	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
754	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").
755		904
756	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
757	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
758	finished (especially in interactive programs), but having a program	907	finished (especially in interactive programs), but having a program
759	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
760	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
761	beauty.	910	beauty.
762		911
763	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
764	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++
765	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
766	will it clear any outstanding C<EVBREAK_ONE> breaks.	915	will it clear any outstanding C<EVBREAK_ONE> breaks.
767		916
768	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
769	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
…		…
781	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
782	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
783	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
784	usually a better approach for this kind of thing.	933	usually a better approach for this kind of thing.
785		934
786	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):
787		938
788	- Increment loop depth.	939	- Increment loop depth.
789	- Reset the ev_break status.	940	- Reset the ev_break status.
790	- Before the first iteration, call any pending watchers.	941	- Before the first iteration, call any pending watchers.
791	LOOP:	942	LOOP:
…		…
824	anymore.	975	anymore.
825		976
826	... queue jobs here, make sure they register event watchers as long	977	... queue jobs here, make sure they register event watchers as long
827	... 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..)
828	ev_run (my_loop, 0);	979	ev_run (my_loop, 0);
829	... jobs done or somebody called unloop. yeah!	980	... jobs done or somebody called break. yeah!
830		981
831	=item ev_break (loop, how)	982	=item ev_break (loop, how)
832		983
833	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
834	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
…		…
867	running when nothing else is active.	1018	running when nothing else is active.
868		1019
869	ev_signal exitsig;	1020	ev_signal exitsig;
870	ev_signal_init (&exitsig, sig_cb, SIGINT);	1021	ev_signal_init (&exitsig, sig_cb, SIGINT);
871	ev_signal_start (loop, &exitsig);	1022	ev_signal_start (loop, &exitsig);
872	evf_unref (loop);	1023	ev_unref (loop);
873		1024
874	Example: For some weird reason, unregister the above signal handler again.	1025	Example: For some weird reason, unregister the above signal handler again.
875		1026
876	ev_ref (loop);	1027	ev_ref (loop);
877	ev_signal_stop (loop, &exitsig);	1028	ev_signal_stop (loop, &exitsig);
…		…
897	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.
898		1049
899	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
900	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,
901	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
902	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
903	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
904	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
905	once per this interval, on average.	1056	once per this interval, on average (as long as the host time resolution is
		1057	good enough).
906		1058
907	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
908	to spend more time collecting timeouts, at the expense of increased	1060	to spend more time collecting timeouts, at the expense of increased
909	latency/jitter/inexactness (the watcher callback will be called	1061	latency/jitter/inexactness (the watcher callback will be called
910	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
…		…
956	invoke the actual watchers inside another context (another thread etc.).	1108	invoke the actual watchers inside another context (another thread etc.).
957		1109
958	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
959	callback.	1111	callback.
960		1112
961	=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 ())
962		1114
963	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
964	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
965	each call to a libev function.	1117	each call to a libev function.
966		1118
967	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
968	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
969	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
970	I<release> and I<acquire> callbacks on the loop.	1122	I<release> and I<acquire> callbacks on the loop.
971		1123
972	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
973	suspended waiting for new events, and C<acquire> is called just	1125	suspended waiting for new events, and C<acquire> is called just
974	afterwards.	1126	afterwards.
…		…
1066	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher	1218	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
1067	*) >>), and you can stop watching for events at any time by calling the	1219	*) >>), and you can stop watching for events at any time by calling the
1068	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.	1220	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
1069		1221
1070	As long as your watcher is active (has been started but not stopped) you	1222	As long as your watcher is active (has been started but not stopped) you
1071	must not touch the values stored in it. Most specifically you must never	1223	must not touch the values stored in it except when explicitly documented
1072	reinitialise it or call its C<ev_TYPE_set> macro.	1224	otherwise. Most specifically you must never reinitialise it or call its
		1225	C<ev_TYPE_set> macro.
1073		1226
1074	Each and every callback receives the event loop pointer as first, the	1227	Each and every callback receives the event loop pointer as first, the
1075	registered watcher structure as second, and a bitset of received events as	1228	registered watcher structure as second, and a bitset of received events as
1076	third argument.	1229	third argument.
1077		1230
…		…
1114		1267
1115	=item C<EV_PREPARE>	1268	=item C<EV_PREPARE>
1116		1269
1117	=item C<EV_CHECK>	1270	=item C<EV_CHECK>
1118		1271
1119	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1272	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1120	to gather new events, and all C<ev_check> watchers are invoked just after	1273	gather new events, and all C<ev_check> watchers are queued (not invoked)
1121	C<ev_run> has gathered them, but before it invokes any callbacks for any	1274	just after C<ev_run> has gathered them, but before it queues any callbacks
		1275	for any received events. That means C<ev_prepare> watchers are the last
		1276	watchers invoked before the event loop sleeps or polls for new events, and
		1277	C<ev_check> watchers will be invoked before any other watchers of the same
		1278	or lower priority within an event loop iteration.
		1279
1122	received events. Callbacks of both watcher types can start and stop as	1280	Callbacks of both watcher types can start and stop as many watchers as
1123	many watchers as they want, and all of them will be taken into account	1281	they want, and all of them will be taken into account (for example, a
1124	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1282	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1125	C<ev_run> from blocking).	1283	blocking).
1126		1284
1127	=item C<EV_EMBED>	1285	=item C<EV_EMBED>
1128		1286
1129	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1287	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1130		1288
…		…
1253		1411
1254	=item callback ev_cb (ev_TYPE *watcher)	1412	=item callback ev_cb (ev_TYPE *watcher)
1255		1413
1256	Returns the callback currently set on the watcher.	1414	Returns the callback currently set on the watcher.
1257		1415
1258	=item ev_cb_set (ev_TYPE *watcher, callback)	1416	=item ev_set_cb (ev_TYPE *watcher, callback)
1259		1417
1260	Change the callback. You can change the callback at virtually any time	1418	Change the callback. You can change the callback at virtually any time
1261	(modulo threads).	1419	(modulo threads).
1262		1420
1263	=item ev_set_priority (ev_TYPE *watcher, int priority)	1421	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1281	or might not have been clamped to the valid range.	1439	or might not have been clamped to the valid range.
1282		1440
1283	The default priority used by watchers when no priority has been set is	1441	The default priority used by watchers when no priority has been set is
1284	always C<0>, which is supposed to not be too high and not be too low :).	1442	always C<0>, which is supposed to not be too high and not be too low :).
1285		1443
1286	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1444	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1287	priorities.	1445	priorities.
1288		1446
1289	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1447	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1290		1448
1291	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1449	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
…		…
1316	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1474	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1317	functions that do not need a watcher.	1475	functions that do not need a watcher.
1318		1476
1319	=back	1477	=back
1320		1478
1321	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1479	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1322		1480	OWN COMPOSITE WATCHERS> idioms.
1323	Each watcher has, by default, a member C<void *data> that you can change
1324	and read at any time: libev will completely ignore it. This can be used
1325	to associate arbitrary data with your watcher. If you need more data and
1326	don't want to allocate memory and store a pointer to it in that data
1327	member, you can also "subclass" the watcher type and provide your own
1328	data:
1329
1330	struct my_io
1331	{
1332	ev_io io;
1333	int otherfd;
1334	void *somedata;
1335	struct whatever *mostinteresting;
1336	};
1337
1338	...
1339	struct my_io w;
1340	ev_io_init (&w.io, my_cb, fd, EV_READ);
1341
1342	And since your callback will be called with a pointer to the watcher, you
1343	can cast it back to your own type:
1344
1345	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1346	{
1347	struct my_io *w = (struct my_io *)w_;
1348	...
1349	}
1350
1351	More interesting and less C-conformant ways of casting your callback type
1352	instead have been omitted.
1353
1354	Another common scenario is to use some data structure with multiple
1355	embedded watchers:
1356
1357	struct my_biggy
1358	{
1359	int some_data;
1360	ev_timer t1;
1361	ev_timer t2;
1362	}
1363
1364	In this case getting the pointer to C<my_biggy> is a bit more
1365	complicated: Either you store the address of your C<my_biggy> struct
1366	in the C<data> member of the watcher (for woozies), or you need to use
1367	some pointer arithmetic using C<offsetof> inside your watchers (for real
1368	programmers):
1369
1370	#include <stddef.h>
1371
1372	static void
1373	t1_cb (EV_P_ ev_timer *w, int revents)
1374	{
1375	struct my_biggy big = (struct my_biggy *)
1376	(((char *)w) - offsetof (struct my_biggy, t1));
1377	}
1378
1379	static void
1380	t2_cb (EV_P_ ev_timer *w, int revents)
1381	{
1382	struct my_biggy big = (struct my_biggy *)
1383	(((char *)w) - offsetof (struct my_biggy, t2));
1384	}
1385		1481
1386	=head2 WATCHER STATES	1482	=head2 WATCHER STATES
1387		1483
1388	There are various watcher states mentioned throughout this manual -	1484	There are various watcher states mentioned throughout this manual -
1389	active, pending and so on. In this section these states and the rules to	1485	active, pending and so on. In this section these states and the rules to
1390	transition between them will be described in more detail - and while these	1486	transition between them will be described in more detail - and while these
1391	rules might look complicated, they usually do "the right thing".	1487	rules might look complicated, they usually do "the right thing".
1392		1488
1393	=over 4	1489	=over 4
1394		1490
1395	=item initialiased	1491	=item initialised
1396		1492
1397	Before a watcher can be registered with the event looop it has to be	1493	Before a watcher can be registered with the event loop it has to be
1398	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1494	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1399	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1495	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1400		1496
1401	In this state it is simply some block of memory that is suitable for use	1497	In this state it is simply some block of memory that is suitable for
1402	in an event loop. It can be moved around, freed, reused etc. at will.	1498	use in an event loop. It can be moved around, freed, reused etc. at
		1499	will - as long as you either keep the memory contents intact, or call
		1500	C<ev_TYPE_init> again.
1403		1501
1404	=item started/running/active	1502	=item started/running/active
1405		1503
1406	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1504	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1407	property of the event loop, and is actively waiting for events. While in	1505	property of the event loop, and is actively waiting for events. While in
…		…
1435	latter will clear any pending state the watcher might be in, regardless	1533	latter will clear any pending state the watcher might be in, regardless
1436	of whether it was active or not, so stopping a watcher explicitly before	1534	of whether it was active or not, so stopping a watcher explicitly before
1437	freeing it is often a good idea.	1535	freeing it is often a good idea.
1438		1536
1439	While stopped (and not pending) the watcher is essentially in the	1537	While stopped (and not pending) the watcher is essentially in the
1440	initialised state, that is it can be reused, moved, modified in any way	1538	initialised state, that is, it can be reused, moved, modified in any way
1441	you wish.	1539	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1540	it again).
1442		1541
1443	=back	1542	=back
1444		1543
1445	=head2 WATCHER PRIORITY MODELS	1544	=head2 WATCHER PRIORITY MODELS
1446		1545
1447	Many event loops support I<watcher priorities>, which are usually small	1546	Many event loops support I<watcher priorities>, which are usually small
1448	integers that influence the ordering of event callback invocation	1547	integers that influence the ordering of event callback invocation
1449	between watchers in some way, all else being equal.	1548	between watchers in some way, all else being equal.
1450		1549
1451	In libev, Watcher priorities can be set using C<ev_set_priority>. See its	1550	In libev, watcher priorities can be set using C<ev_set_priority>. See its
1452	description for the more technical details such as the actual priority	1551	description for the more technical details such as the actual priority
1453	range.	1552	range.
1454		1553
1455	There are two common ways how these these priorities are being interpreted	1554	There are two common ways how these these priorities are being interpreted
1456	by event loops:	1555	by event loops:
…		…
1550		1649
1551	This section describes each watcher in detail, but will not repeat	1650	This section describes each watcher in detail, but will not repeat
1552	information given in the last section. Any initialisation/set macros,	1651	information given in the last section. Any initialisation/set macros,
1553	functions and members specific to the watcher type are explained.	1652	functions and members specific to the watcher type are explained.
1554		1653
1555	Members are additionally marked with either I<[read-only]>, meaning that,	1654	Most members are additionally marked with either I<[read-only]>, meaning
1556	while the watcher is active, you can look at the member and expect some	1655	that, while the watcher is active, you can look at the member and expect
1557	sensible content, but you must not modify it (you can modify it while the	1656	some sensible content, but you must not modify it (you can modify it while
1558	watcher is stopped to your hearts content), or I<[read-write]>, which	1657	the watcher is stopped to your hearts content), or I<[read-write]>, which
1559	means you can expect it to have some sensible content while the watcher	1658	means you can expect it to have some sensible content while the watcher
1560	is active, but you can also modify it. Modifying it may not do something	1659	is active, but you can also modify it. Modifying it may not do something
1561	sensible or take immediate effect (or do anything at all), but libev will	1660	sensible or take immediate effect (or do anything at all), but libev will
1562	not crash or malfunction in any way.	1661	not crash or malfunction in any way.
1563		1662
		1663	In any case, the documentation for each member will explain what the
		1664	effects are, and if there are any additional access restrictions.
1564		1665
1565	=head2 C<ev_io> - is this file descriptor readable or writable?	1666	=head2 C<ev_io> - is this file descriptor readable or writable?
1566		1667
1567	I/O watchers check whether a file descriptor is readable or writable	1668	I/O watchers check whether a file descriptor is readable or writable
1568	in each iteration of the event loop, or, more precisely, when reading	1669	in each iteration of the event loop, or, more precisely, when reading
…		…
1575	In general you can register as many read and/or write event watchers per	1676	In general you can register as many read and/or write event watchers per
1576	fd as you want (as long as you don't confuse yourself). Setting all file	1677	fd as you want (as long as you don't confuse yourself). Setting all file
1577	descriptors to non-blocking mode is also usually a good idea (but not	1678	descriptors to non-blocking mode is also usually a good idea (but not
1578	required if you know what you are doing).	1679	required if you know what you are doing).
1579		1680
1580	If you cannot use non-blocking mode, then force the use of a
1581	known-to-be-good backend (at the time of this writing, this includes only
1582	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1583	descriptors for which non-blocking operation makes no sense (such as
1584	files) - libev doesn't guarantee any specific behaviour in that case.
1585
1586	Another thing you have to watch out for is that it is quite easy to	1681	Another thing you have to watch out for is that it is quite easy to
1587	receive "spurious" readiness notifications, that is your callback might	1682	receive "spurious" readiness notifications, that is, your callback might
1588	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1683	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1589	because there is no data. Not only are some backends known to create a	1684	because there is no data. It is very easy to get into this situation even
1590	lot of those (for example Solaris ports), it is very easy to get into	1685	with a relatively standard program structure. Thus it is best to always
1591	this situation even with a relatively standard program structure. Thus	1686	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1592	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1593	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1687	preferable to a program hanging until some data arrives.
1594		1688
1595	If you cannot run the fd in non-blocking mode (for example you should	1689	If you cannot run the fd in non-blocking mode (for example you should
1596	not play around with an Xlib connection), then you have to separately	1690	not play around with an Xlib connection), then you have to separately
1597	re-test whether a file descriptor is really ready with a known-to-be good	1691	re-test whether a file descriptor is really ready with a known-to-be good
1598	interface such as poll (fortunately in our Xlib example, Xlib already	1692	interface such as poll (fortunately in the case of Xlib, it already does
1599	does this on its own, so its quite safe to use). Some people additionally	1693	this on its own, so its quite safe to use). Some people additionally
1600	use C<SIGALRM> and an interval timer, just to be sure you won't block	1694	use C<SIGALRM> and an interval timer, just to be sure you won't block
1601	indefinitely.	1695	indefinitely.
1602		1696
1603	But really, best use non-blocking mode.	1697	But really, best use non-blocking mode.
1604		1698
1605	=head3 The special problem of disappearing file descriptors	1699	=head3 The special problem of disappearing file descriptors
1606		1700
1607	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1701	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1608	descriptor (either due to calling C<close> explicitly or any other means,	1702	a file descriptor (either due to calling C<close> explicitly or any other
1609	such as C<dup2>). The reason is that you register interest in some file	1703	means, such as C<dup2>). The reason is that you register interest in some
1610	descriptor, but when it goes away, the operating system will silently drop	1704	file descriptor, but when it goes away, the operating system will silently
1611	this interest. If another file descriptor with the same number then is	1705	drop this interest. If another file descriptor with the same number then
1612	registered with libev, there is no efficient way to see that this is, in	1706	is registered with libev, there is no efficient way to see that this is,
1613	fact, a different file descriptor.	1707	in fact, a different file descriptor.
1614		1708
1615	To avoid having to explicitly tell libev about such cases, libev follows	1709	To avoid having to explicitly tell libev about such cases, libev follows
1616	the following policy: Each time C<ev_io_set> is being called, libev	1710	the following policy: Each time C<ev_io_set> is being called, libev
1617	will assume that this is potentially a new file descriptor, otherwise	1711	will assume that this is potentially a new file descriptor, otherwise
1618	it is assumed that the file descriptor stays the same. That means that	1712	it is assumed that the file descriptor stays the same. That means that
…		…
1632		1726
1633	There is no workaround possible except not registering events	1727	There is no workaround possible except not registering events
1634	for potentially C<dup ()>'ed file descriptors, or to resort to	1728	for potentially C<dup ()>'ed file descriptors, or to resort to
1635	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1729	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1636		1730
		1731	=head3 The special problem of files
		1732
		1733	Many people try to use C<select> (or libev) on file descriptors
		1734	representing files, and expect it to become ready when their program
		1735	doesn't block on disk accesses (which can take a long time on their own).
		1736
		1737	However, this cannot ever work in the "expected" way - you get a readiness
		1738	notification as soon as the kernel knows whether and how much data is
		1739	there, and in the case of open files, that's always the case, so you
		1740	always get a readiness notification instantly, and your read (or possibly
		1741	write) will still block on the disk I/O.
		1742
		1743	Another way to view it is that in the case of sockets, pipes, character
		1744	devices and so on, there is another party (the sender) that delivers data
		1745	on its own, but in the case of files, there is no such thing: the disk
		1746	will not send data on its own, simply because it doesn't know what you
		1747	wish to read - you would first have to request some data.
		1748
		1749	Since files are typically not-so-well supported by advanced notification
		1750	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1751	to files, even though you should not use it. The reason for this is
		1752	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1753	usually a tty, often a pipe, but also sometimes files or special devices
		1754	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1755	F</dev/urandom>), and even though the file might better be served with
		1756	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1757	it "just works" instead of freezing.
		1758
		1759	So avoid file descriptors pointing to files when you know it (e.g. use
		1760	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1761	when you rarely read from a file instead of from a socket, and want to
		1762	reuse the same code path.
		1763
1637	=head3 The special problem of fork	1764	=head3 The special problem of fork
1638		1765
1639	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1766	Some backends (epoll, kqueue, linuxaio, iouring) do not support C<fork ()>
1640	useless behaviour. Libev fully supports fork, but needs to be told about	1767	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1641	it in the child.	1768	to be told about it in the child if you want to continue to use it in the
		1769	child.
1642		1770
1643	To support fork in your programs, you either have to call	1771	To support fork in your child processes, you have to call C<ev_loop_fork
1644	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1772	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1645	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1773	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1646	C<EVBACKEND_POLL>.
1647		1774
1648	=head3 The special problem of SIGPIPE	1775	=head3 The special problem of SIGPIPE
1649		1776
1650	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1777	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1651	when writing to a pipe whose other end has been closed, your program gets	1778	when writing to a pipe whose other end has been closed, your program gets
…		…
1702	=item ev_io_init (ev_io *, callback, int fd, int events)	1829	=item ev_io_init (ev_io *, callback, int fd, int events)
1703		1830
1704	=item ev_io_set (ev_io *, int fd, int events)	1831	=item ev_io_set (ev_io *, int fd, int events)
1705		1832
1706	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1833	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1707	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or	1834	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE>, both
1708	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.	1835	C<EV_READ | EV_WRITE> or C<0>, to express the desire to receive the given
		1836	events.
1709		1837
1710	=item int fd [read-only]	1838	Note that setting the C<events> to C<0> and starting the watcher is
		1839	supported, but not specially optimized - if your program sometimes happens
		1840	to generate this combination this is fine, but if it is easy to avoid
		1841	starting an io watcher watching for no events you should do so.
1711		1842
1712	The file descriptor being watched.	1843	=item ev_io_modify (ev_io *, int events)
1713		1844
		1845	Similar to C<ev_io_set>, but only changes the event mask. Using this might
		1846	be faster with some backends, as libev can assume that the C<fd> still
		1847	refers to the same underlying file description, something it cannot do
		1848	when using C<ev_io_set>.
		1849
		1850	=item int fd [no-modify]
		1851
		1852	The file descriptor being watched. While it can be read at any time, you
		1853	must not modify this member even when the watcher is stopped - always use
		1854	C<ev_io_set> for that.
		1855
1714	=item int events [read-only]	1856	=item int events [no-modify]
1715		1857
1716	The events being watched.	1858	The set of events the fd is being watched for, among other flags. Remember
		1859	that this is a bit set - to test for C<EV_READ>, use C<< w->events &
		1860	EV_READ >>, and similarly for C<EV_WRITE>.
		1861
		1862	As with C<fd>, you must not modify this member even when the watcher is
		1863	stopped, always use C<ev_io_set> or C<ev_io_modify> for that.
1717		1864
1718	=back	1865	=back
1719		1866
1720	=head3 Examples	1867	=head3 Examples
1721		1868
…		…
1749	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1896	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1750	monotonic clock option helps a lot here).	1897	monotonic clock option helps a lot here).
1751		1898
1752	The callback is guaranteed to be invoked only I<after> its timeout has	1899	The callback is guaranteed to be invoked only I<after> its timeout has
1753	passed (not I<at>, so on systems with very low-resolution clocks this	1900	passed (not I<at>, so on systems with very low-resolution clocks this
1754	might introduce a small delay). If multiple timers become ready during the	1901	might introduce a small delay, see "the special problem of being too
		1902	early", below). If multiple timers become ready during the same loop
1755	same loop iteration then the ones with earlier time-out values are invoked	1903	iteration then the ones with earlier time-out values are invoked before
1756	before ones of the same priority with later time-out values (but this is	1904	ones of the same priority with later time-out values (but this is no
1757	no longer true when a callback calls C<ev_run> recursively).	1905	longer true when a callback calls C<ev_run> recursively).
1758		1906
1759	=head3 Be smart about timeouts	1907	=head3 Be smart about timeouts
1760		1908
1761	Many real-world problems involve some kind of timeout, usually for error	1909	Many real-world problems involve some kind of timeout, usually for error
1762	recovery. A typical example is an HTTP request - if the other side hangs,	1910	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1837		1985
1838	In this case, it would be more efficient to leave the C<ev_timer> alone,	1986	In this case, it would be more efficient to leave the C<ev_timer> alone,
1839	but remember the time of last activity, and check for a real timeout only	1987	but remember the time of last activity, and check for a real timeout only
1840	within the callback:	1988	within the callback:
1841		1989
		1990	ev_tstamp timeout = 60.;
1842	ev_tstamp last_activity; // time of last activity	1991	ev_tstamp last_activity; // time of last activity
		1992	ev_timer timer;
1843		1993
1844	static void	1994	static void
1845	callback (EV_P_ ev_timer *w, int revents)	1995	callback (EV_P_ ev_timer *w, int revents)
1846	{	1996	{
1847	ev_tstamp now = ev_now (EV_A);	1997	// calculate when the timeout would happen
1848	ev_tstamp timeout = last_activity + 60.;	1998	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1849		1999
1850	// if last_activity + 60. is older than now, we did time out	2000	// if negative, it means we the timeout already occurred
1851	if (timeout < now)	2001	if (after < 0.)
1852	{	2002	{
1853	// timeout occurred, take action	2003	// timeout occurred, take action
1854	}	2004	}
1855	else	2005	else
1856	{	2006	{
1857	// callback was invoked, but there was some activity, re-arm	2007	// callback was invoked, but there was some recent
1858	// the watcher to fire in last_activity + 60, which is	2008	// activity. simply restart the timer to time out
1859	// guaranteed to be in the future, so "again" is positive:	2009	// after "after" seconds, which is the earliest time
1860	w->repeat = timeout - now;	2010	// the timeout can occur.
		2011	ev_timer_set (w, after, 0.);
1861	ev_timer_again (EV_A_ w);	2012	ev_timer_start (EV_A_ w);
1862	}	2013	}
1863	}	2014	}
1864		2015
1865	To summarise the callback: first calculate the real timeout (defined	2016	To summarise the callback: first calculate in how many seconds the
1866	as "60 seconds after the last activity"), then check if that time has	2017	timeout will occur (by calculating the absolute time when it would occur,
1867	been reached, which means something I<did>, in fact, time out. Otherwise	2018	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1868	the callback was invoked too early (C<timeout> is in the future), so	2019	(EV_A)> from that).
1869	re-schedule the timer to fire at that future time, to see if maybe we have
1870	a timeout then.
1871		2020
1872	Note how C<ev_timer_again> is used, taking advantage of the	2021	If this value is negative, then we are already past the timeout, i.e. we
1873	C<ev_timer_again> optimisation when the timer is already running.	2022	timed out, and need to do whatever is needed in this case.
		2023
		2024	Otherwise, we now the earliest time at which the timeout would trigger,
		2025	and simply start the timer with this timeout value.
		2026
		2027	In other words, each time the callback is invoked it will check whether
		2028	the timeout occurred. If not, it will simply reschedule itself to check
		2029	again at the earliest time it could time out. Rinse. Repeat.
1874		2030
1875	This scheme causes more callback invocations (about one every 60 seconds	2031	This scheme causes more callback invocations (about one every 60 seconds
1876	minus half the average time between activity), but virtually no calls to	2032	minus half the average time between activity), but virtually no calls to
1877	libev to change the timeout.	2033	libev to change the timeout.
1878		2034
1879	To start the timer, simply initialise the watcher and set C<last_activity>	2035	To start the machinery, simply initialise the watcher and set
1880	to the current time (meaning we just have some activity :), then call the	2036	C<last_activity> to the current time (meaning there was some activity just
1881	callback, which will "do the right thing" and start the timer:	2037	now), then call the callback, which will "do the right thing" and start
		2038	the timer:
1882		2039
		2040	last_activity = ev_now (EV_A);
1883	ev_init (timer, callback);	2041	ev_init (&timer, callback);
1884	last_activity = ev_now (loop);	2042	callback (EV_A_ &timer, 0);
1885	callback (loop, timer, EV_TIMER);
1886		2043
1887	And when there is some activity, simply store the current time in	2044	When there is some activity, simply store the current time in
1888	C<last_activity>, no libev calls at all:	2045	C<last_activity>, no libev calls at all:
1889		2046
		2047	if (activity detected)
1890	last_activity = ev_now (loop);	2048	last_activity = ev_now (EV_A);
		2049
		2050	When your timeout value changes, then the timeout can be changed by simply
		2051	providing a new value, stopping the timer and calling the callback, which
		2052	will again do the right thing (for example, time out immediately :).
		2053
		2054	timeout = new_value;
		2055	ev_timer_stop (EV_A_ &timer);
		2056	callback (EV_A_ &timer, 0);
1891		2057
1892	This technique is slightly more complex, but in most cases where the	2058	This technique is slightly more complex, but in most cases where the
1893	time-out is unlikely to be triggered, much more efficient.	2059	time-out is unlikely to be triggered, much more efficient.
1894
1895	Changing the timeout is trivial as well (if it isn't hard-coded in the
1896	callback :) - just change the timeout and invoke the callback, which will
1897	fix things for you.
1898		2060
1899	=item 4. Wee, just use a double-linked list for your timeouts.	2061	=item 4. Wee, just use a double-linked list for your timeouts.
1900		2062
1901	If there is not one request, but many thousands (millions...), all	2063	If there is not one request, but many thousands (millions...), all
1902	employing some kind of timeout with the same timeout value, then one can	2064	employing some kind of timeout with the same timeout value, then one can
…		…
1929	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2091	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1930	rather complicated, but extremely efficient, something that really pays	2092	rather complicated, but extremely efficient, something that really pays
1931	off after the first million or so of active timers, i.e. it's usually	2093	off after the first million or so of active timers, i.e. it's usually
1932	overkill :)	2094	overkill :)
1933		2095
		2096	=head3 The special problem of being too early
		2097
		2098	If you ask a timer to call your callback after three seconds, then
		2099	you expect it to be invoked after three seconds - but of course, this
		2100	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2101	guaranteed to any precision by libev - imagine somebody suspending the
		2102	process with a STOP signal for a few hours for example.
		2103
		2104	So, libev tries to invoke your callback as soon as possible I<after> the
		2105	delay has occurred, but cannot guarantee this.
		2106
		2107	A less obvious failure mode is calling your callback too early: many event
		2108	loops compare timestamps with a "elapsed delay >= requested delay", but
		2109	this can cause your callback to be invoked much earlier than you would
		2110	expect.
		2111
		2112	To see why, imagine a system with a clock that only offers full second
		2113	resolution (think windows if you can't come up with a broken enough OS
		2114	yourself). If you schedule a one-second timer at the time 500.9, then the
		2115	event loop will schedule your timeout to elapse at a system time of 500
		2116	(500.9 truncated to the resolution) + 1, or 501.
		2117
		2118	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2119	501" and invoke the callback 0.1s after it was started, even though a
		2120	one-second delay was requested - this is being "too early", despite best
		2121	intentions.
		2122
		2123	This is the reason why libev will never invoke the callback if the elapsed
		2124	delay equals the requested delay, but only when the elapsed delay is
		2125	larger than the requested delay. In the example above, libev would only invoke
		2126	the callback at system time 502, or 1.1s after the timer was started.
		2127
		2128	So, while libev cannot guarantee that your callback will be invoked
		2129	exactly when requested, it I<can> and I<does> guarantee that the requested
		2130	delay has actually elapsed, or in other words, it always errs on the "too
		2131	late" side of things.
		2132
1934	=head3 The special problem of time updates	2133	=head3 The special problem of time updates
1935		2134
1936	Establishing the current time is a costly operation (it usually takes at	2135	Establishing the current time is a costly operation (it usually takes
1937	least two system calls): EV therefore updates its idea of the current	2136	at least one system call): EV therefore updates its idea of the current
1938	time only before and after C<ev_run> collects new events, which causes a	2137	time only before and after C<ev_run> collects new events, which causes a
1939	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2138	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1940	lots of events in one iteration.	2139	lots of events in one iteration.
1941		2140
1942	The relative timeouts are calculated relative to the C<ev_now ()>	2141	The relative timeouts are calculated relative to the C<ev_now ()>
1943	time. This is usually the right thing as this timestamp refers to the time	2142	time. This is usually the right thing as this timestamp refers to the time
1944	of the event triggering whatever timeout you are modifying/starting. If	2143	of the event triggering whatever timeout you are modifying/starting. If
1945	you suspect event processing to be delayed and you I<need> to base the	2144	you suspect event processing to be delayed and you I<need> to base the
1946	timeout on the current time, use something like this to adjust for this:	2145	timeout on the current time, use something like the following to adjust
		2146	for it:
1947		2147
1948	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2148	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1949		2149
1950	If the event loop is suspended for a long time, you can also force an	2150	If the event loop is suspended for a long time, you can also force an
1951	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2151	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1952	()>.	2152	()>, although that will push the event time of all outstanding events
		2153	further into the future.
		2154
		2155	=head3 The special problem of unsynchronised clocks
		2156
		2157	Modern systems have a variety of clocks - libev itself uses the normal
		2158	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2159	jumps).
		2160
		2161	Neither of these clocks is synchronised with each other or any other clock
		2162	on the system, so C<ev_time ()> might return a considerably different time
		2163	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2164	a call to C<gettimeofday> might return a second count that is one higher
		2165	than a directly following call to C<time>.
		2166
		2167	The moral of this is to only compare libev-related timestamps with
		2168	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2169	a second or so.
		2170
		2171	One more problem arises due to this lack of synchronisation: if libev uses
		2172	the system monotonic clock and you compare timestamps from C<ev_time>
		2173	or C<ev_now> from when you started your timer and when your callback is
		2174	invoked, you will find that sometimes the callback is a bit "early".
		2175
		2176	This is because C<ev_timer>s work in real time, not wall clock time, so
		2177	libev makes sure your callback is not invoked before the delay happened,
		2178	I<measured according to the real time>, not the system clock.
		2179
		2180	If your timeouts are based on a physical timescale (e.g. "time out this
		2181	connection after 100 seconds") then this shouldn't bother you as it is
		2182	exactly the right behaviour.
		2183
		2184	If you want to compare wall clock/system timestamps to your timers, then
		2185	you need to use C<ev_periodic>s, as these are based on the wall clock
		2186	time, where your comparisons will always generate correct results.
1953		2187
1954	=head3 The special problems of suspended animation	2188	=head3 The special problems of suspended animation
1955		2189
1956	When you leave the server world it is quite customary to hit machines that	2190	When you leave the server world it is quite customary to hit machines that
1957	can suspend/hibernate - what happens to the clocks during such a suspend?	2191	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1987		2221
1988	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2222	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1989		2223
1990	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2224	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1991		2225
1992	Configure the timer to trigger after C<after> seconds. If C<repeat>	2226	Configure the timer to trigger after C<after> seconds (fractional and
1993	is C<0.>, then it will automatically be stopped once the timeout is	2227	negative values are supported). If C<repeat> is C<0.>, then it will
1994	reached. If it is positive, then the timer will automatically be	2228	automatically be stopped once the timeout is reached. If it is positive,
1995	configured to trigger again C<repeat> seconds later, again, and again,	2229	then the timer will automatically be configured to trigger again C<repeat>
1996	until stopped manually.	2230	seconds later, again, and again, until stopped manually.
1997		2231
1998	The timer itself will do a best-effort at avoiding drift, that is, if	2232	The timer itself will do a best-effort at avoiding drift, that is, if
1999	you configure a timer to trigger every 10 seconds, then it will normally	2233	you configure a timer to trigger every 10 seconds, then it will normally
2000	trigger at exactly 10 second intervals. If, however, your program cannot	2234	trigger at exactly 10 second intervals. If, however, your program cannot
2001	keep up with the timer (because it takes longer than those 10 seconds to	2235	keep up with the timer (because it takes longer than those 10 seconds to
2002	do stuff) the timer will not fire more than once per event loop iteration.	2236	do stuff) the timer will not fire more than once per event loop iteration.
2003		2237
2004	=item ev_timer_again (loop, ev_timer *)	2238	=item ev_timer_again (loop, ev_timer *)
2005		2239
2006	This will act as if the timer timed out and restart it again if it is	2240	This will act as if the timer timed out, and restarts it again if it is
2007	repeating. The exact semantics are:	2241	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2242	timeout to the C<repeat> value and calling C<ev_timer_start>.
2008		2243
		2244	The exact semantics are as in the following rules, all of which will be
		2245	applied to the watcher:
		2246
		2247	=over 4
		2248
2009	If the timer is pending, its pending status is cleared.	2249	=item If the timer is pending, the pending status is always cleared.
2010		2250
2011	If the timer is started but non-repeating, stop it (as if it timed out).	2251	=item If the timer is started but non-repeating, stop it (as if it timed
		2252	out, without invoking it).
2012		2253
2013	If the timer is repeating, either start it if necessary (with the	2254	=item If the timer is repeating, make the C<repeat> value the new timeout
2014	C<repeat> value), or reset the running timer to the C<repeat> value.	2255	and start the timer, if necessary.
2015		2256
		2257	=back
		2258
2016	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2259	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2017	usage example.	2260	usage example.
2018		2261
2019	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2262	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2020		2263
2021	Returns the remaining time until a timer fires. If the timer is active,	2264	Returns the remaining time until a timer fires. If the timer is active,
…		…
2074	Periodic watchers are also timers of a kind, but they are very versatile	2317	Periodic watchers are also timers of a kind, but they are very versatile
2075	(and unfortunately a bit complex).	2318	(and unfortunately a bit complex).
2076		2319
2077	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2320	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2078	relative time, the physical time that passes) but on wall clock time	2321	relative time, the physical time that passes) but on wall clock time
2079	(absolute time, the thing you can read on your calender or clock). The	2322	(absolute time, the thing you can read on your calendar or clock). The
2080	difference is that wall clock time can run faster or slower than real	2323	difference is that wall clock time can run faster or slower than real
2081	time, and time jumps are not uncommon (e.g. when you adjust your	2324	time, and time jumps are not uncommon (e.g. when you adjust your
2082	wrist-watch).	2325	wrist-watch).
2083		2326
2084	You can tell a periodic watcher to trigger after some specific point	2327	You can tell a periodic watcher to trigger after some specific point
…		…
2089	C<ev_timer>, which would still trigger roughly 10 seconds after starting	2332	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2090	it, as it uses a relative timeout).	2333	it, as it uses a relative timeout).
2091		2334
2092	C<ev_periodic> watchers can also be used to implement vastly more complex	2335	C<ev_periodic> watchers can also be used to implement vastly more complex
2093	timers, such as triggering an event on each "midnight, local time", or	2336	timers, such as triggering an event on each "midnight, local time", or
2094	other complicated rules. This cannot be done with C<ev_timer> watchers, as	2337	other complicated rules. This cannot easily be done with C<ev_timer>
2095	those cannot react to time jumps.	2338	watchers, as those cannot react to time jumps.
2096		2339
2097	As with timers, the callback is guaranteed to be invoked only when the	2340	As with timers, the callback is guaranteed to be invoked only when the
2098	point in time where it is supposed to trigger has passed. If multiple	2341	point in time where it is supposed to trigger has passed. If multiple
2099	timers become ready during the same loop iteration then the ones with	2342	timers become ready during the same loop iteration then the ones with
2100	earlier time-out values are invoked before ones with later time-out values	2343	earlier time-out values are invoked before ones with later time-out values
…		…
2141		2384
2142	Another way to think about it (for the mathematically inclined) is that	2385	Another way to think about it (for the mathematically inclined) is that
2143	C<ev_periodic> will try to run the callback in this mode at the next possible	2386	C<ev_periodic> will try to run the callback in this mode at the next possible
2144	time where C<time = offset (mod interval)>, regardless of any time jumps.	2387	time where C<time = offset (mod interval)>, regardless of any time jumps.
2145		2388
2146	For numerical stability it is preferable that the C<offset> value is near	2389	The C<interval> I<MUST> be positive, and for numerical stability, the
2147	C<ev_now ()> (the current time), but there is no range requirement for	2390	interval value should be higher than C<1/8192> (which is around 100
2148	this value, and in fact is often specified as zero.	2391	microseconds) and C<offset> should be higher than C<0> and should have
		2392	at most a similar magnitude as the current time (say, within a factor of
		2393	ten). Typical values for offset are, in fact, C<0> or something between
		2394	C<0> and C<interval>, which is also the recommended range.
2149		2395
2150	Note also that there is an upper limit to how often a timer can fire (CPU	2396	Note also that there is an upper limit to how often a timer can fire (CPU
2151	speed for example), so if C<interval> is very small then timing stability	2397	speed for example), so if C<interval> is very small then timing stability
2152	will of course deteriorate. Libev itself tries to be exact to be about one	2398	will of course deteriorate. Libev itself tries to be exact to be about one
2153	millisecond (if the OS supports it and the machine is fast enough).	2399	millisecond (if the OS supports it and the machine is fast enough).
…		…
2183		2429
2184	NOTE: I<< This callback must always return a time that is higher than or	2430	NOTE: I<< This callback must always return a time that is higher than or
2185	equal to the passed C<now> value >>.	2431	equal to the passed C<now> value >>.
2186		2432
2187	This can be used to create very complex timers, such as a timer that	2433	This can be used to create very complex timers, such as a timer that
2188	triggers on "next midnight, local time". To do this, you would calculate the	2434	triggers on "next midnight, local time". To do this, you would calculate
2189	next midnight after C<now> and return the timestamp value for this. How	2435	the next midnight after C<now> and return the timestamp value for
2190	you do this is, again, up to you (but it is not trivial, which is the main	2436	this. Here is a (completely untested, no error checking) example on how to
2191	reason I omitted it as an example).	2437	do this:
		2438
		2439	#include <time.h>
		2440
		2441	static ev_tstamp
		2442	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2443	{
		2444	time_t tnow = (time_t)now;
		2445	struct tm tm;
		2446	localtime_r (&tnow, &tm);
		2447
		2448	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2449	++tm.tm_mday; // midnight next day
		2450
		2451	return mktime (&tm);
		2452	}
		2453
		2454	Note: this code might run into trouble on days that have more then two
		2455	midnights (beginning and end).
2192		2456
2193	=back	2457	=back
2194		2458
2195	=item ev_periodic_again (loop, ev_periodic *)	2459	=item ev_periodic_again (loop, ev_periodic *)
2196		2460
…		…
2261		2525
2262	ev_periodic hourly_tick;	2526	ev_periodic hourly_tick;
2263	ev_periodic_init (&hourly_tick, clock_cb,	2527	ev_periodic_init (&hourly_tick, clock_cb,
2264	fmod (ev_now (loop), 3600.), 3600., 0);	2528	fmod (ev_now (loop), 3600.), 3600., 0);
2265	ev_periodic_start (loop, &hourly_tick);	2529	ev_periodic_start (loop, &hourly_tick);
2266		2530
2267		2531
2268	=head2 C<ev_signal> - signal me when a signal gets signalled!	2532	=head2 C<ev_signal> - signal me when a signal gets signalled!
2269		2533
2270	Signal watchers will trigger an event when the process receives a specific	2534	Signal watchers will trigger an event when the process receives a specific
2271	signal one or more times. Even though signals are very asynchronous, libev	2535	signal one or more times. Even though signals are very asynchronous, libev
…		…
2281	only within the same loop, i.e. you can watch for C<SIGINT> in your	2545	only within the same loop, i.e. you can watch for C<SIGINT> in your
2282	default loop and for C<SIGIO> in another loop, but you cannot watch for	2546	default loop and for C<SIGIO> in another loop, but you cannot watch for
2283	C<SIGINT> in both the default loop and another loop at the same time. At	2547	C<SIGINT> in both the default loop and another loop at the same time. At
2284	the moment, C<SIGCHLD> is permanently tied to the default loop.	2548	the moment, C<SIGCHLD> is permanently tied to the default loop.
2285		2549
2286	When the first watcher gets started will libev actually register something	2550	Only after the first watcher for a signal is started will libev actually
2287	with the kernel (thus it coexists with your own signal handlers as long as	2551	register something with the kernel. It thus coexists with your own signal
2288	you don't register any with libev for the same signal).	2552	handlers as long as you don't register any with libev for the same signal.
2289		2553
2290	If possible and supported, libev will install its handlers with	2554	If possible and supported, libev will install its handlers with
2291	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2555	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2292	not be unduly interrupted. If you have a problem with system calls getting	2556	not be unduly interrupted. If you have a problem with system calls getting
2293	interrupted by signals you can block all signals in an C<ev_check> watcher	2557	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2296	=head3 The special problem of inheritance over fork/execve/pthread_create	2560	=head3 The special problem of inheritance over fork/execve/pthread_create
2297		2561
2298	Both the signal mask (C<sigprocmask>) and the signal disposition	2562	Both the signal mask (C<sigprocmask>) and the signal disposition
2299	(C<sigaction>) are unspecified after starting a signal watcher (and after	2563	(C<sigaction>) are unspecified after starting a signal watcher (and after
2300	stopping it again), that is, libev might or might not block the signal,	2564	stopping it again), that is, libev might or might not block the signal,
2301	and might or might not set or restore the installed signal handler.	2565	and might or might not set or restore the installed signal handler (but
		2566	see C<EVFLAG_NOSIGMASK>).
2302		2567
2303	While this does not matter for the signal disposition (libev never	2568	While this does not matter for the signal disposition (libev never
2304	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2569	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2305	C<execve>), this matters for the signal mask: many programs do not expect	2570	C<execve>), this matters for the signal mask: many programs do not expect
2306	certain signals to be blocked.	2571	certain signals to be blocked.
…		…
2319	I<has> to modify the signal mask, at least temporarily.	2584	I<has> to modify the signal mask, at least temporarily.
2320		2585
2321	So I can't stress this enough: I<If you do not reset your signal mask when	2586	So I can't stress this enough: I<If you do not reset your signal mask when
2322	you expect it to be empty, you have a race condition in your code>. This	2587	you expect it to be empty, you have a race condition in your code>. This
2323	is not a libev-specific thing, this is true for most event libraries.	2588	is not a libev-specific thing, this is true for most event libraries.
		2589
		2590	=head3 The special problem of threads signal handling
		2591
		2592	POSIX threads has problematic signal handling semantics, specifically,
		2593	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2594	threads in a process block signals, which is hard to achieve.
		2595
		2596	When you want to use sigwait (or mix libev signal handling with your own
		2597	for the same signals), you can tackle this problem by globally blocking
		2598	all signals before creating any threads (or creating them with a fully set
		2599	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2600	loops. Then designate one thread as "signal receiver thread" which handles
		2601	these signals. You can pass on any signals that libev might be interested
		2602	in by calling C<ev_feed_signal>.
2324		2603
2325	=head3 Watcher-Specific Functions and Data Members	2604	=head3 Watcher-Specific Functions and Data Members
2326		2605
2327	=over 4	2606	=over 4
2328		2607
…		…
2463		2742
2464	=head2 C<ev_stat> - did the file attributes just change?	2743	=head2 C<ev_stat> - did the file attributes just change?
2465		2744
2466	This watches a file system path for attribute changes. That is, it calls	2745	This watches a file system path for attribute changes. That is, it calls
2467	C<stat> on that path in regular intervals (or when the OS says it changed)	2746	C<stat> on that path in regular intervals (or when the OS says it changed)
2468	and sees if it changed compared to the last time, invoking the callback if	2747	and sees if it changed compared to the last time, invoking the callback
2469	it did.	2748	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2749	happen after the watcher has been started will be reported.
2470		2750
2471	The path does not need to exist: changing from "path exists" to "path does	2751	The path does not need to exist: changing from "path exists" to "path does
2472	not exist" is a status change like any other. The condition "path does not	2752	not exist" is a status change like any other. The condition "path does not
2473	exist" (or more correctly "path cannot be stat'ed") is signified by the	2753	exist" (or more correctly "path cannot be stat'ed") is signified by the
2474	C<st_nlink> field being zero (which is otherwise always forced to be at	2754	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2704	Apart from keeping your process non-blocking (which is a useful	2984	Apart from keeping your process non-blocking (which is a useful
2705	effect on its own sometimes), idle watchers are a good place to do	2985	effect on its own sometimes), idle watchers are a good place to do
2706	"pseudo-background processing", or delay processing stuff to after the	2986	"pseudo-background processing", or delay processing stuff to after the
2707	event loop has handled all outstanding events.	2987	event loop has handled all outstanding events.
2708		2988
		2989	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2990
		2991	As long as there is at least one active idle watcher, libev will never
		2992	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2993	For this to work, the idle watcher doesn't need to be invoked at all - the
		2994	lowest priority will do.
		2995
		2996	This mode of operation can be useful together with an C<ev_check> watcher,
		2997	to do something on each event loop iteration - for example to balance load
		2998	between different connections.
		2999
		3000	See L</Abusing an ev_check watcher for its side-effect> for a longer
		3001	example.
		3002
2709	=head3 Watcher-Specific Functions and Data Members	3003	=head3 Watcher-Specific Functions and Data Members
2710		3004
2711	=over 4	3005	=over 4
2712		3006
2713	=item ev_idle_init (ev_idle *, callback)	3007	=item ev_idle_init (ev_idle *, callback)
…		…
2724	callback, free it. Also, use no error checking, as usual.	3018	callback, free it. Also, use no error checking, as usual.
2725		3019
2726	static void	3020	static void
2727	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	3021	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2728	{	3022	{
		3023	// stop the watcher
		3024	ev_idle_stop (loop, w);
		3025
		3026	// now we can free it
2729	free (w);	3027	free (w);
		3028
2730	// now do something you wanted to do when the program has	3029	// now do something you wanted to do when the program has
2731	// no longer anything immediate to do.	3030	// no longer anything immediate to do.
2732	}	3031	}
2733		3032
2734	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	3033	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2736	ev_idle_start (loop, idle_watcher);	3035	ev_idle_start (loop, idle_watcher);
2737		3036
2738		3037
2739	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3038	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2740		3039
2741	Prepare and check watchers are usually (but not always) used in pairs:	3040	Prepare and check watchers are often (but not always) used in pairs:
2742	prepare watchers get invoked before the process blocks and check watchers	3041	prepare watchers get invoked before the process blocks and check watchers
2743	afterwards.	3042	afterwards.
2744		3043
2745	You I<must not> call C<ev_run> or similar functions that enter	3044	You I<must not> call C<ev_run> (or similar functions that enter the
2746	the current event loop from either C<ev_prepare> or C<ev_check>	3045	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2747	watchers. Other loops than the current one are fine, however. The	3046	C<ev_check> watchers. Other loops than the current one are fine,
2748	rationale behind this is that you do not need to check for recursion in	3047	however. The rationale behind this is that you do not need to check
2749	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3048	for recursion in those watchers, i.e. the sequence will always be
2750	C<ev_check> so if you have one watcher of each kind they will always be	3049	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2751	called in pairs bracketing the blocking call.	3050	kind they will always be called in pairs bracketing the blocking call.
2752		3051
2753	Their main purpose is to integrate other event mechanisms into libev and	3052	Their main purpose is to integrate other event mechanisms into libev and
2754	their use is somewhat advanced. They could be used, for example, to track	3053	their use is somewhat advanced. They could be used, for example, to track
2755	variable changes, implement your own watchers, integrate net-snmp or a	3054	variable changes, implement your own watchers, integrate net-snmp or a
2756	coroutine library and lots more. They are also occasionally useful if	3055	coroutine library and lots more. They are also occasionally useful if
…		…
2774	with priority higher than or equal to the event loop and one coroutine	3073	with priority higher than or equal to the event loop and one coroutine
2775	of lower priority, but only once, using idle watchers to keep the event	3074	of lower priority, but only once, using idle watchers to keep the event
2776	loop from blocking if lower-priority coroutines are active, thus mapping	3075	loop from blocking if lower-priority coroutines are active, thus mapping
2777	low-priority coroutines to idle/background tasks).	3076	low-priority coroutines to idle/background tasks).
2778		3077
2779	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3078	When used for this purpose, it is recommended to give C<ev_check> watchers
2780	priority, to ensure that they are being run before any other watchers	3079	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2781	after the poll (this doesn't matter for C<ev_prepare> watchers).	3080	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3081	watchers).
2782		3082
2783	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3083	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2784	activate ("feed") events into libev. While libev fully supports this, they	3084	activate ("feed") events into libev. While libev fully supports this, they
2785	might get executed before other C<ev_check> watchers did their job. As	3085	might get executed before other C<ev_check> watchers did their job. As
2786	C<ev_check> watchers are often used to embed other (non-libev) event	3086	C<ev_check> watchers are often used to embed other (non-libev) event
2787	loops those other event loops might be in an unusable state until their	3087	loops those other event loops might be in an unusable state until their
2788	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3088	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2789	others).	3089	others).
		3090
		3091	=head3 Abusing an C<ev_check> watcher for its side-effect
		3092
		3093	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3094	useful because they are called once per event loop iteration. For
		3095	example, if you want to handle a large number of connections fairly, you
		3096	normally only do a bit of work for each active connection, and if there
		3097	is more work to do, you wait for the next event loop iteration, so other
		3098	connections have a chance of making progress.
		3099
		3100	Using an C<ev_check> watcher is almost enough: it will be called on the
		3101	next event loop iteration. However, that isn't as soon as possible -
		3102	without external events, your C<ev_check> watcher will not be invoked.
		3103
		3104	This is where C<ev_idle> watchers come in handy - all you need is a
		3105	single global idle watcher that is active as long as you have one active
		3106	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3107	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3108	invoked. Neither watcher alone can do that.
2790		3109
2791	=head3 Watcher-Specific Functions and Data Members	3110	=head3 Watcher-Specific Functions and Data Members
2792		3111
2793	=over 4	3112	=over 4
2794		3113
…		…
2995		3314
2996	=over 4	3315	=over 4
2997		3316
2998	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3317	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2999		3318
3000	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3319	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
3001		3320
3002	Configures the watcher to embed the given loop, which must be	3321	Configures the watcher to embed the given loop, which must be
3003	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3322	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
3004	invoked automatically, otherwise it is the responsibility of the callback	3323	invoked automatically, otherwise it is the responsibility of the callback
3005	to invoke it (it will continue to be called until the sweep has been done,	3324	to invoke it (it will continue to be called until the sweep has been done,
…		…
3026	used).	3345	used).
3027		3346
3028	struct ev_loop *loop_hi = ev_default_init (0);	3347	struct ev_loop *loop_hi = ev_default_init (0);
3029	struct ev_loop *loop_lo = 0;	3348	struct ev_loop *loop_lo = 0;
3030	ev_embed embed;	3349	ev_embed embed;
3031		3350
3032	// see if there is a chance of getting one that works	3351	// see if there is a chance of getting one that works
3033	// (remember that a flags value of 0 means autodetection)	3352	// (remember that a flags value of 0 means autodetection)
3034	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3353	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3035	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3354	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3036	: 0;	3355	: 0;
…		…
3050	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3369	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3051		3370
3052	struct ev_loop *loop = ev_default_init (0);	3371	struct ev_loop *loop = ev_default_init (0);
3053	struct ev_loop *loop_socket = 0;	3372	struct ev_loop *loop_socket = 0;
3054	ev_embed embed;	3373	ev_embed embed;
3055		3374
3056	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3375	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3057	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3376	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3058	{	3377	{
3059	ev_embed_init (&embed, 0, loop_socket);	3378	ev_embed_init (&embed, 0, loop_socket);
3060	ev_embed_start (loop, &embed);	3379	ev_embed_start (loop, &embed);
…		…
3068		3387
3069	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3388	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3070		3389
3071	Fork watchers are called when a C<fork ()> was detected (usually because	3390	Fork watchers are called when a C<fork ()> was detected (usually because
3072	whoever is a good citizen cared to tell libev about it by calling	3391	whoever is a good citizen cared to tell libev about it by calling
3073	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3392	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3074	event loop blocks next and before C<ev_check> watchers are being called,	3393	and before C<ev_check> watchers are being called, and only in the child
3075	and only in the child after the fork. If whoever good citizen calling	3394	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3076	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3395	and calls it in the wrong process, the fork handlers will be invoked, too,
3077	handlers will be invoked, too, of course.	3396	of course.
3078		3397
3079	=head3 The special problem of life after fork - how is it possible?	3398	=head3 The special problem of life after fork - how is it possible?
3080		3399
3081	Most uses of C<fork()> consist of forking, then some simple calls to set	3400	Most uses of C<fork ()> consist of forking, then some simple calls to set
3082	up/change the process environment, followed by a call to C<exec()>. This	3401	up/change the process environment, followed by a call to C<exec()>. This
3083	sequence should be handled by libev without any problems.	3402	sequence should be handled by libev without any problems.
3084		3403
3085	This changes when the application actually wants to do event handling	3404	This changes when the application actually wants to do event handling
3086	in the child, or both parent in child, in effect "continuing" after the	3405	in the child, or both parent in child, in effect "continuing" after the
…		…
3163	atexit (program_exits);	3482	atexit (program_exits);
3164		3483
3165		3484
3166	=head2 C<ev_async> - how to wake up an event loop	3485	=head2 C<ev_async> - how to wake up an event loop
3167		3486
3168	In general, you cannot use an C<ev_run> from multiple threads or other	3487	In general, you cannot use an C<ev_loop> from multiple threads or other
3169	asynchronous sources such as signal handlers (as opposed to multiple event	3488	asynchronous sources such as signal handlers (as opposed to multiple event
3170	loops - those are of course safe to use in different threads).	3489	loops - those are of course safe to use in different threads).
3171		3490
3172	Sometimes, however, you need to wake up an event loop you do not control,	3491	Sometimes, however, you need to wake up an event loop you do not control,
3173	for example because it belongs to another thread. This is what C<ev_async>	3492	for example because it belongs to another thread. This is what C<ev_async>
…		…
3175	it by calling C<ev_async_send>, which is thread- and signal safe.	3494	it by calling C<ev_async_send>, which is thread- and signal safe.
3176		3495
3177	This functionality is very similar to C<ev_signal> watchers, as signals,	3496	This functionality is very similar to C<ev_signal> watchers, as signals,
3178	too, are asynchronous in nature, and signals, too, will be compressed	3497	too, are asynchronous in nature, and signals, too, will be compressed
3179	(i.e. the number of callback invocations may be less than the number of	3498	(i.e. the number of callback invocations may be less than the number of
3180	C<ev_async_sent> calls).	3499	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3181		3500	of "global async watchers" by using a watcher on an otherwise unused
3182	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3501	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3183	just the default loop.	3502	even without knowing which loop owns the signal.
3184		3503
3185	=head3 Queueing	3504	=head3 Queueing
3186		3505
3187	C<ev_async> does not support queueing of data in any way. The reason	3506	C<ev_async> does not support queueing of data in any way. The reason
3188	is that the author does not know of a simple (or any) algorithm for a	3507	is that the author does not know of a simple (or any) algorithm for a
…		…
3280	trust me.	3599	trust me.
3281		3600
3282	=item ev_async_send (loop, ev_async *)	3601	=item ev_async_send (loop, ev_async *)
3283		3602
3284	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3603	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3285	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3604	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3605	returns.
		3606
3286	C<ev_feed_event>, this call is safe to do from other threads, signal or	3607	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3287	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3608	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3288	section below on what exactly this means).	3609	embedding section below on what exactly this means).
3289		3610
3290	Note that, as with other watchers in libev, multiple events might get	3611	Note that, as with other watchers in libev, multiple events might get
3291	compressed into a single callback invocation (another way to look at this	3612	compressed into a single callback invocation (another way to look at
3292	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3613	this is that C<ev_async> watchers are level-triggered: they are set on
3293	reset when the event loop detects that).	3614	C<ev_async_send>, reset when the event loop detects that).
3294		3615
3295	This call incurs the overhead of a system call only once per event loop	3616	This call incurs the overhead of at most one extra system call per event
3296	iteration, so while the overhead might be noticeable, it doesn't apply to	3617	loop iteration, if the event loop is blocked, and no syscall at all if
3297	repeated calls to C<ev_async_send> for the same event loop.	3618	the event loop (or your program) is processing events. That means that
		3619	repeated calls are basically free (there is no need to avoid calls for
		3620	performance reasons) and that the overhead becomes smaller (typically
		3621	zero) under load.
3298		3622
3299	=item bool = ev_async_pending (ev_async *)	3623	=item bool = ev_async_pending (ev_async *)
3300		3624
3301	Returns a non-zero value when C<ev_async_send> has been called on the	3625	Returns a non-zero value when C<ev_async_send> has been called on the
3302	watcher but the event has not yet been processed (or even noted) by the	3626	watcher but the event has not yet been processed (or even noted) by the
…		…
3319		3643
3320	There are some other functions of possible interest. Described. Here. Now.	3644	There are some other functions of possible interest. Described. Here. Now.
3321		3645
3322	=over 4	3646	=over 4
3323		3647
3324	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3648	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3325		3649
3326	This function combines a simple timer and an I/O watcher, calls your	3650	This function combines a simple timer and an I/O watcher, calls your
3327	callback on whichever event happens first and automatically stops both	3651	callback on whichever event happens first and automatically stops both
3328	watchers. This is useful if you want to wait for a single event on an fd	3652	watchers. This is useful if you want to wait for a single event on an fd
3329	or timeout without having to allocate/configure/start/stop/free one or	3653	or timeout without having to allocate/configure/start/stop/free one or
…		…
3357	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3681	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3358		3682
3359	=item ev_feed_fd_event (loop, int fd, int revents)	3683	=item ev_feed_fd_event (loop, int fd, int revents)
3360		3684
3361	Feed an event on the given fd, as if a file descriptor backend detected	3685	Feed an event on the given fd, as if a file descriptor backend detected
3362	the given events it.	3686	the given events.
3363		3687
3364	=item ev_feed_signal_event (loop, int signum)	3688	=item ev_feed_signal_event (loop, int signum)
3365		3689
3366	Feed an event as if the given signal occurred (C<loop> must be the default	3690	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3367	loop!).	3691	which is async-safe.
3368		3692
3369	=back	3693	=back
3370		3694
3371		3695
3372	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)	3696	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
3373		3697
3374	This section explains some common idioms that are not immediately	3698	This section explains some common idioms that are not immediately
3375	obvious. Note that examples are sprinkled over the whole manual, and this	3699	obvious. Note that examples are sprinkled over the whole manual, and this
3376	section only contains stuff that wouldn't fit anywhere else.	3700	section only contains stuff that wouldn't fit anywhere else.
3377		3701
3378	=over 4	3702	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3379		3703
3380	=item Model/nested event loop invocations and exit conditions.	3704	Each watcher has, by default, a C<void *data> member that you can read
		3705	or modify at any time: libev will completely ignore it. This can be used
		3706	to associate arbitrary data with your watcher. If you need more data and
		3707	don't want to allocate memory separately and store a pointer to it in that
		3708	data member, you can also "subclass" the watcher type and provide your own
		3709	data:
		3710
		3711	struct my_io
		3712	{
		3713	ev_io io;
		3714	int otherfd;
		3715	void *somedata;
		3716	struct whatever *mostinteresting;
		3717	};
		3718
		3719	...
		3720	struct my_io w;
		3721	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3722
		3723	And since your callback will be called with a pointer to the watcher, you
		3724	can cast it back to your own type:
		3725
		3726	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3727	{
		3728	struct my_io *w = (struct my_io *)w_;
		3729	...
		3730	}
		3731
		3732	More interesting and less C-conformant ways of casting your callback
		3733	function type instead have been omitted.
		3734
		3735	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3736
		3737	Another common scenario is to use some data structure with multiple
		3738	embedded watchers, in effect creating your own watcher that combines
		3739	multiple libev event sources into one "super-watcher":
		3740
		3741	struct my_biggy
		3742	{
		3743	int some_data;
		3744	ev_timer t1;
		3745	ev_timer t2;
		3746	}
		3747
		3748	In this case getting the pointer to C<my_biggy> is a bit more
		3749	complicated: Either you store the address of your C<my_biggy> struct in
		3750	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3751	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3752	real programmers):
		3753
		3754	#include <stddef.h>
		3755
		3756	static void
		3757	t1_cb (EV_P_ ev_timer *w, int revents)
		3758	{
		3759	struct my_biggy big = (struct my_biggy *)
		3760	(((char *)w) - offsetof (struct my_biggy, t1));
		3761	}
		3762
		3763	static void
		3764	t2_cb (EV_P_ ev_timer *w, int revents)
		3765	{
		3766	struct my_biggy big = (struct my_biggy *)
		3767	(((char *)w) - offsetof (struct my_biggy, t2));
		3768	}
		3769
		3770	=head2 AVOIDING FINISHING BEFORE RETURNING
		3771
		3772	Often you have structures like this in event-based programs:
		3773
		3774	callback ()
		3775	{
		3776	free (request);
		3777	}
		3778
		3779	request = start_new_request (..., callback);
		3780
		3781	The intent is to start some "lengthy" operation. The C<request> could be
		3782	used to cancel the operation, or do other things with it.
		3783
		3784	It's not uncommon to have code paths in C<start_new_request> that
		3785	immediately invoke the callback, for example, to report errors. Or you add
		3786	some caching layer that finds that it can skip the lengthy aspects of the
		3787	operation and simply invoke the callback with the result.
		3788
		3789	The problem here is that this will happen I<before> C<start_new_request>
		3790	has returned, so C<request> is not set.
		3791
		3792	Even if you pass the request by some safer means to the callback, you
		3793	might want to do something to the request after starting it, such as
		3794	canceling it, which probably isn't working so well when the callback has
		3795	already been invoked.
		3796
		3797	A common way around all these issues is to make sure that
		3798	C<start_new_request> I<always> returns before the callback is invoked. If
		3799	C<start_new_request> immediately knows the result, it can artificially
		3800	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3801	example, or more sneakily, by reusing an existing (stopped) watcher and
		3802	pushing it into the pending queue:
		3803
		3804	ev_set_cb (watcher, callback);
		3805	ev_feed_event (EV_A_ watcher, 0);
		3806
		3807	This way, C<start_new_request> can safely return before the callback is
		3808	invoked, while not delaying callback invocation too much.
		3809
		3810	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3381		3811
3382	Often (especially in GUI toolkits) there are places where you have	3812	Often (especially in GUI toolkits) there are places where you have
3383	I<modal> interaction, which is most easily implemented by recursively	3813	I<modal> interaction, which is most easily implemented by recursively
3384	invoking C<ev_run>.	3814	invoking C<ev_run>.
3385		3815
3386	This brings the problem of exiting - a callback might want to finish the	3816	This brings the problem of exiting - a callback might want to finish the
3387	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but	3817	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
3388	a modal "Are you sure?" dialog is still waiting), or just the nested one	3818	a modal "Are you sure?" dialog is still waiting), or just the nested one
3389	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some	3819	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
3390	other combination: In these cases, C<ev_break> will not work alone.	3820	other combination: In these cases, a simple C<ev_break> will not work.
3391		3821
3392	The solution is to maintain "break this loop" variable for each C<ev_run>	3822	The solution is to maintain "break this loop" variable for each C<ev_run>
3393	invocation, and use a loop around C<ev_run> until the condition is	3823	invocation, and use a loop around C<ev_run> until the condition is
3394	triggered, using C<EVRUN_ONCE>:	3824	triggered, using C<EVRUN_ONCE>:
3395		3825
…		…
3397	int exit_main_loop = 0;	3827	int exit_main_loop = 0;
3398		3828
3399	while (!exit_main_loop)	3829	while (!exit_main_loop)
3400	ev_run (EV_DEFAULT_ EVRUN_ONCE);	3830	ev_run (EV_DEFAULT_ EVRUN_ONCE);
3401		3831
3402	// in a model watcher	3832	// in a modal watcher
3403	int exit_nested_loop = 0;	3833	int exit_nested_loop = 0;
3404		3834
3405	while (!exit_nested_loop)	3835	while (!exit_nested_loop)
3406	ev_run (EV_A_ EVRUN_ONCE);	3836	ev_run (EV_A_ EVRUN_ONCE);
3407		3837
…		…
3414	exit_main_loop = 1;	3844	exit_main_loop = 1;
3415		3845
3416	// exit both	3846	// exit both
3417	exit_main_loop = exit_nested_loop = 1;	3847	exit_main_loop = exit_nested_loop = 1;
3418		3848
3419	=back	3849	=head2 THREAD LOCKING EXAMPLE
		3850
		3851	Here is a fictitious example of how to run an event loop in a different
		3852	thread from where callbacks are being invoked and watchers are
		3853	created/added/removed.
		3854
		3855	For a real-world example, see the C<EV::Loop::Async> perl module,
		3856	which uses exactly this technique (which is suited for many high-level
		3857	languages).
		3858
		3859	The example uses a pthread mutex to protect the loop data, a condition
		3860	variable to wait for callback invocations, an async watcher to notify the
		3861	event loop thread and an unspecified mechanism to wake up the main thread.
		3862
		3863	First, you need to associate some data with the event loop:
		3864
		3865	typedef struct {
		3866	mutex_t lock; /* global loop lock */
		3867	ev_async async_w;
		3868	thread_t tid;
		3869	cond_t invoke_cv;
		3870	} userdata;
		3871
		3872	void prepare_loop (EV_P)
		3873	{
		3874	// for simplicity, we use a static userdata struct.
		3875	static userdata u;
		3876
		3877	ev_async_init (&u->async_w, async_cb);
		3878	ev_async_start (EV_A_ &u->async_w);
		3879
		3880	pthread_mutex_init (&u->lock, 0);
		3881	pthread_cond_init (&u->invoke_cv, 0);
		3882
		3883	// now associate this with the loop
		3884	ev_set_userdata (EV_A_ u);
		3885	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3886	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3887
		3888	// then create the thread running ev_run
		3889	pthread_create (&u->tid, 0, l_run, EV_A);
		3890	}
		3891
		3892	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3893	solely to wake up the event loop so it takes notice of any new watchers
		3894	that might have been added:
		3895
		3896	static void
		3897	async_cb (EV_P_ ev_async *w, int revents)
		3898	{
		3899	// just used for the side effects
		3900	}
		3901
		3902	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3903	protecting the loop data, respectively.
		3904
		3905	static void
		3906	l_release (EV_P)
		3907	{
		3908	userdata *u = ev_userdata (EV_A);
		3909	pthread_mutex_unlock (&u->lock);
		3910	}
		3911
		3912	static void
		3913	l_acquire (EV_P)
		3914	{
		3915	userdata *u = ev_userdata (EV_A);
		3916	pthread_mutex_lock (&u->lock);
		3917	}
		3918
		3919	The event loop thread first acquires the mutex, and then jumps straight
		3920	into C<ev_run>:
		3921
		3922	void *
		3923	l_run (void *thr_arg)
		3924	{
		3925	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3926
		3927	l_acquire (EV_A);
		3928	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3929	ev_run (EV_A_ 0);
		3930	l_release (EV_A);
		3931
		3932	return 0;
		3933	}
		3934
		3935	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3936	signal the main thread via some unspecified mechanism (signals? pipe
		3937	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3938	have been called (in a while loop because a) spurious wakeups are possible
		3939	and b) skipping inter-thread-communication when there are no pending
		3940	watchers is very beneficial):
		3941
		3942	static void
		3943	l_invoke (EV_P)
		3944	{
		3945	userdata *u = ev_userdata (EV_A);
		3946
		3947	while (ev_pending_count (EV_A))
		3948	{
		3949	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3950	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3951	}
		3952	}
		3953
		3954	Now, whenever the main thread gets told to invoke pending watchers, it
		3955	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3956	thread to continue:
		3957
		3958	static void
		3959	real_invoke_pending (EV_P)
		3960	{
		3961	userdata *u = ev_userdata (EV_A);
		3962
		3963	pthread_mutex_lock (&u->lock);
		3964	ev_invoke_pending (EV_A);
		3965	pthread_cond_signal (&u->invoke_cv);
		3966	pthread_mutex_unlock (&u->lock);
		3967	}
		3968
		3969	Whenever you want to start/stop a watcher or do other modifications to an
		3970	event loop, you will now have to lock:
		3971
		3972	ev_timer timeout_watcher;
		3973	userdata *u = ev_userdata (EV_A);
		3974
		3975	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3976
		3977	pthread_mutex_lock (&u->lock);
		3978	ev_timer_start (EV_A_ &timeout_watcher);
		3979	ev_async_send (EV_A_ &u->async_w);
		3980	pthread_mutex_unlock (&u->lock);
		3981
		3982	Note that sending the C<ev_async> watcher is required because otherwise
		3983	an event loop currently blocking in the kernel will have no knowledge
		3984	about the newly added timer. By waking up the loop it will pick up any new
		3985	watchers in the next event loop iteration.
		3986
		3987	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3988
		3989	While the overhead of a callback that e.g. schedules a thread is small, it
		3990	is still an overhead. If you embed libev, and your main usage is with some
		3991	kind of threads or coroutines, you might want to customise libev so that
		3992	doesn't need callbacks anymore.
		3993
		3994	Imagine you have coroutines that you can switch to using a function
		3995	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3996	and that due to some magic, the currently active coroutine is stored in a
		3997	global called C<current_coro>. Then you can build your own "wait for libev
		3998	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3999	the differing C<;> conventions):
		4000
		4001	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4002	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4003
		4004	That means instead of having a C callback function, you store the
		4005	coroutine to switch to in each watcher, and instead of having libev call
		4006	your callback, you instead have it switch to that coroutine.
		4007
		4008	A coroutine might now wait for an event with a function called
		4009	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		4010	matter when, or whether the watcher is active or not when this function is
		4011	called):
		4012
		4013	void
		4014	wait_for_event (ev_watcher *w)
		4015	{
		4016	ev_set_cb (w, current_coro);
		4017	switch_to (libev_coro);
		4018	}
		4019
		4020	That basically suspends the coroutine inside C<wait_for_event> and
		4021	continues the libev coroutine, which, when appropriate, switches back to
		4022	this or any other coroutine.
		4023
		4024	You can do similar tricks if you have, say, threads with an event queue -
		4025	instead of storing a coroutine, you store the queue object and instead of
		4026	switching to a coroutine, you push the watcher onto the queue and notify
		4027	any waiters.
		4028
		4029	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		4030	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		4031
		4032	// my_ev.h
		4033	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4034	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4035	#include "../libev/ev.h"
		4036
		4037	// my_ev.c
		4038	#define EV_H "my_ev.h"
		4039	#include "../libev/ev.c"
		4040
		4041	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4042	F<my_ev.c> into your project. When properly specifying include paths, you
		4043	can even use F<ev.h> as header file name directly.
3420		4044
3421		4045
3422	=head1 LIBEVENT EMULATION	4046	=head1 LIBEVENT EMULATION
3423		4047
3424	Libev offers a compatibility emulation layer for libevent. It cannot	4048	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3427	=over 4	4051	=over 4
3428		4052
3429	=item * Only the libevent-1.4.1-beta API is being emulated.	4053	=item * Only the libevent-1.4.1-beta API is being emulated.
3430		4054
3431	This was the newest libevent version available when libev was implemented,	4055	This was the newest libevent version available when libev was implemented,
3432	and is still mostly uncanged in 2010.	4056	and is still mostly unchanged in 2010.
3433		4057
3434	=item * Use it by including <event.h>, as usual.	4058	=item * Use it by including <event.h>, as usual.
3435		4059
3436	=item * The following members are fully supported: ev_base, ev_callback,	4060	=item * The following members are fully supported: ev_base, ev_callback,
3437	ev_arg, ev_fd, ev_res, ev_events.	4061	ev_arg, ev_fd, ev_res, ev_events.
…		…
3454		4078
3455	=back	4079	=back
3456		4080
3457	=head1 C++ SUPPORT	4081	=head1 C++ SUPPORT
3458		4082
		4083	=head2 C API
		4084
		4085	The normal C API should work fine when used from C++: both ev.h and the
		4086	libev sources can be compiled as C++. Therefore, code that uses the C API
		4087	will work fine.
		4088
		4089	Proper exception specifications might have to be added to callbacks passed
		4090	to libev: exceptions may be thrown only from watcher callbacks, all other
		4091	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4092	callbacks) must not throw exceptions, and might need a C<noexcept>
		4093	specification. If you have code that needs to be compiled as both C and
		4094	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4095
		4096	static void
		4097	fatal_error (const char *msg) EV_NOEXCEPT
		4098	{
		4099	perror (msg);
		4100	abort ();
		4101	}
		4102
		4103	...
		4104	ev_set_syserr_cb (fatal_error);
		4105
		4106	The only API functions that can currently throw exceptions are C<ev_run>,
		4107	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4108	because it runs cleanup watchers).
		4109
		4110	Throwing exceptions in watcher callbacks is only supported if libev itself
		4111	is compiled with a C++ compiler or your C and C++ environments allow
		4112	throwing exceptions through C libraries (most do).
		4113
		4114	=head2 C++ API
		4115
3459	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4116	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3460	you to use some convenience methods to start/stop watchers and also change	4117	you to use some convenience methods to start/stop watchers and also change
3461	the callback model to a model using method callbacks on objects.	4118	the callback model to a model using method callbacks on objects.
3462		4119
3463	To use it,	4120	To use it,
3464		4121
3465	#include <ev++.h>	4122	#include <ev++.h>
3466		4123
3467	This automatically includes F<ev.h> and puts all of its definitions (many	4124	This automatically includes F<ev.h> and puts all of its definitions (many
3468	of them macros) into the global namespace. All C++ specific things are	4125	of them macros) into the global namespace. All C++ specific things are
3469	put into the C<ev> namespace. It should support all the same embedding	4126	put into the C<ev> namespace. It should support all the same embedding
…		…
3478	with C<operator ()> can be used as callbacks. Other types should be easy	4135	with C<operator ()> can be used as callbacks. Other types should be easy
3479	to add as long as they only need one additional pointer for context. If	4136	to add as long as they only need one additional pointer for context. If
3480	you need support for other types of functors please contact the author	4137	you need support for other types of functors please contact the author
3481	(preferably after implementing it).	4138	(preferably after implementing it).
3482		4139
		4140	For all this to work, your C++ compiler either has to use the same calling
		4141	conventions as your C compiler (for static member functions), or you have
		4142	to embed libev and compile libev itself as C++.
		4143
3483	Here is a list of things available in the C<ev> namespace:	4144	Here is a list of things available in the C<ev> namespace:
3484		4145
3485	=over 4	4146	=over 4
3486		4147
3487	=item C<ev::READ>, C<ev::WRITE> etc.	4148	=item C<ev::READ>, C<ev::WRITE> etc.
…		…
3496	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4157	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3497		4158
3498	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4159	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3499	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4160	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3500	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4161	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3501	defines by many implementations.	4162	defined by many implementations.
3502		4163
3503	All of those classes have these methods:	4164	All of those classes have these methods:
3504		4165
3505	=over 4	4166	=over 4
3506		4167
…		…
3568	void operator() (ev::io &w, int revents)	4229	void operator() (ev::io &w, int revents)
3569	{	4230	{
3570	...	4231	...
3571	}	4232	}
3572	}	4233	}
3573		4234
3574	myfunctor f;	4235	myfunctor f;
3575		4236
3576	ev::io w;	4237	ev::io w;
3577	w.set (&f);	4238	w.set (&f);
3578		4239
…		…
3596	Associates a different C<struct ev_loop> with this watcher. You can only	4257	Associates a different C<struct ev_loop> with this watcher. You can only
3597	do this when the watcher is inactive (and not pending either).	4258	do this when the watcher is inactive (and not pending either).
3598		4259
3599	=item w->set ([arguments])	4260	=item w->set ([arguments])
3600		4261
3601	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4262	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3602	method or a suitable start method must be called at least once. Unlike the	4263	with the same arguments. Either this method or a suitable start method
3603	C counterpart, an active watcher gets automatically stopped and restarted	4264	must be called at least once. Unlike the C counterpart, an active watcher
3604	when reconfiguring it with this method.	4265	gets automatically stopped and restarted when reconfiguring it with this
		4266	method.
		4267
		4268	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4269	clashing with the C<set (loop)> method.
		4270
		4271	For C<ev::io> watchers there is an additional C<set> method that acepts a
		4272	new event mask only, and internally calls C<ev_io_modfify>.
3605		4273
3606	=item w->start ()	4274	=item w->start ()
3607		4275
3608	Starts the watcher. Note that there is no C<loop> argument, as the	4276	Starts the watcher. Note that there is no C<loop> argument, as the
3609	constructor already stores the event loop.	4277	constructor already stores the event loop.
…		…
3639	watchers in the constructor.	4307	watchers in the constructor.
3640		4308
3641	class myclass	4309	class myclass
3642	{	4310	{
3643	ev::io io ; void io_cb (ev::io &w, int revents);	4311	ev::io io ; void io_cb (ev::io &w, int revents);
3644	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4312	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3645	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4313	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3646		4314
3647	myclass (int fd)	4315	myclass (int fd)
3648	{	4316	{
3649	io .set <myclass, &myclass::io_cb > (this);	4317	io .set <myclass, &myclass::io_cb > (this);
…		…
3700	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4368	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3701		4369
3702	=item D	4370	=item D
3703		4371
3704	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4372	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3705	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4373	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3706		4374
3707	=item Ocaml	4375	=item Ocaml
3708		4376
3709	Erkki Seppala has written Ocaml bindings for libev, to be found at	4377	Erkki Seppala has written Ocaml bindings for libev, to be found at
3710	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4378	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3713		4381
3714	Brian Maher has written a partial interface to libev for lua (at the	4382	Brian Maher has written a partial interface to libev for lua (at the
3715	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4383	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3716	L<http://github.com/brimworks/lua-ev>.	4384	L<http://github.com/brimworks/lua-ev>.
3717		4385
		4386	=item Javascript
		4387
		4388	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4389
		4390	=item Others
		4391
		4392	There are others, and I stopped counting.
		4393
3718	=back	4394	=back
3719		4395
3720		4396
3721	=head1 MACRO MAGIC	4397	=head1 MACRO MAGIC
3722		4398
…		…
3758	suitable for use with C<EV_A>.	4434	suitable for use with C<EV_A>.
3759		4435
3760	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4436	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3761		4437
3762	Similar to the other two macros, this gives you the value of the default	4438	Similar to the other two macros, this gives you the value of the default
3763	loop, if multiple loops are supported ("ev loop default").	4439	loop, if multiple loops are supported ("ev loop default"). The default loop
		4440	will be initialised if it isn't already initialised.
		4441
		4442	For non-multiplicity builds, these macros do nothing, so you always have
		4443	to initialise the loop somewhere.
3764		4444
3765	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4445	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3766		4446
3767	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4447	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3768	default loop has been initialised (C<UC> == unchecked). Their behaviour	4448	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3835	ev_vars.h	4515	ev_vars.h
3836	ev_wrap.h	4516	ev_wrap.h
3837		4517
3838	ev_win32.c required on win32 platforms only	4518	ev_win32.c required on win32 platforms only
3839		4519
3840	ev_select.c only when select backend is enabled (which is enabled by default)	4520	ev_select.c only when select backend is enabled
3841	ev_poll.c only when poll backend is enabled (disabled by default)	4521	ev_poll.c only when poll backend is enabled
3842	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4522	ev_epoll.c only when the epoll backend is enabled
		4523	ev_linuxaio.c only when the linux aio backend is enabled
		4524	ev_iouring.c only when the linux io_uring backend is enabled
3843	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4525	ev_kqueue.c only when the kqueue backend is enabled
3844	ev_port.c only when the solaris port backend is enabled (disabled by default)	4526	ev_port.c only when the solaris port backend is enabled
3845		4527
3846	F<ev.c> includes the backend files directly when enabled, so you only need	4528	F<ev.c> includes the backend files directly when enabled, so you only need
3847	to compile this single file.	4529	to compile this single file.
3848		4530
3849	=head3 LIBEVENT COMPATIBILITY API	4531	=head3 LIBEVENT COMPATIBILITY API
…		…
3913	supported). It will also not define any of the structs usually found in	4595	supported). It will also not define any of the structs usually found in
3914	F<event.h> that are not directly supported by the libev core alone.	4596	F<event.h> that are not directly supported by the libev core alone.
3915		4597
3916	In standalone mode, libev will still try to automatically deduce the	4598	In standalone mode, libev will still try to automatically deduce the
3917	configuration, but has to be more conservative.	4599	configuration, but has to be more conservative.
		4600
		4601	=item EV_USE_FLOOR
		4602
		4603	If defined to be C<1>, libev will use the C<floor ()> function for its
		4604	periodic reschedule calculations, otherwise libev will fall back on a
		4605	portable (slower) implementation. If you enable this, you usually have to
		4606	link against libm or something equivalent. Enabling this when the C<floor>
		4607	function is not available will fail, so the safe default is to not enable
		4608	this.
3918		4609
3919	=item EV_USE_MONOTONIC	4610	=item EV_USE_MONOTONIC
3920		4611
3921	If defined to be C<1>, libev will try to detect the availability of the	4612	If defined to be C<1>, libev will try to detect the availability of the
3922	monotonic clock option at both compile time and runtime. Otherwise no	4613	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3959	available and will probe for kernel support at runtime. This will improve	4650	available and will probe for kernel support at runtime. This will improve
3960	C<ev_signal> and C<ev_async> performance and reduce resource consumption.	4651	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
3961	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc	4652	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
3962	2.7 or newer, otherwise disabled.	4653	2.7 or newer, otherwise disabled.
3963		4654
		4655	=item EV_USE_SIGNALFD
		4656
		4657	If defined to be C<1>, then libev will assume that C<signalfd ()> is
		4658	available and will probe for kernel support at runtime. This enables
		4659	the use of EVFLAG_SIGNALFD for faster and simpler signal handling. If
		4660	undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4661	2.7 or newer, otherwise disabled.
		4662
		4663	=item EV_USE_TIMERFD
		4664
		4665	If defined to be C<1>, then libev will assume that C<timerfd ()> is
		4666	available and will probe for kernel support at runtime. This allows
		4667	libev to detect time jumps accurately. If undefined, it will be enabled
		4668	if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
		4669	C<TFD_TIMER_CANCEL_ON_SET>, otherwise disabled.
		4670
		4671	=item EV_USE_EVENTFD
		4672
		4673	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4674	available and will probe for kernel support at runtime. This will improve
		4675	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4676	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4677	2.7 or newer, otherwise disabled.
		4678
3964	=item EV_USE_SELECT	4679	=item EV_USE_SELECT
3965		4680
3966	If undefined or defined to be C<1>, libev will compile in support for the	4681	If undefined or defined to be C<1>, libev will compile in support for the
3967	C<select>(2) backend. No attempt at auto-detection will be done: if no	4682	C<select>(2) backend. No attempt at auto-detection will be done: if no
3968	other method takes over, select will be it. Otherwise the select backend	4683	other method takes over, select will be it. Otherwise the select backend
…		…
4008	If programs implement their own fd to handle mapping on win32, then this	4723	If programs implement their own fd to handle mapping on win32, then this
4009	macro can be used to override the C<close> function, useful to unregister	4724	macro can be used to override the C<close> function, useful to unregister
4010	file descriptors again. Note that the replacement function has to close	4725	file descriptors again. Note that the replacement function has to close
4011	the underlying OS handle.	4726	the underlying OS handle.
4012		4727
		4728	=item EV_USE_WSASOCKET
		4729
		4730	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4731	communication socket, which works better in some environments. Otherwise,
		4732	the normal C<socket> function will be used, which works better in other
		4733	environments.
		4734
4013	=item EV_USE_POLL	4735	=item EV_USE_POLL
4014		4736
4015	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4737	If defined to be C<1>, libev will compile in support for the C<poll>(2)
4016	backend. Otherwise it will be enabled on non-win32 platforms. It	4738	backend. Otherwise it will be enabled on non-win32 platforms. It
4017	takes precedence over select.	4739	takes precedence over select.
…		…
4021	If defined to be C<1>, libev will compile in support for the Linux	4743	If defined to be C<1>, libev will compile in support for the Linux
4022	C<epoll>(7) backend. Its availability will be detected at runtime,	4744	C<epoll>(7) backend. Its availability will be detected at runtime,
4023	otherwise another method will be used as fallback. This is the preferred	4745	otherwise another method will be used as fallback. This is the preferred
4024	backend for GNU/Linux systems. If undefined, it will be enabled if the	4746	backend for GNU/Linux systems. If undefined, it will be enabled if the
4025	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4747	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4748
		4749	=item EV_USE_LINUXAIO
		4750
		4751	If defined to be C<1>, libev will compile in support for the Linux aio
		4752	backend (C<EV_USE_EPOLL> must also be enabled). If undefined, it will be
		4753	enabled on linux, otherwise disabled.
		4754
		4755	=item EV_USE_IOURING
		4756
		4757	If defined to be C<1>, libev will compile in support for the Linux
		4758	io_uring backend (C<EV_USE_EPOLL> must also be enabled). Due to it's
		4759	current limitations it has to be requested explicitly. If undefined, it
		4760	will be enabled on linux, otherwise disabled.
4026		4761
4027	=item EV_USE_KQUEUE	4762	=item EV_USE_KQUEUE
4028		4763
4029	If defined to be C<1>, libev will compile in support for the BSD style	4764	If defined to be C<1>, libev will compile in support for the BSD style
4030	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4765	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
4052	If defined to be C<1>, libev will compile in support for the Linux inotify	4787	If defined to be C<1>, libev will compile in support for the Linux inotify
4053	interface to speed up C<ev_stat> watchers. Its actual availability will	4788	interface to speed up C<ev_stat> watchers. Its actual availability will
4054	be detected at runtime. If undefined, it will be enabled if the headers	4789	be detected at runtime. If undefined, it will be enabled if the headers
4055	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4790	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4056		4791
		4792	=item EV_NO_SMP
		4793
		4794	If defined to be C<1>, libev will assume that memory is always coherent
		4795	between threads, that is, threads can be used, but threads never run on
		4796	different cpus (or different cpu cores). This reduces dependencies
		4797	and makes libev faster.
		4798
		4799	=item EV_NO_THREADS
		4800
		4801	If defined to be C<1>, libev will assume that it will never be called from
		4802	different threads (that includes signal handlers), which is a stronger
		4803	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4804	libev faster.
		4805
4057	=item EV_ATOMIC_T	4806	=item EV_ATOMIC_T
4058		4807
4059	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4808	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4060	access is atomic with respect to other threads or signal contexts. No such	4809	access is atomic with respect to other threads or signal contexts. No
4061	type is easily found in the C language, so you can provide your own type	4810	such type is easily found in the C language, so you can provide your own
4062	that you know is safe for your purposes. It is used both for signal handler "locking"	4811	type that you know is safe for your purposes. It is used both for signal
4063	as well as for signal and thread safety in C<ev_async> watchers.	4812	handler "locking" as well as for signal and thread safety in C<ev_async>
		4813	watchers.
4064		4814
4065	In the absence of this define, libev will use C<sig_atomic_t volatile>	4815	In the absence of this define, libev will use C<sig_atomic_t volatile>
4066	(from F<signal.h>), which is usually good enough on most platforms.	4816	(from F<signal.h>), which is usually good enough on most platforms.
4067		4817
4068	=item EV_H (h)	4818	=item EV_H (h)
…		…
4095	will have the C<struct ev_loop *> as first argument, and you can create	4845	will have the C<struct ev_loop *> as first argument, and you can create
4096	additional independent event loops. Otherwise there will be no support	4846	additional independent event loops. Otherwise there will be no support
4097	for multiple event loops and there is no first event loop pointer	4847	for multiple event loops and there is no first event loop pointer
4098	argument. Instead, all functions act on the single default loop.	4848	argument. Instead, all functions act on the single default loop.
4099		4849
		4850	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4851	default loop when multiplicity is switched off - you always have to
		4852	initialise the loop manually in this case.
		4853
4100	=item EV_MINPRI	4854	=item EV_MINPRI
4101		4855
4102	=item EV_MAXPRI	4856	=item EV_MAXPRI
4103		4857
4104	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4858	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4140	#define EV_USE_POLL 1	4894	#define EV_USE_POLL 1
4141	#define EV_CHILD_ENABLE 1	4895	#define EV_CHILD_ENABLE 1
4142	#define EV_ASYNC_ENABLE 1	4896	#define EV_ASYNC_ENABLE 1
4143		4897
4144	The actual value is a bitset, it can be a combination of the following	4898	The actual value is a bitset, it can be a combination of the following
4145	values:	4899	values (by default, all of these are enabled):
4146		4900
4147	=over 4	4901	=over 4
4148		4902
4149	=item C<1> - faster/larger code	4903	=item C<1> - faster/larger code
4150		4904
…		…
4154	code size by roughly 30% on amd64).	4908	code size by roughly 30% on amd64).
4155		4909
4156	When optimising for size, use of compiler flags such as C<-Os> with	4910	When optimising for size, use of compiler flags such as C<-Os> with
4157	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4911	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4158	assertions.	4912	assertions.
		4913
		4914	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4915	(e.g. gcc with C<-Os>).
4159		4916
4160	=item C<2> - faster/larger data structures	4917	=item C<2> - faster/larger data structures
4161		4918
4162	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4919	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4163	hash table sizes and so on. This will usually further increase code size	4920	hash table sizes and so on. This will usually further increase code size
4164	and can additionally have an effect on the size of data structures at	4921	and can additionally have an effect on the size of data structures at
4165	runtime.	4922	runtime.
4166		4923
		4924	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4925	(e.g. gcc with C<-Os>).
		4926
4167	=item C<4> - full API configuration	4927	=item C<4> - full API configuration
4168		4928
4169	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4929	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4170	enables multiplicity (C<EV_MULTIPLICITY>=1).	4930	enables multiplicity (C<EV_MULTIPLICITY>=1).
4171		4931
…		…
4201		4961
4202	With an intelligent-enough linker (gcc+binutils are intelligent enough	4962	With an intelligent-enough linker (gcc+binutils are intelligent enough
4203	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4963	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4204	your program might be left out as well - a binary starting a timer and an	4964	your program might be left out as well - a binary starting a timer and an
4205	I/O watcher then might come out at only 5Kb.	4965	I/O watcher then might come out at only 5Kb.
		4966
		4967	=item EV_API_STATIC
		4968
		4969	If this symbol is defined (by default it is not), then all identifiers
		4970	will have static linkage. This means that libev will not export any
		4971	identifiers, and you cannot link against libev anymore. This can be useful
		4972	when you embed libev, only want to use libev functions in a single file,
		4973	and do not want its identifiers to be visible.
		4974
		4975	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4976	wants to use libev.
		4977
		4978	This option only works when libev is compiled with a C compiler, as C++
		4979	doesn't support the required declaration syntax.
4206		4980
4207	=item EV_AVOID_STDIO	4981	=item EV_AVOID_STDIO
4208		4982
4209	If this is set to C<1> at compiletime, then libev will avoid using stdio	4983	If this is set to C<1> at compiletime, then libev will avoid using stdio
4210	functions (printf, scanf, perror etc.). This will increase the code size	4984	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4268	in. If set to C<1>, then verification code will be compiled in, but not	5042	in. If set to C<1>, then verification code will be compiled in, but not
4269	called. If set to C<2>, then the internal verification code will be	5043	called. If set to C<2>, then the internal verification code will be
4270	called once per loop, which can slow down libev. If set to C<3>, then the	5044	called once per loop, which can slow down libev. If set to C<3>, then the
4271	verification code will be called very frequently, which will slow down	5045	verification code will be called very frequently, which will slow down
4272	libev considerably.	5046	libev considerably.
		5047
		5048	Verification errors are reported via C's C<assert> mechanism, so if you
		5049	disable that (e.g. by defining C<NDEBUG>) then no errors will be reported.
4273		5050
4274	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it	5051	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
4275	will be C<0>.	5052	will be C<0>.
4276		5053
4277	=item EV_COMMON	5054	=item EV_COMMON
…		…
4354	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5131	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4355		5132
4356	#include "ev_cpp.h"	5133	#include "ev_cpp.h"
4357	#include "ev.c"	5134	#include "ev.c"
4358		5135
4359	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5136	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4360		5137
4361	=head2 THREADS AND COROUTINES	5138	=head2 THREADS AND COROUTINES
4362		5139
4363	=head3 THREADS	5140	=head3 THREADS
4364		5141
…		…
4415	default loop and triggering an C<ev_async> watcher from the default loop	5192	default loop and triggering an C<ev_async> watcher from the default loop
4416	watcher callback into the event loop interested in the signal.	5193	watcher callback into the event loop interested in the signal.
4417		5194
4418	=back	5195	=back
4419		5196
4420	=head4 THREAD LOCKING EXAMPLE	5197	See also L</THREAD LOCKING EXAMPLE>.
4421
4422	Here is a fictitious example of how to run an event loop in a different
4423	thread than where callbacks are being invoked and watchers are
4424	created/added/removed.
4425
4426	For a real-world example, see the C<EV::Loop::Async> perl module,
4427	which uses exactly this technique (which is suited for many high-level
4428	languages).
4429
4430	The example uses a pthread mutex to protect the loop data, a condition
4431	variable to wait for callback invocations, an async watcher to notify the
4432	event loop thread and an unspecified mechanism to wake up the main thread.
4433
4434	First, you need to associate some data with the event loop:
4435
4436	typedef struct {
4437	mutex_t lock; /* global loop lock */
4438	ev_async async_w;
4439	thread_t tid;
4440	cond_t invoke_cv;
4441	} userdata;
4442
4443	void prepare_loop (EV_P)
4444	{
4445	// for simplicity, we use a static userdata struct.
4446	static userdata u;
4447
4448	ev_async_init (&u->async_w, async_cb);
4449	ev_async_start (EV_A_ &u->async_w);
4450
4451	pthread_mutex_init (&u->lock, 0);
4452	pthread_cond_init (&u->invoke_cv, 0);
4453
4454	// now associate this with the loop
4455	ev_set_userdata (EV_A_ u);
4456	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4457	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4458
4459	// then create the thread running ev_loop
4460	pthread_create (&u->tid, 0, l_run, EV_A);
4461	}
4462
4463	The callback for the C<ev_async> watcher does nothing: the watcher is used
4464	solely to wake up the event loop so it takes notice of any new watchers
4465	that might have been added:
4466
4467	static void
4468	async_cb (EV_P_ ev_async *w, int revents)
4469	{
4470	// just used for the side effects
4471	}
4472
4473	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4474	protecting the loop data, respectively.
4475
4476	static void
4477	l_release (EV_P)
4478	{
4479	userdata *u = ev_userdata (EV_A);
4480	pthread_mutex_unlock (&u->lock);
4481	}
4482
4483	static void
4484	l_acquire (EV_P)
4485	{
4486	userdata *u = ev_userdata (EV_A);
4487	pthread_mutex_lock (&u->lock);
4488	}
4489
4490	The event loop thread first acquires the mutex, and then jumps straight
4491	into C<ev_run>:
4492
4493	void *
4494	l_run (void *thr_arg)
4495	{
4496	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4497
4498	l_acquire (EV_A);
4499	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4500	ev_run (EV_A_ 0);
4501	l_release (EV_A);
4502
4503	return 0;
4504	}
4505
4506	Instead of invoking all pending watchers, the C<l_invoke> callback will
4507	signal the main thread via some unspecified mechanism (signals? pipe
4508	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4509	have been called (in a while loop because a) spurious wakeups are possible
4510	and b) skipping inter-thread-communication when there are no pending
4511	watchers is very beneficial):
4512
4513	static void
4514	l_invoke (EV_P)
4515	{
4516	userdata *u = ev_userdata (EV_A);
4517
4518	while (ev_pending_count (EV_A))
4519	{
4520	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4521	pthread_cond_wait (&u->invoke_cv, &u->lock);
4522	}
4523	}
4524
4525	Now, whenever the main thread gets told to invoke pending watchers, it
4526	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4527	thread to continue:
4528
4529	static void
4530	real_invoke_pending (EV_P)
4531	{
4532	userdata *u = ev_userdata (EV_A);
4533
4534	pthread_mutex_lock (&u->lock);
4535	ev_invoke_pending (EV_A);
4536	pthread_cond_signal (&u->invoke_cv);
4537	pthread_mutex_unlock (&u->lock);
4538	}
4539
4540	Whenever you want to start/stop a watcher or do other modifications to an
4541	event loop, you will now have to lock:
4542
4543	ev_timer timeout_watcher;
4544	userdata *u = ev_userdata (EV_A);
4545
4546	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4547
4548	pthread_mutex_lock (&u->lock);
4549	ev_timer_start (EV_A_ &timeout_watcher);
4550	ev_async_send (EV_A_ &u->async_w);
4551	pthread_mutex_unlock (&u->lock);
4552
4553	Note that sending the C<ev_async> watcher is required because otherwise
4554	an event loop currently blocking in the kernel will have no knowledge
4555	about the newly added timer. By waking up the loop it will pick up any new
4556	watchers in the next event loop iteration.
4557		5198
4558	=head3 COROUTINES	5199	=head3 COROUTINES
4559		5200
4560	Libev is very accommodating to coroutines ("cooperative threads"):	5201	Libev is very accommodating to coroutines ("cooperative threads"):
4561	libev fully supports nesting calls to its functions from different	5202	libev fully supports nesting calls to its functions from different
…		…
4726	requires, and its I/O model is fundamentally incompatible with the POSIX	5367	requires, and its I/O model is fundamentally incompatible with the POSIX
4727	model. Libev still offers limited functionality on this platform in	5368	model. Libev still offers limited functionality on this platform in
4728	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5369	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4729	descriptors. This only applies when using Win32 natively, not when using	5370	descriptors. This only applies when using Win32 natively, not when using
4730	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5371	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4731	as every compielr comes with a slightly differently broken/incompatible	5372	as every compiler comes with a slightly differently broken/incompatible
4732	environment.	5373	environment.
4733		5374
4734	Lifting these limitations would basically require the full	5375	Lifting these limitations would basically require the full
4735	re-implementation of the I/O system. If you are into this kind of thing,	5376	re-implementation of the I/O system. If you are into this kind of thing,
4736	then note that glib does exactly that for you in a very portable way (note	5377	then note that glib does exactly that for you in a very portable way (note
…		…
4830	structure (guaranteed by POSIX but not by ISO C for example), but it also	5471	structure (guaranteed by POSIX but not by ISO C for example), but it also
4831	assumes that the same (machine) code can be used to call any watcher	5472	assumes that the same (machine) code can be used to call any watcher
4832	callback: The watcher callbacks have different type signatures, but libev	5473	callback: The watcher callbacks have different type signatures, but libev
4833	calls them using an C<ev_watcher *> internally.	5474	calls them using an C<ev_watcher *> internally.
4834		5475
		5476	=item null pointers and integer zero are represented by 0 bytes
		5477
		5478	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5479	relies on this setting pointers and integers to null.
		5480
4835	=item pointer accesses must be thread-atomic	5481	=item pointer accesses must be thread-atomic
4836		5482
4837	Accessing a pointer value must be atomic, it must both be readable and	5483	Accessing a pointer value must be atomic, it must both be readable and
4838	writable in one piece - this is the case on all current architectures.	5484	writable in one piece - this is the case on all current architectures.
4839		5485
…		…
4852	thread" or will block signals process-wide, both behaviours would	5498	thread" or will block signals process-wide, both behaviours would
4853	be compatible with libev. Interaction between C<sigprocmask> and	5499	be compatible with libev. Interaction between C<sigprocmask> and
4854	C<pthread_sigmask> could complicate things, however.	5500	C<pthread_sigmask> could complicate things, however.
4855		5501
4856	The most portable way to handle signals is to block signals in all threads	5502	The most portable way to handle signals is to block signals in all threads
4857	except the initial one, and run the default loop in the initial thread as	5503	except the initial one, and run the signal handling loop in the initial
4858	well.	5504	thread as well.
4859		5505
4860	=item C<long> must be large enough for common memory allocation sizes	5506	=item C<long> must be large enough for common memory allocation sizes
4861		5507
4862	To improve portability and simplify its API, libev uses C<long> internally	5508	To improve portability and simplify its API, libev uses C<long> internally
4863	instead of C<size_t> when allocating its data structures. On non-POSIX	5509	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4869		5515
4870	The type C<double> is used to represent timestamps. It is required to	5516	The type C<double> is used to represent timestamps. It is required to
4871	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5517	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4872	good enough for at least into the year 4000 with millisecond accuracy	5518	good enough for at least into the year 4000 with millisecond accuracy
4873	(the design goal for libev). This requirement is overfulfilled by	5519	(the design goal for libev). This requirement is overfulfilled by
4874	implementations using IEEE 754, which is basically all existing ones. With	5520	implementations using IEEE 754, which is basically all existing ones.
		5521
4875	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5522	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5523	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5524	is either obsolete or somebody patched it to use C<long double> or
		5525	something like that, just kidding).
4876		5526
4877	=back	5527	=back
4878		5528
4879	If you know of other additional requirements drop me a note.	5529	If you know of other additional requirements drop me a note.
4880		5530
…		…
4942	=item Processing ev_async_send: O(number_of_async_watchers)	5592	=item Processing ev_async_send: O(number_of_async_watchers)
4943		5593
4944	=item Processing signals: O(max_signal_number)	5594	=item Processing signals: O(max_signal_number)
4945		5595
4946	Sending involves a system call I<iff> there were no other C<ev_async_send>	5596	Sending involves a system call I<iff> there were no other C<ev_async_send>
4947	calls in the current loop iteration. Checking for async and signal events	5597	calls in the current loop iteration and the loop is currently
		5598	blocked. Checking for async and signal events involves iterating over all
4948	involves iterating over all running async watchers or all signal numbers.	5599	running async watchers or all signal numbers.
4949		5600
4950	=back	5601	=back
4951		5602
4952		5603
4953	=head1 PORTING FROM LIBEV 3.X TO 4.X	5604	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
4962	=over 4	5613	=over 4
4963		5614
4964	=item C<EV_COMPAT3> backwards compatibility mechanism	5615	=item C<EV_COMPAT3> backwards compatibility mechanism
4965		5616
4966	The backward compatibility mechanism can be controlled by	5617	The backward compatibility mechanism can be controlled by
4967	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5618	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
4968	section.	5619	section.
4969		5620
4970	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5621	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4971		5622
4972	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5623	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
5015	=over 4	5666	=over 4
5016		5667
5017	=item active	5668	=item active
5018		5669
5019	A watcher is active as long as it has been started and not yet stopped.	5670	A watcher is active as long as it has been started and not yet stopped.
5020	See L<WATCHER STATES> for details.	5671	See L</WATCHER STATES> for details.
5021		5672
5022	=item application	5673	=item application
5023		5674
5024	In this document, an application is whatever is using libev.	5675	In this document, an application is whatever is using libev.
5025		5676
…		…
5061	watchers and events.	5712	watchers and events.
5062		5713
5063	=item pending	5714	=item pending
5064		5715
5065	A watcher is pending as soon as the corresponding event has been	5716	A watcher is pending as soon as the corresponding event has been
5066	detected. See L<WATCHER STATES> for details.	5717	detected. See L</WATCHER STATES> for details.
5067		5718
5068	=item real time	5719	=item real time
5069		5720
5070	The physical time that is observed. It is apparently strictly monotonic :)	5721	The physical time that is observed. It is apparently strictly monotonic :)
5071		5722
5072	=item wall-clock time	5723	=item wall-clock time
5073		5724
5074	The time and date as shown on clocks. Unlike real time, it can actually	5725	The time and date as shown on clocks. Unlike real time, it can actually
5075	be wrong and jump forwards and backwards, e.g. when the you adjust your	5726	be wrong and jump forwards and backwards, e.g. when you adjust your
5076	clock.	5727	clock.
5077		5728
5078	=item watcher	5729	=item watcher
5079		5730
5080	A data structure that describes interest in certain events. Watchers need	5731	A data structure that describes interest in certain events. Watchers need
…		…
5083	=back	5734	=back
5084		5735
5085	=head1 AUTHOR	5736	=head1 AUTHOR
5086		5737
5087	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5738	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5088	Magnusson and Emanuele Giaquinta.	5739	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5089		5740

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