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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
…		…
43		45
44	int	46	int
45	main (void)	47	main (void)
46	{	48	{
47	// use the default event loop unless you have special needs	49	// use the default event loop unless you have special needs
48	struct ev_loop *loop = ev_default_loop (0);	50	struct ev_loop *loop = EV_DEFAULT;
49		51
50	// initialise an io watcher, then start it	52	// initialise an io watcher, then start it
51	// this one will watch for stdin to become readable	53	// this one will watch for stdin to become readable
52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	54	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
53	ev_io_start (loop, &stdin_watcher);	55	ev_io_start (loop, &stdin_watcher);
…		…
58	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
59		61
60	// now wait for events to arrive	62	// now wait for events to arrive
61	ev_run (loop, 0);	63	ev_run (loop, 0);
62		64
63	// unloop was called, so exit	65	// break was called, so exit
64	return 0;	66	return 0;
65	}	67	}
66		68
67	=head1 ABOUT THIS DOCUMENT	69	=head1 ABOUT THIS DOCUMENT
68		70
…		…
78	with libev.	80	with libev.
79		81
80	Familiarity with event based programming techniques in general is assumed	82	Familiarity with event based programming techniques in general is assumed
81	throughout this document.	83	throughout this document.
82		84
		85	=head1 WHAT TO READ WHEN IN A HURRY
		86
		87	This manual tries to be very detailed, but unfortunately, this also makes
		88	it very long. If you just want to know the basics of libev, I suggest
		89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
		90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
		91	C<ev_timer> sections in L</WATCHER TYPES>.
		92
83	=head1 ABOUT LIBEV	93	=head1 ABOUT LIBEV
84		94
85	Libev is an event loop: you register interest in certain events (such as a	95	Libev is an event loop: you register interest in certain events (such as a
86	file descriptor being readable or a timeout occurring), and it will manage	96	file descriptor being readable or a timeout occurring), and it will manage
87	these event sources and provide your program with events.	97	these event sources and provide your program with events.
…		…
95	details of the event, and then hand it over to libev by I<starting> the	105	details of the event, and then hand it over to libev by I<starting> the
96	watcher.	106	watcher.
97		107
98	=head2 FEATURES	108	=head2 FEATURES
99		109
100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	110	Libev supports C<select>, C<poll>, the Linux-specific aio and C<epoll>
101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port
102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	112	mechanisms for file descriptor events (C<ev_io>), the Linux C<inotify>
103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner	113	interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative	114	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
105	timers (C<ev_timer>), absolute timers with customised rescheduling	115	timers (C<ev_timer>), absolute timers with customised rescheduling
106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status	116	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
107	change events (C<ev_child>), and event watchers dealing with the event	117	change events (C<ev_child>), and event watchers dealing with the event
108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and	118	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
…		…
149	When libev detects a usage error such as a negative timer interval, then	159	When libev detects a usage error such as a negative timer interval, then
150	it will print a diagnostic message and abort (via the C<assert> mechanism,	160	it will print a diagnostic message and abort (via the C<assert> mechanism,
151	so C<NDEBUG> will disable this checking): these are programming errors in	161	so C<NDEBUG> will disable this checking): these are programming errors in
152	the libev caller and need to be fixed there.	162	the libev caller and need to be fixed there.
153		163
		164	Via the C<EV_FREQUENT> macro you can compile in and/or enable extensive
		165	consistency checking code inside libev that can be used to check for
		166	internal inconsistencies, suually caused by application bugs.
		167
154	Libev also has a few internal error-checking C<assert>ions, and also has	168	Libev also has a few internal error-checking C<assert>ions. These do not
155	extensive consistency checking code. These do not trigger under normal
156	circumstances, as they indicate either a bug in libev or worse.	169	trigger under normal circumstances, as they indicate either a bug in libev
		170	or worse.
157		171
158		172
159	=head1 GLOBAL FUNCTIONS	173	=head1 GLOBAL FUNCTIONS
160		174
161	These functions can be called anytime, even before initialising the	175	These functions can be called anytime, even before initialising the
…		…
165		179
166	=item ev_tstamp ev_time ()	180	=item ev_tstamp ev_time ()
167		181
168	Returns the current time as libev would use it. Please note that the	182	Returns the current time as libev would use it. Please note that the
169	C<ev_now> function is usually faster and also often returns the timestamp	183	C<ev_now> function is usually faster and also often returns the timestamp
170	you actually want to know. Also interetsing is the combination of	184	you actually want to know. Also interesting is the combination of
171	C<ev_update_now> and C<ev_now>.	185	C<ev_now_update> and C<ev_now>.
172		186
173	=item ev_sleep (ev_tstamp interval)	187	=item ev_sleep (ev_tstamp interval)
174		188
175	Sleep for the given interval: The current thread will be blocked until	189	Sleep for the given interval: The current thread will be blocked
176	either it is interrupted or the given time interval has passed. Basically	190	until either it is interrupted or the given time interval has
		191	passed (approximately - it might return a bit earlier even if not
		192	interrupted). Returns immediately if C<< interval <= 0 >>.
		193
177	this is a sub-second-resolution C<sleep ()>.	194	Basically this is a sub-second-resolution C<sleep ()>.
		195
		196	The range of the C<interval> is limited - libev only guarantees to work
		197	with sleep times of up to one day (C<< interval <= 86400 >>).
178		198
179	=item int ev_version_major ()	199	=item int ev_version_major ()
180		200
181	=item int ev_version_minor ()	201	=item int ev_version_minor ()
182		202
…		…
193	as this indicates an incompatible change. Minor versions are usually	213	as this indicates an incompatible change. Minor versions are usually
194	compatible to older versions, so a larger minor version alone is usually	214	compatible to older versions, so a larger minor version alone is usually
195	not a problem.	215	not a problem.
196		216
197	Example: Make sure we haven't accidentally been linked against the wrong	217	Example: Make sure we haven't accidentally been linked against the wrong
198	version (note, however, that this will not detect ABI mismatches :).	218	version (note, however, that this will not detect other ABI mismatches,
		219	such as LFS or reentrancy).
199		220
200	assert (("libev version mismatch",	221	assert (("libev version mismatch",
201	ev_version_major () == EV_VERSION_MAJOR	222	ev_version_major () == EV_VERSION_MAJOR
202	&& ev_version_minor () >= EV_VERSION_MINOR));	223	&& ev_version_minor () >= EV_VERSION_MINOR));
203		224
…		…
225	probe for if you specify no backends explicitly.	246	probe for if you specify no backends explicitly.
226		247
227	=item unsigned int ev_embeddable_backends ()	248	=item unsigned int ev_embeddable_backends ()
228		249
229	Returns the set of backends that are embeddable in other event loops. This	250	Returns the set of backends that are embeddable in other event loops. This
230	is the theoretical, all-platform, value. To find which backends	251	value is platform-specific but can include backends not available on the
231	might be supported on the current system, you would need to look at	252	current system. To find which embeddable backends might be supported on
232	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	253	the current system, you would need to look at C<ev_embeddable_backends ()
233	recommended ones.	254	& ev_supported_backends ()>, likewise for recommended ones.
234		255
235	See the description of C<ev_embed> watchers for more info.	256	See the description of C<ev_embed> watchers for more info.
236		257
237	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	258	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
238		259
239	Sets the allocation function to use (the prototype is similar - the	260	Sets the allocation function to use (the prototype is similar - the
240	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
241	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
242	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
…		…
248		269
249	You could override this function in high-availability programs to, say,	270	You could override this function in high-availability programs to, say,
250	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,
251	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.
252		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
253	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
254	retries (example requires a standards-compliant C<realloc>).	289	retries.
255		290
256	static void *	291	static void *
257	persistent_realloc (void *ptr, size_t size)	292	persistent_realloc (void *ptr, size_t size)
258	{	293	{
		294	if (!size)
		295	{
		296	free (ptr);
		297	return 0;
		298	}
		299
259	for (;;)	300	for (;;)
260	{	301	{
261	void *newptr = realloc (ptr, size);	302	void *newptr = realloc (ptr, size);
262		303
263	if (newptr)	304	if (newptr)
…		…
268	}	309	}
269		310
270	...	311	...
271	ev_set_allocator (persistent_realloc);	312	ev_set_allocator (persistent_realloc);
272		313
273	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	314	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
274		315
275	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
276	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
277	indicating the system call or subsystem causing the problem. If this	318	indicating the system call or subsystem causing the problem. If this
278	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
…		…
290	}	331	}
291		332
292	...	333	...
293	ev_set_syserr_cb (fatal_error);	334	ev_set_syserr_cb (fatal_error);
294		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
295	=back	349	=back
296		350
297	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	351	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
298		352
299	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
300	I<not> optional in this case unless libev 3 compatibility is disabled, as	354	I<not> optional in this case unless libev 3 compatibility is disabled, as
301	libev 3 had an C<ev_loop> function colliding with the struct name).	355	libev 3 had an C<ev_loop> function colliding with the struct name).
302		356
303	The library knows two types of such loops, the I<default> loop, which	357	The library knows two types of such loops, the I<default> loop, which
304	supports signals and child events, and dynamically created event loops	358	supports child process events, and dynamically created event loops which
305	which do not.	359	do not.
306		360
307	=over 4	361	=over 4
308		362
309	=item struct ev_loop *ev_default_loop (unsigned int flags)	363	=item struct ev_loop *ev_default_loop (unsigned int flags)
310		364
311	This will initialise the default event loop if it hasn't been initialised	365	This returns the "default" event loop object, which is what you should
312	yet and return it. If the default loop could not be initialised, returns	366	normally use when you just need "the event loop". Event loop objects and
313	false. If it already was initialised it simply returns it (and ignores the	367	the C<flags> parameter are described in more detail in the entry for
314	flags. If that is troubling you, check C<ev_backend ()> afterwards).	368	C<ev_loop_new>.
		369
		370	If the default loop is already initialised then this function simply
		371	returns it (and ignores the flags. If that is troubling you, check
		372	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		373	flags, which should almost always be C<0>, unless the caller is also the
		374	one calling C<ev_run> or otherwise qualifies as "the main program".
315		375
316	If you don't know what event loop to use, use the one returned from this	376	If you don't know what event loop to use, use the one returned from this
317	function.	377	function (or via the C<EV_DEFAULT> macro).
318		378
319	Note that this function is I<not> thread-safe, so if you want to use it	379	Note that this function is I<not> thread-safe, so if you want to use it
320	from multiple threads, you have to lock (note also that this is unlikely,	380	from multiple threads, you have to employ some kind of mutex (note also
321	as loops cannot be shared easily between threads anyway).	381	that this case is unlikely, as loops cannot be shared easily between
		382	threads anyway).
322		383
323	The default loop is the only loop that can handle C<ev_signal> and	384	The default loop is the only loop that can handle C<ev_child> watchers,
324	C<ev_child> watchers, and to do this, it always registers a handler	385	and to do this, it always registers a handler for C<SIGCHLD>. If this is
325	for C<SIGCHLD>. If this is a problem for your application you can either	386	a problem for your application you can either create a dynamic loop with
326	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	387	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
327	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	388	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
328	C<ev_default_init>.	389
		390	Example: This is the most typical usage.
		391
		392	if (!ev_default_loop (0))
		393	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		394
		395	Example: Restrict libev to the select and poll backends, and do not allow
		396	environment settings to be taken into account:
		397
		398	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		399
		400	=item struct ev_loop *ev_loop_new (unsigned int flags)
		401
		402	This will create and initialise a new event loop object. If the loop
		403	could not be initialised, returns false.
		404
		405	This function is thread-safe, and one common way to use libev with
		406	threads is indeed to create one loop per thread, and using the default
		407	loop in the "main" or "initial" thread.
329		408
330	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
331	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>).
332		411
333	The following flags are supported:	412	The following flags are supported:
…		…
343		422
344	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
345	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
346	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	425	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
347	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
348	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
349	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).
350		431
351	=item C<EVFLAG_FORKCHECK>	432	=item C<EVFLAG_FORKCHECK>
352		433
353	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
354	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.
355		436
356	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,
357	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
358	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
359	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
360	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
361	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).
362		444
363	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
364	forget about forgetting to tell libev about forking) when you use this	446	forget about forgetting to tell libev about forking, although you still
365	flag.	447	have to ignore C<SIGPIPE>) when you use this flag.
366		448
367	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>
368	environment variable.	450	environment variable.
369		451
370	=item C<EVFLAG_NOINOTIFY>	452	=item C<EVFLAG_NOINOTIFY>
371		453
372	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
373	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
374	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
375	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.
376		458
377	=item C<EVFLAG_SIGNALFD>	459	=item C<EVFLAG_SIGNALFD>
378		460
379	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
380	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
381	delivers signals synchronously, which makes it both faster and might make	463	delivers signals synchronously, which makes it both faster and might make
382	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
383	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
384	threads that are not interested in handling them.	466	threads that are not interested in handling them.
385		467
386	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
387	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
388	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.
389		495
390	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	496	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
391		497
392	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
393	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,
…		…
418	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
419	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	525	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
420		526
421	=item C<EVBACKEND_EPOLL> (value 4, Linux)	527	=item C<EVBACKEND_EPOLL> (value 4, Linux)
422		528
423	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
424	kernels).	530	kernels).
425		531
426	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
427	but it scales phenomenally better. While poll and select usually scale	533	it scales phenomenally better. While poll and select usually scale like
428	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
429	epoll scales either O(1) or O(active_fds).	535	fd), epoll scales either O(1) or O(active_fds).
430		536
431	The epoll mechanism deserves honorable mention as the most misdesigned	537	The epoll mechanism deserves honorable mention as the most misdesigned
432	of the more advanced event mechanisms: mere annoyances include silently	538	of the more advanced event mechanisms: mere annoyances include silently
433	dropping file descriptors, requiring a system call per change per file	539	dropping file descriptors, requiring a system call per change per file
434	descriptor (and unnecessary guessing of parameters), problems with dup and	540	descriptor (and unnecessary guessing of parameters), problems with dup,
		541	returning before the timeout value, resulting in additional iterations
		542	(and only giving 5ms accuracy while select on the same platform gives
435	so on. The biggest issue is fork races, however - if a program forks then	543	0.1ms) and so on. The biggest issue is fork races, however - if a program
436	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
437	take considerable time (one syscall per file descriptor) and is of course	545	set, which can take considerable time (one syscall per file descriptor)
438	hard to detect.	546	and is of course hard to detect.
439		547
440	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	548	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
441	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
442	I<different> file descriptors (even already closed ones, so one cannot	550	totally I<different> file descriptors (even already closed ones, so
443	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
444	on SMP systems). Libev tries to counter these spurious notifications by	552	(especially on SMP systems). Libev tries to counter these spurious
445	employing an additional generation counter and comparing that against the	553	notifications by employing an additional generation counter and comparing
446	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
447	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
448	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...
449		564
450	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
451	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
452	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
453	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
…		…
465	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
466	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
467	the usage. So sad.	582	the usage. So sad.
468		583
469	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
470	all kernel versions tested so far.	585	a lot of kernel revisions, but probably(!) works in current versions.
471		586
472	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
473	C<EVBACKEND_POLL>.	588	C<EVBACKEND_POLL>.
474		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
475	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	634	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
476		635
477	Kqueue deserves special mention, as at the time of this writing, it	636	Kqueue deserves special mention, as at the time this backend was
478	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
479	with anything but sockets and pipes, except on Darwin, where of course	638	work reliably with anything but sockets and pipes, except on Darwin,
480	it's completely useless). Unlike epoll, however, whose brokenness	639	where of course it's completely useless). Unlike epoll, however, whose
481	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)
482	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
483	"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
484	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
485	system like NetBSD.	644	known-to-be-good (-enough) system like NetBSD.
486		645
487	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
488	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
489	the target platform). See C<ev_embed> watchers for more info.	648	the target platform). See C<ev_embed> watchers for more info.
490		649
491	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
492	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
493	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
494	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
495	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
496	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
497	cases	656	drops fds silently in similarly hard-to-detect cases.
498		657
499	This backend usually performs well under most conditions.	658	This backend usually performs well under most conditions.
500		659
501	While nominally embeddable in other event loops, this doesn't work	660	While nominally embeddable in other event loops, this doesn't work
502	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
…		…
516	and is not embeddable, which would limit the usefulness of this backend	675	and is not embeddable, which would limit the usefulness of this backend
517	immensely.	676	immensely.
518		677
519	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	678	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
520		679
521	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
522	it's really slow, but it still scales very well (O(active_fds)).	681	Solaris, it's really slow, but it still scales very well (O(active_fds)).
523
524	Please note that Solaris event ports can deliver a lot of spurious
525	notifications, so you need to use non-blocking I/O or other means to avoid
526	blocking when no data (or space) is available.
527		682
528	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
529	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
530	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	685	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
531	might perform better.	686	might perform better.
532		687
533	On the positive side, with the exception of the spurious readiness	688	On the positive side, this backend actually performed fully to
534	notifications, this backend actually performed fully to specification
535	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
536	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.
537		702
538	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
539	C<EVBACKEND_POLL>.	704	C<EVBACKEND_POLL>.
540		705
541	=item C<EVBACKEND_ALL>	706	=item C<EVBACKEND_ALL>
542		707
543	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
544	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
545	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	710	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
546		711
547	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).
548		721
549	=back	722	=back
550		723
551	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,
552	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
553	here). If none are specified, all backends in C<ev_recommended_backends	726	here). If none are specified, all backends in C<ev_recommended_backends
554	()> will be tried.	727	()> will be tried.
555		728
556	Example: This is the most typical usage.
557
558	if (!ev_default_loop (0))
559	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
560
561	Example: Restrict libev to the select and poll backends, and do not allow
562	environment settings to be taken into account:
563
564	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
565
566	Example: Use whatever libev has to offer, but make sure that kqueue is
567	used if available (warning, breaks stuff, best use only with your own
568	private event loop and only if you know the OS supports your types of
569	fds):
570
571	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
572
573	=item struct ev_loop *ev_loop_new (unsigned int flags)
574
575	Similar to C<ev_default_loop>, but always creates a new event loop that is
576	always distinct from the default loop.
577
578	Note that this function I<is> thread-safe, and one common way to use
579	libev with threads is indeed to create one loop per thread, and using the
580	default loop in the "main" or "initial" thread.
581
582	Example: Try to create a event loop that uses epoll and nothing else.	729	Example: Try to create a event loop that uses epoll and nothing else.
583		730
584	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	731	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
585	if (!epoller)	732	if (!epoller)
586	fatal ("no epoll found here, maybe it hides under your chair");	733	fatal ("no epoll found here, maybe it hides under your chair");
587		734
		735	Example: Use whatever libev has to offer, but make sure that kqueue is
		736	used if available.
		737
		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);
		745
588	=item ev_default_destroy ()	746	=item ev_loop_destroy (loop)
589		747
590	Destroys the default loop (frees all memory and kernel state etc.). None	748	Destroys an event loop object (frees all memory and kernel state
591	of the active event watchers will be stopped in the normal sense, so	749	etc.). None of the active event watchers will be stopped in the normal
592	e.g. C<ev_is_active> might still return true. It is your responsibility to	750	sense, so e.g. C<ev_is_active> might still return true. It is your
593	either stop all watchers cleanly yourself I<before> calling this function,	751	responsibility to either stop all watchers cleanly yourself I<before>
594	or cope with the fact afterwards (which is usually the easiest thing, you	752	calling this function, or cope with the fact afterwards (which is usually
595	can just ignore the watchers and/or C<free ()> them for example).	753	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		754	for example).
596		755
597	Note that certain global state, such as signal state (and installed signal	756	Note that certain global state, such as signal state (and installed signal
598	handlers), will not be freed by this function, and related watchers (such	757	handlers), will not be freed by this function, and related watchers (such
599	as signal and child watchers) would need to be stopped manually.	758	as signal and child watchers) would need to be stopped manually.
600		759
601	In general it is not advisable to call this function except in the	760	This function is normally used on loop objects allocated by
602	rare occasion where you really need to free e.g. the signal handling	761	C<ev_loop_new>, but it can also be used on the default loop returned by
		762	C<ev_default_loop>, in which case it is not thread-safe.
		763
		764	Note that it is not advisable to call this function on the default loop
		765	except in the rare occasion where you really need to free its resources.
603	pipe fds. If you need dynamically allocated loops it is better to use	766	If you need dynamically allocated loops it is better to use C<ev_loop_new>
604	C<ev_loop_new> and C<ev_loop_destroy>.	767	and C<ev_loop_destroy>.
605		768
606	=item ev_loop_destroy (loop)	769	=item ev_loop_fork (loop)
607
608	Like C<ev_default_destroy>, but destroys an event loop created by an
609	earlier call to C<ev_loop_new>.
610
611	=item ev_default_fork ()
612		770
613	This function sets a flag that causes subsequent C<ev_run> iterations	771	This function sets a flag that causes subsequent C<ev_run> iterations
614	to reinitialise the kernel state for backends that have one. Despite the	772	to reinitialise the kernel state for backends that have one. Despite
615	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
616	the child process (or both child and parent, but that again makes little	774	watchers (except inside an C<ev_prepare> callback), but it makes most
617	sense). You I<must> call it in the child before using any of the libev	775	sense after forking, in the child process. You I<must> call it (or use
618	functions, and it will only take effect at the next C<ev_run> iteration.	776	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
619		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
620	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
621	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
622	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	783	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
623	during fork.	784	during fork.
624		785
625	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
…		…
628	call it at all (in fact, C<epoll> is so badly broken that it makes a	789	call it at all (in fact, C<epoll> is so badly broken that it makes a
629	difference, but libev will usually detect this case on its own and do a	790	difference, but libev will usually detect this case on its own and do a
630	costly reset of the backend).	791	costly reset of the backend).
631		792
632	The function itself is quite fast and it's usually not a problem to call	793	The function itself is quite fast and it's usually not a problem to call
633	it just in case after a fork. To make this easy, the function will fit in	794	it just in case after a fork.
634	quite nicely into a call to C<pthread_atfork>:
635		795
		796	Example: Automate calling C<ev_loop_fork> on the default loop when
		797	using pthreads.
		798
		799	static void
		800	post_fork_child (void)
		801	{
		802	ev_loop_fork (EV_DEFAULT);
		803	}
		804
		805	...
636	pthread_atfork (0, 0, ev_default_fork);	806	pthread_atfork (0, 0, post_fork_child);
637
638	=item ev_loop_fork (loop)
639
640	Like C<ev_default_fork>, but acts on an event loop created by
641	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
642	after fork that you want to re-use in the child, and how you keep track of
643	them is entirely your own problem.
644		807
645	=item int ev_is_default_loop (loop)	808	=item int ev_is_default_loop (loop)
646		809
647	Returns true when the given loop is, in fact, the default loop, and false	810	Returns true when the given loop is, in fact, the default loop, and false
648	otherwise.	811	otherwise.
…		…
659	prepare and check phases.	822	prepare and check phases.
660		823
661	=item unsigned int ev_depth (loop)	824	=item unsigned int ev_depth (loop)
662		825
663	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
664	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.
665		828
666	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
667	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),
668	in which case it is higher.	831	in which case it is higher.
669		832
670	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	833	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
671	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
672	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.
673		837
674	=item unsigned int ev_backend (loop)	838	=item unsigned int ev_backend (loop)
675		839
676	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
677	use.	841	use.
…		…
692		856
693	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
694	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
695	the current time is a good idea.	859	the current time is a good idea.
696		860
697	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.
698		862
699	=item ev_suspend (loop)	863	=item ev_suspend (loop)
700		864
701	=item ev_resume (loop)	865	=item ev_resume (loop)
702		866
…		…
720	without a previous call to C<ev_suspend>.	884	without a previous call to C<ev_suspend>.
721		885
722	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
723	event loop time (see C<ev_now_update>).	887	event loop time (see C<ev_now_update>).
724		888
725	=item ev_run (loop, int flags)	889	=item bool ev_run (loop, int flags)
726		890
727	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
728	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
729	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
730	the watcher callbacks, an then repeat the whole process indefinitely: This	894	the watcher callbacks, and then repeat the whole process indefinitely: This
731	is why event loops are called I<loops>.	895	is why event loops are called I<loops>.
732		896
733	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
734	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
735	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").
736		904
737	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
738	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
739	finished (especially in interactive programs), but having a program	907	finished (especially in interactive programs), but having a program
740	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
741	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
742	beauty.	910	beauty.
743		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
744	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
745	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
746	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
747	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
748	events while doing lengthy calculations, to keep the program responsive.	921	events while doing lengthy calculations, to keep the program responsive.
…		…
757	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
758	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
759	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
760	usually a better approach for this kind of thing.	933	usually a better approach for this kind of thing.
761		934
762	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):
763		938
764	- Increment loop depth.	939	- Increment loop depth.
765	- Reset the ev_break status.	940	- Reset the ev_break status.
766	- Before the first iteration, call any pending watchers.	941	- Before the first iteration, call any pending watchers.
767	LOOP:	942	LOOP:
…		…
784	- Queue all expired timers.	959	- Queue all expired timers.
785	- Queue all expired periodics.	960	- Queue all expired periodics.
786	- Queue all idle watchers with priority higher than that of pending events.	961	- Queue all idle watchers with priority higher than that of pending events.
787	- Queue all check watchers.	962	- Queue all check watchers.
788	- Call all queued watchers in reverse order (i.e. check watchers first).	963	- Call all queued watchers in reverse order (i.e. check watchers first).
789	Signals and child watchers are implemented as I/O watchers, and will	964	Signals, async and child watchers are implemented as I/O watchers, and
790	be handled here by queueing them when their watcher gets executed.	965	will be handled here by queueing them when their watcher gets executed.
791	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT	966	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
792	were used, or there are no active watchers, goto FINISH, otherwise	967	were used, or there are no active watchers, goto FINISH, otherwise
793	continue with step LOOP.	968	continue with step LOOP.
794	FINISH:	969	FINISH:
795	- Reset the ev_break status iff it was EVBREAK_ONE.	970	- Reset the ev_break status iff it was EVBREAK_ONE.
…		…
800	anymore.	975	anymore.
801		976
802	... queue jobs here, make sure they register event watchers as long	977	... queue jobs here, make sure they register event watchers as long
803	... 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..)
804	ev_run (my_loop, 0);	979	ev_run (my_loop, 0);
805	... jobs done or somebody called unloop. yeah!	980	... jobs done or somebody called break. yeah!
806		981
807	=item ev_break (loop, how)	982	=item ev_break (loop, how)
808		983
809	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
810	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
811	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
812	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.
813		988
814	This "unloop state" will be cleared when entering C<ev_run> again.	989	This "break state" will be cleared on the next call to C<ev_run>.
815		990
816	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	991	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		992	which case it will have no effect.
817		993
818	=item ev_ref (loop)	994	=item ev_ref (loop)
819		995
820	=item ev_unref (loop)	996	=item ev_unref (loop)
821		997
…		…
842	running when nothing else is active.	1018	running when nothing else is active.
843		1019
844	ev_signal exitsig;	1020	ev_signal exitsig;
845	ev_signal_init (&exitsig, sig_cb, SIGINT);	1021	ev_signal_init (&exitsig, sig_cb, SIGINT);
846	ev_signal_start (loop, &exitsig);	1022	ev_signal_start (loop, &exitsig);
847	evf_unref (loop);	1023	ev_unref (loop);
848		1024
849	Example: For some weird reason, unregister the above signal handler again.	1025	Example: For some weird reason, unregister the above signal handler again.
850		1026
851	ev_ref (loop);	1027	ev_ref (loop);
852	ev_signal_stop (loop, &exitsig);	1028	ev_signal_stop (loop, &exitsig);
…		…
872	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.
873		1049
874	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
875	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,
876	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
877	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
878	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
879	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
880	once per this interval, on average.	1056	once per this interval, on average (as long as the host time resolution is
		1057	good enough).
881		1058
882	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
883	to spend more time collecting timeouts, at the expense of increased	1060	to spend more time collecting timeouts, at the expense of increased
884	latency/jitter/inexactness (the watcher callback will be called	1061	latency/jitter/inexactness (the watcher callback will be called
885	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
…		…
931	invoke the actual watchers inside another context (another thread etc.).	1108	invoke the actual watchers inside another context (another thread etc.).
932		1109
933	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
934	callback.	1111	callback.
935		1112
936	=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 ())
937		1114
938	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
939	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
940	each call to a libev function.	1117	each call to a libev function.
941		1118
942	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
943	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
944	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
945	I<release> and I<acquire> callbacks on the loop.	1122	I<release> and I<acquire> callbacks on the loop.
946		1123
947	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
948	suspended waiting for new events, and C<acquire> is called just	1125	suspended waiting for new events, and C<acquire> is called just
949	afterwards.	1126	afterwards.
…		…
964	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
965	document.	1142	document.
966		1143
967	=item ev_set_userdata (loop, void *data)	1144	=item ev_set_userdata (loop, void *data)
968		1145
969	=item ev_userdata (loop)	1146	=item void *ev_userdata (loop)
970		1147
971	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
972	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
973	C<0.>	1150	C<0>.
974		1151
975	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,
976	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
977	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
978	any other purpose as well.	1155	any other purpose as well.
…		…
1041	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
1042	*) >>), 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
1043	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.	1220	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
1044		1221
1045	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
1046	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
1047	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.
1048		1226
1049	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
1050	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
1051	third argument.	1229	third argument.
1052		1230
…		…
1089		1267
1090	=item C<EV_PREPARE>	1268	=item C<EV_PREPARE>
1091		1269
1092	=item C<EV_CHECK>	1270	=item C<EV_CHECK>
1093		1271
1094	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
1095	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)
1096	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
1097	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
1098	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
1099	(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
1100	C<ev_run> from blocking).	1283	blocking).
1101		1284
1102	=item C<EV_EMBED>	1285	=item C<EV_EMBED>
1103		1286
1104	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.
1105		1288
1106	=item C<EV_FORK>	1289	=item C<EV_FORK>
1107		1290
1108	The event loop has been resumed in the child process after fork (see	1291	The event loop has been resumed in the child process after fork (see
1109	C<ev_fork>).	1292	C<ev_fork>).
		1293
		1294	=item C<EV_CLEANUP>
		1295
		1296	The event loop is about to be destroyed (see C<ev_cleanup>).
1110		1297
1111	=item C<EV_ASYNC>	1298	=item C<EV_ASYNC>
1112		1299
1113	The given async watcher has been asynchronously notified (see C<ev_async>).	1300	The given async watcher has been asynchronously notified (see C<ev_async>).
1114		1301
…		…
1136	programs, though, as the fd could already be closed and reused for another	1323	programs, though, as the fd could already be closed and reused for another
1137	thing, so beware.	1324	thing, so beware.
1138		1325
1139	=back	1326	=back
1140		1327
1141	=head2 WATCHER STATES
1142
1143	There are various watcher states mentioned throughout this manual -
1144	active, pending and so on. In this section these states and the rules to
1145	transition between them will be described in more detail - and while these
1146	rules might look complicated, they usually do "the right thing".
1147
1148	=over 4
1149
1150	=item initialiased
1151
1152	Before a watcher can be registered with the event looop it has to be
1153	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1154	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1155
1156	In this state it is simply some block of memory that is suitable for use
1157	in an event loop. It can be moved around, freed, reused etc. at will.
1158
1159	=item started/running/active
1160
1161	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1162	property of the event loop, and is actively waiting for events. While in
1163	this state it cannot be accessed (except in a few documented ways), moved,
1164	freed or anything else - the only legal thing is to keep a pointer to it,
1165	and call libev functions on it that are documented to work on active watchers.
1166
1167	=item pending
1168
1169	If a watcher is active and libev determines that an event it is interested
1170	in has occurred (such as a timer expiring), it will become pending. It will
1171	stay in this pending state until either it is stopped or its callback is
1172	about to be invoked, so it is not normally pending inside the watcher
1173	callback.
1174
1175	The watcher might or might not be active while it is pending (for example,
1176	an expired non-repeating timer can be pending but no longer active). If it
1177	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
1178	but it is still property of the event loop at this time, so cannot be
1179	moved, freed or reused. And if it is active the rules described in the
1180	previous item still apply.
1181
1182	It is also possible to feed an event on a watcher that is not active (e.g.
1183	via C<ev_feed_event>), in which case it becomes pending without being
1184	active.
1185
1186	=item stopped
1187
1188	A watcher can be stopped implicitly by libev (in which case it might still
1189	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
1190	latter will clear any pending state the watcher might be in, regardless
1191	of whether it was active or not, so stopping a watcher explicitly before
1192	freeing it is often a good idea.
1193
1194	While stopped (and not pending) the watcher is essentially in the
1195	initialised state, that is it can be reused, moved, modified in any way
1196	you wish.
1197
1198	=back
1199
1200	=head2 GENERIC WATCHER FUNCTIONS	1328	=head2 GENERIC WATCHER FUNCTIONS
1201		1329
1202	=over 4	1330	=over 4
1203		1331
1204	=item C<ev_init> (ev_TYPE *watcher, callback)	1332	=item C<ev_init> (ev_TYPE *watcher, callback)
…		…
1268		1396
1269	=item bool ev_is_active (ev_TYPE *watcher)	1397	=item bool ev_is_active (ev_TYPE *watcher)
1270		1398
1271	Returns a true value iff the watcher is active (i.e. it has been started	1399	Returns a true value iff the watcher is active (i.e. it has been started
1272	and not yet been stopped). As long as a watcher is active you must not modify	1400	and not yet been stopped). As long as a watcher is active you must not modify
1273	it.	1401	it unless documented otherwise.
		1402
		1403	Obviously, it is safe to call this on an active watcher, or actually any
		1404	watcher that is initialised.
1274		1405
1275	=item bool ev_is_pending (ev_TYPE *watcher)	1406	=item bool ev_is_pending (ev_TYPE *watcher)
1276		1407
1277	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1408	Returns a true value iff the watcher is pending, (i.e. it has outstanding
1278	events but its callback has not yet been invoked). As long as a watcher	1409	events but its callback has not yet been invoked). As long as a watcher
1279	is pending (but not active) you must not call an init function on it (but	1410	is pending (but not active) you must not call an init function on it (but
1280	C<ev_TYPE_set> is safe), you must not change its priority, and you must	1411	C<ev_TYPE_set> is safe), you must not change its priority, and you must
1281	make sure the watcher is available to libev (e.g. you cannot C<free ()>	1412	make sure the watcher is available to libev (e.g. you cannot C<free ()>
1282	it).	1413	it).
1283		1414
		1415	It is safe to call this on any watcher in any state as long as it is
		1416	initialised.
		1417
1284	=item callback ev_cb (ev_TYPE *watcher)	1418	=item callback ev_cb (ev_TYPE *watcher)
1285		1419
1286	Returns the callback currently set on the watcher.	1420	Returns the callback currently set on the watcher.
1287		1421
1288	=item ev_cb_set (ev_TYPE *watcher, callback)	1422	=item ev_set_cb (ev_TYPE *watcher, callback)
1289		1423
1290	Change the callback. You can change the callback at virtually any time	1424	Change the callback. You can change the callback at virtually any time
1291	(modulo threads).	1425	(modulo threads).
1292		1426
1293	=item ev_set_priority (ev_TYPE *watcher, int priority)	1427	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1301	from being executed (except for C<ev_idle> watchers).	1435	from being executed (except for C<ev_idle> watchers).
1302		1436
1303	If you need to suppress invocation when higher priority events are pending	1437	If you need to suppress invocation when higher priority events are pending
1304	you need to look at C<ev_idle> watchers, which provide this functionality.	1438	you need to look at C<ev_idle> watchers, which provide this functionality.
1305		1439
1306	You I<must not> change the priority of a watcher as long as it is active or	1440	You I<must not> change the priority of a watcher as long as it is active
1307	pending.	1441	or pending. Reading the priority with C<ev_priority> is fine in any state.
1308		1442
1309	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1443	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1310	fine, as long as you do not mind that the priority value you query might	1444	fine, as long as you do not mind that the priority value you query might
1311	or might not have been clamped to the valid range.	1445	or might not have been clamped to the valid range.
1312		1446
1313	The default priority used by watchers when no priority has been set is	1447	The default priority used by watchers when no priority has been set is
1314	always C<0>, which is supposed to not be too high and not be too low :).	1448	always C<0>, which is supposed to not be too high and not be too low :).
1315		1449
1316	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1450	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1317	priorities.	1451	priorities.
1318		1452
1319	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1453	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1320		1454
1321	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1455	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
…		…
1334		1468
1335	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)	1469	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
1336		1470
1337	Feeds the given event set into the event loop, as if the specified event	1471	Feeds the given event set into the event loop, as if the specified event
1338	had happened for the specified watcher (which must be a pointer to an	1472	had happened for the specified watcher (which must be a pointer to an
1339	initialised but not necessarily started event watcher). Obviously you must	1473	initialised but not necessarily started event watcher, though it can be
1340	not free the watcher as long as it has pending events.	1474	active). Obviously you must not free the watcher as long as it has pending
		1475	events.
1341		1476
1342	Stopping the watcher, letting libev invoke it, or calling	1477	Stopping the watcher, letting libev invoke it, or calling
1343	C<ev_clear_pending> will clear the pending event, even if the watcher was	1478	C<ev_clear_pending> will clear the pending event, even if the watcher was
1344	not started in the first place.	1479	not started in the first place.
1345		1480
1346	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1481	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1347	functions that do not need a watcher.	1482	functions that do not need a watcher.
1348		1483
1349	=back	1484	=back
1350		1485
		1486	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1487	OWN COMPOSITE WATCHERS> idioms.
1351		1488
1352	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1489	=head2 WATCHER STATES
1353		1490
1354	Each watcher has, by default, a member C<void *data> that you can change	1491	There are various watcher states mentioned throughout this manual -
1355	and read at any time: libev will completely ignore it. This can be used	1492	active, pending and so on. In this section these states and the rules to
1356	to associate arbitrary data with your watcher. If you need more data and	1493	transition between them will be described in more detail - and while these
1357	don't want to allocate memory and store a pointer to it in that data	1494	rules might look complicated, they usually do "the right thing".
1358	member, you can also "subclass" the watcher type and provide your own
1359	data:
1360		1495
1361	struct my_io	1496	=over 4
1362	{
1363	ev_io io;
1364	int otherfd;
1365	void *somedata;
1366	struct whatever *mostinteresting;
1367	};
1368		1497
1369	...	1498	=item initialised
1370	struct my_io w;
1371	ev_io_init (&w.io, my_cb, fd, EV_READ);
1372		1499
1373	And since your callback will be called with a pointer to the watcher, you	1500	Before a watcher can be registered with the event loop it has to be
1374	can cast it back to your own type:	1501	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1502	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1375		1503
1376	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)	1504	In this state it is simply some block of memory that is suitable for
1377	{	1505	use in an event loop. It can be moved around, freed, reused etc. at
1378	struct my_io *w = (struct my_io *)w_;	1506	will - as long as you either keep the memory contents intact, or call
1379	...	1507	C<ev_TYPE_init> again.
1380	}
1381		1508
1382	More interesting and less C-conformant ways of casting your callback type	1509	=item started/running/active
1383	instead have been omitted.
1384		1510
1385	Another common scenario is to use some data structure with multiple	1511	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1386	embedded watchers:	1512	property of the event loop, and is actively waiting for events. While in
		1513	this state it cannot be accessed (except in a few documented ways, such as
		1514	stoping it), moved, freed or anything else - the only legal thing is to
		1515	keep a pointer to it, and call libev functions on it that are documented
		1516	to work on active watchers.
1387		1517
1388	struct my_biggy	1518	As a rule of thumb, before accessing a member or calling any function on
1389	{	1519	a watcher, it should be stopped (or freshly initialised). If that is not
1390	int some_data;	1520	convenient, you can check the documentation for that function or member to
1391	ev_timer t1;	1521	see if it is safe to use on an active watcher.
1392	ev_timer t2;
1393	}
1394		1522
1395	In this case getting the pointer to C<my_biggy> is a bit more	1523	=item pending
1396	complicated: Either you store the address of your C<my_biggy> struct
1397	in the C<data> member of the watcher (for woozies), or you need to use
1398	some pointer arithmetic using C<offsetof> inside your watchers (for real
1399	programmers):
1400		1524
1401	#include <stddef.h>	1525	If a watcher is active and libev determines that an event it is interested
		1526	in has occurred (such as a timer expiring), it will become pending. It
		1527	will stay in this pending state until either it is explicitly stopped or
		1528	its callback is about to be invoked, so it is not normally pending inside
		1529	the watcher callback.
1402		1530
1403	static void	1531	Generally, the watcher might or might not be active while it is pending
1404	t1_cb (EV_P_ ev_timer *w, int revents)	1532	(for example, an expired non-repeating timer can be pending but no longer
1405	{	1533	active). If it is pending but not active, it can be freely accessed (e.g.
1406	struct my_biggy big = (struct my_biggy *)	1534	by calling C<ev_TYPE_set>), but it is still property of the event loop at
1407	(((char *)w) - offsetof (struct my_biggy, t1));	1535	this time, so cannot be moved, freed or reused. And if it is active the
1408	}	1536	rules described in the previous item still apply.
1409		1537
1410	static void	1538	Explicitly stopping a watcher will also clear the pending state
1411	t2_cb (EV_P_ ev_timer *w, int revents)	1539	unconditionally, so it is safe to stop a watcher and then free it.
1412	{	1540
1413	struct my_biggy big = (struct my_biggy *)	1541	It is also possible to feed an event on a watcher that is not active (e.g.
1414	(((char *)w) - offsetof (struct my_biggy, t2));	1542	via C<ev_feed_event>), in which case it becomes pending without being
1415	}	1543	active.
		1544
		1545	=item stopped
		1546
		1547	A watcher can be stopped implicitly by libev (in which case it might still
		1548	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1549	latter will clear any pending state the watcher might be in, regardless
		1550	of whether it was active or not, so stopping a watcher explicitly before
		1551	freeing it is often a good idea.
		1552
		1553	While stopped (and not pending) the watcher is essentially in the
		1554	initialised state, that is, it can be reused, moved, modified in any way
		1555	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1556	it again).
		1557
		1558	=back
1416		1559
1417	=head2 WATCHER PRIORITY MODELS	1560	=head2 WATCHER PRIORITY MODELS
1418		1561
1419	Many event loops support I<watcher priorities>, which are usually small	1562	Many event loops support I<watcher priorities>, which are usually small
1420	integers that influence the ordering of event callback invocation	1563	integers that influence the ordering of event callback invocation
1421	between watchers in some way, all else being equal.	1564	between watchers in some way, all else being equal.
1422		1565
1423	In libev, Watcher priorities can be set using C<ev_set_priority>. See its	1566	In libev, watcher priorities can be set using C<ev_set_priority>. See its
1424	description for the more technical details such as the actual priority	1567	description for the more technical details such as the actual priority
1425	range.	1568	range.
1426		1569
1427	There are two common ways how these these priorities are being interpreted	1570	There are two common ways how these these priorities are being interpreted
1428	by event loops:	1571	by event loops:
…		…
1522		1665
1523	This section describes each watcher in detail, but will not repeat	1666	This section describes each watcher in detail, but will not repeat
1524	information given in the last section. Any initialisation/set macros,	1667	information given in the last section. Any initialisation/set macros,
1525	functions and members specific to the watcher type are explained.	1668	functions and members specific to the watcher type are explained.
1526		1669
1527	Members are additionally marked with either I<[read-only]>, meaning that,	1670	Most members are additionally marked with either I<[read-only]>, meaning
1528	while the watcher is active, you can look at the member and expect some	1671	that, while the watcher is active, you can look at the member and expect
1529	sensible content, but you must not modify it (you can modify it while the	1672	some sensible content, but you must not modify it (you can modify it while
1530	watcher is stopped to your hearts content), or I<[read-write]>, which	1673	the watcher is stopped to your hearts content), or I<[read-write]>, which
1531	means you can expect it to have some sensible content while the watcher	1674	means you can expect it to have some sensible content while the watcher is
1532	is active, but you can also modify it. Modifying it may not do something	1675	active, but you can also modify it (within the same thread as the event
		1676	loop, i.e. without creating data races). Modifying it may not do something
1533	sensible or take immediate effect (or do anything at all), but libev will	1677	sensible or take immediate effect (or do anything at all), but libev will
1534	not crash or malfunction in any way.	1678	not crash or malfunction in any way.
1535		1679
		1680	In any case, the documentation for each member will explain what the
		1681	effects are, and if there are any additional access restrictions.
1536		1682
1537	=head2 C<ev_io> - is this file descriptor readable or writable?	1683	=head2 C<ev_io> - is this file descriptor readable or writable?
1538		1684
1539	I/O watchers check whether a file descriptor is readable or writable	1685	I/O watchers check whether a file descriptor is readable or writable
1540	in each iteration of the event loop, or, more precisely, when reading	1686	in each iteration of the event loop, or, more precisely, when reading
…		…
1547	In general you can register as many read and/or write event watchers per	1693	In general you can register as many read and/or write event watchers per
1548	fd as you want (as long as you don't confuse yourself). Setting all file	1694	fd as you want (as long as you don't confuse yourself). Setting all file
1549	descriptors to non-blocking mode is also usually a good idea (but not	1695	descriptors to non-blocking mode is also usually a good idea (but not
1550	required if you know what you are doing).	1696	required if you know what you are doing).
1551		1697
1552	If you cannot use non-blocking mode, then force the use of a
1553	known-to-be-good backend (at the time of this writing, this includes only
1554	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1555	descriptors for which non-blocking operation makes no sense (such as
1556	files) - libev doesn't guarantee any specific behaviour in that case.
1557
1558	Another thing you have to watch out for is that it is quite easy to	1698	Another thing you have to watch out for is that it is quite easy to
1559	receive "spurious" readiness notifications, that is your callback might	1699	receive "spurious" readiness notifications, that is, your callback might
1560	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1700	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1561	because there is no data. Not only are some backends known to create a	1701	because there is no data. It is very easy to get into this situation even
1562	lot of those (for example Solaris ports), it is very easy to get into	1702	with a relatively standard program structure. Thus it is best to always
1563	this situation even with a relatively standard program structure. Thus	1703	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1564	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1565	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1704	preferable to a program hanging until some data arrives.
1566		1705
1567	If you cannot run the fd in non-blocking mode (for example you should	1706	If you cannot run the fd in non-blocking mode (for example you should
1568	not play around with an Xlib connection), then you have to separately	1707	not play around with an Xlib connection), then you have to separately
1569	re-test whether a file descriptor is really ready with a known-to-be good	1708	re-test whether a file descriptor is really ready with a known-to-be good
1570	interface such as poll (fortunately in our Xlib example, Xlib already	1709	interface such as poll (fortunately in the case of Xlib, it already does
1571	does this on its own, so its quite safe to use). Some people additionally	1710	this on its own, so its quite safe to use). Some people additionally
1572	use C<SIGALRM> and an interval timer, just to be sure you won't block	1711	use C<SIGALRM> and an interval timer, just to be sure you won't block
1573	indefinitely.	1712	indefinitely.
1574		1713
1575	But really, best use non-blocking mode.	1714	But really, best use non-blocking mode.
1576		1715
1577	=head3 The special problem of disappearing file descriptors	1716	=head3 The special problem of disappearing file descriptors
1578		1717
1579	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1718	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1580	descriptor (either due to calling C<close> explicitly or any other means,	1719	a file descriptor (either due to calling C<close> explicitly or any other
1581	such as C<dup2>). The reason is that you register interest in some file	1720	means, such as C<dup2>). The reason is that you register interest in some
1582	descriptor, but when it goes away, the operating system will silently drop	1721	file descriptor, but when it goes away, the operating system will silently
1583	this interest. If another file descriptor with the same number then is	1722	drop this interest. If another file descriptor with the same number then
1584	registered with libev, there is no efficient way to see that this is, in	1723	is registered with libev, there is no efficient way to see that this is,
1585	fact, a different file descriptor.	1724	in fact, a different file descriptor.
1586		1725
1587	To avoid having to explicitly tell libev about such cases, libev follows	1726	To avoid having to explicitly tell libev about such cases, libev follows
1588	the following policy: Each time C<ev_io_set> is being called, libev	1727	the following policy: Each time C<ev_io_set> is being called, libev
1589	will assume that this is potentially a new file descriptor, otherwise	1728	will assume that this is potentially a new file descriptor, otherwise
1590	it is assumed that the file descriptor stays the same. That means that	1729	it is assumed that the file descriptor stays the same. That means that
…		…
1604		1743
1605	There is no workaround possible except not registering events	1744	There is no workaround possible except not registering events
1606	for potentially C<dup ()>'ed file descriptors, or to resort to	1745	for potentially C<dup ()>'ed file descriptors, or to resort to
1607	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1746	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1608		1747
		1748	=head3 The special problem of files
		1749
		1750	Many people try to use C<select> (or libev) on file descriptors
		1751	representing files, and expect it to become ready when their program
		1752	doesn't block on disk accesses (which can take a long time on their own).
		1753
		1754	However, this cannot ever work in the "expected" way - you get a readiness
		1755	notification as soon as the kernel knows whether and how much data is
		1756	there, and in the case of open files, that's always the case, so you
		1757	always get a readiness notification instantly, and your read (or possibly
		1758	write) will still block on the disk I/O.
		1759
		1760	Another way to view it is that in the case of sockets, pipes, character
		1761	devices and so on, there is another party (the sender) that delivers data
		1762	on its own, but in the case of files, there is no such thing: the disk
		1763	will not send data on its own, simply because it doesn't know what you
		1764	wish to read - you would first have to request some data.
		1765
		1766	Since files are typically not-so-well supported by advanced notification
		1767	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1768	to files, even though you should not use it. The reason for this is
		1769	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1770	usually a tty, often a pipe, but also sometimes files or special devices
		1771	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1772	F</dev/urandom>), and even though the file might better be served with
		1773	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1774	it "just works" instead of freezing.
		1775
		1776	So avoid file descriptors pointing to files when you know it (e.g. use
		1777	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1778	when you rarely read from a file instead of from a socket, and want to
		1779	reuse the same code path.
		1780
1609	=head3 The special problem of fork	1781	=head3 The special problem of fork
1610		1782
1611	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1783	Some backends (epoll, kqueue, linuxaio, iouring) do not support C<fork ()>
1612	useless behaviour. Libev fully supports fork, but needs to be told about	1784	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1613	it in the child.	1785	to be told about it in the child if you want to continue to use it in the
		1786	child.
1614		1787
1615	To support fork in your programs, you either have to call	1788	To support fork in your child processes, you have to call C<ev_loop_fork
1616	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1789	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1617	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1790	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1618	C<EVBACKEND_POLL>.
1619		1791
1620	=head3 The special problem of SIGPIPE	1792	=head3 The special problem of SIGPIPE
1621		1793
1622	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1794	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1623	when writing to a pipe whose other end has been closed, your program gets	1795	when writing to a pipe whose other end has been closed, your program gets
…		…
1674	=item ev_io_init (ev_io *, callback, int fd, int events)	1846	=item ev_io_init (ev_io *, callback, int fd, int events)
1675		1847
1676	=item ev_io_set (ev_io *, int fd, int events)	1848	=item ev_io_set (ev_io *, int fd, int events)
1677		1849
1678	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1850	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1679	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or	1851	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE>, both
1680	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.	1852	C<EV_READ | EV_WRITE> or C<0>, to express the desire to receive the given
		1853	events.
1681		1854
1682	=item int fd [read-only]	1855	Note that setting the C<events> to C<0> and starting the watcher is
		1856	supported, but not specially optimized - if your program sometimes happens
		1857	to generate this combination this is fine, but if it is easy to avoid
		1858	starting an io watcher watching for no events you should do so.
1683		1859
1684	The file descriptor being watched.	1860	=item ev_io_modify (ev_io *, int events)
1685		1861
		1862	Similar to C<ev_io_set>, but only changes the requested events. Using this
		1863	might be faster with some backends, as libev can assume that the C<fd>
		1864	still refers to the same underlying file description, something it cannot
		1865	do when using C<ev_io_set>.
		1866
		1867	=item int fd [no-modify]
		1868
		1869	The file descriptor being watched. While it can be read at any time, you
		1870	must not modify this member even when the watcher is stopped - always use
		1871	C<ev_io_set> for that.
		1872
1686	=item int events [read-only]	1873	=item int events [no-modify]
1687		1874
1688	The events being watched.	1875	The set of events the fd is being watched for, among other flags. Remember
		1876	that this is a bit set - to test for C<EV_READ>, use C<< w->events &
		1877	EV_READ >>, and similarly for C<EV_WRITE>.
		1878
		1879	As with C<fd>, you must not modify this member even when the watcher is
		1880	stopped, always use C<ev_io_set> or C<ev_io_modify> for that.
1689		1881
1690	=back	1882	=back
1691		1883
1692	=head3 Examples	1884	=head3 Examples
1693		1885
…		…
1721	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1913	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1722	monotonic clock option helps a lot here).	1914	monotonic clock option helps a lot here).
1723		1915
1724	The callback is guaranteed to be invoked only I<after> its timeout has	1916	The callback is guaranteed to be invoked only I<after> its timeout has
1725	passed (not I<at>, so on systems with very low-resolution clocks this	1917	passed (not I<at>, so on systems with very low-resolution clocks this
1726	might introduce a small delay). If multiple timers become ready during the	1918	might introduce a small delay, see "the special problem of being too
		1919	early", below). If multiple timers become ready during the same loop
1727	same loop iteration then the ones with earlier time-out values are invoked	1920	iteration then the ones with earlier time-out values are invoked before
1728	before ones of the same priority with later time-out values (but this is	1921	ones of the same priority with later time-out values (but this is no
1729	no longer true when a callback calls C<ev_run> recursively).	1922	longer true when a callback calls C<ev_run> recursively).
1730		1923
1731	=head3 Be smart about timeouts	1924	=head3 Be smart about timeouts
1732		1925
1733	Many real-world problems involve some kind of timeout, usually for error	1926	Many real-world problems involve some kind of timeout, usually for error
1734	recovery. A typical example is an HTTP request - if the other side hangs,	1927	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1809		2002
1810	In this case, it would be more efficient to leave the C<ev_timer> alone,	2003	In this case, it would be more efficient to leave the C<ev_timer> alone,
1811	but remember the time of last activity, and check for a real timeout only	2004	but remember the time of last activity, and check for a real timeout only
1812	within the callback:	2005	within the callback:
1813		2006
		2007	ev_tstamp timeout = 60.;
1814	ev_tstamp last_activity; // time of last activity	2008	ev_tstamp last_activity; // time of last activity
		2009	ev_timer timer;
1815		2010
1816	static void	2011	static void
1817	callback (EV_P_ ev_timer *w, int revents)	2012	callback (EV_P_ ev_timer *w, int revents)
1818	{	2013	{
1819	ev_tstamp now = ev_now (EV_A);	2014	// calculate when the timeout would happen
1820	ev_tstamp timeout = last_activity + 60.;	2015	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1821		2016
1822	// if last_activity + 60. is older than now, we did time out	2017	// if negative, it means we the timeout already occurred
1823	if (timeout < now)	2018	if (after < 0.)
1824	{	2019	{
1825	// timeout occurred, take action	2020	// timeout occurred, take action
1826	}	2021	}
1827	else	2022	else
1828	{	2023	{
1829	// callback was invoked, but there was some activity, re-arm	2024	// callback was invoked, but there was some recent
1830	// the watcher to fire in last_activity + 60, which is	2025	// activity. simply restart the timer to time out
1831	// guaranteed to be in the future, so "again" is positive:	2026	// after "after" seconds, which is the earliest time
1832	w->repeat = timeout - now;	2027	// the timeout can occur.
		2028	ev_timer_set (w, after, 0.);
1833	ev_timer_again (EV_A_ w);	2029	ev_timer_start (EV_A_ w);
1834	}	2030	}
1835	}	2031	}
1836		2032
1837	To summarise the callback: first calculate the real timeout (defined	2033	To summarise the callback: first calculate in how many seconds the
1838	as "60 seconds after the last activity"), then check if that time has	2034	timeout will occur (by calculating the absolute time when it would occur,
1839	been reached, which means something I<did>, in fact, time out. Otherwise	2035	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1840	the callback was invoked too early (C<timeout> is in the future), so	2036	(EV_A)> from that).
1841	re-schedule the timer to fire at that future time, to see if maybe we have
1842	a timeout then.
1843		2037
1844	Note how C<ev_timer_again> is used, taking advantage of the	2038	If this value is negative, then we are already past the timeout, i.e. we
1845	C<ev_timer_again> optimisation when the timer is already running.	2039	timed out, and need to do whatever is needed in this case.
		2040
		2041	Otherwise, we now the earliest time at which the timeout would trigger,
		2042	and simply start the timer with this timeout value.
		2043
		2044	In other words, each time the callback is invoked it will check whether
		2045	the timeout occurred. If not, it will simply reschedule itself to check
		2046	again at the earliest time it could time out. Rinse. Repeat.
1846		2047
1847	This scheme causes more callback invocations (about one every 60 seconds	2048	This scheme causes more callback invocations (about one every 60 seconds
1848	minus half the average time between activity), but virtually no calls to	2049	minus half the average time between activity), but virtually no calls to
1849	libev to change the timeout.	2050	libev to change the timeout.
1850		2051
1851	To start the timer, simply initialise the watcher and set C<last_activity>	2052	To start the machinery, simply initialise the watcher and set
1852	to the current time (meaning we just have some activity :), then call the	2053	C<last_activity> to the current time (meaning there was some activity just
1853	callback, which will "do the right thing" and start the timer:	2054	now), then call the callback, which will "do the right thing" and start
		2055	the timer:
1854		2056
		2057	last_activity = ev_now (EV_A);
1855	ev_init (timer, callback);	2058	ev_init (&timer, callback);
1856	last_activity = ev_now (loop);	2059	callback (EV_A_ &timer, 0);
1857	callback (loop, timer, EV_TIMER);
1858		2060
1859	And when there is some activity, simply store the current time in	2061	When there is some activity, simply store the current time in
1860	C<last_activity>, no libev calls at all:	2062	C<last_activity>, no libev calls at all:
1861		2063
		2064	if (activity detected)
1862	last_activity = ev_now (loop);	2065	last_activity = ev_now (EV_A);
		2066
		2067	When your timeout value changes, then the timeout can be changed by simply
		2068	providing a new value, stopping the timer and calling the callback, which
		2069	will again do the right thing (for example, time out immediately :).
		2070
		2071	timeout = new_value;
		2072	ev_timer_stop (EV_A_ &timer);
		2073	callback (EV_A_ &timer, 0);
1863		2074
1864	This technique is slightly more complex, but in most cases where the	2075	This technique is slightly more complex, but in most cases where the
1865	time-out is unlikely to be triggered, much more efficient.	2076	time-out is unlikely to be triggered, much more efficient.
1866
1867	Changing the timeout is trivial as well (if it isn't hard-coded in the
1868	callback :) - just change the timeout and invoke the callback, which will
1869	fix things for you.
1870		2077
1871	=item 4. Wee, just use a double-linked list for your timeouts.	2078	=item 4. Wee, just use a double-linked list for your timeouts.
1872		2079
1873	If there is not one request, but many thousands (millions...), all	2080	If there is not one request, but many thousands (millions...), all
1874	employing some kind of timeout with the same timeout value, then one can	2081	employing some kind of timeout with the same timeout value, then one can
…		…
1901	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2108	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1902	rather complicated, but extremely efficient, something that really pays	2109	rather complicated, but extremely efficient, something that really pays
1903	off after the first million or so of active timers, i.e. it's usually	2110	off after the first million or so of active timers, i.e. it's usually
1904	overkill :)	2111	overkill :)
1905		2112
		2113	=head3 The special problem of being too early
		2114
		2115	If you ask a timer to call your callback after three seconds, then
		2116	you expect it to be invoked after three seconds - but of course, this
		2117	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2118	guaranteed to any precision by libev - imagine somebody suspending the
		2119	process with a STOP signal for a few hours for example.
		2120
		2121	So, libev tries to invoke your callback as soon as possible I<after> the
		2122	delay has occurred, but cannot guarantee this.
		2123
		2124	A less obvious failure mode is calling your callback too early: many event
		2125	loops compare timestamps with a "elapsed delay >= requested delay", but
		2126	this can cause your callback to be invoked much earlier than you would
		2127	expect.
		2128
		2129	To see why, imagine a system with a clock that only offers full second
		2130	resolution (think windows if you can't come up with a broken enough OS
		2131	yourself). If you schedule a one-second timer at the time 500.9, then the
		2132	event loop will schedule your timeout to elapse at a system time of 500
		2133	(500.9 truncated to the resolution) + 1, or 501.
		2134
		2135	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2136	501" and invoke the callback 0.1s after it was started, even though a
		2137	one-second delay was requested - this is being "too early", despite best
		2138	intentions.
		2139
		2140	This is the reason why libev will never invoke the callback if the elapsed
		2141	delay equals the requested delay, but only when the elapsed delay is
		2142	larger than the requested delay. In the example above, libev would only invoke
		2143	the callback at system time 502, or 1.1s after the timer was started.
		2144
		2145	So, while libev cannot guarantee that your callback will be invoked
		2146	exactly when requested, it I<can> and I<does> guarantee that the requested
		2147	delay has actually elapsed, or in other words, it always errs on the "too
		2148	late" side of things.
		2149
1906	=head3 The special problem of time updates	2150	=head3 The special problem of time updates
1907		2151
1908	Establishing the current time is a costly operation (it usually takes at	2152	Establishing the current time is a costly operation (it usually takes
1909	least two system calls): EV therefore updates its idea of the current	2153	at least one system call): EV therefore updates its idea of the current
1910	time only before and after C<ev_run> collects new events, which causes a	2154	time only before and after C<ev_run> collects new events, which causes a
1911	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2155	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1912	lots of events in one iteration.	2156	lots of events in one iteration.
1913		2157
1914	The relative timeouts are calculated relative to the C<ev_now ()>	2158	The relative timeouts are calculated relative to the C<ev_now ()>
1915	time. This is usually the right thing as this timestamp refers to the time	2159	time. This is usually the right thing as this timestamp refers to the time
1916	of the event triggering whatever timeout you are modifying/starting. If	2160	of the event triggering whatever timeout you are modifying/starting. If
1917	you suspect event processing to be delayed and you I<need> to base the	2161	you suspect event processing to be delayed and you I<need> to base the
1918	timeout on the current time, use something like this to adjust for this:	2162	timeout on the current time, use something like the following to adjust
		2163	for it:
1919		2164
1920	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2165	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1921		2166
1922	If the event loop is suspended for a long time, you can also force an	2167	If the event loop is suspended for a long time, you can also force an
1923	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2168	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1924	()>.	2169	()>, although that will push the event time of all outstanding events
		2170	further into the future.
		2171
		2172	=head3 The special problem of unsynchronised clocks
		2173
		2174	Modern systems have a variety of clocks - libev itself uses the normal
		2175	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2176	jumps).
		2177
		2178	Neither of these clocks is synchronised with each other or any other clock
		2179	on the system, so C<ev_time ()> might return a considerably different time
		2180	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2181	a call to C<gettimeofday> might return a second count that is one higher
		2182	than a directly following call to C<time>.
		2183
		2184	The moral of this is to only compare libev-related timestamps with
		2185	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2186	a second or so.
		2187
		2188	One more problem arises due to this lack of synchronisation: if libev uses
		2189	the system monotonic clock and you compare timestamps from C<ev_time>
		2190	or C<ev_now> from when you started your timer and when your callback is
		2191	invoked, you will find that sometimes the callback is a bit "early".
		2192
		2193	This is because C<ev_timer>s work in real time, not wall clock time, so
		2194	libev makes sure your callback is not invoked before the delay happened,
		2195	I<measured according to the real time>, not the system clock.
		2196
		2197	If your timeouts are based on a physical timescale (e.g. "time out this
		2198	connection after 100 seconds") then this shouldn't bother you as it is
		2199	exactly the right behaviour.
		2200
		2201	If you want to compare wall clock/system timestamps to your timers, then
		2202	you need to use C<ev_periodic>s, as these are based on the wall clock
		2203	time, where your comparisons will always generate correct results.
1925		2204
1926	=head3 The special problems of suspended animation	2205	=head3 The special problems of suspended animation
1927		2206
1928	When you leave the server world it is quite customary to hit machines that	2207	When you leave the server world it is quite customary to hit machines that
1929	can suspend/hibernate - what happens to the clocks during such a suspend?	2208	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1959		2238
1960	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2239	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1961		2240
1962	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2241	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1963		2242
1964	Configure the timer to trigger after C<after> seconds. If C<repeat>	2243	Configure the timer to trigger after C<after> seconds (fractional and
1965	is C<0.>, then it will automatically be stopped once the timeout is	2244	negative values are supported). If C<repeat> is C<0.>, then it will
1966	reached. If it is positive, then the timer will automatically be	2245	automatically be stopped once the timeout is reached. If it is positive,
1967	configured to trigger again C<repeat> seconds later, again, and again,	2246	then the timer will automatically be configured to trigger again C<repeat>
1968	until stopped manually.	2247	seconds later, again, and again, until stopped manually.
1969		2248
1970	The timer itself will do a best-effort at avoiding drift, that is, if	2249	The timer itself will do a best-effort at avoiding drift, that is, if
1971	you configure a timer to trigger every 10 seconds, then it will normally	2250	you configure a timer to trigger every 10 seconds, then it will normally
1972	trigger at exactly 10 second intervals. If, however, your program cannot	2251	trigger at exactly 10 second intervals. If, however, your program cannot
1973	keep up with the timer (because it takes longer than those 10 seconds to	2252	keep up with the timer (because it takes longer than those 10 seconds to
1974	do stuff) the timer will not fire more than once per event loop iteration.	2253	do stuff) the timer will not fire more than once per event loop iteration.
1975		2254
1976	=item ev_timer_again (loop, ev_timer *)	2255	=item ev_timer_again (loop, ev_timer *)
1977		2256
1978	This will act as if the timer timed out and restart it again if it is	2257	This will act as if the timer timed out, and restarts it again if it is
1979	repeating. The exact semantics are:	2258	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2259	timeout to the C<repeat> value and calling C<ev_timer_start>.
1980		2260
		2261	The exact semantics are as in the following rules, all of which will be
		2262	applied to the watcher:
		2263
		2264	=over 4
		2265
1981	If the timer is pending, its pending status is cleared.	2266	=item If the timer is pending, the pending status is always cleared.
1982		2267
1983	If the timer is started but non-repeating, stop it (as if it timed out).	2268	=item If the timer is started but non-repeating, stop it (as if it timed
		2269	out, without invoking it).
1984		2270
1985	If the timer is repeating, either start it if necessary (with the	2271	=item If the timer is repeating, make the C<repeat> value the new timeout
1986	C<repeat> value), or reset the running timer to the C<repeat> value.	2272	and start the timer, if necessary.
1987		2273
		2274	=back
		2275
1988	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2276	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1989	usage example.	2277	usage example.
1990		2278
1991	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2279	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1992		2280
1993	Returns the remaining time until a timer fires. If the timer is active,	2281	Returns the remaining time until a timer fires. If the timer is active,
…		…
2046	Periodic watchers are also timers of a kind, but they are very versatile	2334	Periodic watchers are also timers of a kind, but they are very versatile
2047	(and unfortunately a bit complex).	2335	(and unfortunately a bit complex).
2048		2336
2049	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2337	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2050	relative time, the physical time that passes) but on wall clock time	2338	relative time, the physical time that passes) but on wall clock time
2051	(absolute time, the thing you can read on your calender or clock). The	2339	(absolute time, the thing you can read on your calendar or clock). The
2052	difference is that wall clock time can run faster or slower than real	2340	difference is that wall clock time can run faster or slower than real
2053	time, and time jumps are not uncommon (e.g. when you adjust your	2341	time, and time jumps are not uncommon (e.g. when you adjust your
2054	wrist-watch).	2342	wrist-watch).
2055		2343
2056	You can tell a periodic watcher to trigger after some specific point	2344	You can tell a periodic watcher to trigger after some specific point
…		…
2061	C<ev_timer>, which would still trigger roughly 10 seconds after starting	2349	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2062	it, as it uses a relative timeout).	2350	it, as it uses a relative timeout).
2063		2351
2064	C<ev_periodic> watchers can also be used to implement vastly more complex	2352	C<ev_periodic> watchers can also be used to implement vastly more complex
2065	timers, such as triggering an event on each "midnight, local time", or	2353	timers, such as triggering an event on each "midnight, local time", or
2066	other complicated rules. This cannot be done with C<ev_timer> watchers, as	2354	other complicated rules. This cannot easily be done with C<ev_timer>
2067	those cannot react to time jumps.	2355	watchers, as those cannot react to time jumps.
2068		2356
2069	As with timers, the callback is guaranteed to be invoked only when the	2357	As with timers, the callback is guaranteed to be invoked only when the
2070	point in time where it is supposed to trigger has passed. If multiple	2358	point in time where it is supposed to trigger has passed. If multiple
2071	timers become ready during the same loop iteration then the ones with	2359	timers become ready during the same loop iteration then the ones with
2072	earlier time-out values are invoked before ones with later time-out values	2360	earlier time-out values are invoked before ones with later time-out values
…		…
2113		2401
2114	Another way to think about it (for the mathematically inclined) is that	2402	Another way to think about it (for the mathematically inclined) is that
2115	C<ev_periodic> will try to run the callback in this mode at the next possible	2403	C<ev_periodic> will try to run the callback in this mode at the next possible
2116	time where C<time = offset (mod interval)>, regardless of any time jumps.	2404	time where C<time = offset (mod interval)>, regardless of any time jumps.
2117		2405
2118	For numerical stability it is preferable that the C<offset> value is near	2406	The C<interval> I<MUST> be positive, and for numerical stability, the
2119	C<ev_now ()> (the current time), but there is no range requirement for	2407	interval value should be higher than C<1/8192> (which is around 100
2120	this value, and in fact is often specified as zero.	2408	microseconds) and C<offset> should be higher than C<0> and should have
		2409	at most a similar magnitude as the current time (say, within a factor of
		2410	ten). Typical values for offset are, in fact, C<0> or something between
		2411	C<0> and C<interval>, which is also the recommended range.
2121		2412
2122	Note also that there is an upper limit to how often a timer can fire (CPU	2413	Note also that there is an upper limit to how often a timer can fire (CPU
2123	speed for example), so if C<interval> is very small then timing stability	2414	speed for example), so if C<interval> is very small then timing stability
2124	will of course deteriorate. Libev itself tries to be exact to be about one	2415	will of course deteriorate. Libev itself tries to be exact to be about one
2125	millisecond (if the OS supports it and the machine is fast enough).	2416	millisecond (if the OS supports it and the machine is fast enough).
…		…
2155		2446
2156	NOTE: I<< This callback must always return a time that is higher than or	2447	NOTE: I<< This callback must always return a time that is higher than or
2157	equal to the passed C<now> value >>.	2448	equal to the passed C<now> value >>.
2158		2449
2159	This can be used to create very complex timers, such as a timer that	2450	This can be used to create very complex timers, such as a timer that
2160	triggers on "next midnight, local time". To do this, you would calculate the	2451	triggers on "next midnight, local time". To do this, you would calculate
2161	next midnight after C<now> and return the timestamp value for this. How	2452	the next midnight after C<now> and return the timestamp value for
2162	you do this is, again, up to you (but it is not trivial, which is the main	2453	this. Here is a (completely untested, no error checking) example on how to
2163	reason I omitted it as an example).	2454	do this:
		2455
		2456	#include <time.h>
		2457
		2458	static ev_tstamp
		2459	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2460	{
		2461	time_t tnow = (time_t)now;
		2462	struct tm tm;
		2463	localtime_r (&tnow, &tm);
		2464
		2465	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2466	++tm.tm_mday; // midnight next day
		2467
		2468	return mktime (&tm);
		2469	}
		2470
		2471	Note: this code might run into trouble on days that have more then two
		2472	midnights (beginning and end).
2164		2473
2165	=back	2474	=back
2166		2475
2167	=item ev_periodic_again (loop, ev_periodic *)	2476	=item ev_periodic_again (loop, ev_periodic *)
2168		2477
…		…
2233		2542
2234	ev_periodic hourly_tick;	2543	ev_periodic hourly_tick;
2235	ev_periodic_init (&hourly_tick, clock_cb,	2544	ev_periodic_init (&hourly_tick, clock_cb,
2236	fmod (ev_now (loop), 3600.), 3600., 0);	2545	fmod (ev_now (loop), 3600.), 3600., 0);
2237	ev_periodic_start (loop, &hourly_tick);	2546	ev_periodic_start (loop, &hourly_tick);
2238		2547
2239		2548
2240	=head2 C<ev_signal> - signal me when a signal gets signalled!	2549	=head2 C<ev_signal> - signal me when a signal gets signalled!
2241		2550
2242	Signal watchers will trigger an event when the process receives a specific	2551	Signal watchers will trigger an event when the process receives a specific
2243	signal one or more times. Even though signals are very asynchronous, libev	2552	signal one or more times. Even though signals are very asynchronous, libev
2244	will try it's best to deliver signals synchronously, i.e. as part of the	2553	will try its best to deliver signals synchronously, i.e. as part of the
2245	normal event processing, like any other event.	2554	normal event processing, like any other event.
2246		2555
2247	If you want signals to be delivered truly asynchronously, just use	2556	If you want signals to be delivered truly asynchronously, just use
2248	C<sigaction> as you would do without libev and forget about sharing	2557	C<sigaction> as you would do without libev and forget about sharing
2249	the signal. You can even use C<ev_async> from a signal handler to	2558	the signal. You can even use C<ev_async> from a signal handler to
…		…
2253	only within the same loop, i.e. you can watch for C<SIGINT> in your	2562	only within the same loop, i.e. you can watch for C<SIGINT> in your
2254	default loop and for C<SIGIO> in another loop, but you cannot watch for	2563	default loop and for C<SIGIO> in another loop, but you cannot watch for
2255	C<SIGINT> in both the default loop and another loop at the same time. At	2564	C<SIGINT> in both the default loop and another loop at the same time. At
2256	the moment, C<SIGCHLD> is permanently tied to the default loop.	2565	the moment, C<SIGCHLD> is permanently tied to the default loop.
2257		2566
2258	When the first watcher gets started will libev actually register something	2567	Only after the first watcher for a signal is started will libev actually
2259	with the kernel (thus it coexists with your own signal handlers as long as	2568	register something with the kernel. It thus coexists with your own signal
2260	you don't register any with libev for the same signal).	2569	handlers as long as you don't register any with libev for the same signal.
2261		2570
2262	If possible and supported, libev will install its handlers with	2571	If possible and supported, libev will install its handlers with
2263	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2572	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2264	not be unduly interrupted. If you have a problem with system calls getting	2573	not be unduly interrupted. If you have a problem with system calls getting
2265	interrupted by signals you can block all signals in an C<ev_check> watcher	2574	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2268	=head3 The special problem of inheritance over fork/execve/pthread_create	2577	=head3 The special problem of inheritance over fork/execve/pthread_create
2269		2578
2270	Both the signal mask (C<sigprocmask>) and the signal disposition	2579	Both the signal mask (C<sigprocmask>) and the signal disposition
2271	(C<sigaction>) are unspecified after starting a signal watcher (and after	2580	(C<sigaction>) are unspecified after starting a signal watcher (and after
2272	stopping it again), that is, libev might or might not block the signal,	2581	stopping it again), that is, libev might or might not block the signal,
2273	and might or might not set or restore the installed signal handler.	2582	and might or might not set or restore the installed signal handler (but
		2583	see C<EVFLAG_NOSIGMASK>).
2274		2584
2275	While this does not matter for the signal disposition (libev never	2585	While this does not matter for the signal disposition (libev never
2276	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2586	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2277	C<execve>), this matters for the signal mask: many programs do not expect	2587	C<execve>), this matters for the signal mask: many programs do not expect
2278	certain signals to be blocked.	2588	certain signals to be blocked.
…		…
2291	I<has> to modify the signal mask, at least temporarily.	2601	I<has> to modify the signal mask, at least temporarily.
2292		2602
2293	So I can't stress this enough: I<If you do not reset your signal mask when	2603	So I can't stress this enough: I<If you do not reset your signal mask when
2294	you expect it to be empty, you have a race condition in your code>. This	2604	you expect it to be empty, you have a race condition in your code>. This
2295	is not a libev-specific thing, this is true for most event libraries.	2605	is not a libev-specific thing, this is true for most event libraries.
		2606
		2607	=head3 The special problem of threads signal handling
		2608
		2609	POSIX threads has problematic signal handling semantics, specifically,
		2610	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2611	threads in a process block signals, which is hard to achieve.
		2612
		2613	When you want to use sigwait (or mix libev signal handling with your own
		2614	for the same signals), you can tackle this problem by globally blocking
		2615	all signals before creating any threads (or creating them with a fully set
		2616	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2617	loops. Then designate one thread as "signal receiver thread" which handles
		2618	these signals. You can pass on any signals that libev might be interested
		2619	in by calling C<ev_feed_signal>.
2296		2620
2297	=head3 Watcher-Specific Functions and Data Members	2621	=head3 Watcher-Specific Functions and Data Members
2298		2622
2299	=over 4	2623	=over 4
2300		2624
…		…
2435		2759
2436	=head2 C<ev_stat> - did the file attributes just change?	2760	=head2 C<ev_stat> - did the file attributes just change?
2437		2761
2438	This watches a file system path for attribute changes. That is, it calls	2762	This watches a file system path for attribute changes. That is, it calls
2439	C<stat> on that path in regular intervals (or when the OS says it changed)	2763	C<stat> on that path in regular intervals (or when the OS says it changed)
2440	and sees if it changed compared to the last time, invoking the callback if	2764	and sees if it changed compared to the last time, invoking the callback
2441	it did.	2765	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2766	happen after the watcher has been started will be reported.
2442		2767
2443	The path does not need to exist: changing from "path exists" to "path does	2768	The path does not need to exist: changing from "path exists" to "path does
2444	not exist" is a status change like any other. The condition "path does not	2769	not exist" is a status change like any other. The condition "path does not
2445	exist" (or more correctly "path cannot be stat'ed") is signified by the	2770	exist" (or more correctly "path cannot be stat'ed") is signified by the
2446	C<st_nlink> field being zero (which is otherwise always forced to be at	2771	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2676	Apart from keeping your process non-blocking (which is a useful	3001	Apart from keeping your process non-blocking (which is a useful
2677	effect on its own sometimes), idle watchers are a good place to do	3002	effect on its own sometimes), idle watchers are a good place to do
2678	"pseudo-background processing", or delay processing stuff to after the	3003	"pseudo-background processing", or delay processing stuff to after the
2679	event loop has handled all outstanding events.	3004	event loop has handled all outstanding events.
2680		3005
		3006	=head3 Abusing an C<ev_idle> watcher for its side-effect
		3007
		3008	As long as there is at least one active idle watcher, libev will never
		3009	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		3010	For this to work, the idle watcher doesn't need to be invoked at all - the
		3011	lowest priority will do.
		3012
		3013	This mode of operation can be useful together with an C<ev_check> watcher,
		3014	to do something on each event loop iteration - for example to balance load
		3015	between different connections.
		3016
		3017	See L</Abusing an ev_check watcher for its side-effect> for a longer
		3018	example.
		3019
2681	=head3 Watcher-Specific Functions and Data Members	3020	=head3 Watcher-Specific Functions and Data Members
2682		3021
2683	=over 4	3022	=over 4
2684		3023
2685	=item ev_idle_init (ev_idle *, callback)	3024	=item ev_idle_init (ev_idle *, callback)
…		…
2696	callback, free it. Also, use no error checking, as usual.	3035	callback, free it. Also, use no error checking, as usual.
2697		3036
2698	static void	3037	static void
2699	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	3038	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2700	{	3039	{
		3040	// stop the watcher
		3041	ev_idle_stop (loop, w);
		3042
		3043	// now we can free it
2701	free (w);	3044	free (w);
		3045
2702	// now do something you wanted to do when the program has	3046	// now do something you wanted to do when the program has
2703	// no longer anything immediate to do.	3047	// no longer anything immediate to do.
2704	}	3048	}
2705		3049
2706	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	3050	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2708	ev_idle_start (loop, idle_watcher);	3052	ev_idle_start (loop, idle_watcher);
2709		3053
2710		3054
2711	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3055	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2712		3056
2713	Prepare and check watchers are usually (but not always) used in pairs:	3057	Prepare and check watchers are often (but not always) used in pairs:
2714	prepare watchers get invoked before the process blocks and check watchers	3058	prepare watchers get invoked before the process blocks and check watchers
2715	afterwards.	3059	afterwards.
2716		3060
2717	You I<must not> call C<ev_run> or similar functions that enter	3061	You I<must not> call C<ev_run> (or similar functions that enter the
2718	the current event loop from either C<ev_prepare> or C<ev_check>	3062	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2719	watchers. Other loops than the current one are fine, however. The	3063	C<ev_check> watchers. Other loops than the current one are fine,
2720	rationale behind this is that you do not need to check for recursion in	3064	however. The rationale behind this is that you do not need to check
2721	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3065	for recursion in those watchers, i.e. the sequence will always be
2722	C<ev_check> so if you have one watcher of each kind they will always be	3066	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2723	called in pairs bracketing the blocking call.	3067	kind they will always be called in pairs bracketing the blocking call.
2724		3068
2725	Their main purpose is to integrate other event mechanisms into libev and	3069	Their main purpose is to integrate other event mechanisms into libev and
2726	their use is somewhat advanced. They could be used, for example, to track	3070	their use is somewhat advanced. They could be used, for example, to track
2727	variable changes, implement your own watchers, integrate net-snmp or a	3071	variable changes, implement your own watchers, integrate net-snmp or a
2728	coroutine library and lots more. They are also occasionally useful if	3072	coroutine library and lots more. They are also occasionally useful if
…		…
2746	with priority higher than or equal to the event loop and one coroutine	3090	with priority higher than or equal to the event loop and one coroutine
2747	of lower priority, but only once, using idle watchers to keep the event	3091	of lower priority, but only once, using idle watchers to keep the event
2748	loop from blocking if lower-priority coroutines are active, thus mapping	3092	loop from blocking if lower-priority coroutines are active, thus mapping
2749	low-priority coroutines to idle/background tasks).	3093	low-priority coroutines to idle/background tasks).
2750		3094
2751	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3095	When used for this purpose, it is recommended to give C<ev_check> watchers
2752	priority, to ensure that they are being run before any other watchers	3096	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2753	after the poll (this doesn't matter for C<ev_prepare> watchers).	3097	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3098	watchers).
2754		3099
2755	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3100	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2756	activate ("feed") events into libev. While libev fully supports this, they	3101	activate ("feed") events into libev. While libev fully supports this, they
2757	might get executed before other C<ev_check> watchers did their job. As	3102	might get executed before other C<ev_check> watchers did their job. As
2758	C<ev_check> watchers are often used to embed other (non-libev) event	3103	C<ev_check> watchers are often used to embed other (non-libev) event
2759	loops those other event loops might be in an unusable state until their	3104	loops those other event loops might be in an unusable state until their
2760	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3105	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2761	others).	3106	others).
		3107
		3108	=head3 Abusing an C<ev_check> watcher for its side-effect
		3109
		3110	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3111	useful because they are called once per event loop iteration. For
		3112	example, if you want to handle a large number of connections fairly, you
		3113	normally only do a bit of work for each active connection, and if there
		3114	is more work to do, you wait for the next event loop iteration, so other
		3115	connections have a chance of making progress.
		3116
		3117	Using an C<ev_check> watcher is almost enough: it will be called on the
		3118	next event loop iteration. However, that isn't as soon as possible -
		3119	without external events, your C<ev_check> watcher will not be invoked.
		3120
		3121	This is where C<ev_idle> watchers come in handy - all you need is a
		3122	single global idle watcher that is active as long as you have one active
		3123	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3124	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3125	invoked. Neither watcher alone can do that.
2762		3126
2763	=head3 Watcher-Specific Functions and Data Members	3127	=head3 Watcher-Specific Functions and Data Members
2764		3128
2765	=over 4	3129	=over 4
2766		3130
…		…
2967		3331
2968	=over 4	3332	=over 4
2969		3333
2970	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3334	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2971		3335
2972	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3336	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2973		3337
2974	Configures the watcher to embed the given loop, which must be	3338	Configures the watcher to embed the given loop, which must be
2975	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3339	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2976	invoked automatically, otherwise it is the responsibility of the callback	3340	invoked automatically, otherwise it is the responsibility of the callback
2977	to invoke it (it will continue to be called until the sweep has been done,	3341	to invoke it (it will continue to be called until the sweep has been done,
…		…
2998	used).	3362	used).
2999		3363
3000	struct ev_loop *loop_hi = ev_default_init (0);	3364	struct ev_loop *loop_hi = ev_default_init (0);
3001	struct ev_loop *loop_lo = 0;	3365	struct ev_loop *loop_lo = 0;
3002	ev_embed embed;	3366	ev_embed embed;
3003		3367
3004	// see if there is a chance of getting one that works	3368	// see if there is a chance of getting one that works
3005	// (remember that a flags value of 0 means autodetection)	3369	// (remember that a flags value of 0 means autodetection)
3006	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3370	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3007	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3371	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3008	: 0;	3372	: 0;
…		…
3022	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3386	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3023		3387
3024	struct ev_loop *loop = ev_default_init (0);	3388	struct ev_loop *loop = ev_default_init (0);
3025	struct ev_loop *loop_socket = 0;	3389	struct ev_loop *loop_socket = 0;
3026	ev_embed embed;	3390	ev_embed embed;
3027		3391
3028	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3392	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3029	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3393	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3030	{	3394	{
3031	ev_embed_init (&embed, 0, loop_socket);	3395	ev_embed_init (&embed, 0, loop_socket);
3032	ev_embed_start (loop, &embed);	3396	ev_embed_start (loop, &embed);
…		…
3040		3404
3041	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3405	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3042		3406
3043	Fork watchers are called when a C<fork ()> was detected (usually because	3407	Fork watchers are called when a C<fork ()> was detected (usually because
3044	whoever is a good citizen cared to tell libev about it by calling	3408	whoever is a good citizen cared to tell libev about it by calling
3045	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3409	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3046	event loop blocks next and before C<ev_check> watchers are being called,	3410	and before C<ev_check> watchers are being called, and only in the child
3047	and only in the child after the fork. If whoever good citizen calling	3411	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3048	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3412	and calls it in the wrong process, the fork handlers will be invoked, too,
3049	handlers will be invoked, too, of course.	3413	of course.
3050		3414
3051	=head3 The special problem of life after fork - how is it possible?	3415	=head3 The special problem of life after fork - how is it possible?
3052		3416
3053	Most uses of C<fork()> consist of forking, then some simple calls to set	3417	Most uses of C<fork ()> consist of forking, then some simple calls to set
3054	up/change the process environment, followed by a call to C<exec()>. This	3418	up/change the process environment, followed by a call to C<exec()>. This
3055	sequence should be handled by libev without any problems.	3419	sequence should be handled by libev without any problems.
3056		3420
3057	This changes when the application actually wants to do event handling	3421	This changes when the application actually wants to do event handling
3058	in the child, or both parent in child, in effect "continuing" after the	3422	in the child, or both parent in child, in effect "continuing" after the
…		…
3074	disadvantage of having to use multiple event loops (which do not support	3438	disadvantage of having to use multiple event loops (which do not support
3075	signal watchers).	3439	signal watchers).
3076		3440
3077	When this is not possible, or you want to use the default loop for	3441	When this is not possible, or you want to use the default loop for
3078	other reasons, then in the process that wants to start "fresh", call	3442	other reasons, then in the process that wants to start "fresh", call
3079	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying	3443	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
3080	the default loop will "orphan" (not stop) all registered watchers, so you	3444	Destroying the default loop will "orphan" (not stop) all registered
3081	have to be careful not to execute code that modifies those watchers. Note	3445	watchers, so you have to be careful not to execute code that modifies
3082	also that in that case, you have to re-register any signal watchers.	3446	those watchers. Note also that in that case, you have to re-register any
		3447	signal watchers.
3083		3448
3084	=head3 Watcher-Specific Functions and Data Members	3449	=head3 Watcher-Specific Functions and Data Members
3085		3450
3086	=over 4	3451	=over 4
3087		3452
3088	=item ev_fork_init (ev_signal *, callback)	3453	=item ev_fork_init (ev_fork *, callback)
3089		3454
3090	Initialises and configures the fork watcher - it has no parameters of any	3455	Initialises and configures the fork watcher - it has no parameters of any
3091	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3456	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3092	believe me.	3457	really.
3093		3458
3094	=back	3459	=back
3095		3460
3096		3461
		3462	=head2 C<ev_cleanup> - even the best things end
		3463
		3464	Cleanup watchers are called just before the event loop is being destroyed
		3465	by a call to C<ev_loop_destroy>.
		3466
		3467	While there is no guarantee that the event loop gets destroyed, cleanup
		3468	watchers provide a convenient method to install cleanup hooks for your
		3469	program, worker threads and so on - you just to make sure to destroy the
		3470	loop when you want them to be invoked.
		3471
		3472	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3473	all other watchers, they do not keep a reference to the event loop (which
		3474	makes a lot of sense if you think about it). Like all other watchers, you
		3475	can call libev functions in the callback, except C<ev_cleanup_start>.
		3476
		3477	=head3 Watcher-Specific Functions and Data Members
		3478
		3479	=over 4
		3480
		3481	=item ev_cleanup_init (ev_cleanup *, callback)
		3482
		3483	Initialises and configures the cleanup watcher - it has no parameters of
		3484	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3485	pointless, I assure you.
		3486
		3487	=back
		3488
		3489	Example: Register an atexit handler to destroy the default loop, so any
		3490	cleanup functions are called.
		3491
		3492	static void
		3493	program_exits (void)
		3494	{
		3495	ev_loop_destroy (EV_DEFAULT_UC);
		3496	}
		3497
		3498	...
		3499	atexit (program_exits);
		3500
		3501
3097	=head2 C<ev_async> - how to wake up an event loop	3502	=head2 C<ev_async> - how to wake up an event loop
3098		3503
3099	In general, you cannot use an C<ev_run> from multiple threads or other	3504	In general, you cannot use an C<ev_loop> from multiple threads or other
3100	asynchronous sources such as signal handlers (as opposed to multiple event	3505	asynchronous sources such as signal handlers (as opposed to multiple event
3101	loops - those are of course safe to use in different threads).	3506	loops - those are of course safe to use in different threads).
3102		3507
3103	Sometimes, however, you need to wake up an event loop you do not control,	3508	Sometimes, however, you need to wake up an event loop you do not control,
3104	for example because it belongs to another thread. This is what C<ev_async>	3509	for example because it belongs to another thread. This is what C<ev_async>
…		…
3106	it by calling C<ev_async_send>, which is thread- and signal safe.	3511	it by calling C<ev_async_send>, which is thread- and signal safe.
3107		3512
3108	This functionality is very similar to C<ev_signal> watchers, as signals,	3513	This functionality is very similar to C<ev_signal> watchers, as signals,
3109	too, are asynchronous in nature, and signals, too, will be compressed	3514	too, are asynchronous in nature, and signals, too, will be compressed
3110	(i.e. the number of callback invocations may be less than the number of	3515	(i.e. the number of callback invocations may be less than the number of
3111	C<ev_async_sent> calls).	3516	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3112		3517	of "global async watchers" by using a watcher on an otherwise unused
3113	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3518	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3114	just the default loop.	3519	even without knowing which loop owns the signal.
3115		3520
3116	=head3 Queueing	3521	=head3 Queueing
3117		3522
3118	C<ev_async> does not support queueing of data in any way. The reason	3523	C<ev_async> does not support queueing of data in any way. The reason
3119	is that the author does not know of a simple (or any) algorithm for a	3524	is that the author does not know of a simple (or any) algorithm for a
…		…
3211	trust me.	3616	trust me.
3212		3617
3213	=item ev_async_send (loop, ev_async *)	3618	=item ev_async_send (loop, ev_async *)
3214		3619
3215	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3620	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3216	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3621	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3622	returns.
		3623
3217	C<ev_feed_event>, this call is safe to do from other threads, signal or	3624	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3218	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3625	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3219	section below on what exactly this means).	3626	embedding section below on what exactly this means).
3220		3627
3221	Note that, as with other watchers in libev, multiple events might get	3628	Note that, as with other watchers in libev, multiple events might get
3222	compressed into a single callback invocation (another way to look at this	3629	compressed into a single callback invocation (another way to look at
3223	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3630	this is that C<ev_async> watchers are level-triggered: they are set on
3224	reset when the event loop detects that).	3631	C<ev_async_send>, reset when the event loop detects that).
3225		3632
3226	This call incurs the overhead of a system call only once per event loop	3633	This call incurs the overhead of at most one extra system call per event
3227	iteration, so while the overhead might be noticeable, it doesn't apply to	3634	loop iteration, if the event loop is blocked, and no syscall at all if
3228	repeated calls to C<ev_async_send> for the same event loop.	3635	the event loop (or your program) is processing events. That means that
		3636	repeated calls are basically free (there is no need to avoid calls for
		3637	performance reasons) and that the overhead becomes smaller (typically
		3638	zero) under load.
3229		3639
3230	=item bool = ev_async_pending (ev_async *)	3640	=item bool = ev_async_pending (ev_async *)
3231		3641
3232	Returns a non-zero value when C<ev_async_send> has been called on the	3642	Returns a non-zero value when C<ev_async_send> has been called on the
3233	watcher but the event has not yet been processed (or even noted) by the	3643	watcher but the event has not yet been processed (or even noted) by the
…		…
3250		3660
3251	There are some other functions of possible interest. Described. Here. Now.	3661	There are some other functions of possible interest. Described. Here. Now.
3252		3662
3253	=over 4	3663	=over 4
3254		3664
3255	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3665	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3256		3666
3257	This function combines a simple timer and an I/O watcher, calls your	3667	This function combines a simple timer and an I/O watcher, calls your
3258	callback on whichever event happens first and automatically stops both	3668	callback on whichever event happens first and automatically stops both
3259	watchers. This is useful if you want to wait for a single event on an fd	3669	watchers. This is useful if you want to wait for a single event on an fd
3260	or timeout without having to allocate/configure/start/stop/free one or	3670	or timeout without having to allocate/configure/start/stop/free one or
…		…
3288	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3698	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3289		3699
3290	=item ev_feed_fd_event (loop, int fd, int revents)	3700	=item ev_feed_fd_event (loop, int fd, int revents)
3291		3701
3292	Feed an event on the given fd, as if a file descriptor backend detected	3702	Feed an event on the given fd, as if a file descriptor backend detected
3293	the given events it.	3703	the given events.
3294		3704
3295	=item ev_feed_signal_event (loop, int signum)	3705	=item ev_feed_signal_event (loop, int signum)
3296		3706
3297	Feed an event as if the given signal occurred (C<loop> must be the default	3707	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3298	loop!).	3708	which is async-safe.
3299		3709
3300	=back	3710	=back
		3711
		3712
		3713	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3714
		3715	This section explains some common idioms that are not immediately
		3716	obvious. Note that examples are sprinkled over the whole manual, and this
		3717	section only contains stuff that wouldn't fit anywhere else.
		3718
		3719	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3720
		3721	Each watcher has, by default, a C<void *data> member that you can read
		3722	or modify at any time: libev will completely ignore it. This can be used
		3723	to associate arbitrary data with your watcher. If you need more data and
		3724	don't want to allocate memory separately and store a pointer to it in that
		3725	data member, you can also "subclass" the watcher type and provide your own
		3726	data:
		3727
		3728	struct my_io
		3729	{
		3730	ev_io io;
		3731	int otherfd;
		3732	void *somedata;
		3733	struct whatever *mostinteresting;
		3734	};
		3735
		3736	...
		3737	struct my_io w;
		3738	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3739
		3740	And since your callback will be called with a pointer to the watcher, you
		3741	can cast it back to your own type:
		3742
		3743	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3744	{
		3745	struct my_io *w = (struct my_io *)w_;
		3746	...
		3747	}
		3748
		3749	More interesting and less C-conformant ways of casting your callback
		3750	function type instead have been omitted.
		3751
		3752	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3753
		3754	Another common scenario is to use some data structure with multiple
		3755	embedded watchers, in effect creating your own watcher that combines
		3756	multiple libev event sources into one "super-watcher":
		3757
		3758	struct my_biggy
		3759	{
		3760	int some_data;
		3761	ev_timer t1;
		3762	ev_timer t2;
		3763	}
		3764
		3765	In this case getting the pointer to C<my_biggy> is a bit more
		3766	complicated: Either you store the address of your C<my_biggy> struct in
		3767	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3768	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3769	real programmers):
		3770
		3771	#include <stddef.h>
		3772
		3773	static void
		3774	t1_cb (EV_P_ ev_timer *w, int revents)
		3775	{
		3776	struct my_biggy big = (struct my_biggy *)
		3777	(((char *)w) - offsetof (struct my_biggy, t1));
		3778	}
		3779
		3780	static void
		3781	t2_cb (EV_P_ ev_timer *w, int revents)
		3782	{
		3783	struct my_biggy big = (struct my_biggy *)
		3784	(((char *)w) - offsetof (struct my_biggy, t2));
		3785	}
		3786
		3787	=head2 AVOIDING FINISHING BEFORE RETURNING
		3788
		3789	Often you have structures like this in event-based programs:
		3790
		3791	callback ()
		3792	{
		3793	free (request);
		3794	}
		3795
		3796	request = start_new_request (..., callback);
		3797
		3798	The intent is to start some "lengthy" operation. The C<request> could be
		3799	used to cancel the operation, or do other things with it.
		3800
		3801	It's not uncommon to have code paths in C<start_new_request> that
		3802	immediately invoke the callback, for example, to report errors. Or you add
		3803	some caching layer that finds that it can skip the lengthy aspects of the
		3804	operation and simply invoke the callback with the result.
		3805
		3806	The problem here is that this will happen I<before> C<start_new_request>
		3807	has returned, so C<request> is not set.
		3808
		3809	Even if you pass the request by some safer means to the callback, you
		3810	might want to do something to the request after starting it, such as
		3811	canceling it, which probably isn't working so well when the callback has
		3812	already been invoked.
		3813
		3814	A common way around all these issues is to make sure that
		3815	C<start_new_request> I<always> returns before the callback is invoked. If
		3816	C<start_new_request> immediately knows the result, it can artificially
		3817	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3818	example, or more sneakily, by reusing an existing (stopped) watcher and
		3819	pushing it into the pending queue:
		3820
		3821	ev_set_cb (watcher, callback);
		3822	ev_feed_event (EV_A_ watcher, 0);
		3823
		3824	This way, C<start_new_request> can safely return before the callback is
		3825	invoked, while not delaying callback invocation too much.
		3826
		3827	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3828
		3829	Often (especially in GUI toolkits) there are places where you have
		3830	I<modal> interaction, which is most easily implemented by recursively
		3831	invoking C<ev_run>.
		3832
		3833	This brings the problem of exiting - a callback might want to finish the
		3834	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3835	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3836	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3837	other combination: In these cases, a simple C<ev_break> will not work.
		3838
		3839	The solution is to maintain "break this loop" variable for each C<ev_run>
		3840	invocation, and use a loop around C<ev_run> until the condition is
		3841	triggered, using C<EVRUN_ONCE>:
		3842
		3843	// main loop
		3844	int exit_main_loop = 0;
		3845
		3846	while (!exit_main_loop)
		3847	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3848
		3849	// in a modal watcher
		3850	int exit_nested_loop = 0;
		3851
		3852	while (!exit_nested_loop)
		3853	ev_run (EV_A_ EVRUN_ONCE);
		3854
		3855	To exit from any of these loops, just set the corresponding exit variable:
		3856
		3857	// exit modal loop
		3858	exit_nested_loop = 1;
		3859
		3860	// exit main program, after modal loop is finished
		3861	exit_main_loop = 1;
		3862
		3863	// exit both
		3864	exit_main_loop = exit_nested_loop = 1;
		3865
		3866	=head2 THREAD LOCKING EXAMPLE
		3867
		3868	Here is a fictitious example of how to run an event loop in a different
		3869	thread from where callbacks are being invoked and watchers are
		3870	created/added/removed.
		3871
		3872	For a real-world example, see the C<EV::Loop::Async> perl module,
		3873	which uses exactly this technique (which is suited for many high-level
		3874	languages).
		3875
		3876	The example uses a pthread mutex to protect the loop data, a condition
		3877	variable to wait for callback invocations, an async watcher to notify the
		3878	event loop thread and an unspecified mechanism to wake up the main thread.
		3879
		3880	First, you need to associate some data with the event loop:
		3881
		3882	typedef struct {
		3883	pthread_mutex_t lock; /* global loop lock */
		3884	pthread_t tid;
		3885	pthread_cond_t invoke_cv;
		3886	ev_async async_w;
		3887	} userdata;
		3888
		3889	void prepare_loop (EV_P)
		3890	{
		3891	// for simplicity, we use a static userdata struct.
		3892	static userdata u;
		3893
		3894	ev_async_init (&u.async_w, async_cb);
		3895	ev_async_start (EV_A_ &u.async_w);
		3896
		3897	pthread_mutex_init (&u.lock, 0);
		3898	pthread_cond_init (&u.invoke_cv, 0);
		3899
		3900	// now associate this with the loop
		3901	ev_set_userdata (EV_A_ &u);
		3902	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3903	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3904
		3905	// then create the thread running ev_run
		3906	pthread_create (&u.tid, 0, l_run, EV_A);
		3907	}
		3908
		3909	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3910	solely to wake up the event loop so it takes notice of any new watchers
		3911	that might have been added:
		3912
		3913	static void
		3914	async_cb (EV_P_ ev_async *w, int revents)
		3915	{
		3916	// just used for the side effects
		3917	}
		3918
		3919	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3920	protecting the loop data, respectively.
		3921
		3922	static void
		3923	l_release (EV_P)
		3924	{
		3925	userdata *u = ev_userdata (EV_A);
		3926	pthread_mutex_unlock (&u->lock);
		3927	}
		3928
		3929	static void
		3930	l_acquire (EV_P)
		3931	{
		3932	userdata *u = ev_userdata (EV_A);
		3933	pthread_mutex_lock (&u->lock);
		3934	}
		3935
		3936	The event loop thread first acquires the mutex, and then jumps straight
		3937	into C<ev_run>:
		3938
		3939	void *
		3940	l_run (void *thr_arg)
		3941	{
		3942	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3943
		3944	l_acquire (EV_A);
		3945	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3946	ev_run (EV_A_ 0);
		3947	l_release (EV_A);
		3948
		3949	return 0;
		3950	}
		3951
		3952	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3953	signal the main thread via some unspecified mechanism (signals? pipe
		3954	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3955	have been called (in a while loop because a) spurious wakeups are possible
		3956	and b) skipping inter-thread-communication when there are no pending
		3957	watchers is very beneficial):
		3958
		3959	static void
		3960	l_invoke (EV_P)
		3961	{
		3962	userdata *u = ev_userdata (EV_A);
		3963
		3964	while (ev_pending_count (EV_A))
		3965	{
		3966	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3967	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3968	}
		3969	}
		3970
		3971	Now, whenever the main thread gets told to invoke pending watchers, it
		3972	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3973	thread to continue:
		3974
		3975	static void
		3976	real_invoke_pending (EV_P)
		3977	{
		3978	userdata *u = ev_userdata (EV_A);
		3979
		3980	pthread_mutex_lock (&u->lock);
		3981	ev_invoke_pending (EV_A);
		3982	pthread_cond_signal (&u->invoke_cv);
		3983	pthread_mutex_unlock (&u->lock);
		3984	}
		3985
		3986	Whenever you want to start/stop a watcher or do other modifications to an
		3987	event loop, you will now have to lock:
		3988
		3989	ev_timer timeout_watcher;
		3990	userdata *u = ev_userdata (EV_A);
		3991
		3992	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3993
		3994	pthread_mutex_lock (&u->lock);
		3995	ev_timer_start (EV_A_ &timeout_watcher);
		3996	ev_async_send (EV_A_ &u->async_w);
		3997	pthread_mutex_unlock (&u->lock);
		3998
		3999	Note that sending the C<ev_async> watcher is required because otherwise
		4000	an event loop currently blocking in the kernel will have no knowledge
		4001	about the newly added timer. By waking up the loop it will pick up any new
		4002	watchers in the next event loop iteration.
		4003
		4004	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		4005
		4006	While the overhead of a callback that e.g. schedules a thread is small, it
		4007	is still an overhead. If you embed libev, and your main usage is with some
		4008	kind of threads or coroutines, you might want to customise libev so that
		4009	doesn't need callbacks anymore.
		4010
		4011	Imagine you have coroutines that you can switch to using a function
		4012	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		4013	and that due to some magic, the currently active coroutine is stored in a
		4014	global called C<current_coro>. Then you can build your own "wait for libev
		4015	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		4016	the differing C<;> conventions):
		4017
		4018	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4019	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4020
		4021	That means instead of having a C callback function, you store the
		4022	coroutine to switch to in each watcher, and instead of having libev call
		4023	your callback, you instead have it switch to that coroutine.
		4024
		4025	A coroutine might now wait for an event with a function called
		4026	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		4027	matter when, or whether the watcher is active or not when this function is
		4028	called):
		4029
		4030	void
		4031	wait_for_event (ev_watcher *w)
		4032	{
		4033	ev_set_cb (w, current_coro);
		4034	switch_to (libev_coro);
		4035	}
		4036
		4037	That basically suspends the coroutine inside C<wait_for_event> and
		4038	continues the libev coroutine, which, when appropriate, switches back to
		4039	this or any other coroutine.
		4040
		4041	You can do similar tricks if you have, say, threads with an event queue -
		4042	instead of storing a coroutine, you store the queue object and instead of
		4043	switching to a coroutine, you push the watcher onto the queue and notify
		4044	any waiters.
		4045
		4046	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		4047	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		4048
		4049	// my_ev.h
		4050	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4051	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4052	#include "../libev/ev.h"
		4053
		4054	// my_ev.c
		4055	#define EV_H "my_ev.h"
		4056	#include "../libev/ev.c"
		4057
		4058	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4059	F<my_ev.c> into your project. When properly specifying include paths, you
		4060	can even use F<ev.h> as header file name directly.
3301		4061
3302		4062
3303	=head1 LIBEVENT EMULATION	4063	=head1 LIBEVENT EMULATION
3304		4064
3305	Libev offers a compatibility emulation layer for libevent. It cannot	4065	Libev offers a compatibility emulation layer for libevent. It cannot
3306	emulate the internals of libevent, so here are some usage hints:	4066	emulate the internals of libevent, so here are some usage hints:
3307		4067
3308	=over 4	4068	=over 4
		4069
		4070	=item * Only the libevent-1.4.1-beta API is being emulated.
		4071
		4072	This was the newest libevent version available when libev was implemented,
		4073	and is still mostly unchanged in 2010.
3309		4074
3310	=item * Use it by including <event.h>, as usual.	4075	=item * Use it by including <event.h>, as usual.
3311		4076
3312	=item * The following members are fully supported: ev_base, ev_callback,	4077	=item * The following members are fully supported: ev_base, ev_callback,
3313	ev_arg, ev_fd, ev_res, ev_events.	4078	ev_arg, ev_fd, ev_res, ev_events.
…		…
3319	=item * Priorities are not currently supported. Initialising priorities	4084	=item * Priorities are not currently supported. Initialising priorities
3320	will fail and all watchers will have the same priority, even though there	4085	will fail and all watchers will have the same priority, even though there
3321	is an ev_pri field.	4086	is an ev_pri field.
3322		4087
3323	=item * In libevent, the last base created gets the signals, in libev, the	4088	=item * In libevent, the last base created gets the signals, in libev, the
3324	first base created (== the default loop) gets the signals.	4089	base that registered the signal gets the signals.
3325		4090
3326	=item * Other members are not supported.	4091	=item * Other members are not supported.
3327		4092
3328	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4093	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3329	to use the libev header file and library.	4094	to use the libev header file and library.
3330		4095
3331	=back	4096	=back
3332		4097
3333	=head1 C++ SUPPORT	4098	=head1 C++ SUPPORT
		4099
		4100	=head2 C API
		4101
		4102	The normal C API should work fine when used from C++: both ev.h and the
		4103	libev sources can be compiled as C++. Therefore, code that uses the C API
		4104	will work fine.
		4105
		4106	Proper exception specifications might have to be added to callbacks passed
		4107	to libev: exceptions may be thrown only from watcher callbacks, all other
		4108	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4109	callbacks) must not throw exceptions, and might need a C<noexcept>
		4110	specification. If you have code that needs to be compiled as both C and
		4111	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4112
		4113	static void
		4114	fatal_error (const char *msg) EV_NOEXCEPT
		4115	{
		4116	perror (msg);
		4117	abort ();
		4118	}
		4119
		4120	...
		4121	ev_set_syserr_cb (fatal_error);
		4122
		4123	The only API functions that can currently throw exceptions are C<ev_run>,
		4124	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4125	because it runs cleanup watchers).
		4126
		4127	Throwing exceptions in watcher callbacks is only supported if libev itself
		4128	is compiled with a C++ compiler or your C and C++ environments allow
		4129	throwing exceptions through C libraries (most do).
		4130
		4131	=head2 C++ API
3334		4132
3335	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4133	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3336	you to use some convenience methods to start/stop watchers and also change	4134	you to use some convenience methods to start/stop watchers and also change
3337	the callback model to a model using method callbacks on objects.	4135	the callback model to a model using method callbacks on objects.
3338		4136
3339	To use it,	4137	To use it,
3340		4138
3341	#include <ev++.h>	4139	#include <ev++.h>
3342		4140
3343	This automatically includes F<ev.h> and puts all of its definitions (many	4141	This automatically includes F<ev.h> and puts all of its definitions (many
3344	of them macros) into the global namespace. All C++ specific things are	4142	of them macros) into the global namespace. All C++ specific things are
3345	put into the C<ev> namespace. It should support all the same embedding	4143	put into the C<ev> namespace. It should support all the same embedding
…		…
3348	Care has been taken to keep the overhead low. The only data member the C++	4146	Care has been taken to keep the overhead low. The only data member the C++
3349	classes add (compared to plain C-style watchers) is the event loop pointer	4147	classes add (compared to plain C-style watchers) is the event loop pointer
3350	that the watcher is associated with (or no additional members at all if	4148	that the watcher is associated with (or no additional members at all if
3351	you disable C<EV_MULTIPLICITY> when embedding libev).	4149	you disable C<EV_MULTIPLICITY> when embedding libev).
3352		4150
3353	Currently, functions, and static and non-static member functions can be	4151	Currently, functions, static and non-static member functions and classes
3354	used as callbacks. Other types should be easy to add as long as they only	4152	with C<operator ()> can be used as callbacks. Other types should be easy
3355	need one additional pointer for context. If you need support for other	4153	to add as long as they only need one additional pointer for context. If
3356	types of functors please contact the author (preferably after implementing	4154	you need support for other types of functors please contact the author
3357	it).	4155	(preferably after implementing it).
		4156
		4157	For all this to work, your C++ compiler either has to use the same calling
		4158	conventions as your C compiler (for static member functions), or you have
		4159	to embed libev and compile libev itself as C++.
3358		4160
3359	Here is a list of things available in the C<ev> namespace:	4161	Here is a list of things available in the C<ev> namespace:
3360		4162
3361	=over 4	4163	=over 4
3362		4164
…		…
3372	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4174	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3373		4175
3374	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4176	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3375	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4177	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3376	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4178	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3377	defines by many implementations.	4179	defined by many implementations.
3378		4180
3379	All of those classes have these methods:	4181	All of those classes have these methods:
3380		4182
3381	=over 4	4183	=over 4
3382		4184
…		…
3444	void operator() (ev::io &w, int revents)	4246	void operator() (ev::io &w, int revents)
3445	{	4247	{
3446	...	4248	...
3447	}	4249	}
3448	}	4250	}
3449		4251
3450	myfunctor f;	4252	myfunctor f;
3451		4253
3452	ev::io w;	4254	ev::io w;
3453	w.set (&f);	4255	w.set (&f);
3454		4256
…		…
3472	Associates a different C<struct ev_loop> with this watcher. You can only	4274	Associates a different C<struct ev_loop> with this watcher. You can only
3473	do this when the watcher is inactive (and not pending either).	4275	do this when the watcher is inactive (and not pending either).
3474		4276
3475	=item w->set ([arguments])	4277	=item w->set ([arguments])
3476		4278
3477	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4279	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3478	method or a suitable start method must be called at least once. Unlike the	4280	with the same arguments. Either this method or a suitable start method
3479	C counterpart, an active watcher gets automatically stopped and restarted	4281	must be called at least once. Unlike the C counterpart, an active watcher
3480	when reconfiguring it with this method.	4282	gets automatically stopped and restarted when reconfiguring it with this
		4283	method.
		4284
		4285	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4286	clashing with the C<set (loop)> method.
		4287
		4288	For C<ev::io> watchers there is an additional C<set> method that acepts a
		4289	new event mask only, and internally calls C<ev_io_modify>.
3481		4290
3482	=item w->start ()	4291	=item w->start ()
3483		4292
3484	Starts the watcher. Note that there is no C<loop> argument, as the	4293	Starts the watcher. Note that there is no C<loop> argument, as the
3485	constructor already stores the event loop.	4294	constructor already stores the event loop.
…		…
3515	watchers in the constructor.	4324	watchers in the constructor.
3516		4325
3517	class myclass	4326	class myclass
3518	{	4327	{
3519	ev::io io ; void io_cb (ev::io &w, int revents);	4328	ev::io io ; void io_cb (ev::io &w, int revents);
3520	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4329	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3521	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4330	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3522		4331
3523	myclass (int fd)	4332	myclass (int fd)
3524	{	4333	{
3525	io .set <myclass, &myclass::io_cb > (this);	4334	io .set <myclass, &myclass::io_cb > (this);
…		…
3576	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4385	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3577		4386
3578	=item D	4387	=item D
3579		4388
3580	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4389	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3581	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4390	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3582		4391
3583	=item Ocaml	4392	=item Ocaml
3584		4393
3585	Erkki Seppala has written Ocaml bindings for libev, to be found at	4394	Erkki Seppala has written Ocaml bindings for libev, to be found at
3586	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4395	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3589		4398
3590	Brian Maher has written a partial interface to libev for lua (at the	4399	Brian Maher has written a partial interface to libev for lua (at the
3591	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4400	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3592	L<http://github.com/brimworks/lua-ev>.	4401	L<http://github.com/brimworks/lua-ev>.
3593		4402
		4403	=item Javascript
		4404
		4405	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4406
		4407	=item Others
		4408
		4409	There are others, and I stopped counting.
		4410
3594	=back	4411	=back
3595		4412
3596		4413
3597	=head1 MACRO MAGIC	4414	=head1 MACRO MAGIC
3598		4415
…		…
3634	suitable for use with C<EV_A>.	4451	suitable for use with C<EV_A>.
3635		4452
3636	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4453	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3637		4454
3638	Similar to the other two macros, this gives you the value of the default	4455	Similar to the other two macros, this gives you the value of the default
3639	loop, if multiple loops are supported ("ev loop default").	4456	loop, if multiple loops are supported ("ev loop default"). The default loop
		4457	will be initialised if it isn't already initialised.
		4458
		4459	For non-multiplicity builds, these macros do nothing, so you always have
		4460	to initialise the loop somewhere.
3640		4461
3641	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4462	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3642		4463
3643	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4464	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3644	default loop has been initialised (C<UC> == unchecked). Their behaviour	4465	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3711	ev_vars.h	4532	ev_vars.h
3712	ev_wrap.h	4533	ev_wrap.h
3713		4534
3714	ev_win32.c required on win32 platforms only	4535	ev_win32.c required on win32 platforms only
3715		4536
3716	ev_select.c only when select backend is enabled (which is enabled by default)	4537	ev_select.c only when select backend is enabled
3717	ev_poll.c only when poll backend is enabled (disabled by default)	4538	ev_poll.c only when poll backend is enabled
3718	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4539	ev_epoll.c only when the epoll backend is enabled
		4540	ev_linuxaio.c only when the linux aio backend is enabled
		4541	ev_iouring.c only when the linux io_uring backend is enabled
3719	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4542	ev_kqueue.c only when the kqueue backend is enabled
3720	ev_port.c only when the solaris port backend is enabled (disabled by default)	4543	ev_port.c only when the solaris port backend is enabled
3721		4544
3722	F<ev.c> includes the backend files directly when enabled, so you only need	4545	F<ev.c> includes the backend files directly when enabled, so you only need
3723	to compile this single file.	4546	to compile this single file.
3724		4547
3725	=head3 LIBEVENT COMPATIBILITY API	4548	=head3 LIBEVENT COMPATIBILITY API
…		…
3789	supported). It will also not define any of the structs usually found in	4612	supported). It will also not define any of the structs usually found in
3790	F<event.h> that are not directly supported by the libev core alone.	4613	F<event.h> that are not directly supported by the libev core alone.
3791		4614
3792	In standalone mode, libev will still try to automatically deduce the	4615	In standalone mode, libev will still try to automatically deduce the
3793	configuration, but has to be more conservative.	4616	configuration, but has to be more conservative.
		4617
		4618	=item EV_USE_FLOOR
		4619
		4620	If defined to be C<1>, libev will use the C<floor ()> function for its
		4621	periodic reschedule calculations, otherwise libev will fall back on a
		4622	portable (slower) implementation. If you enable this, you usually have to
		4623	link against libm or something equivalent. Enabling this when the C<floor>
		4624	function is not available will fail, so the safe default is to not enable
		4625	this.
3794		4626
3795	=item EV_USE_MONOTONIC	4627	=item EV_USE_MONOTONIC
3796		4628
3797	If defined to be C<1>, libev will try to detect the availability of the	4629	If defined to be C<1>, libev will try to detect the availability of the
3798	monotonic clock option at both compile time and runtime. Otherwise no	4630	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3835	available and will probe for kernel support at runtime. This will improve	4667	available and will probe for kernel support at runtime. This will improve
3836	C<ev_signal> and C<ev_async> performance and reduce resource consumption.	4668	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
3837	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc	4669	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
3838	2.7 or newer, otherwise disabled.	4670	2.7 or newer, otherwise disabled.
3839		4671
		4672	=item EV_USE_SIGNALFD
		4673
		4674	If defined to be C<1>, then libev will assume that C<signalfd ()> is
		4675	available and will probe for kernel support at runtime. This enables
		4676	the use of EVFLAG_SIGNALFD for faster and simpler signal handling. If
		4677	undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4678	2.7 or newer, otherwise disabled.
		4679
		4680	=item EV_USE_TIMERFD
		4681
		4682	If defined to be C<1>, then libev will assume that C<timerfd ()> is
		4683	available and will probe for kernel support at runtime. This allows
		4684	libev to detect time jumps accurately. If undefined, it will be enabled
		4685	if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
		4686	C<TFD_TIMER_CANCEL_ON_SET>, otherwise disabled.
		4687
		4688	=item EV_USE_EVENTFD
		4689
		4690	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4691	available and will probe for kernel support at runtime. This will improve
		4692	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4693	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4694	2.7 or newer, otherwise disabled.
		4695
3840	=item EV_USE_SELECT	4696	=item EV_USE_SELECT
3841		4697
3842	If undefined or defined to be C<1>, libev will compile in support for the	4698	If undefined or defined to be C<1>, libev will compile in support for the
3843	C<select>(2) backend. No attempt at auto-detection will be done: if no	4699	C<select>(2) backend. No attempt at auto-detection will be done: if no
3844	other method takes over, select will be it. Otherwise the select backend	4700	other method takes over, select will be it. Otherwise the select backend
…		…
3884	If programs implement their own fd to handle mapping on win32, then this	4740	If programs implement their own fd to handle mapping on win32, then this
3885	macro can be used to override the C<close> function, useful to unregister	4741	macro can be used to override the C<close> function, useful to unregister
3886	file descriptors again. Note that the replacement function has to close	4742	file descriptors again. Note that the replacement function has to close
3887	the underlying OS handle.	4743	the underlying OS handle.
3888		4744
		4745	=item EV_USE_WSASOCKET
		4746
		4747	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4748	communication socket, which works better in some environments. Otherwise,
		4749	the normal C<socket> function will be used, which works better in other
		4750	environments.
		4751
3889	=item EV_USE_POLL	4752	=item EV_USE_POLL
3890		4753
3891	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4754	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3892	backend. Otherwise it will be enabled on non-win32 platforms. It	4755	backend. Otherwise it will be enabled on non-win32 platforms. It
3893	takes precedence over select.	4756	takes precedence over select.
…		…
3897	If defined to be C<1>, libev will compile in support for the Linux	4760	If defined to be C<1>, libev will compile in support for the Linux
3898	C<epoll>(7) backend. Its availability will be detected at runtime,	4761	C<epoll>(7) backend. Its availability will be detected at runtime,
3899	otherwise another method will be used as fallback. This is the preferred	4762	otherwise another method will be used as fallback. This is the preferred
3900	backend for GNU/Linux systems. If undefined, it will be enabled if the	4763	backend for GNU/Linux systems. If undefined, it will be enabled if the
3901	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4764	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4765
		4766	=item EV_USE_LINUXAIO
		4767
		4768	If defined to be C<1>, libev will compile in support for the Linux aio
		4769	backend (C<EV_USE_EPOLL> must also be enabled). If undefined, it will be
		4770	enabled on linux, otherwise disabled.
		4771
		4772	=item EV_USE_IOURING
		4773
		4774	If defined to be C<1>, libev will compile in support for the Linux
		4775	io_uring backend (C<EV_USE_EPOLL> must also be enabled). Due to it's
		4776	current limitations it has to be requested explicitly. If undefined, it
		4777	will be enabled on linux, otherwise disabled.
3902		4778
3903	=item EV_USE_KQUEUE	4779	=item EV_USE_KQUEUE
3904		4780
3905	If defined to be C<1>, libev will compile in support for the BSD style	4781	If defined to be C<1>, libev will compile in support for the BSD style
3906	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4782	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
3928	If defined to be C<1>, libev will compile in support for the Linux inotify	4804	If defined to be C<1>, libev will compile in support for the Linux inotify
3929	interface to speed up C<ev_stat> watchers. Its actual availability will	4805	interface to speed up C<ev_stat> watchers. Its actual availability will
3930	be detected at runtime. If undefined, it will be enabled if the headers	4806	be detected at runtime. If undefined, it will be enabled if the headers
3931	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4807	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3932		4808
		4809	=item EV_NO_SMP
		4810
		4811	If defined to be C<1>, libev will assume that memory is always coherent
		4812	between threads, that is, threads can be used, but threads never run on
		4813	different cpus (or different cpu cores). This reduces dependencies
		4814	and makes libev faster.
		4815
		4816	=item EV_NO_THREADS
		4817
		4818	If defined to be C<1>, libev will assume that it will never be called from
		4819	different threads (that includes signal handlers), which is a stronger
		4820	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4821	libev faster.
		4822
3933	=item EV_ATOMIC_T	4823	=item EV_ATOMIC_T
3934		4824
3935	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4825	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3936	access is atomic with respect to other threads or signal contexts. No such	4826	access is atomic with respect to other threads or signal contexts. No
3937	type is easily found in the C language, so you can provide your own type	4827	such type is easily found in the C language, so you can provide your own
3938	that you know is safe for your purposes. It is used both for signal handler "locking"	4828	type that you know is safe for your purposes. It is used both for signal
3939	as well as for signal and thread safety in C<ev_async> watchers.	4829	handler "locking" as well as for signal and thread safety in C<ev_async>
		4830	watchers.
3940		4831
3941	In the absence of this define, libev will use C<sig_atomic_t volatile>	4832	In the absence of this define, libev will use C<sig_atomic_t volatile>
3942	(from F<signal.h>), which is usually good enough on most platforms.	4833	(from F<signal.h>), which is usually good enough on most platforms.
3943		4834
3944	=item EV_H (h)	4835	=item EV_H (h)
…		…
3971	will have the C<struct ev_loop *> as first argument, and you can create	4862	will have the C<struct ev_loop *> as first argument, and you can create
3972	additional independent event loops. Otherwise there will be no support	4863	additional independent event loops. Otherwise there will be no support
3973	for multiple event loops and there is no first event loop pointer	4864	for multiple event loops and there is no first event loop pointer
3974	argument. Instead, all functions act on the single default loop.	4865	argument. Instead, all functions act on the single default loop.
3975		4866
		4867	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4868	default loop when multiplicity is switched off - you always have to
		4869	initialise the loop manually in this case.
		4870
3976	=item EV_MINPRI	4871	=item EV_MINPRI
3977		4872
3978	=item EV_MAXPRI	4873	=item EV_MAXPRI
3979		4874
3980	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4875	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4016	#define EV_USE_POLL 1	4911	#define EV_USE_POLL 1
4017	#define EV_CHILD_ENABLE 1	4912	#define EV_CHILD_ENABLE 1
4018	#define EV_ASYNC_ENABLE 1	4913	#define EV_ASYNC_ENABLE 1
4019		4914
4020	The actual value is a bitset, it can be a combination of the following	4915	The actual value is a bitset, it can be a combination of the following
4021	values:	4916	values (by default, all of these are enabled):
4022		4917
4023	=over 4	4918	=over 4
4024		4919
4025	=item C<1> - faster/larger code	4920	=item C<1> - faster/larger code
4026		4921
…		…
4030	code size by roughly 30% on amd64).	4925	code size by roughly 30% on amd64).
4031		4926
4032	When optimising for size, use of compiler flags such as C<-Os> with	4927	When optimising for size, use of compiler flags such as C<-Os> with
4033	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4928	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4034	assertions.	4929	assertions.
		4930
		4931	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4932	(e.g. gcc with C<-Os>).
4035		4933
4036	=item C<2> - faster/larger data structures	4934	=item C<2> - faster/larger data structures
4037		4935
4038	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4936	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4039	hash table sizes and so on. This will usually further increase code size	4937	hash table sizes and so on. This will usually further increase code size
4040	and can additionally have an effect on the size of data structures at	4938	and can additionally have an effect on the size of data structures at
4041	runtime.	4939	runtime.
4042		4940
		4941	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4942	(e.g. gcc with C<-Os>).
		4943
4043	=item C<4> - full API configuration	4944	=item C<4> - full API configuration
4044		4945
4045	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4946	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4046	enables multiplicity (C<EV_MULTIPLICITY>=1).	4947	enables multiplicity (C<EV_MULTIPLICITY>=1).
4047		4948
…		…
4077		4978
4078	With an intelligent-enough linker (gcc+binutils are intelligent enough	4979	With an intelligent-enough linker (gcc+binutils are intelligent enough
4079	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4980	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4080	your program might be left out as well - a binary starting a timer and an	4981	your program might be left out as well - a binary starting a timer and an
4081	I/O watcher then might come out at only 5Kb.	4982	I/O watcher then might come out at only 5Kb.
		4983
		4984	=item EV_API_STATIC
		4985
		4986	If this symbol is defined (by default it is not), then all identifiers
		4987	will have static linkage. This means that libev will not export any
		4988	identifiers, and you cannot link against libev anymore. This can be useful
		4989	when you embed libev, only want to use libev functions in a single file,
		4990	and do not want its identifiers to be visible.
		4991
		4992	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4993	wants to use libev.
		4994
		4995	This option only works when libev is compiled with a C compiler, as C++
		4996	doesn't support the required declaration syntax.
4082		4997
4083	=item EV_AVOID_STDIO	4998	=item EV_AVOID_STDIO
4084		4999
4085	If this is set to C<1> at compiletime, then libev will avoid using stdio	5000	If this is set to C<1> at compiletime, then libev will avoid using stdio
4086	functions (printf, scanf, perror etc.). This will increase the code size	5001	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4144	in. If set to C<1>, then verification code will be compiled in, but not	5059	in. If set to C<1>, then verification code will be compiled in, but not
4145	called. If set to C<2>, then the internal verification code will be	5060	called. If set to C<2>, then the internal verification code will be
4146	called once per loop, which can slow down libev. If set to C<3>, then the	5061	called once per loop, which can slow down libev. If set to C<3>, then the
4147	verification code will be called very frequently, which will slow down	5062	verification code will be called very frequently, which will slow down
4148	libev considerably.	5063	libev considerably.
		5064
		5065	Verification errors are reported via C's C<assert> mechanism, so if you
		5066	disable that (e.g. by defining C<NDEBUG>) then no errors will be reported.
4149		5067
4150	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it	5068	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
4151	will be C<0>.	5069	will be C<0>.
4152		5070
4153	=item EV_COMMON	5071	=item EV_COMMON
…		…
4230	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5148	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4231		5149
4232	#include "ev_cpp.h"	5150	#include "ev_cpp.h"
4233	#include "ev.c"	5151	#include "ev.c"
4234		5152
4235	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5153	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4236		5154
4237	=head2 THREADS AND COROUTINES	5155	=head2 THREADS AND COROUTINES
4238		5156
4239	=head3 THREADS	5157	=head3 THREADS
4240		5158
…		…
4291	default loop and triggering an C<ev_async> watcher from the default loop	5209	default loop and triggering an C<ev_async> watcher from the default loop
4292	watcher callback into the event loop interested in the signal.	5210	watcher callback into the event loop interested in the signal.
4293		5211
4294	=back	5212	=back
4295		5213
4296	=head4 THREAD LOCKING EXAMPLE	5214	See also L</THREAD LOCKING EXAMPLE>.
4297
4298	Here is a fictitious example of how to run an event loop in a different
4299	thread than where callbacks are being invoked and watchers are
4300	created/added/removed.
4301
4302	For a real-world example, see the C<EV::Loop::Async> perl module,
4303	which uses exactly this technique (which is suited for many high-level
4304	languages).
4305
4306	The example uses a pthread mutex to protect the loop data, a condition
4307	variable to wait for callback invocations, an async watcher to notify the
4308	event loop thread and an unspecified mechanism to wake up the main thread.
4309
4310	First, you need to associate some data with the event loop:
4311
4312	typedef struct {
4313	mutex_t lock; /* global loop lock */
4314	ev_async async_w;
4315	thread_t tid;
4316	cond_t invoke_cv;
4317	} userdata;
4318
4319	void prepare_loop (EV_P)
4320	{
4321	// for simplicity, we use a static userdata struct.
4322	static userdata u;
4323
4324	ev_async_init (&u->async_w, async_cb);
4325	ev_async_start (EV_A_ &u->async_w);
4326
4327	pthread_mutex_init (&u->lock, 0);
4328	pthread_cond_init (&u->invoke_cv, 0);
4329
4330	// now associate this with the loop
4331	ev_set_userdata (EV_A_ u);
4332	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4333	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4334
4335	// then create the thread running ev_loop
4336	pthread_create (&u->tid, 0, l_run, EV_A);
4337	}
4338
4339	The callback for the C<ev_async> watcher does nothing: the watcher is used
4340	solely to wake up the event loop so it takes notice of any new watchers
4341	that might have been added:
4342
4343	static void
4344	async_cb (EV_P_ ev_async *w, int revents)
4345	{
4346	// just used for the side effects
4347	}
4348
4349	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4350	protecting the loop data, respectively.
4351
4352	static void
4353	l_release (EV_P)
4354	{
4355	userdata *u = ev_userdata (EV_A);
4356	pthread_mutex_unlock (&u->lock);
4357	}
4358
4359	static void
4360	l_acquire (EV_P)
4361	{
4362	userdata *u = ev_userdata (EV_A);
4363	pthread_mutex_lock (&u->lock);
4364	}
4365
4366	The event loop thread first acquires the mutex, and then jumps straight
4367	into C<ev_run>:
4368
4369	void *
4370	l_run (void *thr_arg)
4371	{
4372	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4373
4374	l_acquire (EV_A);
4375	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4376	ev_run (EV_A_ 0);
4377	l_release (EV_A);
4378
4379	return 0;
4380	}
4381
4382	Instead of invoking all pending watchers, the C<l_invoke> callback will
4383	signal the main thread via some unspecified mechanism (signals? pipe
4384	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4385	have been called (in a while loop because a) spurious wakeups are possible
4386	and b) skipping inter-thread-communication when there are no pending
4387	watchers is very beneficial):
4388
4389	static void
4390	l_invoke (EV_P)
4391	{
4392	userdata *u = ev_userdata (EV_A);
4393
4394	while (ev_pending_count (EV_A))
4395	{
4396	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4397	pthread_cond_wait (&u->invoke_cv, &u->lock);
4398	}
4399	}
4400
4401	Now, whenever the main thread gets told to invoke pending watchers, it
4402	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4403	thread to continue:
4404
4405	static void
4406	real_invoke_pending (EV_P)
4407	{
4408	userdata *u = ev_userdata (EV_A);
4409
4410	pthread_mutex_lock (&u->lock);
4411	ev_invoke_pending (EV_A);
4412	pthread_cond_signal (&u->invoke_cv);
4413	pthread_mutex_unlock (&u->lock);
4414	}
4415
4416	Whenever you want to start/stop a watcher or do other modifications to an
4417	event loop, you will now have to lock:
4418
4419	ev_timer timeout_watcher;
4420	userdata *u = ev_userdata (EV_A);
4421
4422	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4423
4424	pthread_mutex_lock (&u->lock);
4425	ev_timer_start (EV_A_ &timeout_watcher);
4426	ev_async_send (EV_A_ &u->async_w);
4427	pthread_mutex_unlock (&u->lock);
4428
4429	Note that sending the C<ev_async> watcher is required because otherwise
4430	an event loop currently blocking in the kernel will have no knowledge
4431	about the newly added timer. By waking up the loop it will pick up any new
4432	watchers in the next event loop iteration.
4433		5215
4434	=head3 COROUTINES	5216	=head3 COROUTINES
4435		5217
4436	Libev is very accommodating to coroutines ("cooperative threads"):	5218	Libev is very accommodating to coroutines ("cooperative threads"):
4437	libev fully supports nesting calls to its functions from different	5219	libev fully supports nesting calls to its functions from different
…		…
4602	requires, and its I/O model is fundamentally incompatible with the POSIX	5384	requires, and its I/O model is fundamentally incompatible with the POSIX
4603	model. Libev still offers limited functionality on this platform in	5385	model. Libev still offers limited functionality on this platform in
4604	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5386	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4605	descriptors. This only applies when using Win32 natively, not when using	5387	descriptors. This only applies when using Win32 natively, not when using
4606	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5388	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4607	as every compielr comes with a slightly differently broken/incompatible	5389	as every compiler comes with a slightly differently broken/incompatible
4608	environment.	5390	environment.
4609		5391
4610	Lifting these limitations would basically require the full	5392	Lifting these limitations would basically require the full
4611	re-implementation of the I/O system. If you are into this kind of thing,	5393	re-implementation of the I/O system. If you are into this kind of thing,
4612	then note that glib does exactly that for you in a very portable way (note	5394	then note that glib does exactly that for you in a very portable way (note
…		…
4706	structure (guaranteed by POSIX but not by ISO C for example), but it also	5488	structure (guaranteed by POSIX but not by ISO C for example), but it also
4707	assumes that the same (machine) code can be used to call any watcher	5489	assumes that the same (machine) code can be used to call any watcher
4708	callback: The watcher callbacks have different type signatures, but libev	5490	callback: The watcher callbacks have different type signatures, but libev
4709	calls them using an C<ev_watcher *> internally.	5491	calls them using an C<ev_watcher *> internally.
4710		5492
		5493	=item null pointers and integer zero are represented by 0 bytes
		5494
		5495	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5496	relies on this setting pointers and integers to null.
		5497
		5498	=item pointer accesses must be thread-atomic
		5499
		5500	Accessing a pointer value must be atomic, it must both be readable and
		5501	writable in one piece - this is the case on all current architectures.
		5502
4711	=item C<sig_atomic_t volatile> must be thread-atomic as well	5503	=item C<sig_atomic_t volatile> must be thread-atomic as well
4712		5504
4713	The type C<sig_atomic_t volatile> (or whatever is defined as	5505	The type C<sig_atomic_t volatile> (or whatever is defined as
4714	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5506	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4715	threads. This is not part of the specification for C<sig_atomic_t>, but is	5507	threads. This is not part of the specification for C<sig_atomic_t>, but is
…		…
4723	thread" or will block signals process-wide, both behaviours would	5515	thread" or will block signals process-wide, both behaviours would
4724	be compatible with libev. Interaction between C<sigprocmask> and	5516	be compatible with libev. Interaction between C<sigprocmask> and
4725	C<pthread_sigmask> could complicate things, however.	5517	C<pthread_sigmask> could complicate things, however.
4726		5518
4727	The most portable way to handle signals is to block signals in all threads	5519	The most portable way to handle signals is to block signals in all threads
4728	except the initial one, and run the default loop in the initial thread as	5520	except the initial one, and run the signal handling loop in the initial
4729	well.	5521	thread as well.
4730		5522
4731	=item C<long> must be large enough for common memory allocation sizes	5523	=item C<long> must be large enough for common memory allocation sizes
4732		5524
4733	To improve portability and simplify its API, libev uses C<long> internally	5525	To improve portability and simplify its API, libev uses C<long> internally
4734	instead of C<size_t> when allocating its data structures. On non-POSIX	5526	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4740		5532
4741	The type C<double> is used to represent timestamps. It is required to	5533	The type C<double> is used to represent timestamps. It is required to
4742	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5534	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4743	good enough for at least into the year 4000 with millisecond accuracy	5535	good enough for at least into the year 4000 with millisecond accuracy
4744	(the design goal for libev). This requirement is overfulfilled by	5536	(the design goal for libev). This requirement is overfulfilled by
4745	implementations using IEEE 754, which is basically all existing ones. With	5537	implementations using IEEE 754, which is basically all existing ones.
		5538
4746	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5539	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5540	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5541	is either obsolete or somebody patched it to use C<long double> or
		5542	something like that, just kidding).
4747		5543
4748	=back	5544	=back
4749		5545
4750	If you know of other additional requirements drop me a note.	5546	If you know of other additional requirements drop me a note.
4751		5547
…		…
4813	=item Processing ev_async_send: O(number_of_async_watchers)	5609	=item Processing ev_async_send: O(number_of_async_watchers)
4814		5610
4815	=item Processing signals: O(max_signal_number)	5611	=item Processing signals: O(max_signal_number)
4816		5612
4817	Sending involves a system call I<iff> there were no other C<ev_async_send>	5613	Sending involves a system call I<iff> there were no other C<ev_async_send>
4818	calls in the current loop iteration. Checking for async and signal events	5614	calls in the current loop iteration and the loop is currently
		5615	blocked. Checking for async and signal events involves iterating over all
4819	involves iterating over all running async watchers or all signal numbers.	5616	running async watchers or all signal numbers.
4820		5617
4821	=back	5618	=back
4822		5619
4823		5620
4824	=head1 PORTING FROM LIBEV 3.X TO 4.X	5621	=head1 PORTING FROM LIBEV 3.X TO 4.X
4825		5622
4826	The major version 4 introduced some minor incompatible changes to the API.	5623	The major version 4 introduced some incompatible changes to the API.
4827		5624
4828	At the moment, the C<ev.h> header file tries to implement superficial	5625	At the moment, the C<ev.h> header file provides compatibility definitions
4829	compatibility, so most programs should still compile. Those might be	5626	for all changes, so most programs should still compile. The compatibility
4830	removed in later versions of libev, so better update early than late.	5627	layer might be removed in later versions of libev, so better update to the
		5628	new API early than late.
4831		5629
4832	=over 4	5630	=over 4
		5631
		5632	=item C<EV_COMPAT3> backwards compatibility mechanism
		5633
		5634	The backward compatibility mechanism can be controlled by
		5635	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5636	section.
		5637
		5638	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5639
		5640	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5641
		5642	ev_loop_destroy (EV_DEFAULT_UC);
		5643	ev_loop_fork (EV_DEFAULT);
4833		5644
4834	=item function/symbol renames	5645	=item function/symbol renames
4835		5646
4836	A number of functions and symbols have been renamed:	5647	A number of functions and symbols have been renamed:
4837		5648
…		…
4856	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5667	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4857	as all other watcher types. Note that C<ev_loop_fork> is still called	5668	as all other watcher types. Note that C<ev_loop_fork> is still called
4858	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>	5669	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4859	typedef.	5670	typedef.
4860		5671
4861	=item C<EV_COMPAT3> backwards compatibility mechanism
4862
4863	The backward compatibility mechanism can be controlled by
4864	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4865	section.
4866
4867	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>	5672	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4868		5673
4869	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5674	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4870	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5675	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4871	and work, but the library code will of course be larger.	5676	and work, but the library code will of course be larger.
…		…
4878	=over 4	5683	=over 4
4879		5684
4880	=item active	5685	=item active
4881		5686
4882	A watcher is active as long as it has been started and not yet stopped.	5687	A watcher is active as long as it has been started and not yet stopped.
4883	See L<WATCHER STATES> for details.	5688	See L</WATCHER STATES> for details.
4884		5689
4885	=item application	5690	=item application
4886		5691
4887	In this document, an application is whatever is using libev.	5692	In this document, an application is whatever is using libev.
4888		5693
…		…
4924	watchers and events.	5729	watchers and events.
4925		5730
4926	=item pending	5731	=item pending
4927		5732
4928	A watcher is pending as soon as the corresponding event has been	5733	A watcher is pending as soon as the corresponding event has been
4929	detected. See L<WATCHER STATES> for details.	5734	detected. See L</WATCHER STATES> for details.
4930		5735
4931	=item real time	5736	=item real time
4932		5737
4933	The physical time that is observed. It is apparently strictly monotonic :)	5738	The physical time that is observed. It is apparently strictly monotonic :)
4934		5739
4935	=item wall-clock time	5740	=item wall-clock time
4936		5741
4937	The time and date as shown on clocks. Unlike real time, it can actually	5742	The time and date as shown on clocks. Unlike real time, it can actually
4938	be wrong and jump forwards and backwards, e.g. when the you adjust your	5743	be wrong and jump forwards and backwards, e.g. when you adjust your
4939	clock.	5744	clock.
4940		5745
4941	=item watcher	5746	=item watcher
4942		5747
4943	A data structure that describes interest in certain events. Watchers need	5748	A data structure that describes interest in certain events. Watchers need
…		…
4945		5750
4946	=back	5751	=back
4947		5752
4948	=head1 AUTHOR	5753	=head1 AUTHOR
4949		5754
4950	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5755	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5756	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
4951		5757

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