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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
…		…
8		10
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>
		15
		16	#include <stdio.h> // for puts
13		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;
…		…
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_ 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	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
…		…
103	Libev is very configurable. In this manual the default (and most common)	128	Libev is very configurable. In this manual the default (and most common)
104	configuration will be described, which supports multiple event loops. For	129	configuration will be described, which supports multiple event loops. For
105	more info about various configuration options please have a look at	130	more info about various configuration options please have a look at
106	B<EMBED> section in this manual. If libev was configured without support	131	B<EMBED> section in this manual. If libev was configured without support
107	for multiple event loops, then all functions taking an initial argument of	132	for multiple event loops, then all functions taking an initial argument of
108	name C<loop> (which is always of type C<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 C<struct>	353	An event loop is described by a C<struct ev_loop *> (the C<struct> is
282	is I<not> optional in this case, as there is also an C<ev_loop>	354	I<not> optional in this case unless libev 3 compatibility is disabled, as
283	I<function>).	355	libev 3 had an C<ev_loop> function colliding with the struct name).
284		356
285	The library knows two types of such loops, the I<default> loop, which	357	The library knows two types of such loops, the I<default> loop, which
286	supports signals and child events, and dynamically created loops which do	358	supports child process events, and dynamically created event loops which
287	not.	359	do not.
288		360
289	=over 4	361	=over 4
290		362
291	=item struct ev_loop *ev_default_loop (unsigned int flags)	363	=item struct ev_loop *ev_default_loop (unsigned int flags)
292		364
293	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
294	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
295	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
296	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".
297		375
298	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
299	function.	377	function (or via the C<EV_DEFAULT> macro).
300		378
301	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
302	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
303	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).
304		383
305	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,
306	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
307	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
308	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
309	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	388	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
310	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.
311		408
312	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
313	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>).
314		411
315	The following flags are supported:	412	The following flags are supported:
…		…
325		422
326	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
327	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
328	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	425	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
329	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
330	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
331	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).
332		431
333	=item C<EVFLAG_FORKCHECK>	432	=item C<EVFLAG_FORKCHECK>
334		433
335	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
336	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.
337	enabling this flag.
338		436
339	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,
340	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
341	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
342	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
343	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
344	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).
345		444
346	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
347	forget about forgetting to tell libev about forking) when you use this	446	forget about forgetting to tell libev about forking, although you still
348	flag.	447	have to ignore C<SIGPIPE>) when you use this flag.
349		448
350	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>
351	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.
352		495
353	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	496	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
354		497
355	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
356	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,
…		…
381	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
382	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	525	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
383		526
384	=item C<EVBACKEND_EPOLL> (value 4, Linux)	527	=item C<EVBACKEND_EPOLL> (value 4, Linux)
385		528
		529	Use the Linux-specific epoll(7) interface (for both pre- and post-2.6.9
		530	kernels).
		531
386	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
387	but it scales phenomenally better. While poll and select usually scale	533	it scales phenomenally better. While poll and select usually scale like
388	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
389	epoll scales either O(1) or O(active_fds).	535	fd), epoll scales either O(1) or O(active_fds).
390		536
391	The epoll syscalls are the most misdesigned of the more advanced event	537	The epoll mechanism deserves honorable mention as the most misdesigned
392	mechanisms: problems include silently dropping fds, requiring a system	538	of the more advanced event mechanisms: mere annoyances include silently
		539	dropping file descriptors, requiring a system call per change per file
393	call per change per fd (and unnecessary guessing of parameters), problems	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
394	with dup and so on. The biggest issue is fork races, however - if a	543	0.1ms) and so on. The biggest issue is fork races, however - if a program
395	program forks then I<both> parent and child process have to recreate the	544	forks then I<both> parent and child process have to recreate the epoll
396	epoll set, which can take considerable time (one syscall per fd) and is of	545	set, which can take considerable time (one syscall per file descriptor)
397	course hard to detect.	546	and is of course hard to detect.
398		547
399	Epoll is also notoriously buggy - embedding epoll fds should work, but	548	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
400	of course doesn't, and epoll just loves to report events for totally	549	but of course I<doesn't>, and epoll just loves to report events for
401	I<different> file descriptors (even already closed ones, so one cannot	550	totally I<different> file descriptors (even already closed ones, so
402	even remove them from the set) than registered in the set (especially	551	one cannot even remove them from the set) than registered in the set
403	on SMP systems). Libev tries to counter these spurious notifications by	552	(especially on SMP systems). Libev tries to counter these spurious
404	employing an additional generation counter and comparing that against the	553	notifications by employing an additional generation counter and comparing
405	events to filter out spurious ones.	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...
406		564
407	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
408	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
409	(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
410	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
411	very well if you register events for both fds.	569	file descriptors might not work very well if you register events for both
		570	file descriptors.
412		571
413	Best performance from this backend is achieved by not unregistering all	572	Best performance from this backend is achieved by not unregistering all
414	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,
415	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
416	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
417	extra overhead. A fork can both result in spurious notifications as well	576	extra overhead. A fork can both result in spurious notifications as well
418	as in libev having to destroy and recreate the epoll object, which can	577	as in libev having to destroy and recreate the epoll object, which can
419	take considerable time and thus should be avoided.	578	take considerable time and thus should be avoided.
420		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.
		583
421	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
422	all kernel versions tested so far.	585	a lot of kernel revisions, but probably(!) works in current versions.
423		586
424	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
425	C<EVBACKEND_POLL>.	588	C<EVBACKEND_POLL>.
426		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
427	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	634	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
428		635
429	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
430	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
431	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,
432	completely useless). For this reason it's not being "auto-detected" unless	639	where of course it's completely useless). Unlike epoll, however, whose
433	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
434	libev was compiled on a known-to-be-good (-enough) system like NetBSD.	644	known-to-be-good (-enough) system like NetBSD.
435		645
436	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
437	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
438	the target platform). See C<ev_embed> watchers for more info.	648	the target platform). See C<ev_embed> watchers for more info.
439		649
440	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
441	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
442	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
443	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
444	two event changes per incident. Support for C<fork ()> is very bad (but	654	two event changes per incident. Support for C<fork ()> is very bad (you
445	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	655	might have to leak fds on fork, but it's more sane than epoll) and it
446	cases	656	drops fds silently in similarly hard-to-detect cases.
447		657
448	This backend usually performs well under most conditions.	658	This backend usually performs well under most conditions.
449		659
450	While nominally embeddable in other event loops, this doesn't work	660	While nominally embeddable in other event loops, this doesn't work
451	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
452	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
453	(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
454	(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
455	using it only for sockets.	665	also broken on OS X)) and, did I mention it, using it only for sockets.
456		666
457	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
458	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
459	C<NOTE_EOF>.	669	C<NOTE_EOF>.
460		670
…		…
465	and is not embeddable, which would limit the usefulness of this backend	675	and is not embeddable, which would limit the usefulness of this backend
466	immensely.	676	immensely.
467		677
468	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	678	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
469		679
470	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
471	it's really slow, but it still scales very well (O(active_fds)).	681	Solaris, it's really slow, but it still scales very well (O(active_fds)).
472
473	Please note that Solaris event ports can deliver a lot of spurious
474	notifications, so you need to use non-blocking I/O or other means to avoid
475	blocking when no data (or space) is available.
476		682
477	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
478	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
479	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	685	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
480	might perform better.	686	might perform better.
481		687
482	On the positive side, with the exception of the spurious readiness	688	On the positive side, this backend actually performed fully to
483	notifications, this backend actually performed fully to specification
484	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
485	OS-specific backends (I vastly prefer correctness over speed hacks).	690	among the OS-specific backends (I vastly prefer correctness over speed
		691	hacks).
		692
		693	On the negative side, the interface is I<bizarre> - so bizarre that
		694	even sun itself gets it wrong in their code examples: The event polling
		695	function sometimes returns events to the caller even though an error
		696	occurred, but with no indication whether it has done so or not (yes, it's
		697	even documented that way) - deadly for edge-triggered interfaces where you
		698	absolutely have to know whether an event occurred or not because you have
		699	to re-arm the watcher.
		700
		701	Fortunately libev seems to be able to work around these idiocies.
486		702
487	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
488	C<EVBACKEND_POLL>.	704	C<EVBACKEND_POLL>.
489		705
490	=item C<EVBACKEND_ALL>	706	=item C<EVBACKEND_ALL>
491		707
492	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
493	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
494	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	710	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
495		711
496	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).
497		721
498	=back	722	=back
499		723
500	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,
501	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
502	specified, all backends in C<ev_recommended_backends ()> will be tried.	726	here). If none are specified, all backends in C<ev_recommended_backends
503		727	()> will be tried.
504	Example: This is the most typical usage.
505
506	if (!ev_default_loop (0))
507	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
508
509	Example: Restrict libev to the select and poll backends, and do not allow
510	environment settings to be taken into account:
511
512	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
513
514	Example: Use whatever libev has to offer, but make sure that kqueue is
515	used if available (warning, breaks stuff, best use only with your own
516	private event loop and only if you know the OS supports your types of
517	fds):
518
519	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
520
521	=item struct ev_loop *ev_loop_new (unsigned int flags)
522
523	Similar to C<ev_default_loop>, but always creates a new event loop that is
524	always distinct from the default loop. Unlike the default loop, it cannot
525	handle signal and child watchers, and attempts to do so will be greeted by
526	undefined behaviour (or a failed assertion if assertions are enabled).
527
528	Note that this function I<is> thread-safe, and the recommended way to use
529	libev with threads is indeed to create one loop per thread, and using the
530	default loop in the "main" or "initial" thread.
531		728
532	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.
533		730
534	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	731	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
535	if (!epoller)	732	if (!epoller)
536	fatal ("no epoll found here, maybe it hides under your chair");	733	fatal ("no epoll found here, maybe it hides under your chair");
537		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
538	=item ev_default_destroy ()	746	=item ev_loop_destroy (loop)
539		747
540	Destroys the default loop again (frees all memory and kernel state	748	Destroys an event loop object (frees all memory and kernel state
541	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
542	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
543	responsibility to either stop all watchers cleanly yourself I<before>	751	responsibility to either stop all watchers cleanly yourself I<before>
544	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
545	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
…		…
547		755
548	Note that certain global state, such as signal state (and installed signal	756	Note that certain global state, such as signal state (and installed signal
549	handlers), will not be freed by this function, and related watchers (such	757	handlers), will not be freed by this function, and related watchers (such
550	as signal and child watchers) would need to be stopped manually.	758	as signal and child watchers) would need to be stopped manually.
551		759
552	In general it is not advisable to call this function except in the	760	This function is normally used on loop objects allocated by
553	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.
554	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>
555	C<ev_loop_new> and C<ev_loop_destroy>).	767	and C<ev_loop_destroy>.
556		768
557	=item ev_loop_destroy (loop)	769	=item ev_loop_fork (loop)
558		770
559	Like C<ev_default_destroy>, but destroys an event loop created by an
560	earlier call to C<ev_loop_new>.
561
562	=item ev_default_fork ()
563
564	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
565	to reinitialise the kernel state for backends that have one. Despite the	772	to reinitialise the kernel state for backends that have one. Despite
566	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
567	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
568	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
569	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.
570		785
571	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
572	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
573	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).
574		792
575	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
576	it just in case after a fork. To make this easy, the function will fit in	794	it just in case after a fork.
577	quite nicely into a call to C<pthread_atfork>:
578		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	...
579	pthread_atfork (0, 0, ev_default_fork);	806	pthread_atfork (0, 0, post_fork_child);
580
581	=item ev_loop_fork (loop)
582
583	Like C<ev_default_fork>, but acts on an event loop created by
584	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
585	after fork that you want to re-use in the child, and how you do this is
586	entirely your own problem.
587		807
588	=item int ev_is_default_loop (loop)	808	=item int ev_is_default_loop (loop)
589		809
590	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
591	otherwise.	811	otherwise.
592		812
593	=item unsigned int ev_loop_count (loop)	813	=item unsigned int ev_iteration (loop)
594		814
595	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
596	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>
597	happily wraps around with enough iterations.	817	and happily wraps around with enough iterations.
598		818
599	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
600	"ticks" the number of loop iterations), as it roughly corresponds with	820	"ticks" the number of loop iterations), as it roughly corresponds with
601	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.
602		837
603	=item unsigned int ev_backend (loop)	838	=item unsigned int ev_backend (loop)
604		839
605	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
606	use.	841	use.
…		…
615		850
616	=item ev_now_update (loop)	851	=item ev_now_update (loop)
617		852
618	Establishes the current time by querying the kernel, updating the time	853	Establishes the current time by querying the kernel, updating the time
619	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
620	is usually done automatically within C<ev_loop ()>.	855	is usually done automatically within C<ev_run ()>.
621		856
622	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
623	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
624	the current time is a good idea.	859	the current time is a good idea.
625		860
626	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.
627		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
628	=item ev_loop (loop, int flags)	889	=item bool ev_run (loop, int flags)
629		890
630	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
631	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
632	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>.
633		896
634	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
635	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.
636		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
637	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
638	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
639	finished (especially in interactive programs), but having a program	907	finished (especially in interactive programs), but having a program
640	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
641	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
642	beauty.	910	beauty.
643		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
644	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
645	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
646	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
647	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.
648		922
649	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
650	necessary) and will handle those and any already outstanding ones. It	924	necessary) and will handle those and any already outstanding ones. It
651	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
652	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
653	user-registered callback will be called), and will return after one	927	user-registered callback will be called), and will return after one
654	iteration of the loop.	928	iteration of the loop.
655		929
656	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
657	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
658	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
659	usually a better approach for this kind of thing.	933	usually a better approach for this kind of thing.
660		934
661	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):
662		938
		939	- Increment loop depth.
		940	- Reset the ev_break status.
663	- Before the first iteration, call any pending watchers.	941	- Before the first iteration, call any pending watchers.
		942	LOOP:
664	* If EVFLAG_FORKCHECK was used, check for a fork.	943	- If EVFLAG_FORKCHECK was used, check for a fork.
665	- 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.
666	- Queue and call all prepare watchers.	945	- Queue and call all prepare watchers.
		946	- If ev_break was called, goto FINISH.
667	- If we have been forked, detach and recreate the kernel state	947	- If we have been forked, detach and recreate the kernel state
668	as to not disturb the other process.	948	as to not disturb the other process.
669	- Update the kernel state with all outstanding changes.	949	- Update the kernel state with all outstanding changes.
670	- Update the "event loop time" (ev_now ()).	950	- Update the "event loop time" (ev_now ()).
671	- Calculate for how long to sleep or block, if at all	951	- Calculate for how long to sleep or block, if at all
672	(active idle watchers, EVLOOP_NONBLOCK or not having	952	(active idle watchers, EVRUN_NOWAIT or not having
673	any active watchers at all will result in not sleeping).	953	any active watchers at all will result in not sleeping).
674	- 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.
675	- Block the process, waiting for any events.	956	- Block the process, waiting for any events.
676	- Queue all outstanding I/O (fd) events.	957	- Queue all outstanding I/O (fd) events.
677	- 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.
678	- Queue all expired timers.	959	- Queue all expired timers.
679	- Queue all expired periodics.	960	- Queue all expired periodics.
680	- Unless any events are pending now, queue all idle watchers.	961	- Queue all idle watchers with priority higher than that of pending events.
681	- Queue all check watchers.	962	- Queue all check watchers.
682	- 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).
683	Signals and child watchers are implemented as I/O watchers, and will	964	Signals, async and child watchers are implemented as I/O watchers, and
684	be handled here by queueing them when their watcher gets executed.	965	will be handled here by queueing them when their watcher gets executed.
685	- 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
686	were used, or there are no active watchers, return, otherwise	967	were used, or there are no active watchers, goto FINISH, otherwise
687	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.
688		973
689	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
690	anymore.	975	anymore.
691		976
692	... queue jobs here, make sure they register event watchers as long	977	... queue jobs here, make sure they register event watchers as long
693	... 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..)
694	ev_loop (my_loop, 0);	979	ev_run (my_loop, 0);
695	... jobs done or somebody called unloop. yeah!	980	... jobs done or somebody called break. yeah!
696		981
697	=item ev_unloop (loop, how)	982	=item ev_break (loop, how)
698		983
699	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
700	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
701	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
702	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.
703		988
704	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>.
705		990
706	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.
707		993
708	=item ev_ref (loop)	994	=item ev_ref (loop)
709		995
710	=item ev_unref (loop)	996	=item ev_unref (loop)
711		997
712	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
713	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
714	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.
715		1001
716	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
717	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>
718	stopping it.	1005	before stopping it.
719		1006
720	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
721	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
722	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
723	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
724	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
725	(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
726	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).
727		1016
728	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>
729	running when nothing else is active.	1018	running when nothing else is active.
730		1019
731	ev_signal exitsig;	1020	ev_signal exitsig;
732	ev_signal_init (&exitsig, sig_cb, SIGINT);	1021	ev_signal_init (&exitsig, sig_cb, SIGINT);
733	ev_signal_start (loop, &exitsig);	1022	ev_signal_start (loop, &exitsig);
734	evf_unref (loop);	1023	ev_unref (loop);
735		1024
736	Example: For some weird reason, unregister the above signal handler again.	1025	Example: For some weird reason, unregister the above signal handler again.
737		1026
738	ev_ref (loop);	1027	ev_ref (loop);
739	ev_signal_stop (loop, &exitsig);	1028	ev_signal_stop (loop, &exitsig);
…		…
759	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.
760		1049
761	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
762	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,
763	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
764	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
765	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).
766		1058
767	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
768	to spend more time collecting timeouts, at the expense of increased	1060	to spend more time collecting timeouts, at the expense of increased
769	latency/jitter/inexactness (the watcher callback will be called	1061	latency/jitter/inexactness (the watcher callback will be called
770	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
…		…
772		1064
773	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
774	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
775	interactive servers (of course not for games), likewise for timeouts. It	1067	interactive servers (of course not for games), likewise for timeouts. It
776	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>,
777	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).
778		1074
779	Setting the I<timeout collect interval> can improve the opportunity for	1075	Setting the I<timeout collect interval> can improve the opportunity for
780	saving power, as the program will "bundle" timer callback invocations that	1076	saving power, as the program will "bundle" timer callback invocations that
781	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
782	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
783	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
784	they fire on, say, one-second boundaries only.	1080	they fire on, say, one-second boundaries only.
785		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
786	=item ev_loop_verify (loop)	1157	=item ev_verify (loop)
787		1158
788	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
789	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
790	through all internal structures and checks them for validity. If anything	1161	through all internal structures and checks them for validity. If anything
791	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
…		…
802		1173
803	In the following description, uppercase C<TYPE> in names stands for the	1174	In the following description, uppercase C<TYPE> in names stands for the
804	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer	1175	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
805	watchers and C<ev_io_start> for I/O watchers.	1176	watchers and C<ev_io_start> for I/O watchers.
806		1177
807	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
808	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
809	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:
810		1182
811	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)	1183	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
812	{	1184	{
813	ev_io_stop (w);	1185	ev_io_stop (w);
814	ev_unloop (loop, EVUNLOOP_ALL);	1186	ev_break (loop, EVBREAK_ALL);
815	}	1187	}
816		1188
817	struct ev_loop *loop = ev_default_loop (0);	1189	struct ev_loop *loop = ev_default_loop (0);
818		1190
819	ev_io stdin_watcher;	1191	ev_io stdin_watcher;
820		1192
821	ev_init (&stdin_watcher, my_cb);	1193	ev_init (&stdin_watcher, my_cb);
822	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1194	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
823	ev_io_start (loop, &stdin_watcher);	1195	ev_io_start (loop, &stdin_watcher);
824		1196
825	ev_loop (loop, 0);	1197	ev_run (loop, 0);
826		1198
827	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
828	watcher structures (and it is I<usually> a bad idea to do this on the	1200	watcher structures (and it is I<usually> a bad idea to do this on the
829	stack).	1201	stack).
830		1202
831	Each watcher has an associated watcher structure (called C<struct ev_TYPE>	1203	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
832	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).	1204	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
833		1205
834	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
835	(watcher *, callback)>, which expects a callback to be provided. This	1207	*, callback)>, which expects a callback to be provided. This callback is
836	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
837	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
838	is readable and/or writable).	1210	and/or writable).
839		1211
840	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>	1212	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
841	macro to configure it, with arguments specific to the watcher type. There	1213	macro to configure it, with arguments specific to the watcher type. There
842	is also a macro to combine initialisation and setting in one call: C<<	1214	is also a macro to combine initialisation and setting in one call: C<<
843	ev_TYPE_init (watcher *, callback, ...) >>.	1215	ev_TYPE_init (watcher *, callback, ...) >>.
…		…
846	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
847	*) >>), 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
848	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.	1220	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
849		1221
850	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
851	must not touch the values stored in it. Most specifically you must never	1223	must not touch the values stored in it except when explicitly documented
852	reinitialise it or call its C<ev_TYPE_set> macro.	1224	otherwise. Most specifically you must never reinitialise it or call its
		1225	C<ev_TYPE_set> macro.
853		1226
854	Each and every callback receives the event loop pointer as first, the	1227	Each and every callback receives the event loop pointer as first, the
855	registered watcher structure as second, and a bitset of received events as	1228	registered watcher structure as second, and a bitset of received events as
856	third argument.	1229	third argument.
857		1230
…		…
866	=item C<EV_WRITE>	1239	=item C<EV_WRITE>
867		1240
868	The file descriptor in the C<ev_io> watcher has become readable and/or	1241	The file descriptor in the C<ev_io> watcher has become readable and/or
869	writable.	1242	writable.
870		1243
871	=item C<EV_TIMEOUT>	1244	=item C<EV_TIMER>
872		1245
873	The C<ev_timer> watcher has timed out.	1246	The C<ev_timer> watcher has timed out.
874		1247
875	=item C<EV_PERIODIC>	1248	=item C<EV_PERIODIC>
876		1249
…		…
894		1267
895	=item C<EV_PREPARE>	1268	=item C<EV_PREPARE>
896		1269
897	=item C<EV_CHECK>	1270	=item C<EV_CHECK>
898		1271
899	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1272	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
900	to gather new events, and all C<ev_check> watchers are invoked just after	1273	gather new events, and all C<ev_check> watchers are queued (not invoked)
901	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1274	just after C<ev_run> has gathered them, but before it queues any callbacks
		1275	for any received events. That means C<ev_prepare> watchers are the last
		1276	watchers invoked before the event loop sleeps or polls for new events, and
		1277	C<ev_check> watchers will be invoked before any other watchers of the same
		1278	or lower priority within an event loop iteration.
		1279
902	received events. Callbacks of both watcher types can start and stop as	1280	Callbacks of both watcher types can start and stop as many watchers as
903	many watchers as they want, and all of them will be taken into account	1281	they want, and all of them will be taken into account (for example, a
904	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1282	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
905	C<ev_loop> from blocking).	1283	blocking).
906		1284
907	=item C<EV_EMBED>	1285	=item C<EV_EMBED>
908		1286
909	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1287	The embedded event loop specified in the C<ev_embed> watcher needs attention.
910		1288
911	=item C<EV_FORK>	1289	=item C<EV_FORK>
912		1290
913	The event loop has been resumed in the child process after fork (see	1291	The event loop has been resumed in the child process after fork (see
914	C<ev_fork>).	1292	C<ev_fork>).
915		1293
		1294	=item C<EV_CLEANUP>
		1295
		1296	The event loop is about to be destroyed (see C<ev_cleanup>).
		1297
916	=item C<EV_ASYNC>	1298	=item C<EV_ASYNC>
917		1299
918	The given async watcher has been asynchronously notified (see C<ev_async>).	1300	The given async watcher has been asynchronously notified (see C<ev_async>).
		1301
		1302	=item C<EV_CUSTOM>
		1303
		1304	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1305	by libev users to signal watchers (e.g. via C<ev_feed_event>).
919		1306
920	=item C<EV_ERROR>	1307	=item C<EV_ERROR>
921		1308
922	An unspecified error has occurred, the watcher has been stopped. This might	1309	An unspecified error has occurred, the watcher has been stopped. This might
923	happen because the watcher could not be properly started because libev	1310	happen because the watcher could not be properly started because libev
…		…
961		1348
962	ev_io w;	1349	ev_io w;
963	ev_init (&w, my_cb);	1350	ev_init (&w, my_cb);
964	ev_io_set (&w, STDIN_FILENO, EV_READ);	1351	ev_io_set (&w, STDIN_FILENO, EV_READ);
965		1352
966	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1353	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
967		1354
968	This macro initialises the type-specific parts of a watcher. You need to	1355	This macro initialises the type-specific parts of a watcher. You need to
969	call C<ev_init> at least once before you call this macro, but you can	1356	call C<ev_init> at least once before you call this macro, but you can
970	call C<ev_TYPE_set> any number of times. You must not, however, call this	1357	call C<ev_TYPE_set> any number of times. You must not, however, call this
971	macro on a watcher that is active (it can be pending, however, which is a	1358	macro on a watcher that is active (it can be pending, however, which is a
…		…
984		1371
985	Example: Initialise and set an C<ev_io> watcher in one step.	1372	Example: Initialise and set an C<ev_io> watcher in one step.
986		1373
987	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);	1374	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
988		1375
989	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1376	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
990		1377
991	Starts (activates) the given watcher. Only active watchers will receive	1378	Starts (activates) the given watcher. Only active watchers will receive
992	events. If the watcher is already active nothing will happen.	1379	events. If the watcher is already active nothing will happen.
993		1380
994	Example: Start the C<ev_io> watcher that is being abused as example in this	1381	Example: Start the C<ev_io> watcher that is being abused as example in this
995	whole section.	1382	whole section.
996		1383
997	ev_io_start (EV_DEFAULT_UC, &w);	1384	ev_io_start (EV_DEFAULT_UC, &w);
998		1385
999	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1386	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
1000		1387
1001	Stops the given watcher if active, and clears the pending status (whether	1388	Stops the given watcher if active, and clears the pending status (whether
1002	the watcher was active or not).	1389	the watcher was active or not).
1003		1390
1004	It is possible that stopped watchers are pending - for example,	1391	It is possible that stopped watchers are pending - for example,
…		…
1009		1396
1010	=item bool ev_is_active (ev_TYPE *watcher)	1397	=item bool ev_is_active (ev_TYPE *watcher)
1011		1398
1012	Returns a true value iff the watcher is active (i.e. it has been started	1399	Returns a true value iff the watcher is active (i.e. it has been started
1013	and not yet been stopped). As long as a watcher is active you must not modify	1400	and not yet been stopped). As long as a watcher is active you must not modify
1014	it.	1401	it unless documented otherwise.
		1402
		1403	Obviously, it is safe to call this on an active watcher, or actually any
		1404	watcher that is initialised.
1015		1405
1016	=item bool ev_is_pending (ev_TYPE *watcher)	1406	=item bool ev_is_pending (ev_TYPE *watcher)
1017		1407
1018	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1408	Returns a true value iff the watcher is pending, (i.e. it has outstanding
1019	events but its callback has not yet been invoked). As long as a watcher	1409	events but its callback has not yet been invoked). As long as a watcher
1020	is pending (but not active) you must not call an init function on it (but	1410	is pending (but not active) you must not call an init function on it (but
1021	C<ev_TYPE_set> is safe), you must not change its priority, and you must	1411	C<ev_TYPE_set> is safe), you must not change its priority, and you must
1022	make sure the watcher is available to libev (e.g. you cannot C<free ()>	1412	make sure the watcher is available to libev (e.g. you cannot C<free ()>
1023	it).	1413	it).
1024		1414
		1415	It is safe to call this on any watcher in any state as long as it is
		1416	initialised.
		1417
1025	=item callback ev_cb (ev_TYPE *watcher)	1418	=item callback ev_cb (ev_TYPE *watcher)
1026		1419
1027	Returns the callback currently set on the watcher.	1420	Returns the callback currently set on the watcher.
1028		1421
1029	=item ev_cb_set (ev_TYPE *watcher, callback)	1422	=item ev_set_cb (ev_TYPE *watcher, callback)
1030		1423
1031	Change the callback. You can change the callback at virtually any time	1424	Change the callback. You can change the callback at virtually any time
1032	(modulo threads).	1425	(modulo threads).
1033		1426
1034	=item ev_set_priority (ev_TYPE *watcher, priority)	1427	=item ev_set_priority (ev_TYPE *watcher, int priority)
1035		1428
1036	=item int ev_priority (ev_TYPE *watcher)	1429	=item int ev_priority (ev_TYPE *watcher)
1037		1430
1038	Set and query the priority of the watcher. The priority is a small	1431	Set and query the priority of the watcher. The priority is a small
1039	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1432	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1040	(default: C<-2>). Pending watchers with higher priority will be invoked	1433	(default: C<-2>). Pending watchers with higher priority will be invoked
1041	before watchers with lower priority, but priority will not keep watchers	1434	before watchers with lower priority, but priority will not keep watchers
1042	from being executed (except for C<ev_idle> watchers).	1435	from being executed (except for C<ev_idle> watchers).
1043		1436
1044	This means that priorities are I<only> used for ordering callback
1045	invocation after new events have been received. This is useful, for
1046	example, to reduce latency after idling, or more often, to bind two
1047	watchers on the same event and make sure one is called first.
1048
1049	If you need to suppress invocation when higher priority events are pending	1437	If you need to suppress invocation when higher priority events are pending
1050	you need to look at C<ev_idle> watchers, which provide this functionality.	1438	you need to look at C<ev_idle> watchers, which provide this functionality.
1051		1439
1052	You I<must not> change the priority of a watcher as long as it is active or	1440	You I<must not> change the priority of a watcher as long as it is active
1053	pending.	1441	or pending. Reading the priority with C<ev_priority> is fine in any state.
1054
1055	The default priority used by watchers when no priority has been set is
1056	always C<0>, which is supposed to not be too high and not be too low :).
1057		1442
1058	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1443	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1059	fine, as long as you do not mind that the priority value you query might	1444	fine, as long as you do not mind that the priority value you query might
1060	or might not have been clamped to the valid range.	1445	or might not have been clamped to the valid range.
		1446
		1447	The default priority used by watchers when no priority has been set is
		1448	always C<0>, which is supposed to not be too high and not be too low :).
		1449
		1450	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1451	priorities.
1061		1452
1062	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1453	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1063		1454
1064	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1455	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1065	C<loop> nor C<revents> need to be valid as long as the watcher callback	1456	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1073	watcher isn't pending it does nothing and returns C<0>.	1464	watcher isn't pending it does nothing and returns C<0>.
1074		1465
1075	Sometimes it can be useful to "poll" a watcher instead of waiting for its	1466	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1076	callback to be invoked, which can be accomplished with this function.	1467	callback to be invoked, which can be accomplished with this function.
1077		1468
		1469	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1470
		1471	Feeds the given event set into the event loop, as if the specified event
		1472	had happened for the specified watcher (which must be a pointer to an
		1473	initialised but not necessarily started event watcher, though it can be
		1474	active). Obviously you must not free the watcher as long as it has pending
		1475	events.
		1476
		1477	Stopping the watcher, letting libev invoke it, or calling
		1478	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1479	not started in the first place.
		1480
		1481	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1482	functions that do not need a watcher.
		1483
1078	=back	1484	=back
1079		1485
		1486	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1487	OWN COMPOSITE WATCHERS> idioms.
1080		1488
1081	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1489	=head2 WATCHER STATES
1082		1490
1083	Each watcher has, by default, a member C<void *data> that you can change	1491	There are various watcher states mentioned throughout this manual -
1084	and read at any time: libev will completely ignore it. This can be used	1492	active, pending and so on. In this section these states and the rules to
1085	to associate arbitrary data with your watcher. If you need more data and	1493	transition between them will be described in more detail - and while these
1086	don't want to allocate memory and store a pointer to it in that data	1494	rules might look complicated, they usually do "the right thing".
1087	member, you can also "subclass" the watcher type and provide your own
1088	data:
1089		1495
1090	struct my_io	1496	=over 4
		1497
		1498	=item initialised
		1499
		1500	Before a watcher can be registered with the event loop it has to be
		1501	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1502	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1503
		1504	In this state it is simply some block of memory that is suitable for
		1505	use in an event loop. It can be moved around, freed, reused etc. at
		1506	will - as long as you either keep the memory contents intact, or call
		1507	C<ev_TYPE_init> again.
		1508
		1509	=item started/running/active
		1510
		1511	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1512	property of the event loop, and is actively waiting for events. While in
		1513	this state it cannot be accessed (except in a few documented ways, such as
		1514	stoping it), moved, freed or anything else - the only legal thing is to
		1515	keep a pointer to it, and call libev functions on it that are documented
		1516	to work on active watchers.
		1517
		1518	As a rule of thumb, before accessing a member or calling any function on
		1519	a watcher, it should be stopped (or freshly initialised). If that is not
		1520	convenient, you can check the documentation for that function or member to
		1521	see if it is safe to use on an active watcher.
		1522
		1523	=item pending
		1524
		1525	If a watcher is active and libev determines that an event it is interested
		1526	in has occurred (such as a timer expiring), it will become pending. It
		1527	will stay in this pending state until either it is explicitly stopped or
		1528	its callback is about to be invoked, so it is not normally pending inside
		1529	the watcher callback.
		1530
		1531	Generally, the watcher might or might not be active while it is pending
		1532	(for example, an expired non-repeating timer can be pending but no longer
		1533	active). If it is pending but not active, it can be freely accessed (e.g.
		1534	by calling C<ev_TYPE_set>), but it is still property of the event loop at
		1535	this time, so cannot be moved, freed or reused. And if it is active the
		1536	rules described in the previous item still apply.
		1537
		1538	Explicitly stopping a watcher will also clear the pending state
		1539	unconditionally, so it is safe to stop a watcher and then free it.
		1540
		1541	It is also possible to feed an event on a watcher that is not active (e.g.
		1542	via C<ev_feed_event>), in which case it becomes pending without being
		1543	active.
		1544
		1545	=item stopped
		1546
		1547	A watcher can be stopped implicitly by libev (in which case it might still
		1548	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1549	latter will clear any pending state the watcher might be in, regardless
		1550	of whether it was active or not, so stopping a watcher explicitly before
		1551	freeing it is often a good idea.
		1552
		1553	While stopped (and not pending) the watcher is essentially in the
		1554	initialised state, that is, it can be reused, moved, modified in any way
		1555	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1556	it again).
		1557
		1558	=back
		1559
		1560	=head2 WATCHER PRIORITY MODELS
		1561
		1562	Many event loops support I<watcher priorities>, which are usually small
		1563	integers that influence the ordering of event callback invocation
		1564	between watchers in some way, all else being equal.
		1565
		1566	In libev, watcher priorities can be set using C<ev_set_priority>. See its
		1567	description for the more technical details such as the actual priority
		1568	range.
		1569
		1570	There are two common ways how these these priorities are being interpreted
		1571	by event loops:
		1572
		1573	In the more common lock-out model, higher priorities "lock out" invocation
		1574	of lower priority watchers, which means as long as higher priority
		1575	watchers receive events, lower priority watchers are not being invoked.
		1576
		1577	The less common only-for-ordering model uses priorities solely to order
		1578	callback invocation within a single event loop iteration: Higher priority
		1579	watchers are invoked before lower priority ones, but they all get invoked
		1580	before polling for new events.
		1581
		1582	Libev uses the second (only-for-ordering) model for all its watchers
		1583	except for idle watchers (which use the lock-out model).
		1584
		1585	The rationale behind this is that implementing the lock-out model for
		1586	watchers is not well supported by most kernel interfaces, and most event
		1587	libraries will just poll for the same events again and again as long as
		1588	their callbacks have not been executed, which is very inefficient in the
		1589	common case of one high-priority watcher locking out a mass of lower
		1590	priority ones.
		1591
		1592	Static (ordering) priorities are most useful when you have two or more
		1593	watchers handling the same resource: a typical usage example is having an
		1594	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1595	timeouts. Under load, data might be received while the program handles
		1596	other jobs, but since timers normally get invoked first, the timeout
		1597	handler will be executed before checking for data. In that case, giving
		1598	the timer a lower priority than the I/O watcher ensures that I/O will be
		1599	handled first even under adverse conditions (which is usually, but not
		1600	always, what you want).
		1601
		1602	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1603	will only be executed when no same or higher priority watchers have
		1604	received events, they can be used to implement the "lock-out" model when
		1605	required.
		1606
		1607	For example, to emulate how many other event libraries handle priorities,
		1608	you can associate an C<ev_idle> watcher to each such watcher, and in
		1609	the normal watcher callback, you just start the idle watcher. The real
		1610	processing is done in the idle watcher callback. This causes libev to
		1611	continuously poll and process kernel event data for the watcher, but when
		1612	the lock-out case is known to be rare (which in turn is rare :), this is
		1613	workable.
		1614
		1615	Usually, however, the lock-out model implemented that way will perform
		1616	miserably under the type of load it was designed to handle. In that case,
		1617	it might be preferable to stop the real watcher before starting the
		1618	idle watcher, so the kernel will not have to process the event in case
		1619	the actual processing will be delayed for considerable time.
		1620
		1621	Here is an example of an I/O watcher that should run at a strictly lower
		1622	priority than the default, and which should only process data when no
		1623	other events are pending:
		1624
		1625	ev_idle idle; // actual processing watcher
		1626	ev_io io; // actual event watcher
		1627
		1628	static void
		1629	io_cb (EV_P_ ev_io *w, int revents)
1091	{	1630	{
1092	ev_io io;	1631	// stop the I/O watcher, we received the event, but
1093	int otherfd;	1632	// are not yet ready to handle it.
1094	void *somedata;	1633	ev_io_stop (EV_A_ w);
1095	struct whatever *mostinteresting;	1634
		1635	// start the idle watcher to handle the actual event.
		1636	// it will not be executed as long as other watchers
		1637	// with the default priority are receiving events.
		1638	ev_idle_start (EV_A_ &idle);
1096	};	1639	}
1097		1640
1098	...	1641	static void
1099	struct my_io w;	1642	idle_cb (EV_P_ ev_idle *w, int revents)
1100	ev_io_init (&w.io, my_cb, fd, EV_READ);
1101
1102	And since your callback will be called with a pointer to the watcher, you
1103	can cast it back to your own type:
1104
1105	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1106	{	1643	{
1107	struct my_io *w = (struct my_io *)w_;	1644	// actual processing
1108	...	1645	read (STDIN_FILENO, ...);
		1646
		1647	// have to start the I/O watcher again, as
		1648	// we have handled the event
		1649	ev_io_start (EV_P_ &io);
1109	}	1650	}
1110		1651
1111	More interesting and less C-conformant ways of casting your callback type	1652	// initialisation
1112	instead have been omitted.	1653	ev_idle_init (&idle, idle_cb);
		1654	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1655	ev_io_start (EV_DEFAULT_ &io);
1113		1656
1114	Another common scenario is to use some data structure with multiple	1657	In the "real" world, it might also be beneficial to start a timer, so that
1115	embedded watchers:	1658	low-priority connections can not be locked out forever under load. This
1116		1659	enables your program to keep a lower latency for important connections
1117	struct my_biggy	1660	during short periods of high load, while not completely locking out less
1118	{	1661	important ones.
1119	int some_data;
1120	ev_timer t1;
1121	ev_timer t2;
1122	}
1123
1124	In this case getting the pointer to C<my_biggy> is a bit more
1125	complicated: Either you store the address of your C<my_biggy> struct
1126	in the C<data> member of the watcher (for woozies), or you need to use
1127	some pointer arithmetic using C<offsetof> inside your watchers (for real
1128	programmers):
1129
1130	#include <stddef.h>
1131
1132	static void
1133	t1_cb (EV_P_ ev_timer *w, int revents)
1134	{
1135	struct my_biggy big = (struct my_biggy *
1136	(((char *)w) - offsetof (struct my_biggy, t1));
1137	}
1138
1139	static void
1140	t2_cb (EV_P_ ev_timer *w, int revents)
1141	{
1142	struct my_biggy big = (struct my_biggy *
1143	(((char *)w) - offsetof (struct my_biggy, t2));
1144	}
1145		1662
1146		1663
1147	=head1 WATCHER TYPES	1664	=head1 WATCHER TYPES
1148		1665
1149	This section describes each watcher in detail, but will not repeat	1666	This section describes each watcher in detail, but will not repeat
1150	information given in the last section. Any initialisation/set macros,	1667	information given in the last section. Any initialisation/set macros,
1151	functions and members specific to the watcher type are explained.	1668	functions and members specific to the watcher type are explained.
1152		1669
1153	Members are additionally marked with either I<[read-only]>, meaning that,	1670	Most members are additionally marked with either I<[read-only]>, meaning
1154	while the watcher is active, you can look at the member and expect some	1671	that, while the watcher is active, you can look at the member and expect
1155	sensible content, but you must not modify it (you can modify it while the	1672	some sensible content, but you must not modify it (you can modify it while
1156	watcher is stopped to your hearts content), or I<[read-write]>, which	1673	the watcher is stopped to your hearts content), or I<[read-write]>, which
1157	means you can expect it to have some sensible content while the watcher	1674	means you can expect it to have some sensible content while the watcher is
1158	is active, but you can also modify it. Modifying it may not do something	1675	active, but you can also modify it (within the same thread as the event
		1676	loop, i.e. without creating data races). Modifying it may not do something
1159	sensible or take immediate effect (or do anything at all), but libev will	1677	sensible or take immediate effect (or do anything at all), but libev will
1160	not crash or malfunction in any way.	1678	not crash or malfunction in any way.
1161		1679
		1680	In any case, the documentation for each member will explain what the
		1681	effects are, and if there are any additional access restrictions.
1162		1682
1163	=head2 C<ev_io> - is this file descriptor readable or writable?	1683	=head2 C<ev_io> - is this file descriptor readable or writable?
1164		1684
1165	I/O watchers check whether a file descriptor is readable or writable	1685	I/O watchers check whether a file descriptor is readable or writable
1166	in each iteration of the event loop, or, more precisely, when reading	1686	in each iteration of the event loop, or, more precisely, when reading
…		…
1173	In general you can register as many read and/or write event watchers per	1693	In general you can register as many read and/or write event watchers per
1174	fd as you want (as long as you don't confuse yourself). Setting all file	1694	fd as you want (as long as you don't confuse yourself). Setting all file
1175	descriptors to non-blocking mode is also usually a good idea (but not	1695	descriptors to non-blocking mode is also usually a good idea (but not
1176	required if you know what you are doing).	1696	required if you know what you are doing).
1177		1697
1178	If you cannot use non-blocking mode, then force the use of a
1179	known-to-be-good backend (at the time of this writing, this includes only
1180	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
1181
1182	Another thing you have to watch out for is that it is quite easy to	1698	Another thing you have to watch out for is that it is quite easy to
1183	receive "spurious" readiness notifications, that is your callback might	1699	receive "spurious" readiness notifications, that is, your callback might
1184	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1700	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1185	because there is no data. Not only are some backends known to create a	1701	because there is no data. It is very easy to get into this situation even
1186	lot of those (for example Solaris ports), it is very easy to get into	1702	with a relatively standard program structure. Thus it is best to always
1187	this situation even with a relatively standard program structure. Thus	1703	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1188	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1189	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1704	preferable to a program hanging until some data arrives.
1190		1705
1191	If you cannot run the fd in non-blocking mode (for example you should	1706	If you cannot run the fd in non-blocking mode (for example you should
1192	not play around with an Xlib connection), then you have to separately	1707	not play around with an Xlib connection), then you have to separately
1193	re-test whether a file descriptor is really ready with a known-to-be good	1708	re-test whether a file descriptor is really ready with a known-to-be good
1194	interface such as poll (fortunately in our Xlib example, Xlib already	1709	interface such as poll (fortunately in the case of Xlib, it already does
1195	does this on its own, so its quite safe to use). Some people additionally	1710	this on its own, so its quite safe to use). Some people additionally
1196	use C<SIGALRM> and an interval timer, just to be sure you won't block	1711	use C<SIGALRM> and an interval timer, just to be sure you won't block
1197	indefinitely.	1712	indefinitely.
1198		1713
1199	But really, best use non-blocking mode.	1714	But really, best use non-blocking mode.
1200		1715
1201	=head3 The special problem of disappearing file descriptors	1716	=head3 The special problem of disappearing file descriptors
1202		1717
1203	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1718	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1204	descriptor (either due to calling C<close> explicitly or any other means,	1719	a file descriptor (either due to calling C<close> explicitly or any other
1205	such as C<dup2>). The reason is that you register interest in some file	1720	means, such as C<dup2>). The reason is that you register interest in some
1206	descriptor, but when it goes away, the operating system will silently drop	1721	file descriptor, but when it goes away, the operating system will silently
1207	this interest. If another file descriptor with the same number then is	1722	drop this interest. If another file descriptor with the same number then
1208	registered with libev, there is no efficient way to see that this is, in	1723	is registered with libev, there is no efficient way to see that this is,
1209	fact, a different file descriptor.	1724	in fact, a different file descriptor.
1210		1725
1211	To avoid having to explicitly tell libev about such cases, libev follows	1726	To avoid having to explicitly tell libev about such cases, libev follows
1212	the following policy: Each time C<ev_io_set> is being called, libev	1727	the following policy: Each time C<ev_io_set> is being called, libev
1213	will assume that this is potentially a new file descriptor, otherwise	1728	will assume that this is potentially a new file descriptor, otherwise
1214	it is assumed that the file descriptor stays the same. That means that	1729	it is assumed that the file descriptor stays the same. That means that
…		…
1228		1743
1229	There is no workaround possible except not registering events	1744	There is no workaround possible except not registering events
1230	for potentially C<dup ()>'ed file descriptors, or to resort to	1745	for potentially C<dup ()>'ed file descriptors, or to resort to
1231	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1746	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1232		1747
		1748	=head3 The special problem of files
		1749
		1750	Many people try to use C<select> (or libev) on file descriptors
		1751	representing files, and expect it to become ready when their program
		1752	doesn't block on disk accesses (which can take a long time on their own).
		1753
		1754	However, this cannot ever work in the "expected" way - you get a readiness
		1755	notification as soon as the kernel knows whether and how much data is
		1756	there, and in the case of open files, that's always the case, so you
		1757	always get a readiness notification instantly, and your read (or possibly
		1758	write) will still block on the disk I/O.
		1759
		1760	Another way to view it is that in the case of sockets, pipes, character
		1761	devices and so on, there is another party (the sender) that delivers data
		1762	on its own, but in the case of files, there is no such thing: the disk
		1763	will not send data on its own, simply because it doesn't know what you
		1764	wish to read - you would first have to request some data.
		1765
		1766	Since files are typically not-so-well supported by advanced notification
		1767	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1768	to files, even though you should not use it. The reason for this is
		1769	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1770	usually a tty, often a pipe, but also sometimes files or special devices
		1771	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1772	F</dev/urandom>), and even though the file might better be served with
		1773	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1774	it "just works" instead of freezing.
		1775
		1776	So avoid file descriptors pointing to files when you know it (e.g. use
		1777	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1778	when you rarely read from a file instead of from a socket, and want to
		1779	reuse the same code path.
		1780
1233	=head3 The special problem of fork	1781	=head3 The special problem of fork
1234		1782
1235	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1783	Some backends (epoll, kqueue, linuxaio, iouring) do not support C<fork ()>
1236	useless behaviour. Libev fully supports fork, but needs to be told about	1784	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1237	it in the child.	1785	to be told about it in the child if you want to continue to use it in the
		1786	child.
1238		1787
1239	To support fork in your programs, you either have to call	1788	To support fork in your child processes, you have to call C<ev_loop_fork
1240	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1789	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1241	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1790	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1242	C<EVBACKEND_POLL>.
1243		1791
1244	=head3 The special problem of SIGPIPE	1792	=head3 The special problem of SIGPIPE
1245		1793
1246	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1794	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1247	when writing to a pipe whose other end has been closed, your program gets	1795	when writing to a pipe whose other end has been closed, your program gets
…		…
1250		1798
1251	So when you encounter spurious, unexplained daemon exits, make sure you	1799	So when you encounter spurious, unexplained daemon exits, make sure you
1252	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1800	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1253	somewhere, as that would have given you a big clue).	1801	somewhere, as that would have given you a big clue).
1254		1802
		1803	=head3 The special problem of accept()ing when you can't
		1804
		1805	Many implementations of the POSIX C<accept> function (for example,
		1806	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1807	connection from the pending queue in all error cases.
		1808
		1809	For example, larger servers often run out of file descriptors (because
		1810	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1811	rejecting the connection, leading to libev signalling readiness on
		1812	the next iteration again (the connection still exists after all), and
		1813	typically causing the program to loop at 100% CPU usage.
		1814
		1815	Unfortunately, the set of errors that cause this issue differs between
		1816	operating systems, there is usually little the app can do to remedy the
		1817	situation, and no known thread-safe method of removing the connection to
		1818	cope with overload is known (to me).
		1819
		1820	One of the easiest ways to handle this situation is to just ignore it
		1821	- when the program encounters an overload, it will just loop until the
		1822	situation is over. While this is a form of busy waiting, no OS offers an
		1823	event-based way to handle this situation, so it's the best one can do.
		1824
		1825	A better way to handle the situation is to log any errors other than
		1826	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1827	messages, and continue as usual, which at least gives the user an idea of
		1828	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1829	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1830	usage.
		1831
		1832	If your program is single-threaded, then you could also keep a dummy file
		1833	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1834	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1835	close that fd, and create a new dummy fd. This will gracefully refuse
		1836	clients under typical overload conditions.
		1837
		1838	The last way to handle it is to simply log the error and C<exit>, as
		1839	is often done with C<malloc> failures, but this results in an easy
		1840	opportunity for a DoS attack.
1255		1841
1256	=head3 Watcher-Specific Functions	1842	=head3 Watcher-Specific Functions
1257		1843
1258	=over 4	1844	=over 4
1259		1845
1260	=item ev_io_init (ev_io *, callback, int fd, int events)	1846	=item ev_io_init (ev_io *, callback, int fd, int events)
1261		1847
1262	=item ev_io_set (ev_io *, int fd, int events)	1848	=item ev_io_set (ev_io *, int fd, int events)
1263		1849
1264	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1850	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1265	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or	1851	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE>, both
1266	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.	1852	C<EV_READ | EV_WRITE> or C<0>, to express the desire to receive the given
		1853	events.
1267		1854
1268	=item int fd [read-only]	1855	Note that setting the C<events> to C<0> and starting the watcher is
		1856	supported, but not specially optimized - if your program sometimes happens
		1857	to generate this combination this is fine, but if it is easy to avoid
		1858	starting an io watcher watching for no events you should do so.
1269		1859
1270	The file descriptor being watched.	1860	=item ev_io_modify (ev_io *, int events)
1271		1861
		1862	Similar to C<ev_io_set>, but only changes the requested events. Using this
		1863	might be faster with some backends, as libev can assume that the C<fd>
		1864	still refers to the same underlying file description, something it cannot
		1865	do when using C<ev_io_set>.
		1866
		1867	=item int fd [no-modify]
		1868
		1869	The file descriptor being watched. While it can be read at any time, you
		1870	must not modify this member even when the watcher is stopped - always use
		1871	C<ev_io_set> for that.
		1872
1272	=item int events [read-only]	1873	=item int events [no-modify]
1273		1874
1274	The events being watched.	1875	The set of events the fd is being watched for, among other flags. Remember
		1876	that this is a bit set - to test for C<EV_READ>, use C<< w->events &
		1877	EV_READ >>, and similarly for C<EV_WRITE>.
		1878
		1879	As with C<fd>, you must not modify this member even when the watcher is
		1880	stopped, always use C<ev_io_set> or C<ev_io_modify> for that.
1275		1881
1276	=back	1882	=back
1277		1883
1278	=head3 Examples	1884	=head3 Examples
1279		1885
…		…
1291	...	1897	...
1292	struct ev_loop *loop = ev_default_init (0);	1898	struct ev_loop *loop = ev_default_init (0);
1293	ev_io stdin_readable;	1899	ev_io stdin_readable;
1294	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1900	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1295	ev_io_start (loop, &stdin_readable);	1901	ev_io_start (loop, &stdin_readable);
1296	ev_loop (loop, 0);	1902	ev_run (loop, 0);
1297		1903
1298		1904
1299	=head2 C<ev_timer> - relative and optionally repeating timeouts	1905	=head2 C<ev_timer> - relative and optionally repeating timeouts
1300		1906
1301	Timer watchers are simple relative timers that generate an event after a	1907	Timer watchers are simple relative timers that generate an event after a
…		…
1306	year, it will still time out after (roughly) one hour. "Roughly" because	1912	year, it will still time out after (roughly) one hour. "Roughly" because
1307	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1913	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1308	monotonic clock option helps a lot here).	1914	monotonic clock option helps a lot here).
1309		1915
1310	The callback is guaranteed to be invoked only I<after> its timeout has	1916	The callback is guaranteed to be invoked only I<after> its timeout has
1311	passed, but if multiple timers become ready during the same loop iteration	1917	passed (not I<at>, so on systems with very low-resolution clocks this
1312	then order of execution is undefined.	1918	might introduce a small delay, see "the special problem of being too
		1919	early", below). If multiple timers become ready during the same loop
		1920	iteration then the ones with earlier time-out values are invoked before
		1921	ones of the same priority with later time-out values (but this is no
		1922	longer true when a callback calls C<ev_run> recursively).
1313		1923
1314	=head3 Be smart about timeouts	1924	=head3 Be smart about timeouts
1315		1925
1316	Many real-world problems involve some kind of timeout, usually for error	1926	Many real-world problems involve some kind of timeout, usually for error
1317	recovery. A typical example is an HTTP request - if the other side hangs,	1927	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1361	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>	1971	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
1362	member and C<ev_timer_again>.	1972	member and C<ev_timer_again>.
1363		1973
1364	At start:	1974	At start:
1365		1975
1366	ev_timer_init (timer, callback);	1976	ev_init (timer, callback);
1367	timer->repeat = 60.;	1977	timer->repeat = 60.;
1368	ev_timer_again (loop, timer);	1978	ev_timer_again (loop, timer);
1369		1979
1370	Each time there is some activity:	1980	Each time there is some activity:
1371		1981
…		…
1392		2002
1393	In this case, it would be more efficient to leave the C<ev_timer> alone,	2003	In this case, it would be more efficient to leave the C<ev_timer> alone,
1394	but remember the time of last activity, and check for a real timeout only	2004	but remember the time of last activity, and check for a real timeout only
1395	within the callback:	2005	within the callback:
1396		2006
		2007	ev_tstamp timeout = 60.;
1397	ev_tstamp last_activity; // time of last activity	2008	ev_tstamp last_activity; // time of last activity
		2009	ev_timer timer;
1398		2010
1399	static void	2011	static void
1400	callback (EV_P_ ev_timer *w, int revents)	2012	callback (EV_P_ ev_timer *w, int revents)
1401	{	2013	{
1402	ev_tstamp now = ev_now (EV_A);	2014	// calculate when the timeout would happen
1403	ev_tstamp timeout = last_activity + 60.;	2015	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1404		2016
1405	// if last_activity + 60. is older than now, we did time out	2017	// if negative, it means we the timeout already occurred
1406	if (timeout < now)	2018	if (after < 0.)
1407	{	2019	{
1408	// timeout occured, take action	2020	// timeout occurred, take action
1409	}	2021	}
1410	else	2022	else
1411	{	2023	{
1412	// callback was invoked, but there was some activity, re-arm	2024	// callback was invoked, but there was some recent
1413	// the watcher to fire in last_activity + 60, which is	2025	// activity. simply restart the timer to time out
1414	// guaranteed to be in the future, so "again" is positive:	2026	// after "after" seconds, which is the earliest time
1415	w->again = timeout - now;	2027	// the timeout can occur.
		2028	ev_timer_set (w, after, 0.);
1416	ev_timer_again (EV_A_ w);	2029	ev_timer_start (EV_A_ w);
1417	}	2030	}
1418	}	2031	}
1419		2032
1420	To summarise the callback: first calculate the real timeout (defined	2033	To summarise the callback: first calculate in how many seconds the
1421	as "60 seconds after the last activity"), then check if that time has	2034	timeout will occur (by calculating the absolute time when it would occur,
1422	been reached, which means something I<did>, in fact, time out. Otherwise	2035	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1423	the callback was invoked too early (C<timeout> is in the future), so	2036	(EV_A)> from that).
1424	re-schedule the timer to fire at that future time, to see if maybe we have
1425	a timeout then.
1426		2037
1427	Note how C<ev_timer_again> is used, taking advantage of the	2038	If this value is negative, then we are already past the timeout, i.e. we
1428	C<ev_timer_again> optimisation when the timer is already running.	2039	timed out, and need to do whatever is needed in this case.
		2040
		2041	Otherwise, we now the earliest time at which the timeout would trigger,
		2042	and simply start the timer with this timeout value.
		2043
		2044	In other words, each time the callback is invoked it will check whether
		2045	the timeout occurred. If not, it will simply reschedule itself to check
		2046	again at the earliest time it could time out. Rinse. Repeat.
1429		2047
1430	This scheme causes more callback invocations (about one every 60 seconds	2048	This scheme causes more callback invocations (about one every 60 seconds
1431	minus half the average time between activity), but virtually no calls to	2049	minus half the average time between activity), but virtually no calls to
1432	libev to change the timeout.	2050	libev to change the timeout.
1433		2051
1434	To start the timer, simply initialise the watcher and set C<last_activity>	2052	To start the machinery, simply initialise the watcher and set
1435	to the current time (meaning we just have some activity :), then call the	2053	C<last_activity> to the current time (meaning there was some activity just
1436	callback, which will "do the right thing" and start the timer:	2054	now), then call the callback, which will "do the right thing" and start
		2055	the timer:
1437		2056
		2057	last_activity = ev_now (EV_A);
1438	ev_timer_init (timer, callback);	2058	ev_init (&timer, callback);
1439	last_activity = ev_now (loop);	2059	callback (EV_A_ &timer, 0);
1440	callback (loop, timer, EV_TIMEOUT);
1441		2060
1442	And when there is some activity, simply store the current time in	2061	When there is some activity, simply store the current time in
1443	C<last_activity>, no libev calls at all:	2062	C<last_activity>, no libev calls at all:
1444		2063
		2064	if (activity detected)
1445	last_actiivty = ev_now (loop);	2065	last_activity = ev_now (EV_A);
		2066
		2067	When your timeout value changes, then the timeout can be changed by simply
		2068	providing a new value, stopping the timer and calling the callback, which
		2069	will again do the right thing (for example, time out immediately :).
		2070
		2071	timeout = new_value;
		2072	ev_timer_stop (EV_A_ &timer);
		2073	callback (EV_A_ &timer, 0);
1446		2074
1447	This technique is slightly more complex, but in most cases where the	2075	This technique is slightly more complex, but in most cases where the
1448	time-out is unlikely to be triggered, much more efficient.	2076	time-out is unlikely to be triggered, much more efficient.
1449
1450	Changing the timeout is trivial as well (if it isn't hard-coded in the
1451	callback :) - just change the timeout and invoke the callback, which will
1452	fix things for you.
1453		2077
1454	=item 4. Wee, just use a double-linked list for your timeouts.	2078	=item 4. Wee, just use a double-linked list for your timeouts.
1455		2079
1456	If there is not one request, but many thousands (millions...), all	2080	If there is not one request, but many thousands (millions...), all
1457	employing some kind of timeout with the same timeout value, then one can	2081	employing some kind of timeout with the same timeout value, then one can
…		…
1484	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2108	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1485	rather complicated, but extremely efficient, something that really pays	2109	rather complicated, but extremely efficient, something that really pays
1486	off after the first million or so of active timers, i.e. it's usually	2110	off after the first million or so of active timers, i.e. it's usually
1487	overkill :)	2111	overkill :)
1488		2112
		2113	=head3 The special problem of being too early
		2114
		2115	If you ask a timer to call your callback after three seconds, then
		2116	you expect it to be invoked after three seconds - but of course, this
		2117	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2118	guaranteed to any precision by libev - imagine somebody suspending the
		2119	process with a STOP signal for a few hours for example.
		2120
		2121	So, libev tries to invoke your callback as soon as possible I<after> the
		2122	delay has occurred, but cannot guarantee this.
		2123
		2124	A less obvious failure mode is calling your callback too early: many event
		2125	loops compare timestamps with a "elapsed delay >= requested delay", but
		2126	this can cause your callback to be invoked much earlier than you would
		2127	expect.
		2128
		2129	To see why, imagine a system with a clock that only offers full second
		2130	resolution (think windows if you can't come up with a broken enough OS
		2131	yourself). If you schedule a one-second timer at the time 500.9, then the
		2132	event loop will schedule your timeout to elapse at a system time of 500
		2133	(500.9 truncated to the resolution) + 1, or 501.
		2134
		2135	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2136	501" and invoke the callback 0.1s after it was started, even though a
		2137	one-second delay was requested - this is being "too early", despite best
		2138	intentions.
		2139
		2140	This is the reason why libev will never invoke the callback if the elapsed
		2141	delay equals the requested delay, but only when the elapsed delay is
		2142	larger than the requested delay. In the example above, libev would only invoke
		2143	the callback at system time 502, or 1.1s after the timer was started.
		2144
		2145	So, while libev cannot guarantee that your callback will be invoked
		2146	exactly when requested, it I<can> and I<does> guarantee that the requested
		2147	delay has actually elapsed, or in other words, it always errs on the "too
		2148	late" side of things.
		2149
1489	=head3 The special problem of time updates	2150	=head3 The special problem of time updates
1490		2151
1491	Establishing the current time is a costly operation (it usually takes at	2152	Establishing the current time is a costly operation (it usually takes
1492	least two system calls): EV therefore updates its idea of the current	2153	at least one system call): EV therefore updates its idea of the current
1493	time only before and after C<ev_loop> collects new events, which causes a	2154	time only before and after C<ev_run> collects new events, which causes a
1494	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2155	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1495	lots of events in one iteration.	2156	lots of events in one iteration.
1496		2157
1497	The relative timeouts are calculated relative to the C<ev_now ()>	2158	The relative timeouts are calculated relative to the C<ev_now ()>
1498	time. This is usually the right thing as this timestamp refers to the time	2159	time. This is usually the right thing as this timestamp refers to the time
1499	of the event triggering whatever timeout you are modifying/starting. If	2160	of the event triggering whatever timeout you are modifying/starting. If
1500	you suspect event processing to be delayed and you I<need> to base the	2161	you suspect event processing to be delayed and you I<need> to base the
1501	timeout on the current time, use something like this to adjust for this:	2162	timeout on the current time, use something like the following to adjust
		2163	for it:
1502		2164
1503	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2165	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1504		2166
1505	If the event loop is suspended for a long time, you can also force an	2167	If the event loop is suspended for a long time, you can also force an
1506	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2168	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1507	()>.	2169	()>, although that will push the event time of all outstanding events
		2170	further into the future.
		2171
		2172	=head3 The special problem of unsynchronised clocks
		2173
		2174	Modern systems have a variety of clocks - libev itself uses the normal
		2175	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2176	jumps).
		2177
		2178	Neither of these clocks is synchronised with each other or any other clock
		2179	on the system, so C<ev_time ()> might return a considerably different time
		2180	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2181	a call to C<gettimeofday> might return a second count that is one higher
		2182	than a directly following call to C<time>.
		2183
		2184	The moral of this is to only compare libev-related timestamps with
		2185	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2186	a second or so.
		2187
		2188	One more problem arises due to this lack of synchronisation: if libev uses
		2189	the system monotonic clock and you compare timestamps from C<ev_time>
		2190	or C<ev_now> from when you started your timer and when your callback is
		2191	invoked, you will find that sometimes the callback is a bit "early".
		2192
		2193	This is because C<ev_timer>s work in real time, not wall clock time, so
		2194	libev makes sure your callback is not invoked before the delay happened,
		2195	I<measured according to the real time>, not the system clock.
		2196
		2197	If your timeouts are based on a physical timescale (e.g. "time out this
		2198	connection after 100 seconds") then this shouldn't bother you as it is
		2199	exactly the right behaviour.
		2200
		2201	If you want to compare wall clock/system timestamps to your timers, then
		2202	you need to use C<ev_periodic>s, as these are based on the wall clock
		2203	time, where your comparisons will always generate correct results.
		2204
		2205	=head3 The special problems of suspended animation
		2206
		2207	When you leave the server world it is quite customary to hit machines that
		2208	can suspend/hibernate - what happens to the clocks during such a suspend?
		2209
		2210	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2211	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2212	to run until the system is suspended, but they will not advance while the
		2213	system is suspended. That means, on resume, it will be as if the program
		2214	was frozen for a few seconds, but the suspend time will not be counted
		2215	towards C<ev_timer> when a monotonic clock source is used. The real time
		2216	clock advanced as expected, but if it is used as sole clocksource, then a
		2217	long suspend would be detected as a time jump by libev, and timers would
		2218	be adjusted accordingly.
		2219
		2220	I would not be surprised to see different behaviour in different between
		2221	operating systems, OS versions or even different hardware.
		2222
		2223	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2224	time jump in the monotonic clocks and the realtime clock. If the program
		2225	is suspended for a very long time, and monotonic clock sources are in use,
		2226	then you can expect C<ev_timer>s to expire as the full suspension time
		2227	will be counted towards the timers. When no monotonic clock source is in
		2228	use, then libev will again assume a timejump and adjust accordingly.
		2229
		2230	It might be beneficial for this latter case to call C<ev_suspend>
		2231	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2232	deterministic behaviour in this case (you can do nothing against
		2233	C<SIGSTOP>).
1508		2234
1509	=head3 Watcher-Specific Functions and Data Members	2235	=head3 Watcher-Specific Functions and Data Members
1510		2236
1511	=over 4	2237	=over 4
1512		2238
1513	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2239	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1514		2240
1515	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2241	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1516		2242
1517	Configure the timer to trigger after C<after> seconds. If C<repeat>	2243	Configure the timer to trigger after C<after> seconds (fractional and
1518	is C<0.>, then it will automatically be stopped once the timeout is	2244	negative values are supported). If C<repeat> is C<0.>, then it will
1519	reached. If it is positive, then the timer will automatically be	2245	automatically be stopped once the timeout is reached. If it is positive,
1520	configured to trigger again C<repeat> seconds later, again, and again,	2246	then the timer will automatically be configured to trigger again C<repeat>
1521	until stopped manually.	2247	seconds later, again, and again, until stopped manually.
1522		2248
1523	The timer itself will do a best-effort at avoiding drift, that is, if	2249	The timer itself will do a best-effort at avoiding drift, that is, if
1524	you configure a timer to trigger every 10 seconds, then it will normally	2250	you configure a timer to trigger every 10 seconds, then it will normally
1525	trigger at exactly 10 second intervals. If, however, your program cannot	2251	trigger at exactly 10 second intervals. If, however, your program cannot
1526	keep up with the timer (because it takes longer than those 10 seconds to	2252	keep up with the timer (because it takes longer than those 10 seconds to
1527	do stuff) the timer will not fire more than once per event loop iteration.	2253	do stuff) the timer will not fire more than once per event loop iteration.
1528		2254
1529	=item ev_timer_again (loop, ev_timer *)	2255	=item ev_timer_again (loop, ev_timer *)
1530		2256
1531	This will act as if the timer timed out and restart it again if it is	2257	This will act as if the timer timed out, and restarts it again if it is
1532	repeating. The exact semantics are:	2258	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2259	timeout to the C<repeat> value and calling C<ev_timer_start>.
1533		2260
		2261	The exact semantics are as in the following rules, all of which will be
		2262	applied to the watcher:
		2263
		2264	=over 4
		2265
1534	If the timer is pending, its pending status is cleared.	2266	=item If the timer is pending, the pending status is always cleared.
1535		2267
1536	If the timer is started but non-repeating, stop it (as if it timed out).	2268	=item If the timer is started but non-repeating, stop it (as if it timed
		2269	out, without invoking it).
1537		2270
1538	If the timer is repeating, either start it if necessary (with the	2271	=item If the timer is repeating, make the C<repeat> value the new timeout
1539	C<repeat> value), or reset the running timer to the C<repeat> value.	2272	and start the timer, if necessary.
1540		2273
		2274	=back
		2275
1541	This sounds a bit complicated, see "Be smart about timeouts", above, for a	2276	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1542	usage example.	2277	usage example.
		2278
		2279	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
		2280
		2281	Returns the remaining time until a timer fires. If the timer is active,
		2282	then this time is relative to the current event loop time, otherwise it's
		2283	the timeout value currently configured.
		2284
		2285	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2286	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2287	will return C<4>. When the timer expires and is restarted, it will return
		2288	roughly C<7> (likely slightly less as callback invocation takes some time,
		2289	too), and so on.
1543		2290
1544	=item ev_tstamp repeat [read-write]	2291	=item ev_tstamp repeat [read-write]
1545		2292
1546	The current C<repeat> value. Will be used each time the watcher times out	2293	The current C<repeat> value. Will be used each time the watcher times out
1547	or C<ev_timer_again> is called, and determines the next timeout (if any),	2294	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1573	}	2320	}
1574		2321
1575	ev_timer mytimer;	2322	ev_timer mytimer;
1576	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2323	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1577	ev_timer_again (&mytimer); /* start timer */	2324	ev_timer_again (&mytimer); /* start timer */
1578	ev_loop (loop, 0);	2325	ev_run (loop, 0);
1579		2326
1580	// and in some piece of code that gets executed on any "activity":	2327	// and in some piece of code that gets executed on any "activity":
1581	// reset the timeout to start ticking again at 10 seconds	2328	// reset the timeout to start ticking again at 10 seconds
1582	ev_timer_again (&mytimer);	2329	ev_timer_again (&mytimer);
1583		2330
…		…
1585	=head2 C<ev_periodic> - to cron or not to cron?	2332	=head2 C<ev_periodic> - to cron or not to cron?
1586		2333
1587	Periodic watchers are also timers of a kind, but they are very versatile	2334	Periodic watchers are also timers of a kind, but they are very versatile
1588	(and unfortunately a bit complex).	2335	(and unfortunately a bit complex).
1589		2336
1590	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2337	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1591	but on wall clock time (absolute time). You can tell a periodic watcher	2338	relative time, the physical time that passes) but on wall clock time
1592	to trigger after some specific point in time. For example, if you tell a	2339	(absolute time, the thing you can read on your calendar or clock). The
1593	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	2340	difference is that wall clock time can run faster or slower than real
1594	+ 10.>, that is, an absolute time not a delay) and then reset your system	2341	time, and time jumps are not uncommon (e.g. when you adjust your
1595	clock to January of the previous year, then it will take more than year	2342	wrist-watch).
1596	to trigger the event (unlike an C<ev_timer>, which would still trigger
1597	roughly 10 seconds later as it uses a relative timeout).
1598		2343
		2344	You can tell a periodic watcher to trigger after some specific point
		2345	in time: for example, if you tell a periodic watcher to trigger "in 10
		2346	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2347	not a delay) and then reset your system clock to January of the previous
		2348	year, then it will take a year or more to trigger the event (unlike an
		2349	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2350	it, as it uses a relative timeout).
		2351
1599	C<ev_periodic>s can also be used to implement vastly more complex timers,	2352	C<ev_periodic> watchers can also be used to implement vastly more complex
1600	such as triggering an event on each "midnight, local time", or other	2353	timers, such as triggering an event on each "midnight, local time", or
1601	complicated rules.	2354	other complicated rules. This cannot easily be done with C<ev_timer>
		2355	watchers, as those cannot react to time jumps.
1602		2356
1603	As with timers, the callback is guaranteed to be invoked only when the	2357	As with timers, the callback is guaranteed to be invoked only when the
1604	time (C<at>) has passed, but if multiple periodic timers become ready	2358	point in time where it is supposed to trigger has passed. If multiple
1605	during the same loop iteration, then order of execution is undefined.	2359	timers become ready during the same loop iteration then the ones with
		2360	earlier time-out values are invoked before ones with later time-out values
		2361	(but this is no longer true when a callback calls C<ev_run> recursively).
1606		2362
1607	=head3 Watcher-Specific Functions and Data Members	2363	=head3 Watcher-Specific Functions and Data Members
1608		2364
1609	=over 4	2365	=over 4
1610		2366
1611	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2367	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1612		2368
1613	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2369	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1614		2370
1615	Lots of arguments, lets sort it out... There are basically three modes of	2371	Lots of arguments, let's sort it out... There are basically three modes of
1616	operation, and we will explain them from simplest to most complex:	2372	operation, and we will explain them from simplest to most complex:
1617		2373
1618	=over 4	2374	=over 4
1619		2375
1620	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2376	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1621		2377
1622	In this configuration the watcher triggers an event after the wall clock	2378	In this configuration the watcher triggers an event after the wall clock
1623	time C<at> has passed. It will not repeat and will not adjust when a time	2379	time C<offset> has passed. It will not repeat and will not adjust when a
1624	jump occurs, that is, if it is to be run at January 1st 2011 then it will	2380	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1625	only run when the system clock reaches or surpasses this time.	2381	will be stopped and invoked when the system clock reaches or surpasses
		2382	this point in time.
1626		2383
1627	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2384	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1628		2385
1629	In this mode the watcher will always be scheduled to time out at the next	2386	In this mode the watcher will always be scheduled to time out at the next
1630	C<at + N * interval> time (for some integer N, which can also be negative)	2387	C<offset + N * interval> time (for some integer N, which can also be
1631	and then repeat, regardless of any time jumps.	2388	negative) and then repeat, regardless of any time jumps. The C<offset>
		2389	argument is merely an offset into the C<interval> periods.
1632		2390
1633	This can be used to create timers that do not drift with respect to the	2391	This can be used to create timers that do not drift with respect to the
1634	system clock, for example, here is a C<ev_periodic> that triggers each	2392	system clock, for example, here is an C<ev_periodic> that triggers each
1635	hour, on the hour:	2393	hour, on the hour (with respect to UTC):
1636		2394
1637	ev_periodic_set (&periodic, 0., 3600., 0);	2395	ev_periodic_set (&periodic, 0., 3600., 0);
1638		2396
1639	This doesn't mean there will always be 3600 seconds in between triggers,	2397	This doesn't mean there will always be 3600 seconds in between triggers,
1640	but only that the callback will be called when the system time shows a	2398	but only that the callback will be called when the system time shows a
1641	full hour (UTC), or more correctly, when the system time is evenly divisible	2399	full hour (UTC), or more correctly, when the system time is evenly divisible
1642	by 3600.	2400	by 3600.
1643		2401
1644	Another way to think about it (for the mathematically inclined) is that	2402	Another way to think about it (for the mathematically inclined) is that
1645	C<ev_periodic> will try to run the callback in this mode at the next possible	2403	C<ev_periodic> will try to run the callback in this mode at the next possible
1646	time where C<time = at (mod interval)>, regardless of any time jumps.	2404	time where C<time = offset (mod interval)>, regardless of any time jumps.
1647		2405
1648	For numerical stability it is preferable that the C<at> value is near	2406	The C<interval> I<MUST> be positive, and for numerical stability, the
1649	C<ev_now ()> (the current time), but there is no range requirement for	2407	interval value should be higher than C<1/8192> (which is around 100
1650	this value, and in fact is often specified as zero.	2408	microseconds) and C<offset> should be higher than C<0> and should have
		2409	at most a similar magnitude as the current time (say, within a factor of
		2410	ten). Typical values for offset are, in fact, C<0> or something between
		2411	C<0> and C<interval>, which is also the recommended range.
1651		2412
1652	Note also that there is an upper limit to how often a timer can fire (CPU	2413	Note also that there is an upper limit to how often a timer can fire (CPU
1653	speed for example), so if C<interval> is very small then timing stability	2414	speed for example), so if C<interval> is very small then timing stability
1654	will of course deteriorate. Libev itself tries to be exact to be about one	2415	will of course deteriorate. Libev itself tries to be exact to be about one
1655	millisecond (if the OS supports it and the machine is fast enough).	2416	millisecond (if the OS supports it and the machine is fast enough).
1656		2417
1657	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2418	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1658		2419
1659	In this mode the values for C<interval> and C<at> are both being	2420	In this mode the values for C<interval> and C<offset> are both being
1660	ignored. Instead, each time the periodic watcher gets scheduled, the	2421	ignored. Instead, each time the periodic watcher gets scheduled, the
1661	reschedule callback will be called with the watcher as first, and the	2422	reschedule callback will be called with the watcher as first, and the
1662	current time as second argument.	2423	current time as second argument.
1663		2424
1664	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2425	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1665	ever, or make ANY event loop modifications whatsoever>.	2426	or make ANY other event loop modifications whatsoever, unless explicitly
		2427	allowed by documentation here>.
1666		2428
1667	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2429	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1668	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	2430	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1669	only event loop modification you are allowed to do).	2431	only event loop modification you are allowed to do).
1670		2432
…		…
1684		2446
1685	NOTE: I<< This callback must always return a time that is higher than or	2447	NOTE: I<< This callback must always return a time that is higher than or
1686	equal to the passed C<now> value >>.	2448	equal to the passed C<now> value >>.
1687		2449
1688	This can be used to create very complex timers, such as a timer that	2450	This can be used to create very complex timers, such as a timer that
1689	triggers on "next midnight, local time". To do this, you would calculate the	2451	triggers on "next midnight, local time". To do this, you would calculate
1690	next midnight after C<now> and return the timestamp value for this. How	2452	the next midnight after C<now> and return the timestamp value for
1691	you do this is, again, up to you (but it is not trivial, which is the main	2453	this. Here is a (completely untested, no error checking) example on how to
1692	reason I omitted it as an example).	2454	do this:
		2455
		2456	#include <time.h>
		2457
		2458	static ev_tstamp
		2459	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2460	{
		2461	time_t tnow = (time_t)now;
		2462	struct tm tm;
		2463	localtime_r (&tnow, &tm);
		2464
		2465	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2466	++tm.tm_mday; // midnight next day
		2467
		2468	return mktime (&tm);
		2469	}
		2470
		2471	Note: this code might run into trouble on days that have more then two
		2472	midnights (beginning and end).
1693		2473
1694	=back	2474	=back
1695		2475
1696	=item ev_periodic_again (loop, ev_periodic *)	2476	=item ev_periodic_again (loop, ev_periodic *)
1697		2477
…		…
1700	a different time than the last time it was called (e.g. in a crond like	2480	a different time than the last time it was called (e.g. in a crond like
1701	program when the crontabs have changed).	2481	program when the crontabs have changed).
1702		2482
1703	=item ev_tstamp ev_periodic_at (ev_periodic *)	2483	=item ev_tstamp ev_periodic_at (ev_periodic *)
1704		2484
1705	When active, returns the absolute time that the watcher is supposed to	2485	When active, returns the absolute time that the watcher is supposed
1706	trigger next.	2486	to trigger next. This is not the same as the C<offset> argument to
		2487	C<ev_periodic_set>, but indeed works even in interval and manual
		2488	rescheduling modes.
1707		2489
1708	=item ev_tstamp offset [read-write]	2490	=item ev_tstamp offset [read-write]
1709		2491
1710	When repeating, this contains the offset value, otherwise this is the	2492	When repeating, this contains the offset value, otherwise this is the
1711	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2493	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2494	although libev might modify this value for better numerical stability).
1712		2495
1713	Can be modified any time, but changes only take effect when the periodic	2496	Can be modified any time, but changes only take effect when the periodic
1714	timer fires or C<ev_periodic_again> is being called.	2497	timer fires or C<ev_periodic_again> is being called.
1715		2498
1716	=item ev_tstamp interval [read-write]	2499	=item ev_tstamp interval [read-write]
…		…
1732	Example: Call a callback every hour, or, more precisely, whenever the	2515	Example: Call a callback every hour, or, more precisely, whenever the
1733	system time is divisible by 3600. The callback invocation times have	2516	system time is divisible by 3600. The callback invocation times have
1734	potentially a lot of jitter, but good long-term stability.	2517	potentially a lot of jitter, but good long-term stability.
1735		2518
1736	static void	2519	static void
1737	clock_cb (struct ev_loop *loop, ev_io *w, int revents)	2520	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1738	{	2521	{
1739	... its now a full hour (UTC, or TAI or whatever your clock follows)	2522	... its now a full hour (UTC, or TAI or whatever your clock follows)
1740	}	2523	}
1741		2524
1742	ev_periodic hourly_tick;	2525	ev_periodic hourly_tick;
…		…
1759		2542
1760	ev_periodic hourly_tick;	2543	ev_periodic hourly_tick;
1761	ev_periodic_init (&hourly_tick, clock_cb,	2544	ev_periodic_init (&hourly_tick, clock_cb,
1762	fmod (ev_now (loop), 3600.), 3600., 0);	2545	fmod (ev_now (loop), 3600.), 3600., 0);
1763	ev_periodic_start (loop, &hourly_tick);	2546	ev_periodic_start (loop, &hourly_tick);
1764		2547
1765		2548
1766	=head2 C<ev_signal> - signal me when a signal gets signalled!	2549	=head2 C<ev_signal> - signal me when a signal gets signalled!
1767		2550
1768	Signal watchers will trigger an event when the process receives a specific	2551	Signal watchers will trigger an event when the process receives a specific
1769	signal one or more times. Even though signals are very asynchronous, libev	2552	signal one or more times. Even though signals are very asynchronous, libev
1770	will try it's best to deliver signals synchronously, i.e. as part of the	2553	will try its best to deliver signals synchronously, i.e. as part of the
1771	normal event processing, like any other event.	2554	normal event processing, like any other event.
1772		2555
1773	If you want signals asynchronously, just use C<sigaction> as you would	2556	If you want signals to be delivered truly asynchronously, just use
1774	do without libev and forget about sharing the signal. You can even use	2557	C<sigaction> as you would do without libev and forget about sharing
1775	C<ev_async> from a signal handler to synchronously wake up an event loop.	2558	the signal. You can even use C<ev_async> from a signal handler to
		2559	synchronously wake up an event loop.
1776		2560
1777	You can configure as many watchers as you like per signal. Only when the	2561	You can configure as many watchers as you like for the same signal, but
1778	first watcher gets started will libev actually register a signal handler	2562	only within the same loop, i.e. you can watch for C<SIGINT> in your
1779	with the kernel (thus it coexists with your own signal handlers as long as	2563	default loop and for C<SIGIO> in another loop, but you cannot watch for
1780	you don't register any with libev for the same signal). Similarly, when	2564	C<SIGINT> in both the default loop and another loop at the same time. At
1781	the last signal watcher for a signal is stopped, libev will reset the	2565	the moment, C<SIGCHLD> is permanently tied to the default loop.
1782	signal handler to SIG_DFL (regardless of what it was set to before).	2566
		2567	Only after the first watcher for a signal is started will libev actually
		2568	register something with the kernel. It thus coexists with your own signal
		2569	handlers as long as you don't register any with libev for the same signal.
1783		2570
1784	If possible and supported, libev will install its handlers with	2571	If possible and supported, libev will install its handlers with
1785	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2572	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1786	interrupted. If you have a problem with system calls getting interrupted by	2573	not be unduly interrupted. If you have a problem with system calls getting
1787	signals you can block all signals in an C<ev_check> watcher and unblock	2574	interrupted by signals you can block all signals in an C<ev_check> watcher
1788	them in an C<ev_prepare> watcher.	2575	and unblock them in an C<ev_prepare> watcher.
		2576
		2577	=head3 The special problem of inheritance over fork/execve/pthread_create
		2578
		2579	Both the signal mask (C<sigprocmask>) and the signal disposition
		2580	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2581	stopping it again), that is, libev might or might not block the signal,
		2582	and might or might not set or restore the installed signal handler (but
		2583	see C<EVFLAG_NOSIGMASK>).
		2584
		2585	While this does not matter for the signal disposition (libev never
		2586	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2587	C<execve>), this matters for the signal mask: many programs do not expect
		2588	certain signals to be blocked.
		2589
		2590	This means that before calling C<exec> (from the child) you should reset
		2591	the signal mask to whatever "default" you expect (all clear is a good
		2592	choice usually).
		2593
		2594	The simplest way to ensure that the signal mask is reset in the child is
		2595	to install a fork handler with C<pthread_atfork> that resets it. That will
		2596	catch fork calls done by libraries (such as the libc) as well.
		2597
		2598	In current versions of libev, the signal will not be blocked indefinitely
		2599	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2600	the window of opportunity for problems, it will not go away, as libev
		2601	I<has> to modify the signal mask, at least temporarily.
		2602
		2603	So I can't stress this enough: I<If you do not reset your signal mask when
		2604	you expect it to be empty, you have a race condition in your code>. This
		2605	is not a libev-specific thing, this is true for most event libraries.
		2606
		2607	=head3 The special problem of threads signal handling
		2608
		2609	POSIX threads has problematic signal handling semantics, specifically,
		2610	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2611	threads in a process block signals, which is hard to achieve.
		2612
		2613	When you want to use sigwait (or mix libev signal handling with your own
		2614	for the same signals), you can tackle this problem by globally blocking
		2615	all signals before creating any threads (or creating them with a fully set
		2616	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2617	loops. Then designate one thread as "signal receiver thread" which handles
		2618	these signals. You can pass on any signals that libev might be interested
		2619	in by calling C<ev_feed_signal>.
1789		2620
1790	=head3 Watcher-Specific Functions and Data Members	2621	=head3 Watcher-Specific Functions and Data Members
1791		2622
1792	=over 4	2623	=over 4
1793		2624
…		…
1809	Example: Try to exit cleanly on SIGINT.	2640	Example: Try to exit cleanly on SIGINT.
1810		2641
1811	static void	2642	static void
1812	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)	2643	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1813	{	2644	{
1814	ev_unloop (loop, EVUNLOOP_ALL);	2645	ev_break (loop, EVBREAK_ALL);
1815	}	2646	}
1816		2647
1817	ev_signal signal_watcher;	2648	ev_signal signal_watcher;
1818	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2649	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1819	ev_signal_start (loop, &signal_watcher);	2650	ev_signal_start (loop, &signal_watcher);
…		…
1825	some child status changes (most typically when a child of yours dies or	2656	some child status changes (most typically when a child of yours dies or
1826	exits). It is permissible to install a child watcher I<after> the child	2657	exits). It is permissible to install a child watcher I<after> the child
1827	has been forked (which implies it might have already exited), as long	2658	has been forked (which implies it might have already exited), as long
1828	as the event loop isn't entered (or is continued from a watcher), i.e.,	2659	as the event loop isn't entered (or is continued from a watcher), i.e.,
1829	forking and then immediately registering a watcher for the child is fine,	2660	forking and then immediately registering a watcher for the child is fine,
1830	but forking and registering a watcher a few event loop iterations later is	2661	but forking and registering a watcher a few event loop iterations later or
1831	not.	2662	in the next callback invocation is not.
1832		2663
1833	Only the default event loop is capable of handling signals, and therefore	2664	Only the default event loop is capable of handling signals, and therefore
1834	you can only register child watchers in the default event loop.	2665	you can only register child watchers in the default event loop.
1835		2666
		2667	Due to some design glitches inside libev, child watchers will always be
		2668	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2669	libev)
		2670
1836	=head3 Process Interaction	2671	=head3 Process Interaction
1837		2672
1838	Libev grabs C<SIGCHLD> as soon as the default event loop is	2673	Libev grabs C<SIGCHLD> as soon as the default event loop is
1839	initialised. This is necessary to guarantee proper behaviour even if	2674	initialised. This is necessary to guarantee proper behaviour even if the
1840	the first child watcher is started after the child exits. The occurrence	2675	first child watcher is started after the child exits. The occurrence
1841	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2676	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1842	synchronously as part of the event loop processing. Libev always reaps all	2677	synchronously as part of the event loop processing. Libev always reaps all
1843	children, even ones not watched.	2678	children, even ones not watched.
1844		2679
1845	=head3 Overriding the Built-In Processing	2680	=head3 Overriding the Built-In Processing
…		…
1855	=head3 Stopping the Child Watcher	2690	=head3 Stopping the Child Watcher
1856		2691
1857	Currently, the child watcher never gets stopped, even when the	2692	Currently, the child watcher never gets stopped, even when the
1858	child terminates, so normally one needs to stop the watcher in the	2693	child terminates, so normally one needs to stop the watcher in the
1859	callback. Future versions of libev might stop the watcher automatically	2694	callback. Future versions of libev might stop the watcher automatically
1860	when a child exit is detected.	2695	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2696	problem).
1861		2697
1862	=head3 Watcher-Specific Functions and Data Members	2698	=head3 Watcher-Specific Functions and Data Members
1863		2699
1864	=over 4	2700	=over 4
1865		2701
…		…
1923		2759
1924	=head2 C<ev_stat> - did the file attributes just change?	2760	=head2 C<ev_stat> - did the file attributes just change?
1925		2761
1926	This watches a file system path for attribute changes. That is, it calls	2762	This watches a file system path for attribute changes. That is, it calls
1927	C<stat> on that path in regular intervals (or when the OS says it changed)	2763	C<stat> on that path in regular intervals (or when the OS says it changed)
1928	and sees if it changed compared to the last time, invoking the callback if	2764	and sees if it changed compared to the last time, invoking the callback
1929	it did.	2765	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2766	happen after the watcher has been started will be reported.
1930		2767
1931	The path does not need to exist: changing from "path exists" to "path does	2768	The path does not need to exist: changing from "path exists" to "path does
1932	not exist" is a status change like any other. The condition "path does	2769	not exist" is a status change like any other. The condition "path does not
1933	not exist" is signified by the C<st_nlink> field being zero (which is	2770	exist" (or more correctly "path cannot be stat'ed") is signified by the
1934	otherwise always forced to be at least one) and all the other fields of	2771	C<st_nlink> field being zero (which is otherwise always forced to be at
1935	the stat buffer having unspecified contents.	2772	least one) and all the other fields of the stat buffer having unspecified
		2773	contents.
1936		2774
1937	The path I<must not> end in a slash or contain special components such as	2775	The path I<must not> end in a slash or contain special components such as
1938	C<.> or C<..>. The path I<should> be absolute: If it is relative and	2776	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1939	your working directory changes, then the behaviour is undefined.	2777	your working directory changes, then the behaviour is undefined.
1940		2778
…		…
1943	to see if it changed somehow. You can specify a recommended polling	2781	to see if it changed somehow. You can specify a recommended polling
1944	interval for this case. If you specify a polling interval of C<0> (highly	2782	interval for this case. If you specify a polling interval of C<0> (highly
1945	recommended!) then a I<suitable, unspecified default> value will be used	2783	recommended!) then a I<suitable, unspecified default> value will be used
1946	(which you can expect to be around five seconds, although this might	2784	(which you can expect to be around five seconds, although this might
1947	change dynamically). Libev will also impose a minimum interval which is	2785	change dynamically). Libev will also impose a minimum interval which is
1948	currently around C<0.1>, but thats usually overkill.	2786	currently around C<0.1>, but that's usually overkill.
1949		2787
1950	This watcher type is not meant for massive numbers of stat watchers,	2788	This watcher type is not meant for massive numbers of stat watchers,
1951	as even with OS-supported change notifications, this can be	2789	as even with OS-supported change notifications, this can be
1952	resource-intensive.	2790	resource-intensive.
1953		2791
1954	At the time of this writing, the only OS-specific interface implemented	2792	At the time of this writing, the only OS-specific interface implemented
1955	is the Linux inotify interface (implementing kqueue support is left as	2793	is the Linux inotify interface (implementing kqueue support is left as an
1956	an exercise for the reader. Note, however, that the author sees no way	2794	exercise for the reader. Note, however, that the author sees no way of
1957	of implementing C<ev_stat> semantics with kqueue).	2795	implementing C<ev_stat> semantics with kqueue, except as a hint).
1958		2796
1959	=head3 ABI Issues (Largefile Support)	2797	=head3 ABI Issues (Largefile Support)
1960		2798
1961	Libev by default (unless the user overrides this) uses the default	2799	Libev by default (unless the user overrides this) uses the default
1962	compilation environment, which means that on systems with large file	2800	compilation environment, which means that on systems with large file
…		…
1973	to exchange stat structures with application programs compiled using the	2811	to exchange stat structures with application programs compiled using the
1974	default compilation environment.	2812	default compilation environment.
1975		2813
1976	=head3 Inotify and Kqueue	2814	=head3 Inotify and Kqueue
1977		2815
1978	When C<inotify (7)> support has been compiled into libev (generally	2816	When C<inotify (7)> support has been compiled into libev and present at
1979	only available with Linux 2.6.25 or above due to bugs in earlier	2817	runtime, it will be used to speed up change detection where possible. The
1980	implementations) and present at runtime, it will be used to speed up	2818	inotify descriptor will be created lazily when the first C<ev_stat>
1981	change detection where possible. The inotify descriptor will be created	2819	watcher is being started.
1982	lazily when the first C<ev_stat> watcher is being started.
1983		2820
1984	Inotify presence does not change the semantics of C<ev_stat> watchers	2821	Inotify presence does not change the semantics of C<ev_stat> watchers
1985	except that changes might be detected earlier, and in some cases, to avoid	2822	except that changes might be detected earlier, and in some cases, to avoid
1986	making regular C<stat> calls. Even in the presence of inotify support	2823	making regular C<stat> calls. Even in the presence of inotify support
1987	there are many cases where libev has to resort to regular C<stat> polling,	2824	there are many cases where libev has to resort to regular C<stat> polling,
1988	but as long as the path exists, libev usually gets away without polling.	2825	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2826	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2827	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2828	xfs are fully working) libev usually gets away without polling.
1989		2829
1990	There is no support for kqueue, as apparently it cannot be used to	2830	There is no support for kqueue, as apparently it cannot be used to
1991	implement this functionality, due to the requirement of having a file	2831	implement this functionality, due to the requirement of having a file
1992	descriptor open on the object at all times, and detecting renames, unlinks	2832	descriptor open on the object at all times, and detecting renames, unlinks
1993	etc. is difficult.	2833	etc. is difficult.
		2834
		2835	=head3 C<stat ()> is a synchronous operation
		2836
		2837	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2838	the process. The exception are C<ev_stat> watchers - those call C<stat
		2839	()>, which is a synchronous operation.
		2840
		2841	For local paths, this usually doesn't matter: unless the system is very
		2842	busy or the intervals between stat's are large, a stat call will be fast,
		2843	as the path data is usually in memory already (except when starting the
		2844	watcher).
		2845
		2846	For networked file systems, calling C<stat ()> can block an indefinite
		2847	time due to network issues, and even under good conditions, a stat call
		2848	often takes multiple milliseconds.
		2849
		2850	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2851	paths, although this is fully supported by libev.
1994		2852
1995	=head3 The special problem of stat time resolution	2853	=head3 The special problem of stat time resolution
1996		2854
1997	The C<stat ()> system call only supports full-second resolution portably,	2855	The C<stat ()> system call only supports full-second resolution portably,
1998	and even on systems where the resolution is higher, most file systems	2856	and even on systems where the resolution is higher, most file systems
…		…
2143	Apart from keeping your process non-blocking (which is a useful	3001	Apart from keeping your process non-blocking (which is a useful
2144	effect on its own sometimes), idle watchers are a good place to do	3002	effect on its own sometimes), idle watchers are a good place to do
2145	"pseudo-background processing", or delay processing stuff to after the	3003	"pseudo-background processing", or delay processing stuff to after the
2146	event loop has handled all outstanding events.	3004	event loop has handled all outstanding events.
2147		3005
		3006	=head3 Abusing an C<ev_idle> watcher for its side-effect
		3007
		3008	As long as there is at least one active idle watcher, libev will never
		3009	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		3010	For this to work, the idle watcher doesn't need to be invoked at all - the
		3011	lowest priority will do.
		3012
		3013	This mode of operation can be useful together with an C<ev_check> watcher,
		3014	to do something on each event loop iteration - for example to balance load
		3015	between different connections.
		3016
		3017	See L</Abusing an ev_check watcher for its side-effect> for a longer
		3018	example.
		3019
2148	=head3 Watcher-Specific Functions and Data Members	3020	=head3 Watcher-Specific Functions and Data Members
2149		3021
2150	=over 4	3022	=over 4
2151		3023
2152	=item ev_idle_init (ev_signal *, callback)	3024	=item ev_idle_init (ev_idle *, callback)
2153		3025
2154	Initialises and configures the idle watcher - it has no parameters of any	3026	Initialises and configures the idle watcher - it has no parameters of any
2155	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	3027	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
2156	believe me.	3028	believe me.
2157		3029
…		…
2163	callback, free it. Also, use no error checking, as usual.	3035	callback, free it. Also, use no error checking, as usual.
2164		3036
2165	static void	3037	static void
2166	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	3038	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2167	{	3039	{
		3040	// stop the watcher
		3041	ev_idle_stop (loop, w);
		3042
		3043	// now we can free it
2168	free (w);	3044	free (w);
		3045
2169	// now do something you wanted to do when the program has	3046	// now do something you wanted to do when the program has
2170	// no longer anything immediate to do.	3047	// no longer anything immediate to do.
2171	}	3048	}
2172		3049
2173	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	3050	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2174	ev_idle_init (idle_watcher, idle_cb);	3051	ev_idle_init (idle_watcher, idle_cb);
2175	ev_idle_start (loop, idle_cb);	3052	ev_idle_start (loop, idle_watcher);
2176		3053
2177		3054
2178	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3055	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2179		3056
2180	Prepare and check watchers are usually (but not always) used in pairs:	3057	Prepare and check watchers are often (but not always) used in pairs:
2181	prepare watchers get invoked before the process blocks and check watchers	3058	prepare watchers get invoked before the process blocks and check watchers
2182	afterwards.	3059	afterwards.
2183		3060
2184	You I<must not> call C<ev_loop> or similar functions that enter	3061	You I<must not> call C<ev_run> (or similar functions that enter the
2185	the current event loop from either C<ev_prepare> or C<ev_check>	3062	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2186	watchers. Other loops than the current one are fine, however. The	3063	C<ev_check> watchers. Other loops than the current one are fine,
2187	rationale behind this is that you do not need to check for recursion in	3064	however. The rationale behind this is that you do not need to check
2188	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3065	for recursion in those watchers, i.e. the sequence will always be
2189	C<ev_check> so if you have one watcher of each kind they will always be	3066	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2190	called in pairs bracketing the blocking call.	3067	kind they will always be called in pairs bracketing the blocking call.
2191		3068
2192	Their main purpose is to integrate other event mechanisms into libev and	3069	Their main purpose is to integrate other event mechanisms into libev and
2193	their use is somewhat advanced. They could be used, for example, to track	3070	their use is somewhat advanced. They could be used, for example, to track
2194	variable changes, implement your own watchers, integrate net-snmp or a	3071	variable changes, implement your own watchers, integrate net-snmp or a
2195	coroutine library and lots more. They are also occasionally useful if	3072	coroutine library and lots more. They are also occasionally useful if
…		…
2213	with priority higher than or equal to the event loop and one coroutine	3090	with priority higher than or equal to the event loop and one coroutine
2214	of lower priority, but only once, using idle watchers to keep the event	3091	of lower priority, but only once, using idle watchers to keep the event
2215	loop from blocking if lower-priority coroutines are active, thus mapping	3092	loop from blocking if lower-priority coroutines are active, thus mapping
2216	low-priority coroutines to idle/background tasks).	3093	low-priority coroutines to idle/background tasks).
2217		3094
2218	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3095	When used for this purpose, it is recommended to give C<ev_check> watchers
2219	priority, to ensure that they are being run before any other watchers	3096	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2220	after the poll (this doesn't matter for C<ev_prepare> watchers).	3097	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3098	watchers).
2221		3099
2222	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3100	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2223	activate ("feed") events into libev. While libev fully supports this, they	3101	activate ("feed") events into libev. While libev fully supports this, they
2224	might get executed before other C<ev_check> watchers did their job. As	3102	might get executed before other C<ev_check> watchers did their job. As
2225	C<ev_check> watchers are often used to embed other (non-libev) event	3103	C<ev_check> watchers are often used to embed other (non-libev) event
2226	loops those other event loops might be in an unusable state until their	3104	loops those other event loops might be in an unusable state until their
2227	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3105	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2228	others).	3106	others).
		3107
		3108	=head3 Abusing an C<ev_check> watcher for its side-effect
		3109
		3110	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3111	useful because they are called once per event loop iteration. For
		3112	example, if you want to handle a large number of connections fairly, you
		3113	normally only do a bit of work for each active connection, and if there
		3114	is more work to do, you wait for the next event loop iteration, so other
		3115	connections have a chance of making progress.
		3116
		3117	Using an C<ev_check> watcher is almost enough: it will be called on the
		3118	next event loop iteration. However, that isn't as soon as possible -
		3119	without external events, your C<ev_check> watcher will not be invoked.
		3120
		3121	This is where C<ev_idle> watchers come in handy - all you need is a
		3122	single global idle watcher that is active as long as you have one active
		3123	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3124	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3125	invoked. Neither watcher alone can do that.
2229		3126
2230	=head3 Watcher-Specific Functions and Data Members	3127	=head3 Watcher-Specific Functions and Data Members
2231		3128
2232	=over 4	3129	=over 4
2233		3130
…		…
2273	struct pollfd fds [nfd];	3170	struct pollfd fds [nfd];
2274	// actual code will need to loop here and realloc etc.	3171	// actual code will need to loop here and realloc etc.
2275	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	3172	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2276		3173
2277	/* the callback is illegal, but won't be called as we stop during check */	3174	/* the callback is illegal, but won't be called as we stop during check */
2278	ev_timer_init (&tw, 0, timeout * 1e-3);	3175	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2279	ev_timer_start (loop, &tw);	3176	ev_timer_start (loop, &tw);
2280		3177
2281	// create one ev_io per pollfd	3178	// create one ev_io per pollfd
2282	for (int i = 0; i < nfd; ++i)	3179	for (int i = 0; i < nfd; ++i)
2283	{	3180	{
…		…
2357		3254
2358	if (timeout >= 0)	3255	if (timeout >= 0)
2359	// create/start timer	3256	// create/start timer
2360		3257
2361	// poll	3258	// poll
2362	ev_loop (EV_A_ 0);	3259	ev_run (EV_A_ 0);
2363		3260
2364	// stop timer again	3261	// stop timer again
2365	if (timeout >= 0)	3262	if (timeout >= 0)
2366	ev_timer_stop (EV_A_ &to);	3263	ev_timer_stop (EV_A_ &to);
2367		3264
…		…
2396	some fds have to be watched and handled very quickly (with low latency),	3293	some fds have to be watched and handled very quickly (with low latency),
2397	and even priorities and idle watchers might have too much overhead. In	3294	and even priorities and idle watchers might have too much overhead. In
2398	this case you would put all the high priority stuff in one loop and all	3295	this case you would put all the high priority stuff in one loop and all
2399	the rest in a second one, and embed the second one in the first.	3296	the rest in a second one, and embed the second one in the first.
2400		3297
2401	As long as the watcher is active, the callback will be invoked every time	3298	As long as the watcher is active, the callback will be invoked every
2402	there might be events pending in the embedded loop. The callback must then	3299	time there might be events pending in the embedded loop. The callback
2403	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3300	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2404	their callbacks (you could also start an idle watcher to give the embedded	3301	sweep and invoke their callbacks (the callback doesn't need to invoke the
2405	loop strictly lower priority for example). You can also set the callback	3302	C<ev_embed_sweep> function directly, it could also start an idle watcher
2406	to C<0>, in which case the embed watcher will automatically execute the	3303	to give the embedded loop strictly lower priority for example).
2407	embedded loop sweep.
2408		3304
2409	As long as the watcher is started it will automatically handle events. The	3305	You can also set the callback to C<0>, in which case the embed watcher
2410	callback will be invoked whenever some events have been handled. You can	3306	will automatically execute the embedded loop sweep whenever necessary.
2411	set the callback to C<0> to avoid having to specify one if you are not
2412	interested in that.
2413		3307
2414	Also, there have not currently been made special provisions for forking:	3308	Fork detection will be handled transparently while the C<ev_embed> watcher
2415	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3309	is active, i.e., the embedded loop will automatically be forked when the
2416	but you will also have to stop and restart any C<ev_embed> watchers	3310	embedding loop forks. In other cases, the user is responsible for calling
2417	yourself - but you can use a fork watcher to handle this automatically,	3311	C<ev_loop_fork> on the embedded loop.
2418	and future versions of libev might do just that.
2419		3312
2420	Unfortunately, not all backends are embeddable: only the ones returned by	3313	Unfortunately, not all backends are embeddable: only the ones returned by
2421	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3314	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2422	portable one.	3315	portable one.
2423		3316
…		…
2438		3331
2439	=over 4	3332	=over 4
2440		3333
2441	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3334	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2442		3335
2443	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3336	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2444		3337
2445	Configures the watcher to embed the given loop, which must be	3338	Configures the watcher to embed the given loop, which must be
2446	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3339	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2447	invoked automatically, otherwise it is the responsibility of the callback	3340	invoked automatically, otherwise it is the responsibility of the callback
2448	to invoke it (it will continue to be called until the sweep has been done,	3341	to invoke it (it will continue to be called until the sweep has been done,
2449	if you do not want that, you need to temporarily stop the embed watcher).	3342	if you do not want that, you need to temporarily stop the embed watcher).
2450		3343
2451	=item ev_embed_sweep (loop, ev_embed *)	3344	=item ev_embed_sweep (loop, ev_embed *)
2452		3345
2453	Make a single, non-blocking sweep over the embedded loop. This works	3346	Make a single, non-blocking sweep over the embedded loop. This works
2454	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3347	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
2455	appropriate way for embedded loops.	3348	appropriate way for embedded loops.
2456		3349
2457	=item struct ev_loop *other [read-only]	3350	=item struct ev_loop *other [read-only]
2458		3351
2459	The embedded event loop.	3352	The embedded event loop.
…		…
2469	used).	3362	used).
2470		3363
2471	struct ev_loop *loop_hi = ev_default_init (0);	3364	struct ev_loop *loop_hi = ev_default_init (0);
2472	struct ev_loop *loop_lo = 0;	3365	struct ev_loop *loop_lo = 0;
2473	ev_embed embed;	3366	ev_embed embed;
2474		3367
2475	// see if there is a chance of getting one that works	3368	// see if there is a chance of getting one that works
2476	// (remember that a flags value of 0 means autodetection)	3369	// (remember that a flags value of 0 means autodetection)
2477	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3370	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2478	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3371	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2479	: 0;	3372	: 0;
…		…
2493	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3386	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2494		3387
2495	struct ev_loop *loop = ev_default_init (0);	3388	struct ev_loop *loop = ev_default_init (0);
2496	struct ev_loop *loop_socket = 0;	3389	struct ev_loop *loop_socket = 0;
2497	ev_embed embed;	3390	ev_embed embed;
2498		3391
2499	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3392	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2500	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3393	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2501	{	3394	{
2502	ev_embed_init (&embed, 0, loop_socket);	3395	ev_embed_init (&embed, 0, loop_socket);
2503	ev_embed_start (loop, &embed);	3396	ev_embed_start (loop, &embed);
…		…
2511		3404
2512	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3405	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2513		3406
2514	Fork watchers are called when a C<fork ()> was detected (usually because	3407	Fork watchers are called when a C<fork ()> was detected (usually because
2515	whoever is a good citizen cared to tell libev about it by calling	3408	whoever is a good citizen cared to tell libev about it by calling
2516	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3409	C<ev_loop_fork>). The invocation is done before the event loop blocks next
2517	event loop blocks next and before C<ev_check> watchers are being called,	3410	and before C<ev_check> watchers are being called, and only in the child
2518	and only in the child after the fork. If whoever good citizen calling	3411	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
2519	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3412	and calls it in the wrong process, the fork handlers will be invoked, too,
2520	handlers will be invoked, too, of course.	3413	of course.
		3414
		3415	=head3 The special problem of life after fork - how is it possible?
		3416
		3417	Most uses of C<fork ()> consist of forking, then some simple calls to set
		3418	up/change the process environment, followed by a call to C<exec()>. This
		3419	sequence should be handled by libev without any problems.
		3420
		3421	This changes when the application actually wants to do event handling
		3422	in the child, or both parent in child, in effect "continuing" after the
		3423	fork.
		3424
		3425	The default mode of operation (for libev, with application help to detect
		3426	forks) is to duplicate all the state in the child, as would be expected
		3427	when I<either> the parent I<or> the child process continues.
		3428
		3429	When both processes want to continue using libev, then this is usually the
		3430	wrong result. In that case, usually one process (typically the parent) is
		3431	supposed to continue with all watchers in place as before, while the other
		3432	process typically wants to start fresh, i.e. without any active watchers.
		3433
		3434	The cleanest and most efficient way to achieve that with libev is to
		3435	simply create a new event loop, which of course will be "empty", and
		3436	use that for new watchers. This has the advantage of not touching more
		3437	memory than necessary, and thus avoiding the copy-on-write, and the
		3438	disadvantage of having to use multiple event loops (which do not support
		3439	signal watchers).
		3440
		3441	When this is not possible, or you want to use the default loop for
		3442	other reasons, then in the process that wants to start "fresh", call
		3443	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3444	Destroying the default loop will "orphan" (not stop) all registered
		3445	watchers, so you have to be careful not to execute code that modifies
		3446	those watchers. Note also that in that case, you have to re-register any
		3447	signal watchers.
2521		3448
2522	=head3 Watcher-Specific Functions and Data Members	3449	=head3 Watcher-Specific Functions and Data Members
2523		3450
2524	=over 4	3451	=over 4
2525		3452
2526	=item ev_fork_init (ev_signal *, callback)	3453	=item ev_fork_init (ev_fork *, callback)
2527		3454
2528	Initialises and configures the fork watcher - it has no parameters of any	3455	Initialises and configures the fork watcher - it has no parameters of any
2529	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3456	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2530	believe me.	3457	really.
2531		3458
2532	=back	3459	=back
2533		3460
2534		3461
		3462	=head2 C<ev_cleanup> - even the best things end
		3463
		3464	Cleanup watchers are called just before the event loop is being destroyed
		3465	by a call to C<ev_loop_destroy>.
		3466
		3467	While there is no guarantee that the event loop gets destroyed, cleanup
		3468	watchers provide a convenient method to install cleanup hooks for your
		3469	program, worker threads and so on - you just to make sure to destroy the
		3470	loop when you want them to be invoked.
		3471
		3472	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3473	all other watchers, they do not keep a reference to the event loop (which
		3474	makes a lot of sense if you think about it). Like all other watchers, you
		3475	can call libev functions in the callback, except C<ev_cleanup_start>.
		3476
		3477	=head3 Watcher-Specific Functions and Data Members
		3478
		3479	=over 4
		3480
		3481	=item ev_cleanup_init (ev_cleanup *, callback)
		3482
		3483	Initialises and configures the cleanup watcher - it has no parameters of
		3484	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3485	pointless, I assure you.
		3486
		3487	=back
		3488
		3489	Example: Register an atexit handler to destroy the default loop, so any
		3490	cleanup functions are called.
		3491
		3492	static void
		3493	program_exits (void)
		3494	{
		3495	ev_loop_destroy (EV_DEFAULT_UC);
		3496	}
		3497
		3498	...
		3499	atexit (program_exits);
		3500
		3501
2535	=head2 C<ev_async> - how to wake up another event loop	3502	=head2 C<ev_async> - how to wake up an event loop
2536		3503
2537	In general, you cannot use an C<ev_loop> from multiple threads or other	3504	In general, you cannot use an C<ev_loop> from multiple threads or other
2538	asynchronous sources such as signal handlers (as opposed to multiple event	3505	asynchronous sources such as signal handlers (as opposed to multiple event
2539	loops - those are of course safe to use in different threads).	3506	loops - those are of course safe to use in different threads).
2540		3507
2541	Sometimes, however, you need to wake up another event loop you do not	3508	Sometimes, however, you need to wake up an event loop you do not control,
2542	control, for example because it belongs to another thread. This is what	3509	for example because it belongs to another thread. This is what C<ev_async>
2543	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3510	watchers do: as long as the C<ev_async> watcher is active, you can signal
2544	can signal it by calling C<ev_async_send>, which is thread- and signal	3511	it by calling C<ev_async_send>, which is thread- and signal safe.
2545	safe.
2546		3512
2547	This functionality is very similar to C<ev_signal> watchers, as signals,	3513	This functionality is very similar to C<ev_signal> watchers, as signals,
2548	too, are asynchronous in nature, and signals, too, will be compressed	3514	too, are asynchronous in nature, and signals, too, will be compressed
2549	(i.e. the number of callback invocations may be less than the number of	3515	(i.e. the number of callback invocations may be less than the number of
2550	C<ev_async_sent> calls).	3516	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
2551		3517	of "global async watchers" by using a watcher on an otherwise unused
2552	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3518	signal, and C<ev_feed_signal> to signal this watcher from another thread,
2553	just the default loop.	3519	even without knowing which loop owns the signal.
2554		3520
2555	=head3 Queueing	3521	=head3 Queueing
2556		3522
2557	C<ev_async> does not support queueing of data in any way. The reason	3523	C<ev_async> does not support queueing of data in any way. The reason
2558	is that the author does not know of a simple (or any) algorithm for a	3524	is that the author does not know of a simple (or any) algorithm for a
2559	multiple-writer-single-reader queue that works in all cases and doesn't	3525	multiple-writer-single-reader queue that works in all cases and doesn't
2560	need elaborate support such as pthreads.	3526	need elaborate support such as pthreads or unportable memory access
		3527	semantics.
2561		3528
2562	That means that if you want to queue data, you have to provide your own	3529	That means that if you want to queue data, you have to provide your own
2563	queue. But at least I can tell you how to implement locking around your	3530	queue. But at least I can tell you how to implement locking around your
2564	queue:	3531	queue:
2565		3532
…		…
2643	=over 4	3610	=over 4
2644		3611
2645	=item ev_async_init (ev_async *, callback)	3612	=item ev_async_init (ev_async *, callback)
2646		3613
2647	Initialises and configures the async watcher - it has no parameters of any	3614	Initialises and configures the async watcher - it has no parameters of any
2648	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3615	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2649	trust me.	3616	trust me.
2650		3617
2651	=item ev_async_send (loop, ev_async *)	3618	=item ev_async_send (loop, ev_async *)
2652		3619
2653	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3620	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2654	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3621	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3622	returns.
		3623
2655	C<ev_feed_event>, this call is safe to do from other threads, signal or	3624	Unlike C<ev_feed_event>, this call is safe to do from other threads,
2656	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3625	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
2657	section below on what exactly this means).	3626	embedding section below on what exactly this means).
2658		3627
2659	This call incurs the overhead of a system call only once per loop iteration,	3628	Note that, as with other watchers in libev, multiple events might get
2660	so while the overhead might be noticeable, it doesn't apply to repeated	3629	compressed into a single callback invocation (another way to look at
2661	calls to C<ev_async_send>.	3630	this is that C<ev_async> watchers are level-triggered: they are set on
		3631	C<ev_async_send>, reset when the event loop detects that).
		3632
		3633	This call incurs the overhead of at most one extra system call per event
		3634	loop iteration, if the event loop is blocked, and no syscall at all if
		3635	the event loop (or your program) is processing events. That means that
		3636	repeated calls are basically free (there is no need to avoid calls for
		3637	performance reasons) and that the overhead becomes smaller (typically
		3638	zero) under load.
2662		3639
2663	=item bool = ev_async_pending (ev_async *)	3640	=item bool = ev_async_pending (ev_async *)
2664		3641
2665	Returns a non-zero value when C<ev_async_send> has been called on the	3642	Returns a non-zero value when C<ev_async_send> has been called on the
2666	watcher but the event has not yet been processed (or even noted) by the	3643	watcher but the event has not yet been processed (or even noted) by the
…		…
2669	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3646	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2670	the loop iterates next and checks for the watcher to have become active,	3647	the loop iterates next and checks for the watcher to have become active,
2671	it will reset the flag again. C<ev_async_pending> can be used to very	3648	it will reset the flag again. C<ev_async_pending> can be used to very
2672	quickly check whether invoking the loop might be a good idea.	3649	quickly check whether invoking the loop might be a good idea.
2673		3650
2674	Not that this does I<not> check whether the watcher itself is pending, only	3651	Not that this does I<not> check whether the watcher itself is pending,
2675	whether it has been requested to make this watcher pending.	3652	only whether it has been requested to make this watcher pending: there
		3653	is a time window between the event loop checking and resetting the async
		3654	notification, and the callback being invoked.
2676		3655
2677	=back	3656	=back
2678		3657
2679		3658
2680	=head1 OTHER FUNCTIONS	3659	=head1 OTHER FUNCTIONS
2681		3660
2682	There are some other functions of possible interest. Described. Here. Now.	3661	There are some other functions of possible interest. Described. Here. Now.
2683		3662
2684	=over 4	3663	=over 4
2685		3664
2686	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3665	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
2687		3666
2688	This function combines a simple timer and an I/O watcher, calls your	3667	This function combines a simple timer and an I/O watcher, calls your
2689	callback on whichever event happens first and automatically stops both	3668	callback on whichever event happens first and automatically stops both
2690	watchers. This is useful if you want to wait for a single event on an fd	3669	watchers. This is useful if you want to wait for a single event on an fd
2691	or timeout without having to allocate/configure/start/stop/free one or	3670	or timeout without having to allocate/configure/start/stop/free one or
…		…
2697		3676
2698	If C<timeout> is less than 0, then no timeout watcher will be	3677	If C<timeout> is less than 0, then no timeout watcher will be
2699	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3678	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2700	repeat = 0) will be started. C<0> is a valid timeout.	3679	repeat = 0) will be started. C<0> is a valid timeout.
2701		3680
2702	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3681	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2703	passed an C<revents> set like normal event callbacks (a combination of	3682	passed an C<revents> set like normal event callbacks (a combination of
2704	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3683	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2705	value passed to C<ev_once>. Note that it is possible to receive I<both>	3684	value passed to C<ev_once>. Note that it is possible to receive I<both>
2706	a timeout and an io event at the same time - you probably should give io	3685	a timeout and an io event at the same time - you probably should give io
2707	events precedence.	3686	events precedence.
2708		3687
2709	Example: wait up to ten seconds for data to appear on STDIN_FILENO.	3688	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2710		3689
2711	static void stdin_ready (int revents, void *arg)	3690	static void stdin_ready (int revents, void *arg)
2712	{	3691	{
2713	if (revents & EV_READ)	3692	if (revents & EV_READ)
2714	/* stdin might have data for us, joy! */;	3693	/* stdin might have data for us, joy! */;
2715	else if (revents & EV_TIMEOUT)	3694	else if (revents & EV_TIMER)
2716	/* doh, nothing entered */;	3695	/* doh, nothing entered */;
2717	}	3696	}
2718		3697
2719	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3698	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2720		3699
2721	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
2722
2723	Feeds the given event set into the event loop, as if the specified event
2724	had happened for the specified watcher (which must be a pointer to an
2725	initialised but not necessarily started event watcher).
2726
2727	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)	3700	=item ev_feed_fd_event (loop, int fd, int revents)
2728		3701
2729	Feed an event on the given fd, as if a file descriptor backend detected	3702	Feed an event on the given fd, as if a file descriptor backend detected
2730	the given events it.	3703	the given events.
2731		3704
2732	=item ev_feed_signal_event (struct ev_loop *loop, int signum)	3705	=item ev_feed_signal_event (loop, int signum)
2733		3706
2734	Feed an event as if the given signal occurred (C<loop> must be the default	3707	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
2735	loop!).	3708	which is async-safe.
2736		3709
2737	=back	3710	=back
		3711
		3712
		3713	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3714
		3715	This section explains some common idioms that are not immediately
		3716	obvious. Note that examples are sprinkled over the whole manual, and this
		3717	section only contains stuff that wouldn't fit anywhere else.
		3718
		3719	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3720
		3721	Each watcher has, by default, a C<void *data> member that you can read
		3722	or modify at any time: libev will completely ignore it. This can be used
		3723	to associate arbitrary data with your watcher. If you need more data and
		3724	don't want to allocate memory separately and store a pointer to it in that
		3725	data member, you can also "subclass" the watcher type and provide your own
		3726	data:
		3727
		3728	struct my_io
		3729	{
		3730	ev_io io;
		3731	int otherfd;
		3732	void *somedata;
		3733	struct whatever *mostinteresting;
		3734	};
		3735
		3736	...
		3737	struct my_io w;
		3738	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3739
		3740	And since your callback will be called with a pointer to the watcher, you
		3741	can cast it back to your own type:
		3742
		3743	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3744	{
		3745	struct my_io *w = (struct my_io *)w_;
		3746	...
		3747	}
		3748
		3749	More interesting and less C-conformant ways of casting your callback
		3750	function type instead have been omitted.
		3751
		3752	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3753
		3754	Another common scenario is to use some data structure with multiple
		3755	embedded watchers, in effect creating your own watcher that combines
		3756	multiple libev event sources into one "super-watcher":
		3757
		3758	struct my_biggy
		3759	{
		3760	int some_data;
		3761	ev_timer t1;
		3762	ev_timer t2;
		3763	}
		3764
		3765	In this case getting the pointer to C<my_biggy> is a bit more
		3766	complicated: Either you store the address of your C<my_biggy> struct in
		3767	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3768	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3769	real programmers):
		3770
		3771	#include <stddef.h>
		3772
		3773	static void
		3774	t1_cb (EV_P_ ev_timer *w, int revents)
		3775	{
		3776	struct my_biggy big = (struct my_biggy *)
		3777	(((char *)w) - offsetof (struct my_biggy, t1));
		3778	}
		3779
		3780	static void
		3781	t2_cb (EV_P_ ev_timer *w, int revents)
		3782	{
		3783	struct my_biggy big = (struct my_biggy *)
		3784	(((char *)w) - offsetof (struct my_biggy, t2));
		3785	}
		3786
		3787	=head2 AVOIDING FINISHING BEFORE RETURNING
		3788
		3789	Often you have structures like this in event-based programs:
		3790
		3791	callback ()
		3792	{
		3793	free (request);
		3794	}
		3795
		3796	request = start_new_request (..., callback);
		3797
		3798	The intent is to start some "lengthy" operation. The C<request> could be
		3799	used to cancel the operation, or do other things with it.
		3800
		3801	It's not uncommon to have code paths in C<start_new_request> that
		3802	immediately invoke the callback, for example, to report errors. Or you add
		3803	some caching layer that finds that it can skip the lengthy aspects of the
		3804	operation and simply invoke the callback with the result.
		3805
		3806	The problem here is that this will happen I<before> C<start_new_request>
		3807	has returned, so C<request> is not set.
		3808
		3809	Even if you pass the request by some safer means to the callback, you
		3810	might want to do something to the request after starting it, such as
		3811	canceling it, which probably isn't working so well when the callback has
		3812	already been invoked.
		3813
		3814	A common way around all these issues is to make sure that
		3815	C<start_new_request> I<always> returns before the callback is invoked. If
		3816	C<start_new_request> immediately knows the result, it can artificially
		3817	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3818	example, or more sneakily, by reusing an existing (stopped) watcher and
		3819	pushing it into the pending queue:
		3820
		3821	ev_set_cb (watcher, callback);
		3822	ev_feed_event (EV_A_ watcher, 0);
		3823
		3824	This way, C<start_new_request> can safely return before the callback is
		3825	invoked, while not delaying callback invocation too much.
		3826
		3827	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3828
		3829	Often (especially in GUI toolkits) there are places where you have
		3830	I<modal> interaction, which is most easily implemented by recursively
		3831	invoking C<ev_run>.
		3832
		3833	This brings the problem of exiting - a callback might want to finish the
		3834	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3835	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3836	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3837	other combination: In these cases, a simple C<ev_break> will not work.
		3838
		3839	The solution is to maintain "break this loop" variable for each C<ev_run>
		3840	invocation, and use a loop around C<ev_run> until the condition is
		3841	triggered, using C<EVRUN_ONCE>:
		3842
		3843	// main loop
		3844	int exit_main_loop = 0;
		3845
		3846	while (!exit_main_loop)
		3847	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3848
		3849	// in a modal watcher
		3850	int exit_nested_loop = 0;
		3851
		3852	while (!exit_nested_loop)
		3853	ev_run (EV_A_ EVRUN_ONCE);
		3854
		3855	To exit from any of these loops, just set the corresponding exit variable:
		3856
		3857	// exit modal loop
		3858	exit_nested_loop = 1;
		3859
		3860	// exit main program, after modal loop is finished
		3861	exit_main_loop = 1;
		3862
		3863	// exit both
		3864	exit_main_loop = exit_nested_loop = 1;
		3865
		3866	=head2 THREAD LOCKING EXAMPLE
		3867
		3868	Here is a fictitious example of how to run an event loop in a different
		3869	thread from where callbacks are being invoked and watchers are
		3870	created/added/removed.
		3871
		3872	For a real-world example, see the C<EV::Loop::Async> perl module,
		3873	which uses exactly this technique (which is suited for many high-level
		3874	languages).
		3875
		3876	The example uses a pthread mutex to protect the loop data, a condition
		3877	variable to wait for callback invocations, an async watcher to notify the
		3878	event loop thread and an unspecified mechanism to wake up the main thread.
		3879
		3880	First, you need to associate some data with the event loop:
		3881
		3882	typedef struct {
		3883	pthread_mutex_t lock; /* global loop lock */
		3884	pthread_t tid;
		3885	pthread_cond_t invoke_cv;
		3886	ev_async async_w;
		3887	} userdata;
		3888
		3889	void prepare_loop (EV_P)
		3890	{
		3891	// for simplicity, we use a static userdata struct.
		3892	static userdata u;
		3893
		3894	ev_async_init (&u.async_w, async_cb);
		3895	ev_async_start (EV_A_ &u.async_w);
		3896
		3897	pthread_mutex_init (&u.lock, 0);
		3898	pthread_cond_init (&u.invoke_cv, 0);
		3899
		3900	// now associate this with the loop
		3901	ev_set_userdata (EV_A_ &u);
		3902	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3903	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3904
		3905	// then create the thread running ev_run
		3906	pthread_create (&u.tid, 0, l_run, EV_A);
		3907	}
		3908
		3909	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3910	solely to wake up the event loop so it takes notice of any new watchers
		3911	that might have been added:
		3912
		3913	static void
		3914	async_cb (EV_P_ ev_async *w, int revents)
		3915	{
		3916	// just used for the side effects
		3917	}
		3918
		3919	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3920	protecting the loop data, respectively.
		3921
		3922	static void
		3923	l_release (EV_P)
		3924	{
		3925	userdata *u = ev_userdata (EV_A);
		3926	pthread_mutex_unlock (&u->lock);
		3927	}
		3928
		3929	static void
		3930	l_acquire (EV_P)
		3931	{
		3932	userdata *u = ev_userdata (EV_A);
		3933	pthread_mutex_lock (&u->lock);
		3934	}
		3935
		3936	The event loop thread first acquires the mutex, and then jumps straight
		3937	into C<ev_run>:
		3938
		3939	void *
		3940	l_run (void *thr_arg)
		3941	{
		3942	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3943
		3944	l_acquire (EV_A);
		3945	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3946	ev_run (EV_A_ 0);
		3947	l_release (EV_A);
		3948
		3949	return 0;
		3950	}
		3951
		3952	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3953	signal the main thread via some unspecified mechanism (signals? pipe
		3954	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3955	have been called (in a while loop because a) spurious wakeups are possible
		3956	and b) skipping inter-thread-communication when there are no pending
		3957	watchers is very beneficial):
		3958
		3959	static void
		3960	l_invoke (EV_P)
		3961	{
		3962	userdata *u = ev_userdata (EV_A);
		3963
		3964	while (ev_pending_count (EV_A))
		3965	{
		3966	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3967	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3968	}
		3969	}
		3970
		3971	Now, whenever the main thread gets told to invoke pending watchers, it
		3972	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3973	thread to continue:
		3974
		3975	static void
		3976	real_invoke_pending (EV_P)
		3977	{
		3978	userdata *u = ev_userdata (EV_A);
		3979
		3980	pthread_mutex_lock (&u->lock);
		3981	ev_invoke_pending (EV_A);
		3982	pthread_cond_signal (&u->invoke_cv);
		3983	pthread_mutex_unlock (&u->lock);
		3984	}
		3985
		3986	Whenever you want to start/stop a watcher or do other modifications to an
		3987	event loop, you will now have to lock:
		3988
		3989	ev_timer timeout_watcher;
		3990	userdata *u = ev_userdata (EV_A);
		3991
		3992	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3993
		3994	pthread_mutex_lock (&u->lock);
		3995	ev_timer_start (EV_A_ &timeout_watcher);
		3996	ev_async_send (EV_A_ &u->async_w);
		3997	pthread_mutex_unlock (&u->lock);
		3998
		3999	Note that sending the C<ev_async> watcher is required because otherwise
		4000	an event loop currently blocking in the kernel will have no knowledge
		4001	about the newly added timer. By waking up the loop it will pick up any new
		4002	watchers in the next event loop iteration.
		4003
		4004	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		4005
		4006	While the overhead of a callback that e.g. schedules a thread is small, it
		4007	is still an overhead. If you embed libev, and your main usage is with some
		4008	kind of threads or coroutines, you might want to customise libev so that
		4009	doesn't need callbacks anymore.
		4010
		4011	Imagine you have coroutines that you can switch to using a function
		4012	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		4013	and that due to some magic, the currently active coroutine is stored in a
		4014	global called C<current_coro>. Then you can build your own "wait for libev
		4015	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		4016	the differing C<;> conventions):
		4017
		4018	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4019	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4020
		4021	That means instead of having a C callback function, you store the
		4022	coroutine to switch to in each watcher, and instead of having libev call
		4023	your callback, you instead have it switch to that coroutine.
		4024
		4025	A coroutine might now wait for an event with a function called
		4026	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		4027	matter when, or whether the watcher is active or not when this function is
		4028	called):
		4029
		4030	void
		4031	wait_for_event (ev_watcher *w)
		4032	{
		4033	ev_set_cb (w, current_coro);
		4034	switch_to (libev_coro);
		4035	}
		4036
		4037	That basically suspends the coroutine inside C<wait_for_event> and
		4038	continues the libev coroutine, which, when appropriate, switches back to
		4039	this or any other coroutine.
		4040
		4041	You can do similar tricks if you have, say, threads with an event queue -
		4042	instead of storing a coroutine, you store the queue object and instead of
		4043	switching to a coroutine, you push the watcher onto the queue and notify
		4044	any waiters.
		4045
		4046	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		4047	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		4048
		4049	// my_ev.h
		4050	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4051	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4052	#include "../libev/ev.h"
		4053
		4054	// my_ev.c
		4055	#define EV_H "my_ev.h"
		4056	#include "../libev/ev.c"
		4057
		4058	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4059	F<my_ev.c> into your project. When properly specifying include paths, you
		4060	can even use F<ev.h> as header file name directly.
2738		4061
2739		4062
2740	=head1 LIBEVENT EMULATION	4063	=head1 LIBEVENT EMULATION
2741		4064
2742	Libev offers a compatibility emulation layer for libevent. It cannot	4065	Libev offers a compatibility emulation layer for libevent. It cannot
2743	emulate the internals of libevent, so here are some usage hints:	4066	emulate the internals of libevent, so here are some usage hints:
2744		4067
2745	=over 4	4068	=over 4
		4069
		4070	=item * Only the libevent-1.4.1-beta API is being emulated.
		4071
		4072	This was the newest libevent version available when libev was implemented,
		4073	and is still mostly unchanged in 2010.
2746		4074
2747	=item * Use it by including <event.h>, as usual.	4075	=item * Use it by including <event.h>, as usual.
2748		4076
2749	=item * The following members are fully supported: ev_base, ev_callback,	4077	=item * The following members are fully supported: ev_base, ev_callback,
2750	ev_arg, ev_fd, ev_res, ev_events.	4078	ev_arg, ev_fd, ev_res, ev_events.
…		…
2756	=item * Priorities are not currently supported. Initialising priorities	4084	=item * Priorities are not currently supported. Initialising priorities
2757	will fail and all watchers will have the same priority, even though there	4085	will fail and all watchers will have the same priority, even though there
2758	is an ev_pri field.	4086	is an ev_pri field.
2759		4087
2760	=item * In libevent, the last base created gets the signals, in libev, the	4088	=item * In libevent, the last base created gets the signals, in libev, the
2761	first base created (== the default loop) gets the signals.	4089	base that registered the signal gets the signals.
2762		4090
2763	=item * Other members are not supported.	4091	=item * Other members are not supported.
2764		4092
2765	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4093	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2766	to use the libev header file and library.	4094	to use the libev header file and library.
2767		4095
2768	=back	4096	=back
2769		4097
2770	=head1 C++ SUPPORT	4098	=head1 C++ SUPPORT
		4099
		4100	=head2 C API
		4101
		4102	The normal C API should work fine when used from C++: both ev.h and the
		4103	libev sources can be compiled as C++. Therefore, code that uses the C API
		4104	will work fine.
		4105
		4106	Proper exception specifications might have to be added to callbacks passed
		4107	to libev: exceptions may be thrown only from watcher callbacks, all other
		4108	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4109	callbacks) must not throw exceptions, and might need a C<noexcept>
		4110	specification. If you have code that needs to be compiled as both C and
		4111	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4112
		4113	static void
		4114	fatal_error (const char *msg) EV_NOEXCEPT
		4115	{
		4116	perror (msg);
		4117	abort ();
		4118	}
		4119
		4120	...
		4121	ev_set_syserr_cb (fatal_error);
		4122
		4123	The only API functions that can currently throw exceptions are C<ev_run>,
		4124	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4125	because it runs cleanup watchers).
		4126
		4127	Throwing exceptions in watcher callbacks is only supported if libev itself
		4128	is compiled with a C++ compiler or your C and C++ environments allow
		4129	throwing exceptions through C libraries (most do).
		4130
		4131	=head2 C++ API
2771		4132
2772	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4133	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2773	you to use some convenience methods to start/stop watchers and also change	4134	you to use some convenience methods to start/stop watchers and also change
2774	the callback model to a model using method callbacks on objects.	4135	the callback model to a model using method callbacks on objects.
2775		4136
2776	To use it,	4137	To use it,
2777		4138
2778	#include <ev++.h>	4139	#include <ev++.h>
2779		4140
2780	This automatically includes F<ev.h> and puts all of its definitions (many	4141	This automatically includes F<ev.h> and puts all of its definitions (many
2781	of them macros) into the global namespace. All C++ specific things are	4142	of them macros) into the global namespace. All C++ specific things are
2782	put into the C<ev> namespace. It should support all the same embedding	4143	put into the C<ev> namespace. It should support all the same embedding
…		…
2785	Care has been taken to keep the overhead low. The only data member the C++	4146	Care has been taken to keep the overhead low. The only data member the C++
2786	classes add (compared to plain C-style watchers) is the event loop pointer	4147	classes add (compared to plain C-style watchers) is the event loop pointer
2787	that the watcher is associated with (or no additional members at all if	4148	that the watcher is associated with (or no additional members at all if
2788	you disable C<EV_MULTIPLICITY> when embedding libev).	4149	you disable C<EV_MULTIPLICITY> when embedding libev).
2789		4150
2790	Currently, functions, and static and non-static member functions can be	4151	Currently, functions, static and non-static member functions and classes
2791	used as callbacks. Other types should be easy to add as long as they only	4152	with C<operator ()> can be used as callbacks. Other types should be easy
2792	need one additional pointer for context. If you need support for other	4153	to add as long as they only need one additional pointer for context. If
2793	types of functors please contact the author (preferably after implementing	4154	you need support for other types of functors please contact the author
2794	it).	4155	(preferably after implementing it).
		4156
		4157	For all this to work, your C++ compiler either has to use the same calling
		4158	conventions as your C compiler (for static member functions), or you have
		4159	to embed libev and compile libev itself as C++.
2795		4160
2796	Here is a list of things available in the C<ev> namespace:	4161	Here is a list of things available in the C<ev> namespace:
2797		4162
2798	=over 4	4163	=over 4
2799		4164
…		…
2809	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4174	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
2810		4175
2811	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4176	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
2812	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4177	the same name in the C<ev> namespace, with the exception of C<ev_signal>
2813	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4178	which is called C<ev::sig> to avoid clashes with the C<signal> macro
2814	defines by many implementations.	4179	defined by many implementations.
2815		4180
2816	All of those classes have these methods:	4181	All of those classes have these methods:
2817		4182
2818	=over 4	4183	=over 4
2819		4184
2820	=item ev::TYPE::TYPE ()	4185	=item ev::TYPE::TYPE ()
2821		4186
2822	=item ev::TYPE::TYPE (struct ev_loop *)	4187	=item ev::TYPE::TYPE (loop)
2823		4188
2824	=item ev::TYPE::~TYPE	4189	=item ev::TYPE::~TYPE
2825		4190
2826	The constructor (optionally) takes an event loop to associate the watcher	4191	The constructor (optionally) takes an event loop to associate the watcher
2827	with. If it is omitted, it will use C<EV_DEFAULT>.	4192	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2859		4224
2860	myclass obj;	4225	myclass obj;
2861	ev::io iow;	4226	ev::io iow;
2862	iow.set <myclass, &myclass::io_cb> (&obj);	4227	iow.set <myclass, &myclass::io_cb> (&obj);
2863		4228
		4229	=item w->set (object *)
		4230
		4231	This is a variation of a method callback - leaving out the method to call
		4232	will default the method to C<operator ()>, which makes it possible to use
		4233	functor objects without having to manually specify the C<operator ()> all
		4234	the time. Incidentally, you can then also leave out the template argument
		4235	list.
		4236
		4237	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4238	int revents)>.
		4239
		4240	See the method-C<set> above for more details.
		4241
		4242	Example: use a functor object as callback.
		4243
		4244	struct myfunctor
		4245	{
		4246	void operator() (ev::io &w, int revents)
		4247	{
		4248	...
		4249	}
		4250	}
		4251
		4252	myfunctor f;
		4253
		4254	ev::io w;
		4255	w.set (&f);
		4256
2864	=item w->set<function> (void *data = 0)	4257	=item w->set<function> (void *data = 0)
2865		4258
2866	Also sets a callback, but uses a static method or plain function as	4259	Also sets a callback, but uses a static method or plain function as
2867	callback. The optional C<data> argument will be stored in the watcher's	4260	callback. The optional C<data> argument will be stored in the watcher's
2868	C<data> member and is free for you to use.	4261	C<data> member and is free for you to use.
…		…
2874	Example: Use a plain function as callback.	4267	Example: Use a plain function as callback.
2875		4268
2876	static void io_cb (ev::io &w, int revents) { }	4269	static void io_cb (ev::io &w, int revents) { }
2877	iow.set <io_cb> ();	4270	iow.set <io_cb> ();
2878		4271
2879	=item w->set (struct ev_loop *)	4272	=item w->set (loop)
2880		4273
2881	Associates a different C<struct ev_loop> with this watcher. You can only	4274	Associates a different C<struct ev_loop> with this watcher. You can only
2882	do this when the watcher is inactive (and not pending either).	4275	do this when the watcher is inactive (and not pending either).
2883		4276
2884	=item w->set ([arguments])	4277	=item w->set ([arguments])
2885		4278
2886	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be	4279	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4280	with the same arguments. Either this method or a suitable start method
2887	called at least once. Unlike the C counterpart, an active watcher gets	4281	must be called at least once. Unlike the C counterpart, an active watcher
2888	automatically stopped and restarted when reconfiguring it with this	4282	gets automatically stopped and restarted when reconfiguring it with this
2889	method.	4283	method.
		4284
		4285	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4286	clashing with the C<set (loop)> method.
		4287
		4288	For C<ev::io> watchers there is an additional C<set> method that acepts a
		4289	new event mask only, and internally calls C<ev_io_modify>.
2890		4290
2891	=item w->start ()	4291	=item w->start ()
2892		4292
2893	Starts the watcher. Note that there is no C<loop> argument, as the	4293	Starts the watcher. Note that there is no C<loop> argument, as the
2894	constructor already stores the event loop.	4294	constructor already stores the event loop.
2895		4295
		4296	=item w->start ([arguments])
		4297
		4298	Instead of calling C<set> and C<start> methods separately, it is often
		4299	convenient to wrap them in one call. Uses the same type of arguments as
		4300	the configure C<set> method of the watcher.
		4301
2896	=item w->stop ()	4302	=item w->stop ()
2897		4303
2898	Stops the watcher if it is active. Again, no C<loop> argument.	4304	Stops the watcher if it is active. Again, no C<loop> argument.
2899		4305
2900	=item w->again () (C<ev::timer>, C<ev::periodic> only)	4306	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2912		4318
2913	=back	4319	=back
2914		4320
2915	=back	4321	=back
2916		4322
2917	Example: Define a class with an IO and idle watcher, start one of them in	4323	Example: Define a class with two I/O and idle watchers, start the I/O
2918	the constructor.	4324	watchers in the constructor.
2919		4325
2920	class myclass	4326	class myclass
2921	{	4327	{
2922	ev::io io ; void io_cb (ev::io &w, int revents);	4328	ev::io io ; void io_cb (ev::io &w, int revents);
		4329	ev::io io2 ; void io2_cb (ev::io &w, int revents);
2923	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4330	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2924		4331
2925	myclass (int fd)	4332	myclass (int fd)
2926	{	4333	{
2927	io .set <myclass, &myclass::io_cb > (this);	4334	io .set <myclass, &myclass::io_cb > (this);
		4335	io2 .set <myclass, &myclass::io2_cb > (this);
2928	idle.set <myclass, &myclass::idle_cb> (this);	4336	idle.set <myclass, &myclass::idle_cb> (this);
2929		4337
2930	io.start (fd, ev::READ);	4338	io.set (fd, ev::WRITE); // configure the watcher
		4339	io.start (); // start it whenever convenient
		4340
		4341	io2.start (fd, ev::READ); // set + start in one call
2931	}	4342	}
2932	};	4343	};
2933		4344
2934		4345
2935	=head1 OTHER LANGUAGE BINDINGS	4346	=head1 OTHER LANGUAGE BINDINGS
…		…
2954	L<http://software.schmorp.de/pkg/EV>.	4365	L<http://software.schmorp.de/pkg/EV>.
2955		4366
2956	=item Python	4367	=item Python
2957		4368
2958	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	4369	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2959	seems to be quite complete and well-documented. Note, however, that the	4370	seems to be quite complete and well-documented.
2960	patch they require for libev is outright dangerous as it breaks the ABI
2961	for everybody else, and therefore, should never be applied in an installed
2962	libev (if python requires an incompatible ABI then it needs to embed
2963	libev).
2964		4371
2965	=item Ruby	4372	=item Ruby
2966		4373
2967	Tony Arcieri has written a ruby extension that offers access to a subset	4374	Tony Arcieri has written a ruby extension that offers access to a subset
2968	of the libev API and adds file handle abstractions, asynchronous DNS and	4375	of the libev API and adds file handle abstractions, asynchronous DNS and
2969	more on top of it. It can be found via gem servers. Its homepage is at	4376	more on top of it. It can be found via gem servers. Its homepage is at
2970	L<http://rev.rubyforge.org/>.	4377	L<http://rev.rubyforge.org/>.
2971		4378
		4379	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4380	makes rev work even on mingw.
		4381
		4382	=item Haskell
		4383
		4384	A haskell binding to libev is available at
		4385	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4386
2972	=item D	4387	=item D
2973		4388
2974	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4389	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2975	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4390	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
2976		4391
2977	=item Ocaml	4392	=item Ocaml
2978		4393
2979	Erkki Seppala has written Ocaml bindings for libev, to be found at	4394	Erkki Seppala has written Ocaml bindings for libev, to be found at
2980	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4395	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4396
		4397	=item Lua
		4398
		4399	Brian Maher has written a partial interface to libev for lua (at the
		4400	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4401	L<http://github.com/brimworks/lua-ev>.
		4402
		4403	=item Javascript
		4404
		4405	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4406
		4407	=item Others
		4408
		4409	There are others, and I stopped counting.
2981		4410
2982	=back	4411	=back
2983		4412
2984		4413
2985	=head1 MACRO MAGIC	4414	=head1 MACRO MAGIC
…		…
2999	loop argument"). The C<EV_A> form is used when this is the sole argument,	4428	loop argument"). The C<EV_A> form is used when this is the sole argument,
3000	C<EV_A_> is used when other arguments are following. Example:	4429	C<EV_A_> is used when other arguments are following. Example:
3001		4430
3002	ev_unref (EV_A);	4431	ev_unref (EV_A);
3003	ev_timer_add (EV_A_ watcher);	4432	ev_timer_add (EV_A_ watcher);
3004	ev_loop (EV_A_ 0);	4433	ev_run (EV_A_ 0);
3005		4434
3006	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4435	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
3007	which is often provided by the following macro.	4436	which is often provided by the following macro.
3008		4437
3009	=item C<EV_P>, C<EV_P_>	4438	=item C<EV_P>, C<EV_P_>
…		…
3022	suitable for use with C<EV_A>.	4451	suitable for use with C<EV_A>.
3023		4452
3024	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4453	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3025		4454
3026	Similar to the other two macros, this gives you the value of the default	4455	Similar to the other two macros, this gives you the value of the default
3027	loop, if multiple loops are supported ("ev loop default").	4456	loop, if multiple loops are supported ("ev loop default"). The default loop
		4457	will be initialised if it isn't already initialised.
		4458
		4459	For non-multiplicity builds, these macros do nothing, so you always have
		4460	to initialise the loop somewhere.
3028		4461
3029	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4462	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3030		4463
3031	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4464	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3032	default loop has been initialised (C<UC> == unchecked). Their behaviour	4465	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3049	}	4482	}
3050		4483
3051	ev_check check;	4484	ev_check check;
3052	ev_check_init (&check, check_cb);	4485	ev_check_init (&check, check_cb);
3053	ev_check_start (EV_DEFAULT_ &check);	4486	ev_check_start (EV_DEFAULT_ &check);
3054	ev_loop (EV_DEFAULT_ 0);	4487	ev_run (EV_DEFAULT_ 0);
3055		4488
3056	=head1 EMBEDDING	4489	=head1 EMBEDDING
3057		4490
3058	Libev can (and often is) directly embedded into host	4491	Libev can (and often is) directly embedded into host
3059	applications. Examples of applications that embed it include the Deliantra	4492	applications. Examples of applications that embed it include the Deliantra
…		…
3086		4519
3087	#define EV_STANDALONE 1	4520	#define EV_STANDALONE 1
3088	#include "ev.h"	4521	#include "ev.h"
3089		4522
3090	Both header files and implementation files can be compiled with a C++	4523	Both header files and implementation files can be compiled with a C++
3091	compiler (at least, thats a stated goal, and breakage will be treated	4524	compiler (at least, that's a stated goal, and breakage will be treated
3092	as a bug).	4525	as a bug).
3093		4526
3094	You need the following files in your source tree, or in a directory	4527	You need the following files in your source tree, or in a directory
3095	in your include path (e.g. in libev/ when using -Ilibev):	4528	in your include path (e.g. in libev/ when using -Ilibev):
3096		4529
…		…
3099	ev_vars.h	4532	ev_vars.h
3100	ev_wrap.h	4533	ev_wrap.h
3101		4534
3102	ev_win32.c required on win32 platforms only	4535	ev_win32.c required on win32 platforms only
3103		4536
3104	ev_select.c only when select backend is enabled (which is enabled by default)	4537	ev_select.c only when select backend is enabled
3105	ev_poll.c only when poll backend is enabled (disabled by default)	4538	ev_poll.c only when poll backend is enabled
3106	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4539	ev_epoll.c only when the epoll backend is enabled
		4540	ev_linuxaio.c only when the linux aio backend is enabled
		4541	ev_iouring.c only when the linux io_uring backend is enabled
3107	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4542	ev_kqueue.c only when the kqueue backend is enabled
3108	ev_port.c only when the solaris port backend is enabled (disabled by default)	4543	ev_port.c only when the solaris port backend is enabled
3109		4544
3110	F<ev.c> includes the backend files directly when enabled, so you only need	4545	F<ev.c> includes the backend files directly when enabled, so you only need
3111	to compile this single file.	4546	to compile this single file.
3112		4547
3113	=head3 LIBEVENT COMPATIBILITY API	4548	=head3 LIBEVENT COMPATIBILITY API
…		…
3139	libev.m4	4574	libev.m4
3140		4575
3141	=head2 PREPROCESSOR SYMBOLS/MACROS	4576	=head2 PREPROCESSOR SYMBOLS/MACROS
3142		4577
3143	Libev can be configured via a variety of preprocessor symbols you have to	4578	Libev can be configured via a variety of preprocessor symbols you have to
3144	define before including any of its files. The default in the absence of	4579	define before including (or compiling) any of its files. The default in
3145	autoconf is documented for every option.	4580	the absence of autoconf is documented for every option.
		4581
		4582	Symbols marked with "(h)" do not change the ABI, and can have different
		4583	values when compiling libev vs. including F<ev.h>, so it is permissible
		4584	to redefine them before including F<ev.h> without breaking compatibility
		4585	to a compiled library. All other symbols change the ABI, which means all
		4586	users of libev and the libev code itself must be compiled with compatible
		4587	settings.
3146		4588
3147	=over 4	4589	=over 4
3148		4590
		4591	=item EV_COMPAT3 (h)
		4592
		4593	Backwards compatibility is a major concern for libev. This is why this
		4594	release of libev comes with wrappers for the functions and symbols that
		4595	have been renamed between libev version 3 and 4.
		4596
		4597	You can disable these wrappers (to test compatibility with future
		4598	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4599	sources. This has the additional advantage that you can drop the C<struct>
		4600	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4601	typedef in that case.
		4602
		4603	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4604	and in some even more future version the compatibility code will be
		4605	removed completely.
		4606
3149	=item EV_STANDALONE	4607	=item EV_STANDALONE (h)
3150		4608
3151	Must always be C<1> if you do not use autoconf configuration, which	4609	Must always be C<1> if you do not use autoconf configuration, which
3152	keeps libev from including F<config.h>, and it also defines dummy	4610	keeps libev from including F<config.h>, and it also defines dummy
3153	implementations for some libevent functions (such as logging, which is not	4611	implementations for some libevent functions (such as logging, which is not
3154	supported). It will also not define any of the structs usually found in	4612	supported). It will also not define any of the structs usually found in
3155	F<event.h> that are not directly supported by the libev core alone.	4613	F<event.h> that are not directly supported by the libev core alone.
3156		4614
		4615	In standalone mode, libev will still try to automatically deduce the
		4616	configuration, but has to be more conservative.
		4617
		4618	=item EV_USE_FLOOR
		4619
		4620	If defined to be C<1>, libev will use the C<floor ()> function for its
		4621	periodic reschedule calculations, otherwise libev will fall back on a
		4622	portable (slower) implementation. If you enable this, you usually have to
		4623	link against libm or something equivalent. Enabling this when the C<floor>
		4624	function is not available will fail, so the safe default is to not enable
		4625	this.
		4626
3157	=item EV_USE_MONOTONIC	4627	=item EV_USE_MONOTONIC
3158		4628
3159	If defined to be C<1>, libev will try to detect the availability of the	4629	If defined to be C<1>, libev will try to detect the availability of the
3160	monotonic clock option at both compile time and runtime. Otherwise no use	4630	monotonic clock option at both compile time and runtime. Otherwise no
3161	of the monotonic clock option will be attempted. If you enable this, you	4631	use of the monotonic clock option will be attempted. If you enable this,
3162	usually have to link against librt or something similar. Enabling it when	4632	you usually have to link against librt or something similar. Enabling it
3163	the functionality isn't available is safe, though, although you have	4633	when the functionality isn't available is safe, though, although you have
3164	to make sure you link against any libraries where the C<clock_gettime>	4634	to make sure you link against any libraries where the C<clock_gettime>
3165	function is hiding in (often F<-lrt>).	4635	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
3166		4636
3167	=item EV_USE_REALTIME	4637	=item EV_USE_REALTIME
3168		4638
3169	If defined to be C<1>, libev will try to detect the availability of the	4639	If defined to be C<1>, libev will try to detect the availability of the
3170	real-time clock option at compile time (and assume its availability at	4640	real-time clock option at compile time (and assume its availability
3171	runtime if successful). Otherwise no use of the real-time clock option will	4641	at runtime if successful). Otherwise no use of the real-time clock
3172	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4642	option will be attempted. This effectively replaces C<gettimeofday>
3173	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4643	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
3174	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4644	correctness. See the note about libraries in the description of
		4645	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4646	C<EV_USE_CLOCK_SYSCALL>.
		4647
		4648	=item EV_USE_CLOCK_SYSCALL
		4649
		4650	If defined to be C<1>, libev will try to use a direct syscall instead
		4651	of calling the system-provided C<clock_gettime> function. This option
		4652	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4653	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4654	programs needlessly. Using a direct syscall is slightly slower (in
		4655	theory), because no optimised vdso implementation can be used, but avoids
		4656	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4657	higher, as it simplifies linking (no need for C<-lrt>).
3175		4658
3176	=item EV_USE_NANOSLEEP	4659	=item EV_USE_NANOSLEEP
3177		4660
3178	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4661	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
3179	and will use it for delays. Otherwise it will use C<select ()>.	4662	and will use it for delays. Otherwise it will use C<select ()>.
…		…
3184	available and will probe for kernel support at runtime. This will improve	4667	available and will probe for kernel support at runtime. This will improve
3185	C<ev_signal> and C<ev_async> performance and reduce resource consumption.	4668	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
3186	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc	4669	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
3187	2.7 or newer, otherwise disabled.	4670	2.7 or newer, otherwise disabled.
3188		4671
		4672	=item EV_USE_SIGNALFD
		4673
		4674	If defined to be C<1>, then libev will assume that C<signalfd ()> is
		4675	available and will probe for kernel support at runtime. This enables
		4676	the use of EVFLAG_SIGNALFD for faster and simpler signal handling. If
		4677	undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4678	2.7 or newer, otherwise disabled.
		4679
		4680	=item EV_USE_TIMERFD
		4681
		4682	If defined to be C<1>, then libev will assume that C<timerfd ()> is
		4683	available and will probe for kernel support at runtime. This allows
		4684	libev to detect time jumps accurately. If undefined, it will be enabled
		4685	if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
		4686	C<TFD_TIMER_CANCEL_ON_SET>, otherwise disabled.
		4687
		4688	=item EV_USE_EVENTFD
		4689
		4690	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4691	available and will probe for kernel support at runtime. This will improve
		4692	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4693	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4694	2.7 or newer, otherwise disabled.
		4695
3189	=item EV_USE_SELECT	4696	=item EV_USE_SELECT
3190		4697
3191	If undefined or defined to be C<1>, libev will compile in support for the	4698	If undefined or defined to be C<1>, libev will compile in support for the
3192	C<select>(2) backend. No attempt at auto-detection will be done: if no	4699	C<select>(2) backend. No attempt at auto-detection will be done: if no
3193	other method takes over, select will be it. Otherwise the select backend	4700	other method takes over, select will be it. Otherwise the select backend
…		…
3195		4702
3196	=item EV_SELECT_USE_FD_SET	4703	=item EV_SELECT_USE_FD_SET
3197		4704
3198	If defined to C<1>, then the select backend will use the system C<fd_set>	4705	If defined to C<1>, then the select backend will use the system C<fd_set>
3199	structure. This is useful if libev doesn't compile due to a missing	4706	structure. This is useful if libev doesn't compile due to a missing
3200	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	4707	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
3201	exotic systems. This usually limits the range of file descriptors to some	4708	on exotic systems. This usually limits the range of file descriptors to
3202	low limit such as 1024 or might have other limitations (winsocket only	4709	some low limit such as 1024 or might have other limitations (winsocket
3203	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4710	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
3204	influence the size of the C<fd_set> used.	4711	configures the maximum size of the C<fd_set>.
3205		4712
3206	=item EV_SELECT_IS_WINSOCKET	4713	=item EV_SELECT_IS_WINSOCKET
3207		4714
3208	When defined to C<1>, the select backend will assume that	4715	When defined to C<1>, the select backend will assume that
3209	select/socket/connect etc. don't understand file descriptors but	4716	select/socket/connect etc. don't understand file descriptors but
…		…
3211	be used is the winsock select). This means that it will call	4718	be used is the winsock select). This means that it will call
3212	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4719	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
3213	it is assumed that all these functions actually work on fds, even	4720	it is assumed that all these functions actually work on fds, even
3214	on win32. Should not be defined on non-win32 platforms.	4721	on win32. Should not be defined on non-win32 platforms.
3215		4722
3216	=item EV_FD_TO_WIN32_HANDLE	4723	=item EV_FD_TO_WIN32_HANDLE(fd)
3217		4724
3218	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4725	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
3219	file descriptors to socket handles. When not defining this symbol (the	4726	file descriptors to socket handles. When not defining this symbol (the
3220	default), then libev will call C<_get_osfhandle>, which is usually	4727	default), then libev will call C<_get_osfhandle>, which is usually
3221	correct. In some cases, programs use their own file descriptor management,	4728	correct. In some cases, programs use their own file descriptor management,
3222	in which case they can provide this function to map fds to socket handles.	4729	in which case they can provide this function to map fds to socket handles.
3223		4730
		4731	=item EV_WIN32_HANDLE_TO_FD(handle)
		4732
		4733	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4734	using the standard C<_open_osfhandle> function. For programs implementing
		4735	their own fd to handle mapping, overwriting this function makes it easier
		4736	to do so. This can be done by defining this macro to an appropriate value.
		4737
		4738	=item EV_WIN32_CLOSE_FD(fd)
		4739
		4740	If programs implement their own fd to handle mapping on win32, then this
		4741	macro can be used to override the C<close> function, useful to unregister
		4742	file descriptors again. Note that the replacement function has to close
		4743	the underlying OS handle.
		4744
		4745	=item EV_USE_WSASOCKET
		4746
		4747	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4748	communication socket, which works better in some environments. Otherwise,
		4749	the normal C<socket> function will be used, which works better in other
		4750	environments.
		4751
3224	=item EV_USE_POLL	4752	=item EV_USE_POLL
3225		4753
3226	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4754	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3227	backend. Otherwise it will be enabled on non-win32 platforms. It	4755	backend. Otherwise it will be enabled on non-win32 platforms. It
3228	takes precedence over select.	4756	takes precedence over select.
…		…
3232	If defined to be C<1>, libev will compile in support for the Linux	4760	If defined to be C<1>, libev will compile in support for the Linux
3233	C<epoll>(7) backend. Its availability will be detected at runtime,	4761	C<epoll>(7) backend. Its availability will be detected at runtime,
3234	otherwise another method will be used as fallback. This is the preferred	4762	otherwise another method will be used as fallback. This is the preferred
3235	backend for GNU/Linux systems. If undefined, it will be enabled if the	4763	backend for GNU/Linux systems. If undefined, it will be enabled if the
3236	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4764	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4765
		4766	=item EV_USE_LINUXAIO
		4767
		4768	If defined to be C<1>, libev will compile in support for the Linux aio
		4769	backend (C<EV_USE_EPOLL> must also be enabled). If undefined, it will be
		4770	enabled on linux, otherwise disabled.
		4771
		4772	=item EV_USE_IOURING
		4773
		4774	If defined to be C<1>, libev will compile in support for the Linux
		4775	io_uring backend (C<EV_USE_EPOLL> must also be enabled). Due to it's
		4776	current limitations it has to be requested explicitly. If undefined, it
		4777	will be enabled on linux, otherwise disabled.
3237		4778
3238	=item EV_USE_KQUEUE	4779	=item EV_USE_KQUEUE
3239		4780
3240	If defined to be C<1>, libev will compile in support for the BSD style	4781	If defined to be C<1>, libev will compile in support for the BSD style
3241	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4782	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
3263	If defined to be C<1>, libev will compile in support for the Linux inotify	4804	If defined to be C<1>, libev will compile in support for the Linux inotify
3264	interface to speed up C<ev_stat> watchers. Its actual availability will	4805	interface to speed up C<ev_stat> watchers. Its actual availability will
3265	be detected at runtime. If undefined, it will be enabled if the headers	4806	be detected at runtime. If undefined, it will be enabled if the headers
3266	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4807	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3267		4808
		4809	=item EV_NO_SMP
		4810
		4811	If defined to be C<1>, libev will assume that memory is always coherent
		4812	between threads, that is, threads can be used, but threads never run on
		4813	different cpus (or different cpu cores). This reduces dependencies
		4814	and makes libev faster.
		4815
		4816	=item EV_NO_THREADS
		4817
		4818	If defined to be C<1>, libev will assume that it will never be called from
		4819	different threads (that includes signal handlers), which is a stronger
		4820	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4821	libev faster.
		4822
3268	=item EV_ATOMIC_T	4823	=item EV_ATOMIC_T
3269		4824
3270	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4825	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3271	access is atomic with respect to other threads or signal contexts. No such	4826	access is atomic with respect to other threads or signal contexts. No
3272	type is easily found in the C language, so you can provide your own type	4827	such type is easily found in the C language, so you can provide your own
3273	that you know is safe for your purposes. It is used both for signal handler "locking"	4828	type that you know is safe for your purposes. It is used both for signal
3274	as well as for signal and thread safety in C<ev_async> watchers.	4829	handler "locking" as well as for signal and thread safety in C<ev_async>
		4830	watchers.
3275		4831
3276	In the absence of this define, libev will use C<sig_atomic_t volatile>	4832	In the absence of this define, libev will use C<sig_atomic_t volatile>
3277	(from F<signal.h>), which is usually good enough on most platforms.	4833	(from F<signal.h>), which is usually good enough on most platforms.
3278		4834
3279	=item EV_H	4835	=item EV_H (h)
3280		4836
3281	The name of the F<ev.h> header file used to include it. The default if	4837	The name of the F<ev.h> header file used to include it. The default if
3282	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4838	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
3283	used to virtually rename the F<ev.h> header file in case of conflicts.	4839	used to virtually rename the F<ev.h> header file in case of conflicts.
3284		4840
3285	=item EV_CONFIG_H	4841	=item EV_CONFIG_H (h)
3286		4842
3287	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4843	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
3288	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4844	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
3289	C<EV_H>, above.	4845	C<EV_H>, above.
3290		4846
3291	=item EV_EVENT_H	4847	=item EV_EVENT_H (h)
3292		4848
3293	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4849	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
3294	of how the F<event.h> header can be found, the default is C<"event.h">.	4850	of how the F<event.h> header can be found, the default is C<"event.h">.
3295		4851
3296	=item EV_PROTOTYPES	4852	=item EV_PROTOTYPES (h)
3297		4853
3298	If defined to be C<0>, then F<ev.h> will not define any function	4854	If defined to be C<0>, then F<ev.h> will not define any function
3299	prototypes, but still define all the structs and other symbols. This is	4855	prototypes, but still define all the structs and other symbols. This is
3300	occasionally useful if you want to provide your own wrapper functions	4856	occasionally useful if you want to provide your own wrapper functions
3301	around libev functions.	4857	around libev functions.
…		…
3306	will have the C<struct ev_loop *> as first argument, and you can create	4862	will have the C<struct ev_loop *> as first argument, and you can create
3307	additional independent event loops. Otherwise there will be no support	4863	additional independent event loops. Otherwise there will be no support
3308	for multiple event loops and there is no first event loop pointer	4864	for multiple event loops and there is no first event loop pointer
3309	argument. Instead, all functions act on the single default loop.	4865	argument. Instead, all functions act on the single default loop.
3310		4866
		4867	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4868	default loop when multiplicity is switched off - you always have to
		4869	initialise the loop manually in this case.
		4870
3311	=item EV_MINPRI	4871	=item EV_MINPRI
3312		4872
3313	=item EV_MAXPRI	4873	=item EV_MAXPRI
3314		4874
3315	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4875	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
3323	fine.	4883	fine.
3324		4884
3325	If your embedding application does not need any priorities, defining these	4885	If your embedding application does not need any priorities, defining these
3326	both to C<0> will save some memory and CPU.	4886	both to C<0> will save some memory and CPU.
3327		4887
3328	=item EV_PERIODIC_ENABLE	4888	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4889	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4890	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
3329		4891
3330	If undefined or defined to be C<1>, then periodic timers are supported. If	4892	If undefined or defined to be C<1> (and the platform supports it), then
3331	defined to be C<0>, then they are not. Disabling them saves a few kB of	4893	the respective watcher type is supported. If defined to be C<0>, then it
3332	code.	4894	is not. Disabling watcher types mainly saves code size.
3333		4895
3334	=item EV_IDLE_ENABLE	4896	=item EV_FEATURES
3335
3336	If undefined or defined to be C<1>, then idle watchers are supported. If
3337	defined to be C<0>, then they are not. Disabling them saves a few kB of
3338	code.
3339
3340	=item EV_EMBED_ENABLE
3341
3342	If undefined or defined to be C<1>, then embed watchers are supported. If
3343	defined to be C<0>, then they are not. Embed watchers rely on most other
3344	watcher types, which therefore must not be disabled.
3345
3346	=item EV_STAT_ENABLE
3347
3348	If undefined or defined to be C<1>, then stat watchers are supported. If
3349	defined to be C<0>, then they are not.
3350
3351	=item EV_FORK_ENABLE
3352
3353	If undefined or defined to be C<1>, then fork watchers are supported. If
3354	defined to be C<0>, then they are not.
3355
3356	=item EV_ASYNC_ENABLE
3357
3358	If undefined or defined to be C<1>, then async watchers are supported. If
3359	defined to be C<0>, then they are not.
3360
3361	=item EV_MINIMAL
3362		4897
3363	If you need to shave off some kilobytes of code at the expense of some	4898	If you need to shave off some kilobytes of code at the expense of some
3364	speed, define this symbol to C<1>. Currently this is used to override some	4899	speed (but with the full API), you can define this symbol to request
3365	inlining decisions, saves roughly 30% code size on amd64. It also selects a	4900	certain subsets of functionality. The default is to enable all features
3366	much smaller 2-heap for timer management over the default 4-heap.	4901	that can be enabled on the platform.
		4902
		4903	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4904	with some broad features you want) and then selectively re-enable
		4905	additional parts you want, for example if you want everything minimal,
		4906	but multiple event loop support, async and child watchers and the poll
		4907	backend, use this:
		4908
		4909	#define EV_FEATURES 0
		4910	#define EV_MULTIPLICITY 1
		4911	#define EV_USE_POLL 1
		4912	#define EV_CHILD_ENABLE 1
		4913	#define EV_ASYNC_ENABLE 1
		4914
		4915	The actual value is a bitset, it can be a combination of the following
		4916	values (by default, all of these are enabled):
		4917
		4918	=over 4
		4919
		4920	=item C<1> - faster/larger code
		4921
		4922	Use larger code to speed up some operations.
		4923
		4924	Currently this is used to override some inlining decisions (enlarging the
		4925	code size by roughly 30% on amd64).
		4926
		4927	When optimising for size, use of compiler flags such as C<-Os> with
		4928	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4929	assertions.
		4930
		4931	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4932	(e.g. gcc with C<-Os>).
		4933
		4934	=item C<2> - faster/larger data structures
		4935
		4936	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4937	hash table sizes and so on. This will usually further increase code size
		4938	and can additionally have an effect on the size of data structures at
		4939	runtime.
		4940
		4941	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4942	(e.g. gcc with C<-Os>).
		4943
		4944	=item C<4> - full API configuration
		4945
		4946	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4947	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4948
		4949	=item C<8> - full API
		4950
		4951	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4952	details on which parts of the API are still available without this
		4953	feature, and do not complain if this subset changes over time.
		4954
		4955	=item C<16> - enable all optional watcher types
		4956
		4957	Enables all optional watcher types. If you want to selectively enable
		4958	only some watcher types other than I/O and timers (e.g. prepare,
		4959	embed, async, child...) you can enable them manually by defining
		4960	C<EV_watchertype_ENABLE> to C<1> instead.
		4961
		4962	=item C<32> - enable all backends
		4963
		4964	This enables all backends - without this feature, you need to enable at
		4965	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4966
		4967	=item C<64> - enable OS-specific "helper" APIs
		4968
		4969	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4970	default.
		4971
		4972	=back
		4973
		4974	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4975	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4976	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4977	watchers, timers and monotonic clock support.
		4978
		4979	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4980	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4981	your program might be left out as well - a binary starting a timer and an
		4982	I/O watcher then might come out at only 5Kb.
		4983
		4984	=item EV_API_STATIC
		4985
		4986	If this symbol is defined (by default it is not), then all identifiers
		4987	will have static linkage. This means that libev will not export any
		4988	identifiers, and you cannot link against libev anymore. This can be useful
		4989	when you embed libev, only want to use libev functions in a single file,
		4990	and do not want its identifiers to be visible.
		4991
		4992	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4993	wants to use libev.
		4994
		4995	This option only works when libev is compiled with a C compiler, as C++
		4996	doesn't support the required declaration syntax.
		4997
		4998	=item EV_AVOID_STDIO
		4999
		5000	If this is set to C<1> at compiletime, then libev will avoid using stdio
		5001	functions (printf, scanf, perror etc.). This will increase the code size
		5002	somewhat, but if your program doesn't otherwise depend on stdio and your
		5003	libc allows it, this avoids linking in the stdio library which is quite
		5004	big.
		5005
		5006	Note that error messages might become less precise when this option is
		5007	enabled.
		5008
		5009	=item EV_NSIG
		5010
		5011	The highest supported signal number, +1 (or, the number of
		5012	signals): Normally, libev tries to deduce the maximum number of signals
		5013	automatically, but sometimes this fails, in which case it can be
		5014	specified. Also, using a lower number than detected (C<32> should be
		5015	good for about any system in existence) can save some memory, as libev
		5016	statically allocates some 12-24 bytes per signal number.
3367		5017
3368	=item EV_PID_HASHSIZE	5018	=item EV_PID_HASHSIZE
3369		5019
3370	C<ev_child> watchers use a small hash table to distribute workload by	5020	C<ev_child> watchers use a small hash table to distribute workload by
3371	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	5021	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
3372	than enough. If you need to manage thousands of children you might want to	5022	usually more than enough. If you need to manage thousands of children you
3373	increase this value (I<must> be a power of two).	5023	might want to increase this value (I<must> be a power of two).
3374		5024
3375	=item EV_INOTIFY_HASHSIZE	5025	=item EV_INOTIFY_HASHSIZE
3376		5026
3377	C<ev_stat> watchers use a small hash table to distribute workload by	5027	C<ev_stat> watchers use a small hash table to distribute workload by
3378	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	5028	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
3379	usually more than enough. If you need to manage thousands of C<ev_stat>	5029	disabled), usually more than enough. If you need to manage thousands of
3380	watchers you might want to increase this value (I<must> be a power of	5030	C<ev_stat> watchers you might want to increase this value (I<must> be a
3381	two).	5031	power of two).
3382		5032
3383	=item EV_USE_4HEAP	5033	=item EV_USE_4HEAP
3384		5034
3385	Heaps are not very cache-efficient. To improve the cache-efficiency of the	5035	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3386	timer and periodics heaps, libev uses a 4-heap when this symbol is defined	5036	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3387	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably	5037	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3388	faster performance with many (thousands) of watchers.	5038	faster performance with many (thousands) of watchers.
3389		5039
3390	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	5040	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3391	(disabled).	5041	will be C<0>.
3392		5042
3393	=item EV_HEAP_CACHE_AT	5043	=item EV_HEAP_CACHE_AT
3394		5044
3395	Heaps are not very cache-efficient. To improve the cache-efficiency of the	5045	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3396	timer and periodics heaps, libev can cache the timestamp (I<at>) within	5046	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3397	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	5047	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3398	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	5048	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3399	but avoids random read accesses on heap changes. This improves performance	5049	but avoids random read accesses on heap changes. This improves performance
3400	noticeably with many (hundreds) of watchers.	5050	noticeably with many (hundreds) of watchers.
3401		5051
3402	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	5052	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3403	(disabled).	5053	will be C<0>.
3404		5054
3405	=item EV_VERIFY	5055	=item EV_VERIFY
3406		5056
3407	Controls how much internal verification (see C<ev_loop_verify ()>) will	5057	Controls how much internal verification (see C<ev_verify ()>) will
3408	be done: If set to C<0>, no internal verification code will be compiled	5058	be done: If set to C<0>, no internal verification code will be compiled
3409	in. If set to C<1>, then verification code will be compiled in, but not	5059	in. If set to C<1>, then verification code will be compiled in, but not
3410	called. If set to C<2>, then the internal verification code will be	5060	called. If set to C<2>, then the internal verification code will be
3411	called once per loop, which can slow down libev. If set to C<3>, then the	5061	called once per loop, which can slow down libev. If set to C<3>, then the
3412	verification code will be called very frequently, which will slow down	5062	verification code will be called very frequently, which will slow down
3413	libev considerably.	5063	libev considerably.
3414		5064
		5065	Verification errors are reported via C's C<assert> mechanism, so if you
		5066	disable that (e.g. by defining C<NDEBUG>) then no errors will be reported.
		5067
3415	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	5068	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3416	C<0>.	5069	will be C<0>.
3417		5070
3418	=item EV_COMMON	5071	=item EV_COMMON
3419		5072
3420	By default, all watchers have a C<void *data> member. By redefining	5073	By default, all watchers have a C<void *data> member. By redefining
3421	this macro to a something else you can include more and other types of	5074	this macro to something else you can include more and other types of
3422	members. You have to define it each time you include one of the files,	5075	members. You have to define it each time you include one of the files,
3423	though, and it must be identical each time.	5076	though, and it must be identical each time.
3424		5077
3425	For example, the perl EV module uses something like this:	5078	For example, the perl EV module uses something like this:
3426		5079
…		…
3479	file.	5132	file.
3480		5133
3481	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	5134	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
3482	that everybody includes and which overrides some configure choices:	5135	that everybody includes and which overrides some configure choices:
3483		5136
3484	#define EV_MINIMAL 1	5137	#define EV_FEATURES 8
3485	#define EV_USE_POLL 0	5138	#define EV_USE_SELECT 1
3486	#define EV_MULTIPLICITY 0
3487	#define EV_PERIODIC_ENABLE 0	5139	#define EV_PREPARE_ENABLE 1
		5140	#define EV_IDLE_ENABLE 1
3488	#define EV_STAT_ENABLE 0	5141	#define EV_SIGNAL_ENABLE 1
3489	#define EV_FORK_ENABLE 0	5142	#define EV_CHILD_ENABLE 1
		5143	#define EV_USE_STDEXCEPT 0
3490	#define EV_CONFIG_H <config.h>	5144	#define EV_CONFIG_H <config.h>
3491	#define EV_MINPRI 0
3492	#define EV_MAXPRI 0
3493		5145
3494	#include "ev++.h"	5146	#include "ev++.h"
3495		5147
3496	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5148	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3497		5149
3498	#include "ev_cpp.h"	5150	#include "ev_cpp.h"
3499	#include "ev.c"	5151	#include "ev.c"
3500		5152
3501	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5153	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
3502		5154
3503	=head2 THREADS AND COROUTINES	5155	=head2 THREADS AND COROUTINES
3504		5156
3505	=head3 THREADS	5157	=head3 THREADS
3506		5158
…		…
3557	default loop and triggering an C<ev_async> watcher from the default loop	5209	default loop and triggering an C<ev_async> watcher from the default loop
3558	watcher callback into the event loop interested in the signal.	5210	watcher callback into the event loop interested in the signal.
3559		5211
3560	=back	5212	=back
3561		5213
		5214	See also L</THREAD LOCKING EXAMPLE>.
		5215
3562	=head3 COROUTINES	5216	=head3 COROUTINES
3563		5217
3564	Libev is very accommodating to coroutines ("cooperative threads"):	5218	Libev is very accommodating to coroutines ("cooperative threads"):
3565	libev fully supports nesting calls to its functions from different	5219	libev fully supports nesting calls to its functions from different
3566	coroutines (e.g. you can call C<ev_loop> on the same loop from two	5220	coroutines (e.g. you can call C<ev_run> on the same loop from two
3567	different coroutines, and switch freely between both coroutines running the	5221	different coroutines, and switch freely between both coroutines running
3568	loop, as long as you don't confuse yourself). The only exception is that	5222	the loop, as long as you don't confuse yourself). The only exception is
3569	you must not do this from C<ev_periodic> reschedule callbacks.	5223	that you must not do this from C<ev_periodic> reschedule callbacks.
3570		5224
3571	Care has been taken to ensure that libev does not keep local state inside	5225	Care has been taken to ensure that libev does not keep local state inside
3572	C<ev_loop>, and other calls do not usually allow for coroutine switches as	5226	C<ev_run>, and other calls do not usually allow for coroutine switches as
3573	they do not clal any callbacks.	5227	they do not call any callbacks.
3574		5228
3575	=head2 COMPILER WARNINGS	5229	=head2 COMPILER WARNINGS
3576		5230
3577	Depending on your compiler and compiler settings, you might get no or a	5231	Depending on your compiler and compiler settings, you might get no or a
3578	lot of warnings when compiling libev code. Some people are apparently	5232	lot of warnings when compiling libev code. Some people are apparently
…		…
3588	maintainable.	5242	maintainable.
3589		5243
3590	And of course, some compiler warnings are just plain stupid, or simply	5244	And of course, some compiler warnings are just plain stupid, or simply
3591	wrong (because they don't actually warn about the condition their message	5245	wrong (because they don't actually warn about the condition their message
3592	seems to warn about). For example, certain older gcc versions had some	5246	seems to warn about). For example, certain older gcc versions had some
3593	warnings that resulted an extreme number of false positives. These have	5247	warnings that resulted in an extreme number of false positives. These have
3594	been fixed, but some people still insist on making code warn-free with	5248	been fixed, but some people still insist on making code warn-free with
3595	such buggy versions.	5249	such buggy versions.
3596		5250
3597	While libev is written to generate as few warnings as possible,	5251	While libev is written to generate as few warnings as possible,
3598	"warn-free" code is not a goal, and it is recommended not to build libev	5252	"warn-free" code is not a goal, and it is recommended not to build libev
…		…
3612	==2274== definitely lost: 0 bytes in 0 blocks.	5266	==2274== definitely lost: 0 bytes in 0 blocks.
3613	==2274== possibly lost: 0 bytes in 0 blocks.	5267	==2274== possibly lost: 0 bytes in 0 blocks.
3614	==2274== still reachable: 256 bytes in 1 blocks.	5268	==2274== still reachable: 256 bytes in 1 blocks.
3615		5269
3616	Then there is no memory leak, just as memory accounted to global variables	5270	Then there is no memory leak, just as memory accounted to global variables
3617	is not a memleak - the memory is still being refernced, and didn't leak.	5271	is not a memleak - the memory is still being referenced, and didn't leak.
3618		5272
3619	Similarly, under some circumstances, valgrind might report kernel bugs	5273	Similarly, under some circumstances, valgrind might report kernel bugs
3620	as if it were a bug in libev (e.g. in realloc or in the poll backend,	5274	as if it were a bug in libev (e.g. in realloc or in the poll backend,
3621	although an acceptable workaround has been found here), or it might be	5275	although an acceptable workaround has been found here), or it might be
3622	confused.	5276	confused.
…		…
3634	I suggest using suppression lists.	5288	I suggest using suppression lists.
3635		5289
3636		5290
3637	=head1 PORTABILITY NOTES	5291	=head1 PORTABILITY NOTES
3638		5292
		5293	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5294
		5295	GNU/Linux is the only common platform that supports 64 bit file/large file
		5296	interfaces but I<disables> them by default.
		5297
		5298	That means that libev compiled in the default environment doesn't support
		5299	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5300
		5301	Unfortunately, many programs try to work around this GNU/Linux issue
		5302	by enabling the large file API, which makes them incompatible with the
		5303	standard libev compiled for their system.
		5304
		5305	Likewise, libev cannot enable the large file API itself as this would
		5306	suddenly make it incompatible to the default compile time environment,
		5307	i.e. all programs not using special compile switches.
		5308
		5309	=head2 OS/X AND DARWIN BUGS
		5310
		5311	The whole thing is a bug if you ask me - basically any system interface
		5312	you touch is broken, whether it is locales, poll, kqueue or even the
		5313	OpenGL drivers.
		5314
		5315	=head3 C<kqueue> is buggy
		5316
		5317	The kqueue syscall is broken in all known versions - most versions support
		5318	only sockets, many support pipes.
		5319
		5320	Libev tries to work around this by not using C<kqueue> by default on this
		5321	rotten platform, but of course you can still ask for it when creating a
		5322	loop - embedding a socket-only kqueue loop into a select-based one is
		5323	probably going to work well.
		5324
		5325	=head3 C<poll> is buggy
		5326
		5327	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5328	implementation by something calling C<kqueue> internally around the 10.5.6
		5329	release, so now C<kqueue> I<and> C<poll> are broken.
		5330
		5331	Libev tries to work around this by not using C<poll> by default on
		5332	this rotten platform, but of course you can still ask for it when creating
		5333	a loop.
		5334
		5335	=head3 C<select> is buggy
		5336
		5337	All that's left is C<select>, and of course Apple found a way to fuck this
		5338	one up as well: On OS/X, C<select> actively limits the number of file
		5339	descriptors you can pass in to 1024 - your program suddenly crashes when
		5340	you use more.
		5341
		5342	There is an undocumented "workaround" for this - defining
		5343	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5344	work on OS/X.
		5345
		5346	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5347
		5348	=head3 C<errno> reentrancy
		5349
		5350	The default compile environment on Solaris is unfortunately so
		5351	thread-unsafe that you can't even use components/libraries compiled
		5352	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5353	defined by default. A valid, if stupid, implementation choice.
		5354
		5355	If you want to use libev in threaded environments you have to make sure
		5356	it's compiled with C<_REENTRANT> defined.
		5357
		5358	=head3 Event port backend
		5359
		5360	The scalable event interface for Solaris is called "event
		5361	ports". Unfortunately, this mechanism is very buggy in all major
		5362	releases. If you run into high CPU usage, your program freezes or you get
		5363	a large number of spurious wakeups, make sure you have all the relevant
		5364	and latest kernel patches applied. No, I don't know which ones, but there
		5365	are multiple ones to apply, and afterwards, event ports actually work
		5366	great.
		5367
		5368	If you can't get it to work, you can try running the program by setting
		5369	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5370	C<select> backends.
		5371
		5372	=head2 AIX POLL BUG
		5373
		5374	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5375	this by trying to avoid the poll backend altogether (i.e. it's not even
		5376	compiled in), which normally isn't a big problem as C<select> works fine
		5377	with large bitsets on AIX, and AIX is dead anyway.
		5378
3639	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	5379	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5380
		5381	=head3 General issues
3640		5382
3641	Win32 doesn't support any of the standards (e.g. POSIX) that libev	5383	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3642	requires, and its I/O model is fundamentally incompatible with the POSIX	5384	requires, and its I/O model is fundamentally incompatible with the POSIX
3643	model. Libev still offers limited functionality on this platform in	5385	model. Libev still offers limited functionality on this platform in
3644	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5386	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3645	descriptors. This only applies when using Win32 natively, not when using	5387	descriptors. This only applies when using Win32 natively, not when using
3646	e.g. cygwin.	5388	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5389	as every compiler comes with a slightly differently broken/incompatible
		5390	environment.
3647		5391
3648	Lifting these limitations would basically require the full	5392	Lifting these limitations would basically require the full
3649	re-implementation of the I/O system. If you are into these kinds of	5393	re-implementation of the I/O system. If you are into this kind of thing,
3650	things, then note that glib does exactly that for you in a very portable	5394	then note that glib does exactly that for you in a very portable way (note
3651	way (note also that glib is the slowest event library known to man).	5395	also that glib is the slowest event library known to man).
3652		5396
3653	There is no supported compilation method available on windows except	5397	There is no supported compilation method available on windows except
3654	embedding it into other applications.	5398	embedding it into other applications.
		5399
		5400	Sensible signal handling is officially unsupported by Microsoft - libev
		5401	tries its best, but under most conditions, signals will simply not work.
3655		5402
3656	Not a libev limitation but worth mentioning: windows apparently doesn't	5403	Not a libev limitation but worth mentioning: windows apparently doesn't
3657	accept large writes: instead of resulting in a partial write, windows will	5404	accept large writes: instead of resulting in a partial write, windows will
3658	either accept everything or return C<ENOBUFS> if the buffer is too large,	5405	either accept everything or return C<ENOBUFS> if the buffer is too large,
3659	so make sure you only write small amounts into your sockets (less than a	5406	so make sure you only write small amounts into your sockets (less than a
…		…
3664	the abysmal performance of winsockets, using a large number of sockets	5411	the abysmal performance of winsockets, using a large number of sockets
3665	is not recommended (and not reasonable). If your program needs to use	5412	is not recommended (and not reasonable). If your program needs to use
3666	more than a hundred or so sockets, then likely it needs to use a totally	5413	more than a hundred or so sockets, then likely it needs to use a totally
3667	different implementation for windows, as libev offers the POSIX readiness	5414	different implementation for windows, as libev offers the POSIX readiness
3668	notification model, which cannot be implemented efficiently on windows	5415	notification model, which cannot be implemented efficiently on windows
3669	(Microsoft monopoly games).	5416	(due to Microsoft monopoly games).
3670		5417
3671	A typical way to use libev under windows is to embed it (see the embedding	5418	A typical way to use libev under windows is to embed it (see the embedding
3672	section for details) and use the following F<evwrap.h> header file instead	5419	section for details) and use the following F<evwrap.h> header file instead
3673	of F<ev.h>:	5420	of F<ev.h>:
3674		5421
…		…
3681	you do I<not> compile the F<ev.c> or any other embedded source files!):	5428	you do I<not> compile the F<ev.c> or any other embedded source files!):
3682		5429
3683	#include "evwrap.h"	5430	#include "evwrap.h"
3684	#include "ev.c"	5431	#include "ev.c"
3685		5432
3686	=over 4
3687
3688	=item The winsocket select function	5433	=head3 The winsocket C<select> function
3689		5434
3690	The winsocket C<select> function doesn't follow POSIX in that it	5435	The winsocket C<select> function doesn't follow POSIX in that it
3691	requires socket I<handles> and not socket I<file descriptors> (it is	5436	requires socket I<handles> and not socket I<file descriptors> (it is
3692	also extremely buggy). This makes select very inefficient, and also	5437	also extremely buggy). This makes select very inefficient, and also
3693	requires a mapping from file descriptors to socket handles (the Microsoft	5438	requires a mapping from file descriptors to socket handles (the Microsoft
…		…
3702	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	5447	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3703		5448
3704	Note that winsockets handling of fd sets is O(n), so you can easily get a	5449	Note that winsockets handling of fd sets is O(n), so you can easily get a
3705	complexity in the O(n²) range when using win32.	5450	complexity in the O(n²) range when using win32.
3706		5451
3707	=item Limited number of file descriptors	5452	=head3 Limited number of file descriptors
3708		5453
3709	Windows has numerous arbitrary (and low) limits on things.	5454	Windows has numerous arbitrary (and low) limits on things.
3710		5455
3711	Early versions of winsocket's select only supported waiting for a maximum	5456	Early versions of winsocket's select only supported waiting for a maximum
3712	of C<64> handles (probably owning to the fact that all windows kernels	5457	of C<64> handles (probably owning to the fact that all windows kernels
3713	can only wait for C<64> things at the same time internally; Microsoft	5458	can only wait for C<64> things at the same time internally; Microsoft
3714	recommends spawning a chain of threads and wait for 63 handles and the	5459	recommends spawning a chain of threads and wait for 63 handles and the
3715	previous thread in each. Great).	5460	previous thread in each. Sounds great!).
3716		5461
3717	Newer versions support more handles, but you need to define C<FD_SETSIZE>	5462	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3718	to some high number (e.g. C<2048>) before compiling the winsocket select	5463	to some high number (e.g. C<2048>) before compiling the winsocket select
3719	call (which might be in libev or elsewhere, for example, perl does its own	5464	call (which might be in libev or elsewhere, for example, perl and many
3720	select emulation on windows).	5465	other interpreters do their own select emulation on windows).
3721		5466
3722	Another limit is the number of file descriptors in the Microsoft runtime	5467	Another limit is the number of file descriptors in the Microsoft runtime
3723	libraries, which by default is C<64> (there must be a hidden I<64> fetish	5468	libraries, which by default is C<64> (there must be a hidden I<64>
3724	or something like this inside Microsoft). You can increase this by calling	5469	fetish or something like this inside Microsoft). You can increase this
3725	C<_setmaxstdio>, which can increase this limit to C<2048> (another	5470	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3726	arbitrary limit), but is broken in many versions of the Microsoft runtime	5471	(another arbitrary limit), but is broken in many versions of the Microsoft
3727	libraries.
3728
3729	This might get you to about C<512> or C<2048> sockets (depending on	5472	runtime libraries. This might get you to about C<512> or C<2048> sockets
3730	windows version and/or the phase of the moon). To get more, you need to	5473	(depending on windows version and/or the phase of the moon). To get more,
3731	wrap all I/O functions and provide your own fd management, but the cost of	5474	you need to wrap all I/O functions and provide your own fd management, but
3732	calling select (O(n²)) will likely make this unworkable.	5475	the cost of calling select (O(n²)) will likely make this unworkable.
3733
3734	=back
3735		5476
3736	=head2 PORTABILITY REQUIREMENTS	5477	=head2 PORTABILITY REQUIREMENTS
3737		5478
3738	In addition to a working ISO-C implementation and of course the	5479	In addition to a working ISO-C implementation and of course the
3739	backend-specific APIs, libev relies on a few additional extensions:	5480	backend-specific APIs, libev relies on a few additional extensions:
…		…
3746	Libev assumes not only that all watcher pointers have the same internal	5487	Libev assumes not only that all watcher pointers have the same internal
3747	structure (guaranteed by POSIX but not by ISO C for example), but it also	5488	structure (guaranteed by POSIX but not by ISO C for example), but it also
3748	assumes that the same (machine) code can be used to call any watcher	5489	assumes that the same (machine) code can be used to call any watcher
3749	callback: The watcher callbacks have different type signatures, but libev	5490	callback: The watcher callbacks have different type signatures, but libev
3750	calls them using an C<ev_watcher *> internally.	5491	calls them using an C<ev_watcher *> internally.
		5492
		5493	=item null pointers and integer zero are represented by 0 bytes
		5494
		5495	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5496	relies on this setting pointers and integers to null.
		5497
		5498	=item pointer accesses must be thread-atomic
		5499
		5500	Accessing a pointer value must be atomic, it must both be readable and
		5501	writable in one piece - this is the case on all current architectures.
3751		5502
3752	=item C<sig_atomic_t volatile> must be thread-atomic as well	5503	=item C<sig_atomic_t volatile> must be thread-atomic as well
3753		5504
3754	The type C<sig_atomic_t volatile> (or whatever is defined as	5505	The type C<sig_atomic_t volatile> (or whatever is defined as
3755	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5506	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
…		…
3764	thread" or will block signals process-wide, both behaviours would	5515	thread" or will block signals process-wide, both behaviours would
3765	be compatible with libev. Interaction between C<sigprocmask> and	5516	be compatible with libev. Interaction between C<sigprocmask> and
3766	C<pthread_sigmask> could complicate things, however.	5517	C<pthread_sigmask> could complicate things, however.
3767		5518
3768	The most portable way to handle signals is to block signals in all threads	5519	The most portable way to handle signals is to block signals in all threads
3769	except the initial one, and run the default loop in the initial thread as	5520	except the initial one, and run the signal handling loop in the initial
3770	well.	5521	thread as well.
3771		5522
3772	=item C<long> must be large enough for common memory allocation sizes	5523	=item C<long> must be large enough for common memory allocation sizes
3773		5524
3774	To improve portability and simplify its API, libev uses C<long> internally	5525	To improve portability and simplify its API, libev uses C<long> internally
3775	instead of C<size_t> when allocating its data structures. On non-POSIX	5526	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
3778	watchers.	5529	watchers.
3779		5530
3780	=item C<double> must hold a time value in seconds with enough accuracy	5531	=item C<double> must hold a time value in seconds with enough accuracy
3781		5532
3782	The type C<double> is used to represent timestamps. It is required to	5533	The type C<double> is used to represent timestamps. It is required to
3783	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	5534	have at least 51 bits of mantissa (and 9 bits of exponent), which is
3784	enough for at least into the year 4000. This requirement is fulfilled by	5535	good enough for at least into the year 4000 with millisecond accuracy
		5536	(the design goal for libev). This requirement is overfulfilled by
3785	implementations implementing IEEE 754 (basically all existing ones).	5537	implementations using IEEE 754, which is basically all existing ones.
		5538
		5539	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5540	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5541	is either obsolete or somebody patched it to use C<long double> or
		5542	something like that, just kidding).
3786		5543
3787	=back	5544	=back
3788		5545
3789	If you know of other additional requirements drop me a note.	5546	If you know of other additional requirements drop me a note.
3790		5547
…		…
3852	=item Processing ev_async_send: O(number_of_async_watchers)	5609	=item Processing ev_async_send: O(number_of_async_watchers)
3853		5610
3854	=item Processing signals: O(max_signal_number)	5611	=item Processing signals: O(max_signal_number)
3855		5612
3856	Sending involves a system call I<iff> there were no other C<ev_async_send>	5613	Sending involves a system call I<iff> there were no other C<ev_async_send>
3857	calls in the current loop iteration. Checking for async and signal events	5614	calls in the current loop iteration and the loop is currently
		5615	blocked. Checking for async and signal events involves iterating over all
3858	involves iterating over all running async watchers or all signal numbers.	5616	running async watchers or all signal numbers.
3859		5617
3860	=back	5618	=back
3861		5619
3862		5620
		5621	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5622
		5623	The major version 4 introduced some incompatible changes to the API.
		5624
		5625	At the moment, the C<ev.h> header file provides compatibility definitions
		5626	for all changes, so most programs should still compile. The compatibility
		5627	layer might be removed in later versions of libev, so better update to the
		5628	new API early than late.
		5629
		5630	=over 4
		5631
		5632	=item C<EV_COMPAT3> backwards compatibility mechanism
		5633
		5634	The backward compatibility mechanism can be controlled by
		5635	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5636	section.
		5637
		5638	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5639
		5640	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5641
		5642	ev_loop_destroy (EV_DEFAULT_UC);
		5643	ev_loop_fork (EV_DEFAULT);
		5644
		5645	=item function/symbol renames
		5646
		5647	A number of functions and symbols have been renamed:
		5648
		5649	ev_loop => ev_run
		5650	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5651	EVLOOP_ONESHOT => EVRUN_ONCE
		5652
		5653	ev_unloop => ev_break
		5654	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5655	EVUNLOOP_ONE => EVBREAK_ONE
		5656	EVUNLOOP_ALL => EVBREAK_ALL
		5657
		5658	EV_TIMEOUT => EV_TIMER
		5659
		5660	ev_loop_count => ev_iteration
		5661	ev_loop_depth => ev_depth
		5662	ev_loop_verify => ev_verify
		5663
		5664	Most functions working on C<struct ev_loop> objects don't have an
		5665	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5666	associated constants have been renamed to not collide with the C<struct
		5667	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5668	as all other watcher types. Note that C<ev_loop_fork> is still called
		5669	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5670	typedef.
		5671
		5672	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5673
		5674	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5675	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5676	and work, but the library code will of course be larger.
		5677
		5678	=back
		5679
		5680
		5681	=head1 GLOSSARY
		5682
		5683	=over 4
		5684
		5685	=item active
		5686
		5687	A watcher is active as long as it has been started and not yet stopped.
		5688	See L</WATCHER STATES> for details.
		5689
		5690	=item application
		5691
		5692	In this document, an application is whatever is using libev.
		5693
		5694	=item backend
		5695
		5696	The part of the code dealing with the operating system interfaces.
		5697
		5698	=item callback
		5699
		5700	The address of a function that is called when some event has been
		5701	detected. Callbacks are being passed the event loop, the watcher that
		5702	received the event, and the actual event bitset.
		5703
		5704	=item callback/watcher invocation
		5705
		5706	The act of calling the callback associated with a watcher.
		5707
		5708	=item event
		5709
		5710	A change of state of some external event, such as data now being available
		5711	for reading on a file descriptor, time having passed or simply not having
		5712	any other events happening anymore.
		5713
		5714	In libev, events are represented as single bits (such as C<EV_READ> or
		5715	C<EV_TIMER>).
		5716
		5717	=item event library
		5718
		5719	A software package implementing an event model and loop.
		5720
		5721	=item event loop
		5722
		5723	An entity that handles and processes external events and converts them
		5724	into callback invocations.
		5725
		5726	=item event model
		5727
		5728	The model used to describe how an event loop handles and processes
		5729	watchers and events.
		5730
		5731	=item pending
		5732
		5733	A watcher is pending as soon as the corresponding event has been
		5734	detected. See L</WATCHER STATES> for details.
		5735
		5736	=item real time
		5737
		5738	The physical time that is observed. It is apparently strictly monotonic :)
		5739
		5740	=item wall-clock time
		5741
		5742	The time and date as shown on clocks. Unlike real time, it can actually
		5743	be wrong and jump forwards and backwards, e.g. when you adjust your
		5744	clock.
		5745
		5746	=item watcher
		5747
		5748	A data structure that describes interest in certain events. Watchers need
		5749	to be started (attached to an event loop) before they can receive events.
		5750
		5751	=back
		5752
3863	=head1 AUTHOR	5753	=head1 AUTHOR
3864		5754
3865	Marc Lehmann <libev@schmorp.de>.	5755	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5756	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
3866		5757

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