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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
		590	the epoll set), and generally sounds too good to be true. Because, this
		591	being the linux kernel, of course it suffers from a whole new set of
		592	limitations.
		593
		594	For one, it is not easily embeddable (but probably could be done using
		595	an event fd at some extra overhead). It also is subject to a system wide
		596	limit that can be configured in F</proc/sys/fs/aio-max-nr> - each loop
		597	currently requires C<61> of this number. If no aio requests are left, this
		598	backend will be skipped during initialisation.
		599
		600	Most problematic in practise, however, is that not all file descriptors
		601	work with it. For example, in linux 5.1, tcp sockets, pipes, event fds,
		602	files, F</dev/null> and a few others are supported, but ttys do not work
		603	properly (a known bug that the kernel developers don't care about, see
		604	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		605	(yet?) a generic event polling interface.
		606
		607	To work around this latter problem, the current version of libev uses
		608	epoll as a fallback for file deescriptor types that do not work. Epoll
		609	is used in, kind of, slow mode that hopefully avoids most of its design
		610	problems and requires 1-3 extra syscalls per active fd every iteration.
469		611
470	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	612	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
471	C<EVBACKEND_POLL>.	613	C<EVBACKEND_POLL>.
472		614
473	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	615	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
…		…
488		630
489	It scales in the same way as the epoll backend, but the interface to the	631	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	632	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	633	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	634	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	635	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	636	might have to leak fd's on fork, but it's more sane than epoll) and it
495	cases	637	drops fds silently in similarly hard-to-detect cases.
496		638
497	This backend usually performs well under most conditions.	639	This backend usually performs well under most conditions.
498		640
499	While nominally embeddable in other event loops, this doesn't work	641	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	642	everywhere, so you might need to test for this. And since it is broken
…		…
517	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	659	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
518		660
519	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	661	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)).	662	it's really slow, but it still scales very well (O(active_fds)).
521		663
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	664	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	665	file descriptor per loop iteration. For small and medium numbers of file
528	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	666	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
529	might perform better.	667	might perform better.
530		668
531	On the positive side, with the exception of the spurious readiness	669	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	670	specification in all tests and is fully embeddable, which is a rare feat
534	OS-specific backends (I vastly prefer correctness over speed hacks).	671	among the OS-specific backends (I vastly prefer correctness over speed
		672	hacks).
		673
		674	On the negative side, the interface is I<bizarre> - so bizarre that
		675	even sun itself gets it wrong in their code examples: The event polling
		676	function sometimes returns events to the caller even though an error
		677	occurred, but with no indication whether it has done so or not (yes, it's
		678	even documented that way) - deadly for edge-triggered interfaces where you
		679	absolutely have to know whether an event occurred or not because you have
		680	to re-arm the watcher.
		681
		682	Fortunately libev seems to be able to work around these idiocies.
535		683
536	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	684	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
537	C<EVBACKEND_POLL>.	685	C<EVBACKEND_POLL>.
538		686
539	=item C<EVBACKEND_ALL>	687	=item C<EVBACKEND_ALL>
540		688
541	Try all backends (even potentially broken ones that wouldn't be tried	689	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	690	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
543	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	691	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
544		692
545	It is definitely not recommended to use this flag.	693	It is definitely not recommended to use this flag, use whatever
		694	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		695	at all.
		696
		697	=item C<EVBACKEND_MASK>
		698
		699	Not a backend at all, but a mask to select all backend bits from a
		700	C<flags> value, in case you want to mask out any backends from a flags
		701	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
546		702
547	=back	703	=back
548		704
549	If one or more of the backend flags are or'ed into the flags value,	705	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	706	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	707	here). If none are specified, all backends in C<ev_recommended_backends
552	()> will be tried.	708	()> will be tried.
553		709
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.	710	Example: Try to create a event loop that uses epoll and nothing else.
581		711
582	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	712	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
583	if (!epoller)	713	if (!epoller)
584	fatal ("no epoll found here, maybe it hides under your chair");	714	fatal ("no epoll found here, maybe it hides under your chair");
585		715
		716	Example: Use whatever libev has to offer, but make sure that kqueue is
		717	used if available.
		718
		719	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		720
		721	Example: Similarly, on linux, you mgiht want to take advantage of the
		722	linux aio backend if possible, but fall back to something else if that
		723	isn't available.
		724
		725	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
		726
586	=item ev_default_destroy ()	727	=item ev_loop_destroy (loop)
587		728
588	Destroys the default loop (frees all memory and kernel state etc.). None	729	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	730	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	731	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,	732	responsibility to either stop all watchers cleanly yourself I<before>
592	or cope with the fact afterwards (which is usually the easiest thing, you	733	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).	734	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		735	for example).
594		736
595	Note that certain global state, such as signal state (and installed signal	737	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	738	handlers), will not be freed by this function, and related watchers (such
597	as signal and child watchers) would need to be stopped manually.	739	as signal and child watchers) would need to be stopped manually.
598		740
599	In general it is not advisable to call this function except in the	741	This function is normally used on loop objects allocated by
600	rare occasion where you really need to free e.g. the signal handling	742	C<ev_loop_new>, but it can also be used on the default loop returned by
		743	C<ev_default_loop>, in which case it is not thread-safe.
		744
		745	Note that it is not advisable to call this function on the default loop
		746	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	747	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>.	748	and C<ev_loop_destroy>.
603		749
604	=item ev_loop_destroy (loop)	750	=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		751
611	This function sets a flag that causes subsequent C<ev_run> iterations	752	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	753	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	754	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	755	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	756	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.	757	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
617		758
		759	In addition, if you want to reuse a loop (via this function or
		760	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		761
618	Again, you I<have> to call it on I<any> loop that you want to re-use after	762	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	763	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	764	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
621	during fork.	765	during fork.
622		766
623	On the other hand, you only need to call this function in the child	767	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	770	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	771	difference, but libev will usually detect this case on its own and do a
628	costly reset of the backend).	772	costly reset of the backend).
629		773
630	The function itself is quite fast and it's usually not a problem to call	774	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	775	it just in case after a fork.
632	quite nicely into a call to C<pthread_atfork>:
633		776
		777	Example: Automate calling C<ev_loop_fork> on the default loop when
		778	using pthreads.
		779
		780	static void
		781	post_fork_child (void)
		782	{
		783	ev_loop_fork (EV_DEFAULT);
		784	}
		785
		786	...
634	pthread_atfork (0, 0, ev_default_fork);	787	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		788
643	=item int ev_is_default_loop (loop)	789	=item int ev_is_default_loop (loop)
644		790
645	Returns true when the given loop is, in fact, the default loop, and false	791	Returns true when the given loop is, in fact, the default loop, and false
646	otherwise.	792	otherwise.
…		…
657	prepare and check phases.	803	prepare and check phases.
658		804
659	=item unsigned int ev_depth (loop)	805	=item unsigned int ev_depth (loop)
660		806
661	Returns the number of times C<ev_run> was entered minus the number of	807	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.	808	times C<ev_run> was exited normally, in other words, the recursion depth.
663		809
664	Outside C<ev_run>, this number is zero. In a callback, this number is	810	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),	811	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
666	in which case it is higher.	812	in which case it is higher.
667		813
668	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	814	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	815	throwing an exception etc.), doesn't count as "exit" - consider this
670	ungentleman-like behaviour unless it's really convenient.	816	as a hint to avoid such ungentleman-like behaviour unless it's really
		817	convenient, in which case it is fully supported.
671		818
672	=item unsigned int ev_backend (loop)	819	=item unsigned int ev_backend (loop)
673		820
674	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	821	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
675	use.	822	use.
…		…
690		837
691	This function is rarely useful, but when some event callback runs for a	838	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	839	very long time without entering the event loop, updating libev's idea of
693	the current time is a good idea.	840	the current time is a good idea.
694		841
695	See also L<The special problem of time updates> in the C<ev_timer> section.	842	See also L</The special problem of time updates> in the C<ev_timer> section.
696		843
697	=item ev_suspend (loop)	844	=item ev_suspend (loop)
698		845
699	=item ev_resume (loop)	846	=item ev_resume (loop)
700		847
…		…
718	without a previous call to C<ev_suspend>.	865	without a previous call to C<ev_suspend>.
719		866
720	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	867	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
721	event loop time (see C<ev_now_update>).	868	event loop time (see C<ev_now_update>).
722		869
723	=item ev_run (loop, int flags)	870	=item bool ev_run (loop, int flags)
724		871
725	Finally, this is it, the event handler. This function usually is called	872	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	873	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	874	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	875	the watcher callbacks, and then repeat the whole process indefinitely: This
729	is why event loops are called I<loops>.	876	is why event loops are called I<loops>.
730		877
731	If the flags argument is specified as C<0>, it will keep handling events	878	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	879	until either no event watchers are active anymore or C<ev_break> was
733	called.	880	called.
		881
		882	The return value is false if there are no more active watchers (which
		883	usually means "all jobs done" or "deadlock"), and true in all other cases
		884	(which usually means " you should call C<ev_run> again").
734		885
735	Please note that an explicit C<ev_break> is usually better than	886	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	887	relying on all watchers to be stopped when deciding when a program has
737	finished (especially in interactive programs), but having a program	888	finished (especially in interactive programs), but having a program
738	that automatically loops as long as it has to and no longer by virtue	889	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	890	of relying on its watchers stopping correctly, that is truly a thing of
740	beauty.	891	beauty.
741		892
		893	This function is I<mostly> exception-safe - you can break out of a
		894	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		895	exception and so on. This does not decrement the C<ev_depth> value, nor
		896	will it clear any outstanding C<EVBREAK_ONE> breaks.
		897
742	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	898	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	899	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	900	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	901	iteration of the loop. This is sometimes useful to poll and handle new
746	events while doing lengthy calculations, to keep the program responsive.	902	events while doing lengthy calculations, to keep the program responsive.
…		…
755	This is useful if you are waiting for some external event in conjunction	911	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	912	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	913	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.	914	usually a better approach for this kind of thing.
759		915
760	Here are the gory details of what C<ev_run> does:	916	Here are the gory details of what C<ev_run> does (this is for your
		917	understanding, not a guarantee that things will work exactly like this in
		918	future versions):
761		919
762	- Increment loop depth.	920	- Increment loop depth.
763	- Reset the ev_break status.	921	- Reset the ev_break status.
764	- Before the first iteration, call any pending watchers.	922	- Before the first iteration, call any pending watchers.
765	LOOP:	923	LOOP:
…		…
798	anymore.	956	anymore.
799		957
800	... queue jobs here, make sure they register event watchers as long	958	... 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..)	959	... as they still have work to do (even an idle watcher will do..)
802	ev_run (my_loop, 0);	960	ev_run (my_loop, 0);
803	... jobs done or somebody called unloop. yeah!	961	... jobs done or somebody called break. yeah!
804		962
805	=item ev_break (loop, how)	963	=item ev_break (loop, how)
806		964
807	Can be used to make a call to C<ev_run> return early (but only after it	965	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	966	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	967	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.	968	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
811		969
812	This "unloop state" will be cleared when entering C<ev_run> again.	970	This "break state" will be cleared on the next call to C<ev_run>.
813		971
814	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	972	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		973	which case it will have no effect.
815		974
816	=item ev_ref (loop)	975	=item ev_ref (loop)
817		976
818	=item ev_unref (loop)	977	=item ev_unref (loop)
819		978
…		…
840	running when nothing else is active.	999	running when nothing else is active.
841		1000
842	ev_signal exitsig;	1001	ev_signal exitsig;
843	ev_signal_init (&exitsig, sig_cb, SIGINT);	1002	ev_signal_init (&exitsig, sig_cb, SIGINT);
844	ev_signal_start (loop, &exitsig);	1003	ev_signal_start (loop, &exitsig);
845	evf_unref (loop);	1004	ev_unref (loop);
846		1005
847	Example: For some weird reason, unregister the above signal handler again.	1006	Example: For some weird reason, unregister the above signal handler again.
848		1007
849	ev_ref (loop);	1008	ev_ref (loop);
850	ev_signal_stop (loop, &exitsig);	1009	ev_signal_stop (loop, &exitsig);
…		…
870	overhead for the actual polling but can deliver many events at once.	1029	overhead for the actual polling but can deliver many events at once.
871		1030
872	By setting a higher I<io collect interval> you allow libev to spend more	1031	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,	1032	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	1033	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	1034	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	1035	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	1036	sleep time ensures that libev will not poll for I/O events more often then
878	once per this interval, on average.	1037	once per this interval, on average (as long as the host time resolution is
		1038	good enough).
879		1039
880	Likewise, by setting a higher I<timeout collect interval> you allow libev	1040	Likewise, by setting a higher I<timeout collect interval> you allow libev
881	to spend more time collecting timeouts, at the expense of increased	1041	to spend more time collecting timeouts, at the expense of increased
882	latency/jitter/inexactness (the watcher callback will be called	1042	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	1043	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.).	1089	invoke the actual watchers inside another context (another thread etc.).
930		1090
931	If you want to reset the callback, use C<ev_invoke_pending> as new	1091	If you want to reset the callback, use C<ev_invoke_pending> as new
932	callback.	1092	callback.
933		1093
934	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1094	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
935		1095
936	Sometimes you want to share the same loop between multiple threads. This	1096	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	1097	can be done relatively simply by putting mutex_lock/unlock calls around
938	each call to a libev function.	1098	each call to a libev function.
939		1099
940	However, C<ev_run> can run an indefinite time, so it is not feasible	1100	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	1101	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	1102	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.	1103	I<release> and I<acquire> callbacks on the loop.
944		1104
945	When set, then C<release> will be called just before the thread is	1105	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	1106	suspended waiting for new events, and C<acquire> is called just
947	afterwards.	1107	afterwards.
…		…
962	See also the locking example in the C<THREADS> section later in this	1122	See also the locking example in the C<THREADS> section later in this
963	document.	1123	document.
964		1124
965	=item ev_set_userdata (loop, void *data)	1125	=item ev_set_userdata (loop, void *data)
966		1126
967	=item ev_userdata (loop)	1127	=item void *ev_userdata (loop)
968		1128
969	Set and retrieve a single C<void *> associated with a loop. When	1129	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	1130	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
971	C<0.>	1131	C<0>.
972		1132
973	These two functions can be used to associate arbitrary data with a loop,	1133	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	1134	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	1135	C<acquire> callbacks described above, but of course can be (ab-)used for
976	any other purpose as well.	1136	any other purpose as well.
…		…
1087		1247
1088	=item C<EV_PREPARE>	1248	=item C<EV_PREPARE>
1089		1249
1090	=item C<EV_CHECK>	1250	=item C<EV_CHECK>
1091		1251
1092	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1252	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	1253	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	1254	just after C<ev_run> has gathered them, but before it queues any callbacks
		1255	for any received events. That means C<ev_prepare> watchers are the last
		1256	watchers invoked before the event loop sleeps or polls for new events, and
		1257	C<ev_check> watchers will be invoked before any other watchers of the same
		1258	or lower priority within an event loop iteration.
		1259
1095	received events. Callbacks of both watcher types can start and stop as	1260	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	1261	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	1262	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1098	C<ev_run> from blocking).	1263	blocking).
1099		1264
1100	=item C<EV_EMBED>	1265	=item C<EV_EMBED>
1101		1266
1102	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1267	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1103		1268
1104	=item C<EV_FORK>	1269	=item C<EV_FORK>
1105		1270
1106	The event loop has been resumed in the child process after fork (see	1271	The event loop has been resumed in the child process after fork (see
1107	C<ev_fork>).	1272	C<ev_fork>).
		1273
		1274	=item C<EV_CLEANUP>
		1275
		1276	The event loop is about to be destroyed (see C<ev_cleanup>).
1108		1277
1109	=item C<EV_ASYNC>	1278	=item C<EV_ASYNC>
1110		1279
1111	The given async watcher has been asynchronously notified (see C<ev_async>).	1280	The given async watcher has been asynchronously notified (see C<ev_async>).
1112		1281
…		…
1134	programs, though, as the fd could already be closed and reused for another	1303	programs, though, as the fd could already be closed and reused for another
1135	thing, so beware.	1304	thing, so beware.
1136		1305
1137	=back	1306	=back
1138		1307
		1308	=head2 GENERIC WATCHER FUNCTIONS
		1309
		1310	=over 4
		1311
		1312	=item C<ev_init> (ev_TYPE *watcher, callback)
		1313
		1314	This macro initialises the generic portion of a watcher. The contents
		1315	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1316	the generic parts of the watcher are initialised, you I<need> to call
		1317	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1318	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1319	which rolls both calls into one.
		1320
		1321	You can reinitialise a watcher at any time as long as it has been stopped
		1322	(or never started) and there are no pending events outstanding.
		1323
		1324	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1325	int revents)>.
		1326
		1327	Example: Initialise an C<ev_io> watcher in two steps.
		1328
		1329	ev_io w;
		1330	ev_init (&w, my_cb);
		1331	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1332
		1333	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1334
		1335	This macro initialises the type-specific parts of a watcher. You need to
		1336	call C<ev_init> at least once before you call this macro, but you can
		1337	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1338	macro on a watcher that is active (it can be pending, however, which is a
		1339	difference to the C<ev_init> macro).
		1340
		1341	Although some watcher types do not have type-specific arguments
		1342	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1343
		1344	See C<ev_init>, above, for an example.
		1345
		1346	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1347
		1348	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1349	calls into a single call. This is the most convenient method to initialise
		1350	a watcher. The same limitations apply, of course.
		1351
		1352	Example: Initialise and set an C<ev_io> watcher in one step.
		1353
		1354	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1355
		1356	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1357
		1358	Starts (activates) the given watcher. Only active watchers will receive
		1359	events. If the watcher is already active nothing will happen.
		1360
		1361	Example: Start the C<ev_io> watcher that is being abused as example in this
		1362	whole section.
		1363
		1364	ev_io_start (EV_DEFAULT_UC, &w);
		1365
		1366	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1367
		1368	Stops the given watcher if active, and clears the pending status (whether
		1369	the watcher was active or not).
		1370
		1371	It is possible that stopped watchers are pending - for example,
		1372	non-repeating timers are being stopped when they become pending - but
		1373	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1374	pending. If you want to free or reuse the memory used by the watcher it is
		1375	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1376
		1377	=item bool ev_is_active (ev_TYPE *watcher)
		1378
		1379	Returns a true value iff the watcher is active (i.e. it has been started
		1380	and not yet been stopped). As long as a watcher is active you must not modify
		1381	it.
		1382
		1383	=item bool ev_is_pending (ev_TYPE *watcher)
		1384
		1385	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1386	events but its callback has not yet been invoked). As long as a watcher
		1387	is pending (but not active) you must not call an init function on it (but
		1388	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1389	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1390	it).
		1391
		1392	=item callback ev_cb (ev_TYPE *watcher)
		1393
		1394	Returns the callback currently set on the watcher.
		1395
		1396	=item ev_set_cb (ev_TYPE *watcher, callback)
		1397
		1398	Change the callback. You can change the callback at virtually any time
		1399	(modulo threads).
		1400
		1401	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1402
		1403	=item int ev_priority (ev_TYPE *watcher)
		1404
		1405	Set and query the priority of the watcher. The priority is a small
		1406	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1407	(default: C<-2>). Pending watchers with higher priority will be invoked
		1408	before watchers with lower priority, but priority will not keep watchers
		1409	from being executed (except for C<ev_idle> watchers).
		1410
		1411	If you need to suppress invocation when higher priority events are pending
		1412	you need to look at C<ev_idle> watchers, which provide this functionality.
		1413
		1414	You I<must not> change the priority of a watcher as long as it is active or
		1415	pending.
		1416
		1417	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1418	fine, as long as you do not mind that the priority value you query might
		1419	or might not have been clamped to the valid range.
		1420
		1421	The default priority used by watchers when no priority has been set is
		1422	always C<0>, which is supposed to not be too high and not be too low :).
		1423
		1424	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1425	priorities.
		1426
		1427	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1428
		1429	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1430	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1431	can deal with that fact, as both are simply passed through to the
		1432	callback.
		1433
		1434	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1435
		1436	If the watcher is pending, this function clears its pending status and
		1437	returns its C<revents> bitset (as if its callback was invoked). If the
		1438	watcher isn't pending it does nothing and returns C<0>.
		1439
		1440	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1441	callback to be invoked, which can be accomplished with this function.
		1442
		1443	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1444
		1445	Feeds the given event set into the event loop, as if the specified event
		1446	had happened for the specified watcher (which must be a pointer to an
		1447	initialised but not necessarily started event watcher). Obviously you must
		1448	not free the watcher as long as it has pending events.
		1449
		1450	Stopping the watcher, letting libev invoke it, or calling
		1451	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1452	not started in the first place.
		1453
		1454	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1455	functions that do not need a watcher.
		1456
		1457	=back
		1458
		1459	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1460	OWN COMPOSITE WATCHERS> idioms.
		1461
1139	=head2 WATCHER STATES	1462	=head2 WATCHER STATES
1140		1463
1141	There are various watcher states mentioned throughout this manual -	1464	There are various watcher states mentioned throughout this manual -
1142	active, pending and so on. In this section these states and the rules to	1465	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	1466	transition between them will be described in more detail - and while these
1144	rules might look complicated, they usually do "the right thing".	1467	rules might look complicated, they usually do "the right thing".
1145		1468
1146	=over 4	1469	=over 4
1147		1470
1148	=item initialiased	1471	=item initialised
1149		1472
1150	Before a watcher can be registered with the event looop it has to be	1473	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	1474	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.	1475	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1153		1476
1154	In this state it is simply some block of memory that is suitable for use	1477	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.	1478	use in an event loop. It can be moved around, freed, reused etc. at
		1479	will - as long as you either keep the memory contents intact, or call
		1480	C<ev_TYPE_init> again.
1156		1481
1157	=item started/running/active	1482	=item started/running/active
1158		1483
1159	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1484	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	1485	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	1513	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	1514	of whether it was active or not, so stopping a watcher explicitly before
1190	freeing it is often a good idea.	1515	freeing it is often a good idea.
1191		1516
1192	While stopped (and not pending) the watcher is essentially in the	1517	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	1518	initialised state, that is, it can be reused, moved, modified in any way
1194	you wish.	1519	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1520	it again).
1195		1521
1196	=back	1522	=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		1523
1415	=head2 WATCHER PRIORITY MODELS	1524	=head2 WATCHER PRIORITY MODELS
1416		1525
1417	Many event loops support I<watcher priorities>, which are usually small	1526	Many event loops support I<watcher priorities>, which are usually small
1418	integers that influence the ordering of event callback invocation	1527	integers that influence the ordering of event callback invocation
…		…
1545	In general you can register as many read and/or write event watchers per	1654	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	1655	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	1656	descriptors to non-blocking mode is also usually a good idea (but not
1548	required if you know what you are doing).	1657	required if you know what you are doing).
1549		1658
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	1659	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	1660	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	1661	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	1662	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	1663	with a relatively standard program structure. Thus it is best to always
1561	this situation even with a relatively standard program structure. Thus	1664	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.	1665	preferable to a program hanging until some data arrives.
1564		1666
1565	If you cannot run the fd in non-blocking mode (for example you should	1667	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	1668	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	1669	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	1670	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	1671	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	1672	use C<SIGALRM> and an interval timer, just to be sure you won't block
1571	indefinitely.	1673	indefinitely.
1572		1674
1573	But really, best use non-blocking mode.	1675	But really, best use non-blocking mode.
1574		1676
1575	=head3 The special problem of disappearing file descriptors	1677	=head3 The special problem of disappearing file descriptors
1576		1678
1577	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1679	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,	1680	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	1681	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	1682	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	1683	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	1684	is registered with libev, there is no efficient way to see that this is,
1583	fact, a different file descriptor.	1685	in fact, a different file descriptor.
1584		1686
1585	To avoid having to explicitly tell libev about such cases, libev follows	1687	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	1688	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	1689	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	1690	it is assumed that the file descriptor stays the same. That means that
…		…
1602		1704
1603	There is no workaround possible except not registering events	1705	There is no workaround possible except not registering events
1604	for potentially C<dup ()>'ed file descriptors, or to resort to	1706	for potentially C<dup ()>'ed file descriptors, or to resort to
1605	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1707	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1606		1708
		1709	=head3 The special problem of files
		1710
		1711	Many people try to use C<select> (or libev) on file descriptors
		1712	representing files, and expect it to become ready when their program
		1713	doesn't block on disk accesses (which can take a long time on their own).
		1714
		1715	However, this cannot ever work in the "expected" way - you get a readiness
		1716	notification as soon as the kernel knows whether and how much data is
		1717	there, and in the case of open files, that's always the case, so you
		1718	always get a readiness notification instantly, and your read (or possibly
		1719	write) will still block on the disk I/O.
		1720
		1721	Another way to view it is that in the case of sockets, pipes, character
		1722	devices and so on, there is another party (the sender) that delivers data
		1723	on its own, but in the case of files, there is no such thing: the disk
		1724	will not send data on its own, simply because it doesn't know what you
		1725	wish to read - you would first have to request some data.
		1726
		1727	Since files are typically not-so-well supported by advanced notification
		1728	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1729	to files, even though you should not use it. The reason for this is
		1730	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1731	usually a tty, often a pipe, but also sometimes files or special devices
		1732	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1733	F</dev/urandom>), and even though the file might better be served with
		1734	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1735	it "just works" instead of freezing.
		1736
		1737	So avoid file descriptors pointing to files when you know it (e.g. use
		1738	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1739	when you rarely read from a file instead of from a socket, and want to
		1740	reuse the same code path.
		1741
1607	=head3 The special problem of fork	1742	=head3 The special problem of fork
1608		1743
1609	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1744	Some backends (epoll, kqueue, probably linuxaio) do not support C<fork ()>
1610	useless behaviour. Libev fully supports fork, but needs to be told about	1745	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1611	it in the child.	1746	to be told about it in the child if you want to continue to use it in the
		1747	child.
1612		1748
1613	To support fork in your programs, you either have to call	1749	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,	1750	()> 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	1751	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1616	C<EVBACKEND_POLL>.
1617		1752
1618	=head3 The special problem of SIGPIPE	1753	=head3 The special problem of SIGPIPE
1619		1754
1620	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1755	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	1756	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	1854	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1720	monotonic clock option helps a lot here).	1855	monotonic clock option helps a lot here).
1721		1856
1722	The callback is guaranteed to be invoked only I<after> its timeout has	1857	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	1858	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	1859	might introduce a small delay, see "the special problem of being too
		1860	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	1861	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	1862	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).	1863	longer true when a callback calls C<ev_run> recursively).
1728		1864
1729	=head3 Be smart about timeouts	1865	=head3 Be smart about timeouts
1730		1866
1731	Many real-world problems involve some kind of timeout, usually for error	1867	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,	1868	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1807		1943
1808	In this case, it would be more efficient to leave the C<ev_timer> alone,	1944	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	1945	but remember the time of last activity, and check for a real timeout only
1810	within the callback:	1946	within the callback:
1811		1947
		1948	ev_tstamp timeout = 60.;
1812	ev_tstamp last_activity; // time of last activity	1949	ev_tstamp last_activity; // time of last activity
		1950	ev_timer timer;
1813		1951
1814	static void	1952	static void
1815	callback (EV_P_ ev_timer *w, int revents)	1953	callback (EV_P_ ev_timer *w, int revents)
1816	{	1954	{
1817	ev_tstamp now = ev_now (EV_A);	1955	// calculate when the timeout would happen
1818	ev_tstamp timeout = last_activity + 60.;	1956	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1819		1957
1820	// if last_activity + 60. is older than now, we did time out	1958	// if negative, it means we the timeout already occurred
1821	if (timeout < now)	1959	if (after < 0.)
1822	{	1960	{
1823	// timeout occurred, take action	1961	// timeout occurred, take action
1824	}	1962	}
1825	else	1963	else
1826	{	1964	{
1827	// callback was invoked, but there was some activity, re-arm	1965	// callback was invoked, but there was some recent
1828	// the watcher to fire in last_activity + 60, which is	1966	// activity. simply restart the timer to time out
1829	// guaranteed to be in the future, so "again" is positive:	1967	// after "after" seconds, which is the earliest time
1830	w->repeat = timeout - now;	1968	// the timeout can occur.
		1969	ev_timer_set (w, after, 0.);
1831	ev_timer_again (EV_A_ w);	1970	ev_timer_start (EV_A_ w);
1832	}	1971	}
1833	}	1972	}
1834		1973
1835	To summarise the callback: first calculate the real timeout (defined	1974	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	1975	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	1976	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	1977	(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		1978
1842	Note how C<ev_timer_again> is used, taking advantage of the	1979	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.	1980	timed out, and need to do whatever is needed in this case.
		1981
		1982	Otherwise, we now the earliest time at which the timeout would trigger,
		1983	and simply start the timer with this timeout value.
		1984
		1985	In other words, each time the callback is invoked it will check whether
		1986	the timeout occurred. If not, it will simply reschedule itself to check
		1987	again at the earliest time it could time out. Rinse. Repeat.
1844		1988
1845	This scheme causes more callback invocations (about one every 60 seconds	1989	This scheme causes more callback invocations (about one every 60 seconds
1846	minus half the average time between activity), but virtually no calls to	1990	minus half the average time between activity), but virtually no calls to
1847	libev to change the timeout.	1991	libev to change the timeout.
1848		1992
1849	To start the timer, simply initialise the watcher and set C<last_activity>	1993	To start the machinery, simply initialise the watcher and set
1850	to the current time (meaning we just have some activity :), then call the	1994	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:	1995	now), then call the callback, which will "do the right thing" and start
		1996	the timer:
1852		1997
		1998	last_activity = ev_now (EV_A);
1853	ev_init (timer, callback);	1999	ev_init (&timer, callback);
1854	last_activity = ev_now (loop);	2000	callback (EV_A_ &timer, 0);
1855	callback (loop, timer, EV_TIMER);
1856		2001
1857	And when there is some activity, simply store the current time in	2002	When there is some activity, simply store the current time in
1858	C<last_activity>, no libev calls at all:	2003	C<last_activity>, no libev calls at all:
1859		2004
		2005	if (activity detected)
1860	last_activity = ev_now (loop);	2006	last_activity = ev_now (EV_A);
		2007
		2008	When your timeout value changes, then the timeout can be changed by simply
		2009	providing a new value, stopping the timer and calling the callback, which
		2010	will again do the right thing (for example, time out immediately :).
		2011
		2012	timeout = new_value;
		2013	ev_timer_stop (EV_A_ &timer);
		2014	callback (EV_A_ &timer, 0);
1861		2015
1862	This technique is slightly more complex, but in most cases where the	2016	This technique is slightly more complex, but in most cases where the
1863	time-out is unlikely to be triggered, much more efficient.	2017	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		2018
1869	=item 4. Wee, just use a double-linked list for your timeouts.	2019	=item 4. Wee, just use a double-linked list for your timeouts.
1870		2020
1871	If there is not one request, but many thousands (millions...), all	2021	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	2022	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	2049	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	2050	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	2051	off after the first million or so of active timers, i.e. it's usually
1902	overkill :)	2052	overkill :)
1903		2053
		2054	=head3 The special problem of being too early
		2055
		2056	If you ask a timer to call your callback after three seconds, then
		2057	you expect it to be invoked after three seconds - but of course, this
		2058	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2059	guaranteed to any precision by libev - imagine somebody suspending the
		2060	process with a STOP signal for a few hours for example.
		2061
		2062	So, libev tries to invoke your callback as soon as possible I<after> the
		2063	delay has occurred, but cannot guarantee this.
		2064
		2065	A less obvious failure mode is calling your callback too early: many event
		2066	loops compare timestamps with a "elapsed delay >= requested delay", but
		2067	this can cause your callback to be invoked much earlier than you would
		2068	expect.
		2069
		2070	To see why, imagine a system with a clock that only offers full second
		2071	resolution (think windows if you can't come up with a broken enough OS
		2072	yourself). If you schedule a one-second timer at the time 500.9, then the
		2073	event loop will schedule your timeout to elapse at a system time of 500
		2074	(500.9 truncated to the resolution) + 1, or 501.
		2075
		2076	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2077	501" and invoke the callback 0.1s after it was started, even though a
		2078	one-second delay was requested - this is being "too early", despite best
		2079	intentions.
		2080
		2081	This is the reason why libev will never invoke the callback if the elapsed
		2082	delay equals the requested delay, but only when the elapsed delay is
		2083	larger than the requested delay. In the example above, libev would only invoke
		2084	the callback at system time 502, or 1.1s after the timer was started.
		2085
		2086	So, while libev cannot guarantee that your callback will be invoked
		2087	exactly when requested, it I<can> and I<does> guarantee that the requested
		2088	delay has actually elapsed, or in other words, it always errs on the "too
		2089	late" side of things.
		2090
1904	=head3 The special problem of time updates	2091	=head3 The special problem of time updates
1905		2092
1906	Establishing the current time is a costly operation (it usually takes at	2093	Establishing the current time is a costly operation (it usually takes
1907	least two system calls): EV therefore updates its idea of the current	2094	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	2095	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	2096	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1910	lots of events in one iteration.	2097	lots of events in one iteration.
1911		2098
1912	The relative timeouts are calculated relative to the C<ev_now ()>	2099	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	2100	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	2101	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	2102	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:	2103	timeout on the current time, use something like the following to adjust
		2104	for it:
1917		2105
1918	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2106	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1919		2107
1920	If the event loop is suspended for a long time, you can also force an	2108	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	2109	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1922	()>.	2110	()>, although that will push the event time of all outstanding events
		2111	further into the future.
		2112
		2113	=head3 The special problem of unsynchronised clocks
		2114
		2115	Modern systems have a variety of clocks - libev itself uses the normal
		2116	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2117	jumps).
		2118
		2119	Neither of these clocks is synchronised with each other or any other clock
		2120	on the system, so C<ev_time ()> might return a considerably different time
		2121	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2122	a call to C<gettimeofday> might return a second count that is one higher
		2123	than a directly following call to C<time>.
		2124
		2125	The moral of this is to only compare libev-related timestamps with
		2126	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2127	a second or so.
		2128
		2129	One more problem arises due to this lack of synchronisation: if libev uses
		2130	the system monotonic clock and you compare timestamps from C<ev_time>
		2131	or C<ev_now> from when you started your timer and when your callback is
		2132	invoked, you will find that sometimes the callback is a bit "early".
		2133
		2134	This is because C<ev_timer>s work in real time, not wall clock time, so
		2135	libev makes sure your callback is not invoked before the delay happened,
		2136	I<measured according to the real time>, not the system clock.
		2137
		2138	If your timeouts are based on a physical timescale (e.g. "time out this
		2139	connection after 100 seconds") then this shouldn't bother you as it is
		2140	exactly the right behaviour.
		2141
		2142	If you want to compare wall clock/system timestamps to your timers, then
		2143	you need to use C<ev_periodic>s, as these are based on the wall clock
		2144	time, where your comparisons will always generate correct results.
1923		2145
1924	=head3 The special problems of suspended animation	2146	=head3 The special problems of suspended animation
1925		2147
1926	When you leave the server world it is quite customary to hit machines that	2148	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?	2149	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1957		2179
1958	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2180	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1959		2181
1960	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2182	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1961		2183
1962	Configure the timer to trigger after C<after> seconds. If C<repeat>	2184	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	2185	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	2186	automatically be stopped once the timeout is reached. If it is positive,
1965	configured to trigger again C<repeat> seconds later, again, and again,	2187	then the timer will automatically be configured to trigger again C<repeat>
1966	until stopped manually.	2188	seconds later, again, and again, until stopped manually.
1967		2189
1968	The timer itself will do a best-effort at avoiding drift, that is, if	2190	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	2191	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	2192	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	2193	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.	2194	do stuff) the timer will not fire more than once per event loop iteration.
1973		2195
1974	=item ev_timer_again (loop, ev_timer *)	2196	=item ev_timer_again (loop, ev_timer *)
1975		2197
1976	This will act as if the timer timed out and restart it again if it is	2198	This will act as if the timer timed out, and restarts it again if it is
1977	repeating. The exact semantics are:	2199	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2200	timeout to the C<repeat> value and calling C<ev_timer_start>.
1978		2201
		2202	The exact semantics are as in the following rules, all of which will be
		2203	applied to the watcher:
		2204
		2205	=over 4
		2206
1979	If the timer is pending, its pending status is cleared.	2207	=item If the timer is pending, the pending status is always cleared.
1980		2208
1981	If the timer is started but non-repeating, stop it (as if it timed out).	2209	=item If the timer is started but non-repeating, stop it (as if it timed
		2210	out, without invoking it).
1982		2211
1983	If the timer is repeating, either start it if necessary (with the	2212	=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.	2213	and start the timer, if necessary.
1985		2214
		2215	=back
		2216
1986	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2217	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1987	usage example.	2218	usage example.
1988		2219
1989	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2220	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1990		2221
1991	Returns the remaining time until a timer fires. If the timer is active,	2222	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	2275	Periodic watchers are also timers of a kind, but they are very versatile
2045	(and unfortunately a bit complex).	2276	(and unfortunately a bit complex).
2046		2277
2047	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2278	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	2279	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	2280	(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	2281	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	2282	time, and time jumps are not uncommon (e.g. when you adjust your
2052	wrist-watch).	2283	wrist-watch).
2053		2284
2054	You can tell a periodic watcher to trigger after some specific point	2285	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	2290	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2060	it, as it uses a relative timeout).	2291	it, as it uses a relative timeout).
2061		2292
2062	C<ev_periodic> watchers can also be used to implement vastly more complex	2293	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	2294	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	2295	other complicated rules. This cannot easily be done with C<ev_timer>
2065	those cannot react to time jumps.	2296	watchers, as those cannot react to time jumps.
2066		2297
2067	As with timers, the callback is guaranteed to be invoked only when the	2298	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	2299	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	2300	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	2301	earlier time-out values are invoked before ones with later time-out values
…		…
2111		2342
2112	Another way to think about it (for the mathematically inclined) is that	2343	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	2344	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.	2345	time where C<time = offset (mod interval)>, regardless of any time jumps.
2115		2346
2116	For numerical stability it is preferable that the C<offset> value is near	2347	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	2348	interval value should be higher than C<1/8192> (which is around 100
2118	this value, and in fact is often specified as zero.	2349	microseconds) and C<offset> should be higher than C<0> and should have
		2350	at most a similar magnitude as the current time (say, within a factor of
		2351	ten). Typical values for offset are, in fact, C<0> or something between
		2352	C<0> and C<interval>, which is also the recommended range.
2119		2353
2120	Note also that there is an upper limit to how often a timer can fire (CPU	2354	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	2355	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	2356	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).	2357	millisecond (if the OS supports it and the machine is fast enough).
…		…
2153		2387
2154	NOTE: I<< This callback must always return a time that is higher than or	2388	NOTE: I<< This callback must always return a time that is higher than or
2155	equal to the passed C<now> value >>.	2389	equal to the passed C<now> value >>.
2156		2390
2157	This can be used to create very complex timers, such as a timer that	2391	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	2392	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	2393	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	2394	this. Here is a (completely untested, no error checking) example on how to
2161	reason I omitted it as an example).	2395	do this:
		2396
		2397	#include <time.h>
		2398
		2399	static ev_tstamp
		2400	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2401	{
		2402	time_t tnow = (time_t)now;
		2403	struct tm tm;
		2404	localtime_r (&tnow, &tm);
		2405
		2406	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2407	++tm.tm_mday; // midnight next day
		2408
		2409	return mktime (&tm);
		2410	}
		2411
		2412	Note: this code might run into trouble on days that have more then two
		2413	midnights (beginning and end).
2162		2414
2163	=back	2415	=back
2164		2416
2165	=item ev_periodic_again (loop, ev_periodic *)	2417	=item ev_periodic_again (loop, ev_periodic *)
2166		2418
…		…
2231		2483
2232	ev_periodic hourly_tick;	2484	ev_periodic hourly_tick;
2233	ev_periodic_init (&hourly_tick, clock_cb,	2485	ev_periodic_init (&hourly_tick, clock_cb,
2234	fmod (ev_now (loop), 3600.), 3600., 0);	2486	fmod (ev_now (loop), 3600.), 3600., 0);
2235	ev_periodic_start (loop, &hourly_tick);	2487	ev_periodic_start (loop, &hourly_tick);
2236		2488
2237		2489
2238	=head2 C<ev_signal> - signal me when a signal gets signalled!	2490	=head2 C<ev_signal> - signal me when a signal gets signalled!
2239		2491
2240	Signal watchers will trigger an event when the process receives a specific	2492	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	2493	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	2494	will try its best to deliver signals synchronously, i.e. as part of the
2243	normal event processing, like any other event.	2495	normal event processing, like any other event.
2244		2496
2245	If you want signals to be delivered truly asynchronously, just use	2497	If you want signals to be delivered truly asynchronously, just use
2246	C<sigaction> as you would do without libev and forget about sharing	2498	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	2499	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	2503	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	2504	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	2505	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.	2506	the moment, C<SIGCHLD> is permanently tied to the default loop.
2255		2507
2256	When the first watcher gets started will libev actually register something	2508	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	2509	register something with the kernel. It thus coexists with your own signal
2258	you don't register any with libev for the same signal).	2510	handlers as long as you don't register any with libev for the same signal.
2259		2511
2260	If possible and supported, libev will install its handlers with	2512	If possible and supported, libev will install its handlers with
2261	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2513	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	2514	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	2515	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	2518	=head3 The special problem of inheritance over fork/execve/pthread_create
2267		2519
2268	Both the signal mask (C<sigprocmask>) and the signal disposition	2520	Both the signal mask (C<sigprocmask>) and the signal disposition
2269	(C<sigaction>) are unspecified after starting a signal watcher (and after	2521	(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,	2522	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.	2523	and might or might not set or restore the installed signal handler (but
		2524	see C<EVFLAG_NOSIGMASK>).
2272		2525
2273	While this does not matter for the signal disposition (libev never	2526	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	2527	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	2528	C<execve>), this matters for the signal mask: many programs do not expect
2276	certain signals to be blocked.	2529	certain signals to be blocked.
…		…
2289	I<has> to modify the signal mask, at least temporarily.	2542	I<has> to modify the signal mask, at least temporarily.
2290		2543
2291	So I can't stress this enough: I<If you do not reset your signal mask when	2544	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	2545	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.	2546	is not a libev-specific thing, this is true for most event libraries.
		2547
		2548	=head3 The special problem of threads signal handling
		2549
		2550	POSIX threads has problematic signal handling semantics, specifically,
		2551	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2552	threads in a process block signals, which is hard to achieve.
		2553
		2554	When you want to use sigwait (or mix libev signal handling with your own
		2555	for the same signals), you can tackle this problem by globally blocking
		2556	all signals before creating any threads (or creating them with a fully set
		2557	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2558	loops. Then designate one thread as "signal receiver thread" which handles
		2559	these signals. You can pass on any signals that libev might be interested
		2560	in by calling C<ev_feed_signal>.
2294		2561
2295	=head3 Watcher-Specific Functions and Data Members	2562	=head3 Watcher-Specific Functions and Data Members
2296		2563
2297	=over 4	2564	=over 4
2298		2565
…		…
2433		2700
2434	=head2 C<ev_stat> - did the file attributes just change?	2701	=head2 C<ev_stat> - did the file attributes just change?
2435		2702
2436	This watches a file system path for attribute changes. That is, it calls	2703	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)	2704	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	2705	and sees if it changed compared to the last time, invoking the callback
2439	it did.	2706	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2707	happen after the watcher has been started will be reported.
2440		2708
2441	The path does not need to exist: changing from "path exists" to "path does	2709	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	2710	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	2711	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	2712	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	2942	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	2943	effect on its own sometimes), idle watchers are a good place to do
2676	"pseudo-background processing", or delay processing stuff to after the	2944	"pseudo-background processing", or delay processing stuff to after the
2677	event loop has handled all outstanding events.	2945	event loop has handled all outstanding events.
2678		2946
		2947	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2948
		2949	As long as there is at least one active idle watcher, libev will never
		2950	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2951	For this to work, the idle watcher doesn't need to be invoked at all - the
		2952	lowest priority will do.
		2953
		2954	This mode of operation can be useful together with an C<ev_check> watcher,
		2955	to do something on each event loop iteration - for example to balance load
		2956	between different connections.
		2957
		2958	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2959	example.
		2960
2679	=head3 Watcher-Specific Functions and Data Members	2961	=head3 Watcher-Specific Functions and Data Members
2680		2962
2681	=over 4	2963	=over 4
2682		2964
2683	=item ev_idle_init (ev_idle *, callback)	2965	=item ev_idle_init (ev_idle *, callback)
…		…
2694	callback, free it. Also, use no error checking, as usual.	2976	callback, free it. Also, use no error checking, as usual.
2695		2977
2696	static void	2978	static void
2697	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2979	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2698	{	2980	{
		2981	// stop the watcher
		2982	ev_idle_stop (loop, w);
		2983
		2984	// now we can free it
2699	free (w);	2985	free (w);
		2986
2700	// now do something you wanted to do when the program has	2987	// now do something you wanted to do when the program has
2701	// no longer anything immediate to do.	2988	// no longer anything immediate to do.
2702	}	2989	}
2703		2990
2704	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2991	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2706	ev_idle_start (loop, idle_watcher);	2993	ev_idle_start (loop, idle_watcher);
2707		2994
2708		2995
2709	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2996	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2710		2997
2711	Prepare and check watchers are usually (but not always) used in pairs:	2998	Prepare and check watchers are often (but not always) used in pairs:
2712	prepare watchers get invoked before the process blocks and check watchers	2999	prepare watchers get invoked before the process blocks and check watchers
2713	afterwards.	3000	afterwards.
2714		3001
2715	You I<must not> call C<ev_run> or similar functions that enter	3002	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>	3003	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	3004	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	3005	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,	3006	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	3007	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2721	called in pairs bracketing the blocking call.	3008	kind they will always be called in pairs bracketing the blocking call.
2722		3009
2723	Their main purpose is to integrate other event mechanisms into libev and	3010	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	3011	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	3012	variable changes, implement your own watchers, integrate net-snmp or a
2726	coroutine library and lots more. They are also occasionally useful if	3013	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	3031	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	3032	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	3033	loop from blocking if lower-priority coroutines are active, thus mapping
2747	low-priority coroutines to idle/background tasks).	3034	low-priority coroutines to idle/background tasks).
2748		3035
2749	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3036	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	3037	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).	3038	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3039	watchers).
2752		3040
2753	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3041	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	3042	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	3043	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	3044	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	3045	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	3046	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2759	others).	3047	others).
		3048
		3049	=head3 Abusing an C<ev_check> watcher for its side-effect
		3050
		3051	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3052	useful because they are called once per event loop iteration. For
		3053	example, if you want to handle a large number of connections fairly, you
		3054	normally only do a bit of work for each active connection, and if there
		3055	is more work to do, you wait for the next event loop iteration, so other
		3056	connections have a chance of making progress.
		3057
		3058	Using an C<ev_check> watcher is almost enough: it will be called on the
		3059	next event loop iteration. However, that isn't as soon as possible -
		3060	without external events, your C<ev_check> watcher will not be invoked.
		3061
		3062	This is where C<ev_idle> watchers come in handy - all you need is a
		3063	single global idle watcher that is active as long as you have one active
		3064	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3065	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3066	invoked. Neither watcher alone can do that.
2760		3067
2761	=head3 Watcher-Specific Functions and Data Members	3068	=head3 Watcher-Specific Functions and Data Members
2762		3069
2763	=over 4	3070	=over 4
2764		3071
…		…
2965		3272
2966	=over 4	3273	=over 4
2967		3274
2968	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3275	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2969		3276
2970	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3277	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2971		3278
2972	Configures the watcher to embed the given loop, which must be	3279	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	3280	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	3281	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,	3282	to invoke it (it will continue to be called until the sweep has been done,
…		…
2996	used).	3303	used).
2997		3304
2998	struct ev_loop *loop_hi = ev_default_init (0);	3305	struct ev_loop *loop_hi = ev_default_init (0);
2999	struct ev_loop *loop_lo = 0;	3306	struct ev_loop *loop_lo = 0;
3000	ev_embed embed;	3307	ev_embed embed;
3001		3308
3002	// see if there is a chance of getting one that works	3309	// see if there is a chance of getting one that works
3003	// (remember that a flags value of 0 means autodetection)	3310	// (remember that a flags value of 0 means autodetection)
3004	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3311	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3005	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3312	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3006	: 0;	3313	: 0;
…		…
3020	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3327	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3021		3328
3022	struct ev_loop *loop = ev_default_init (0);	3329	struct ev_loop *loop = ev_default_init (0);
3023	struct ev_loop *loop_socket = 0;	3330	struct ev_loop *loop_socket = 0;
3024	ev_embed embed;	3331	ev_embed embed;
3025		3332
3026	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3333	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3027	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3334	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3028	{	3335	{
3029	ev_embed_init (&embed, 0, loop_socket);	3336	ev_embed_init (&embed, 0, loop_socket);
3030	ev_embed_start (loop, &embed);	3337	ev_embed_start (loop, &embed);
…		…
3038		3345
3039	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3346	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3040		3347
3041	Fork watchers are called when a C<fork ()> was detected (usually because	3348	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	3349	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	3350	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,	3351	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	3352	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	3353	and calls it in the wrong process, the fork handlers will be invoked, too,
3047	handlers will be invoked, too, of course.	3354	of course.
3048		3355
3049	=head3 The special problem of life after fork - how is it possible?	3356	=head3 The special problem of life after fork - how is it possible?
3050		3357
3051	Most uses of C<fork()> consist of forking, then some simple calls to set	3358	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	3359	up/change the process environment, followed by a call to C<exec()>. This
3053	sequence should be handled by libev without any problems.	3360	sequence should be handled by libev without any problems.
3054		3361
3055	This changes when the application actually wants to do event handling	3362	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	3363	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	3379	disadvantage of having to use multiple event loops (which do not support
3073	signal watchers).	3380	signal watchers).
3074		3381
3075	When this is not possible, or you want to use the default loop for	3382	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	3383	other reasons, then in the process that wants to start "fresh", call
3077	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying	3384	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	3385	Destroying the default loop will "orphan" (not stop) all registered
3079	have to be careful not to execute code that modifies those watchers. Note	3386	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.	3387	those watchers. Note also that in that case, you have to re-register any
		3388	signal watchers.
3081		3389
3082	=head3 Watcher-Specific Functions and Data Members	3390	=head3 Watcher-Specific Functions and Data Members
3083		3391
3084	=over 4	3392	=over 4
3085		3393
3086	=item ev_fork_init (ev_signal *, callback)	3394	=item ev_fork_init (ev_fork *, callback)
3087		3395
3088	Initialises and configures the fork watcher - it has no parameters of any	3396	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,	3397	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3090	believe me.	3398	really.
3091		3399
3092	=back	3400	=back
3093		3401
3094		3402
		3403	=head2 C<ev_cleanup> - even the best things end
		3404
		3405	Cleanup watchers are called just before the event loop is being destroyed
		3406	by a call to C<ev_loop_destroy>.
		3407
		3408	While there is no guarantee that the event loop gets destroyed, cleanup
		3409	watchers provide a convenient method to install cleanup hooks for your
		3410	program, worker threads and so on - you just to make sure to destroy the
		3411	loop when you want them to be invoked.
		3412
		3413	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3414	all other watchers, they do not keep a reference to the event loop (which
		3415	makes a lot of sense if you think about it). Like all other watchers, you
		3416	can call libev functions in the callback, except C<ev_cleanup_start>.
		3417
		3418	=head3 Watcher-Specific Functions and Data Members
		3419
		3420	=over 4
		3421
		3422	=item ev_cleanup_init (ev_cleanup *, callback)
		3423
		3424	Initialises and configures the cleanup watcher - it has no parameters of
		3425	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3426	pointless, I assure you.
		3427
		3428	=back
		3429
		3430	Example: Register an atexit handler to destroy the default loop, so any
		3431	cleanup functions are called.
		3432
		3433	static void
		3434	program_exits (void)
		3435	{
		3436	ev_loop_destroy (EV_DEFAULT_UC);
		3437	}
		3438
		3439	...
		3440	atexit (program_exits);
		3441
		3442
3095	=head2 C<ev_async> - how to wake up an event loop	3443	=head2 C<ev_async> - how to wake up an event loop
3096		3444
3097	In general, you cannot use an C<ev_run> from multiple threads or other	3445	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	3446	asynchronous sources such as signal handlers (as opposed to multiple event
3099	loops - those are of course safe to use in different threads).	3447	loops - those are of course safe to use in different threads).
3100		3448
3101	Sometimes, however, you need to wake up an event loop you do not control,	3449	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>	3450	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.	3452	it by calling C<ev_async_send>, which is thread- and signal safe.
3105		3453
3106	This functionality is very similar to C<ev_signal> watchers, as signals,	3454	This functionality is very similar to C<ev_signal> watchers, as signals,
3107	too, are asynchronous in nature, and signals, too, will be compressed	3455	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	3456	(i.e. the number of callback invocations may be less than the number of
3109	C<ev_async_sent> calls).	3457	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3110		3458	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	3459	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3112	just the default loop.	3460	even without knowing which loop owns the signal.
3113		3461
3114	=head3 Queueing	3462	=head3 Queueing
3115		3463
3116	C<ev_async> does not support queueing of data in any way. The reason	3464	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	3465	is that the author does not know of a simple (or any) algorithm for a
…		…
3209	trust me.	3557	trust me.
3210		3558
3211	=item ev_async_send (loop, ev_async *)	3559	=item ev_async_send (loop, ev_async *)
3212		3560
3213	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3561	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	3562	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3563	returns.
		3564
3215	C<ev_feed_event>, this call is safe to do from other threads, signal or	3565	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	3566	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3217	section below on what exactly this means).	3567	embedding section below on what exactly this means).
3218		3568
3219	Note that, as with other watchers in libev, multiple events might get	3569	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	3570	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>,	3571	this is that C<ev_async> watchers are level-triggered: they are set on
3222	reset when the event loop detects that).	3572	C<ev_async_send>, reset when the event loop detects that).
3223		3573
3224	This call incurs the overhead of a system call only once per event loop	3574	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	3575	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.	3576	the event loop (or your program) is processing events. That means that
		3577	repeated calls are basically free (there is no need to avoid calls for
		3578	performance reasons) and that the overhead becomes smaller (typically
		3579	zero) under load.
3227		3580
3228	=item bool = ev_async_pending (ev_async *)	3581	=item bool = ev_async_pending (ev_async *)
3229		3582
3230	Returns a non-zero value when C<ev_async_send> has been called on the	3583	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	3584	watcher but the event has not yet been processed (or even noted) by the
…		…
3248		3601
3249	There are some other functions of possible interest. Described. Here. Now.	3602	There are some other functions of possible interest. Described. Here. Now.
3250		3603
3251	=over 4	3604	=over 4
3252		3605
3253	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3606	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3254		3607
3255	This function combines a simple timer and an I/O watcher, calls your	3608	This function combines a simple timer and an I/O watcher, calls your
3256	callback on whichever event happens first and automatically stops both	3609	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	3610	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	3611	or timeout without having to allocate/configure/start/stop/free one or
…		…
3286	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3639	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3287		3640
3288	=item ev_feed_fd_event (loop, int fd, int revents)	3641	=item ev_feed_fd_event (loop, int fd, int revents)
3289		3642
3290	Feed an event on the given fd, as if a file descriptor backend detected	3643	Feed an event on the given fd, as if a file descriptor backend detected
3291	the given events it.	3644	the given events.
3292		3645
3293	=item ev_feed_signal_event (loop, int signum)	3646	=item ev_feed_signal_event (loop, int signum)
3294		3647
3295	Feed an event as if the given signal occurred (C<loop> must be the default	3648	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3296	loop!).	3649	which is async-safe.
3297		3650
3298	=back	3651	=back
		3652
		3653
		3654	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3655
		3656	This section explains some common idioms that are not immediately
		3657	obvious. Note that examples are sprinkled over the whole manual, and this
		3658	section only contains stuff that wouldn't fit anywhere else.
		3659
		3660	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3661
		3662	Each watcher has, by default, a C<void *data> member that you can read
		3663	or modify at any time: libev will completely ignore it. This can be used
		3664	to associate arbitrary data with your watcher. If you need more data and
		3665	don't want to allocate memory separately and store a pointer to it in that
		3666	data member, you can also "subclass" the watcher type and provide your own
		3667	data:
		3668
		3669	struct my_io
		3670	{
		3671	ev_io io;
		3672	int otherfd;
		3673	void *somedata;
		3674	struct whatever *mostinteresting;
		3675	};
		3676
		3677	...
		3678	struct my_io w;
		3679	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3680
		3681	And since your callback will be called with a pointer to the watcher, you
		3682	can cast it back to your own type:
		3683
		3684	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3685	{
		3686	struct my_io *w = (struct my_io *)w_;
		3687	...
		3688	}
		3689
		3690	More interesting and less C-conformant ways of casting your callback
		3691	function type instead have been omitted.
		3692
		3693	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3694
		3695	Another common scenario is to use some data structure with multiple
		3696	embedded watchers, in effect creating your own watcher that combines
		3697	multiple libev event sources into one "super-watcher":
		3698
		3699	struct my_biggy
		3700	{
		3701	int some_data;
		3702	ev_timer t1;
		3703	ev_timer t2;
		3704	}
		3705
		3706	In this case getting the pointer to C<my_biggy> is a bit more
		3707	complicated: Either you store the address of your C<my_biggy> struct in
		3708	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3709	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3710	real programmers):
		3711
		3712	#include <stddef.h>
		3713
		3714	static void
		3715	t1_cb (EV_P_ ev_timer *w, int revents)
		3716	{
		3717	struct my_biggy big = (struct my_biggy *)
		3718	(((char *)w) - offsetof (struct my_biggy, t1));
		3719	}
		3720
		3721	static void
		3722	t2_cb (EV_P_ ev_timer *w, int revents)
		3723	{
		3724	struct my_biggy big = (struct my_biggy *)
		3725	(((char *)w) - offsetof (struct my_biggy, t2));
		3726	}
		3727
		3728	=head2 AVOIDING FINISHING BEFORE RETURNING
		3729
		3730	Often you have structures like this in event-based programs:
		3731
		3732	callback ()
		3733	{
		3734	free (request);
		3735	}
		3736
		3737	request = start_new_request (..., callback);
		3738
		3739	The intent is to start some "lengthy" operation. The C<request> could be
		3740	used to cancel the operation, or do other things with it.
		3741
		3742	It's not uncommon to have code paths in C<start_new_request> that
		3743	immediately invoke the callback, for example, to report errors. Or you add
		3744	some caching layer that finds that it can skip the lengthy aspects of the
		3745	operation and simply invoke the callback with the result.
		3746
		3747	The problem here is that this will happen I<before> C<start_new_request>
		3748	has returned, so C<request> is not set.
		3749
		3750	Even if you pass the request by some safer means to the callback, you
		3751	might want to do something to the request after starting it, such as
		3752	canceling it, which probably isn't working so well when the callback has
		3753	already been invoked.
		3754
		3755	A common way around all these issues is to make sure that
		3756	C<start_new_request> I<always> returns before the callback is invoked. If
		3757	C<start_new_request> immediately knows the result, it can artificially
		3758	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3759	example, or more sneakily, by reusing an existing (stopped) watcher and
		3760	pushing it into the pending queue:
		3761
		3762	ev_set_cb (watcher, callback);
		3763	ev_feed_event (EV_A_ watcher, 0);
		3764
		3765	This way, C<start_new_request> can safely return before the callback is
		3766	invoked, while not delaying callback invocation too much.
		3767
		3768	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3769
		3770	Often (especially in GUI toolkits) there are places where you have
		3771	I<modal> interaction, which is most easily implemented by recursively
		3772	invoking C<ev_run>.
		3773
		3774	This brings the problem of exiting - a callback might want to finish the
		3775	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3776	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3777	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3778	other combination: In these cases, a simple C<ev_break> will not work.
		3779
		3780	The solution is to maintain "break this loop" variable for each C<ev_run>
		3781	invocation, and use a loop around C<ev_run> until the condition is
		3782	triggered, using C<EVRUN_ONCE>:
		3783
		3784	// main loop
		3785	int exit_main_loop = 0;
		3786
		3787	while (!exit_main_loop)
		3788	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3789
		3790	// in a modal watcher
		3791	int exit_nested_loop = 0;
		3792
		3793	while (!exit_nested_loop)
		3794	ev_run (EV_A_ EVRUN_ONCE);
		3795
		3796	To exit from any of these loops, just set the corresponding exit variable:
		3797
		3798	// exit modal loop
		3799	exit_nested_loop = 1;
		3800
		3801	// exit main program, after modal loop is finished
		3802	exit_main_loop = 1;
		3803
		3804	// exit both
		3805	exit_main_loop = exit_nested_loop = 1;
		3806
		3807	=head2 THREAD LOCKING EXAMPLE
		3808
		3809	Here is a fictitious example of how to run an event loop in a different
		3810	thread from where callbacks are being invoked and watchers are
		3811	created/added/removed.
		3812
		3813	For a real-world example, see the C<EV::Loop::Async> perl module,
		3814	which uses exactly this technique (which is suited for many high-level
		3815	languages).
		3816
		3817	The example uses a pthread mutex to protect the loop data, a condition
		3818	variable to wait for callback invocations, an async watcher to notify the
		3819	event loop thread and an unspecified mechanism to wake up the main thread.
		3820
		3821	First, you need to associate some data with the event loop:
		3822
		3823	typedef struct {
		3824	mutex_t lock; /* global loop lock */
		3825	ev_async async_w;
		3826	thread_t tid;
		3827	cond_t invoke_cv;
		3828	} userdata;
		3829
		3830	void prepare_loop (EV_P)
		3831	{
		3832	// for simplicity, we use a static userdata struct.
		3833	static userdata u;
		3834
		3835	ev_async_init (&u->async_w, async_cb);
		3836	ev_async_start (EV_A_ &u->async_w);
		3837
		3838	pthread_mutex_init (&u->lock, 0);
		3839	pthread_cond_init (&u->invoke_cv, 0);
		3840
		3841	// now associate this with the loop
		3842	ev_set_userdata (EV_A_ u);
		3843	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3844	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3845
		3846	// then create the thread running ev_run
		3847	pthread_create (&u->tid, 0, l_run, EV_A);
		3848	}
		3849
		3850	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3851	solely to wake up the event loop so it takes notice of any new watchers
		3852	that might have been added:
		3853
		3854	static void
		3855	async_cb (EV_P_ ev_async *w, int revents)
		3856	{
		3857	// just used for the side effects
		3858	}
		3859
		3860	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3861	protecting the loop data, respectively.
		3862
		3863	static void
		3864	l_release (EV_P)
		3865	{
		3866	userdata *u = ev_userdata (EV_A);
		3867	pthread_mutex_unlock (&u->lock);
		3868	}
		3869
		3870	static void
		3871	l_acquire (EV_P)
		3872	{
		3873	userdata *u = ev_userdata (EV_A);
		3874	pthread_mutex_lock (&u->lock);
		3875	}
		3876
		3877	The event loop thread first acquires the mutex, and then jumps straight
		3878	into C<ev_run>:
		3879
		3880	void *
		3881	l_run (void *thr_arg)
		3882	{
		3883	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3884
		3885	l_acquire (EV_A);
		3886	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3887	ev_run (EV_A_ 0);
		3888	l_release (EV_A);
		3889
		3890	return 0;
		3891	}
		3892
		3893	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3894	signal the main thread via some unspecified mechanism (signals? pipe
		3895	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3896	have been called (in a while loop because a) spurious wakeups are possible
		3897	and b) skipping inter-thread-communication when there are no pending
		3898	watchers is very beneficial):
		3899
		3900	static void
		3901	l_invoke (EV_P)
		3902	{
		3903	userdata *u = ev_userdata (EV_A);
		3904
		3905	while (ev_pending_count (EV_A))
		3906	{
		3907	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3908	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3909	}
		3910	}
		3911
		3912	Now, whenever the main thread gets told to invoke pending watchers, it
		3913	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3914	thread to continue:
		3915
		3916	static void
		3917	real_invoke_pending (EV_P)
		3918	{
		3919	userdata *u = ev_userdata (EV_A);
		3920
		3921	pthread_mutex_lock (&u->lock);
		3922	ev_invoke_pending (EV_A);
		3923	pthread_cond_signal (&u->invoke_cv);
		3924	pthread_mutex_unlock (&u->lock);
		3925	}
		3926
		3927	Whenever you want to start/stop a watcher or do other modifications to an
		3928	event loop, you will now have to lock:
		3929
		3930	ev_timer timeout_watcher;
		3931	userdata *u = ev_userdata (EV_A);
		3932
		3933	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3934
		3935	pthread_mutex_lock (&u->lock);
		3936	ev_timer_start (EV_A_ &timeout_watcher);
		3937	ev_async_send (EV_A_ &u->async_w);
		3938	pthread_mutex_unlock (&u->lock);
		3939
		3940	Note that sending the C<ev_async> watcher is required because otherwise
		3941	an event loop currently blocking in the kernel will have no knowledge
		3942	about the newly added timer. By waking up the loop it will pick up any new
		3943	watchers in the next event loop iteration.
		3944
		3945	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3946
		3947	While the overhead of a callback that e.g. schedules a thread is small, it
		3948	is still an overhead. If you embed libev, and your main usage is with some
		3949	kind of threads or coroutines, you might want to customise libev so that
		3950	doesn't need callbacks anymore.
		3951
		3952	Imagine you have coroutines that you can switch to using a function
		3953	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3954	and that due to some magic, the currently active coroutine is stored in a
		3955	global called C<current_coro>. Then you can build your own "wait for libev
		3956	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3957	the differing C<;> conventions):
		3958
		3959	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3960	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3961
		3962	That means instead of having a C callback function, you store the
		3963	coroutine to switch to in each watcher, and instead of having libev call
		3964	your callback, you instead have it switch to that coroutine.
		3965
		3966	A coroutine might now wait for an event with a function called
		3967	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3968	matter when, or whether the watcher is active or not when this function is
		3969	called):
		3970
		3971	void
		3972	wait_for_event (ev_watcher *w)
		3973	{
		3974	ev_set_cb (w, current_coro);
		3975	switch_to (libev_coro);
		3976	}
		3977
		3978	That basically suspends the coroutine inside C<wait_for_event> and
		3979	continues the libev coroutine, which, when appropriate, switches back to
		3980	this or any other coroutine.
		3981
		3982	You can do similar tricks if you have, say, threads with an event queue -
		3983	instead of storing a coroutine, you store the queue object and instead of
		3984	switching to a coroutine, you push the watcher onto the queue and notify
		3985	any waiters.
		3986
		3987	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3988	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3989
		3990	// my_ev.h
		3991	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3992	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3993	#include "../libev/ev.h"
		3994
		3995	// my_ev.c
		3996	#define EV_H "my_ev.h"
		3997	#include "../libev/ev.c"
		3998
		3999	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4000	F<my_ev.c> into your project. When properly specifying include paths, you
		4001	can even use F<ev.h> as header file name directly.
3299		4002
3300		4003
3301	=head1 LIBEVENT EMULATION	4004	=head1 LIBEVENT EMULATION
3302		4005
3303	Libev offers a compatibility emulation layer for libevent. It cannot	4006	Libev offers a compatibility emulation layer for libevent. It cannot
3304	emulate the internals of libevent, so here are some usage hints:	4007	emulate the internals of libevent, so here are some usage hints:
3305		4008
3306	=over 4	4009	=over 4
		4010
		4011	=item * Only the libevent-1.4.1-beta API is being emulated.
		4012
		4013	This was the newest libevent version available when libev was implemented,
		4014	and is still mostly unchanged in 2010.
3307		4015
3308	=item * Use it by including <event.h>, as usual.	4016	=item * Use it by including <event.h>, as usual.
3309		4017
3310	=item * The following members are fully supported: ev_base, ev_callback,	4018	=item * The following members are fully supported: ev_base, ev_callback,
3311	ev_arg, ev_fd, ev_res, ev_events.	4019	ev_arg, ev_fd, ev_res, ev_events.
…		…
3317	=item * Priorities are not currently supported. Initialising priorities	4025	=item * Priorities are not currently supported. Initialising priorities
3318	will fail and all watchers will have the same priority, even though there	4026	will fail and all watchers will have the same priority, even though there
3319	is an ev_pri field.	4027	is an ev_pri field.
3320		4028
3321	=item * In libevent, the last base created gets the signals, in libev, the	4029	=item * In libevent, the last base created gets the signals, in libev, the
3322	first base created (== the default loop) gets the signals.	4030	base that registered the signal gets the signals.
3323		4031
3324	=item * Other members are not supported.	4032	=item * Other members are not supported.
3325		4033
3326	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4034	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3327	to use the libev header file and library.	4035	to use the libev header file and library.
3328		4036
3329	=back	4037	=back
3330		4038
3331	=head1 C++ SUPPORT	4039	=head1 C++ SUPPORT
		4040
		4041	=head2 C API
		4042
		4043	The normal C API should work fine when used from C++: both ev.h and the
		4044	libev sources can be compiled as C++. Therefore, code that uses the C API
		4045	will work fine.
		4046
		4047	Proper exception specifications might have to be added to callbacks passed
		4048	to libev: exceptions may be thrown only from watcher callbacks, all other
		4049	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4050	callbacks) must not throw exceptions, and might need a C<noexcept>
		4051	specification. If you have code that needs to be compiled as both C and
		4052	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4053
		4054	static void
		4055	fatal_error (const char *msg) EV_NOEXCEPT
		4056	{
		4057	perror (msg);
		4058	abort ();
		4059	}
		4060
		4061	...
		4062	ev_set_syserr_cb (fatal_error);
		4063
		4064	The only API functions that can currently throw exceptions are C<ev_run>,
		4065	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4066	because it runs cleanup watchers).
		4067
		4068	Throwing exceptions in watcher callbacks is only supported if libev itself
		4069	is compiled with a C++ compiler or your C and C++ environments allow
		4070	throwing exceptions through C libraries (most do).
		4071
		4072	=head2 C++ API
3332		4073
3333	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4074	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	4075	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.	4076	the callback model to a model using method callbacks on objects.
3336		4077
3337	To use it,	4078	To use it,
3338		4079
3339	#include <ev++.h>	4080	#include <ev++.h>
3340		4081
3341	This automatically includes F<ev.h> and puts all of its definitions (many	4082	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	4083	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	4084	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++	4087	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	4088	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	4089	that the watcher is associated with (or no additional members at all if
3349	you disable C<EV_MULTIPLICITY> when embedding libev).	4090	you disable C<EV_MULTIPLICITY> when embedding libev).
3350		4091
3351	Currently, functions, and static and non-static member functions can be	4092	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	4093	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	4094	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	4095	you need support for other types of functors please contact the author
3355	it).	4096	(preferably after implementing it).
		4097
		4098	For all this to work, your C++ compiler either has to use the same calling
		4099	conventions as your C compiler (for static member functions), or you have
		4100	to embed libev and compile libev itself as C++.
3356		4101
3357	Here is a list of things available in the C<ev> namespace:	4102	Here is a list of things available in the C<ev> namespace:
3358		4103
3359	=over 4	4104	=over 4
3360		4105
…		…
3370	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4115	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3371		4116
3372	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4117	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>	4118	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	4119	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3375	defines by many implementations.	4120	defined by many implementations.
3376		4121
3377	All of those classes have these methods:	4122	All of those classes have these methods:
3378		4123
3379	=over 4	4124	=over 4
3380		4125
…		…
3442	void operator() (ev::io &w, int revents)	4187	void operator() (ev::io &w, int revents)
3443	{	4188	{
3444	...	4189	...
3445	}	4190	}
3446	}	4191	}
3447		4192
3448	myfunctor f;	4193	myfunctor f;
3449		4194
3450	ev::io w;	4195	ev::io w;
3451	w.set (&f);	4196	w.set (&f);
3452		4197
…		…
3470	Associates a different C<struct ev_loop> with this watcher. You can only	4215	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).	4216	do this when the watcher is inactive (and not pending either).
3472		4217
3473	=item w->set ([arguments])	4218	=item w->set ([arguments])
3474		4219
3475	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4220	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	4221	with the same arguments. Either this method or a suitable start method
3477	C counterpart, an active watcher gets automatically stopped and restarted	4222	must be called at least once. Unlike the C counterpart, an active watcher
3478	when reconfiguring it with this method.	4223	gets automatically stopped and restarted when reconfiguring it with this
		4224	method.
		4225
		4226	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4227	clashing with the C<set (loop)> method.
3479		4228
3480	=item w->start ()	4229	=item w->start ()
3481		4230
3482	Starts the watcher. Note that there is no C<loop> argument, as the	4231	Starts the watcher. Note that there is no C<loop> argument, as the
3483	constructor already stores the event loop.	4232	constructor already stores the event loop.
…		…
3513	watchers in the constructor.	4262	watchers in the constructor.
3514		4263
3515	class myclass	4264	class myclass
3516	{	4265	{
3517	ev::io io ; void io_cb (ev::io &w, int revents);	4266	ev::io io ; void io_cb (ev::io &w, int revents);
3518	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4267	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3519	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4268	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3520		4269
3521	myclass (int fd)	4270	myclass (int fd)
3522	{	4271	{
3523	io .set <myclass, &myclass::io_cb > (this);	4272	io .set <myclass, &myclass::io_cb > (this);
…		…
3574	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4323	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3575		4324
3576	=item D	4325	=item D
3577		4326
3578	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4327	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>.	4328	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3580		4329
3581	=item Ocaml	4330	=item Ocaml
3582		4331
3583	Erkki Seppala has written Ocaml bindings for libev, to be found at	4332	Erkki Seppala has written Ocaml bindings for libev, to be found at
3584	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4333	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3587		4336
3588	Brian Maher has written a partial interface to libev for lua (at the	4337	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	4338	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3590	L<http://github.com/brimworks/lua-ev>.	4339	L<http://github.com/brimworks/lua-ev>.
3591		4340
		4341	=item Javascript
		4342
		4343	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4344
		4345	=item Others
		4346
		4347	There are others, and I stopped counting.
		4348
3592	=back	4349	=back
3593		4350
3594		4351
3595	=head1 MACRO MAGIC	4352	=head1 MACRO MAGIC
3596		4353
…		…
3632	suitable for use with C<EV_A>.	4389	suitable for use with C<EV_A>.
3633		4390
3634	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4391	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3635		4392
3636	Similar to the other two macros, this gives you the value of the default	4393	Similar to the other two macros, this gives you the value of the default
3637	loop, if multiple loops are supported ("ev loop default").	4394	loop, if multiple loops are supported ("ev loop default"). The default loop
		4395	will be initialised if it isn't already initialised.
		4396
		4397	For non-multiplicity builds, these macros do nothing, so you always have
		4398	to initialise the loop somewhere.
3638		4399
3639	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4400	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3640		4401
3641	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4402	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	4403	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3709	ev_vars.h	4470	ev_vars.h
3710	ev_wrap.h	4471	ev_wrap.h
3711		4472
3712	ev_win32.c required on win32 platforms only	4473	ev_win32.c required on win32 platforms only
3713		4474
3714	ev_select.c only when select backend is enabled (which is enabled by default)	4475	ev_select.c only when select backend is enabled
3715	ev_poll.c only when poll backend is enabled (disabled by default)	4476	ev_poll.c only when poll backend is enabled
3716	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4477	ev_epoll.c only when the epoll backend is enabled
		4478	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)	4479	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)	4480	ev_port.c only when the solaris port backend is enabled
3719		4481
3720	F<ev.c> includes the backend files directly when enabled, so you only need	4482	F<ev.c> includes the backend files directly when enabled, so you only need
3721	to compile this single file.	4483	to compile this single file.
3722		4484
3723	=head3 LIBEVENT COMPATIBILITY API	4485	=head3 LIBEVENT COMPATIBILITY API
…		…
3787	supported). It will also not define any of the structs usually found in	4549	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.	4550	F<event.h> that are not directly supported by the libev core alone.
3789		4551
3790	In standalone mode, libev will still try to automatically deduce the	4552	In standalone mode, libev will still try to automatically deduce the
3791	configuration, but has to be more conservative.	4553	configuration, but has to be more conservative.
		4554
		4555	=item EV_USE_FLOOR
		4556
		4557	If defined to be C<1>, libev will use the C<floor ()> function for its
		4558	periodic reschedule calculations, otherwise libev will fall back on a
		4559	portable (slower) implementation. If you enable this, you usually have to
		4560	link against libm or something equivalent. Enabling this when the C<floor>
		4561	function is not available will fail, so the safe default is to not enable
		4562	this.
3792		4563
3793	=item EV_USE_MONOTONIC	4564	=item EV_USE_MONOTONIC
3794		4565
3795	If defined to be C<1>, libev will try to detect the availability of the	4566	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	4567	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	4653	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	4654	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	4655	file descriptors again. Note that the replacement function has to close
3885	the underlying OS handle.	4656	the underlying OS handle.
3886		4657
		4658	=item EV_USE_WSASOCKET
		4659
		4660	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4661	communication socket, which works better in some environments. Otherwise,
		4662	the normal C<socket> function will be used, which works better in other
		4663	environments.
		4664
3887	=item EV_USE_POLL	4665	=item EV_USE_POLL
3888		4666
3889	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4667	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	4668	backend. Otherwise it will be enabled on non-win32 platforms. It
3891	takes precedence over select.	4669	takes precedence over select.
…		…
3895	If defined to be C<1>, libev will compile in support for the Linux	4673	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,	4674	C<epoll>(7) backend. Its availability will be detected at runtime,
3897	otherwise another method will be used as fallback. This is the preferred	4675	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	4676	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.	4677	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4678
		4679	=item EV_USE_LINUXAIO
		4680
		4681	If defined to be C<1>, libev will compile in support for the Linux
		4682	aio backend. Due to it's currenbt limitations it has to be requested
		4683	explicitly. If undefined, it will be enabled on linux, otherwise
		4684	disabled.
3900		4685
3901	=item EV_USE_KQUEUE	4686	=item EV_USE_KQUEUE
3902		4687
3903	If defined to be C<1>, libev will compile in support for the BSD style	4688	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,	4689	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	4711	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	4712	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	4713	be detected at runtime. If undefined, it will be enabled if the headers
3929	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4714	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3930		4715
		4716	=item EV_NO_SMP
		4717
		4718	If defined to be C<1>, libev will assume that memory is always coherent
		4719	between threads, that is, threads can be used, but threads never run on
		4720	different cpus (or different cpu cores). This reduces dependencies
		4721	and makes libev faster.
		4722
		4723	=item EV_NO_THREADS
		4724
		4725	If defined to be C<1>, libev will assume that it will never be called from
		4726	different threads (that includes signal handlers), which is a stronger
		4727	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4728	libev faster.
		4729
3931	=item EV_ATOMIC_T	4730	=item EV_ATOMIC_T
3932		4731
3933	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4732	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	4733	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	4734	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"	4735	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.	4736	handler "locking" as well as for signal and thread safety in C<ev_async>
		4737	watchers.
3938		4738
3939	In the absence of this define, libev will use C<sig_atomic_t volatile>	4739	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.	4740	(from F<signal.h>), which is usually good enough on most platforms.
3941		4741
3942	=item EV_H (h)	4742	=item EV_H (h)
…		…
3969	will have the C<struct ev_loop *> as first argument, and you can create	4769	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	4770	additional independent event loops. Otherwise there will be no support
3971	for multiple event loops and there is no first event loop pointer	4771	for multiple event loops and there is no first event loop pointer
3972	argument. Instead, all functions act on the single default loop.	4772	argument. Instead, all functions act on the single default loop.
3973		4773
		4774	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4775	default loop when multiplicity is switched off - you always have to
		4776	initialise the loop manually in this case.
		4777
3974	=item EV_MINPRI	4778	=item EV_MINPRI
3975		4779
3976	=item EV_MAXPRI	4780	=item EV_MAXPRI
3977		4781
3978	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4782	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4014	#define EV_USE_POLL 1	4818	#define EV_USE_POLL 1
4015	#define EV_CHILD_ENABLE 1	4819	#define EV_CHILD_ENABLE 1
4016	#define EV_ASYNC_ENABLE 1	4820	#define EV_ASYNC_ENABLE 1
4017		4821
4018	The actual value is a bitset, it can be a combination of the following	4822	The actual value is a bitset, it can be a combination of the following
4019	values:	4823	values (by default, all of these are enabled):
4020		4824
4021	=over 4	4825	=over 4
4022		4826
4023	=item C<1> - faster/larger code	4827	=item C<1> - faster/larger code
4024		4828
…		…
4028	code size by roughly 30% on amd64).	4832	code size by roughly 30% on amd64).
4029		4833
4030	When optimising for size, use of compiler flags such as C<-Os> with	4834	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	4835	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4032	assertions.	4836	assertions.
		4837
		4838	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4839	(e.g. gcc with C<-Os>).
4033		4840
4034	=item C<2> - faster/larger data structures	4841	=item C<2> - faster/larger data structures
4035		4842
4036	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4843	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	4844	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	4845	and can additionally have an effect on the size of data structures at
4039	runtime.	4846	runtime.
4040		4847
		4848	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4849	(e.g. gcc with C<-Os>).
		4850
4041	=item C<4> - full API configuration	4851	=item C<4> - full API configuration
4042		4852
4043	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4853	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4044	enables multiplicity (C<EV_MULTIPLICITY>=1).	4854	enables multiplicity (C<EV_MULTIPLICITY>=1).
4045		4855
…		…
4075		4885
4076	With an intelligent-enough linker (gcc+binutils are intelligent enough	4886	With an intelligent-enough linker (gcc+binutils are intelligent enough
4077	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4887	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	4888	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.	4889	I/O watcher then might come out at only 5Kb.
		4890
		4891	=item EV_API_STATIC
		4892
		4893	If this symbol is defined (by default it is not), then all identifiers
		4894	will have static linkage. This means that libev will not export any
		4895	identifiers, and you cannot link against libev anymore. This can be useful
		4896	when you embed libev, only want to use libev functions in a single file,
		4897	and do not want its identifiers to be visible.
		4898
		4899	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4900	wants to use libev.
		4901
		4902	This option only works when libev is compiled with a C compiler, as C++
		4903	doesn't support the required declaration syntax.
4080		4904
4081	=item EV_AVOID_STDIO	4905	=item EV_AVOID_STDIO
4082		4906
4083	If this is set to C<1> at compiletime, then libev will avoid using stdio	4907	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	4908	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:	5052	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4229		5053
4230	#include "ev_cpp.h"	5054	#include "ev_cpp.h"
4231	#include "ev.c"	5055	#include "ev.c"
4232		5056
4233	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5057	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4234		5058
4235	=head2 THREADS AND COROUTINES	5059	=head2 THREADS AND COROUTINES
4236		5060
4237	=head3 THREADS	5061	=head3 THREADS
4238		5062
…		…
4289	default loop and triggering an C<ev_async> watcher from the default loop	5113	default loop and triggering an C<ev_async> watcher from the default loop
4290	watcher callback into the event loop interested in the signal.	5114	watcher callback into the event loop interested in the signal.
4291		5115
4292	=back	5116	=back
4293		5117
4294	=head4 THREAD LOCKING EXAMPLE	5118	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		5119
4432	=head3 COROUTINES	5120	=head3 COROUTINES
4433		5121
4434	Libev is very accommodating to coroutines ("cooperative threads"):	5122	Libev is very accommodating to coroutines ("cooperative threads"):
4435	libev fully supports nesting calls to its functions from different	5123	libev fully supports nesting calls to its functions from different
…		…
4600	requires, and its I/O model is fundamentally incompatible with the POSIX	5288	requires, and its I/O model is fundamentally incompatible with the POSIX
4601	model. Libev still offers limited functionality on this platform in	5289	model. Libev still offers limited functionality on this platform in
4602	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5290	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4603	descriptors. This only applies when using Win32 natively, not when using	5291	descriptors. This only applies when using Win32 natively, not when using
4604	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5292	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4605	as every compielr comes with a slightly differently broken/incompatible	5293	as every compiler comes with a slightly differently broken/incompatible
4606	environment.	5294	environment.
4607		5295
4608	Lifting these limitations would basically require the full	5296	Lifting these limitations would basically require the full
4609	re-implementation of the I/O system. If you are into this kind of thing,	5297	re-implementation of the I/O system. If you are into this kind of thing,
4610	then note that glib does exactly that for you in a very portable way (note	5298	then note that glib does exactly that for you in a very portable way (note
…		…
4704	structure (guaranteed by POSIX but not by ISO C for example), but it also	5392	structure (guaranteed by POSIX but not by ISO C for example), but it also
4705	assumes that the same (machine) code can be used to call any watcher	5393	assumes that the same (machine) code can be used to call any watcher
4706	callback: The watcher callbacks have different type signatures, but libev	5394	callback: The watcher callbacks have different type signatures, but libev
4707	calls them using an C<ev_watcher *> internally.	5395	calls them using an C<ev_watcher *> internally.
4708		5396
		5397	=item null pointers and integer zero are represented by 0 bytes
		5398
		5399	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5400	relies on this setting pointers and integers to null.
		5401
		5402	=item pointer accesses must be thread-atomic
		5403
		5404	Accessing a pointer value must be atomic, it must both be readable and
		5405	writable in one piece - this is the case on all current architectures.
		5406
4709	=item C<sig_atomic_t volatile> must be thread-atomic as well	5407	=item C<sig_atomic_t volatile> must be thread-atomic as well
4710		5408
4711	The type C<sig_atomic_t volatile> (or whatever is defined as	5409	The type C<sig_atomic_t volatile> (or whatever is defined as
4712	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5410	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4713	threads. This is not part of the specification for C<sig_atomic_t>, but is	5411	threads. This is not part of the specification for C<sig_atomic_t>, but is
…		…
4721	thread" or will block signals process-wide, both behaviours would	5419	thread" or will block signals process-wide, both behaviours would
4722	be compatible with libev. Interaction between C<sigprocmask> and	5420	be compatible with libev. Interaction between C<sigprocmask> and
4723	C<pthread_sigmask> could complicate things, however.	5421	C<pthread_sigmask> could complicate things, however.
4724		5422
4725	The most portable way to handle signals is to block signals in all threads	5423	The most portable way to handle signals is to block signals in all threads
4726	except the initial one, and run the default loop in the initial thread as	5424	except the initial one, and run the signal handling loop in the initial
4727	well.	5425	thread as well.
4728		5426
4729	=item C<long> must be large enough for common memory allocation sizes	5427	=item C<long> must be large enough for common memory allocation sizes
4730		5428
4731	To improve portability and simplify its API, libev uses C<long> internally	5429	To improve portability and simplify its API, libev uses C<long> internally
4732	instead of C<size_t> when allocating its data structures. On non-POSIX	5430	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4738		5436
4739	The type C<double> is used to represent timestamps. It is required to	5437	The type C<double> is used to represent timestamps. It is required to
4740	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5438	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4741	good enough for at least into the year 4000 with millisecond accuracy	5439	good enough for at least into the year 4000 with millisecond accuracy
4742	(the design goal for libev). This requirement is overfulfilled by	5440	(the design goal for libev). This requirement is overfulfilled by
4743	implementations using IEEE 754, which is basically all existing ones. With	5441	implementations using IEEE 754, which is basically all existing ones.
		5442
4744	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5443	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5444	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5445	is either obsolete or somebody patched it to use C<long double> or
		5446	something like that, just kidding).
4745		5447
4746	=back	5448	=back
4747		5449
4748	If you know of other additional requirements drop me a note.	5450	If you know of other additional requirements drop me a note.
4749		5451
…		…
4811	=item Processing ev_async_send: O(number_of_async_watchers)	5513	=item Processing ev_async_send: O(number_of_async_watchers)
4812		5514
4813	=item Processing signals: O(max_signal_number)	5515	=item Processing signals: O(max_signal_number)
4814		5516
4815	Sending involves a system call I<iff> there were no other C<ev_async_send>	5517	Sending involves a system call I<iff> there were no other C<ev_async_send>
4816	calls in the current loop iteration. Checking for async and signal events	5518	calls in the current loop iteration and the loop is currently
		5519	blocked. Checking for async and signal events involves iterating over all
4817	involves iterating over all running async watchers or all signal numbers.	5520	running async watchers or all signal numbers.
4818		5521
4819	=back	5522	=back
4820		5523
4821		5524
4822	=head1 PORTING FROM LIBEV 3.X TO 4.X	5525	=head1 PORTING FROM LIBEV 3.X TO 4.X
4823		5526
4824	The major version 4 introduced some minor incompatible changes to the API.	5527	The major version 4 introduced some incompatible changes to the API.
4825		5528
4826	At the moment, the C<ev.h> header file tries to implement superficial	5529	At the moment, the C<ev.h> header file provides compatibility definitions
4827	compatibility, so most programs should still compile. Those might be	5530	for all changes, so most programs should still compile. The compatibility
4828	removed in later versions of libev, so better update early than late.	5531	layer might be removed in later versions of libev, so better update to the
		5532	new API early than late.
4829		5533
4830	=over 4	5534	=over 4
		5535
		5536	=item C<EV_COMPAT3> backwards compatibility mechanism
		5537
		5538	The backward compatibility mechanism can be controlled by
		5539	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5540	section.
		5541
		5542	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5543
		5544	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5545
		5546	ev_loop_destroy (EV_DEFAULT_UC);
		5547	ev_loop_fork (EV_DEFAULT);
4831		5548
4832	=item function/symbol renames	5549	=item function/symbol renames
4833		5550
4834	A number of functions and symbols have been renamed:	5551	A number of functions and symbols have been renamed:
4835		5552
…		…
4854	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5571	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4855	as all other watcher types. Note that C<ev_loop_fork> is still called	5572	as all other watcher types. Note that C<ev_loop_fork> is still called
4856	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>	5573	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4857	typedef.	5574	typedef.
4858		5575
4859	=item C<EV_COMPAT3> backwards compatibility mechanism
4860
4861	The backward compatibility mechanism can be controlled by
4862	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4863	section.
4864
4865	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>	5576	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4866		5577
4867	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5578	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4868	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5579	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4869	and work, but the library code will of course be larger.	5580	and work, but the library code will of course be larger.
…		…
4876	=over 4	5587	=over 4
4877		5588
4878	=item active	5589	=item active
4879		5590
4880	A watcher is active as long as it has been started and not yet stopped.	5591	A watcher is active as long as it has been started and not yet stopped.
4881	See L<WATCHER STATES> for details.	5592	See L</WATCHER STATES> for details.
4882		5593
4883	=item application	5594	=item application
4884		5595
4885	In this document, an application is whatever is using libev.	5596	In this document, an application is whatever is using libev.
4886		5597
…		…
4922	watchers and events.	5633	watchers and events.
4923		5634
4924	=item pending	5635	=item pending
4925		5636
4926	A watcher is pending as soon as the corresponding event has been	5637	A watcher is pending as soon as the corresponding event has been
4927	detected. See L<WATCHER STATES> for details.	5638	detected. See L</WATCHER STATES> for details.
4928		5639
4929	=item real time	5640	=item real time
4930		5641
4931	The physical time that is observed. It is apparently strictly monotonic :)	5642	The physical time that is observed. It is apparently strictly monotonic :)
4932		5643
4933	=item wall-clock time	5644	=item wall-clock time
4934		5645
4935	The time and date as shown on clocks. Unlike real time, it can actually	5646	The time and date as shown on clocks. Unlike real time, it can actually
4936	be wrong and jump forwards and backwards, e.g. when the you adjust your	5647	be wrong and jump forwards and backwards, e.g. when you adjust your
4937	clock.	5648	clock.
4938		5649
4939	=item watcher	5650	=item watcher
4940		5651
4941	A data structure that describes interest in certain events. Watchers need	5652	A data structure that describes interest in certain events. Watchers need
…		…
4943		5654
4944	=back	5655	=back
4945		5656
4946	=head1 AUTHOR	5657	=head1 AUTHOR
4947		5658
4948	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5659	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5660	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
4949		5661

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