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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 (but libev
		581	only tries to use it in 4.19+).
		582
		583	This is another linux trainwreck of an event interface.
		584
		585	If this backend works for you (as of this writing, it was very
		586	experimental), it is the best event interface available on linux and might
		587	be well worth enabling it - if it isn't available in your kernel this will
		588	be detected and this backend will be skipped.
		589
		590	This backend can batch oneshot requests and supports a user-space ring
		591	buffer to receive events. It also doesn't suffer from most of the design
		592	problems of epoll (such as not being able to remove event sources from
		593	the epoll set), and generally sounds too good to be true. Because, this
		594	being the linux kernel, of course it suffers from a whole new set of
		595	limitations, forcing you to fall back to epoll, inheriting all its design
		596	issues.
		597
		598	For one, it is not easily embeddable (but probably could be done using
		599	an event fd at some extra overhead). It also is subject to a system wide
		600	limit that can be configured in F</proc/sys/fs/aio-max-nr>. If no aio
		601	requests are left, this backend will be skipped during initialisation, and
		602	will switch to epoll when the loop is active.
		603
		604	Most problematic in practice, however, is that not all file descriptors
		605	work with it. For example, in linux 5.1, tcp sockets, pipes, event fds,
		606	files, F</dev/null> and a few others are supported, but ttys do not work
		607	properly (a known bug that the kernel developers don't care about, see
		608	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		609	(yet?) a generic event polling interface.
		610
		611	Overall, it seems the linux developers just don't want it to have a
		612	generic event handling mechanism other than C<select> or C<poll>.
		613
		614	To work around all these problem, the current version of libev uses its
		615	epoll backend as a fallback for file descriptor types that do not work. Or
		616	falls back completely to epoll if the kernel acts up.
469		617
470	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	618	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
471	C<EVBACKEND_POLL>.	619	C<EVBACKEND_POLL>.
472		620
473	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	621	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
…		…
488		636
489	It scales in the same way as the epoll backend, but the interface to the	637	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	638	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	639	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	640	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	641	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	642	might have to leak fd's on fork, but it's more sane than epoll) and it
495	cases	643	drops fds silently in similarly hard-to-detect cases.
496		644
497	This backend usually performs well under most conditions.	645	This backend usually performs well under most conditions.
498		646
499	While nominally embeddable in other event loops, this doesn't work	647	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	648	everywhere, so you might need to test for this. And since it is broken
…		…
517	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	665	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
518		666
519	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	667	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)).	668	it's really slow, but it still scales very well (O(active_fds)).
521		669
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	670	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	671	file descriptor per loop iteration. For small and medium numbers of file
528	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	672	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
529	might perform better.	673	might perform better.
530		674
531	On the positive side, with the exception of the spurious readiness	675	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	676	specification in all tests and is fully embeddable, which is a rare feat
534	OS-specific backends (I vastly prefer correctness over speed hacks).	677	among the OS-specific backends (I vastly prefer correctness over speed
		678	hacks).
		679
		680	On the negative side, the interface is I<bizarre> - so bizarre that
		681	even sun itself gets it wrong in their code examples: The event polling
		682	function sometimes returns events to the caller even though an error
		683	occurred, but with no indication whether it has done so or not (yes, it's
		684	even documented that way) - deadly for edge-triggered interfaces where you
		685	absolutely have to know whether an event occurred or not because you have
		686	to re-arm the watcher.
		687
		688	Fortunately libev seems to be able to work around these idiocies.
535		689
536	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	690	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
537	C<EVBACKEND_POLL>.	691	C<EVBACKEND_POLL>.
538		692
539	=item C<EVBACKEND_ALL>	693	=item C<EVBACKEND_ALL>
540		694
541	Try all backends (even potentially broken ones that wouldn't be tried	695	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	696	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
543	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	697	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
544		698
545	It is definitely not recommended to use this flag.	699	It is definitely not recommended to use this flag, use whatever
		700	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		701	at all.
		702
		703	=item C<EVBACKEND_MASK>
		704
		705	Not a backend at all, but a mask to select all backend bits from a
		706	C<flags> value, in case you want to mask out any backends from a flags
		707	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
546		708
547	=back	709	=back
548		710
549	If one or more of the backend flags are or'ed into the flags value,	711	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	712	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	713	here). If none are specified, all backends in C<ev_recommended_backends
552	()> will be tried.	714	()> will be tried.
553		715
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.	716	Example: Try to create a event loop that uses epoll and nothing else.
581		717
582	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	718	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
583	if (!epoller)	719	if (!epoller)
584	fatal ("no epoll found here, maybe it hides under your chair");	720	fatal ("no epoll found here, maybe it hides under your chair");
585		721
		722	Example: Use whatever libev has to offer, but make sure that kqueue is
		723	used if available.
		724
		725	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		726
		727	Example: Similarly, on linux, you mgiht want to take advantage of the
		728	linux aio backend if possible, but fall back to something else if that
		729	isn't available.
		730
		731	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
		732
586	=item ev_default_destroy ()	733	=item ev_loop_destroy (loop)
587		734
588	Destroys the default loop (frees all memory and kernel state etc.). None	735	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	736	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	737	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,	738	responsibility to either stop all watchers cleanly yourself I<before>
592	or cope with the fact afterwards (which is usually the easiest thing, you	739	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).	740	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		741	for example).
594		742
595	Note that certain global state, such as signal state (and installed signal	743	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	744	handlers), will not be freed by this function, and related watchers (such
597	as signal and child watchers) would need to be stopped manually.	745	as signal and child watchers) would need to be stopped manually.
598		746
599	In general it is not advisable to call this function except in the	747	This function is normally used on loop objects allocated by
600	rare occasion where you really need to free e.g. the signal handling	748	C<ev_loop_new>, but it can also be used on the default loop returned by
		749	C<ev_default_loop>, in which case it is not thread-safe.
		750
		751	Note that it is not advisable to call this function on the default loop
		752	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	753	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>.	754	and C<ev_loop_destroy>.
603		755
604	=item ev_loop_destroy (loop)	756	=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		757
611	This function sets a flag that causes subsequent C<ev_run> iterations	758	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	759	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	760	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	761	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	762	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.	763	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
617		764
		765	In addition, if you want to reuse a loop (via this function or
		766	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		767
618	Again, you I<have> to call it on I<any> loop that you want to re-use after	768	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	769	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	770	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
621	during fork.	771	during fork.
622		772
623	On the other hand, you only need to call this function in the child	773	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	776	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	777	difference, but libev will usually detect this case on its own and do a
628	costly reset of the backend).	778	costly reset of the backend).
629		779
630	The function itself is quite fast and it's usually not a problem to call	780	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	781	it just in case after a fork.
632	quite nicely into a call to C<pthread_atfork>:
633		782
		783	Example: Automate calling C<ev_loop_fork> on the default loop when
		784	using pthreads.
		785
		786	static void
		787	post_fork_child (void)
		788	{
		789	ev_loop_fork (EV_DEFAULT);
		790	}
		791
		792	...
634	pthread_atfork (0, 0, ev_default_fork);	793	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		794
643	=item int ev_is_default_loop (loop)	795	=item int ev_is_default_loop (loop)
644		796
645	Returns true when the given loop is, in fact, the default loop, and false	797	Returns true when the given loop is, in fact, the default loop, and false
646	otherwise.	798	otherwise.
…		…
657	prepare and check phases.	809	prepare and check phases.
658		810
659	=item unsigned int ev_depth (loop)	811	=item unsigned int ev_depth (loop)
660		812
661	Returns the number of times C<ev_run> was entered minus the number of	813	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.	814	times C<ev_run> was exited normally, in other words, the recursion depth.
663		815
664	Outside C<ev_run>, this number is zero. In a callback, this number is	816	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),	817	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
666	in which case it is higher.	818	in which case it is higher.
667		819
668	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	820	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	821	throwing an exception etc.), doesn't count as "exit" - consider this
670	ungentleman-like behaviour unless it's really convenient.	822	as a hint to avoid such ungentleman-like behaviour unless it's really
		823	convenient, in which case it is fully supported.
671		824
672	=item unsigned int ev_backend (loop)	825	=item unsigned int ev_backend (loop)
673		826
674	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	827	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
675	use.	828	use.
…		…
690		843
691	This function is rarely useful, but when some event callback runs for a	844	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	845	very long time without entering the event loop, updating libev's idea of
693	the current time is a good idea.	846	the current time is a good idea.
694		847
695	See also L<The special problem of time updates> in the C<ev_timer> section.	848	See also L</The special problem of time updates> in the C<ev_timer> section.
696		849
697	=item ev_suspend (loop)	850	=item ev_suspend (loop)
698		851
699	=item ev_resume (loop)	852	=item ev_resume (loop)
700		853
…		…
718	without a previous call to C<ev_suspend>.	871	without a previous call to C<ev_suspend>.
719		872
720	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	873	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
721	event loop time (see C<ev_now_update>).	874	event loop time (see C<ev_now_update>).
722		875
723	=item ev_run (loop, int flags)	876	=item bool ev_run (loop, int flags)
724		877
725	Finally, this is it, the event handler. This function usually is called	878	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	879	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	880	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	881	the watcher callbacks, and then repeat the whole process indefinitely: This
729	is why event loops are called I<loops>.	882	is why event loops are called I<loops>.
730		883
731	If the flags argument is specified as C<0>, it will keep handling events	884	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	885	until either no event watchers are active anymore or C<ev_break> was
733	called.	886	called.
		887
		888	The return value is false if there are no more active watchers (which
		889	usually means "all jobs done" or "deadlock"), and true in all other cases
		890	(which usually means " you should call C<ev_run> again").
734		891
735	Please note that an explicit C<ev_break> is usually better than	892	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	893	relying on all watchers to be stopped when deciding when a program has
737	finished (especially in interactive programs), but having a program	894	finished (especially in interactive programs), but having a program
738	that automatically loops as long as it has to and no longer by virtue	895	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	896	of relying on its watchers stopping correctly, that is truly a thing of
740	beauty.	897	beauty.
741		898
		899	This function is I<mostly> exception-safe - you can break out of a
		900	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		901	exception and so on. This does not decrement the C<ev_depth> value, nor
		902	will it clear any outstanding C<EVBREAK_ONE> breaks.
		903
742	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	904	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	905	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	906	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	907	iteration of the loop. This is sometimes useful to poll and handle new
746	events while doing lengthy calculations, to keep the program responsive.	908	events while doing lengthy calculations, to keep the program responsive.
…		…
755	This is useful if you are waiting for some external event in conjunction	917	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	918	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	919	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.	920	usually a better approach for this kind of thing.
759		921
760	Here are the gory details of what C<ev_run> does:	922	Here are the gory details of what C<ev_run> does (this is for your
		923	understanding, not a guarantee that things will work exactly like this in
		924	future versions):
761		925
762	- Increment loop depth.	926	- Increment loop depth.
763	- Reset the ev_break status.	927	- Reset the ev_break status.
764	- Before the first iteration, call any pending watchers.	928	- Before the first iteration, call any pending watchers.
765	LOOP:	929	LOOP:
…		…
798	anymore.	962	anymore.
799		963
800	... queue jobs here, make sure they register event watchers as long	964	... 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..)	965	... as they still have work to do (even an idle watcher will do..)
802	ev_run (my_loop, 0);	966	ev_run (my_loop, 0);
803	... jobs done or somebody called unloop. yeah!	967	... jobs done or somebody called break. yeah!
804		968
805	=item ev_break (loop, how)	969	=item ev_break (loop, how)
806		970
807	Can be used to make a call to C<ev_run> return early (but only after it	971	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	972	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	973	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.	974	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
811		975
812	This "unloop state" will be cleared when entering C<ev_run> again.	976	This "break state" will be cleared on the next call to C<ev_run>.
813		977
814	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	978	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		979	which case it will have no effect.
815		980
816	=item ev_ref (loop)	981	=item ev_ref (loop)
817		982
818	=item ev_unref (loop)	983	=item ev_unref (loop)
819		984
…		…
840	running when nothing else is active.	1005	running when nothing else is active.
841		1006
842	ev_signal exitsig;	1007	ev_signal exitsig;
843	ev_signal_init (&exitsig, sig_cb, SIGINT);	1008	ev_signal_init (&exitsig, sig_cb, SIGINT);
844	ev_signal_start (loop, &exitsig);	1009	ev_signal_start (loop, &exitsig);
845	evf_unref (loop);	1010	ev_unref (loop);
846		1011
847	Example: For some weird reason, unregister the above signal handler again.	1012	Example: For some weird reason, unregister the above signal handler again.
848		1013
849	ev_ref (loop);	1014	ev_ref (loop);
850	ev_signal_stop (loop, &exitsig);	1015	ev_signal_stop (loop, &exitsig);
…		…
870	overhead for the actual polling but can deliver many events at once.	1035	overhead for the actual polling but can deliver many events at once.
871		1036
872	By setting a higher I<io collect interval> you allow libev to spend more	1037	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,	1038	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	1039	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	1040	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	1041	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	1042	sleep time ensures that libev will not poll for I/O events more often then
878	once per this interval, on average.	1043	once per this interval, on average (as long as the host time resolution is
		1044	good enough).
879		1045
880	Likewise, by setting a higher I<timeout collect interval> you allow libev	1046	Likewise, by setting a higher I<timeout collect interval> you allow libev
881	to spend more time collecting timeouts, at the expense of increased	1047	to spend more time collecting timeouts, at the expense of increased
882	latency/jitter/inexactness (the watcher callback will be called	1048	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	1049	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.).	1095	invoke the actual watchers inside another context (another thread etc.).
930		1096
931	If you want to reset the callback, use C<ev_invoke_pending> as new	1097	If you want to reset the callback, use C<ev_invoke_pending> as new
932	callback.	1098	callback.
933		1099
934	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1100	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
935		1101
936	Sometimes you want to share the same loop between multiple threads. This	1102	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	1103	can be done relatively simply by putting mutex_lock/unlock calls around
938	each call to a libev function.	1104	each call to a libev function.
939		1105
940	However, C<ev_run> can run an indefinite time, so it is not feasible	1106	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	1107	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	1108	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.	1109	I<release> and I<acquire> callbacks on the loop.
944		1110
945	When set, then C<release> will be called just before the thread is	1111	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	1112	suspended waiting for new events, and C<acquire> is called just
947	afterwards.	1113	afterwards.
…		…
962	See also the locking example in the C<THREADS> section later in this	1128	See also the locking example in the C<THREADS> section later in this
963	document.	1129	document.
964		1130
965	=item ev_set_userdata (loop, void *data)	1131	=item ev_set_userdata (loop, void *data)
966		1132
967	=item ev_userdata (loop)	1133	=item void *ev_userdata (loop)
968		1134
969	Set and retrieve a single C<void *> associated with a loop. When	1135	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	1136	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
971	C<0.>	1137	C<0>.
972		1138
973	These two functions can be used to associate arbitrary data with a loop,	1139	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	1140	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	1141	C<acquire> callbacks described above, but of course can be (ab-)used for
976	any other purpose as well.	1142	any other purpose as well.
…		…
1087		1253
1088	=item C<EV_PREPARE>	1254	=item C<EV_PREPARE>
1089		1255
1090	=item C<EV_CHECK>	1256	=item C<EV_CHECK>
1091		1257
1092	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1258	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	1259	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	1260	just after C<ev_run> has gathered them, but before it queues any callbacks
		1261	for any received events. That means C<ev_prepare> watchers are the last
		1262	watchers invoked before the event loop sleeps or polls for new events, and
		1263	C<ev_check> watchers will be invoked before any other watchers of the same
		1264	or lower priority within an event loop iteration.
		1265
1095	received events. Callbacks of both watcher types can start and stop as	1266	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	1267	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	1268	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1098	C<ev_run> from blocking).	1269	blocking).
1099		1270
1100	=item C<EV_EMBED>	1271	=item C<EV_EMBED>
1101		1272
1102	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1273	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1103		1274
1104	=item C<EV_FORK>	1275	=item C<EV_FORK>
1105		1276
1106	The event loop has been resumed in the child process after fork (see	1277	The event loop has been resumed in the child process after fork (see
1107	C<ev_fork>).	1278	C<ev_fork>).
		1279
		1280	=item C<EV_CLEANUP>
		1281
		1282	The event loop is about to be destroyed (see C<ev_cleanup>).
1108		1283
1109	=item C<EV_ASYNC>	1284	=item C<EV_ASYNC>
1110		1285
1111	The given async watcher has been asynchronously notified (see C<ev_async>).	1286	The given async watcher has been asynchronously notified (see C<ev_async>).
1112		1287
…		…
1134	programs, though, as the fd could already be closed and reused for another	1309	programs, though, as the fd could already be closed and reused for another
1135	thing, so beware.	1310	thing, so beware.
1136		1311
1137	=back	1312	=back
1138		1313
		1314	=head2 GENERIC WATCHER FUNCTIONS
		1315
		1316	=over 4
		1317
		1318	=item C<ev_init> (ev_TYPE *watcher, callback)
		1319
		1320	This macro initialises the generic portion of a watcher. The contents
		1321	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1322	the generic parts of the watcher are initialised, you I<need> to call
		1323	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1324	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1325	which rolls both calls into one.
		1326
		1327	You can reinitialise a watcher at any time as long as it has been stopped
		1328	(or never started) and there are no pending events outstanding.
		1329
		1330	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1331	int revents)>.
		1332
		1333	Example: Initialise an C<ev_io> watcher in two steps.
		1334
		1335	ev_io w;
		1336	ev_init (&w, my_cb);
		1337	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1338
		1339	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1340
		1341	This macro initialises the type-specific parts of a watcher. You need to
		1342	call C<ev_init> at least once before you call this macro, but you can
		1343	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1344	macro on a watcher that is active (it can be pending, however, which is a
		1345	difference to the C<ev_init> macro).
		1346
		1347	Although some watcher types do not have type-specific arguments
		1348	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1349
		1350	See C<ev_init>, above, for an example.
		1351
		1352	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1353
		1354	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1355	calls into a single call. This is the most convenient method to initialise
		1356	a watcher. The same limitations apply, of course.
		1357
		1358	Example: Initialise and set an C<ev_io> watcher in one step.
		1359
		1360	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1361
		1362	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1363
		1364	Starts (activates) the given watcher. Only active watchers will receive
		1365	events. If the watcher is already active nothing will happen.
		1366
		1367	Example: Start the C<ev_io> watcher that is being abused as example in this
		1368	whole section.
		1369
		1370	ev_io_start (EV_DEFAULT_UC, &w);
		1371
		1372	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1373
		1374	Stops the given watcher if active, and clears the pending status (whether
		1375	the watcher was active or not).
		1376
		1377	It is possible that stopped watchers are pending - for example,
		1378	non-repeating timers are being stopped when they become pending - but
		1379	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1380	pending. If you want to free or reuse the memory used by the watcher it is
		1381	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1382
		1383	=item bool ev_is_active (ev_TYPE *watcher)
		1384
		1385	Returns a true value iff the watcher is active (i.e. it has been started
		1386	and not yet been stopped). As long as a watcher is active you must not modify
		1387	it.
		1388
		1389	=item bool ev_is_pending (ev_TYPE *watcher)
		1390
		1391	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1392	events but its callback has not yet been invoked). As long as a watcher
		1393	is pending (but not active) you must not call an init function on it (but
		1394	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1395	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1396	it).
		1397
		1398	=item callback ev_cb (ev_TYPE *watcher)
		1399
		1400	Returns the callback currently set on the watcher.
		1401
		1402	=item ev_set_cb (ev_TYPE *watcher, callback)
		1403
		1404	Change the callback. You can change the callback at virtually any time
		1405	(modulo threads).
		1406
		1407	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1408
		1409	=item int ev_priority (ev_TYPE *watcher)
		1410
		1411	Set and query the priority of the watcher. The priority is a small
		1412	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1413	(default: C<-2>). Pending watchers with higher priority will be invoked
		1414	before watchers with lower priority, but priority will not keep watchers
		1415	from being executed (except for C<ev_idle> watchers).
		1416
		1417	If you need to suppress invocation when higher priority events are pending
		1418	you need to look at C<ev_idle> watchers, which provide this functionality.
		1419
		1420	You I<must not> change the priority of a watcher as long as it is active or
		1421	pending.
		1422
		1423	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1424	fine, as long as you do not mind that the priority value you query might
		1425	or might not have been clamped to the valid range.
		1426
		1427	The default priority used by watchers when no priority has been set is
		1428	always C<0>, which is supposed to not be too high and not be too low :).
		1429
		1430	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1431	priorities.
		1432
		1433	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1434
		1435	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1436	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1437	can deal with that fact, as both are simply passed through to the
		1438	callback.
		1439
		1440	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1441
		1442	If the watcher is pending, this function clears its pending status and
		1443	returns its C<revents> bitset (as if its callback was invoked). If the
		1444	watcher isn't pending it does nothing and returns C<0>.
		1445
		1446	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1447	callback to be invoked, which can be accomplished with this function.
		1448
		1449	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1450
		1451	Feeds the given event set into the event loop, as if the specified event
		1452	had happened for the specified watcher (which must be a pointer to an
		1453	initialised but not necessarily started event watcher). Obviously you must
		1454	not free the watcher as long as it has pending events.
		1455
		1456	Stopping the watcher, letting libev invoke it, or calling
		1457	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1458	not started in the first place.
		1459
		1460	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1461	functions that do not need a watcher.
		1462
		1463	=back
		1464
		1465	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1466	OWN COMPOSITE WATCHERS> idioms.
		1467
1139	=head2 WATCHER STATES	1468	=head2 WATCHER STATES
1140		1469
1141	There are various watcher states mentioned throughout this manual -	1470	There are various watcher states mentioned throughout this manual -
1142	active, pending and so on. In this section these states and the rules to	1471	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	1472	transition between them will be described in more detail - and while these
1144	rules might look complicated, they usually do "the right thing".	1473	rules might look complicated, they usually do "the right thing".
1145		1474
1146	=over 4	1475	=over 4
1147		1476
1148	=item initialiased	1477	=item initialised
1149		1478
1150	Before a watcher can be registered with the event looop it has to be	1479	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	1480	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.	1481	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1153		1482
1154	In this state it is simply some block of memory that is suitable for use	1483	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.	1484	use in an event loop. It can be moved around, freed, reused etc. at
		1485	will - as long as you either keep the memory contents intact, or call
		1486	C<ev_TYPE_init> again.
1156		1487
1157	=item started/running/active	1488	=item started/running/active
1158		1489
1159	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1490	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	1491	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	1519	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	1520	of whether it was active or not, so stopping a watcher explicitly before
1190	freeing it is often a good idea.	1521	freeing it is often a good idea.
1191		1522
1192	While stopped (and not pending) the watcher is essentially in the	1523	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	1524	initialised state, that is, it can be reused, moved, modified in any way
1194	you wish.	1525	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1526	it again).
1195		1527
1196	=back	1528	=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		1529
1415	=head2 WATCHER PRIORITY MODELS	1530	=head2 WATCHER PRIORITY MODELS
1416		1531
1417	Many event loops support I<watcher priorities>, which are usually small	1532	Many event loops support I<watcher priorities>, which are usually small
1418	integers that influence the ordering of event callback invocation	1533	integers that influence the ordering of event callback invocation
…		…
1545	In general you can register as many read and/or write event watchers per	1660	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	1661	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	1662	descriptors to non-blocking mode is also usually a good idea (but not
1548	required if you know what you are doing).	1663	required if you know what you are doing).
1549		1664
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	1665	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	1666	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	1667	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	1668	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	1669	with a relatively standard program structure. Thus it is best to always
1561	this situation even with a relatively standard program structure. Thus	1670	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.	1671	preferable to a program hanging until some data arrives.
1564		1672
1565	If you cannot run the fd in non-blocking mode (for example you should	1673	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	1674	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	1675	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	1676	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	1677	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	1678	use C<SIGALRM> and an interval timer, just to be sure you won't block
1571	indefinitely.	1679	indefinitely.
1572		1680
1573	But really, best use non-blocking mode.	1681	But really, best use non-blocking mode.
1574		1682
1575	=head3 The special problem of disappearing file descriptors	1683	=head3 The special problem of disappearing file descriptors
1576		1684
1577	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1685	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,	1686	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	1687	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	1688	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	1689	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	1690	is registered with libev, there is no efficient way to see that this is,
1583	fact, a different file descriptor.	1691	in fact, a different file descriptor.
1584		1692
1585	To avoid having to explicitly tell libev about such cases, libev follows	1693	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	1694	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	1695	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	1696	it is assumed that the file descriptor stays the same. That means that
…		…
1602		1710
1603	There is no workaround possible except not registering events	1711	There is no workaround possible except not registering events
1604	for potentially C<dup ()>'ed file descriptors, or to resort to	1712	for potentially C<dup ()>'ed file descriptors, or to resort to
1605	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1713	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1606		1714
		1715	=head3 The special problem of files
		1716
		1717	Many people try to use C<select> (or libev) on file descriptors
		1718	representing files, and expect it to become ready when their program
		1719	doesn't block on disk accesses (which can take a long time on their own).
		1720
		1721	However, this cannot ever work in the "expected" way - you get a readiness
		1722	notification as soon as the kernel knows whether and how much data is
		1723	there, and in the case of open files, that's always the case, so you
		1724	always get a readiness notification instantly, and your read (or possibly
		1725	write) will still block on the disk I/O.
		1726
		1727	Another way to view it is that in the case of sockets, pipes, character
		1728	devices and so on, there is another party (the sender) that delivers data
		1729	on its own, but in the case of files, there is no such thing: the disk
		1730	will not send data on its own, simply because it doesn't know what you
		1731	wish to read - you would first have to request some data.
		1732
		1733	Since files are typically not-so-well supported by advanced notification
		1734	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1735	to files, even though you should not use it. The reason for this is
		1736	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1737	usually a tty, often a pipe, but also sometimes files or special devices
		1738	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1739	F</dev/urandom>), and even though the file might better be served with
		1740	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1741	it "just works" instead of freezing.
		1742
		1743	So avoid file descriptors pointing to files when you know it (e.g. use
		1744	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1745	when you rarely read from a file instead of from a socket, and want to
		1746	reuse the same code path.
		1747
1607	=head3 The special problem of fork	1748	=head3 The special problem of fork
1608		1749
1609	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1750	Some backends (epoll, kqueue, probably linuxaio) do not support C<fork ()>
1610	useless behaviour. Libev fully supports fork, but needs to be told about	1751	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1611	it in the child.	1752	to be told about it in the child if you want to continue to use it in the
		1753	child.
1612		1754
1613	To support fork in your programs, you either have to call	1755	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,	1756	()> 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	1757	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1616	C<EVBACKEND_POLL>.
1617		1758
1618	=head3 The special problem of SIGPIPE	1759	=head3 The special problem of SIGPIPE
1619		1760
1620	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1761	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	1762	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	1860	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1720	monotonic clock option helps a lot here).	1861	monotonic clock option helps a lot here).
1721		1862
1722	The callback is guaranteed to be invoked only I<after> its timeout has	1863	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	1864	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	1865	might introduce a small delay, see "the special problem of being too
		1866	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	1867	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	1868	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).	1869	longer true when a callback calls C<ev_run> recursively).
1728		1870
1729	=head3 Be smart about timeouts	1871	=head3 Be smart about timeouts
1730		1872
1731	Many real-world problems involve some kind of timeout, usually for error	1873	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,	1874	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1807		1949
1808	In this case, it would be more efficient to leave the C<ev_timer> alone,	1950	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	1951	but remember the time of last activity, and check for a real timeout only
1810	within the callback:	1952	within the callback:
1811		1953
		1954	ev_tstamp timeout = 60.;
1812	ev_tstamp last_activity; // time of last activity	1955	ev_tstamp last_activity; // time of last activity
		1956	ev_timer timer;
1813		1957
1814	static void	1958	static void
1815	callback (EV_P_ ev_timer *w, int revents)	1959	callback (EV_P_ ev_timer *w, int revents)
1816	{	1960	{
1817	ev_tstamp now = ev_now (EV_A);	1961	// calculate when the timeout would happen
1818	ev_tstamp timeout = last_activity + 60.;	1962	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1819		1963
1820	// if last_activity + 60. is older than now, we did time out	1964	// if negative, it means we the timeout already occurred
1821	if (timeout < now)	1965	if (after < 0.)
1822	{	1966	{
1823	// timeout occurred, take action	1967	// timeout occurred, take action
1824	}	1968	}
1825	else	1969	else
1826	{	1970	{
1827	// callback was invoked, but there was some activity, re-arm	1971	// callback was invoked, but there was some recent
1828	// the watcher to fire in last_activity + 60, which is	1972	// activity. simply restart the timer to time out
1829	// guaranteed to be in the future, so "again" is positive:	1973	// after "after" seconds, which is the earliest time
1830	w->repeat = timeout - now;	1974	// the timeout can occur.
		1975	ev_timer_set (w, after, 0.);
1831	ev_timer_again (EV_A_ w);	1976	ev_timer_start (EV_A_ w);
1832	}	1977	}
1833	}	1978	}
1834		1979
1835	To summarise the callback: first calculate the real timeout (defined	1980	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	1981	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	1982	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	1983	(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		1984
1842	Note how C<ev_timer_again> is used, taking advantage of the	1985	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.	1986	timed out, and need to do whatever is needed in this case.
		1987
		1988	Otherwise, we now the earliest time at which the timeout would trigger,
		1989	and simply start the timer with this timeout value.
		1990
		1991	In other words, each time the callback is invoked it will check whether
		1992	the timeout occurred. If not, it will simply reschedule itself to check
		1993	again at the earliest time it could time out. Rinse. Repeat.
1844		1994
1845	This scheme causes more callback invocations (about one every 60 seconds	1995	This scheme causes more callback invocations (about one every 60 seconds
1846	minus half the average time between activity), but virtually no calls to	1996	minus half the average time between activity), but virtually no calls to
1847	libev to change the timeout.	1997	libev to change the timeout.
1848		1998
1849	To start the timer, simply initialise the watcher and set C<last_activity>	1999	To start the machinery, simply initialise the watcher and set
1850	to the current time (meaning we just have some activity :), then call the	2000	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:	2001	now), then call the callback, which will "do the right thing" and start
		2002	the timer:
1852		2003
		2004	last_activity = ev_now (EV_A);
1853	ev_init (timer, callback);	2005	ev_init (&timer, callback);
1854	last_activity = ev_now (loop);	2006	callback (EV_A_ &timer, 0);
1855	callback (loop, timer, EV_TIMER);
1856		2007
1857	And when there is some activity, simply store the current time in	2008	When there is some activity, simply store the current time in
1858	C<last_activity>, no libev calls at all:	2009	C<last_activity>, no libev calls at all:
1859		2010
		2011	if (activity detected)
1860	last_activity = ev_now (loop);	2012	last_activity = ev_now (EV_A);
		2013
		2014	When your timeout value changes, then the timeout can be changed by simply
		2015	providing a new value, stopping the timer and calling the callback, which
		2016	will again do the right thing (for example, time out immediately :).
		2017
		2018	timeout = new_value;
		2019	ev_timer_stop (EV_A_ &timer);
		2020	callback (EV_A_ &timer, 0);
1861		2021
1862	This technique is slightly more complex, but in most cases where the	2022	This technique is slightly more complex, but in most cases where the
1863	time-out is unlikely to be triggered, much more efficient.	2023	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		2024
1869	=item 4. Wee, just use a double-linked list for your timeouts.	2025	=item 4. Wee, just use a double-linked list for your timeouts.
1870		2026
1871	If there is not one request, but many thousands (millions...), all	2027	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	2028	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	2055	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	2056	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	2057	off after the first million or so of active timers, i.e. it's usually
1902	overkill :)	2058	overkill :)
1903		2059
		2060	=head3 The special problem of being too early
		2061
		2062	If you ask a timer to call your callback after three seconds, then
		2063	you expect it to be invoked after three seconds - but of course, this
		2064	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2065	guaranteed to any precision by libev - imagine somebody suspending the
		2066	process with a STOP signal for a few hours for example.
		2067
		2068	So, libev tries to invoke your callback as soon as possible I<after> the
		2069	delay has occurred, but cannot guarantee this.
		2070
		2071	A less obvious failure mode is calling your callback too early: many event
		2072	loops compare timestamps with a "elapsed delay >= requested delay", but
		2073	this can cause your callback to be invoked much earlier than you would
		2074	expect.
		2075
		2076	To see why, imagine a system with a clock that only offers full second
		2077	resolution (think windows if you can't come up with a broken enough OS
		2078	yourself). If you schedule a one-second timer at the time 500.9, then the
		2079	event loop will schedule your timeout to elapse at a system time of 500
		2080	(500.9 truncated to the resolution) + 1, or 501.
		2081
		2082	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2083	501" and invoke the callback 0.1s after it was started, even though a
		2084	one-second delay was requested - this is being "too early", despite best
		2085	intentions.
		2086
		2087	This is the reason why libev will never invoke the callback if the elapsed
		2088	delay equals the requested delay, but only when the elapsed delay is
		2089	larger than the requested delay. In the example above, libev would only invoke
		2090	the callback at system time 502, or 1.1s after the timer was started.
		2091
		2092	So, while libev cannot guarantee that your callback will be invoked
		2093	exactly when requested, it I<can> and I<does> guarantee that the requested
		2094	delay has actually elapsed, or in other words, it always errs on the "too
		2095	late" side of things.
		2096
1904	=head3 The special problem of time updates	2097	=head3 The special problem of time updates
1905		2098
1906	Establishing the current time is a costly operation (it usually takes at	2099	Establishing the current time is a costly operation (it usually takes
1907	least two system calls): EV therefore updates its idea of the current	2100	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	2101	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	2102	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1910	lots of events in one iteration.	2103	lots of events in one iteration.
1911		2104
1912	The relative timeouts are calculated relative to the C<ev_now ()>	2105	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	2106	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	2107	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	2108	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:	2109	timeout on the current time, use something like the following to adjust
		2110	for it:
1917		2111
1918	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2112	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1919		2113
1920	If the event loop is suspended for a long time, you can also force an	2114	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	2115	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1922	()>.	2116	()>, although that will push the event time of all outstanding events
		2117	further into the future.
		2118
		2119	=head3 The special problem of unsynchronised clocks
		2120
		2121	Modern systems have a variety of clocks - libev itself uses the normal
		2122	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2123	jumps).
		2124
		2125	Neither of these clocks is synchronised with each other or any other clock
		2126	on the system, so C<ev_time ()> might return a considerably different time
		2127	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2128	a call to C<gettimeofday> might return a second count that is one higher
		2129	than a directly following call to C<time>.
		2130
		2131	The moral of this is to only compare libev-related timestamps with
		2132	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2133	a second or so.
		2134
		2135	One more problem arises due to this lack of synchronisation: if libev uses
		2136	the system monotonic clock and you compare timestamps from C<ev_time>
		2137	or C<ev_now> from when you started your timer and when your callback is
		2138	invoked, you will find that sometimes the callback is a bit "early".
		2139
		2140	This is because C<ev_timer>s work in real time, not wall clock time, so
		2141	libev makes sure your callback is not invoked before the delay happened,
		2142	I<measured according to the real time>, not the system clock.
		2143
		2144	If your timeouts are based on a physical timescale (e.g. "time out this
		2145	connection after 100 seconds") then this shouldn't bother you as it is
		2146	exactly the right behaviour.
		2147
		2148	If you want to compare wall clock/system timestamps to your timers, then
		2149	you need to use C<ev_periodic>s, as these are based on the wall clock
		2150	time, where your comparisons will always generate correct results.
1923		2151
1924	=head3 The special problems of suspended animation	2152	=head3 The special problems of suspended animation
1925		2153
1926	When you leave the server world it is quite customary to hit machines that	2154	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?	2155	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1957		2185
1958	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2186	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1959		2187
1960	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2188	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1961		2189
1962	Configure the timer to trigger after C<after> seconds. If C<repeat>	2190	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	2191	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	2192	automatically be stopped once the timeout is reached. If it is positive,
1965	configured to trigger again C<repeat> seconds later, again, and again,	2193	then the timer will automatically be configured to trigger again C<repeat>
1966	until stopped manually.	2194	seconds later, again, and again, until stopped manually.
1967		2195
1968	The timer itself will do a best-effort at avoiding drift, that is, if	2196	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	2197	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	2198	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	2199	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.	2200	do stuff) the timer will not fire more than once per event loop iteration.
1973		2201
1974	=item ev_timer_again (loop, ev_timer *)	2202	=item ev_timer_again (loop, ev_timer *)
1975		2203
1976	This will act as if the timer timed out and restart it again if it is	2204	This will act as if the timer timed out, and restarts it again if it is
1977	repeating. The exact semantics are:	2205	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2206	timeout to the C<repeat> value and calling C<ev_timer_start>.
1978		2207
		2208	The exact semantics are as in the following rules, all of which will be
		2209	applied to the watcher:
		2210
		2211	=over 4
		2212
1979	If the timer is pending, its pending status is cleared.	2213	=item If the timer is pending, the pending status is always cleared.
1980		2214
1981	If the timer is started but non-repeating, stop it (as if it timed out).	2215	=item If the timer is started but non-repeating, stop it (as if it timed
		2216	out, without invoking it).
1982		2217
1983	If the timer is repeating, either start it if necessary (with the	2218	=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.	2219	and start the timer, if necessary.
1985		2220
		2221	=back
		2222
1986	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2223	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1987	usage example.	2224	usage example.
1988		2225
1989	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2226	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1990		2227
1991	Returns the remaining time until a timer fires. If the timer is active,	2228	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	2281	Periodic watchers are also timers of a kind, but they are very versatile
2045	(and unfortunately a bit complex).	2282	(and unfortunately a bit complex).
2046		2283
2047	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2284	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	2285	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	2286	(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	2287	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	2288	time, and time jumps are not uncommon (e.g. when you adjust your
2052	wrist-watch).	2289	wrist-watch).
2053		2290
2054	You can tell a periodic watcher to trigger after some specific point	2291	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	2296	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2060	it, as it uses a relative timeout).	2297	it, as it uses a relative timeout).
2061		2298
2062	C<ev_periodic> watchers can also be used to implement vastly more complex	2299	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	2300	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	2301	other complicated rules. This cannot easily be done with C<ev_timer>
2065	those cannot react to time jumps.	2302	watchers, as those cannot react to time jumps.
2066		2303
2067	As with timers, the callback is guaranteed to be invoked only when the	2304	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	2305	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	2306	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	2307	earlier time-out values are invoked before ones with later time-out values
…		…
2111		2348
2112	Another way to think about it (for the mathematically inclined) is that	2349	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	2350	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.	2351	time where C<time = offset (mod interval)>, regardless of any time jumps.
2115		2352
2116	For numerical stability it is preferable that the C<offset> value is near	2353	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	2354	interval value should be higher than C<1/8192> (which is around 100
2118	this value, and in fact is often specified as zero.	2355	microseconds) and C<offset> should be higher than C<0> and should have
		2356	at most a similar magnitude as the current time (say, within a factor of
		2357	ten). Typical values for offset are, in fact, C<0> or something between
		2358	C<0> and C<interval>, which is also the recommended range.
2119		2359
2120	Note also that there is an upper limit to how often a timer can fire (CPU	2360	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	2361	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	2362	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).	2363	millisecond (if the OS supports it and the machine is fast enough).
…		…
2153		2393
2154	NOTE: I<< This callback must always return a time that is higher than or	2394	NOTE: I<< This callback must always return a time that is higher than or
2155	equal to the passed C<now> value >>.	2395	equal to the passed C<now> value >>.
2156		2396
2157	This can be used to create very complex timers, such as a timer that	2397	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	2398	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	2399	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	2400	this. Here is a (completely untested, no error checking) example on how to
2161	reason I omitted it as an example).	2401	do this:
		2402
		2403	#include <time.h>
		2404
		2405	static ev_tstamp
		2406	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2407	{
		2408	time_t tnow = (time_t)now;
		2409	struct tm tm;
		2410	localtime_r (&tnow, &tm);
		2411
		2412	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2413	++tm.tm_mday; // midnight next day
		2414
		2415	return mktime (&tm);
		2416	}
		2417
		2418	Note: this code might run into trouble on days that have more then two
		2419	midnights (beginning and end).
2162		2420
2163	=back	2421	=back
2164		2422
2165	=item ev_periodic_again (loop, ev_periodic *)	2423	=item ev_periodic_again (loop, ev_periodic *)
2166		2424
…		…
2231		2489
2232	ev_periodic hourly_tick;	2490	ev_periodic hourly_tick;
2233	ev_periodic_init (&hourly_tick, clock_cb,	2491	ev_periodic_init (&hourly_tick, clock_cb,
2234	fmod (ev_now (loop), 3600.), 3600., 0);	2492	fmod (ev_now (loop), 3600.), 3600., 0);
2235	ev_periodic_start (loop, &hourly_tick);	2493	ev_periodic_start (loop, &hourly_tick);
2236		2494
2237		2495
2238	=head2 C<ev_signal> - signal me when a signal gets signalled!	2496	=head2 C<ev_signal> - signal me when a signal gets signalled!
2239		2497
2240	Signal watchers will trigger an event when the process receives a specific	2498	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	2499	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	2500	will try its best to deliver signals synchronously, i.e. as part of the
2243	normal event processing, like any other event.	2501	normal event processing, like any other event.
2244		2502
2245	If you want signals to be delivered truly asynchronously, just use	2503	If you want signals to be delivered truly asynchronously, just use
2246	C<sigaction> as you would do without libev and forget about sharing	2504	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	2505	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	2509	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	2510	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	2511	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.	2512	the moment, C<SIGCHLD> is permanently tied to the default loop.
2255		2513
2256	When the first watcher gets started will libev actually register something	2514	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	2515	register something with the kernel. It thus coexists with your own signal
2258	you don't register any with libev for the same signal).	2516	handlers as long as you don't register any with libev for the same signal.
2259		2517
2260	If possible and supported, libev will install its handlers with	2518	If possible and supported, libev will install its handlers with
2261	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2519	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	2520	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	2521	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	2524	=head3 The special problem of inheritance over fork/execve/pthread_create
2267		2525
2268	Both the signal mask (C<sigprocmask>) and the signal disposition	2526	Both the signal mask (C<sigprocmask>) and the signal disposition
2269	(C<sigaction>) are unspecified after starting a signal watcher (and after	2527	(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,	2528	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.	2529	and might or might not set or restore the installed signal handler (but
		2530	see C<EVFLAG_NOSIGMASK>).
2272		2531
2273	While this does not matter for the signal disposition (libev never	2532	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	2533	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	2534	C<execve>), this matters for the signal mask: many programs do not expect
2276	certain signals to be blocked.	2535	certain signals to be blocked.
…		…
2289	I<has> to modify the signal mask, at least temporarily.	2548	I<has> to modify the signal mask, at least temporarily.
2290		2549
2291	So I can't stress this enough: I<If you do not reset your signal mask when	2550	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	2551	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.	2552	is not a libev-specific thing, this is true for most event libraries.
		2553
		2554	=head3 The special problem of threads signal handling
		2555
		2556	POSIX threads has problematic signal handling semantics, specifically,
		2557	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2558	threads in a process block signals, which is hard to achieve.
		2559
		2560	When you want to use sigwait (or mix libev signal handling with your own
		2561	for the same signals), you can tackle this problem by globally blocking
		2562	all signals before creating any threads (or creating them with a fully set
		2563	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2564	loops. Then designate one thread as "signal receiver thread" which handles
		2565	these signals. You can pass on any signals that libev might be interested
		2566	in by calling C<ev_feed_signal>.
2294		2567
2295	=head3 Watcher-Specific Functions and Data Members	2568	=head3 Watcher-Specific Functions and Data Members
2296		2569
2297	=over 4	2570	=over 4
2298		2571
…		…
2433		2706
2434	=head2 C<ev_stat> - did the file attributes just change?	2707	=head2 C<ev_stat> - did the file attributes just change?
2435		2708
2436	This watches a file system path for attribute changes. That is, it calls	2709	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)	2710	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	2711	and sees if it changed compared to the last time, invoking the callback
2439	it did.	2712	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2713	happen after the watcher has been started will be reported.
2440		2714
2441	The path does not need to exist: changing from "path exists" to "path does	2715	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	2716	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	2717	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	2718	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	2948	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	2949	effect on its own sometimes), idle watchers are a good place to do
2676	"pseudo-background processing", or delay processing stuff to after the	2950	"pseudo-background processing", or delay processing stuff to after the
2677	event loop has handled all outstanding events.	2951	event loop has handled all outstanding events.
2678		2952
		2953	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2954
		2955	As long as there is at least one active idle watcher, libev will never
		2956	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2957	For this to work, the idle watcher doesn't need to be invoked at all - the
		2958	lowest priority will do.
		2959
		2960	This mode of operation can be useful together with an C<ev_check> watcher,
		2961	to do something on each event loop iteration - for example to balance load
		2962	between different connections.
		2963
		2964	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2965	example.
		2966
2679	=head3 Watcher-Specific Functions and Data Members	2967	=head3 Watcher-Specific Functions and Data Members
2680		2968
2681	=over 4	2969	=over 4
2682		2970
2683	=item ev_idle_init (ev_idle *, callback)	2971	=item ev_idle_init (ev_idle *, callback)
…		…
2694	callback, free it. Also, use no error checking, as usual.	2982	callback, free it. Also, use no error checking, as usual.
2695		2983
2696	static void	2984	static void
2697	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2985	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2698	{	2986	{
		2987	// stop the watcher
		2988	ev_idle_stop (loop, w);
		2989
		2990	// now we can free it
2699	free (w);	2991	free (w);
		2992
2700	// now do something you wanted to do when the program has	2993	// now do something you wanted to do when the program has
2701	// no longer anything immediate to do.	2994	// no longer anything immediate to do.
2702	}	2995	}
2703		2996
2704	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2997	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2706	ev_idle_start (loop, idle_watcher);	2999	ev_idle_start (loop, idle_watcher);
2707		3000
2708		3001
2709	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3002	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2710		3003
2711	Prepare and check watchers are usually (but not always) used in pairs:	3004	Prepare and check watchers are often (but not always) used in pairs:
2712	prepare watchers get invoked before the process blocks and check watchers	3005	prepare watchers get invoked before the process blocks and check watchers
2713	afterwards.	3006	afterwards.
2714		3007
2715	You I<must not> call C<ev_run> or similar functions that enter	3008	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>	3009	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	3010	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	3011	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,	3012	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	3013	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2721	called in pairs bracketing the blocking call.	3014	kind they will always be called in pairs bracketing the blocking call.
2722		3015
2723	Their main purpose is to integrate other event mechanisms into libev and	3016	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	3017	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	3018	variable changes, implement your own watchers, integrate net-snmp or a
2726	coroutine library and lots more. They are also occasionally useful if	3019	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	3037	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	3038	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	3039	loop from blocking if lower-priority coroutines are active, thus mapping
2747	low-priority coroutines to idle/background tasks).	3040	low-priority coroutines to idle/background tasks).
2748		3041
2749	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3042	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	3043	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).	3044	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3045	watchers).
2752		3046
2753	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3047	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	3048	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	3049	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	3050	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	3051	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	3052	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2759	others).	3053	others).
		3054
		3055	=head3 Abusing an C<ev_check> watcher for its side-effect
		3056
		3057	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3058	useful because they are called once per event loop iteration. For
		3059	example, if you want to handle a large number of connections fairly, you
		3060	normally only do a bit of work for each active connection, and if there
		3061	is more work to do, you wait for the next event loop iteration, so other
		3062	connections have a chance of making progress.
		3063
		3064	Using an C<ev_check> watcher is almost enough: it will be called on the
		3065	next event loop iteration. However, that isn't as soon as possible -
		3066	without external events, your C<ev_check> watcher will not be invoked.
		3067
		3068	This is where C<ev_idle> watchers come in handy - all you need is a
		3069	single global idle watcher that is active as long as you have one active
		3070	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3071	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3072	invoked. Neither watcher alone can do that.
2760		3073
2761	=head3 Watcher-Specific Functions and Data Members	3074	=head3 Watcher-Specific Functions and Data Members
2762		3075
2763	=over 4	3076	=over 4
2764		3077
…		…
2965		3278
2966	=over 4	3279	=over 4
2967		3280
2968	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3281	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2969		3282
2970	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3283	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2971		3284
2972	Configures the watcher to embed the given loop, which must be	3285	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	3286	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	3287	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,	3288	to invoke it (it will continue to be called until the sweep has been done,
…		…
2996	used).	3309	used).
2997		3310
2998	struct ev_loop *loop_hi = ev_default_init (0);	3311	struct ev_loop *loop_hi = ev_default_init (0);
2999	struct ev_loop *loop_lo = 0;	3312	struct ev_loop *loop_lo = 0;
3000	ev_embed embed;	3313	ev_embed embed;
3001		3314
3002	// see if there is a chance of getting one that works	3315	// see if there is a chance of getting one that works
3003	// (remember that a flags value of 0 means autodetection)	3316	// (remember that a flags value of 0 means autodetection)
3004	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3317	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3005	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3318	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3006	: 0;	3319	: 0;
…		…
3020	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3333	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3021		3334
3022	struct ev_loop *loop = ev_default_init (0);	3335	struct ev_loop *loop = ev_default_init (0);
3023	struct ev_loop *loop_socket = 0;	3336	struct ev_loop *loop_socket = 0;
3024	ev_embed embed;	3337	ev_embed embed;
3025		3338
3026	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3339	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3027	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3340	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3028	{	3341	{
3029	ev_embed_init (&embed, 0, loop_socket);	3342	ev_embed_init (&embed, 0, loop_socket);
3030	ev_embed_start (loop, &embed);	3343	ev_embed_start (loop, &embed);
…		…
3038		3351
3039	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3352	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3040		3353
3041	Fork watchers are called when a C<fork ()> was detected (usually because	3354	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	3355	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	3356	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,	3357	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	3358	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	3359	and calls it in the wrong process, the fork handlers will be invoked, too,
3047	handlers will be invoked, too, of course.	3360	of course.
3048		3361
3049	=head3 The special problem of life after fork - how is it possible?	3362	=head3 The special problem of life after fork - how is it possible?
3050		3363
3051	Most uses of C<fork()> consist of forking, then some simple calls to set	3364	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	3365	up/change the process environment, followed by a call to C<exec()>. This
3053	sequence should be handled by libev without any problems.	3366	sequence should be handled by libev without any problems.
3054		3367
3055	This changes when the application actually wants to do event handling	3368	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	3369	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	3385	disadvantage of having to use multiple event loops (which do not support
3073	signal watchers).	3386	signal watchers).
3074		3387
3075	When this is not possible, or you want to use the default loop for	3388	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	3389	other reasons, then in the process that wants to start "fresh", call
3077	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying	3390	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	3391	Destroying the default loop will "orphan" (not stop) all registered
3079	have to be careful not to execute code that modifies those watchers. Note	3392	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.	3393	those watchers. Note also that in that case, you have to re-register any
		3394	signal watchers.
3081		3395
3082	=head3 Watcher-Specific Functions and Data Members	3396	=head3 Watcher-Specific Functions and Data Members
3083		3397
3084	=over 4	3398	=over 4
3085		3399
3086	=item ev_fork_init (ev_signal *, callback)	3400	=item ev_fork_init (ev_fork *, callback)
3087		3401
3088	Initialises and configures the fork watcher - it has no parameters of any	3402	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,	3403	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3090	believe me.	3404	really.
3091		3405
3092	=back	3406	=back
3093		3407
3094		3408
		3409	=head2 C<ev_cleanup> - even the best things end
		3410
		3411	Cleanup watchers are called just before the event loop is being destroyed
		3412	by a call to C<ev_loop_destroy>.
		3413
		3414	While there is no guarantee that the event loop gets destroyed, cleanup
		3415	watchers provide a convenient method to install cleanup hooks for your
		3416	program, worker threads and so on - you just to make sure to destroy the
		3417	loop when you want them to be invoked.
		3418
		3419	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3420	all other watchers, they do not keep a reference to the event loop (which
		3421	makes a lot of sense if you think about it). Like all other watchers, you
		3422	can call libev functions in the callback, except C<ev_cleanup_start>.
		3423
		3424	=head3 Watcher-Specific Functions and Data Members
		3425
		3426	=over 4
		3427
		3428	=item ev_cleanup_init (ev_cleanup *, callback)
		3429
		3430	Initialises and configures the cleanup watcher - it has no parameters of
		3431	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3432	pointless, I assure you.
		3433
		3434	=back
		3435
		3436	Example: Register an atexit handler to destroy the default loop, so any
		3437	cleanup functions are called.
		3438
		3439	static void
		3440	program_exits (void)
		3441	{
		3442	ev_loop_destroy (EV_DEFAULT_UC);
		3443	}
		3444
		3445	...
		3446	atexit (program_exits);
		3447
		3448
3095	=head2 C<ev_async> - how to wake up an event loop	3449	=head2 C<ev_async> - how to wake up an event loop
3096		3450
3097	In general, you cannot use an C<ev_run> from multiple threads or other	3451	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	3452	asynchronous sources such as signal handlers (as opposed to multiple event
3099	loops - those are of course safe to use in different threads).	3453	loops - those are of course safe to use in different threads).
3100		3454
3101	Sometimes, however, you need to wake up an event loop you do not control,	3455	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>	3456	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.	3458	it by calling C<ev_async_send>, which is thread- and signal safe.
3105		3459
3106	This functionality is very similar to C<ev_signal> watchers, as signals,	3460	This functionality is very similar to C<ev_signal> watchers, as signals,
3107	too, are asynchronous in nature, and signals, too, will be compressed	3461	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	3462	(i.e. the number of callback invocations may be less than the number of
3109	C<ev_async_sent> calls).	3463	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3110		3464	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	3465	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3112	just the default loop.	3466	even without knowing which loop owns the signal.
3113		3467
3114	=head3 Queueing	3468	=head3 Queueing
3115		3469
3116	C<ev_async> does not support queueing of data in any way. The reason	3470	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	3471	is that the author does not know of a simple (or any) algorithm for a
…		…
3209	trust me.	3563	trust me.
3210		3564
3211	=item ev_async_send (loop, ev_async *)	3565	=item ev_async_send (loop, ev_async *)
3212		3566
3213	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3567	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	3568	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3569	returns.
		3570
3215	C<ev_feed_event>, this call is safe to do from other threads, signal or	3571	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	3572	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3217	section below on what exactly this means).	3573	embedding section below on what exactly this means).
3218		3574
3219	Note that, as with other watchers in libev, multiple events might get	3575	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	3576	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>,	3577	this is that C<ev_async> watchers are level-triggered: they are set on
3222	reset when the event loop detects that).	3578	C<ev_async_send>, reset when the event loop detects that).
3223		3579
3224	This call incurs the overhead of a system call only once per event loop	3580	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	3581	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.	3582	the event loop (or your program) is processing events. That means that
		3583	repeated calls are basically free (there is no need to avoid calls for
		3584	performance reasons) and that the overhead becomes smaller (typically
		3585	zero) under load.
3227		3586
3228	=item bool = ev_async_pending (ev_async *)	3587	=item bool = ev_async_pending (ev_async *)
3229		3588
3230	Returns a non-zero value when C<ev_async_send> has been called on the	3589	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	3590	watcher but the event has not yet been processed (or even noted) by the
…		…
3248		3607
3249	There are some other functions of possible interest. Described. Here. Now.	3608	There are some other functions of possible interest. Described. Here. Now.
3250		3609
3251	=over 4	3610	=over 4
3252		3611
3253	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3612	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3254		3613
3255	This function combines a simple timer and an I/O watcher, calls your	3614	This function combines a simple timer and an I/O watcher, calls your
3256	callback on whichever event happens first and automatically stops both	3615	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	3616	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	3617	or timeout without having to allocate/configure/start/stop/free one or
…		…
3286	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3645	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3287		3646
3288	=item ev_feed_fd_event (loop, int fd, int revents)	3647	=item ev_feed_fd_event (loop, int fd, int revents)
3289		3648
3290	Feed an event on the given fd, as if a file descriptor backend detected	3649	Feed an event on the given fd, as if a file descriptor backend detected
3291	the given events it.	3650	the given events.
3292		3651
3293	=item ev_feed_signal_event (loop, int signum)	3652	=item ev_feed_signal_event (loop, int signum)
3294		3653
3295	Feed an event as if the given signal occurred (C<loop> must be the default	3654	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3296	loop!).	3655	which is async-safe.
3297		3656
3298	=back	3657	=back
		3658
		3659
		3660	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3661
		3662	This section explains some common idioms that are not immediately
		3663	obvious. Note that examples are sprinkled over the whole manual, and this
		3664	section only contains stuff that wouldn't fit anywhere else.
		3665
		3666	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3667
		3668	Each watcher has, by default, a C<void *data> member that you can read
		3669	or modify at any time: libev will completely ignore it. This can be used
		3670	to associate arbitrary data with your watcher. If you need more data and
		3671	don't want to allocate memory separately and store a pointer to it in that
		3672	data member, you can also "subclass" the watcher type and provide your own
		3673	data:
		3674
		3675	struct my_io
		3676	{
		3677	ev_io io;
		3678	int otherfd;
		3679	void *somedata;
		3680	struct whatever *mostinteresting;
		3681	};
		3682
		3683	...
		3684	struct my_io w;
		3685	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3686
		3687	And since your callback will be called with a pointer to the watcher, you
		3688	can cast it back to your own type:
		3689
		3690	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3691	{
		3692	struct my_io *w = (struct my_io *)w_;
		3693	...
		3694	}
		3695
		3696	More interesting and less C-conformant ways of casting your callback
		3697	function type instead have been omitted.
		3698
		3699	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3700
		3701	Another common scenario is to use some data structure with multiple
		3702	embedded watchers, in effect creating your own watcher that combines
		3703	multiple libev event sources into one "super-watcher":
		3704
		3705	struct my_biggy
		3706	{
		3707	int some_data;
		3708	ev_timer t1;
		3709	ev_timer t2;
		3710	}
		3711
		3712	In this case getting the pointer to C<my_biggy> is a bit more
		3713	complicated: Either you store the address of your C<my_biggy> struct in
		3714	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3715	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3716	real programmers):
		3717
		3718	#include <stddef.h>
		3719
		3720	static void
		3721	t1_cb (EV_P_ ev_timer *w, int revents)
		3722	{
		3723	struct my_biggy big = (struct my_biggy *)
		3724	(((char *)w) - offsetof (struct my_biggy, t1));
		3725	}
		3726
		3727	static void
		3728	t2_cb (EV_P_ ev_timer *w, int revents)
		3729	{
		3730	struct my_biggy big = (struct my_biggy *)
		3731	(((char *)w) - offsetof (struct my_biggy, t2));
		3732	}
		3733
		3734	=head2 AVOIDING FINISHING BEFORE RETURNING
		3735
		3736	Often you have structures like this in event-based programs:
		3737
		3738	callback ()
		3739	{
		3740	free (request);
		3741	}
		3742
		3743	request = start_new_request (..., callback);
		3744
		3745	The intent is to start some "lengthy" operation. The C<request> could be
		3746	used to cancel the operation, or do other things with it.
		3747
		3748	It's not uncommon to have code paths in C<start_new_request> that
		3749	immediately invoke the callback, for example, to report errors. Or you add
		3750	some caching layer that finds that it can skip the lengthy aspects of the
		3751	operation and simply invoke the callback with the result.
		3752
		3753	The problem here is that this will happen I<before> C<start_new_request>
		3754	has returned, so C<request> is not set.
		3755
		3756	Even if you pass the request by some safer means to the callback, you
		3757	might want to do something to the request after starting it, such as
		3758	canceling it, which probably isn't working so well when the callback has
		3759	already been invoked.
		3760
		3761	A common way around all these issues is to make sure that
		3762	C<start_new_request> I<always> returns before the callback is invoked. If
		3763	C<start_new_request> immediately knows the result, it can artificially
		3764	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3765	example, or more sneakily, by reusing an existing (stopped) watcher and
		3766	pushing it into the pending queue:
		3767
		3768	ev_set_cb (watcher, callback);
		3769	ev_feed_event (EV_A_ watcher, 0);
		3770
		3771	This way, C<start_new_request> can safely return before the callback is
		3772	invoked, while not delaying callback invocation too much.
		3773
		3774	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3775
		3776	Often (especially in GUI toolkits) there are places where you have
		3777	I<modal> interaction, which is most easily implemented by recursively
		3778	invoking C<ev_run>.
		3779
		3780	This brings the problem of exiting - a callback might want to finish the
		3781	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3782	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3783	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3784	other combination: In these cases, a simple C<ev_break> will not work.
		3785
		3786	The solution is to maintain "break this loop" variable for each C<ev_run>
		3787	invocation, and use a loop around C<ev_run> until the condition is
		3788	triggered, using C<EVRUN_ONCE>:
		3789
		3790	// main loop
		3791	int exit_main_loop = 0;
		3792
		3793	while (!exit_main_loop)
		3794	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3795
		3796	// in a modal watcher
		3797	int exit_nested_loop = 0;
		3798
		3799	while (!exit_nested_loop)
		3800	ev_run (EV_A_ EVRUN_ONCE);
		3801
		3802	To exit from any of these loops, just set the corresponding exit variable:
		3803
		3804	// exit modal loop
		3805	exit_nested_loop = 1;
		3806
		3807	// exit main program, after modal loop is finished
		3808	exit_main_loop = 1;
		3809
		3810	// exit both
		3811	exit_main_loop = exit_nested_loop = 1;
		3812
		3813	=head2 THREAD LOCKING EXAMPLE
		3814
		3815	Here is a fictitious example of how to run an event loop in a different
		3816	thread from where callbacks are being invoked and watchers are
		3817	created/added/removed.
		3818
		3819	For a real-world example, see the C<EV::Loop::Async> perl module,
		3820	which uses exactly this technique (which is suited for many high-level
		3821	languages).
		3822
		3823	The example uses a pthread mutex to protect the loop data, a condition
		3824	variable to wait for callback invocations, an async watcher to notify the
		3825	event loop thread and an unspecified mechanism to wake up the main thread.
		3826
		3827	First, you need to associate some data with the event loop:
		3828
		3829	typedef struct {
		3830	mutex_t lock; /* global loop lock */
		3831	ev_async async_w;
		3832	thread_t tid;
		3833	cond_t invoke_cv;
		3834	} userdata;
		3835
		3836	void prepare_loop (EV_P)
		3837	{
		3838	// for simplicity, we use a static userdata struct.
		3839	static userdata u;
		3840
		3841	ev_async_init (&u->async_w, async_cb);
		3842	ev_async_start (EV_A_ &u->async_w);
		3843
		3844	pthread_mutex_init (&u->lock, 0);
		3845	pthread_cond_init (&u->invoke_cv, 0);
		3846
		3847	// now associate this with the loop
		3848	ev_set_userdata (EV_A_ u);
		3849	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3850	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3851
		3852	// then create the thread running ev_run
		3853	pthread_create (&u->tid, 0, l_run, EV_A);
		3854	}
		3855
		3856	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3857	solely to wake up the event loop so it takes notice of any new watchers
		3858	that might have been added:
		3859
		3860	static void
		3861	async_cb (EV_P_ ev_async *w, int revents)
		3862	{
		3863	// just used for the side effects
		3864	}
		3865
		3866	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3867	protecting the loop data, respectively.
		3868
		3869	static void
		3870	l_release (EV_P)
		3871	{
		3872	userdata *u = ev_userdata (EV_A);
		3873	pthread_mutex_unlock (&u->lock);
		3874	}
		3875
		3876	static void
		3877	l_acquire (EV_P)
		3878	{
		3879	userdata *u = ev_userdata (EV_A);
		3880	pthread_mutex_lock (&u->lock);
		3881	}
		3882
		3883	The event loop thread first acquires the mutex, and then jumps straight
		3884	into C<ev_run>:
		3885
		3886	void *
		3887	l_run (void *thr_arg)
		3888	{
		3889	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3890
		3891	l_acquire (EV_A);
		3892	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3893	ev_run (EV_A_ 0);
		3894	l_release (EV_A);
		3895
		3896	return 0;
		3897	}
		3898
		3899	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3900	signal the main thread via some unspecified mechanism (signals? pipe
		3901	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3902	have been called (in a while loop because a) spurious wakeups are possible
		3903	and b) skipping inter-thread-communication when there are no pending
		3904	watchers is very beneficial):
		3905
		3906	static void
		3907	l_invoke (EV_P)
		3908	{
		3909	userdata *u = ev_userdata (EV_A);
		3910
		3911	while (ev_pending_count (EV_A))
		3912	{
		3913	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3914	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3915	}
		3916	}
		3917
		3918	Now, whenever the main thread gets told to invoke pending watchers, it
		3919	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3920	thread to continue:
		3921
		3922	static void
		3923	real_invoke_pending (EV_P)
		3924	{
		3925	userdata *u = ev_userdata (EV_A);
		3926
		3927	pthread_mutex_lock (&u->lock);
		3928	ev_invoke_pending (EV_A);
		3929	pthread_cond_signal (&u->invoke_cv);
		3930	pthread_mutex_unlock (&u->lock);
		3931	}
		3932
		3933	Whenever you want to start/stop a watcher or do other modifications to an
		3934	event loop, you will now have to lock:
		3935
		3936	ev_timer timeout_watcher;
		3937	userdata *u = ev_userdata (EV_A);
		3938
		3939	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3940
		3941	pthread_mutex_lock (&u->lock);
		3942	ev_timer_start (EV_A_ &timeout_watcher);
		3943	ev_async_send (EV_A_ &u->async_w);
		3944	pthread_mutex_unlock (&u->lock);
		3945
		3946	Note that sending the C<ev_async> watcher is required because otherwise
		3947	an event loop currently blocking in the kernel will have no knowledge
		3948	about the newly added timer. By waking up the loop it will pick up any new
		3949	watchers in the next event loop iteration.
		3950
		3951	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3952
		3953	While the overhead of a callback that e.g. schedules a thread is small, it
		3954	is still an overhead. If you embed libev, and your main usage is with some
		3955	kind of threads or coroutines, you might want to customise libev so that
		3956	doesn't need callbacks anymore.
		3957
		3958	Imagine you have coroutines that you can switch to using a function
		3959	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3960	and that due to some magic, the currently active coroutine is stored in a
		3961	global called C<current_coro>. Then you can build your own "wait for libev
		3962	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3963	the differing C<;> conventions):
		3964
		3965	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3966	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3967
		3968	That means instead of having a C callback function, you store the
		3969	coroutine to switch to in each watcher, and instead of having libev call
		3970	your callback, you instead have it switch to that coroutine.
		3971
		3972	A coroutine might now wait for an event with a function called
		3973	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3974	matter when, or whether the watcher is active or not when this function is
		3975	called):
		3976
		3977	void
		3978	wait_for_event (ev_watcher *w)
		3979	{
		3980	ev_set_cb (w, current_coro);
		3981	switch_to (libev_coro);
		3982	}
		3983
		3984	That basically suspends the coroutine inside C<wait_for_event> and
		3985	continues the libev coroutine, which, when appropriate, switches back to
		3986	this or any other coroutine.
		3987
		3988	You can do similar tricks if you have, say, threads with an event queue -
		3989	instead of storing a coroutine, you store the queue object and instead of
		3990	switching to a coroutine, you push the watcher onto the queue and notify
		3991	any waiters.
		3992
		3993	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3994	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3995
		3996	// my_ev.h
		3997	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3998	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3999	#include "../libev/ev.h"
		4000
		4001	// my_ev.c
		4002	#define EV_H "my_ev.h"
		4003	#include "../libev/ev.c"
		4004
		4005	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4006	F<my_ev.c> into your project. When properly specifying include paths, you
		4007	can even use F<ev.h> as header file name directly.
3299		4008
3300		4009
3301	=head1 LIBEVENT EMULATION	4010	=head1 LIBEVENT EMULATION
3302		4011
3303	Libev offers a compatibility emulation layer for libevent. It cannot	4012	Libev offers a compatibility emulation layer for libevent. It cannot
3304	emulate the internals of libevent, so here are some usage hints:	4013	emulate the internals of libevent, so here are some usage hints:
3305		4014
3306	=over 4	4015	=over 4
		4016
		4017	=item * Only the libevent-1.4.1-beta API is being emulated.
		4018
		4019	This was the newest libevent version available when libev was implemented,
		4020	and is still mostly unchanged in 2010.
3307		4021
3308	=item * Use it by including <event.h>, as usual.	4022	=item * Use it by including <event.h>, as usual.
3309		4023
3310	=item * The following members are fully supported: ev_base, ev_callback,	4024	=item * The following members are fully supported: ev_base, ev_callback,
3311	ev_arg, ev_fd, ev_res, ev_events.	4025	ev_arg, ev_fd, ev_res, ev_events.
…		…
3317	=item * Priorities are not currently supported. Initialising priorities	4031	=item * Priorities are not currently supported. Initialising priorities
3318	will fail and all watchers will have the same priority, even though there	4032	will fail and all watchers will have the same priority, even though there
3319	is an ev_pri field.	4033	is an ev_pri field.
3320		4034
3321	=item * In libevent, the last base created gets the signals, in libev, the	4035	=item * In libevent, the last base created gets the signals, in libev, the
3322	first base created (== the default loop) gets the signals.	4036	base that registered the signal gets the signals.
3323		4037
3324	=item * Other members are not supported.	4038	=item * Other members are not supported.
3325		4039
3326	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4040	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3327	to use the libev header file and library.	4041	to use the libev header file and library.
3328		4042
3329	=back	4043	=back
3330		4044
3331	=head1 C++ SUPPORT	4045	=head1 C++ SUPPORT
		4046
		4047	=head2 C API
		4048
		4049	The normal C API should work fine when used from C++: both ev.h and the
		4050	libev sources can be compiled as C++. Therefore, code that uses the C API
		4051	will work fine.
		4052
		4053	Proper exception specifications might have to be added to callbacks passed
		4054	to libev: exceptions may be thrown only from watcher callbacks, all other
		4055	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4056	callbacks) must not throw exceptions, and might need a C<noexcept>
		4057	specification. If you have code that needs to be compiled as both C and
		4058	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4059
		4060	static void
		4061	fatal_error (const char *msg) EV_NOEXCEPT
		4062	{
		4063	perror (msg);
		4064	abort ();
		4065	}
		4066
		4067	...
		4068	ev_set_syserr_cb (fatal_error);
		4069
		4070	The only API functions that can currently throw exceptions are C<ev_run>,
		4071	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4072	because it runs cleanup watchers).
		4073
		4074	Throwing exceptions in watcher callbacks is only supported if libev itself
		4075	is compiled with a C++ compiler or your C and C++ environments allow
		4076	throwing exceptions through C libraries (most do).
		4077
		4078	=head2 C++ API
3332		4079
3333	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4080	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	4081	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.	4082	the callback model to a model using method callbacks on objects.
3336		4083
3337	To use it,	4084	To use it,
3338		4085
3339	#include <ev++.h>	4086	#include <ev++.h>
3340		4087
3341	This automatically includes F<ev.h> and puts all of its definitions (many	4088	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	4089	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	4090	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++	4093	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	4094	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	4095	that the watcher is associated with (or no additional members at all if
3349	you disable C<EV_MULTIPLICITY> when embedding libev).	4096	you disable C<EV_MULTIPLICITY> when embedding libev).
3350		4097
3351	Currently, functions, and static and non-static member functions can be	4098	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	4099	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	4100	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	4101	you need support for other types of functors please contact the author
3355	it).	4102	(preferably after implementing it).
		4103
		4104	For all this to work, your C++ compiler either has to use the same calling
		4105	conventions as your C compiler (for static member functions), or you have
		4106	to embed libev and compile libev itself as C++.
3356		4107
3357	Here is a list of things available in the C<ev> namespace:	4108	Here is a list of things available in the C<ev> namespace:
3358		4109
3359	=over 4	4110	=over 4
3360		4111
…		…
3370	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4121	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3371		4122
3372	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4123	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>	4124	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	4125	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3375	defines by many implementations.	4126	defined by many implementations.
3376		4127
3377	All of those classes have these methods:	4128	All of those classes have these methods:
3378		4129
3379	=over 4	4130	=over 4
3380		4131
…		…
3442	void operator() (ev::io &w, int revents)	4193	void operator() (ev::io &w, int revents)
3443	{	4194	{
3444	...	4195	...
3445	}	4196	}
3446	}	4197	}
3447		4198
3448	myfunctor f;	4199	myfunctor f;
3449		4200
3450	ev::io w;	4201	ev::io w;
3451	w.set (&f);	4202	w.set (&f);
3452		4203
…		…
3470	Associates a different C<struct ev_loop> with this watcher. You can only	4221	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).	4222	do this when the watcher is inactive (and not pending either).
3472		4223
3473	=item w->set ([arguments])	4224	=item w->set ([arguments])
3474		4225
3475	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4226	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	4227	with the same arguments. Either this method or a suitable start method
3477	C counterpart, an active watcher gets automatically stopped and restarted	4228	must be called at least once. Unlike the C counterpart, an active watcher
3478	when reconfiguring it with this method.	4229	gets automatically stopped and restarted when reconfiguring it with this
		4230	method.
		4231
		4232	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4233	clashing with the C<set (loop)> method.
3479		4234
3480	=item w->start ()	4235	=item w->start ()
3481		4236
3482	Starts the watcher. Note that there is no C<loop> argument, as the	4237	Starts the watcher. Note that there is no C<loop> argument, as the
3483	constructor already stores the event loop.	4238	constructor already stores the event loop.
…		…
3513	watchers in the constructor.	4268	watchers in the constructor.
3514		4269
3515	class myclass	4270	class myclass
3516	{	4271	{
3517	ev::io io ; void io_cb (ev::io &w, int revents);	4272	ev::io io ; void io_cb (ev::io &w, int revents);
3518	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4273	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3519	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4274	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3520		4275
3521	myclass (int fd)	4276	myclass (int fd)
3522	{	4277	{
3523	io .set <myclass, &myclass::io_cb > (this);	4278	io .set <myclass, &myclass::io_cb > (this);
…		…
3574	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4329	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3575		4330
3576	=item D	4331	=item D
3577		4332
3578	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4333	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>.	4334	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3580		4335
3581	=item Ocaml	4336	=item Ocaml
3582		4337
3583	Erkki Seppala has written Ocaml bindings for libev, to be found at	4338	Erkki Seppala has written Ocaml bindings for libev, to be found at
3584	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4339	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3587		4342
3588	Brian Maher has written a partial interface to libev for lua (at the	4343	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	4344	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3590	L<http://github.com/brimworks/lua-ev>.	4345	L<http://github.com/brimworks/lua-ev>.
3591		4346
		4347	=item Javascript
		4348
		4349	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4350
		4351	=item Others
		4352
		4353	There are others, and I stopped counting.
		4354
3592	=back	4355	=back
3593		4356
3594		4357
3595	=head1 MACRO MAGIC	4358	=head1 MACRO MAGIC
3596		4359
…		…
3632	suitable for use with C<EV_A>.	4395	suitable for use with C<EV_A>.
3633		4396
3634	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4397	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3635		4398
3636	Similar to the other two macros, this gives you the value of the default	4399	Similar to the other two macros, this gives you the value of the default
3637	loop, if multiple loops are supported ("ev loop default").	4400	loop, if multiple loops are supported ("ev loop default"). The default loop
		4401	will be initialised if it isn't already initialised.
		4402
		4403	For non-multiplicity builds, these macros do nothing, so you always have
		4404	to initialise the loop somewhere.
3638		4405
3639	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4406	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3640		4407
3641	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4408	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	4409	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3709	ev_vars.h	4476	ev_vars.h
3710	ev_wrap.h	4477	ev_wrap.h
3711		4478
3712	ev_win32.c required on win32 platforms only	4479	ev_win32.c required on win32 platforms only
3713		4480
3714	ev_select.c only when select backend is enabled (which is enabled by default)	4481	ev_select.c only when select backend is enabled
3715	ev_poll.c only when poll backend is enabled (disabled by default)	4482	ev_poll.c only when poll backend is enabled
3716	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4483	ev_epoll.c only when the epoll backend is enabled
		4484	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)	4485	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)	4486	ev_port.c only when the solaris port backend is enabled
3719		4487
3720	F<ev.c> includes the backend files directly when enabled, so you only need	4488	F<ev.c> includes the backend files directly when enabled, so you only need
3721	to compile this single file.	4489	to compile this single file.
3722		4490
3723	=head3 LIBEVENT COMPATIBILITY API	4491	=head3 LIBEVENT COMPATIBILITY API
…		…
3787	supported). It will also not define any of the structs usually found in	4555	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.	4556	F<event.h> that are not directly supported by the libev core alone.
3789		4557
3790	In standalone mode, libev will still try to automatically deduce the	4558	In standalone mode, libev will still try to automatically deduce the
3791	configuration, but has to be more conservative.	4559	configuration, but has to be more conservative.
		4560
		4561	=item EV_USE_FLOOR
		4562
		4563	If defined to be C<1>, libev will use the C<floor ()> function for its
		4564	periodic reschedule calculations, otherwise libev will fall back on a
		4565	portable (slower) implementation. If you enable this, you usually have to
		4566	link against libm or something equivalent. Enabling this when the C<floor>
		4567	function is not available will fail, so the safe default is to not enable
		4568	this.
3792		4569
3793	=item EV_USE_MONOTONIC	4570	=item EV_USE_MONOTONIC
3794		4571
3795	If defined to be C<1>, libev will try to detect the availability of the	4572	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	4573	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	4659	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	4660	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	4661	file descriptors again. Note that the replacement function has to close
3885	the underlying OS handle.	4662	the underlying OS handle.
3886		4663
		4664	=item EV_USE_WSASOCKET
		4665
		4666	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4667	communication socket, which works better in some environments. Otherwise,
		4668	the normal C<socket> function will be used, which works better in other
		4669	environments.
		4670
3887	=item EV_USE_POLL	4671	=item EV_USE_POLL
3888		4672
3889	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4673	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	4674	backend. Otherwise it will be enabled on non-win32 platforms. It
3891	takes precedence over select.	4675	takes precedence over select.
…		…
3895	If defined to be C<1>, libev will compile in support for the Linux	4679	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,	4680	C<epoll>(7) backend. Its availability will be detected at runtime,
3897	otherwise another method will be used as fallback. This is the preferred	4681	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	4682	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.	4683	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4684
		4685	=item EV_USE_LINUXAIO
		4686
		4687	If defined to be C<1>, libev will compile in support for the Linux
		4688	aio backend. Due to it's currenbt limitations it has to be requested
		4689	explicitly. If undefined, it will be enabled on linux, otherwise
		4690	disabled.
3900		4691
3901	=item EV_USE_KQUEUE	4692	=item EV_USE_KQUEUE
3902		4693
3903	If defined to be C<1>, libev will compile in support for the BSD style	4694	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,	4695	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	4717	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	4718	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	4719	be detected at runtime. If undefined, it will be enabled if the headers
3929	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4720	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3930		4721
		4722	=item EV_NO_SMP
		4723
		4724	If defined to be C<1>, libev will assume that memory is always coherent
		4725	between threads, that is, threads can be used, but threads never run on
		4726	different cpus (or different cpu cores). This reduces dependencies
		4727	and makes libev faster.
		4728
		4729	=item EV_NO_THREADS
		4730
		4731	If defined to be C<1>, libev will assume that it will never be called from
		4732	different threads (that includes signal handlers), which is a stronger
		4733	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4734	libev faster.
		4735
3931	=item EV_ATOMIC_T	4736	=item EV_ATOMIC_T
3932		4737
3933	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4738	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	4739	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	4740	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"	4741	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.	4742	handler "locking" as well as for signal and thread safety in C<ev_async>
		4743	watchers.
3938		4744
3939	In the absence of this define, libev will use C<sig_atomic_t volatile>	4745	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.	4746	(from F<signal.h>), which is usually good enough on most platforms.
3941		4747
3942	=item EV_H (h)	4748	=item EV_H (h)
…		…
3969	will have the C<struct ev_loop *> as first argument, and you can create	4775	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	4776	additional independent event loops. Otherwise there will be no support
3971	for multiple event loops and there is no first event loop pointer	4777	for multiple event loops and there is no first event loop pointer
3972	argument. Instead, all functions act on the single default loop.	4778	argument. Instead, all functions act on the single default loop.
3973		4779
		4780	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4781	default loop when multiplicity is switched off - you always have to
		4782	initialise the loop manually in this case.
		4783
3974	=item EV_MINPRI	4784	=item EV_MINPRI
3975		4785
3976	=item EV_MAXPRI	4786	=item EV_MAXPRI
3977		4787
3978	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4788	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4014	#define EV_USE_POLL 1	4824	#define EV_USE_POLL 1
4015	#define EV_CHILD_ENABLE 1	4825	#define EV_CHILD_ENABLE 1
4016	#define EV_ASYNC_ENABLE 1	4826	#define EV_ASYNC_ENABLE 1
4017		4827
4018	The actual value is a bitset, it can be a combination of the following	4828	The actual value is a bitset, it can be a combination of the following
4019	values:	4829	values (by default, all of these are enabled):
4020		4830
4021	=over 4	4831	=over 4
4022		4832
4023	=item C<1> - faster/larger code	4833	=item C<1> - faster/larger code
4024		4834
…		…
4028	code size by roughly 30% on amd64).	4838	code size by roughly 30% on amd64).
4029		4839
4030	When optimising for size, use of compiler flags such as C<-Os> with	4840	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	4841	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4032	assertions.	4842	assertions.
		4843
		4844	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4845	(e.g. gcc with C<-Os>).
4033		4846
4034	=item C<2> - faster/larger data structures	4847	=item C<2> - faster/larger data structures
4035		4848
4036	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4849	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	4850	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	4851	and can additionally have an effect on the size of data structures at
4039	runtime.	4852	runtime.
4040		4853
		4854	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4855	(e.g. gcc with C<-Os>).
		4856
4041	=item C<4> - full API configuration	4857	=item C<4> - full API configuration
4042		4858
4043	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4859	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4044	enables multiplicity (C<EV_MULTIPLICITY>=1).	4860	enables multiplicity (C<EV_MULTIPLICITY>=1).
4045		4861
…		…
4075		4891
4076	With an intelligent-enough linker (gcc+binutils are intelligent enough	4892	With an intelligent-enough linker (gcc+binutils are intelligent enough
4077	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4893	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	4894	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.	4895	I/O watcher then might come out at only 5Kb.
		4896
		4897	=item EV_API_STATIC
		4898
		4899	If this symbol is defined (by default it is not), then all identifiers
		4900	will have static linkage. This means that libev will not export any
		4901	identifiers, and you cannot link against libev anymore. This can be useful
		4902	when you embed libev, only want to use libev functions in a single file,
		4903	and do not want its identifiers to be visible.
		4904
		4905	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4906	wants to use libev.
		4907
		4908	This option only works when libev is compiled with a C compiler, as C++
		4909	doesn't support the required declaration syntax.
4080		4910
4081	=item EV_AVOID_STDIO	4911	=item EV_AVOID_STDIO
4082		4912
4083	If this is set to C<1> at compiletime, then libev will avoid using stdio	4913	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	4914	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:	5058	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4229		5059
4230	#include "ev_cpp.h"	5060	#include "ev_cpp.h"
4231	#include "ev.c"	5061	#include "ev.c"
4232		5062
4233	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5063	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4234		5064
4235	=head2 THREADS AND COROUTINES	5065	=head2 THREADS AND COROUTINES
4236		5066
4237	=head3 THREADS	5067	=head3 THREADS
4238		5068
…		…
4289	default loop and triggering an C<ev_async> watcher from the default loop	5119	default loop and triggering an C<ev_async> watcher from the default loop
4290	watcher callback into the event loop interested in the signal.	5120	watcher callback into the event loop interested in the signal.
4291		5121
4292	=back	5122	=back
4293		5123
4294	=head4 THREAD LOCKING EXAMPLE	5124	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		5125
4432	=head3 COROUTINES	5126	=head3 COROUTINES
4433		5127
4434	Libev is very accommodating to coroutines ("cooperative threads"):	5128	Libev is very accommodating to coroutines ("cooperative threads"):
4435	libev fully supports nesting calls to its functions from different	5129	libev fully supports nesting calls to its functions from different
…		…
4600	requires, and its I/O model is fundamentally incompatible with the POSIX	5294	requires, and its I/O model is fundamentally incompatible with the POSIX
4601	model. Libev still offers limited functionality on this platform in	5295	model. Libev still offers limited functionality on this platform in
4602	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5296	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4603	descriptors. This only applies when using Win32 natively, not when using	5297	descriptors. This only applies when using Win32 natively, not when using
4604	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5298	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4605	as every compielr comes with a slightly differently broken/incompatible	5299	as every compiler comes with a slightly differently broken/incompatible
4606	environment.	5300	environment.
4607		5301
4608	Lifting these limitations would basically require the full	5302	Lifting these limitations would basically require the full
4609	re-implementation of the I/O system. If you are into this kind of thing,	5303	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	5304	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	5398	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	5399	assumes that the same (machine) code can be used to call any watcher
4706	callback: The watcher callbacks have different type signatures, but libev	5400	callback: The watcher callbacks have different type signatures, but libev
4707	calls them using an C<ev_watcher *> internally.	5401	calls them using an C<ev_watcher *> internally.
4708		5402
		5403	=item null pointers and integer zero are represented by 0 bytes
		5404
		5405	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5406	relies on this setting pointers and integers to null.
		5407
		5408	=item pointer accesses must be thread-atomic
		5409
		5410	Accessing a pointer value must be atomic, it must both be readable and
		5411	writable in one piece - this is the case on all current architectures.
		5412
4709	=item C<sig_atomic_t volatile> must be thread-atomic as well	5413	=item C<sig_atomic_t volatile> must be thread-atomic as well
4710		5414
4711	The type C<sig_atomic_t volatile> (or whatever is defined as	5415	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	5416	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	5417	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	5425	thread" or will block signals process-wide, both behaviours would
4722	be compatible with libev. Interaction between C<sigprocmask> and	5426	be compatible with libev. Interaction between C<sigprocmask> and
4723	C<pthread_sigmask> could complicate things, however.	5427	C<pthread_sigmask> could complicate things, however.
4724		5428
4725	The most portable way to handle signals is to block signals in all threads	5429	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	5430	except the initial one, and run the signal handling loop in the initial
4727	well.	5431	thread as well.
4728		5432
4729	=item C<long> must be large enough for common memory allocation sizes	5433	=item C<long> must be large enough for common memory allocation sizes
4730		5434
4731	To improve portability and simplify its API, libev uses C<long> internally	5435	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	5436	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4738		5442
4739	The type C<double> is used to represent timestamps. It is required to	5443	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	5444	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	5445	good enough for at least into the year 4000 with millisecond accuracy
4742	(the design goal for libev). This requirement is overfulfilled by	5446	(the design goal for libev). This requirement is overfulfilled by
4743	implementations using IEEE 754, which is basically all existing ones. With	5447	implementations using IEEE 754, which is basically all existing ones.
		5448
4744	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5449	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5450	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5451	is either obsolete or somebody patched it to use C<long double> or
		5452	something like that, just kidding).
4745		5453
4746	=back	5454	=back
4747		5455
4748	If you know of other additional requirements drop me a note.	5456	If you know of other additional requirements drop me a note.
4749		5457
…		…
4811	=item Processing ev_async_send: O(number_of_async_watchers)	5519	=item Processing ev_async_send: O(number_of_async_watchers)
4812		5520
4813	=item Processing signals: O(max_signal_number)	5521	=item Processing signals: O(max_signal_number)
4814		5522
4815	Sending involves a system call I<iff> there were no other C<ev_async_send>	5523	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	5524	calls in the current loop iteration and the loop is currently
		5525	blocked. Checking for async and signal events involves iterating over all
4817	involves iterating over all running async watchers or all signal numbers.	5526	running async watchers or all signal numbers.
4818		5527
4819	=back	5528	=back
4820		5529
4821		5530
4822	=head1 PORTING FROM LIBEV 3.X TO 4.X	5531	=head1 PORTING FROM LIBEV 3.X TO 4.X
4823		5532
4824	The major version 4 introduced some minor incompatible changes to the API.	5533	The major version 4 introduced some incompatible changes to the API.
4825		5534
4826	At the moment, the C<ev.h> header file tries to implement superficial	5535	At the moment, the C<ev.h> header file provides compatibility definitions
4827	compatibility, so most programs should still compile. Those might be	5536	for all changes, so most programs should still compile. The compatibility
4828	removed in later versions of libev, so better update early than late.	5537	layer might be removed in later versions of libev, so better update to the
		5538	new API early than late.
4829		5539
4830	=over 4	5540	=over 4
		5541
		5542	=item C<EV_COMPAT3> backwards compatibility mechanism
		5543
		5544	The backward compatibility mechanism can be controlled by
		5545	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5546	section.
		5547
		5548	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5549
		5550	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5551
		5552	ev_loop_destroy (EV_DEFAULT_UC);
		5553	ev_loop_fork (EV_DEFAULT);
4831		5554
4832	=item function/symbol renames	5555	=item function/symbol renames
4833		5556
4834	A number of functions and symbols have been renamed:	5557	A number of functions and symbols have been renamed:
4835		5558
…		…
4854	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5577	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	5578	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>	5579	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4857	typedef.	5580	typedef.
4858		5581
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>	5582	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4866		5583
4867	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5584	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4868	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5585	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4869	and work, but the library code will of course be larger.	5586	and work, but the library code will of course be larger.
…		…
4876	=over 4	5593	=over 4
4877		5594
4878	=item active	5595	=item active
4879		5596
4880	A watcher is active as long as it has been started and not yet stopped.	5597	A watcher is active as long as it has been started and not yet stopped.
4881	See L<WATCHER STATES> for details.	5598	See L</WATCHER STATES> for details.
4882		5599
4883	=item application	5600	=item application
4884		5601
4885	In this document, an application is whatever is using libev.	5602	In this document, an application is whatever is using libev.
4886		5603
…		…
4922	watchers and events.	5639	watchers and events.
4923		5640
4924	=item pending	5641	=item pending
4925		5642
4926	A watcher is pending as soon as the corresponding event has been	5643	A watcher is pending as soon as the corresponding event has been
4927	detected. See L<WATCHER STATES> for details.	5644	detected. See L</WATCHER STATES> for details.
4928		5645
4929	=item real time	5646	=item real time
4930		5647
4931	The physical time that is observed. It is apparently strictly monotonic :)	5648	The physical time that is observed. It is apparently strictly monotonic :)
4932		5649
4933	=item wall-clock time	5650	=item wall-clock time
4934		5651
4935	The time and date as shown on clocks. Unlike real time, it can actually	5652	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	5653	be wrong and jump forwards and backwards, e.g. when you adjust your
4937	clock.	5654	clock.
4938		5655
4939	=item watcher	5656	=item watcher
4940		5657
4941	A data structure that describes interest in certain events. Watchers need	5658	A data structure that describes interest in certain events. Watchers need
…		…
4943		5660
4944	=back	5661	=back
4945		5662
4946	=head1 AUTHOR	5663	=head1 AUTHOR
4947		5664
4948	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5665	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5666	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
4949		5667

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