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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
…		…
124	this argument.	134	this argument.
125		135
126	=head2 TIME REPRESENTATION	136	=head2 TIME REPRESENTATION
127		137
128	Libev represents time as a single floating point number, representing	138	Libev represents time as a single floating point number, representing
129	the (fractional) number of seconds since the (POSIX) epoch (in practise	139	the (fractional) number of seconds since the (POSIX) epoch (in practice
130	somewhere near the beginning of 1970, details are complicated, don't	140	somewhere near the beginning of 1970, details are complicated, don't
131	ask). This type is called C<ev_tstamp>, which is what you should use	141	ask). This type is called C<ev_tstamp>, which is what you should use
132	too. It usually aliases to the C<double> type in C. When you need to do	142	too. It usually aliases to the C<double> type in C. When you need to do
133	any calculations on it, you should treat it as some floating point value.	143	any calculations on it, you should treat it as some floating point value.
134		144
…		…
165		175
166	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
167		177
168	Returns the current time as libev would use it. Please note that the	178	Returns the current time as libev would use it. Please note that the
169	C<ev_now> function is usually faster and also often returns the timestamp	179	C<ev_now> function is usually faster and also often returns the timestamp
170	you actually want to know.	180	you actually want to know. Also interesting is the combination of
		181	C<ev_now_update> and C<ev_now>.
171		182
172	=item ev_sleep (ev_tstamp interval)	183	=item ev_sleep (ev_tstamp interval)
173		184
174	Sleep for the given interval: The current thread will be blocked until	185	Sleep for the given interval: The current thread will be blocked
175	either it is interrupted or the given time interval has passed. Basically	186	until either it is interrupted or the given time interval has
		187	passed (approximately - it might return a bit earlier even if not
		188	interrupted). Returns immediately if C<< interval <= 0 >>.
		189
176	this is a sub-second-resolution C<sleep ()>.	190	Basically this is a sub-second-resolution C<sleep ()>.
		191
		192	The range of the C<interval> is limited - libev only guarantees to work
		193	with sleep times of up to one day (C<< interval <= 86400 >>).
177		194
178	=item int ev_version_major ()	195	=item int ev_version_major ()
179		196
180	=item int ev_version_minor ()	197	=item int ev_version_minor ()
181		198
…		…
192	as this indicates an incompatible change. Minor versions are usually	209	as this indicates an incompatible change. Minor versions are usually
193	compatible to older versions, so a larger minor version alone is usually	210	compatible to older versions, so a larger minor version alone is usually
194	not a problem.	211	not a problem.
195		212
196	Example: Make sure we haven't accidentally been linked against the wrong	213	Example: Make sure we haven't accidentally been linked against the wrong
197	version (note, however, that this will not detect ABI mismatches :).	214	version (note, however, that this will not detect other ABI mismatches,
		215	such as LFS or reentrancy).
198		216
199	assert (("libev version mismatch",	217	assert (("libev version mismatch",
200	ev_version_major () == EV_VERSION_MAJOR	218	ev_version_major () == EV_VERSION_MAJOR
201	&& ev_version_minor () >= EV_VERSION_MINOR));	219	&& ev_version_minor () >= EV_VERSION_MINOR));
202		220
…		…
213	assert (("sorry, no epoll, no sex",	231	assert (("sorry, no epoll, no sex",
214	ev_supported_backends () & EVBACKEND_EPOLL));	232	ev_supported_backends () & EVBACKEND_EPOLL));
215		233
216	=item unsigned int ev_recommended_backends ()	234	=item unsigned int ev_recommended_backends ()
217		235
218	Return the set of all backends compiled into this binary of libev and also	236	Return the set of all backends compiled into this binary of libev and
219	recommended for this platform. This set is often smaller than the one	237	also recommended for this platform, meaning it will work for most file
		238	descriptor types. This set is often smaller than the one returned by
220	returned by C<ev_supported_backends>, as for example kqueue is broken on	239	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
221	most BSDs and will not be auto-detected unless you explicitly request it	240	and will not be auto-detected unless you explicitly request it (assuming
222	(assuming you know what you are doing). This is the set of backends that	241	you know what you are doing). This is the set of backends that libev will
223	libev will probe for if you specify no backends explicitly.	242	probe for if you specify no backends explicitly.
224		243
225	=item unsigned int ev_embeddable_backends ()	244	=item unsigned int ev_embeddable_backends ()
226		245
227	Returns the set of backends that are embeddable in other event loops. This	246	Returns the set of backends that are embeddable in other event loops. This
228	is the theoretical, all-platform, value. To find which backends	247	value is platform-specific but can include backends not available on the
229	might be supported on the current system, you would need to look at	248	current system. To find which embeddable backends might be supported on
230	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	249	the current system, you would need to look at C<ev_embeddable_backends ()
231	recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
232		251
233	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
234		253
235	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
236		255
237	Sets the allocation function to use (the prototype is similar - the	256	Sets the allocation function to use (the prototype is similar - the
238	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	257	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
239	used to allocate and free memory (no surprises here). If it returns zero	258	used to allocate and free memory (no surprises here). If it returns zero
240	when memory needs to be allocated (C<size != 0>), the library might abort	259	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
246		265
247	You could override this function in high-availability programs to, say,	266	You could override this function in high-availability programs to, say,
248	free some memory if it cannot allocate memory, to use a special allocator,	267	free some memory if it cannot allocate memory, to use a special allocator,
249	or even to sleep a while and retry until some memory is available.	268	or even to sleep a while and retry until some memory is available.
250		269
		270	Example: The following is the C<realloc> function that libev itself uses
		271	which should work with C<realloc> and C<free> functions of all kinds and
		272	is probably a good basis for your own implementation.
		273
		274	static void *
		275	ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
		276	{
		277	if (size)
		278	return realloc (ptr, size);
		279
		280	free (ptr);
		281	return 0;
		282	}
		283
251	Example: Replace the libev allocator with one that waits a bit and then	284	Example: Replace the libev allocator with one that waits a bit and then
252	retries (example requires a standards-compliant C<realloc>).	285	retries.
253		286
254	static void *	287	static void *
255	persistent_realloc (void *ptr, size_t size)	288	persistent_realloc (void *ptr, size_t size)
256	{	289	{
		290	if (!size)
		291	{
		292	free (ptr);
		293	return 0;
		294	}
		295
257	for (;;)	296	for (;;)
258	{	297	{
259	void *newptr = realloc (ptr, size);	298	void *newptr = realloc (ptr, size);
260		299
261	if (newptr)	300	if (newptr)
…		…
266	}	305	}
267		306
268	...	307	...
269	ev_set_allocator (persistent_realloc);	308	ev_set_allocator (persistent_realloc);
270		309
271	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	310	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
272		311
273	Set the callback function to call on a retryable system call error (such	312	Set the callback function to call on a retryable system call error (such
274	as failed select, poll, epoll_wait). The message is a printable string	313	as failed select, poll, epoll_wait). The message is a printable string
275	indicating the system call or subsystem causing the problem. If this	314	indicating the system call or subsystem causing the problem. If this
276	callback is set, then libev will expect it to remedy the situation, no	315	callback is set, then libev will expect it to remedy the situation, no
…		…
288	}	327	}
289		328
290	...	329	...
291	ev_set_syserr_cb (fatal_error);	330	ev_set_syserr_cb (fatal_error);
292		331
		332	=item ev_feed_signal (int signum)
		333
		334	This function can be used to "simulate" a signal receive. It is completely
		335	safe to call this function at any time, from any context, including signal
		336	handlers or random threads.
		337
		338	Its main use is to customise signal handling in your process, especially
		339	in the presence of threads. For example, you could block signals
		340	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		341	creating any loops), and in one thread, use C<sigwait> or any other
		342	mechanism to wait for signals, then "deliver" them to libev by calling
		343	C<ev_feed_signal>.
		344
293	=back	345	=back
294		346
295	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	347	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
296		348
297	An event loop is described by a C<struct ev_loop *> (the C<struct> is	349	An event loop is described by a C<struct ev_loop *> (the C<struct> is
298	I<not> optional in this case unless libev 3 compatibility is disabled, as	350	I<not> optional in this case unless libev 3 compatibility is disabled, as
299	libev 3 had an C<ev_loop> function colliding with the struct name).	351	libev 3 had an C<ev_loop> function colliding with the struct name).
300		352
301	The library knows two types of such loops, the I<default> loop, which	353	The library knows two types of such loops, the I<default> loop, which
302	supports signals and child events, and dynamically created event loops	354	supports child process events, and dynamically created event loops which
303	which do not.	355	do not.
304		356
305	=over 4	357	=over 4
306		358
307	=item struct ev_loop *ev_default_loop (unsigned int flags)	359	=item struct ev_loop *ev_default_loop (unsigned int flags)
308		360
309	This will initialise the default event loop if it hasn't been initialised	361	This returns the "default" event loop object, which is what you should
310	yet and return it. If the default loop could not be initialised, returns	362	normally use when you just need "the event loop". Event loop objects and
311	false. If it already was initialised it simply returns it (and ignores the	363	the C<flags> parameter are described in more detail in the entry for
312	flags. If that is troubling you, check C<ev_backend ()> afterwards).	364	C<ev_loop_new>.
		365
		366	If the default loop is already initialised then this function simply
		367	returns it (and ignores the flags. If that is troubling you, check
		368	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		369	flags, which should almost always be C<0>, unless the caller is also the
		370	one calling C<ev_run> or otherwise qualifies as "the main program".
313		371
314	If you don't know what event loop to use, use the one returned from this	372	If you don't know what event loop to use, use the one returned from this
315	function.	373	function (or via the C<EV_DEFAULT> macro).
316		374
317	Note that this function is I<not> thread-safe, so if you want to use it	375	Note that this function is I<not> thread-safe, so if you want to use it
318	from multiple threads, you have to lock (note also that this is unlikely,	376	from multiple threads, you have to employ some kind of mutex (note also
319	as loops cannot be shared easily between threads anyway).	377	that this case is unlikely, as loops cannot be shared easily between
		378	threads anyway).
320		379
321	The default loop is the only loop that can handle C<ev_signal> and	380	The default loop is the only loop that can handle C<ev_child> watchers,
322	C<ev_child> watchers, and to do this, it always registers a handler	381	and to do this, it always registers a handler for C<SIGCHLD>. If this is
323	for C<SIGCHLD>. If this is a problem for your application you can either	382	a problem for your application you can either create a dynamic loop with
324	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	383	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
325	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	384	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
326	C<ev_default_init>.	385
		386	Example: This is the most typical usage.
		387
		388	if (!ev_default_loop (0))
		389	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		390
		391	Example: Restrict libev to the select and poll backends, and do not allow
		392	environment settings to be taken into account:
		393
		394	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		395
		396	=item struct ev_loop *ev_loop_new (unsigned int flags)
		397
		398	This will create and initialise a new event loop object. If the loop
		399	could not be initialised, returns false.
		400
		401	This function is thread-safe, and one common way to use libev with
		402	threads is indeed to create one loop per thread, and using the default
		403	loop in the "main" or "initial" thread.
327		404
328	The flags argument can be used to specify special behaviour or specific	405	The flags argument can be used to specify special behaviour or specific
329	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	406	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
330		407
331	The following flags are supported:	408	The following flags are supported:
…		…
341		418
342	If this flag bit is or'ed into the flag value (or the program runs setuid	419	If this flag bit is or'ed into the flag value (or the program runs setuid
343	or setgid) then libev will I<not> look at the environment variable	420	or setgid) then libev will I<not> look at the environment variable
344	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	421	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
345	override the flags completely if it is found in the environment. This is	422	override the flags completely if it is found in the environment. This is
346	useful to try out specific backends to test their performance, or to work	423	useful to try out specific backends to test their performance, to work
347	around bugs.	424	around bugs, or to make libev threadsafe (accessing environment variables
		425	cannot be done in a threadsafe way, but usually it works if no other
		426	thread modifies them).
348		427
349	=item C<EVFLAG_FORKCHECK>	428	=item C<EVFLAG_FORKCHECK>
350		429
351	Instead of calling C<ev_loop_fork> manually after a fork, you can also	430	Instead of calling C<ev_loop_fork> manually after a fork, you can also
352	make libev check for a fork in each iteration by enabling this flag.	431	make libev check for a fork in each iteration by enabling this flag.
353		432
354	This works by calling C<getpid ()> on every iteration of the loop,	433	This works by calling C<getpid ()> on every iteration of the loop,
355	and thus this might slow down your event loop if you do a lot of loop	434	and thus this might slow down your event loop if you do a lot of loop
356	iterations and little real work, but is usually not noticeable (on my	435	iterations and little real work, but is usually not noticeable (on my
357	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	436	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
358	without a system call and thus I<very> fast, but my GNU/Linux system also has	437	sequence without a system call and thus I<very> fast, but my GNU/Linux
359	C<pthread_atfork> which is even faster).	438	system also has C<pthread_atfork> which is even faster). (Update: glibc
		439	versions 2.25 apparently removed the C<getpid> optimisation again).
360		440
361	The big advantage of this flag is that you can forget about fork (and	441	The big advantage of this flag is that you can forget about fork (and
362	forget about forgetting to tell libev about forking) when you use this	442	forget about forgetting to tell libev about forking, although you still
363	flag.	443	have to ignore C<SIGPIPE>) when you use this flag.
364		444
365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	445	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
366	environment variable.	446	environment variable.
367		447
368	=item C<EVFLAG_NOINOTIFY>	448	=item C<EVFLAG_NOINOTIFY>
369		449
370	When this flag is specified, then libev will not attempt to use the	450	When this flag is specified, then libev will not attempt to use the
371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and	451	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
372	testing, this flag can be useful to conserve inotify file descriptors, as	452	testing, this flag can be useful to conserve inotify file descriptors, as
373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.	453	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
374		454
375	=item C<EVFLAG_SIGNALFD>	455	=item C<EVFLAG_SIGNALFD>
376		456
377	When this flag is specified, then libev will attempt to use the	457	When this flag is specified, then libev will attempt to use the
378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API	458	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
379	delivers signals synchronously, which makes it both faster and might make	459	delivers signals synchronously, which makes it both faster and might make
380	it possible to get the queued signal data. It can also simplify signal	460	it possible to get the queued signal data. It can also simplify signal
381	handling with threads, as long as you properly block signals in your	461	handling with threads, as long as you properly block signals in your
382	threads that are not interested in handling them.	462	threads that are not interested in handling them.
383		463
384	Signalfd will not be used by default as this changes your signal mask, and	464	Signalfd will not be used by default as this changes your signal mask, and
385	there are a lot of shoddy libraries and programs (glib's threadpool for	465	there are a lot of shoddy libraries and programs (glib's threadpool for
386	example) that can't properly initialise their signal masks.	466	example) that can't properly initialise their signal masks.
		467
		468	=item C<EVFLAG_NOSIGMASK>
		469
		470	When this flag is specified, then libev will avoid to modify the signal
		471	mask. Specifically, this means you have to make sure signals are unblocked
		472	when you want to receive them.
		473
		474	This behaviour is useful when you want to do your own signal handling, or
		475	want to handle signals only in specific threads and want to avoid libev
		476	unblocking the signals.
		477
		478	It's also required by POSIX in a threaded program, as libev calls
		479	C<sigprocmask>, whose behaviour is officially unspecified.
		480
		481	This flag's behaviour will become the default in future versions of libev.
387		482
388	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	483	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
389		484
390	This is your standard select(2) backend. Not I<completely> standard, as	485	This is your standard select(2) backend. Not I<completely> standard, as
391	libev tries to roll its own fd_set with no limits on the number of fds,	486	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
419	=item C<EVBACKEND_EPOLL> (value 4, Linux)	514	=item C<EVBACKEND_EPOLL> (value 4, Linux)
420		515
421	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	516	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
422	kernels).	517	kernels).
423		518
424	For few fds, this backend is a bit little slower than poll and select,	519	For few fds, this backend is a bit little slower than poll and select, but
425	but it scales phenomenally better. While poll and select usually scale	520	it scales phenomenally better. While poll and select usually scale like
426	like O(total_fds) where n is the total number of fds (or the highest fd),	521	O(total_fds) where total_fds is the total number of fds (or the highest
427	epoll scales either O(1) or O(active_fds).	522	fd), epoll scales either O(1) or O(active_fds).
428		523
429	The epoll mechanism deserves honorable mention as the most misdesigned	524	The epoll mechanism deserves honorable mention as the most misdesigned
430	of the more advanced event mechanisms: mere annoyances include silently	525	of the more advanced event mechanisms: mere annoyances include silently
431	dropping file descriptors, requiring a system call per change per file	526	dropping file descriptors, requiring a system call per change per file
432	descriptor (and unnecessary guessing of parameters), problems with dup and	527	descriptor (and unnecessary guessing of parameters), problems with dup,
		528	returning before the timeout value, resulting in additional iterations
		529	(and only giving 5ms accuracy while select on the same platform gives
433	so on. The biggest issue is fork races, however - if a program forks then	530	0.1ms) and so on. The biggest issue is fork races, however - if a program
434	I<both> parent and child process have to recreate the epoll set, which can	531	forks then I<both> parent and child process have to recreate the epoll
435	take considerable time (one syscall per file descriptor) and is of course	532	set, which can take considerable time (one syscall per file descriptor)
436	hard to detect.	533	and is of course hard to detect.
437		534
438	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	535	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
439	of course I<doesn't>, and epoll just loves to report events for totally	536	but of course I<doesn't>, and epoll just loves to report events for
440	I<different> file descriptors (even already closed ones, so one cannot	537	totally I<different> file descriptors (even already closed ones, so
441	even remove them from the set) than registered in the set (especially	538	one cannot even remove them from the set) than registered in the set
442	on SMP systems). Libev tries to counter these spurious notifications by	539	(especially on SMP systems). Libev tries to counter these spurious
443	employing an additional generation counter and comparing that against the	540	notifications by employing an additional generation counter and comparing
444	events to filter out spurious ones, recreating the set when required. Last	541	that against the events to filter out spurious ones, recreating the set
		542	when required. Epoll also erroneously rounds down timeouts, but gives you
		543	no way to know when and by how much, so sometimes you have to busy-wait
		544	because epoll returns immediately despite a nonzero timeout. And last
445	not least, it also refuses to work with some file descriptors which work	545	not least, it also refuses to work with some file descriptors which work
446	perfectly fine with C<select> (files, many character devices...).	546	perfectly fine with C<select> (files, many character devices...).
		547
		548	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		549	cobbled together in a hurry, no thought to design or interaction with
		550	others. Oh, the pain, will it ever stop...
447		551
448	While stopping, setting and starting an I/O watcher in the same iteration	552	While stopping, setting and starting an I/O watcher in the same iteration
449	will result in some caching, there is still a system call per such	553	will result in some caching, there is still a system call per such
450	incident (because the same I<file descriptor> could point to a different	554	incident (because the same I<file descriptor> could point to a different
451	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	555	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
463	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or	567	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
464	faster than epoll for maybe up to a hundred file descriptors, depending on	568	faster than epoll for maybe up to a hundred file descriptors, depending on
465	the usage. So sad.	569	the usage. So sad.
466		570
467	While nominally embeddable in other event loops, this feature is broken in	571	While nominally embeddable in other event loops, this feature is broken in
468	all kernel versions tested so far.	572	a lot of kernel revisions, but probably(!) works in current versions.
		573
		574	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		575	C<EVBACKEND_POLL>.
		576
		577	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		578
		579	Use the linux-specific linux aio (I<not> C<< aio(7) >> but C<<
		580	io_submit(2) >>) event interface available in post-4.18 kernels.
		581
		582	If this backend works for you (as of this writing, it was very
		583	experimental), it is the best event interface available on linux and might
		584	be well worth enabling it - if it isn't available in your kernel this will
		585	be detected and this backend will be skipped.
		586
		587	This backend can batch oneshot requests and supports a user-space ring
		588	buffer to receive events. It also doesn't suffer from most of the design
		589	problems of epoll (such as not being able to remove event sources from the
		590	epoll set), and generally sounds too good to be true. Because, this being
		591	the linux kernel, of course it suffers from a whole new set of limitations.
		592
		593	For one, it is not easily embeddable (but probably could be done using
		594	an event fd at some extra overhead). It also is subject to a system wide
		595	limit that can be configured in F</proc/sys/fs/aio-max-nr> - each loop
		596	currently requires C<61> of this number. If no aio requests are left, this
		597	backend will be skipped during initialisation.
		598
		599	Most problematic in practise, however, is that not all file descriptors
		600	work with it. For example, in linux 5.1, tcp sockets, pipes, event fds,
		601	files, F</dev/null> and a few others are supported, but ttys do not work
		602	properly (a known bug that the kernel developers don't care about, see
		603	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		604	(yet?) a generic event polling interface.
		605
		606	Overall, it seems the linux developers just don't want it to have a
		607	generic event handling mechanism other than C<select> or C<poll>.
		608
		609	To work around the fd type problem, the current version of libev uses
		610	epoll as a fallback for file deescriptor types that do not work. Epoll
		611	is used in, kind of, slow mode that hopefully avoids most of its design
		612	problems and requires 1-3 extra syscalls per active fd every iteration.
469		613
470	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	614	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
471	C<EVBACKEND_POLL>.	615	C<EVBACKEND_POLL>.
472		616
473	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	617	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
…		…
488		632
489	It scales in the same way as the epoll backend, but the interface to the	633	It scales in the same way as the epoll backend, but the interface to the
490	kernel is more efficient (which says nothing about its actual speed, of	634	kernel is more efficient (which says nothing about its actual speed, of
491	course). While stopping, setting and starting an I/O watcher does never	635	course). While stopping, setting and starting an I/O watcher does never
492	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	636	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
493	two event changes per incident. Support for C<fork ()> is very bad (but	637	two event changes per incident. Support for C<fork ()> is very bad (you
494	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	638	might have to leak fd's on fork, but it's more sane than epoll) and it
495	cases	639	drops fds silently in similarly hard-to-detect cases.
496		640
497	This backend usually performs well under most conditions.	641	This backend usually performs well under most conditions.
498		642
499	While nominally embeddable in other event loops, this doesn't work	643	While nominally embeddable in other event loops, this doesn't work
500	everywhere, so you might need to test for this. And since it is broken	644	everywhere, so you might need to test for this. And since it is broken
…		…
517	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	661	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
518		662
519	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	663	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
520	it's really slow, but it still scales very well (O(active_fds)).	664	it's really slow, but it still scales very well (O(active_fds)).
521		665
522	Please note that Solaris event ports can deliver a lot of spurious
523	notifications, so you need to use non-blocking I/O or other means to avoid
524	blocking when no data (or space) is available.
525
526	While this backend scales well, it requires one system call per active	666	While this backend scales well, it requires one system call per active
527	file descriptor per loop iteration. For small and medium numbers of file	667	file descriptor per loop iteration. For small and medium numbers of file
528	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	668	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
529	might perform better.	669	might perform better.
530		670
531	On the positive side, with the exception of the spurious readiness	671	On the positive side, this backend actually performed fully to
532	notifications, this backend actually performed fully to specification
533	in all tests and is fully embeddable, which is a rare feat among the	672	specification in all tests and is fully embeddable, which is a rare feat
534	OS-specific backends (I vastly prefer correctness over speed hacks).	673	among the OS-specific backends (I vastly prefer correctness over speed
		674	hacks).
		675
		676	On the negative side, the interface is I<bizarre> - so bizarre that
		677	even sun itself gets it wrong in their code examples: The event polling
		678	function sometimes returns events to the caller even though an error
		679	occurred, but with no indication whether it has done so or not (yes, it's
		680	even documented that way) - deadly for edge-triggered interfaces where you
		681	absolutely have to know whether an event occurred or not because you have
		682	to re-arm the watcher.
		683
		684	Fortunately libev seems to be able to work around these idiocies.
535		685
536	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	686	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
537	C<EVBACKEND_POLL>.	687	C<EVBACKEND_POLL>.
538		688
539	=item C<EVBACKEND_ALL>	689	=item C<EVBACKEND_ALL>
540		690
541	Try all backends (even potentially broken ones that wouldn't be tried	691	Try all backends (even potentially broken ones that wouldn't be tried
542	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	692	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
543	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	693	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
544		694
545	It is definitely not recommended to use this flag.	695	It is definitely not recommended to use this flag, use whatever
		696	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		697	at all.
		698
		699	=item C<EVBACKEND_MASK>
		700
		701	Not a backend at all, but a mask to select all backend bits from a
		702	C<flags> value, in case you want to mask out any backends from a flags
		703	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
546		704
547	=back	705	=back
548		706
549	If one or more of the backend flags are or'ed into the flags value,	707	If one or more of the backend flags are or'ed into the flags value,
550	then only these backends will be tried (in the reverse order as listed	708	then only these backends will be tried (in the reverse order as listed
551	here). If none are specified, all backends in C<ev_recommended_backends	709	here). If none are specified, all backends in C<ev_recommended_backends
552	()> will be tried.	710	()> will be tried.
553		711
554	Example: This is the most typical usage.
555
556	if (!ev_default_loop (0))
557	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
558
559	Example: Restrict libev to the select and poll backends, and do not allow
560	environment settings to be taken into account:
561
562	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
563
564	Example: Use whatever libev has to offer, but make sure that kqueue is
565	used if available (warning, breaks stuff, best use only with your own
566	private event loop and only if you know the OS supports your types of
567	fds):
568
569	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
570
571	=item struct ev_loop *ev_loop_new (unsigned int flags)
572
573	Similar to C<ev_default_loop>, but always creates a new event loop that is
574	always distinct from the default loop.
575
576	Note that this function I<is> thread-safe, and one common way to use
577	libev with threads is indeed to create one loop per thread, and using the
578	default loop in the "main" or "initial" thread.
579
580	Example: Try to create a event loop that uses epoll and nothing else.	712	Example: Try to create a event loop that uses epoll and nothing else.
581		713
582	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	714	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
583	if (!epoller)	715	if (!epoller)
584	fatal ("no epoll found here, maybe it hides under your chair");	716	fatal ("no epoll found here, maybe it hides under your chair");
585		717
		718	Example: Use whatever libev has to offer, but make sure that kqueue is
		719	used if available.
		720
		721	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		722
		723	Example: Similarly, on linux, you mgiht want to take advantage of the
		724	linux aio backend if possible, but fall back to something else if that
		725	isn't available.
		726
		727	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
		728
586	=item ev_default_destroy ()	729	=item ev_loop_destroy (loop)
587		730
588	Destroys the default loop (frees all memory and kernel state etc.). None	731	Destroys an event loop object (frees all memory and kernel state
589	of the active event watchers will be stopped in the normal sense, so	732	etc.). None of the active event watchers will be stopped in the normal
590	e.g. C<ev_is_active> might still return true. It is your responsibility to	733	sense, so e.g. C<ev_is_active> might still return true. It is your
591	either stop all watchers cleanly yourself I<before> calling this function,	734	responsibility to either stop all watchers cleanly yourself I<before>
592	or cope with the fact afterwards (which is usually the easiest thing, you	735	calling this function, or cope with the fact afterwards (which is usually
593	can just ignore the watchers and/or C<free ()> them for example).	736	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		737	for example).
594		738
595	Note that certain global state, such as signal state (and installed signal	739	Note that certain global state, such as signal state (and installed signal
596	handlers), will not be freed by this function, and related watchers (such	740	handlers), will not be freed by this function, and related watchers (such
597	as signal and child watchers) would need to be stopped manually.	741	as signal and child watchers) would need to be stopped manually.
598		742
599	In general it is not advisable to call this function except in the	743	This function is normally used on loop objects allocated by
600	rare occasion where you really need to free e.g. the signal handling	744	C<ev_loop_new>, but it can also be used on the default loop returned by
		745	C<ev_default_loop>, in which case it is not thread-safe.
		746
		747	Note that it is not advisable to call this function on the default loop
		748	except in the rare occasion where you really need to free its resources.
601	pipe fds. If you need dynamically allocated loops it is better to use	749	If you need dynamically allocated loops it is better to use C<ev_loop_new>
602	C<ev_loop_new> and C<ev_loop_destroy>.	750	and C<ev_loop_destroy>.
603		751
604	=item ev_loop_destroy (loop)	752	=item ev_loop_fork (loop)
605
606	Like C<ev_default_destroy>, but destroys an event loop created by an
607	earlier call to C<ev_loop_new>.
608
609	=item ev_default_fork ()
610		753
611	This function sets a flag that causes subsequent C<ev_run> iterations	754	This function sets a flag that causes subsequent C<ev_run> iterations
612	to reinitialise the kernel state for backends that have one. Despite the	755	to reinitialise the kernel state for backends that have one. Despite
613	name, you can call it anytime, but it makes most sense after forking, in	756	the name, you can call it anytime you are allowed to start or stop
614	the child process (or both child and parent, but that again makes little	757	watchers (except inside an C<ev_prepare> callback), but it makes most
615	sense). You I<must> call it in the child before using any of the libev	758	sense after forking, in the child process. You I<must> call it (or use
616	functions, and it will only take effect at the next C<ev_run> iteration.	759	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
617		760
		761	In addition, if you want to reuse a loop (via this function or
		762	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		763
618	Again, you I<have> to call it on I<any> loop that you want to re-use after	764	Again, you I<have> to call it on I<any> loop that you want to re-use after
619	a fork, I<even if you do not plan to use the loop in the parent>. This is	765	a fork, I<even if you do not plan to use the loop in the parent>. This is
620	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	766	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
621	during fork.	767	during fork.
622		768
623	On the other hand, you only need to call this function in the child	769	On the other hand, you only need to call this function in the child
…		…
626	call it at all (in fact, C<epoll> is so badly broken that it makes a	772	call it at all (in fact, C<epoll> is so badly broken that it makes a
627	difference, but libev will usually detect this case on its own and do a	773	difference, but libev will usually detect this case on its own and do a
628	costly reset of the backend).	774	costly reset of the backend).
629		775
630	The function itself is quite fast and it's usually not a problem to call	776	The function itself is quite fast and it's usually not a problem to call
631	it just in case after a fork. To make this easy, the function will fit in	777	it just in case after a fork.
632	quite nicely into a call to C<pthread_atfork>:
633		778
		779	Example: Automate calling C<ev_loop_fork> on the default loop when
		780	using pthreads.
		781
		782	static void
		783	post_fork_child (void)
		784	{
		785	ev_loop_fork (EV_DEFAULT);
		786	}
		787
		788	...
634	pthread_atfork (0, 0, ev_default_fork);	789	pthread_atfork (0, 0, post_fork_child);
635
636	=item ev_loop_fork (loop)
637
638	Like C<ev_default_fork>, but acts on an event loop created by
639	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
640	after fork that you want to re-use in the child, and how you keep track of
641	them is entirely your own problem.
642		790
643	=item int ev_is_default_loop (loop)	791	=item int ev_is_default_loop (loop)
644		792
645	Returns true when the given loop is, in fact, the default loop, and false	793	Returns true when the given loop is, in fact, the default loop, and false
646	otherwise.	794	otherwise.
…		…
657	prepare and check phases.	805	prepare and check phases.
658		806
659	=item unsigned int ev_depth (loop)	807	=item unsigned int ev_depth (loop)
660		808
661	Returns the number of times C<ev_run> was entered minus the number of	809	Returns the number of times C<ev_run> was entered minus the number of
662	times C<ev_run> was exited, in other words, the recursion depth.	810	times C<ev_run> was exited normally, in other words, the recursion depth.
663		811
664	Outside C<ev_run>, this number is zero. In a callback, this number is	812	Outside C<ev_run>, this number is zero. In a callback, this number is
665	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	813	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
666	in which case it is higher.	814	in which case it is higher.
667		815
668	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	816	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
669	etc.), doesn't count as "exit" - consider this as a hint to avoid such	817	throwing an exception etc.), doesn't count as "exit" - consider this
670	ungentleman-like behaviour unless it's really convenient.	818	as a hint to avoid such ungentleman-like behaviour unless it's really
		819	convenient, in which case it is fully supported.
671		820
672	=item unsigned int ev_backend (loop)	821	=item unsigned int ev_backend (loop)
673		822
674	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	823	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
675	use.	824	use.
…		…
690		839
691	This function is rarely useful, but when some event callback runs for a	840	This function is rarely useful, but when some event callback runs for a
692	very long time without entering the event loop, updating libev's idea of	841	very long time without entering the event loop, updating libev's idea of
693	the current time is a good idea.	842	the current time is a good idea.
694		843
695	See also L<The special problem of time updates> in the C<ev_timer> section.	844	See also L</The special problem of time updates> in the C<ev_timer> section.
696		845
697	=item ev_suspend (loop)	846	=item ev_suspend (loop)
698		847
699	=item ev_resume (loop)	848	=item ev_resume (loop)
700		849
…		…
718	without a previous call to C<ev_suspend>.	867	without a previous call to C<ev_suspend>.
719		868
720	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	869	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
721	event loop time (see C<ev_now_update>).	870	event loop time (see C<ev_now_update>).
722		871
723	=item ev_run (loop, int flags)	872	=item bool ev_run (loop, int flags)
724		873
725	Finally, this is it, the event handler. This function usually is called	874	Finally, this is it, the event handler. This function usually is called
726	after you have initialised all your watchers and you want to start	875	after you have initialised all your watchers and you want to start
727	handling events. It will ask the operating system for any new events, call	876	handling events. It will ask the operating system for any new events, call
728	the watcher callbacks, an then repeat the whole process indefinitely: This	877	the watcher callbacks, and then repeat the whole process indefinitely: This
729	is why event loops are called I<loops>.	878	is why event loops are called I<loops>.
730		879
731	If the flags argument is specified as C<0>, it will keep handling events	880	If the flags argument is specified as C<0>, it will keep handling events
732	until either no event watchers are active anymore or C<ev_break> was	881	until either no event watchers are active anymore or C<ev_break> was
733	called.	882	called.
		883
		884	The return value is false if there are no more active watchers (which
		885	usually means "all jobs done" or "deadlock"), and true in all other cases
		886	(which usually means " you should call C<ev_run> again").
734		887
735	Please note that an explicit C<ev_break> is usually better than	888	Please note that an explicit C<ev_break> is usually better than
736	relying on all watchers to be stopped when deciding when a program has	889	relying on all watchers to be stopped when deciding when a program has
737	finished (especially in interactive programs), but having a program	890	finished (especially in interactive programs), but having a program
738	that automatically loops as long as it has to and no longer by virtue	891	that automatically loops as long as it has to and no longer by virtue
739	of relying on its watchers stopping correctly, that is truly a thing of	892	of relying on its watchers stopping correctly, that is truly a thing of
740	beauty.	893	beauty.
741		894
		895	This function is I<mostly> exception-safe - you can break out of a
		896	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		897	exception and so on. This does not decrement the C<ev_depth> value, nor
		898	will it clear any outstanding C<EVBREAK_ONE> breaks.
		899
742	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	900	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
743	those events and any already outstanding ones, but will not wait and	901	those events and any already outstanding ones, but will not wait and
744	block your process in case there are no events and will return after one	902	block your process in case there are no events and will return after one
745	iteration of the loop. This is sometimes useful to poll and handle new	903	iteration of the loop. This is sometimes useful to poll and handle new
746	events while doing lengthy calculations, to keep the program responsive.	904	events while doing lengthy calculations, to keep the program responsive.
…		…
755	This is useful if you are waiting for some external event in conjunction	913	This is useful if you are waiting for some external event in conjunction
756	with something not expressible using other libev watchers (i.e. "roll your	914	with something not expressible using other libev watchers (i.e. "roll your
757	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	915	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
758	usually a better approach for this kind of thing.	916	usually a better approach for this kind of thing.
759		917
760	Here are the gory details of what C<ev_run> does:	918	Here are the gory details of what C<ev_run> does (this is for your
		919	understanding, not a guarantee that things will work exactly like this in
		920	future versions):
761		921
762	- Increment loop depth.	922	- Increment loop depth.
763	- Reset the ev_break status.	923	- Reset the ev_break status.
764	- Before the first iteration, call any pending watchers.	924	- Before the first iteration, call any pending watchers.
765	LOOP:	925	LOOP:
…		…
798	anymore.	958	anymore.
799		959
800	... queue jobs here, make sure they register event watchers as long	960	... queue jobs here, make sure they register event watchers as long
801	... as they still have work to do (even an idle watcher will do..)	961	... as they still have work to do (even an idle watcher will do..)
802	ev_run (my_loop, 0);	962	ev_run (my_loop, 0);
803	... jobs done or somebody called unloop. yeah!	963	... jobs done or somebody called break. yeah!
804		964
805	=item ev_break (loop, how)	965	=item ev_break (loop, how)
806		966
807	Can be used to make a call to C<ev_run> return early (but only after it	967	Can be used to make a call to C<ev_run> return early (but only after it
808	has processed all outstanding events). The C<how> argument must be either	968	has processed all outstanding events). The C<how> argument must be either
809	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	969	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
810	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	970	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
811		971
812	This "unloop state" will be cleared when entering C<ev_run> again.	972	This "break state" will be cleared on the next call to C<ev_run>.
813		973
814	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	974	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		975	which case it will have no effect.
815		976
816	=item ev_ref (loop)	977	=item ev_ref (loop)
817		978
818	=item ev_unref (loop)	979	=item ev_unref (loop)
819		980
…		…
840	running when nothing else is active.	1001	running when nothing else is active.
841		1002
842	ev_signal exitsig;	1003	ev_signal exitsig;
843	ev_signal_init (&exitsig, sig_cb, SIGINT);	1004	ev_signal_init (&exitsig, sig_cb, SIGINT);
844	ev_signal_start (loop, &exitsig);	1005	ev_signal_start (loop, &exitsig);
845	evf_unref (loop);	1006	ev_unref (loop);
846		1007
847	Example: For some weird reason, unregister the above signal handler again.	1008	Example: For some weird reason, unregister the above signal handler again.
848		1009
849	ev_ref (loop);	1010	ev_ref (loop);
850	ev_signal_stop (loop, &exitsig);	1011	ev_signal_stop (loop, &exitsig);
…		…
870	overhead for the actual polling but can deliver many events at once.	1031	overhead for the actual polling but can deliver many events at once.
871		1032
872	By setting a higher I<io collect interval> you allow libev to spend more	1033	By setting a higher I<io collect interval> you allow libev to spend more
873	time collecting I/O events, so you can handle more events per iteration,	1034	time collecting I/O events, so you can handle more events per iteration,
874	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	1035	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
875	C<ev_timer>) will be not affected. Setting this to a non-null value will	1036	C<ev_timer>) will not be affected. Setting this to a non-null value will
876	introduce an additional C<ev_sleep ()> call into most loop iterations. The	1037	introduce an additional C<ev_sleep ()> call into most loop iterations. The
877	sleep time ensures that libev will not poll for I/O events more often then	1038	sleep time ensures that libev will not poll for I/O events more often then
878	once per this interval, on average.	1039	once per this interval, on average (as long as the host time resolution is
		1040	good enough).
879		1041
880	Likewise, by setting a higher I<timeout collect interval> you allow libev	1042	Likewise, by setting a higher I<timeout collect interval> you allow libev
881	to spend more time collecting timeouts, at the expense of increased	1043	to spend more time collecting timeouts, at the expense of increased
882	latency/jitter/inexactness (the watcher callback will be called	1044	latency/jitter/inexactness (the watcher callback will be called
883	later). C<ev_io> watchers will not be affected. Setting this to a non-null	1045	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
929	invoke the actual watchers inside another context (another thread etc.).	1091	invoke the actual watchers inside another context (another thread etc.).
930		1092
931	If you want to reset the callback, use C<ev_invoke_pending> as new	1093	If you want to reset the callback, use C<ev_invoke_pending> as new
932	callback.	1094	callback.
933		1095
934	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1096	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
935		1097
936	Sometimes you want to share the same loop between multiple threads. This	1098	Sometimes you want to share the same loop between multiple threads. This
937	can be done relatively simply by putting mutex_lock/unlock calls around	1099	can be done relatively simply by putting mutex_lock/unlock calls around
938	each call to a libev function.	1100	each call to a libev function.
939		1101
940	However, C<ev_run> can run an indefinite time, so it is not feasible	1102	However, C<ev_run> can run an indefinite time, so it is not feasible
941	to wait for it to return. One way around this is to wake up the event	1103	to wait for it to return. One way around this is to wake up the event
942	loop via C<ev_break> and C<av_async_send>, another way is to set these	1104	loop via C<ev_break> and C<ev_async_send>, another way is to set these
943	I<release> and I<acquire> callbacks on the loop.	1105	I<release> and I<acquire> callbacks on the loop.
944		1106
945	When set, then C<release> will be called just before the thread is	1107	When set, then C<release> will be called just before the thread is
946	suspended waiting for new events, and C<acquire> is called just	1108	suspended waiting for new events, and C<acquire> is called just
947	afterwards.	1109	afterwards.
…		…
962	See also the locking example in the C<THREADS> section later in this	1124	See also the locking example in the C<THREADS> section later in this
963	document.	1125	document.
964		1126
965	=item ev_set_userdata (loop, void *data)	1127	=item ev_set_userdata (loop, void *data)
966		1128
967	=item ev_userdata (loop)	1129	=item void *ev_userdata (loop)
968		1130
969	Set and retrieve a single C<void *> associated with a loop. When	1131	Set and retrieve a single C<void *> associated with a loop. When
970	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1132	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
971	C<0.>	1133	C<0>.
972		1134
973	These two functions can be used to associate arbitrary data with a loop,	1135	These two functions can be used to associate arbitrary data with a loop,
974	and are intended solely for the C<invoke_pending_cb>, C<release> and	1136	and are intended solely for the C<invoke_pending_cb>, C<release> and
975	C<acquire> callbacks described above, but of course can be (ab-)used for	1137	C<acquire> callbacks described above, but of course can be (ab-)used for
976	any other purpose as well.	1138	any other purpose as well.
…		…
1087		1249
1088	=item C<EV_PREPARE>	1250	=item C<EV_PREPARE>
1089		1251
1090	=item C<EV_CHECK>	1252	=item C<EV_CHECK>
1091		1253
1092	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1254	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1093	to gather new events, and all C<ev_check> watchers are invoked just after	1255	gather new events, and all C<ev_check> watchers are queued (not invoked)
1094	C<ev_run> has gathered them, but before it invokes any callbacks for any	1256	just after C<ev_run> has gathered them, but before it queues any callbacks
		1257	for any received events. That means C<ev_prepare> watchers are the last
		1258	watchers invoked before the event loop sleeps or polls for new events, and
		1259	C<ev_check> watchers will be invoked before any other watchers of the same
		1260	or lower priority within an event loop iteration.
		1261
1095	received events. Callbacks of both watcher types can start and stop as	1262	Callbacks of both watcher types can start and stop as many watchers as
1096	many watchers as they want, and all of them will be taken into account	1263	they want, and all of them will be taken into account (for example, a
1097	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1264	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1098	C<ev_run> from blocking).	1265	blocking).
1099		1266
1100	=item C<EV_EMBED>	1267	=item C<EV_EMBED>
1101		1268
1102	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1269	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1103		1270
1104	=item C<EV_FORK>	1271	=item C<EV_FORK>
1105		1272
1106	The event loop has been resumed in the child process after fork (see	1273	The event loop has been resumed in the child process after fork (see
1107	C<ev_fork>).	1274	C<ev_fork>).
		1275
		1276	=item C<EV_CLEANUP>
		1277
		1278	The event loop is about to be destroyed (see C<ev_cleanup>).
1108		1279
1109	=item C<EV_ASYNC>	1280	=item C<EV_ASYNC>
1110		1281
1111	The given async watcher has been asynchronously notified (see C<ev_async>).	1282	The given async watcher has been asynchronously notified (see C<ev_async>).
1112		1283
…		…
1134	programs, though, as the fd could already be closed and reused for another	1305	programs, though, as the fd could already be closed and reused for another
1135	thing, so beware.	1306	thing, so beware.
1136		1307
1137	=back	1308	=back
1138		1309
		1310	=head2 GENERIC WATCHER FUNCTIONS
		1311
		1312	=over 4
		1313
		1314	=item C<ev_init> (ev_TYPE *watcher, callback)
		1315
		1316	This macro initialises the generic portion of a watcher. The contents
		1317	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1318	the generic parts of the watcher are initialised, you I<need> to call
		1319	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1320	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1321	which rolls both calls into one.
		1322
		1323	You can reinitialise a watcher at any time as long as it has been stopped
		1324	(or never started) and there are no pending events outstanding.
		1325
		1326	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1327	int revents)>.
		1328
		1329	Example: Initialise an C<ev_io> watcher in two steps.
		1330
		1331	ev_io w;
		1332	ev_init (&w, my_cb);
		1333	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1334
		1335	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1336
		1337	This macro initialises the type-specific parts of a watcher. You need to
		1338	call C<ev_init> at least once before you call this macro, but you can
		1339	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1340	macro on a watcher that is active (it can be pending, however, which is a
		1341	difference to the C<ev_init> macro).
		1342
		1343	Although some watcher types do not have type-specific arguments
		1344	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1345
		1346	See C<ev_init>, above, for an example.
		1347
		1348	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1349
		1350	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1351	calls into a single call. This is the most convenient method to initialise
		1352	a watcher. The same limitations apply, of course.
		1353
		1354	Example: Initialise and set an C<ev_io> watcher in one step.
		1355
		1356	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1357
		1358	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1359
		1360	Starts (activates) the given watcher. Only active watchers will receive
		1361	events. If the watcher is already active nothing will happen.
		1362
		1363	Example: Start the C<ev_io> watcher that is being abused as example in this
		1364	whole section.
		1365
		1366	ev_io_start (EV_DEFAULT_UC, &w);
		1367
		1368	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1369
		1370	Stops the given watcher if active, and clears the pending status (whether
		1371	the watcher was active or not).
		1372
		1373	It is possible that stopped watchers are pending - for example,
		1374	non-repeating timers are being stopped when they become pending - but
		1375	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1376	pending. If you want to free or reuse the memory used by the watcher it is
		1377	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1378
		1379	=item bool ev_is_active (ev_TYPE *watcher)
		1380
		1381	Returns a true value iff the watcher is active (i.e. it has been started
		1382	and not yet been stopped). As long as a watcher is active you must not modify
		1383	it.
		1384
		1385	=item bool ev_is_pending (ev_TYPE *watcher)
		1386
		1387	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1388	events but its callback has not yet been invoked). As long as a watcher
		1389	is pending (but not active) you must not call an init function on it (but
		1390	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1391	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1392	it).
		1393
		1394	=item callback ev_cb (ev_TYPE *watcher)
		1395
		1396	Returns the callback currently set on the watcher.
		1397
		1398	=item ev_set_cb (ev_TYPE *watcher, callback)
		1399
		1400	Change the callback. You can change the callback at virtually any time
		1401	(modulo threads).
		1402
		1403	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1404
		1405	=item int ev_priority (ev_TYPE *watcher)
		1406
		1407	Set and query the priority of the watcher. The priority is a small
		1408	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1409	(default: C<-2>). Pending watchers with higher priority will be invoked
		1410	before watchers with lower priority, but priority will not keep watchers
		1411	from being executed (except for C<ev_idle> watchers).
		1412
		1413	If you need to suppress invocation when higher priority events are pending
		1414	you need to look at C<ev_idle> watchers, which provide this functionality.
		1415
		1416	You I<must not> change the priority of a watcher as long as it is active or
		1417	pending.
		1418
		1419	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1420	fine, as long as you do not mind that the priority value you query might
		1421	or might not have been clamped to the valid range.
		1422
		1423	The default priority used by watchers when no priority has been set is
		1424	always C<0>, which is supposed to not be too high and not be too low :).
		1425
		1426	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1427	priorities.
		1428
		1429	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1430
		1431	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1432	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1433	can deal with that fact, as both are simply passed through to the
		1434	callback.
		1435
		1436	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1437
		1438	If the watcher is pending, this function clears its pending status and
		1439	returns its C<revents> bitset (as if its callback was invoked). If the
		1440	watcher isn't pending it does nothing and returns C<0>.
		1441
		1442	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1443	callback to be invoked, which can be accomplished with this function.
		1444
		1445	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1446
		1447	Feeds the given event set into the event loop, as if the specified event
		1448	had happened for the specified watcher (which must be a pointer to an
		1449	initialised but not necessarily started event watcher). Obviously you must
		1450	not free the watcher as long as it has pending events.
		1451
		1452	Stopping the watcher, letting libev invoke it, or calling
		1453	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1454	not started in the first place.
		1455
		1456	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1457	functions that do not need a watcher.
		1458
		1459	=back
		1460
		1461	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1462	OWN COMPOSITE WATCHERS> idioms.
		1463
1139	=head2 WATCHER STATES	1464	=head2 WATCHER STATES
1140		1465
1141	There are various watcher states mentioned throughout this manual -	1466	There are various watcher states mentioned throughout this manual -
1142	active, pending and so on. In this section these states and the rules to	1467	active, pending and so on. In this section these states and the rules to
1143	transition between them will be described in more detail - and while these	1468	transition between them will be described in more detail - and while these
1144	rules might look complicated, they usually do "the right thing".	1469	rules might look complicated, they usually do "the right thing".
1145		1470
1146	=over 4	1471	=over 4
1147		1472
1148	=item initialiased	1473	=item initialised
1149		1474
1150	Before a watcher can be registered with the event looop it has to be	1475	Before a watcher can be registered with the event loop it has to be
1151	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1476	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1152	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1477	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1153		1478
1154	In this state it is simply some block of memory that is suitable for use	1479	In this state it is simply some block of memory that is suitable for
1155	in an event loop. It can be moved around, freed, reused etc. at will.	1480	use in an event loop. It can be moved around, freed, reused etc. at
		1481	will - as long as you either keep the memory contents intact, or call
		1482	C<ev_TYPE_init> again.
1156		1483
1157	=item started/running/active	1484	=item started/running/active
1158		1485
1159	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1486	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1160	property of the event loop, and is actively waiting for events. While in	1487	property of the event loop, and is actively waiting for events. While in
…		…
1188	latter will clear any pending state the watcher might be in, regardless	1515	latter will clear any pending state the watcher might be in, regardless
1189	of whether it was active or not, so stopping a watcher explicitly before	1516	of whether it was active or not, so stopping a watcher explicitly before
1190	freeing it is often a good idea.	1517	freeing it is often a good idea.
1191		1518
1192	While stopped (and not pending) the watcher is essentially in the	1519	While stopped (and not pending) the watcher is essentially in the
1193	initialised state, that is it can be reused, moved, modified in any way	1520	initialised state, that is, it can be reused, moved, modified in any way
1194	you wish.	1521	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1522	it again).
1195		1523
1196	=back	1524	=back
1197
1198	=head2 GENERIC WATCHER FUNCTIONS
1199
1200	=over 4
1201
1202	=item C<ev_init> (ev_TYPE *watcher, callback)
1203
1204	This macro initialises the generic portion of a watcher. The contents
1205	of the watcher object can be arbitrary (so C<malloc> will do). Only
1206	the generic parts of the watcher are initialised, you I<need> to call
1207	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
1208	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
1209	which rolls both calls into one.
1210
1211	You can reinitialise a watcher at any time as long as it has been stopped
1212	(or never started) and there are no pending events outstanding.
1213
1214	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1215	int revents)>.
1216
1217	Example: Initialise an C<ev_io> watcher in two steps.
1218
1219	ev_io w;
1220	ev_init (&w, my_cb);
1221	ev_io_set (&w, STDIN_FILENO, EV_READ);
1222
1223	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
1224
1225	This macro initialises the type-specific parts of a watcher. You need to
1226	call C<ev_init> at least once before you call this macro, but you can
1227	call C<ev_TYPE_set> any number of times. You must not, however, call this
1228	macro on a watcher that is active (it can be pending, however, which is a
1229	difference to the C<ev_init> macro).
1230
1231	Although some watcher types do not have type-specific arguments
1232	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
1233
1234	See C<ev_init>, above, for an example.
1235
1236	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
1237
1238	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
1239	calls into a single call. This is the most convenient method to initialise
1240	a watcher. The same limitations apply, of course.
1241
1242	Example: Initialise and set an C<ev_io> watcher in one step.
1243
1244	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1245
1246	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
1247
1248	Starts (activates) the given watcher. Only active watchers will receive
1249	events. If the watcher is already active nothing will happen.
1250
1251	Example: Start the C<ev_io> watcher that is being abused as example in this
1252	whole section.
1253
1254	ev_io_start (EV_DEFAULT_UC, &w);
1255
1256	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
1257
1258	Stops the given watcher if active, and clears the pending status (whether
1259	the watcher was active or not).
1260
1261	It is possible that stopped watchers are pending - for example,
1262	non-repeating timers are being stopped when they become pending - but
1263	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
1264	pending. If you want to free or reuse the memory used by the watcher it is
1265	therefore a good idea to always call its C<ev_TYPE_stop> function.
1266
1267	=item bool ev_is_active (ev_TYPE *watcher)
1268
1269	Returns a true value iff the watcher is active (i.e. it has been started
1270	and not yet been stopped). As long as a watcher is active you must not modify
1271	it.
1272
1273	=item bool ev_is_pending (ev_TYPE *watcher)
1274
1275	Returns a true value iff the watcher is pending, (i.e. it has outstanding
1276	events but its callback has not yet been invoked). As long as a watcher
1277	is pending (but not active) you must not call an init function on it (but
1278	C<ev_TYPE_set> is safe), you must not change its priority, and you must
1279	make sure the watcher is available to libev (e.g. you cannot C<free ()>
1280	it).
1281
1282	=item callback ev_cb (ev_TYPE *watcher)
1283
1284	Returns the callback currently set on the watcher.
1285
1286	=item ev_cb_set (ev_TYPE *watcher, callback)
1287
1288	Change the callback. You can change the callback at virtually any time
1289	(modulo threads).
1290
1291	=item ev_set_priority (ev_TYPE *watcher, int priority)
1292
1293	=item int ev_priority (ev_TYPE *watcher)
1294
1295	Set and query the priority of the watcher. The priority is a small
1296	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1297	(default: C<-2>). Pending watchers with higher priority will be invoked
1298	before watchers with lower priority, but priority will not keep watchers
1299	from being executed (except for C<ev_idle> watchers).
1300
1301	If you need to suppress invocation when higher priority events are pending
1302	you need to look at C<ev_idle> watchers, which provide this functionality.
1303
1304	You I<must not> change the priority of a watcher as long as it is active or
1305	pending.
1306
1307	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1308	fine, as long as you do not mind that the priority value you query might
1309	or might not have been clamped to the valid range.
1310
1311	The default priority used by watchers when no priority has been set is
1312	always C<0>, which is supposed to not be too high and not be too low :).
1313
1314	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1315	priorities.
1316
1317	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1318
1319	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1320	C<loop> nor C<revents> need to be valid as long as the watcher callback
1321	can deal with that fact, as both are simply passed through to the
1322	callback.
1323
1324	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1325
1326	If the watcher is pending, this function clears its pending status and
1327	returns its C<revents> bitset (as if its callback was invoked). If the
1328	watcher isn't pending it does nothing and returns C<0>.
1329
1330	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1331	callback to be invoked, which can be accomplished with this function.
1332
1333	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
1334
1335	Feeds the given event set into the event loop, as if the specified event
1336	had happened for the specified watcher (which must be a pointer to an
1337	initialised but not necessarily started event watcher). Obviously you must
1338	not free the watcher as long as it has pending events.
1339
1340	Stopping the watcher, letting libev invoke it, or calling
1341	C<ev_clear_pending> will clear the pending event, even if the watcher was
1342	not started in the first place.
1343
1344	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1345	functions that do not need a watcher.
1346
1347	=back
1348
1349
1350	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1351
1352	Each watcher has, by default, a member C<void *data> that you can change
1353	and read at any time: libev will completely ignore it. This can be used
1354	to associate arbitrary data with your watcher. If you need more data and
1355	don't want to allocate memory and store a pointer to it in that data
1356	member, you can also "subclass" the watcher type and provide your own
1357	data:
1358
1359	struct my_io
1360	{
1361	ev_io io;
1362	int otherfd;
1363	void *somedata;
1364	struct whatever *mostinteresting;
1365	};
1366
1367	...
1368	struct my_io w;
1369	ev_io_init (&w.io, my_cb, fd, EV_READ);
1370
1371	And since your callback will be called with a pointer to the watcher, you
1372	can cast it back to your own type:
1373
1374	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1375	{
1376	struct my_io *w = (struct my_io *)w_;
1377	...
1378	}
1379
1380	More interesting and less C-conformant ways of casting your callback type
1381	instead have been omitted.
1382
1383	Another common scenario is to use some data structure with multiple
1384	embedded watchers:
1385
1386	struct my_biggy
1387	{
1388	int some_data;
1389	ev_timer t1;
1390	ev_timer t2;
1391	}
1392
1393	In this case getting the pointer to C<my_biggy> is a bit more
1394	complicated: Either you store the address of your C<my_biggy> struct
1395	in the C<data> member of the watcher (for woozies), or you need to use
1396	some pointer arithmetic using C<offsetof> inside your watchers (for real
1397	programmers):
1398
1399	#include <stddef.h>
1400
1401	static void
1402	t1_cb (EV_P_ ev_timer *w, int revents)
1403	{
1404	struct my_biggy big = (struct my_biggy *)
1405	(((char *)w) - offsetof (struct my_biggy, t1));
1406	}
1407
1408	static void
1409	t2_cb (EV_P_ ev_timer *w, int revents)
1410	{
1411	struct my_biggy big = (struct my_biggy *)
1412	(((char *)w) - offsetof (struct my_biggy, t2));
1413	}
1414		1525
1415	=head2 WATCHER PRIORITY MODELS	1526	=head2 WATCHER PRIORITY MODELS
1416		1527
1417	Many event loops support I<watcher priorities>, which are usually small	1528	Many event loops support I<watcher priorities>, which are usually small
1418	integers that influence the ordering of event callback invocation	1529	integers that influence the ordering of event callback invocation
…		…
1545	In general you can register as many read and/or write event watchers per	1656	In general you can register as many read and/or write event watchers per
1546	fd as you want (as long as you don't confuse yourself). Setting all file	1657	fd as you want (as long as you don't confuse yourself). Setting all file
1547	descriptors to non-blocking mode is also usually a good idea (but not	1658	descriptors to non-blocking mode is also usually a good idea (but not
1548	required if you know what you are doing).	1659	required if you know what you are doing).
1549		1660
1550	If you cannot use non-blocking mode, then force the use of a
1551	known-to-be-good backend (at the time of this writing, this includes only
1552	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1553	descriptors for which non-blocking operation makes no sense (such as
1554	files) - libev doesn't guarantee any specific behaviour in that case.
1555
1556	Another thing you have to watch out for is that it is quite easy to	1661	Another thing you have to watch out for is that it is quite easy to
1557	receive "spurious" readiness notifications, that is your callback might	1662	receive "spurious" readiness notifications, that is, your callback might
1558	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1663	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1559	because there is no data. Not only are some backends known to create a	1664	because there is no data. It is very easy to get into this situation even
1560	lot of those (for example Solaris ports), it is very easy to get into	1665	with a relatively standard program structure. Thus it is best to always
1561	this situation even with a relatively standard program structure. Thus	1666	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1562	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1563	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1667	preferable to a program hanging until some data arrives.
1564		1668
1565	If you cannot run the fd in non-blocking mode (for example you should	1669	If you cannot run the fd in non-blocking mode (for example you should
1566	not play around with an Xlib connection), then you have to separately	1670	not play around with an Xlib connection), then you have to separately
1567	re-test whether a file descriptor is really ready with a known-to-be good	1671	re-test whether a file descriptor is really ready with a known-to-be good
1568	interface such as poll (fortunately in our Xlib example, Xlib already	1672	interface such as poll (fortunately in the case of Xlib, it already does
1569	does this on its own, so its quite safe to use). Some people additionally	1673	this on its own, so its quite safe to use). Some people additionally
1570	use C<SIGALRM> and an interval timer, just to be sure you won't block	1674	use C<SIGALRM> and an interval timer, just to be sure you won't block
1571	indefinitely.	1675	indefinitely.
1572		1676
1573	But really, best use non-blocking mode.	1677	But really, best use non-blocking mode.
1574		1678
1575	=head3 The special problem of disappearing file descriptors	1679	=head3 The special problem of disappearing file descriptors
1576		1680
1577	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1681	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1578	descriptor (either due to calling C<close> explicitly or any other means,	1682	a file descriptor (either due to calling C<close> explicitly or any other
1579	such as C<dup2>). The reason is that you register interest in some file	1683	means, such as C<dup2>). The reason is that you register interest in some
1580	descriptor, but when it goes away, the operating system will silently drop	1684	file descriptor, but when it goes away, the operating system will silently
1581	this interest. If another file descriptor with the same number then is	1685	drop this interest. If another file descriptor with the same number then
1582	registered with libev, there is no efficient way to see that this is, in	1686	is registered with libev, there is no efficient way to see that this is,
1583	fact, a different file descriptor.	1687	in fact, a different file descriptor.
1584		1688
1585	To avoid having to explicitly tell libev about such cases, libev follows	1689	To avoid having to explicitly tell libev about such cases, libev follows
1586	the following policy: Each time C<ev_io_set> is being called, libev	1690	the following policy: Each time C<ev_io_set> is being called, libev
1587	will assume that this is potentially a new file descriptor, otherwise	1691	will assume that this is potentially a new file descriptor, otherwise
1588	it is assumed that the file descriptor stays the same. That means that	1692	it is assumed that the file descriptor stays the same. That means that
…		…
1602		1706
1603	There is no workaround possible except not registering events	1707	There is no workaround possible except not registering events
1604	for potentially C<dup ()>'ed file descriptors, or to resort to	1708	for potentially C<dup ()>'ed file descriptors, or to resort to
1605	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1709	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1606		1710
		1711	=head3 The special problem of files
		1712
		1713	Many people try to use C<select> (or libev) on file descriptors
		1714	representing files, and expect it to become ready when their program
		1715	doesn't block on disk accesses (which can take a long time on their own).
		1716
		1717	However, this cannot ever work in the "expected" way - you get a readiness
		1718	notification as soon as the kernel knows whether and how much data is
		1719	there, and in the case of open files, that's always the case, so you
		1720	always get a readiness notification instantly, and your read (or possibly
		1721	write) will still block on the disk I/O.
		1722
		1723	Another way to view it is that in the case of sockets, pipes, character
		1724	devices and so on, there is another party (the sender) that delivers data
		1725	on its own, but in the case of files, there is no such thing: the disk
		1726	will not send data on its own, simply because it doesn't know what you
		1727	wish to read - you would first have to request some data.
		1728
		1729	Since files are typically not-so-well supported by advanced notification
		1730	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1731	to files, even though you should not use it. The reason for this is
		1732	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1733	usually a tty, often a pipe, but also sometimes files or special devices
		1734	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1735	F</dev/urandom>), and even though the file might better be served with
		1736	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1737	it "just works" instead of freezing.
		1738
		1739	So avoid file descriptors pointing to files when you know it (e.g. use
		1740	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1741	when you rarely read from a file instead of from a socket, and want to
		1742	reuse the same code path.
		1743
1607	=head3 The special problem of fork	1744	=head3 The special problem of fork
1608		1745
1609	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1746	Some backends (epoll, kqueue, probably linuxaio) do not support C<fork ()>
1610	useless behaviour. Libev fully supports fork, but needs to be told about	1747	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1611	it in the child.	1748	to be told about it in the child if you want to continue to use it in the
		1749	child.
1612		1750
1613	To support fork in your programs, you either have to call	1751	To support fork in your child processes, you have to call C<ev_loop_fork
1614	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1752	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1615	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1753	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1616	C<EVBACKEND_POLL>.
1617		1754
1618	=head3 The special problem of SIGPIPE	1755	=head3 The special problem of SIGPIPE
1619		1756
1620	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1757	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1621	when writing to a pipe whose other end has been closed, your program gets	1758	when writing to a pipe whose other end has been closed, your program gets
…		…
1719	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1856	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1720	monotonic clock option helps a lot here).	1857	monotonic clock option helps a lot here).
1721		1858
1722	The callback is guaranteed to be invoked only I<after> its timeout has	1859	The callback is guaranteed to be invoked only I<after> its timeout has
1723	passed (not I<at>, so on systems with very low-resolution clocks this	1860	passed (not I<at>, so on systems with very low-resolution clocks this
1724	might introduce a small delay). If multiple timers become ready during the	1861	might introduce a small delay, see "the special problem of being too
		1862	early", below). If multiple timers become ready during the same loop
1725	same loop iteration then the ones with earlier time-out values are invoked	1863	iteration then the ones with earlier time-out values are invoked before
1726	before ones of the same priority with later time-out values (but this is	1864	ones of the same priority with later time-out values (but this is no
1727	no longer true when a callback calls C<ev_run> recursively).	1865	longer true when a callback calls C<ev_run> recursively).
1728		1866
1729	=head3 Be smart about timeouts	1867	=head3 Be smart about timeouts
1730		1868
1731	Many real-world problems involve some kind of timeout, usually for error	1869	Many real-world problems involve some kind of timeout, usually for error
1732	recovery. A typical example is an HTTP request - if the other side hangs,	1870	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1807		1945
1808	In this case, it would be more efficient to leave the C<ev_timer> alone,	1946	In this case, it would be more efficient to leave the C<ev_timer> alone,
1809	but remember the time of last activity, and check for a real timeout only	1947	but remember the time of last activity, and check for a real timeout only
1810	within the callback:	1948	within the callback:
1811		1949
		1950	ev_tstamp timeout = 60.;
1812	ev_tstamp last_activity; // time of last activity	1951	ev_tstamp last_activity; // time of last activity
		1952	ev_timer timer;
1813		1953
1814	static void	1954	static void
1815	callback (EV_P_ ev_timer *w, int revents)	1955	callback (EV_P_ ev_timer *w, int revents)
1816	{	1956	{
1817	ev_tstamp now = ev_now (EV_A);	1957	// calculate when the timeout would happen
1818	ev_tstamp timeout = last_activity + 60.;	1958	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1819		1959
1820	// if last_activity + 60. is older than now, we did time out	1960	// if negative, it means we the timeout already occurred
1821	if (timeout < now)	1961	if (after < 0.)
1822	{	1962	{
1823	// timeout occurred, take action	1963	// timeout occurred, take action
1824	}	1964	}
1825	else	1965	else
1826	{	1966	{
1827	// callback was invoked, but there was some activity, re-arm	1967	// callback was invoked, but there was some recent
1828	// the watcher to fire in last_activity + 60, which is	1968	// activity. simply restart the timer to time out
1829	// guaranteed to be in the future, so "again" is positive:	1969	// after "after" seconds, which is the earliest time
1830	w->repeat = timeout - now;	1970	// the timeout can occur.
		1971	ev_timer_set (w, after, 0.);
1831	ev_timer_again (EV_A_ w);	1972	ev_timer_start (EV_A_ w);
1832	}	1973	}
1833	}	1974	}
1834		1975
1835	To summarise the callback: first calculate the real timeout (defined	1976	To summarise the callback: first calculate in how many seconds the
1836	as "60 seconds after the last activity"), then check if that time has	1977	timeout will occur (by calculating the absolute time when it would occur,
1837	been reached, which means something I<did>, in fact, time out. Otherwise	1978	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1838	the callback was invoked too early (C<timeout> is in the future), so	1979	(EV_A)> from that).
1839	re-schedule the timer to fire at that future time, to see if maybe we have
1840	a timeout then.
1841		1980
1842	Note how C<ev_timer_again> is used, taking advantage of the	1981	If this value is negative, then we are already past the timeout, i.e. we
1843	C<ev_timer_again> optimisation when the timer is already running.	1982	timed out, and need to do whatever is needed in this case.
		1983
		1984	Otherwise, we now the earliest time at which the timeout would trigger,
		1985	and simply start the timer with this timeout value.
		1986
		1987	In other words, each time the callback is invoked it will check whether
		1988	the timeout occurred. If not, it will simply reschedule itself to check
		1989	again at the earliest time it could time out. Rinse. Repeat.
1844		1990
1845	This scheme causes more callback invocations (about one every 60 seconds	1991	This scheme causes more callback invocations (about one every 60 seconds
1846	minus half the average time between activity), but virtually no calls to	1992	minus half the average time between activity), but virtually no calls to
1847	libev to change the timeout.	1993	libev to change the timeout.
1848		1994
1849	To start the timer, simply initialise the watcher and set C<last_activity>	1995	To start the machinery, simply initialise the watcher and set
1850	to the current time (meaning we just have some activity :), then call the	1996	C<last_activity> to the current time (meaning there was some activity just
1851	callback, which will "do the right thing" and start the timer:	1997	now), then call the callback, which will "do the right thing" and start
		1998	the timer:
1852		1999
		2000	last_activity = ev_now (EV_A);
1853	ev_init (timer, callback);	2001	ev_init (&timer, callback);
1854	last_activity = ev_now (loop);	2002	callback (EV_A_ &timer, 0);
1855	callback (loop, timer, EV_TIMER);
1856		2003
1857	And when there is some activity, simply store the current time in	2004	When there is some activity, simply store the current time in
1858	C<last_activity>, no libev calls at all:	2005	C<last_activity>, no libev calls at all:
1859		2006
		2007	if (activity detected)
1860	last_activity = ev_now (loop);	2008	last_activity = ev_now (EV_A);
		2009
		2010	When your timeout value changes, then the timeout can be changed by simply
		2011	providing a new value, stopping the timer and calling the callback, which
		2012	will again do the right thing (for example, time out immediately :).
		2013
		2014	timeout = new_value;
		2015	ev_timer_stop (EV_A_ &timer);
		2016	callback (EV_A_ &timer, 0);
1861		2017
1862	This technique is slightly more complex, but in most cases where the	2018	This technique is slightly more complex, but in most cases where the
1863	time-out is unlikely to be triggered, much more efficient.	2019	time-out is unlikely to be triggered, much more efficient.
1864
1865	Changing the timeout is trivial as well (if it isn't hard-coded in the
1866	callback :) - just change the timeout and invoke the callback, which will
1867	fix things for you.
1868		2020
1869	=item 4. Wee, just use a double-linked list for your timeouts.	2021	=item 4. Wee, just use a double-linked list for your timeouts.
1870		2022
1871	If there is not one request, but many thousands (millions...), all	2023	If there is not one request, but many thousands (millions...), all
1872	employing some kind of timeout with the same timeout value, then one can	2024	employing some kind of timeout with the same timeout value, then one can
…		…
1899	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2051	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1900	rather complicated, but extremely efficient, something that really pays	2052	rather complicated, but extremely efficient, something that really pays
1901	off after the first million or so of active timers, i.e. it's usually	2053	off after the first million or so of active timers, i.e. it's usually
1902	overkill :)	2054	overkill :)
1903		2055
		2056	=head3 The special problem of being too early
		2057
		2058	If you ask a timer to call your callback after three seconds, then
		2059	you expect it to be invoked after three seconds - but of course, this
		2060	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2061	guaranteed to any precision by libev - imagine somebody suspending the
		2062	process with a STOP signal for a few hours for example.
		2063
		2064	So, libev tries to invoke your callback as soon as possible I<after> the
		2065	delay has occurred, but cannot guarantee this.
		2066
		2067	A less obvious failure mode is calling your callback too early: many event
		2068	loops compare timestamps with a "elapsed delay >= requested delay", but
		2069	this can cause your callback to be invoked much earlier than you would
		2070	expect.
		2071
		2072	To see why, imagine a system with a clock that only offers full second
		2073	resolution (think windows if you can't come up with a broken enough OS
		2074	yourself). If you schedule a one-second timer at the time 500.9, then the
		2075	event loop will schedule your timeout to elapse at a system time of 500
		2076	(500.9 truncated to the resolution) + 1, or 501.
		2077
		2078	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2079	501" and invoke the callback 0.1s after it was started, even though a
		2080	one-second delay was requested - this is being "too early", despite best
		2081	intentions.
		2082
		2083	This is the reason why libev will never invoke the callback if the elapsed
		2084	delay equals the requested delay, but only when the elapsed delay is
		2085	larger than the requested delay. In the example above, libev would only invoke
		2086	the callback at system time 502, or 1.1s after the timer was started.
		2087
		2088	So, while libev cannot guarantee that your callback will be invoked
		2089	exactly when requested, it I<can> and I<does> guarantee that the requested
		2090	delay has actually elapsed, or in other words, it always errs on the "too
		2091	late" side of things.
		2092
1904	=head3 The special problem of time updates	2093	=head3 The special problem of time updates
1905		2094
1906	Establishing the current time is a costly operation (it usually takes at	2095	Establishing the current time is a costly operation (it usually takes
1907	least two system calls): EV therefore updates its idea of the current	2096	at least one system call): EV therefore updates its idea of the current
1908	time only before and after C<ev_run> collects new events, which causes a	2097	time only before and after C<ev_run> collects new events, which causes a
1909	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2098	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1910	lots of events in one iteration.	2099	lots of events in one iteration.
1911		2100
1912	The relative timeouts are calculated relative to the C<ev_now ()>	2101	The relative timeouts are calculated relative to the C<ev_now ()>
1913	time. This is usually the right thing as this timestamp refers to the time	2102	time. This is usually the right thing as this timestamp refers to the time
1914	of the event triggering whatever timeout you are modifying/starting. If	2103	of the event triggering whatever timeout you are modifying/starting. If
1915	you suspect event processing to be delayed and you I<need> to base the	2104	you suspect event processing to be delayed and you I<need> to base the
1916	timeout on the current time, use something like this to adjust for this:	2105	timeout on the current time, use something like the following to adjust
		2106	for it:
1917		2107
1918	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2108	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1919		2109
1920	If the event loop is suspended for a long time, you can also force an	2110	If the event loop is suspended for a long time, you can also force an
1921	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2111	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1922	()>.	2112	()>, although that will push the event time of all outstanding events
		2113	further into the future.
		2114
		2115	=head3 The special problem of unsynchronised clocks
		2116
		2117	Modern systems have a variety of clocks - libev itself uses the normal
		2118	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2119	jumps).
		2120
		2121	Neither of these clocks is synchronised with each other or any other clock
		2122	on the system, so C<ev_time ()> might return a considerably different time
		2123	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2124	a call to C<gettimeofday> might return a second count that is one higher
		2125	than a directly following call to C<time>.
		2126
		2127	The moral of this is to only compare libev-related timestamps with
		2128	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2129	a second or so.
		2130
		2131	One more problem arises due to this lack of synchronisation: if libev uses
		2132	the system monotonic clock and you compare timestamps from C<ev_time>
		2133	or C<ev_now> from when you started your timer and when your callback is
		2134	invoked, you will find that sometimes the callback is a bit "early".
		2135
		2136	This is because C<ev_timer>s work in real time, not wall clock time, so
		2137	libev makes sure your callback is not invoked before the delay happened,
		2138	I<measured according to the real time>, not the system clock.
		2139
		2140	If your timeouts are based on a physical timescale (e.g. "time out this
		2141	connection after 100 seconds") then this shouldn't bother you as it is
		2142	exactly the right behaviour.
		2143
		2144	If you want to compare wall clock/system timestamps to your timers, then
		2145	you need to use C<ev_periodic>s, as these are based on the wall clock
		2146	time, where your comparisons will always generate correct results.
1923		2147
1924	=head3 The special problems of suspended animation	2148	=head3 The special problems of suspended animation
1925		2149
1926	When you leave the server world it is quite customary to hit machines that	2150	When you leave the server world it is quite customary to hit machines that
1927	can suspend/hibernate - what happens to the clocks during such a suspend?	2151	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1957		2181
1958	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2182	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1959		2183
1960	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2184	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1961		2185
1962	Configure the timer to trigger after C<after> seconds. If C<repeat>	2186	Configure the timer to trigger after C<after> seconds (fractional and
1963	is C<0.>, then it will automatically be stopped once the timeout is	2187	negative values are supported). If C<repeat> is C<0.>, then it will
1964	reached. If it is positive, then the timer will automatically be	2188	automatically be stopped once the timeout is reached. If it is positive,
1965	configured to trigger again C<repeat> seconds later, again, and again,	2189	then the timer will automatically be configured to trigger again C<repeat>
1966	until stopped manually.	2190	seconds later, again, and again, until stopped manually.
1967		2191
1968	The timer itself will do a best-effort at avoiding drift, that is, if	2192	The timer itself will do a best-effort at avoiding drift, that is, if
1969	you configure a timer to trigger every 10 seconds, then it will normally	2193	you configure a timer to trigger every 10 seconds, then it will normally
1970	trigger at exactly 10 second intervals. If, however, your program cannot	2194	trigger at exactly 10 second intervals. If, however, your program cannot
1971	keep up with the timer (because it takes longer than those 10 seconds to	2195	keep up with the timer (because it takes longer than those 10 seconds to
1972	do stuff) the timer will not fire more than once per event loop iteration.	2196	do stuff) the timer will not fire more than once per event loop iteration.
1973		2197
1974	=item ev_timer_again (loop, ev_timer *)	2198	=item ev_timer_again (loop, ev_timer *)
1975		2199
1976	This will act as if the timer timed out and restart it again if it is	2200	This will act as if the timer timed out, and restarts it again if it is
1977	repeating. The exact semantics are:	2201	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2202	timeout to the C<repeat> value and calling C<ev_timer_start>.
1978		2203
		2204	The exact semantics are as in the following rules, all of which will be
		2205	applied to the watcher:
		2206
		2207	=over 4
		2208
1979	If the timer is pending, its pending status is cleared.	2209	=item If the timer is pending, the pending status is always cleared.
1980		2210
1981	If the timer is started but non-repeating, stop it (as if it timed out).	2211	=item If the timer is started but non-repeating, stop it (as if it timed
		2212	out, without invoking it).
1982		2213
1983	If the timer is repeating, either start it if necessary (with the	2214	=item If the timer is repeating, make the C<repeat> value the new timeout
1984	C<repeat> value), or reset the running timer to the C<repeat> value.	2215	and start the timer, if necessary.
1985		2216
		2217	=back
		2218
1986	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2219	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1987	usage example.	2220	usage example.
1988		2221
1989	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2222	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1990		2223
1991	Returns the remaining time until a timer fires. If the timer is active,	2224	Returns the remaining time until a timer fires. If the timer is active,
…		…
2044	Periodic watchers are also timers of a kind, but they are very versatile	2277	Periodic watchers are also timers of a kind, but they are very versatile
2045	(and unfortunately a bit complex).	2278	(and unfortunately a bit complex).
2046		2279
2047	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2280	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2048	relative time, the physical time that passes) but on wall clock time	2281	relative time, the physical time that passes) but on wall clock time
2049	(absolute time, the thing you can read on your calender or clock). The	2282	(absolute time, the thing you can read on your calendar or clock). The
2050	difference is that wall clock time can run faster or slower than real	2283	difference is that wall clock time can run faster or slower than real
2051	time, and time jumps are not uncommon (e.g. when you adjust your	2284	time, and time jumps are not uncommon (e.g. when you adjust your
2052	wrist-watch).	2285	wrist-watch).
2053		2286
2054	You can tell a periodic watcher to trigger after some specific point	2287	You can tell a periodic watcher to trigger after some specific point
…		…
2059	C<ev_timer>, which would still trigger roughly 10 seconds after starting	2292	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2060	it, as it uses a relative timeout).	2293	it, as it uses a relative timeout).
2061		2294
2062	C<ev_periodic> watchers can also be used to implement vastly more complex	2295	C<ev_periodic> watchers can also be used to implement vastly more complex
2063	timers, such as triggering an event on each "midnight, local time", or	2296	timers, such as triggering an event on each "midnight, local time", or
2064	other complicated rules. This cannot be done with C<ev_timer> watchers, as	2297	other complicated rules. This cannot easily be done with C<ev_timer>
2065	those cannot react to time jumps.	2298	watchers, as those cannot react to time jumps.
2066		2299
2067	As with timers, the callback is guaranteed to be invoked only when the	2300	As with timers, the callback is guaranteed to be invoked only when the
2068	point in time where it is supposed to trigger has passed. If multiple	2301	point in time where it is supposed to trigger has passed. If multiple
2069	timers become ready during the same loop iteration then the ones with	2302	timers become ready during the same loop iteration then the ones with
2070	earlier time-out values are invoked before ones with later time-out values	2303	earlier time-out values are invoked before ones with later time-out values
…		…
2111		2344
2112	Another way to think about it (for the mathematically inclined) is that	2345	Another way to think about it (for the mathematically inclined) is that
2113	C<ev_periodic> will try to run the callback in this mode at the next possible	2346	C<ev_periodic> will try to run the callback in this mode at the next possible
2114	time where C<time = offset (mod interval)>, regardless of any time jumps.	2347	time where C<time = offset (mod interval)>, regardless of any time jumps.
2115		2348
2116	For numerical stability it is preferable that the C<offset> value is near	2349	The C<interval> I<MUST> be positive, and for numerical stability, the
2117	C<ev_now ()> (the current time), but there is no range requirement for	2350	interval value should be higher than C<1/8192> (which is around 100
2118	this value, and in fact is often specified as zero.	2351	microseconds) and C<offset> should be higher than C<0> and should have
		2352	at most a similar magnitude as the current time (say, within a factor of
		2353	ten). Typical values for offset are, in fact, C<0> or something between
		2354	C<0> and C<interval>, which is also the recommended range.
2119		2355
2120	Note also that there is an upper limit to how often a timer can fire (CPU	2356	Note also that there is an upper limit to how often a timer can fire (CPU
2121	speed for example), so if C<interval> is very small then timing stability	2357	speed for example), so if C<interval> is very small then timing stability
2122	will of course deteriorate. Libev itself tries to be exact to be about one	2358	will of course deteriorate. Libev itself tries to be exact to be about one
2123	millisecond (if the OS supports it and the machine is fast enough).	2359	millisecond (if the OS supports it and the machine is fast enough).
…		…
2153		2389
2154	NOTE: I<< This callback must always return a time that is higher than or	2390	NOTE: I<< This callback must always return a time that is higher than or
2155	equal to the passed C<now> value >>.	2391	equal to the passed C<now> value >>.
2156		2392
2157	This can be used to create very complex timers, such as a timer that	2393	This can be used to create very complex timers, such as a timer that
2158	triggers on "next midnight, local time". To do this, you would calculate the	2394	triggers on "next midnight, local time". To do this, you would calculate
2159	next midnight after C<now> and return the timestamp value for this. How	2395	the next midnight after C<now> and return the timestamp value for
2160	you do this is, again, up to you (but it is not trivial, which is the main	2396	this. Here is a (completely untested, no error checking) example on how to
2161	reason I omitted it as an example).	2397	do this:
		2398
		2399	#include <time.h>
		2400
		2401	static ev_tstamp
		2402	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2403	{
		2404	time_t tnow = (time_t)now;
		2405	struct tm tm;
		2406	localtime_r (&tnow, &tm);
		2407
		2408	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2409	++tm.tm_mday; // midnight next day
		2410
		2411	return mktime (&tm);
		2412	}
		2413
		2414	Note: this code might run into trouble on days that have more then two
		2415	midnights (beginning and end).
2162		2416
2163	=back	2417	=back
2164		2418
2165	=item ev_periodic_again (loop, ev_periodic *)	2419	=item ev_periodic_again (loop, ev_periodic *)
2166		2420
…		…
2231		2485
2232	ev_periodic hourly_tick;	2486	ev_periodic hourly_tick;
2233	ev_periodic_init (&hourly_tick, clock_cb,	2487	ev_periodic_init (&hourly_tick, clock_cb,
2234	fmod (ev_now (loop), 3600.), 3600., 0);	2488	fmod (ev_now (loop), 3600.), 3600., 0);
2235	ev_periodic_start (loop, &hourly_tick);	2489	ev_periodic_start (loop, &hourly_tick);
2236		2490
2237		2491
2238	=head2 C<ev_signal> - signal me when a signal gets signalled!	2492	=head2 C<ev_signal> - signal me when a signal gets signalled!
2239		2493
2240	Signal watchers will trigger an event when the process receives a specific	2494	Signal watchers will trigger an event when the process receives a specific
2241	signal one or more times. Even though signals are very asynchronous, libev	2495	signal one or more times. Even though signals are very asynchronous, libev
2242	will try it's best to deliver signals synchronously, i.e. as part of the	2496	will try its best to deliver signals synchronously, i.e. as part of the
2243	normal event processing, like any other event.	2497	normal event processing, like any other event.
2244		2498
2245	If you want signals to be delivered truly asynchronously, just use	2499	If you want signals to be delivered truly asynchronously, just use
2246	C<sigaction> as you would do without libev and forget about sharing	2500	C<sigaction> as you would do without libev and forget about sharing
2247	the signal. You can even use C<ev_async> from a signal handler to	2501	the signal. You can even use C<ev_async> from a signal handler to
…		…
2251	only within the same loop, i.e. you can watch for C<SIGINT> in your	2505	only within the same loop, i.e. you can watch for C<SIGINT> in your
2252	default loop and for C<SIGIO> in another loop, but you cannot watch for	2506	default loop and for C<SIGIO> in another loop, but you cannot watch for
2253	C<SIGINT> in both the default loop and another loop at the same time. At	2507	C<SIGINT> in both the default loop and another loop at the same time. At
2254	the moment, C<SIGCHLD> is permanently tied to the default loop.	2508	the moment, C<SIGCHLD> is permanently tied to the default loop.
2255		2509
2256	When the first watcher gets started will libev actually register something	2510	Only after the first watcher for a signal is started will libev actually
2257	with the kernel (thus it coexists with your own signal handlers as long as	2511	register something with the kernel. It thus coexists with your own signal
2258	you don't register any with libev for the same signal).	2512	handlers as long as you don't register any with libev for the same signal.
2259		2513
2260	If possible and supported, libev will install its handlers with	2514	If possible and supported, libev will install its handlers with
2261	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2515	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2262	not be unduly interrupted. If you have a problem with system calls getting	2516	not be unduly interrupted. If you have a problem with system calls getting
2263	interrupted by signals you can block all signals in an C<ev_check> watcher	2517	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2266	=head3 The special problem of inheritance over fork/execve/pthread_create	2520	=head3 The special problem of inheritance over fork/execve/pthread_create
2267		2521
2268	Both the signal mask (C<sigprocmask>) and the signal disposition	2522	Both the signal mask (C<sigprocmask>) and the signal disposition
2269	(C<sigaction>) are unspecified after starting a signal watcher (and after	2523	(C<sigaction>) are unspecified after starting a signal watcher (and after
2270	stopping it again), that is, libev might or might not block the signal,	2524	stopping it again), that is, libev might or might not block the signal,
2271	and might or might not set or restore the installed signal handler.	2525	and might or might not set or restore the installed signal handler (but
		2526	see C<EVFLAG_NOSIGMASK>).
2272		2527
2273	While this does not matter for the signal disposition (libev never	2528	While this does not matter for the signal disposition (libev never
2274	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2529	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2275	C<execve>), this matters for the signal mask: many programs do not expect	2530	C<execve>), this matters for the signal mask: many programs do not expect
2276	certain signals to be blocked.	2531	certain signals to be blocked.
…		…
2289	I<has> to modify the signal mask, at least temporarily.	2544	I<has> to modify the signal mask, at least temporarily.
2290		2545
2291	So I can't stress this enough: I<If you do not reset your signal mask when	2546	So I can't stress this enough: I<If you do not reset your signal mask when
2292	you expect it to be empty, you have a race condition in your code>. This	2547	you expect it to be empty, you have a race condition in your code>. This
2293	is not a libev-specific thing, this is true for most event libraries.	2548	is not a libev-specific thing, this is true for most event libraries.
		2549
		2550	=head3 The special problem of threads signal handling
		2551
		2552	POSIX threads has problematic signal handling semantics, specifically,
		2553	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2554	threads in a process block signals, which is hard to achieve.
		2555
		2556	When you want to use sigwait (or mix libev signal handling with your own
		2557	for the same signals), you can tackle this problem by globally blocking
		2558	all signals before creating any threads (or creating them with a fully set
		2559	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2560	loops. Then designate one thread as "signal receiver thread" which handles
		2561	these signals. You can pass on any signals that libev might be interested
		2562	in by calling C<ev_feed_signal>.
2294		2563
2295	=head3 Watcher-Specific Functions and Data Members	2564	=head3 Watcher-Specific Functions and Data Members
2296		2565
2297	=over 4	2566	=over 4
2298		2567
…		…
2433		2702
2434	=head2 C<ev_stat> - did the file attributes just change?	2703	=head2 C<ev_stat> - did the file attributes just change?
2435		2704
2436	This watches a file system path for attribute changes. That is, it calls	2705	This watches a file system path for attribute changes. That is, it calls
2437	C<stat> on that path in regular intervals (or when the OS says it changed)	2706	C<stat> on that path in regular intervals (or when the OS says it changed)
2438	and sees if it changed compared to the last time, invoking the callback if	2707	and sees if it changed compared to the last time, invoking the callback
2439	it did.	2708	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2709	happen after the watcher has been started will be reported.
2440		2710
2441	The path does not need to exist: changing from "path exists" to "path does	2711	The path does not need to exist: changing from "path exists" to "path does
2442	not exist" is a status change like any other. The condition "path does not	2712	not exist" is a status change like any other. The condition "path does not
2443	exist" (or more correctly "path cannot be stat'ed") is signified by the	2713	exist" (or more correctly "path cannot be stat'ed") is signified by the
2444	C<st_nlink> field being zero (which is otherwise always forced to be at	2714	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2674	Apart from keeping your process non-blocking (which is a useful	2944	Apart from keeping your process non-blocking (which is a useful
2675	effect on its own sometimes), idle watchers are a good place to do	2945	effect on its own sometimes), idle watchers are a good place to do
2676	"pseudo-background processing", or delay processing stuff to after the	2946	"pseudo-background processing", or delay processing stuff to after the
2677	event loop has handled all outstanding events.	2947	event loop has handled all outstanding events.
2678		2948
		2949	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2950
		2951	As long as there is at least one active idle watcher, libev will never
		2952	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2953	For this to work, the idle watcher doesn't need to be invoked at all - the
		2954	lowest priority will do.
		2955
		2956	This mode of operation can be useful together with an C<ev_check> watcher,
		2957	to do something on each event loop iteration - for example to balance load
		2958	between different connections.
		2959
		2960	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2961	example.
		2962
2679	=head3 Watcher-Specific Functions and Data Members	2963	=head3 Watcher-Specific Functions and Data Members
2680		2964
2681	=over 4	2965	=over 4
2682		2966
2683	=item ev_idle_init (ev_idle *, callback)	2967	=item ev_idle_init (ev_idle *, callback)
…		…
2694	callback, free it. Also, use no error checking, as usual.	2978	callback, free it. Also, use no error checking, as usual.
2695		2979
2696	static void	2980	static void
2697	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2981	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2698	{	2982	{
		2983	// stop the watcher
		2984	ev_idle_stop (loop, w);
		2985
		2986	// now we can free it
2699	free (w);	2987	free (w);
		2988
2700	// now do something you wanted to do when the program has	2989	// now do something you wanted to do when the program has
2701	// no longer anything immediate to do.	2990	// no longer anything immediate to do.
2702	}	2991	}
2703		2992
2704	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2993	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2706	ev_idle_start (loop, idle_watcher);	2995	ev_idle_start (loop, idle_watcher);
2707		2996
2708		2997
2709	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2998	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2710		2999
2711	Prepare and check watchers are usually (but not always) used in pairs:	3000	Prepare and check watchers are often (but not always) used in pairs:
2712	prepare watchers get invoked before the process blocks and check watchers	3001	prepare watchers get invoked before the process blocks and check watchers
2713	afterwards.	3002	afterwards.
2714		3003
2715	You I<must not> call C<ev_run> or similar functions that enter	3004	You I<must not> call C<ev_run> (or similar functions that enter the
2716	the current event loop from either C<ev_prepare> or C<ev_check>	3005	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2717	watchers. Other loops than the current one are fine, however. The	3006	C<ev_check> watchers. Other loops than the current one are fine,
2718	rationale behind this is that you do not need to check for recursion in	3007	however. The rationale behind this is that you do not need to check
2719	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3008	for recursion in those watchers, i.e. the sequence will always be
2720	C<ev_check> so if you have one watcher of each kind they will always be	3009	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2721	called in pairs bracketing the blocking call.	3010	kind they will always be called in pairs bracketing the blocking call.
2722		3011
2723	Their main purpose is to integrate other event mechanisms into libev and	3012	Their main purpose is to integrate other event mechanisms into libev and
2724	their use is somewhat advanced. They could be used, for example, to track	3013	their use is somewhat advanced. They could be used, for example, to track
2725	variable changes, implement your own watchers, integrate net-snmp or a	3014	variable changes, implement your own watchers, integrate net-snmp or a
2726	coroutine library and lots more. They are also occasionally useful if	3015	coroutine library and lots more. They are also occasionally useful if
…		…
2744	with priority higher than or equal to the event loop and one coroutine	3033	with priority higher than or equal to the event loop and one coroutine
2745	of lower priority, but only once, using idle watchers to keep the event	3034	of lower priority, but only once, using idle watchers to keep the event
2746	loop from blocking if lower-priority coroutines are active, thus mapping	3035	loop from blocking if lower-priority coroutines are active, thus mapping
2747	low-priority coroutines to idle/background tasks).	3036	low-priority coroutines to idle/background tasks).
2748		3037
2749	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3038	When used for this purpose, it is recommended to give C<ev_check> watchers
2750	priority, to ensure that they are being run before any other watchers	3039	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2751	after the poll (this doesn't matter for C<ev_prepare> watchers).	3040	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3041	watchers).
2752		3042
2753	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3043	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2754	activate ("feed") events into libev. While libev fully supports this, they	3044	activate ("feed") events into libev. While libev fully supports this, they
2755	might get executed before other C<ev_check> watchers did their job. As	3045	might get executed before other C<ev_check> watchers did their job. As
2756	C<ev_check> watchers are often used to embed other (non-libev) event	3046	C<ev_check> watchers are often used to embed other (non-libev) event
2757	loops those other event loops might be in an unusable state until their	3047	loops those other event loops might be in an unusable state until their
2758	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3048	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2759	others).	3049	others).
		3050
		3051	=head3 Abusing an C<ev_check> watcher for its side-effect
		3052
		3053	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3054	useful because they are called once per event loop iteration. For
		3055	example, if you want to handle a large number of connections fairly, you
		3056	normally only do a bit of work for each active connection, and if there
		3057	is more work to do, you wait for the next event loop iteration, so other
		3058	connections have a chance of making progress.
		3059
		3060	Using an C<ev_check> watcher is almost enough: it will be called on the
		3061	next event loop iteration. However, that isn't as soon as possible -
		3062	without external events, your C<ev_check> watcher will not be invoked.
		3063
		3064	This is where C<ev_idle> watchers come in handy - all you need is a
		3065	single global idle watcher that is active as long as you have one active
		3066	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3067	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3068	invoked. Neither watcher alone can do that.
2760		3069
2761	=head3 Watcher-Specific Functions and Data Members	3070	=head3 Watcher-Specific Functions and Data Members
2762		3071
2763	=over 4	3072	=over 4
2764		3073
…		…
2965		3274
2966	=over 4	3275	=over 4
2967		3276
2968	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3277	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2969		3278
2970	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3279	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2971		3280
2972	Configures the watcher to embed the given loop, which must be	3281	Configures the watcher to embed the given loop, which must be
2973	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3282	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2974	invoked automatically, otherwise it is the responsibility of the callback	3283	invoked automatically, otherwise it is the responsibility of the callback
2975	to invoke it (it will continue to be called until the sweep has been done,	3284	to invoke it (it will continue to be called until the sweep has been done,
…		…
2996	used).	3305	used).
2997		3306
2998	struct ev_loop *loop_hi = ev_default_init (0);	3307	struct ev_loop *loop_hi = ev_default_init (0);
2999	struct ev_loop *loop_lo = 0;	3308	struct ev_loop *loop_lo = 0;
3000	ev_embed embed;	3309	ev_embed embed;
3001		3310
3002	// see if there is a chance of getting one that works	3311	// see if there is a chance of getting one that works
3003	// (remember that a flags value of 0 means autodetection)	3312	// (remember that a flags value of 0 means autodetection)
3004	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3313	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3005	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3314	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3006	: 0;	3315	: 0;
…		…
3020	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3329	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3021		3330
3022	struct ev_loop *loop = ev_default_init (0);	3331	struct ev_loop *loop = ev_default_init (0);
3023	struct ev_loop *loop_socket = 0;	3332	struct ev_loop *loop_socket = 0;
3024	ev_embed embed;	3333	ev_embed embed;
3025		3334
3026	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3335	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3027	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3336	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3028	{	3337	{
3029	ev_embed_init (&embed, 0, loop_socket);	3338	ev_embed_init (&embed, 0, loop_socket);
3030	ev_embed_start (loop, &embed);	3339	ev_embed_start (loop, &embed);
…		…
3038		3347
3039	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3348	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3040		3349
3041	Fork watchers are called when a C<fork ()> was detected (usually because	3350	Fork watchers are called when a C<fork ()> was detected (usually because
3042	whoever is a good citizen cared to tell libev about it by calling	3351	whoever is a good citizen cared to tell libev about it by calling
3043	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3352	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3044	event loop blocks next and before C<ev_check> watchers are being called,	3353	and before C<ev_check> watchers are being called, and only in the child
3045	and only in the child after the fork. If whoever good citizen calling	3354	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3046	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3355	and calls it in the wrong process, the fork handlers will be invoked, too,
3047	handlers will be invoked, too, of course.	3356	of course.
3048		3357
3049	=head3 The special problem of life after fork - how is it possible?	3358	=head3 The special problem of life after fork - how is it possible?
3050		3359
3051	Most uses of C<fork()> consist of forking, then some simple calls to set	3360	Most uses of C<fork ()> consist of forking, then some simple calls to set
3052	up/change the process environment, followed by a call to C<exec()>. This	3361	up/change the process environment, followed by a call to C<exec()>. This
3053	sequence should be handled by libev without any problems.	3362	sequence should be handled by libev without any problems.
3054		3363
3055	This changes when the application actually wants to do event handling	3364	This changes when the application actually wants to do event handling
3056	in the child, or both parent in child, in effect "continuing" after the	3365	in the child, or both parent in child, in effect "continuing" after the
…		…
3072	disadvantage of having to use multiple event loops (which do not support	3381	disadvantage of having to use multiple event loops (which do not support
3073	signal watchers).	3382	signal watchers).
3074		3383
3075	When this is not possible, or you want to use the default loop for	3384	When this is not possible, or you want to use the default loop for
3076	other reasons, then in the process that wants to start "fresh", call	3385	other reasons, then in the process that wants to start "fresh", call
3077	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying	3386	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
3078	the default loop will "orphan" (not stop) all registered watchers, so you	3387	Destroying the default loop will "orphan" (not stop) all registered
3079	have to be careful not to execute code that modifies those watchers. Note	3388	watchers, so you have to be careful not to execute code that modifies
3080	also that in that case, you have to re-register any signal watchers.	3389	those watchers. Note also that in that case, you have to re-register any
		3390	signal watchers.
3081		3391
3082	=head3 Watcher-Specific Functions and Data Members	3392	=head3 Watcher-Specific Functions and Data Members
3083		3393
3084	=over 4	3394	=over 4
3085		3395
3086	=item ev_fork_init (ev_signal *, callback)	3396	=item ev_fork_init (ev_fork *, callback)
3087		3397
3088	Initialises and configures the fork watcher - it has no parameters of any	3398	Initialises and configures the fork watcher - it has no parameters of any
3089	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3399	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3090	believe me.	3400	really.
3091		3401
3092	=back	3402	=back
3093		3403
3094		3404
		3405	=head2 C<ev_cleanup> - even the best things end
		3406
		3407	Cleanup watchers are called just before the event loop is being destroyed
		3408	by a call to C<ev_loop_destroy>.
		3409
		3410	While there is no guarantee that the event loop gets destroyed, cleanup
		3411	watchers provide a convenient method to install cleanup hooks for your
		3412	program, worker threads and so on - you just to make sure to destroy the
		3413	loop when you want them to be invoked.
		3414
		3415	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3416	all other watchers, they do not keep a reference to the event loop (which
		3417	makes a lot of sense if you think about it). Like all other watchers, you
		3418	can call libev functions in the callback, except C<ev_cleanup_start>.
		3419
		3420	=head3 Watcher-Specific Functions and Data Members
		3421
		3422	=over 4
		3423
		3424	=item ev_cleanup_init (ev_cleanup *, callback)
		3425
		3426	Initialises and configures the cleanup watcher - it has no parameters of
		3427	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3428	pointless, I assure you.
		3429
		3430	=back
		3431
		3432	Example: Register an atexit handler to destroy the default loop, so any
		3433	cleanup functions are called.
		3434
		3435	static void
		3436	program_exits (void)
		3437	{
		3438	ev_loop_destroy (EV_DEFAULT_UC);
		3439	}
		3440
		3441	...
		3442	atexit (program_exits);
		3443
		3444
3095	=head2 C<ev_async> - how to wake up an event loop	3445	=head2 C<ev_async> - how to wake up an event loop
3096		3446
3097	In general, you cannot use an C<ev_run> from multiple threads or other	3447	In general, you cannot use an C<ev_loop> from multiple threads or other
3098	asynchronous sources such as signal handlers (as opposed to multiple event	3448	asynchronous sources such as signal handlers (as opposed to multiple event
3099	loops - those are of course safe to use in different threads).	3449	loops - those are of course safe to use in different threads).
3100		3450
3101	Sometimes, however, you need to wake up an event loop you do not control,	3451	Sometimes, however, you need to wake up an event loop you do not control,
3102	for example because it belongs to another thread. This is what C<ev_async>	3452	for example because it belongs to another thread. This is what C<ev_async>
…		…
3104	it by calling C<ev_async_send>, which is thread- and signal safe.	3454	it by calling C<ev_async_send>, which is thread- and signal safe.
3105		3455
3106	This functionality is very similar to C<ev_signal> watchers, as signals,	3456	This functionality is very similar to C<ev_signal> watchers, as signals,
3107	too, are asynchronous in nature, and signals, too, will be compressed	3457	too, are asynchronous in nature, and signals, too, will be compressed
3108	(i.e. the number of callback invocations may be less than the number of	3458	(i.e. the number of callback invocations may be less than the number of
3109	C<ev_async_sent> calls).	3459	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3110		3460	of "global async watchers" by using a watcher on an otherwise unused
3111	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3461	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3112	just the default loop.	3462	even without knowing which loop owns the signal.
3113		3463
3114	=head3 Queueing	3464	=head3 Queueing
3115		3465
3116	C<ev_async> does not support queueing of data in any way. The reason	3466	C<ev_async> does not support queueing of data in any way. The reason
3117	is that the author does not know of a simple (or any) algorithm for a	3467	is that the author does not know of a simple (or any) algorithm for a
…		…
3209	trust me.	3559	trust me.
3210		3560
3211	=item ev_async_send (loop, ev_async *)	3561	=item ev_async_send (loop, ev_async *)
3212		3562
3213	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3563	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3214	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3564	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3565	returns.
		3566
3215	C<ev_feed_event>, this call is safe to do from other threads, signal or	3567	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3216	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3568	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3217	section below on what exactly this means).	3569	embedding section below on what exactly this means).
3218		3570
3219	Note that, as with other watchers in libev, multiple events might get	3571	Note that, as with other watchers in libev, multiple events might get
3220	compressed into a single callback invocation (another way to look at this	3572	compressed into a single callback invocation (another way to look at
3221	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3573	this is that C<ev_async> watchers are level-triggered: they are set on
3222	reset when the event loop detects that).	3574	C<ev_async_send>, reset when the event loop detects that).
3223		3575
3224	This call incurs the overhead of a system call only once per event loop	3576	This call incurs the overhead of at most one extra system call per event
3225	iteration, so while the overhead might be noticeable, it doesn't apply to	3577	loop iteration, if the event loop is blocked, and no syscall at all if
3226	repeated calls to C<ev_async_send> for the same event loop.	3578	the event loop (or your program) is processing events. That means that
		3579	repeated calls are basically free (there is no need to avoid calls for
		3580	performance reasons) and that the overhead becomes smaller (typically
		3581	zero) under load.
3227		3582
3228	=item bool = ev_async_pending (ev_async *)	3583	=item bool = ev_async_pending (ev_async *)
3229		3584
3230	Returns a non-zero value when C<ev_async_send> has been called on the	3585	Returns a non-zero value when C<ev_async_send> has been called on the
3231	watcher but the event has not yet been processed (or even noted) by the	3586	watcher but the event has not yet been processed (or even noted) by the
…		…
3248		3603
3249	There are some other functions of possible interest. Described. Here. Now.	3604	There are some other functions of possible interest. Described. Here. Now.
3250		3605
3251	=over 4	3606	=over 4
3252		3607
3253	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3608	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3254		3609
3255	This function combines a simple timer and an I/O watcher, calls your	3610	This function combines a simple timer and an I/O watcher, calls your
3256	callback on whichever event happens first and automatically stops both	3611	callback on whichever event happens first and automatically stops both
3257	watchers. This is useful if you want to wait for a single event on an fd	3612	watchers. This is useful if you want to wait for a single event on an fd
3258	or timeout without having to allocate/configure/start/stop/free one or	3613	or timeout without having to allocate/configure/start/stop/free one or
…		…
3286	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3641	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3287		3642
3288	=item ev_feed_fd_event (loop, int fd, int revents)	3643	=item ev_feed_fd_event (loop, int fd, int revents)
3289		3644
3290	Feed an event on the given fd, as if a file descriptor backend detected	3645	Feed an event on the given fd, as if a file descriptor backend detected
3291	the given events it.	3646	the given events.
3292		3647
3293	=item ev_feed_signal_event (loop, int signum)	3648	=item ev_feed_signal_event (loop, int signum)
3294		3649
3295	Feed an event as if the given signal occurred (C<loop> must be the default	3650	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3296	loop!).	3651	which is async-safe.
3297		3652
3298	=back	3653	=back
		3654
		3655
		3656	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3657
		3658	This section explains some common idioms that are not immediately
		3659	obvious. Note that examples are sprinkled over the whole manual, and this
		3660	section only contains stuff that wouldn't fit anywhere else.
		3661
		3662	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3663
		3664	Each watcher has, by default, a C<void *data> member that you can read
		3665	or modify at any time: libev will completely ignore it. This can be used
		3666	to associate arbitrary data with your watcher. If you need more data and
		3667	don't want to allocate memory separately and store a pointer to it in that
		3668	data member, you can also "subclass" the watcher type and provide your own
		3669	data:
		3670
		3671	struct my_io
		3672	{
		3673	ev_io io;
		3674	int otherfd;
		3675	void *somedata;
		3676	struct whatever *mostinteresting;
		3677	};
		3678
		3679	...
		3680	struct my_io w;
		3681	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3682
		3683	And since your callback will be called with a pointer to the watcher, you
		3684	can cast it back to your own type:
		3685
		3686	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3687	{
		3688	struct my_io *w = (struct my_io *)w_;
		3689	...
		3690	}
		3691
		3692	More interesting and less C-conformant ways of casting your callback
		3693	function type instead have been omitted.
		3694
		3695	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3696
		3697	Another common scenario is to use some data structure with multiple
		3698	embedded watchers, in effect creating your own watcher that combines
		3699	multiple libev event sources into one "super-watcher":
		3700
		3701	struct my_biggy
		3702	{
		3703	int some_data;
		3704	ev_timer t1;
		3705	ev_timer t2;
		3706	}
		3707
		3708	In this case getting the pointer to C<my_biggy> is a bit more
		3709	complicated: Either you store the address of your C<my_biggy> struct in
		3710	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3711	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3712	real programmers):
		3713
		3714	#include <stddef.h>
		3715
		3716	static void
		3717	t1_cb (EV_P_ ev_timer *w, int revents)
		3718	{
		3719	struct my_biggy big = (struct my_biggy *)
		3720	(((char *)w) - offsetof (struct my_biggy, t1));
		3721	}
		3722
		3723	static void
		3724	t2_cb (EV_P_ ev_timer *w, int revents)
		3725	{
		3726	struct my_biggy big = (struct my_biggy *)
		3727	(((char *)w) - offsetof (struct my_biggy, t2));
		3728	}
		3729
		3730	=head2 AVOIDING FINISHING BEFORE RETURNING
		3731
		3732	Often you have structures like this in event-based programs:
		3733
		3734	callback ()
		3735	{
		3736	free (request);
		3737	}
		3738
		3739	request = start_new_request (..., callback);
		3740
		3741	The intent is to start some "lengthy" operation. The C<request> could be
		3742	used to cancel the operation, or do other things with it.
		3743
		3744	It's not uncommon to have code paths in C<start_new_request> that
		3745	immediately invoke the callback, for example, to report errors. Or you add
		3746	some caching layer that finds that it can skip the lengthy aspects of the
		3747	operation and simply invoke the callback with the result.
		3748
		3749	The problem here is that this will happen I<before> C<start_new_request>
		3750	has returned, so C<request> is not set.
		3751
		3752	Even if you pass the request by some safer means to the callback, you
		3753	might want to do something to the request after starting it, such as
		3754	canceling it, which probably isn't working so well when the callback has
		3755	already been invoked.
		3756
		3757	A common way around all these issues is to make sure that
		3758	C<start_new_request> I<always> returns before the callback is invoked. If
		3759	C<start_new_request> immediately knows the result, it can artificially
		3760	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3761	example, or more sneakily, by reusing an existing (stopped) watcher and
		3762	pushing it into the pending queue:
		3763
		3764	ev_set_cb (watcher, callback);
		3765	ev_feed_event (EV_A_ watcher, 0);
		3766
		3767	This way, C<start_new_request> can safely return before the callback is
		3768	invoked, while not delaying callback invocation too much.
		3769
		3770	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3771
		3772	Often (especially in GUI toolkits) there are places where you have
		3773	I<modal> interaction, which is most easily implemented by recursively
		3774	invoking C<ev_run>.
		3775
		3776	This brings the problem of exiting - a callback might want to finish the
		3777	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3778	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3779	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3780	other combination: In these cases, a simple C<ev_break> will not work.
		3781
		3782	The solution is to maintain "break this loop" variable for each C<ev_run>
		3783	invocation, and use a loop around C<ev_run> until the condition is
		3784	triggered, using C<EVRUN_ONCE>:
		3785
		3786	// main loop
		3787	int exit_main_loop = 0;
		3788
		3789	while (!exit_main_loop)
		3790	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3791
		3792	// in a modal watcher
		3793	int exit_nested_loop = 0;
		3794
		3795	while (!exit_nested_loop)
		3796	ev_run (EV_A_ EVRUN_ONCE);
		3797
		3798	To exit from any of these loops, just set the corresponding exit variable:
		3799
		3800	// exit modal loop
		3801	exit_nested_loop = 1;
		3802
		3803	// exit main program, after modal loop is finished
		3804	exit_main_loop = 1;
		3805
		3806	// exit both
		3807	exit_main_loop = exit_nested_loop = 1;
		3808
		3809	=head2 THREAD LOCKING EXAMPLE
		3810
		3811	Here is a fictitious example of how to run an event loop in a different
		3812	thread from where callbacks are being invoked and watchers are
		3813	created/added/removed.
		3814
		3815	For a real-world example, see the C<EV::Loop::Async> perl module,
		3816	which uses exactly this technique (which is suited for many high-level
		3817	languages).
		3818
		3819	The example uses a pthread mutex to protect the loop data, a condition
		3820	variable to wait for callback invocations, an async watcher to notify the
		3821	event loop thread and an unspecified mechanism to wake up the main thread.
		3822
		3823	First, you need to associate some data with the event loop:
		3824
		3825	typedef struct {
		3826	mutex_t lock; /* global loop lock */
		3827	ev_async async_w;
		3828	thread_t tid;
		3829	cond_t invoke_cv;
		3830	} userdata;
		3831
		3832	void prepare_loop (EV_P)
		3833	{
		3834	// for simplicity, we use a static userdata struct.
		3835	static userdata u;
		3836
		3837	ev_async_init (&u->async_w, async_cb);
		3838	ev_async_start (EV_A_ &u->async_w);
		3839
		3840	pthread_mutex_init (&u->lock, 0);
		3841	pthread_cond_init (&u->invoke_cv, 0);
		3842
		3843	// now associate this with the loop
		3844	ev_set_userdata (EV_A_ u);
		3845	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3846	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3847
		3848	// then create the thread running ev_run
		3849	pthread_create (&u->tid, 0, l_run, EV_A);
		3850	}
		3851
		3852	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3853	solely to wake up the event loop so it takes notice of any new watchers
		3854	that might have been added:
		3855
		3856	static void
		3857	async_cb (EV_P_ ev_async *w, int revents)
		3858	{
		3859	// just used for the side effects
		3860	}
		3861
		3862	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3863	protecting the loop data, respectively.
		3864
		3865	static void
		3866	l_release (EV_P)
		3867	{
		3868	userdata *u = ev_userdata (EV_A);
		3869	pthread_mutex_unlock (&u->lock);
		3870	}
		3871
		3872	static void
		3873	l_acquire (EV_P)
		3874	{
		3875	userdata *u = ev_userdata (EV_A);
		3876	pthread_mutex_lock (&u->lock);
		3877	}
		3878
		3879	The event loop thread first acquires the mutex, and then jumps straight
		3880	into C<ev_run>:
		3881
		3882	void *
		3883	l_run (void *thr_arg)
		3884	{
		3885	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3886
		3887	l_acquire (EV_A);
		3888	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3889	ev_run (EV_A_ 0);
		3890	l_release (EV_A);
		3891
		3892	return 0;
		3893	}
		3894
		3895	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3896	signal the main thread via some unspecified mechanism (signals? pipe
		3897	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3898	have been called (in a while loop because a) spurious wakeups are possible
		3899	and b) skipping inter-thread-communication when there are no pending
		3900	watchers is very beneficial):
		3901
		3902	static void
		3903	l_invoke (EV_P)
		3904	{
		3905	userdata *u = ev_userdata (EV_A);
		3906
		3907	while (ev_pending_count (EV_A))
		3908	{
		3909	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3910	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3911	}
		3912	}
		3913
		3914	Now, whenever the main thread gets told to invoke pending watchers, it
		3915	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3916	thread to continue:
		3917
		3918	static void
		3919	real_invoke_pending (EV_P)
		3920	{
		3921	userdata *u = ev_userdata (EV_A);
		3922
		3923	pthread_mutex_lock (&u->lock);
		3924	ev_invoke_pending (EV_A);
		3925	pthread_cond_signal (&u->invoke_cv);
		3926	pthread_mutex_unlock (&u->lock);
		3927	}
		3928
		3929	Whenever you want to start/stop a watcher or do other modifications to an
		3930	event loop, you will now have to lock:
		3931
		3932	ev_timer timeout_watcher;
		3933	userdata *u = ev_userdata (EV_A);
		3934
		3935	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3936
		3937	pthread_mutex_lock (&u->lock);
		3938	ev_timer_start (EV_A_ &timeout_watcher);
		3939	ev_async_send (EV_A_ &u->async_w);
		3940	pthread_mutex_unlock (&u->lock);
		3941
		3942	Note that sending the C<ev_async> watcher is required because otherwise
		3943	an event loop currently blocking in the kernel will have no knowledge
		3944	about the newly added timer. By waking up the loop it will pick up any new
		3945	watchers in the next event loop iteration.
		3946
		3947	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3948
		3949	While the overhead of a callback that e.g. schedules a thread is small, it
		3950	is still an overhead. If you embed libev, and your main usage is with some
		3951	kind of threads or coroutines, you might want to customise libev so that
		3952	doesn't need callbacks anymore.
		3953
		3954	Imagine you have coroutines that you can switch to using a function
		3955	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3956	and that due to some magic, the currently active coroutine is stored in a
		3957	global called C<current_coro>. Then you can build your own "wait for libev
		3958	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3959	the differing C<;> conventions):
		3960
		3961	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3962	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3963
		3964	That means instead of having a C callback function, you store the
		3965	coroutine to switch to in each watcher, and instead of having libev call
		3966	your callback, you instead have it switch to that coroutine.
		3967
		3968	A coroutine might now wait for an event with a function called
		3969	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3970	matter when, or whether the watcher is active or not when this function is
		3971	called):
		3972
		3973	void
		3974	wait_for_event (ev_watcher *w)
		3975	{
		3976	ev_set_cb (w, current_coro);
		3977	switch_to (libev_coro);
		3978	}
		3979
		3980	That basically suspends the coroutine inside C<wait_for_event> and
		3981	continues the libev coroutine, which, when appropriate, switches back to
		3982	this or any other coroutine.
		3983
		3984	You can do similar tricks if you have, say, threads with an event queue -
		3985	instead of storing a coroutine, you store the queue object and instead of
		3986	switching to a coroutine, you push the watcher onto the queue and notify
		3987	any waiters.
		3988
		3989	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3990	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3991
		3992	// my_ev.h
		3993	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3994	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3995	#include "../libev/ev.h"
		3996
		3997	// my_ev.c
		3998	#define EV_H "my_ev.h"
		3999	#include "../libev/ev.c"
		4000
		4001	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4002	F<my_ev.c> into your project. When properly specifying include paths, you
		4003	can even use F<ev.h> as header file name directly.
3299		4004
3300		4005
3301	=head1 LIBEVENT EMULATION	4006	=head1 LIBEVENT EMULATION
3302		4007
3303	Libev offers a compatibility emulation layer for libevent. It cannot	4008	Libev offers a compatibility emulation layer for libevent. It cannot
3304	emulate the internals of libevent, so here are some usage hints:	4009	emulate the internals of libevent, so here are some usage hints:
3305		4010
3306	=over 4	4011	=over 4
		4012
		4013	=item * Only the libevent-1.4.1-beta API is being emulated.
		4014
		4015	This was the newest libevent version available when libev was implemented,
		4016	and is still mostly unchanged in 2010.
3307		4017
3308	=item * Use it by including <event.h>, as usual.	4018	=item * Use it by including <event.h>, as usual.
3309		4019
3310	=item * The following members are fully supported: ev_base, ev_callback,	4020	=item * The following members are fully supported: ev_base, ev_callback,
3311	ev_arg, ev_fd, ev_res, ev_events.	4021	ev_arg, ev_fd, ev_res, ev_events.
…		…
3317	=item * Priorities are not currently supported. Initialising priorities	4027	=item * Priorities are not currently supported. Initialising priorities
3318	will fail and all watchers will have the same priority, even though there	4028	will fail and all watchers will have the same priority, even though there
3319	is an ev_pri field.	4029	is an ev_pri field.
3320		4030
3321	=item * In libevent, the last base created gets the signals, in libev, the	4031	=item * In libevent, the last base created gets the signals, in libev, the
3322	first base created (== the default loop) gets the signals.	4032	base that registered the signal gets the signals.
3323		4033
3324	=item * Other members are not supported.	4034	=item * Other members are not supported.
3325		4035
3326	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4036	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3327	to use the libev header file and library.	4037	to use the libev header file and library.
3328		4038
3329	=back	4039	=back
3330		4040
3331	=head1 C++ SUPPORT	4041	=head1 C++ SUPPORT
		4042
		4043	=head2 C API
		4044
		4045	The normal C API should work fine when used from C++: both ev.h and the
		4046	libev sources can be compiled as C++. Therefore, code that uses the C API
		4047	will work fine.
		4048
		4049	Proper exception specifications might have to be added to callbacks passed
		4050	to libev: exceptions may be thrown only from watcher callbacks, all other
		4051	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4052	callbacks) must not throw exceptions, and might need a C<noexcept>
		4053	specification. If you have code that needs to be compiled as both C and
		4054	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4055
		4056	static void
		4057	fatal_error (const char *msg) EV_NOEXCEPT
		4058	{
		4059	perror (msg);
		4060	abort ();
		4061	}
		4062
		4063	...
		4064	ev_set_syserr_cb (fatal_error);
		4065
		4066	The only API functions that can currently throw exceptions are C<ev_run>,
		4067	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4068	because it runs cleanup watchers).
		4069
		4070	Throwing exceptions in watcher callbacks is only supported if libev itself
		4071	is compiled with a C++ compiler or your C and C++ environments allow
		4072	throwing exceptions through C libraries (most do).
		4073
		4074	=head2 C++ API
3332		4075
3333	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4076	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3334	you to use some convenience methods to start/stop watchers and also change	4077	you to use some convenience methods to start/stop watchers and also change
3335	the callback model to a model using method callbacks on objects.	4078	the callback model to a model using method callbacks on objects.
3336		4079
3337	To use it,	4080	To use it,
3338		4081
3339	#include <ev++.h>	4082	#include <ev++.h>
3340		4083
3341	This automatically includes F<ev.h> and puts all of its definitions (many	4084	This automatically includes F<ev.h> and puts all of its definitions (many
3342	of them macros) into the global namespace. All C++ specific things are	4085	of them macros) into the global namespace. All C++ specific things are
3343	put into the C<ev> namespace. It should support all the same embedding	4086	put into the C<ev> namespace. It should support all the same embedding
…		…
3346	Care has been taken to keep the overhead low. The only data member the C++	4089	Care has been taken to keep the overhead low. The only data member the C++
3347	classes add (compared to plain C-style watchers) is the event loop pointer	4090	classes add (compared to plain C-style watchers) is the event loop pointer
3348	that the watcher is associated with (or no additional members at all if	4091	that the watcher is associated with (or no additional members at all if
3349	you disable C<EV_MULTIPLICITY> when embedding libev).	4092	you disable C<EV_MULTIPLICITY> when embedding libev).
3350		4093
3351	Currently, functions, and static and non-static member functions can be	4094	Currently, functions, static and non-static member functions and classes
3352	used as callbacks. Other types should be easy to add as long as they only	4095	with C<operator ()> can be used as callbacks. Other types should be easy
3353	need one additional pointer for context. If you need support for other	4096	to add as long as they only need one additional pointer for context. If
3354	types of functors please contact the author (preferably after implementing	4097	you need support for other types of functors please contact the author
3355	it).	4098	(preferably after implementing it).
		4099
		4100	For all this to work, your C++ compiler either has to use the same calling
		4101	conventions as your C compiler (for static member functions), or you have
		4102	to embed libev and compile libev itself as C++.
3356		4103
3357	Here is a list of things available in the C<ev> namespace:	4104	Here is a list of things available in the C<ev> namespace:
3358		4105
3359	=over 4	4106	=over 4
3360		4107
…		…
3370	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4117	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3371		4118
3372	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4119	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3373	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4120	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3374	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4121	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3375	defines by many implementations.	4122	defined by many implementations.
3376		4123
3377	All of those classes have these methods:	4124	All of those classes have these methods:
3378		4125
3379	=over 4	4126	=over 4
3380		4127
…		…
3442	void operator() (ev::io &w, int revents)	4189	void operator() (ev::io &w, int revents)
3443	{	4190	{
3444	...	4191	...
3445	}	4192	}
3446	}	4193	}
3447		4194
3448	myfunctor f;	4195	myfunctor f;
3449		4196
3450	ev::io w;	4197	ev::io w;
3451	w.set (&f);	4198	w.set (&f);
3452		4199
…		…
3470	Associates a different C<struct ev_loop> with this watcher. You can only	4217	Associates a different C<struct ev_loop> with this watcher. You can only
3471	do this when the watcher is inactive (and not pending either).	4218	do this when the watcher is inactive (and not pending either).
3472		4219
3473	=item w->set ([arguments])	4220	=item w->set ([arguments])
3474		4221
3475	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4222	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3476	method or a suitable start method must be called at least once. Unlike the	4223	with the same arguments. Either this method or a suitable start method
3477	C counterpart, an active watcher gets automatically stopped and restarted	4224	must be called at least once. Unlike the C counterpart, an active watcher
3478	when reconfiguring it with this method.	4225	gets automatically stopped and restarted when reconfiguring it with this
		4226	method.
		4227
		4228	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4229	clashing with the C<set (loop)> method.
3479		4230
3480	=item w->start ()	4231	=item w->start ()
3481		4232
3482	Starts the watcher. Note that there is no C<loop> argument, as the	4233	Starts the watcher. Note that there is no C<loop> argument, as the
3483	constructor already stores the event loop.	4234	constructor already stores the event loop.
…		…
3513	watchers in the constructor.	4264	watchers in the constructor.
3514		4265
3515	class myclass	4266	class myclass
3516	{	4267	{
3517	ev::io io ; void io_cb (ev::io &w, int revents);	4268	ev::io io ; void io_cb (ev::io &w, int revents);
3518	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4269	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3519	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4270	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3520		4271
3521	myclass (int fd)	4272	myclass (int fd)
3522	{	4273	{
3523	io .set <myclass, &myclass::io_cb > (this);	4274	io .set <myclass, &myclass::io_cb > (this);
…		…
3574	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4325	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3575		4326
3576	=item D	4327	=item D
3577		4328
3578	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4329	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3579	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4330	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3580		4331
3581	=item Ocaml	4332	=item Ocaml
3582		4333
3583	Erkki Seppala has written Ocaml bindings for libev, to be found at	4334	Erkki Seppala has written Ocaml bindings for libev, to be found at
3584	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4335	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3587		4338
3588	Brian Maher has written a partial interface to libev for lua (at the	4339	Brian Maher has written a partial interface to libev for lua (at the
3589	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4340	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3590	L<http://github.com/brimworks/lua-ev>.	4341	L<http://github.com/brimworks/lua-ev>.
3591		4342
		4343	=item Javascript
		4344
		4345	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4346
		4347	=item Others
		4348
		4349	There are others, and I stopped counting.
		4350
3592	=back	4351	=back
3593		4352
3594		4353
3595	=head1 MACRO MAGIC	4354	=head1 MACRO MAGIC
3596		4355
…		…
3632	suitable for use with C<EV_A>.	4391	suitable for use with C<EV_A>.
3633		4392
3634	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4393	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3635		4394
3636	Similar to the other two macros, this gives you the value of the default	4395	Similar to the other two macros, this gives you the value of the default
3637	loop, if multiple loops are supported ("ev loop default").	4396	loop, if multiple loops are supported ("ev loop default"). The default loop
		4397	will be initialised if it isn't already initialised.
		4398
		4399	For non-multiplicity builds, these macros do nothing, so you always have
		4400	to initialise the loop somewhere.
3638		4401
3639	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4402	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3640		4403
3641	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4404	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3642	default loop has been initialised (C<UC> == unchecked). Their behaviour	4405	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3709	ev_vars.h	4472	ev_vars.h
3710	ev_wrap.h	4473	ev_wrap.h
3711		4474
3712	ev_win32.c required on win32 platforms only	4475	ev_win32.c required on win32 platforms only
3713		4476
3714	ev_select.c only when select backend is enabled (which is enabled by default)	4477	ev_select.c only when select backend is enabled
3715	ev_poll.c only when poll backend is enabled (disabled by default)	4478	ev_poll.c only when poll backend is enabled
3716	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4479	ev_epoll.c only when the epoll backend is enabled
		4480	ev_linuxaio.c only when the linux aio backend is enabled
3717	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4481	ev_kqueue.c only when the kqueue backend is enabled
3718	ev_port.c only when the solaris port backend is enabled (disabled by default)	4482	ev_port.c only when the solaris port backend is enabled
3719		4483
3720	F<ev.c> includes the backend files directly when enabled, so you only need	4484	F<ev.c> includes the backend files directly when enabled, so you only need
3721	to compile this single file.	4485	to compile this single file.
3722		4486
3723	=head3 LIBEVENT COMPATIBILITY API	4487	=head3 LIBEVENT COMPATIBILITY API
…		…
3787	supported). It will also not define any of the structs usually found in	4551	supported). It will also not define any of the structs usually found in
3788	F<event.h> that are not directly supported by the libev core alone.	4552	F<event.h> that are not directly supported by the libev core alone.
3789		4553
3790	In standalone mode, libev will still try to automatically deduce the	4554	In standalone mode, libev will still try to automatically deduce the
3791	configuration, but has to be more conservative.	4555	configuration, but has to be more conservative.
		4556
		4557	=item EV_USE_FLOOR
		4558
		4559	If defined to be C<1>, libev will use the C<floor ()> function for its
		4560	periodic reschedule calculations, otherwise libev will fall back on a
		4561	portable (slower) implementation. If you enable this, you usually have to
		4562	link against libm or something equivalent. Enabling this when the C<floor>
		4563	function is not available will fail, so the safe default is to not enable
		4564	this.
3792		4565
3793	=item EV_USE_MONOTONIC	4566	=item EV_USE_MONOTONIC
3794		4567
3795	If defined to be C<1>, libev will try to detect the availability of the	4568	If defined to be C<1>, libev will try to detect the availability of the
3796	monotonic clock option at both compile time and runtime. Otherwise no	4569	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3882	If programs implement their own fd to handle mapping on win32, then this	4655	If programs implement their own fd to handle mapping on win32, then this
3883	macro can be used to override the C<close> function, useful to unregister	4656	macro can be used to override the C<close> function, useful to unregister
3884	file descriptors again. Note that the replacement function has to close	4657	file descriptors again. Note that the replacement function has to close
3885	the underlying OS handle.	4658	the underlying OS handle.
3886		4659
		4660	=item EV_USE_WSASOCKET
		4661
		4662	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4663	communication socket, which works better in some environments. Otherwise,
		4664	the normal C<socket> function will be used, which works better in other
		4665	environments.
		4666
3887	=item EV_USE_POLL	4667	=item EV_USE_POLL
3888		4668
3889	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4669	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3890	backend. Otherwise it will be enabled on non-win32 platforms. It	4670	backend. Otherwise it will be enabled on non-win32 platforms. It
3891	takes precedence over select.	4671	takes precedence over select.
…		…
3895	If defined to be C<1>, libev will compile in support for the Linux	4675	If defined to be C<1>, libev will compile in support for the Linux
3896	C<epoll>(7) backend. Its availability will be detected at runtime,	4676	C<epoll>(7) backend. Its availability will be detected at runtime,
3897	otherwise another method will be used as fallback. This is the preferred	4677	otherwise another method will be used as fallback. This is the preferred
3898	backend for GNU/Linux systems. If undefined, it will be enabled if the	4678	backend for GNU/Linux systems. If undefined, it will be enabled if the
3899	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4679	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4680
		4681	=item EV_USE_LINUXAIO
		4682
		4683	If defined to be C<1>, libev will compile in support for the Linux
		4684	aio backend. Due to it's currenbt limitations it has to be requested
		4685	explicitly. If undefined, it will be enabled on linux, otherwise
		4686	disabled.
3900		4687
3901	=item EV_USE_KQUEUE	4688	=item EV_USE_KQUEUE
3902		4689
3903	If defined to be C<1>, libev will compile in support for the BSD style	4690	If defined to be C<1>, libev will compile in support for the BSD style
3904	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4691	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
3926	If defined to be C<1>, libev will compile in support for the Linux inotify	4713	If defined to be C<1>, libev will compile in support for the Linux inotify
3927	interface to speed up C<ev_stat> watchers. Its actual availability will	4714	interface to speed up C<ev_stat> watchers. Its actual availability will
3928	be detected at runtime. If undefined, it will be enabled if the headers	4715	be detected at runtime. If undefined, it will be enabled if the headers
3929	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4716	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3930		4717
		4718	=item EV_NO_SMP
		4719
		4720	If defined to be C<1>, libev will assume that memory is always coherent
		4721	between threads, that is, threads can be used, but threads never run on
		4722	different cpus (or different cpu cores). This reduces dependencies
		4723	and makes libev faster.
		4724
		4725	=item EV_NO_THREADS
		4726
		4727	If defined to be C<1>, libev will assume that it will never be called from
		4728	different threads (that includes signal handlers), which is a stronger
		4729	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4730	libev faster.
		4731
3931	=item EV_ATOMIC_T	4732	=item EV_ATOMIC_T
3932		4733
3933	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4734	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3934	access is atomic with respect to other threads or signal contexts. No such	4735	access is atomic with respect to other threads or signal contexts. No
3935	type is easily found in the C language, so you can provide your own type	4736	such type is easily found in the C language, so you can provide your own
3936	that you know is safe for your purposes. It is used both for signal handler "locking"	4737	type that you know is safe for your purposes. It is used both for signal
3937	as well as for signal and thread safety in C<ev_async> watchers.	4738	handler "locking" as well as for signal and thread safety in C<ev_async>
		4739	watchers.
3938		4740
3939	In the absence of this define, libev will use C<sig_atomic_t volatile>	4741	In the absence of this define, libev will use C<sig_atomic_t volatile>
3940	(from F<signal.h>), which is usually good enough on most platforms.	4742	(from F<signal.h>), which is usually good enough on most platforms.
3941		4743
3942	=item EV_H (h)	4744	=item EV_H (h)
…		…
3969	will have the C<struct ev_loop *> as first argument, and you can create	4771	will have the C<struct ev_loop *> as first argument, and you can create
3970	additional independent event loops. Otherwise there will be no support	4772	additional independent event loops. Otherwise there will be no support
3971	for multiple event loops and there is no first event loop pointer	4773	for multiple event loops and there is no first event loop pointer
3972	argument. Instead, all functions act on the single default loop.	4774	argument. Instead, all functions act on the single default loop.
3973		4775
		4776	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4777	default loop when multiplicity is switched off - you always have to
		4778	initialise the loop manually in this case.
		4779
3974	=item EV_MINPRI	4780	=item EV_MINPRI
3975		4781
3976	=item EV_MAXPRI	4782	=item EV_MAXPRI
3977		4783
3978	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4784	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4014	#define EV_USE_POLL 1	4820	#define EV_USE_POLL 1
4015	#define EV_CHILD_ENABLE 1	4821	#define EV_CHILD_ENABLE 1
4016	#define EV_ASYNC_ENABLE 1	4822	#define EV_ASYNC_ENABLE 1
4017		4823
4018	The actual value is a bitset, it can be a combination of the following	4824	The actual value is a bitset, it can be a combination of the following
4019	values:	4825	values (by default, all of these are enabled):
4020		4826
4021	=over 4	4827	=over 4
4022		4828
4023	=item C<1> - faster/larger code	4829	=item C<1> - faster/larger code
4024		4830
…		…
4028	code size by roughly 30% on amd64).	4834	code size by roughly 30% on amd64).
4029		4835
4030	When optimising for size, use of compiler flags such as C<-Os> with	4836	When optimising for size, use of compiler flags such as C<-Os> with
4031	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4837	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4032	assertions.	4838	assertions.
		4839
		4840	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4841	(e.g. gcc with C<-Os>).
4033		4842
4034	=item C<2> - faster/larger data structures	4843	=item C<2> - faster/larger data structures
4035		4844
4036	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4845	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4037	hash table sizes and so on. This will usually further increase code size	4846	hash table sizes and so on. This will usually further increase code size
4038	and can additionally have an effect on the size of data structures at	4847	and can additionally have an effect on the size of data structures at
4039	runtime.	4848	runtime.
4040		4849
		4850	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4851	(e.g. gcc with C<-Os>).
		4852
4041	=item C<4> - full API configuration	4853	=item C<4> - full API configuration
4042		4854
4043	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4855	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4044	enables multiplicity (C<EV_MULTIPLICITY>=1).	4856	enables multiplicity (C<EV_MULTIPLICITY>=1).
4045		4857
…		…
4075		4887
4076	With an intelligent-enough linker (gcc+binutils are intelligent enough	4888	With an intelligent-enough linker (gcc+binutils are intelligent enough
4077	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4889	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4078	your program might be left out as well - a binary starting a timer and an	4890	your program might be left out as well - a binary starting a timer and an
4079	I/O watcher then might come out at only 5Kb.	4891	I/O watcher then might come out at only 5Kb.
		4892
		4893	=item EV_API_STATIC
		4894
		4895	If this symbol is defined (by default it is not), then all identifiers
		4896	will have static linkage. This means that libev will not export any
		4897	identifiers, and you cannot link against libev anymore. This can be useful
		4898	when you embed libev, only want to use libev functions in a single file,
		4899	and do not want its identifiers to be visible.
		4900
		4901	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4902	wants to use libev.
		4903
		4904	This option only works when libev is compiled with a C compiler, as C++
		4905	doesn't support the required declaration syntax.
4080		4906
4081	=item EV_AVOID_STDIO	4907	=item EV_AVOID_STDIO
4082		4908
4083	If this is set to C<1> at compiletime, then libev will avoid using stdio	4909	If this is set to C<1> at compiletime, then libev will avoid using stdio
4084	functions (printf, scanf, perror etc.). This will increase the code size	4910	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4228	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5054	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4229		5055
4230	#include "ev_cpp.h"	5056	#include "ev_cpp.h"
4231	#include "ev.c"	5057	#include "ev.c"
4232		5058
4233	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5059	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4234		5060
4235	=head2 THREADS AND COROUTINES	5061	=head2 THREADS AND COROUTINES
4236		5062
4237	=head3 THREADS	5063	=head3 THREADS
4238		5064
…		…
4289	default loop and triggering an C<ev_async> watcher from the default loop	5115	default loop and triggering an C<ev_async> watcher from the default loop
4290	watcher callback into the event loop interested in the signal.	5116	watcher callback into the event loop interested in the signal.
4291		5117
4292	=back	5118	=back
4293		5119
4294	=head4 THREAD LOCKING EXAMPLE	5120	See also L</THREAD LOCKING EXAMPLE>.
4295
4296	Here is a fictitious example of how to run an event loop in a different
4297	thread than where callbacks are being invoked and watchers are
4298	created/added/removed.
4299
4300	For a real-world example, see the C<EV::Loop::Async> perl module,
4301	which uses exactly this technique (which is suited for many high-level
4302	languages).
4303
4304	The example uses a pthread mutex to protect the loop data, a condition
4305	variable to wait for callback invocations, an async watcher to notify the
4306	event loop thread and an unspecified mechanism to wake up the main thread.
4307
4308	First, you need to associate some data with the event loop:
4309
4310	typedef struct {
4311	mutex_t lock; /* global loop lock */
4312	ev_async async_w;
4313	thread_t tid;
4314	cond_t invoke_cv;
4315	} userdata;
4316
4317	void prepare_loop (EV_P)
4318	{
4319	// for simplicity, we use a static userdata struct.
4320	static userdata u;
4321
4322	ev_async_init (&u->async_w, async_cb);
4323	ev_async_start (EV_A_ &u->async_w);
4324
4325	pthread_mutex_init (&u->lock, 0);
4326	pthread_cond_init (&u->invoke_cv, 0);
4327
4328	// now associate this with the loop
4329	ev_set_userdata (EV_A_ u);
4330	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4331	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4332
4333	// then create the thread running ev_loop
4334	pthread_create (&u->tid, 0, l_run, EV_A);
4335	}
4336
4337	The callback for the C<ev_async> watcher does nothing: the watcher is used
4338	solely to wake up the event loop so it takes notice of any new watchers
4339	that might have been added:
4340
4341	static void
4342	async_cb (EV_P_ ev_async *w, int revents)
4343	{
4344	// just used for the side effects
4345	}
4346
4347	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4348	protecting the loop data, respectively.
4349
4350	static void
4351	l_release (EV_P)
4352	{
4353	userdata *u = ev_userdata (EV_A);
4354	pthread_mutex_unlock (&u->lock);
4355	}
4356
4357	static void
4358	l_acquire (EV_P)
4359	{
4360	userdata *u = ev_userdata (EV_A);
4361	pthread_mutex_lock (&u->lock);
4362	}
4363
4364	The event loop thread first acquires the mutex, and then jumps straight
4365	into C<ev_run>:
4366
4367	void *
4368	l_run (void *thr_arg)
4369	{
4370	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4371
4372	l_acquire (EV_A);
4373	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4374	ev_run (EV_A_ 0);
4375	l_release (EV_A);
4376
4377	return 0;
4378	}
4379
4380	Instead of invoking all pending watchers, the C<l_invoke> callback will
4381	signal the main thread via some unspecified mechanism (signals? pipe
4382	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4383	have been called (in a while loop because a) spurious wakeups are possible
4384	and b) skipping inter-thread-communication when there are no pending
4385	watchers is very beneficial):
4386
4387	static void
4388	l_invoke (EV_P)
4389	{
4390	userdata *u = ev_userdata (EV_A);
4391
4392	while (ev_pending_count (EV_A))
4393	{
4394	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4395	pthread_cond_wait (&u->invoke_cv, &u->lock);
4396	}
4397	}
4398
4399	Now, whenever the main thread gets told to invoke pending watchers, it
4400	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4401	thread to continue:
4402
4403	static void
4404	real_invoke_pending (EV_P)
4405	{
4406	userdata *u = ev_userdata (EV_A);
4407
4408	pthread_mutex_lock (&u->lock);
4409	ev_invoke_pending (EV_A);
4410	pthread_cond_signal (&u->invoke_cv);
4411	pthread_mutex_unlock (&u->lock);
4412	}
4413
4414	Whenever you want to start/stop a watcher or do other modifications to an
4415	event loop, you will now have to lock:
4416
4417	ev_timer timeout_watcher;
4418	userdata *u = ev_userdata (EV_A);
4419
4420	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4421
4422	pthread_mutex_lock (&u->lock);
4423	ev_timer_start (EV_A_ &timeout_watcher);
4424	ev_async_send (EV_A_ &u->async_w);
4425	pthread_mutex_unlock (&u->lock);
4426
4427	Note that sending the C<ev_async> watcher is required because otherwise
4428	an event loop currently blocking in the kernel will have no knowledge
4429	about the newly added timer. By waking up the loop it will pick up any new
4430	watchers in the next event loop iteration.
4431		5121
4432	=head3 COROUTINES	5122	=head3 COROUTINES
4433		5123
4434	Libev is very accommodating to coroutines ("cooperative threads"):	5124	Libev is very accommodating to coroutines ("cooperative threads"):
4435	libev fully supports nesting calls to its functions from different	5125	libev fully supports nesting calls to its functions from different
…		…
4531	=head3 C<kqueue> is buggy	5221	=head3 C<kqueue> is buggy
4532		5222
4533	The kqueue syscall is broken in all known versions - most versions support	5223	The kqueue syscall is broken in all known versions - most versions support
4534	only sockets, many support pipes.	5224	only sockets, many support pipes.
4535		5225
4536	Libev tries to work around this by not using C<kqueue> by default on	5226	Libev tries to work around this by not using C<kqueue> by default on this
4537	this rotten platform, but of course you can still ask for it when creating	5227	rotten platform, but of course you can still ask for it when creating a
4538	a loop.	5228	loop - embedding a socket-only kqueue loop into a select-based one is
		5229	probably going to work well.
4539		5230
4540	=head3 C<poll> is buggy	5231	=head3 C<poll> is buggy
4541		5232
4542	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>	5233	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
4543	implementation by something calling C<kqueue> internally around the 10.5.6	5234	implementation by something calling C<kqueue> internally around the 10.5.6
…		…
4562		5253
4563	=head3 C<errno> reentrancy	5254	=head3 C<errno> reentrancy
4564		5255
4565	The default compile environment on Solaris is unfortunately so	5256	The default compile environment on Solaris is unfortunately so
4566	thread-unsafe that you can't even use components/libraries compiled	5257	thread-unsafe that you can't even use components/libraries compiled
4567	without C<-D_REENTRANT> (as long as they use C<errno>), which, of course,	5258	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
4568	isn't defined by default.	5259	defined by default. A valid, if stupid, implementation choice.
4569		5260
4570	If you want to use libev in threaded environments you have to make sure	5261	If you want to use libev in threaded environments you have to make sure
4571	it's compiled with C<_REENTRANT> defined.	5262	it's compiled with C<_REENTRANT> defined.
4572		5263
4573	=head3 Event port backend	5264	=head3 Event port backend
4574		5265
4575	The scalable event interface for Solaris is called "event ports". Unfortunately,	5266	The scalable event interface for Solaris is called "event
4576	this mechanism is very buggy. If you run into high CPU usage, your program	5267	ports". Unfortunately, this mechanism is very buggy in all major
		5268	releases. If you run into high CPU usage, your program freezes or you get
4577	freezes or you get a large number of spurious wakeups, make sure you have	5269	a large number of spurious wakeups, make sure you have all the relevant
4578	all the relevant and latest kernel patches applied. No, I don't know which	5270	and latest kernel patches applied. No, I don't know which ones, but there
4579	ones, but there are multiple ones.	5271	are multiple ones to apply, and afterwards, event ports actually work
		5272	great.
4580		5273
4581	If you can't get it to work, you can try running the program by setting	5274	If you can't get it to work, you can try running the program by setting
4582	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and	5275	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
4583	C<select> backends.	5276	C<select> backends.
4584		5277
4585	=head2 AIX POLL BUG	5278	=head2 AIX POLL BUG
4586		5279
4587	AIX unfortunately has a broken C<poll.h> header. Libev works around	5280	AIX unfortunately has a broken C<poll.h> header. Libev works around
4588	this by trying to avoid the poll backend altogether (i.e. it's not even	5281	this by trying to avoid the poll backend altogether (i.e. it's not even
4589	compiled in), which normally isn't a big problem as C<select> works fine	5282	compiled in), which normally isn't a big problem as C<select> works fine
4590	with large bitsets, and AIX is dead anyway.	5283	with large bitsets on AIX, and AIX is dead anyway.
4591		5284
4592	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	5285	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
4593		5286
4594	=head3 General issues	5287	=head3 General issues
4595		5288
…		…
4597	requires, and its I/O model is fundamentally incompatible with the POSIX	5290	requires, and its I/O model is fundamentally incompatible with the POSIX
4598	model. Libev still offers limited functionality on this platform in	5291	model. Libev still offers limited functionality on this platform in
4599	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5292	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4600	descriptors. This only applies when using Win32 natively, not when using	5293	descriptors. This only applies when using Win32 natively, not when using
4601	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5294	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4602	as every compielr comes with a slightly differently broken/incompatible	5295	as every compiler comes with a slightly differently broken/incompatible
4603	environment.	5296	environment.
4604		5297
4605	Lifting these limitations would basically require the full	5298	Lifting these limitations would basically require the full
4606	re-implementation of the I/O system. If you are into this kind of thing,	5299	re-implementation of the I/O system. If you are into this kind of thing,
4607	then note that glib does exactly that for you in a very portable way (note	5300	then note that glib does exactly that for you in a very portable way (note
…		…
4701	structure (guaranteed by POSIX but not by ISO C for example), but it also	5394	structure (guaranteed by POSIX but not by ISO C for example), but it also
4702	assumes that the same (machine) code can be used to call any watcher	5395	assumes that the same (machine) code can be used to call any watcher
4703	callback: The watcher callbacks have different type signatures, but libev	5396	callback: The watcher callbacks have different type signatures, but libev
4704	calls them using an C<ev_watcher *> internally.	5397	calls them using an C<ev_watcher *> internally.
4705		5398
		5399	=item null pointers and integer zero are represented by 0 bytes
		5400
		5401	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5402	relies on this setting pointers and integers to null.
		5403
		5404	=item pointer accesses must be thread-atomic
		5405
		5406	Accessing a pointer value must be atomic, it must both be readable and
		5407	writable in one piece - this is the case on all current architectures.
		5408
4706	=item C<sig_atomic_t volatile> must be thread-atomic as well	5409	=item C<sig_atomic_t volatile> must be thread-atomic as well
4707		5410
4708	The type C<sig_atomic_t volatile> (or whatever is defined as	5411	The type C<sig_atomic_t volatile> (or whatever is defined as
4709	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5412	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4710	threads. This is not part of the specification for C<sig_atomic_t>, but is	5413	threads. This is not part of the specification for C<sig_atomic_t>, but is
…		…
4718	thread" or will block signals process-wide, both behaviours would	5421	thread" or will block signals process-wide, both behaviours would
4719	be compatible with libev. Interaction between C<sigprocmask> and	5422	be compatible with libev. Interaction between C<sigprocmask> and
4720	C<pthread_sigmask> could complicate things, however.	5423	C<pthread_sigmask> could complicate things, however.
4721		5424
4722	The most portable way to handle signals is to block signals in all threads	5425	The most portable way to handle signals is to block signals in all threads
4723	except the initial one, and run the default loop in the initial thread as	5426	except the initial one, and run the signal handling loop in the initial
4724	well.	5427	thread as well.
4725		5428
4726	=item C<long> must be large enough for common memory allocation sizes	5429	=item C<long> must be large enough for common memory allocation sizes
4727		5430
4728	To improve portability and simplify its API, libev uses C<long> internally	5431	To improve portability and simplify its API, libev uses C<long> internally
4729	instead of C<size_t> when allocating its data structures. On non-POSIX	5432	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4735		5438
4736	The type C<double> is used to represent timestamps. It is required to	5439	The type C<double> is used to represent timestamps. It is required to
4737	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5440	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4738	good enough for at least into the year 4000 with millisecond accuracy	5441	good enough for at least into the year 4000 with millisecond accuracy
4739	(the design goal for libev). This requirement is overfulfilled by	5442	(the design goal for libev). This requirement is overfulfilled by
4740	implementations using IEEE 754, which is basically all existing ones. With	5443	implementations using IEEE 754, which is basically all existing ones.
		5444
4741	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5445	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5446	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5447	is either obsolete or somebody patched it to use C<long double> or
		5448	something like that, just kidding).
4742		5449
4743	=back	5450	=back
4744		5451
4745	If you know of other additional requirements drop me a note.	5452	If you know of other additional requirements drop me a note.
4746		5453
…		…
4808	=item Processing ev_async_send: O(number_of_async_watchers)	5515	=item Processing ev_async_send: O(number_of_async_watchers)
4809		5516
4810	=item Processing signals: O(max_signal_number)	5517	=item Processing signals: O(max_signal_number)
4811		5518
4812	Sending involves a system call I<iff> there were no other C<ev_async_send>	5519	Sending involves a system call I<iff> there were no other C<ev_async_send>
4813	calls in the current loop iteration. Checking for async and signal events	5520	calls in the current loop iteration and the loop is currently
		5521	blocked. Checking for async and signal events involves iterating over all
4814	involves iterating over all running async watchers or all signal numbers.	5522	running async watchers or all signal numbers.
4815		5523
4816	=back	5524	=back
4817		5525
4818		5526
4819	=head1 PORTING FROM LIBEV 3.X TO 4.X	5527	=head1 PORTING FROM LIBEV 3.X TO 4.X
4820		5528
4821	The major version 4 introduced some minor incompatible changes to the API.	5529	The major version 4 introduced some incompatible changes to the API.
4822		5530
4823	At the moment, the C<ev.h> header file tries to implement superficial	5531	At the moment, the C<ev.h> header file provides compatibility definitions
4824	compatibility, so most programs should still compile. Those might be	5532	for all changes, so most programs should still compile. The compatibility
4825	removed in later versions of libev, so better update early than late.	5533	layer might be removed in later versions of libev, so better update to the
		5534	new API early than late.
4826		5535
4827	=over 4	5536	=over 4
		5537
		5538	=item C<EV_COMPAT3> backwards compatibility mechanism
		5539
		5540	The backward compatibility mechanism can be controlled by
		5541	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5542	section.
		5543
		5544	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5545
		5546	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5547
		5548	ev_loop_destroy (EV_DEFAULT_UC);
		5549	ev_loop_fork (EV_DEFAULT);
4828		5550
4829	=item function/symbol renames	5551	=item function/symbol renames
4830		5552
4831	A number of functions and symbols have been renamed:	5553	A number of functions and symbols have been renamed:
4832		5554
…		…
4851	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5573	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4852	as all other watcher types. Note that C<ev_loop_fork> is still called	5574	as all other watcher types. Note that C<ev_loop_fork> is still called
4853	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>	5575	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4854	typedef.	5576	typedef.
4855		5577
4856	=item C<EV_COMPAT3> backwards compatibility mechanism
4857
4858	The backward compatibility mechanism can be controlled by
4859	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4860	section.
4861
4862	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>	5578	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4863		5579
4864	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5580	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4865	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5581	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4866	and work, but the library code will of course be larger.	5582	and work, but the library code will of course be larger.
…		…
4872		5588
4873	=over 4	5589	=over 4
4874		5590
4875	=item active	5591	=item active
4876		5592
4877	A watcher is active as long as it has been started (has been attached to	5593	A watcher is active as long as it has been started and not yet stopped.
4878	an event loop) but not yet stopped (disassociated from the event loop).	5594	See L</WATCHER STATES> for details.
4879		5595
4880	=item application	5596	=item application
4881		5597
4882	In this document, an application is whatever is using libev.	5598	In this document, an application is whatever is using libev.
		5599
		5600	=item backend
		5601
		5602	The part of the code dealing with the operating system interfaces.
4883		5603
4884	=item callback	5604	=item callback
4885		5605
4886	The address of a function that is called when some event has been	5606	The address of a function that is called when some event has been
4887	detected. Callbacks are being passed the event loop, the watcher that	5607	detected. Callbacks are being passed the event loop, the watcher that
4888	received the event, and the actual event bitset.	5608	received the event, and the actual event bitset.
4889		5609
4890	=item callback invocation	5610	=item callback/watcher invocation
4891		5611
4892	The act of calling the callback associated with a watcher.	5612	The act of calling the callback associated with a watcher.
4893		5613
4894	=item event	5614	=item event
4895		5615
…		…
4914	The model used to describe how an event loop handles and processes	5634	The model used to describe how an event loop handles and processes
4915	watchers and events.	5635	watchers and events.
4916		5636
4917	=item pending	5637	=item pending
4918		5638
4919	A watcher is pending as soon as the corresponding event has been detected,	5639	A watcher is pending as soon as the corresponding event has been
4920	and stops being pending as soon as the watcher will be invoked or its	5640	detected. See L</WATCHER STATES> for details.
4921	pending status is explicitly cleared by the application.
4922
4923	A watcher can be pending, but not active. Stopping a watcher also clears
4924	its pending status.
4925		5641
4926	=item real time	5642	=item real time
4927		5643
4928	The physical time that is observed. It is apparently strictly monotonic :)	5644	The physical time that is observed. It is apparently strictly monotonic :)
4929		5645
4930	=item wall-clock time	5646	=item wall-clock time
4931		5647
4932	The time and date as shown on clocks. Unlike real time, it can actually	5648	The time and date as shown on clocks. Unlike real time, it can actually
4933	be wrong and jump forwards and backwards, e.g. when the you adjust your	5649	be wrong and jump forwards and backwards, e.g. when you adjust your
4934	clock.	5650	clock.
4935		5651
4936	=item watcher	5652	=item watcher
4937		5653
4938	A data structure that describes interest in certain events. Watchers need	5654	A data structure that describes interest in certain events. Watchers need
4939	to be started (attached to an event loop) before they can receive events.	5655	to be started (attached to an event loop) before they can receive events.
4940		5656
4941	=item watcher invocation
4942
4943	The act of calling the callback associated with a watcher.
4944
4945	=back	5657	=back
4946		5658
4947	=head1 AUTHOR	5659	=head1 AUTHOR
4948		5660
4949	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5661	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5662	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
4950		5663

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