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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
…		…
9	=head2 EXAMPLE PROGRAM	11	=head2 EXAMPLE PROGRAM
10		12
11	// a single header file is required	13	// a single header file is required
12	#include <ev.h>	14	#include <ev.h>
13		15
		16	#include <stdio.h> // for puts
		17
14	// every watcher type has its own typedef'd struct	18	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	19	// with the name ev_TYPE
16	ev_io stdin_watcher;	20	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	21	ev_timer timeout_watcher;
18		22
19	// all watcher callbacks have a similar signature	23	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	24	// this callback is called when data is readable on stdin
21	static void	25	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	26	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	27	{
24	puts ("stdin ready");	28	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	29	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	30	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	31	ev_io_stop (EV_A_ w);
28		32
29	// this causes all nested ev_loop's to stop iterating	33	// this causes all nested ev_run's to stop iterating
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	34	ev_break (EV_A_ EVBREAK_ALL);
31	}	35	}
32		36
33	// another callback, this time for a time-out	37	// another callback, this time for a time-out
34	static void	38	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	39	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	40	{
37	puts ("timeout");	41	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	42	// this causes the innermost ev_run to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	43	ev_break (EV_A_ EVBREAK_ONE);
40	}	44	}
41		45
42	int	46	int
43	main (void)	47	main (void)
44	{	48	{
45	// use the default event loop unless you have special needs	49	// use the default event loop unless you have special needs
46	struct ev_loop *loop = ev_default_loop (0);	50	struct ev_loop *loop = EV_DEFAULT;
47		51
48	// initialise an io watcher, then start it	52	// initialise an io watcher, then start it
49	// this one will watch for stdin to become readable	53	// this one will watch for stdin to become readable
50	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);
51	ev_io_start (loop, &stdin_watcher);	55	ev_io_start (loop, &stdin_watcher);
…		…
54	// simple non-repeating 5.5 second timeout	58	// simple non-repeating 5.5 second timeout
55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	59	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
56	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
57		61
58	// now wait for events to arrive	62	// now wait for events to arrive
59	ev_loop (loop, 0);	63	ev_run (loop, 0);
60		64
61	// unloop was called, so exit	65	// break was called, so exit
62	return 0;	66	return 0;
63	}	67	}
64		68
65	=head1 DESCRIPTION	69	=head1 ABOUT THIS DOCUMENT
		70
		71	This document documents the libev software package.
66		72
67	The newest version of this document is also available as an html-formatted	73	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	74	web page you might find easier to navigate when reading it for the first
69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.	75	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		76
		77	While this document tries to be as complete as possible in documenting
		78	libev, its usage and the rationale behind its design, it is not a tutorial
		79	on event-based programming, nor will it introduce event-based programming
		80	with libev.
		81
		82	Familiarity with event based programming techniques in general is assumed
		83	throughout this document.
		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
		93	=head1 ABOUT LIBEV
70		94
71	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
72	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
73	these event sources and provide your program with events.	97	these event sources and provide your program with events.
74		98
…		…
81	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
82	watcher.	106	watcher.
83		107
84	=head2 FEATURES	108	=head2 FEATURES
85		109
86	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>
87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port
88	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>
89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	113	interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
90	with customised rescheduling (C<ev_periodic>), synchronous signals	114	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
91	(C<ev_signal>), process status change events (C<ev_child>), and event	115	timers (C<ev_timer>), absolute timers with customised rescheduling
92	watchers dealing with the event loop mechanism itself (C<ev_idle>,	116	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	117	change events (C<ev_child>), and event watchers dealing with the event
94	file watchers (C<ev_stat>) and even limited support for fork events	118	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
95	(C<ev_fork>).	119	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		120	limited support for fork events (C<ev_fork>).
96		121
97	It also is quite fast (see this	122	It also is quite fast (see this
98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	123	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
99	for example).	124	for example).
100		125
…		…
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	133	name C<loop> (which is always of type C<struct ev_loop *>) will not have
109	this argument.	134	this argument.
110		135
111	=head2 TIME REPRESENTATION	136	=head2 TIME REPRESENTATION
112		137
113	Libev represents time as a single floating point number, representing the	138	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	139	the (fractional) number of seconds since the (POSIX) epoch (in practice
115	the beginning of 1970, details are complicated, don't ask). This type is	140	somewhere near the beginning of 1970, details are complicated, don't
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	141	ask). This type is called C<ev_tstamp>, which is what you should use
117	to the C<double> type in C, and when you need to do any calculations on	142	too. It usually aliases to the C<double> type in C. When you need to do
118	it, you should treat it as some floating point value. Unlike the name	143	any calculations on it, you should treat it as some floating point value.
		144
119	component C<stamp> might indicate, it is also used for time differences	145	Unlike the name component C<stamp> might indicate, it is also used for
120	throughout libev.	146	time differences (e.g. delays) throughout libev.
121		147
122	=head1 ERROR HANDLING	148	=head1 ERROR HANDLING
123		149
124	Libev knows three classes of errors: operating system errors, usage errors	150	Libev knows three classes of errors: operating system errors, usage errors
125	and internal errors (bugs).	151	and internal errors (bugs).
…		…
133	When libev detects a usage error such as a negative timer interval, then	159	When libev detects a usage error such as a negative timer interval, then
134	it will print a diagnostic message and abort (via the C<assert> mechanism,	160	it will print a diagnostic message and abort (via the C<assert> mechanism,
135	so C<NDEBUG> will disable this checking): these are programming errors in	161	so C<NDEBUG> will disable this checking): these are programming errors in
136	the libev caller and need to be fixed there.	162	the libev caller and need to be fixed there.
137		163
		164	Via the C<EV_FREQUENT> macro you can compile in and/or enable extensive
		165	consistency checking code inside libev that can be used to check for
		166	internal inconsistencies, suually caused by application bugs.
		167
138	Libev also has a few internal error-checking C<assert>ions, and also has	168	Libev also has a few internal error-checking C<assert>ions. These do not
139	extensive consistency checking code. These do not trigger under normal
140	circumstances, as they indicate either a bug in libev or worse.	169	trigger under normal circumstances, as they indicate either a bug in libev
		170	or worse.
141		171
142		172
143	=head1 GLOBAL FUNCTIONS	173	=head1 GLOBAL FUNCTIONS
144		174
145	These functions can be called anytime, even before initialising the	175	These functions can be called anytime, even before initialising the
…		…
149		179
150	=item ev_tstamp ev_time ()	180	=item ev_tstamp ev_time ()
151		181
152	Returns the current time as libev would use it. Please note that the	182	Returns the current time as libev would use it. Please note that the
153	C<ev_now> function is usually faster and also often returns the timestamp	183	C<ev_now> function is usually faster and also often returns the timestamp
154	you actually want to know.	184	you actually want to know. Also interesting is the combination of
		185	C<ev_now_update> and C<ev_now>.
155		186
156	=item ev_sleep (ev_tstamp interval)	187	=item ev_sleep (ev_tstamp interval)
157		188
158	Sleep for the given interval: The current thread will be blocked until	189	Sleep for the given interval: The current thread will be blocked
159	either it is interrupted or the given time interval has passed. Basically	190	until either it is interrupted or the given time interval has
		191	passed (approximately - it might return a bit earlier even if not
		192	interrupted). Returns immediately if C<< interval <= 0 >>.
		193
160	this is a sub-second-resolution C<sleep ()>.	194	Basically this is a sub-second-resolution C<sleep ()>.
		195
		196	The range of the C<interval> is limited - libev only guarantees to work
		197	with sleep times of up to one day (C<< interval <= 86400 >>).
161		198
162	=item int ev_version_major ()	199	=item int ev_version_major ()
163		200
164	=item int ev_version_minor ()	201	=item int ev_version_minor ()
165		202
…		…
176	as this indicates an incompatible change. Minor versions are usually	213	as this indicates an incompatible change. Minor versions are usually
177	compatible to older versions, so a larger minor version alone is usually	214	compatible to older versions, so a larger minor version alone is usually
178	not a problem.	215	not a problem.
179		216
180	Example: Make sure we haven't accidentally been linked against the wrong	217	Example: Make sure we haven't accidentally been linked against the wrong
181	version.	218	version (note, however, that this will not detect other ABI mismatches,
		219	such as LFS or reentrancy).
182		220
183	assert (("libev version mismatch",	221	assert (("libev version mismatch",
184	ev_version_major () == EV_VERSION_MAJOR	222	ev_version_major () == EV_VERSION_MAJOR
185	&& ev_version_minor () >= EV_VERSION_MINOR));	223	&& ev_version_minor () >= EV_VERSION_MINOR));
186		224
…		…
197	assert (("sorry, no epoll, no sex",	235	assert (("sorry, no epoll, no sex",
198	ev_supported_backends () & EVBACKEND_EPOLL));	236	ev_supported_backends () & EVBACKEND_EPOLL));
199		237
200	=item unsigned int ev_recommended_backends ()	238	=item unsigned int ev_recommended_backends ()
201		239
202	Return the set of all backends compiled into this binary of libev and also	240	Return the set of all backends compiled into this binary of libev and
203	recommended for this platform. This set is often smaller than the one	241	also recommended for this platform, meaning it will work for most file
		242	descriptor types. This set is often smaller than the one returned by
204	returned by C<ev_supported_backends>, as for example kqueue is broken on	243	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
205	most BSDs and will not be auto-detected unless you explicitly request it	244	and will not be auto-detected unless you explicitly request it (assuming
206	(assuming you know what you are doing). This is the set of backends that	245	you know what you are doing). This is the set of backends that libev will
207	libev will probe for if you specify no backends explicitly.	246	probe for if you specify no backends explicitly.
208		247
209	=item unsigned int ev_embeddable_backends ()	248	=item unsigned int ev_embeddable_backends ()
210		249
211	Returns the set of backends that are embeddable in other event loops. This	250	Returns the set of backends that are embeddable in other event loops. This
212	is the theoretical, all-platform, value. To find which backends	251	value is platform-specific but can include backends not available on the
213	might be supported on the current system, you would need to look at	252	current system. To find which embeddable backends might be supported on
214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	253	the current system, you would need to look at C<ev_embeddable_backends ()
215	recommended ones.	254	& ev_supported_backends ()>, likewise for recommended ones.
216		255
217	See the description of C<ev_embed> watchers for more info.	256	See the description of C<ev_embed> watchers for more info.
218		257
219	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	258	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
220		259
221	Sets the allocation function to use (the prototype is similar - the	260	Sets the allocation function to use (the prototype is similar - the
222	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	261	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
223	used to allocate and free memory (no surprises here). If it returns zero	262	used to allocate and free memory (no surprises here). If it returns zero
224	when memory needs to be allocated (C<size != 0>), the library might abort	263	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
230		269
231	You could override this function in high-availability programs to, say,	270	You could override this function in high-availability programs to, say,
232	free some memory if it cannot allocate memory, to use a special allocator,	271	free some memory if it cannot allocate memory, to use a special allocator,
233	or even to sleep a while and retry until some memory is available.	272	or even to sleep a while and retry until some memory is available.
234		273
		274	Example: The following is the C<realloc> function that libev itself uses
		275	which should work with C<realloc> and C<free> functions of all kinds and
		276	is probably a good basis for your own implementation.
		277
		278	static void *
		279	ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
		280	{
		281	if (size)
		282	return realloc (ptr, size);
		283
		284	free (ptr);
		285	return 0;
		286	}
		287
235	Example: Replace the libev allocator with one that waits a bit and then	288	Example: Replace the libev allocator with one that waits a bit and then
236	retries (example requires a standards-compliant C<realloc>).	289	retries.
237		290
238	static void *	291	static void *
239	persistent_realloc (void *ptr, size_t size)	292	persistent_realloc (void *ptr, size_t size)
240	{	293	{
		294	if (!size)
		295	{
		296	free (ptr);
		297	return 0;
		298	}
		299
241	for (;;)	300	for (;;)
242	{	301	{
243	void *newptr = realloc (ptr, size);	302	void *newptr = realloc (ptr, size);
244		303
245	if (newptr)	304	if (newptr)
…		…
250	}	309	}
251		310
252	...	311	...
253	ev_set_allocator (persistent_realloc);	312	ev_set_allocator (persistent_realloc);
254		313
255	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	314	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
256		315
257	Set the callback function to call on a retryable system call error (such	316	Set the callback function to call on a retryable system call error (such
258	as failed select, poll, epoll_wait). The message is a printable string	317	as failed select, poll, epoll_wait). The message is a printable string
259	indicating the system call or subsystem causing the problem. If this	318	indicating the system call or subsystem causing the problem. If this
260	callback is set, then libev will expect it to remedy the situation, no	319	callback is set, then libev will expect it to remedy the situation, no
…		…
272	}	331	}
273		332
274	...	333	...
275	ev_set_syserr_cb (fatal_error);	334	ev_set_syserr_cb (fatal_error);
276		335
		336	=item ev_feed_signal (int signum)
		337
		338	This function can be used to "simulate" a signal receive. It is completely
		339	safe to call this function at any time, from any context, including signal
		340	handlers or random threads.
		341
		342	Its main use is to customise signal handling in your process, especially
		343	in the presence of threads. For example, you could block signals
		344	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		345	creating any loops), and in one thread, use C<sigwait> or any other
		346	mechanism to wait for signals, then "deliver" them to libev by calling
		347	C<ev_feed_signal>.
		348
277	=back	349	=back
278		350
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	351	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
280		352
281	An event loop is described by a C<struct ev_loop *>. The library knows two	353	An event loop is described by a C<struct ev_loop *> (the C<struct> is
282	types of such loops, the I<default> loop, which supports signals and child	354	I<not> optional in this case unless libev 3 compatibility is disabled, as
283	events, and dynamically created loops which do not.	355	libev 3 had an C<ev_loop> function colliding with the struct name).
		356
		357	The library knows two types of such loops, the I<default> loop, which
		358	supports child process events, and dynamically created event loops which
		359	do not.
284		360
285	=over 4	361	=over 4
286		362
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	363	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		364
289	This will initialise the default event loop if it hasn't been initialised	365	This returns the "default" event loop object, which is what you should
290	yet and return it. If the default loop could not be initialised, returns	366	normally use when you just need "the event loop". Event loop objects and
291	false. If it already was initialised it simply returns it (and ignores the	367	the C<flags> parameter are described in more detail in the entry for
292	flags. If that is troubling you, check C<ev_backend ()> afterwards).	368	C<ev_loop_new>.
		369
		370	If the default loop is already initialised then this function simply
		371	returns it (and ignores the flags. If that is troubling you, check
		372	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		373	flags, which should almost always be C<0>, unless the caller is also the
		374	one calling C<ev_run> or otherwise qualifies as "the main program".
293		375
294	If you don't know what event loop to use, use the one returned from this	376	If you don't know what event loop to use, use the one returned from this
295	function.	377	function (or via the C<EV_DEFAULT> macro).
296		378
297	Note that this function is I<not> thread-safe, so if you want to use it	379	Note that this function is I<not> thread-safe, so if you want to use it
298	from multiple threads, you have to lock (note also that this is unlikely,	380	from multiple threads, you have to employ some kind of mutex (note also
299	as loops cannot bes hared easily between threads anyway).	381	that this case is unlikely, as loops cannot be shared easily between
		382	threads anyway).
300		383
301	The default loop is the only loop that can handle C<ev_signal> and	384	The default loop is the only loop that can handle C<ev_child> watchers,
302	C<ev_child> watchers, and to do this, it always registers a handler	385	and to do this, it always registers a handler for C<SIGCHLD>. If this is
303	for C<SIGCHLD>. If this is a problem for your application you can either	386	a problem for your application you can either create a dynamic loop with
304	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	387	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
305	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	388	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
306	C<ev_default_init>.	389
		390	Example: This is the most typical usage.
		391
		392	if (!ev_default_loop (0))
		393	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		394
		395	Example: Restrict libev to the select and poll backends, and do not allow
		396	environment settings to be taken into account:
		397
		398	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		399
		400	=item struct ev_loop *ev_loop_new (unsigned int flags)
		401
		402	This will create and initialise a new event loop object. If the loop
		403	could not be initialised, returns false.
		404
		405	This function is thread-safe, and one common way to use libev with
		406	threads is indeed to create one loop per thread, and using the default
		407	loop in the "main" or "initial" thread.
307		408
308	The flags argument can be used to specify special behaviour or specific	409	The flags argument can be used to specify special behaviour or specific
309	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	410	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
310		411
311	The following flags are supported:	412	The following flags are supported:
…		…
321		422
322	If this flag bit is or'ed into the flag value (or the program runs setuid	423	If this flag bit is or'ed into the flag value (or the program runs setuid
323	or setgid) then libev will I<not> look at the environment variable	424	or setgid) then libev will I<not> look at the environment variable
324	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	425	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
325	override the flags completely if it is found in the environment. This is	426	override the flags completely if it is found in the environment. This is
326	useful to try out specific backends to test their performance, or to work	427	useful to try out specific backends to test their performance, to work
327	around bugs.	428	around bugs, or to make libev threadsafe (accessing environment variables
		429	cannot be done in a threadsafe way, but usually it works if no other
		430	thread modifies them).
328		431
329	=item C<EVFLAG_FORKCHECK>	432	=item C<EVFLAG_FORKCHECK>
330		433
331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	434	Instead of calling C<ev_loop_fork> manually after a fork, you can also
332	a fork, you can also make libev check for a fork in each iteration by	435	make libev check for a fork in each iteration by enabling this flag.
333	enabling this flag.
334		436
335	This works by calling C<getpid ()> on every iteration of the loop,	437	This works by calling C<getpid ()> on every iteration of the loop,
336	and thus this might slow down your event loop if you do a lot of loop	438	and thus this might slow down your event loop if you do a lot of loop
337	iterations and little real work, but is usually not noticeable (on my	439	iterations and little real work, but is usually not noticeable (on my
338	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	440	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
339	without a system call and thus I<very> fast, but my GNU/Linux system also has	441	sequence without a system call and thus I<very> fast, but my GNU/Linux
340	C<pthread_atfork> which is even faster).	442	system also has C<pthread_atfork> which is even faster). (Update: glibc
		443	versions 2.25 apparently removed the C<getpid> optimisation again).
341		444
342	The big advantage of this flag is that you can forget about fork (and	445	The big advantage of this flag is that you can forget about fork (and
343	forget about forgetting to tell libev about forking) when you use this	446	forget about forgetting to tell libev about forking, although you still
344	flag.	447	have to ignore C<SIGPIPE>) when you use this flag.
345		448
346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	449	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
347	environment variable.	450	environment variable.
		451
		452	=item C<EVFLAG_NOINOTIFY>
		453
		454	When this flag is specified, then libev will not attempt to use the
		455	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		456	testing, this flag can be useful to conserve inotify file descriptors, as
		457	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		458
		459	=item C<EVFLAG_SIGNALFD>
		460
		461	When this flag is specified, then libev will attempt to use the
		462	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		463	delivers signals synchronously, which makes it both faster and might make
		464	it possible to get the queued signal data. It can also simplify signal
		465	handling with threads, as long as you properly block signals in your
		466	threads that are not interested in handling them.
		467
		468	Signalfd will not be used by default as this changes your signal mask, and
		469	there are a lot of shoddy libraries and programs (glib's threadpool for
		470	example) that can't properly initialise their signal masks.
		471
		472	=item C<EVFLAG_NOSIGMASK>
		473
		474	When this flag is specified, then libev will avoid to modify the signal
		475	mask. Specifically, this means you have to make sure signals are unblocked
		476	when you want to receive them.
		477
		478	This behaviour is useful when you want to do your own signal handling, or
		479	want to handle signals only in specific threads and want to avoid libev
		480	unblocking the signals.
		481
		482	It's also required by POSIX in a threaded program, as libev calls
		483	C<sigprocmask>, whose behaviour is officially unspecified.
		484
		485	=item C<EVFLAG_NOTIMERFD>
		486
		487	When this flag is specified, the libev will avoid using a C<timerfd> to
		488	detect time jumps. It will still be able to detect time jumps, but takes
		489	longer and has a lower accuracy in doing so, but saves a file descriptor
		490	per loop.
		491
		492	The current implementation only tries to use a C<timerfd> when the first
		493	C<ev_periodic> watcher is started and falls back on other methods if it
		494	cannot be created, but this behaviour might change in the future.
348		495
349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	496	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
350		497
351	This is your standard select(2) backend. Not I<completely> standard, as	498	This is your standard select(2) backend. Not I<completely> standard, as
352	libev tries to roll its own fd_set with no limits on the number of fds,	499	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
377	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and	524	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
378	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	525	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
379		526
380	=item C<EVBACKEND_EPOLL> (value 4, Linux)	527	=item C<EVBACKEND_EPOLL> (value 4, Linux)
381		528
		529	Use the Linux-specific epoll(7) interface (for both pre- and post-2.6.9
		530	kernels).
		531
382	For few fds, this backend is a bit little slower than poll and select,	532	For few fds, this backend is a bit little slower than poll and select, but
383	but it scales phenomenally better. While poll and select usually scale	533	it scales phenomenally better. While poll and select usually scale like
384	like O(total_fds) where n is the total number of fds (or the highest fd),	534	O(total_fds) where total_fds is the total number of fds (or the highest
385	epoll scales either O(1) or O(active_fds). The epoll design has a number	535	fd), epoll scales either O(1) or O(active_fds).
386	of shortcomings, such as silently dropping events in some hard-to-detect	536
387	cases and requiring a system call per fd change, no fork support and bad	537	The epoll mechanism deserves honorable mention as the most misdesigned
388	support for dup.	538	of the more advanced event mechanisms: mere annoyances include silently
		539	dropping file descriptors, requiring a system call per change per file
		540	descriptor (and unnecessary guessing of parameters), problems with dup,
		541	returning before the timeout value, resulting in additional iterations
		542	(and only giving 5ms accuracy while select on the same platform gives
		543	0.1ms) and so on. The biggest issue is fork races, however - if a program
		544	forks then I<both> parent and child process have to recreate the epoll
		545	set, which can take considerable time (one syscall per file descriptor)
		546	and is of course hard to detect.
		547
		548	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		549	but of course I<doesn't>, and epoll just loves to report events for
		550	totally I<different> file descriptors (even already closed ones, so
		551	one cannot even remove them from the set) than registered in the set
		552	(especially on SMP systems). Libev tries to counter these spurious
		553	notifications by employing an additional generation counter and comparing
		554	that against the events to filter out spurious ones, recreating the set
		555	when required. Epoll also erroneously rounds down timeouts, but gives you
		556	no way to know when and by how much, so sometimes you have to busy-wait
		557	because epoll returns immediately despite a nonzero timeout. And last
		558	not least, it also refuses to work with some file descriptors which work
		559	perfectly fine with C<select> (files, many character devices...).
		560
		561	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		562	cobbled together in a hurry, no thought to design or interaction with
		563	others. Oh, the pain, will it ever stop...
389		564
390	While stopping, setting and starting an I/O watcher in the same iteration	565	While stopping, setting and starting an I/O watcher in the same iteration
391	will result in some caching, there is still a system call per such incident	566	will result in some caching, there is still a system call per such
392	(because the fd could point to a different file description now), so its	567	incident (because the same I<file descriptor> could point to a different
393	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	568	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
394	very well if you register events for both fds.	569	file descriptors might not work very well if you register events for both
395		570	file descriptors.
396	Please note that epoll sometimes generates spurious notifications, so you
397	need to use non-blocking I/O or other means to avoid blocking when no data
398	(or space) is available.
399		571
400	Best performance from this backend is achieved by not unregistering all	572	Best performance from this backend is achieved by not unregistering all
401	watchers for a file descriptor until it has been closed, if possible,	573	watchers for a file descriptor until it has been closed, if possible,
402	i.e. keep at least one watcher active per fd at all times. Stopping and	574	i.e. keep at least one watcher active per fd at all times. Stopping and
403	starting a watcher (without re-setting it) also usually doesn't cause	575	starting a watcher (without re-setting it) also usually doesn't cause
404	extra overhead.	576	extra overhead. A fork can both result in spurious notifications as well
		577	as in libev having to destroy and recreate the epoll object, which can
		578	take considerable time and thus should be avoided.
		579
		580	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		581	faster than epoll for maybe up to a hundred file descriptors, depending on
		582	the usage. So sad.
405		583
406	While nominally embeddable in other event loops, this feature is broken in	584	While nominally embeddable in other event loops, this feature is broken in
407	all kernel versions tested so far.	585	a lot of kernel revisions, but probably(!) works in current versions.
408		586
409	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	587	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
410	C<EVBACKEND_POLL>.	588	C<EVBACKEND_POLL>.
411		589
		590	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		591
		592	Use the Linux-specific Linux AIO (I<not> C<< aio(7) >> but C<<
		593	io_submit(2) >>) event interface available in post-4.18 kernels (but libev
		594	only tries to use it in 4.19+).
		595
		596	This is another Linux train wreck of an event interface.
		597
		598	If this backend works for you (as of this writing, it was very
		599	experimental), it is the best event interface available on Linux and might
		600	be well worth enabling it - if it isn't available in your kernel this will
		601	be detected and this backend will be skipped.
		602
		603	This backend can batch oneshot requests and supports a user-space ring
		604	buffer to receive events. It also doesn't suffer from most of the design
		605	problems of epoll (such as not being able to remove event sources from
		606	the epoll set), and generally sounds too good to be true. Because, this
		607	being the Linux kernel, of course it suffers from a whole new set of
		608	limitations, forcing you to fall back to epoll, inheriting all its design
		609	issues.
		610
		611	For one, it is not easily embeddable (but probably could be done using
		612	an event fd at some extra overhead). It also is subject to a system wide
		613	limit that can be configured in F</proc/sys/fs/aio-max-nr>. If no AIO
		614	requests are left, this backend will be skipped during initialisation, and
		615	will switch to epoll when the loop is active.
		616
		617	Most problematic in practice, however, is that not all file descriptors
		618	work with it. For example, in Linux 5.1, TCP sockets, pipes, event fds,
		619	files, F</dev/null> and many others are supported, but ttys do not work
		620	properly (a known bug that the kernel developers don't care about, see
		621	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		622	(yet?) a generic event polling interface.
		623
		624	Overall, it seems the Linux developers just don't want it to have a
		625	generic event handling mechanism other than C<select> or C<poll>.
		626
		627	To work around all these problem, the current version of libev uses its
		628	epoll backend as a fallback for file descriptor types that do not work. Or
		629	falls back completely to epoll if the kernel acts up.
		630
		631	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		632	C<EVBACKEND_POLL>.
		633
412	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	634	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
413		635
414	Kqueue deserves special mention, as at the time of this writing, it was	636	Kqueue deserves special mention, as at the time this backend was
415	broken on all BSDs except NetBSD (usually it doesn't work reliably with	637	implemented, it was broken on all BSDs except NetBSD (usually it doesn't
416	anything but sockets and pipes, except on Darwin, where of course it's	638	work reliably with anything but sockets and pipes, except on Darwin,
417	completely useless). For this reason it's not being "auto-detected" unless	639	where of course it's completely useless). Unlike epoll, however, whose
418	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or	640	brokenness is by design, these kqueue bugs can be (and mostly have been)
		641	fixed without API changes to existing programs. For this reason it's not
		642	being "auto-detected" on all platforms unless you explicitly specify it
		643	in the flags (i.e. using C<EVBACKEND_KQUEUE>) or libev was compiled on a
419	libev was compiled on a known-to-be-good (-enough) system like NetBSD.	644	known-to-be-good (-enough) system like NetBSD.
420		645
421	You still can embed kqueue into a normal poll or select backend and use it	646	You still can embed kqueue into a normal poll or select backend and use it
422	only for sockets (after having made sure that sockets work with kqueue on	647	only for sockets (after having made sure that sockets work with kqueue on
423	the target platform). See C<ev_embed> watchers for more info.	648	the target platform). See C<ev_embed> watchers for more info.
424		649
425	It scales in the same way as the epoll backend, but the interface to the	650	It scales in the same way as the epoll backend, but the interface to the
426	kernel is more efficient (which says nothing about its actual speed, of	651	kernel is more efficient (which says nothing about its actual speed, of
427	course). While stopping, setting and starting an I/O watcher does never	652	course). While stopping, setting and starting an I/O watcher does never
428	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	653	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
429	two event changes per incident. Support for C<fork ()> is very bad and it	654	two event changes per incident. Support for C<fork ()> is very bad (you
		655	might have to leak fds on fork, but it's more sane than epoll) and it
430	drops fds silently in similarly hard-to-detect cases.	656	drops fds silently in similarly hard-to-detect cases.
431		657
432	This backend usually performs well under most conditions.	658	This backend usually performs well under most conditions.
433		659
434	While nominally embeddable in other event loops, this doesn't work	660	While nominally embeddable in other event loops, this doesn't work
435	everywhere, so you might need to test for this. And since it is broken	661	everywhere, so you might need to test for this. And since it is broken
436	almost everywhere, you should only use it when you have a lot of sockets	662	almost everywhere, you should only use it when you have a lot of sockets
437	(for which it usually works), by embedding it into another event loop	663	(for which it usually works), by embedding it into another event loop
438	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,	664	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
439	using it only for sockets.	665	also broken on OS X)) and, did I mention it, using it only for sockets.
440		666
441	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with	667	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
442	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with	668	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
443	C<NOTE_EOF>.	669	C<NOTE_EOF>.
444		670
…		…
452	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	678	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
453		679
454	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	680	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
455	it's really slow, but it still scales very well (O(active_fds)).	681	it's really slow, but it still scales very well (O(active_fds)).
456		682
457	Please note that Solaris event ports can deliver a lot of spurious
458	notifications, so you need to use non-blocking I/O or other means to avoid
459	blocking when no data (or space) is available.
460
461	While this backend scales well, it requires one system call per active	683	While this backend scales well, it requires one system call per active
462	file descriptor per loop iteration. For small and medium numbers of file	684	file descriptor per loop iteration. For small and medium numbers of file
463	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	685	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
464	might perform better.	686	might perform better.
465		687
466	On the positive side, with the exception of the spurious readiness	688	On the positive side, this backend actually performed fully to
467	notifications, this backend actually performed fully to specification
468	in all tests and is fully embeddable, which is a rare feat among the	689	specification in all tests and is fully embeddable, which is a rare feat
469	OS-specific backends.	690	among the OS-specific backends (I vastly prefer correctness over speed
		691	hacks).
		692
		693	On the negative side, the interface is I<bizarre> - so bizarre that
		694	even sun itself gets it wrong in their code examples: The event polling
		695	function sometimes returns events to the caller even though an error
		696	occurred, but with no indication whether it has done so or not (yes, it's
		697	even documented that way) - deadly for edge-triggered interfaces where you
		698	absolutely have to know whether an event occurred or not because you have
		699	to re-arm the watcher.
		700
		701	Fortunately libev seems to be able to work around these idiocies.
470		702
471	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	703	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
472	C<EVBACKEND_POLL>.	704	C<EVBACKEND_POLL>.
473		705
474	=item C<EVBACKEND_ALL>	706	=item C<EVBACKEND_ALL>
475		707
476	Try all backends (even potentially broken ones that wouldn't be tried	708	Try all backends (even potentially broken ones that wouldn't be tried
477	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	709	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
478	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	710	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
479		711
480	It is definitely not recommended to use this flag.	712	It is definitely not recommended to use this flag, use whatever
		713	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		714	at all.
		715
		716	=item C<EVBACKEND_MASK>
		717
		718	Not a backend at all, but a mask to select all backend bits from a
		719	C<flags> value, in case you want to mask out any backends from a flags
		720	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
481		721
482	=back	722	=back
483		723
484	If one or more of these are or'ed into the flags value, then only these	724	If one or more of the backend flags are or'ed into the flags value,
485	backends will be tried (in the reverse order as listed here). If none are	725	then only these backends will be tried (in the reverse order as listed
486	specified, all backends in C<ev_recommended_backends ()> will be tried.	726	here). If none are specified, all backends in C<ev_recommended_backends
487		727	()> will be tried.
488	Example: This is the most typical usage.
489
490	if (!ev_default_loop (0))
491	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
492
493	Example: Restrict libev to the select and poll backends, and do not allow
494	environment settings to be taken into account:
495
496	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
497
498	Example: Use whatever libev has to offer, but make sure that kqueue is
499	used if available (warning, breaks stuff, best use only with your own
500	private event loop and only if you know the OS supports your types of
501	fds):
502
503	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
504
505	=item struct ev_loop *ev_loop_new (unsigned int flags)
506
507	Similar to C<ev_default_loop>, but always creates a new event loop that is
508	always distinct from the default loop. Unlike the default loop, it cannot
509	handle signal and child watchers, and attempts to do so will be greeted by
510	undefined behaviour (or a failed assertion if assertions are enabled).
511
512	Note that this function I<is> thread-safe, and the recommended way to use
513	libev with threads is indeed to create one loop per thread, and using the
514	default loop in the "main" or "initial" thread.
515		728
516	Example: Try to create a event loop that uses epoll and nothing else.	729	Example: Try to create a event loop that uses epoll and nothing else.
517		730
518	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	731	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
519	if (!epoller)	732	if (!epoller)
520	fatal ("no epoll found here, maybe it hides under your chair");	733	fatal ("no epoll found here, maybe it hides under your chair");
521		734
		735	Example: Use whatever libev has to offer, but make sure that kqueue is
		736	used if available.
		737
		738	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		739
		740	Example: Similarly, on linux, you mgiht want to take advantage of the
		741	linux aio backend if possible, but fall back to something else if that
		742	isn't available.
		743
		744	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
		745
522	=item ev_default_destroy ()	746	=item ev_loop_destroy (loop)
523		747
524	Destroys the default loop again (frees all memory and kernel state	748	Destroys an event loop object (frees all memory and kernel state
525	etc.). None of the active event watchers will be stopped in the normal	749	etc.). None of the active event watchers will be stopped in the normal
526	sense, so e.g. C<ev_is_active> might still return true. It is your	750	sense, so e.g. C<ev_is_active> might still return true. It is your
527	responsibility to either stop all watchers cleanly yourself I<before>	751	responsibility to either stop all watchers cleanly yourself I<before>
528	calling this function, or cope with the fact afterwards (which is usually	752	calling this function, or cope with the fact afterwards (which is usually
529	the easiest thing, you can just ignore the watchers and/or C<free ()> them	753	the easiest thing, you can just ignore the watchers and/or C<free ()> them
530	for example).	754	for example).
531		755
532	Note that certain global state, such as signal state, will not be freed by	756	Note that certain global state, such as signal state (and installed signal
533	this function, and related watchers (such as signal and child watchers)	757	handlers), will not be freed by this function, and related watchers (such
534	would need to be stopped manually.	758	as signal and child watchers) would need to be stopped manually.
535		759
536	In general it is not advisable to call this function except in the	760	This function is normally used on loop objects allocated by
537	rare occasion where you really need to free e.g. the signal handling	761	C<ev_loop_new>, but it can also be used on the default loop returned by
		762	C<ev_default_loop>, in which case it is not thread-safe.
		763
		764	Note that it is not advisable to call this function on the default loop
		765	except in the rare occasion where you really need to free its resources.
538	pipe fds. If you need dynamically allocated loops it is better to use	766	If you need dynamically allocated loops it is better to use C<ev_loop_new>
539	C<ev_loop_new> and C<ev_loop_destroy>).	767	and C<ev_loop_destroy>.
540		768
541	=item ev_loop_destroy (loop)	769	=item ev_loop_fork (loop)
542		770
543	Like C<ev_default_destroy>, but destroys an event loop created by an
544	earlier call to C<ev_loop_new>.
545
546	=item ev_default_fork ()
547
548	This function sets a flag that causes subsequent C<ev_loop> iterations	771	This function sets a flag that causes subsequent C<ev_run> iterations
549	to reinitialise the kernel state for backends that have one. Despite the	772	to reinitialise the kernel state for backends that have one. Despite
550	name, you can call it anytime, but it makes most sense after forking, in	773	the name, you can call it anytime you are allowed to start or stop
551	the child process (or both child and parent, but that again makes little	774	watchers (except inside an C<ev_prepare> callback), but it makes most
552	sense). You I<must> call it in the child before using any of the libev	775	sense after forking, in the child process. You I<must> call it (or use
553	functions, and it will only take effect at the next C<ev_loop> iteration.	776	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
		777
		778	In addition, if you want to reuse a loop (via this function or
		779	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		780
		781	Again, you I<have> to call it on I<any> loop that you want to re-use after
		782	a fork, I<even if you do not plan to use the loop in the parent>. This is
		783	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		784	during fork.
554		785
555	On the other hand, you only need to call this function in the child	786	On the other hand, you only need to call this function in the child
556	process if and only if you want to use the event library in the child. If	787	process if and only if you want to use the event loop in the child. If
557	you just fork+exec, you don't have to call it at all.	788	you just fork+exec or create a new loop in the child, you don't have to
		789	call it at all (in fact, C<epoll> is so badly broken that it makes a
		790	difference, but libev will usually detect this case on its own and do a
		791	costly reset of the backend).
558		792
559	The function itself is quite fast and it's usually not a problem to call	793	The function itself is quite fast and it's usually not a problem to call
560	it just in case after a fork. To make this easy, the function will fit in	794	it just in case after a fork.
561	quite nicely into a call to C<pthread_atfork>:
562		795
		796	Example: Automate calling C<ev_loop_fork> on the default loop when
		797	using pthreads.
		798
		799	static void
		800	post_fork_child (void)
		801	{
		802	ev_loop_fork (EV_DEFAULT);
		803	}
		804
		805	...
563	pthread_atfork (0, 0, ev_default_fork);	806	pthread_atfork (0, 0, post_fork_child);
564
565	=item ev_loop_fork (loop)
566
567	Like C<ev_default_fork>, but acts on an event loop created by
568	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
569	after fork that you want to re-use in the child, and how you do this is
570	entirely your own problem.
571		807
572	=item int ev_is_default_loop (loop)	808	=item int ev_is_default_loop (loop)
573		809
574	Returns true when the given loop is, in fact, the default loop, and false	810	Returns true when the given loop is, in fact, the default loop, and false
575	otherwise.	811	otherwise.
576		812
577	=item unsigned int ev_loop_count (loop)	813	=item unsigned int ev_iteration (loop)
578		814
579	Returns the count of loop iterations for the loop, which is identical to	815	Returns the current iteration count for the event loop, which is identical
580	the number of times libev did poll for new events. It starts at C<0> and	816	to the number of times libev did poll for new events. It starts at C<0>
581	happily wraps around with enough iterations.	817	and happily wraps around with enough iterations.
582		818
583	This value can sometimes be useful as a generation counter of sorts (it	819	This value can sometimes be useful as a generation counter of sorts (it
584	"ticks" the number of loop iterations), as it roughly corresponds with	820	"ticks" the number of loop iterations), as it roughly corresponds with
585	C<ev_prepare> and C<ev_check> calls.	821	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		822	prepare and check phases.
		823
		824	=item unsigned int ev_depth (loop)
		825
		826	Returns the number of times C<ev_run> was entered minus the number of
		827	times C<ev_run> was exited normally, in other words, the recursion depth.
		828
		829	Outside C<ev_run>, this number is zero. In a callback, this number is
		830	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		831	in which case it is higher.
		832
		833	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		834	throwing an exception etc.), doesn't count as "exit" - consider this
		835	as a hint to avoid such ungentleman-like behaviour unless it's really
		836	convenient, in which case it is fully supported.
586		837
587	=item unsigned int ev_backend (loop)	838	=item unsigned int ev_backend (loop)
588		839
589	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	840	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
590	use.	841	use.
…		…
599		850
600	=item ev_now_update (loop)	851	=item ev_now_update (loop)
601		852
602	Establishes the current time by querying the kernel, updating the time	853	Establishes the current time by querying the kernel, updating the time
603	returned by C<ev_now ()> in the progress. This is a costly operation and	854	returned by C<ev_now ()> in the progress. This is a costly operation and
604	is usually done automatically within C<ev_loop ()>.	855	is usually done automatically within C<ev_run ()>.
605		856
606	This function is rarely useful, but when some event callback runs for a	857	This function is rarely useful, but when some event callback runs for a
607	very long time without entering the event loop, updating libev's idea of	858	very long time without entering the event loop, updating libev's idea of
608	the current time is a good idea.	859	the current time is a good idea.
609		860
610	See also "The special problem of time updates" in the C<ev_timer> section.	861	See also L</The special problem of time updates> in the C<ev_timer> section.
611		862
		863	=item ev_suspend (loop)
		864
		865	=item ev_resume (loop)
		866
		867	These two functions suspend and resume an event loop, for use when the
		868	loop is not used for a while and timeouts should not be processed.
		869
		870	A typical use case would be an interactive program such as a game: When
		871	the user presses C<^Z> to suspend the game and resumes it an hour later it
		872	would be best to handle timeouts as if no time had actually passed while
		873	the program was suspended. This can be achieved by calling C<ev_suspend>
		874	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		875	C<ev_resume> directly afterwards to resume timer processing.
		876
		877	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		878	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		879	will be rescheduled (that is, they will lose any events that would have
		880	occurred while suspended).
		881
		882	After calling C<ev_suspend> you B<must not> call I<any> function on the
		883	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		884	without a previous call to C<ev_suspend>.
		885
		886	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		887	event loop time (see C<ev_now_update>).
		888
612	=item ev_loop (loop, int flags)	889	=item bool ev_run (loop, int flags)
613		890
614	Finally, this is it, the event handler. This function usually is called	891	Finally, this is it, the event handler. This function usually is called
615	after you initialised all your watchers and you want to start handling	892	after you have initialised all your watchers and you want to start
616	events.	893	handling events. It will ask the operating system for any new events, call
		894	the watcher callbacks, and then repeat the whole process indefinitely: This
		895	is why event loops are called I<loops>.
617		896
618	If the flags argument is specified as C<0>, it will not return until	897	If the flags argument is specified as C<0>, it will keep handling events
619	either no event watchers are active anymore or C<ev_unloop> was called.	898	until either no event watchers are active anymore or C<ev_break> was
		899	called.
620		900
		901	The return value is false if there are no more active watchers (which
		902	usually means "all jobs done" or "deadlock"), and true in all other cases
		903	(which usually means " you should call C<ev_run> again").
		904
621	Please note that an explicit C<ev_unloop> is usually better than	905	Please note that an explicit C<ev_break> is usually better than
622	relying on all watchers to be stopped when deciding when a program has	906	relying on all watchers to be stopped when deciding when a program has
623	finished (especially in interactive programs), but having a program	907	finished (especially in interactive programs), but having a program
624	that automatically loops as long as it has to and no longer by virtue	908	that automatically loops as long as it has to and no longer by virtue
625	of relying on its watchers stopping correctly, that is truly a thing of	909	of relying on its watchers stopping correctly, that is truly a thing of
626	beauty.	910	beauty.
627		911
		912	This function is I<mostly> exception-safe - you can break out of a
		913	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		914	exception and so on. This does not decrement the C<ev_depth> value, nor
		915	will it clear any outstanding C<EVBREAK_ONE> breaks.
		916
628	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	917	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
629	those events and any already outstanding ones, but will not block your	918	those events and any already outstanding ones, but will not wait and
630	process in case there are no events and will return after one iteration of	919	block your process in case there are no events and will return after one
631	the loop.	920	iteration of the loop. This is sometimes useful to poll and handle new
		921	events while doing lengthy calculations, to keep the program responsive.
632		922
633	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	923	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
634	necessary) and will handle those and any already outstanding ones. It	924	necessary) and will handle those and any already outstanding ones. It
635	will block your process until at least one new event arrives (which could	925	will block your process until at least one new event arrives (which could
636	be an event internal to libev itself, so there is no guarentee that a	926	be an event internal to libev itself, so there is no guarantee that a
637	user-registered callback will be called), and will return after one	927	user-registered callback will be called), and will return after one
638	iteration of the loop.	928	iteration of the loop.
639		929
640	This is useful if you are waiting for some external event in conjunction	930	This is useful if you are waiting for some external event in conjunction
641	with something not expressible using other libev watchers (i.e. "roll your	931	with something not expressible using other libev watchers (i.e. "roll your
642	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	932	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
643	usually a better approach for this kind of thing.	933	usually a better approach for this kind of thing.
644		934
645	Here are the gory details of what C<ev_loop> does:	935	Here are the gory details of what C<ev_run> does (this is for your
		936	understanding, not a guarantee that things will work exactly like this in
		937	future versions):
646		938
		939	- Increment loop depth.
		940	- Reset the ev_break status.
647	- Before the first iteration, call any pending watchers.	941	- Before the first iteration, call any pending watchers.
		942	LOOP:
648	* If EVFLAG_FORKCHECK was used, check for a fork.	943	- If EVFLAG_FORKCHECK was used, check for a fork.
649	- If a fork was detected (by any means), queue and call all fork watchers.	944	- If a fork was detected (by any means), queue and call all fork watchers.
650	- Queue and call all prepare watchers.	945	- Queue and call all prepare watchers.
		946	- If ev_break was called, goto FINISH.
651	- If we have been forked, detach and recreate the kernel state	947	- If we have been forked, detach and recreate the kernel state
652	as to not disturb the other process.	948	as to not disturb the other process.
653	- Update the kernel state with all outstanding changes.	949	- Update the kernel state with all outstanding changes.
654	- Update the "event loop time" (ev_now ()).	950	- Update the "event loop time" (ev_now ()).
655	- Calculate for how long to sleep or block, if at all	951	- Calculate for how long to sleep or block, if at all
656	(active idle watchers, EVLOOP_NONBLOCK or not having	952	(active idle watchers, EVRUN_NOWAIT or not having
657	any active watchers at all will result in not sleeping).	953	any active watchers at all will result in not sleeping).
658	- Sleep if the I/O and timer collect interval say so.	954	- Sleep if the I/O and timer collect interval say so.
		955	- Increment loop iteration counter.
659	- Block the process, waiting for any events.	956	- Block the process, waiting for any events.
660	- Queue all outstanding I/O (fd) events.	957	- Queue all outstanding I/O (fd) events.
661	- Update the "event loop time" (ev_now ()), and do time jump adjustments.	958	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
662	- Queue all expired timers.	959	- Queue all expired timers.
663	- Queue all expired periodics.	960	- Queue all expired periodics.
664	- Unless any events are pending now, queue all idle watchers.	961	- Queue all idle watchers with priority higher than that of pending events.
665	- Queue all check watchers.	962	- Queue all check watchers.
666	- Call all queued watchers in reverse order (i.e. check watchers first).	963	- Call all queued watchers in reverse order (i.e. check watchers first).
667	Signals and child watchers are implemented as I/O watchers, and will	964	Signals and child watchers are implemented as I/O watchers, and will
668	be handled here by queueing them when their watcher gets executed.	965	be handled here by queueing them when their watcher gets executed.
669	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	966	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
670	were used, or there are no active watchers, return, otherwise	967	were used, or there are no active watchers, goto FINISH, otherwise
671	continue with step *.	968	continue with step LOOP.
		969	FINISH:
		970	- Reset the ev_break status iff it was EVBREAK_ONE.
		971	- Decrement the loop depth.
		972	- Return.
672		973
673	Example: Queue some jobs and then loop until no events are outstanding	974	Example: Queue some jobs and then loop until no events are outstanding
674	anymore.	975	anymore.
675		976
676	... queue jobs here, make sure they register event watchers as long	977	... queue jobs here, make sure they register event watchers as long
677	... as they still have work to do (even an idle watcher will do..)	978	... as they still have work to do (even an idle watcher will do..)
678	ev_loop (my_loop, 0);	979	ev_run (my_loop, 0);
679	... jobs done or somebody called unloop. yeah!	980	... jobs done or somebody called break. yeah!
680		981
681	=item ev_unloop (loop, how)	982	=item ev_break (loop, how)
682		983
683	Can be used to make a call to C<ev_loop> return early (but only after it	984	Can be used to make a call to C<ev_run> return early (but only after it
684	has processed all outstanding events). The C<how> argument must be either	985	has processed all outstanding events). The C<how> argument must be either
685	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	986	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
686	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	987	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
687		988
688	This "unloop state" will be cleared when entering C<ev_loop> again.	989	This "break state" will be cleared on the next call to C<ev_run>.
689		990
690	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.	991	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		992	which case it will have no effect.
691		993
692	=item ev_ref (loop)	994	=item ev_ref (loop)
693		995
694	=item ev_unref (loop)	996	=item ev_unref (loop)
695		997
696	Ref/unref can be used to add or remove a reference count on the event	998	Ref/unref can be used to add or remove a reference count on the event
697	loop: Every watcher keeps one reference, and as long as the reference	999	loop: Every watcher keeps one reference, and as long as the reference
698	count is nonzero, C<ev_loop> will not return on its own.	1000	count is nonzero, C<ev_run> will not return on its own.
699		1001
700	If you have a watcher you never unregister that should not keep C<ev_loop>	1002	This is useful when you have a watcher that you never intend to
701	from returning, call ev_unref() after starting, and ev_ref() before	1003	unregister, but that nevertheless should not keep C<ev_run> from
		1004	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
702	stopping it.	1005	before stopping it.
703		1006
704	As an example, libev itself uses this for its internal signal pipe: It is	1007	As an example, libev itself uses this for its internal signal pipe: It
705	not visible to the libev user and should not keep C<ev_loop> from exiting	1008	is not visible to the libev user and should not keep C<ev_run> from
706	if no event watchers registered by it are active. It is also an excellent	1009	exiting if no event watchers registered by it are active. It is also an
707	way to do this for generic recurring timers or from within third-party	1010	excellent way to do this for generic recurring timers or from within
708	libraries. Just remember to I<unref after start> and I<ref before stop>	1011	third-party libraries. Just remember to I<unref after start> and I<ref
709	(but only if the watcher wasn't active before, or was active before,	1012	before stop> (but only if the watcher wasn't active before, or was active
710	respectively).	1013	before, respectively. Note also that libev might stop watchers itself
		1014	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		1015	in the callback).
711		1016
712	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	1017	Example: Create a signal watcher, but keep it from keeping C<ev_run>
713	running when nothing else is active.	1018	running when nothing else is active.
714		1019
715	struct ev_signal exitsig;	1020	ev_signal exitsig;
716	ev_signal_init (&exitsig, sig_cb, SIGINT);	1021	ev_signal_init (&exitsig, sig_cb, SIGINT);
717	ev_signal_start (loop, &exitsig);	1022	ev_signal_start (loop, &exitsig);
718	evf_unref (loop);	1023	ev_unref (loop);
719		1024
720	Example: For some weird reason, unregister the above signal handler again.	1025	Example: For some weird reason, unregister the above signal handler again.
721		1026
722	ev_ref (loop);	1027	ev_ref (loop);
723	ev_signal_stop (loop, &exitsig);	1028	ev_signal_stop (loop, &exitsig);
…		…
743	overhead for the actual polling but can deliver many events at once.	1048	overhead for the actual polling but can deliver many events at once.
744		1049
745	By setting a higher I<io collect interval> you allow libev to spend more	1050	By setting a higher I<io collect interval> you allow libev to spend more
746	time collecting I/O events, so you can handle more events per iteration,	1051	time collecting I/O events, so you can handle more events per iteration,
747	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	1052	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
748	C<ev_timer>) will be not affected. Setting this to a non-null value will	1053	C<ev_timer>) will not be affected. Setting this to a non-null value will
749	introduce an additional C<ev_sleep ()> call into most loop iterations.	1054	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		1055	sleep time ensures that libev will not poll for I/O events more often then
		1056	once per this interval, on average (as long as the host time resolution is
		1057	good enough).
750		1058
751	Likewise, by setting a higher I<timeout collect interval> you allow libev	1059	Likewise, by setting a higher I<timeout collect interval> you allow libev
752	to spend more time collecting timeouts, at the expense of increased	1060	to spend more time collecting timeouts, at the expense of increased
753	latency/jitter/inexactness (the watcher callback will be called	1061	latency/jitter/inexactness (the watcher callback will be called
754	later). C<ev_io> watchers will not be affected. Setting this to a non-null	1062	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
756		1064
757	Many (busy) programs can usually benefit by setting the I/O collect	1065	Many (busy) programs can usually benefit by setting the I/O collect
758	interval to a value near C<0.1> or so, which is often enough for	1066	interval to a value near C<0.1> or so, which is often enough for
759	interactive servers (of course not for games), likewise for timeouts. It	1067	interactive servers (of course not for games), likewise for timeouts. It
760	usually doesn't make much sense to set it to a lower value than C<0.01>,	1068	usually doesn't make much sense to set it to a lower value than C<0.01>,
761	as this approaches the timing granularity of most systems.	1069	as this approaches the timing granularity of most systems. Note that if
		1070	you do transactions with the outside world and you can't increase the
		1071	parallelity, then this setting will limit your transaction rate (if you
		1072	need to poll once per transaction and the I/O collect interval is 0.01,
		1073	then you can't do more than 100 transactions per second).
762		1074
763	Setting the I<timeout collect interval> can improve the opportunity for	1075	Setting the I<timeout collect interval> can improve the opportunity for
764	saving power, as the program will "bundle" timer callback invocations that	1076	saving power, as the program will "bundle" timer callback invocations that
765	are "near" in time together, by delaying some, thus reducing the number of	1077	are "near" in time together, by delaying some, thus reducing the number of
766	times the process sleeps and wakes up again. Another useful technique to	1078	times the process sleeps and wakes up again. Another useful technique to
767	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	1079	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
768	they fire on, say, one-second boundaries only.	1080	they fire on, say, one-second boundaries only.
769		1081
		1082	Example: we only need 0.1s timeout granularity, and we wish not to poll
		1083	more often than 100 times per second:
		1084
		1085	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		1086	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		1087
		1088	=item ev_invoke_pending (loop)
		1089
		1090	This call will simply invoke all pending watchers while resetting their
		1091	pending state. Normally, C<ev_run> does this automatically when required,
		1092	but when overriding the invoke callback this call comes handy. This
		1093	function can be invoked from a watcher - this can be useful for example
		1094	when you want to do some lengthy calculation and want to pass further
		1095	event handling to another thread (you still have to make sure only one
		1096	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1097
		1098	=item int ev_pending_count (loop)
		1099
		1100	Returns the number of pending watchers - zero indicates that no watchers
		1101	are pending.
		1102
		1103	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1104
		1105	This overrides the invoke pending functionality of the loop: Instead of
		1106	invoking all pending watchers when there are any, C<ev_run> will call
		1107	this callback instead. This is useful, for example, when you want to
		1108	invoke the actual watchers inside another context (another thread etc.).
		1109
		1110	If you want to reset the callback, use C<ev_invoke_pending> as new
		1111	callback.
		1112
		1113	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1114
		1115	Sometimes you want to share the same loop between multiple threads. This
		1116	can be done relatively simply by putting mutex_lock/unlock calls around
		1117	each call to a libev function.
		1118
		1119	However, C<ev_run> can run an indefinite time, so it is not feasible
		1120	to wait for it to return. One way around this is to wake up the event
		1121	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1122	I<release> and I<acquire> callbacks on the loop.
		1123
		1124	When set, then C<release> will be called just before the thread is
		1125	suspended waiting for new events, and C<acquire> is called just
		1126	afterwards.
		1127
		1128	Ideally, C<release> will just call your mutex_unlock function, and
		1129	C<acquire> will just call the mutex_lock function again.
		1130
		1131	While event loop modifications are allowed between invocations of
		1132	C<release> and C<acquire> (that's their only purpose after all), no
		1133	modifications done will affect the event loop, i.e. adding watchers will
		1134	have no effect on the set of file descriptors being watched, or the time
		1135	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1136	to take note of any changes you made.
		1137
		1138	In theory, threads executing C<ev_run> will be async-cancel safe between
		1139	invocations of C<release> and C<acquire>.
		1140
		1141	See also the locking example in the C<THREADS> section later in this
		1142	document.
		1143
		1144	=item ev_set_userdata (loop, void *data)
		1145
		1146	=item void *ev_userdata (loop)
		1147
		1148	Set and retrieve a single C<void *> associated with a loop. When
		1149	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1150	C<0>.
		1151
		1152	These two functions can be used to associate arbitrary data with a loop,
		1153	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1154	C<acquire> callbacks described above, but of course can be (ab-)used for
		1155	any other purpose as well.
		1156
770	=item ev_loop_verify (loop)	1157	=item ev_verify (loop)
771		1158
772	This function only does something when C<EV_VERIFY> support has been	1159	This function only does something when C<EV_VERIFY> support has been
773	compiled in. which is the default for non-minimal builds. It tries to go	1160	compiled in, which is the default for non-minimal builds. It tries to go
774	through all internal structures and checks them for validity. If anything	1161	through all internal structures and checks them for validity. If anything
775	is found to be inconsistent, it will print an error message to standard	1162	is found to be inconsistent, it will print an error message to standard
776	error and call C<abort ()>.	1163	error and call C<abort ()>.
777		1164
778	This can be used to catch bugs inside libev itself: under normal	1165	This can be used to catch bugs inside libev itself: under normal
…		…
782	=back	1169	=back
783		1170
784		1171
785	=head1 ANATOMY OF A WATCHER	1172	=head1 ANATOMY OF A WATCHER
786		1173
		1174	In the following description, uppercase C<TYPE> in names stands for the
		1175	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1176	watchers and C<ev_io_start> for I/O watchers.
		1177
787	A watcher is a structure that you create and register to record your	1178	A watcher is an opaque structure that you allocate and register to record
788	interest in some event. For instance, if you want to wait for STDIN to	1179	your interest in some event. To make a concrete example, imagine you want
789	become readable, you would create an C<ev_io> watcher for that:	1180	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1181	for that:
790		1182
791	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1183	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
792	{	1184	{
793	ev_io_stop (w);	1185	ev_io_stop (w);
794	ev_unloop (loop, EVUNLOOP_ALL);	1186	ev_break (loop, EVBREAK_ALL);
795	}	1187	}
796		1188
797	struct ev_loop *loop = ev_default_loop (0);	1189	struct ev_loop *loop = ev_default_loop (0);
		1190
798	struct ev_io stdin_watcher;	1191	ev_io stdin_watcher;
		1192
799	ev_init (&stdin_watcher, my_cb);	1193	ev_init (&stdin_watcher, my_cb);
800	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1194	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
801	ev_io_start (loop, &stdin_watcher);	1195	ev_io_start (loop, &stdin_watcher);
		1196
802	ev_loop (loop, 0);	1197	ev_run (loop, 0);
803		1198
804	As you can see, you are responsible for allocating the memory for your	1199	As you can see, you are responsible for allocating the memory for your
805	watcher structures (and it is usually a bad idea to do this on the stack,	1200	watcher structures (and it is I<usually> a bad idea to do this on the
806	although this can sometimes be quite valid).	1201	stack).
807		1202
		1203	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1204	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1205
808	Each watcher structure must be initialised by a call to C<ev_init	1206	Each watcher structure must be initialised by a call to C<ev_init (watcher
809	(watcher *, callback)>, which expects a callback to be provided. This	1207	*, callback)>, which expects a callback to be provided. This callback is
810	callback gets invoked each time the event occurs (or, in the case of I/O	1208	invoked each time the event occurs (or, in the case of I/O watchers, each
811	watchers, each time the event loop detects that the file descriptor given	1209	time the event loop detects that the file descriptor given is readable
812	is readable and/or writable).	1210	and/or writable).
813		1211
814	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1212	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
815	with arguments specific to this watcher type. There is also a macro	1213	macro to configure it, with arguments specific to the watcher type. There
816	to combine initialisation and setting in one call: C<< ev_<type>_init	1214	is also a macro to combine initialisation and setting in one call: C<<
817	(watcher *, callback, ...) >>.	1215	ev_TYPE_init (watcher *, callback, ...) >>.
818		1216
819	To make the watcher actually watch out for events, you have to start it	1217	To make the watcher actually watch out for events, you have to start it
820	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1218	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
821	*) >>), and you can stop watching for events at any time by calling the	1219	*) >>), and you can stop watching for events at any time by calling the
822	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1220	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
823		1221
824	As long as your watcher is active (has been started but not stopped) you	1222	As long as your watcher is active (has been started but not stopped) you
825	must not touch the values stored in it. Most specifically you must never	1223	must not touch the values stored in it. Most specifically you must never
826	reinitialise it or call its C<set> macro.	1224	reinitialise it or call its C<ev_TYPE_set> macro.
827		1225
828	Each and every callback receives the event loop pointer as first, the	1226	Each and every callback receives the event loop pointer as first, the
829	registered watcher structure as second, and a bitset of received events as	1227	registered watcher structure as second, and a bitset of received events as
830	third argument.	1228	third argument.
831		1229
…		…
840	=item C<EV_WRITE>	1238	=item C<EV_WRITE>
841		1239
842	The file descriptor in the C<ev_io> watcher has become readable and/or	1240	The file descriptor in the C<ev_io> watcher has become readable and/or
843	writable.	1241	writable.
844		1242
845	=item C<EV_TIMEOUT>	1243	=item C<EV_TIMER>
846		1244
847	The C<ev_timer> watcher has timed out.	1245	The C<ev_timer> watcher has timed out.
848		1246
849	=item C<EV_PERIODIC>	1247	=item C<EV_PERIODIC>
850		1248
…		…
868		1266
869	=item C<EV_PREPARE>	1267	=item C<EV_PREPARE>
870		1268
871	=item C<EV_CHECK>	1269	=item C<EV_CHECK>
872		1270
873	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1271	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
874	to gather new events, and all C<ev_check> watchers are invoked just after	1272	gather new events, and all C<ev_check> watchers are queued (not invoked)
875	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1273	just after C<ev_run> has gathered them, but before it queues any callbacks
		1274	for any received events. That means C<ev_prepare> watchers are the last
		1275	watchers invoked before the event loop sleeps or polls for new events, and
		1276	C<ev_check> watchers will be invoked before any other watchers of the same
		1277	or lower priority within an event loop iteration.
		1278
876	received events. Callbacks of both watcher types can start and stop as	1279	Callbacks of both watcher types can start and stop as many watchers as
877	many watchers as they want, and all of them will be taken into account	1280	they want, and all of them will be taken into account (for example, a
878	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1281	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
879	C<ev_loop> from blocking).	1282	blocking).
880		1283
881	=item C<EV_EMBED>	1284	=item C<EV_EMBED>
882		1285
883	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1286	The embedded event loop specified in the C<ev_embed> watcher needs attention.
884		1287
885	=item C<EV_FORK>	1288	=item C<EV_FORK>
886		1289
887	The event loop has been resumed in the child process after fork (see	1290	The event loop has been resumed in the child process after fork (see
888	C<ev_fork>).	1291	C<ev_fork>).
889		1292
		1293	=item C<EV_CLEANUP>
		1294
		1295	The event loop is about to be destroyed (see C<ev_cleanup>).
		1296
890	=item C<EV_ASYNC>	1297	=item C<EV_ASYNC>
891		1298
892	The given async watcher has been asynchronously notified (see C<ev_async>).	1299	The given async watcher has been asynchronously notified (see C<ev_async>).
		1300
		1301	=item C<EV_CUSTOM>
		1302
		1303	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1304	by libev users to signal watchers (e.g. via C<ev_feed_event>).
893		1305
894	=item C<EV_ERROR>	1306	=item C<EV_ERROR>
895		1307
896	An unspecified error has occurred, the watcher has been stopped. This might	1308	An unspecified error has occurred, the watcher has been stopped. This might
897	happen because the watcher could not be properly started because libev	1309	happen because the watcher could not be properly started because libev
898	ran out of memory, a file descriptor was found to be closed or any other	1310	ran out of memory, a file descriptor was found to be closed or any other
		1311	problem. Libev considers these application bugs.
		1312
899	problem. You best act on it by reporting the problem and somehow coping	1313	You best act on it by reporting the problem and somehow coping with the
900	with the watcher being stopped.	1314	watcher being stopped. Note that well-written programs should not receive
		1315	an error ever, so when your watcher receives it, this usually indicates a
		1316	bug in your program.
901		1317
902	Libev will usually signal a few "dummy" events together with an error, for	1318	Libev will usually signal a few "dummy" events together with an error, for
903	example it might indicate that a fd is readable or writable, and if your	1319	example it might indicate that a fd is readable or writable, and if your
904	callbacks is well-written it can just attempt the operation and cope with	1320	callbacks is well-written it can just attempt the operation and cope with
905	the error from read() or write(). This will not work in multi-threaded	1321	the error from read() or write(). This will not work in multi-threaded
…		…
908		1324
909	=back	1325	=back
910		1326
911	=head2 GENERIC WATCHER FUNCTIONS	1327	=head2 GENERIC WATCHER FUNCTIONS
912		1328
913	In the following description, C<TYPE> stands for the watcher type,
914	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
915
916	=over 4	1329	=over 4
917		1330
918	=item C<ev_init> (ev_TYPE *watcher, callback)	1331	=item C<ev_init> (ev_TYPE *watcher, callback)
919		1332
920	This macro initialises the generic portion of a watcher. The contents	1333	This macro initialises the generic portion of a watcher. The contents
…		…
925	which rolls both calls into one.	1338	which rolls both calls into one.
926		1339
927	You can reinitialise a watcher at any time as long as it has been stopped	1340	You can reinitialise a watcher at any time as long as it has been stopped
928	(or never started) and there are no pending events outstanding.	1341	(or never started) and there are no pending events outstanding.
929		1342
930	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1343	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
931	int revents)>.	1344	int revents)>.
932		1345
933	Example: Initialise an C<ev_io> watcher in two steps.	1346	Example: Initialise an C<ev_io> watcher in two steps.
934		1347
935	ev_io w;	1348	ev_io w;
936	ev_init (&w, my_cb);	1349	ev_init (&w, my_cb);
937	ev_io_set (&w, STDIN_FILENO, EV_READ);	1350	ev_io_set (&w, STDIN_FILENO, EV_READ);
938		1351
939	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1352	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
940		1353
941	This macro initialises the type-specific parts of a watcher. You need to	1354	This macro initialises the type-specific parts of a watcher. You need to
942	call C<ev_init> at least once before you call this macro, but you can	1355	call C<ev_init> at least once before you call this macro, but you can
943	call C<ev_TYPE_set> any number of times. You must not, however, call this	1356	call C<ev_TYPE_set> any number of times. You must not, however, call this
944	macro on a watcher that is active (it can be pending, however, which is a	1357	macro on a watcher that is active (it can be pending, however, which is a
…		…
957		1370
958	Example: Initialise and set an C<ev_io> watcher in one step.	1371	Example: Initialise and set an C<ev_io> watcher in one step.
959		1372
960	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);	1373	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
961		1374
962	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1375	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
963		1376
964	Starts (activates) the given watcher. Only active watchers will receive	1377	Starts (activates) the given watcher. Only active watchers will receive
965	events. If the watcher is already active nothing will happen.	1378	events. If the watcher is already active nothing will happen.
966		1379
967	Example: Start the C<ev_io> watcher that is being abused as example in this	1380	Example: Start the C<ev_io> watcher that is being abused as example in this
968	whole section.	1381	whole section.
969		1382
970	ev_io_start (EV_DEFAULT_UC, &w);	1383	ev_io_start (EV_DEFAULT_UC, &w);
971		1384
972	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1385	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
973		1386
974	Stops the given watcher if active, and clears the pending status (whether	1387	Stops the given watcher if active, and clears the pending status (whether
975	the watcher was active or not).	1388	the watcher was active or not).
976		1389
977	It is possible that stopped watchers are pending - for example,	1390	It is possible that stopped watchers are pending - for example,
…		…
997		1410
998	=item callback ev_cb (ev_TYPE *watcher)	1411	=item callback ev_cb (ev_TYPE *watcher)
999		1412
1000	Returns the callback currently set on the watcher.	1413	Returns the callback currently set on the watcher.
1001		1414
1002	=item ev_cb_set (ev_TYPE *watcher, callback)	1415	=item ev_set_cb (ev_TYPE *watcher, callback)
1003		1416
1004	Change the callback. You can change the callback at virtually any time	1417	Change the callback. You can change the callback at virtually any time
1005	(modulo threads).	1418	(modulo threads).
1006		1419
1007	=item ev_set_priority (ev_TYPE *watcher, priority)	1420	=item ev_set_priority (ev_TYPE *watcher, int priority)
1008		1421
1009	=item int ev_priority (ev_TYPE *watcher)	1422	=item int ev_priority (ev_TYPE *watcher)
1010		1423
1011	Set and query the priority of the watcher. The priority is a small	1424	Set and query the priority of the watcher. The priority is a small
1012	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1425	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1013	(default: C<-2>). Pending watchers with higher priority will be invoked	1426	(default: C<-2>). Pending watchers with higher priority will be invoked
1014	before watchers with lower priority, but priority will not keep watchers	1427	before watchers with lower priority, but priority will not keep watchers
1015	from being executed (except for C<ev_idle> watchers).	1428	from being executed (except for C<ev_idle> watchers).
1016		1429
1017	This means that priorities are I<only> used for ordering callback
1018	invocation after new events have been received. This is useful, for
1019	example, to reduce latency after idling, or more often, to bind two
1020	watchers on the same event and make sure one is called first.
1021
1022	If you need to suppress invocation when higher priority events are pending	1430	If you need to suppress invocation when higher priority events are pending
1023	you need to look at C<ev_idle> watchers, which provide this functionality.	1431	you need to look at C<ev_idle> watchers, which provide this functionality.
1024		1432
1025	You I<must not> change the priority of a watcher as long as it is active or	1433	You I<must not> change the priority of a watcher as long as it is active or
1026	pending.	1434	pending.
1027		1435
		1436	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1437	fine, as long as you do not mind that the priority value you query might
		1438	or might not have been clamped to the valid range.
		1439
1028	The default priority used by watchers when no priority has been set is	1440	The default priority used by watchers when no priority has been set is
1029	always C<0>, which is supposed to not be too high and not be too low :).	1441	always C<0>, which is supposed to not be too high and not be too low :).
1030		1442
1031	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1443	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1032	fine, as long as you do not mind that the priority value you query might	1444	priorities.
1033	or might not have been adjusted to be within valid range.
1034		1445
1035	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1446	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1036		1447
1037	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1448	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1038	C<loop> nor C<revents> need to be valid as long as the watcher callback	1449	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1046	watcher isn't pending it does nothing and returns C<0>.	1457	watcher isn't pending it does nothing and returns C<0>.
1047		1458
1048	Sometimes it can be useful to "poll" a watcher instead of waiting for its	1459	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1049	callback to be invoked, which can be accomplished with this function.	1460	callback to be invoked, which can be accomplished with this function.
1050		1461
		1462	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1463
		1464	Feeds the given event set into the event loop, as if the specified event
		1465	had happened for the specified watcher (which must be a pointer to an
		1466	initialised but not necessarily started event watcher). Obviously you must
		1467	not free the watcher as long as it has pending events.
		1468
		1469	Stopping the watcher, letting libev invoke it, or calling
		1470	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1471	not started in the first place.
		1472
		1473	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1474	functions that do not need a watcher.
		1475
1051	=back	1476	=back
1052		1477
		1478	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1479	OWN COMPOSITE WATCHERS> idioms.
1053		1480
1054	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1481	=head2 WATCHER STATES
1055		1482
1056	Each watcher has, by default, a member C<void *data> that you can change	1483	There are various watcher states mentioned throughout this manual -
1057	and read at any time: libev will completely ignore it. This can be used	1484	active, pending and so on. In this section these states and the rules to
1058	to associate arbitrary data with your watcher. If you need more data and	1485	transition between them will be described in more detail - and while these
1059	don't want to allocate memory and store a pointer to it in that data	1486	rules might look complicated, they usually do "the right thing".
1060	member, you can also "subclass" the watcher type and provide your own
1061	data:
1062		1487
1063	struct my_io	1488	=over 4
		1489
		1490	=item initialised
		1491
		1492	Before a watcher can be registered with the event loop it has to be
		1493	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1494	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1495
		1496	In this state it is simply some block of memory that is suitable for
		1497	use in an event loop. It can be moved around, freed, reused etc. at
		1498	will - as long as you either keep the memory contents intact, or call
		1499	C<ev_TYPE_init> again.
		1500
		1501	=item started/running/active
		1502
		1503	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1504	property of the event loop, and is actively waiting for events. While in
		1505	this state it cannot be accessed (except in a few documented ways), moved,
		1506	freed or anything else - the only legal thing is to keep a pointer to it,
		1507	and call libev functions on it that are documented to work on active watchers.
		1508
		1509	=item pending
		1510
		1511	If a watcher is active and libev determines that an event it is interested
		1512	in has occurred (such as a timer expiring), it will become pending. It will
		1513	stay in this pending state until either it is stopped or its callback is
		1514	about to be invoked, so it is not normally pending inside the watcher
		1515	callback.
		1516
		1517	The watcher might or might not be active while it is pending (for example,
		1518	an expired non-repeating timer can be pending but no longer active). If it
		1519	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1520	but it is still property of the event loop at this time, so cannot be
		1521	moved, freed or reused. And if it is active the rules described in the
		1522	previous item still apply.
		1523
		1524	It is also possible to feed an event on a watcher that is not active (e.g.
		1525	via C<ev_feed_event>), in which case it becomes pending without being
		1526	active.
		1527
		1528	=item stopped
		1529
		1530	A watcher can be stopped implicitly by libev (in which case it might still
		1531	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1532	latter will clear any pending state the watcher might be in, regardless
		1533	of whether it was active or not, so stopping a watcher explicitly before
		1534	freeing it is often a good idea.
		1535
		1536	While stopped (and not pending) the watcher is essentially in the
		1537	initialised state, that is, it can be reused, moved, modified in any way
		1538	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1539	it again).
		1540
		1541	=back
		1542
		1543	=head2 WATCHER PRIORITY MODELS
		1544
		1545	Many event loops support I<watcher priorities>, which are usually small
		1546	integers that influence the ordering of event callback invocation
		1547	between watchers in some way, all else being equal.
		1548
		1549	In libev, watcher priorities can be set using C<ev_set_priority>. See its
		1550	description for the more technical details such as the actual priority
		1551	range.
		1552
		1553	There are two common ways how these these priorities are being interpreted
		1554	by event loops:
		1555
		1556	In the more common lock-out model, higher priorities "lock out" invocation
		1557	of lower priority watchers, which means as long as higher priority
		1558	watchers receive events, lower priority watchers are not being invoked.
		1559
		1560	The less common only-for-ordering model uses priorities solely to order
		1561	callback invocation within a single event loop iteration: Higher priority
		1562	watchers are invoked before lower priority ones, but they all get invoked
		1563	before polling for new events.
		1564
		1565	Libev uses the second (only-for-ordering) model for all its watchers
		1566	except for idle watchers (which use the lock-out model).
		1567
		1568	The rationale behind this is that implementing the lock-out model for
		1569	watchers is not well supported by most kernel interfaces, and most event
		1570	libraries will just poll for the same events again and again as long as
		1571	their callbacks have not been executed, which is very inefficient in the
		1572	common case of one high-priority watcher locking out a mass of lower
		1573	priority ones.
		1574
		1575	Static (ordering) priorities are most useful when you have two or more
		1576	watchers handling the same resource: a typical usage example is having an
		1577	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1578	timeouts. Under load, data might be received while the program handles
		1579	other jobs, but since timers normally get invoked first, the timeout
		1580	handler will be executed before checking for data. In that case, giving
		1581	the timer a lower priority than the I/O watcher ensures that I/O will be
		1582	handled first even under adverse conditions (which is usually, but not
		1583	always, what you want).
		1584
		1585	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1586	will only be executed when no same or higher priority watchers have
		1587	received events, they can be used to implement the "lock-out" model when
		1588	required.
		1589
		1590	For example, to emulate how many other event libraries handle priorities,
		1591	you can associate an C<ev_idle> watcher to each such watcher, and in
		1592	the normal watcher callback, you just start the idle watcher. The real
		1593	processing is done in the idle watcher callback. This causes libev to
		1594	continuously poll and process kernel event data for the watcher, but when
		1595	the lock-out case is known to be rare (which in turn is rare :), this is
		1596	workable.
		1597
		1598	Usually, however, the lock-out model implemented that way will perform
		1599	miserably under the type of load it was designed to handle. In that case,
		1600	it might be preferable to stop the real watcher before starting the
		1601	idle watcher, so the kernel will not have to process the event in case
		1602	the actual processing will be delayed for considerable time.
		1603
		1604	Here is an example of an I/O watcher that should run at a strictly lower
		1605	priority than the default, and which should only process data when no
		1606	other events are pending:
		1607
		1608	ev_idle idle; // actual processing watcher
		1609	ev_io io; // actual event watcher
		1610
		1611	static void
		1612	io_cb (EV_P_ ev_io *w, int revents)
1064	{	1613	{
1065	struct ev_io io;	1614	// stop the I/O watcher, we received the event, but
1066	int otherfd;	1615	// are not yet ready to handle it.
1067	void *somedata;	1616	ev_io_stop (EV_A_ w);
1068	struct whatever *mostinteresting;	1617
		1618	// start the idle watcher to handle the actual event.
		1619	// it will not be executed as long as other watchers
		1620	// with the default priority are receiving events.
		1621	ev_idle_start (EV_A_ &idle);
1069	};	1622	}
1070		1623
1071	...	1624	static void
1072	struct my_io w;	1625	idle_cb (EV_P_ ev_idle *w, int revents)
1073	ev_io_init (&w.io, my_cb, fd, EV_READ);
1074
1075	And since your callback will be called with a pointer to the watcher, you
1076	can cast it back to your own type:
1077
1078	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
1079	{	1626	{
1080	struct my_io *w = (struct my_io *)w_;	1627	// actual processing
1081	...	1628	read (STDIN_FILENO, ...);
		1629
		1630	// have to start the I/O watcher again, as
		1631	// we have handled the event
		1632	ev_io_start (EV_P_ &io);
1082	}	1633	}
1083		1634
1084	More interesting and less C-conformant ways of casting your callback type	1635	// initialisation
1085	instead have been omitted.	1636	ev_idle_init (&idle, idle_cb);
		1637	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1638	ev_io_start (EV_DEFAULT_ &io);
1086		1639
1087	Another common scenario is to use some data structure with multiple	1640	In the "real" world, it might also be beneficial to start a timer, so that
1088	embedded watchers:	1641	low-priority connections can not be locked out forever under load. This
1089		1642	enables your program to keep a lower latency for important connections
1090	struct my_biggy	1643	during short periods of high load, while not completely locking out less
1091	{	1644	important ones.
1092	int some_data;
1093	ev_timer t1;
1094	ev_timer t2;
1095	}
1096
1097	In this case getting the pointer to C<my_biggy> is a bit more
1098	complicated: Either you store the address of your C<my_biggy> struct
1099	in the C<data> member of the watcher (for woozies), or you need to use
1100	some pointer arithmetic using C<offsetof> inside your watchers (for real
1101	programmers):
1102
1103	#include <stddef.h>
1104
1105	static void
1106	t1_cb (EV_P_ struct ev_timer *w, int revents)
1107	{
1108	struct my_biggy big = (struct my_biggy *
1109	(((char *)w) - offsetof (struct my_biggy, t1));
1110	}
1111
1112	static void
1113	t2_cb (EV_P_ struct ev_timer *w, int revents)
1114	{
1115	struct my_biggy big = (struct my_biggy *
1116	(((char *)w) - offsetof (struct my_biggy, t2));
1117	}
1118		1645
1119		1646
1120	=head1 WATCHER TYPES	1647	=head1 WATCHER TYPES
1121		1648
1122	This section describes each watcher in detail, but will not repeat	1649	This section describes each watcher in detail, but will not repeat
…		…
1146	In general you can register as many read and/or write event watchers per	1673	In general you can register as many read and/or write event watchers per
1147	fd as you want (as long as you don't confuse yourself). Setting all file	1674	fd as you want (as long as you don't confuse yourself). Setting all file
1148	descriptors to non-blocking mode is also usually a good idea (but not	1675	descriptors to non-blocking mode is also usually a good idea (but not
1149	required if you know what you are doing).	1676	required if you know what you are doing).
1150		1677
1151	If you cannot use non-blocking mode, then force the use of a
1152	known-to-be-good backend (at the time of this writing, this includes only
1153	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
1154
1155	Another thing you have to watch out for is that it is quite easy to	1678	Another thing you have to watch out for is that it is quite easy to
1156	receive "spurious" readiness notifications, that is your callback might	1679	receive "spurious" readiness notifications, that is, your callback might
1157	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1680	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1158	because there is no data. Not only are some backends known to create a	1681	because there is no data. It is very easy to get into this situation even
1159	lot of those (for example Solaris ports), it is very easy to get into	1682	with a relatively standard program structure. Thus it is best to always
1160	this situation even with a relatively standard program structure. Thus	1683	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1161	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1162	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1684	preferable to a program hanging until some data arrives.
1163		1685
1164	If you cannot run the fd in non-blocking mode (for example you should	1686	If you cannot run the fd in non-blocking mode (for example you should
1165	not play around with an Xlib connection), then you have to separately	1687	not play around with an Xlib connection), then you have to separately
1166	re-test whether a file descriptor is really ready with a known-to-be good	1688	re-test whether a file descriptor is really ready with a known-to-be good
1167	interface such as poll (fortunately in our Xlib example, Xlib already	1689	interface such as poll (fortunately in the case of Xlib, it already does
1168	does this on its own, so its quite safe to use). Some people additionally	1690	this on its own, so its quite safe to use). Some people additionally
1169	use C<SIGALRM> and an interval timer, just to be sure you won't block	1691	use C<SIGALRM> and an interval timer, just to be sure you won't block
1170	indefinitely.	1692	indefinitely.
1171		1693
1172	But really, best use non-blocking mode.	1694	But really, best use non-blocking mode.
1173		1695
1174	=head3 The special problem of disappearing file descriptors	1696	=head3 The special problem of disappearing file descriptors
1175		1697
1176	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1698	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1177	descriptor (either due to calling C<close> explicitly or any other means,	1699	a file descriptor (either due to calling C<close> explicitly or any other
1178	such as C<dup2>). The reason is that you register interest in some file	1700	means, such as C<dup2>). The reason is that you register interest in some
1179	descriptor, but when it goes away, the operating system will silently drop	1701	file descriptor, but when it goes away, the operating system will silently
1180	this interest. If another file descriptor with the same number then is	1702	drop this interest. If another file descriptor with the same number then
1181	registered with libev, there is no efficient way to see that this is, in	1703	is registered with libev, there is no efficient way to see that this is,
1182	fact, a different file descriptor.	1704	in fact, a different file descriptor.
1183		1705
1184	To avoid having to explicitly tell libev about such cases, libev follows	1706	To avoid having to explicitly tell libev about such cases, libev follows
1185	the following policy: Each time C<ev_io_set> is being called, libev	1707	the following policy: Each time C<ev_io_set> is being called, libev
1186	will assume that this is potentially a new file descriptor, otherwise	1708	will assume that this is potentially a new file descriptor, otherwise
1187	it is assumed that the file descriptor stays the same. That means that	1709	it is assumed that the file descriptor stays the same. That means that
…		…
1201		1723
1202	There is no workaround possible except not registering events	1724	There is no workaround possible except not registering events
1203	for potentially C<dup ()>'ed file descriptors, or to resort to	1725	for potentially C<dup ()>'ed file descriptors, or to resort to
1204	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1726	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1205		1727
		1728	=head3 The special problem of files
		1729
		1730	Many people try to use C<select> (or libev) on file descriptors
		1731	representing files, and expect it to become ready when their program
		1732	doesn't block on disk accesses (which can take a long time on their own).
		1733
		1734	However, this cannot ever work in the "expected" way - you get a readiness
		1735	notification as soon as the kernel knows whether and how much data is
		1736	there, and in the case of open files, that's always the case, so you
		1737	always get a readiness notification instantly, and your read (or possibly
		1738	write) will still block on the disk I/O.
		1739
		1740	Another way to view it is that in the case of sockets, pipes, character
		1741	devices and so on, there is another party (the sender) that delivers data
		1742	on its own, but in the case of files, there is no such thing: the disk
		1743	will not send data on its own, simply because it doesn't know what you
		1744	wish to read - you would first have to request some data.
		1745
		1746	Since files are typically not-so-well supported by advanced notification
		1747	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1748	to files, even though you should not use it. The reason for this is
		1749	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1750	usually a tty, often a pipe, but also sometimes files or special devices
		1751	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1752	F</dev/urandom>), and even though the file might better be served with
		1753	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1754	it "just works" instead of freezing.
		1755
		1756	So avoid file descriptors pointing to files when you know it (e.g. use
		1757	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1758	when you rarely read from a file instead of from a socket, and want to
		1759	reuse the same code path.
		1760
1206	=head3 The special problem of fork	1761	=head3 The special problem of fork
1207		1762
1208	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1763	Some backends (epoll, kqueue, linuxaio, iouring) do not support C<fork ()>
1209	useless behaviour. Libev fully supports fork, but needs to be told about	1764	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1210	it in the child.	1765	to be told about it in the child if you want to continue to use it in the
		1766	child.
1211		1767
1212	To support fork in your programs, you either have to call	1768	To support fork in your child processes, you have to call C<ev_loop_fork
1213	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1769	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1214	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1770	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1215	C<EVBACKEND_POLL>.
1216		1771
1217	=head3 The special problem of SIGPIPE	1772	=head3 The special problem of SIGPIPE
1218		1773
1219	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1774	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1220	when writing to a pipe whose other end has been closed, your program gets	1775	when writing to a pipe whose other end has been closed, your program gets
…		…
1223		1778
1224	So when you encounter spurious, unexplained daemon exits, make sure you	1779	So when you encounter spurious, unexplained daemon exits, make sure you
1225	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1780	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1226	somewhere, as that would have given you a big clue).	1781	somewhere, as that would have given you a big clue).
1227		1782
		1783	=head3 The special problem of accept()ing when you can't
		1784
		1785	Many implementations of the POSIX C<accept> function (for example,
		1786	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1787	connection from the pending queue in all error cases.
		1788
		1789	For example, larger servers often run out of file descriptors (because
		1790	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1791	rejecting the connection, leading to libev signalling readiness on
		1792	the next iteration again (the connection still exists after all), and
		1793	typically causing the program to loop at 100% CPU usage.
		1794
		1795	Unfortunately, the set of errors that cause this issue differs between
		1796	operating systems, there is usually little the app can do to remedy the
		1797	situation, and no known thread-safe method of removing the connection to
		1798	cope with overload is known (to me).
		1799
		1800	One of the easiest ways to handle this situation is to just ignore it
		1801	- when the program encounters an overload, it will just loop until the
		1802	situation is over. While this is a form of busy waiting, no OS offers an
		1803	event-based way to handle this situation, so it's the best one can do.
		1804
		1805	A better way to handle the situation is to log any errors other than
		1806	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1807	messages, and continue as usual, which at least gives the user an idea of
		1808	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1809	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1810	usage.
		1811
		1812	If your program is single-threaded, then you could also keep a dummy file
		1813	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1814	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1815	close that fd, and create a new dummy fd. This will gracefully refuse
		1816	clients under typical overload conditions.
		1817
		1818	The last way to handle it is to simply log the error and C<exit>, as
		1819	is often done with C<malloc> failures, but this results in an easy
		1820	opportunity for a DoS attack.
1228		1821
1229	=head3 Watcher-Specific Functions	1822	=head3 Watcher-Specific Functions
1230		1823
1231	=over 4	1824	=over 4
1232		1825
…		…
1253	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1846	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1254	readable, but only once. Since it is likely line-buffered, you could	1847	readable, but only once. Since it is likely line-buffered, you could
1255	attempt to read a whole line in the callback.	1848	attempt to read a whole line in the callback.
1256		1849
1257	static void	1850	static void
1258	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1851	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1259	{	1852	{
1260	ev_io_stop (loop, w);	1853	ev_io_stop (loop, w);
1261	.. read from stdin here (or from w->fd) and handle any I/O errors	1854	.. read from stdin here (or from w->fd) and handle any I/O errors
1262	}	1855	}
1263		1856
1264	...	1857	...
1265	struct ev_loop *loop = ev_default_init (0);	1858	struct ev_loop *loop = ev_default_init (0);
1266	struct ev_io stdin_readable;	1859	ev_io stdin_readable;
1267	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1860	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1268	ev_io_start (loop, &stdin_readable);	1861	ev_io_start (loop, &stdin_readable);
1269	ev_loop (loop, 0);	1862	ev_run (loop, 0);
1270		1863
1271		1864
1272	=head2 C<ev_timer> - relative and optionally repeating timeouts	1865	=head2 C<ev_timer> - relative and optionally repeating timeouts
1273		1866
1274	Timer watchers are simple relative timers that generate an event after a	1867	Timer watchers are simple relative timers that generate an event after a
…		…
1279	year, it will still time out after (roughly) one hour. "Roughly" because	1872	year, it will still time out after (roughly) one hour. "Roughly" because
1280	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1873	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1281	monotonic clock option helps a lot here).	1874	monotonic clock option helps a lot here).
1282		1875
1283	The callback is guaranteed to be invoked only I<after> its timeout has	1876	The callback is guaranteed to be invoked only I<after> its timeout has
1284	passed, but if multiple timers become ready during the same loop iteration	1877	passed (not I<at>, so on systems with very low-resolution clocks this
1285	then order of execution is undefined.	1878	might introduce a small delay, see "the special problem of being too
		1879	early", below). If multiple timers become ready during the same loop
		1880	iteration then the ones with earlier time-out values are invoked before
		1881	ones of the same priority with later time-out values (but this is no
		1882	longer true when a callback calls C<ev_run> recursively).
		1883
		1884	=head3 Be smart about timeouts
		1885
		1886	Many real-world problems involve some kind of timeout, usually for error
		1887	recovery. A typical example is an HTTP request - if the other side hangs,
		1888	you want to raise some error after a while.
		1889
		1890	What follows are some ways to handle this problem, from obvious and
		1891	inefficient to smart and efficient.
		1892
		1893	In the following, a 60 second activity timeout is assumed - a timeout that
		1894	gets reset to 60 seconds each time there is activity (e.g. each time some
		1895	data or other life sign was received).
		1896
		1897	=over 4
		1898
		1899	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1900
		1901	This is the most obvious, but not the most simple way: In the beginning,
		1902	start the watcher:
		1903
		1904	ev_timer_init (timer, callback, 60., 0.);
		1905	ev_timer_start (loop, timer);
		1906
		1907	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1908	and start it again:
		1909
		1910	ev_timer_stop (loop, timer);
		1911	ev_timer_set (timer, 60., 0.);
		1912	ev_timer_start (loop, timer);
		1913
		1914	This is relatively simple to implement, but means that each time there is
		1915	some activity, libev will first have to remove the timer from its internal
		1916	data structure and then add it again. Libev tries to be fast, but it's
		1917	still not a constant-time operation.
		1918
		1919	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1920
		1921	This is the easiest way, and involves using C<ev_timer_again> instead of
		1922	C<ev_timer_start>.
		1923
		1924	To implement this, configure an C<ev_timer> with a C<repeat> value
		1925	of C<60> and then call C<ev_timer_again> at start and each time you
		1926	successfully read or write some data. If you go into an idle state where
		1927	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1928	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1929
		1930	That means you can ignore both the C<ev_timer_start> function and the
		1931	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1932	member and C<ev_timer_again>.
		1933
		1934	At start:
		1935
		1936	ev_init (timer, callback);
		1937	timer->repeat = 60.;
		1938	ev_timer_again (loop, timer);
		1939
		1940	Each time there is some activity:
		1941
		1942	ev_timer_again (loop, timer);
		1943
		1944	It is even possible to change the time-out on the fly, regardless of
		1945	whether the watcher is active or not:
		1946
		1947	timer->repeat = 30.;
		1948	ev_timer_again (loop, timer);
		1949
		1950	This is slightly more efficient then stopping/starting the timer each time
		1951	you want to modify its timeout value, as libev does not have to completely
		1952	remove and re-insert the timer from/into its internal data structure.
		1953
		1954	It is, however, even simpler than the "obvious" way to do it.
		1955
		1956	=item 3. Let the timer time out, but then re-arm it as required.
		1957
		1958	This method is more tricky, but usually most efficient: Most timeouts are
		1959	relatively long compared to the intervals between other activity - in
		1960	our example, within 60 seconds, there are usually many I/O events with
		1961	associated activity resets.
		1962
		1963	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1964	but remember the time of last activity, and check for a real timeout only
		1965	within the callback:
		1966
		1967	ev_tstamp timeout = 60.;
		1968	ev_tstamp last_activity; // time of last activity
		1969	ev_timer timer;
		1970
		1971	static void
		1972	callback (EV_P_ ev_timer *w, int revents)
		1973	{
		1974	// calculate when the timeout would happen
		1975	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1976
		1977	// if negative, it means we the timeout already occurred
		1978	if (after < 0.)
		1979	{
		1980	// timeout occurred, take action
		1981	}
		1982	else
		1983	{
		1984	// callback was invoked, but there was some recent
		1985	// activity. simply restart the timer to time out
		1986	// after "after" seconds, which is the earliest time
		1987	// the timeout can occur.
		1988	ev_timer_set (w, after, 0.);
		1989	ev_timer_start (EV_A_ w);
		1990	}
		1991	}
		1992
		1993	To summarise the callback: first calculate in how many seconds the
		1994	timeout will occur (by calculating the absolute time when it would occur,
		1995	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1996	(EV_A)> from that).
		1997
		1998	If this value is negative, then we are already past the timeout, i.e. we
		1999	timed out, and need to do whatever is needed in this case.
		2000
		2001	Otherwise, we now the earliest time at which the timeout would trigger,
		2002	and simply start the timer with this timeout value.
		2003
		2004	In other words, each time the callback is invoked it will check whether
		2005	the timeout occurred. If not, it will simply reschedule itself to check
		2006	again at the earliest time it could time out. Rinse. Repeat.
		2007
		2008	This scheme causes more callback invocations (about one every 60 seconds
		2009	minus half the average time between activity), but virtually no calls to
		2010	libev to change the timeout.
		2011
		2012	To start the machinery, simply initialise the watcher and set
		2013	C<last_activity> to the current time (meaning there was some activity just
		2014	now), then call the callback, which will "do the right thing" and start
		2015	the timer:
		2016
		2017	last_activity = ev_now (EV_A);
		2018	ev_init (&timer, callback);
		2019	callback (EV_A_ &timer, 0);
		2020
		2021	When there is some activity, simply store the current time in
		2022	C<last_activity>, no libev calls at all:
		2023
		2024	if (activity detected)
		2025	last_activity = ev_now (EV_A);
		2026
		2027	When your timeout value changes, then the timeout can be changed by simply
		2028	providing a new value, stopping the timer and calling the callback, which
		2029	will again do the right thing (for example, time out immediately :).
		2030
		2031	timeout = new_value;
		2032	ev_timer_stop (EV_A_ &timer);
		2033	callback (EV_A_ &timer, 0);
		2034
		2035	This technique is slightly more complex, but in most cases where the
		2036	time-out is unlikely to be triggered, much more efficient.
		2037
		2038	=item 4. Wee, just use a double-linked list for your timeouts.
		2039
		2040	If there is not one request, but many thousands (millions...), all
		2041	employing some kind of timeout with the same timeout value, then one can
		2042	do even better:
		2043
		2044	When starting the timeout, calculate the timeout value and put the timeout
		2045	at the I<end> of the list.
		2046
		2047	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		2048	the list is expected to fire (for example, using the technique #3).
		2049
		2050	When there is some activity, remove the timer from the list, recalculate
		2051	the timeout, append it to the end of the list again, and make sure to
		2052	update the C<ev_timer> if it was taken from the beginning of the list.
		2053
		2054	This way, one can manage an unlimited number of timeouts in O(1) time for
		2055	starting, stopping and updating the timers, at the expense of a major
		2056	complication, and having to use a constant timeout. The constant timeout
		2057	ensures that the list stays sorted.
		2058
		2059	=back
		2060
		2061	So which method the best?
		2062
		2063	Method #2 is a simple no-brain-required solution that is adequate in most
		2064	situations. Method #3 requires a bit more thinking, but handles many cases
		2065	better, and isn't very complicated either. In most case, choosing either
		2066	one is fine, with #3 being better in typical situations.
		2067
		2068	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		2069	rather complicated, but extremely efficient, something that really pays
		2070	off after the first million or so of active timers, i.e. it's usually
		2071	overkill :)
		2072
		2073	=head3 The special problem of being too early
		2074
		2075	If you ask a timer to call your callback after three seconds, then
		2076	you expect it to be invoked after three seconds - but of course, this
		2077	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2078	guaranteed to any precision by libev - imagine somebody suspending the
		2079	process with a STOP signal for a few hours for example.
		2080
		2081	So, libev tries to invoke your callback as soon as possible I<after> the
		2082	delay has occurred, but cannot guarantee this.
		2083
		2084	A less obvious failure mode is calling your callback too early: many event
		2085	loops compare timestamps with a "elapsed delay >= requested delay", but
		2086	this can cause your callback to be invoked much earlier than you would
		2087	expect.
		2088
		2089	To see why, imagine a system with a clock that only offers full second
		2090	resolution (think windows if you can't come up with a broken enough OS
		2091	yourself). If you schedule a one-second timer at the time 500.9, then the
		2092	event loop will schedule your timeout to elapse at a system time of 500
		2093	(500.9 truncated to the resolution) + 1, or 501.
		2094
		2095	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2096	501" and invoke the callback 0.1s after it was started, even though a
		2097	one-second delay was requested - this is being "too early", despite best
		2098	intentions.
		2099
		2100	This is the reason why libev will never invoke the callback if the elapsed
		2101	delay equals the requested delay, but only when the elapsed delay is
		2102	larger than the requested delay. In the example above, libev would only invoke
		2103	the callback at system time 502, or 1.1s after the timer was started.
		2104
		2105	So, while libev cannot guarantee that your callback will be invoked
		2106	exactly when requested, it I<can> and I<does> guarantee that the requested
		2107	delay has actually elapsed, or in other words, it always errs on the "too
		2108	late" side of things.
1286		2109
1287	=head3 The special problem of time updates	2110	=head3 The special problem of time updates
1288		2111
1289	Establishing the current time is a costly operation (it usually takes at	2112	Establishing the current time is a costly operation (it usually takes
1290	least two system calls): EV therefore updates its idea of the current	2113	at least one system call): EV therefore updates its idea of the current
1291	time only before and after C<ev_loop> collects new events, which causes a	2114	time only before and after C<ev_run> collects new events, which causes a
1292	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2115	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1293	lots of events in one iteration.	2116	lots of events in one iteration.
1294		2117
1295	The relative timeouts are calculated relative to the C<ev_now ()>	2118	The relative timeouts are calculated relative to the C<ev_now ()>
1296	time. This is usually the right thing as this timestamp refers to the time	2119	time. This is usually the right thing as this timestamp refers to the time
1297	of the event triggering whatever timeout you are modifying/starting. If	2120	of the event triggering whatever timeout you are modifying/starting. If
1298	you suspect event processing to be delayed and you I<need> to base the	2121	you suspect event processing to be delayed and you I<need> to base the
1299	timeout on the current time, use something like this to adjust for this:	2122	timeout on the current time, use something like the following to adjust
		2123	for it:
1300		2124
1301	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2125	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1302		2126
1303	If the event loop is suspended for a long time, you can also force an	2127	If the event loop is suspended for a long time, you can also force an
1304	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2128	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1305	()>.	2129	()>, although that will push the event time of all outstanding events
		2130	further into the future.
		2131
		2132	=head3 The special problem of unsynchronised clocks
		2133
		2134	Modern systems have a variety of clocks - libev itself uses the normal
		2135	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2136	jumps).
		2137
		2138	Neither of these clocks is synchronised with each other or any other clock
		2139	on the system, so C<ev_time ()> might return a considerably different time
		2140	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2141	a call to C<gettimeofday> might return a second count that is one higher
		2142	than a directly following call to C<time>.
		2143
		2144	The moral of this is to only compare libev-related timestamps with
		2145	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2146	a second or so.
		2147
		2148	One more problem arises due to this lack of synchronisation: if libev uses
		2149	the system monotonic clock and you compare timestamps from C<ev_time>
		2150	or C<ev_now> from when you started your timer and when your callback is
		2151	invoked, you will find that sometimes the callback is a bit "early".
		2152
		2153	This is because C<ev_timer>s work in real time, not wall clock time, so
		2154	libev makes sure your callback is not invoked before the delay happened,
		2155	I<measured according to the real time>, not the system clock.
		2156
		2157	If your timeouts are based on a physical timescale (e.g. "time out this
		2158	connection after 100 seconds") then this shouldn't bother you as it is
		2159	exactly the right behaviour.
		2160
		2161	If you want to compare wall clock/system timestamps to your timers, then
		2162	you need to use C<ev_periodic>s, as these are based on the wall clock
		2163	time, where your comparisons will always generate correct results.
		2164
		2165	=head3 The special problems of suspended animation
		2166
		2167	When you leave the server world it is quite customary to hit machines that
		2168	can suspend/hibernate - what happens to the clocks during such a suspend?
		2169
		2170	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2171	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2172	to run until the system is suspended, but they will not advance while the
		2173	system is suspended. That means, on resume, it will be as if the program
		2174	was frozen for a few seconds, but the suspend time will not be counted
		2175	towards C<ev_timer> when a monotonic clock source is used. The real time
		2176	clock advanced as expected, but if it is used as sole clocksource, then a
		2177	long suspend would be detected as a time jump by libev, and timers would
		2178	be adjusted accordingly.
		2179
		2180	I would not be surprised to see different behaviour in different between
		2181	operating systems, OS versions or even different hardware.
		2182
		2183	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2184	time jump in the monotonic clocks and the realtime clock. If the program
		2185	is suspended for a very long time, and monotonic clock sources are in use,
		2186	then you can expect C<ev_timer>s to expire as the full suspension time
		2187	will be counted towards the timers. When no monotonic clock source is in
		2188	use, then libev will again assume a timejump and adjust accordingly.
		2189
		2190	It might be beneficial for this latter case to call C<ev_suspend>
		2191	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2192	deterministic behaviour in this case (you can do nothing against
		2193	C<SIGSTOP>).
1306		2194
1307	=head3 Watcher-Specific Functions and Data Members	2195	=head3 Watcher-Specific Functions and Data Members
1308		2196
1309	=over 4	2197	=over 4
1310		2198
1311	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2199	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1312		2200
1313	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2201	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1314		2202
1315	Configure the timer to trigger after C<after> seconds. If C<repeat>	2203	Configure the timer to trigger after C<after> seconds (fractional and
1316	is C<0.>, then it will automatically be stopped once the timeout is	2204	negative values are supported). If C<repeat> is C<0.>, then it will
1317	reached. If it is positive, then the timer will automatically be	2205	automatically be stopped once the timeout is reached. If it is positive,
1318	configured to trigger again C<repeat> seconds later, again, and again,	2206	then the timer will automatically be configured to trigger again C<repeat>
1319	until stopped manually.	2207	seconds later, again, and again, until stopped manually.
1320		2208
1321	The timer itself will do a best-effort at avoiding drift, that is, if	2209	The timer itself will do a best-effort at avoiding drift, that is, if
1322	you configure a timer to trigger every 10 seconds, then it will normally	2210	you configure a timer to trigger every 10 seconds, then it will normally
1323	trigger at exactly 10 second intervals. If, however, your program cannot	2211	trigger at exactly 10 second intervals. If, however, your program cannot
1324	keep up with the timer (because it takes longer than those 10 seconds to	2212	keep up with the timer (because it takes longer than those 10 seconds to
1325	do stuff) the timer will not fire more than once per event loop iteration.	2213	do stuff) the timer will not fire more than once per event loop iteration.
1326		2214
1327	=item ev_timer_again (loop, ev_timer *)	2215	=item ev_timer_again (loop, ev_timer *)
1328		2216
1329	This will act as if the timer timed out and restart it again if it is	2217	This will act as if the timer timed out, and restarts it again if it is
1330	repeating. The exact semantics are:	2218	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2219	timeout to the C<repeat> value and calling C<ev_timer_start>.
1331		2220
		2221	The exact semantics are as in the following rules, all of which will be
		2222	applied to the watcher:
		2223
		2224	=over 4
		2225
1332	If the timer is pending, its pending status is cleared.	2226	=item If the timer is pending, the pending status is always cleared.
1333		2227
1334	If the timer is started but non-repeating, stop it (as if it timed out).	2228	=item If the timer is started but non-repeating, stop it (as if it timed
		2229	out, without invoking it).
1335		2230
1336	If the timer is repeating, either start it if necessary (with the	2231	=item If the timer is repeating, make the C<repeat> value the new timeout
1337	C<repeat> value), or reset the running timer to the C<repeat> value.	2232	and start the timer, if necessary.
1338		2233
1339	This sounds a bit complicated, but here is a useful and typical	2234	=back
1340	example: Imagine you have a TCP connection and you want a so-called idle
1341	timeout, that is, you want to be called when there have been, say, 60
1342	seconds of inactivity on the socket. The easiest way to do this is to
1343	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1344	C<ev_timer_again> each time you successfully read or write some data. If
1345	you go into an idle state where you do not expect data to travel on the
1346	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1347	automatically restart it if need be.
1348		2235
1349	That means you can ignore the C<after> value and C<ev_timer_start>	2236	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1350	altogether and only ever use the C<repeat> value and C<ev_timer_again>:	2237	usage example.
1351		2238
1352	ev_timer_init (timer, callback, 0., 5.);	2239	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1353	ev_timer_again (loop, timer);
1354	...
1355	timer->again = 17.;
1356	ev_timer_again (loop, timer);
1357	...
1358	timer->again = 10.;
1359	ev_timer_again (loop, timer);
1360		2240
1361	This is more slightly efficient then stopping/starting the timer each time	2241	Returns the remaining time until a timer fires. If the timer is active,
1362	you want to modify its timeout value.	2242	then this time is relative to the current event loop time, otherwise it's
		2243	the timeout value currently configured.
1363		2244
1364	Note, however, that it is often even more efficient to remember the	2245	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1365	time of the last activity and let the timer time-out naturally. In the	2246	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
1366	callback, you then check whether the time-out is real, or, if there was	2247	will return C<4>. When the timer expires and is restarted, it will return
1367	some activity, you reschedule the watcher to time-out in "last_activity +	2248	roughly C<7> (likely slightly less as callback invocation takes some time,
1368	timeout - ev_now ()" seconds.	2249	too), and so on.
1369		2250
1370	=item ev_tstamp repeat [read-write]	2251	=item ev_tstamp repeat [read-write]
1371		2252
1372	The current C<repeat> value. Will be used each time the watcher times out	2253	The current C<repeat> value. Will be used each time the watcher times out
1373	or C<ev_timer_again> is called, and determines the next timeout (if any),	2254	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1378	=head3 Examples	2259	=head3 Examples
1379		2260
1380	Example: Create a timer that fires after 60 seconds.	2261	Example: Create a timer that fires after 60 seconds.
1381		2262
1382	static void	2263	static void
1383	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2264	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1384	{	2265	{
1385	.. one minute over, w is actually stopped right here	2266	.. one minute over, w is actually stopped right here
1386	}	2267	}
1387		2268
1388	struct ev_timer mytimer;	2269	ev_timer mytimer;
1389	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2270	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1390	ev_timer_start (loop, &mytimer);	2271	ev_timer_start (loop, &mytimer);
1391		2272
1392	Example: Create a timeout timer that times out after 10 seconds of	2273	Example: Create a timeout timer that times out after 10 seconds of
1393	inactivity.	2274	inactivity.
1394		2275
1395	static void	2276	static void
1396	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2277	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1397	{	2278	{
1398	.. ten seconds without any activity	2279	.. ten seconds without any activity
1399	}	2280	}
1400		2281
1401	struct ev_timer mytimer;	2282	ev_timer mytimer;
1402	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2283	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1403	ev_timer_again (&mytimer); /* start timer */	2284	ev_timer_again (&mytimer); /* start timer */
1404	ev_loop (loop, 0);	2285	ev_run (loop, 0);
1405		2286
1406	// and in some piece of code that gets executed on any "activity":	2287	// and in some piece of code that gets executed on any "activity":
1407	// reset the timeout to start ticking again at 10 seconds	2288	// reset the timeout to start ticking again at 10 seconds
1408	ev_timer_again (&mytimer);	2289	ev_timer_again (&mytimer);
1409		2290
…		…
1411	=head2 C<ev_periodic> - to cron or not to cron?	2292	=head2 C<ev_periodic> - to cron or not to cron?
1412		2293
1413	Periodic watchers are also timers of a kind, but they are very versatile	2294	Periodic watchers are also timers of a kind, but they are very versatile
1414	(and unfortunately a bit complex).	2295	(and unfortunately a bit complex).
1415		2296
1416	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2297	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1417	but on wall clock time (absolute time). You can tell a periodic watcher	2298	relative time, the physical time that passes) but on wall clock time
1418	to trigger after some specific point in time. For example, if you tell a	2299	(absolute time, the thing you can read on your calendar or clock). The
1419	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	2300	difference is that wall clock time can run faster or slower than real
1420	+ 10.>, that is, an absolute time not a delay) and then reset your system	2301	time, and time jumps are not uncommon (e.g. when you adjust your
1421	clock to January of the previous year, then it will take more than year	2302	wrist-watch).
1422	to trigger the event (unlike an C<ev_timer>, which would still trigger
1423	roughly 10 seconds later as it uses a relative timeout).
1424		2303
		2304	You can tell a periodic watcher to trigger after some specific point
		2305	in time: for example, if you tell a periodic watcher to trigger "in 10
		2306	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2307	not a delay) and then reset your system clock to January of the previous
		2308	year, then it will take a year or more to trigger the event (unlike an
		2309	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2310	it, as it uses a relative timeout).
		2311
1425	C<ev_periodic>s can also be used to implement vastly more complex timers,	2312	C<ev_periodic> watchers can also be used to implement vastly more complex
1426	such as triggering an event on each "midnight, local time", or other	2313	timers, such as triggering an event on each "midnight, local time", or
1427	complicated rules.	2314	other complicated rules. This cannot easily be done with C<ev_timer>
		2315	watchers, as those cannot react to time jumps.
1428		2316
1429	As with timers, the callback is guaranteed to be invoked only when the	2317	As with timers, the callback is guaranteed to be invoked only when the
1430	time (C<at>) has passed, but if multiple periodic timers become ready	2318	point in time where it is supposed to trigger has passed. If multiple
1431	during the same loop iteration, then order of execution is undefined.	2319	timers become ready during the same loop iteration then the ones with
		2320	earlier time-out values are invoked before ones with later time-out values
		2321	(but this is no longer true when a callback calls C<ev_run> recursively).
1432		2322
1433	=head3 Watcher-Specific Functions and Data Members	2323	=head3 Watcher-Specific Functions and Data Members
1434		2324
1435	=over 4	2325	=over 4
1436		2326
1437	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2327	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1438		2328
1439	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2329	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1440		2330
1441	Lots of arguments, lets sort it out... There are basically three modes of	2331	Lots of arguments, let's sort it out... There are basically three modes of
1442	operation, and we will explain them from simplest to most complex:	2332	operation, and we will explain them from simplest to most complex:
1443		2333
1444	=over 4	2334	=over 4
1445		2335
1446	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2336	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1447		2337
1448	In this configuration the watcher triggers an event after the wall clock	2338	In this configuration the watcher triggers an event after the wall clock
1449	time C<at> has passed. It will not repeat and will not adjust when a time	2339	time C<offset> has passed. It will not repeat and will not adjust when a
1450	jump occurs, that is, if it is to be run at January 1st 2011 then it will	2340	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1451	only run when the system clock reaches or surpasses this time.	2341	will be stopped and invoked when the system clock reaches or surpasses
		2342	this point in time.
1452		2343
1453	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2344	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1454		2345
1455	In this mode the watcher will always be scheduled to time out at the next	2346	In this mode the watcher will always be scheduled to time out at the next
1456	C<at + N * interval> time (for some integer N, which can also be negative)	2347	C<offset + N * interval> time (for some integer N, which can also be
1457	and then repeat, regardless of any time jumps.	2348	negative) and then repeat, regardless of any time jumps. The C<offset>
		2349	argument is merely an offset into the C<interval> periods.
1458		2350
1459	This can be used to create timers that do not drift with respect to the	2351	This can be used to create timers that do not drift with respect to the
1460	system clock, for example, here is a C<ev_periodic> that triggers each	2352	system clock, for example, here is an C<ev_periodic> that triggers each
1461	hour, on the hour:	2353	hour, on the hour (with respect to UTC):
1462		2354
1463	ev_periodic_set (&periodic, 0., 3600., 0);	2355	ev_periodic_set (&periodic, 0., 3600., 0);
1464		2356
1465	This doesn't mean there will always be 3600 seconds in between triggers,	2357	This doesn't mean there will always be 3600 seconds in between triggers,
1466	but only that the callback will be called when the system time shows a	2358	but only that the callback will be called when the system time shows a
1467	full hour (UTC), or more correctly, when the system time is evenly divisible	2359	full hour (UTC), or more correctly, when the system time is evenly divisible
1468	by 3600.	2360	by 3600.
1469		2361
1470	Another way to think about it (for the mathematically inclined) is that	2362	Another way to think about it (for the mathematically inclined) is that
1471	C<ev_periodic> will try to run the callback in this mode at the next possible	2363	C<ev_periodic> will try to run the callback in this mode at the next possible
1472	time where C<time = at (mod interval)>, regardless of any time jumps.	2364	time where C<time = offset (mod interval)>, regardless of any time jumps.
1473		2365
1474	For numerical stability it is preferable that the C<at> value is near	2366	The C<interval> I<MUST> be positive, and for numerical stability, the
1475	C<ev_now ()> (the current time), but there is no range requirement for	2367	interval value should be higher than C<1/8192> (which is around 100
1476	this value, and in fact is often specified as zero.	2368	microseconds) and C<offset> should be higher than C<0> and should have
		2369	at most a similar magnitude as the current time (say, within a factor of
		2370	ten). Typical values for offset are, in fact, C<0> or something between
		2371	C<0> and C<interval>, which is also the recommended range.
1477		2372
1478	Note also that there is an upper limit to how often a timer can fire (CPU	2373	Note also that there is an upper limit to how often a timer can fire (CPU
1479	speed for example), so if C<interval> is very small then timing stability	2374	speed for example), so if C<interval> is very small then timing stability
1480	will of course deteriorate. Libev itself tries to be exact to be about one	2375	will of course deteriorate. Libev itself tries to be exact to be about one
1481	millisecond (if the OS supports it and the machine is fast enough).	2376	millisecond (if the OS supports it and the machine is fast enough).
1482		2377
1483	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2378	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1484		2379
1485	In this mode the values for C<interval> and C<at> are both being	2380	In this mode the values for C<interval> and C<offset> are both being
1486	ignored. Instead, each time the periodic watcher gets scheduled, the	2381	ignored. Instead, each time the periodic watcher gets scheduled, the
1487	reschedule callback will be called with the watcher as first, and the	2382	reschedule callback will be called with the watcher as first, and the
1488	current time as second argument.	2383	current time as second argument.
1489		2384
1490	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2385	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1491	ever, or make ANY event loop modifications whatsoever>.	2386	or make ANY other event loop modifications whatsoever, unless explicitly
		2387	allowed by documentation here>.
1492		2388
1493	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2389	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1494	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	2390	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1495	only event loop modification you are allowed to do).	2391	only event loop modification you are allowed to do).
1496		2392
1497	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	2393	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1498	*w, ev_tstamp now)>, e.g.:	2394	*w, ev_tstamp now)>, e.g.:
1499		2395
		2396	static ev_tstamp
1500	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2397	my_rescheduler (ev_periodic *w, ev_tstamp now)
1501	{	2398	{
1502	return now + 60.;	2399	return now + 60.;
1503	}	2400	}
1504		2401
1505	It must return the next time to trigger, based on the passed time value	2402	It must return the next time to trigger, based on the passed time value
…		…
1509		2406
1510	NOTE: I<< This callback must always return a time that is higher than or	2407	NOTE: I<< This callback must always return a time that is higher than or
1511	equal to the passed C<now> value >>.	2408	equal to the passed C<now> value >>.
1512		2409
1513	This can be used to create very complex timers, such as a timer that	2410	This can be used to create very complex timers, such as a timer that
1514	triggers on "next midnight, local time". To do this, you would calculate the	2411	triggers on "next midnight, local time". To do this, you would calculate
1515	next midnight after C<now> and return the timestamp value for this. How	2412	the next midnight after C<now> and return the timestamp value for
1516	you do this is, again, up to you (but it is not trivial, which is the main	2413	this. Here is a (completely untested, no error checking) example on how to
1517	reason I omitted it as an example).	2414	do this:
		2415
		2416	#include <time.h>
		2417
		2418	static ev_tstamp
		2419	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2420	{
		2421	time_t tnow = (time_t)now;
		2422	struct tm tm;
		2423	localtime_r (&tnow, &tm);
		2424
		2425	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2426	++tm.tm_mday; // midnight next day
		2427
		2428	return mktime (&tm);
		2429	}
		2430
		2431	Note: this code might run into trouble on days that have more then two
		2432	midnights (beginning and end).
1518		2433
1519	=back	2434	=back
1520		2435
1521	=item ev_periodic_again (loop, ev_periodic *)	2436	=item ev_periodic_again (loop, ev_periodic *)
1522		2437
…		…
1525	a different time than the last time it was called (e.g. in a crond like	2440	a different time than the last time it was called (e.g. in a crond like
1526	program when the crontabs have changed).	2441	program when the crontabs have changed).
1527		2442
1528	=item ev_tstamp ev_periodic_at (ev_periodic *)	2443	=item ev_tstamp ev_periodic_at (ev_periodic *)
1529		2444
1530	When active, returns the absolute time that the watcher is supposed to	2445	When active, returns the absolute time that the watcher is supposed
1531	trigger next.	2446	to trigger next. This is not the same as the C<offset> argument to
		2447	C<ev_periodic_set>, but indeed works even in interval and manual
		2448	rescheduling modes.
1532		2449
1533	=item ev_tstamp offset [read-write]	2450	=item ev_tstamp offset [read-write]
1534		2451
1535	When repeating, this contains the offset value, otherwise this is the	2452	When repeating, this contains the offset value, otherwise this is the
1536	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2453	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2454	although libev might modify this value for better numerical stability).
1537		2455
1538	Can be modified any time, but changes only take effect when the periodic	2456	Can be modified any time, but changes only take effect when the periodic
1539	timer fires or C<ev_periodic_again> is being called.	2457	timer fires or C<ev_periodic_again> is being called.
1540		2458
1541	=item ev_tstamp interval [read-write]	2459	=item ev_tstamp interval [read-write]
1542		2460
1543	The current interval value. Can be modified any time, but changes only	2461	The current interval value. Can be modified any time, but changes only
1544	take effect when the periodic timer fires or C<ev_periodic_again> is being	2462	take effect when the periodic timer fires or C<ev_periodic_again> is being
1545	called.	2463	called.
1546		2464
1547	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2465	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1548		2466
1549	The current reschedule callback, or C<0>, if this functionality is	2467	The current reschedule callback, or C<0>, if this functionality is
1550	switched off. Can be changed any time, but changes only take effect when	2468	switched off. Can be changed any time, but changes only take effect when
1551	the periodic timer fires or C<ev_periodic_again> is being called.	2469	the periodic timer fires or C<ev_periodic_again> is being called.
1552		2470
…		…
1557	Example: Call a callback every hour, or, more precisely, whenever the	2475	Example: Call a callback every hour, or, more precisely, whenever the
1558	system time is divisible by 3600. The callback invocation times have	2476	system time is divisible by 3600. The callback invocation times have
1559	potentially a lot of jitter, but good long-term stability.	2477	potentially a lot of jitter, but good long-term stability.
1560		2478
1561	static void	2479	static void
1562	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2480	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1563	{	2481	{
1564	... its now a full hour (UTC, or TAI or whatever your clock follows)	2482	... its now a full hour (UTC, or TAI or whatever your clock follows)
1565	}	2483	}
1566		2484
1567	struct ev_periodic hourly_tick;	2485	ev_periodic hourly_tick;
1568	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2486	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1569	ev_periodic_start (loop, &hourly_tick);	2487	ev_periodic_start (loop, &hourly_tick);
1570		2488
1571	Example: The same as above, but use a reschedule callback to do it:	2489	Example: The same as above, but use a reschedule callback to do it:
1572		2490
1573	#include <math.h>	2491	#include <math.h>
1574		2492
1575	static ev_tstamp	2493	static ev_tstamp
1576	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2494	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1577	{	2495	{
1578	return now + (3600. - fmod (now, 3600.));	2496	return now + (3600. - fmod (now, 3600.));
1579	}	2497	}
1580		2498
1581	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2499	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1582		2500
1583	Example: Call a callback every hour, starting now:	2501	Example: Call a callback every hour, starting now:
1584		2502
1585	struct ev_periodic hourly_tick;	2503	ev_periodic hourly_tick;
1586	ev_periodic_init (&hourly_tick, clock_cb,	2504	ev_periodic_init (&hourly_tick, clock_cb,
1587	fmod (ev_now (loop), 3600.), 3600., 0);	2505	fmod (ev_now (loop), 3600.), 3600., 0);
1588	ev_periodic_start (loop, &hourly_tick);	2506	ev_periodic_start (loop, &hourly_tick);
1589		2507
1590		2508
1591	=head2 C<ev_signal> - signal me when a signal gets signalled!	2509	=head2 C<ev_signal> - signal me when a signal gets signalled!
1592		2510
1593	Signal watchers will trigger an event when the process receives a specific	2511	Signal watchers will trigger an event when the process receives a specific
1594	signal one or more times. Even though signals are very asynchronous, libev	2512	signal one or more times. Even though signals are very asynchronous, libev
1595	will try it's best to deliver signals synchronously, i.e. as part of the	2513	will try its best to deliver signals synchronously, i.e. as part of the
1596	normal event processing, like any other event.	2514	normal event processing, like any other event.
1597		2515
1598	If you want signals asynchronously, just use C<sigaction> as you would	2516	If you want signals to be delivered truly asynchronously, just use
1599	do without libev and forget about sharing the signal. You can even use	2517	C<sigaction> as you would do without libev and forget about sharing
1600	C<ev_async> from a signal handler to synchronously wake up an event loop.	2518	the signal. You can even use C<ev_async> from a signal handler to
		2519	synchronously wake up an event loop.
1601		2520
1602	You can configure as many watchers as you like per signal. Only when the	2521	You can configure as many watchers as you like for the same signal, but
1603	first watcher gets started will libev actually register a signal handler	2522	only within the same loop, i.e. you can watch for C<SIGINT> in your
1604	with the kernel (thus it coexists with your own signal handlers as long as	2523	default loop and for C<SIGIO> in another loop, but you cannot watch for
1605	you don't register any with libev for the same signal). Similarly, when	2524	C<SIGINT> in both the default loop and another loop at the same time. At
1606	the last signal watcher for a signal is stopped, libev will reset the	2525	the moment, C<SIGCHLD> is permanently tied to the default loop.
1607	signal handler to SIG_DFL (regardless of what it was set to before).	2526
		2527	Only after the first watcher for a signal is started will libev actually
		2528	register something with the kernel. It thus coexists with your own signal
		2529	handlers as long as you don't register any with libev for the same signal.
1608		2530
1609	If possible and supported, libev will install its handlers with	2531	If possible and supported, libev will install its handlers with
1610	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2532	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1611	interrupted. If you have a problem with system calls getting interrupted by	2533	not be unduly interrupted. If you have a problem with system calls getting
1612	signals you can block all signals in an C<ev_check> watcher and unblock	2534	interrupted by signals you can block all signals in an C<ev_check> watcher
1613	them in an C<ev_prepare> watcher.	2535	and unblock them in an C<ev_prepare> watcher.
		2536
		2537	=head3 The special problem of inheritance over fork/execve/pthread_create
		2538
		2539	Both the signal mask (C<sigprocmask>) and the signal disposition
		2540	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2541	stopping it again), that is, libev might or might not block the signal,
		2542	and might or might not set or restore the installed signal handler (but
		2543	see C<EVFLAG_NOSIGMASK>).
		2544
		2545	While this does not matter for the signal disposition (libev never
		2546	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2547	C<execve>), this matters for the signal mask: many programs do not expect
		2548	certain signals to be blocked.
		2549
		2550	This means that before calling C<exec> (from the child) you should reset
		2551	the signal mask to whatever "default" you expect (all clear is a good
		2552	choice usually).
		2553
		2554	The simplest way to ensure that the signal mask is reset in the child is
		2555	to install a fork handler with C<pthread_atfork> that resets it. That will
		2556	catch fork calls done by libraries (such as the libc) as well.
		2557
		2558	In current versions of libev, the signal will not be blocked indefinitely
		2559	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2560	the window of opportunity for problems, it will not go away, as libev
		2561	I<has> to modify the signal mask, at least temporarily.
		2562
		2563	So I can't stress this enough: I<If you do not reset your signal mask when
		2564	you expect it to be empty, you have a race condition in your code>. This
		2565	is not a libev-specific thing, this is true for most event libraries.
		2566
		2567	=head3 The special problem of threads signal handling
		2568
		2569	POSIX threads has problematic signal handling semantics, specifically,
		2570	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2571	threads in a process block signals, which is hard to achieve.
		2572
		2573	When you want to use sigwait (or mix libev signal handling with your own
		2574	for the same signals), you can tackle this problem by globally blocking
		2575	all signals before creating any threads (or creating them with a fully set
		2576	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2577	loops. Then designate one thread as "signal receiver thread" which handles
		2578	these signals. You can pass on any signals that libev might be interested
		2579	in by calling C<ev_feed_signal>.
1614		2580
1615	=head3 Watcher-Specific Functions and Data Members	2581	=head3 Watcher-Specific Functions and Data Members
1616		2582
1617	=over 4	2583	=over 4
1618		2584
…		…
1632	=head3 Examples	2598	=head3 Examples
1633		2599
1634	Example: Try to exit cleanly on SIGINT.	2600	Example: Try to exit cleanly on SIGINT.
1635		2601
1636	static void	2602	static void
1637	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2603	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1638	{	2604	{
1639	ev_unloop (loop, EVUNLOOP_ALL);	2605	ev_break (loop, EVBREAK_ALL);
1640	}	2606	}
1641		2607
1642	struct ev_signal signal_watcher;	2608	ev_signal signal_watcher;
1643	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2609	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1644	ev_signal_start (loop, &signal_watcher);	2610	ev_signal_start (loop, &signal_watcher);
1645		2611
1646		2612
1647	=head2 C<ev_child> - watch out for process status changes	2613	=head2 C<ev_child> - watch out for process status changes
…		…
1650	some child status changes (most typically when a child of yours dies or	2616	some child status changes (most typically when a child of yours dies or
1651	exits). It is permissible to install a child watcher I<after> the child	2617	exits). It is permissible to install a child watcher I<after> the child
1652	has been forked (which implies it might have already exited), as long	2618	has been forked (which implies it might have already exited), as long
1653	as the event loop isn't entered (or is continued from a watcher), i.e.,	2619	as the event loop isn't entered (or is continued from a watcher), i.e.,
1654	forking and then immediately registering a watcher for the child is fine,	2620	forking and then immediately registering a watcher for the child is fine,
1655	but forking and registering a watcher a few event loop iterations later is	2621	but forking and registering a watcher a few event loop iterations later or
1656	not.	2622	in the next callback invocation is not.
1657		2623
1658	Only the default event loop is capable of handling signals, and therefore	2624	Only the default event loop is capable of handling signals, and therefore
1659	you can only register child watchers in the default event loop.	2625	you can only register child watchers in the default event loop.
1660		2626
		2627	Due to some design glitches inside libev, child watchers will always be
		2628	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2629	libev)
		2630
1661	=head3 Process Interaction	2631	=head3 Process Interaction
1662		2632
1663	Libev grabs C<SIGCHLD> as soon as the default event loop is	2633	Libev grabs C<SIGCHLD> as soon as the default event loop is
1664	initialised. This is necessary to guarantee proper behaviour even if	2634	initialised. This is necessary to guarantee proper behaviour even if the
1665	the first child watcher is started after the child exits. The occurrence	2635	first child watcher is started after the child exits. The occurrence
1666	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2636	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1667	synchronously as part of the event loop processing. Libev always reaps all	2637	synchronously as part of the event loop processing. Libev always reaps all
1668	children, even ones not watched.	2638	children, even ones not watched.
1669		2639
1670	=head3 Overriding the Built-In Processing	2640	=head3 Overriding the Built-In Processing
…		…
1680	=head3 Stopping the Child Watcher	2650	=head3 Stopping the Child Watcher
1681		2651
1682	Currently, the child watcher never gets stopped, even when the	2652	Currently, the child watcher never gets stopped, even when the
1683	child terminates, so normally one needs to stop the watcher in the	2653	child terminates, so normally one needs to stop the watcher in the
1684	callback. Future versions of libev might stop the watcher automatically	2654	callback. Future versions of libev might stop the watcher automatically
1685	when a child exit is detected.	2655	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2656	problem).
1686		2657
1687	=head3 Watcher-Specific Functions and Data Members	2658	=head3 Watcher-Specific Functions and Data Members
1688		2659
1689	=over 4	2660	=over 4
1690		2661
…		…
1722	its completion.	2693	its completion.
1723		2694
1724	ev_child cw;	2695	ev_child cw;
1725		2696
1726	static void	2697	static void
1727	child_cb (EV_P_ struct ev_child *w, int revents)	2698	child_cb (EV_P_ ev_child *w, int revents)
1728	{	2699	{
1729	ev_child_stop (EV_A_ w);	2700	ev_child_stop (EV_A_ w);
1730	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2701	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1731	}	2702	}
1732		2703
…		…
1747		2718
1748		2719
1749	=head2 C<ev_stat> - did the file attributes just change?	2720	=head2 C<ev_stat> - did the file attributes just change?
1750		2721
1751	This watches a file system path for attribute changes. That is, it calls	2722	This watches a file system path for attribute changes. That is, it calls
1752	C<stat> regularly (or when the OS says it changed) and sees if it changed	2723	C<stat> on that path in regular intervals (or when the OS says it changed)
1753	compared to the last time, invoking the callback if it did.	2724	and sees if it changed compared to the last time, invoking the callback
		2725	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2726	happen after the watcher has been started will be reported.
1754		2727
1755	The path does not need to exist: changing from "path exists" to "path does	2728	The path does not need to exist: changing from "path exists" to "path does
1756	not exist" is a status change like any other. The condition "path does	2729	not exist" is a status change like any other. The condition "path does not
1757	not exist" is signified by the C<st_nlink> field being zero (which is	2730	exist" (or more correctly "path cannot be stat'ed") is signified by the
1758	otherwise always forced to be at least one) and all the other fields of	2731	C<st_nlink> field being zero (which is otherwise always forced to be at
1759	the stat buffer having unspecified contents.	2732	least one) and all the other fields of the stat buffer having unspecified
		2733	contents.
1760		2734
1761	The path I<should> be absolute and I<must not> end in a slash. If it is	2735	The path I<must not> end in a slash or contain special components such as
		2736	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1762	relative and your working directory changes, the behaviour is undefined.	2737	your working directory changes, then the behaviour is undefined.
1763		2738
1764	Since there is no standard kernel interface to do this, the portable	2739	Since there is no portable change notification interface available, the
1765	implementation simply calls C<stat (2)> regularly on the path to see if	2740	portable implementation simply calls C<stat(2)> regularly on the path
1766	it changed somehow. You can specify a recommended polling interval for	2741	to see if it changed somehow. You can specify a recommended polling
1767	this case. If you specify a polling interval of C<0> (highly recommended!)	2742	interval for this case. If you specify a polling interval of C<0> (highly
1768	then a I<suitable, unspecified default> value will be used (which	2743	recommended!) then a I<suitable, unspecified default> value will be used
1769	you can expect to be around five seconds, although this might change	2744	(which you can expect to be around five seconds, although this might
1770	dynamically). Libev will also impose a minimum interval which is currently	2745	change dynamically). Libev will also impose a minimum interval which is
1771	around C<0.1>, but thats usually overkill.	2746	currently around C<0.1>, but that's usually overkill.
1772		2747
1773	This watcher type is not meant for massive numbers of stat watchers,	2748	This watcher type is not meant for massive numbers of stat watchers,
1774	as even with OS-supported change notifications, this can be	2749	as even with OS-supported change notifications, this can be
1775	resource-intensive.	2750	resource-intensive.
1776		2751
1777	At the time of this writing, the only OS-specific interface implemented	2752	At the time of this writing, the only OS-specific interface implemented
1778	is the Linux inotify interface (implementing kqueue support is left as	2753	is the Linux inotify interface (implementing kqueue support is left as an
1779	an exercise for the reader. Note, however, that the author sees no way	2754	exercise for the reader. Note, however, that the author sees no way of
1780	of implementing C<ev_stat> semantics with kqueue).	2755	implementing C<ev_stat> semantics with kqueue, except as a hint).
1781		2756
1782	=head3 ABI Issues (Largefile Support)	2757	=head3 ABI Issues (Largefile Support)
1783		2758
1784	Libev by default (unless the user overrides this) uses the default	2759	Libev by default (unless the user overrides this) uses the default
1785	compilation environment, which means that on systems with large file	2760	compilation environment, which means that on systems with large file
1786	support disabled by default, you get the 32 bit version of the stat	2761	support disabled by default, you get the 32 bit version of the stat
1787	structure. When using the library from programs that change the ABI to	2762	structure. When using the library from programs that change the ABI to
1788	use 64 bit file offsets the programs will fail. In that case you have to	2763	use 64 bit file offsets the programs will fail. In that case you have to
1789	compile libev with the same flags to get binary compatibility. This is	2764	compile libev with the same flags to get binary compatibility. This is
1790	obviously the case with any flags that change the ABI, but the problem is	2765	obviously the case with any flags that change the ABI, but the problem is
1791	most noticeably disabled with ev_stat and large file support.	2766	most noticeably displayed with ev_stat and large file support.
1792		2767
1793	The solution for this is to lobby your distribution maker to make large	2768	The solution for this is to lobby your distribution maker to make large
1794	file interfaces available by default (as e.g. FreeBSD does) and not	2769	file interfaces available by default (as e.g. FreeBSD does) and not
1795	optional. Libev cannot simply switch on large file support because it has	2770	optional. Libev cannot simply switch on large file support because it has
1796	to exchange stat structures with application programs compiled using the	2771	to exchange stat structures with application programs compiled using the
1797	default compilation environment.	2772	default compilation environment.
1798		2773
1799	=head3 Inotify and Kqueue	2774	=head3 Inotify and Kqueue
1800		2775
1801	When C<inotify (7)> support has been compiled into libev (generally	2776	When C<inotify (7)> support has been compiled into libev and present at
1802	only available with Linux 2.6.25 or above due to bugs in earlier	2777	runtime, it will be used to speed up change detection where possible. The
1803	implementations) and present at runtime, it will be used to speed up	2778	inotify descriptor will be created lazily when the first C<ev_stat>
1804	change detection where possible. The inotify descriptor will be created	2779	watcher is being started.
1805	lazily when the first C<ev_stat> watcher is being started.
1806		2780
1807	Inotify presence does not change the semantics of C<ev_stat> watchers	2781	Inotify presence does not change the semantics of C<ev_stat> watchers
1808	except that changes might be detected earlier, and in some cases, to avoid	2782	except that changes might be detected earlier, and in some cases, to avoid
1809	making regular C<stat> calls. Even in the presence of inotify support	2783	making regular C<stat> calls. Even in the presence of inotify support
1810	there are many cases where libev has to resort to regular C<stat> polling,	2784	there are many cases where libev has to resort to regular C<stat> polling,
1811	but as long as the path exists, libev usually gets away without polling.	2785	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2786	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2787	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2788	xfs are fully working) libev usually gets away without polling.
1812		2789
1813	There is no support for kqueue, as apparently it cannot be used to	2790	There is no support for kqueue, as apparently it cannot be used to
1814	implement this functionality, due to the requirement of having a file	2791	implement this functionality, due to the requirement of having a file
1815	descriptor open on the object at all times, and detecting renames, unlinks	2792	descriptor open on the object at all times, and detecting renames, unlinks
1816	etc. is difficult.	2793	etc. is difficult.
1817		2794
		2795	=head3 C<stat ()> is a synchronous operation
		2796
		2797	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2798	the process. The exception are C<ev_stat> watchers - those call C<stat
		2799	()>, which is a synchronous operation.
		2800
		2801	For local paths, this usually doesn't matter: unless the system is very
		2802	busy or the intervals between stat's are large, a stat call will be fast,
		2803	as the path data is usually in memory already (except when starting the
		2804	watcher).
		2805
		2806	For networked file systems, calling C<stat ()> can block an indefinite
		2807	time due to network issues, and even under good conditions, a stat call
		2808	often takes multiple milliseconds.
		2809
		2810	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2811	paths, although this is fully supported by libev.
		2812
1818	=head3 The special problem of stat time resolution	2813	=head3 The special problem of stat time resolution
1819		2814
1820	The C<stat ()> system call only supports full-second resolution portably, and	2815	The C<stat ()> system call only supports full-second resolution portably,
1821	even on systems where the resolution is higher, most file systems still	2816	and even on systems where the resolution is higher, most file systems
1822	only support whole seconds.	2817	still only support whole seconds.
1823		2818
1824	That means that, if the time is the only thing that changes, you can	2819	That means that, if the time is the only thing that changes, you can
1825	easily miss updates: on the first update, C<ev_stat> detects a change and	2820	easily miss updates: on the first update, C<ev_stat> detects a change and
1826	calls your callback, which does something. When there is another update	2821	calls your callback, which does something. When there is another update
1827	within the same second, C<ev_stat> will be unable to detect unless the	2822	within the same second, C<ev_stat> will be unable to detect unless the
…		…
1966	Apart from keeping your process non-blocking (which is a useful	2961	Apart from keeping your process non-blocking (which is a useful
1967	effect on its own sometimes), idle watchers are a good place to do	2962	effect on its own sometimes), idle watchers are a good place to do
1968	"pseudo-background processing", or delay processing stuff to after the	2963	"pseudo-background processing", or delay processing stuff to after the
1969	event loop has handled all outstanding events.	2964	event loop has handled all outstanding events.
1970		2965
		2966	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2967
		2968	As long as there is at least one active idle watcher, libev will never
		2969	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2970	For this to work, the idle watcher doesn't need to be invoked at all - the
		2971	lowest priority will do.
		2972
		2973	This mode of operation can be useful together with an C<ev_check> watcher,
		2974	to do something on each event loop iteration - for example to balance load
		2975	between different connections.
		2976
		2977	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2978	example.
		2979
1971	=head3 Watcher-Specific Functions and Data Members	2980	=head3 Watcher-Specific Functions and Data Members
1972		2981
1973	=over 4	2982	=over 4
1974		2983
1975	=item ev_idle_init (ev_signal *, callback)	2984	=item ev_idle_init (ev_idle *, callback)
1976		2985
1977	Initialises and configures the idle watcher - it has no parameters of any	2986	Initialises and configures the idle watcher - it has no parameters of any
1978	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2987	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1979	believe me.	2988	believe me.
1980		2989
…		…
1984		2993
1985	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2994	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1986	callback, free it. Also, use no error checking, as usual.	2995	callback, free it. Also, use no error checking, as usual.
1987		2996
1988	static void	2997	static void
1989	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2998	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1990	{	2999	{
		3000	// stop the watcher
		3001	ev_idle_stop (loop, w);
		3002
		3003	// now we can free it
1991	free (w);	3004	free (w);
		3005
1992	// now do something you wanted to do when the program has	3006	// now do something you wanted to do when the program has
1993	// no longer anything immediate to do.	3007	// no longer anything immediate to do.
1994	}	3008	}
1995		3009
1996	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	3010	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1997	ev_idle_init (idle_watcher, idle_cb);	3011	ev_idle_init (idle_watcher, idle_cb);
1998	ev_idle_start (loop, idle_cb);	3012	ev_idle_start (loop, idle_watcher);
1999		3013
2000		3014
2001	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3015	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2002		3016
2003	Prepare and check watchers are usually (but not always) used in pairs:	3017	Prepare and check watchers are often (but not always) used in pairs:
2004	prepare watchers get invoked before the process blocks and check watchers	3018	prepare watchers get invoked before the process blocks and check watchers
2005	afterwards.	3019	afterwards.
2006		3020
2007	You I<must not> call C<ev_loop> or similar functions that enter	3021	You I<must not> call C<ev_run> (or similar functions that enter the
2008	the current event loop from either C<ev_prepare> or C<ev_check>	3022	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2009	watchers. Other loops than the current one are fine, however. The	3023	C<ev_check> watchers. Other loops than the current one are fine,
2010	rationale behind this is that you do not need to check for recursion in	3024	however. The rationale behind this is that you do not need to check
2011	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3025	for recursion in those watchers, i.e. the sequence will always be
2012	C<ev_check> so if you have one watcher of each kind they will always be	3026	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2013	called in pairs bracketing the blocking call.	3027	kind they will always be called in pairs bracketing the blocking call.
2014		3028
2015	Their main purpose is to integrate other event mechanisms into libev and	3029	Their main purpose is to integrate other event mechanisms into libev and
2016	their use is somewhat advanced. They could be used, for example, to track	3030	their use is somewhat advanced. They could be used, for example, to track
2017	variable changes, implement your own watchers, integrate net-snmp or a	3031	variable changes, implement your own watchers, integrate net-snmp or a
2018	coroutine library and lots more. They are also occasionally useful if	3032	coroutine library and lots more. They are also occasionally useful if
…		…
2036	with priority higher than or equal to the event loop and one coroutine	3050	with priority higher than or equal to the event loop and one coroutine
2037	of lower priority, but only once, using idle watchers to keep the event	3051	of lower priority, but only once, using idle watchers to keep the event
2038	loop from blocking if lower-priority coroutines are active, thus mapping	3052	loop from blocking if lower-priority coroutines are active, thus mapping
2039	low-priority coroutines to idle/background tasks).	3053	low-priority coroutines to idle/background tasks).
2040		3054
2041	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3055	When used for this purpose, it is recommended to give C<ev_check> watchers
2042	priority, to ensure that they are being run before any other watchers	3056	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2043	after the poll (this doesn't matter for C<ev_prepare> watchers).	3057	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3058	watchers).
2044		3059
2045	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3060	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2046	activate ("feed") events into libev. While libev fully supports this, they	3061	activate ("feed") events into libev. While libev fully supports this, they
2047	might get executed before other C<ev_check> watchers did their job. As	3062	might get executed before other C<ev_check> watchers did their job. As
2048	C<ev_check> watchers are often used to embed other (non-libev) event	3063	C<ev_check> watchers are often used to embed other (non-libev) event
2049	loops those other event loops might be in an unusable state until their	3064	loops those other event loops might be in an unusable state until their
2050	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3065	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2051	others).	3066	others).
2052		3067
		3068	=head3 Abusing an C<ev_check> watcher for its side-effect
		3069
		3070	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3071	useful because they are called once per event loop iteration. For
		3072	example, if you want to handle a large number of connections fairly, you
		3073	normally only do a bit of work for each active connection, and if there
		3074	is more work to do, you wait for the next event loop iteration, so other
		3075	connections have a chance of making progress.
		3076
		3077	Using an C<ev_check> watcher is almost enough: it will be called on the
		3078	next event loop iteration. However, that isn't as soon as possible -
		3079	without external events, your C<ev_check> watcher will not be invoked.
		3080
		3081	This is where C<ev_idle> watchers come in handy - all you need is a
		3082	single global idle watcher that is active as long as you have one active
		3083	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3084	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3085	invoked. Neither watcher alone can do that.
		3086
2053	=head3 Watcher-Specific Functions and Data Members	3087	=head3 Watcher-Specific Functions and Data Members
2054		3088
2055	=over 4	3089	=over 4
2056		3090
2057	=item ev_prepare_init (ev_prepare *, callback)	3091	=item ev_prepare_init (ev_prepare *, callback)
…		…
2082		3116
2083	static ev_io iow [nfd];	3117	static ev_io iow [nfd];
2084	static ev_timer tw;	3118	static ev_timer tw;
2085		3119
2086	static void	3120	static void
2087	io_cb (ev_loop *loop, ev_io *w, int revents)	3121	io_cb (struct ev_loop *loop, ev_io *w, int revents)
2088	{	3122	{
2089	}	3123	}
2090		3124
2091	// create io watchers for each fd and a timer before blocking	3125	// create io watchers for each fd and a timer before blocking
2092	static void	3126	static void
2093	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	3127	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2094	{	3128	{
2095	int timeout = 3600000;	3129	int timeout = 3600000;
2096	struct pollfd fds [nfd];	3130	struct pollfd fds [nfd];
2097	// actual code will need to loop here and realloc etc.	3131	// actual code will need to loop here and realloc etc.
2098	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	3132	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2099		3133
2100	/* the callback is illegal, but won't be called as we stop during check */	3134	/* the callback is illegal, but won't be called as we stop during check */
2101	ev_timer_init (&tw, 0, timeout * 1e-3);	3135	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2102	ev_timer_start (loop, &tw);	3136	ev_timer_start (loop, &tw);
2103		3137
2104	// create one ev_io per pollfd	3138	// create one ev_io per pollfd
2105	for (int i = 0; i < nfd; ++i)	3139	for (int i = 0; i < nfd; ++i)
2106	{	3140	{
…		…
2113	}	3147	}
2114	}	3148	}
2115		3149
2116	// stop all watchers after blocking	3150	// stop all watchers after blocking
2117	static void	3151	static void
2118	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	3152	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2119	{	3153	{
2120	ev_timer_stop (loop, &tw);	3154	ev_timer_stop (loop, &tw);
2121		3155
2122	for (int i = 0; i < nfd; ++i)	3156	for (int i = 0; i < nfd; ++i)
2123	{	3157	{
…		…
2180		3214
2181	if (timeout >= 0)	3215	if (timeout >= 0)
2182	// create/start timer	3216	// create/start timer
2183		3217
2184	// poll	3218	// poll
2185	ev_loop (EV_A_ 0);	3219	ev_run (EV_A_ 0);
2186		3220
2187	// stop timer again	3221	// stop timer again
2188	if (timeout >= 0)	3222	if (timeout >= 0)
2189	ev_timer_stop (EV_A_ &to);	3223	ev_timer_stop (EV_A_ &to);
2190		3224
…		…
2219	some fds have to be watched and handled very quickly (with low latency),	3253	some fds have to be watched and handled very quickly (with low latency),
2220	and even priorities and idle watchers might have too much overhead. In	3254	and even priorities and idle watchers might have too much overhead. In
2221	this case you would put all the high priority stuff in one loop and all	3255	this case you would put all the high priority stuff in one loop and all
2222	the rest in a second one, and embed the second one in the first.	3256	the rest in a second one, and embed the second one in the first.
2223		3257
2224	As long as the watcher is active, the callback will be invoked every time	3258	As long as the watcher is active, the callback will be invoked every
2225	there might be events pending in the embedded loop. The callback must then	3259	time there might be events pending in the embedded loop. The callback
2226	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3260	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2227	their callbacks (you could also start an idle watcher to give the embedded	3261	sweep and invoke their callbacks (the callback doesn't need to invoke the
2228	loop strictly lower priority for example). You can also set the callback	3262	C<ev_embed_sweep> function directly, it could also start an idle watcher
2229	to C<0>, in which case the embed watcher will automatically execute the	3263	to give the embedded loop strictly lower priority for example).
2230	embedded loop sweep.
2231		3264
2232	As long as the watcher is started it will automatically handle events. The	3265	You can also set the callback to C<0>, in which case the embed watcher
2233	callback will be invoked whenever some events have been handled. You can	3266	will automatically execute the embedded loop sweep whenever necessary.
2234	set the callback to C<0> to avoid having to specify one if you are not
2235	interested in that.
2236		3267
2237	Also, there have not currently been made special provisions for forking:	3268	Fork detection will be handled transparently while the C<ev_embed> watcher
2238	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3269	is active, i.e., the embedded loop will automatically be forked when the
2239	but you will also have to stop and restart any C<ev_embed> watchers	3270	embedding loop forks. In other cases, the user is responsible for calling
2240	yourself - but you can use a fork watcher to handle this automatically,	3271	C<ev_loop_fork> on the embedded loop.
2241	and future versions of libev might do just that.
2242		3272
2243	Unfortunately, not all backends are embeddable: only the ones returned by	3273	Unfortunately, not all backends are embeddable: only the ones returned by
2244	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3274	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2245	portable one.	3275	portable one.
2246		3276
…		…
2261		3291
2262	=over 4	3292	=over 4
2263		3293
2264	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3294	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2265		3295
2266	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3296	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2267		3297
2268	Configures the watcher to embed the given loop, which must be	3298	Configures the watcher to embed the given loop, which must be
2269	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3299	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2270	invoked automatically, otherwise it is the responsibility of the callback	3300	invoked automatically, otherwise it is the responsibility of the callback
2271	to invoke it (it will continue to be called until the sweep has been done,	3301	to invoke it (it will continue to be called until the sweep has been done,
2272	if you do not want that, you need to temporarily stop the embed watcher).	3302	if you do not want that, you need to temporarily stop the embed watcher).
2273		3303
2274	=item ev_embed_sweep (loop, ev_embed *)	3304	=item ev_embed_sweep (loop, ev_embed *)
2275		3305
2276	Make a single, non-blocking sweep over the embedded loop. This works	3306	Make a single, non-blocking sweep over the embedded loop. This works
2277	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3307	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
2278	appropriate way for embedded loops.	3308	appropriate way for embedded loops.
2279		3309
2280	=item struct ev_loop *other [read-only]	3310	=item struct ev_loop *other [read-only]
2281		3311
2282	The embedded event loop.	3312	The embedded event loop.
…		…
2291	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	3321	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2292	used).	3322	used).
2293		3323
2294	struct ev_loop *loop_hi = ev_default_init (0);	3324	struct ev_loop *loop_hi = ev_default_init (0);
2295	struct ev_loop *loop_lo = 0;	3325	struct ev_loop *loop_lo = 0;
2296	struct ev_embed embed;	3326	ev_embed embed;
2297		3327
2298	// see if there is a chance of getting one that works	3328	// see if there is a chance of getting one that works
2299	// (remember that a flags value of 0 means autodetection)	3329	// (remember that a flags value of 0 means autodetection)
2300	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3330	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2301	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3331	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2302	: 0;	3332	: 0;
…		…
2315	kqueue implementation). Store the kqueue/socket-only event loop in	3345	kqueue implementation). Store the kqueue/socket-only event loop in
2316	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3346	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2317		3347
2318	struct ev_loop *loop = ev_default_init (0);	3348	struct ev_loop *loop = ev_default_init (0);
2319	struct ev_loop *loop_socket = 0;	3349	struct ev_loop *loop_socket = 0;
2320	struct ev_embed embed;	3350	ev_embed embed;
2321		3351
2322	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3352	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2323	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3353	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2324	{	3354	{
2325	ev_embed_init (&embed, 0, loop_socket);	3355	ev_embed_init (&embed, 0, loop_socket);
2326	ev_embed_start (loop, &embed);	3356	ev_embed_start (loop, &embed);
…		…
2334		3364
2335	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3365	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2336		3366
2337	Fork watchers are called when a C<fork ()> was detected (usually because	3367	Fork watchers are called when a C<fork ()> was detected (usually because
2338	whoever is a good citizen cared to tell libev about it by calling	3368	whoever is a good citizen cared to tell libev about it by calling
2339	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3369	C<ev_loop_fork>). The invocation is done before the event loop blocks next
2340	event loop blocks next and before C<ev_check> watchers are being called,	3370	and before C<ev_check> watchers are being called, and only in the child
2341	and only in the child after the fork. If whoever good citizen calling	3371	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
2342	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3372	and calls it in the wrong process, the fork handlers will be invoked, too,
2343	handlers will be invoked, too, of course.	3373	of course.
		3374
		3375	=head3 The special problem of life after fork - how is it possible?
		3376
		3377	Most uses of C<fork ()> consist of forking, then some simple calls to set
		3378	up/change the process environment, followed by a call to C<exec()>. This
		3379	sequence should be handled by libev without any problems.
		3380
		3381	This changes when the application actually wants to do event handling
		3382	in the child, or both parent in child, in effect "continuing" after the
		3383	fork.
		3384
		3385	The default mode of operation (for libev, with application help to detect
		3386	forks) is to duplicate all the state in the child, as would be expected
		3387	when I<either> the parent I<or> the child process continues.
		3388
		3389	When both processes want to continue using libev, then this is usually the
		3390	wrong result. In that case, usually one process (typically the parent) is
		3391	supposed to continue with all watchers in place as before, while the other
		3392	process typically wants to start fresh, i.e. without any active watchers.
		3393
		3394	The cleanest and most efficient way to achieve that with libev is to
		3395	simply create a new event loop, which of course will be "empty", and
		3396	use that for new watchers. This has the advantage of not touching more
		3397	memory than necessary, and thus avoiding the copy-on-write, and the
		3398	disadvantage of having to use multiple event loops (which do not support
		3399	signal watchers).
		3400
		3401	When this is not possible, or you want to use the default loop for
		3402	other reasons, then in the process that wants to start "fresh", call
		3403	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3404	Destroying the default loop will "orphan" (not stop) all registered
		3405	watchers, so you have to be careful not to execute code that modifies
		3406	those watchers. Note also that in that case, you have to re-register any
		3407	signal watchers.
2344		3408
2345	=head3 Watcher-Specific Functions and Data Members	3409	=head3 Watcher-Specific Functions and Data Members
2346		3410
2347	=over 4	3411	=over 4
2348		3412
2349	=item ev_fork_init (ev_signal *, callback)	3413	=item ev_fork_init (ev_fork *, callback)
2350		3414
2351	Initialises and configures the fork watcher - it has no parameters of any	3415	Initialises and configures the fork watcher - it has no parameters of any
2352	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3416	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2353	believe me.	3417	really.
2354		3418
2355	=back	3419	=back
2356		3420
2357		3421
		3422	=head2 C<ev_cleanup> - even the best things end
		3423
		3424	Cleanup watchers are called just before the event loop is being destroyed
		3425	by a call to C<ev_loop_destroy>.
		3426
		3427	While there is no guarantee that the event loop gets destroyed, cleanup
		3428	watchers provide a convenient method to install cleanup hooks for your
		3429	program, worker threads and so on - you just to make sure to destroy the
		3430	loop when you want them to be invoked.
		3431
		3432	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3433	all other watchers, they do not keep a reference to the event loop (which
		3434	makes a lot of sense if you think about it). Like all other watchers, you
		3435	can call libev functions in the callback, except C<ev_cleanup_start>.
		3436
		3437	=head3 Watcher-Specific Functions and Data Members
		3438
		3439	=over 4
		3440
		3441	=item ev_cleanup_init (ev_cleanup *, callback)
		3442
		3443	Initialises and configures the cleanup watcher - it has no parameters of
		3444	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3445	pointless, I assure you.
		3446
		3447	=back
		3448
		3449	Example: Register an atexit handler to destroy the default loop, so any
		3450	cleanup functions are called.
		3451
		3452	static void
		3453	program_exits (void)
		3454	{
		3455	ev_loop_destroy (EV_DEFAULT_UC);
		3456	}
		3457
		3458	...
		3459	atexit (program_exits);
		3460
		3461
2358	=head2 C<ev_async> - how to wake up another event loop	3462	=head2 C<ev_async> - how to wake up an event loop
2359		3463
2360	In general, you cannot use an C<ev_loop> from multiple threads or other	3464	In general, you cannot use an C<ev_loop> from multiple threads or other
2361	asynchronous sources such as signal handlers (as opposed to multiple event	3465	asynchronous sources such as signal handlers (as opposed to multiple event
2362	loops - those are of course safe to use in different threads).	3466	loops - those are of course safe to use in different threads).
2363		3467
2364	Sometimes, however, you need to wake up another event loop you do not	3468	Sometimes, however, you need to wake up an event loop you do not control,
2365	control, for example because it belongs to another thread. This is what	3469	for example because it belongs to another thread. This is what C<ev_async>
2366	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3470	watchers do: as long as the C<ev_async> watcher is active, you can signal
2367	can signal it by calling C<ev_async_send>, which is thread- and signal	3471	it by calling C<ev_async_send>, which is thread- and signal safe.
2368	safe.
2369		3472
2370	This functionality is very similar to C<ev_signal> watchers, as signals,	3473	This functionality is very similar to C<ev_signal> watchers, as signals,
2371	too, are asynchronous in nature, and signals, too, will be compressed	3474	too, are asynchronous in nature, and signals, too, will be compressed
2372	(i.e. the number of callback invocations may be less than the number of	3475	(i.e. the number of callback invocations may be less than the number of
2373	C<ev_async_sent> calls).	3476	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
2374		3477	of "global async watchers" by using a watcher on an otherwise unused
2375	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3478	signal, and C<ev_feed_signal> to signal this watcher from another thread,
2376	just the default loop.	3479	even without knowing which loop owns the signal.
2377		3480
2378	=head3 Queueing	3481	=head3 Queueing
2379		3482
2380	C<ev_async> does not support queueing of data in any way. The reason	3483	C<ev_async> does not support queueing of data in any way. The reason
2381	is that the author does not know of a simple (or any) algorithm for a	3484	is that the author does not know of a simple (or any) algorithm for a
2382	multiple-writer-single-reader queue that works in all cases and doesn't	3485	multiple-writer-single-reader queue that works in all cases and doesn't
2383	need elaborate support such as pthreads.	3486	need elaborate support such as pthreads or unportable memory access
		3487	semantics.
2384		3488
2385	That means that if you want to queue data, you have to provide your own	3489	That means that if you want to queue data, you have to provide your own
2386	queue. But at least I can tell you how to implement locking around your	3490	queue. But at least I can tell you how to implement locking around your
2387	queue:	3491	queue:
2388		3492
…		…
2466	=over 4	3570	=over 4
2467		3571
2468	=item ev_async_init (ev_async *, callback)	3572	=item ev_async_init (ev_async *, callback)
2469		3573
2470	Initialises and configures the async watcher - it has no parameters of any	3574	Initialises and configures the async watcher - it has no parameters of any
2471	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3575	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2472	trust me.	3576	trust me.
2473		3577
2474	=item ev_async_send (loop, ev_async *)	3578	=item ev_async_send (loop, ev_async *)
2475		3579
2476	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3580	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2477	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3581	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3582	returns.
		3583
2478	C<ev_feed_event>, this call is safe to do from other threads, signal or	3584	Unlike C<ev_feed_event>, this call is safe to do from other threads,
2479	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3585	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
2480	section below on what exactly this means).	3586	embedding section below on what exactly this means).
2481		3587
2482	This call incurs the overhead of a system call only once per loop iteration,	3588	Note that, as with other watchers in libev, multiple events might get
2483	so while the overhead might be noticeable, it doesn't apply to repeated	3589	compressed into a single callback invocation (another way to look at
2484	calls to C<ev_async_send>.	3590	this is that C<ev_async> watchers are level-triggered: they are set on
		3591	C<ev_async_send>, reset when the event loop detects that).
		3592
		3593	This call incurs the overhead of at most one extra system call per event
		3594	loop iteration, if the event loop is blocked, and no syscall at all if
		3595	the event loop (or your program) is processing events. That means that
		3596	repeated calls are basically free (there is no need to avoid calls for
		3597	performance reasons) and that the overhead becomes smaller (typically
		3598	zero) under load.
2485		3599
2486	=item bool = ev_async_pending (ev_async *)	3600	=item bool = ev_async_pending (ev_async *)
2487		3601
2488	Returns a non-zero value when C<ev_async_send> has been called on the	3602	Returns a non-zero value when C<ev_async_send> has been called on the
2489	watcher but the event has not yet been processed (or even noted) by the	3603	watcher but the event has not yet been processed (or even noted) by the
…		…
2492	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3606	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2493	the loop iterates next and checks for the watcher to have become active,	3607	the loop iterates next and checks for the watcher to have become active,
2494	it will reset the flag again. C<ev_async_pending> can be used to very	3608	it will reset the flag again. C<ev_async_pending> can be used to very
2495	quickly check whether invoking the loop might be a good idea.	3609	quickly check whether invoking the loop might be a good idea.
2496		3610
2497	Not that this does I<not> check whether the watcher itself is pending, only	3611	Not that this does I<not> check whether the watcher itself is pending,
2498	whether it has been requested to make this watcher pending.	3612	only whether it has been requested to make this watcher pending: there
		3613	is a time window between the event loop checking and resetting the async
		3614	notification, and the callback being invoked.
2499		3615
2500	=back	3616	=back
2501		3617
2502		3618
2503	=head1 OTHER FUNCTIONS	3619	=head1 OTHER FUNCTIONS
2504		3620
2505	There are some other functions of possible interest. Described. Here. Now.	3621	There are some other functions of possible interest. Described. Here. Now.
2506		3622
2507	=over 4	3623	=over 4
2508		3624
2509	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3625	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
2510		3626
2511	This function combines a simple timer and an I/O watcher, calls your	3627	This function combines a simple timer and an I/O watcher, calls your
2512	callback on whichever event happens first and automatically stops both	3628	callback on whichever event happens first and automatically stops both
2513	watchers. This is useful if you want to wait for a single event on an fd	3629	watchers. This is useful if you want to wait for a single event on an fd
2514	or timeout without having to allocate/configure/start/stop/free one or	3630	or timeout without having to allocate/configure/start/stop/free one or
…		…
2520		3636
2521	If C<timeout> is less than 0, then no timeout watcher will be	3637	If C<timeout> is less than 0, then no timeout watcher will be
2522	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3638	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2523	repeat = 0) will be started. C<0> is a valid timeout.	3639	repeat = 0) will be started. C<0> is a valid timeout.
2524		3640
2525	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3641	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2526	passed an C<revents> set like normal event callbacks (a combination of	3642	passed an C<revents> set like normal event callbacks (a combination of
2527	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3643	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2528	value passed to C<ev_once>. Note that it is possible to receive I<both>	3644	value passed to C<ev_once>. Note that it is possible to receive I<both>
2529	a timeout and an io event at the same time - you probably should give io	3645	a timeout and an io event at the same time - you probably should give io
2530	events precedence.	3646	events precedence.
2531		3647
2532	Example: wait up to ten seconds for data to appear on STDIN_FILENO.	3648	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2533		3649
2534	static void stdin_ready (int revents, void *arg)	3650	static void stdin_ready (int revents, void *arg)
2535	{	3651	{
2536	if (revents & EV_READ)	3652	if (revents & EV_READ)
2537	/* stdin might have data for us, joy! */;	3653	/* stdin might have data for us, joy! */;
2538	else if (revents & EV_TIMEOUT)	3654	else if (revents & EV_TIMER)
2539	/* doh, nothing entered */;	3655	/* doh, nothing entered */;
2540	}	3656	}
2541		3657
2542	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3658	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2543		3659
2544	=item ev_feed_event (ev_loop *, watcher *, int revents)
2545
2546	Feeds the given event set into the event loop, as if the specified event
2547	had happened for the specified watcher (which must be a pointer to an
2548	initialised but not necessarily started event watcher).
2549
2550	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3660	=item ev_feed_fd_event (loop, int fd, int revents)
2551		3661
2552	Feed an event on the given fd, as if a file descriptor backend detected	3662	Feed an event on the given fd, as if a file descriptor backend detected
2553	the given events it.	3663	the given events.
2554		3664
2555	=item ev_feed_signal_event (ev_loop *loop, int signum)	3665	=item ev_feed_signal_event (loop, int signum)
2556		3666
2557	Feed an event as if the given signal occurred (C<loop> must be the default	3667	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
2558	loop!).	3668	which is async-safe.
2559		3669
2560	=back	3670	=back
		3671
		3672
		3673	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3674
		3675	This section explains some common idioms that are not immediately
		3676	obvious. Note that examples are sprinkled over the whole manual, and this
		3677	section only contains stuff that wouldn't fit anywhere else.
		3678
		3679	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3680
		3681	Each watcher has, by default, a C<void *data> member that you can read
		3682	or modify at any time: libev will completely ignore it. This can be used
		3683	to associate arbitrary data with your watcher. If you need more data and
		3684	don't want to allocate memory separately and store a pointer to it in that
		3685	data member, you can also "subclass" the watcher type and provide your own
		3686	data:
		3687
		3688	struct my_io
		3689	{
		3690	ev_io io;
		3691	int otherfd;
		3692	void *somedata;
		3693	struct whatever *mostinteresting;
		3694	};
		3695
		3696	...
		3697	struct my_io w;
		3698	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3699
		3700	And since your callback will be called with a pointer to the watcher, you
		3701	can cast it back to your own type:
		3702
		3703	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3704	{
		3705	struct my_io *w = (struct my_io *)w_;
		3706	...
		3707	}
		3708
		3709	More interesting and less C-conformant ways of casting your callback
		3710	function type instead have been omitted.
		3711
		3712	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3713
		3714	Another common scenario is to use some data structure with multiple
		3715	embedded watchers, in effect creating your own watcher that combines
		3716	multiple libev event sources into one "super-watcher":
		3717
		3718	struct my_biggy
		3719	{
		3720	int some_data;
		3721	ev_timer t1;
		3722	ev_timer t2;
		3723	}
		3724
		3725	In this case getting the pointer to C<my_biggy> is a bit more
		3726	complicated: Either you store the address of your C<my_biggy> struct in
		3727	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3728	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3729	real programmers):
		3730
		3731	#include <stddef.h>
		3732
		3733	static void
		3734	t1_cb (EV_P_ ev_timer *w, int revents)
		3735	{
		3736	struct my_biggy big = (struct my_biggy *)
		3737	(((char *)w) - offsetof (struct my_biggy, t1));
		3738	}
		3739
		3740	static void
		3741	t2_cb (EV_P_ ev_timer *w, int revents)
		3742	{
		3743	struct my_biggy big = (struct my_biggy *)
		3744	(((char *)w) - offsetof (struct my_biggy, t2));
		3745	}
		3746
		3747	=head2 AVOIDING FINISHING BEFORE RETURNING
		3748
		3749	Often you have structures like this in event-based programs:
		3750
		3751	callback ()
		3752	{
		3753	free (request);
		3754	}
		3755
		3756	request = start_new_request (..., callback);
		3757
		3758	The intent is to start some "lengthy" operation. The C<request> could be
		3759	used to cancel the operation, or do other things with it.
		3760
		3761	It's not uncommon to have code paths in C<start_new_request> that
		3762	immediately invoke the callback, for example, to report errors. Or you add
		3763	some caching layer that finds that it can skip the lengthy aspects of the
		3764	operation and simply invoke the callback with the result.
		3765
		3766	The problem here is that this will happen I<before> C<start_new_request>
		3767	has returned, so C<request> is not set.
		3768
		3769	Even if you pass the request by some safer means to the callback, you
		3770	might want to do something to the request after starting it, such as
		3771	canceling it, which probably isn't working so well when the callback has
		3772	already been invoked.
		3773
		3774	A common way around all these issues is to make sure that
		3775	C<start_new_request> I<always> returns before the callback is invoked. If
		3776	C<start_new_request> immediately knows the result, it can artificially
		3777	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3778	example, or more sneakily, by reusing an existing (stopped) watcher and
		3779	pushing it into the pending queue:
		3780
		3781	ev_set_cb (watcher, callback);
		3782	ev_feed_event (EV_A_ watcher, 0);
		3783
		3784	This way, C<start_new_request> can safely return before the callback is
		3785	invoked, while not delaying callback invocation too much.
		3786
		3787	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3788
		3789	Often (especially in GUI toolkits) there are places where you have
		3790	I<modal> interaction, which is most easily implemented by recursively
		3791	invoking C<ev_run>.
		3792
		3793	This brings the problem of exiting - a callback might want to finish the
		3794	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3795	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3796	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3797	other combination: In these cases, a simple C<ev_break> will not work.
		3798
		3799	The solution is to maintain "break this loop" variable for each C<ev_run>
		3800	invocation, and use a loop around C<ev_run> until the condition is
		3801	triggered, using C<EVRUN_ONCE>:
		3802
		3803	// main loop
		3804	int exit_main_loop = 0;
		3805
		3806	while (!exit_main_loop)
		3807	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3808
		3809	// in a modal watcher
		3810	int exit_nested_loop = 0;
		3811
		3812	while (!exit_nested_loop)
		3813	ev_run (EV_A_ EVRUN_ONCE);
		3814
		3815	To exit from any of these loops, just set the corresponding exit variable:
		3816
		3817	// exit modal loop
		3818	exit_nested_loop = 1;
		3819
		3820	// exit main program, after modal loop is finished
		3821	exit_main_loop = 1;
		3822
		3823	// exit both
		3824	exit_main_loop = exit_nested_loop = 1;
		3825
		3826	=head2 THREAD LOCKING EXAMPLE
		3827
		3828	Here is a fictitious example of how to run an event loop in a different
		3829	thread from where callbacks are being invoked and watchers are
		3830	created/added/removed.
		3831
		3832	For a real-world example, see the C<EV::Loop::Async> perl module,
		3833	which uses exactly this technique (which is suited for many high-level
		3834	languages).
		3835
		3836	The example uses a pthread mutex to protect the loop data, a condition
		3837	variable to wait for callback invocations, an async watcher to notify the
		3838	event loop thread and an unspecified mechanism to wake up the main thread.
		3839
		3840	First, you need to associate some data with the event loop:
		3841
		3842	typedef struct {
		3843	mutex_t lock; /* global loop lock */
		3844	ev_async async_w;
		3845	thread_t tid;
		3846	cond_t invoke_cv;
		3847	} userdata;
		3848
		3849	void prepare_loop (EV_P)
		3850	{
		3851	// for simplicity, we use a static userdata struct.
		3852	static userdata u;
		3853
		3854	ev_async_init (&u->async_w, async_cb);
		3855	ev_async_start (EV_A_ &u->async_w);
		3856
		3857	pthread_mutex_init (&u->lock, 0);
		3858	pthread_cond_init (&u->invoke_cv, 0);
		3859
		3860	// now associate this with the loop
		3861	ev_set_userdata (EV_A_ u);
		3862	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3863	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3864
		3865	// then create the thread running ev_run
		3866	pthread_create (&u->tid, 0, l_run, EV_A);
		3867	}
		3868
		3869	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3870	solely to wake up the event loop so it takes notice of any new watchers
		3871	that might have been added:
		3872
		3873	static void
		3874	async_cb (EV_P_ ev_async *w, int revents)
		3875	{
		3876	// just used for the side effects
		3877	}
		3878
		3879	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3880	protecting the loop data, respectively.
		3881
		3882	static void
		3883	l_release (EV_P)
		3884	{
		3885	userdata *u = ev_userdata (EV_A);
		3886	pthread_mutex_unlock (&u->lock);
		3887	}
		3888
		3889	static void
		3890	l_acquire (EV_P)
		3891	{
		3892	userdata *u = ev_userdata (EV_A);
		3893	pthread_mutex_lock (&u->lock);
		3894	}
		3895
		3896	The event loop thread first acquires the mutex, and then jumps straight
		3897	into C<ev_run>:
		3898
		3899	void *
		3900	l_run (void *thr_arg)
		3901	{
		3902	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3903
		3904	l_acquire (EV_A);
		3905	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3906	ev_run (EV_A_ 0);
		3907	l_release (EV_A);
		3908
		3909	return 0;
		3910	}
		3911
		3912	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3913	signal the main thread via some unspecified mechanism (signals? pipe
		3914	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3915	have been called (in a while loop because a) spurious wakeups are possible
		3916	and b) skipping inter-thread-communication when there are no pending
		3917	watchers is very beneficial):
		3918
		3919	static void
		3920	l_invoke (EV_P)
		3921	{
		3922	userdata *u = ev_userdata (EV_A);
		3923
		3924	while (ev_pending_count (EV_A))
		3925	{
		3926	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3927	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3928	}
		3929	}
		3930
		3931	Now, whenever the main thread gets told to invoke pending watchers, it
		3932	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3933	thread to continue:
		3934
		3935	static void
		3936	real_invoke_pending (EV_P)
		3937	{
		3938	userdata *u = ev_userdata (EV_A);
		3939
		3940	pthread_mutex_lock (&u->lock);
		3941	ev_invoke_pending (EV_A);
		3942	pthread_cond_signal (&u->invoke_cv);
		3943	pthread_mutex_unlock (&u->lock);
		3944	}
		3945
		3946	Whenever you want to start/stop a watcher or do other modifications to an
		3947	event loop, you will now have to lock:
		3948
		3949	ev_timer timeout_watcher;
		3950	userdata *u = ev_userdata (EV_A);
		3951
		3952	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3953
		3954	pthread_mutex_lock (&u->lock);
		3955	ev_timer_start (EV_A_ &timeout_watcher);
		3956	ev_async_send (EV_A_ &u->async_w);
		3957	pthread_mutex_unlock (&u->lock);
		3958
		3959	Note that sending the C<ev_async> watcher is required because otherwise
		3960	an event loop currently blocking in the kernel will have no knowledge
		3961	about the newly added timer. By waking up the loop it will pick up any new
		3962	watchers in the next event loop iteration.
		3963
		3964	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3965
		3966	While the overhead of a callback that e.g. schedules a thread is small, it
		3967	is still an overhead. If you embed libev, and your main usage is with some
		3968	kind of threads or coroutines, you might want to customise libev so that
		3969	doesn't need callbacks anymore.
		3970
		3971	Imagine you have coroutines that you can switch to using a function
		3972	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3973	and that due to some magic, the currently active coroutine is stored in a
		3974	global called C<current_coro>. Then you can build your own "wait for libev
		3975	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3976	the differing C<;> conventions):
		3977
		3978	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3979	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3980
		3981	That means instead of having a C callback function, you store the
		3982	coroutine to switch to in each watcher, and instead of having libev call
		3983	your callback, you instead have it switch to that coroutine.
		3984
		3985	A coroutine might now wait for an event with a function called
		3986	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3987	matter when, or whether the watcher is active or not when this function is
		3988	called):
		3989
		3990	void
		3991	wait_for_event (ev_watcher *w)
		3992	{
		3993	ev_set_cb (w, current_coro);
		3994	switch_to (libev_coro);
		3995	}
		3996
		3997	That basically suspends the coroutine inside C<wait_for_event> and
		3998	continues the libev coroutine, which, when appropriate, switches back to
		3999	this or any other coroutine.
		4000
		4001	You can do similar tricks if you have, say, threads with an event queue -
		4002	instead of storing a coroutine, you store the queue object and instead of
		4003	switching to a coroutine, you push the watcher onto the queue and notify
		4004	any waiters.
		4005
		4006	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		4007	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		4008
		4009	// my_ev.h
		4010	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4011	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4012	#include "../libev/ev.h"
		4013
		4014	// my_ev.c
		4015	#define EV_H "my_ev.h"
		4016	#include "../libev/ev.c"
		4017
		4018	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4019	F<my_ev.c> into your project. When properly specifying include paths, you
		4020	can even use F<ev.h> as header file name directly.
2561		4021
2562		4022
2563	=head1 LIBEVENT EMULATION	4023	=head1 LIBEVENT EMULATION
2564		4024
2565	Libev offers a compatibility emulation layer for libevent. It cannot	4025	Libev offers a compatibility emulation layer for libevent. It cannot
2566	emulate the internals of libevent, so here are some usage hints:	4026	emulate the internals of libevent, so here are some usage hints:
2567		4027
2568	=over 4	4028	=over 4
		4029
		4030	=item * Only the libevent-1.4.1-beta API is being emulated.
		4031
		4032	This was the newest libevent version available when libev was implemented,
		4033	and is still mostly unchanged in 2010.
2569		4034
2570	=item * Use it by including <event.h>, as usual.	4035	=item * Use it by including <event.h>, as usual.
2571		4036
2572	=item * The following members are fully supported: ev_base, ev_callback,	4037	=item * The following members are fully supported: ev_base, ev_callback,
2573	ev_arg, ev_fd, ev_res, ev_events.	4038	ev_arg, ev_fd, ev_res, ev_events.
…		…
2579	=item * Priorities are not currently supported. Initialising priorities	4044	=item * Priorities are not currently supported. Initialising priorities
2580	will fail and all watchers will have the same priority, even though there	4045	will fail and all watchers will have the same priority, even though there
2581	is an ev_pri field.	4046	is an ev_pri field.
2582		4047
2583	=item * In libevent, the last base created gets the signals, in libev, the	4048	=item * In libevent, the last base created gets the signals, in libev, the
2584	first base created (== the default loop) gets the signals.	4049	base that registered the signal gets the signals.
2585		4050
2586	=item * Other members are not supported.	4051	=item * Other members are not supported.
2587		4052
2588	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4053	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2589	to use the libev header file and library.	4054	to use the libev header file and library.
2590		4055
2591	=back	4056	=back
2592		4057
2593	=head1 C++ SUPPORT	4058	=head1 C++ SUPPORT
		4059
		4060	=head2 C API
		4061
		4062	The normal C API should work fine when used from C++: both ev.h and the
		4063	libev sources can be compiled as C++. Therefore, code that uses the C API
		4064	will work fine.
		4065
		4066	Proper exception specifications might have to be added to callbacks passed
		4067	to libev: exceptions may be thrown only from watcher callbacks, all other
		4068	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4069	callbacks) must not throw exceptions, and might need a C<noexcept>
		4070	specification. If you have code that needs to be compiled as both C and
		4071	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4072
		4073	static void
		4074	fatal_error (const char *msg) EV_NOEXCEPT
		4075	{
		4076	perror (msg);
		4077	abort ();
		4078	}
		4079
		4080	...
		4081	ev_set_syserr_cb (fatal_error);
		4082
		4083	The only API functions that can currently throw exceptions are C<ev_run>,
		4084	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4085	because it runs cleanup watchers).
		4086
		4087	Throwing exceptions in watcher callbacks is only supported if libev itself
		4088	is compiled with a C++ compiler or your C and C++ environments allow
		4089	throwing exceptions through C libraries (most do).
		4090
		4091	=head2 C++ API
2594		4092
2595	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4093	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2596	you to use some convenience methods to start/stop watchers and also change	4094	you to use some convenience methods to start/stop watchers and also change
2597	the callback model to a model using method callbacks on objects.	4095	the callback model to a model using method callbacks on objects.
2598		4096
2599	To use it,	4097	To use it,
2600		4098
2601	#include <ev++.h>	4099	#include <ev++.h>
2602		4100
2603	This automatically includes F<ev.h> and puts all of its definitions (many	4101	This automatically includes F<ev.h> and puts all of its definitions (many
2604	of them macros) into the global namespace. All C++ specific things are	4102	of them macros) into the global namespace. All C++ specific things are
2605	put into the C<ev> namespace. It should support all the same embedding	4103	put into the C<ev> namespace. It should support all the same embedding
…		…
2608	Care has been taken to keep the overhead low. The only data member the C++	4106	Care has been taken to keep the overhead low. The only data member the C++
2609	classes add (compared to plain C-style watchers) is the event loop pointer	4107	classes add (compared to plain C-style watchers) is the event loop pointer
2610	that the watcher is associated with (or no additional members at all if	4108	that the watcher is associated with (or no additional members at all if
2611	you disable C<EV_MULTIPLICITY> when embedding libev).	4109	you disable C<EV_MULTIPLICITY> when embedding libev).
2612		4110
2613	Currently, functions, and static and non-static member functions can be	4111	Currently, functions, static and non-static member functions and classes
2614	used as callbacks. Other types should be easy to add as long as they only	4112	with C<operator ()> can be used as callbacks. Other types should be easy
2615	need one additional pointer for context. If you need support for other	4113	to add as long as they only need one additional pointer for context. If
2616	types of functors please contact the author (preferably after implementing	4114	you need support for other types of functors please contact the author
2617	it).	4115	(preferably after implementing it).
		4116
		4117	For all this to work, your C++ compiler either has to use the same calling
		4118	conventions as your C compiler (for static member functions), or you have
		4119	to embed libev and compile libev itself as C++.
2618		4120
2619	Here is a list of things available in the C<ev> namespace:	4121	Here is a list of things available in the C<ev> namespace:
2620		4122
2621	=over 4	4123	=over 4
2622		4124
…		…
2632	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4134	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
2633		4135
2634	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4136	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
2635	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4137	the same name in the C<ev> namespace, with the exception of C<ev_signal>
2636	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4138	which is called C<ev::sig> to avoid clashes with the C<signal> macro
2637	defines by many implementations.	4139	defined by many implementations.
2638		4140
2639	All of those classes have these methods:	4141	All of those classes have these methods:
2640		4142
2641	=over 4	4143	=over 4
2642		4144
2643	=item ev::TYPE::TYPE ()	4145	=item ev::TYPE::TYPE ()
2644		4146
2645	=item ev::TYPE::TYPE (struct ev_loop *)	4147	=item ev::TYPE::TYPE (loop)
2646		4148
2647	=item ev::TYPE::~TYPE	4149	=item ev::TYPE::~TYPE
2648		4150
2649	The constructor (optionally) takes an event loop to associate the watcher	4151	The constructor (optionally) takes an event loop to associate the watcher
2650	with. If it is omitted, it will use C<EV_DEFAULT>.	4152	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2682		4184
2683	myclass obj;	4185	myclass obj;
2684	ev::io iow;	4186	ev::io iow;
2685	iow.set <myclass, &myclass::io_cb> (&obj);	4187	iow.set <myclass, &myclass::io_cb> (&obj);
2686		4188
		4189	=item w->set (object *)
		4190
		4191	This is a variation of a method callback - leaving out the method to call
		4192	will default the method to C<operator ()>, which makes it possible to use
		4193	functor objects without having to manually specify the C<operator ()> all
		4194	the time. Incidentally, you can then also leave out the template argument
		4195	list.
		4196
		4197	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4198	int revents)>.
		4199
		4200	See the method-C<set> above for more details.
		4201
		4202	Example: use a functor object as callback.
		4203
		4204	struct myfunctor
		4205	{
		4206	void operator() (ev::io &w, int revents)
		4207	{
		4208	...
		4209	}
		4210	}
		4211
		4212	myfunctor f;
		4213
		4214	ev::io w;
		4215	w.set (&f);
		4216
2687	=item w->set<function> (void *data = 0)	4217	=item w->set<function> (void *data = 0)
2688		4218
2689	Also sets a callback, but uses a static method or plain function as	4219	Also sets a callback, but uses a static method or plain function as
2690	callback. The optional C<data> argument will be stored in the watcher's	4220	callback. The optional C<data> argument will be stored in the watcher's
2691	C<data> member and is free for you to use.	4221	C<data> member and is free for you to use.
…		…
2697	Example: Use a plain function as callback.	4227	Example: Use a plain function as callback.
2698		4228
2699	static void io_cb (ev::io &w, int revents) { }	4229	static void io_cb (ev::io &w, int revents) { }
2700	iow.set <io_cb> ();	4230	iow.set <io_cb> ();
2701		4231
2702	=item w->set (struct ev_loop *)	4232	=item w->set (loop)
2703		4233
2704	Associates a different C<struct ev_loop> with this watcher. You can only	4234	Associates a different C<struct ev_loop> with this watcher. You can only
2705	do this when the watcher is inactive (and not pending either).	4235	do this when the watcher is inactive (and not pending either).
2706		4236
2707	=item w->set ([arguments])	4237	=item w->set ([arguments])
2708		4238
2709	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be	4239	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4240	with the same arguments. Either this method or a suitable start method
2710	called at least once. Unlike the C counterpart, an active watcher gets	4241	must be called at least once. Unlike the C counterpart, an active watcher
2711	automatically stopped and restarted when reconfiguring it with this	4242	gets automatically stopped and restarted when reconfiguring it with this
2712	method.	4243	method.
		4244
		4245	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4246	clashing with the C<set (loop)> method.
2713		4247
2714	=item w->start ()	4248	=item w->start ()
2715		4249
2716	Starts the watcher. Note that there is no C<loop> argument, as the	4250	Starts the watcher. Note that there is no C<loop> argument, as the
2717	constructor already stores the event loop.	4251	constructor already stores the event loop.
2718		4252
		4253	=item w->start ([arguments])
		4254
		4255	Instead of calling C<set> and C<start> methods separately, it is often
		4256	convenient to wrap them in one call. Uses the same type of arguments as
		4257	the configure C<set> method of the watcher.
		4258
2719	=item w->stop ()	4259	=item w->stop ()
2720		4260
2721	Stops the watcher if it is active. Again, no C<loop> argument.	4261	Stops the watcher if it is active. Again, no C<loop> argument.
2722		4262
2723	=item w->again () (C<ev::timer>, C<ev::periodic> only)	4263	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2735		4275
2736	=back	4276	=back
2737		4277
2738	=back	4278	=back
2739		4279
2740	Example: Define a class with an IO and idle watcher, start one of them in	4280	Example: Define a class with two I/O and idle watchers, start the I/O
2741	the constructor.	4281	watchers in the constructor.
2742		4282
2743	class myclass	4283	class myclass
2744	{	4284	{
2745	ev::io io ; void io_cb (ev::io &w, int revents);	4285	ev::io io ; void io_cb (ev::io &w, int revents);
		4286	ev::io io2 ; void io2_cb (ev::io &w, int revents);
2746	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4287	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2747		4288
2748	myclass (int fd)	4289	myclass (int fd)
2749	{	4290	{
2750	io .set <myclass, &myclass::io_cb > (this);	4291	io .set <myclass, &myclass::io_cb > (this);
		4292	io2 .set <myclass, &myclass::io2_cb > (this);
2751	idle.set <myclass, &myclass::idle_cb> (this);	4293	idle.set <myclass, &myclass::idle_cb> (this);
2752		4294
2753	io.start (fd, ev::READ);	4295	io.set (fd, ev::WRITE); // configure the watcher
		4296	io.start (); // start it whenever convenient
		4297
		4298	io2.start (fd, ev::READ); // set + start in one call
2754	}	4299	}
2755	};	4300	};
2756		4301
2757		4302
2758	=head1 OTHER LANGUAGE BINDINGS	4303	=head1 OTHER LANGUAGE BINDINGS
…		…
2777	L<http://software.schmorp.de/pkg/EV>.	4322	L<http://software.schmorp.de/pkg/EV>.
2778		4323
2779	=item Python	4324	=item Python
2780		4325
2781	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	4326	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2782	seems to be quite complete and well-documented. Note, however, that the	4327	seems to be quite complete and well-documented.
2783	patch they require for libev is outright dangerous as it breaks the ABI
2784	for everybody else, and therefore, should never be applied in an installed
2785	libev (if python requires an incompatible ABI then it needs to embed
2786	libev).
2787		4328
2788	=item Ruby	4329	=item Ruby
2789		4330
2790	Tony Arcieri has written a ruby extension that offers access to a subset	4331	Tony Arcieri has written a ruby extension that offers access to a subset
2791	of the libev API and adds file handle abstractions, asynchronous DNS and	4332	of the libev API and adds file handle abstractions, asynchronous DNS and
2792	more on top of it. It can be found via gem servers. Its homepage is at	4333	more on top of it. It can be found via gem servers. Its homepage is at
2793	L<http://rev.rubyforge.org/>.	4334	L<http://rev.rubyforge.org/>.
2794		4335
		4336	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4337	makes rev work even on mingw.
		4338
		4339	=item Haskell
		4340
		4341	A haskell binding to libev is available at
		4342	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4343
2795	=item D	4344	=item D
2796		4345
2797	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4346	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2798	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4347	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4348
		4349	=item Ocaml
		4350
		4351	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4352	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4353
		4354	=item Lua
		4355
		4356	Brian Maher has written a partial interface to libev for lua (at the
		4357	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4358	L<http://github.com/brimworks/lua-ev>.
		4359
		4360	=item Javascript
		4361
		4362	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4363
		4364	=item Others
		4365
		4366	There are others, and I stopped counting.
2799		4367
2800	=back	4368	=back
2801		4369
2802		4370
2803	=head1 MACRO MAGIC	4371	=head1 MACRO MAGIC
…		…
2817	loop argument"). The C<EV_A> form is used when this is the sole argument,	4385	loop argument"). The C<EV_A> form is used when this is the sole argument,
2818	C<EV_A_> is used when other arguments are following. Example:	4386	C<EV_A_> is used when other arguments are following. Example:
2819		4387
2820	ev_unref (EV_A);	4388	ev_unref (EV_A);
2821	ev_timer_add (EV_A_ watcher);	4389	ev_timer_add (EV_A_ watcher);
2822	ev_loop (EV_A_ 0);	4390	ev_run (EV_A_ 0);
2823		4391
2824	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4392	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2825	which is often provided by the following macro.	4393	which is often provided by the following macro.
2826		4394
2827	=item C<EV_P>, C<EV_P_>	4395	=item C<EV_P>, C<EV_P_>
…		…
2840	suitable for use with C<EV_A>.	4408	suitable for use with C<EV_A>.
2841		4409
2842	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4410	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2843		4411
2844	Similar to the other two macros, this gives you the value of the default	4412	Similar to the other two macros, this gives you the value of the default
2845	loop, if multiple loops are supported ("ev loop default").	4413	loop, if multiple loops are supported ("ev loop default"). The default loop
		4414	will be initialised if it isn't already initialised.
		4415
		4416	For non-multiplicity builds, these macros do nothing, so you always have
		4417	to initialise the loop somewhere.
2846		4418
2847	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4419	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
2848		4420
2849	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4421	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
2850	default loop has been initialised (C<UC> == unchecked). Their behaviour	4422	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
2867	}	4439	}
2868		4440
2869	ev_check check;	4441	ev_check check;
2870	ev_check_init (&check, check_cb);	4442	ev_check_init (&check, check_cb);
2871	ev_check_start (EV_DEFAULT_ &check);	4443	ev_check_start (EV_DEFAULT_ &check);
2872	ev_loop (EV_DEFAULT_ 0);	4444	ev_run (EV_DEFAULT_ 0);
2873		4445
2874	=head1 EMBEDDING	4446	=head1 EMBEDDING
2875		4447
2876	Libev can (and often is) directly embedded into host	4448	Libev can (and often is) directly embedded into host
2877	applications. Examples of applications that embed it include the Deliantra	4449	applications. Examples of applications that embed it include the Deliantra
…		…
2904		4476
2905	#define EV_STANDALONE 1	4477	#define EV_STANDALONE 1
2906	#include "ev.h"	4478	#include "ev.h"
2907		4479
2908	Both header files and implementation files can be compiled with a C++	4480	Both header files and implementation files can be compiled with a C++
2909	compiler (at least, thats a stated goal, and breakage will be treated	4481	compiler (at least, that's a stated goal, and breakage will be treated
2910	as a bug).	4482	as a bug).
2911		4483
2912	You need the following files in your source tree, or in a directory	4484	You need the following files in your source tree, or in a directory
2913	in your include path (e.g. in libev/ when using -Ilibev):	4485	in your include path (e.g. in libev/ when using -Ilibev):
2914		4486
…		…
2917	ev_vars.h	4489	ev_vars.h
2918	ev_wrap.h	4490	ev_wrap.h
2919		4491
2920	ev_win32.c required on win32 platforms only	4492	ev_win32.c required on win32 platforms only
2921		4493
2922	ev_select.c only when select backend is enabled (which is enabled by default)	4494	ev_select.c only when select backend is enabled
2923	ev_poll.c only when poll backend is enabled (disabled by default)	4495	ev_poll.c only when poll backend is enabled
2924	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4496	ev_epoll.c only when the epoll backend is enabled
		4497	ev_linuxaio.c only when the linux aio backend is enabled
		4498	ev_iouring.c only when the linux io_uring backend is enabled
2925	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4499	ev_kqueue.c only when the kqueue backend is enabled
2926	ev_port.c only when the solaris port backend is enabled (disabled by default)	4500	ev_port.c only when the solaris port backend is enabled
2927		4501
2928	F<ev.c> includes the backend files directly when enabled, so you only need	4502	F<ev.c> includes the backend files directly when enabled, so you only need
2929	to compile this single file.	4503	to compile this single file.
2930		4504
2931	=head3 LIBEVENT COMPATIBILITY API	4505	=head3 LIBEVENT COMPATIBILITY API
…		…
2957	libev.m4	4531	libev.m4
2958		4532
2959	=head2 PREPROCESSOR SYMBOLS/MACROS	4533	=head2 PREPROCESSOR SYMBOLS/MACROS
2960		4534
2961	Libev can be configured via a variety of preprocessor symbols you have to	4535	Libev can be configured via a variety of preprocessor symbols you have to
2962	define before including any of its files. The default in the absence of	4536	define before including (or compiling) any of its files. The default in
2963	autoconf is documented for every option.	4537	the absence of autoconf is documented for every option.
		4538
		4539	Symbols marked with "(h)" do not change the ABI, and can have different
		4540	values when compiling libev vs. including F<ev.h>, so it is permissible
		4541	to redefine them before including F<ev.h> without breaking compatibility
		4542	to a compiled library. All other symbols change the ABI, which means all
		4543	users of libev and the libev code itself must be compiled with compatible
		4544	settings.
2964		4545
2965	=over 4	4546	=over 4
2966		4547
		4548	=item EV_COMPAT3 (h)
		4549
		4550	Backwards compatibility is a major concern for libev. This is why this
		4551	release of libev comes with wrappers for the functions and symbols that
		4552	have been renamed between libev version 3 and 4.
		4553
		4554	You can disable these wrappers (to test compatibility with future
		4555	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4556	sources. This has the additional advantage that you can drop the C<struct>
		4557	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4558	typedef in that case.
		4559
		4560	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4561	and in some even more future version the compatibility code will be
		4562	removed completely.
		4563
2967	=item EV_STANDALONE	4564	=item EV_STANDALONE (h)
2968		4565
2969	Must always be C<1> if you do not use autoconf configuration, which	4566	Must always be C<1> if you do not use autoconf configuration, which
2970	keeps libev from including F<config.h>, and it also defines dummy	4567	keeps libev from including F<config.h>, and it also defines dummy
2971	implementations for some libevent functions (such as logging, which is not	4568	implementations for some libevent functions (such as logging, which is not
2972	supported). It will also not define any of the structs usually found in	4569	supported). It will also not define any of the structs usually found in
2973	F<event.h> that are not directly supported by the libev core alone.	4570	F<event.h> that are not directly supported by the libev core alone.
2974		4571
		4572	In standalone mode, libev will still try to automatically deduce the
		4573	configuration, but has to be more conservative.
		4574
		4575	=item EV_USE_FLOOR
		4576
		4577	If defined to be C<1>, libev will use the C<floor ()> function for its
		4578	periodic reschedule calculations, otherwise libev will fall back on a
		4579	portable (slower) implementation. If you enable this, you usually have to
		4580	link against libm or something equivalent. Enabling this when the C<floor>
		4581	function is not available will fail, so the safe default is to not enable
		4582	this.
		4583
2975	=item EV_USE_MONOTONIC	4584	=item EV_USE_MONOTONIC
2976		4585
2977	If defined to be C<1>, libev will try to detect the availability of the	4586	If defined to be C<1>, libev will try to detect the availability of the
2978	monotonic clock option at both compile time and runtime. Otherwise no use	4587	monotonic clock option at both compile time and runtime. Otherwise no
2979	of the monotonic clock option will be attempted. If you enable this, you	4588	use of the monotonic clock option will be attempted. If you enable this,
2980	usually have to link against librt or something similar. Enabling it when	4589	you usually have to link against librt or something similar. Enabling it
2981	the functionality isn't available is safe, though, although you have	4590	when the functionality isn't available is safe, though, although you have
2982	to make sure you link against any libraries where the C<clock_gettime>	4591	to make sure you link against any libraries where the C<clock_gettime>
2983	function is hiding in (often F<-lrt>).	4592	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2984		4593
2985	=item EV_USE_REALTIME	4594	=item EV_USE_REALTIME
2986		4595
2987	If defined to be C<1>, libev will try to detect the availability of the	4596	If defined to be C<1>, libev will try to detect the availability of the
2988	real-time clock option at compile time (and assume its availability at	4597	real-time clock option at compile time (and assume its availability
2989	runtime if successful). Otherwise no use of the real-time clock option will	4598	at runtime if successful). Otherwise no use of the real-time clock
2990	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4599	option will be attempted. This effectively replaces C<gettimeofday>
2991	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4600	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2992	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4601	correctness. See the note about libraries in the description of
		4602	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4603	C<EV_USE_CLOCK_SYSCALL>.
		4604
		4605	=item EV_USE_CLOCK_SYSCALL
		4606
		4607	If defined to be C<1>, libev will try to use a direct syscall instead
		4608	of calling the system-provided C<clock_gettime> function. This option
		4609	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4610	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4611	programs needlessly. Using a direct syscall is slightly slower (in
		4612	theory), because no optimised vdso implementation can be used, but avoids
		4613	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4614	higher, as it simplifies linking (no need for C<-lrt>).
2993		4615
2994	=item EV_USE_NANOSLEEP	4616	=item EV_USE_NANOSLEEP
2995		4617
2996	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4618	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2997	and will use it for delays. Otherwise it will use C<select ()>.	4619	and will use it for delays. Otherwise it will use C<select ()>.
…		…
3002	available and will probe for kernel support at runtime. This will improve	4624	available and will probe for kernel support at runtime. This will improve
3003	C<ev_signal> and C<ev_async> performance and reduce resource consumption.	4625	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
3004	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc	4626	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
3005	2.7 or newer, otherwise disabled.	4627	2.7 or newer, otherwise disabled.
3006		4628
		4629	=item EV_USE_SIGNALFD
		4630
		4631	If defined to be C<1>, then libev will assume that C<signalfd ()> is
		4632	available and will probe for kernel support at runtime. This enables
		4633	the use of EVFLAG_SIGNALFD for faster and simpler signal handling. If
		4634	undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4635	2.7 or newer, otherwise disabled.
		4636
		4637	=item EV_USE_TIMERFD
		4638
		4639	If defined to be C<1>, then libev will assume that C<timerfd ()> is
		4640	available and will probe for kernel support at runtime. This allows
		4641	libev to detect time jumps accurately. If undefined, it will be enabled
		4642	if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
		4643	C<TFD_TIMER_CANCEL_ON_SET>, otherwise disabled.
		4644
		4645	=item EV_USE_EVENTFD
		4646
		4647	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4648	available and will probe for kernel support at runtime. This will improve
		4649	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4650	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4651	2.7 or newer, otherwise disabled.
		4652
3007	=item EV_USE_SELECT	4653	=item EV_USE_SELECT
3008		4654
3009	If undefined or defined to be C<1>, libev will compile in support for the	4655	If undefined or defined to be C<1>, libev will compile in support for the
3010	C<select>(2) backend. No attempt at auto-detection will be done: if no	4656	C<select>(2) backend. No attempt at auto-detection will be done: if no
3011	other method takes over, select will be it. Otherwise the select backend	4657	other method takes over, select will be it. Otherwise the select backend
…		…
3013		4659
3014	=item EV_SELECT_USE_FD_SET	4660	=item EV_SELECT_USE_FD_SET
3015		4661
3016	If defined to C<1>, then the select backend will use the system C<fd_set>	4662	If defined to C<1>, then the select backend will use the system C<fd_set>
3017	structure. This is useful if libev doesn't compile due to a missing	4663	structure. This is useful if libev doesn't compile due to a missing
3018	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	4664	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
3019	exotic systems. This usually limits the range of file descriptors to some	4665	on exotic systems. This usually limits the range of file descriptors to
3020	low limit such as 1024 or might have other limitations (winsocket only	4666	some low limit such as 1024 or might have other limitations (winsocket
3021	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4667	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
3022	influence the size of the C<fd_set> used.	4668	configures the maximum size of the C<fd_set>.
3023		4669
3024	=item EV_SELECT_IS_WINSOCKET	4670	=item EV_SELECT_IS_WINSOCKET
3025		4671
3026	When defined to C<1>, the select backend will assume that	4672	When defined to C<1>, the select backend will assume that
3027	select/socket/connect etc. don't understand file descriptors but	4673	select/socket/connect etc. don't understand file descriptors but
…		…
3029	be used is the winsock select). This means that it will call	4675	be used is the winsock select). This means that it will call
3030	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4676	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
3031	it is assumed that all these functions actually work on fds, even	4677	it is assumed that all these functions actually work on fds, even
3032	on win32. Should not be defined on non-win32 platforms.	4678	on win32. Should not be defined on non-win32 platforms.
3033		4679
3034	=item EV_FD_TO_WIN32_HANDLE	4680	=item EV_FD_TO_WIN32_HANDLE(fd)
3035		4681
3036	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4682	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
3037	file descriptors to socket handles. When not defining this symbol (the	4683	file descriptors to socket handles. When not defining this symbol (the
3038	default), then libev will call C<_get_osfhandle>, which is usually	4684	default), then libev will call C<_get_osfhandle>, which is usually
3039	correct. In some cases, programs use their own file descriptor management,	4685	correct. In some cases, programs use their own file descriptor management,
3040	in which case they can provide this function to map fds to socket handles.	4686	in which case they can provide this function to map fds to socket handles.
3041		4687
		4688	=item EV_WIN32_HANDLE_TO_FD(handle)
		4689
		4690	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4691	using the standard C<_open_osfhandle> function. For programs implementing
		4692	their own fd to handle mapping, overwriting this function makes it easier
		4693	to do so. This can be done by defining this macro to an appropriate value.
		4694
		4695	=item EV_WIN32_CLOSE_FD(fd)
		4696
		4697	If programs implement their own fd to handle mapping on win32, then this
		4698	macro can be used to override the C<close> function, useful to unregister
		4699	file descriptors again. Note that the replacement function has to close
		4700	the underlying OS handle.
		4701
		4702	=item EV_USE_WSASOCKET
		4703
		4704	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4705	communication socket, which works better in some environments. Otherwise,
		4706	the normal C<socket> function will be used, which works better in other
		4707	environments.
		4708
3042	=item EV_USE_POLL	4709	=item EV_USE_POLL
3043		4710
3044	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4711	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3045	backend. Otherwise it will be enabled on non-win32 platforms. It	4712	backend. Otherwise it will be enabled on non-win32 platforms. It
3046	takes precedence over select.	4713	takes precedence over select.
…		…
3050	If defined to be C<1>, libev will compile in support for the Linux	4717	If defined to be C<1>, libev will compile in support for the Linux
3051	C<epoll>(7) backend. Its availability will be detected at runtime,	4718	C<epoll>(7) backend. Its availability will be detected at runtime,
3052	otherwise another method will be used as fallback. This is the preferred	4719	otherwise another method will be used as fallback. This is the preferred
3053	backend for GNU/Linux systems. If undefined, it will be enabled if the	4720	backend for GNU/Linux systems. If undefined, it will be enabled if the
3054	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4721	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4722
		4723	=item EV_USE_LINUXAIO
		4724
		4725	If defined to be C<1>, libev will compile in support for the Linux aio
		4726	backend (C<EV_USE_EPOLL> must also be enabled). If undefined, it will be
		4727	enabled on linux, otherwise disabled.
		4728
		4729	=item EV_USE_IOURING
		4730
		4731	If defined to be C<1>, libev will compile in support for the Linux
		4732	io_uring backend (C<EV_USE_EPOLL> must also be enabled). Due to it's
		4733	current limitations it has to be requested explicitly. If undefined, it
		4734	will be enabled on linux, otherwise disabled.
3055		4735
3056	=item EV_USE_KQUEUE	4736	=item EV_USE_KQUEUE
3057		4737
3058	If defined to be C<1>, libev will compile in support for the BSD style	4738	If defined to be C<1>, libev will compile in support for the BSD style
3059	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4739	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
3081	If defined to be C<1>, libev will compile in support for the Linux inotify	4761	If defined to be C<1>, libev will compile in support for the Linux inotify
3082	interface to speed up C<ev_stat> watchers. Its actual availability will	4762	interface to speed up C<ev_stat> watchers. Its actual availability will
3083	be detected at runtime. If undefined, it will be enabled if the headers	4763	be detected at runtime. If undefined, it will be enabled if the headers
3084	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4764	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3085		4765
		4766	=item EV_NO_SMP
		4767
		4768	If defined to be C<1>, libev will assume that memory is always coherent
		4769	between threads, that is, threads can be used, but threads never run on
		4770	different cpus (or different cpu cores). This reduces dependencies
		4771	and makes libev faster.
		4772
		4773	=item EV_NO_THREADS
		4774
		4775	If defined to be C<1>, libev will assume that it will never be called from
		4776	different threads (that includes signal handlers), which is a stronger
		4777	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4778	libev faster.
		4779
3086	=item EV_ATOMIC_T	4780	=item EV_ATOMIC_T
3087		4781
3088	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4782	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3089	access is atomic with respect to other threads or signal contexts. No such	4783	access is atomic with respect to other threads or signal contexts. No
3090	type is easily found in the C language, so you can provide your own type	4784	such type is easily found in the C language, so you can provide your own
3091	that you know is safe for your purposes. It is used both for signal handler "locking"	4785	type that you know is safe for your purposes. It is used both for signal
3092	as well as for signal and thread safety in C<ev_async> watchers.	4786	handler "locking" as well as for signal and thread safety in C<ev_async>
		4787	watchers.
3093		4788
3094	In the absence of this define, libev will use C<sig_atomic_t volatile>	4789	In the absence of this define, libev will use C<sig_atomic_t volatile>
3095	(from F<signal.h>), which is usually good enough on most platforms.	4790	(from F<signal.h>), which is usually good enough on most platforms.
3096		4791
3097	=item EV_H	4792	=item EV_H (h)
3098		4793
3099	The name of the F<ev.h> header file used to include it. The default if	4794	The name of the F<ev.h> header file used to include it. The default if
3100	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4795	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
3101	used to virtually rename the F<ev.h> header file in case of conflicts.	4796	used to virtually rename the F<ev.h> header file in case of conflicts.
3102		4797
3103	=item EV_CONFIG_H	4798	=item EV_CONFIG_H (h)
3104		4799
3105	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4800	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
3106	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4801	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
3107	C<EV_H>, above.	4802	C<EV_H>, above.
3108		4803
3109	=item EV_EVENT_H	4804	=item EV_EVENT_H (h)
3110		4805
3111	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4806	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
3112	of how the F<event.h> header can be found, the default is C<"event.h">.	4807	of how the F<event.h> header can be found, the default is C<"event.h">.
3113		4808
3114	=item EV_PROTOTYPES	4809	=item EV_PROTOTYPES (h)
3115		4810
3116	If defined to be C<0>, then F<ev.h> will not define any function	4811	If defined to be C<0>, then F<ev.h> will not define any function
3117	prototypes, but still define all the structs and other symbols. This is	4812	prototypes, but still define all the structs and other symbols. This is
3118	occasionally useful if you want to provide your own wrapper functions	4813	occasionally useful if you want to provide your own wrapper functions
3119	around libev functions.	4814	around libev functions.
…		…
3124	will have the C<struct ev_loop *> as first argument, and you can create	4819	will have the C<struct ev_loop *> as first argument, and you can create
3125	additional independent event loops. Otherwise there will be no support	4820	additional independent event loops. Otherwise there will be no support
3126	for multiple event loops and there is no first event loop pointer	4821	for multiple event loops and there is no first event loop pointer
3127	argument. Instead, all functions act on the single default loop.	4822	argument. Instead, all functions act on the single default loop.
3128		4823
		4824	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4825	default loop when multiplicity is switched off - you always have to
		4826	initialise the loop manually in this case.
		4827
3129	=item EV_MINPRI	4828	=item EV_MINPRI
3130		4829
3131	=item EV_MAXPRI	4830	=item EV_MAXPRI
3132		4831
3133	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4832	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
3141	fine.	4840	fine.
3142		4841
3143	If your embedding application does not need any priorities, defining these	4842	If your embedding application does not need any priorities, defining these
3144	both to C<0> will save some memory and CPU.	4843	both to C<0> will save some memory and CPU.
3145		4844
3146	=item EV_PERIODIC_ENABLE	4845	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4846	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4847	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
3147		4848
3148	If undefined or defined to be C<1>, then periodic timers are supported. If	4849	If undefined or defined to be C<1> (and the platform supports it), then
3149	defined to be C<0>, then they are not. Disabling them saves a few kB of	4850	the respective watcher type is supported. If defined to be C<0>, then it
3150	code.	4851	is not. Disabling watcher types mainly saves code size.
3151		4852
3152	=item EV_IDLE_ENABLE	4853	=item EV_FEATURES
3153
3154	If undefined or defined to be C<1>, then idle watchers are supported. If
3155	defined to be C<0>, then they are not. Disabling them saves a few kB of
3156	code.
3157
3158	=item EV_EMBED_ENABLE
3159
3160	If undefined or defined to be C<1>, then embed watchers are supported. If
3161	defined to be C<0>, then they are not. Embed watchers rely on most other
3162	watcher types, which therefore must not be disabled.
3163
3164	=item EV_STAT_ENABLE
3165
3166	If undefined or defined to be C<1>, then stat watchers are supported. If
3167	defined to be C<0>, then they are not.
3168
3169	=item EV_FORK_ENABLE
3170
3171	If undefined or defined to be C<1>, then fork watchers are supported. If
3172	defined to be C<0>, then they are not.
3173
3174	=item EV_ASYNC_ENABLE
3175
3176	If undefined or defined to be C<1>, then async watchers are supported. If
3177	defined to be C<0>, then they are not.
3178
3179	=item EV_MINIMAL
3180		4854
3181	If you need to shave off some kilobytes of code at the expense of some	4855	If you need to shave off some kilobytes of code at the expense of some
3182	speed, define this symbol to C<1>. Currently this is used to override some	4856	speed (but with the full API), you can define this symbol to request
3183	inlining decisions, saves roughly 30% code size on amd64. It also selects a	4857	certain subsets of functionality. The default is to enable all features
3184	much smaller 2-heap for timer management over the default 4-heap.	4858	that can be enabled on the platform.
		4859
		4860	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4861	with some broad features you want) and then selectively re-enable
		4862	additional parts you want, for example if you want everything minimal,
		4863	but multiple event loop support, async and child watchers and the poll
		4864	backend, use this:
		4865
		4866	#define EV_FEATURES 0
		4867	#define EV_MULTIPLICITY 1
		4868	#define EV_USE_POLL 1
		4869	#define EV_CHILD_ENABLE 1
		4870	#define EV_ASYNC_ENABLE 1
		4871
		4872	The actual value is a bitset, it can be a combination of the following
		4873	values (by default, all of these are enabled):
		4874
		4875	=over 4
		4876
		4877	=item C<1> - faster/larger code
		4878
		4879	Use larger code to speed up some operations.
		4880
		4881	Currently this is used to override some inlining decisions (enlarging the
		4882	code size by roughly 30% on amd64).
		4883
		4884	When optimising for size, use of compiler flags such as C<-Os> with
		4885	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4886	assertions.
		4887
		4888	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4889	(e.g. gcc with C<-Os>).
		4890
		4891	=item C<2> - faster/larger data structures
		4892
		4893	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4894	hash table sizes and so on. This will usually further increase code size
		4895	and can additionally have an effect on the size of data structures at
		4896	runtime.
		4897
		4898	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4899	(e.g. gcc with C<-Os>).
		4900
		4901	=item C<4> - full API configuration
		4902
		4903	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4904	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4905
		4906	=item C<8> - full API
		4907
		4908	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4909	details on which parts of the API are still available without this
		4910	feature, and do not complain if this subset changes over time.
		4911
		4912	=item C<16> - enable all optional watcher types
		4913
		4914	Enables all optional watcher types. If you want to selectively enable
		4915	only some watcher types other than I/O and timers (e.g. prepare,
		4916	embed, async, child...) you can enable them manually by defining
		4917	C<EV_watchertype_ENABLE> to C<1> instead.
		4918
		4919	=item C<32> - enable all backends
		4920
		4921	This enables all backends - without this feature, you need to enable at
		4922	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4923
		4924	=item C<64> - enable OS-specific "helper" APIs
		4925
		4926	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4927	default.
		4928
		4929	=back
		4930
		4931	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4932	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4933	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4934	watchers, timers and monotonic clock support.
		4935
		4936	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4937	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4938	your program might be left out as well - a binary starting a timer and an
		4939	I/O watcher then might come out at only 5Kb.
		4940
		4941	=item EV_API_STATIC
		4942
		4943	If this symbol is defined (by default it is not), then all identifiers
		4944	will have static linkage. This means that libev will not export any
		4945	identifiers, and you cannot link against libev anymore. This can be useful
		4946	when you embed libev, only want to use libev functions in a single file,
		4947	and do not want its identifiers to be visible.
		4948
		4949	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4950	wants to use libev.
		4951
		4952	This option only works when libev is compiled with a C compiler, as C++
		4953	doesn't support the required declaration syntax.
		4954
		4955	=item EV_AVOID_STDIO
		4956
		4957	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4958	functions (printf, scanf, perror etc.). This will increase the code size
		4959	somewhat, but if your program doesn't otherwise depend on stdio and your
		4960	libc allows it, this avoids linking in the stdio library which is quite
		4961	big.
		4962
		4963	Note that error messages might become less precise when this option is
		4964	enabled.
		4965
		4966	=item EV_NSIG
		4967
		4968	The highest supported signal number, +1 (or, the number of
		4969	signals): Normally, libev tries to deduce the maximum number of signals
		4970	automatically, but sometimes this fails, in which case it can be
		4971	specified. Also, using a lower number than detected (C<32> should be
		4972	good for about any system in existence) can save some memory, as libev
		4973	statically allocates some 12-24 bytes per signal number.
3185		4974
3186	=item EV_PID_HASHSIZE	4975	=item EV_PID_HASHSIZE
3187		4976
3188	C<ev_child> watchers use a small hash table to distribute workload by	4977	C<ev_child> watchers use a small hash table to distribute workload by
3189	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4978	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
3190	than enough. If you need to manage thousands of children you might want to	4979	usually more than enough. If you need to manage thousands of children you
3191	increase this value (I<must> be a power of two).	4980	might want to increase this value (I<must> be a power of two).
3192		4981
3193	=item EV_INOTIFY_HASHSIZE	4982	=item EV_INOTIFY_HASHSIZE
3194		4983
3195	C<ev_stat> watchers use a small hash table to distribute workload by	4984	C<ev_stat> watchers use a small hash table to distribute workload by
3196	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4985	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
3197	usually more than enough. If you need to manage thousands of C<ev_stat>	4986	disabled), usually more than enough. If you need to manage thousands of
3198	watchers you might want to increase this value (I<must> be a power of	4987	C<ev_stat> watchers you might want to increase this value (I<must> be a
3199	two).	4988	power of two).
3200		4989
3201	=item EV_USE_4HEAP	4990	=item EV_USE_4HEAP
3202		4991
3203	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4992	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3204	timer and periodics heaps, libev uses a 4-heap when this symbol is defined	4993	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3205	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably	4994	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3206	faster performance with many (thousands) of watchers.	4995	faster performance with many (thousands) of watchers.
3207		4996
3208	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4997	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3209	(disabled).	4998	will be C<0>.
3210		4999
3211	=item EV_HEAP_CACHE_AT	5000	=item EV_HEAP_CACHE_AT
3212		5001
3213	Heaps are not very cache-efficient. To improve the cache-efficiency of the	5002	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3214	timer and periodics heaps, libev can cache the timestamp (I<at>) within	5003	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3215	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	5004	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3216	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	5005	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3217	but avoids random read accesses on heap changes. This improves performance	5006	but avoids random read accesses on heap changes. This improves performance
3218	noticeably with many (hundreds) of watchers.	5007	noticeably with many (hundreds) of watchers.
3219		5008
3220	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	5009	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3221	(disabled).	5010	will be C<0>.
3222		5011
3223	=item EV_VERIFY	5012	=item EV_VERIFY
3224		5013
3225	Controls how much internal verification (see C<ev_loop_verify ()>) will	5014	Controls how much internal verification (see C<ev_verify ()>) will
3226	be done: If set to C<0>, no internal verification code will be compiled	5015	be done: If set to C<0>, no internal verification code will be compiled
3227	in. If set to C<1>, then verification code will be compiled in, but not	5016	in. If set to C<1>, then verification code will be compiled in, but not
3228	called. If set to C<2>, then the internal verification code will be	5017	called. If set to C<2>, then the internal verification code will be
3229	called once per loop, which can slow down libev. If set to C<3>, then the	5018	called once per loop, which can slow down libev. If set to C<3>, then the
3230	verification code will be called very frequently, which will slow down	5019	verification code will be called very frequently, which will slow down
3231	libev considerably.	5020	libev considerably.
3232		5021
		5022	Verification errors are reported via C's C<assert> mechanism, so if you
		5023	disable that (e.g. by defining C<NDEBUG>) then no errors will be reported.
		5024
3233	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	5025	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3234	C<0>.	5026	will be C<0>.
3235		5027
3236	=item EV_COMMON	5028	=item EV_COMMON
3237		5029
3238	By default, all watchers have a C<void *data> member. By redefining	5030	By default, all watchers have a C<void *data> member. By redefining
3239	this macro to a something else you can include more and other types of	5031	this macro to something else you can include more and other types of
3240	members. You have to define it each time you include one of the files,	5032	members. You have to define it each time you include one of the files,
3241	though, and it must be identical each time.	5033	though, and it must be identical each time.
3242		5034
3243	For example, the perl EV module uses something like this:	5035	For example, the perl EV module uses something like this:
3244		5036
…		…
3297	file.	5089	file.
3298		5090
3299	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	5091	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
3300	that everybody includes and which overrides some configure choices:	5092	that everybody includes and which overrides some configure choices:
3301		5093
3302	#define EV_MINIMAL 1	5094	#define EV_FEATURES 8
3303	#define EV_USE_POLL 0	5095	#define EV_USE_SELECT 1
3304	#define EV_MULTIPLICITY 0
3305	#define EV_PERIODIC_ENABLE 0	5096	#define EV_PREPARE_ENABLE 1
		5097	#define EV_IDLE_ENABLE 1
3306	#define EV_STAT_ENABLE 0	5098	#define EV_SIGNAL_ENABLE 1
3307	#define EV_FORK_ENABLE 0	5099	#define EV_CHILD_ENABLE 1
		5100	#define EV_USE_STDEXCEPT 0
3308	#define EV_CONFIG_H <config.h>	5101	#define EV_CONFIG_H <config.h>
3309	#define EV_MINPRI 0
3310	#define EV_MAXPRI 0
3311		5102
3312	#include "ev++.h"	5103	#include "ev++.h"
3313		5104
3314	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5105	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3315		5106
3316	#include "ev_cpp.h"	5107	#include "ev_cpp.h"
3317	#include "ev.c"	5108	#include "ev.c"
3318		5109
3319	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5110	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
3320		5111
3321	=head2 THREADS AND COROUTINES	5112	=head2 THREADS AND COROUTINES
3322		5113
3323	=head3 THREADS	5114	=head3 THREADS
3324		5115
…		…
3375	default loop and triggering an C<ev_async> watcher from the default loop	5166	default loop and triggering an C<ev_async> watcher from the default loop
3376	watcher callback into the event loop interested in the signal.	5167	watcher callback into the event loop interested in the signal.
3377		5168
3378	=back	5169	=back
3379		5170
		5171	See also L</THREAD LOCKING EXAMPLE>.
		5172
3380	=head3 COROUTINES	5173	=head3 COROUTINES
3381		5174
3382	Libev is very accommodating to coroutines ("cooperative threads"):	5175	Libev is very accommodating to coroutines ("cooperative threads"):
3383	libev fully supports nesting calls to its functions from different	5176	libev fully supports nesting calls to its functions from different
3384	coroutines (e.g. you can call C<ev_loop> on the same loop from two	5177	coroutines (e.g. you can call C<ev_run> on the same loop from two
3385	different coroutines, and switch freely between both coroutines running the	5178	different coroutines, and switch freely between both coroutines running
3386	loop, as long as you don't confuse yourself). The only exception is that	5179	the loop, as long as you don't confuse yourself). The only exception is
3387	you must not do this from C<ev_periodic> reschedule callbacks.	5180	that you must not do this from C<ev_periodic> reschedule callbacks.
3388		5181
3389	Care has been taken to ensure that libev does not keep local state inside	5182	Care has been taken to ensure that libev does not keep local state inside
3390	C<ev_loop>, and other calls do not usually allow for coroutine switches as	5183	C<ev_run>, and other calls do not usually allow for coroutine switches as
3391	they do not clal any callbacks.	5184	they do not call any callbacks.
3392		5185
3393	=head2 COMPILER WARNINGS	5186	=head2 COMPILER WARNINGS
3394		5187
3395	Depending on your compiler and compiler settings, you might get no or a	5188	Depending on your compiler and compiler settings, you might get no or a
3396	lot of warnings when compiling libev code. Some people are apparently	5189	lot of warnings when compiling libev code. Some people are apparently
…		…
3406	maintainable.	5199	maintainable.
3407		5200
3408	And of course, some compiler warnings are just plain stupid, or simply	5201	And of course, some compiler warnings are just plain stupid, or simply
3409	wrong (because they don't actually warn about the condition their message	5202	wrong (because they don't actually warn about the condition their message
3410	seems to warn about). For example, certain older gcc versions had some	5203	seems to warn about). For example, certain older gcc versions had some
3411	warnings that resulted an extreme number of false positives. These have	5204	warnings that resulted in an extreme number of false positives. These have
3412	been fixed, but some people still insist on making code warn-free with	5205	been fixed, but some people still insist on making code warn-free with
3413	such buggy versions.	5206	such buggy versions.
3414		5207
3415	While libev is written to generate as few warnings as possible,	5208	While libev is written to generate as few warnings as possible,
3416	"warn-free" code is not a goal, and it is recommended not to build libev	5209	"warn-free" code is not a goal, and it is recommended not to build libev
…		…
3430	==2274== definitely lost: 0 bytes in 0 blocks.	5223	==2274== definitely lost: 0 bytes in 0 blocks.
3431	==2274== possibly lost: 0 bytes in 0 blocks.	5224	==2274== possibly lost: 0 bytes in 0 blocks.
3432	==2274== still reachable: 256 bytes in 1 blocks.	5225	==2274== still reachable: 256 bytes in 1 blocks.
3433		5226
3434	Then there is no memory leak, just as memory accounted to global variables	5227	Then there is no memory leak, just as memory accounted to global variables
3435	is not a memleak - the memory is still being refernced, and didn't leak.	5228	is not a memleak - the memory is still being referenced, and didn't leak.
3436		5229
3437	Similarly, under some circumstances, valgrind might report kernel bugs	5230	Similarly, under some circumstances, valgrind might report kernel bugs
3438	as if it were a bug in libev (e.g. in realloc or in the poll backend,	5231	as if it were a bug in libev (e.g. in realloc or in the poll backend,
3439	although an acceptable workaround has been found here), or it might be	5232	although an acceptable workaround has been found here), or it might be
3440	confused.	5233	confused.
…		…
3452	I suggest using suppression lists.	5245	I suggest using suppression lists.
3453		5246
3454		5247
3455	=head1 PORTABILITY NOTES	5248	=head1 PORTABILITY NOTES
3456		5249
		5250	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5251
		5252	GNU/Linux is the only common platform that supports 64 bit file/large file
		5253	interfaces but I<disables> them by default.
		5254
		5255	That means that libev compiled in the default environment doesn't support
		5256	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5257
		5258	Unfortunately, many programs try to work around this GNU/Linux issue
		5259	by enabling the large file API, which makes them incompatible with the
		5260	standard libev compiled for their system.
		5261
		5262	Likewise, libev cannot enable the large file API itself as this would
		5263	suddenly make it incompatible to the default compile time environment,
		5264	i.e. all programs not using special compile switches.
		5265
		5266	=head2 OS/X AND DARWIN BUGS
		5267
		5268	The whole thing is a bug if you ask me - basically any system interface
		5269	you touch is broken, whether it is locales, poll, kqueue or even the
		5270	OpenGL drivers.
		5271
		5272	=head3 C<kqueue> is buggy
		5273
		5274	The kqueue syscall is broken in all known versions - most versions support
		5275	only sockets, many support pipes.
		5276
		5277	Libev tries to work around this by not using C<kqueue> by default on this
		5278	rotten platform, but of course you can still ask for it when creating a
		5279	loop - embedding a socket-only kqueue loop into a select-based one is
		5280	probably going to work well.
		5281
		5282	=head3 C<poll> is buggy
		5283
		5284	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5285	implementation by something calling C<kqueue> internally around the 10.5.6
		5286	release, so now C<kqueue> I<and> C<poll> are broken.
		5287
		5288	Libev tries to work around this by not using C<poll> by default on
		5289	this rotten platform, but of course you can still ask for it when creating
		5290	a loop.
		5291
		5292	=head3 C<select> is buggy
		5293
		5294	All that's left is C<select>, and of course Apple found a way to fuck this
		5295	one up as well: On OS/X, C<select> actively limits the number of file
		5296	descriptors you can pass in to 1024 - your program suddenly crashes when
		5297	you use more.
		5298
		5299	There is an undocumented "workaround" for this - defining
		5300	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5301	work on OS/X.
		5302
		5303	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5304
		5305	=head3 C<errno> reentrancy
		5306
		5307	The default compile environment on Solaris is unfortunately so
		5308	thread-unsafe that you can't even use components/libraries compiled
		5309	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5310	defined by default. A valid, if stupid, implementation choice.
		5311
		5312	If you want to use libev in threaded environments you have to make sure
		5313	it's compiled with C<_REENTRANT> defined.
		5314
		5315	=head3 Event port backend
		5316
		5317	The scalable event interface for Solaris is called "event
		5318	ports". Unfortunately, this mechanism is very buggy in all major
		5319	releases. If you run into high CPU usage, your program freezes or you get
		5320	a large number of spurious wakeups, make sure you have all the relevant
		5321	and latest kernel patches applied. No, I don't know which ones, but there
		5322	are multiple ones to apply, and afterwards, event ports actually work
		5323	great.
		5324
		5325	If you can't get it to work, you can try running the program by setting
		5326	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5327	C<select> backends.
		5328
		5329	=head2 AIX POLL BUG
		5330
		5331	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5332	this by trying to avoid the poll backend altogether (i.e. it's not even
		5333	compiled in), which normally isn't a big problem as C<select> works fine
		5334	with large bitsets on AIX, and AIX is dead anyway.
		5335
3457	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	5336	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5337
		5338	=head3 General issues
3458		5339
3459	Win32 doesn't support any of the standards (e.g. POSIX) that libev	5340	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3460	requires, and its I/O model is fundamentally incompatible with the POSIX	5341	requires, and its I/O model is fundamentally incompatible with the POSIX
3461	model. Libev still offers limited functionality on this platform in	5342	model. Libev still offers limited functionality on this platform in
3462	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5343	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3463	descriptors. This only applies when using Win32 natively, not when using	5344	descriptors. This only applies when using Win32 natively, not when using
3464	e.g. cygwin.	5345	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5346	as every compiler comes with a slightly differently broken/incompatible
		5347	environment.
3465		5348
3466	Lifting these limitations would basically require the full	5349	Lifting these limitations would basically require the full
3467	re-implementation of the I/O system. If you are into these kinds of	5350	re-implementation of the I/O system. If you are into this kind of thing,
3468	things, then note that glib does exactly that for you in a very portable	5351	then note that glib does exactly that for you in a very portable way (note
3469	way (note also that glib is the slowest event library known to man).	5352	also that glib is the slowest event library known to man).
3470		5353
3471	There is no supported compilation method available on windows except	5354	There is no supported compilation method available on windows except
3472	embedding it into other applications.	5355	embedding it into other applications.
		5356
		5357	Sensible signal handling is officially unsupported by Microsoft - libev
		5358	tries its best, but under most conditions, signals will simply not work.
3473		5359
3474	Not a libev limitation but worth mentioning: windows apparently doesn't	5360	Not a libev limitation but worth mentioning: windows apparently doesn't
3475	accept large writes: instead of resulting in a partial write, windows will	5361	accept large writes: instead of resulting in a partial write, windows will
3476	either accept everything or return C<ENOBUFS> if the buffer is too large,	5362	either accept everything or return C<ENOBUFS> if the buffer is too large,
3477	so make sure you only write small amounts into your sockets (less than a	5363	so make sure you only write small amounts into your sockets (less than a
…		…
3482	the abysmal performance of winsockets, using a large number of sockets	5368	the abysmal performance of winsockets, using a large number of sockets
3483	is not recommended (and not reasonable). If your program needs to use	5369	is not recommended (and not reasonable). If your program needs to use
3484	more than a hundred or so sockets, then likely it needs to use a totally	5370	more than a hundred or so sockets, then likely it needs to use a totally
3485	different implementation for windows, as libev offers the POSIX readiness	5371	different implementation for windows, as libev offers the POSIX readiness
3486	notification model, which cannot be implemented efficiently on windows	5372	notification model, which cannot be implemented efficiently on windows
3487	(Microsoft monopoly games).	5373	(due to Microsoft monopoly games).
3488		5374
3489	A typical way to use libev under windows is to embed it (see the embedding	5375	A typical way to use libev under windows is to embed it (see the embedding
3490	section for details) and use the following F<evwrap.h> header file instead	5376	section for details) and use the following F<evwrap.h> header file instead
3491	of F<ev.h>:	5377	of F<ev.h>:
3492		5378
…		…
3499	you do I<not> compile the F<ev.c> or any other embedded source files!):	5385	you do I<not> compile the F<ev.c> or any other embedded source files!):
3500		5386
3501	#include "evwrap.h"	5387	#include "evwrap.h"
3502	#include "ev.c"	5388	#include "ev.c"
3503		5389
3504	=over 4
3505
3506	=item The winsocket select function	5390	=head3 The winsocket C<select> function
3507		5391
3508	The winsocket C<select> function doesn't follow POSIX in that it	5392	The winsocket C<select> function doesn't follow POSIX in that it
3509	requires socket I<handles> and not socket I<file descriptors> (it is	5393	requires socket I<handles> and not socket I<file descriptors> (it is
3510	also extremely buggy). This makes select very inefficient, and also	5394	also extremely buggy). This makes select very inefficient, and also
3511	requires a mapping from file descriptors to socket handles (the Microsoft	5395	requires a mapping from file descriptors to socket handles (the Microsoft
…		…
3520	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	5404	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3521		5405
3522	Note that winsockets handling of fd sets is O(n), so you can easily get a	5406	Note that winsockets handling of fd sets is O(n), so you can easily get a
3523	complexity in the O(n²) range when using win32.	5407	complexity in the O(n²) range when using win32.
3524		5408
3525	=item Limited number of file descriptors	5409	=head3 Limited number of file descriptors
3526		5410
3527	Windows has numerous arbitrary (and low) limits on things.	5411	Windows has numerous arbitrary (and low) limits on things.
3528		5412
3529	Early versions of winsocket's select only supported waiting for a maximum	5413	Early versions of winsocket's select only supported waiting for a maximum
3530	of C<64> handles (probably owning to the fact that all windows kernels	5414	of C<64> handles (probably owning to the fact that all windows kernels
3531	can only wait for C<64> things at the same time internally; Microsoft	5415	can only wait for C<64> things at the same time internally; Microsoft
3532	recommends spawning a chain of threads and wait for 63 handles and the	5416	recommends spawning a chain of threads and wait for 63 handles and the
3533	previous thread in each. Great).	5417	previous thread in each. Sounds great!).
3534		5418
3535	Newer versions support more handles, but you need to define C<FD_SETSIZE>	5419	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3536	to some high number (e.g. C<2048>) before compiling the winsocket select	5420	to some high number (e.g. C<2048>) before compiling the winsocket select
3537	call (which might be in libev or elsewhere, for example, perl does its own	5421	call (which might be in libev or elsewhere, for example, perl and many
3538	select emulation on windows).	5422	other interpreters do their own select emulation on windows).
3539		5423
3540	Another limit is the number of file descriptors in the Microsoft runtime	5424	Another limit is the number of file descriptors in the Microsoft runtime
3541	libraries, which by default is C<64> (there must be a hidden I<64> fetish	5425	libraries, which by default is C<64> (there must be a hidden I<64>
3542	or something like this inside Microsoft). You can increase this by calling	5426	fetish or something like this inside Microsoft). You can increase this
3543	C<_setmaxstdio>, which can increase this limit to C<2048> (another	5427	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3544	arbitrary limit), but is broken in many versions of the Microsoft runtime	5428	(another arbitrary limit), but is broken in many versions of the Microsoft
3545	libraries.
3546
3547	This might get you to about C<512> or C<2048> sockets (depending on	5429	runtime libraries. This might get you to about C<512> or C<2048> sockets
3548	windows version and/or the phase of the moon). To get more, you need to	5430	(depending on windows version and/or the phase of the moon). To get more,
3549	wrap all I/O functions and provide your own fd management, but the cost of	5431	you need to wrap all I/O functions and provide your own fd management, but
3550	calling select (O(n²)) will likely make this unworkable.	5432	the cost of calling select (O(n²)) will likely make this unworkable.
3551
3552	=back
3553		5433
3554	=head2 PORTABILITY REQUIREMENTS	5434	=head2 PORTABILITY REQUIREMENTS
3555		5435
3556	In addition to a working ISO-C implementation and of course the	5436	In addition to a working ISO-C implementation and of course the
3557	backend-specific APIs, libev relies on a few additional extensions:	5437	backend-specific APIs, libev relies on a few additional extensions:
…		…
3564	Libev assumes not only that all watcher pointers have the same internal	5444	Libev assumes not only that all watcher pointers have the same internal
3565	structure (guaranteed by POSIX but not by ISO C for example), but it also	5445	structure (guaranteed by POSIX but not by ISO C for example), but it also
3566	assumes that the same (machine) code can be used to call any watcher	5446	assumes that the same (machine) code can be used to call any watcher
3567	callback: The watcher callbacks have different type signatures, but libev	5447	callback: The watcher callbacks have different type signatures, but libev
3568	calls them using an C<ev_watcher *> internally.	5448	calls them using an C<ev_watcher *> internally.
		5449
		5450	=item null pointers and integer zero are represented by 0 bytes
		5451
		5452	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5453	relies on this setting pointers and integers to null.
		5454
		5455	=item pointer accesses must be thread-atomic
		5456
		5457	Accessing a pointer value must be atomic, it must both be readable and
		5458	writable in one piece - this is the case on all current architectures.
3569		5459
3570	=item C<sig_atomic_t volatile> must be thread-atomic as well	5460	=item C<sig_atomic_t volatile> must be thread-atomic as well
3571		5461
3572	The type C<sig_atomic_t volatile> (or whatever is defined as	5462	The type C<sig_atomic_t volatile> (or whatever is defined as
3573	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5463	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
…		…
3582	thread" or will block signals process-wide, both behaviours would	5472	thread" or will block signals process-wide, both behaviours would
3583	be compatible with libev. Interaction between C<sigprocmask> and	5473	be compatible with libev. Interaction between C<sigprocmask> and
3584	C<pthread_sigmask> could complicate things, however.	5474	C<pthread_sigmask> could complicate things, however.
3585		5475
3586	The most portable way to handle signals is to block signals in all threads	5476	The most portable way to handle signals is to block signals in all threads
3587	except the initial one, and run the default loop in the initial thread as	5477	except the initial one, and run the signal handling loop in the initial
3588	well.	5478	thread as well.
3589		5479
3590	=item C<long> must be large enough for common memory allocation sizes	5480	=item C<long> must be large enough for common memory allocation sizes
3591		5481
3592	To improve portability and simplify its API, libev uses C<long> internally	5482	To improve portability and simplify its API, libev uses C<long> internally
3593	instead of C<size_t> when allocating its data structures. On non-POSIX	5483	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
3596	watchers.	5486	watchers.
3597		5487
3598	=item C<double> must hold a time value in seconds with enough accuracy	5488	=item C<double> must hold a time value in seconds with enough accuracy
3599		5489
3600	The type C<double> is used to represent timestamps. It is required to	5490	The type C<double> is used to represent timestamps. It is required to
3601	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	5491	have at least 51 bits of mantissa (and 9 bits of exponent), which is
3602	enough for at least into the year 4000. This requirement is fulfilled by	5492	good enough for at least into the year 4000 with millisecond accuracy
		5493	(the design goal for libev). This requirement is overfulfilled by
3603	implementations implementing IEEE 754 (basically all existing ones).	5494	implementations using IEEE 754, which is basically all existing ones.
		5495
		5496	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5497	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5498	is either obsolete or somebody patched it to use C<long double> or
		5499	something like that, just kidding).
3604		5500
3605	=back	5501	=back
3606		5502
3607	If you know of other additional requirements drop me a note.	5503	If you know of other additional requirements drop me a note.
3608		5504
…		…
3670	=item Processing ev_async_send: O(number_of_async_watchers)	5566	=item Processing ev_async_send: O(number_of_async_watchers)
3671		5567
3672	=item Processing signals: O(max_signal_number)	5568	=item Processing signals: O(max_signal_number)
3673		5569
3674	Sending involves a system call I<iff> there were no other C<ev_async_send>	5570	Sending involves a system call I<iff> there were no other C<ev_async_send>
3675	calls in the current loop iteration. Checking for async and signal events	5571	calls in the current loop iteration and the loop is currently
		5572	blocked. Checking for async and signal events involves iterating over all
3676	involves iterating over all running async watchers or all signal numbers.	5573	running async watchers or all signal numbers.
3677		5574
3678	=back	5575	=back
3679		5576
3680		5577
		5578	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5579
		5580	The major version 4 introduced some incompatible changes to the API.
		5581
		5582	At the moment, the C<ev.h> header file provides compatibility definitions
		5583	for all changes, so most programs should still compile. The compatibility
		5584	layer might be removed in later versions of libev, so better update to the
		5585	new API early than late.
		5586
		5587	=over 4
		5588
		5589	=item C<EV_COMPAT3> backwards compatibility mechanism
		5590
		5591	The backward compatibility mechanism can be controlled by
		5592	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5593	section.
		5594
		5595	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5596
		5597	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5598
		5599	ev_loop_destroy (EV_DEFAULT_UC);
		5600	ev_loop_fork (EV_DEFAULT);
		5601
		5602	=item function/symbol renames
		5603
		5604	A number of functions and symbols have been renamed:
		5605
		5606	ev_loop => ev_run
		5607	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5608	EVLOOP_ONESHOT => EVRUN_ONCE
		5609
		5610	ev_unloop => ev_break
		5611	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5612	EVUNLOOP_ONE => EVBREAK_ONE
		5613	EVUNLOOP_ALL => EVBREAK_ALL
		5614
		5615	EV_TIMEOUT => EV_TIMER
		5616
		5617	ev_loop_count => ev_iteration
		5618	ev_loop_depth => ev_depth
		5619	ev_loop_verify => ev_verify
		5620
		5621	Most functions working on C<struct ev_loop> objects don't have an
		5622	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5623	associated constants have been renamed to not collide with the C<struct
		5624	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5625	as all other watcher types. Note that C<ev_loop_fork> is still called
		5626	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5627	typedef.
		5628
		5629	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5630
		5631	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5632	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5633	and work, but the library code will of course be larger.
		5634
		5635	=back
		5636
		5637
		5638	=head1 GLOSSARY
		5639
		5640	=over 4
		5641
		5642	=item active
		5643
		5644	A watcher is active as long as it has been started and not yet stopped.
		5645	See L</WATCHER STATES> for details.
		5646
		5647	=item application
		5648
		5649	In this document, an application is whatever is using libev.
		5650
		5651	=item backend
		5652
		5653	The part of the code dealing with the operating system interfaces.
		5654
		5655	=item callback
		5656
		5657	The address of a function that is called when some event has been
		5658	detected. Callbacks are being passed the event loop, the watcher that
		5659	received the event, and the actual event bitset.
		5660
		5661	=item callback/watcher invocation
		5662
		5663	The act of calling the callback associated with a watcher.
		5664
		5665	=item event
		5666
		5667	A change of state of some external event, such as data now being available
		5668	for reading on a file descriptor, time having passed or simply not having
		5669	any other events happening anymore.
		5670
		5671	In libev, events are represented as single bits (such as C<EV_READ> or
		5672	C<EV_TIMER>).
		5673
		5674	=item event library
		5675
		5676	A software package implementing an event model and loop.
		5677
		5678	=item event loop
		5679
		5680	An entity that handles and processes external events and converts them
		5681	into callback invocations.
		5682
		5683	=item event model
		5684
		5685	The model used to describe how an event loop handles and processes
		5686	watchers and events.
		5687
		5688	=item pending
		5689
		5690	A watcher is pending as soon as the corresponding event has been
		5691	detected. See L</WATCHER STATES> for details.
		5692
		5693	=item real time
		5694
		5695	The physical time that is observed. It is apparently strictly monotonic :)
		5696
		5697	=item wall-clock time
		5698
		5699	The time and date as shown on clocks. Unlike real time, it can actually
		5700	be wrong and jump forwards and backwards, e.g. when you adjust your
		5701	clock.
		5702
		5703	=item watcher
		5704
		5705	A data structure that describes interest in certain events. Watchers need
		5706	to be started (attached to an event loop) before they can receive events.
		5707
		5708	=back
		5709
3681	=head1 AUTHOR	5710	=head1 AUTHOR
3682		5711
3683	Marc Lehmann <libev@schmorp.de>.	5712	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5713	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
3684		5714

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