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		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	libev - a high performance full-featured event loop written in C	5	libev - a high performance full-featured event loop written in C
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
…		…
58	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
59		61
60	// now wait for events to arrive	62	// now wait for events to arrive
61	ev_run (loop, 0);	63	ev_run (loop, 0);
62		64
63	// unloop was called, so exit	65	// break was called, so exit
64	return 0;	66	return 0;
65	}	67	}
66		68
67	=head1 ABOUT THIS DOCUMENT	69	=head1 ABOUT THIS DOCUMENT
68		70
…		…
82		84
83	=head1 WHAT TO READ WHEN IN A HURRY	85	=head1 WHAT TO READ WHEN IN A HURRY
84		86
85	This manual tries to be very detailed, but unfortunately, this also makes	87	This manual tries to be very detailed, but unfortunately, this also makes
86	it very long. If you just want to know the basics of libev, I suggest	88	it very long. If you just want to know the basics of libev, I suggest
87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and	89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and	90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
89	C<ev_timer> sections in L<WATCHER TYPES>.	91	C<ev_timer> sections in L</WATCHER TYPES>.
90		92
91	=head1 ABOUT LIBEV	93	=head1 ABOUT LIBEV
92		94
93	Libev is an event loop: you register interest in certain events (such as a	95	Libev is an event loop: you register interest in certain events (such as a
94	file descriptor being readable or a timeout occurring), and it will manage	96	file descriptor being readable or a timeout occurring), and it will manage
…		…
103	details of the event, and then hand it over to libev by I<starting> the	105	details of the event, and then hand it over to libev by I<starting> the
104	watcher.	106	watcher.
105		107
106	=head2 FEATURES	108	=head2 FEATURES
107		109
108	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	110	Libev supports C<select>, C<poll>, the Linux-specific aio and C<epoll>
109	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port
110	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	112	mechanisms for file descriptor events (C<ev_io>), the Linux C<inotify>
111	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner	113	interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
112	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative	114	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
113	timers (C<ev_timer>), absolute timers with customised rescheduling	115	timers (C<ev_timer>), absolute timers with customised rescheduling
114	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status	116	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
115	change events (C<ev_child>), and event watchers dealing with the event	117	change events (C<ev_child>), and event watchers dealing with the event
116	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and	118	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
…		…
157	When libev detects a usage error such as a negative timer interval, then	159	When libev detects a usage error such as a negative timer interval, then
158	it will print a diagnostic message and abort (via the C<assert> mechanism,	160	it will print a diagnostic message and abort (via the C<assert> mechanism,
159	so C<NDEBUG> will disable this checking): these are programming errors in	161	so C<NDEBUG> will disable this checking): these are programming errors in
160	the libev caller and need to be fixed there.	162	the libev caller and need to be fixed there.
161		163
		164	Via the C<EV_FREQUENT> macro you can compile in and/or enable extensive
		165	consistency checking code inside libev that can be used to check for
		166	internal inconsistencies, suually caused by application bugs.
		167
162	Libev also has a few internal error-checking C<assert>ions, and also has	168	Libev also has a few internal error-checking C<assert>ions. These do not
163	extensive consistency checking code. These do not trigger under normal
164	circumstances, as they indicate either a bug in libev or worse.	169	trigger under normal circumstances, as they indicate either a bug in libev
		170	or worse.
165		171
166		172
167	=head1 GLOBAL FUNCTIONS	173	=head1 GLOBAL FUNCTIONS
168		174
169	These functions can be called anytime, even before initialising the	175	These functions can be called anytime, even before initialising the
…		…
174	=item ev_tstamp ev_time ()	180	=item ev_tstamp ev_time ()
175		181
176	Returns the current time as libev would use it. Please note that the	182	Returns the current time as libev would use it. Please note that the
177	C<ev_now> function is usually faster and also often returns the timestamp	183	C<ev_now> function is usually faster and also often returns the timestamp
178	you actually want to know. Also interesting is the combination of	184	you actually want to know. Also interesting is the combination of
179	C<ev_update_now> and C<ev_now>.	185	C<ev_now_update> and C<ev_now>.
180		186
181	=item ev_sleep (ev_tstamp interval)	187	=item ev_sleep (ev_tstamp interval)
182		188
183	Sleep for the given interval: The current thread will be blocked until	189	Sleep for the given interval: The current thread will be blocked
184	either it is interrupted or the given time interval has passed. Basically	190	until either it is interrupted or the given time interval has
		191	passed (approximately - it might return a bit earlier even if not
		192	interrupted). Returns immediately if C<< interval <= 0 >>.
		193
185	this is a sub-second-resolution C<sleep ()>.	194	Basically this is a sub-second-resolution C<sleep ()>.
		195
		196	The range of the C<interval> is limited - libev only guarantees to work
		197	with sleep times of up to one day (C<< interval <= 86400 >>).
186		198
187	=item int ev_version_major ()	199	=item int ev_version_major ()
188		200
189	=item int ev_version_minor ()	201	=item int ev_version_minor ()
190		202
…		…
241	the current system, you would need to look at C<ev_embeddable_backends ()	253	the current system, you would need to look at C<ev_embeddable_backends ()
242	& ev_supported_backends ()>, likewise for recommended ones.	254	& ev_supported_backends ()>, likewise for recommended ones.
243		255
244	See the description of C<ev_embed> watchers for more info.	256	See the description of C<ev_embed> watchers for more info.
245		257
246	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	258	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
247		259
248	Sets the allocation function to use (the prototype is similar - the	260	Sets the allocation function to use (the prototype is similar - the
249	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	261	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
250	used to allocate and free memory (no surprises here). If it returns zero	262	used to allocate and free memory (no surprises here). If it returns zero
251	when memory needs to be allocated (C<size != 0>), the library might abort	263	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
257		269
258	You could override this function in high-availability programs to, say,	270	You could override this function in high-availability programs to, say,
259	free some memory if it cannot allocate memory, to use a special allocator,	271	free some memory if it cannot allocate memory, to use a special allocator,
260	or even to sleep a while and retry until some memory is available.	272	or even to sleep a while and retry until some memory is available.
261		273
		274	Example: The following is the C<realloc> function that libev itself uses
		275	which should work with C<realloc> and C<free> functions of all kinds and
		276	is probably a good basis for your own implementation.
		277
		278	static void *
		279	ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
		280	{
		281	if (size)
		282	return realloc (ptr, size);
		283
		284	free (ptr);
		285	return 0;
		286	}
		287
262	Example: Replace the libev allocator with one that waits a bit and then	288	Example: Replace the libev allocator with one that waits a bit and then
263	retries (example requires a standards-compliant C<realloc>).	289	retries.
264		290
265	static void *	291	static void *
266	persistent_realloc (void *ptr, size_t size)	292	persistent_realloc (void *ptr, size_t size)
267	{	293	{
		294	if (!size)
		295	{
		296	free (ptr);
		297	return 0;
		298	}
		299
268	for (;;)	300	for (;;)
269	{	301	{
270	void *newptr = realloc (ptr, size);	302	void *newptr = realloc (ptr, size);
271		303
272	if (newptr)	304	if (newptr)
…		…
277	}	309	}
278		310
279	...	311	...
280	ev_set_allocator (persistent_realloc);	312	ev_set_allocator (persistent_realloc);
281		313
282	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	314	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
283		315
284	Set the callback function to call on a retryable system call error (such	316	Set the callback function to call on a retryable system call error (such
285	as failed select, poll, epoll_wait). The message is a printable string	317	as failed select, poll, epoll_wait). The message is a printable string
286	indicating the system call or subsystem causing the problem. If this	318	indicating the system call or subsystem causing the problem. If this
287	callback is set, then libev will expect it to remedy the situation, no	319	callback is set, then libev will expect it to remedy the situation, no
…		…
299	}	331	}
300		332
301	...	333	...
302	ev_set_syserr_cb (fatal_error);	334	ev_set_syserr_cb (fatal_error);
303		335
		336	=item ev_feed_signal (int signum)
		337
		338	This function can be used to "simulate" a signal receive. It is completely
		339	safe to call this function at any time, from any context, including signal
		340	handlers or random threads.
		341
		342	Its main use is to customise signal handling in your process, especially
		343	in the presence of threads. For example, you could block signals
		344	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		345	creating any loops), and in one thread, use C<sigwait> or any other
		346	mechanism to wait for signals, then "deliver" them to libev by calling
		347	C<ev_feed_signal>.
		348
304	=back	349	=back
305		350
306	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	351	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
307		352
308	An event loop is described by a C<struct ev_loop *> (the C<struct> is	353	An event loop is described by a C<struct ev_loop *> (the C<struct> is
…		…
355	=item struct ev_loop *ev_loop_new (unsigned int flags)	400	=item struct ev_loop *ev_loop_new (unsigned int flags)
356		401
357	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
358	could not be initialised, returns false.	403	could not be initialised, returns false.
359		404
360	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
361	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
362	default loop in the "main" or "initial" thread.	407	loop in the "main" or "initial" thread.
363		408
364	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
365	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>).
366		411
367	The following flags are supported:	412	The following flags are supported:
…		…
377		422
378	If this flag bit is or'ed into the flag value (or the program runs setuid	423	If this flag bit is or'ed into the flag value (or the program runs setuid
379	or setgid) then libev will I<not> look at the environment variable	424	or setgid) then libev will I<not> look at the environment variable
380	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	425	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
381	override the flags completely if it is found in the environment. This is	426	override the flags completely if it is found in the environment. This is
382	useful to try out specific backends to test their performance, or to work	427	useful to try out specific backends to test their performance, to work
383	around bugs.	428	around bugs, or to make libev threadsafe (accessing environment variables
		429	cannot be done in a threadsafe way, but usually it works if no other
		430	thread modifies them).
384		431
385	=item C<EVFLAG_FORKCHECK>	432	=item C<EVFLAG_FORKCHECK>
386		433
387	Instead of calling C<ev_loop_fork> manually after a fork, you can also	434	Instead of calling C<ev_loop_fork> manually after a fork, you can also
388	make libev check for a fork in each iteration by enabling this flag.	435	make libev check for a fork in each iteration by enabling this flag.
389		436
390	This works by calling C<getpid ()> on every iteration of the loop,	437	This works by calling C<getpid ()> on every iteration of the loop,
391	and thus this might slow down your event loop if you do a lot of loop	438	and thus this might slow down your event loop if you do a lot of loop
392	iterations and little real work, but is usually not noticeable (on my	439	iterations and little real work, but is usually not noticeable (on my
393	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	440	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
394	without a system call and thus I<very> fast, but my GNU/Linux system also has	441	sequence without a system call and thus I<very> fast, but my GNU/Linux
395	C<pthread_atfork> which is even faster).	442	system also has C<pthread_atfork> which is even faster). (Update: glibc
		443	versions 2.25 apparently removed the C<getpid> optimisation again).
396		444
397	The big advantage of this flag is that you can forget about fork (and	445	The big advantage of this flag is that you can forget about fork (and
398	forget about forgetting to tell libev about forking) when you use this	446	forget about forgetting to tell libev about forking, although you still
399	flag.	447	have to ignore C<SIGPIPE>) when you use this flag.
400		448
401	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	449	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
402	environment variable.	450	environment variable.
403		451
404	=item C<EVFLAG_NOINOTIFY>	452	=item C<EVFLAG_NOINOTIFY>
405		453
406	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
407	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
408	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
409	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.
410		458
411	=item C<EVFLAG_SIGNALFD>	459	=item C<EVFLAG_SIGNALFD>
412		460
413	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
414	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
415	delivers signals synchronously, which makes it both faster and might make	463	delivers signals synchronously, which makes it both faster and might make
416	it possible to get the queued signal data. It can also simplify signal	464	it possible to get the queued signal data. It can also simplify signal
417	handling with threads, as long as you properly block signals in your	465	handling with threads, as long as you properly block signals in your
418	threads that are not interested in handling them.	466	threads that are not interested in handling them.
419		467
420	Signalfd will not be used by default as this changes your signal mask, and	468	Signalfd will not be used by default as this changes your signal mask, and
421	there are a lot of shoddy libraries and programs (glib's threadpool for	469	there are a lot of shoddy libraries and programs (glib's threadpool for
422	example) that can't properly initialise their signal masks.	470	example) that can't properly initialise their signal masks.
		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.
423		495
424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	496	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
425		497
426	This is your standard select(2) backend. Not I<completely> standard, as	498	This is your standard select(2) backend. Not I<completely> standard, as
427	libev tries to roll its own fd_set with no limits on the number of fds,	499	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
452	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and	524	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
453	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	525	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
454		526
455	=item C<EVBACKEND_EPOLL> (value 4, Linux)	527	=item C<EVBACKEND_EPOLL> (value 4, Linux)
456		528
457	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	529	Use the Linux-specific epoll(7) interface (for both pre- and post-2.6.9
458	kernels).	530	kernels).
459		531
460	For few fds, this backend is a bit little slower than poll and select,	532	For few fds, this backend is a bit little slower than poll and select, but
461	but it scales phenomenally better. While poll and select usually scale	533	it scales phenomenally better. While poll and select usually scale like
462	like O(total_fds) where n is the total number of fds (or the highest fd),	534	O(total_fds) where total_fds is the total number of fds (or the highest
463	epoll scales either O(1) or O(active_fds).	535	fd), epoll scales either O(1) or O(active_fds).
464		536
465	The epoll mechanism deserves honorable mention as the most misdesigned	537	The epoll mechanism deserves honorable mention as the most misdesigned
466	of the more advanced event mechanisms: mere annoyances include silently	538	of the more advanced event mechanisms: mere annoyances include silently
467	dropping file descriptors, requiring a system call per change per file	539	dropping file descriptors, requiring a system call per change per file
468	descriptor (and unnecessary guessing of parameters), problems with dup,	540	descriptor (and unnecessary guessing of parameters), problems with dup,
469	returning before the timeout value requiring additional iterations and so	541	returning before the timeout value, resulting in additional iterations
		542	(and only giving 5ms accuracy while select on the same platform gives
470	on. The biggest issue is fork races, however - if a program forks then	543	0.1ms) and so on. The biggest issue is fork races, however - if a program
471	I<both> parent and child process have to recreate the epoll set, which can	544	forks then I<both> parent and child process have to recreate the epoll
472	take considerable time (one syscall per file descriptor) and is of course	545	set, which can take considerable time (one syscall per file descriptor)
473	hard to detect.	546	and is of course hard to detect.
474		547
475	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	548	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
476	of course I<doesn't>, and epoll just loves to report events for totally	549	but of course I<doesn't>, and epoll just loves to report events for
477	I<different> file descriptors (even already closed ones, so one cannot	550	totally I<different> file descriptors (even already closed ones, so
478	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
479	on SMP systems). Libev tries to counter these spurious notifications by	552	(especially on SMP systems). Libev tries to counter these spurious
480	employing an additional generation counter and comparing that against the	553	notifications by employing an additional generation counter and comparing
481	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
482	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
483	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...
484		564
485	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
486	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
487	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
488	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
…		…
500	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
501	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
502	the usage. So sad.	582	the usage. So sad.
503		583
504	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
505	all kernel versions tested so far.	585	a lot of kernel revisions, but probably(!) works in current versions.
506		586
507	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
508	C<EVBACKEND_POLL>.	588	C<EVBACKEND_POLL>.
509		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
510	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	634	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
511		635
512	Kqueue deserves special mention, as at the time of this writing, it	636	Kqueue deserves special mention, as at the time this backend was
513	was broken on all BSDs except NetBSD (usually it doesn't work reliably	637	implemented, it was broken on all BSDs except NetBSD (usually it doesn't
514	with anything but sockets and pipes, except on Darwin, where of course	638	work reliably with anything but sockets and pipes, except on Darwin,
515	it's completely useless). Unlike epoll, however, whose brokenness	639	where of course it's completely useless). Unlike epoll, however, whose
516	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)
517	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
518	"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
519	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
520	system like NetBSD.	644	known-to-be-good (-enough) system like NetBSD.
521		645
522	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
523	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
524	the target platform). See C<ev_embed> watchers for more info.	648	the target platform). See C<ev_embed> watchers for more info.
525		649
526	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
527	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
528	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
529	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
530	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
531	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
532	cases	656	drops fds silently in similarly hard-to-detect cases.
533		657
534	This backend usually performs well under most conditions.	658	This backend usually performs well under most conditions.
535		659
536	While nominally embeddable in other event loops, this doesn't work	660	While nominally embeddable in other event loops, this doesn't work
537	everywhere, so you might need to test for this. And since it is broken	661	everywhere, so you might need to test for this. And since it is broken
…		…
554	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	678	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
555		679
556	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,
557	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)).
558		682
559	Please note that Solaris event ports can deliver a lot of spurious
560	notifications, so you need to use non-blocking I/O or other means to avoid
561	blocking when no data (or space) is available.
562
563	While this backend scales well, it requires one system call per active	683	While this backend scales well, it requires one system call per active
564	file descriptor per loop iteration. For small and medium numbers of file	684	file descriptor per loop iteration. For small and medium numbers of file
565	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	685	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
566	might perform better.	686	might perform better.
567		687
568	On the positive side, with the exception of the spurious readiness	688	On the positive side, this backend actually performed fully to
569	notifications, this backend actually performed fully to specification
570	in all tests and is fully embeddable, which is a rare feat among the	689	specification in all tests and is fully embeddable, which is a rare feat
571	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.
572		702
573	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
574	C<EVBACKEND_POLL>.	704	C<EVBACKEND_POLL>.
575		705
576	=item C<EVBACKEND_ALL>	706	=item C<EVBACKEND_ALL>
577		707
578	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
579	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
580	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	710	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
581		711
582	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).
583		721
584	=back	722	=back
585		723
586	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,
587	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
…		…
596		734
597	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
598	used if available.	736	used if available.
599		737
600	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);
601		745
602	=item ev_loop_destroy (loop)	746	=item ev_loop_destroy (loop)
603		747
604	Destroys an event loop object (frees all memory and kernel state	748	Destroys an event loop object (frees all memory and kernel state
605	etc.). None of the active event watchers will be stopped in the normal	749	etc.). None of the active event watchers will be stopped in the normal
…		…
616	This function is normally used on loop objects allocated by	760	This function is normally used on loop objects allocated by
617	C<ev_loop_new>, but it can also be used on the default loop returned by	761	C<ev_loop_new>, but it can also be used on the default loop returned by
618	C<ev_default_loop>, in which case it is not thread-safe.	762	C<ev_default_loop>, in which case it is not thread-safe.
619		763
620	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
621	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.
622	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>
623	and C<ev_loop_destroy>.	767	and C<ev_loop_destroy>.
624		768
625	=item ev_loop_fork (loop)	769	=item ev_loop_fork (loop)
626		770
627	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
628	reinitialise the kernel state for backends that have one. Despite the	772	to reinitialise the kernel state for backends that have one. Despite
629	name, you can call it anytime, but it makes most sense after forking, in	773	the name, you can call it anytime you are allowed to start or stop
630	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the	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
631	child before resuming or calling C<ev_run>.	776	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
632		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
633	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
634	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
635	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	783	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
636	during fork.	784	during fork.
637		785
638	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
…		…
674	prepare and check phases.	822	prepare and check phases.
675		823
676	=item unsigned int ev_depth (loop)	824	=item unsigned int ev_depth (loop)
677		825
678	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
679	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.
680		828
681	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
682	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),
683	in which case it is higher.	831	in which case it is higher.
684		832
685	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	833	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
686	etc.), doesn't count as "exit" - consider this as a hint to avoid such	834	throwing an exception etc.), doesn't count as "exit" - consider this
687	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.
688		837
689	=item unsigned int ev_backend (loop)	838	=item unsigned int ev_backend (loop)
690		839
691	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
692	use.	841	use.
…		…
707		856
708	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
709	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
710	the current time is a good idea.	859	the current time is a good idea.
711		860
712	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.
713		862
714	=item ev_suspend (loop)	863	=item ev_suspend (loop)
715		864
716	=item ev_resume (loop)	865	=item ev_resume (loop)
717		866
…		…
735	without a previous call to C<ev_suspend>.	884	without a previous call to C<ev_suspend>.
736		885
737	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
738	event loop time (see C<ev_now_update>).	887	event loop time (see C<ev_now_update>).
739		888
740	=item ev_run (loop, int flags)	889	=item bool ev_run (loop, int flags)
741		890
742	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
743	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
744	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
745	the watcher callbacks, an then repeat the whole process indefinitely: This	894	the watcher callbacks, and then repeat the whole process indefinitely: This
746	is why event loops are called I<loops>.	895	is why event loops are called I<loops>.
747		896
748	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
749	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
750	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").
751		904
752	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
753	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
754	finished (especially in interactive programs), but having a program	907	finished (especially in interactive programs), but having a program
755	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
756	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
757	beauty.	910	beauty.
758		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
759	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
760	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
761	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
762	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
763	events while doing lengthy calculations, to keep the program responsive.	921	events while doing lengthy calculations, to keep the program responsive.
…		…
772	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
773	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
774	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
775	usually a better approach for this kind of thing.	933	usually a better approach for this kind of thing.
776		934
777	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):
778		938
779	- Increment loop depth.	939	- Increment loop depth.
780	- Reset the ev_break status.	940	- Reset the ev_break status.
781	- Before the first iteration, call any pending watchers.	941	- Before the first iteration, call any pending watchers.
782	LOOP:	942	LOOP:
…		…
815	anymore.	975	anymore.
816		976
817	... queue jobs here, make sure they register event watchers as long	977	... queue jobs here, make sure they register event watchers as long
818	... as they still have work to do (even an idle watcher will do..)	978	... as they still have work to do (even an idle watcher will do..)
819	ev_run (my_loop, 0);	979	ev_run (my_loop, 0);
820	... jobs done or somebody called unloop. yeah!	980	... jobs done or somebody called break. yeah!
821		981
822	=item ev_break (loop, how)	982	=item ev_break (loop, how)
823		983
824	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
825	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
826	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
827	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.
828		988
829	This "break 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>.
830		990
831	It is safe to call C<ev_break> from outside any C<ev_run> calls, too.	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.
832		993
833	=item ev_ref (loop)	994	=item ev_ref (loop)
834		995
835	=item ev_unref (loop)	996	=item ev_unref (loop)
836		997
…		…
857	running when nothing else is active.	1018	running when nothing else is active.
858		1019
859	ev_signal exitsig;	1020	ev_signal exitsig;
860	ev_signal_init (&exitsig, sig_cb, SIGINT);	1021	ev_signal_init (&exitsig, sig_cb, SIGINT);
861	ev_signal_start (loop, &exitsig);	1022	ev_signal_start (loop, &exitsig);
862	evf_unref (loop);	1023	ev_unref (loop);
863		1024
864	Example: For some weird reason, unregister the above signal handler again.	1025	Example: For some weird reason, unregister the above signal handler again.
865		1026
866	ev_ref (loop);	1027	ev_ref (loop);
867	ev_signal_stop (loop, &exitsig);	1028	ev_signal_stop (loop, &exitsig);
…		…
887	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.
888		1049
889	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
890	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,
891	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
892	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
893	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
894	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
895	once per this interval, on average.	1056	once per this interval, on average (as long as the host time resolution is
		1057	good enough).
896		1058
897	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
898	to spend more time collecting timeouts, at the expense of increased	1060	to spend more time collecting timeouts, at the expense of increased
899	latency/jitter/inexactness (the watcher callback will be called	1061	latency/jitter/inexactness (the watcher callback will be called
900	later). C<ev_io> watchers will not be affected. Setting this to a non-null	1062	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
946	invoke the actual watchers inside another context (another thread etc.).	1108	invoke the actual watchers inside another context (another thread etc.).
947		1109
948	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
949	callback.	1111	callback.
950		1112
951	=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 ())
952		1114
953	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
954	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
955	each call to a libev function.	1117	each call to a libev function.
956		1118
957	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
958	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
959	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
960	I<release> and I<acquire> callbacks on the loop.	1122	I<release> and I<acquire> callbacks on the loop.
961		1123
962	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
963	suspended waiting for new events, and C<acquire> is called just	1125	suspended waiting for new events, and C<acquire> is called just
964	afterwards.	1126	afterwards.
…		…
979	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
980	document.	1142	document.
981		1143
982	=item ev_set_userdata (loop, void *data)	1144	=item ev_set_userdata (loop, void *data)
983		1145
984	=item ev_userdata (loop)	1146	=item void *ev_userdata (loop)
985		1147
986	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
987	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
988	C<0.>	1150	C<0>.
989		1151
990	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,
991	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
992	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
993	any other purpose as well.	1155	any other purpose as well.
…		…
1056	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
1057	*) >>), 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
1058	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.	1220	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
1059		1221
1060	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
1061	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
1062	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.
1063		1226
1064	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
1065	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
1066	third argument.	1229	third argument.
1067		1230
…		…
1104		1267
1105	=item C<EV_PREPARE>	1268	=item C<EV_PREPARE>
1106		1269
1107	=item C<EV_CHECK>	1270	=item C<EV_CHECK>
1108		1271
1109	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
1110	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)
1111	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
1112	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
1113	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
1114	(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
1115	C<ev_run> from blocking).	1283	blocking).
1116		1284
1117	=item C<EV_EMBED>	1285	=item C<EV_EMBED>
1118		1286
1119	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.
1120		1288
…		…
1243		1411
1244	=item callback ev_cb (ev_TYPE *watcher)	1412	=item callback ev_cb (ev_TYPE *watcher)
1245		1413
1246	Returns the callback currently set on the watcher.	1414	Returns the callback currently set on the watcher.
1247		1415
1248	=item ev_cb_set (ev_TYPE *watcher, callback)	1416	=item ev_set_cb (ev_TYPE *watcher, callback)
1249		1417
1250	Change the callback. You can change the callback at virtually any time	1418	Change the callback. You can change the callback at virtually any time
1251	(modulo threads).	1419	(modulo threads).
1252		1420
1253	=item ev_set_priority (ev_TYPE *watcher, int priority)	1421	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1271	or might not have been clamped to the valid range.	1439	or might not have been clamped to the valid range.
1272		1440
1273	The default priority used by watchers when no priority has been set is	1441	The default priority used by watchers when no priority has been set is
1274	always C<0>, which is supposed to not be too high and not be too low :).	1442	always C<0>, which is supposed to not be too high and not be too low :).
1275		1443
1276	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1444	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1277	priorities.	1445	priorities.
1278		1446
1279	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1447	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1280		1448
1281	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1449	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
…		…
1306	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1474	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1307	functions that do not need a watcher.	1475	functions that do not need a watcher.
1308		1476
1309	=back	1477	=back
1310		1478
1311	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1479	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
1312		1480	OWN COMPOSITE WATCHERS> idioms.
1313	Each watcher has, by default, a member C<void *data> that you can change
1314	and read at any time: libev will completely ignore it. This can be used
1315	to associate arbitrary data with your watcher. If you need more data and
1316	don't want to allocate memory and store a pointer to it in that data
1317	member, you can also "subclass" the watcher type and provide your own
1318	data:
1319
1320	struct my_io
1321	{
1322	ev_io io;
1323	int otherfd;
1324	void *somedata;
1325	struct whatever *mostinteresting;
1326	};
1327
1328	...
1329	struct my_io w;
1330	ev_io_init (&w.io, my_cb, fd, EV_READ);
1331
1332	And since your callback will be called with a pointer to the watcher, you
1333	can cast it back to your own type:
1334
1335	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1336	{
1337	struct my_io *w = (struct my_io *)w_;
1338	...
1339	}
1340
1341	More interesting and less C-conformant ways of casting your callback type
1342	instead have been omitted.
1343
1344	Another common scenario is to use some data structure with multiple
1345	embedded watchers:
1346
1347	struct my_biggy
1348	{
1349	int some_data;
1350	ev_timer t1;
1351	ev_timer t2;
1352	}
1353
1354	In this case getting the pointer to C<my_biggy> is a bit more
1355	complicated: Either you store the address of your C<my_biggy> struct
1356	in the C<data> member of the watcher (for woozies), or you need to use
1357	some pointer arithmetic using C<offsetof> inside your watchers (for real
1358	programmers):
1359
1360	#include <stddef.h>
1361
1362	static void
1363	t1_cb (EV_P_ ev_timer *w, int revents)
1364	{
1365	struct my_biggy big = (struct my_biggy *)
1366	(((char *)w) - offsetof (struct my_biggy, t1));
1367	}
1368
1369	static void
1370	t2_cb (EV_P_ ev_timer *w, int revents)
1371	{
1372	struct my_biggy big = (struct my_biggy *)
1373	(((char *)w) - offsetof (struct my_biggy, t2));
1374	}
1375		1481
1376	=head2 WATCHER STATES	1482	=head2 WATCHER STATES
1377		1483
1378	There are various watcher states mentioned throughout this manual -	1484	There are various watcher states mentioned throughout this manual -
1379	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
1380	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
1381	rules might look complicated, they usually do "the right thing".	1487	rules might look complicated, they usually do "the right thing".
1382		1488
1383	=over 4	1489	=over 4
1384		1490
1385	=item initialiased	1491	=item initialised
1386		1492
1387	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
1388	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
1389	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.
1390		1496
1391	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
1392	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.
1393		1501
1394	=item started/running/active	1502	=item started/running/active
1395		1503
1396	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
1397	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
…		…
1425	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
1426	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
1427	freeing it is often a good idea.	1535	freeing it is often a good idea.
1428		1536
1429	While stopped (and not pending) the watcher is essentially in the	1537	While stopped (and not pending) the watcher is essentially in the
1430	initialised state, that is it can be reused, moved, modified in any way	1538	initialised state, that is, it can be reused, moved, modified in any way
1431	you wish.	1539	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1540	it again).
1432		1541
1433	=back	1542	=back
1434		1543
1435	=head2 WATCHER PRIORITY MODELS	1544	=head2 WATCHER PRIORITY MODELS
1436		1545
1437	Many event loops support I<watcher priorities>, which are usually small	1546	Many event loops support I<watcher priorities>, which are usually small
1438	integers that influence the ordering of event callback invocation	1547	integers that influence the ordering of event callback invocation
1439	between watchers in some way, all else being equal.	1548	between watchers in some way, all else being equal.
1440		1549
1441	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
1442	description for the more technical details such as the actual priority	1551	description for the more technical details such as the actual priority
1443	range.	1552	range.
1444		1553
1445	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
1446	by event loops:	1555	by event loops:
…		…
1540		1649
1541	This section describes each watcher in detail, but will not repeat	1650	This section describes each watcher in detail, but will not repeat
1542	information given in the last section. Any initialisation/set macros,	1651	information given in the last section. Any initialisation/set macros,
1543	functions and members specific to the watcher type are explained.	1652	functions and members specific to the watcher type are explained.
1544		1653
1545	Members are additionally marked with either I<[read-only]>, meaning that,	1654	Most members are additionally marked with either I<[read-only]>, meaning
1546	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
1547	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
1548	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
1549	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
1550	is active, but you can also modify it. Modifying it may not do something	1659	is active, but you can also modify it. Modifying it may not do something
1551	sensible or take immediate effect (or do anything at all), but libev will	1660	sensible or take immediate effect (or do anything at all), but libev will
1552	not crash or malfunction in any way.	1661	not crash or malfunction in any way.
1553		1662
		1663	In any case, the documentation for each member will explain what the
		1664	effects are, and if there are any additional access restrictions.
1554		1665
1555	=head2 C<ev_io> - is this file descriptor readable or writable?	1666	=head2 C<ev_io> - is this file descriptor readable or writable?
1556		1667
1557	I/O watchers check whether a file descriptor is readable or writable	1668	I/O watchers check whether a file descriptor is readable or writable
1558	in each iteration of the event loop, or, more precisely, when reading	1669	in each iteration of the event loop, or, more precisely, when reading
…		…
1565	In general you can register as many read and/or write event watchers per	1676	In general you can register as many read and/or write event watchers per
1566	fd as you want (as long as you don't confuse yourself). Setting all file	1677	fd as you want (as long as you don't confuse yourself). Setting all file
1567	descriptors to non-blocking mode is also usually a good idea (but not	1678	descriptors to non-blocking mode is also usually a good idea (but not
1568	required if you know what you are doing).	1679	required if you know what you are doing).
1569		1680
1570	If you cannot use non-blocking mode, then force the use of a
1571	known-to-be-good backend (at the time of this writing, this includes only
1572	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1573	descriptors for which non-blocking operation makes no sense (such as
1574	files) - libev doesn't guarantee any specific behaviour in that case.
1575
1576	Another thing you have to watch out for is that it is quite easy to	1681	Another thing you have to watch out for is that it is quite easy to
1577	receive "spurious" readiness notifications, that is your callback might	1682	receive "spurious" readiness notifications, that is, your callback might
1578	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1683	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1579	because there is no data. Not only are some backends known to create a	1684	because there is no data. It is very easy to get into this situation even
1580	lot of those (for example Solaris ports), it is very easy to get into	1685	with a relatively standard program structure. Thus it is best to always
1581	this situation even with a relatively standard program structure. Thus	1686	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1582	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1583	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1687	preferable to a program hanging until some data arrives.
1584		1688
1585	If you cannot run the fd in non-blocking mode (for example you should	1689	If you cannot run the fd in non-blocking mode (for example you should
1586	not play around with an Xlib connection), then you have to separately	1690	not play around with an Xlib connection), then you have to separately
1587	re-test whether a file descriptor is really ready with a known-to-be good	1691	re-test whether a file descriptor is really ready with a known-to-be good
1588	interface such as poll (fortunately in our Xlib example, Xlib already	1692	interface such as poll (fortunately in the case of Xlib, it already does
1589	does this on its own, so its quite safe to use). Some people additionally	1693	this on its own, so its quite safe to use). Some people additionally
1590	use C<SIGALRM> and an interval timer, just to be sure you won't block	1694	use C<SIGALRM> and an interval timer, just to be sure you won't block
1591	indefinitely.	1695	indefinitely.
1592		1696
1593	But really, best use non-blocking mode.	1697	But really, best use non-blocking mode.
1594		1698
1595	=head3 The special problem of disappearing file descriptors	1699	=head3 The special problem of disappearing file descriptors
1596		1700
1597	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1701	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1598	descriptor (either due to calling C<close> explicitly or any other means,	1702	a file descriptor (either due to calling C<close> explicitly or any other
1599	such as C<dup2>). The reason is that you register interest in some file	1703	means, such as C<dup2>). The reason is that you register interest in some
1600	descriptor, but when it goes away, the operating system will silently drop	1704	file descriptor, but when it goes away, the operating system will silently
1601	this interest. If another file descriptor with the same number then is	1705	drop this interest. If another file descriptor with the same number then
1602	registered with libev, there is no efficient way to see that this is, in	1706	is registered with libev, there is no efficient way to see that this is,
1603	fact, a different file descriptor.	1707	in fact, a different file descriptor.
1604		1708
1605	To avoid having to explicitly tell libev about such cases, libev follows	1709	To avoid having to explicitly tell libev about such cases, libev follows
1606	the following policy: Each time C<ev_io_set> is being called, libev	1710	the following policy: Each time C<ev_io_set> is being called, libev
1607	will assume that this is potentially a new file descriptor, otherwise	1711	will assume that this is potentially a new file descriptor, otherwise
1608	it is assumed that the file descriptor stays the same. That means that	1712	it is assumed that the file descriptor stays the same. That means that
…		…
1622		1726
1623	There is no workaround possible except not registering events	1727	There is no workaround possible except not registering events
1624	for potentially C<dup ()>'ed file descriptors, or to resort to	1728	for potentially C<dup ()>'ed file descriptors, or to resort to
1625	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1729	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1626		1730
		1731	=head3 The special problem of files
		1732
		1733	Many people try to use C<select> (or libev) on file descriptors
		1734	representing files, and expect it to become ready when their program
		1735	doesn't block on disk accesses (which can take a long time on their own).
		1736
		1737	However, this cannot ever work in the "expected" way - you get a readiness
		1738	notification as soon as the kernel knows whether and how much data is
		1739	there, and in the case of open files, that's always the case, so you
		1740	always get a readiness notification instantly, and your read (or possibly
		1741	write) will still block on the disk I/O.
		1742
		1743	Another way to view it is that in the case of sockets, pipes, character
		1744	devices and so on, there is another party (the sender) that delivers data
		1745	on its own, but in the case of files, there is no such thing: the disk
		1746	will not send data on its own, simply because it doesn't know what you
		1747	wish to read - you would first have to request some data.
		1748
		1749	Since files are typically not-so-well supported by advanced notification
		1750	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1751	to files, even though you should not use it. The reason for this is
		1752	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1753	usually a tty, often a pipe, but also sometimes files or special devices
		1754	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1755	F</dev/urandom>), and even though the file might better be served with
		1756	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1757	it "just works" instead of freezing.
		1758
		1759	So avoid file descriptors pointing to files when you know it (e.g. use
		1760	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1761	when you rarely read from a file instead of from a socket, and want to
		1762	reuse the same code path.
		1763
1627	=head3 The special problem of fork	1764	=head3 The special problem of fork
1628		1765
1629	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1766	Some backends (epoll, kqueue, linuxaio, iouring) do not support C<fork ()>
1630	useless behaviour. Libev fully supports fork, but needs to be told about	1767	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1631	it in the child.	1768	to be told about it in the child if you want to continue to use it in the
		1769	child.
1632		1770
1633	To support fork in your programs, you either have to call	1771	To support fork in your child processes, you have to call C<ev_loop_fork
1634	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1772	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1635	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1773	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1636	C<EVBACKEND_POLL>.
1637		1774
1638	=head3 The special problem of SIGPIPE	1775	=head3 The special problem of SIGPIPE
1639		1776
1640	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1777	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1641	when writing to a pipe whose other end has been closed, your program gets	1778	when writing to a pipe whose other end has been closed, your program gets
…		…
1695		1832
1696	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1833	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1697	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or	1834	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1698	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.	1835	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1699		1836
1700	=item int fd [read-only]	1837	=item ev_io_modify (ev_io *, int events)
1701		1838
1702	The file descriptor being watched.	1839	Similar to C<ev_io_set>, but only changes the event mask. Using this might
		1840	be faster with some backends, as libev can assume that the C<fd> still
		1841	refers to the same underlying file description, something it cannot do
		1842	when using C<ev_io_set>.
1703		1843
		1844	=item int fd [no-modify]
		1845
		1846	The file descriptor being watched. While it can be read at any time, you
		1847	must not modify this member even when the watcher is stopped - always use
		1848	C<ev_io_set> for that.
		1849
1704	=item int events [read-only]	1850	=item int events [no-modify]
1705		1851
1706	The events being watched.	1852	The set of events the fd is being watched for, among other flags. Remember
		1853	that this is a bit set - to test for C<EV_READ>, use C<< w->events &
		1854	EV_READ >>, and similarly for C<EV_WRITE>.
		1855
		1856	As with C<fd>, you must not modify this member even when the watcher is
		1857	stopped, always use C<ev_io_set> or C<ev_io_modify> for that.
1707		1858
1708	=back	1859	=back
1709		1860
1710	=head3 Examples	1861	=head3 Examples
1711		1862
…		…
1739	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1890	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1740	monotonic clock option helps a lot here).	1891	monotonic clock option helps a lot here).
1741		1892
1742	The callback is guaranteed to be invoked only I<after> its timeout has	1893	The callback is guaranteed to be invoked only I<after> its timeout has
1743	passed (not I<at>, so on systems with very low-resolution clocks this	1894	passed (not I<at>, so on systems with very low-resolution clocks this
1744	might introduce a small delay). If multiple timers become ready during the	1895	might introduce a small delay, see "the special problem of being too
		1896	early", below). If multiple timers become ready during the same loop
1745	same loop iteration then the ones with earlier time-out values are invoked	1897	iteration then the ones with earlier time-out values are invoked before
1746	before ones of the same priority with later time-out values (but this is	1898	ones of the same priority with later time-out values (but this is no
1747	no longer true when a callback calls C<ev_run> recursively).	1899	longer true when a callback calls C<ev_run> recursively).
1748		1900
1749	=head3 Be smart about timeouts	1901	=head3 Be smart about timeouts
1750		1902
1751	Many real-world problems involve some kind of timeout, usually for error	1903	Many real-world problems involve some kind of timeout, usually for error
1752	recovery. A typical example is an HTTP request - if the other side hangs,	1904	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1827		1979
1828	In this case, it would be more efficient to leave the C<ev_timer> alone,	1980	In this case, it would be more efficient to leave the C<ev_timer> alone,
1829	but remember the time of last activity, and check for a real timeout only	1981	but remember the time of last activity, and check for a real timeout only
1830	within the callback:	1982	within the callback:
1831		1983
		1984	ev_tstamp timeout = 60.;
1832	ev_tstamp last_activity; // time of last activity	1985	ev_tstamp last_activity; // time of last activity
		1986	ev_timer timer;
1833		1987
1834	static void	1988	static void
1835	callback (EV_P_ ev_timer *w, int revents)	1989	callback (EV_P_ ev_timer *w, int revents)
1836	{	1990	{
1837	ev_tstamp now = ev_now (EV_A);	1991	// calculate when the timeout would happen
1838	ev_tstamp timeout = last_activity + 60.;	1992	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1839		1993
1840	// if last_activity + 60. is older than now, we did time out	1994	// if negative, it means we the timeout already occurred
1841	if (timeout < now)	1995	if (after < 0.)
1842	{	1996	{
1843	// timeout occurred, take action	1997	// timeout occurred, take action
1844	}	1998	}
1845	else	1999	else
1846	{	2000	{
1847	// callback was invoked, but there was some activity, re-arm	2001	// callback was invoked, but there was some recent
1848	// the watcher to fire in last_activity + 60, which is	2002	// activity. simply restart the timer to time out
1849	// guaranteed to be in the future, so "again" is positive:	2003	// after "after" seconds, which is the earliest time
1850	w->repeat = timeout - now;	2004	// the timeout can occur.
		2005	ev_timer_set (w, after, 0.);
1851	ev_timer_again (EV_A_ w);	2006	ev_timer_start (EV_A_ w);
1852	}	2007	}
1853	}	2008	}
1854		2009
1855	To summarise the callback: first calculate the real timeout (defined	2010	To summarise the callback: first calculate in how many seconds the
1856	as "60 seconds after the last activity"), then check if that time has	2011	timeout will occur (by calculating the absolute time when it would occur,
1857	been reached, which means something I<did>, in fact, time out. Otherwise	2012	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1858	the callback was invoked too early (C<timeout> is in the future), so	2013	(EV_A)> from that).
1859	re-schedule the timer to fire at that future time, to see if maybe we have
1860	a timeout then.
1861		2014
1862	Note how C<ev_timer_again> is used, taking advantage of the	2015	If this value is negative, then we are already past the timeout, i.e. we
1863	C<ev_timer_again> optimisation when the timer is already running.	2016	timed out, and need to do whatever is needed in this case.
		2017
		2018	Otherwise, we now the earliest time at which the timeout would trigger,
		2019	and simply start the timer with this timeout value.
		2020
		2021	In other words, each time the callback is invoked it will check whether
		2022	the timeout occurred. If not, it will simply reschedule itself to check
		2023	again at the earliest time it could time out. Rinse. Repeat.
1864		2024
1865	This scheme causes more callback invocations (about one every 60 seconds	2025	This scheme causes more callback invocations (about one every 60 seconds
1866	minus half the average time between activity), but virtually no calls to	2026	minus half the average time between activity), but virtually no calls to
1867	libev to change the timeout.	2027	libev to change the timeout.
1868		2028
1869	To start the timer, simply initialise the watcher and set C<last_activity>	2029	To start the machinery, simply initialise the watcher and set
1870	to the current time (meaning we just have some activity :), then call the	2030	C<last_activity> to the current time (meaning there was some activity just
1871	callback, which will "do the right thing" and start the timer:	2031	now), then call the callback, which will "do the right thing" and start
		2032	the timer:
1872		2033
		2034	last_activity = ev_now (EV_A);
1873	ev_init (timer, callback);	2035	ev_init (&timer, callback);
1874	last_activity = ev_now (loop);	2036	callback (EV_A_ &timer, 0);
1875	callback (loop, timer, EV_TIMER);
1876		2037
1877	And when there is some activity, simply store the current time in	2038	When there is some activity, simply store the current time in
1878	C<last_activity>, no libev calls at all:	2039	C<last_activity>, no libev calls at all:
1879		2040
		2041	if (activity detected)
1880	last_activity = ev_now (loop);	2042	last_activity = ev_now (EV_A);
		2043
		2044	When your timeout value changes, then the timeout can be changed by simply
		2045	providing a new value, stopping the timer and calling the callback, which
		2046	will again do the right thing (for example, time out immediately :).
		2047
		2048	timeout = new_value;
		2049	ev_timer_stop (EV_A_ &timer);
		2050	callback (EV_A_ &timer, 0);
1881		2051
1882	This technique is slightly more complex, but in most cases where the	2052	This technique is slightly more complex, but in most cases where the
1883	time-out is unlikely to be triggered, much more efficient.	2053	time-out is unlikely to be triggered, much more efficient.
1884
1885	Changing the timeout is trivial as well (if it isn't hard-coded in the
1886	callback :) - just change the timeout and invoke the callback, which will
1887	fix things for you.
1888		2054
1889	=item 4. Wee, just use a double-linked list for your timeouts.	2055	=item 4. Wee, just use a double-linked list for your timeouts.
1890		2056
1891	If there is not one request, but many thousands (millions...), all	2057	If there is not one request, but many thousands (millions...), all
1892	employing some kind of timeout with the same timeout value, then one can	2058	employing some kind of timeout with the same timeout value, then one can
…		…
1919	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2085	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1920	rather complicated, but extremely efficient, something that really pays	2086	rather complicated, but extremely efficient, something that really pays
1921	off after the first million or so of active timers, i.e. it's usually	2087	off after the first million or so of active timers, i.e. it's usually
1922	overkill :)	2088	overkill :)
1923		2089
		2090	=head3 The special problem of being too early
		2091
		2092	If you ask a timer to call your callback after three seconds, then
		2093	you expect it to be invoked after three seconds - but of course, this
		2094	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2095	guaranteed to any precision by libev - imagine somebody suspending the
		2096	process with a STOP signal for a few hours for example.
		2097
		2098	So, libev tries to invoke your callback as soon as possible I<after> the
		2099	delay has occurred, but cannot guarantee this.
		2100
		2101	A less obvious failure mode is calling your callback too early: many event
		2102	loops compare timestamps with a "elapsed delay >= requested delay", but
		2103	this can cause your callback to be invoked much earlier than you would
		2104	expect.
		2105
		2106	To see why, imagine a system with a clock that only offers full second
		2107	resolution (think windows if you can't come up with a broken enough OS
		2108	yourself). If you schedule a one-second timer at the time 500.9, then the
		2109	event loop will schedule your timeout to elapse at a system time of 500
		2110	(500.9 truncated to the resolution) + 1, or 501.
		2111
		2112	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2113	501" and invoke the callback 0.1s after it was started, even though a
		2114	one-second delay was requested - this is being "too early", despite best
		2115	intentions.
		2116
		2117	This is the reason why libev will never invoke the callback if the elapsed
		2118	delay equals the requested delay, but only when the elapsed delay is
		2119	larger than the requested delay. In the example above, libev would only invoke
		2120	the callback at system time 502, or 1.1s after the timer was started.
		2121
		2122	So, while libev cannot guarantee that your callback will be invoked
		2123	exactly when requested, it I<can> and I<does> guarantee that the requested
		2124	delay has actually elapsed, or in other words, it always errs on the "too
		2125	late" side of things.
		2126
1924	=head3 The special problem of time updates	2127	=head3 The special problem of time updates
1925		2128
1926	Establishing the current time is a costly operation (it usually takes at	2129	Establishing the current time is a costly operation (it usually takes
1927	least two system calls): EV therefore updates its idea of the current	2130	at least one system call): EV therefore updates its idea of the current
1928	time only before and after C<ev_run> collects new events, which causes a	2131	time only before and after C<ev_run> collects new events, which causes a
1929	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2132	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1930	lots of events in one iteration.	2133	lots of events in one iteration.
1931		2134
1932	The relative timeouts are calculated relative to the C<ev_now ()>	2135	The relative timeouts are calculated relative to the C<ev_now ()>
1933	time. This is usually the right thing as this timestamp refers to the time	2136	time. This is usually the right thing as this timestamp refers to the time
1934	of the event triggering whatever timeout you are modifying/starting. If	2137	of the event triggering whatever timeout you are modifying/starting. If
1935	you suspect event processing to be delayed and you I<need> to base the	2138	you suspect event processing to be delayed and you I<need> to base the
1936	timeout on the current time, use something like this to adjust for this:	2139	timeout on the current time, use something like the following to adjust
		2140	for it:
1937		2141
1938	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2142	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1939		2143
1940	If the event loop is suspended for a long time, you can also force an	2144	If the event loop is suspended for a long time, you can also force an
1941	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2145	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1942	()>.	2146	()>, although that will push the event time of all outstanding events
		2147	further into the future.
		2148
		2149	=head3 The special problem of unsynchronised clocks
		2150
		2151	Modern systems have a variety of clocks - libev itself uses the normal
		2152	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2153	jumps).
		2154
		2155	Neither of these clocks is synchronised with each other or any other clock
		2156	on the system, so C<ev_time ()> might return a considerably different time
		2157	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2158	a call to C<gettimeofday> might return a second count that is one higher
		2159	than a directly following call to C<time>.
		2160
		2161	The moral of this is to only compare libev-related timestamps with
		2162	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2163	a second or so.
		2164
		2165	One more problem arises due to this lack of synchronisation: if libev uses
		2166	the system monotonic clock and you compare timestamps from C<ev_time>
		2167	or C<ev_now> from when you started your timer and when your callback is
		2168	invoked, you will find that sometimes the callback is a bit "early".
		2169
		2170	This is because C<ev_timer>s work in real time, not wall clock time, so
		2171	libev makes sure your callback is not invoked before the delay happened,
		2172	I<measured according to the real time>, not the system clock.
		2173
		2174	If your timeouts are based on a physical timescale (e.g. "time out this
		2175	connection after 100 seconds") then this shouldn't bother you as it is
		2176	exactly the right behaviour.
		2177
		2178	If you want to compare wall clock/system timestamps to your timers, then
		2179	you need to use C<ev_periodic>s, as these are based on the wall clock
		2180	time, where your comparisons will always generate correct results.
1943		2181
1944	=head3 The special problems of suspended animation	2182	=head3 The special problems of suspended animation
1945		2183
1946	When you leave the server world it is quite customary to hit machines that	2184	When you leave the server world it is quite customary to hit machines that
1947	can suspend/hibernate - what happens to the clocks during such a suspend?	2185	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1977		2215
1978	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2216	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1979		2217
1980	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2218	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1981		2219
1982	Configure the timer to trigger after C<after> seconds. If C<repeat>	2220	Configure the timer to trigger after C<after> seconds (fractional and
1983	is C<0.>, then it will automatically be stopped once the timeout is	2221	negative values are supported). If C<repeat> is C<0.>, then it will
1984	reached. If it is positive, then the timer will automatically be	2222	automatically be stopped once the timeout is reached. If it is positive,
1985	configured to trigger again C<repeat> seconds later, again, and again,	2223	then the timer will automatically be configured to trigger again C<repeat>
1986	until stopped manually.	2224	seconds later, again, and again, until stopped manually.
1987		2225
1988	The timer itself will do a best-effort at avoiding drift, that is, if	2226	The timer itself will do a best-effort at avoiding drift, that is, if
1989	you configure a timer to trigger every 10 seconds, then it will normally	2227	you configure a timer to trigger every 10 seconds, then it will normally
1990	trigger at exactly 10 second intervals. If, however, your program cannot	2228	trigger at exactly 10 second intervals. If, however, your program cannot
1991	keep up with the timer (because it takes longer than those 10 seconds to	2229	keep up with the timer (because it takes longer than those 10 seconds to
1992	do stuff) the timer will not fire more than once per event loop iteration.	2230	do stuff) the timer will not fire more than once per event loop iteration.
1993		2231
1994	=item ev_timer_again (loop, ev_timer *)	2232	=item ev_timer_again (loop, ev_timer *)
1995		2233
1996	This will act as if the timer timed out and restart it again if it is	2234	This will act as if the timer timed out, and restarts it again if it is
1997	repeating. The exact semantics are:	2235	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2236	timeout to the C<repeat> value and calling C<ev_timer_start>.
1998		2237
		2238	The exact semantics are as in the following rules, all of which will be
		2239	applied to the watcher:
		2240
		2241	=over 4
		2242
1999	If the timer is pending, its pending status is cleared.	2243	=item If the timer is pending, the pending status is always cleared.
2000		2244
2001	If the timer is started but non-repeating, stop it (as if it timed out).	2245	=item If the timer is started but non-repeating, stop it (as if it timed
		2246	out, without invoking it).
2002		2247
2003	If the timer is repeating, either start it if necessary (with the	2248	=item If the timer is repeating, make the C<repeat> value the new timeout
2004	C<repeat> value), or reset the running timer to the C<repeat> value.	2249	and start the timer, if necessary.
2005		2250
		2251	=back
		2252
2006	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2253	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
2007	usage example.	2254	usage example.
2008		2255
2009	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2256	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2010		2257
2011	Returns the remaining time until a timer fires. If the timer is active,	2258	Returns the remaining time until a timer fires. If the timer is active,
…		…
2064	Periodic watchers are also timers of a kind, but they are very versatile	2311	Periodic watchers are also timers of a kind, but they are very versatile
2065	(and unfortunately a bit complex).	2312	(and unfortunately a bit complex).
2066		2313
2067	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2314	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2068	relative time, the physical time that passes) but on wall clock time	2315	relative time, the physical time that passes) but on wall clock time
2069	(absolute time, the thing you can read on your calender or clock). The	2316	(absolute time, the thing you can read on your calendar or clock). The
2070	difference is that wall clock time can run faster or slower than real	2317	difference is that wall clock time can run faster or slower than real
2071	time, and time jumps are not uncommon (e.g. when you adjust your	2318	time, and time jumps are not uncommon (e.g. when you adjust your
2072	wrist-watch).	2319	wrist-watch).
2073		2320
2074	You can tell a periodic watcher to trigger after some specific point	2321	You can tell a periodic watcher to trigger after some specific point
…		…
2079	C<ev_timer>, which would still trigger roughly 10 seconds after starting	2326	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2080	it, as it uses a relative timeout).	2327	it, as it uses a relative timeout).
2081		2328
2082	C<ev_periodic> watchers can also be used to implement vastly more complex	2329	C<ev_periodic> watchers can also be used to implement vastly more complex
2083	timers, such as triggering an event on each "midnight, local time", or	2330	timers, such as triggering an event on each "midnight, local time", or
2084	other complicated rules. This cannot be done with C<ev_timer> watchers, as	2331	other complicated rules. This cannot easily be done with C<ev_timer>
2085	those cannot react to time jumps.	2332	watchers, as those cannot react to time jumps.
2086		2333
2087	As with timers, the callback is guaranteed to be invoked only when the	2334	As with timers, the callback is guaranteed to be invoked only when the
2088	point in time where it is supposed to trigger has passed. If multiple	2335	point in time where it is supposed to trigger has passed. If multiple
2089	timers become ready during the same loop iteration then the ones with	2336	timers become ready during the same loop iteration then the ones with
2090	earlier time-out values are invoked before ones with later time-out values	2337	earlier time-out values are invoked before ones with later time-out values
…		…
2131		2378
2132	Another way to think about it (for the mathematically inclined) is that	2379	Another way to think about it (for the mathematically inclined) is that
2133	C<ev_periodic> will try to run the callback in this mode at the next possible	2380	C<ev_periodic> will try to run the callback in this mode at the next possible
2134	time where C<time = offset (mod interval)>, regardless of any time jumps.	2381	time where C<time = offset (mod interval)>, regardless of any time jumps.
2135		2382
2136	For numerical stability it is preferable that the C<offset> value is near	2383	The C<interval> I<MUST> be positive, and for numerical stability, the
2137	C<ev_now ()> (the current time), but there is no range requirement for	2384	interval value should be higher than C<1/8192> (which is around 100
2138	this value, and in fact is often specified as zero.	2385	microseconds) and C<offset> should be higher than C<0> and should have
		2386	at most a similar magnitude as the current time (say, within a factor of
		2387	ten). Typical values for offset are, in fact, C<0> or something between
		2388	C<0> and C<interval>, which is also the recommended range.
2139		2389
2140	Note also that there is an upper limit to how often a timer can fire (CPU	2390	Note also that there is an upper limit to how often a timer can fire (CPU
2141	speed for example), so if C<interval> is very small then timing stability	2391	speed for example), so if C<interval> is very small then timing stability
2142	will of course deteriorate. Libev itself tries to be exact to be about one	2392	will of course deteriorate. Libev itself tries to be exact to be about one
2143	millisecond (if the OS supports it and the machine is fast enough).	2393	millisecond (if the OS supports it and the machine is fast enough).
…		…
2173		2423
2174	NOTE: I<< This callback must always return a time that is higher than or	2424	NOTE: I<< This callback must always return a time that is higher than or
2175	equal to the passed C<now> value >>.	2425	equal to the passed C<now> value >>.
2176		2426
2177	This can be used to create very complex timers, such as a timer that	2427	This can be used to create very complex timers, such as a timer that
2178	triggers on "next midnight, local time". To do this, you would calculate the	2428	triggers on "next midnight, local time". To do this, you would calculate
2179	next midnight after C<now> and return the timestamp value for this. How	2429	the next midnight after C<now> and return the timestamp value for
2180	you do this is, again, up to you (but it is not trivial, which is the main	2430	this. Here is a (completely untested, no error checking) example on how to
2181	reason I omitted it as an example).	2431	do this:
		2432
		2433	#include <time.h>
		2434
		2435	static ev_tstamp
		2436	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2437	{
		2438	time_t tnow = (time_t)now;
		2439	struct tm tm;
		2440	localtime_r (&tnow, &tm);
		2441
		2442	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2443	++tm.tm_mday; // midnight next day
		2444
		2445	return mktime (&tm);
		2446	}
		2447
		2448	Note: this code might run into trouble on days that have more then two
		2449	midnights (beginning and end).
2182		2450
2183	=back	2451	=back
2184		2452
2185	=item ev_periodic_again (loop, ev_periodic *)	2453	=item ev_periodic_again (loop, ev_periodic *)
2186		2454
…		…
2251		2519
2252	ev_periodic hourly_tick;	2520	ev_periodic hourly_tick;
2253	ev_periodic_init (&hourly_tick, clock_cb,	2521	ev_periodic_init (&hourly_tick, clock_cb,
2254	fmod (ev_now (loop), 3600.), 3600., 0);	2522	fmod (ev_now (loop), 3600.), 3600., 0);
2255	ev_periodic_start (loop, &hourly_tick);	2523	ev_periodic_start (loop, &hourly_tick);
2256		2524
2257		2525
2258	=head2 C<ev_signal> - signal me when a signal gets signalled!	2526	=head2 C<ev_signal> - signal me when a signal gets signalled!
2259		2527
2260	Signal watchers will trigger an event when the process receives a specific	2528	Signal watchers will trigger an event when the process receives a specific
2261	signal one or more times. Even though signals are very asynchronous, libev	2529	signal one or more times. Even though signals are very asynchronous, libev
2262	will try it's best to deliver signals synchronously, i.e. as part of the	2530	will try its best to deliver signals synchronously, i.e. as part of the
2263	normal event processing, like any other event.	2531	normal event processing, like any other event.
2264		2532
2265	If you want signals to be delivered truly asynchronously, just use	2533	If you want signals to be delivered truly asynchronously, just use
2266	C<sigaction> as you would do without libev and forget about sharing	2534	C<sigaction> as you would do without libev and forget about sharing
2267	the signal. You can even use C<ev_async> from a signal handler to	2535	the signal. You can even use C<ev_async> from a signal handler to
…		…
2271	only within the same loop, i.e. you can watch for C<SIGINT> in your	2539	only within the same loop, i.e. you can watch for C<SIGINT> in your
2272	default loop and for C<SIGIO> in another loop, but you cannot watch for	2540	default loop and for C<SIGIO> in another loop, but you cannot watch for
2273	C<SIGINT> in both the default loop and another loop at the same time. At	2541	C<SIGINT> in both the default loop and another loop at the same time. At
2274	the moment, C<SIGCHLD> is permanently tied to the default loop.	2542	the moment, C<SIGCHLD> is permanently tied to the default loop.
2275		2543
2276	When the first watcher gets started will libev actually register something	2544	Only after the first watcher for a signal is started will libev actually
2277	with the kernel (thus it coexists with your own signal handlers as long as	2545	register something with the kernel. It thus coexists with your own signal
2278	you don't register any with libev for the same signal).	2546	handlers as long as you don't register any with libev for the same signal.
2279		2547
2280	If possible and supported, libev will install its handlers with	2548	If possible and supported, libev will install its handlers with
2281	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2549	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2282	not be unduly interrupted. If you have a problem with system calls getting	2550	not be unduly interrupted. If you have a problem with system calls getting
2283	interrupted by signals you can block all signals in an C<ev_check> watcher	2551	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2286	=head3 The special problem of inheritance over fork/execve/pthread_create	2554	=head3 The special problem of inheritance over fork/execve/pthread_create
2287		2555
2288	Both the signal mask (C<sigprocmask>) and the signal disposition	2556	Both the signal mask (C<sigprocmask>) and the signal disposition
2289	(C<sigaction>) are unspecified after starting a signal watcher (and after	2557	(C<sigaction>) are unspecified after starting a signal watcher (and after
2290	stopping it again), that is, libev might or might not block the signal,	2558	stopping it again), that is, libev might or might not block the signal,
2291	and might or might not set or restore the installed signal handler.	2559	and might or might not set or restore the installed signal handler (but
		2560	see C<EVFLAG_NOSIGMASK>).
2292		2561
2293	While this does not matter for the signal disposition (libev never	2562	While this does not matter for the signal disposition (libev never
2294	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2563	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2295	C<execve>), this matters for the signal mask: many programs do not expect	2564	C<execve>), this matters for the signal mask: many programs do not expect
2296	certain signals to be blocked.	2565	certain signals to be blocked.
…		…
2309	I<has> to modify the signal mask, at least temporarily.	2578	I<has> to modify the signal mask, at least temporarily.
2310		2579
2311	So I can't stress this enough: I<If you do not reset your signal mask when	2580	So I can't stress this enough: I<If you do not reset your signal mask when
2312	you expect it to be empty, you have a race condition in your code>. This	2581	you expect it to be empty, you have a race condition in your code>. This
2313	is not a libev-specific thing, this is true for most event libraries.	2582	is not a libev-specific thing, this is true for most event libraries.
		2583
		2584	=head3 The special problem of threads signal handling
		2585
		2586	POSIX threads has problematic signal handling semantics, specifically,
		2587	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2588	threads in a process block signals, which is hard to achieve.
		2589
		2590	When you want to use sigwait (or mix libev signal handling with your own
		2591	for the same signals), you can tackle this problem by globally blocking
		2592	all signals before creating any threads (or creating them with a fully set
		2593	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2594	loops. Then designate one thread as "signal receiver thread" which handles
		2595	these signals. You can pass on any signals that libev might be interested
		2596	in by calling C<ev_feed_signal>.
2314		2597
2315	=head3 Watcher-Specific Functions and Data Members	2598	=head3 Watcher-Specific Functions and Data Members
2316		2599
2317	=over 4	2600	=over 4
2318		2601
…		…
2453		2736
2454	=head2 C<ev_stat> - did the file attributes just change?	2737	=head2 C<ev_stat> - did the file attributes just change?
2455		2738
2456	This watches a file system path for attribute changes. That is, it calls	2739	This watches a file system path for attribute changes. That is, it calls
2457	C<stat> on that path in regular intervals (or when the OS says it changed)	2740	C<stat> on that path in regular intervals (or when the OS says it changed)
2458	and sees if it changed compared to the last time, invoking the callback if	2741	and sees if it changed compared to the last time, invoking the callback
2459	it did.	2742	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2743	happen after the watcher has been started will be reported.
2460		2744
2461	The path does not need to exist: changing from "path exists" to "path does	2745	The path does not need to exist: changing from "path exists" to "path does
2462	not exist" is a status change like any other. The condition "path does not	2746	not exist" is a status change like any other. The condition "path does not
2463	exist" (or more correctly "path cannot be stat'ed") is signified by the	2747	exist" (or more correctly "path cannot be stat'ed") is signified by the
2464	C<st_nlink> field being zero (which is otherwise always forced to be at	2748	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2694	Apart from keeping your process non-blocking (which is a useful	2978	Apart from keeping your process non-blocking (which is a useful
2695	effect on its own sometimes), idle watchers are a good place to do	2979	effect on its own sometimes), idle watchers are a good place to do
2696	"pseudo-background processing", or delay processing stuff to after the	2980	"pseudo-background processing", or delay processing stuff to after the
2697	event loop has handled all outstanding events.	2981	event loop has handled all outstanding events.
2698		2982
		2983	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2984
		2985	As long as there is at least one active idle watcher, libev will never
		2986	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2987	For this to work, the idle watcher doesn't need to be invoked at all - the
		2988	lowest priority will do.
		2989
		2990	This mode of operation can be useful together with an C<ev_check> watcher,
		2991	to do something on each event loop iteration - for example to balance load
		2992	between different connections.
		2993
		2994	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2995	example.
		2996
2699	=head3 Watcher-Specific Functions and Data Members	2997	=head3 Watcher-Specific Functions and Data Members
2700		2998
2701	=over 4	2999	=over 4
2702		3000
2703	=item ev_idle_init (ev_idle *, callback)	3001	=item ev_idle_init (ev_idle *, callback)
…		…
2714	callback, free it. Also, use no error checking, as usual.	3012	callback, free it. Also, use no error checking, as usual.
2715		3013
2716	static void	3014	static void
2717	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	3015	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2718	{	3016	{
		3017	// stop the watcher
		3018	ev_idle_stop (loop, w);
		3019
		3020	// now we can free it
2719	free (w);	3021	free (w);
		3022
2720	// now do something you wanted to do when the program has	3023	// now do something you wanted to do when the program has
2721	// no longer anything immediate to do.	3024	// no longer anything immediate to do.
2722	}	3025	}
2723		3026
2724	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	3027	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2726	ev_idle_start (loop, idle_watcher);	3029	ev_idle_start (loop, idle_watcher);
2727		3030
2728		3031
2729	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3032	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2730		3033
2731	Prepare and check watchers are usually (but not always) used in pairs:	3034	Prepare and check watchers are often (but not always) used in pairs:
2732	prepare watchers get invoked before the process blocks and check watchers	3035	prepare watchers get invoked before the process blocks and check watchers
2733	afterwards.	3036	afterwards.
2734		3037
2735	You I<must not> call C<ev_run> or similar functions that enter	3038	You I<must not> call C<ev_run> (or similar functions that enter the
2736	the current event loop from either C<ev_prepare> or C<ev_check>	3039	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2737	watchers. Other loops than the current one are fine, however. The	3040	C<ev_check> watchers. Other loops than the current one are fine,
2738	rationale behind this is that you do not need to check for recursion in	3041	however. The rationale behind this is that you do not need to check
2739	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3042	for recursion in those watchers, i.e. the sequence will always be
2740	C<ev_check> so if you have one watcher of each kind they will always be	3043	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2741	called in pairs bracketing the blocking call.	3044	kind they will always be called in pairs bracketing the blocking call.
2742		3045
2743	Their main purpose is to integrate other event mechanisms into libev and	3046	Their main purpose is to integrate other event mechanisms into libev and
2744	their use is somewhat advanced. They could be used, for example, to track	3047	their use is somewhat advanced. They could be used, for example, to track
2745	variable changes, implement your own watchers, integrate net-snmp or a	3048	variable changes, implement your own watchers, integrate net-snmp or a
2746	coroutine library and lots more. They are also occasionally useful if	3049	coroutine library and lots more. They are also occasionally useful if
…		…
2764	with priority higher than or equal to the event loop and one coroutine	3067	with priority higher than or equal to the event loop and one coroutine
2765	of lower priority, but only once, using idle watchers to keep the event	3068	of lower priority, but only once, using idle watchers to keep the event
2766	loop from blocking if lower-priority coroutines are active, thus mapping	3069	loop from blocking if lower-priority coroutines are active, thus mapping
2767	low-priority coroutines to idle/background tasks).	3070	low-priority coroutines to idle/background tasks).
2768		3071
2769	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3072	When used for this purpose, it is recommended to give C<ev_check> watchers
2770	priority, to ensure that they are being run before any other watchers	3073	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2771	after the poll (this doesn't matter for C<ev_prepare> watchers).	3074	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3075	watchers).
2772		3076
2773	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3077	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2774	activate ("feed") events into libev. While libev fully supports this, they	3078	activate ("feed") events into libev. While libev fully supports this, they
2775	might get executed before other C<ev_check> watchers did their job. As	3079	might get executed before other C<ev_check> watchers did their job. As
2776	C<ev_check> watchers are often used to embed other (non-libev) event	3080	C<ev_check> watchers are often used to embed other (non-libev) event
2777	loops those other event loops might be in an unusable state until their	3081	loops those other event loops might be in an unusable state until their
2778	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3082	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2779	others).	3083	others).
		3084
		3085	=head3 Abusing an C<ev_check> watcher for its side-effect
		3086
		3087	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3088	useful because they are called once per event loop iteration. For
		3089	example, if you want to handle a large number of connections fairly, you
		3090	normally only do a bit of work for each active connection, and if there
		3091	is more work to do, you wait for the next event loop iteration, so other
		3092	connections have a chance of making progress.
		3093
		3094	Using an C<ev_check> watcher is almost enough: it will be called on the
		3095	next event loop iteration. However, that isn't as soon as possible -
		3096	without external events, your C<ev_check> watcher will not be invoked.
		3097
		3098	This is where C<ev_idle> watchers come in handy - all you need is a
		3099	single global idle watcher that is active as long as you have one active
		3100	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3101	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3102	invoked. Neither watcher alone can do that.
2780		3103
2781	=head3 Watcher-Specific Functions and Data Members	3104	=head3 Watcher-Specific Functions and Data Members
2782		3105
2783	=over 4	3106	=over 4
2784		3107
…		…
2985		3308
2986	=over 4	3309	=over 4
2987		3310
2988	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3311	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2989		3312
2990	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3313	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2991		3314
2992	Configures the watcher to embed the given loop, which must be	3315	Configures the watcher to embed the given loop, which must be
2993	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3316	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2994	invoked automatically, otherwise it is the responsibility of the callback	3317	invoked automatically, otherwise it is the responsibility of the callback
2995	to invoke it (it will continue to be called until the sweep has been done,	3318	to invoke it (it will continue to be called until the sweep has been done,
…		…
3016	used).	3339	used).
3017		3340
3018	struct ev_loop *loop_hi = ev_default_init (0);	3341	struct ev_loop *loop_hi = ev_default_init (0);
3019	struct ev_loop *loop_lo = 0;	3342	struct ev_loop *loop_lo = 0;
3020	ev_embed embed;	3343	ev_embed embed;
3021		3344
3022	// see if there is a chance of getting one that works	3345	// see if there is a chance of getting one that works
3023	// (remember that a flags value of 0 means autodetection)	3346	// (remember that a flags value of 0 means autodetection)
3024	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3347	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3025	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3348	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3026	: 0;	3349	: 0;
…		…
3040	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3363	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3041		3364
3042	struct ev_loop *loop = ev_default_init (0);	3365	struct ev_loop *loop = ev_default_init (0);
3043	struct ev_loop *loop_socket = 0;	3366	struct ev_loop *loop_socket = 0;
3044	ev_embed embed;	3367	ev_embed embed;
3045		3368
3046	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3369	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3047	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3370	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3048	{	3371	{
3049	ev_embed_init (&embed, 0, loop_socket);	3372	ev_embed_init (&embed, 0, loop_socket);
3050	ev_embed_start (loop, &embed);	3373	ev_embed_start (loop, &embed);
…		…
3058		3381
3059	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3382	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3060		3383
3061	Fork watchers are called when a C<fork ()> was detected (usually because	3384	Fork watchers are called when a C<fork ()> was detected (usually because
3062	whoever is a good citizen cared to tell libev about it by calling	3385	whoever is a good citizen cared to tell libev about it by calling
3063	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3386	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3064	event loop blocks next and before C<ev_check> watchers are being called,	3387	and before C<ev_check> watchers are being called, and only in the child
3065	and only in the child after the fork. If whoever good citizen calling	3388	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3066	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3389	and calls it in the wrong process, the fork handlers will be invoked, too,
3067	handlers will be invoked, too, of course.	3390	of course.
3068		3391
3069	=head3 The special problem of life after fork - how is it possible?	3392	=head3 The special problem of life after fork - how is it possible?
3070		3393
3071	Most uses of C<fork()> consist of forking, then some simple calls to set	3394	Most uses of C<fork ()> consist of forking, then some simple calls to set
3072	up/change the process environment, followed by a call to C<exec()>. This	3395	up/change the process environment, followed by a call to C<exec()>. This
3073	sequence should be handled by libev without any problems.	3396	sequence should be handled by libev without any problems.
3074		3397
3075	This changes when the application actually wants to do event handling	3398	This changes when the application actually wants to do event handling
3076	in the child, or both parent in child, in effect "continuing" after the	3399	in the child, or both parent in child, in effect "continuing" after the
…		…
3153	atexit (program_exits);	3476	atexit (program_exits);
3154		3477
3155		3478
3156	=head2 C<ev_async> - how to wake up an event loop	3479	=head2 C<ev_async> - how to wake up an event loop
3157		3480
3158	In general, you cannot use an C<ev_run> from multiple threads or other	3481	In general, you cannot use an C<ev_loop> from multiple threads or other
3159	asynchronous sources such as signal handlers (as opposed to multiple event	3482	asynchronous sources such as signal handlers (as opposed to multiple event
3160	loops - those are of course safe to use in different threads).	3483	loops - those are of course safe to use in different threads).
3161		3484
3162	Sometimes, however, you need to wake up an event loop you do not control,	3485	Sometimes, however, you need to wake up an event loop you do not control,
3163	for example because it belongs to another thread. This is what C<ev_async>	3486	for example because it belongs to another thread. This is what C<ev_async>
…		…
3165	it by calling C<ev_async_send>, which is thread- and signal safe.	3488	it by calling C<ev_async_send>, which is thread- and signal safe.
3166		3489
3167	This functionality is very similar to C<ev_signal> watchers, as signals,	3490	This functionality is very similar to C<ev_signal> watchers, as signals,
3168	too, are asynchronous in nature, and signals, too, will be compressed	3491	too, are asynchronous in nature, and signals, too, will be compressed
3169	(i.e. the number of callback invocations may be less than the number of	3492	(i.e. the number of callback invocations may be less than the number of
3170	C<ev_async_sent> calls).	3493	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3171		3494	of "global async watchers" by using a watcher on an otherwise unused
3172	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3495	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3173	just the default loop.	3496	even without knowing which loop owns the signal.
3174		3497
3175	=head3 Queueing	3498	=head3 Queueing
3176		3499
3177	C<ev_async> does not support queueing of data in any way. The reason	3500	C<ev_async> does not support queueing of data in any way. The reason
3178	is that the author does not know of a simple (or any) algorithm for a	3501	is that the author does not know of a simple (or any) algorithm for a
…		…
3270	trust me.	3593	trust me.
3271		3594
3272	=item ev_async_send (loop, ev_async *)	3595	=item ev_async_send (loop, ev_async *)
3273		3596
3274	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3597	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3275	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3598	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3599	returns.
		3600
3276	C<ev_feed_event>, this call is safe to do from other threads, signal or	3601	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3277	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3602	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3278	section below on what exactly this means).	3603	embedding section below on what exactly this means).
3279		3604
3280	Note that, as with other watchers in libev, multiple events might get	3605	Note that, as with other watchers in libev, multiple events might get
3281	compressed into a single callback invocation (another way to look at this	3606	compressed into a single callback invocation (another way to look at
3282	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3607	this is that C<ev_async> watchers are level-triggered: they are set on
3283	reset when the event loop detects that).	3608	C<ev_async_send>, reset when the event loop detects that).
3284		3609
3285	This call incurs the overhead of a system call only once per event loop	3610	This call incurs the overhead of at most one extra system call per event
3286	iteration, so while the overhead might be noticeable, it doesn't apply to	3611	loop iteration, if the event loop is blocked, and no syscall at all if
3287	repeated calls to C<ev_async_send> for the same event loop.	3612	the event loop (or your program) is processing events. That means that
		3613	repeated calls are basically free (there is no need to avoid calls for
		3614	performance reasons) and that the overhead becomes smaller (typically
		3615	zero) under load.
3288		3616
3289	=item bool = ev_async_pending (ev_async *)	3617	=item bool = ev_async_pending (ev_async *)
3290		3618
3291	Returns a non-zero value when C<ev_async_send> has been called on the	3619	Returns a non-zero value when C<ev_async_send> has been called on the
3292	watcher but the event has not yet been processed (or even noted) by the	3620	watcher but the event has not yet been processed (or even noted) by the
…		…
3309		3637
3310	There are some other functions of possible interest. Described. Here. Now.	3638	There are some other functions of possible interest. Described. Here. Now.
3311		3639
3312	=over 4	3640	=over 4
3313		3641
3314	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3642	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3315		3643
3316	This function combines a simple timer and an I/O watcher, calls your	3644	This function combines a simple timer and an I/O watcher, calls your
3317	callback on whichever event happens first and automatically stops both	3645	callback on whichever event happens first and automatically stops both
3318	watchers. This is useful if you want to wait for a single event on an fd	3646	watchers. This is useful if you want to wait for a single event on an fd
3319	or timeout without having to allocate/configure/start/stop/free one or	3647	or timeout without having to allocate/configure/start/stop/free one or
…		…
3347	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3675	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3348		3676
3349	=item ev_feed_fd_event (loop, int fd, int revents)	3677	=item ev_feed_fd_event (loop, int fd, int revents)
3350		3678
3351	Feed an event on the given fd, as if a file descriptor backend detected	3679	Feed an event on the given fd, as if a file descriptor backend detected
3352	the given events it.	3680	the given events.
3353		3681
3354	=item ev_feed_signal_event (loop, int signum)	3682	=item ev_feed_signal_event (loop, int signum)
3355		3683
3356	Feed an event as if the given signal occurred (C<loop> must be the default	3684	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3357	loop!).	3685	which is async-safe.
3358		3686
3359	=back	3687	=back
		3688
		3689
		3690	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3691
		3692	This section explains some common idioms that are not immediately
		3693	obvious. Note that examples are sprinkled over the whole manual, and this
		3694	section only contains stuff that wouldn't fit anywhere else.
		3695
		3696	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3697
		3698	Each watcher has, by default, a C<void *data> member that you can read
		3699	or modify at any time: libev will completely ignore it. This can be used
		3700	to associate arbitrary data with your watcher. If you need more data and
		3701	don't want to allocate memory separately and store a pointer to it in that
		3702	data member, you can also "subclass" the watcher type and provide your own
		3703	data:
		3704
		3705	struct my_io
		3706	{
		3707	ev_io io;
		3708	int otherfd;
		3709	void *somedata;
		3710	struct whatever *mostinteresting;
		3711	};
		3712
		3713	...
		3714	struct my_io w;
		3715	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3716
		3717	And since your callback will be called with a pointer to the watcher, you
		3718	can cast it back to your own type:
		3719
		3720	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3721	{
		3722	struct my_io *w = (struct my_io *)w_;
		3723	...
		3724	}
		3725
		3726	More interesting and less C-conformant ways of casting your callback
		3727	function type instead have been omitted.
		3728
		3729	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3730
		3731	Another common scenario is to use some data structure with multiple
		3732	embedded watchers, in effect creating your own watcher that combines
		3733	multiple libev event sources into one "super-watcher":
		3734
		3735	struct my_biggy
		3736	{
		3737	int some_data;
		3738	ev_timer t1;
		3739	ev_timer t2;
		3740	}
		3741
		3742	In this case getting the pointer to C<my_biggy> is a bit more
		3743	complicated: Either you store the address of your C<my_biggy> struct in
		3744	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3745	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3746	real programmers):
		3747
		3748	#include <stddef.h>
		3749
		3750	static void
		3751	t1_cb (EV_P_ ev_timer *w, int revents)
		3752	{
		3753	struct my_biggy big = (struct my_biggy *)
		3754	(((char *)w) - offsetof (struct my_biggy, t1));
		3755	}
		3756
		3757	static void
		3758	t2_cb (EV_P_ ev_timer *w, int revents)
		3759	{
		3760	struct my_biggy big = (struct my_biggy *)
		3761	(((char *)w) - offsetof (struct my_biggy, t2));
		3762	}
		3763
		3764	=head2 AVOIDING FINISHING BEFORE RETURNING
		3765
		3766	Often you have structures like this in event-based programs:
		3767
		3768	callback ()
		3769	{
		3770	free (request);
		3771	}
		3772
		3773	request = start_new_request (..., callback);
		3774
		3775	The intent is to start some "lengthy" operation. The C<request> could be
		3776	used to cancel the operation, or do other things with it.
		3777
		3778	It's not uncommon to have code paths in C<start_new_request> that
		3779	immediately invoke the callback, for example, to report errors. Or you add
		3780	some caching layer that finds that it can skip the lengthy aspects of the
		3781	operation and simply invoke the callback with the result.
		3782
		3783	The problem here is that this will happen I<before> C<start_new_request>
		3784	has returned, so C<request> is not set.
		3785
		3786	Even if you pass the request by some safer means to the callback, you
		3787	might want to do something to the request after starting it, such as
		3788	canceling it, which probably isn't working so well when the callback has
		3789	already been invoked.
		3790
		3791	A common way around all these issues is to make sure that
		3792	C<start_new_request> I<always> returns before the callback is invoked. If
		3793	C<start_new_request> immediately knows the result, it can artificially
		3794	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3795	example, or more sneakily, by reusing an existing (stopped) watcher and
		3796	pushing it into the pending queue:
		3797
		3798	ev_set_cb (watcher, callback);
		3799	ev_feed_event (EV_A_ watcher, 0);
		3800
		3801	This way, C<start_new_request> can safely return before the callback is
		3802	invoked, while not delaying callback invocation too much.
		3803
		3804	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3805
		3806	Often (especially in GUI toolkits) there are places where you have
		3807	I<modal> interaction, which is most easily implemented by recursively
		3808	invoking C<ev_run>.
		3809
		3810	This brings the problem of exiting - a callback might want to finish the
		3811	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3812	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3813	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3814	other combination: In these cases, a simple C<ev_break> will not work.
		3815
		3816	The solution is to maintain "break this loop" variable for each C<ev_run>
		3817	invocation, and use a loop around C<ev_run> until the condition is
		3818	triggered, using C<EVRUN_ONCE>:
		3819
		3820	// main loop
		3821	int exit_main_loop = 0;
		3822
		3823	while (!exit_main_loop)
		3824	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3825
		3826	// in a modal watcher
		3827	int exit_nested_loop = 0;
		3828
		3829	while (!exit_nested_loop)
		3830	ev_run (EV_A_ EVRUN_ONCE);
		3831
		3832	To exit from any of these loops, just set the corresponding exit variable:
		3833
		3834	// exit modal loop
		3835	exit_nested_loop = 1;
		3836
		3837	// exit main program, after modal loop is finished
		3838	exit_main_loop = 1;
		3839
		3840	// exit both
		3841	exit_main_loop = exit_nested_loop = 1;
		3842
		3843	=head2 THREAD LOCKING EXAMPLE
		3844
		3845	Here is a fictitious example of how to run an event loop in a different
		3846	thread from where callbacks are being invoked and watchers are
		3847	created/added/removed.
		3848
		3849	For a real-world example, see the C<EV::Loop::Async> perl module,
		3850	which uses exactly this technique (which is suited for many high-level
		3851	languages).
		3852
		3853	The example uses a pthread mutex to protect the loop data, a condition
		3854	variable to wait for callback invocations, an async watcher to notify the
		3855	event loop thread and an unspecified mechanism to wake up the main thread.
		3856
		3857	First, you need to associate some data with the event loop:
		3858
		3859	typedef struct {
		3860	mutex_t lock; /* global loop lock */
		3861	ev_async async_w;
		3862	thread_t tid;
		3863	cond_t invoke_cv;
		3864	} userdata;
		3865
		3866	void prepare_loop (EV_P)
		3867	{
		3868	// for simplicity, we use a static userdata struct.
		3869	static userdata u;
		3870
		3871	ev_async_init (&u->async_w, async_cb);
		3872	ev_async_start (EV_A_ &u->async_w);
		3873
		3874	pthread_mutex_init (&u->lock, 0);
		3875	pthread_cond_init (&u->invoke_cv, 0);
		3876
		3877	// now associate this with the loop
		3878	ev_set_userdata (EV_A_ u);
		3879	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3880	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3881
		3882	// then create the thread running ev_run
		3883	pthread_create (&u->tid, 0, l_run, EV_A);
		3884	}
		3885
		3886	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3887	solely to wake up the event loop so it takes notice of any new watchers
		3888	that might have been added:
		3889
		3890	static void
		3891	async_cb (EV_P_ ev_async *w, int revents)
		3892	{
		3893	// just used for the side effects
		3894	}
		3895
		3896	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3897	protecting the loop data, respectively.
		3898
		3899	static void
		3900	l_release (EV_P)
		3901	{
		3902	userdata *u = ev_userdata (EV_A);
		3903	pthread_mutex_unlock (&u->lock);
		3904	}
		3905
		3906	static void
		3907	l_acquire (EV_P)
		3908	{
		3909	userdata *u = ev_userdata (EV_A);
		3910	pthread_mutex_lock (&u->lock);
		3911	}
		3912
		3913	The event loop thread first acquires the mutex, and then jumps straight
		3914	into C<ev_run>:
		3915
		3916	void *
		3917	l_run (void *thr_arg)
		3918	{
		3919	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3920
		3921	l_acquire (EV_A);
		3922	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3923	ev_run (EV_A_ 0);
		3924	l_release (EV_A);
		3925
		3926	return 0;
		3927	}
		3928
		3929	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3930	signal the main thread via some unspecified mechanism (signals? pipe
		3931	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3932	have been called (in a while loop because a) spurious wakeups are possible
		3933	and b) skipping inter-thread-communication when there are no pending
		3934	watchers is very beneficial):
		3935
		3936	static void
		3937	l_invoke (EV_P)
		3938	{
		3939	userdata *u = ev_userdata (EV_A);
		3940
		3941	while (ev_pending_count (EV_A))
		3942	{
		3943	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3944	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3945	}
		3946	}
		3947
		3948	Now, whenever the main thread gets told to invoke pending watchers, it
		3949	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3950	thread to continue:
		3951
		3952	static void
		3953	real_invoke_pending (EV_P)
		3954	{
		3955	userdata *u = ev_userdata (EV_A);
		3956
		3957	pthread_mutex_lock (&u->lock);
		3958	ev_invoke_pending (EV_A);
		3959	pthread_cond_signal (&u->invoke_cv);
		3960	pthread_mutex_unlock (&u->lock);
		3961	}
		3962
		3963	Whenever you want to start/stop a watcher or do other modifications to an
		3964	event loop, you will now have to lock:
		3965
		3966	ev_timer timeout_watcher;
		3967	userdata *u = ev_userdata (EV_A);
		3968
		3969	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3970
		3971	pthread_mutex_lock (&u->lock);
		3972	ev_timer_start (EV_A_ &timeout_watcher);
		3973	ev_async_send (EV_A_ &u->async_w);
		3974	pthread_mutex_unlock (&u->lock);
		3975
		3976	Note that sending the C<ev_async> watcher is required because otherwise
		3977	an event loop currently blocking in the kernel will have no knowledge
		3978	about the newly added timer. By waking up the loop it will pick up any new
		3979	watchers in the next event loop iteration.
		3980
		3981	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3982
		3983	While the overhead of a callback that e.g. schedules a thread is small, it
		3984	is still an overhead. If you embed libev, and your main usage is with some
		3985	kind of threads or coroutines, you might want to customise libev so that
		3986	doesn't need callbacks anymore.
		3987
		3988	Imagine you have coroutines that you can switch to using a function
		3989	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3990	and that due to some magic, the currently active coroutine is stored in a
		3991	global called C<current_coro>. Then you can build your own "wait for libev
		3992	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3993	the differing C<;> conventions):
		3994
		3995	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3996	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3997
		3998	That means instead of having a C callback function, you store the
		3999	coroutine to switch to in each watcher, and instead of having libev call
		4000	your callback, you instead have it switch to that coroutine.
		4001
		4002	A coroutine might now wait for an event with a function called
		4003	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		4004	matter when, or whether the watcher is active or not when this function is
		4005	called):
		4006
		4007	void
		4008	wait_for_event (ev_watcher *w)
		4009	{
		4010	ev_set_cb (w, current_coro);
		4011	switch_to (libev_coro);
		4012	}
		4013
		4014	That basically suspends the coroutine inside C<wait_for_event> and
		4015	continues the libev coroutine, which, when appropriate, switches back to
		4016	this or any other coroutine.
		4017
		4018	You can do similar tricks if you have, say, threads with an event queue -
		4019	instead of storing a coroutine, you store the queue object and instead of
		4020	switching to a coroutine, you push the watcher onto the queue and notify
		4021	any waiters.
		4022
		4023	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		4024	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		4025
		4026	// my_ev.h
		4027	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4028	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4029	#include "../libev/ev.h"
		4030
		4031	// my_ev.c
		4032	#define EV_H "my_ev.h"
		4033	#include "../libev/ev.c"
		4034
		4035	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4036	F<my_ev.c> into your project. When properly specifying include paths, you
		4037	can even use F<ev.h> as header file name directly.
3360		4038
3361		4039
3362	=head1 LIBEVENT EMULATION	4040	=head1 LIBEVENT EMULATION
3363		4041
3364	Libev offers a compatibility emulation layer for libevent. It cannot	4042	Libev offers a compatibility emulation layer for libevent. It cannot
3365	emulate the internals of libevent, so here are some usage hints:	4043	emulate the internals of libevent, so here are some usage hints:
3366		4044
3367	=over 4	4045	=over 4
		4046
		4047	=item * Only the libevent-1.4.1-beta API is being emulated.
		4048
		4049	This was the newest libevent version available when libev was implemented,
		4050	and is still mostly unchanged in 2010.
3368		4051
3369	=item * Use it by including <event.h>, as usual.	4052	=item * Use it by including <event.h>, as usual.
3370		4053
3371	=item * The following members are fully supported: ev_base, ev_callback,	4054	=item * The following members are fully supported: ev_base, ev_callback,
3372	ev_arg, ev_fd, ev_res, ev_events.	4055	ev_arg, ev_fd, ev_res, ev_events.
…		…
3378	=item * Priorities are not currently supported. Initialising priorities	4061	=item * Priorities are not currently supported. Initialising priorities
3379	will fail and all watchers will have the same priority, even though there	4062	will fail and all watchers will have the same priority, even though there
3380	is an ev_pri field.	4063	is an ev_pri field.
3381		4064
3382	=item * In libevent, the last base created gets the signals, in libev, the	4065	=item * In libevent, the last base created gets the signals, in libev, the
3383	first base created (== the default loop) gets the signals.	4066	base that registered the signal gets the signals.
3384		4067
3385	=item * Other members are not supported.	4068	=item * Other members are not supported.
3386		4069
3387	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4070	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3388	to use the libev header file and library.	4071	to use the libev header file and library.
3389		4072
3390	=back	4073	=back
3391		4074
3392	=head1 C++ SUPPORT	4075	=head1 C++ SUPPORT
		4076
		4077	=head2 C API
		4078
		4079	The normal C API should work fine when used from C++: both ev.h and the
		4080	libev sources can be compiled as C++. Therefore, code that uses the C API
		4081	will work fine.
		4082
		4083	Proper exception specifications might have to be added to callbacks passed
		4084	to libev: exceptions may be thrown only from watcher callbacks, all other
		4085	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4086	callbacks) must not throw exceptions, and might need a C<noexcept>
		4087	specification. If you have code that needs to be compiled as both C and
		4088	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4089
		4090	static void
		4091	fatal_error (const char *msg) EV_NOEXCEPT
		4092	{
		4093	perror (msg);
		4094	abort ();
		4095	}
		4096
		4097	...
		4098	ev_set_syserr_cb (fatal_error);
		4099
		4100	The only API functions that can currently throw exceptions are C<ev_run>,
		4101	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4102	because it runs cleanup watchers).
		4103
		4104	Throwing exceptions in watcher callbacks is only supported if libev itself
		4105	is compiled with a C++ compiler or your C and C++ environments allow
		4106	throwing exceptions through C libraries (most do).
		4107
		4108	=head2 C++ API
3393		4109
3394	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4110	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3395	you to use some convenience methods to start/stop watchers and also change	4111	you to use some convenience methods to start/stop watchers and also change
3396	the callback model to a model using method callbacks on objects.	4112	the callback model to a model using method callbacks on objects.
3397		4113
3398	To use it,	4114	To use it,
3399		4115
3400	#include <ev++.h>	4116	#include <ev++.h>
3401		4117
3402	This automatically includes F<ev.h> and puts all of its definitions (many	4118	This automatically includes F<ev.h> and puts all of its definitions (many
3403	of them macros) into the global namespace. All C++ specific things are	4119	of them macros) into the global namespace. All C++ specific things are
3404	put into the C<ev> namespace. It should support all the same embedding	4120	put into the C<ev> namespace. It should support all the same embedding
…		…
3407	Care has been taken to keep the overhead low. The only data member the C++	4123	Care has been taken to keep the overhead low. The only data member the C++
3408	classes add (compared to plain C-style watchers) is the event loop pointer	4124	classes add (compared to plain C-style watchers) is the event loop pointer
3409	that the watcher is associated with (or no additional members at all if	4125	that the watcher is associated with (or no additional members at all if
3410	you disable C<EV_MULTIPLICITY> when embedding libev).	4126	you disable C<EV_MULTIPLICITY> when embedding libev).
3411		4127
3412	Currently, functions, and static and non-static member functions can be	4128	Currently, functions, static and non-static member functions and classes
3413	used as callbacks. Other types should be easy to add as long as they only	4129	with C<operator ()> can be used as callbacks. Other types should be easy
3414	need one additional pointer for context. If you need support for other	4130	to add as long as they only need one additional pointer for context. If
3415	types of functors please contact the author (preferably after implementing	4131	you need support for other types of functors please contact the author
3416	it).	4132	(preferably after implementing it).
		4133
		4134	For all this to work, your C++ compiler either has to use the same calling
		4135	conventions as your C compiler (for static member functions), or you have
		4136	to embed libev and compile libev itself as C++.
3417		4137
3418	Here is a list of things available in the C<ev> namespace:	4138	Here is a list of things available in the C<ev> namespace:
3419		4139
3420	=over 4	4140	=over 4
3421		4141
…		…
3431	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4151	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3432		4152
3433	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4153	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3434	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4154	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3435	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4155	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3436	defines by many implementations.	4156	defined by many implementations.
3437		4157
3438	All of those classes have these methods:	4158	All of those classes have these methods:
3439		4159
3440	=over 4	4160	=over 4
3441		4161
…		…
3503	void operator() (ev::io &w, int revents)	4223	void operator() (ev::io &w, int revents)
3504	{	4224	{
3505	...	4225	...
3506	}	4226	}
3507	}	4227	}
3508		4228
3509	myfunctor f;	4229	myfunctor f;
3510		4230
3511	ev::io w;	4231	ev::io w;
3512	w.set (&f);	4232	w.set (&f);
3513		4233
…		…
3531	Associates a different C<struct ev_loop> with this watcher. You can only	4251	Associates a different C<struct ev_loop> with this watcher. You can only
3532	do this when the watcher is inactive (and not pending either).	4252	do this when the watcher is inactive (and not pending either).
3533		4253
3534	=item w->set ([arguments])	4254	=item w->set ([arguments])
3535		4255
3536	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4256	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3537	method or a suitable start method must be called at least once. Unlike the	4257	with the same arguments. Either this method or a suitable start method
3538	C counterpart, an active watcher gets automatically stopped and restarted	4258	must be called at least once. Unlike the C counterpart, an active watcher
3539	when reconfiguring it with this method.	4259	gets automatically stopped and restarted when reconfiguring it with this
		4260	method.
		4261
		4262	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4263	clashing with the C<set (loop)> method.
3540		4264
3541	=item w->start ()	4265	=item w->start ()
3542		4266
3543	Starts the watcher. Note that there is no C<loop> argument, as the	4267	Starts the watcher. Note that there is no C<loop> argument, as the
3544	constructor already stores the event loop.	4268	constructor already stores the event loop.
…		…
3574	watchers in the constructor.	4298	watchers in the constructor.
3575		4299
3576	class myclass	4300	class myclass
3577	{	4301	{
3578	ev::io io ; void io_cb (ev::io &w, int revents);	4302	ev::io io ; void io_cb (ev::io &w, int revents);
3579	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4303	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3580	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4304	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3581		4305
3582	myclass (int fd)	4306	myclass (int fd)
3583	{	4307	{
3584	io .set <myclass, &myclass::io_cb > (this);	4308	io .set <myclass, &myclass::io_cb > (this);
…		…
3635	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4359	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3636		4360
3637	=item D	4361	=item D
3638		4362
3639	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4363	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3640	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4364	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3641		4365
3642	=item Ocaml	4366	=item Ocaml
3643		4367
3644	Erkki Seppala has written Ocaml bindings for libev, to be found at	4368	Erkki Seppala has written Ocaml bindings for libev, to be found at
3645	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4369	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3648		4372
3649	Brian Maher has written a partial interface to libev for lua (at the	4373	Brian Maher has written a partial interface to libev for lua (at the
3650	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4374	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3651	L<http://github.com/brimworks/lua-ev>.	4375	L<http://github.com/brimworks/lua-ev>.
3652		4376
		4377	=item Javascript
		4378
		4379	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4380
		4381	=item Others
		4382
		4383	There are others, and I stopped counting.
		4384
3653	=back	4385	=back
3654		4386
3655		4387
3656	=head1 MACRO MAGIC	4388	=head1 MACRO MAGIC
3657		4389
…		…
3693	suitable for use with C<EV_A>.	4425	suitable for use with C<EV_A>.
3694		4426
3695	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4427	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3696		4428
3697	Similar to the other two macros, this gives you the value of the default	4429	Similar to the other two macros, this gives you the value of the default
3698	loop, if multiple loops are supported ("ev loop default").	4430	loop, if multiple loops are supported ("ev loop default"). The default loop
		4431	will be initialised if it isn't already initialised.
		4432
		4433	For non-multiplicity builds, these macros do nothing, so you always have
		4434	to initialise the loop somewhere.
3699		4435
3700	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4436	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3701		4437
3702	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4438	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3703	default loop has been initialised (C<UC> == unchecked). Their behaviour	4439	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3770	ev_vars.h	4506	ev_vars.h
3771	ev_wrap.h	4507	ev_wrap.h
3772		4508
3773	ev_win32.c required on win32 platforms only	4509	ev_win32.c required on win32 platforms only
3774		4510
3775	ev_select.c only when select backend is enabled (which is enabled by default)	4511	ev_select.c only when select backend is enabled
3776	ev_poll.c only when poll backend is enabled (disabled by default)	4512	ev_poll.c only when poll backend is enabled
3777	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4513	ev_epoll.c only when the epoll backend is enabled
		4514	ev_linuxaio.c only when the linux aio backend is enabled
		4515	ev_iouring.c only when the linux io_uring backend is enabled
3778	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4516	ev_kqueue.c only when the kqueue backend is enabled
3779	ev_port.c only when the solaris port backend is enabled (disabled by default)	4517	ev_port.c only when the solaris port backend is enabled
3780		4518
3781	F<ev.c> includes the backend files directly when enabled, so you only need	4519	F<ev.c> includes the backend files directly when enabled, so you only need
3782	to compile this single file.	4520	to compile this single file.
3783		4521
3784	=head3 LIBEVENT COMPATIBILITY API	4522	=head3 LIBEVENT COMPATIBILITY API
…		…
3848	supported). It will also not define any of the structs usually found in	4586	supported). It will also not define any of the structs usually found in
3849	F<event.h> that are not directly supported by the libev core alone.	4587	F<event.h> that are not directly supported by the libev core alone.
3850		4588
3851	In standalone mode, libev will still try to automatically deduce the	4589	In standalone mode, libev will still try to automatically deduce the
3852	configuration, but has to be more conservative.	4590	configuration, but has to be more conservative.
		4591
		4592	=item EV_USE_FLOOR
		4593
		4594	If defined to be C<1>, libev will use the C<floor ()> function for its
		4595	periodic reschedule calculations, otherwise libev will fall back on a
		4596	portable (slower) implementation. If you enable this, you usually have to
		4597	link against libm or something equivalent. Enabling this when the C<floor>
		4598	function is not available will fail, so the safe default is to not enable
		4599	this.
3853		4600
3854	=item EV_USE_MONOTONIC	4601	=item EV_USE_MONOTONIC
3855		4602
3856	If defined to be C<1>, libev will try to detect the availability of the	4603	If defined to be C<1>, libev will try to detect the availability of the
3857	monotonic clock option at both compile time and runtime. Otherwise no	4604	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3894	available and will probe for kernel support at runtime. This will improve	4641	available and will probe for kernel support at runtime. This will improve
3895	C<ev_signal> and C<ev_async> performance and reduce resource consumption.	4642	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
3896	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc	4643	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
3897	2.7 or newer, otherwise disabled.	4644	2.7 or newer, otherwise disabled.
3898		4645
		4646	=item EV_USE_SIGNALFD
		4647
		4648	If defined to be C<1>, then libev will assume that C<signalfd ()> is
		4649	available and will probe for kernel support at runtime. This enables
		4650	the use of EVFLAG_SIGNALFD for faster and simpler signal handling. If
		4651	undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4652	2.7 or newer, otherwise disabled.
		4653
		4654	=item EV_USE_TIMERFD
		4655
		4656	If defined to be C<1>, then libev will assume that C<timerfd ()> is
		4657	available and will probe for kernel support at runtime. This allows
		4658	libev to detect time jumps accurately. If undefined, it will be enabled
		4659	if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
		4660	C<TFD_TIMER_CANCEL_ON_SET>, otherwise disabled.
		4661
		4662	=item EV_USE_EVENTFD
		4663
		4664	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4665	available and will probe for kernel support at runtime. This will improve
		4666	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4667	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4668	2.7 or newer, otherwise disabled.
		4669
3899	=item EV_USE_SELECT	4670	=item EV_USE_SELECT
3900		4671
3901	If undefined or defined to be C<1>, libev will compile in support for the	4672	If undefined or defined to be C<1>, libev will compile in support for the
3902	C<select>(2) backend. No attempt at auto-detection will be done: if no	4673	C<select>(2) backend. No attempt at auto-detection will be done: if no
3903	other method takes over, select will be it. Otherwise the select backend	4674	other method takes over, select will be it. Otherwise the select backend
…		…
3943	If programs implement their own fd to handle mapping on win32, then this	4714	If programs implement their own fd to handle mapping on win32, then this
3944	macro can be used to override the C<close> function, useful to unregister	4715	macro can be used to override the C<close> function, useful to unregister
3945	file descriptors again. Note that the replacement function has to close	4716	file descriptors again. Note that the replacement function has to close
3946	the underlying OS handle.	4717	the underlying OS handle.
3947		4718
		4719	=item EV_USE_WSASOCKET
		4720
		4721	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4722	communication socket, which works better in some environments. Otherwise,
		4723	the normal C<socket> function will be used, which works better in other
		4724	environments.
		4725
3948	=item EV_USE_POLL	4726	=item EV_USE_POLL
3949		4727
3950	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4728	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3951	backend. Otherwise it will be enabled on non-win32 platforms. It	4729	backend. Otherwise it will be enabled on non-win32 platforms. It
3952	takes precedence over select.	4730	takes precedence over select.
…		…
3956	If defined to be C<1>, libev will compile in support for the Linux	4734	If defined to be C<1>, libev will compile in support for the Linux
3957	C<epoll>(7) backend. Its availability will be detected at runtime,	4735	C<epoll>(7) backend. Its availability will be detected at runtime,
3958	otherwise another method will be used as fallback. This is the preferred	4736	otherwise another method will be used as fallback. This is the preferred
3959	backend for GNU/Linux systems. If undefined, it will be enabled if the	4737	backend for GNU/Linux systems. If undefined, it will be enabled if the
3960	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4738	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4739
		4740	=item EV_USE_LINUXAIO
		4741
		4742	If defined to be C<1>, libev will compile in support for the Linux aio
		4743	backend (C<EV_USE_EPOLL> must also be enabled). If undefined, it will be
		4744	enabled on linux, otherwise disabled.
		4745
		4746	=item EV_USE_IOURING
		4747
		4748	If defined to be C<1>, libev will compile in support for the Linux
		4749	io_uring backend (C<EV_USE_EPOLL> must also be enabled). Due to it's
		4750	current limitations it has to be requested explicitly. If undefined, it
		4751	will be enabled on linux, otherwise disabled.
3961		4752
3962	=item EV_USE_KQUEUE	4753	=item EV_USE_KQUEUE
3963		4754
3964	If defined to be C<1>, libev will compile in support for the BSD style	4755	If defined to be C<1>, libev will compile in support for the BSD style
3965	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4756	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
3987	If defined to be C<1>, libev will compile in support for the Linux inotify	4778	If defined to be C<1>, libev will compile in support for the Linux inotify
3988	interface to speed up C<ev_stat> watchers. Its actual availability will	4779	interface to speed up C<ev_stat> watchers. Its actual availability will
3989	be detected at runtime. If undefined, it will be enabled if the headers	4780	be detected at runtime. If undefined, it will be enabled if the headers
3990	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4781	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3991		4782
		4783	=item EV_NO_SMP
		4784
		4785	If defined to be C<1>, libev will assume that memory is always coherent
		4786	between threads, that is, threads can be used, but threads never run on
		4787	different cpus (or different cpu cores). This reduces dependencies
		4788	and makes libev faster.
		4789
		4790	=item EV_NO_THREADS
		4791
		4792	If defined to be C<1>, libev will assume that it will never be called from
		4793	different threads (that includes signal handlers), which is a stronger
		4794	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4795	libev faster.
		4796
3992	=item EV_ATOMIC_T	4797	=item EV_ATOMIC_T
3993		4798
3994	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4799	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3995	access is atomic with respect to other threads or signal contexts. No such	4800	access is atomic with respect to other threads or signal contexts. No
3996	type is easily found in the C language, so you can provide your own type	4801	such type is easily found in the C language, so you can provide your own
3997	that you know is safe for your purposes. It is used both for signal handler "locking"	4802	type that you know is safe for your purposes. It is used both for signal
3998	as well as for signal and thread safety in C<ev_async> watchers.	4803	handler "locking" as well as for signal and thread safety in C<ev_async>
		4804	watchers.
3999		4805
4000	In the absence of this define, libev will use C<sig_atomic_t volatile>	4806	In the absence of this define, libev will use C<sig_atomic_t volatile>
4001	(from F<signal.h>), which is usually good enough on most platforms.	4807	(from F<signal.h>), which is usually good enough on most platforms.
4002		4808
4003	=item EV_H (h)	4809	=item EV_H (h)
…		…
4030	will have the C<struct ev_loop *> as first argument, and you can create	4836	will have the C<struct ev_loop *> as first argument, and you can create
4031	additional independent event loops. Otherwise there will be no support	4837	additional independent event loops. Otherwise there will be no support
4032	for multiple event loops and there is no first event loop pointer	4838	for multiple event loops and there is no first event loop pointer
4033	argument. Instead, all functions act on the single default loop.	4839	argument. Instead, all functions act on the single default loop.
4034		4840
		4841	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4842	default loop when multiplicity is switched off - you always have to
		4843	initialise the loop manually in this case.
		4844
4035	=item EV_MINPRI	4845	=item EV_MINPRI
4036		4846
4037	=item EV_MAXPRI	4847	=item EV_MAXPRI
4038		4848
4039	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4849	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4075	#define EV_USE_POLL 1	4885	#define EV_USE_POLL 1
4076	#define EV_CHILD_ENABLE 1	4886	#define EV_CHILD_ENABLE 1
4077	#define EV_ASYNC_ENABLE 1	4887	#define EV_ASYNC_ENABLE 1
4078		4888
4079	The actual value is a bitset, it can be a combination of the following	4889	The actual value is a bitset, it can be a combination of the following
4080	values:	4890	values (by default, all of these are enabled):
4081		4891
4082	=over 4	4892	=over 4
4083		4893
4084	=item C<1> - faster/larger code	4894	=item C<1> - faster/larger code
4085		4895
…		…
4089	code size by roughly 30% on amd64).	4899	code size by roughly 30% on amd64).
4090		4900
4091	When optimising for size, use of compiler flags such as C<-Os> with	4901	When optimising for size, use of compiler flags such as C<-Os> with
4092	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4902	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4093	assertions.	4903	assertions.
		4904
		4905	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4906	(e.g. gcc with C<-Os>).
4094		4907
4095	=item C<2> - faster/larger data structures	4908	=item C<2> - faster/larger data structures
4096		4909
4097	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4910	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4098	hash table sizes and so on. This will usually further increase code size	4911	hash table sizes and so on. This will usually further increase code size
4099	and can additionally have an effect on the size of data structures at	4912	and can additionally have an effect on the size of data structures at
4100	runtime.	4913	runtime.
4101		4914
		4915	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4916	(e.g. gcc with C<-Os>).
		4917
4102	=item C<4> - full API configuration	4918	=item C<4> - full API configuration
4103		4919
4104	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4920	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4105	enables multiplicity (C<EV_MULTIPLICITY>=1).	4921	enables multiplicity (C<EV_MULTIPLICITY>=1).
4106		4922
…		…
4136		4952
4137	With an intelligent-enough linker (gcc+binutils are intelligent enough	4953	With an intelligent-enough linker (gcc+binutils are intelligent enough
4138	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4954	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4139	your program might be left out as well - a binary starting a timer and an	4955	your program might be left out as well - a binary starting a timer and an
4140	I/O watcher then might come out at only 5Kb.	4956	I/O watcher then might come out at only 5Kb.
		4957
		4958	=item EV_API_STATIC
		4959
		4960	If this symbol is defined (by default it is not), then all identifiers
		4961	will have static linkage. This means that libev will not export any
		4962	identifiers, and you cannot link against libev anymore. This can be useful
		4963	when you embed libev, only want to use libev functions in a single file,
		4964	and do not want its identifiers to be visible.
		4965
		4966	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4967	wants to use libev.
		4968
		4969	This option only works when libev is compiled with a C compiler, as C++
		4970	doesn't support the required declaration syntax.
4141		4971
4142	=item EV_AVOID_STDIO	4972	=item EV_AVOID_STDIO
4143		4973
4144	If this is set to C<1> at compiletime, then libev will avoid using stdio	4974	If this is set to C<1> at compiletime, then libev will avoid using stdio
4145	functions (printf, scanf, perror etc.). This will increase the code size	4975	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4203	in. If set to C<1>, then verification code will be compiled in, but not	5033	in. If set to C<1>, then verification code will be compiled in, but not
4204	called. If set to C<2>, then the internal verification code will be	5034	called. If set to C<2>, then the internal verification code will be
4205	called once per loop, which can slow down libev. If set to C<3>, then the	5035	called once per loop, which can slow down libev. If set to C<3>, then the
4206	verification code will be called very frequently, which will slow down	5036	verification code will be called very frequently, which will slow down
4207	libev considerably.	5037	libev considerably.
		5038
		5039	Verification errors are reported via C's C<assert> mechanism, so if you
		5040	disable that (e.g. by defining C<NDEBUG>) then no errors will be reported.
4208		5041
4209	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it	5042	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
4210	will be C<0>.	5043	will be C<0>.
4211		5044
4212	=item EV_COMMON	5045	=item EV_COMMON
…		…
4289	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5122	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4290		5123
4291	#include "ev_cpp.h"	5124	#include "ev_cpp.h"
4292	#include "ev.c"	5125	#include "ev.c"
4293		5126
4294	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5127	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4295		5128
4296	=head2 THREADS AND COROUTINES	5129	=head2 THREADS AND COROUTINES
4297		5130
4298	=head3 THREADS	5131	=head3 THREADS
4299		5132
…		…
4350	default loop and triggering an C<ev_async> watcher from the default loop	5183	default loop and triggering an C<ev_async> watcher from the default loop
4351	watcher callback into the event loop interested in the signal.	5184	watcher callback into the event loop interested in the signal.
4352		5185
4353	=back	5186	=back
4354		5187
4355	=head4 THREAD LOCKING EXAMPLE	5188	See also L</THREAD LOCKING EXAMPLE>.
4356
4357	Here is a fictitious example of how to run an event loop in a different
4358	thread than where callbacks are being invoked and watchers are
4359	created/added/removed.
4360
4361	For a real-world example, see the C<EV::Loop::Async> perl module,
4362	which uses exactly this technique (which is suited for many high-level
4363	languages).
4364
4365	The example uses a pthread mutex to protect the loop data, a condition
4366	variable to wait for callback invocations, an async watcher to notify the
4367	event loop thread and an unspecified mechanism to wake up the main thread.
4368
4369	First, you need to associate some data with the event loop:
4370
4371	typedef struct {
4372	mutex_t lock; /* global loop lock */
4373	ev_async async_w;
4374	thread_t tid;
4375	cond_t invoke_cv;
4376	} userdata;
4377
4378	void prepare_loop (EV_P)
4379	{
4380	// for simplicity, we use a static userdata struct.
4381	static userdata u;
4382
4383	ev_async_init (&u->async_w, async_cb);
4384	ev_async_start (EV_A_ &u->async_w);
4385
4386	pthread_mutex_init (&u->lock, 0);
4387	pthread_cond_init (&u->invoke_cv, 0);
4388
4389	// now associate this with the loop
4390	ev_set_userdata (EV_A_ u);
4391	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4392	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4393
4394	// then create the thread running ev_loop
4395	pthread_create (&u->tid, 0, l_run, EV_A);
4396	}
4397
4398	The callback for the C<ev_async> watcher does nothing: the watcher is used
4399	solely to wake up the event loop so it takes notice of any new watchers
4400	that might have been added:
4401
4402	static void
4403	async_cb (EV_P_ ev_async *w, int revents)
4404	{
4405	// just used for the side effects
4406	}
4407
4408	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4409	protecting the loop data, respectively.
4410
4411	static void
4412	l_release (EV_P)
4413	{
4414	userdata *u = ev_userdata (EV_A);
4415	pthread_mutex_unlock (&u->lock);
4416	}
4417
4418	static void
4419	l_acquire (EV_P)
4420	{
4421	userdata *u = ev_userdata (EV_A);
4422	pthread_mutex_lock (&u->lock);
4423	}
4424
4425	The event loop thread first acquires the mutex, and then jumps straight
4426	into C<ev_run>:
4427
4428	void *
4429	l_run (void *thr_arg)
4430	{
4431	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4432
4433	l_acquire (EV_A);
4434	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4435	ev_run (EV_A_ 0);
4436	l_release (EV_A);
4437
4438	return 0;
4439	}
4440
4441	Instead of invoking all pending watchers, the C<l_invoke> callback will
4442	signal the main thread via some unspecified mechanism (signals? pipe
4443	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4444	have been called (in a while loop because a) spurious wakeups are possible
4445	and b) skipping inter-thread-communication when there are no pending
4446	watchers is very beneficial):
4447
4448	static void
4449	l_invoke (EV_P)
4450	{
4451	userdata *u = ev_userdata (EV_A);
4452
4453	while (ev_pending_count (EV_A))
4454	{
4455	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4456	pthread_cond_wait (&u->invoke_cv, &u->lock);
4457	}
4458	}
4459
4460	Now, whenever the main thread gets told to invoke pending watchers, it
4461	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4462	thread to continue:
4463
4464	static void
4465	real_invoke_pending (EV_P)
4466	{
4467	userdata *u = ev_userdata (EV_A);
4468
4469	pthread_mutex_lock (&u->lock);
4470	ev_invoke_pending (EV_A);
4471	pthread_cond_signal (&u->invoke_cv);
4472	pthread_mutex_unlock (&u->lock);
4473	}
4474
4475	Whenever you want to start/stop a watcher or do other modifications to an
4476	event loop, you will now have to lock:
4477
4478	ev_timer timeout_watcher;
4479	userdata *u = ev_userdata (EV_A);
4480
4481	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4482
4483	pthread_mutex_lock (&u->lock);
4484	ev_timer_start (EV_A_ &timeout_watcher);
4485	ev_async_send (EV_A_ &u->async_w);
4486	pthread_mutex_unlock (&u->lock);
4487
4488	Note that sending the C<ev_async> watcher is required because otherwise
4489	an event loop currently blocking in the kernel will have no knowledge
4490	about the newly added timer. By waking up the loop it will pick up any new
4491	watchers in the next event loop iteration.
4492		5189
4493	=head3 COROUTINES	5190	=head3 COROUTINES
4494		5191
4495	Libev is very accommodating to coroutines ("cooperative threads"):	5192	Libev is very accommodating to coroutines ("cooperative threads"):
4496	libev fully supports nesting calls to its functions from different	5193	libev fully supports nesting calls to its functions from different
…		…
4661	requires, and its I/O model is fundamentally incompatible with the POSIX	5358	requires, and its I/O model is fundamentally incompatible with the POSIX
4662	model. Libev still offers limited functionality on this platform in	5359	model. Libev still offers limited functionality on this platform in
4663	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5360	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4664	descriptors. This only applies when using Win32 natively, not when using	5361	descriptors. This only applies when using Win32 natively, not when using
4665	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5362	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4666	as every compielr comes with a slightly differently broken/incompatible	5363	as every compiler comes with a slightly differently broken/incompatible
4667	environment.	5364	environment.
4668		5365
4669	Lifting these limitations would basically require the full	5366	Lifting these limitations would basically require the full
4670	re-implementation of the I/O system. If you are into this kind of thing,	5367	re-implementation of the I/O system. If you are into this kind of thing,
4671	then note that glib does exactly that for you in a very portable way (note	5368	then note that glib does exactly that for you in a very portable way (note
…		…
4765	structure (guaranteed by POSIX but not by ISO C for example), but it also	5462	structure (guaranteed by POSIX but not by ISO C for example), but it also
4766	assumes that the same (machine) code can be used to call any watcher	5463	assumes that the same (machine) code can be used to call any watcher
4767	callback: The watcher callbacks have different type signatures, but libev	5464	callback: The watcher callbacks have different type signatures, but libev
4768	calls them using an C<ev_watcher *> internally.	5465	calls them using an C<ev_watcher *> internally.
4769		5466
		5467	=item null pointers and integer zero are represented by 0 bytes
		5468
		5469	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5470	relies on this setting pointers and integers to null.
		5471
4770	=item pointer accesses must be thread-atomic	5472	=item pointer accesses must be thread-atomic
4771		5473
4772	Accessing a pointer value must be atomic, it must both be readable and	5474	Accessing a pointer value must be atomic, it must both be readable and
4773	writable in one piece - this is the case on all current architectures.	5475	writable in one piece - this is the case on all current architectures.
4774		5476
…		…
4787	thread" or will block signals process-wide, both behaviours would	5489	thread" or will block signals process-wide, both behaviours would
4788	be compatible with libev. Interaction between C<sigprocmask> and	5490	be compatible with libev. Interaction between C<sigprocmask> and
4789	C<pthread_sigmask> could complicate things, however.	5491	C<pthread_sigmask> could complicate things, however.
4790		5492
4791	The most portable way to handle signals is to block signals in all threads	5493	The most portable way to handle signals is to block signals in all threads
4792	except the initial one, and run the default loop in the initial thread as	5494	except the initial one, and run the signal handling loop in the initial
4793	well.	5495	thread as well.
4794		5496
4795	=item C<long> must be large enough for common memory allocation sizes	5497	=item C<long> must be large enough for common memory allocation sizes
4796		5498
4797	To improve portability and simplify its API, libev uses C<long> internally	5499	To improve portability and simplify its API, libev uses C<long> internally
4798	instead of C<size_t> when allocating its data structures. On non-POSIX	5500	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4804		5506
4805	The type C<double> is used to represent timestamps. It is required to	5507	The type C<double> is used to represent timestamps. It is required to
4806	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5508	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4807	good enough for at least into the year 4000 with millisecond accuracy	5509	good enough for at least into the year 4000 with millisecond accuracy
4808	(the design goal for libev). This requirement is overfulfilled by	5510	(the design goal for libev). This requirement is overfulfilled by
4809	implementations using IEEE 754, which is basically all existing ones. With	5511	implementations using IEEE 754, which is basically all existing ones.
		5512
4810	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5513	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5514	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5515	is either obsolete or somebody patched it to use C<long double> or
		5516	something like that, just kidding).
4811		5517
4812	=back	5518	=back
4813		5519
4814	If you know of other additional requirements drop me a note.	5520	If you know of other additional requirements drop me a note.
4815		5521
…		…
4877	=item Processing ev_async_send: O(number_of_async_watchers)	5583	=item Processing ev_async_send: O(number_of_async_watchers)
4878		5584
4879	=item Processing signals: O(max_signal_number)	5585	=item Processing signals: O(max_signal_number)
4880		5586
4881	Sending involves a system call I<iff> there were no other C<ev_async_send>	5587	Sending involves a system call I<iff> there were no other C<ev_async_send>
4882	calls in the current loop iteration. Checking for async and signal events	5588	calls in the current loop iteration and the loop is currently
		5589	blocked. Checking for async and signal events involves iterating over all
4883	involves iterating over all running async watchers or all signal numbers.	5590	running async watchers or all signal numbers.
4884		5591
4885	=back	5592	=back
4886		5593
4887		5594
4888	=head1 PORTING FROM LIBEV 3.X TO 4.X	5595	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
4897	=over 4	5604	=over 4
4898		5605
4899	=item C<EV_COMPAT3> backwards compatibility mechanism	5606	=item C<EV_COMPAT3> backwards compatibility mechanism
4900		5607
4901	The backward compatibility mechanism can be controlled by	5608	The backward compatibility mechanism can be controlled by
4902	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>	5609	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
4903	section.	5610	section.
4904		5611
4905	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5612	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4906		5613
4907	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5614	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
…		…
4950	=over 4	5657	=over 4
4951		5658
4952	=item active	5659	=item active
4953		5660
4954	A watcher is active as long as it has been started and not yet stopped.	5661	A watcher is active as long as it has been started and not yet stopped.
4955	See L<WATCHER STATES> for details.	5662	See L</WATCHER STATES> for details.
4956		5663
4957	=item application	5664	=item application
4958		5665
4959	In this document, an application is whatever is using libev.	5666	In this document, an application is whatever is using libev.
4960		5667
…		…
4996	watchers and events.	5703	watchers and events.
4997		5704
4998	=item pending	5705	=item pending
4999		5706
5000	A watcher is pending as soon as the corresponding event has been	5707	A watcher is pending as soon as the corresponding event has been
5001	detected. See L<WATCHER STATES> for details.	5708	detected. See L</WATCHER STATES> for details.
5002		5709
5003	=item real time	5710	=item real time
5004		5711
5005	The physical time that is observed. It is apparently strictly monotonic :)	5712	The physical time that is observed. It is apparently strictly monotonic :)
5006		5713
5007	=item wall-clock time	5714	=item wall-clock time
5008		5715
5009	The time and date as shown on clocks. Unlike real time, it can actually	5716	The time and date as shown on clocks. Unlike real time, it can actually
5010	be wrong and jump forwards and backwards, e.g. when the you adjust your	5717	be wrong and jump forwards and backwards, e.g. when you adjust your
5011	clock.	5718	clock.
5012		5719
5013	=item watcher	5720	=item watcher
5014		5721
5015	A data structure that describes interest in certain events. Watchers need	5722	A data structure that describes interest in certain events. Watchers need
…		…
5018	=back	5725	=back
5019		5726
5020	=head1 AUTHOR	5727	=head1 AUTHOR
5021		5728
5022	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5729	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5023	Magnusson and Emanuele Giaquinta.	5730	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5024		5731

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