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		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	libev - a high performance full-featured event loop written in C	5	libev - a high performance full-featured event loop written in C
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
…		…
58	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
59		61
60	// now wait for events to arrive	62	// now wait for events to arrive
61	ev_run (loop, 0);	63	ev_run (loop, 0);
62		64
63	// unloop was called, so exit	65	// break was called, so exit
64	return 0;	66	return 0;
65	}	67	}
66		68
67	=head1 ABOUT THIS DOCUMENT	69	=head1 ABOUT THIS DOCUMENT
68		70
…		…
82		84
83	=head1 WHAT TO READ WHEN IN A HURRY	85	=head1 WHAT TO READ WHEN IN A HURRY
84		86
85	This manual tries to be very detailed, but unfortunately, this also makes	87	This manual tries to be very detailed, but unfortunately, this also makes
86	it very long. If you just want to know the basics of libev, I suggest	88	it very long. If you just want to know the basics of libev, I suggest
87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and	89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and	90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
89	C<ev_timer> sections in L<WATCHER TYPES>.	91	C<ev_timer> sections in L</WATCHER TYPES>.
90		92
91	=head1 ABOUT LIBEV	93	=head1 ABOUT LIBEV
92		94
93	Libev is an event loop: you register interest in certain events (such as a	95	Libev is an event loop: you register interest in certain events (such as a
94	file descriptor being readable or a timeout occurring), and it will manage	96	file descriptor being readable or a timeout occurring), and it will manage
…		…
103	details of the event, and then hand it over to libev by I<starting> the	105	details of the event, and then hand it over to libev by I<starting> the
104	watcher.	106	watcher.
105		107
106	=head2 FEATURES	108	=head2 FEATURES
107		109
108	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	110	Libev supports C<select>, C<poll>, the Linux-specific aio and C<epoll>
109	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port
110	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	112	mechanisms for file descriptor events (C<ev_io>), the Linux C<inotify>
111	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner	113	interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
112	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative	114	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
113	timers (C<ev_timer>), absolute timers with customised rescheduling	115	timers (C<ev_timer>), absolute timers with customised rescheduling
114	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status	116	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
115	change events (C<ev_child>), and event watchers dealing with the event	117	change events (C<ev_child>), and event watchers dealing with the event
116	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and	118	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
…		…
174	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
175		177
176	Returns the current time as libev would use it. Please note that the	178	Returns the current time as libev would use it. Please note that the
177	C<ev_now> function is usually faster and also often returns the timestamp	179	C<ev_now> function is usually faster and also often returns the timestamp
178	you actually want to know. Also interesting is the combination of	180	you actually want to know. Also interesting is the combination of
179	C<ev_update_now> and C<ev_now>.	181	C<ev_now_update> and C<ev_now>.
180		182
181	=item ev_sleep (ev_tstamp interval)	183	=item ev_sleep (ev_tstamp interval)
182		184
183	Sleep for the given interval: The current thread will be blocked until	185	Sleep for the given interval: The current thread will be blocked
184	either it is interrupted or the given time interval has passed. Basically	186	until either it is interrupted or the given time interval has
		187	passed (approximately - it might return a bit earlier even if not
		188	interrupted). Returns immediately if C<< interval <= 0 >>.
		189
185	this is a sub-second-resolution C<sleep ()>.	190	Basically this is a sub-second-resolution C<sleep ()>.
		191
		192	The range of the C<interval> is limited - libev only guarantees to work
		193	with sleep times of up to one day (C<< interval <= 86400 >>).
186		194
187	=item int ev_version_major ()	195	=item int ev_version_major ()
188		196
189	=item int ev_version_minor ()	197	=item int ev_version_minor ()
190		198
…		…
241	the current system, you would need to look at C<ev_embeddable_backends ()	249	the current system, you would need to look at C<ev_embeddable_backends ()
242	& ev_supported_backends ()>, likewise for recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
243		251
244	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
245		253
246	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
247		255
248	Sets the allocation function to use (the prototype is similar - the	256	Sets the allocation function to use (the prototype is similar - the
249	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	257	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
250	used to allocate and free memory (no surprises here). If it returns zero	258	used to allocate and free memory (no surprises here). If it returns zero
251	when memory needs to be allocated (C<size != 0>), the library might abort	259	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
257		265
258	You could override this function in high-availability programs to, say,	266	You could override this function in high-availability programs to, say,
259	free some memory if it cannot allocate memory, to use a special allocator,	267	free some memory if it cannot allocate memory, to use a special allocator,
260	or even to sleep a while and retry until some memory is available.	268	or even to sleep a while and retry until some memory is available.
261		269
		270	Example: The following is the C<realloc> function that libev itself uses
		271	which should work with C<realloc> and C<free> functions of all kinds and
		272	is probably a good basis for your own implementation.
		273
		274	static void *
		275	ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
		276	{
		277	if (size)
		278	return realloc (ptr, size);
		279
		280	free (ptr);
		281	return 0;
		282	}
		283
262	Example: Replace the libev allocator with one that waits a bit and then	284	Example: Replace the libev allocator with one that waits a bit and then
263	retries (example requires a standards-compliant C<realloc>).	285	retries.
264		286
265	static void *	287	static void *
266	persistent_realloc (void *ptr, size_t size)	288	persistent_realloc (void *ptr, size_t size)
267	{	289	{
		290	if (!size)
		291	{
		292	free (ptr);
		293	return 0;
		294	}
		295
268	for (;;)	296	for (;;)
269	{	297	{
270	void *newptr = realloc (ptr, size);	298	void *newptr = realloc (ptr, size);
271		299
272	if (newptr)	300	if (newptr)
…		…
277	}	305	}
278		306
279	...	307	...
280	ev_set_allocator (persistent_realloc);	308	ev_set_allocator (persistent_realloc);
281		309
282	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	310	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
283		311
284	Set the callback function to call on a retryable system call error (such	312	Set the callback function to call on a retryable system call error (such
285	as failed select, poll, epoll_wait). The message is a printable string	313	as failed select, poll, epoll_wait). The message is a printable string
286	indicating the system call or subsystem causing the problem. If this	314	indicating the system call or subsystem causing the problem. If this
287	callback is set, then libev will expect it to remedy the situation, no	315	callback is set, then libev will expect it to remedy the situation, no
…		…
299	}	327	}
300		328
301	...	329	...
302	ev_set_syserr_cb (fatal_error);	330	ev_set_syserr_cb (fatal_error);
303		331
		332	=item ev_feed_signal (int signum)
		333
		334	This function can be used to "simulate" a signal receive. It is completely
		335	safe to call this function at any time, from any context, including signal
		336	handlers or random threads.
		337
		338	Its main use is to customise signal handling in your process, especially
		339	in the presence of threads. For example, you could block signals
		340	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		341	creating any loops), and in one thread, use C<sigwait> or any other
		342	mechanism to wait for signals, then "deliver" them to libev by calling
		343	C<ev_feed_signal>.
		344
304	=back	345	=back
305		346
306	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	347	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
307		348
308	An event loop is described by a C<struct ev_loop *> (the C<struct> is	349	An event loop is described by a C<struct ev_loop *> (the C<struct> is
…		…
355	=item struct ev_loop *ev_loop_new (unsigned int flags)	396	=item struct ev_loop *ev_loop_new (unsigned int flags)
356		397
357	This will create and initialise a new event loop object. If the loop	398	This will create and initialise a new event loop object. If the loop
358	could not be initialised, returns false.	399	could not be initialised, returns false.
359		400
360	Note that this function I<is> thread-safe, and one common way to use	401	This function is thread-safe, and one common way to use libev with
361	libev with threads is indeed to create one loop per thread, and using the	402	threads is indeed to create one loop per thread, and using the default
362	default loop in the "main" or "initial" thread.	403	loop in the "main" or "initial" thread.
363		404
364	The flags argument can be used to specify special behaviour or specific	405	The flags argument can be used to specify special behaviour or specific
365	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	406	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
366		407
367	The following flags are supported:	408	The following flags are supported:
…		…
377		418
378	If this flag bit is or'ed into the flag value (or the program runs setuid	419	If this flag bit is or'ed into the flag value (or the program runs setuid
379	or setgid) then libev will I<not> look at the environment variable	420	or setgid) then libev will I<not> look at the environment variable
380	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	421	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
381	override the flags completely if it is found in the environment. This is	422	override the flags completely if it is found in the environment. This is
382	useful to try out specific backends to test their performance, or to work	423	useful to try out specific backends to test their performance, to work
383	around bugs.	424	around bugs, or to make libev threadsafe (accessing environment variables
		425	cannot be done in a threadsafe way, but usually it works if no other
		426	thread modifies them).
384		427
385	=item C<EVFLAG_FORKCHECK>	428	=item C<EVFLAG_FORKCHECK>
386		429
387	Instead of calling C<ev_loop_fork> manually after a fork, you can also	430	Instead of calling C<ev_loop_fork> manually after a fork, you can also
388	make libev check for a fork in each iteration by enabling this flag.	431	make libev check for a fork in each iteration by enabling this flag.
389		432
390	This works by calling C<getpid ()> on every iteration of the loop,	433	This works by calling C<getpid ()> on every iteration of the loop,
391	and thus this might slow down your event loop if you do a lot of loop	434	and thus this might slow down your event loop if you do a lot of loop
392	iterations and little real work, but is usually not noticeable (on my	435	iterations and little real work, but is usually not noticeable (on my
393	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	436	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
394	without a system call and thus I<very> fast, but my GNU/Linux system also has	437	sequence without a system call and thus I<very> fast, but my GNU/Linux
395	C<pthread_atfork> which is even faster).	438	system also has C<pthread_atfork> which is even faster). (Update: glibc
		439	versions 2.25 apparently removed the C<getpid> optimisation again).
396		440
397	The big advantage of this flag is that you can forget about fork (and	441	The big advantage of this flag is that you can forget about fork (and
398	forget about forgetting to tell libev about forking) when you use this	442	forget about forgetting to tell libev about forking, although you still
399	flag.	443	have to ignore C<SIGPIPE>) when you use this flag.
400		444
401	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	445	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
402	environment variable.	446	environment variable.
403		447
404	=item C<EVFLAG_NOINOTIFY>	448	=item C<EVFLAG_NOINOTIFY>
405		449
406	When this flag is specified, then libev will not attempt to use the	450	When this flag is specified, then libev will not attempt to use the
407	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and	451	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
408	testing, this flag can be useful to conserve inotify file descriptors, as	452	testing, this flag can be useful to conserve inotify file descriptors, as
409	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.	453	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
410		454
411	=item C<EVFLAG_SIGNALFD>	455	=item C<EVFLAG_SIGNALFD>
412		456
413	When this flag is specified, then libev will attempt to use the	457	When this flag is specified, then libev will attempt to use the
414	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API	458	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
415	delivers signals synchronously, which makes it both faster and might make	459	delivers signals synchronously, which makes it both faster and might make
416	it possible to get the queued signal data. It can also simplify signal	460	it possible to get the queued signal data. It can also simplify signal
417	handling with threads, as long as you properly block signals in your	461	handling with threads, as long as you properly block signals in your
418	threads that are not interested in handling them.	462	threads that are not interested in handling them.
419		463
420	Signalfd will not be used by default as this changes your signal mask, and	464	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	465	there are a lot of shoddy libraries and programs (glib's threadpool for
422	example) that can't properly initialise their signal masks.	466	example) that can't properly initialise their signal masks.
		467
		468	=item C<EVFLAG_NOSIGMASK>
		469
		470	When this flag is specified, then libev will avoid to modify the signal
		471	mask. Specifically, this means you have to make sure signals are unblocked
		472	when you want to receive them.
		473
		474	This behaviour is useful when you want to do your own signal handling, or
		475	want to handle signals only in specific threads and want to avoid libev
		476	unblocking the signals.
		477
		478	It's also required by POSIX in a threaded program, as libev calls
		479	C<sigprocmask>, whose behaviour is officially unspecified.
		480
		481	This flag's behaviour will become the default in future versions of libev.
423		482
424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	483	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
425		484
426	This is your standard select(2) backend. Not I<completely> standard, as	485	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,	486	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
455	=item C<EVBACKEND_EPOLL> (value 4, Linux)	514	=item C<EVBACKEND_EPOLL> (value 4, Linux)
456		515
457	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	516	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
458	kernels).	517	kernels).
459		518
460	For few fds, this backend is a bit little slower than poll and select,	519	For few fds, this backend is a bit little slower than poll and select, but
461	but it scales phenomenally better. While poll and select usually scale	520	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),	521	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).	522	fd), epoll scales either O(1) or O(active_fds).
464		523
465	The epoll mechanism deserves honorable mention as the most misdesigned	524	The epoll mechanism deserves honorable mention as the most misdesigned
466	of the more advanced event mechanisms: mere annoyances include silently	525	of the more advanced event mechanisms: mere annoyances include silently
467	dropping file descriptors, requiring a system call per change per file	526	dropping file descriptors, requiring a system call per change per file
468	descriptor (and unnecessary guessing of parameters), problems with dup,	527	descriptor (and unnecessary guessing of parameters), problems with dup,
469	returning before the timeout value requiring additional iterations and so	528	returning before the timeout value, resulting in additional iterations
		529	(and only giving 5ms accuracy while select on the same platform gives
470	on. The biggest issue is fork races, however - if a program forks then	530	0.1ms) and so on. The biggest issue is fork races, however - if a program
471	I<both> parent and child process have to recreate the epoll set, which can	531	forks then I<both> parent and child process have to recreate the epoll
472	take considerable time (one syscall per file descriptor) and is of course	532	set, which can take considerable time (one syscall per file descriptor)
473	hard to detect.	533	and is of course hard to detect.
474		534
475	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	535	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
476	of course I<doesn't>, and epoll just loves to report events for totally	536	but of course I<doesn't>, and epoll just loves to report events for
477	I<different> file descriptors (even already closed ones, so one cannot	537	totally I<different> file descriptors (even already closed ones, so
478	even remove them from the set) than registered in the set (especially	538	one cannot even remove them from the set) than registered in the set
479	on SMP systems). Libev tries to counter these spurious notifications by	539	(especially on SMP systems). Libev tries to counter these spurious
480	employing an additional generation counter and comparing that against the	540	notifications by employing an additional generation counter and comparing
481	events to filter out spurious ones, recreating the set when required. Last	541	that against the events to filter out spurious ones, recreating the set
		542	when required. Epoll also erroneously rounds down timeouts, but gives you
		543	no way to know when and by how much, so sometimes you have to busy-wait
		544	because epoll returns immediately despite a nonzero timeout. And last
482	not least, it also refuses to work with some file descriptors which work	545	not least, it also refuses to work with some file descriptors which work
483	perfectly fine with C<select> (files, many character devices...).	546	perfectly fine with C<select> (files, many character devices...).
		547
		548	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		549	cobbled together in a hurry, no thought to design or interaction with
		550	others. Oh, the pain, will it ever stop...
484		551
485	While stopping, setting and starting an I/O watcher in the same iteration	552	While stopping, setting and starting an I/O watcher in the same iteration
486	will result in some caching, there is still a system call per such	553	will result in some caching, there is still a system call per such
487	incident (because the same I<file descriptor> could point to a different	554	incident (because the same I<file descriptor> could point to a different
488	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	555	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
500	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or	567	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
501	faster than epoll for maybe up to a hundred file descriptors, depending on	568	faster than epoll for maybe up to a hundred file descriptors, depending on
502	the usage. So sad.	569	the usage. So sad.
503		570
504	While nominally embeddable in other event loops, this feature is broken in	571	While nominally embeddable in other event loops, this feature is broken in
505	all kernel versions tested so far.	572	a lot of kernel revisions, but probably(!) works in current versions.
506		573
507	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	574	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
508	C<EVBACKEND_POLL>.	575	C<EVBACKEND_POLL>.
509		576
		577	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		578
		579	Use the linux-specific linux aio (I<not> C<< aio(7) >> but C<<
		580	io_submit(2) >>) event interface available in post-4.18 kernels (but libev
		581	only tries to use it in 4.19+).
		582
		583	This is another linux trainwreck of an event interface.
		584
		585	If this backend works for you (as of this writing, it was very
		586	experimental), it is the best event interface available on linux and might
		587	be well worth enabling it - if it isn't available in your kernel this will
		588	be detected and this backend will be skipped.
		589
		590	This backend can batch oneshot requests and supports a user-space ring
		591	buffer to receive events. It also doesn't suffer from most of the design
		592	problems of epoll (such as not being able to remove event sources from
		593	the epoll set), and generally sounds too good to be true. Because, this
		594	being the linux kernel, of course it suffers from a whole new set of
		595	limitations, forcing you to fall back to epoll, inheriting all its design
		596	issues.
		597
		598	For one, it is not easily embeddable (but probably could be done using
		599	an event fd at some extra overhead). It also is subject to a system wide
		600	limit that can be configured in F</proc/sys/fs/aio-max-nr>. If no aio
		601	requests are left, this backend will be skipped during initialisation, and
		602	will switch to epoll when the loop is active.
		603
		604	Most problematic in practice, however, is that not all file descriptors
		605	work with it. For example, in linux 5.1, tcp sockets, pipes, event fds,
		606	files, F</dev/null> and a few others are supported, but ttys do not work
		607	properly (a known bug that the kernel developers don't care about, see
		608	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		609	(yet?) a generic event polling interface.
		610
		611	Overall, it seems the linux developers just don't want it to have a
		612	generic event handling mechanism other than C<select> or C<poll>.
		613
		614	To work around all these problem, the current version of libev uses its
		615	epoll backend as a fallback for file descriptor types that do not work. Or
		616	falls back completely to epoll if the kernel acts up.
		617
		618	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		619	C<EVBACKEND_POLL>.
		620
510	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	621	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
511		622
512	Kqueue deserves special mention, as at the time of this writing, it	623	Kqueue deserves special mention, as at the time this backend was
513	was broken on all BSDs except NetBSD (usually it doesn't work reliably	624	implemented, it was broken on all BSDs except NetBSD (usually it doesn't
514	with anything but sockets and pipes, except on Darwin, where of course	625	work reliably with anything but sockets and pipes, except on Darwin,
515	it's completely useless). Unlike epoll, however, whose brokenness	626	where of course it's completely useless). Unlike epoll, however, whose
516	is by design, these kqueue bugs can (and eventually will) be fixed	627	brokenness is by design, these kqueue bugs can be (and mostly have been)
517	without API changes to existing programs. For this reason it's not being	628	fixed without API changes to existing programs. For this reason it's not
518	"auto-detected" unless you explicitly specify it in the flags (i.e. using	629	being "auto-detected" on all platforms unless you explicitly specify it
519	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	630	in the flags (i.e. using C<EVBACKEND_KQUEUE>) or libev was compiled on a
520	system like NetBSD.	631	known-to-be-good (-enough) system like NetBSD.
521		632
522	You still can embed kqueue into a normal poll or select backend and use it	633	You still can embed kqueue into a normal poll or select backend and use it
523	only for sockets (after having made sure that sockets work with kqueue on	634	only for sockets (after having made sure that sockets work with kqueue on
524	the target platform). See C<ev_embed> watchers for more info.	635	the target platform). See C<ev_embed> watchers for more info.
525		636
526	It scales in the same way as the epoll backend, but the interface to the	637	It scales in the same way as the epoll backend, but the interface to the
527	kernel is more efficient (which says nothing about its actual speed, of	638	kernel is more efficient (which says nothing about its actual speed, of
528	course). While stopping, setting and starting an I/O watcher does never	639	course). While stopping, setting and starting an I/O watcher does never
529	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	640	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
530	two event changes per incident. Support for C<fork ()> is very bad (but	641	two event changes per incident. Support for C<fork ()> is very bad (you
531	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	642	might have to leak fd's on fork, but it's more sane than epoll) and it
532	cases	643	drops fds silently in similarly hard-to-detect cases.
533		644
534	This backend usually performs well under most conditions.	645	This backend usually performs well under most conditions.
535		646
536	While nominally embeddable in other event loops, this doesn't work	647	While nominally embeddable in other event loops, this doesn't work
537	everywhere, so you might need to test for this. And since it is broken	648	everywhere, so you might need to test for this. And since it is broken
…		…
554	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	665	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
555		666
556	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	667	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
557	it's really slow, but it still scales very well (O(active_fds)).	668	it's really slow, but it still scales very well (O(active_fds)).
558		669
559	Please note that Solaris event ports can deliver a lot of spurious
560	notifications, so you need to use non-blocking I/O or other means to avoid
561	blocking when no data (or space) is available.
562
563	While this backend scales well, it requires one system call per active	670	While this backend scales well, it requires one system call per active
564	file descriptor per loop iteration. For small and medium numbers of file	671	file descriptor per loop iteration. For small and medium numbers of file
565	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	672	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
566	might perform better.	673	might perform better.
567		674
568	On the positive side, with the exception of the spurious readiness	675	On the positive side, this backend actually performed fully to
569	notifications, this backend actually performed fully to specification
570	in all tests and is fully embeddable, which is a rare feat among the	676	specification in all tests and is fully embeddable, which is a rare feat
571	OS-specific backends (I vastly prefer correctness over speed hacks).	677	among the OS-specific backends (I vastly prefer correctness over speed
		678	hacks).
		679
		680	On the negative side, the interface is I<bizarre> - so bizarre that
		681	even sun itself gets it wrong in their code examples: The event polling
		682	function sometimes returns events to the caller even though an error
		683	occurred, but with no indication whether it has done so or not (yes, it's
		684	even documented that way) - deadly for edge-triggered interfaces where you
		685	absolutely have to know whether an event occurred or not because you have
		686	to re-arm the watcher.
		687
		688	Fortunately libev seems to be able to work around these idiocies.
572		689
573	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	690	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
574	C<EVBACKEND_POLL>.	691	C<EVBACKEND_POLL>.
575		692
576	=item C<EVBACKEND_ALL>	693	=item C<EVBACKEND_ALL>
577		694
578	Try all backends (even potentially broken ones that wouldn't be tried	695	Try all backends (even potentially broken ones that wouldn't be tried
579	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	696	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
580	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	697	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
581		698
582	It is definitely not recommended to use this flag.	699	It is definitely not recommended to use this flag, use whatever
		700	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		701	at all.
		702
		703	=item C<EVBACKEND_MASK>
		704
		705	Not a backend at all, but a mask to select all backend bits from a
		706	C<flags> value, in case you want to mask out any backends from a flags
		707	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
583		708
584	=back	709	=back
585		710
586	If one or more of the backend flags are or'ed into the flags value,	711	If one or more of the backend flags are or'ed into the flags value,
587	then only these backends will be tried (in the reverse order as listed	712	then only these backends will be tried (in the reverse order as listed
…		…
596		721
597	Example: Use whatever libev has to offer, but make sure that kqueue is	722	Example: Use whatever libev has to offer, but make sure that kqueue is
598	used if available.	723	used if available.
599		724
600	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);	725	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		726
		727	Example: Similarly, on linux, you mgiht want to take advantage of the
		728	linux aio backend if possible, but fall back to something else if that
		729	isn't available.
		730
		731	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
601		732
602	=item ev_loop_destroy (loop)	733	=item ev_loop_destroy (loop)
603		734
604	Destroys an event loop object (frees all memory and kernel state	735	Destroys an event loop object (frees all memory and kernel state
605	etc.). None of the active event watchers will be stopped in the normal	736	etc.). None of the active event watchers will be stopped in the normal
…		…
616	This function is normally used on loop objects allocated by	747	This function is normally used on loop objects allocated by
617	C<ev_loop_new>, but it can also be used on the default loop returned by	748	C<ev_loop_new>, but it can also be used on the default loop returned by
618	C<ev_default_loop>, in which case it is not thread-safe.	749	C<ev_default_loop>, in which case it is not thread-safe.
619		750
620	Note that it is not advisable to call this function on the default loop	751	Note that it is not advisable to call this function on the default loop
621	except in the rare occasion where you really need to free it's resources.	752	except in the rare occasion where you really need to free its resources.
622	If you need dynamically allocated loops it is better to use C<ev_loop_new>	753	If you need dynamically allocated loops it is better to use C<ev_loop_new>
623	and C<ev_loop_destroy>.	754	and C<ev_loop_destroy>.
624		755
625	=item ev_loop_fork (loop)	756	=item ev_loop_fork (loop)
626		757
627	This function sets a flag that causes subsequent C<ev_run> iterations to	758	This function sets a flag that causes subsequent C<ev_run> iterations
628	reinitialise the kernel state for backends that have one. Despite the	759	to reinitialise the kernel state for backends that have one. Despite
629	name, you can call it anytime, but it makes most sense after forking, in	760	the name, you can call it anytime you are allowed to start or stop
630	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the	761	watchers (except inside an C<ev_prepare> callback), but it makes most
		762	sense after forking, in the child process. You I<must> call it (or use
631	child before resuming or calling C<ev_run>.	763	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
632		764
		765	In addition, if you want to reuse a loop (via this function or
		766	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		767
633	Again, you I<have> to call it on I<any> loop that you want to re-use after	768	Again, you I<have> to call it on I<any> loop that you want to re-use after
634	a fork, I<even if you do not plan to use the loop in the parent>. This is	769	a fork, I<even if you do not plan to use the loop in the parent>. This is
635	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	770	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
636	during fork.	771	during fork.
637		772
638	On the other hand, you only need to call this function in the child	773	On the other hand, you only need to call this function in the child
…		…
674	prepare and check phases.	809	prepare and check phases.
675		810
676	=item unsigned int ev_depth (loop)	811	=item unsigned int ev_depth (loop)
677		812
678	Returns the number of times C<ev_run> was entered minus the number of	813	Returns the number of times C<ev_run> was entered minus the number of
679	times C<ev_run> was exited, in other words, the recursion depth.	814	times C<ev_run> was exited normally, in other words, the recursion depth.
680		815
681	Outside C<ev_run>, this number is zero. In a callback, this number is	816	Outside C<ev_run>, this number is zero. In a callback, this number is
682	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	817	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
683	in which case it is higher.	818	in which case it is higher.
684		819
685	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	820	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
686	etc.), doesn't count as "exit" - consider this as a hint to avoid such	821	throwing an exception etc.), doesn't count as "exit" - consider this
687	ungentleman-like behaviour unless it's really convenient.	822	as a hint to avoid such ungentleman-like behaviour unless it's really
		823	convenient, in which case it is fully supported.
688		824
689	=item unsigned int ev_backend (loop)	825	=item unsigned int ev_backend (loop)
690		826
691	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	827	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
692	use.	828	use.
…		…
707		843
708	This function is rarely useful, but when some event callback runs for a	844	This function is rarely useful, but when some event callback runs for a
709	very long time without entering the event loop, updating libev's idea of	845	very long time without entering the event loop, updating libev's idea of
710	the current time is a good idea.	846	the current time is a good idea.
711		847
712	See also L<The special problem of time updates> in the C<ev_timer> section.	848	See also L</The special problem of time updates> in the C<ev_timer> section.
713		849
714	=item ev_suspend (loop)	850	=item ev_suspend (loop)
715		851
716	=item ev_resume (loop)	852	=item ev_resume (loop)
717		853
…		…
735	without a previous call to C<ev_suspend>.	871	without a previous call to C<ev_suspend>.
736		872
737	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	873	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
738	event loop time (see C<ev_now_update>).	874	event loop time (see C<ev_now_update>).
739		875
740	=item ev_run (loop, int flags)	876	=item bool ev_run (loop, int flags)
741		877
742	Finally, this is it, the event handler. This function usually is called	878	Finally, this is it, the event handler. This function usually is called
743	after you have initialised all your watchers and you want to start	879	after you have initialised all your watchers and you want to start
744	handling events. It will ask the operating system for any new events, call	880	handling events. It will ask the operating system for any new events, call
745	the watcher callbacks, an then repeat the whole process indefinitely: This	881	the watcher callbacks, and then repeat the whole process indefinitely: This
746	is why event loops are called I<loops>.	882	is why event loops are called I<loops>.
747		883
748	If the flags argument is specified as C<0>, it will keep handling events	884	If the flags argument is specified as C<0>, it will keep handling events
749	until either no event watchers are active anymore or C<ev_break> was	885	until either no event watchers are active anymore or C<ev_break> was
750	called.	886	called.
		887
		888	The return value is false if there are no more active watchers (which
		889	usually means "all jobs done" or "deadlock"), and true in all other cases
		890	(which usually means " you should call C<ev_run> again").
751		891
752	Please note that an explicit C<ev_break> is usually better than	892	Please note that an explicit C<ev_break> is usually better than
753	relying on all watchers to be stopped when deciding when a program has	893	relying on all watchers to be stopped when deciding when a program has
754	finished (especially in interactive programs), but having a program	894	finished (especially in interactive programs), but having a program
755	that automatically loops as long as it has to and no longer by virtue	895	that automatically loops as long as it has to and no longer by virtue
756	of relying on its watchers stopping correctly, that is truly a thing of	896	of relying on its watchers stopping correctly, that is truly a thing of
757	beauty.	897	beauty.
758		898
		899	This function is I<mostly> exception-safe - you can break out of a
		900	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		901	exception and so on. This does not decrement the C<ev_depth> value, nor
		902	will it clear any outstanding C<EVBREAK_ONE> breaks.
		903
759	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	904	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
760	those events and any already outstanding ones, but will not wait and	905	those events and any already outstanding ones, but will not wait and
761	block your process in case there are no events and will return after one	906	block your process in case there are no events and will return after one
762	iteration of the loop. This is sometimes useful to poll and handle new	907	iteration of the loop. This is sometimes useful to poll and handle new
763	events while doing lengthy calculations, to keep the program responsive.	908	events while doing lengthy calculations, to keep the program responsive.
…		…
772	This is useful if you are waiting for some external event in conjunction	917	This is useful if you are waiting for some external event in conjunction
773	with something not expressible using other libev watchers (i.e. "roll your	918	with something not expressible using other libev watchers (i.e. "roll your
774	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	919	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
775	usually a better approach for this kind of thing.	920	usually a better approach for this kind of thing.
776		921
777	Here are the gory details of what C<ev_run> does:	922	Here are the gory details of what C<ev_run> does (this is for your
		923	understanding, not a guarantee that things will work exactly like this in
		924	future versions):
778		925
779	- Increment loop depth.	926	- Increment loop depth.
780	- Reset the ev_break status.	927	- Reset the ev_break status.
781	- Before the first iteration, call any pending watchers.	928	- Before the first iteration, call any pending watchers.
782	LOOP:	929	LOOP:
…		…
815	anymore.	962	anymore.
816		963
817	... queue jobs here, make sure they register event watchers as long	964	... queue jobs here, make sure they register event watchers as long
818	... as they still have work to do (even an idle watcher will do..)	965	... as they still have work to do (even an idle watcher will do..)
819	ev_run (my_loop, 0);	966	ev_run (my_loop, 0);
820	... jobs done or somebody called unloop. yeah!	967	... jobs done or somebody called break. yeah!
821		968
822	=item ev_break (loop, how)	969	=item ev_break (loop, how)
823		970
824	Can be used to make a call to C<ev_run> return early (but only after it	971	Can be used to make a call to C<ev_run> return early (but only after it
825	has processed all outstanding events). The C<how> argument must be either	972	has processed all outstanding events). The C<how> argument must be either
826	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	973	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
827	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	974	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
828		975
829	This "break state" will be cleared when entering C<ev_run> again.	976	This "break state" will be cleared on the next call to C<ev_run>.
830		977
831	It is safe to call C<ev_break> from outside any C<ev_run> calls, too.	978	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		979	which case it will have no effect.
832		980
833	=item ev_ref (loop)	981	=item ev_ref (loop)
834		982
835	=item ev_unref (loop)	983	=item ev_unref (loop)
836		984
…		…
857	running when nothing else is active.	1005	running when nothing else is active.
858		1006
859	ev_signal exitsig;	1007	ev_signal exitsig;
860	ev_signal_init (&exitsig, sig_cb, SIGINT);	1008	ev_signal_init (&exitsig, sig_cb, SIGINT);
861	ev_signal_start (loop, &exitsig);	1009	ev_signal_start (loop, &exitsig);
862	evf_unref (loop);	1010	ev_unref (loop);
863		1011
864	Example: For some weird reason, unregister the above signal handler again.	1012	Example: For some weird reason, unregister the above signal handler again.
865		1013
866	ev_ref (loop);	1014	ev_ref (loop);
867	ev_signal_stop (loop, &exitsig);	1015	ev_signal_stop (loop, &exitsig);
…		…
887	overhead for the actual polling but can deliver many events at once.	1035	overhead for the actual polling but can deliver many events at once.
888		1036
889	By setting a higher I<io collect interval> you allow libev to spend more	1037	By setting a higher I<io collect interval> you allow libev to spend more
890	time collecting I/O events, so you can handle more events per iteration,	1038	time collecting I/O events, so you can handle more events per iteration,
891	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	1039	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
892	C<ev_timer>) will be not affected. Setting this to a non-null value will	1040	C<ev_timer>) will not be affected. Setting this to a non-null value will
893	introduce an additional C<ev_sleep ()> call into most loop iterations. The	1041	introduce an additional C<ev_sleep ()> call into most loop iterations. The
894	sleep time ensures that libev will not poll for I/O events more often then	1042	sleep time ensures that libev will not poll for I/O events more often then
895	once per this interval, on average.	1043	once per this interval, on average (as long as the host time resolution is
		1044	good enough).
896		1045
897	Likewise, by setting a higher I<timeout collect interval> you allow libev	1046	Likewise, by setting a higher I<timeout collect interval> you allow libev
898	to spend more time collecting timeouts, at the expense of increased	1047	to spend more time collecting timeouts, at the expense of increased
899	latency/jitter/inexactness (the watcher callback will be called	1048	latency/jitter/inexactness (the watcher callback will be called
900	later). C<ev_io> watchers will not be affected. Setting this to a non-null	1049	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
946	invoke the actual watchers inside another context (another thread etc.).	1095	invoke the actual watchers inside another context (another thread etc.).
947		1096
948	If you want to reset the callback, use C<ev_invoke_pending> as new	1097	If you want to reset the callback, use C<ev_invoke_pending> as new
949	callback.	1098	callback.
950		1099
951	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1100	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
952		1101
953	Sometimes you want to share the same loop between multiple threads. This	1102	Sometimes you want to share the same loop between multiple threads. This
954	can be done relatively simply by putting mutex_lock/unlock calls around	1103	can be done relatively simply by putting mutex_lock/unlock calls around
955	each call to a libev function.	1104	each call to a libev function.
956		1105
957	However, C<ev_run> can run an indefinite time, so it is not feasible	1106	However, C<ev_run> can run an indefinite time, so it is not feasible
958	to wait for it to return. One way around this is to wake up the event	1107	to wait for it to return. One way around this is to wake up the event
959	loop via C<ev_break> and C<av_async_send>, another way is to set these	1108	loop via C<ev_break> and C<ev_async_send>, another way is to set these
960	I<release> and I<acquire> callbacks on the loop.	1109	I<release> and I<acquire> callbacks on the loop.
961		1110
962	When set, then C<release> will be called just before the thread is	1111	When set, then C<release> will be called just before the thread is
963	suspended waiting for new events, and C<acquire> is called just	1112	suspended waiting for new events, and C<acquire> is called just
964	afterwards.	1113	afterwards.
…		…
979	See also the locking example in the C<THREADS> section later in this	1128	See also the locking example in the C<THREADS> section later in this
980	document.	1129	document.
981		1130
982	=item ev_set_userdata (loop, void *data)	1131	=item ev_set_userdata (loop, void *data)
983		1132
984	=item ev_userdata (loop)	1133	=item void *ev_userdata (loop)
985		1134
986	Set and retrieve a single C<void *> associated with a loop. When	1135	Set and retrieve a single C<void *> associated with a loop. When
987	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1136	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
988	C<0.>	1137	C<0>.
989		1138
990	These two functions can be used to associate arbitrary data with a loop,	1139	These two functions can be used to associate arbitrary data with a loop,
991	and are intended solely for the C<invoke_pending_cb>, C<release> and	1140	and are intended solely for the C<invoke_pending_cb>, C<release> and
992	C<acquire> callbacks described above, but of course can be (ab-)used for	1141	C<acquire> callbacks described above, but of course can be (ab-)used for
993	any other purpose as well.	1142	any other purpose as well.
…		…
1104		1253
1105	=item C<EV_PREPARE>	1254	=item C<EV_PREPARE>
1106		1255
1107	=item C<EV_CHECK>	1256	=item C<EV_CHECK>
1108		1257
1109	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1258	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1110	to gather new events, and all C<ev_check> watchers are invoked just after	1259	gather new events, and all C<ev_check> watchers are queued (not invoked)
1111	C<ev_run> has gathered them, but before it invokes any callbacks for any	1260	just after C<ev_run> has gathered them, but before it queues any callbacks
		1261	for any received events. That means C<ev_prepare> watchers are the last
		1262	watchers invoked before the event loop sleeps or polls for new events, and
		1263	C<ev_check> watchers will be invoked before any other watchers of the same
		1264	or lower priority within an event loop iteration.
		1265
1112	received events. Callbacks of both watcher types can start and stop as	1266	Callbacks of both watcher types can start and stop as many watchers as
1113	many watchers as they want, and all of them will be taken into account	1267	they want, and all of them will be taken into account (for example, a
1114	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1268	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1115	C<ev_run> from blocking).	1269	blocking).
1116		1270
1117	=item C<EV_EMBED>	1271	=item C<EV_EMBED>
1118		1272
1119	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1273	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1120		1274
…		…
1243		1397
1244	=item callback ev_cb (ev_TYPE *watcher)	1398	=item callback ev_cb (ev_TYPE *watcher)
1245		1399
1246	Returns the callback currently set on the watcher.	1400	Returns the callback currently set on the watcher.
1247		1401
1248	=item ev_cb_set (ev_TYPE *watcher, callback)	1402	=item ev_set_cb (ev_TYPE *watcher, callback)
1249		1403
1250	Change the callback. You can change the callback at virtually any time	1404	Change the callback. You can change the callback at virtually any time
1251	(modulo threads).	1405	(modulo threads).
1252		1406
1253	=item ev_set_priority (ev_TYPE *watcher, int priority)	1407	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1271	or might not have been clamped to the valid range.	1425	or might not have been clamped to the valid range.
1272		1426
1273	The default priority used by watchers when no priority has been set is	1427	The default priority used by watchers when no priority has been set is
1274	always C<0>, which is supposed to not be too high and not be too low :).	1428	always C<0>, which is supposed to not be too high and not be too low :).
1275		1429
1276	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1430	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1277	priorities.	1431	priorities.
1278		1432
1279	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1433	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1280		1434
1281	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1435	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
…		…
1306	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1460	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1307	functions that do not need a watcher.	1461	functions that do not need a watcher.
1308		1462
1309	=back	1463	=back
1310		1464
1311	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1465	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1312		1466	OWN COMPOSITE WATCHERS> idioms.
1313	Each watcher has, by default, a member C<void *data> that you can change
1314	and read at any time: libev will completely ignore it. This can be used
1315	to associate arbitrary data with your watcher. If you need more data and
1316	don't want to allocate memory and store a pointer to it in that data
1317	member, you can also "subclass" the watcher type and provide your own
1318	data:
1319
1320	struct my_io
1321	{
1322	ev_io io;
1323	int otherfd;
1324	void *somedata;
1325	struct whatever *mostinteresting;
1326	};
1327
1328	...
1329	struct my_io w;
1330	ev_io_init (&w.io, my_cb, fd, EV_READ);
1331
1332	And since your callback will be called with a pointer to the watcher, you
1333	can cast it back to your own type:
1334
1335	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1336	{
1337	struct my_io *w = (struct my_io *)w_;
1338	...
1339	}
1340
1341	More interesting and less C-conformant ways of casting your callback type
1342	instead have been omitted.
1343
1344	Another common scenario is to use some data structure with multiple
1345	embedded watchers:
1346
1347	struct my_biggy
1348	{
1349	int some_data;
1350	ev_timer t1;
1351	ev_timer t2;
1352	}
1353
1354	In this case getting the pointer to C<my_biggy> is a bit more
1355	complicated: Either you store the address of your C<my_biggy> struct
1356	in the C<data> member of the watcher (for woozies), or you need to use
1357	some pointer arithmetic using C<offsetof> inside your watchers (for real
1358	programmers):
1359
1360	#include <stddef.h>
1361
1362	static void
1363	t1_cb (EV_P_ ev_timer *w, int revents)
1364	{
1365	struct my_biggy big = (struct my_biggy *)
1366	(((char *)w) - offsetof (struct my_biggy, t1));
1367	}
1368
1369	static void
1370	t2_cb (EV_P_ ev_timer *w, int revents)
1371	{
1372	struct my_biggy big = (struct my_biggy *)
1373	(((char *)w) - offsetof (struct my_biggy, t2));
1374	}
1375		1467
1376	=head2 WATCHER STATES	1468	=head2 WATCHER STATES
1377		1469
1378	There are various watcher states mentioned throughout this manual -	1470	There are various watcher states mentioned throughout this manual -
1379	active, pending and so on. In this section these states and the rules to	1471	active, pending and so on. In this section these states and the rules to
1380	transition between them will be described in more detail - and while these	1472	transition between them will be described in more detail - and while these
1381	rules might look complicated, they usually do "the right thing".	1473	rules might look complicated, they usually do "the right thing".
1382		1474
1383	=over 4	1475	=over 4
1384		1476
1385	=item initialiased	1477	=item initialised
1386		1478
1387	Before a watcher can be registered with the event looop it has to be	1479	Before a watcher can be registered with the event loop it has to be
1388	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1480	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1389	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1481	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1390		1482
1391	In this state it is simply some block of memory that is suitable for use	1483	In this state it is simply some block of memory that is suitable for
1392	in an event loop. It can be moved around, freed, reused etc. at will.	1484	use in an event loop. It can be moved around, freed, reused etc. at
		1485	will - as long as you either keep the memory contents intact, or call
		1486	C<ev_TYPE_init> again.
1393		1487
1394	=item started/running/active	1488	=item started/running/active
1395		1489
1396	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1490	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1397	property of the event loop, and is actively waiting for events. While in	1491	property of the event loop, and is actively waiting for events. While in
…		…
1425	latter will clear any pending state the watcher might be in, regardless	1519	latter will clear any pending state the watcher might be in, regardless
1426	of whether it was active or not, so stopping a watcher explicitly before	1520	of whether it was active or not, so stopping a watcher explicitly before
1427	freeing it is often a good idea.	1521	freeing it is often a good idea.
1428		1522
1429	While stopped (and not pending) the watcher is essentially in the	1523	While stopped (and not pending) the watcher is essentially in the
1430	initialised state, that is it can be reused, moved, modified in any way	1524	initialised state, that is, it can be reused, moved, modified in any way
1431	you wish.	1525	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1526	it again).
1432		1527
1433	=back	1528	=back
1434		1529
1435	=head2 WATCHER PRIORITY MODELS	1530	=head2 WATCHER PRIORITY MODELS
1436		1531
…		…
1565	In general you can register as many read and/or write event watchers per	1660	In general you can register as many read and/or write event watchers per
1566	fd as you want (as long as you don't confuse yourself). Setting all file	1661	fd as you want (as long as you don't confuse yourself). Setting all file
1567	descriptors to non-blocking mode is also usually a good idea (but not	1662	descriptors to non-blocking mode is also usually a good idea (but not
1568	required if you know what you are doing).	1663	required if you know what you are doing).
1569		1664
1570	If you cannot use non-blocking mode, then force the use of a
1571	known-to-be-good backend (at the time of this writing, this includes only
1572	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1573	descriptors for which non-blocking operation makes no sense (such as
1574	files) - libev doesn't guarantee any specific behaviour in that case.
1575
1576	Another thing you have to watch out for is that it is quite easy to	1665	Another thing you have to watch out for is that it is quite easy to
1577	receive "spurious" readiness notifications, that is your callback might	1666	receive "spurious" readiness notifications, that is, your callback might
1578	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1667	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1579	because there is no data. Not only are some backends known to create a	1668	because there is no data. It is very easy to get into this situation even
1580	lot of those (for example Solaris ports), it is very easy to get into	1669	with a relatively standard program structure. Thus it is best to always
1581	this situation even with a relatively standard program structure. Thus	1670	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1582	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1583	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1671	preferable to a program hanging until some data arrives.
1584		1672
1585	If you cannot run the fd in non-blocking mode (for example you should	1673	If you cannot run the fd in non-blocking mode (for example you should
1586	not play around with an Xlib connection), then you have to separately	1674	not play around with an Xlib connection), then you have to separately
1587	re-test whether a file descriptor is really ready with a known-to-be good	1675	re-test whether a file descriptor is really ready with a known-to-be good
1588	interface such as poll (fortunately in our Xlib example, Xlib already	1676	interface such as poll (fortunately in the case of Xlib, it already does
1589	does this on its own, so its quite safe to use). Some people additionally	1677	this on its own, so its quite safe to use). Some people additionally
1590	use C<SIGALRM> and an interval timer, just to be sure you won't block	1678	use C<SIGALRM> and an interval timer, just to be sure you won't block
1591	indefinitely.	1679	indefinitely.
1592		1680
1593	But really, best use non-blocking mode.	1681	But really, best use non-blocking mode.
1594		1682
1595	=head3 The special problem of disappearing file descriptors	1683	=head3 The special problem of disappearing file descriptors
1596		1684
1597	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1685	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1598	descriptor (either due to calling C<close> explicitly or any other means,	1686	a file descriptor (either due to calling C<close> explicitly or any other
1599	such as C<dup2>). The reason is that you register interest in some file	1687	means, such as C<dup2>). The reason is that you register interest in some
1600	descriptor, but when it goes away, the operating system will silently drop	1688	file descriptor, but when it goes away, the operating system will silently
1601	this interest. If another file descriptor with the same number then is	1689	drop this interest. If another file descriptor with the same number then
1602	registered with libev, there is no efficient way to see that this is, in	1690	is registered with libev, there is no efficient way to see that this is,
1603	fact, a different file descriptor.	1691	in fact, a different file descriptor.
1604		1692
1605	To avoid having to explicitly tell libev about such cases, libev follows	1693	To avoid having to explicitly tell libev about such cases, libev follows
1606	the following policy: Each time C<ev_io_set> is being called, libev	1694	the following policy: Each time C<ev_io_set> is being called, libev
1607	will assume that this is potentially a new file descriptor, otherwise	1695	will assume that this is potentially a new file descriptor, otherwise
1608	it is assumed that the file descriptor stays the same. That means that	1696	it is assumed that the file descriptor stays the same. That means that
…		…
1622		1710
1623	There is no workaround possible except not registering events	1711	There is no workaround possible except not registering events
1624	for potentially C<dup ()>'ed file descriptors, or to resort to	1712	for potentially C<dup ()>'ed file descriptors, or to resort to
1625	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1713	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1626		1714
		1715	=head3 The special problem of files
		1716
		1717	Many people try to use C<select> (or libev) on file descriptors
		1718	representing files, and expect it to become ready when their program
		1719	doesn't block on disk accesses (which can take a long time on their own).
		1720
		1721	However, this cannot ever work in the "expected" way - you get a readiness
		1722	notification as soon as the kernel knows whether and how much data is
		1723	there, and in the case of open files, that's always the case, so you
		1724	always get a readiness notification instantly, and your read (or possibly
		1725	write) will still block on the disk I/O.
		1726
		1727	Another way to view it is that in the case of sockets, pipes, character
		1728	devices and so on, there is another party (the sender) that delivers data
		1729	on its own, but in the case of files, there is no such thing: the disk
		1730	will not send data on its own, simply because it doesn't know what you
		1731	wish to read - you would first have to request some data.
		1732
		1733	Since files are typically not-so-well supported by advanced notification
		1734	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1735	to files, even though you should not use it. The reason for this is
		1736	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1737	usually a tty, often a pipe, but also sometimes files or special devices
		1738	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1739	F</dev/urandom>), and even though the file might better be served with
		1740	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1741	it "just works" instead of freezing.
		1742
		1743	So avoid file descriptors pointing to files when you know it (e.g. use
		1744	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1745	when you rarely read from a file instead of from a socket, and want to
		1746	reuse the same code path.
		1747
1627	=head3 The special problem of fork	1748	=head3 The special problem of fork
1628		1749
1629	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1750	Some backends (epoll, kqueue, probably linuxaio) do not support C<fork ()>
1630	useless behaviour. Libev fully supports fork, but needs to be told about	1751	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1631	it in the child.	1752	to be told about it in the child if you want to continue to use it in the
		1753	child.
1632		1754
1633	To support fork in your programs, you either have to call	1755	To support fork in your child processes, you have to call C<ev_loop_fork
1634	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1756	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1635	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1757	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1636	C<EVBACKEND_POLL>.
1637		1758
1638	=head3 The special problem of SIGPIPE	1759	=head3 The special problem of SIGPIPE
1639		1760
1640	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1761	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1641	when writing to a pipe whose other end has been closed, your program gets	1762	when writing to a pipe whose other end has been closed, your program gets
…		…
1739	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1860	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1740	monotonic clock option helps a lot here).	1861	monotonic clock option helps a lot here).
1741		1862
1742	The callback is guaranteed to be invoked only I<after> its timeout has	1863	The callback is guaranteed to be invoked only I<after> its timeout has
1743	passed (not I<at>, so on systems with very low-resolution clocks this	1864	passed (not I<at>, so on systems with very low-resolution clocks this
1744	might introduce a small delay). If multiple timers become ready during the	1865	might introduce a small delay, see "the special problem of being too
		1866	early", below). If multiple timers become ready during the same loop
1745	same loop iteration then the ones with earlier time-out values are invoked	1867	iteration then the ones with earlier time-out values are invoked before
1746	before ones of the same priority with later time-out values (but this is	1868	ones of the same priority with later time-out values (but this is no
1747	no longer true when a callback calls C<ev_run> recursively).	1869	longer true when a callback calls C<ev_run> recursively).
1748		1870
1749	=head3 Be smart about timeouts	1871	=head3 Be smart about timeouts
1750		1872
1751	Many real-world problems involve some kind of timeout, usually for error	1873	Many real-world problems involve some kind of timeout, usually for error
1752	recovery. A typical example is an HTTP request - if the other side hangs,	1874	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1827		1949
1828	In this case, it would be more efficient to leave the C<ev_timer> alone,	1950	In this case, it would be more efficient to leave the C<ev_timer> alone,
1829	but remember the time of last activity, and check for a real timeout only	1951	but remember the time of last activity, and check for a real timeout only
1830	within the callback:	1952	within the callback:
1831		1953
		1954	ev_tstamp timeout = 60.;
1832	ev_tstamp last_activity; // time of last activity	1955	ev_tstamp last_activity; // time of last activity
		1956	ev_timer timer;
1833		1957
1834	static void	1958	static void
1835	callback (EV_P_ ev_timer *w, int revents)	1959	callback (EV_P_ ev_timer *w, int revents)
1836	{	1960	{
1837	ev_tstamp now = ev_now (EV_A);	1961	// calculate when the timeout would happen
1838	ev_tstamp timeout = last_activity + 60.;	1962	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1839		1963
1840	// if last_activity + 60. is older than now, we did time out	1964	// if negative, it means we the timeout already occurred
1841	if (timeout < now)	1965	if (after < 0.)
1842	{	1966	{
1843	// timeout occurred, take action	1967	// timeout occurred, take action
1844	}	1968	}
1845	else	1969	else
1846	{	1970	{
1847	// callback was invoked, but there was some activity, re-arm	1971	// callback was invoked, but there was some recent
1848	// the watcher to fire in last_activity + 60, which is	1972	// activity. simply restart the timer to time out
1849	// guaranteed to be in the future, so "again" is positive:	1973	// after "after" seconds, which is the earliest time
1850	w->repeat = timeout - now;	1974	// the timeout can occur.
		1975	ev_timer_set (w, after, 0.);
1851	ev_timer_again (EV_A_ w);	1976	ev_timer_start (EV_A_ w);
1852	}	1977	}
1853	}	1978	}
1854		1979
1855	To summarise the callback: first calculate the real timeout (defined	1980	To summarise the callback: first calculate in how many seconds the
1856	as "60 seconds after the last activity"), then check if that time has	1981	timeout will occur (by calculating the absolute time when it would occur,
1857	been reached, which means something I<did>, in fact, time out. Otherwise	1982	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1858	the callback was invoked too early (C<timeout> is in the future), so	1983	(EV_A)> from that).
1859	re-schedule the timer to fire at that future time, to see if maybe we have
1860	a timeout then.
1861		1984
1862	Note how C<ev_timer_again> is used, taking advantage of the	1985	If this value is negative, then we are already past the timeout, i.e. we
1863	C<ev_timer_again> optimisation when the timer is already running.	1986	timed out, and need to do whatever is needed in this case.
		1987
		1988	Otherwise, we now the earliest time at which the timeout would trigger,
		1989	and simply start the timer with this timeout value.
		1990
		1991	In other words, each time the callback is invoked it will check whether
		1992	the timeout occurred. If not, it will simply reschedule itself to check
		1993	again at the earliest time it could time out. Rinse. Repeat.
1864		1994
1865	This scheme causes more callback invocations (about one every 60 seconds	1995	This scheme causes more callback invocations (about one every 60 seconds
1866	minus half the average time between activity), but virtually no calls to	1996	minus half the average time between activity), but virtually no calls to
1867	libev to change the timeout.	1997	libev to change the timeout.
1868		1998
1869	To start the timer, simply initialise the watcher and set C<last_activity>	1999	To start the machinery, simply initialise the watcher and set
1870	to the current time (meaning we just have some activity :), then call the	2000	C<last_activity> to the current time (meaning there was some activity just
1871	callback, which will "do the right thing" and start the timer:	2001	now), then call the callback, which will "do the right thing" and start
		2002	the timer:
1872		2003
		2004	last_activity = ev_now (EV_A);
1873	ev_init (timer, callback);	2005	ev_init (&timer, callback);
1874	last_activity = ev_now (loop);	2006	callback (EV_A_ &timer, 0);
1875	callback (loop, timer, EV_TIMER);
1876		2007
1877	And when there is some activity, simply store the current time in	2008	When there is some activity, simply store the current time in
1878	C<last_activity>, no libev calls at all:	2009	C<last_activity>, no libev calls at all:
1879		2010
		2011	if (activity detected)
1880	last_activity = ev_now (loop);	2012	last_activity = ev_now (EV_A);
		2013
		2014	When your timeout value changes, then the timeout can be changed by simply
		2015	providing a new value, stopping the timer and calling the callback, which
		2016	will again do the right thing (for example, time out immediately :).
		2017
		2018	timeout = new_value;
		2019	ev_timer_stop (EV_A_ &timer);
		2020	callback (EV_A_ &timer, 0);
1881		2021
1882	This technique is slightly more complex, but in most cases where the	2022	This technique is slightly more complex, but in most cases where the
1883	time-out is unlikely to be triggered, much more efficient.	2023	time-out is unlikely to be triggered, much more efficient.
1884
1885	Changing the timeout is trivial as well (if it isn't hard-coded in the
1886	callback :) - just change the timeout and invoke the callback, which will
1887	fix things for you.
1888		2024
1889	=item 4. Wee, just use a double-linked list for your timeouts.	2025	=item 4. Wee, just use a double-linked list for your timeouts.
1890		2026
1891	If there is not one request, but many thousands (millions...), all	2027	If there is not one request, but many thousands (millions...), all
1892	employing some kind of timeout with the same timeout value, then one can	2028	employing some kind of timeout with the same timeout value, then one can
…		…
1919	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2055	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1920	rather complicated, but extremely efficient, something that really pays	2056	rather complicated, but extremely efficient, something that really pays
1921	off after the first million or so of active timers, i.e. it's usually	2057	off after the first million or so of active timers, i.e. it's usually
1922	overkill :)	2058	overkill :)
1923		2059
		2060	=head3 The special problem of being too early
		2061
		2062	If you ask a timer to call your callback after three seconds, then
		2063	you expect it to be invoked after three seconds - but of course, this
		2064	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2065	guaranteed to any precision by libev - imagine somebody suspending the
		2066	process with a STOP signal for a few hours for example.
		2067
		2068	So, libev tries to invoke your callback as soon as possible I<after> the
		2069	delay has occurred, but cannot guarantee this.
		2070
		2071	A less obvious failure mode is calling your callback too early: many event
		2072	loops compare timestamps with a "elapsed delay >= requested delay", but
		2073	this can cause your callback to be invoked much earlier than you would
		2074	expect.
		2075
		2076	To see why, imagine a system with a clock that only offers full second
		2077	resolution (think windows if you can't come up with a broken enough OS
		2078	yourself). If you schedule a one-second timer at the time 500.9, then the
		2079	event loop will schedule your timeout to elapse at a system time of 500
		2080	(500.9 truncated to the resolution) + 1, or 501.
		2081
		2082	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2083	501" and invoke the callback 0.1s after it was started, even though a
		2084	one-second delay was requested - this is being "too early", despite best
		2085	intentions.
		2086
		2087	This is the reason why libev will never invoke the callback if the elapsed
		2088	delay equals the requested delay, but only when the elapsed delay is
		2089	larger than the requested delay. In the example above, libev would only invoke
		2090	the callback at system time 502, or 1.1s after the timer was started.
		2091
		2092	So, while libev cannot guarantee that your callback will be invoked
		2093	exactly when requested, it I<can> and I<does> guarantee that the requested
		2094	delay has actually elapsed, or in other words, it always errs on the "too
		2095	late" side of things.
		2096
1924	=head3 The special problem of time updates	2097	=head3 The special problem of time updates
1925		2098
1926	Establishing the current time is a costly operation (it usually takes at	2099	Establishing the current time is a costly operation (it usually takes
1927	least two system calls): EV therefore updates its idea of the current	2100	at least one system call): EV therefore updates its idea of the current
1928	time only before and after C<ev_run> collects new events, which causes a	2101	time only before and after C<ev_run> collects new events, which causes a
1929	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2102	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1930	lots of events in one iteration.	2103	lots of events in one iteration.
1931		2104
1932	The relative timeouts are calculated relative to the C<ev_now ()>	2105	The relative timeouts are calculated relative to the C<ev_now ()>
1933	time. This is usually the right thing as this timestamp refers to the time	2106	time. This is usually the right thing as this timestamp refers to the time
1934	of the event triggering whatever timeout you are modifying/starting. If	2107	of the event triggering whatever timeout you are modifying/starting. If
1935	you suspect event processing to be delayed and you I<need> to base the	2108	you suspect event processing to be delayed and you I<need> to base the
1936	timeout on the current time, use something like this to adjust for this:	2109	timeout on the current time, use something like the following to adjust
		2110	for it:
1937		2111
1938	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2112	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1939		2113
1940	If the event loop is suspended for a long time, you can also force an	2114	If the event loop is suspended for a long time, you can also force an
1941	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2115	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1942	()>.	2116	()>, although that will push the event time of all outstanding events
		2117	further into the future.
		2118
		2119	=head3 The special problem of unsynchronised clocks
		2120
		2121	Modern systems have a variety of clocks - libev itself uses the normal
		2122	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2123	jumps).
		2124
		2125	Neither of these clocks is synchronised with each other or any other clock
		2126	on the system, so C<ev_time ()> might return a considerably different time
		2127	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2128	a call to C<gettimeofday> might return a second count that is one higher
		2129	than a directly following call to C<time>.
		2130
		2131	The moral of this is to only compare libev-related timestamps with
		2132	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2133	a second or so.
		2134
		2135	One more problem arises due to this lack of synchronisation: if libev uses
		2136	the system monotonic clock and you compare timestamps from C<ev_time>
		2137	or C<ev_now> from when you started your timer and when your callback is
		2138	invoked, you will find that sometimes the callback is a bit "early".
		2139
		2140	This is because C<ev_timer>s work in real time, not wall clock time, so
		2141	libev makes sure your callback is not invoked before the delay happened,
		2142	I<measured according to the real time>, not the system clock.
		2143
		2144	If your timeouts are based on a physical timescale (e.g. "time out this
		2145	connection after 100 seconds") then this shouldn't bother you as it is
		2146	exactly the right behaviour.
		2147
		2148	If you want to compare wall clock/system timestamps to your timers, then
		2149	you need to use C<ev_periodic>s, as these are based on the wall clock
		2150	time, where your comparisons will always generate correct results.
1943		2151
1944	=head3 The special problems of suspended animation	2152	=head3 The special problems of suspended animation
1945		2153
1946	When you leave the server world it is quite customary to hit machines that	2154	When you leave the server world it is quite customary to hit machines that
1947	can suspend/hibernate - what happens to the clocks during such a suspend?	2155	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1977		2185
1978	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2186	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1979		2187
1980	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2188	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1981		2189
1982	Configure the timer to trigger after C<after> seconds. If C<repeat>	2190	Configure the timer to trigger after C<after> seconds (fractional and
1983	is C<0.>, then it will automatically be stopped once the timeout is	2191	negative values are supported). If C<repeat> is C<0.>, then it will
1984	reached. If it is positive, then the timer will automatically be	2192	automatically be stopped once the timeout is reached. If it is positive,
1985	configured to trigger again C<repeat> seconds later, again, and again,	2193	then the timer will automatically be configured to trigger again C<repeat>
1986	until stopped manually.	2194	seconds later, again, and again, until stopped manually.
1987		2195
1988	The timer itself will do a best-effort at avoiding drift, that is, if	2196	The timer itself will do a best-effort at avoiding drift, that is, if
1989	you configure a timer to trigger every 10 seconds, then it will normally	2197	you configure a timer to trigger every 10 seconds, then it will normally
1990	trigger at exactly 10 second intervals. If, however, your program cannot	2198	trigger at exactly 10 second intervals. If, however, your program cannot
1991	keep up with the timer (because it takes longer than those 10 seconds to	2199	keep up with the timer (because it takes longer than those 10 seconds to
1992	do stuff) the timer will not fire more than once per event loop iteration.	2200	do stuff) the timer will not fire more than once per event loop iteration.
1993		2201
1994	=item ev_timer_again (loop, ev_timer *)	2202	=item ev_timer_again (loop, ev_timer *)
1995		2203
1996	This will act as if the timer timed out and restart it again if it is	2204	This will act as if the timer timed out, and restarts it again if it is
1997	repeating. The exact semantics are:	2205	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2206	timeout to the C<repeat> value and calling C<ev_timer_start>.
1998		2207
		2208	The exact semantics are as in the following rules, all of which will be
		2209	applied to the watcher:
		2210
		2211	=over 4
		2212
1999	If the timer is pending, its pending status is cleared.	2213	=item If the timer is pending, the pending status is always cleared.
2000		2214
2001	If the timer is started but non-repeating, stop it (as if it timed out).	2215	=item If the timer is started but non-repeating, stop it (as if it timed
		2216	out, without invoking it).
2002		2217
2003	If the timer is repeating, either start it if necessary (with the	2218	=item If the timer is repeating, make the C<repeat> value the new timeout
2004	C<repeat> value), or reset the running timer to the C<repeat> value.	2219	and start the timer, if necessary.
2005		2220
		2221	=back
		2222
2006	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2223	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2007	usage example.	2224	usage example.
2008		2225
2009	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2226	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2010		2227
2011	Returns the remaining time until a timer fires. If the timer is active,	2228	Returns the remaining time until a timer fires. If the timer is active,
…		…
2064	Periodic watchers are also timers of a kind, but they are very versatile	2281	Periodic watchers are also timers of a kind, but they are very versatile
2065	(and unfortunately a bit complex).	2282	(and unfortunately a bit complex).
2066		2283
2067	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2284	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2068	relative time, the physical time that passes) but on wall clock time	2285	relative time, the physical time that passes) but on wall clock time
2069	(absolute time, the thing you can read on your calender or clock). The	2286	(absolute time, the thing you can read on your calendar or clock). The
2070	difference is that wall clock time can run faster or slower than real	2287	difference is that wall clock time can run faster or slower than real
2071	time, and time jumps are not uncommon (e.g. when you adjust your	2288	time, and time jumps are not uncommon (e.g. when you adjust your
2072	wrist-watch).	2289	wrist-watch).
2073		2290
2074	You can tell a periodic watcher to trigger after some specific point	2291	You can tell a periodic watcher to trigger after some specific point
…		…
2079	C<ev_timer>, which would still trigger roughly 10 seconds after starting	2296	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2080	it, as it uses a relative timeout).	2297	it, as it uses a relative timeout).
2081		2298
2082	C<ev_periodic> watchers can also be used to implement vastly more complex	2299	C<ev_periodic> watchers can also be used to implement vastly more complex
2083	timers, such as triggering an event on each "midnight, local time", or	2300	timers, such as triggering an event on each "midnight, local time", or
2084	other complicated rules. This cannot be done with C<ev_timer> watchers, as	2301	other complicated rules. This cannot easily be done with C<ev_timer>
2085	those cannot react to time jumps.	2302	watchers, as those cannot react to time jumps.
2086		2303
2087	As with timers, the callback is guaranteed to be invoked only when the	2304	As with timers, the callback is guaranteed to be invoked only when the
2088	point in time where it is supposed to trigger has passed. If multiple	2305	point in time where it is supposed to trigger has passed. If multiple
2089	timers become ready during the same loop iteration then the ones with	2306	timers become ready during the same loop iteration then the ones with
2090	earlier time-out values are invoked before ones with later time-out values	2307	earlier time-out values are invoked before ones with later time-out values
…		…
2131		2348
2132	Another way to think about it (for the mathematically inclined) is that	2349	Another way to think about it (for the mathematically inclined) is that
2133	C<ev_periodic> will try to run the callback in this mode at the next possible	2350	C<ev_periodic> will try to run the callback in this mode at the next possible
2134	time where C<time = offset (mod interval)>, regardless of any time jumps.	2351	time where C<time = offset (mod interval)>, regardless of any time jumps.
2135		2352
2136	For numerical stability it is preferable that the C<offset> value is near	2353	The C<interval> I<MUST> be positive, and for numerical stability, the
2137	C<ev_now ()> (the current time), but there is no range requirement for	2354	interval value should be higher than C<1/8192> (which is around 100
2138	this value, and in fact is often specified as zero.	2355	microseconds) and C<offset> should be higher than C<0> and should have
		2356	at most a similar magnitude as the current time (say, within a factor of
		2357	ten). Typical values for offset are, in fact, C<0> or something between
		2358	C<0> and C<interval>, which is also the recommended range.
2139		2359
2140	Note also that there is an upper limit to how often a timer can fire (CPU	2360	Note also that there is an upper limit to how often a timer can fire (CPU
2141	speed for example), so if C<interval> is very small then timing stability	2361	speed for example), so if C<interval> is very small then timing stability
2142	will of course deteriorate. Libev itself tries to be exact to be about one	2362	will of course deteriorate. Libev itself tries to be exact to be about one
2143	millisecond (if the OS supports it and the machine is fast enough).	2363	millisecond (if the OS supports it and the machine is fast enough).
…		…
2173		2393
2174	NOTE: I<< This callback must always return a time that is higher than or	2394	NOTE: I<< This callback must always return a time that is higher than or
2175	equal to the passed C<now> value >>.	2395	equal to the passed C<now> value >>.
2176		2396
2177	This can be used to create very complex timers, such as a timer that	2397	This can be used to create very complex timers, such as a timer that
2178	triggers on "next midnight, local time". To do this, you would calculate the	2398	triggers on "next midnight, local time". To do this, you would calculate
2179	next midnight after C<now> and return the timestamp value for this. How	2399	the next midnight after C<now> and return the timestamp value for
2180	you do this is, again, up to you (but it is not trivial, which is the main	2400	this. Here is a (completely untested, no error checking) example on how to
2181	reason I omitted it as an example).	2401	do this:
		2402
		2403	#include <time.h>
		2404
		2405	static ev_tstamp
		2406	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2407	{
		2408	time_t tnow = (time_t)now;
		2409	struct tm tm;
		2410	localtime_r (&tnow, &tm);
		2411
		2412	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2413	++tm.tm_mday; // midnight next day
		2414
		2415	return mktime (&tm);
		2416	}
		2417
		2418	Note: this code might run into trouble on days that have more then two
		2419	midnights (beginning and end).
2182		2420
2183	=back	2421	=back
2184		2422
2185	=item ev_periodic_again (loop, ev_periodic *)	2423	=item ev_periodic_again (loop, ev_periodic *)
2186		2424
…		…
2251		2489
2252	ev_periodic hourly_tick;	2490	ev_periodic hourly_tick;
2253	ev_periodic_init (&hourly_tick, clock_cb,	2491	ev_periodic_init (&hourly_tick, clock_cb,
2254	fmod (ev_now (loop), 3600.), 3600., 0);	2492	fmod (ev_now (loop), 3600.), 3600., 0);
2255	ev_periodic_start (loop, &hourly_tick);	2493	ev_periodic_start (loop, &hourly_tick);
2256		2494
2257		2495
2258	=head2 C<ev_signal> - signal me when a signal gets signalled!	2496	=head2 C<ev_signal> - signal me when a signal gets signalled!
2259		2497
2260	Signal watchers will trigger an event when the process receives a specific	2498	Signal watchers will trigger an event when the process receives a specific
2261	signal one or more times. Even though signals are very asynchronous, libev	2499	signal one or more times. Even though signals are very asynchronous, libev
2262	will try it's best to deliver signals synchronously, i.e. as part of the	2500	will try its best to deliver signals synchronously, i.e. as part of the
2263	normal event processing, like any other event.	2501	normal event processing, like any other event.
2264		2502
2265	If you want signals to be delivered truly asynchronously, just use	2503	If you want signals to be delivered truly asynchronously, just use
2266	C<sigaction> as you would do without libev and forget about sharing	2504	C<sigaction> as you would do without libev and forget about sharing
2267	the signal. You can even use C<ev_async> from a signal handler to	2505	the signal. You can even use C<ev_async> from a signal handler to
…		…
2271	only within the same loop, i.e. you can watch for C<SIGINT> in your	2509	only within the same loop, i.e. you can watch for C<SIGINT> in your
2272	default loop and for C<SIGIO> in another loop, but you cannot watch for	2510	default loop and for C<SIGIO> in another loop, but you cannot watch for
2273	C<SIGINT> in both the default loop and another loop at the same time. At	2511	C<SIGINT> in both the default loop and another loop at the same time. At
2274	the moment, C<SIGCHLD> is permanently tied to the default loop.	2512	the moment, C<SIGCHLD> is permanently tied to the default loop.
2275		2513
2276	When the first watcher gets started will libev actually register something	2514	Only after the first watcher for a signal is started will libev actually
2277	with the kernel (thus it coexists with your own signal handlers as long as	2515	register something with the kernel. It thus coexists with your own signal
2278	you don't register any with libev for the same signal).	2516	handlers as long as you don't register any with libev for the same signal.
2279		2517
2280	If possible and supported, libev will install its handlers with	2518	If possible and supported, libev will install its handlers with
2281	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2519	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2282	not be unduly interrupted. If you have a problem with system calls getting	2520	not be unduly interrupted. If you have a problem with system calls getting
2283	interrupted by signals you can block all signals in an C<ev_check> watcher	2521	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2286	=head3 The special problem of inheritance over fork/execve/pthread_create	2524	=head3 The special problem of inheritance over fork/execve/pthread_create
2287		2525
2288	Both the signal mask (C<sigprocmask>) and the signal disposition	2526	Both the signal mask (C<sigprocmask>) and the signal disposition
2289	(C<sigaction>) are unspecified after starting a signal watcher (and after	2527	(C<sigaction>) are unspecified after starting a signal watcher (and after
2290	stopping it again), that is, libev might or might not block the signal,	2528	stopping it again), that is, libev might or might not block the signal,
2291	and might or might not set or restore the installed signal handler.	2529	and might or might not set or restore the installed signal handler (but
		2530	see C<EVFLAG_NOSIGMASK>).
2292		2531
2293	While this does not matter for the signal disposition (libev never	2532	While this does not matter for the signal disposition (libev never
2294	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2533	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2295	C<execve>), this matters for the signal mask: many programs do not expect	2534	C<execve>), this matters for the signal mask: many programs do not expect
2296	certain signals to be blocked.	2535	certain signals to be blocked.
…		…
2309	I<has> to modify the signal mask, at least temporarily.	2548	I<has> to modify the signal mask, at least temporarily.
2310		2549
2311	So I can't stress this enough: I<If you do not reset your signal mask when	2550	So I can't stress this enough: I<If you do not reset your signal mask when
2312	you expect it to be empty, you have a race condition in your code>. This	2551	you expect it to be empty, you have a race condition in your code>. This
2313	is not a libev-specific thing, this is true for most event libraries.	2552	is not a libev-specific thing, this is true for most event libraries.
		2553
		2554	=head3 The special problem of threads signal handling
		2555
		2556	POSIX threads has problematic signal handling semantics, specifically,
		2557	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2558	threads in a process block signals, which is hard to achieve.
		2559
		2560	When you want to use sigwait (or mix libev signal handling with your own
		2561	for the same signals), you can tackle this problem by globally blocking
		2562	all signals before creating any threads (or creating them with a fully set
		2563	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2564	loops. Then designate one thread as "signal receiver thread" which handles
		2565	these signals. You can pass on any signals that libev might be interested
		2566	in by calling C<ev_feed_signal>.
2314		2567
2315	=head3 Watcher-Specific Functions and Data Members	2568	=head3 Watcher-Specific Functions and Data Members
2316		2569
2317	=over 4	2570	=over 4
2318		2571
…		…
2453		2706
2454	=head2 C<ev_stat> - did the file attributes just change?	2707	=head2 C<ev_stat> - did the file attributes just change?
2455		2708
2456	This watches a file system path for attribute changes. That is, it calls	2709	This watches a file system path for attribute changes. That is, it calls
2457	C<stat> on that path in regular intervals (or when the OS says it changed)	2710	C<stat> on that path in regular intervals (or when the OS says it changed)
2458	and sees if it changed compared to the last time, invoking the callback if	2711	and sees if it changed compared to the last time, invoking the callback
2459	it did.	2712	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2713	happen after the watcher has been started will be reported.
2460		2714
2461	The path does not need to exist: changing from "path exists" to "path does	2715	The path does not need to exist: changing from "path exists" to "path does
2462	not exist" is a status change like any other. The condition "path does not	2716	not exist" is a status change like any other. The condition "path does not
2463	exist" (or more correctly "path cannot be stat'ed") is signified by the	2717	exist" (or more correctly "path cannot be stat'ed") is signified by the
2464	C<st_nlink> field being zero (which is otherwise always forced to be at	2718	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2694	Apart from keeping your process non-blocking (which is a useful	2948	Apart from keeping your process non-blocking (which is a useful
2695	effect on its own sometimes), idle watchers are a good place to do	2949	effect on its own sometimes), idle watchers are a good place to do
2696	"pseudo-background processing", or delay processing stuff to after the	2950	"pseudo-background processing", or delay processing stuff to after the
2697	event loop has handled all outstanding events.	2951	event loop has handled all outstanding events.
2698		2952
		2953	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2954
		2955	As long as there is at least one active idle watcher, libev will never
		2956	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2957	For this to work, the idle watcher doesn't need to be invoked at all - the
		2958	lowest priority will do.
		2959
		2960	This mode of operation can be useful together with an C<ev_check> watcher,
		2961	to do something on each event loop iteration - for example to balance load
		2962	between different connections.
		2963
		2964	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2965	example.
		2966
2699	=head3 Watcher-Specific Functions and Data Members	2967	=head3 Watcher-Specific Functions and Data Members
2700		2968
2701	=over 4	2969	=over 4
2702		2970
2703	=item ev_idle_init (ev_idle *, callback)	2971	=item ev_idle_init (ev_idle *, callback)
…		…
2714	callback, free it. Also, use no error checking, as usual.	2982	callback, free it. Also, use no error checking, as usual.
2715		2983
2716	static void	2984	static void
2717	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2985	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2718	{	2986	{
		2987	// stop the watcher
		2988	ev_idle_stop (loop, w);
		2989
		2990	// now we can free it
2719	free (w);	2991	free (w);
		2992
2720	// now do something you wanted to do when the program has	2993	// now do something you wanted to do when the program has
2721	// no longer anything immediate to do.	2994	// no longer anything immediate to do.
2722	}	2995	}
2723		2996
2724	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2997	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2726	ev_idle_start (loop, idle_watcher);	2999	ev_idle_start (loop, idle_watcher);
2727		3000
2728		3001
2729	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3002	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2730		3003
2731	Prepare and check watchers are usually (but not always) used in pairs:	3004	Prepare and check watchers are often (but not always) used in pairs:
2732	prepare watchers get invoked before the process blocks and check watchers	3005	prepare watchers get invoked before the process blocks and check watchers
2733	afterwards.	3006	afterwards.
2734		3007
2735	You I<must not> call C<ev_run> or similar functions that enter	3008	You I<must not> call C<ev_run> (or similar functions that enter the
2736	the current event loop from either C<ev_prepare> or C<ev_check>	3009	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2737	watchers. Other loops than the current one are fine, however. The	3010	C<ev_check> watchers. Other loops than the current one are fine,
2738	rationale behind this is that you do not need to check for recursion in	3011	however. The rationale behind this is that you do not need to check
2739	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3012	for recursion in those watchers, i.e. the sequence will always be
2740	C<ev_check> so if you have one watcher of each kind they will always be	3013	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2741	called in pairs bracketing the blocking call.	3014	kind they will always be called in pairs bracketing the blocking call.
2742		3015
2743	Their main purpose is to integrate other event mechanisms into libev and	3016	Their main purpose is to integrate other event mechanisms into libev and
2744	their use is somewhat advanced. They could be used, for example, to track	3017	their use is somewhat advanced. They could be used, for example, to track
2745	variable changes, implement your own watchers, integrate net-snmp or a	3018	variable changes, implement your own watchers, integrate net-snmp or a
2746	coroutine library and lots more. They are also occasionally useful if	3019	coroutine library and lots more. They are also occasionally useful if
…		…
2764	with priority higher than or equal to the event loop and one coroutine	3037	with priority higher than or equal to the event loop and one coroutine
2765	of lower priority, but only once, using idle watchers to keep the event	3038	of lower priority, but only once, using idle watchers to keep the event
2766	loop from blocking if lower-priority coroutines are active, thus mapping	3039	loop from blocking if lower-priority coroutines are active, thus mapping
2767	low-priority coroutines to idle/background tasks).	3040	low-priority coroutines to idle/background tasks).
2768		3041
2769	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3042	When used for this purpose, it is recommended to give C<ev_check> watchers
2770	priority, to ensure that they are being run before any other watchers	3043	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2771	after the poll (this doesn't matter for C<ev_prepare> watchers).	3044	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3045	watchers).
2772		3046
2773	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3047	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2774	activate ("feed") events into libev. While libev fully supports this, they	3048	activate ("feed") events into libev. While libev fully supports this, they
2775	might get executed before other C<ev_check> watchers did their job. As	3049	might get executed before other C<ev_check> watchers did their job. As
2776	C<ev_check> watchers are often used to embed other (non-libev) event	3050	C<ev_check> watchers are often used to embed other (non-libev) event
2777	loops those other event loops might be in an unusable state until their	3051	loops those other event loops might be in an unusable state until their
2778	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3052	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2779	others).	3053	others).
		3054
		3055	=head3 Abusing an C<ev_check> watcher for its side-effect
		3056
		3057	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3058	useful because they are called once per event loop iteration. For
		3059	example, if you want to handle a large number of connections fairly, you
		3060	normally only do a bit of work for each active connection, and if there
		3061	is more work to do, you wait for the next event loop iteration, so other
		3062	connections have a chance of making progress.
		3063
		3064	Using an C<ev_check> watcher is almost enough: it will be called on the
		3065	next event loop iteration. However, that isn't as soon as possible -
		3066	without external events, your C<ev_check> watcher will not be invoked.
		3067
		3068	This is where C<ev_idle> watchers come in handy - all you need is a
		3069	single global idle watcher that is active as long as you have one active
		3070	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3071	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3072	invoked. Neither watcher alone can do that.
2780		3073
2781	=head3 Watcher-Specific Functions and Data Members	3074	=head3 Watcher-Specific Functions and Data Members
2782		3075
2783	=over 4	3076	=over 4
2784		3077
…		…
2985		3278
2986	=over 4	3279	=over 4
2987		3280
2988	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3281	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2989		3282
2990	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3283	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2991		3284
2992	Configures the watcher to embed the given loop, which must be	3285	Configures the watcher to embed the given loop, which must be
2993	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3286	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2994	invoked automatically, otherwise it is the responsibility of the callback	3287	invoked automatically, otherwise it is the responsibility of the callback
2995	to invoke it (it will continue to be called until the sweep has been done,	3288	to invoke it (it will continue to be called until the sweep has been done,
…		…
3016	used).	3309	used).
3017		3310
3018	struct ev_loop *loop_hi = ev_default_init (0);	3311	struct ev_loop *loop_hi = ev_default_init (0);
3019	struct ev_loop *loop_lo = 0;	3312	struct ev_loop *loop_lo = 0;
3020	ev_embed embed;	3313	ev_embed embed;
3021		3314
3022	// see if there is a chance of getting one that works	3315	// see if there is a chance of getting one that works
3023	// (remember that a flags value of 0 means autodetection)	3316	// (remember that a flags value of 0 means autodetection)
3024	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3317	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3025	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3318	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3026	: 0;	3319	: 0;
…		…
3040	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3333	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3041		3334
3042	struct ev_loop *loop = ev_default_init (0);	3335	struct ev_loop *loop = ev_default_init (0);
3043	struct ev_loop *loop_socket = 0;	3336	struct ev_loop *loop_socket = 0;
3044	ev_embed embed;	3337	ev_embed embed;
3045		3338
3046	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3339	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3047	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3340	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3048	{	3341	{
3049	ev_embed_init (&embed, 0, loop_socket);	3342	ev_embed_init (&embed, 0, loop_socket);
3050	ev_embed_start (loop, &embed);	3343	ev_embed_start (loop, &embed);
…		…
3058		3351
3059	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3352	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3060		3353
3061	Fork watchers are called when a C<fork ()> was detected (usually because	3354	Fork watchers are called when a C<fork ()> was detected (usually because
3062	whoever is a good citizen cared to tell libev about it by calling	3355	whoever is a good citizen cared to tell libev about it by calling
3063	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3356	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3064	event loop blocks next and before C<ev_check> watchers are being called,	3357	and before C<ev_check> watchers are being called, and only in the child
3065	and only in the child after the fork. If whoever good citizen calling	3358	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3066	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3359	and calls it in the wrong process, the fork handlers will be invoked, too,
3067	handlers will be invoked, too, of course.	3360	of course.
3068		3361
3069	=head3 The special problem of life after fork - how is it possible?	3362	=head3 The special problem of life after fork - how is it possible?
3070		3363
3071	Most uses of C<fork()> consist of forking, then some simple calls to set	3364	Most uses of C<fork ()> consist of forking, then some simple calls to set
3072	up/change the process environment, followed by a call to C<exec()>. This	3365	up/change the process environment, followed by a call to C<exec()>. This
3073	sequence should be handled by libev without any problems.	3366	sequence should be handled by libev without any problems.
3074		3367
3075	This changes when the application actually wants to do event handling	3368	This changes when the application actually wants to do event handling
3076	in the child, or both parent in child, in effect "continuing" after the	3369	in the child, or both parent in child, in effect "continuing" after the
…		…
3153	atexit (program_exits);	3446	atexit (program_exits);
3154		3447
3155		3448
3156	=head2 C<ev_async> - how to wake up an event loop	3449	=head2 C<ev_async> - how to wake up an event loop
3157		3450
3158	In general, you cannot use an C<ev_run> from multiple threads or other	3451	In general, you cannot use an C<ev_loop> from multiple threads or other
3159	asynchronous sources such as signal handlers (as opposed to multiple event	3452	asynchronous sources such as signal handlers (as opposed to multiple event
3160	loops - those are of course safe to use in different threads).	3453	loops - those are of course safe to use in different threads).
3161		3454
3162	Sometimes, however, you need to wake up an event loop you do not control,	3455	Sometimes, however, you need to wake up an event loop you do not control,
3163	for example because it belongs to another thread. This is what C<ev_async>	3456	for example because it belongs to another thread. This is what C<ev_async>
…		…
3165	it by calling C<ev_async_send>, which is thread- and signal safe.	3458	it by calling C<ev_async_send>, which is thread- and signal safe.
3166		3459
3167	This functionality is very similar to C<ev_signal> watchers, as signals,	3460	This functionality is very similar to C<ev_signal> watchers, as signals,
3168	too, are asynchronous in nature, and signals, too, will be compressed	3461	too, are asynchronous in nature, and signals, too, will be compressed
3169	(i.e. the number of callback invocations may be less than the number of	3462	(i.e. the number of callback invocations may be less than the number of
3170	C<ev_async_sent> calls).	3463	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3171		3464	of "global async watchers" by using a watcher on an otherwise unused
3172	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3465	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3173	just the default loop.	3466	even without knowing which loop owns the signal.
3174		3467
3175	=head3 Queueing	3468	=head3 Queueing
3176		3469
3177	C<ev_async> does not support queueing of data in any way. The reason	3470	C<ev_async> does not support queueing of data in any way. The reason
3178	is that the author does not know of a simple (or any) algorithm for a	3471	is that the author does not know of a simple (or any) algorithm for a
…		…
3270	trust me.	3563	trust me.
3271		3564
3272	=item ev_async_send (loop, ev_async *)	3565	=item ev_async_send (loop, ev_async *)
3273		3566
3274	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3567	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3275	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3568	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3569	returns.
		3570
3276	C<ev_feed_event>, this call is safe to do from other threads, signal or	3571	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3277	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3572	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3278	section below on what exactly this means).	3573	embedding section below on what exactly this means).
3279		3574
3280	Note that, as with other watchers in libev, multiple events might get	3575	Note that, as with other watchers in libev, multiple events might get
3281	compressed into a single callback invocation (another way to look at this	3576	compressed into a single callback invocation (another way to look at
3282	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3577	this is that C<ev_async> watchers are level-triggered: they are set on
3283	reset when the event loop detects that).	3578	C<ev_async_send>, reset when the event loop detects that).
3284		3579
3285	This call incurs the overhead of a system call only once per event loop	3580	This call incurs the overhead of at most one extra system call per event
3286	iteration, so while the overhead might be noticeable, it doesn't apply to	3581	loop iteration, if the event loop is blocked, and no syscall at all if
3287	repeated calls to C<ev_async_send> for the same event loop.	3582	the event loop (or your program) is processing events. That means that
		3583	repeated calls are basically free (there is no need to avoid calls for
		3584	performance reasons) and that the overhead becomes smaller (typically
		3585	zero) under load.
3288		3586
3289	=item bool = ev_async_pending (ev_async *)	3587	=item bool = ev_async_pending (ev_async *)
3290		3588
3291	Returns a non-zero value when C<ev_async_send> has been called on the	3589	Returns a non-zero value when C<ev_async_send> has been called on the
3292	watcher but the event has not yet been processed (or even noted) by the	3590	watcher but the event has not yet been processed (or even noted) by the
…		…
3309		3607
3310	There are some other functions of possible interest. Described. Here. Now.	3608	There are some other functions of possible interest. Described. Here. Now.
3311		3609
3312	=over 4	3610	=over 4
3313		3611
3314	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3612	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3315		3613
3316	This function combines a simple timer and an I/O watcher, calls your	3614	This function combines a simple timer and an I/O watcher, calls your
3317	callback on whichever event happens first and automatically stops both	3615	callback on whichever event happens first and automatically stops both
3318	watchers. This is useful if you want to wait for a single event on an fd	3616	watchers. This is useful if you want to wait for a single event on an fd
3319	or timeout without having to allocate/configure/start/stop/free one or	3617	or timeout without having to allocate/configure/start/stop/free one or
…		…
3347	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3645	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3348		3646
3349	=item ev_feed_fd_event (loop, int fd, int revents)	3647	=item ev_feed_fd_event (loop, int fd, int revents)
3350		3648
3351	Feed an event on the given fd, as if a file descriptor backend detected	3649	Feed an event on the given fd, as if a file descriptor backend detected
3352	the given events it.	3650	the given events.
3353		3651
3354	=item ev_feed_signal_event (loop, int signum)	3652	=item ev_feed_signal_event (loop, int signum)
3355		3653
3356	Feed an event as if the given signal occurred (C<loop> must be the default	3654	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3357	loop!).	3655	which is async-safe.
3358		3656
3359	=back	3657	=back
		3658
		3659
		3660	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3661
		3662	This section explains some common idioms that are not immediately
		3663	obvious. Note that examples are sprinkled over the whole manual, and this
		3664	section only contains stuff that wouldn't fit anywhere else.
		3665
		3666	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3667
		3668	Each watcher has, by default, a C<void *data> member that you can read
		3669	or modify at any time: libev will completely ignore it. This can be used
		3670	to associate arbitrary data with your watcher. If you need more data and
		3671	don't want to allocate memory separately and store a pointer to it in that
		3672	data member, you can also "subclass" the watcher type and provide your own
		3673	data:
		3674
		3675	struct my_io
		3676	{
		3677	ev_io io;
		3678	int otherfd;
		3679	void *somedata;
		3680	struct whatever *mostinteresting;
		3681	};
		3682
		3683	...
		3684	struct my_io w;
		3685	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3686
		3687	And since your callback will be called with a pointer to the watcher, you
		3688	can cast it back to your own type:
		3689
		3690	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3691	{
		3692	struct my_io *w = (struct my_io *)w_;
		3693	...
		3694	}
		3695
		3696	More interesting and less C-conformant ways of casting your callback
		3697	function type instead have been omitted.
		3698
		3699	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3700
		3701	Another common scenario is to use some data structure with multiple
		3702	embedded watchers, in effect creating your own watcher that combines
		3703	multiple libev event sources into one "super-watcher":
		3704
		3705	struct my_biggy
		3706	{
		3707	int some_data;
		3708	ev_timer t1;
		3709	ev_timer t2;
		3710	}
		3711
		3712	In this case getting the pointer to C<my_biggy> is a bit more
		3713	complicated: Either you store the address of your C<my_biggy> struct in
		3714	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3715	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3716	real programmers):
		3717
		3718	#include <stddef.h>
		3719
		3720	static void
		3721	t1_cb (EV_P_ ev_timer *w, int revents)
		3722	{
		3723	struct my_biggy big = (struct my_biggy *)
		3724	(((char *)w) - offsetof (struct my_biggy, t1));
		3725	}
		3726
		3727	static void
		3728	t2_cb (EV_P_ ev_timer *w, int revents)
		3729	{
		3730	struct my_biggy big = (struct my_biggy *)
		3731	(((char *)w) - offsetof (struct my_biggy, t2));
		3732	}
		3733
		3734	=head2 AVOIDING FINISHING BEFORE RETURNING
		3735
		3736	Often you have structures like this in event-based programs:
		3737
		3738	callback ()
		3739	{
		3740	free (request);
		3741	}
		3742
		3743	request = start_new_request (..., callback);
		3744
		3745	The intent is to start some "lengthy" operation. The C<request> could be
		3746	used to cancel the operation, or do other things with it.
		3747
		3748	It's not uncommon to have code paths in C<start_new_request> that
		3749	immediately invoke the callback, for example, to report errors. Or you add
		3750	some caching layer that finds that it can skip the lengthy aspects of the
		3751	operation and simply invoke the callback with the result.
		3752
		3753	The problem here is that this will happen I<before> C<start_new_request>
		3754	has returned, so C<request> is not set.
		3755
		3756	Even if you pass the request by some safer means to the callback, you
		3757	might want to do something to the request after starting it, such as
		3758	canceling it, which probably isn't working so well when the callback has
		3759	already been invoked.
		3760
		3761	A common way around all these issues is to make sure that
		3762	C<start_new_request> I<always> returns before the callback is invoked. If
		3763	C<start_new_request> immediately knows the result, it can artificially
		3764	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3765	example, or more sneakily, by reusing an existing (stopped) watcher and
		3766	pushing it into the pending queue:
		3767
		3768	ev_set_cb (watcher, callback);
		3769	ev_feed_event (EV_A_ watcher, 0);
		3770
		3771	This way, C<start_new_request> can safely return before the callback is
		3772	invoked, while not delaying callback invocation too much.
		3773
		3774	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3775
		3776	Often (especially in GUI toolkits) there are places where you have
		3777	I<modal> interaction, which is most easily implemented by recursively
		3778	invoking C<ev_run>.
		3779
		3780	This brings the problem of exiting - a callback might want to finish the
		3781	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3782	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3783	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3784	other combination: In these cases, a simple C<ev_break> will not work.
		3785
		3786	The solution is to maintain "break this loop" variable for each C<ev_run>
		3787	invocation, and use a loop around C<ev_run> until the condition is
		3788	triggered, using C<EVRUN_ONCE>:
		3789
		3790	// main loop
		3791	int exit_main_loop = 0;
		3792
		3793	while (!exit_main_loop)
		3794	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3795
		3796	// in a modal watcher
		3797	int exit_nested_loop = 0;
		3798
		3799	while (!exit_nested_loop)
		3800	ev_run (EV_A_ EVRUN_ONCE);
		3801
		3802	To exit from any of these loops, just set the corresponding exit variable:
		3803
		3804	// exit modal loop
		3805	exit_nested_loop = 1;
		3806
		3807	// exit main program, after modal loop is finished
		3808	exit_main_loop = 1;
		3809
		3810	// exit both
		3811	exit_main_loop = exit_nested_loop = 1;
		3812
		3813	=head2 THREAD LOCKING EXAMPLE
		3814
		3815	Here is a fictitious example of how to run an event loop in a different
		3816	thread from where callbacks are being invoked and watchers are
		3817	created/added/removed.
		3818
		3819	For a real-world example, see the C<EV::Loop::Async> perl module,
		3820	which uses exactly this technique (which is suited for many high-level
		3821	languages).
		3822
		3823	The example uses a pthread mutex to protect the loop data, a condition
		3824	variable to wait for callback invocations, an async watcher to notify the
		3825	event loop thread and an unspecified mechanism to wake up the main thread.
		3826
		3827	First, you need to associate some data with the event loop:
		3828
		3829	typedef struct {
		3830	mutex_t lock; /* global loop lock */
		3831	ev_async async_w;
		3832	thread_t tid;
		3833	cond_t invoke_cv;
		3834	} userdata;
		3835
		3836	void prepare_loop (EV_P)
		3837	{
		3838	// for simplicity, we use a static userdata struct.
		3839	static userdata u;
		3840
		3841	ev_async_init (&u->async_w, async_cb);
		3842	ev_async_start (EV_A_ &u->async_w);
		3843
		3844	pthread_mutex_init (&u->lock, 0);
		3845	pthread_cond_init (&u->invoke_cv, 0);
		3846
		3847	// now associate this with the loop
		3848	ev_set_userdata (EV_A_ u);
		3849	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3850	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3851
		3852	// then create the thread running ev_run
		3853	pthread_create (&u->tid, 0, l_run, EV_A);
		3854	}
		3855
		3856	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3857	solely to wake up the event loop so it takes notice of any new watchers
		3858	that might have been added:
		3859
		3860	static void
		3861	async_cb (EV_P_ ev_async *w, int revents)
		3862	{
		3863	// just used for the side effects
		3864	}
		3865
		3866	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3867	protecting the loop data, respectively.
		3868
		3869	static void
		3870	l_release (EV_P)
		3871	{
		3872	userdata *u = ev_userdata (EV_A);
		3873	pthread_mutex_unlock (&u->lock);
		3874	}
		3875
		3876	static void
		3877	l_acquire (EV_P)
		3878	{
		3879	userdata *u = ev_userdata (EV_A);
		3880	pthread_mutex_lock (&u->lock);
		3881	}
		3882
		3883	The event loop thread first acquires the mutex, and then jumps straight
		3884	into C<ev_run>:
		3885
		3886	void *
		3887	l_run (void *thr_arg)
		3888	{
		3889	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3890
		3891	l_acquire (EV_A);
		3892	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3893	ev_run (EV_A_ 0);
		3894	l_release (EV_A);
		3895
		3896	return 0;
		3897	}
		3898
		3899	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3900	signal the main thread via some unspecified mechanism (signals? pipe
		3901	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3902	have been called (in a while loop because a) spurious wakeups are possible
		3903	and b) skipping inter-thread-communication when there are no pending
		3904	watchers is very beneficial):
		3905
		3906	static void
		3907	l_invoke (EV_P)
		3908	{
		3909	userdata *u = ev_userdata (EV_A);
		3910
		3911	while (ev_pending_count (EV_A))
		3912	{
		3913	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3914	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3915	}
		3916	}
		3917
		3918	Now, whenever the main thread gets told to invoke pending watchers, it
		3919	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3920	thread to continue:
		3921
		3922	static void
		3923	real_invoke_pending (EV_P)
		3924	{
		3925	userdata *u = ev_userdata (EV_A);
		3926
		3927	pthread_mutex_lock (&u->lock);
		3928	ev_invoke_pending (EV_A);
		3929	pthread_cond_signal (&u->invoke_cv);
		3930	pthread_mutex_unlock (&u->lock);
		3931	}
		3932
		3933	Whenever you want to start/stop a watcher or do other modifications to an
		3934	event loop, you will now have to lock:
		3935
		3936	ev_timer timeout_watcher;
		3937	userdata *u = ev_userdata (EV_A);
		3938
		3939	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3940
		3941	pthread_mutex_lock (&u->lock);
		3942	ev_timer_start (EV_A_ &timeout_watcher);
		3943	ev_async_send (EV_A_ &u->async_w);
		3944	pthread_mutex_unlock (&u->lock);
		3945
		3946	Note that sending the C<ev_async> watcher is required because otherwise
		3947	an event loop currently blocking in the kernel will have no knowledge
		3948	about the newly added timer. By waking up the loop it will pick up any new
		3949	watchers in the next event loop iteration.
		3950
		3951	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3952
		3953	While the overhead of a callback that e.g. schedules a thread is small, it
		3954	is still an overhead. If you embed libev, and your main usage is with some
		3955	kind of threads or coroutines, you might want to customise libev so that
		3956	doesn't need callbacks anymore.
		3957
		3958	Imagine you have coroutines that you can switch to using a function
		3959	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3960	and that due to some magic, the currently active coroutine is stored in a
		3961	global called C<current_coro>. Then you can build your own "wait for libev
		3962	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3963	the differing C<;> conventions):
		3964
		3965	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3966	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3967
		3968	That means instead of having a C callback function, you store the
		3969	coroutine to switch to in each watcher, and instead of having libev call
		3970	your callback, you instead have it switch to that coroutine.
		3971
		3972	A coroutine might now wait for an event with a function called
		3973	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3974	matter when, or whether the watcher is active or not when this function is
		3975	called):
		3976
		3977	void
		3978	wait_for_event (ev_watcher *w)
		3979	{
		3980	ev_set_cb (w, current_coro);
		3981	switch_to (libev_coro);
		3982	}
		3983
		3984	That basically suspends the coroutine inside C<wait_for_event> and
		3985	continues the libev coroutine, which, when appropriate, switches back to
		3986	this or any other coroutine.
		3987
		3988	You can do similar tricks if you have, say, threads with an event queue -
		3989	instead of storing a coroutine, you store the queue object and instead of
		3990	switching to a coroutine, you push the watcher onto the queue and notify
		3991	any waiters.
		3992
		3993	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3994	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3995
		3996	// my_ev.h
		3997	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3998	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3999	#include "../libev/ev.h"
		4000
		4001	// my_ev.c
		4002	#define EV_H "my_ev.h"
		4003	#include "../libev/ev.c"
		4004
		4005	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4006	F<my_ev.c> into your project. When properly specifying include paths, you
		4007	can even use F<ev.h> as header file name directly.
3360		4008
3361		4009
3362	=head1 LIBEVENT EMULATION	4010	=head1 LIBEVENT EMULATION
3363		4011
3364	Libev offers a compatibility emulation layer for libevent. It cannot	4012	Libev offers a compatibility emulation layer for libevent. It cannot
3365	emulate the internals of libevent, so here are some usage hints:	4013	emulate the internals of libevent, so here are some usage hints:
3366		4014
3367	=over 4	4015	=over 4
		4016
		4017	=item * Only the libevent-1.4.1-beta API is being emulated.
		4018
		4019	This was the newest libevent version available when libev was implemented,
		4020	and is still mostly unchanged in 2010.
3368		4021
3369	=item * Use it by including <event.h>, as usual.	4022	=item * Use it by including <event.h>, as usual.
3370		4023
3371	=item * The following members are fully supported: ev_base, ev_callback,	4024	=item * The following members are fully supported: ev_base, ev_callback,
3372	ev_arg, ev_fd, ev_res, ev_events.	4025	ev_arg, ev_fd, ev_res, ev_events.
…		…
3378	=item * Priorities are not currently supported. Initialising priorities	4031	=item * Priorities are not currently supported. Initialising priorities
3379	will fail and all watchers will have the same priority, even though there	4032	will fail and all watchers will have the same priority, even though there
3380	is an ev_pri field.	4033	is an ev_pri field.
3381		4034
3382	=item * In libevent, the last base created gets the signals, in libev, the	4035	=item * In libevent, the last base created gets the signals, in libev, the
3383	first base created (== the default loop) gets the signals.	4036	base that registered the signal gets the signals.
3384		4037
3385	=item * Other members are not supported.	4038	=item * Other members are not supported.
3386		4039
3387	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4040	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3388	to use the libev header file and library.	4041	to use the libev header file and library.
3389		4042
3390	=back	4043	=back
3391		4044
3392	=head1 C++ SUPPORT	4045	=head1 C++ SUPPORT
		4046
		4047	=head2 C API
		4048
		4049	The normal C API should work fine when used from C++: both ev.h and the
		4050	libev sources can be compiled as C++. Therefore, code that uses the C API
		4051	will work fine.
		4052
		4053	Proper exception specifications might have to be added to callbacks passed
		4054	to libev: exceptions may be thrown only from watcher callbacks, all other
		4055	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4056	callbacks) must not throw exceptions, and might need a C<noexcept>
		4057	specification. If you have code that needs to be compiled as both C and
		4058	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4059
		4060	static void
		4061	fatal_error (const char *msg) EV_NOEXCEPT
		4062	{
		4063	perror (msg);
		4064	abort ();
		4065	}
		4066
		4067	...
		4068	ev_set_syserr_cb (fatal_error);
		4069
		4070	The only API functions that can currently throw exceptions are C<ev_run>,
		4071	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4072	because it runs cleanup watchers).
		4073
		4074	Throwing exceptions in watcher callbacks is only supported if libev itself
		4075	is compiled with a C++ compiler or your C and C++ environments allow
		4076	throwing exceptions through C libraries (most do).
		4077
		4078	=head2 C++ API
3393		4079
3394	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4080	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3395	you to use some convenience methods to start/stop watchers and also change	4081	you to use some convenience methods to start/stop watchers and also change
3396	the callback model to a model using method callbacks on objects.	4082	the callback model to a model using method callbacks on objects.
3397		4083
3398	To use it,	4084	To use it,
3399		4085
3400	#include <ev++.h>	4086	#include <ev++.h>
3401		4087
3402	This automatically includes F<ev.h> and puts all of its definitions (many	4088	This automatically includes F<ev.h> and puts all of its definitions (many
3403	of them macros) into the global namespace. All C++ specific things are	4089	of them macros) into the global namespace. All C++ specific things are
3404	put into the C<ev> namespace. It should support all the same embedding	4090	put into the C<ev> namespace. It should support all the same embedding
…		…
3407	Care has been taken to keep the overhead low. The only data member the C++	4093	Care has been taken to keep the overhead low. The only data member the C++
3408	classes add (compared to plain C-style watchers) is the event loop pointer	4094	classes add (compared to plain C-style watchers) is the event loop pointer
3409	that the watcher is associated with (or no additional members at all if	4095	that the watcher is associated with (or no additional members at all if
3410	you disable C<EV_MULTIPLICITY> when embedding libev).	4096	you disable C<EV_MULTIPLICITY> when embedding libev).
3411		4097
3412	Currently, functions, and static and non-static member functions can be	4098	Currently, functions, static and non-static member functions and classes
3413	used as callbacks. Other types should be easy to add as long as they only	4099	with C<operator ()> can be used as callbacks. Other types should be easy
3414	need one additional pointer for context. If you need support for other	4100	to add as long as they only need one additional pointer for context. If
3415	types of functors please contact the author (preferably after implementing	4101	you need support for other types of functors please contact the author
3416	it).	4102	(preferably after implementing it).
		4103
		4104	For all this to work, your C++ compiler either has to use the same calling
		4105	conventions as your C compiler (for static member functions), or you have
		4106	to embed libev and compile libev itself as C++.
3417		4107
3418	Here is a list of things available in the C<ev> namespace:	4108	Here is a list of things available in the C<ev> namespace:
3419		4109
3420	=over 4	4110	=over 4
3421		4111
…		…
3431	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4121	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3432		4122
3433	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4123	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3434	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4124	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3435	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4125	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3436	defines by many implementations.	4126	defined by many implementations.
3437		4127
3438	All of those classes have these methods:	4128	All of those classes have these methods:
3439		4129
3440	=over 4	4130	=over 4
3441		4131
…		…
3503	void operator() (ev::io &w, int revents)	4193	void operator() (ev::io &w, int revents)
3504	{	4194	{
3505	...	4195	...
3506	}	4196	}
3507	}	4197	}
3508		4198
3509	myfunctor f;	4199	myfunctor f;
3510		4200
3511	ev::io w;	4201	ev::io w;
3512	w.set (&f);	4202	w.set (&f);
3513		4203
…		…
3531	Associates a different C<struct ev_loop> with this watcher. You can only	4221	Associates a different C<struct ev_loop> with this watcher. You can only
3532	do this when the watcher is inactive (and not pending either).	4222	do this when the watcher is inactive (and not pending either).
3533		4223
3534	=item w->set ([arguments])	4224	=item w->set ([arguments])
3535		4225
3536	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4226	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3537	method or a suitable start method must be called at least once. Unlike the	4227	with the same arguments. Either this method or a suitable start method
3538	C counterpart, an active watcher gets automatically stopped and restarted	4228	must be called at least once. Unlike the C counterpart, an active watcher
3539	when reconfiguring it with this method.	4229	gets automatically stopped and restarted when reconfiguring it with this
		4230	method.
		4231
		4232	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4233	clashing with the C<set (loop)> method.
3540		4234
3541	=item w->start ()	4235	=item w->start ()
3542		4236
3543	Starts the watcher. Note that there is no C<loop> argument, as the	4237	Starts the watcher. Note that there is no C<loop> argument, as the
3544	constructor already stores the event loop.	4238	constructor already stores the event loop.
…		…
3574	watchers in the constructor.	4268	watchers in the constructor.
3575		4269
3576	class myclass	4270	class myclass
3577	{	4271	{
3578	ev::io io ; void io_cb (ev::io &w, int revents);	4272	ev::io io ; void io_cb (ev::io &w, int revents);
3579	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4273	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3580	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4274	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3581		4275
3582	myclass (int fd)	4276	myclass (int fd)
3583	{	4277	{
3584	io .set <myclass, &myclass::io_cb > (this);	4278	io .set <myclass, &myclass::io_cb > (this);
…		…
3635	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4329	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3636		4330
3637	=item D	4331	=item D
3638		4332
3639	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4333	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3640	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4334	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3641		4335
3642	=item Ocaml	4336	=item Ocaml
3643		4337
3644	Erkki Seppala has written Ocaml bindings for libev, to be found at	4338	Erkki Seppala has written Ocaml bindings for libev, to be found at
3645	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4339	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3648		4342
3649	Brian Maher has written a partial interface to libev for lua (at the	4343	Brian Maher has written a partial interface to libev for lua (at the
3650	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4344	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3651	L<http://github.com/brimworks/lua-ev>.	4345	L<http://github.com/brimworks/lua-ev>.
3652		4346
		4347	=item Javascript
		4348
		4349	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4350
		4351	=item Others
		4352
		4353	There are others, and I stopped counting.
		4354
3653	=back	4355	=back
3654		4356
3655		4357
3656	=head1 MACRO MAGIC	4358	=head1 MACRO MAGIC
3657		4359
…		…
3693	suitable for use with C<EV_A>.	4395	suitable for use with C<EV_A>.
3694		4396
3695	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4397	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3696		4398
3697	Similar to the other two macros, this gives you the value of the default	4399	Similar to the other two macros, this gives you the value of the default
3698	loop, if multiple loops are supported ("ev loop default").	4400	loop, if multiple loops are supported ("ev loop default"). The default loop
		4401	will be initialised if it isn't already initialised.
		4402
		4403	For non-multiplicity builds, these macros do nothing, so you always have
		4404	to initialise the loop somewhere.
3699		4405
3700	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4406	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3701		4407
3702	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4408	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3703	default loop has been initialised (C<UC> == unchecked). Their behaviour	4409	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3770	ev_vars.h	4476	ev_vars.h
3771	ev_wrap.h	4477	ev_wrap.h
3772		4478
3773	ev_win32.c required on win32 platforms only	4479	ev_win32.c required on win32 platforms only
3774		4480
3775	ev_select.c only when select backend is enabled (which is enabled by default)	4481	ev_select.c only when select backend is enabled
3776	ev_poll.c only when poll backend is enabled (disabled by default)	4482	ev_poll.c only when poll backend is enabled
3777	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4483	ev_epoll.c only when the epoll backend is enabled
		4484	ev_linuxaio.c only when the linux aio backend is enabled
3778	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4485	ev_kqueue.c only when the kqueue backend is enabled
3779	ev_port.c only when the solaris port backend is enabled (disabled by default)	4486	ev_port.c only when the solaris port backend is enabled
3780		4487
3781	F<ev.c> includes the backend files directly when enabled, so you only need	4488	F<ev.c> includes the backend files directly when enabled, so you only need
3782	to compile this single file.	4489	to compile this single file.
3783		4490
3784	=head3 LIBEVENT COMPATIBILITY API	4491	=head3 LIBEVENT COMPATIBILITY API
…		…
3848	supported). It will also not define any of the structs usually found in	4555	supported). It will also not define any of the structs usually found in
3849	F<event.h> that are not directly supported by the libev core alone.	4556	F<event.h> that are not directly supported by the libev core alone.
3850		4557
3851	In standalone mode, libev will still try to automatically deduce the	4558	In standalone mode, libev will still try to automatically deduce the
3852	configuration, but has to be more conservative.	4559	configuration, but has to be more conservative.
		4560
		4561	=item EV_USE_FLOOR
		4562
		4563	If defined to be C<1>, libev will use the C<floor ()> function for its
		4564	periodic reschedule calculations, otherwise libev will fall back on a
		4565	portable (slower) implementation. If you enable this, you usually have to
		4566	link against libm or something equivalent. Enabling this when the C<floor>
		4567	function is not available will fail, so the safe default is to not enable
		4568	this.
3853		4569
3854	=item EV_USE_MONOTONIC	4570	=item EV_USE_MONOTONIC
3855		4571
3856	If defined to be C<1>, libev will try to detect the availability of the	4572	If defined to be C<1>, libev will try to detect the availability of the
3857	monotonic clock option at both compile time and runtime. Otherwise no	4573	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3943	If programs implement their own fd to handle mapping on win32, then this	4659	If programs implement their own fd to handle mapping on win32, then this
3944	macro can be used to override the C<close> function, useful to unregister	4660	macro can be used to override the C<close> function, useful to unregister
3945	file descriptors again. Note that the replacement function has to close	4661	file descriptors again. Note that the replacement function has to close
3946	the underlying OS handle.	4662	the underlying OS handle.
3947		4663
		4664	=item EV_USE_WSASOCKET
		4665
		4666	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4667	communication socket, which works better in some environments. Otherwise,
		4668	the normal C<socket> function will be used, which works better in other
		4669	environments.
		4670
3948	=item EV_USE_POLL	4671	=item EV_USE_POLL
3949		4672
3950	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4673	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3951	backend. Otherwise it will be enabled on non-win32 platforms. It	4674	backend. Otherwise it will be enabled on non-win32 platforms. It
3952	takes precedence over select.	4675	takes precedence over select.
…		…
3956	If defined to be C<1>, libev will compile in support for the Linux	4679	If defined to be C<1>, libev will compile in support for the Linux
3957	C<epoll>(7) backend. Its availability will be detected at runtime,	4680	C<epoll>(7) backend. Its availability will be detected at runtime,
3958	otherwise another method will be used as fallback. This is the preferred	4681	otherwise another method will be used as fallback. This is the preferred
3959	backend for GNU/Linux systems. If undefined, it will be enabled if the	4682	backend for GNU/Linux systems. If undefined, it will be enabled if the
3960	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4683	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4684
		4685	=item EV_USE_LINUXAIO
		4686
		4687	If defined to be C<1>, libev will compile in support for the Linux
		4688	aio backend. Due to it's currenbt limitations it has to be requested
		4689	explicitly. If undefined, it will be enabled on linux, otherwise
		4690	disabled.
3961		4691
3962	=item EV_USE_KQUEUE	4692	=item EV_USE_KQUEUE
3963		4693
3964	If defined to be C<1>, libev will compile in support for the BSD style	4694	If defined to be C<1>, libev will compile in support for the BSD style
3965	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4695	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
3987	If defined to be C<1>, libev will compile in support for the Linux inotify	4717	If defined to be C<1>, libev will compile in support for the Linux inotify
3988	interface to speed up C<ev_stat> watchers. Its actual availability will	4718	interface to speed up C<ev_stat> watchers. Its actual availability will
3989	be detected at runtime. If undefined, it will be enabled if the headers	4719	be detected at runtime. If undefined, it will be enabled if the headers
3990	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4720	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3991		4721
		4722	=item EV_NO_SMP
		4723
		4724	If defined to be C<1>, libev will assume that memory is always coherent
		4725	between threads, that is, threads can be used, but threads never run on
		4726	different cpus (or different cpu cores). This reduces dependencies
		4727	and makes libev faster.
		4728
		4729	=item EV_NO_THREADS
		4730
		4731	If defined to be C<1>, libev will assume that it will never be called from
		4732	different threads (that includes signal handlers), which is a stronger
		4733	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4734	libev faster.
		4735
3992	=item EV_ATOMIC_T	4736	=item EV_ATOMIC_T
3993		4737
3994	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4738	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3995	access is atomic with respect to other threads or signal contexts. No such	4739	access is atomic with respect to other threads or signal contexts. No
3996	type is easily found in the C language, so you can provide your own type	4740	such type is easily found in the C language, so you can provide your own
3997	that you know is safe for your purposes. It is used both for signal handler "locking"	4741	type that you know is safe for your purposes. It is used both for signal
3998	as well as for signal and thread safety in C<ev_async> watchers.	4742	handler "locking" as well as for signal and thread safety in C<ev_async>
		4743	watchers.
3999		4744
4000	In the absence of this define, libev will use C<sig_atomic_t volatile>	4745	In the absence of this define, libev will use C<sig_atomic_t volatile>
4001	(from F<signal.h>), which is usually good enough on most platforms.	4746	(from F<signal.h>), which is usually good enough on most platforms.
4002		4747
4003	=item EV_H (h)	4748	=item EV_H (h)
…		…
4030	will have the C<struct ev_loop *> as first argument, and you can create	4775	will have the C<struct ev_loop *> as first argument, and you can create
4031	additional independent event loops. Otherwise there will be no support	4776	additional independent event loops. Otherwise there will be no support
4032	for multiple event loops and there is no first event loop pointer	4777	for multiple event loops and there is no first event loop pointer
4033	argument. Instead, all functions act on the single default loop.	4778	argument. Instead, all functions act on the single default loop.
4034		4779
		4780	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4781	default loop when multiplicity is switched off - you always have to
		4782	initialise the loop manually in this case.
		4783
4035	=item EV_MINPRI	4784	=item EV_MINPRI
4036		4785
4037	=item EV_MAXPRI	4786	=item EV_MAXPRI
4038		4787
4039	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4788	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4075	#define EV_USE_POLL 1	4824	#define EV_USE_POLL 1
4076	#define EV_CHILD_ENABLE 1	4825	#define EV_CHILD_ENABLE 1
4077	#define EV_ASYNC_ENABLE 1	4826	#define EV_ASYNC_ENABLE 1
4078		4827
4079	The actual value is a bitset, it can be a combination of the following	4828	The actual value is a bitset, it can be a combination of the following
4080	values:	4829	values (by default, all of these are enabled):
4081		4830
4082	=over 4	4831	=over 4
4083		4832
4084	=item C<1> - faster/larger code	4833	=item C<1> - faster/larger code
4085		4834
…		…
4089	code size by roughly 30% on amd64).	4838	code size by roughly 30% on amd64).
4090		4839
4091	When optimising for size, use of compiler flags such as C<-Os> with	4840	When optimising for size, use of compiler flags such as C<-Os> with
4092	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4841	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4093	assertions.	4842	assertions.
		4843
		4844	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4845	(e.g. gcc with C<-Os>).
4094		4846
4095	=item C<2> - faster/larger data structures	4847	=item C<2> - faster/larger data structures
4096		4848
4097	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4849	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4098	hash table sizes and so on. This will usually further increase code size	4850	hash table sizes and so on. This will usually further increase code size
4099	and can additionally have an effect on the size of data structures at	4851	and can additionally have an effect on the size of data structures at
4100	runtime.	4852	runtime.
4101		4853
		4854	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4855	(e.g. gcc with C<-Os>).
		4856
4102	=item C<4> - full API configuration	4857	=item C<4> - full API configuration
4103		4858
4104	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4859	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4105	enables multiplicity (C<EV_MULTIPLICITY>=1).	4860	enables multiplicity (C<EV_MULTIPLICITY>=1).
4106		4861
…		…
4136		4891
4137	With an intelligent-enough linker (gcc+binutils are intelligent enough	4892	With an intelligent-enough linker (gcc+binutils are intelligent enough
4138	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4893	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4139	your program might be left out as well - a binary starting a timer and an	4894	your program might be left out as well - a binary starting a timer and an
4140	I/O watcher then might come out at only 5Kb.	4895	I/O watcher then might come out at only 5Kb.
		4896
		4897	=item EV_API_STATIC
		4898
		4899	If this symbol is defined (by default it is not), then all identifiers
		4900	will have static linkage. This means that libev will not export any
		4901	identifiers, and you cannot link against libev anymore. This can be useful
		4902	when you embed libev, only want to use libev functions in a single file,
		4903	and do not want its identifiers to be visible.
		4904
		4905	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4906	wants to use libev.
		4907
		4908	This option only works when libev is compiled with a C compiler, as C++
		4909	doesn't support the required declaration syntax.
4141		4910
4142	=item EV_AVOID_STDIO	4911	=item EV_AVOID_STDIO
4143		4912
4144	If this is set to C<1> at compiletime, then libev will avoid using stdio	4913	If this is set to C<1> at compiletime, then libev will avoid using stdio
4145	functions (printf, scanf, perror etc.). This will increase the code size	4914	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4289	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5058	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4290		5059
4291	#include "ev_cpp.h"	5060	#include "ev_cpp.h"
4292	#include "ev.c"	5061	#include "ev.c"
4293		5062
4294	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5063	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4295		5064
4296	=head2 THREADS AND COROUTINES	5065	=head2 THREADS AND COROUTINES
4297		5066
4298	=head3 THREADS	5067	=head3 THREADS
4299		5068
…		…
4350	default loop and triggering an C<ev_async> watcher from the default loop	5119	default loop and triggering an C<ev_async> watcher from the default loop
4351	watcher callback into the event loop interested in the signal.	5120	watcher callback into the event loop interested in the signal.
4352		5121
4353	=back	5122	=back
4354		5123
4355	=head4 THREAD LOCKING EXAMPLE	5124	See also L</THREAD LOCKING EXAMPLE>.
4356
4357	Here is a fictitious example of how to run an event loop in a different
4358	thread than where callbacks are being invoked and watchers are
4359	created/added/removed.
4360
4361	For a real-world example, see the C<EV::Loop::Async> perl module,
4362	which uses exactly this technique (which is suited for many high-level
4363	languages).
4364
4365	The example uses a pthread mutex to protect the loop data, a condition
4366	variable to wait for callback invocations, an async watcher to notify the
4367	event loop thread and an unspecified mechanism to wake up the main thread.
4368
4369	First, you need to associate some data with the event loop:
4370
4371	typedef struct {
4372	mutex_t lock; /* global loop lock */
4373	ev_async async_w;
4374	thread_t tid;
4375	cond_t invoke_cv;
4376	} userdata;
4377
4378	void prepare_loop (EV_P)
4379	{
4380	// for simplicity, we use a static userdata struct.
4381	static userdata u;
4382
4383	ev_async_init (&u->async_w, async_cb);
4384	ev_async_start (EV_A_ &u->async_w);
4385
4386	pthread_mutex_init (&u->lock, 0);
4387	pthread_cond_init (&u->invoke_cv, 0);
4388
4389	// now associate this with the loop
4390	ev_set_userdata (EV_A_ u);
4391	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4392	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4393
4394	// then create the thread running ev_loop
4395	pthread_create (&u->tid, 0, l_run, EV_A);
4396	}
4397
4398	The callback for the C<ev_async> watcher does nothing: the watcher is used
4399	solely to wake up the event loop so it takes notice of any new watchers
4400	that might have been added:
4401
4402	static void
4403	async_cb (EV_P_ ev_async *w, int revents)
4404	{
4405	// just used for the side effects
4406	}
4407
4408	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4409	protecting the loop data, respectively.
4410
4411	static void
4412	l_release (EV_P)
4413	{
4414	userdata *u = ev_userdata (EV_A);
4415	pthread_mutex_unlock (&u->lock);
4416	}
4417
4418	static void
4419	l_acquire (EV_P)
4420	{
4421	userdata *u = ev_userdata (EV_A);
4422	pthread_mutex_lock (&u->lock);
4423	}
4424
4425	The event loop thread first acquires the mutex, and then jumps straight
4426	into C<ev_run>:
4427
4428	void *
4429	l_run (void *thr_arg)
4430	{
4431	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4432
4433	l_acquire (EV_A);
4434	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4435	ev_run (EV_A_ 0);
4436	l_release (EV_A);
4437
4438	return 0;
4439	}
4440
4441	Instead of invoking all pending watchers, the C<l_invoke> callback will
4442	signal the main thread via some unspecified mechanism (signals? pipe
4443	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4444	have been called (in a while loop because a) spurious wakeups are possible
4445	and b) skipping inter-thread-communication when there are no pending
4446	watchers is very beneficial):
4447
4448	static void
4449	l_invoke (EV_P)
4450	{
4451	userdata *u = ev_userdata (EV_A);
4452
4453	while (ev_pending_count (EV_A))
4454	{
4455	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4456	pthread_cond_wait (&u->invoke_cv, &u->lock);
4457	}
4458	}
4459
4460	Now, whenever the main thread gets told to invoke pending watchers, it
4461	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4462	thread to continue:
4463
4464	static void
4465	real_invoke_pending (EV_P)
4466	{
4467	userdata *u = ev_userdata (EV_A);
4468
4469	pthread_mutex_lock (&u->lock);
4470	ev_invoke_pending (EV_A);
4471	pthread_cond_signal (&u->invoke_cv);
4472	pthread_mutex_unlock (&u->lock);
4473	}
4474
4475	Whenever you want to start/stop a watcher or do other modifications to an
4476	event loop, you will now have to lock:
4477
4478	ev_timer timeout_watcher;
4479	userdata *u = ev_userdata (EV_A);
4480
4481	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4482
4483	pthread_mutex_lock (&u->lock);
4484	ev_timer_start (EV_A_ &timeout_watcher);
4485	ev_async_send (EV_A_ &u->async_w);
4486	pthread_mutex_unlock (&u->lock);
4487
4488	Note that sending the C<ev_async> watcher is required because otherwise
4489	an event loop currently blocking in the kernel will have no knowledge
4490	about the newly added timer. By waking up the loop it will pick up any new
4491	watchers in the next event loop iteration.
4492		5125
4493	=head3 COROUTINES	5126	=head3 COROUTINES
4494		5127
4495	Libev is very accommodating to coroutines ("cooperative threads"):	5128	Libev is very accommodating to coroutines ("cooperative threads"):
4496	libev fully supports nesting calls to its functions from different	5129	libev fully supports nesting calls to its functions from different
…		…
4661	requires, and its I/O model is fundamentally incompatible with the POSIX	5294	requires, and its I/O model is fundamentally incompatible with the POSIX
4662	model. Libev still offers limited functionality on this platform in	5295	model. Libev still offers limited functionality on this platform in
4663	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5296	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4664	descriptors. This only applies when using Win32 natively, not when using	5297	descriptors. This only applies when using Win32 natively, not when using
4665	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5298	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4666	as every compielr comes with a slightly differently broken/incompatible	5299	as every compiler comes with a slightly differently broken/incompatible
4667	environment.	5300	environment.
4668		5301
4669	Lifting these limitations would basically require the full	5302	Lifting these limitations would basically require the full
4670	re-implementation of the I/O system. If you are into this kind of thing,	5303	re-implementation of the I/O system. If you are into this kind of thing,
4671	then note that glib does exactly that for you in a very portable way (note	5304	then note that glib does exactly that for you in a very portable way (note
…		…
4765	structure (guaranteed by POSIX but not by ISO C for example), but it also	5398	structure (guaranteed by POSIX but not by ISO C for example), but it also
4766	assumes that the same (machine) code can be used to call any watcher	5399	assumes that the same (machine) code can be used to call any watcher
4767	callback: The watcher callbacks have different type signatures, but libev	5400	callback: The watcher callbacks have different type signatures, but libev
4768	calls them using an C<ev_watcher *> internally.	5401	calls them using an C<ev_watcher *> internally.
4769		5402
		5403	=item null pointers and integer zero are represented by 0 bytes
		5404
		5405	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5406	relies on this setting pointers and integers to null.
		5407
4770	=item pointer accesses must be thread-atomic	5408	=item pointer accesses must be thread-atomic
4771		5409
4772	Accessing a pointer value must be atomic, it must both be readable and	5410	Accessing a pointer value must be atomic, it must both be readable and
4773	writable in one piece - this is the case on all current architectures.	5411	writable in one piece - this is the case on all current architectures.
4774		5412
…		…
4787	thread" or will block signals process-wide, both behaviours would	5425	thread" or will block signals process-wide, both behaviours would
4788	be compatible with libev. Interaction between C<sigprocmask> and	5426	be compatible with libev. Interaction between C<sigprocmask> and
4789	C<pthread_sigmask> could complicate things, however.	5427	C<pthread_sigmask> could complicate things, however.
4790		5428
4791	The most portable way to handle signals is to block signals in all threads	5429	The most portable way to handle signals is to block signals in all threads
4792	except the initial one, and run the default loop in the initial thread as	5430	except the initial one, and run the signal handling loop in the initial
4793	well.	5431	thread as well.
4794		5432
4795	=item C<long> must be large enough for common memory allocation sizes	5433	=item C<long> must be large enough for common memory allocation sizes
4796		5434
4797	To improve portability and simplify its API, libev uses C<long> internally	5435	To improve portability and simplify its API, libev uses C<long> internally
4798	instead of C<size_t> when allocating its data structures. On non-POSIX	5436	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4804		5442
4805	The type C<double> is used to represent timestamps. It is required to	5443	The type C<double> is used to represent timestamps. It is required to
4806	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5444	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4807	good enough for at least into the year 4000 with millisecond accuracy	5445	good enough for at least into the year 4000 with millisecond accuracy
4808	(the design goal for libev). This requirement is overfulfilled by	5446	(the design goal for libev). This requirement is overfulfilled by
4809	implementations using IEEE 754, which is basically all existing ones. With	5447	implementations using IEEE 754, which is basically all existing ones.
		5448
4810	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5449	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5450	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5451	is either obsolete or somebody patched it to use C<long double> or
		5452	something like that, just kidding).
4811		5453
4812	=back	5454	=back
4813		5455
4814	If you know of other additional requirements drop me a note.	5456	If you know of other additional requirements drop me a note.
4815		5457
…		…
4877	=item Processing ev_async_send: O(number_of_async_watchers)	5519	=item Processing ev_async_send: O(number_of_async_watchers)
4878		5520
4879	=item Processing signals: O(max_signal_number)	5521	=item Processing signals: O(max_signal_number)
4880		5522
4881	Sending involves a system call I<iff> there were no other C<ev_async_send>	5523	Sending involves a system call I<iff> there were no other C<ev_async_send>
4882	calls in the current loop iteration. Checking for async and signal events	5524	calls in the current loop iteration and the loop is currently
		5525	blocked. Checking for async and signal events involves iterating over all
4883	involves iterating over all running async watchers or all signal numbers.	5526	running async watchers or all signal numbers.
4884		5527
4885	=back	5528	=back
4886		5529
4887		5530
4888	=head1 PORTING FROM LIBEV 3.X TO 4.X	5531	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
4897	=over 4	5540	=over 4
4898		5541
4899	=item C<EV_COMPAT3> backwards compatibility mechanism	5542	=item C<EV_COMPAT3> backwards compatibility mechanism
4900		5543
4901	The backward compatibility mechanism can be controlled by	5544	The backward compatibility mechanism can be controlled by
4902	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5545	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
4903	section.	5546	section.
4904		5547
4905	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5548	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4906		5549
4907	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5550	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
4950	=over 4	5593	=over 4
4951		5594
4952	=item active	5595	=item active
4953		5596
4954	A watcher is active as long as it has been started and not yet stopped.	5597	A watcher is active as long as it has been started and not yet stopped.
4955	See L<WATCHER STATES> for details.	5598	See L</WATCHER STATES> for details.
4956		5599
4957	=item application	5600	=item application
4958		5601
4959	In this document, an application is whatever is using libev.	5602	In this document, an application is whatever is using libev.
4960		5603
…		…
4996	watchers and events.	5639	watchers and events.
4997		5640
4998	=item pending	5641	=item pending
4999		5642
5000	A watcher is pending as soon as the corresponding event has been	5643	A watcher is pending as soon as the corresponding event has been
5001	detected. See L<WATCHER STATES> for details.	5644	detected. See L</WATCHER STATES> for details.
5002		5645
5003	=item real time	5646	=item real time
5004		5647
5005	The physical time that is observed. It is apparently strictly monotonic :)	5648	The physical time that is observed. It is apparently strictly monotonic :)
5006		5649
5007	=item wall-clock time	5650	=item wall-clock time
5008		5651
5009	The time and date as shown on clocks. Unlike real time, it can actually	5652	The time and date as shown on clocks. Unlike real time, it can actually
5010	be wrong and jump forwards and backwards, e.g. when the you adjust your	5653	be wrong and jump forwards and backwards, e.g. when you adjust your
5011	clock.	5654	clock.
5012		5655
5013	=item watcher	5656	=item watcher
5014		5657
5015	A data structure that describes interest in certain events. Watchers need	5658	A data structure that describes interest in certain events. Watchers need
…		…
5018	=back	5661	=back
5019		5662
5020	=head1 AUTHOR	5663	=head1 AUTHOR
5021		5664
5022	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5665	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5023	Magnusson and Emanuele Giaquinta.	5666	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5024		5667

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