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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
…		…
78	with libev.	80	with libev.
79		81
80	Familiarity with event based programming techniques in general is assumed	82	Familiarity with event based programming techniques in general is assumed
81	throughout this document.	83	throughout this document.
82		84
		85	=head1 WHAT TO READ WHEN IN A HURRY
		86
		87	This manual tries to be very detailed, but unfortunately, this also makes
		88	it very long. If you just want to know the basics of libev, I suggest
		89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
		90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
		91	C<ev_timer> sections in L</WATCHER TYPES>.
		92
83	=head1 ABOUT LIBEV	93	=head1 ABOUT LIBEV
84		94
85	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
86	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
87	these event sources and provide your program with events.	97	these event sources and provide your program with events.
…		…
95	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
96	watcher.	106	watcher.
97		107
98	=head2 FEATURES	108	=head2 FEATURES
99		109
100	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>
101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port
102	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>
103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner	113	interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
104	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
105	timers (C<ev_timer>), absolute timers with customised rescheduling	115	timers (C<ev_timer>), absolute timers with customised rescheduling
106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status	116	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
107	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
108	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
…		…
149	When libev detects a usage error such as a negative timer interval, then	159	When libev detects a usage error such as a negative timer interval, then
150	it will print a diagnostic message and abort (via the C<assert> mechanism,	160	it will print a diagnostic message and abort (via the C<assert> mechanism,
151	so C<NDEBUG> will disable this checking): these are programming errors in	161	so C<NDEBUG> will disable this checking): these are programming errors in
152	the libev caller and need to be fixed there.	162	the libev caller and need to be fixed there.
153		163
		164	Via the C<EV_FREQUENT> macro you can compile in and/or enable extensive
		165	consistency checking code inside libev that can be used to check for
		166	internal inconsistencies, suually caused by application bugs.
		167
154	Libev also has a few internal error-checking C<assert>ions, and also has	168	Libev also has a few internal error-checking C<assert>ions. These do not
155	extensive consistency checking code. These do not trigger under normal
156	circumstances, as they indicate either a bug in libev or worse.	169	trigger under normal circumstances, as they indicate either a bug in libev
		170	or worse.
157		171
158		172
159	=head1 GLOBAL FUNCTIONS	173	=head1 GLOBAL FUNCTIONS
160		174
161	These functions can be called anytime, even before initialising the	175	These functions can be called anytime, even before initialising the
…		…
166	=item ev_tstamp ev_time ()	180	=item ev_tstamp ev_time ()
167		181
168	Returns the current time as libev would use it. Please note that the	182	Returns the current time as libev would use it. Please note that the
169	C<ev_now> function is usually faster and also often returns the timestamp	183	C<ev_now> function is usually faster and also often returns the timestamp
170	you actually want to know. Also interesting is the combination of	184	you actually want to know. Also interesting is the combination of
171	C<ev_update_now> and C<ev_now>.	185	C<ev_now_update> and C<ev_now>.
172		186
173	=item ev_sleep (ev_tstamp interval)	187	=item ev_sleep (ev_tstamp interval)
174		188
175	Sleep for the given interval: The current thread will be blocked until	189	Sleep for the given interval: The current thread will be blocked
176	either it is interrupted or the given time interval has passed. Basically	190	until either it is interrupted or the given time interval has
		191	passed (approximately - it might return a bit earlier even if not
		192	interrupted). Returns immediately if C<< interval <= 0 >>.
		193
177	this is a sub-second-resolution C<sleep ()>.	194	Basically this is a sub-second-resolution C<sleep ()>.
		195
		196	The range of the C<interval> is limited - libev only guarantees to work
		197	with sleep times of up to one day (C<< interval <= 86400 >>).
178		198
179	=item int ev_version_major ()	199	=item int ev_version_major ()
180		200
181	=item int ev_version_minor ()	201	=item int ev_version_minor ()
182		202
…		…
233	the current system, you would need to look at C<ev_embeddable_backends ()	253	the current system, you would need to look at C<ev_embeddable_backends ()
234	& ev_supported_backends ()>, likewise for recommended ones.	254	& ev_supported_backends ()>, likewise for recommended ones.
235		255
236	See the description of C<ev_embed> watchers for more info.	256	See the description of C<ev_embed> watchers for more info.
237		257
238	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	258	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
239		259
240	Sets the allocation function to use (the prototype is similar - the	260	Sets the allocation function to use (the prototype is similar - the
241	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	261	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
242	used to allocate and free memory (no surprises here). If it returns zero	262	used to allocate and free memory (no surprises here). If it returns zero
243	when memory needs to be allocated (C<size != 0>), the library might abort	263	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
249		269
250	You could override this function in high-availability programs to, say,	270	You could override this function in high-availability programs to, say,
251	free some memory if it cannot allocate memory, to use a special allocator,	271	free some memory if it cannot allocate memory, to use a special allocator,
252	or even to sleep a while and retry until some memory is available.	272	or even to sleep a while and retry until some memory is available.
253		273
		274	Example: The following is the C<realloc> function that libev itself uses
		275	which should work with C<realloc> and C<free> functions of all kinds and
		276	is probably a good basis for your own implementation.
		277
		278	static void *
		279	ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
		280	{
		281	if (size)
		282	return realloc (ptr, size);
		283
		284	free (ptr);
		285	return 0;
		286	}
		287
254	Example: Replace the libev allocator with one that waits a bit and then	288	Example: Replace the libev allocator with one that waits a bit and then
255	retries (example requires a standards-compliant C<realloc>).	289	retries.
256		290
257	static void *	291	static void *
258	persistent_realloc (void *ptr, size_t size)	292	persistent_realloc (void *ptr, size_t size)
259	{	293	{
		294	if (!size)
		295	{
		296	free (ptr);
		297	return 0;
		298	}
		299
260	for (;;)	300	for (;;)
261	{	301	{
262	void *newptr = realloc (ptr, size);	302	void *newptr = realloc (ptr, size);
263		303
264	if (newptr)	304	if (newptr)
…		…
269	}	309	}
270		310
271	...	311	...
272	ev_set_allocator (persistent_realloc);	312	ev_set_allocator (persistent_realloc);
273		313
274	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	314	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
275		315
276	Set the callback function to call on a retryable system call error (such	316	Set the callback function to call on a retryable system call error (such
277	as failed select, poll, epoll_wait). The message is a printable string	317	as failed select, poll, epoll_wait). The message is a printable string
278	indicating the system call or subsystem causing the problem. If this	318	indicating the system call or subsystem causing the problem. If this
279	callback is set, then libev will expect it to remedy the situation, no	319	callback is set, then libev will expect it to remedy the situation, no
…		…
291	}	331	}
292		332
293	...	333	...
294	ev_set_syserr_cb (fatal_error);	334	ev_set_syserr_cb (fatal_error);
295		335
		336	=item ev_feed_signal (int signum)
		337
		338	This function can be used to "simulate" a signal receive. It is completely
		339	safe to call this function at any time, from any context, including signal
		340	handlers or random threads.
		341
		342	Its main use is to customise signal handling in your process, especially
		343	in the presence of threads. For example, you could block signals
		344	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		345	creating any loops), and in one thread, use C<sigwait> or any other
		346	mechanism to wait for signals, then "deliver" them to libev by calling
		347	C<ev_feed_signal>.
		348
296	=back	349	=back
297		350
298	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	351	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
299		352
300	An event loop is described by a C<struct ev_loop *> (the C<struct> is	353	An event loop is described by a C<struct ev_loop *> (the C<struct> is
301	I<not> optional in this case unless libev 3 compatibility is disabled, as	354	I<not> optional in this case unless libev 3 compatibility is disabled, as
302	libev 3 had an C<ev_loop> function colliding with the struct name).	355	libev 3 had an C<ev_loop> function colliding with the struct name).
303		356
304	The library knows two types of such loops, the I<default> loop, which	357	The library knows two types of such loops, the I<default> loop, which
305	supports signals and child events, and dynamically created event loops	358	supports child process events, and dynamically created event loops which
306	which do not.	359	do not.
307		360
308	=over 4	361	=over 4
309		362
310	=item struct ev_loop *ev_default_loop (unsigned int flags)	363	=item struct ev_loop *ev_default_loop (unsigned int flags)
311		364
…		…
347	=item struct ev_loop *ev_loop_new (unsigned int flags)	400	=item struct ev_loop *ev_loop_new (unsigned int flags)
348		401
349	This will create and initialise a new event loop object. If the loop	402	This will create and initialise a new event loop object. If the loop
350	could not be initialised, returns false.	403	could not be initialised, returns false.
351		404
352	Note that this function I<is> thread-safe, and one common way to use	405	This function is thread-safe, and one common way to use libev with
353	libev with threads is indeed to create one loop per thread, and using the	406	threads is indeed to create one loop per thread, and using the default
354	default loop in the "main" or "initial" thread.	407	loop in the "main" or "initial" thread.
355		408
356	The flags argument can be used to specify special behaviour or specific	409	The flags argument can be used to specify special behaviour or specific
357	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	410	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
358		411
359	The following flags are supported:	412	The following flags are supported:
…		…
369		422
370	If this flag bit is or'ed into the flag value (or the program runs setuid	423	If this flag bit is or'ed into the flag value (or the program runs setuid
371	or setgid) then libev will I<not> look at the environment variable	424	or setgid) then libev will I<not> look at the environment variable
372	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	425	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
373	override the flags completely if it is found in the environment. This is	426	override the flags completely if it is found in the environment. This is
374	useful to try out specific backends to test their performance, or to work	427	useful to try out specific backends to test their performance, to work
375	around bugs.	428	around bugs, or to make libev threadsafe (accessing environment variables
		429	cannot be done in a threadsafe way, but usually it works if no other
		430	thread modifies them).
376		431
377	=item C<EVFLAG_FORKCHECK>	432	=item C<EVFLAG_FORKCHECK>
378		433
379	Instead of calling C<ev_loop_fork> manually after a fork, you can also	434	Instead of calling C<ev_loop_fork> manually after a fork, you can also
380	make libev check for a fork in each iteration by enabling this flag.	435	make libev check for a fork in each iteration by enabling this flag.
381		436
382	This works by calling C<getpid ()> on every iteration of the loop,	437	This works by calling C<getpid ()> on every iteration of the loop,
383	and thus this might slow down your event loop if you do a lot of loop	438	and thus this might slow down your event loop if you do a lot of loop
384	iterations and little real work, but is usually not noticeable (on my	439	iterations and little real work, but is usually not noticeable (on my
385	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	440	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
386	without a system call and thus I<very> fast, but my GNU/Linux system also has	441	sequence without a system call and thus I<very> fast, but my GNU/Linux
387	C<pthread_atfork> which is even faster).	442	system also has C<pthread_atfork> which is even faster). (Update: glibc
		443	versions 2.25 apparently removed the C<getpid> optimisation again).
388		444
389	The big advantage of this flag is that you can forget about fork (and	445	The big advantage of this flag is that you can forget about fork (and
390	forget about forgetting to tell libev about forking) when you use this	446	forget about forgetting to tell libev about forking, although you still
391	flag.	447	have to ignore C<SIGPIPE>) when you use this flag.
392		448
393	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	449	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
394	environment variable.	450	environment variable.
395		451
396	=item C<EVFLAG_NOINOTIFY>	452	=item C<EVFLAG_NOINOTIFY>
397		453
398	When this flag is specified, then libev will not attempt to use the	454	When this flag is specified, then libev will not attempt to use the
399	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and	455	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
400	testing, this flag can be useful to conserve inotify file descriptors, as	456	testing, this flag can be useful to conserve inotify file descriptors, as
401	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.	457	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
402		458
403	=item C<EVFLAG_SIGNALFD>	459	=item C<EVFLAG_SIGNALFD>
404		460
405	When this flag is specified, then libev will attempt to use the	461	When this flag is specified, then libev will attempt to use the
406	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API	462	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
407	delivers signals synchronously, which makes it both faster and might make	463	delivers signals synchronously, which makes it both faster and might make
408	it possible to get the queued signal data. It can also simplify signal	464	it possible to get the queued signal data. It can also simplify signal
409	handling with threads, as long as you properly block signals in your	465	handling with threads, as long as you properly block signals in your
410	threads that are not interested in handling them.	466	threads that are not interested in handling them.
411		467
412	Signalfd will not be used by default as this changes your signal mask, and	468	Signalfd will not be used by default as this changes your signal mask, and
413	there are a lot of shoddy libraries and programs (glib's threadpool for	469	there are a lot of shoddy libraries and programs (glib's threadpool for
414	example) that can't properly initialise their signal masks.	470	example) that can't properly initialise their signal masks.
		471
		472	=item C<EVFLAG_NOSIGMASK>
		473
		474	When this flag is specified, then libev will avoid to modify the signal
		475	mask. Specifically, this means you have to make sure signals are unblocked
		476	when you want to receive them.
		477
		478	This behaviour is useful when you want to do your own signal handling, or
		479	want to handle signals only in specific threads and want to avoid libev
		480	unblocking the signals.
		481
		482	It's also required by POSIX in a threaded program, as libev calls
		483	C<sigprocmask>, whose behaviour is officially unspecified.
		484
		485	=item C<EVFLAG_NOTIMERFD>
		486
		487	When this flag is specified, the libev will avoid using a C<timerfd> to
		488	detect time jumps. It will still be able to detect time jumps, but takes
		489	longer and has a lower accuracy in doing so, but saves a file descriptor
		490	per loop.
		491
		492	The current implementation only tries to use a C<timerfd> when the first
		493	C<ev_periodic> watcher is started and falls back on other methods if it
		494	cannot be created, but this behaviour might change in the future.
415		495
416	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	496	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
417		497
418	This is your standard select(2) backend. Not I<completely> standard, as	498	This is your standard select(2) backend. Not I<completely> standard, as
419	libev tries to roll its own fd_set with no limits on the number of fds,	499	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
444	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and	524	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
445	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	525	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
446		526
447	=item C<EVBACKEND_EPOLL> (value 4, Linux)	527	=item C<EVBACKEND_EPOLL> (value 4, Linux)
448		528
449	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	529	Use the Linux-specific epoll(7) interface (for both pre- and post-2.6.9
450	kernels).	530	kernels).
451		531
452	For few fds, this backend is a bit little slower than poll and select,	532	For few fds, this backend is a bit little slower than poll and select, but
453	but it scales phenomenally better. While poll and select usually scale	533	it scales phenomenally better. While poll and select usually scale like
454	like O(total_fds) where n is the total number of fds (or the highest fd),	534	O(total_fds) where total_fds is the total number of fds (or the highest
455	epoll scales either O(1) or O(active_fds).	535	fd), epoll scales either O(1) or O(active_fds).
456		536
457	The epoll mechanism deserves honorable mention as the most misdesigned	537	The epoll mechanism deserves honorable mention as the most misdesigned
458	of the more advanced event mechanisms: mere annoyances include silently	538	of the more advanced event mechanisms: mere annoyances include silently
459	dropping file descriptors, requiring a system call per change per file	539	dropping file descriptors, requiring a system call per change per file
460	descriptor (and unnecessary guessing of parameters), problems with dup and	540	descriptor (and unnecessary guessing of parameters), problems with dup,
		541	returning before the timeout value, resulting in additional iterations
		542	(and only giving 5ms accuracy while select on the same platform gives
461	so on. The biggest issue is fork races, however - if a program forks then	543	0.1ms) and so on. The biggest issue is fork races, however - if a program
462	I<both> parent and child process have to recreate the epoll set, which can	544	forks then I<both> parent and child process have to recreate the epoll
463	take considerable time (one syscall per file descriptor) and is of course	545	set, which can take considerable time (one syscall per file descriptor)
464	hard to detect.	546	and is of course hard to detect.
465		547
466	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	548	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
467	of course I<doesn't>, and epoll just loves to report events for totally	549	but of course I<doesn't>, and epoll just loves to report events for
468	I<different> file descriptors (even already closed ones, so one cannot	550	totally I<different> file descriptors (even already closed ones, so
469	even remove them from the set) than registered in the set (especially	551	one cannot even remove them from the set) than registered in the set
470	on SMP systems). Libev tries to counter these spurious notifications by	552	(especially on SMP systems). Libev tries to counter these spurious
471	employing an additional generation counter and comparing that against the	553	notifications by employing an additional generation counter and comparing
472	events to filter out spurious ones, recreating the set when required. Last	554	that against the events to filter out spurious ones, recreating the set
		555	when required. Epoll also erroneously rounds down timeouts, but gives you
		556	no way to know when and by how much, so sometimes you have to busy-wait
		557	because epoll returns immediately despite a nonzero timeout. And last
473	not least, it also refuses to work with some file descriptors which work	558	not least, it also refuses to work with some file descriptors which work
474	perfectly fine with C<select> (files, many character devices...).	559	perfectly fine with C<select> (files, many character devices...).
		560
		561	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		562	cobbled together in a hurry, no thought to design or interaction with
		563	others. Oh, the pain, will it ever stop...
475		564
476	While stopping, setting and starting an I/O watcher in the same iteration	565	While stopping, setting and starting an I/O watcher in the same iteration
477	will result in some caching, there is still a system call per such	566	will result in some caching, there is still a system call per such
478	incident (because the same I<file descriptor> could point to a different	567	incident (because the same I<file descriptor> could point to a different
479	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	568	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
491	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or	580	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
492	faster than epoll for maybe up to a hundred file descriptors, depending on	581	faster than epoll for maybe up to a hundred file descriptors, depending on
493	the usage. So sad.	582	the usage. So sad.
494		583
495	While nominally embeddable in other event loops, this feature is broken in	584	While nominally embeddable in other event loops, this feature is broken in
496	all kernel versions tested so far.	585	a lot of kernel revisions, but probably(!) works in current versions.
497		586
498	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	587	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
499	C<EVBACKEND_POLL>.	588	C<EVBACKEND_POLL>.
500		589
		590	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		591
		592	Use the Linux-specific Linux AIO (I<not> C<< aio(7) >> but C<<
		593	io_submit(2) >>) event interface available in post-4.18 kernels (but libev
		594	only tries to use it in 4.19+).
		595
		596	This is another Linux train wreck of an event interface.
		597
		598	If this backend works for you (as of this writing, it was very
		599	experimental), it is the best event interface available on Linux and might
		600	be well worth enabling it - if it isn't available in your kernel this will
		601	be detected and this backend will be skipped.
		602
		603	This backend can batch oneshot requests and supports a user-space ring
		604	buffer to receive events. It also doesn't suffer from most of the design
		605	problems of epoll (such as not being able to remove event sources from
		606	the epoll set), and generally sounds too good to be true. Because, this
		607	being the Linux kernel, of course it suffers from a whole new set of
		608	limitations, forcing you to fall back to epoll, inheriting all its design
		609	issues.
		610
		611	For one, it is not easily embeddable (but probably could be done using
		612	an event fd at some extra overhead). It also is subject to a system wide
		613	limit that can be configured in F</proc/sys/fs/aio-max-nr>. If no AIO
		614	requests are left, this backend will be skipped during initialisation, and
		615	will switch to epoll when the loop is active.
		616
		617	Most problematic in practice, however, is that not all file descriptors
		618	work with it. For example, in Linux 5.1, TCP sockets, pipes, event fds,
		619	files, F</dev/null> and many others are supported, but ttys do not work
		620	properly (a known bug that the kernel developers don't care about, see
		621	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		622	(yet?) a generic event polling interface.
		623
		624	Overall, it seems the Linux developers just don't want it to have a
		625	generic event handling mechanism other than C<select> or C<poll>.
		626
		627	To work around all these problem, the current version of libev uses its
		628	epoll backend as a fallback for file descriptor types that do not work. Or
		629	falls back completely to epoll if the kernel acts up.
		630
		631	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		632	C<EVBACKEND_POLL>.
		633
501	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	634	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
502		635
503	Kqueue deserves special mention, as at the time of this writing, it	636	Kqueue deserves special mention, as at the time this backend was
504	was broken on all BSDs except NetBSD (usually it doesn't work reliably	637	implemented, it was broken on all BSDs except NetBSD (usually it doesn't
505	with anything but sockets and pipes, except on Darwin, where of course	638	work reliably with anything but sockets and pipes, except on Darwin,
506	it's completely useless). Unlike epoll, however, whose brokenness	639	where of course it's completely useless). Unlike epoll, however, whose
507	is by design, these kqueue bugs can (and eventually will) be fixed	640	brokenness is by design, these kqueue bugs can be (and mostly have been)
508	without API changes to existing programs. For this reason it's not being	641	fixed without API changes to existing programs. For this reason it's not
509	"auto-detected" unless you explicitly specify it in the flags (i.e. using	642	being "auto-detected" on all platforms unless you explicitly specify it
510	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	643	in the flags (i.e. using C<EVBACKEND_KQUEUE>) or libev was compiled on a
511	system like NetBSD.	644	known-to-be-good (-enough) system like NetBSD.
512		645
513	You still can embed kqueue into a normal poll or select backend and use it	646	You still can embed kqueue into a normal poll or select backend and use it
514	only for sockets (after having made sure that sockets work with kqueue on	647	only for sockets (after having made sure that sockets work with kqueue on
515	the target platform). See C<ev_embed> watchers for more info.	648	the target platform). See C<ev_embed> watchers for more info.
516		649
517	It scales in the same way as the epoll backend, but the interface to the	650	It scales in the same way as the epoll backend, but the interface to the
518	kernel is more efficient (which says nothing about its actual speed, of	651	kernel is more efficient (which says nothing about its actual speed, of
519	course). While stopping, setting and starting an I/O watcher does never	652	course). While stopping, setting and starting an I/O watcher does never
520	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	653	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
521	two event changes per incident. Support for C<fork ()> is very bad (but	654	two event changes per incident. Support for C<fork ()> is very bad (you
522	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	655	might have to leak fds on fork, but it's more sane than epoll) and it
523	cases	656	drops fds silently in similarly hard-to-detect cases.
524		657
525	This backend usually performs well under most conditions.	658	This backend usually performs well under most conditions.
526		659
527	While nominally embeddable in other event loops, this doesn't work	660	While nominally embeddable in other event loops, this doesn't work
528	everywhere, so you might need to test for this. And since it is broken	661	everywhere, so you might need to test for this. And since it is broken
…		…
545	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	678	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
546		679
547	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	680	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
548	it's really slow, but it still scales very well (O(active_fds)).	681	it's really slow, but it still scales very well (O(active_fds)).
549		682
550	Please note that Solaris event ports can deliver a lot of spurious
551	notifications, so you need to use non-blocking I/O or other means to avoid
552	blocking when no data (or space) is available.
553
554	While this backend scales well, it requires one system call per active	683	While this backend scales well, it requires one system call per active
555	file descriptor per loop iteration. For small and medium numbers of file	684	file descriptor per loop iteration. For small and medium numbers of file
556	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	685	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
557	might perform better.	686	might perform better.
558		687
559	On the positive side, with the exception of the spurious readiness	688	On the positive side, this backend actually performed fully to
560	notifications, this backend actually performed fully to specification
561	in all tests and is fully embeddable, which is a rare feat among the	689	specification in all tests and is fully embeddable, which is a rare feat
562	OS-specific backends (I vastly prefer correctness over speed hacks).	690	among the OS-specific backends (I vastly prefer correctness over speed
		691	hacks).
		692
		693	On the negative side, the interface is I<bizarre> - so bizarre that
		694	even sun itself gets it wrong in their code examples: The event polling
		695	function sometimes returns events to the caller even though an error
		696	occurred, but with no indication whether it has done so or not (yes, it's
		697	even documented that way) - deadly for edge-triggered interfaces where you
		698	absolutely have to know whether an event occurred or not because you have
		699	to re-arm the watcher.
		700
		701	Fortunately libev seems to be able to work around these idiocies.
563		702
564	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	703	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
565	C<EVBACKEND_POLL>.	704	C<EVBACKEND_POLL>.
566		705
567	=item C<EVBACKEND_ALL>	706	=item C<EVBACKEND_ALL>
568		707
569	Try all backends (even potentially broken ones that wouldn't be tried	708	Try all backends (even potentially broken ones that wouldn't be tried
570	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	709	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
571	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	710	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
572		711
573	It is definitely not recommended to use this flag.	712	It is definitely not recommended to use this flag, use whatever
		713	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		714	at all.
		715
		716	=item C<EVBACKEND_MASK>
		717
		718	Not a backend at all, but a mask to select all backend bits from a
		719	C<flags> value, in case you want to mask out any backends from a flags
		720	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
574		721
575	=back	722	=back
576		723
577	If one or more of the backend flags are or'ed into the flags value,	724	If one or more of the backend flags are or'ed into the flags value,
578	then only these backends will be tried (in the reverse order as listed	725	then only these backends will be tried (in the reverse order as listed
…		…
587		734
588	Example: Use whatever libev has to offer, but make sure that kqueue is	735	Example: Use whatever libev has to offer, but make sure that kqueue is
589	used if available.	736	used if available.
590		737
591	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);	738	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		739
		740	Example: Similarly, on linux, you mgiht want to take advantage of the
		741	linux aio backend if possible, but fall back to something else if that
		742	isn't available.
		743
		744	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
592		745
593	=item ev_loop_destroy (loop)	746	=item ev_loop_destroy (loop)
594		747
595	Destroys an event loop object (frees all memory and kernel state	748	Destroys an event loop object (frees all memory and kernel state
596	etc.). None of the active event watchers will be stopped in the normal	749	etc.). None of the active event watchers will be stopped in the normal
…		…
607	This function is normally used on loop objects allocated by	760	This function is normally used on loop objects allocated by
608	C<ev_loop_new>, but it can also be used on the default loop returned by	761	C<ev_loop_new>, but it can also be used on the default loop returned by
609	C<ev_default_loop>, in which case it is not thread-safe.	762	C<ev_default_loop>, in which case it is not thread-safe.
610		763
611	Note that it is not advisable to call this function on the default loop	764	Note that it is not advisable to call this function on the default loop
612	except in the rare occasion where you really need to free it's resources.	765	except in the rare occasion where you really need to free its resources.
613	If you need dynamically allocated loops it is better to use C<ev_loop_new>	766	If you need dynamically allocated loops it is better to use C<ev_loop_new>
614	and C<ev_loop_destroy>.	767	and C<ev_loop_destroy>.
615		768
616	=item ev_loop_fork (loop)	769	=item ev_loop_fork (loop)
617		770
618	This function sets a flag that causes subsequent C<ev_run> iterations to	771	This function sets a flag that causes subsequent C<ev_run> iterations
619	reinitialise the kernel state for backends that have one. Despite the	772	to reinitialise the kernel state for backends that have one. Despite
620	name, you can call it anytime, but it makes most sense after forking, in	773	the name, you can call it anytime you are allowed to start or stop
621	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the	774	watchers (except inside an C<ev_prepare> callback), but it makes most
		775	sense after forking, in the child process. You I<must> call it (or use
622	child before resuming or calling C<ev_run>.	776	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
623		777
		778	In addition, if you want to reuse a loop (via this function or
		779	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		780
624	Again, you I<have> to call it on I<any> loop that you want to re-use after	781	Again, you I<have> to call it on I<any> loop that you want to re-use after
625	a fork, I<even if you do not plan to use the loop in the parent>. This is	782	a fork, I<even if you do not plan to use the loop in the parent>. This is
626	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	783	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
627	during fork.	784	during fork.
628		785
629	On the other hand, you only need to call this function in the child	786	On the other hand, you only need to call this function in the child
…		…
665	prepare and check phases.	822	prepare and check phases.
666		823
667	=item unsigned int ev_depth (loop)	824	=item unsigned int ev_depth (loop)
668		825
669	Returns the number of times C<ev_run> was entered minus the number of	826	Returns the number of times C<ev_run> was entered minus the number of
670	times C<ev_run> was exited, in other words, the recursion depth.	827	times C<ev_run> was exited normally, in other words, the recursion depth.
671		828
672	Outside C<ev_run>, this number is zero. In a callback, this number is	829	Outside C<ev_run>, this number is zero. In a callback, this number is
673	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	830	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
674	in which case it is higher.	831	in which case it is higher.
675		832
676	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	833	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
677	etc.), doesn't count as "exit" - consider this as a hint to avoid such	834	throwing an exception etc.), doesn't count as "exit" - consider this
678	ungentleman-like behaviour unless it's really convenient.	835	as a hint to avoid such ungentleman-like behaviour unless it's really
		836	convenient, in which case it is fully supported.
679		837
680	=item unsigned int ev_backend (loop)	838	=item unsigned int ev_backend (loop)
681		839
682	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	840	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
683	use.	841	use.
…		…
698		856
699	This function is rarely useful, but when some event callback runs for a	857	This function is rarely useful, but when some event callback runs for a
700	very long time without entering the event loop, updating libev's idea of	858	very long time without entering the event loop, updating libev's idea of
701	the current time is a good idea.	859	the current time is a good idea.
702		860
703	See also L<The special problem of time updates> in the C<ev_timer> section.	861	See also L</The special problem of time updates> in the C<ev_timer> section.
704		862
705	=item ev_suspend (loop)	863	=item ev_suspend (loop)
706		864
707	=item ev_resume (loop)	865	=item ev_resume (loop)
708		866
…		…
726	without a previous call to C<ev_suspend>.	884	without a previous call to C<ev_suspend>.
727		885
728	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	886	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
729	event loop time (see C<ev_now_update>).	887	event loop time (see C<ev_now_update>).
730		888
731	=item ev_run (loop, int flags)	889	=item bool ev_run (loop, int flags)
732		890
733	Finally, this is it, the event handler. This function usually is called	891	Finally, this is it, the event handler. This function usually is called
734	after you have initialised all your watchers and you want to start	892	after you have initialised all your watchers and you want to start
735	handling events. It will ask the operating system for any new events, call	893	handling events. It will ask the operating system for any new events, call
736	the watcher callbacks, an then repeat the whole process indefinitely: This	894	the watcher callbacks, and then repeat the whole process indefinitely: This
737	is why event loops are called I<loops>.	895	is why event loops are called I<loops>.
738		896
739	If the flags argument is specified as C<0>, it will keep handling events	897	If the flags argument is specified as C<0>, it will keep handling events
740	until either no event watchers are active anymore or C<ev_break> was	898	until either no event watchers are active anymore or C<ev_break> was
741	called.	899	called.
		900
		901	The return value is false if there are no more active watchers (which
		902	usually means "all jobs done" or "deadlock"), and true in all other cases
		903	(which usually means " you should call C<ev_run> again").
742		904
743	Please note that an explicit C<ev_break> is usually better than	905	Please note that an explicit C<ev_break> is usually better than
744	relying on all watchers to be stopped when deciding when a program has	906	relying on all watchers to be stopped when deciding when a program has
745	finished (especially in interactive programs), but having a program	907	finished (especially in interactive programs), but having a program
746	that automatically loops as long as it has to and no longer by virtue	908	that automatically loops as long as it has to and no longer by virtue
747	of relying on its watchers stopping correctly, that is truly a thing of	909	of relying on its watchers stopping correctly, that is truly a thing of
748	beauty.	910	beauty.
749		911
		912	This function is I<mostly> exception-safe - you can break out of a
		913	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		914	exception and so on. This does not decrement the C<ev_depth> value, nor
		915	will it clear any outstanding C<EVBREAK_ONE> breaks.
		916
750	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	917	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
751	those events and any already outstanding ones, but will not wait and	918	those events and any already outstanding ones, but will not wait and
752	block your process in case there are no events and will return after one	919	block your process in case there are no events and will return after one
753	iteration of the loop. This is sometimes useful to poll and handle new	920	iteration of the loop. This is sometimes useful to poll and handle new
754	events while doing lengthy calculations, to keep the program responsive.	921	events while doing lengthy calculations, to keep the program responsive.
…		…
763	This is useful if you are waiting for some external event in conjunction	930	This is useful if you are waiting for some external event in conjunction
764	with something not expressible using other libev watchers (i.e. "roll your	931	with something not expressible using other libev watchers (i.e. "roll your
765	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	932	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
766	usually a better approach for this kind of thing.	933	usually a better approach for this kind of thing.
767		934
768	Here are the gory details of what C<ev_run> does:	935	Here are the gory details of what C<ev_run> does (this is for your
		936	understanding, not a guarantee that things will work exactly like this in
		937	future versions):
769		938
770	- Increment loop depth.	939	- Increment loop depth.
771	- Reset the ev_break status.	940	- Reset the ev_break status.
772	- Before the first iteration, call any pending watchers.	941	- Before the first iteration, call any pending watchers.
773	LOOP:	942	LOOP:
…		…
790	- Queue all expired timers.	959	- Queue all expired timers.
791	- Queue all expired periodics.	960	- Queue all expired periodics.
792	- Queue all idle watchers with priority higher than that of pending events.	961	- Queue all idle watchers with priority higher than that of pending events.
793	- Queue all check watchers.	962	- Queue all check watchers.
794	- Call all queued watchers in reverse order (i.e. check watchers first).	963	- Call all queued watchers in reverse order (i.e. check watchers first).
795	Signals and child watchers are implemented as I/O watchers, and will	964	Signals, async and child watchers are implemented as I/O watchers, and
796	be handled here by queueing them when their watcher gets executed.	965	will be handled here by queueing them when their watcher gets executed.
797	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT	966	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
798	were used, or there are no active watchers, goto FINISH, otherwise	967	were used, or there are no active watchers, goto FINISH, otherwise
799	continue with step LOOP.	968	continue with step LOOP.
800	FINISH:	969	FINISH:
801	- Reset the ev_break status iff it was EVBREAK_ONE.	970	- Reset the ev_break status iff it was EVBREAK_ONE.
…		…
806	anymore.	975	anymore.
807		976
808	... queue jobs here, make sure they register event watchers as long	977	... queue jobs here, make sure they register event watchers as long
809	... as they still have work to do (even an idle watcher will do..)	978	... as they still have work to do (even an idle watcher will do..)
810	ev_run (my_loop, 0);	979	ev_run (my_loop, 0);
811	... jobs done or somebody called unloop. yeah!	980	... jobs done or somebody called break. yeah!
812		981
813	=item ev_break (loop, how)	982	=item ev_break (loop, how)
814		983
815	Can be used to make a call to C<ev_run> return early (but only after it	984	Can be used to make a call to C<ev_run> return early (but only after it
816	has processed all outstanding events). The C<how> argument must be either	985	has processed all outstanding events). The C<how> argument must be either
817	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	986	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
818	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	987	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
819		988
820	This "unloop state" will be cleared when entering C<ev_run> again.	989	This "break state" will be cleared on the next call to C<ev_run>.
821		990
822	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	991	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		992	which case it will have no effect.
823		993
824	=item ev_ref (loop)	994	=item ev_ref (loop)
825		995
826	=item ev_unref (loop)	996	=item ev_unref (loop)
827		997
…		…
848	running when nothing else is active.	1018	running when nothing else is active.
849		1019
850	ev_signal exitsig;	1020	ev_signal exitsig;
851	ev_signal_init (&exitsig, sig_cb, SIGINT);	1021	ev_signal_init (&exitsig, sig_cb, SIGINT);
852	ev_signal_start (loop, &exitsig);	1022	ev_signal_start (loop, &exitsig);
853	evf_unref (loop);	1023	ev_unref (loop);
854		1024
855	Example: For some weird reason, unregister the above signal handler again.	1025	Example: For some weird reason, unregister the above signal handler again.
856		1026
857	ev_ref (loop);	1027	ev_ref (loop);
858	ev_signal_stop (loop, &exitsig);	1028	ev_signal_stop (loop, &exitsig);
…		…
878	overhead for the actual polling but can deliver many events at once.	1048	overhead for the actual polling but can deliver many events at once.
879		1049
880	By setting a higher I<io collect interval> you allow libev to spend more	1050	By setting a higher I<io collect interval> you allow libev to spend more
881	time collecting I/O events, so you can handle more events per iteration,	1051	time collecting I/O events, so you can handle more events per iteration,
882	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	1052	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
883	C<ev_timer>) will be not affected. Setting this to a non-null value will	1053	C<ev_timer>) will not be affected. Setting this to a non-null value will
884	introduce an additional C<ev_sleep ()> call into most loop iterations. The	1054	introduce an additional C<ev_sleep ()> call into most loop iterations. The
885	sleep time ensures that libev will not poll for I/O events more often then	1055	sleep time ensures that libev will not poll for I/O events more often then
886	once per this interval, on average.	1056	once per this interval, on average (as long as the host time resolution is
		1057	good enough).
887		1058
888	Likewise, by setting a higher I<timeout collect interval> you allow libev	1059	Likewise, by setting a higher I<timeout collect interval> you allow libev
889	to spend more time collecting timeouts, at the expense of increased	1060	to spend more time collecting timeouts, at the expense of increased
890	latency/jitter/inexactness (the watcher callback will be called	1061	latency/jitter/inexactness (the watcher callback will be called
891	later). C<ev_io> watchers will not be affected. Setting this to a non-null	1062	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
937	invoke the actual watchers inside another context (another thread etc.).	1108	invoke the actual watchers inside another context (another thread etc.).
938		1109
939	If you want to reset the callback, use C<ev_invoke_pending> as new	1110	If you want to reset the callback, use C<ev_invoke_pending> as new
940	callback.	1111	callback.
941		1112
942	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1113	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
943		1114
944	Sometimes you want to share the same loop between multiple threads. This	1115	Sometimes you want to share the same loop between multiple threads. This
945	can be done relatively simply by putting mutex_lock/unlock calls around	1116	can be done relatively simply by putting mutex_lock/unlock calls around
946	each call to a libev function.	1117	each call to a libev function.
947		1118
948	However, C<ev_run> can run an indefinite time, so it is not feasible	1119	However, C<ev_run> can run an indefinite time, so it is not feasible
949	to wait for it to return. One way around this is to wake up the event	1120	to wait for it to return. One way around this is to wake up the event
950	loop via C<ev_break> and C<av_async_send>, another way is to set these	1121	loop via C<ev_break> and C<ev_async_send>, another way is to set these
951	I<release> and I<acquire> callbacks on the loop.	1122	I<release> and I<acquire> callbacks on the loop.
952		1123
953	When set, then C<release> will be called just before the thread is	1124	When set, then C<release> will be called just before the thread is
954	suspended waiting for new events, and C<acquire> is called just	1125	suspended waiting for new events, and C<acquire> is called just
955	afterwards.	1126	afterwards.
…		…
970	See also the locking example in the C<THREADS> section later in this	1141	See also the locking example in the C<THREADS> section later in this
971	document.	1142	document.
972		1143
973	=item ev_set_userdata (loop, void *data)	1144	=item ev_set_userdata (loop, void *data)
974		1145
975	=item ev_userdata (loop)	1146	=item void *ev_userdata (loop)
976		1147
977	Set and retrieve a single C<void *> associated with a loop. When	1148	Set and retrieve a single C<void *> associated with a loop. When
978	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1149	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
979	C<0.>	1150	C<0>.
980		1151
981	These two functions can be used to associate arbitrary data with a loop,	1152	These two functions can be used to associate arbitrary data with a loop,
982	and are intended solely for the C<invoke_pending_cb>, C<release> and	1153	and are intended solely for the C<invoke_pending_cb>, C<release> and
983	C<acquire> callbacks described above, but of course can be (ab-)used for	1154	C<acquire> callbacks described above, but of course can be (ab-)used for
984	any other purpose as well.	1155	any other purpose as well.
…		…
1047	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher	1218	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
1048	*) >>), and you can stop watching for events at any time by calling the	1219	*) >>), and you can stop watching for events at any time by calling the
1049	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.	1220	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
1050		1221
1051	As long as your watcher is active (has been started but not stopped) you	1222	As long as your watcher is active (has been started but not stopped) you
1052	must not touch the values stored in it. Most specifically you must never	1223	must not touch the values stored in it except when explicitly documented
1053	reinitialise it or call its C<ev_TYPE_set> macro.	1224	otherwise. Most specifically you must never reinitialise it or call its
		1225	C<ev_TYPE_set> macro.
1054		1226
1055	Each and every callback receives the event loop pointer as first, the	1227	Each and every callback receives the event loop pointer as first, the
1056	registered watcher structure as second, and a bitset of received events as	1228	registered watcher structure as second, and a bitset of received events as
1057	third argument.	1229	third argument.
1058		1230
…		…
1095		1267
1096	=item C<EV_PREPARE>	1268	=item C<EV_PREPARE>
1097		1269
1098	=item C<EV_CHECK>	1270	=item C<EV_CHECK>
1099		1271
1100	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1272	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1101	to gather new events, and all C<ev_check> watchers are invoked just after	1273	gather new events, and all C<ev_check> watchers are queued (not invoked)
1102	C<ev_run> has gathered them, but before it invokes any callbacks for any	1274	just after C<ev_run> has gathered them, but before it queues any callbacks
		1275	for any received events. That means C<ev_prepare> watchers are the last
		1276	watchers invoked before the event loop sleeps or polls for new events, and
		1277	C<ev_check> watchers will be invoked before any other watchers of the same
		1278	or lower priority within an event loop iteration.
		1279
1103	received events. Callbacks of both watcher types can start and stop as	1280	Callbacks of both watcher types can start and stop as many watchers as
1104	many watchers as they want, and all of them will be taken into account	1281	they want, and all of them will be taken into account (for example, a
1105	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1282	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1106	C<ev_run> from blocking).	1283	blocking).
1107		1284
1108	=item C<EV_EMBED>	1285	=item C<EV_EMBED>
1109		1286
1110	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1287	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1111		1288
1112	=item C<EV_FORK>	1289	=item C<EV_FORK>
1113		1290
1114	The event loop has been resumed in the child process after fork (see	1291	The event loop has been resumed in the child process after fork (see
1115	C<ev_fork>).	1292	C<ev_fork>).
		1293
		1294	=item C<EV_CLEANUP>
		1295
		1296	The event loop is about to be destroyed (see C<ev_cleanup>).
1116		1297
1117	=item C<EV_ASYNC>	1298	=item C<EV_ASYNC>
1118		1299
1119	The given async watcher has been asynchronously notified (see C<ev_async>).	1300	The given async watcher has been asynchronously notified (see C<ev_async>).
1120		1301
…		…
1142	programs, though, as the fd could already be closed and reused for another	1323	programs, though, as the fd could already be closed and reused for another
1143	thing, so beware.	1324	thing, so beware.
1144		1325
1145	=back	1326	=back
1146		1327
		1328	=head2 GENERIC WATCHER FUNCTIONS
		1329
		1330	=over 4
		1331
		1332	=item C<ev_init> (ev_TYPE *watcher, callback)
		1333
		1334	This macro initialises the generic portion of a watcher. The contents
		1335	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1336	the generic parts of the watcher are initialised, you I<need> to call
		1337	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1338	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1339	which rolls both calls into one.
		1340
		1341	You can reinitialise a watcher at any time as long as it has been stopped
		1342	(or never started) and there are no pending events outstanding.
		1343
		1344	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1345	int revents)>.
		1346
		1347	Example: Initialise an C<ev_io> watcher in two steps.
		1348
		1349	ev_io w;
		1350	ev_init (&w, my_cb);
		1351	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1352
		1353	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1354
		1355	This macro initialises the type-specific parts of a watcher. You need to
		1356	call C<ev_init> at least once before you call this macro, but you can
		1357	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1358	macro on a watcher that is active (it can be pending, however, which is a
		1359	difference to the C<ev_init> macro).
		1360
		1361	Although some watcher types do not have type-specific arguments
		1362	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1363
		1364	See C<ev_init>, above, for an example.
		1365
		1366	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1367
		1368	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1369	calls into a single call. This is the most convenient method to initialise
		1370	a watcher. The same limitations apply, of course.
		1371
		1372	Example: Initialise and set an C<ev_io> watcher in one step.
		1373
		1374	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1375
		1376	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1377
		1378	Starts (activates) the given watcher. Only active watchers will receive
		1379	events. If the watcher is already active nothing will happen.
		1380
		1381	Example: Start the C<ev_io> watcher that is being abused as example in this
		1382	whole section.
		1383
		1384	ev_io_start (EV_DEFAULT_UC, &w);
		1385
		1386	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1387
		1388	Stops the given watcher if active, and clears the pending status (whether
		1389	the watcher was active or not).
		1390
		1391	It is possible that stopped watchers are pending - for example,
		1392	non-repeating timers are being stopped when they become pending - but
		1393	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1394	pending. If you want to free or reuse the memory used by the watcher it is
		1395	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1396
		1397	=item bool ev_is_active (ev_TYPE *watcher)
		1398
		1399	Returns a true value iff the watcher is active (i.e. it has been started
		1400	and not yet been stopped). As long as a watcher is active you must not modify
		1401	it unless documented otherwise.
		1402
		1403	=item bool ev_is_pending (ev_TYPE *watcher)
		1404
		1405	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1406	events but its callback has not yet been invoked). As long as a watcher
		1407	is pending (but not active) you must not call an init function on it (but
		1408	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1409	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1410	it).
		1411
		1412	=item callback ev_cb (ev_TYPE *watcher)
		1413
		1414	Returns the callback currently set on the watcher.
		1415
		1416	=item ev_set_cb (ev_TYPE *watcher, callback)
		1417
		1418	Change the callback. You can change the callback at virtually any time
		1419	(modulo threads).
		1420
		1421	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1422
		1423	=item int ev_priority (ev_TYPE *watcher)
		1424
		1425	Set and query the priority of the watcher. The priority is a small
		1426	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1427	(default: C<-2>). Pending watchers with higher priority will be invoked
		1428	before watchers with lower priority, but priority will not keep watchers
		1429	from being executed (except for C<ev_idle> watchers).
		1430
		1431	If you need to suppress invocation when higher priority events are pending
		1432	you need to look at C<ev_idle> watchers, which provide this functionality.
		1433
		1434	You I<must not> change the priority of a watcher as long as it is active or
		1435	pending.
		1436
		1437	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1438	fine, as long as you do not mind that the priority value you query might
		1439	or might not have been clamped to the valid range.
		1440
		1441	The default priority used by watchers when no priority has been set is
		1442	always C<0>, which is supposed to not be too high and not be too low :).
		1443
		1444	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1445	priorities.
		1446
		1447	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1448
		1449	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1450	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1451	can deal with that fact, as both are simply passed through to the
		1452	callback.
		1453
		1454	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1455
		1456	If the watcher is pending, this function clears its pending status and
		1457	returns its C<revents> bitset (as if its callback was invoked). If the
		1458	watcher isn't pending it does nothing and returns C<0>.
		1459
		1460	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1461	callback to be invoked, which can be accomplished with this function.
		1462
		1463	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1464
		1465	Feeds the given event set into the event loop, as if the specified event
		1466	had happened for the specified watcher (which must be a pointer to an
		1467	initialised but not necessarily started event watcher). Obviously you must
		1468	not free the watcher as long as it has pending events.
		1469
		1470	Stopping the watcher, letting libev invoke it, or calling
		1471	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1472	not started in the first place.
		1473
		1474	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1475	functions that do not need a watcher.
		1476
		1477	=back
		1478
		1479	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1480	OWN COMPOSITE WATCHERS> idioms.
		1481
1147	=head2 WATCHER STATES	1482	=head2 WATCHER STATES
1148		1483
1149	There are various watcher states mentioned throughout this manual -	1484	There are various watcher states mentioned throughout this manual -
1150	active, pending and so on. In this section these states and the rules to	1485	active, pending and so on. In this section these states and the rules to
1151	transition between them will be described in more detail - and while these	1486	transition between them will be described in more detail - and while these
1152	rules might look complicated, they usually do "the right thing".	1487	rules might look complicated, they usually do "the right thing".
1153		1488
1154	=over 4	1489	=over 4
1155		1490
1156	=item initialiased	1491	=item initialised
1157		1492
1158	Before a watcher can be registered with the event looop it has to be	1493	Before a watcher can be registered with the event loop it has to be
1159	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1494	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1160	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1495	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1161		1496
1162	In this state it is simply some block of memory that is suitable for use	1497	In this state it is simply some block of memory that is suitable for
1163	in an event loop. It can be moved around, freed, reused etc. at will.	1498	use in an event loop. It can be moved around, freed, reused etc. at
		1499	will - as long as you either keep the memory contents intact, or call
		1500	C<ev_TYPE_init> again.
1164		1501
1165	=item started/running/active	1502	=item started/running/active
1166		1503
1167	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1504	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1168	property of the event loop, and is actively waiting for events. While in	1505	property of the event loop, and is actively waiting for events. While in
…		…
1196	latter will clear any pending state the watcher might be in, regardless	1533	latter will clear any pending state the watcher might be in, regardless
1197	of whether it was active or not, so stopping a watcher explicitly before	1534	of whether it was active or not, so stopping a watcher explicitly before
1198	freeing it is often a good idea.	1535	freeing it is often a good idea.
1199		1536
1200	While stopped (and not pending) the watcher is essentially in the	1537	While stopped (and not pending) the watcher is essentially in the
1201	initialised state, that is it can be reused, moved, modified in any way	1538	initialised state, that is, it can be reused, moved, modified in any way
1202	you wish.	1539	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1540	it again).
1203		1541
1204	=back	1542	=back
1205
1206	=head2 GENERIC WATCHER FUNCTIONS
1207
1208	=over 4
1209
1210	=item C<ev_init> (ev_TYPE *watcher, callback)
1211
1212	This macro initialises the generic portion of a watcher. The contents
1213	of the watcher object can be arbitrary (so C<malloc> will do). Only
1214	the generic parts of the watcher are initialised, you I<need> to call
1215	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
1216	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
1217	which rolls both calls into one.
1218
1219	You can reinitialise a watcher at any time as long as it has been stopped
1220	(or never started) and there are no pending events outstanding.
1221
1222	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1223	int revents)>.
1224
1225	Example: Initialise an C<ev_io> watcher in two steps.
1226
1227	ev_io w;
1228	ev_init (&w, my_cb);
1229	ev_io_set (&w, STDIN_FILENO, EV_READ);
1230
1231	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
1232
1233	This macro initialises the type-specific parts of a watcher. You need to
1234	call C<ev_init> at least once before you call this macro, but you can
1235	call C<ev_TYPE_set> any number of times. You must not, however, call this
1236	macro on a watcher that is active (it can be pending, however, which is a
1237	difference to the C<ev_init> macro).
1238
1239	Although some watcher types do not have type-specific arguments
1240	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
1241
1242	See C<ev_init>, above, for an example.
1243
1244	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
1245
1246	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
1247	calls into a single call. This is the most convenient method to initialise
1248	a watcher. The same limitations apply, of course.
1249
1250	Example: Initialise and set an C<ev_io> watcher in one step.
1251
1252	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1253
1254	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
1255
1256	Starts (activates) the given watcher. Only active watchers will receive
1257	events. If the watcher is already active nothing will happen.
1258
1259	Example: Start the C<ev_io> watcher that is being abused as example in this
1260	whole section.
1261
1262	ev_io_start (EV_DEFAULT_UC, &w);
1263
1264	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
1265
1266	Stops the given watcher if active, and clears the pending status (whether
1267	the watcher was active or not).
1268
1269	It is possible that stopped watchers are pending - for example,
1270	non-repeating timers are being stopped when they become pending - but
1271	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
1272	pending. If you want to free or reuse the memory used by the watcher it is
1273	therefore a good idea to always call its C<ev_TYPE_stop> function.
1274
1275	=item bool ev_is_active (ev_TYPE *watcher)
1276
1277	Returns a true value iff the watcher is active (i.e. it has been started
1278	and not yet been stopped). As long as a watcher is active you must not modify
1279	it.
1280
1281	=item bool ev_is_pending (ev_TYPE *watcher)
1282
1283	Returns a true value iff the watcher is pending, (i.e. it has outstanding
1284	events but its callback has not yet been invoked). As long as a watcher
1285	is pending (but not active) you must not call an init function on it (but
1286	C<ev_TYPE_set> is safe), you must not change its priority, and you must
1287	make sure the watcher is available to libev (e.g. you cannot C<free ()>
1288	it).
1289
1290	=item callback ev_cb (ev_TYPE *watcher)
1291
1292	Returns the callback currently set on the watcher.
1293
1294	=item ev_cb_set (ev_TYPE *watcher, callback)
1295
1296	Change the callback. You can change the callback at virtually any time
1297	(modulo threads).
1298
1299	=item ev_set_priority (ev_TYPE *watcher, int priority)
1300
1301	=item int ev_priority (ev_TYPE *watcher)
1302
1303	Set and query the priority of the watcher. The priority is a small
1304	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1305	(default: C<-2>). Pending watchers with higher priority will be invoked
1306	before watchers with lower priority, but priority will not keep watchers
1307	from being executed (except for C<ev_idle> watchers).
1308
1309	If you need to suppress invocation when higher priority events are pending
1310	you need to look at C<ev_idle> watchers, which provide this functionality.
1311
1312	You I<must not> change the priority of a watcher as long as it is active or
1313	pending.
1314
1315	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1316	fine, as long as you do not mind that the priority value you query might
1317	or might not have been clamped to the valid range.
1318
1319	The default priority used by watchers when no priority has been set is
1320	always C<0>, which is supposed to not be too high and not be too low :).
1321
1322	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1323	priorities.
1324
1325	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1326
1327	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1328	C<loop> nor C<revents> need to be valid as long as the watcher callback
1329	can deal with that fact, as both are simply passed through to the
1330	callback.
1331
1332	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1333
1334	If the watcher is pending, this function clears its pending status and
1335	returns its C<revents> bitset (as if its callback was invoked). If the
1336	watcher isn't pending it does nothing and returns C<0>.
1337
1338	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1339	callback to be invoked, which can be accomplished with this function.
1340
1341	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
1342
1343	Feeds the given event set into the event loop, as if the specified event
1344	had happened for the specified watcher (which must be a pointer to an
1345	initialised but not necessarily started event watcher). Obviously you must
1346	not free the watcher as long as it has pending events.
1347
1348	Stopping the watcher, letting libev invoke it, or calling
1349	C<ev_clear_pending> will clear the pending event, even if the watcher was
1350	not started in the first place.
1351
1352	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1353	functions that do not need a watcher.
1354
1355	=back
1356
1357
1358	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1359
1360	Each watcher has, by default, a member C<void *data> that you can change
1361	and read at any time: libev will completely ignore it. This can be used
1362	to associate arbitrary data with your watcher. If you need more data and
1363	don't want to allocate memory and store a pointer to it in that data
1364	member, you can also "subclass" the watcher type and provide your own
1365	data:
1366
1367	struct my_io
1368	{
1369	ev_io io;
1370	int otherfd;
1371	void *somedata;
1372	struct whatever *mostinteresting;
1373	};
1374
1375	...
1376	struct my_io w;
1377	ev_io_init (&w.io, my_cb, fd, EV_READ);
1378
1379	And since your callback will be called with a pointer to the watcher, you
1380	can cast it back to your own type:
1381
1382	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1383	{
1384	struct my_io *w = (struct my_io *)w_;
1385	...
1386	}
1387
1388	More interesting and less C-conformant ways of casting your callback type
1389	instead have been omitted.
1390
1391	Another common scenario is to use some data structure with multiple
1392	embedded watchers:
1393
1394	struct my_biggy
1395	{
1396	int some_data;
1397	ev_timer t1;
1398	ev_timer t2;
1399	}
1400
1401	In this case getting the pointer to C<my_biggy> is a bit more
1402	complicated: Either you store the address of your C<my_biggy> struct
1403	in the C<data> member of the watcher (for woozies), or you need to use
1404	some pointer arithmetic using C<offsetof> inside your watchers (for real
1405	programmers):
1406
1407	#include <stddef.h>
1408
1409	static void
1410	t1_cb (EV_P_ ev_timer *w, int revents)
1411	{
1412	struct my_biggy big = (struct my_biggy *)
1413	(((char *)w) - offsetof (struct my_biggy, t1));
1414	}
1415
1416	static void
1417	t2_cb (EV_P_ ev_timer *w, int revents)
1418	{
1419	struct my_biggy big = (struct my_biggy *)
1420	(((char *)w) - offsetof (struct my_biggy, t2));
1421	}
1422		1543
1423	=head2 WATCHER PRIORITY MODELS	1544	=head2 WATCHER PRIORITY MODELS
1424		1545
1425	Many event loops support I<watcher priorities>, which are usually small	1546	Many event loops support I<watcher priorities>, which are usually small
1426	integers that influence the ordering of event callback invocation	1547	integers that influence the ordering of event callback invocation
1427	between watchers in some way, all else being equal.	1548	between watchers in some way, all else being equal.
1428		1549
1429	In libev, Watcher priorities can be set using C<ev_set_priority>. See its	1550	In libev, watcher priorities can be set using C<ev_set_priority>. See its
1430	description for the more technical details such as the actual priority	1551	description for the more technical details such as the actual priority
1431	range.	1552	range.
1432		1553
1433	There are two common ways how these these priorities are being interpreted	1554	There are two common ways how these these priorities are being interpreted
1434	by event loops:	1555	by event loops:
…		…
1528		1649
1529	This section describes each watcher in detail, but will not repeat	1650	This section describes each watcher in detail, but will not repeat
1530	information given in the last section. Any initialisation/set macros,	1651	information given in the last section. Any initialisation/set macros,
1531	functions and members specific to the watcher type are explained.	1652	functions and members specific to the watcher type are explained.
1532		1653
1533	Members are additionally marked with either I<[read-only]>, meaning that,	1654	Most members are additionally marked with either I<[read-only]>, meaning
1534	while the watcher is active, you can look at the member and expect some	1655	that, while the watcher is active, you can look at the member and expect
1535	sensible content, but you must not modify it (you can modify it while the	1656	some sensible content, but you must not modify it (you can modify it while
1536	watcher is stopped to your hearts content), or I<[read-write]>, which	1657	the watcher is stopped to your hearts content), or I<[read-write]>, which
1537	means you can expect it to have some sensible content while the watcher	1658	means you can expect it to have some sensible content while the watcher is
1538	is active, but you can also modify it. Modifying it may not do something	1659	active, but you can also modify it (within the same thread as the event
		1660	loop, i.e. without creating data races). Modifying it may not do something
1539	sensible or take immediate effect (or do anything at all), but libev will	1661	sensible or take immediate effect (or do anything at all), but libev will
1540	not crash or malfunction in any way.	1662	not crash or malfunction in any way.
1541		1663
		1664	In any case, the documentation for each member will explain what the
		1665	effects are, and if there are any additional access restrictions.
1542		1666
1543	=head2 C<ev_io> - is this file descriptor readable or writable?	1667	=head2 C<ev_io> - is this file descriptor readable or writable?
1544		1668
1545	I/O watchers check whether a file descriptor is readable or writable	1669	I/O watchers check whether a file descriptor is readable or writable
1546	in each iteration of the event loop, or, more precisely, when reading	1670	in each iteration of the event loop, or, more precisely, when reading
…		…
1553	In general you can register as many read and/or write event watchers per	1677	In general you can register as many read and/or write event watchers per
1554	fd as you want (as long as you don't confuse yourself). Setting all file	1678	fd as you want (as long as you don't confuse yourself). Setting all file
1555	descriptors to non-blocking mode is also usually a good idea (but not	1679	descriptors to non-blocking mode is also usually a good idea (but not
1556	required if you know what you are doing).	1680	required if you know what you are doing).
1557		1681
1558	If you cannot use non-blocking mode, then force the use of a
1559	known-to-be-good backend (at the time of this writing, this includes only
1560	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1561	descriptors for which non-blocking operation makes no sense (such as
1562	files) - libev doesn't guarantee any specific behaviour in that case.
1563
1564	Another thing you have to watch out for is that it is quite easy to	1682	Another thing you have to watch out for is that it is quite easy to
1565	receive "spurious" readiness notifications, that is your callback might	1683	receive "spurious" readiness notifications, that is, your callback might
1566	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1684	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1567	because there is no data. Not only are some backends known to create a	1685	because there is no data. It is very easy to get into this situation even
1568	lot of those (for example Solaris ports), it is very easy to get into	1686	with a relatively standard program structure. Thus it is best to always
1569	this situation even with a relatively standard program structure. Thus	1687	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1570	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1571	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1688	preferable to a program hanging until some data arrives.
1572		1689
1573	If you cannot run the fd in non-blocking mode (for example you should	1690	If you cannot run the fd in non-blocking mode (for example you should
1574	not play around with an Xlib connection), then you have to separately	1691	not play around with an Xlib connection), then you have to separately
1575	re-test whether a file descriptor is really ready with a known-to-be good	1692	re-test whether a file descriptor is really ready with a known-to-be good
1576	interface such as poll (fortunately in our Xlib example, Xlib already	1693	interface such as poll (fortunately in the case of Xlib, it already does
1577	does this on its own, so its quite safe to use). Some people additionally	1694	this on its own, so its quite safe to use). Some people additionally
1578	use C<SIGALRM> and an interval timer, just to be sure you won't block	1695	use C<SIGALRM> and an interval timer, just to be sure you won't block
1579	indefinitely.	1696	indefinitely.
1580		1697
1581	But really, best use non-blocking mode.	1698	But really, best use non-blocking mode.
1582		1699
1583	=head3 The special problem of disappearing file descriptors	1700	=head3 The special problem of disappearing file descriptors
1584		1701
1585	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1702	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1586	descriptor (either due to calling C<close> explicitly or any other means,	1703	a file descriptor (either due to calling C<close> explicitly or any other
1587	such as C<dup2>). The reason is that you register interest in some file	1704	means, such as C<dup2>). The reason is that you register interest in some
1588	descriptor, but when it goes away, the operating system will silently drop	1705	file descriptor, but when it goes away, the operating system will silently
1589	this interest. If another file descriptor with the same number then is	1706	drop this interest. If another file descriptor with the same number then
1590	registered with libev, there is no efficient way to see that this is, in	1707	is registered with libev, there is no efficient way to see that this is,
1591	fact, a different file descriptor.	1708	in fact, a different file descriptor.
1592		1709
1593	To avoid having to explicitly tell libev about such cases, libev follows	1710	To avoid having to explicitly tell libev about such cases, libev follows
1594	the following policy: Each time C<ev_io_set> is being called, libev	1711	the following policy: Each time C<ev_io_set> is being called, libev
1595	will assume that this is potentially a new file descriptor, otherwise	1712	will assume that this is potentially a new file descriptor, otherwise
1596	it is assumed that the file descriptor stays the same. That means that	1713	it is assumed that the file descriptor stays the same. That means that
…		…
1610		1727
1611	There is no workaround possible except not registering events	1728	There is no workaround possible except not registering events
1612	for potentially C<dup ()>'ed file descriptors, or to resort to	1729	for potentially C<dup ()>'ed file descriptors, or to resort to
1613	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1730	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1614		1731
		1732	=head3 The special problem of files
		1733
		1734	Many people try to use C<select> (or libev) on file descriptors
		1735	representing files, and expect it to become ready when their program
		1736	doesn't block on disk accesses (which can take a long time on their own).
		1737
		1738	However, this cannot ever work in the "expected" way - you get a readiness
		1739	notification as soon as the kernel knows whether and how much data is
		1740	there, and in the case of open files, that's always the case, so you
		1741	always get a readiness notification instantly, and your read (or possibly
		1742	write) will still block on the disk I/O.
		1743
		1744	Another way to view it is that in the case of sockets, pipes, character
		1745	devices and so on, there is another party (the sender) that delivers data
		1746	on its own, but in the case of files, there is no such thing: the disk
		1747	will not send data on its own, simply because it doesn't know what you
		1748	wish to read - you would first have to request some data.
		1749
		1750	Since files are typically not-so-well supported by advanced notification
		1751	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1752	to files, even though you should not use it. The reason for this is
		1753	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1754	usually a tty, often a pipe, but also sometimes files or special devices
		1755	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1756	F</dev/urandom>), and even though the file might better be served with
		1757	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1758	it "just works" instead of freezing.
		1759
		1760	So avoid file descriptors pointing to files when you know it (e.g. use
		1761	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1762	when you rarely read from a file instead of from a socket, and want to
		1763	reuse the same code path.
		1764
1615	=head3 The special problem of fork	1765	=head3 The special problem of fork
1616		1766
1617	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1767	Some backends (epoll, kqueue, linuxaio, iouring) do not support C<fork ()>
1618	useless behaviour. Libev fully supports fork, but needs to be told about	1768	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1619	it in the child.	1769	to be told about it in the child if you want to continue to use it in the
		1770	child.
1620		1771
1621	To support fork in your programs, you either have to call	1772	To support fork in your child processes, you have to call C<ev_loop_fork
1622	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1773	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1623	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1774	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1624	C<EVBACKEND_POLL>.
1625		1775
1626	=head3 The special problem of SIGPIPE	1776	=head3 The special problem of SIGPIPE
1627		1777
1628	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1778	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1629	when writing to a pipe whose other end has been closed, your program gets	1779	when writing to a pipe whose other end has been closed, your program gets
…		…
1680	=item ev_io_init (ev_io *, callback, int fd, int events)	1830	=item ev_io_init (ev_io *, callback, int fd, int events)
1681		1831
1682	=item ev_io_set (ev_io *, int fd, int events)	1832	=item ev_io_set (ev_io *, int fd, int events)
1683		1833
1684	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1834	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1685	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or	1835	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE>, both
1686	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.	1836	C<EV_READ | EV_WRITE> or C<0>, to express the desire to receive the given
		1837	events.
1687		1838
1688	=item int fd [read-only]	1839	Note that setting the C<events> to C<0> and starting the watcher is
		1840	supported, but not specially optimized - if your program sometimes happens
		1841	to generate this combination this is fine, but if it is easy to avoid
		1842	starting an io watcher watching for no events you should do so.
1689		1843
1690	The file descriptor being watched.	1844	=item ev_io_modify (ev_io *, int events)
1691		1845
		1846	Similar to C<ev_io_set>, but only changes the requested events. Using this
		1847	might be faster with some backends, as libev can assume that the C<fd>
		1848	still refers to the same underlying file description, something it cannot
		1849	do when using C<ev_io_set>.
		1850
		1851	=item int fd [no-modify]
		1852
		1853	The file descriptor being watched. While it can be read at any time, you
		1854	must not modify this member even when the watcher is stopped - always use
		1855	C<ev_io_set> for that.
		1856
1692	=item int events [read-only]	1857	=item int events [no-modify]
1693		1858
1694	The events being watched.	1859	The set of events the fd is being watched for, among other flags. Remember
		1860	that this is a bit set - to test for C<EV_READ>, use C<< w->events &
		1861	EV_READ >>, and similarly for C<EV_WRITE>.
		1862
		1863	As with C<fd>, you must not modify this member even when the watcher is
		1864	stopped, always use C<ev_io_set> or C<ev_io_modify> for that.
1695		1865
1696	=back	1866	=back
1697		1867
1698	=head3 Examples	1868	=head3 Examples
1699		1869
…		…
1727	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1897	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1728	monotonic clock option helps a lot here).	1898	monotonic clock option helps a lot here).
1729		1899
1730	The callback is guaranteed to be invoked only I<after> its timeout has	1900	The callback is guaranteed to be invoked only I<after> its timeout has
1731	passed (not I<at>, so on systems with very low-resolution clocks this	1901	passed (not I<at>, so on systems with very low-resolution clocks this
1732	might introduce a small delay). If multiple timers become ready during the	1902	might introduce a small delay, see "the special problem of being too
		1903	early", below). If multiple timers become ready during the same loop
1733	same loop iteration then the ones with earlier time-out values are invoked	1904	iteration then the ones with earlier time-out values are invoked before
1734	before ones of the same priority with later time-out values (but this is	1905	ones of the same priority with later time-out values (but this is no
1735	no longer true when a callback calls C<ev_run> recursively).	1906	longer true when a callback calls C<ev_run> recursively).
1736		1907
1737	=head3 Be smart about timeouts	1908	=head3 Be smart about timeouts
1738		1909
1739	Many real-world problems involve some kind of timeout, usually for error	1910	Many real-world problems involve some kind of timeout, usually for error
1740	recovery. A typical example is an HTTP request - if the other side hangs,	1911	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1815		1986
1816	In this case, it would be more efficient to leave the C<ev_timer> alone,	1987	In this case, it would be more efficient to leave the C<ev_timer> alone,
1817	but remember the time of last activity, and check for a real timeout only	1988	but remember the time of last activity, and check for a real timeout only
1818	within the callback:	1989	within the callback:
1819		1990
		1991	ev_tstamp timeout = 60.;
1820	ev_tstamp last_activity; // time of last activity	1992	ev_tstamp last_activity; // time of last activity
		1993	ev_timer timer;
1821		1994
1822	static void	1995	static void
1823	callback (EV_P_ ev_timer *w, int revents)	1996	callback (EV_P_ ev_timer *w, int revents)
1824	{	1997	{
1825	ev_tstamp now = ev_now (EV_A);	1998	// calculate when the timeout would happen
1826	ev_tstamp timeout = last_activity + 60.;	1999	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1827		2000
1828	// if last_activity + 60. is older than now, we did time out	2001	// if negative, it means we the timeout already occurred
1829	if (timeout < now)	2002	if (after < 0.)
1830	{	2003	{
1831	// timeout occurred, take action	2004	// timeout occurred, take action
1832	}	2005	}
1833	else	2006	else
1834	{	2007	{
1835	// callback was invoked, but there was some activity, re-arm	2008	// callback was invoked, but there was some recent
1836	// the watcher to fire in last_activity + 60, which is	2009	// activity. simply restart the timer to time out
1837	// guaranteed to be in the future, so "again" is positive:	2010	// after "after" seconds, which is the earliest time
1838	w->repeat = timeout - now;	2011	// the timeout can occur.
		2012	ev_timer_set (w, after, 0.);
1839	ev_timer_again (EV_A_ w);	2013	ev_timer_start (EV_A_ w);
1840	}	2014	}
1841	}	2015	}
1842		2016
1843	To summarise the callback: first calculate the real timeout (defined	2017	To summarise the callback: first calculate in how many seconds the
1844	as "60 seconds after the last activity"), then check if that time has	2018	timeout will occur (by calculating the absolute time when it would occur,
1845	been reached, which means something I<did>, in fact, time out. Otherwise	2019	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1846	the callback was invoked too early (C<timeout> is in the future), so	2020	(EV_A)> from that).
1847	re-schedule the timer to fire at that future time, to see if maybe we have
1848	a timeout then.
1849		2021
1850	Note how C<ev_timer_again> is used, taking advantage of the	2022	If this value is negative, then we are already past the timeout, i.e. we
1851	C<ev_timer_again> optimisation when the timer is already running.	2023	timed out, and need to do whatever is needed in this case.
		2024
		2025	Otherwise, we now the earliest time at which the timeout would trigger,
		2026	and simply start the timer with this timeout value.
		2027
		2028	In other words, each time the callback is invoked it will check whether
		2029	the timeout occurred. If not, it will simply reschedule itself to check
		2030	again at the earliest time it could time out. Rinse. Repeat.
1852		2031
1853	This scheme causes more callback invocations (about one every 60 seconds	2032	This scheme causes more callback invocations (about one every 60 seconds
1854	minus half the average time between activity), but virtually no calls to	2033	minus half the average time between activity), but virtually no calls to
1855	libev to change the timeout.	2034	libev to change the timeout.
1856		2035
1857	To start the timer, simply initialise the watcher and set C<last_activity>	2036	To start the machinery, simply initialise the watcher and set
1858	to the current time (meaning we just have some activity :), then call the	2037	C<last_activity> to the current time (meaning there was some activity just
1859	callback, which will "do the right thing" and start the timer:	2038	now), then call the callback, which will "do the right thing" and start
		2039	the timer:
1860		2040
		2041	last_activity = ev_now (EV_A);
1861	ev_init (timer, callback);	2042	ev_init (&timer, callback);
1862	last_activity = ev_now (loop);	2043	callback (EV_A_ &timer, 0);
1863	callback (loop, timer, EV_TIMER);
1864		2044
1865	And when there is some activity, simply store the current time in	2045	When there is some activity, simply store the current time in
1866	C<last_activity>, no libev calls at all:	2046	C<last_activity>, no libev calls at all:
1867		2047
		2048	if (activity detected)
1868	last_activity = ev_now (loop);	2049	last_activity = ev_now (EV_A);
		2050
		2051	When your timeout value changes, then the timeout can be changed by simply
		2052	providing a new value, stopping the timer and calling the callback, which
		2053	will again do the right thing (for example, time out immediately :).
		2054
		2055	timeout = new_value;
		2056	ev_timer_stop (EV_A_ &timer);
		2057	callback (EV_A_ &timer, 0);
1869		2058
1870	This technique is slightly more complex, but in most cases where the	2059	This technique is slightly more complex, but in most cases where the
1871	time-out is unlikely to be triggered, much more efficient.	2060	time-out is unlikely to be triggered, much more efficient.
1872
1873	Changing the timeout is trivial as well (if it isn't hard-coded in the
1874	callback :) - just change the timeout and invoke the callback, which will
1875	fix things for you.
1876		2061
1877	=item 4. Wee, just use a double-linked list for your timeouts.	2062	=item 4. Wee, just use a double-linked list for your timeouts.
1878		2063
1879	If there is not one request, but many thousands (millions...), all	2064	If there is not one request, but many thousands (millions...), all
1880	employing some kind of timeout with the same timeout value, then one can	2065	employing some kind of timeout with the same timeout value, then one can
…		…
1907	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2092	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1908	rather complicated, but extremely efficient, something that really pays	2093	rather complicated, but extremely efficient, something that really pays
1909	off after the first million or so of active timers, i.e. it's usually	2094	off after the first million or so of active timers, i.e. it's usually
1910	overkill :)	2095	overkill :)
1911		2096
		2097	=head3 The special problem of being too early
		2098
		2099	If you ask a timer to call your callback after three seconds, then
		2100	you expect it to be invoked after three seconds - but of course, this
		2101	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2102	guaranteed to any precision by libev - imagine somebody suspending the
		2103	process with a STOP signal for a few hours for example.
		2104
		2105	So, libev tries to invoke your callback as soon as possible I<after> the
		2106	delay has occurred, but cannot guarantee this.
		2107
		2108	A less obvious failure mode is calling your callback too early: many event
		2109	loops compare timestamps with a "elapsed delay >= requested delay", but
		2110	this can cause your callback to be invoked much earlier than you would
		2111	expect.
		2112
		2113	To see why, imagine a system with a clock that only offers full second
		2114	resolution (think windows if you can't come up with a broken enough OS
		2115	yourself). If you schedule a one-second timer at the time 500.9, then the
		2116	event loop will schedule your timeout to elapse at a system time of 500
		2117	(500.9 truncated to the resolution) + 1, or 501.
		2118
		2119	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2120	501" and invoke the callback 0.1s after it was started, even though a
		2121	one-second delay was requested - this is being "too early", despite best
		2122	intentions.
		2123
		2124	This is the reason why libev will never invoke the callback if the elapsed
		2125	delay equals the requested delay, but only when the elapsed delay is
		2126	larger than the requested delay. In the example above, libev would only invoke
		2127	the callback at system time 502, or 1.1s after the timer was started.
		2128
		2129	So, while libev cannot guarantee that your callback will be invoked
		2130	exactly when requested, it I<can> and I<does> guarantee that the requested
		2131	delay has actually elapsed, or in other words, it always errs on the "too
		2132	late" side of things.
		2133
1912	=head3 The special problem of time updates	2134	=head3 The special problem of time updates
1913		2135
1914	Establishing the current time is a costly operation (it usually takes at	2136	Establishing the current time is a costly operation (it usually takes
1915	least two system calls): EV therefore updates its idea of the current	2137	at least one system call): EV therefore updates its idea of the current
1916	time only before and after C<ev_run> collects new events, which causes a	2138	time only before and after C<ev_run> collects new events, which causes a
1917	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2139	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1918	lots of events in one iteration.	2140	lots of events in one iteration.
1919		2141
1920	The relative timeouts are calculated relative to the C<ev_now ()>	2142	The relative timeouts are calculated relative to the C<ev_now ()>
1921	time. This is usually the right thing as this timestamp refers to the time	2143	time. This is usually the right thing as this timestamp refers to the time
1922	of the event triggering whatever timeout you are modifying/starting. If	2144	of the event triggering whatever timeout you are modifying/starting. If
1923	you suspect event processing to be delayed and you I<need> to base the	2145	you suspect event processing to be delayed and you I<need> to base the
1924	timeout on the current time, use something like this to adjust for this:	2146	timeout on the current time, use something like the following to adjust
		2147	for it:
1925		2148
1926	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2149	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1927		2150
1928	If the event loop is suspended for a long time, you can also force an	2151	If the event loop is suspended for a long time, you can also force an
1929	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2152	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1930	()>.	2153	()>, although that will push the event time of all outstanding events
		2154	further into the future.
		2155
		2156	=head3 The special problem of unsynchronised clocks
		2157
		2158	Modern systems have a variety of clocks - libev itself uses the normal
		2159	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2160	jumps).
		2161
		2162	Neither of these clocks is synchronised with each other or any other clock
		2163	on the system, so C<ev_time ()> might return a considerably different time
		2164	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2165	a call to C<gettimeofday> might return a second count that is one higher
		2166	than a directly following call to C<time>.
		2167
		2168	The moral of this is to only compare libev-related timestamps with
		2169	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2170	a second or so.
		2171
		2172	One more problem arises due to this lack of synchronisation: if libev uses
		2173	the system monotonic clock and you compare timestamps from C<ev_time>
		2174	or C<ev_now> from when you started your timer and when your callback is
		2175	invoked, you will find that sometimes the callback is a bit "early".
		2176
		2177	This is because C<ev_timer>s work in real time, not wall clock time, so
		2178	libev makes sure your callback is not invoked before the delay happened,
		2179	I<measured according to the real time>, not the system clock.
		2180
		2181	If your timeouts are based on a physical timescale (e.g. "time out this
		2182	connection after 100 seconds") then this shouldn't bother you as it is
		2183	exactly the right behaviour.
		2184
		2185	If you want to compare wall clock/system timestamps to your timers, then
		2186	you need to use C<ev_periodic>s, as these are based on the wall clock
		2187	time, where your comparisons will always generate correct results.
1931		2188
1932	=head3 The special problems of suspended animation	2189	=head3 The special problems of suspended animation
1933		2190
1934	When you leave the server world it is quite customary to hit machines that	2191	When you leave the server world it is quite customary to hit machines that
1935	can suspend/hibernate - what happens to the clocks during such a suspend?	2192	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1965		2222
1966	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2223	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1967		2224
1968	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2225	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1969		2226
1970	Configure the timer to trigger after C<after> seconds. If C<repeat>	2227	Configure the timer to trigger after C<after> seconds (fractional and
1971	is C<0.>, then it will automatically be stopped once the timeout is	2228	negative values are supported). If C<repeat> is C<0.>, then it will
1972	reached. If it is positive, then the timer will automatically be	2229	automatically be stopped once the timeout is reached. If it is positive,
1973	configured to trigger again C<repeat> seconds later, again, and again,	2230	then the timer will automatically be configured to trigger again C<repeat>
1974	until stopped manually.	2231	seconds later, again, and again, until stopped manually.
1975		2232
1976	The timer itself will do a best-effort at avoiding drift, that is, if	2233	The timer itself will do a best-effort at avoiding drift, that is, if
1977	you configure a timer to trigger every 10 seconds, then it will normally	2234	you configure a timer to trigger every 10 seconds, then it will normally
1978	trigger at exactly 10 second intervals. If, however, your program cannot	2235	trigger at exactly 10 second intervals. If, however, your program cannot
1979	keep up with the timer (because it takes longer than those 10 seconds to	2236	keep up with the timer (because it takes longer than those 10 seconds to
1980	do stuff) the timer will not fire more than once per event loop iteration.	2237	do stuff) the timer will not fire more than once per event loop iteration.
1981		2238
1982	=item ev_timer_again (loop, ev_timer *)	2239	=item ev_timer_again (loop, ev_timer *)
1983		2240
1984	This will act as if the timer timed out and restart it again if it is	2241	This will act as if the timer timed out, and restarts it again if it is
1985	repeating. The exact semantics are:	2242	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2243	timeout to the C<repeat> value and calling C<ev_timer_start>.
1986		2244
		2245	The exact semantics are as in the following rules, all of which will be
		2246	applied to the watcher:
		2247
		2248	=over 4
		2249
1987	If the timer is pending, its pending status is cleared.	2250	=item If the timer is pending, the pending status is always cleared.
1988		2251
1989	If the timer is started but non-repeating, stop it (as if it timed out).	2252	=item If the timer is started but non-repeating, stop it (as if it timed
		2253	out, without invoking it).
1990		2254
1991	If the timer is repeating, either start it if necessary (with the	2255	=item If the timer is repeating, make the C<repeat> value the new timeout
1992	C<repeat> value), or reset the running timer to the C<repeat> value.	2256	and start the timer, if necessary.
1993		2257
		2258	=back
		2259
1994	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2260	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1995	usage example.	2261	usage example.
1996		2262
1997	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2263	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1998		2264
1999	Returns the remaining time until a timer fires. If the timer is active,	2265	Returns the remaining time until a timer fires. If the timer is active,
…		…
2052	Periodic watchers are also timers of a kind, but they are very versatile	2318	Periodic watchers are also timers of a kind, but they are very versatile
2053	(and unfortunately a bit complex).	2319	(and unfortunately a bit complex).
2054		2320
2055	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2321	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2056	relative time, the physical time that passes) but on wall clock time	2322	relative time, the physical time that passes) but on wall clock time
2057	(absolute time, the thing you can read on your calender or clock). The	2323	(absolute time, the thing you can read on your calendar or clock). The
2058	difference is that wall clock time can run faster or slower than real	2324	difference is that wall clock time can run faster or slower than real
2059	time, and time jumps are not uncommon (e.g. when you adjust your	2325	time, and time jumps are not uncommon (e.g. when you adjust your
2060	wrist-watch).	2326	wrist-watch).
2061		2327
2062	You can tell a periodic watcher to trigger after some specific point	2328	You can tell a periodic watcher to trigger after some specific point
…		…
2067	C<ev_timer>, which would still trigger roughly 10 seconds after starting	2333	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2068	it, as it uses a relative timeout).	2334	it, as it uses a relative timeout).
2069		2335
2070	C<ev_periodic> watchers can also be used to implement vastly more complex	2336	C<ev_periodic> watchers can also be used to implement vastly more complex
2071	timers, such as triggering an event on each "midnight, local time", or	2337	timers, such as triggering an event on each "midnight, local time", or
2072	other complicated rules. This cannot be done with C<ev_timer> watchers, as	2338	other complicated rules. This cannot easily be done with C<ev_timer>
2073	those cannot react to time jumps.	2339	watchers, as those cannot react to time jumps.
2074		2340
2075	As with timers, the callback is guaranteed to be invoked only when the	2341	As with timers, the callback is guaranteed to be invoked only when the
2076	point in time where it is supposed to trigger has passed. If multiple	2342	point in time where it is supposed to trigger has passed. If multiple
2077	timers become ready during the same loop iteration then the ones with	2343	timers become ready during the same loop iteration then the ones with
2078	earlier time-out values are invoked before ones with later time-out values	2344	earlier time-out values are invoked before ones with later time-out values
…		…
2119		2385
2120	Another way to think about it (for the mathematically inclined) is that	2386	Another way to think about it (for the mathematically inclined) is that
2121	C<ev_periodic> will try to run the callback in this mode at the next possible	2387	C<ev_periodic> will try to run the callback in this mode at the next possible
2122	time where C<time = offset (mod interval)>, regardless of any time jumps.	2388	time where C<time = offset (mod interval)>, regardless of any time jumps.
2123		2389
2124	For numerical stability it is preferable that the C<offset> value is near	2390	The C<interval> I<MUST> be positive, and for numerical stability, the
2125	C<ev_now ()> (the current time), but there is no range requirement for	2391	interval value should be higher than C<1/8192> (which is around 100
2126	this value, and in fact is often specified as zero.	2392	microseconds) and C<offset> should be higher than C<0> and should have
		2393	at most a similar magnitude as the current time (say, within a factor of
		2394	ten). Typical values for offset are, in fact, C<0> or something between
		2395	C<0> and C<interval>, which is also the recommended range.
2127		2396
2128	Note also that there is an upper limit to how often a timer can fire (CPU	2397	Note also that there is an upper limit to how often a timer can fire (CPU
2129	speed for example), so if C<interval> is very small then timing stability	2398	speed for example), so if C<interval> is very small then timing stability
2130	will of course deteriorate. Libev itself tries to be exact to be about one	2399	will of course deteriorate. Libev itself tries to be exact to be about one
2131	millisecond (if the OS supports it and the machine is fast enough).	2400	millisecond (if the OS supports it and the machine is fast enough).
…		…
2161		2430
2162	NOTE: I<< This callback must always return a time that is higher than or	2431	NOTE: I<< This callback must always return a time that is higher than or
2163	equal to the passed C<now> value >>.	2432	equal to the passed C<now> value >>.
2164		2433
2165	This can be used to create very complex timers, such as a timer that	2434	This can be used to create very complex timers, such as a timer that
2166	triggers on "next midnight, local time". To do this, you would calculate the	2435	triggers on "next midnight, local time". To do this, you would calculate
2167	next midnight after C<now> and return the timestamp value for this. How	2436	the next midnight after C<now> and return the timestamp value for
2168	you do this is, again, up to you (but it is not trivial, which is the main	2437	this. Here is a (completely untested, no error checking) example on how to
2169	reason I omitted it as an example).	2438	do this:
		2439
		2440	#include <time.h>
		2441
		2442	static ev_tstamp
		2443	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2444	{
		2445	time_t tnow = (time_t)now;
		2446	struct tm tm;
		2447	localtime_r (&tnow, &tm);
		2448
		2449	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2450	++tm.tm_mday; // midnight next day
		2451
		2452	return mktime (&tm);
		2453	}
		2454
		2455	Note: this code might run into trouble on days that have more then two
		2456	midnights (beginning and end).
2170		2457
2171	=back	2458	=back
2172		2459
2173	=item ev_periodic_again (loop, ev_periodic *)	2460	=item ev_periodic_again (loop, ev_periodic *)
2174		2461
…		…
2239		2526
2240	ev_periodic hourly_tick;	2527	ev_periodic hourly_tick;
2241	ev_periodic_init (&hourly_tick, clock_cb,	2528	ev_periodic_init (&hourly_tick, clock_cb,
2242	fmod (ev_now (loop), 3600.), 3600., 0);	2529	fmod (ev_now (loop), 3600.), 3600., 0);
2243	ev_periodic_start (loop, &hourly_tick);	2530	ev_periodic_start (loop, &hourly_tick);
2244		2531
2245		2532
2246	=head2 C<ev_signal> - signal me when a signal gets signalled!	2533	=head2 C<ev_signal> - signal me when a signal gets signalled!
2247		2534
2248	Signal watchers will trigger an event when the process receives a specific	2535	Signal watchers will trigger an event when the process receives a specific
2249	signal one or more times. Even though signals are very asynchronous, libev	2536	signal one or more times. Even though signals are very asynchronous, libev
2250	will try it's best to deliver signals synchronously, i.e. as part of the	2537	will try its best to deliver signals synchronously, i.e. as part of the
2251	normal event processing, like any other event.	2538	normal event processing, like any other event.
2252		2539
2253	If you want signals to be delivered truly asynchronously, just use	2540	If you want signals to be delivered truly asynchronously, just use
2254	C<sigaction> as you would do without libev and forget about sharing	2541	C<sigaction> as you would do without libev and forget about sharing
2255	the signal. You can even use C<ev_async> from a signal handler to	2542	the signal. You can even use C<ev_async> from a signal handler to
…		…
2259	only within the same loop, i.e. you can watch for C<SIGINT> in your	2546	only within the same loop, i.e. you can watch for C<SIGINT> in your
2260	default loop and for C<SIGIO> in another loop, but you cannot watch for	2547	default loop and for C<SIGIO> in another loop, but you cannot watch for
2261	C<SIGINT> in both the default loop and another loop at the same time. At	2548	C<SIGINT> in both the default loop and another loop at the same time. At
2262	the moment, C<SIGCHLD> is permanently tied to the default loop.	2549	the moment, C<SIGCHLD> is permanently tied to the default loop.
2263		2550
2264	When the first watcher gets started will libev actually register something	2551	Only after the first watcher for a signal is started will libev actually
2265	with the kernel (thus it coexists with your own signal handlers as long as	2552	register something with the kernel. It thus coexists with your own signal
2266	you don't register any with libev for the same signal).	2553	handlers as long as you don't register any with libev for the same signal.
2267		2554
2268	If possible and supported, libev will install its handlers with	2555	If possible and supported, libev will install its handlers with
2269	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2556	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2270	not be unduly interrupted. If you have a problem with system calls getting	2557	not be unduly interrupted. If you have a problem with system calls getting
2271	interrupted by signals you can block all signals in an C<ev_check> watcher	2558	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2274	=head3 The special problem of inheritance over fork/execve/pthread_create	2561	=head3 The special problem of inheritance over fork/execve/pthread_create
2275		2562
2276	Both the signal mask (C<sigprocmask>) and the signal disposition	2563	Both the signal mask (C<sigprocmask>) and the signal disposition
2277	(C<sigaction>) are unspecified after starting a signal watcher (and after	2564	(C<sigaction>) are unspecified after starting a signal watcher (and after
2278	stopping it again), that is, libev might or might not block the signal,	2565	stopping it again), that is, libev might or might not block the signal,
2279	and might or might not set or restore the installed signal handler.	2566	and might or might not set or restore the installed signal handler (but
		2567	see C<EVFLAG_NOSIGMASK>).
2280		2568
2281	While this does not matter for the signal disposition (libev never	2569	While this does not matter for the signal disposition (libev never
2282	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2570	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2283	C<execve>), this matters for the signal mask: many programs do not expect	2571	C<execve>), this matters for the signal mask: many programs do not expect
2284	certain signals to be blocked.	2572	certain signals to be blocked.
…		…
2297	I<has> to modify the signal mask, at least temporarily.	2585	I<has> to modify the signal mask, at least temporarily.
2298		2586
2299	So I can't stress this enough: I<If you do not reset your signal mask when	2587	So I can't stress this enough: I<If you do not reset your signal mask when
2300	you expect it to be empty, you have a race condition in your code>. This	2588	you expect it to be empty, you have a race condition in your code>. This
2301	is not a libev-specific thing, this is true for most event libraries.	2589	is not a libev-specific thing, this is true for most event libraries.
		2590
		2591	=head3 The special problem of threads signal handling
		2592
		2593	POSIX threads has problematic signal handling semantics, specifically,
		2594	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2595	threads in a process block signals, which is hard to achieve.
		2596
		2597	When you want to use sigwait (or mix libev signal handling with your own
		2598	for the same signals), you can tackle this problem by globally blocking
		2599	all signals before creating any threads (or creating them with a fully set
		2600	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2601	loops. Then designate one thread as "signal receiver thread" which handles
		2602	these signals. You can pass on any signals that libev might be interested
		2603	in by calling C<ev_feed_signal>.
2302		2604
2303	=head3 Watcher-Specific Functions and Data Members	2605	=head3 Watcher-Specific Functions and Data Members
2304		2606
2305	=over 4	2607	=over 4
2306		2608
…		…
2441		2743
2442	=head2 C<ev_stat> - did the file attributes just change?	2744	=head2 C<ev_stat> - did the file attributes just change?
2443		2745
2444	This watches a file system path for attribute changes. That is, it calls	2746	This watches a file system path for attribute changes. That is, it calls
2445	C<stat> on that path in regular intervals (or when the OS says it changed)	2747	C<stat> on that path in regular intervals (or when the OS says it changed)
2446	and sees if it changed compared to the last time, invoking the callback if	2748	and sees if it changed compared to the last time, invoking the callback
2447	it did.	2749	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2750	happen after the watcher has been started will be reported.
2448		2751
2449	The path does not need to exist: changing from "path exists" to "path does	2752	The path does not need to exist: changing from "path exists" to "path does
2450	not exist" is a status change like any other. The condition "path does not	2753	not exist" is a status change like any other. The condition "path does not
2451	exist" (or more correctly "path cannot be stat'ed") is signified by the	2754	exist" (or more correctly "path cannot be stat'ed") is signified by the
2452	C<st_nlink> field being zero (which is otherwise always forced to be at	2755	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2682	Apart from keeping your process non-blocking (which is a useful	2985	Apart from keeping your process non-blocking (which is a useful
2683	effect on its own sometimes), idle watchers are a good place to do	2986	effect on its own sometimes), idle watchers are a good place to do
2684	"pseudo-background processing", or delay processing stuff to after the	2987	"pseudo-background processing", or delay processing stuff to after the
2685	event loop has handled all outstanding events.	2988	event loop has handled all outstanding events.
2686		2989
		2990	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2991
		2992	As long as there is at least one active idle watcher, libev will never
		2993	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2994	For this to work, the idle watcher doesn't need to be invoked at all - the
		2995	lowest priority will do.
		2996
		2997	This mode of operation can be useful together with an C<ev_check> watcher,
		2998	to do something on each event loop iteration - for example to balance load
		2999	between different connections.
		3000
		3001	See L</Abusing an ev_check watcher for its side-effect> for a longer
		3002	example.
		3003
2687	=head3 Watcher-Specific Functions and Data Members	3004	=head3 Watcher-Specific Functions and Data Members
2688		3005
2689	=over 4	3006	=over 4
2690		3007
2691	=item ev_idle_init (ev_idle *, callback)	3008	=item ev_idle_init (ev_idle *, callback)
…		…
2702	callback, free it. Also, use no error checking, as usual.	3019	callback, free it. Also, use no error checking, as usual.
2703		3020
2704	static void	3021	static void
2705	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	3022	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2706	{	3023	{
		3024	// stop the watcher
		3025	ev_idle_stop (loop, w);
		3026
		3027	// now we can free it
2707	free (w);	3028	free (w);
		3029
2708	// now do something you wanted to do when the program has	3030	// now do something you wanted to do when the program has
2709	// no longer anything immediate to do.	3031	// no longer anything immediate to do.
2710	}	3032	}
2711		3033
2712	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	3034	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2714	ev_idle_start (loop, idle_watcher);	3036	ev_idle_start (loop, idle_watcher);
2715		3037
2716		3038
2717	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3039	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2718		3040
2719	Prepare and check watchers are usually (but not always) used in pairs:	3041	Prepare and check watchers are often (but not always) used in pairs:
2720	prepare watchers get invoked before the process blocks and check watchers	3042	prepare watchers get invoked before the process blocks and check watchers
2721	afterwards.	3043	afterwards.
2722		3044
2723	You I<must not> call C<ev_run> or similar functions that enter	3045	You I<must not> call C<ev_run> (or similar functions that enter the
2724	the current event loop from either C<ev_prepare> or C<ev_check>	3046	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2725	watchers. Other loops than the current one are fine, however. The	3047	C<ev_check> watchers. Other loops than the current one are fine,
2726	rationale behind this is that you do not need to check for recursion in	3048	however. The rationale behind this is that you do not need to check
2727	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3049	for recursion in those watchers, i.e. the sequence will always be
2728	C<ev_check> so if you have one watcher of each kind they will always be	3050	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2729	called in pairs bracketing the blocking call.	3051	kind they will always be called in pairs bracketing the blocking call.
2730		3052
2731	Their main purpose is to integrate other event mechanisms into libev and	3053	Their main purpose is to integrate other event mechanisms into libev and
2732	their use is somewhat advanced. They could be used, for example, to track	3054	their use is somewhat advanced. They could be used, for example, to track
2733	variable changes, implement your own watchers, integrate net-snmp or a	3055	variable changes, implement your own watchers, integrate net-snmp or a
2734	coroutine library and lots more. They are also occasionally useful if	3056	coroutine library and lots more. They are also occasionally useful if
…		…
2752	with priority higher than or equal to the event loop and one coroutine	3074	with priority higher than or equal to the event loop and one coroutine
2753	of lower priority, but only once, using idle watchers to keep the event	3075	of lower priority, but only once, using idle watchers to keep the event
2754	loop from blocking if lower-priority coroutines are active, thus mapping	3076	loop from blocking if lower-priority coroutines are active, thus mapping
2755	low-priority coroutines to idle/background tasks).	3077	low-priority coroutines to idle/background tasks).
2756		3078
2757	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3079	When used for this purpose, it is recommended to give C<ev_check> watchers
2758	priority, to ensure that they are being run before any other watchers	3080	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2759	after the poll (this doesn't matter for C<ev_prepare> watchers).	3081	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3082	watchers).
2760		3083
2761	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3084	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2762	activate ("feed") events into libev. While libev fully supports this, they	3085	activate ("feed") events into libev. While libev fully supports this, they
2763	might get executed before other C<ev_check> watchers did their job. As	3086	might get executed before other C<ev_check> watchers did their job. As
2764	C<ev_check> watchers are often used to embed other (non-libev) event	3087	C<ev_check> watchers are often used to embed other (non-libev) event
2765	loops those other event loops might be in an unusable state until their	3088	loops those other event loops might be in an unusable state until their
2766	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3089	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2767	others).	3090	others).
		3091
		3092	=head3 Abusing an C<ev_check> watcher for its side-effect
		3093
		3094	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3095	useful because they are called once per event loop iteration. For
		3096	example, if you want to handle a large number of connections fairly, you
		3097	normally only do a bit of work for each active connection, and if there
		3098	is more work to do, you wait for the next event loop iteration, so other
		3099	connections have a chance of making progress.
		3100
		3101	Using an C<ev_check> watcher is almost enough: it will be called on the
		3102	next event loop iteration. However, that isn't as soon as possible -
		3103	without external events, your C<ev_check> watcher will not be invoked.
		3104
		3105	This is where C<ev_idle> watchers come in handy - all you need is a
		3106	single global idle watcher that is active as long as you have one active
		3107	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3108	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3109	invoked. Neither watcher alone can do that.
2768		3110
2769	=head3 Watcher-Specific Functions and Data Members	3111	=head3 Watcher-Specific Functions and Data Members
2770		3112
2771	=over 4	3113	=over 4
2772		3114
…		…
2973		3315
2974	=over 4	3316	=over 4
2975		3317
2976	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3318	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2977		3319
2978	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3320	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2979		3321
2980	Configures the watcher to embed the given loop, which must be	3322	Configures the watcher to embed the given loop, which must be
2981	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3323	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2982	invoked automatically, otherwise it is the responsibility of the callback	3324	invoked automatically, otherwise it is the responsibility of the callback
2983	to invoke it (it will continue to be called until the sweep has been done,	3325	to invoke it (it will continue to be called until the sweep has been done,
…		…
3004	used).	3346	used).
3005		3347
3006	struct ev_loop *loop_hi = ev_default_init (0);	3348	struct ev_loop *loop_hi = ev_default_init (0);
3007	struct ev_loop *loop_lo = 0;	3349	struct ev_loop *loop_lo = 0;
3008	ev_embed embed;	3350	ev_embed embed;
3009		3351
3010	// see if there is a chance of getting one that works	3352	// see if there is a chance of getting one that works
3011	// (remember that a flags value of 0 means autodetection)	3353	// (remember that a flags value of 0 means autodetection)
3012	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3354	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3013	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3355	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3014	: 0;	3356	: 0;
…		…
3028	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3370	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3029		3371
3030	struct ev_loop *loop = ev_default_init (0);	3372	struct ev_loop *loop = ev_default_init (0);
3031	struct ev_loop *loop_socket = 0;	3373	struct ev_loop *loop_socket = 0;
3032	ev_embed embed;	3374	ev_embed embed;
3033		3375
3034	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3376	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3035	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3377	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3036	{	3378	{
3037	ev_embed_init (&embed, 0, loop_socket);	3379	ev_embed_init (&embed, 0, loop_socket);
3038	ev_embed_start (loop, &embed);	3380	ev_embed_start (loop, &embed);
…		…
3046		3388
3047	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3389	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3048		3390
3049	Fork watchers are called when a C<fork ()> was detected (usually because	3391	Fork watchers are called when a C<fork ()> was detected (usually because
3050	whoever is a good citizen cared to tell libev about it by calling	3392	whoever is a good citizen cared to tell libev about it by calling
3051	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3393	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3052	event loop blocks next and before C<ev_check> watchers are being called,	3394	and before C<ev_check> watchers are being called, and only in the child
3053	and only in the child after the fork. If whoever good citizen calling	3395	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3054	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3396	and calls it in the wrong process, the fork handlers will be invoked, too,
3055	handlers will be invoked, too, of course.	3397	of course.
3056		3398
3057	=head3 The special problem of life after fork - how is it possible?	3399	=head3 The special problem of life after fork - how is it possible?
3058		3400
3059	Most uses of C<fork()> consist of forking, then some simple calls to set	3401	Most uses of C<fork ()> consist of forking, then some simple calls to set
3060	up/change the process environment, followed by a call to C<exec()>. This	3402	up/change the process environment, followed by a call to C<exec()>. This
3061	sequence should be handled by libev without any problems.	3403	sequence should be handled by libev without any problems.
3062		3404
3063	This changes when the application actually wants to do event handling	3405	This changes when the application actually wants to do event handling
3064	in the child, or both parent in child, in effect "continuing" after the	3406	in the child, or both parent in child, in effect "continuing" after the
…		…
3090		3432
3091	=head3 Watcher-Specific Functions and Data Members	3433	=head3 Watcher-Specific Functions and Data Members
3092		3434
3093	=over 4	3435	=over 4
3094		3436
3095	=item ev_fork_init (ev_signal *, callback)	3437	=item ev_fork_init (ev_fork *, callback)
3096		3438
3097	Initialises and configures the fork watcher - it has no parameters of any	3439	Initialises and configures the fork watcher - it has no parameters of any
3098	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3440	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3099	believe me.	3441	really.
3100		3442
3101	=back	3443	=back
3102		3444
3103		3445
		3446	=head2 C<ev_cleanup> - even the best things end
		3447
		3448	Cleanup watchers are called just before the event loop is being destroyed
		3449	by a call to C<ev_loop_destroy>.
		3450
		3451	While there is no guarantee that the event loop gets destroyed, cleanup
		3452	watchers provide a convenient method to install cleanup hooks for your
		3453	program, worker threads and so on - you just to make sure to destroy the
		3454	loop when you want them to be invoked.
		3455
		3456	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3457	all other watchers, they do not keep a reference to the event loop (which
		3458	makes a lot of sense if you think about it). Like all other watchers, you
		3459	can call libev functions in the callback, except C<ev_cleanup_start>.
		3460
		3461	=head3 Watcher-Specific Functions and Data Members
		3462
		3463	=over 4
		3464
		3465	=item ev_cleanup_init (ev_cleanup *, callback)
		3466
		3467	Initialises and configures the cleanup watcher - it has no parameters of
		3468	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3469	pointless, I assure you.
		3470
		3471	=back
		3472
		3473	Example: Register an atexit handler to destroy the default loop, so any
		3474	cleanup functions are called.
		3475
		3476	static void
		3477	program_exits (void)
		3478	{
		3479	ev_loop_destroy (EV_DEFAULT_UC);
		3480	}
		3481
		3482	...
		3483	atexit (program_exits);
		3484
		3485
3104	=head2 C<ev_async> - how to wake up an event loop	3486	=head2 C<ev_async> - how to wake up an event loop
3105		3487
3106	In general, you cannot use an C<ev_run> from multiple threads or other	3488	In general, you cannot use an C<ev_loop> from multiple threads or other
3107	asynchronous sources such as signal handlers (as opposed to multiple event	3489	asynchronous sources such as signal handlers (as opposed to multiple event
3108	loops - those are of course safe to use in different threads).	3490	loops - those are of course safe to use in different threads).
3109		3491
3110	Sometimes, however, you need to wake up an event loop you do not control,	3492	Sometimes, however, you need to wake up an event loop you do not control,
3111	for example because it belongs to another thread. This is what C<ev_async>	3493	for example because it belongs to another thread. This is what C<ev_async>
…		…
3113	it by calling C<ev_async_send>, which is thread- and signal safe.	3495	it by calling C<ev_async_send>, which is thread- and signal safe.
3114		3496
3115	This functionality is very similar to C<ev_signal> watchers, as signals,	3497	This functionality is very similar to C<ev_signal> watchers, as signals,
3116	too, are asynchronous in nature, and signals, too, will be compressed	3498	too, are asynchronous in nature, and signals, too, will be compressed
3117	(i.e. the number of callback invocations may be less than the number of	3499	(i.e. the number of callback invocations may be less than the number of
3118	C<ev_async_sent> calls).	3500	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3119		3501	of "global async watchers" by using a watcher on an otherwise unused
3120	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3502	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3121	just the default loop.	3503	even without knowing which loop owns the signal.
3122		3504
3123	=head3 Queueing	3505	=head3 Queueing
3124		3506
3125	C<ev_async> does not support queueing of data in any way. The reason	3507	C<ev_async> does not support queueing of data in any way. The reason
3126	is that the author does not know of a simple (or any) algorithm for a	3508	is that the author does not know of a simple (or any) algorithm for a
…		…
3218	trust me.	3600	trust me.
3219		3601
3220	=item ev_async_send (loop, ev_async *)	3602	=item ev_async_send (loop, ev_async *)
3221		3603
3222	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3604	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3223	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3605	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3606	returns.
		3607
3224	C<ev_feed_event>, this call is safe to do from other threads, signal or	3608	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3225	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3609	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3226	section below on what exactly this means).	3610	embedding section below on what exactly this means).
3227		3611
3228	Note that, as with other watchers in libev, multiple events might get	3612	Note that, as with other watchers in libev, multiple events might get
3229	compressed into a single callback invocation (another way to look at this	3613	compressed into a single callback invocation (another way to look at
3230	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3614	this is that C<ev_async> watchers are level-triggered: they are set on
3231	reset when the event loop detects that).	3615	C<ev_async_send>, reset when the event loop detects that).
3232		3616
3233	This call incurs the overhead of a system call only once per event loop	3617	This call incurs the overhead of at most one extra system call per event
3234	iteration, so while the overhead might be noticeable, it doesn't apply to	3618	loop iteration, if the event loop is blocked, and no syscall at all if
3235	repeated calls to C<ev_async_send> for the same event loop.	3619	the event loop (or your program) is processing events. That means that
		3620	repeated calls are basically free (there is no need to avoid calls for
		3621	performance reasons) and that the overhead becomes smaller (typically
		3622	zero) under load.
3236		3623
3237	=item bool = ev_async_pending (ev_async *)	3624	=item bool = ev_async_pending (ev_async *)
3238		3625
3239	Returns a non-zero value when C<ev_async_send> has been called on the	3626	Returns a non-zero value when C<ev_async_send> has been called on the
3240	watcher but the event has not yet been processed (or even noted) by the	3627	watcher but the event has not yet been processed (or even noted) by the
…		…
3257		3644
3258	There are some other functions of possible interest. Described. Here. Now.	3645	There are some other functions of possible interest. Described. Here. Now.
3259		3646
3260	=over 4	3647	=over 4
3261		3648
3262	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3649	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3263		3650
3264	This function combines a simple timer and an I/O watcher, calls your	3651	This function combines a simple timer and an I/O watcher, calls your
3265	callback on whichever event happens first and automatically stops both	3652	callback on whichever event happens first and automatically stops both
3266	watchers. This is useful if you want to wait for a single event on an fd	3653	watchers. This is useful if you want to wait for a single event on an fd
3267	or timeout without having to allocate/configure/start/stop/free one or	3654	or timeout without having to allocate/configure/start/stop/free one or
…		…
3295	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3682	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3296		3683
3297	=item ev_feed_fd_event (loop, int fd, int revents)	3684	=item ev_feed_fd_event (loop, int fd, int revents)
3298		3685
3299	Feed an event on the given fd, as if a file descriptor backend detected	3686	Feed an event on the given fd, as if a file descriptor backend detected
3300	the given events it.	3687	the given events.
3301		3688
3302	=item ev_feed_signal_event (loop, int signum)	3689	=item ev_feed_signal_event (loop, int signum)
3303		3690
3304	Feed an event as if the given signal occurred (C<loop> must be the default	3691	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3305	loop!).	3692	which is async-safe.
3306		3693
3307	=back	3694	=back
		3695
		3696
		3697	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3698
		3699	This section explains some common idioms that are not immediately
		3700	obvious. Note that examples are sprinkled over the whole manual, and this
		3701	section only contains stuff that wouldn't fit anywhere else.
		3702
		3703	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3704
		3705	Each watcher has, by default, a C<void *data> member that you can read
		3706	or modify at any time: libev will completely ignore it. This can be used
		3707	to associate arbitrary data with your watcher. If you need more data and
		3708	don't want to allocate memory separately and store a pointer to it in that
		3709	data member, you can also "subclass" the watcher type and provide your own
		3710	data:
		3711
		3712	struct my_io
		3713	{
		3714	ev_io io;
		3715	int otherfd;
		3716	void *somedata;
		3717	struct whatever *mostinteresting;
		3718	};
		3719
		3720	...
		3721	struct my_io w;
		3722	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3723
		3724	And since your callback will be called with a pointer to the watcher, you
		3725	can cast it back to your own type:
		3726
		3727	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3728	{
		3729	struct my_io *w = (struct my_io *)w_;
		3730	...
		3731	}
		3732
		3733	More interesting and less C-conformant ways of casting your callback
		3734	function type instead have been omitted.
		3735
		3736	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3737
		3738	Another common scenario is to use some data structure with multiple
		3739	embedded watchers, in effect creating your own watcher that combines
		3740	multiple libev event sources into one "super-watcher":
		3741
		3742	struct my_biggy
		3743	{
		3744	int some_data;
		3745	ev_timer t1;
		3746	ev_timer t2;
		3747	}
		3748
		3749	In this case getting the pointer to C<my_biggy> is a bit more
		3750	complicated: Either you store the address of your C<my_biggy> struct in
		3751	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3752	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3753	real programmers):
		3754
		3755	#include <stddef.h>
		3756
		3757	static void
		3758	t1_cb (EV_P_ ev_timer *w, int revents)
		3759	{
		3760	struct my_biggy big = (struct my_biggy *)
		3761	(((char *)w) - offsetof (struct my_biggy, t1));
		3762	}
		3763
		3764	static void
		3765	t2_cb (EV_P_ ev_timer *w, int revents)
		3766	{
		3767	struct my_biggy big = (struct my_biggy *)
		3768	(((char *)w) - offsetof (struct my_biggy, t2));
		3769	}
		3770
		3771	=head2 AVOIDING FINISHING BEFORE RETURNING
		3772
		3773	Often you have structures like this in event-based programs:
		3774
		3775	callback ()
		3776	{
		3777	free (request);
		3778	}
		3779
		3780	request = start_new_request (..., callback);
		3781
		3782	The intent is to start some "lengthy" operation. The C<request> could be
		3783	used to cancel the operation, or do other things with it.
		3784
		3785	It's not uncommon to have code paths in C<start_new_request> that
		3786	immediately invoke the callback, for example, to report errors. Or you add
		3787	some caching layer that finds that it can skip the lengthy aspects of the
		3788	operation and simply invoke the callback with the result.
		3789
		3790	The problem here is that this will happen I<before> C<start_new_request>
		3791	has returned, so C<request> is not set.
		3792
		3793	Even if you pass the request by some safer means to the callback, you
		3794	might want to do something to the request after starting it, such as
		3795	canceling it, which probably isn't working so well when the callback has
		3796	already been invoked.
		3797
		3798	A common way around all these issues is to make sure that
		3799	C<start_new_request> I<always> returns before the callback is invoked. If
		3800	C<start_new_request> immediately knows the result, it can artificially
		3801	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3802	example, or more sneakily, by reusing an existing (stopped) watcher and
		3803	pushing it into the pending queue:
		3804
		3805	ev_set_cb (watcher, callback);
		3806	ev_feed_event (EV_A_ watcher, 0);
		3807
		3808	This way, C<start_new_request> can safely return before the callback is
		3809	invoked, while not delaying callback invocation too much.
		3810
		3811	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3812
		3813	Often (especially in GUI toolkits) there are places where you have
		3814	I<modal> interaction, which is most easily implemented by recursively
		3815	invoking C<ev_run>.
		3816
		3817	This brings the problem of exiting - a callback might want to finish the
		3818	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3819	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3820	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3821	other combination: In these cases, a simple C<ev_break> will not work.
		3822
		3823	The solution is to maintain "break this loop" variable for each C<ev_run>
		3824	invocation, and use a loop around C<ev_run> until the condition is
		3825	triggered, using C<EVRUN_ONCE>:
		3826
		3827	// main loop
		3828	int exit_main_loop = 0;
		3829
		3830	while (!exit_main_loop)
		3831	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3832
		3833	// in a modal watcher
		3834	int exit_nested_loop = 0;
		3835
		3836	while (!exit_nested_loop)
		3837	ev_run (EV_A_ EVRUN_ONCE);
		3838
		3839	To exit from any of these loops, just set the corresponding exit variable:
		3840
		3841	// exit modal loop
		3842	exit_nested_loop = 1;
		3843
		3844	// exit main program, after modal loop is finished
		3845	exit_main_loop = 1;
		3846
		3847	// exit both
		3848	exit_main_loop = exit_nested_loop = 1;
		3849
		3850	=head2 THREAD LOCKING EXAMPLE
		3851
		3852	Here is a fictitious example of how to run an event loop in a different
		3853	thread from where callbacks are being invoked and watchers are
		3854	created/added/removed.
		3855
		3856	For a real-world example, see the C<EV::Loop::Async> perl module,
		3857	which uses exactly this technique (which is suited for many high-level
		3858	languages).
		3859
		3860	The example uses a pthread mutex to protect the loop data, a condition
		3861	variable to wait for callback invocations, an async watcher to notify the
		3862	event loop thread and an unspecified mechanism to wake up the main thread.
		3863
		3864	First, you need to associate some data with the event loop:
		3865
		3866	typedef struct {
		3867	pthread_mutex_t lock; /* global loop lock */
		3868	pthread_t tid;
		3869	pthread_cond_t invoke_cv;
		3870	ev_async async_w;
		3871	} userdata;
		3872
		3873	void prepare_loop (EV_P)
		3874	{
		3875	// for simplicity, we use a static userdata struct.
		3876	static userdata u;
		3877
		3878	ev_async_init (&u.async_w, async_cb);
		3879	ev_async_start (EV_A_ &u.async_w);
		3880
		3881	pthread_mutex_init (&u.lock, 0);
		3882	pthread_cond_init (&u.invoke_cv, 0);
		3883
		3884	// now associate this with the loop
		3885	ev_set_userdata (EV_A_ &u);
		3886	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3887	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3888
		3889	// then create the thread running ev_run
		3890	pthread_create (&u.tid, 0, l_run, EV_A);
		3891	}
		3892
		3893	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3894	solely to wake up the event loop so it takes notice of any new watchers
		3895	that might have been added:
		3896
		3897	static void
		3898	async_cb (EV_P_ ev_async *w, int revents)
		3899	{
		3900	// just used for the side effects
		3901	}
		3902
		3903	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3904	protecting the loop data, respectively.
		3905
		3906	static void
		3907	l_release (EV_P)
		3908	{
		3909	userdata *u = ev_userdata (EV_A);
		3910	pthread_mutex_unlock (&u->lock);
		3911	}
		3912
		3913	static void
		3914	l_acquire (EV_P)
		3915	{
		3916	userdata *u = ev_userdata (EV_A);
		3917	pthread_mutex_lock (&u->lock);
		3918	}
		3919
		3920	The event loop thread first acquires the mutex, and then jumps straight
		3921	into C<ev_run>:
		3922
		3923	void *
		3924	l_run (void *thr_arg)
		3925	{
		3926	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3927
		3928	l_acquire (EV_A);
		3929	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3930	ev_run (EV_A_ 0);
		3931	l_release (EV_A);
		3932
		3933	return 0;
		3934	}
		3935
		3936	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3937	signal the main thread via some unspecified mechanism (signals? pipe
		3938	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3939	have been called (in a while loop because a) spurious wakeups are possible
		3940	and b) skipping inter-thread-communication when there are no pending
		3941	watchers is very beneficial):
		3942
		3943	static void
		3944	l_invoke (EV_P)
		3945	{
		3946	userdata *u = ev_userdata (EV_A);
		3947
		3948	while (ev_pending_count (EV_A))
		3949	{
		3950	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3951	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3952	}
		3953	}
		3954
		3955	Now, whenever the main thread gets told to invoke pending watchers, it
		3956	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3957	thread to continue:
		3958
		3959	static void
		3960	real_invoke_pending (EV_P)
		3961	{
		3962	userdata *u = ev_userdata (EV_A);
		3963
		3964	pthread_mutex_lock (&u->lock);
		3965	ev_invoke_pending (EV_A);
		3966	pthread_cond_signal (&u->invoke_cv);
		3967	pthread_mutex_unlock (&u->lock);
		3968	}
		3969
		3970	Whenever you want to start/stop a watcher or do other modifications to an
		3971	event loop, you will now have to lock:
		3972
		3973	ev_timer timeout_watcher;
		3974	userdata *u = ev_userdata (EV_A);
		3975
		3976	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3977
		3978	pthread_mutex_lock (&u->lock);
		3979	ev_timer_start (EV_A_ &timeout_watcher);
		3980	ev_async_send (EV_A_ &u->async_w);
		3981	pthread_mutex_unlock (&u->lock);
		3982
		3983	Note that sending the C<ev_async> watcher is required because otherwise
		3984	an event loop currently blocking in the kernel will have no knowledge
		3985	about the newly added timer. By waking up the loop it will pick up any new
		3986	watchers in the next event loop iteration.
		3987
		3988	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3989
		3990	While the overhead of a callback that e.g. schedules a thread is small, it
		3991	is still an overhead. If you embed libev, and your main usage is with some
		3992	kind of threads or coroutines, you might want to customise libev so that
		3993	doesn't need callbacks anymore.
		3994
		3995	Imagine you have coroutines that you can switch to using a function
		3996	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3997	and that due to some magic, the currently active coroutine is stored in a
		3998	global called C<current_coro>. Then you can build your own "wait for libev
		3999	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		4000	the differing C<;> conventions):
		4001
		4002	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4003	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4004
		4005	That means instead of having a C callback function, you store the
		4006	coroutine to switch to in each watcher, and instead of having libev call
		4007	your callback, you instead have it switch to that coroutine.
		4008
		4009	A coroutine might now wait for an event with a function called
		4010	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		4011	matter when, or whether the watcher is active or not when this function is
		4012	called):
		4013
		4014	void
		4015	wait_for_event (ev_watcher *w)
		4016	{
		4017	ev_set_cb (w, current_coro);
		4018	switch_to (libev_coro);
		4019	}
		4020
		4021	That basically suspends the coroutine inside C<wait_for_event> and
		4022	continues the libev coroutine, which, when appropriate, switches back to
		4023	this or any other coroutine.
		4024
		4025	You can do similar tricks if you have, say, threads with an event queue -
		4026	instead of storing a coroutine, you store the queue object and instead of
		4027	switching to a coroutine, you push the watcher onto the queue and notify
		4028	any waiters.
		4029
		4030	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		4031	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		4032
		4033	// my_ev.h
		4034	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4035	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4036	#include "../libev/ev.h"
		4037
		4038	// my_ev.c
		4039	#define EV_H "my_ev.h"
		4040	#include "../libev/ev.c"
		4041
		4042	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4043	F<my_ev.c> into your project. When properly specifying include paths, you
		4044	can even use F<ev.h> as header file name directly.
3308		4045
3309		4046
3310	=head1 LIBEVENT EMULATION	4047	=head1 LIBEVENT EMULATION
3311		4048
3312	Libev offers a compatibility emulation layer for libevent. It cannot	4049	Libev offers a compatibility emulation layer for libevent. It cannot
3313	emulate the internals of libevent, so here are some usage hints:	4050	emulate the internals of libevent, so here are some usage hints:
3314		4051
3315	=over 4	4052	=over 4
		4053
		4054	=item * Only the libevent-1.4.1-beta API is being emulated.
		4055
		4056	This was the newest libevent version available when libev was implemented,
		4057	and is still mostly unchanged in 2010.
3316		4058
3317	=item * Use it by including <event.h>, as usual.	4059	=item * Use it by including <event.h>, as usual.
3318		4060
3319	=item * The following members are fully supported: ev_base, ev_callback,	4061	=item * The following members are fully supported: ev_base, ev_callback,
3320	ev_arg, ev_fd, ev_res, ev_events.	4062	ev_arg, ev_fd, ev_res, ev_events.
…		…
3326	=item * Priorities are not currently supported. Initialising priorities	4068	=item * Priorities are not currently supported. Initialising priorities
3327	will fail and all watchers will have the same priority, even though there	4069	will fail and all watchers will have the same priority, even though there
3328	is an ev_pri field.	4070	is an ev_pri field.
3329		4071
3330	=item * In libevent, the last base created gets the signals, in libev, the	4072	=item * In libevent, the last base created gets the signals, in libev, the
3331	first base created (== the default loop) gets the signals.	4073	base that registered the signal gets the signals.
3332		4074
3333	=item * Other members are not supported.	4075	=item * Other members are not supported.
3334		4076
3335	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4077	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3336	to use the libev header file and library.	4078	to use the libev header file and library.
3337		4079
3338	=back	4080	=back
3339		4081
3340	=head1 C++ SUPPORT	4082	=head1 C++ SUPPORT
		4083
		4084	=head2 C API
		4085
		4086	The normal C API should work fine when used from C++: both ev.h and the
		4087	libev sources can be compiled as C++. Therefore, code that uses the C API
		4088	will work fine.
		4089
		4090	Proper exception specifications might have to be added to callbacks passed
		4091	to libev: exceptions may be thrown only from watcher callbacks, all other
		4092	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4093	callbacks) must not throw exceptions, and might need a C<noexcept>
		4094	specification. If you have code that needs to be compiled as both C and
		4095	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4096
		4097	static void
		4098	fatal_error (const char *msg) EV_NOEXCEPT
		4099	{
		4100	perror (msg);
		4101	abort ();
		4102	}
		4103
		4104	...
		4105	ev_set_syserr_cb (fatal_error);
		4106
		4107	The only API functions that can currently throw exceptions are C<ev_run>,
		4108	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4109	because it runs cleanup watchers).
		4110
		4111	Throwing exceptions in watcher callbacks is only supported if libev itself
		4112	is compiled with a C++ compiler or your C and C++ environments allow
		4113	throwing exceptions through C libraries (most do).
		4114
		4115	=head2 C++ API
3341		4116
3342	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4117	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3343	you to use some convenience methods to start/stop watchers and also change	4118	you to use some convenience methods to start/stop watchers and also change
3344	the callback model to a model using method callbacks on objects.	4119	the callback model to a model using method callbacks on objects.
3345		4120
3346	To use it,	4121	To use it,
3347		4122
3348	#include <ev++.h>	4123	#include <ev++.h>
3349		4124
3350	This automatically includes F<ev.h> and puts all of its definitions (many	4125	This automatically includes F<ev.h> and puts all of its definitions (many
3351	of them macros) into the global namespace. All C++ specific things are	4126	of them macros) into the global namespace. All C++ specific things are
3352	put into the C<ev> namespace. It should support all the same embedding	4127	put into the C<ev> namespace. It should support all the same embedding
…		…
3355	Care has been taken to keep the overhead low. The only data member the C++	4130	Care has been taken to keep the overhead low. The only data member the C++
3356	classes add (compared to plain C-style watchers) is the event loop pointer	4131	classes add (compared to plain C-style watchers) is the event loop pointer
3357	that the watcher is associated with (or no additional members at all if	4132	that the watcher is associated with (or no additional members at all if
3358	you disable C<EV_MULTIPLICITY> when embedding libev).	4133	you disable C<EV_MULTIPLICITY> when embedding libev).
3359		4134
3360	Currently, functions, and static and non-static member functions can be	4135	Currently, functions, static and non-static member functions and classes
3361	used as callbacks. Other types should be easy to add as long as they only	4136	with C<operator ()> can be used as callbacks. Other types should be easy
3362	need one additional pointer for context. If you need support for other	4137	to add as long as they only need one additional pointer for context. If
3363	types of functors please contact the author (preferably after implementing	4138	you need support for other types of functors please contact the author
3364	it).	4139	(preferably after implementing it).
		4140
		4141	For all this to work, your C++ compiler either has to use the same calling
		4142	conventions as your C compiler (for static member functions), or you have
		4143	to embed libev and compile libev itself as C++.
3365		4144
3366	Here is a list of things available in the C<ev> namespace:	4145	Here is a list of things available in the C<ev> namespace:
3367		4146
3368	=over 4	4147	=over 4
3369		4148
…		…
3379	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4158	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3380		4159
3381	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4160	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3382	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4161	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3383	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4162	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3384	defines by many implementations.	4163	defined by many implementations.
3385		4164
3386	All of those classes have these methods:	4165	All of those classes have these methods:
3387		4166
3388	=over 4	4167	=over 4
3389		4168
…		…
3451	void operator() (ev::io &w, int revents)	4230	void operator() (ev::io &w, int revents)
3452	{	4231	{
3453	...	4232	...
3454	}	4233	}
3455	}	4234	}
3456		4235
3457	myfunctor f;	4236	myfunctor f;
3458		4237
3459	ev::io w;	4238	ev::io w;
3460	w.set (&f);	4239	w.set (&f);
3461		4240
…		…
3479	Associates a different C<struct ev_loop> with this watcher. You can only	4258	Associates a different C<struct ev_loop> with this watcher. You can only
3480	do this when the watcher is inactive (and not pending either).	4259	do this when the watcher is inactive (and not pending either).
3481		4260
3482	=item w->set ([arguments])	4261	=item w->set ([arguments])
3483		4262
3484	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4263	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3485	method or a suitable start method must be called at least once. Unlike the	4264	with the same arguments. Either this method or a suitable start method
3486	C counterpart, an active watcher gets automatically stopped and restarted	4265	must be called at least once. Unlike the C counterpart, an active watcher
3487	when reconfiguring it with this method.	4266	gets automatically stopped and restarted when reconfiguring it with this
		4267	method.
		4268
		4269	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4270	clashing with the C<set (loop)> method.
		4271
		4272	For C<ev::io> watchers there is an additional C<set> method that acepts a
		4273	new event mask only, and internally calls C<ev_io_modify>.
3488		4274
3489	=item w->start ()	4275	=item w->start ()
3490		4276
3491	Starts the watcher. Note that there is no C<loop> argument, as the	4277	Starts the watcher. Note that there is no C<loop> argument, as the
3492	constructor already stores the event loop.	4278	constructor already stores the event loop.
…		…
3522	watchers in the constructor.	4308	watchers in the constructor.
3523		4309
3524	class myclass	4310	class myclass
3525	{	4311	{
3526	ev::io io ; void io_cb (ev::io &w, int revents);	4312	ev::io io ; void io_cb (ev::io &w, int revents);
3527	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4313	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3528	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4314	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3529		4315
3530	myclass (int fd)	4316	myclass (int fd)
3531	{	4317	{
3532	io .set <myclass, &myclass::io_cb > (this);	4318	io .set <myclass, &myclass::io_cb > (this);
…		…
3583	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4369	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3584		4370
3585	=item D	4371	=item D
3586		4372
3587	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4373	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3588	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4374	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3589		4375
3590	=item Ocaml	4376	=item Ocaml
3591		4377
3592	Erkki Seppala has written Ocaml bindings for libev, to be found at	4378	Erkki Seppala has written Ocaml bindings for libev, to be found at
3593	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4379	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3596		4382
3597	Brian Maher has written a partial interface to libev for lua (at the	4383	Brian Maher has written a partial interface to libev for lua (at the
3598	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4384	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3599	L<http://github.com/brimworks/lua-ev>.	4385	L<http://github.com/brimworks/lua-ev>.
3600		4386
		4387	=item Javascript
		4388
		4389	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4390
		4391	=item Others
		4392
		4393	There are others, and I stopped counting.
		4394
3601	=back	4395	=back
3602		4396
3603		4397
3604	=head1 MACRO MAGIC	4398	=head1 MACRO MAGIC
3605		4399
…		…
3641	suitable for use with C<EV_A>.	4435	suitable for use with C<EV_A>.
3642		4436
3643	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4437	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3644		4438
3645	Similar to the other two macros, this gives you the value of the default	4439	Similar to the other two macros, this gives you the value of the default
3646	loop, if multiple loops are supported ("ev loop default").	4440	loop, if multiple loops are supported ("ev loop default"). The default loop
		4441	will be initialised if it isn't already initialised.
		4442
		4443	For non-multiplicity builds, these macros do nothing, so you always have
		4444	to initialise the loop somewhere.
3647		4445
3648	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4446	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3649		4447
3650	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4448	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3651	default loop has been initialised (C<UC> == unchecked). Their behaviour	4449	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3718	ev_vars.h	4516	ev_vars.h
3719	ev_wrap.h	4517	ev_wrap.h
3720		4518
3721	ev_win32.c required on win32 platforms only	4519	ev_win32.c required on win32 platforms only
3722		4520
3723	ev_select.c only when select backend is enabled (which is enabled by default)	4521	ev_select.c only when select backend is enabled
3724	ev_poll.c only when poll backend is enabled (disabled by default)	4522	ev_poll.c only when poll backend is enabled
3725	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4523	ev_epoll.c only when the epoll backend is enabled
		4524	ev_linuxaio.c only when the linux aio backend is enabled
		4525	ev_iouring.c only when the linux io_uring backend is enabled
3726	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4526	ev_kqueue.c only when the kqueue backend is enabled
3727	ev_port.c only when the solaris port backend is enabled (disabled by default)	4527	ev_port.c only when the solaris port backend is enabled
3728		4528
3729	F<ev.c> includes the backend files directly when enabled, so you only need	4529	F<ev.c> includes the backend files directly when enabled, so you only need
3730	to compile this single file.	4530	to compile this single file.
3731		4531
3732	=head3 LIBEVENT COMPATIBILITY API	4532	=head3 LIBEVENT COMPATIBILITY API
…		…
3796	supported). It will also not define any of the structs usually found in	4596	supported). It will also not define any of the structs usually found in
3797	F<event.h> that are not directly supported by the libev core alone.	4597	F<event.h> that are not directly supported by the libev core alone.
3798		4598
3799	In standalone mode, libev will still try to automatically deduce the	4599	In standalone mode, libev will still try to automatically deduce the
3800	configuration, but has to be more conservative.	4600	configuration, but has to be more conservative.
		4601
		4602	=item EV_USE_FLOOR
		4603
		4604	If defined to be C<1>, libev will use the C<floor ()> function for its
		4605	periodic reschedule calculations, otherwise libev will fall back on a
		4606	portable (slower) implementation. If you enable this, you usually have to
		4607	link against libm or something equivalent. Enabling this when the C<floor>
		4608	function is not available will fail, so the safe default is to not enable
		4609	this.
3801		4610
3802	=item EV_USE_MONOTONIC	4611	=item EV_USE_MONOTONIC
3803		4612
3804	If defined to be C<1>, libev will try to detect the availability of the	4613	If defined to be C<1>, libev will try to detect the availability of the
3805	monotonic clock option at both compile time and runtime. Otherwise no	4614	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3842	available and will probe for kernel support at runtime. This will improve	4651	available and will probe for kernel support at runtime. This will improve
3843	C<ev_signal> and C<ev_async> performance and reduce resource consumption.	4652	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
3844	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc	4653	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
3845	2.7 or newer, otherwise disabled.	4654	2.7 or newer, otherwise disabled.
3846		4655
		4656	=item EV_USE_SIGNALFD
		4657
		4658	If defined to be C<1>, then libev will assume that C<signalfd ()> is
		4659	available and will probe for kernel support at runtime. This enables
		4660	the use of EVFLAG_SIGNALFD for faster and simpler signal handling. If
		4661	undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4662	2.7 or newer, otherwise disabled.
		4663
		4664	=item EV_USE_TIMERFD
		4665
		4666	If defined to be C<1>, then libev will assume that C<timerfd ()> is
		4667	available and will probe for kernel support at runtime. This allows
		4668	libev to detect time jumps accurately. If undefined, it will be enabled
		4669	if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
		4670	C<TFD_TIMER_CANCEL_ON_SET>, otherwise disabled.
		4671
		4672	=item EV_USE_EVENTFD
		4673
		4674	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4675	available and will probe for kernel support at runtime. This will improve
		4676	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4677	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4678	2.7 or newer, otherwise disabled.
		4679
3847	=item EV_USE_SELECT	4680	=item EV_USE_SELECT
3848		4681
3849	If undefined or defined to be C<1>, libev will compile in support for the	4682	If undefined or defined to be C<1>, libev will compile in support for the
3850	C<select>(2) backend. No attempt at auto-detection will be done: if no	4683	C<select>(2) backend. No attempt at auto-detection will be done: if no
3851	other method takes over, select will be it. Otherwise the select backend	4684	other method takes over, select will be it. Otherwise the select backend
…		…
3891	If programs implement their own fd to handle mapping on win32, then this	4724	If programs implement their own fd to handle mapping on win32, then this
3892	macro can be used to override the C<close> function, useful to unregister	4725	macro can be used to override the C<close> function, useful to unregister
3893	file descriptors again. Note that the replacement function has to close	4726	file descriptors again. Note that the replacement function has to close
3894	the underlying OS handle.	4727	the underlying OS handle.
3895		4728
		4729	=item EV_USE_WSASOCKET
		4730
		4731	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4732	communication socket, which works better in some environments. Otherwise,
		4733	the normal C<socket> function will be used, which works better in other
		4734	environments.
		4735
3896	=item EV_USE_POLL	4736	=item EV_USE_POLL
3897		4737
3898	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4738	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3899	backend. Otherwise it will be enabled on non-win32 platforms. It	4739	backend. Otherwise it will be enabled on non-win32 platforms. It
3900	takes precedence over select.	4740	takes precedence over select.
…		…
3904	If defined to be C<1>, libev will compile in support for the Linux	4744	If defined to be C<1>, libev will compile in support for the Linux
3905	C<epoll>(7) backend. Its availability will be detected at runtime,	4745	C<epoll>(7) backend. Its availability will be detected at runtime,
3906	otherwise another method will be used as fallback. This is the preferred	4746	otherwise another method will be used as fallback. This is the preferred
3907	backend for GNU/Linux systems. If undefined, it will be enabled if the	4747	backend for GNU/Linux systems. If undefined, it will be enabled if the
3908	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4748	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4749
		4750	=item EV_USE_LINUXAIO
		4751
		4752	If defined to be C<1>, libev will compile in support for the Linux aio
		4753	backend (C<EV_USE_EPOLL> must also be enabled). If undefined, it will be
		4754	enabled on linux, otherwise disabled.
		4755
		4756	=item EV_USE_IOURING
		4757
		4758	If defined to be C<1>, libev will compile in support for the Linux
		4759	io_uring backend (C<EV_USE_EPOLL> must also be enabled). Due to it's
		4760	current limitations it has to be requested explicitly. If undefined, it
		4761	will be enabled on linux, otherwise disabled.
3909		4762
3910	=item EV_USE_KQUEUE	4763	=item EV_USE_KQUEUE
3911		4764
3912	If defined to be C<1>, libev will compile in support for the BSD style	4765	If defined to be C<1>, libev will compile in support for the BSD style
3913	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4766	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
3935	If defined to be C<1>, libev will compile in support for the Linux inotify	4788	If defined to be C<1>, libev will compile in support for the Linux inotify
3936	interface to speed up C<ev_stat> watchers. Its actual availability will	4789	interface to speed up C<ev_stat> watchers. Its actual availability will
3937	be detected at runtime. If undefined, it will be enabled if the headers	4790	be detected at runtime. If undefined, it will be enabled if the headers
3938	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4791	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3939		4792
		4793	=item EV_NO_SMP
		4794
		4795	If defined to be C<1>, libev will assume that memory is always coherent
		4796	between threads, that is, threads can be used, but threads never run on
		4797	different cpus (or different cpu cores). This reduces dependencies
		4798	and makes libev faster.
		4799
		4800	=item EV_NO_THREADS
		4801
		4802	If defined to be C<1>, libev will assume that it will never be called from
		4803	different threads (that includes signal handlers), which is a stronger
		4804	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4805	libev faster.
		4806
3940	=item EV_ATOMIC_T	4807	=item EV_ATOMIC_T
3941		4808
3942	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4809	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3943	access is atomic with respect to other threads or signal contexts. No such	4810	access is atomic with respect to other threads or signal contexts. No
3944	type is easily found in the C language, so you can provide your own type	4811	such type is easily found in the C language, so you can provide your own
3945	that you know is safe for your purposes. It is used both for signal handler "locking"	4812	type that you know is safe for your purposes. It is used both for signal
3946	as well as for signal and thread safety in C<ev_async> watchers.	4813	handler "locking" as well as for signal and thread safety in C<ev_async>
		4814	watchers.
3947		4815
3948	In the absence of this define, libev will use C<sig_atomic_t volatile>	4816	In the absence of this define, libev will use C<sig_atomic_t volatile>
3949	(from F<signal.h>), which is usually good enough on most platforms.	4817	(from F<signal.h>), which is usually good enough on most platforms.
3950		4818
3951	=item EV_H (h)	4819	=item EV_H (h)
…		…
3978	will have the C<struct ev_loop *> as first argument, and you can create	4846	will have the C<struct ev_loop *> as first argument, and you can create
3979	additional independent event loops. Otherwise there will be no support	4847	additional independent event loops. Otherwise there will be no support
3980	for multiple event loops and there is no first event loop pointer	4848	for multiple event loops and there is no first event loop pointer
3981	argument. Instead, all functions act on the single default loop.	4849	argument. Instead, all functions act on the single default loop.
3982		4850
		4851	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4852	default loop when multiplicity is switched off - you always have to
		4853	initialise the loop manually in this case.
		4854
3983	=item EV_MINPRI	4855	=item EV_MINPRI
3984		4856
3985	=item EV_MAXPRI	4857	=item EV_MAXPRI
3986		4858
3987	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4859	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4023	#define EV_USE_POLL 1	4895	#define EV_USE_POLL 1
4024	#define EV_CHILD_ENABLE 1	4896	#define EV_CHILD_ENABLE 1
4025	#define EV_ASYNC_ENABLE 1	4897	#define EV_ASYNC_ENABLE 1
4026		4898
4027	The actual value is a bitset, it can be a combination of the following	4899	The actual value is a bitset, it can be a combination of the following
4028	values:	4900	values (by default, all of these are enabled):
4029		4901
4030	=over 4	4902	=over 4
4031		4903
4032	=item C<1> - faster/larger code	4904	=item C<1> - faster/larger code
4033		4905
…		…
4037	code size by roughly 30% on amd64).	4909	code size by roughly 30% on amd64).
4038		4910
4039	When optimising for size, use of compiler flags such as C<-Os> with	4911	When optimising for size, use of compiler flags such as C<-Os> with
4040	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4912	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4041	assertions.	4913	assertions.
		4914
		4915	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4916	(e.g. gcc with C<-Os>).
4042		4917
4043	=item C<2> - faster/larger data structures	4918	=item C<2> - faster/larger data structures
4044		4919
4045	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4920	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4046	hash table sizes and so on. This will usually further increase code size	4921	hash table sizes and so on. This will usually further increase code size
4047	and can additionally have an effect on the size of data structures at	4922	and can additionally have an effect on the size of data structures at
4048	runtime.	4923	runtime.
4049		4924
		4925	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4926	(e.g. gcc with C<-Os>).
		4927
4050	=item C<4> - full API configuration	4928	=item C<4> - full API configuration
4051		4929
4052	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4930	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4053	enables multiplicity (C<EV_MULTIPLICITY>=1).	4931	enables multiplicity (C<EV_MULTIPLICITY>=1).
4054		4932
…		…
4084		4962
4085	With an intelligent-enough linker (gcc+binutils are intelligent enough	4963	With an intelligent-enough linker (gcc+binutils are intelligent enough
4086	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4964	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4087	your program might be left out as well - a binary starting a timer and an	4965	your program might be left out as well - a binary starting a timer and an
4088	I/O watcher then might come out at only 5Kb.	4966	I/O watcher then might come out at only 5Kb.
		4967
		4968	=item EV_API_STATIC
		4969
		4970	If this symbol is defined (by default it is not), then all identifiers
		4971	will have static linkage. This means that libev will not export any
		4972	identifiers, and you cannot link against libev anymore. This can be useful
		4973	when you embed libev, only want to use libev functions in a single file,
		4974	and do not want its identifiers to be visible.
		4975
		4976	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4977	wants to use libev.
		4978
		4979	This option only works when libev is compiled with a C compiler, as C++
		4980	doesn't support the required declaration syntax.
4089		4981
4090	=item EV_AVOID_STDIO	4982	=item EV_AVOID_STDIO
4091		4983
4092	If this is set to C<1> at compiletime, then libev will avoid using stdio	4984	If this is set to C<1> at compiletime, then libev will avoid using stdio
4093	functions (printf, scanf, perror etc.). This will increase the code size	4985	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4151	in. If set to C<1>, then verification code will be compiled in, but not	5043	in. If set to C<1>, then verification code will be compiled in, but not
4152	called. If set to C<2>, then the internal verification code will be	5044	called. If set to C<2>, then the internal verification code will be
4153	called once per loop, which can slow down libev. If set to C<3>, then the	5045	called once per loop, which can slow down libev. If set to C<3>, then the
4154	verification code will be called very frequently, which will slow down	5046	verification code will be called very frequently, which will slow down
4155	libev considerably.	5047	libev considerably.
		5048
		5049	Verification errors are reported via C's C<assert> mechanism, so if you
		5050	disable that (e.g. by defining C<NDEBUG>) then no errors will be reported.
4156		5051
4157	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it	5052	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
4158	will be C<0>.	5053	will be C<0>.
4159		5054
4160	=item EV_COMMON	5055	=item EV_COMMON
…		…
4237	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5132	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4238		5133
4239	#include "ev_cpp.h"	5134	#include "ev_cpp.h"
4240	#include "ev.c"	5135	#include "ev.c"
4241		5136
4242	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5137	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4243		5138
4244	=head2 THREADS AND COROUTINES	5139	=head2 THREADS AND COROUTINES
4245		5140
4246	=head3 THREADS	5141	=head3 THREADS
4247		5142
…		…
4298	default loop and triggering an C<ev_async> watcher from the default loop	5193	default loop and triggering an C<ev_async> watcher from the default loop
4299	watcher callback into the event loop interested in the signal.	5194	watcher callback into the event loop interested in the signal.
4300		5195
4301	=back	5196	=back
4302		5197
4303	=head4 THREAD LOCKING EXAMPLE	5198	See also L</THREAD LOCKING EXAMPLE>.
4304
4305	Here is a fictitious example of how to run an event loop in a different
4306	thread than where callbacks are being invoked and watchers are
4307	created/added/removed.
4308
4309	For a real-world example, see the C<EV::Loop::Async> perl module,
4310	which uses exactly this technique (which is suited for many high-level
4311	languages).
4312
4313	The example uses a pthread mutex to protect the loop data, a condition
4314	variable to wait for callback invocations, an async watcher to notify the
4315	event loop thread and an unspecified mechanism to wake up the main thread.
4316
4317	First, you need to associate some data with the event loop:
4318
4319	typedef struct {
4320	mutex_t lock; /* global loop lock */
4321	ev_async async_w;
4322	thread_t tid;
4323	cond_t invoke_cv;
4324	} userdata;
4325
4326	void prepare_loop (EV_P)
4327	{
4328	// for simplicity, we use a static userdata struct.
4329	static userdata u;
4330
4331	ev_async_init (&u->async_w, async_cb);
4332	ev_async_start (EV_A_ &u->async_w);
4333
4334	pthread_mutex_init (&u->lock, 0);
4335	pthread_cond_init (&u->invoke_cv, 0);
4336
4337	// now associate this with the loop
4338	ev_set_userdata (EV_A_ u);
4339	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4340	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4341
4342	// then create the thread running ev_loop
4343	pthread_create (&u->tid, 0, l_run, EV_A);
4344	}
4345
4346	The callback for the C<ev_async> watcher does nothing: the watcher is used
4347	solely to wake up the event loop so it takes notice of any new watchers
4348	that might have been added:
4349
4350	static void
4351	async_cb (EV_P_ ev_async *w, int revents)
4352	{
4353	// just used for the side effects
4354	}
4355
4356	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4357	protecting the loop data, respectively.
4358
4359	static void
4360	l_release (EV_P)
4361	{
4362	userdata *u = ev_userdata (EV_A);
4363	pthread_mutex_unlock (&u->lock);
4364	}
4365
4366	static void
4367	l_acquire (EV_P)
4368	{
4369	userdata *u = ev_userdata (EV_A);
4370	pthread_mutex_lock (&u->lock);
4371	}
4372
4373	The event loop thread first acquires the mutex, and then jumps straight
4374	into C<ev_run>:
4375
4376	void *
4377	l_run (void *thr_arg)
4378	{
4379	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4380
4381	l_acquire (EV_A);
4382	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4383	ev_run (EV_A_ 0);
4384	l_release (EV_A);
4385
4386	return 0;
4387	}
4388
4389	Instead of invoking all pending watchers, the C<l_invoke> callback will
4390	signal the main thread via some unspecified mechanism (signals? pipe
4391	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4392	have been called (in a while loop because a) spurious wakeups are possible
4393	and b) skipping inter-thread-communication when there are no pending
4394	watchers is very beneficial):
4395
4396	static void
4397	l_invoke (EV_P)
4398	{
4399	userdata *u = ev_userdata (EV_A);
4400
4401	while (ev_pending_count (EV_A))
4402	{
4403	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4404	pthread_cond_wait (&u->invoke_cv, &u->lock);
4405	}
4406	}
4407
4408	Now, whenever the main thread gets told to invoke pending watchers, it
4409	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4410	thread to continue:
4411
4412	static void
4413	real_invoke_pending (EV_P)
4414	{
4415	userdata *u = ev_userdata (EV_A);
4416
4417	pthread_mutex_lock (&u->lock);
4418	ev_invoke_pending (EV_A);
4419	pthread_cond_signal (&u->invoke_cv);
4420	pthread_mutex_unlock (&u->lock);
4421	}
4422
4423	Whenever you want to start/stop a watcher or do other modifications to an
4424	event loop, you will now have to lock:
4425
4426	ev_timer timeout_watcher;
4427	userdata *u = ev_userdata (EV_A);
4428
4429	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4430
4431	pthread_mutex_lock (&u->lock);
4432	ev_timer_start (EV_A_ &timeout_watcher);
4433	ev_async_send (EV_A_ &u->async_w);
4434	pthread_mutex_unlock (&u->lock);
4435
4436	Note that sending the C<ev_async> watcher is required because otherwise
4437	an event loop currently blocking in the kernel will have no knowledge
4438	about the newly added timer. By waking up the loop it will pick up any new
4439	watchers in the next event loop iteration.
4440		5199
4441	=head3 COROUTINES	5200	=head3 COROUTINES
4442		5201
4443	Libev is very accommodating to coroutines ("cooperative threads"):	5202	Libev is very accommodating to coroutines ("cooperative threads"):
4444	libev fully supports nesting calls to its functions from different	5203	libev fully supports nesting calls to its functions from different
…		…
4609	requires, and its I/O model is fundamentally incompatible with the POSIX	5368	requires, and its I/O model is fundamentally incompatible with the POSIX
4610	model. Libev still offers limited functionality on this platform in	5369	model. Libev still offers limited functionality on this platform in
4611	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5370	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4612	descriptors. This only applies when using Win32 natively, not when using	5371	descriptors. This only applies when using Win32 natively, not when using
4613	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5372	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4614	as every compielr comes with a slightly differently broken/incompatible	5373	as every compiler comes with a slightly differently broken/incompatible
4615	environment.	5374	environment.
4616		5375
4617	Lifting these limitations would basically require the full	5376	Lifting these limitations would basically require the full
4618	re-implementation of the I/O system. If you are into this kind of thing,	5377	re-implementation of the I/O system. If you are into this kind of thing,
4619	then note that glib does exactly that for you in a very portable way (note	5378	then note that glib does exactly that for you in a very portable way (note
…		…
4713	structure (guaranteed by POSIX but not by ISO C for example), but it also	5472	structure (guaranteed by POSIX but not by ISO C for example), but it also
4714	assumes that the same (machine) code can be used to call any watcher	5473	assumes that the same (machine) code can be used to call any watcher
4715	callback: The watcher callbacks have different type signatures, but libev	5474	callback: The watcher callbacks have different type signatures, but libev
4716	calls them using an C<ev_watcher *> internally.	5475	calls them using an C<ev_watcher *> internally.
4717		5476
		5477	=item null pointers and integer zero are represented by 0 bytes
		5478
		5479	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5480	relies on this setting pointers and integers to null.
		5481
		5482	=item pointer accesses must be thread-atomic
		5483
		5484	Accessing a pointer value must be atomic, it must both be readable and
		5485	writable in one piece - this is the case on all current architectures.
		5486
4718	=item C<sig_atomic_t volatile> must be thread-atomic as well	5487	=item C<sig_atomic_t volatile> must be thread-atomic as well
4719		5488
4720	The type C<sig_atomic_t volatile> (or whatever is defined as	5489	The type C<sig_atomic_t volatile> (or whatever is defined as
4721	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5490	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4722	threads. This is not part of the specification for C<sig_atomic_t>, but is	5491	threads. This is not part of the specification for C<sig_atomic_t>, but is
…		…
4730	thread" or will block signals process-wide, both behaviours would	5499	thread" or will block signals process-wide, both behaviours would
4731	be compatible with libev. Interaction between C<sigprocmask> and	5500	be compatible with libev. Interaction between C<sigprocmask> and
4732	C<pthread_sigmask> could complicate things, however.	5501	C<pthread_sigmask> could complicate things, however.
4733		5502
4734	The most portable way to handle signals is to block signals in all threads	5503	The most portable way to handle signals is to block signals in all threads
4735	except the initial one, and run the default loop in the initial thread as	5504	except the initial one, and run the signal handling loop in the initial
4736	well.	5505	thread as well.
4737		5506
4738	=item C<long> must be large enough for common memory allocation sizes	5507	=item C<long> must be large enough for common memory allocation sizes
4739		5508
4740	To improve portability and simplify its API, libev uses C<long> internally	5509	To improve portability and simplify its API, libev uses C<long> internally
4741	instead of C<size_t> when allocating its data structures. On non-POSIX	5510	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4747		5516
4748	The type C<double> is used to represent timestamps. It is required to	5517	The type C<double> is used to represent timestamps. It is required to
4749	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5518	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4750	good enough for at least into the year 4000 with millisecond accuracy	5519	good enough for at least into the year 4000 with millisecond accuracy
4751	(the design goal for libev). This requirement is overfulfilled by	5520	(the design goal for libev). This requirement is overfulfilled by
4752	implementations using IEEE 754, which is basically all existing ones. With	5521	implementations using IEEE 754, which is basically all existing ones.
		5522
4753	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5523	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5524	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5525	is either obsolete or somebody patched it to use C<long double> or
		5526	something like that, just kidding).
4754		5527
4755	=back	5528	=back
4756		5529
4757	If you know of other additional requirements drop me a note.	5530	If you know of other additional requirements drop me a note.
4758		5531
…		…
4820	=item Processing ev_async_send: O(number_of_async_watchers)	5593	=item Processing ev_async_send: O(number_of_async_watchers)
4821		5594
4822	=item Processing signals: O(max_signal_number)	5595	=item Processing signals: O(max_signal_number)
4823		5596
4824	Sending involves a system call I<iff> there were no other C<ev_async_send>	5597	Sending involves a system call I<iff> there were no other C<ev_async_send>
4825	calls in the current loop iteration. Checking for async and signal events	5598	calls in the current loop iteration and the loop is currently
		5599	blocked. Checking for async and signal events involves iterating over all
4826	involves iterating over all running async watchers or all signal numbers.	5600	running async watchers or all signal numbers.
4827		5601
4828	=back	5602	=back
4829		5603
4830		5604
4831	=head1 PORTING FROM LIBEV 3.X TO 4.X	5605	=head1 PORTING FROM LIBEV 3.X TO 4.X
4832		5606
4833	The major version 4 introduced some minor incompatible changes to the API.	5607	The major version 4 introduced some incompatible changes to the API.
4834		5608
4835	At the moment, the C<ev.h> header file tries to implement superficial	5609	At the moment, the C<ev.h> header file provides compatibility definitions
4836	compatibility, so most programs should still compile. Those might be	5610	for all changes, so most programs should still compile. The compatibility
4837	removed in later versions of libev, so better update early than late.	5611	layer might be removed in later versions of libev, so better update to the
		5612	new API early than late.
4838		5613
4839	=over 4	5614	=over 4
4840		5615
		5616	=item C<EV_COMPAT3> backwards compatibility mechanism
		5617
		5618	The backward compatibility mechanism can be controlled by
		5619	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5620	section.
		5621
4841	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5622	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4842		5623
4843	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5624	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
4844		5625
4845	ev_loop_destroy (EV_DEFAULT);	5626	ev_loop_destroy (EV_DEFAULT_UC);
4846	ev_loop_fork (EV_DEFAULT);	5627	ev_loop_fork (EV_DEFAULT);
4847		5628
4848	=item function/symbol renames	5629	=item function/symbol renames
4849		5630
4850	A number of functions and symbols have been renamed:	5631	A number of functions and symbols have been renamed:
…		…
4870	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5651	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4871	as all other watcher types. Note that C<ev_loop_fork> is still called	5652	as all other watcher types. Note that C<ev_loop_fork> is still called
4872	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>	5653	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4873	typedef.	5654	typedef.
4874		5655
4875	=item C<EV_COMPAT3> backwards compatibility mechanism
4876
4877	The backward compatibility mechanism can be controlled by
4878	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4879	section.
4880
4881	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>	5656	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4882		5657
4883	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5658	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4884	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5659	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4885	and work, but the library code will of course be larger.	5660	and work, but the library code will of course be larger.
…		…
4892	=over 4	5667	=over 4
4893		5668
4894	=item active	5669	=item active
4895		5670
4896	A watcher is active as long as it has been started and not yet stopped.	5671	A watcher is active as long as it has been started and not yet stopped.
4897	See L<WATCHER STATES> for details.	5672	See L</WATCHER STATES> for details.
4898		5673
4899	=item application	5674	=item application
4900		5675
4901	In this document, an application is whatever is using libev.	5676	In this document, an application is whatever is using libev.
4902		5677
…		…
4938	watchers and events.	5713	watchers and events.
4939		5714
4940	=item pending	5715	=item pending
4941		5716
4942	A watcher is pending as soon as the corresponding event has been	5717	A watcher is pending as soon as the corresponding event has been
4943	detected. See L<WATCHER STATES> for details.	5718	detected. See L</WATCHER STATES> for details.
4944		5719
4945	=item real time	5720	=item real time
4946		5721
4947	The physical time that is observed. It is apparently strictly monotonic :)	5722	The physical time that is observed. It is apparently strictly monotonic :)
4948		5723
4949	=item wall-clock time	5724	=item wall-clock time
4950		5725
4951	The time and date as shown on clocks. Unlike real time, it can actually	5726	The time and date as shown on clocks. Unlike real time, it can actually
4952	be wrong and jump forwards and backwards, e.g. when the you adjust your	5727	be wrong and jump forwards and backwards, e.g. when you adjust your
4953	clock.	5728	clock.
4954		5729
4955	=item watcher	5730	=item watcher
4956		5731
4957	A data structure that describes interest in certain events. Watchers need	5732	A data structure that describes interest in certain events. Watchers need
…		…
4959		5734
4960	=back	5735	=back
4961		5736
4962	=head1 AUTHOR	5737	=head1 AUTHOR
4963		5738
4964	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5739	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5740	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
4965		5741

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