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		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	libev - a high performance full-featured event loop written in C	5	libev - a high performance full-featured event loop written in C
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
…		…
9	=head2 EXAMPLE PROGRAM	11	=head2 EXAMPLE PROGRAM
10		12
11	// a single header file is required	13	// a single header file is required
12	#include <ev.h>	14	#include <ev.h>
13		15
		16	#include <stdio.h> // for puts
		17
14	// every watcher type has its own typedef'd struct	18	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	19	// with the name ev_TYPE
16	ev_io stdin_watcher;	20	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	21	ev_timer timeout_watcher;
18		22
19	// all watcher callbacks have a similar signature	23	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	24	// this callback is called when data is readable on stdin
…		…
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<ev_loop *>. The library knows two	353	An event loop is described by a C<struct ev_loop *> (the C<struct> is
282	types of such loops, the I<default> loop, which supports signals and child	354	I<not> optional in this case unless libev 3 compatibility is disabled, as
283	events, and dynamically created loops which do not.	355	libev 3 had an C<ev_loop> function colliding with the struct name).
		356
		357	The library knows two types of such loops, the I<default> loop, which
		358	supports child process events, and dynamically created event loops which
		359	do not.
284		360
285	=over 4	361	=over 4
286		362
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	363	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		364
289	This will initialise the default event loop if it hasn't been initialised	365	This returns the "default" event loop object, which is what you should
290	yet and return it. If the default loop could not be initialised, returns	366	normally use when you just need "the event loop". Event loop objects and
291	false. If it already was initialised it simply returns it (and ignores the	367	the C<flags> parameter are described in more detail in the entry for
292	flags. If that is troubling you, check C<ev_backend ()> afterwards).	368	C<ev_loop_new>.
		369
		370	If the default loop is already initialised then this function simply
		371	returns it (and ignores the flags. If that is troubling you, check
		372	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		373	flags, which should almost always be C<0>, unless the caller is also the
		374	one calling C<ev_run> or otherwise qualifies as "the main program".
293		375
294	If you don't know what event loop to use, use the one returned from this	376	If you don't know what event loop to use, use the one returned from this
295	function.	377	function (or via the C<EV_DEFAULT> macro).
296		378
297	Note that this function is I<not> thread-safe, so if you want to use it	379	Note that this function is I<not> thread-safe, so if you want to use it
298	from multiple threads, you have to lock (note also that this is unlikely,	380	from multiple threads, you have to employ some kind of mutex (note also
299	as loops cannot bes hared easily between threads anyway).	381	that this case is unlikely, as loops cannot be shared easily between
		382	threads anyway).
300		383
301	The default loop is the only loop that can handle C<ev_signal> and	384	The default loop is the only loop that can handle C<ev_child> watchers,
302	C<ev_child> watchers, and to do this, it always registers a handler	385	and to do this, it always registers a handler for C<SIGCHLD>. If this is
303	for C<SIGCHLD>. If this is a problem for your application you can either	386	a problem for your application you can either create a dynamic loop with
304	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	387	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
305	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	388	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
306	C<ev_default_init>.	389
		390	Example: This is the most typical usage.
		391
		392	if (!ev_default_loop (0))
		393	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		394
		395	Example: Restrict libev to the select and poll backends, and do not allow
		396	environment settings to be taken into account:
		397
		398	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		399
		400	=item struct ev_loop *ev_loop_new (unsigned int flags)
		401
		402	This will create and initialise a new event loop object. If the loop
		403	could not be initialised, returns false.
		404
		405	This function is thread-safe, and one common way to use libev with
		406	threads is indeed to create one loop per thread, and using the default
		407	loop in the "main" or "initial" thread.
307		408
308	The flags argument can be used to specify special behaviour or specific	409	The flags argument can be used to specify special behaviour or specific
309	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	410	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
310		411
311	The following flags are supported:	412	The following flags are supported:
…		…
321		422
322	If this flag bit is or'ed into the flag value (or the program runs setuid	423	If this flag bit is or'ed into the flag value (or the program runs setuid
323	or setgid) then libev will I<not> look at the environment variable	424	or setgid) then libev will I<not> look at the environment variable
324	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	425	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
325	override the flags completely if it is found in the environment. This is	426	override the flags completely if it is found in the environment. This is
326	useful to try out specific backends to test their performance, or to work	427	useful to try out specific backends to test their performance, to work
327	around bugs.	428	around bugs, or to make libev threadsafe (accessing environment variables
		429	cannot be done in a threadsafe way, but usually it works if no other
		430	thread modifies them).
328		431
329	=item C<EVFLAG_FORKCHECK>	432	=item C<EVFLAG_FORKCHECK>
330		433
331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	434	Instead of calling C<ev_loop_fork> manually after a fork, you can also
332	a fork, you can also make libev check for a fork in each iteration by	435	make libev check for a fork in each iteration by enabling this flag.
333	enabling this flag.
334		436
335	This works by calling C<getpid ()> on every iteration of the loop,	437	This works by calling C<getpid ()> on every iteration of the loop,
336	and thus this might slow down your event loop if you do a lot of loop	438	and thus this might slow down your event loop if you do a lot of loop
337	iterations and little real work, but is usually not noticeable (on my	439	iterations and little real work, but is usually not noticeable (on my
338	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	440	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
339	without a system call and thus I<very> fast, but my GNU/Linux system also has	441	sequence without a system call and thus I<very> fast, but my GNU/Linux
340	C<pthread_atfork> which is even faster).	442	system also has C<pthread_atfork> which is even faster). (Update: glibc
		443	versions 2.25 apparently removed the C<getpid> optimisation again).
341		444
342	The big advantage of this flag is that you can forget about fork (and	445	The big advantage of this flag is that you can forget about fork (and
343	forget about forgetting to tell libev about forking) when you use this	446	forget about forgetting to tell libev about forking, although you still
344	flag.	447	have to ignore C<SIGPIPE>) when you use this flag.
345		448
346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	449	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
347	environment variable.	450	environment variable.
		451
		452	=item C<EVFLAG_NOINOTIFY>
		453
		454	When this flag is specified, then libev will not attempt to use the
		455	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		456	testing, this flag can be useful to conserve inotify file descriptors, as
		457	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		458
		459	=item C<EVFLAG_SIGNALFD>
		460
		461	When this flag is specified, then libev will attempt to use the
		462	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		463	delivers signals synchronously, which makes it both faster and might make
		464	it possible to get the queued signal data. It can also simplify signal
		465	handling with threads, as long as you properly block signals in your
		466	threads that are not interested in handling them.
		467
		468	Signalfd will not be used by default as this changes your signal mask, and
		469	there are a lot of shoddy libraries and programs (glib's threadpool for
		470	example) that can't properly initialise their signal masks.
		471
		472	=item C<EVFLAG_NOSIGMASK>
		473
		474	When this flag is specified, then libev will avoid to modify the signal
		475	mask. Specifically, this means you have to make sure signals are unblocked
		476	when you want to receive them.
		477
		478	This behaviour is useful when you want to do your own signal handling, or
		479	want to handle signals only in specific threads and want to avoid libev
		480	unblocking the signals.
		481
		482	It's also required by POSIX in a threaded program, as libev calls
		483	C<sigprocmask>, whose behaviour is officially unspecified.
		484
		485	=item C<EVFLAG_NOTIMERFD>
		486
		487	When this flag is specified, the libev will avoid using a C<timerfd> to
		488	detect time jumps. It will still be able to detect time jumps, but takes
		489	longer and has a lower accuracy in doing so, but saves a file descriptor
		490	per loop.
		491
		492	The current implementation only tries to use a C<timerfd> when the first
		493	C<ev_periodic> watcher is started and falls back on other methods if it
		494	cannot be created, but this behaviour might change in the future.
348		495
349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	496	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
350		497
351	This is your standard select(2) backend. Not I<completely> standard, as	498	This is your standard select(2) backend. Not I<completely> standard, as
352	libev tries to roll its own fd_set with no limits on the number of fds,	499	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
377	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and	524	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
378	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.	525	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
379		526
380	=item C<EVBACKEND_EPOLL> (value 4, Linux)	527	=item C<EVBACKEND_EPOLL> (value 4, Linux)
381		528
		529	Use the Linux-specific epoll(7) interface (for both pre- and post-2.6.9
		530	kernels).
		531
382	For few fds, this backend is a bit little slower than poll and select,	532	For few fds, this backend is a bit little slower than poll and select, but
383	but it scales phenomenally better. While poll and select usually scale	533	it scales phenomenally better. While poll and select usually scale like
384	like O(total_fds) where n is the total number of fds (or the highest fd),	534	O(total_fds) where total_fds is the total number of fds (or the highest
385	epoll scales either O(1) or O(active_fds). The epoll design has a number	535	fd), epoll scales either O(1) or O(active_fds).
386	of shortcomings, such as silently dropping events in some hard-to-detect	536
387	cases and requiring a system call per fd change, no fork support and bad	537	The epoll mechanism deserves honorable mention as the most misdesigned
388	support for dup.	538	of the more advanced event mechanisms: mere annoyances include silently
		539	dropping file descriptors, requiring a system call per change per file
		540	descriptor (and unnecessary guessing of parameters), problems with dup,
		541	returning before the timeout value, resulting in additional iterations
		542	(and only giving 5ms accuracy while select on the same platform gives
		543	0.1ms) and so on. The biggest issue is fork races, however - if a program
		544	forks then I<both> parent and child process have to recreate the epoll
		545	set, which can take considerable time (one syscall per file descriptor)
		546	and is of course hard to detect.
		547
		548	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		549	but of course I<doesn't>, and epoll just loves to report events for
		550	totally I<different> file descriptors (even already closed ones, so
		551	one cannot even remove them from the set) than registered in the set
		552	(especially on SMP systems). Libev tries to counter these spurious
		553	notifications by employing an additional generation counter and comparing
		554	that against the events to filter out spurious ones, recreating the set
		555	when required. Epoll also erroneously rounds down timeouts, but gives you
		556	no way to know when and by how much, so sometimes you have to busy-wait
		557	because epoll returns immediately despite a nonzero timeout. And last
		558	not least, it also refuses to work with some file descriptors which work
		559	perfectly fine with C<select> (files, many character devices...).
		560
		561	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		562	cobbled together in a hurry, no thought to design or interaction with
		563	others. Oh, the pain, will it ever stop...
389		564
390	While stopping, setting and starting an I/O watcher in the same iteration	565	While stopping, setting and starting an I/O watcher in the same iteration
391	will result in some caching, there is still a system call per such incident	566	will result in some caching, there is still a system call per such
392	(because the fd could point to a different file description now), so its	567	incident (because the same I<file descriptor> could point to a different
393	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	568	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
394	very well if you register events for both fds.	569	file descriptors might not work very well if you register events for both
395		570	file descriptors.
396	Please note that epoll sometimes generates spurious notifications, so you
397	need to use non-blocking I/O or other means to avoid blocking when no data
398	(or space) is available.
399		571
400	Best performance from this backend is achieved by not unregistering all	572	Best performance from this backend is achieved by not unregistering all
401	watchers for a file descriptor until it has been closed, if possible,	573	watchers for a file descriptor until it has been closed, if possible,
402	i.e. keep at least one watcher active per fd at all times. Stopping and	574	i.e. keep at least one watcher active per fd at all times. Stopping and
403	starting a watcher (without re-setting it) also usually doesn't cause	575	starting a watcher (without re-setting it) also usually doesn't cause
404	extra overhead.	576	extra overhead. A fork can both result in spurious notifications as well
		577	as in libev having to destroy and recreate the epoll object, which can
		578	take considerable time and thus should be avoided.
		579
		580	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		581	faster than epoll for maybe up to a hundred file descriptors, depending on
		582	the usage. So sad.
405		583
406	While nominally embeddable in other event loops, this feature is broken in	584	While nominally embeddable in other event loops, this feature is broken in
407	all kernel versions tested so far.	585	a lot of kernel revisions, but probably(!) works in current versions.
408		586
409	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	587	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
410	C<EVBACKEND_POLL>.	588	C<EVBACKEND_POLL>.
411		589
		590	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		591
		592	Use the Linux-specific Linux AIO (I<not> C<< aio(7) >> but C<<
		593	io_submit(2) >>) event interface available in post-4.18 kernels (but libev
		594	only tries to use it in 4.19+).
		595
		596	This is another Linux train wreck of an event interface.
		597
		598	If this backend works for you (as of this writing, it was very
		599	experimental), it is the best event interface available on Linux and might
		600	be well worth enabling it - if it isn't available in your kernel this will
		601	be detected and this backend will be skipped.
		602
		603	This backend can batch oneshot requests and supports a user-space ring
		604	buffer to receive events. It also doesn't suffer from most of the design
		605	problems of epoll (such as not being able to remove event sources from
		606	the epoll set), and generally sounds too good to be true. Because, this
		607	being the Linux kernel, of course it suffers from a whole new set of
		608	limitations, forcing you to fall back to epoll, inheriting all its design
		609	issues.
		610
		611	For one, it is not easily embeddable (but probably could be done using
		612	an event fd at some extra overhead). It also is subject to a system wide
		613	limit that can be configured in F</proc/sys/fs/aio-max-nr>. If no AIO
		614	requests are left, this backend will be skipped during initialisation, and
		615	will switch to epoll when the loop is active.
		616
		617	Most problematic in practice, however, is that not all file descriptors
		618	work with it. For example, in Linux 5.1, TCP sockets, pipes, event fds,
		619	files, F</dev/null> and many others are supported, but ttys do not work
		620	properly (a known bug that the kernel developers don't care about, see
		621	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		622	(yet?) a generic event polling interface.
		623
		624	Overall, it seems the Linux developers just don't want it to have a
		625	generic event handling mechanism other than C<select> or C<poll>.
		626
		627	To work around all these problem, the current version of libev uses its
		628	epoll backend as a fallback for file descriptor types that do not work. Or
		629	falls back completely to epoll if the kernel acts up.
		630
		631	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		632	C<EVBACKEND_POLL>.
		633
412	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	634	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
413		635
414	Kqueue deserves special mention, as at the time of this writing, it was	636	Kqueue deserves special mention, as at the time this backend was
415	broken on all BSDs except NetBSD (usually it doesn't work reliably with	637	implemented, it was broken on all BSDs except NetBSD (usually it doesn't
416	anything but sockets and pipes, except on Darwin, where of course it's	638	work reliably with anything but sockets and pipes, except on Darwin,
417	completely useless). For this reason it's not being "auto-detected" unless	639	where of course it's completely useless). Unlike epoll, however, whose
418	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or	640	brokenness is by design, these kqueue bugs can be (and mostly have been)
		641	fixed without API changes to existing programs. For this reason it's not
		642	being "auto-detected" on all platforms unless you explicitly specify it
		643	in the flags (i.e. using C<EVBACKEND_KQUEUE>) or libev was compiled on a
419	libev was compiled on a known-to-be-good (-enough) system like NetBSD.	644	known-to-be-good (-enough) system like NetBSD.
420		645
421	You still can embed kqueue into a normal poll or select backend and use it	646	You still can embed kqueue into a normal poll or select backend and use it
422	only for sockets (after having made sure that sockets work with kqueue on	647	only for sockets (after having made sure that sockets work with kqueue on
423	the target platform). See C<ev_embed> watchers for more info.	648	the target platform). See C<ev_embed> watchers for more info.
424		649
425	It scales in the same way as the epoll backend, but the interface to the	650	It scales in the same way as the epoll backend, but the interface to the
426	kernel is more efficient (which says nothing about its actual speed, of	651	kernel is more efficient (which says nothing about its actual speed, of
427	course). While stopping, setting and starting an I/O watcher does never	652	course). While stopping, setting and starting an I/O watcher does never
428	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	653	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
429	two event changes per incident. Support for C<fork ()> is very bad and it	654	two event changes per incident. Support for C<fork ()> is very bad (you
		655	might have to leak fds on fork, but it's more sane than epoll) and it
430	drops fds silently in similarly hard-to-detect cases.	656	drops fds silently in similarly hard-to-detect cases.
431		657
432	This backend usually performs well under most conditions.	658	This backend usually performs well under most conditions.
433		659
434	While nominally embeddable in other event loops, this doesn't work	660	While nominally embeddable in other event loops, this doesn't work
435	everywhere, so you might need to test for this. And since it is broken	661	everywhere, so you might need to test for this. And since it is broken
436	almost everywhere, you should only use it when you have a lot of sockets	662	almost everywhere, you should only use it when you have a lot of sockets
437	(for which it usually works), by embedding it into another event loop	663	(for which it usually works), by embedding it into another event loop
438	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,	664	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
439	using it only for sockets.	665	also broken on OS X)) and, did I mention it, using it only for sockets.
440		666
441	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with	667	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
442	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with	668	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
443	C<NOTE_EOF>.	669	C<NOTE_EOF>.
444		670
…		…
452	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	678	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
453		679
454	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	680	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
455	it's really slow, but it still scales very well (O(active_fds)).	681	it's really slow, but it still scales very well (O(active_fds)).
456		682
457	Please note that Solaris event ports can deliver a lot of spurious
458	notifications, so you need to use non-blocking I/O or other means to avoid
459	blocking when no data (or space) is available.
460
461	While this backend scales well, it requires one system call per active	683	While this backend scales well, it requires one system call per active
462	file descriptor per loop iteration. For small and medium numbers of file	684	file descriptor per loop iteration. For small and medium numbers of file
463	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	685	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
464	might perform better.	686	might perform better.
465		687
466	On the positive side, with the exception of the spurious readiness	688	On the positive side, this backend actually performed fully to
467	notifications, this backend actually performed fully to specification
468	in all tests and is fully embeddable, which is a rare feat among the	689	specification in all tests and is fully embeddable, which is a rare feat
469	OS-specific backends.	690	among the OS-specific backends (I vastly prefer correctness over speed
		691	hacks).
		692
		693	On the negative side, the interface is I<bizarre> - so bizarre that
		694	even sun itself gets it wrong in their code examples: The event polling
		695	function sometimes returns events to the caller even though an error
		696	occurred, but with no indication whether it has done so or not (yes, it's
		697	even documented that way) - deadly for edge-triggered interfaces where you
		698	absolutely have to know whether an event occurred or not because you have
		699	to re-arm the watcher.
		700
		701	Fortunately libev seems to be able to work around these idiocies.
470		702
471	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	703	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
472	C<EVBACKEND_POLL>.	704	C<EVBACKEND_POLL>.
473		705
474	=item C<EVBACKEND_ALL>	706	=item C<EVBACKEND_ALL>
475		707
476	Try all backends (even potentially broken ones that wouldn't be tried	708	Try all backends (even potentially broken ones that wouldn't be tried
477	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	709	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
478	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	710	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
479		711
480	It is definitely not recommended to use this flag.	712	It is definitely not recommended to use this flag, use whatever
		713	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		714	at all.
		715
		716	=item C<EVBACKEND_MASK>
		717
		718	Not a backend at all, but a mask to select all backend bits from a
		719	C<flags> value, in case you want to mask out any backends from a flags
		720	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
481		721
482	=back	722	=back
483		723
484	If one or more of these are or'ed into the flags value, then only these	724	If one or more of the backend flags are or'ed into the flags value,
485	backends will be tried (in the reverse order as listed here). If none are	725	then only these backends will be tried (in the reverse order as listed
486	specified, all backends in C<ev_recommended_backends ()> will be tried.	726	here). If none are specified, all backends in C<ev_recommended_backends
487		727	()> will be tried.
488	Example: This is the most typical usage.
489
490	if (!ev_default_loop (0))
491	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
492
493	Example: Restrict libev to the select and poll backends, and do not allow
494	environment settings to be taken into account:
495
496	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
497
498	Example: Use whatever libev has to offer, but make sure that kqueue is
499	used if available (warning, breaks stuff, best use only with your own
500	private event loop and only if you know the OS supports your types of
501	fds):
502
503	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
504
505	=item struct ev_loop *ev_loop_new (unsigned int flags)
506
507	Similar to C<ev_default_loop>, but always creates a new event loop that is
508	always distinct from the default loop. Unlike the default loop, it cannot
509	handle signal and child watchers, and attempts to do so will be greeted by
510	undefined behaviour (or a failed assertion if assertions are enabled).
511
512	Note that this function I<is> thread-safe, and the recommended way to use
513	libev with threads is indeed to create one loop per thread, and using the
514	default loop in the "main" or "initial" thread.
515		728
516	Example: Try to create a event loop that uses epoll and nothing else.	729	Example: Try to create a event loop that uses epoll and nothing else.
517		730
518	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	731	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
519	if (!epoller)	732	if (!epoller)
520	fatal ("no epoll found here, maybe it hides under your chair");	733	fatal ("no epoll found here, maybe it hides under your chair");
521		734
		735	Example: Use whatever libev has to offer, but make sure that kqueue is
		736	used if available.
		737
		738	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		739
		740	Example: Similarly, on linux, you mgiht want to take advantage of the
		741	linux aio backend if possible, but fall back to something else if that
		742	isn't available.
		743
		744	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
		745
522	=item ev_default_destroy ()	746	=item ev_loop_destroy (loop)
523		747
524	Destroys the default loop again (frees all memory and kernel state	748	Destroys an event loop object (frees all memory and kernel state
525	etc.). None of the active event watchers will be stopped in the normal	749	etc.). None of the active event watchers will be stopped in the normal
526	sense, so e.g. C<ev_is_active> might still return true. It is your	750	sense, so e.g. C<ev_is_active> might still return true. It is your
527	responsibility to either stop all watchers cleanly yourself I<before>	751	responsibility to either stop all watchers cleanly yourself I<before>
528	calling this function, or cope with the fact afterwards (which is usually	752	calling this function, or cope with the fact afterwards (which is usually
529	the easiest thing, you can just ignore the watchers and/or C<free ()> them	753	the easiest thing, you can just ignore the watchers and/or C<free ()> them
530	for example).	754	for example).
531		755
532	Note that certain global state, such as signal state, will not be freed by	756	Note that certain global state, such as signal state (and installed signal
533	this function, and related watchers (such as signal and child watchers)	757	handlers), will not be freed by this function, and related watchers (such
534	would need to be stopped manually.	758	as signal and child watchers) would need to be stopped manually.
535		759
536	In general it is not advisable to call this function except in the	760	This function is normally used on loop objects allocated by
537	rare occasion where you really need to free e.g. the signal handling	761	C<ev_loop_new>, but it can also be used on the default loop returned by
		762	C<ev_default_loop>, in which case it is not thread-safe.
		763
		764	Note that it is not advisable to call this function on the default loop
		765	except in the rare occasion where you really need to free its resources.
538	pipe fds. If you need dynamically allocated loops it is better to use	766	If you need dynamically allocated loops it is better to use C<ev_loop_new>
539	C<ev_loop_new> and C<ev_loop_destroy>).	767	and C<ev_loop_destroy>.
540		768
541	=item ev_loop_destroy (loop)	769	=item ev_loop_fork (loop)
542		770
543	Like C<ev_default_destroy>, but destroys an event loop created by an
544	earlier call to C<ev_loop_new>.
545
546	=item ev_default_fork ()
547
548	This function sets a flag that causes subsequent C<ev_loop> iterations	771	This function sets a flag that causes subsequent C<ev_run> iterations
549	to reinitialise the kernel state for backends that have one. Despite the	772	to reinitialise the kernel state for backends that have one. Despite
550	name, you can call it anytime, but it makes most sense after forking, in	773	the name, you can call it anytime you are allowed to start or stop
551	the child process (or both child and parent, but that again makes little	774	watchers (except inside an C<ev_prepare> callback), but it makes most
552	sense). You I<must> call it in the child before using any of the libev	775	sense after forking, in the child process. You I<must> call it (or use
553	functions, and it will only take effect at the next C<ev_loop> iteration.	776	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
		777
		778	In addition, if you want to reuse a loop (via this function or
		779	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		780
		781	Again, you I<have> to call it on I<any> loop that you want to re-use after
		782	a fork, I<even if you do not plan to use the loop in the parent>. This is
		783	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		784	during fork.
554		785
555	On the other hand, you only need to call this function in the child	786	On the other hand, you only need to call this function in the child
556	process if and only if you want to use the event library in the child. If	787	process if and only if you want to use the event loop in the child. If
557	you just fork+exec, you don't have to call it at all.	788	you just fork+exec or create a new loop in the child, you don't have to
		789	call it at all (in fact, C<epoll> is so badly broken that it makes a
		790	difference, but libev will usually detect this case on its own and do a
		791	costly reset of the backend).
558		792
559	The function itself is quite fast and it's usually not a problem to call	793	The function itself is quite fast and it's usually not a problem to call
560	it just in case after a fork. To make this easy, the function will fit in	794	it just in case after a fork.
561	quite nicely into a call to C<pthread_atfork>:
562		795
		796	Example: Automate calling C<ev_loop_fork> on the default loop when
		797	using pthreads.
		798
		799	static void
		800	post_fork_child (void)
		801	{
		802	ev_loop_fork (EV_DEFAULT);
		803	}
		804
		805	...
563	pthread_atfork (0, 0, ev_default_fork);	806	pthread_atfork (0, 0, post_fork_child);
564
565	=item ev_loop_fork (loop)
566
567	Like C<ev_default_fork>, but acts on an event loop created by
568	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
569	after fork that you want to re-use in the child, and how you do this is
570	entirely your own problem.
571		807
572	=item int ev_is_default_loop (loop)	808	=item int ev_is_default_loop (loop)
573		809
574	Returns true when the given loop is, in fact, the default loop, and false	810	Returns true when the given loop is, in fact, the default loop, and false
575	otherwise.	811	otherwise.
576		812
577	=item unsigned int ev_loop_count (loop)	813	=item unsigned int ev_iteration (loop)
578		814
579	Returns the count of loop iterations for the loop, which is identical to	815	Returns the current iteration count for the event loop, which is identical
580	the number of times libev did poll for new events. It starts at C<0> and	816	to the number of times libev did poll for new events. It starts at C<0>
581	happily wraps around with enough iterations.	817	and happily wraps around with enough iterations.
582		818
583	This value can sometimes be useful as a generation counter of sorts (it	819	This value can sometimes be useful as a generation counter of sorts (it
584	"ticks" the number of loop iterations), as it roughly corresponds with	820	"ticks" the number of loop iterations), as it roughly corresponds with
585	C<ev_prepare> and C<ev_check> calls.	821	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		822	prepare and check phases.
		823
		824	=item unsigned int ev_depth (loop)
		825
		826	Returns the number of times C<ev_run> was entered minus the number of
		827	times C<ev_run> was exited normally, in other words, the recursion depth.
		828
		829	Outside C<ev_run>, this number is zero. In a callback, this number is
		830	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		831	in which case it is higher.
		832
		833	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		834	throwing an exception etc.), doesn't count as "exit" - consider this
		835	as a hint to avoid such ungentleman-like behaviour unless it's really
		836	convenient, in which case it is fully supported.
586		837
587	=item unsigned int ev_backend (loop)	838	=item unsigned int ev_backend (loop)
588		839
589	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	840	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
590	use.	841	use.
…		…
599		850
600	=item ev_now_update (loop)	851	=item ev_now_update (loop)
601		852
602	Establishes the current time by querying the kernel, updating the time	853	Establishes the current time by querying the kernel, updating the time
603	returned by C<ev_now ()> in the progress. This is a costly operation and	854	returned by C<ev_now ()> in the progress. This is a costly operation and
604	is usually done automatically within C<ev_loop ()>.	855	is usually done automatically within C<ev_run ()>.
605		856
606	This function is rarely useful, but when some event callback runs for a	857	This function is rarely useful, but when some event callback runs for a
607	very long time without entering the event loop, updating libev's idea of	858	very long time without entering the event loop, updating libev's idea of
608	the current time is a good idea.	859	the current time is a good idea.
609		860
610	See also "The special problem of time updates" in the C<ev_timer> section.	861	See also L</The special problem of time updates> in the C<ev_timer> section.
611		862
		863	=item ev_suspend (loop)
		864
		865	=item ev_resume (loop)
		866
		867	These two functions suspend and resume an event loop, for use when the
		868	loop is not used for a while and timeouts should not be processed.
		869
		870	A typical use case would be an interactive program such as a game: When
		871	the user presses C<^Z> to suspend the game and resumes it an hour later it
		872	would be best to handle timeouts as if no time had actually passed while
		873	the program was suspended. This can be achieved by calling C<ev_suspend>
		874	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		875	C<ev_resume> directly afterwards to resume timer processing.
		876
		877	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		878	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		879	will be rescheduled (that is, they will lose any events that would have
		880	occurred while suspended).
		881
		882	After calling C<ev_suspend> you B<must not> call I<any> function on the
		883	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		884	without a previous call to C<ev_suspend>.
		885
		886	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		887	event loop time (see C<ev_now_update>).
		888
612	=item ev_loop (loop, int flags)	889	=item bool ev_run (loop, int flags)
613		890
614	Finally, this is it, the event handler. This function usually is called	891	Finally, this is it, the event handler. This function usually is called
615	after you initialised all your watchers and you want to start handling	892	after you have initialised all your watchers and you want to start
616	events.	893	handling events. It will ask the operating system for any new events, call
		894	the watcher callbacks, and then repeat the whole process indefinitely: This
		895	is why event loops are called I<loops>.
617		896
618	If the flags argument is specified as C<0>, it will not return until	897	If the flags argument is specified as C<0>, it will keep handling events
619	either no event watchers are active anymore or C<ev_unloop> was called.	898	until either no event watchers are active anymore or C<ev_break> was
		899	called.
620		900
		901	The return value is false if there are no more active watchers (which
		902	usually means "all jobs done" or "deadlock"), and true in all other cases
		903	(which usually means " you should call C<ev_run> again").
		904
621	Please note that an explicit C<ev_unloop> is usually better than	905	Please note that an explicit C<ev_break> is usually better than
622	relying on all watchers to be stopped when deciding when a program has	906	relying on all watchers to be stopped when deciding when a program has
623	finished (especially in interactive programs), but having a program	907	finished (especially in interactive programs), but having a program
624	that automatically loops as long as it has to and no longer by virtue	908	that automatically loops as long as it has to and no longer by virtue
625	of relying on its watchers stopping correctly, that is truly a thing of	909	of relying on its watchers stopping correctly, that is truly a thing of
626	beauty.	910	beauty.
627		911
		912	This function is I<mostly> exception-safe - you can break out of a
		913	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		914	exception and so on. This does not decrement the C<ev_depth> value, nor
		915	will it clear any outstanding C<EVBREAK_ONE> breaks.
		916
628	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	917	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
629	those events and any already outstanding ones, but will not block your	918	those events and any already outstanding ones, but will not wait and
630	process in case there are no events and will return after one iteration of	919	block your process in case there are no events and will return after one
631	the loop.	920	iteration of the loop. This is sometimes useful to poll and handle new
		921	events while doing lengthy calculations, to keep the program responsive.
632		922
633	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	923	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
634	necessary) and will handle those and any already outstanding ones. It	924	necessary) and will handle those and any already outstanding ones. It
635	will block your process until at least one new event arrives (which could	925	will block your process until at least one new event arrives (which could
636	be an event internal to libev itself, so there is no guarentee that a	926	be an event internal to libev itself, so there is no guarantee that a
637	user-registered callback will be called), and will return after one	927	user-registered callback will be called), and will return after one
638	iteration of the loop.	928	iteration of the loop.
639		929
640	This is useful if you are waiting for some external event in conjunction	930	This is useful if you are waiting for some external event in conjunction
641	with something not expressible using other libev watchers (i.e. "roll your	931	with something not expressible using other libev watchers (i.e. "roll your
642	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	932	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
643	usually a better approach for this kind of thing.	933	usually a better approach for this kind of thing.
644		934
645	Here are the gory details of what C<ev_loop> does:	935	Here are the gory details of what C<ev_run> does (this is for your
		936	understanding, not a guarantee that things will work exactly like this in
		937	future versions):
646		938
		939	- Increment loop depth.
		940	- Reset the ev_break status.
647	- Before the first iteration, call any pending watchers.	941	- Before the first iteration, call any pending watchers.
		942	LOOP:
648	* If EVFLAG_FORKCHECK was used, check for a fork.	943	- If EVFLAG_FORKCHECK was used, check for a fork.
649	- If a fork was detected (by any means), queue and call all fork watchers.	944	- If a fork was detected (by any means), queue and call all fork watchers.
650	- Queue and call all prepare watchers.	945	- Queue and call all prepare watchers.
		946	- If ev_break was called, goto FINISH.
651	- If we have been forked, detach and recreate the kernel state	947	- If we have been forked, detach and recreate the kernel state
652	as to not disturb the other process.	948	as to not disturb the other process.
653	- Update the kernel state with all outstanding changes.	949	- Update the kernel state with all outstanding changes.
654	- Update the "event loop time" (ev_now ()).	950	- Update the "event loop time" (ev_now ()).
655	- Calculate for how long to sleep or block, if at all	951	- Calculate for how long to sleep or block, if at all
656	(active idle watchers, EVLOOP_NONBLOCK or not having	952	(active idle watchers, EVRUN_NOWAIT or not having
657	any active watchers at all will result in not sleeping).	953	any active watchers at all will result in not sleeping).
658	- Sleep if the I/O and timer collect interval say so.	954	- Sleep if the I/O and timer collect interval say so.
		955	- Increment loop iteration counter.
659	- Block the process, waiting for any events.	956	- Block the process, waiting for any events.
660	- Queue all outstanding I/O (fd) events.	957	- Queue all outstanding I/O (fd) events.
661	- Update the "event loop time" (ev_now ()), and do time jump adjustments.	958	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
662	- Queue all expired timers.	959	- Queue all expired timers.
663	- Queue all expired periodics.	960	- Queue all expired periodics.
664	- Unless any events are pending now, queue all idle watchers.	961	- Queue all idle watchers with priority higher than that of pending events.
665	- Queue all check watchers.	962	- Queue all check watchers.
666	- Call all queued watchers in reverse order (i.e. check watchers first).	963	- Call all queued watchers in reverse order (i.e. check watchers first).
667	Signals and child watchers are implemented as I/O watchers, and will	964	Signals and child watchers are implemented as I/O watchers, and will
668	be handled here by queueing them when their watcher gets executed.	965	be handled here by queueing them when their watcher gets executed.
669	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	966	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
670	were used, or there are no active watchers, return, otherwise	967	were used, or there are no active watchers, goto FINISH, otherwise
671	continue with step *.	968	continue with step LOOP.
		969	FINISH:
		970	- Reset the ev_break status iff it was EVBREAK_ONE.
		971	- Decrement the loop depth.
		972	- Return.
672		973
673	Example: Queue some jobs and then loop until no events are outstanding	974	Example: Queue some jobs and then loop until no events are outstanding
674	anymore.	975	anymore.
675		976
676	... queue jobs here, make sure they register event watchers as long	977	... queue jobs here, make sure they register event watchers as long
677	... as they still have work to do (even an idle watcher will do..)	978	... as they still have work to do (even an idle watcher will do..)
678	ev_loop (my_loop, 0);	979	ev_run (my_loop, 0);
679	... jobs done or somebody called unloop. yeah!	980	... jobs done or somebody called break. yeah!
680		981
681	=item ev_unloop (loop, how)	982	=item ev_break (loop, how)
682		983
683	Can be used to make a call to C<ev_loop> return early (but only after it	984	Can be used to make a call to C<ev_run> return early (but only after it
684	has processed all outstanding events). The C<how> argument must be either	985	has processed all outstanding events). The C<how> argument must be either
685	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	986	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
686	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	987	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
687		988
688	This "unloop state" will be cleared when entering C<ev_loop> again.	989	This "break state" will be cleared on the next call to C<ev_run>.
689		990
690	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.	991	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		992	which case it will have no effect.
691		993
692	=item ev_ref (loop)	994	=item ev_ref (loop)
693		995
694	=item ev_unref (loop)	996	=item ev_unref (loop)
695		997
696	Ref/unref can be used to add or remove a reference count on the event	998	Ref/unref can be used to add or remove a reference count on the event
697	loop: Every watcher keeps one reference, and as long as the reference	999	loop: Every watcher keeps one reference, and as long as the reference
698	count is nonzero, C<ev_loop> will not return on its own.	1000	count is nonzero, C<ev_run> will not return on its own.
699		1001
700	If you have a watcher you never unregister that should not keep C<ev_loop>	1002	This is useful when you have a watcher that you never intend to
701	from returning, call ev_unref() after starting, and ev_ref() before	1003	unregister, but that nevertheless should not keep C<ev_run> from
		1004	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
702	stopping it.	1005	before stopping it.
703		1006
704	As an example, libev itself uses this for its internal signal pipe: It is	1007	As an example, libev itself uses this for its internal signal pipe: It
705	not visible to the libev user and should not keep C<ev_loop> from exiting	1008	is not visible to the libev user and should not keep C<ev_run> from
706	if no event watchers registered by it are active. It is also an excellent	1009	exiting if no event watchers registered by it are active. It is also an
707	way to do this for generic recurring timers or from within third-party	1010	excellent way to do this for generic recurring timers or from within
708	libraries. Just remember to I<unref after start> and I<ref before stop>	1011	third-party libraries. Just remember to I<unref after start> and I<ref
709	(but only if the watcher wasn't active before, or was active before,	1012	before stop> (but only if the watcher wasn't active before, or was active
710	respectively).	1013	before, respectively. Note also that libev might stop watchers itself
		1014	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		1015	in the callback).
711		1016
712	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	1017	Example: Create a signal watcher, but keep it from keeping C<ev_run>
713	running when nothing else is active.	1018	running when nothing else is active.
714		1019
715	ev_signal exitsig;	1020	ev_signal exitsig;
716	ev_signal_init (&exitsig, sig_cb, SIGINT);	1021	ev_signal_init (&exitsig, sig_cb, SIGINT);
717	ev_signal_start (loop, &exitsig);	1022	ev_signal_start (loop, &exitsig);
718	evf_unref (loop);	1023	ev_unref (loop);
719		1024
720	Example: For some weird reason, unregister the above signal handler again.	1025	Example: For some weird reason, unregister the above signal handler again.
721		1026
722	ev_ref (loop);	1027	ev_ref (loop);
723	ev_signal_stop (loop, &exitsig);	1028	ev_signal_stop (loop, &exitsig);
…		…
743	overhead for the actual polling but can deliver many events at once.	1048	overhead for the actual polling but can deliver many events at once.
744		1049
745	By setting a higher I<io collect interval> you allow libev to spend more	1050	By setting a higher I<io collect interval> you allow libev to spend more
746	time collecting I/O events, so you can handle more events per iteration,	1051	time collecting I/O events, so you can handle more events per iteration,
747	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	1052	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
748	C<ev_timer>) will be not affected. Setting this to a non-null value will	1053	C<ev_timer>) will not be affected. Setting this to a non-null value will
749	introduce an additional C<ev_sleep ()> call into most loop iterations.	1054	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		1055	sleep time ensures that libev will not poll for I/O events more often then
		1056	once per this interval, on average (as long as the host time resolution is
		1057	good enough).
750		1058
751	Likewise, by setting a higher I<timeout collect interval> you allow libev	1059	Likewise, by setting a higher I<timeout collect interval> you allow libev
752	to spend more time collecting timeouts, at the expense of increased	1060	to spend more time collecting timeouts, at the expense of increased
753	latency/jitter/inexactness (the watcher callback will be called	1061	latency/jitter/inexactness (the watcher callback will be called
754	later). C<ev_io> watchers will not be affected. Setting this to a non-null	1062	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
756		1064
757	Many (busy) programs can usually benefit by setting the I/O collect	1065	Many (busy) programs can usually benefit by setting the I/O collect
758	interval to a value near C<0.1> or so, which is often enough for	1066	interval to a value near C<0.1> or so, which is often enough for
759	interactive servers (of course not for games), likewise for timeouts. It	1067	interactive servers (of course not for games), likewise for timeouts. It
760	usually doesn't make much sense to set it to a lower value than C<0.01>,	1068	usually doesn't make much sense to set it to a lower value than C<0.01>,
761	as this approaches the timing granularity of most systems.	1069	as this approaches the timing granularity of most systems. Note that if
		1070	you do transactions with the outside world and you can't increase the
		1071	parallelity, then this setting will limit your transaction rate (if you
		1072	need to poll once per transaction and the I/O collect interval is 0.01,
		1073	then you can't do more than 100 transactions per second).
762		1074
763	Setting the I<timeout collect interval> can improve the opportunity for	1075	Setting the I<timeout collect interval> can improve the opportunity for
764	saving power, as the program will "bundle" timer callback invocations that	1076	saving power, as the program will "bundle" timer callback invocations that
765	are "near" in time together, by delaying some, thus reducing the number of	1077	are "near" in time together, by delaying some, thus reducing the number of
766	times the process sleeps and wakes up again. Another useful technique to	1078	times the process sleeps and wakes up again. Another useful technique to
767	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	1079	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
768	they fire on, say, one-second boundaries only.	1080	they fire on, say, one-second boundaries only.
769		1081
		1082	Example: we only need 0.1s timeout granularity, and we wish not to poll
		1083	more often than 100 times per second:
		1084
		1085	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		1086	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		1087
		1088	=item ev_invoke_pending (loop)
		1089
		1090	This call will simply invoke all pending watchers while resetting their
		1091	pending state. Normally, C<ev_run> does this automatically when required,
		1092	but when overriding the invoke callback this call comes handy. This
		1093	function can be invoked from a watcher - this can be useful for example
		1094	when you want to do some lengthy calculation and want to pass further
		1095	event handling to another thread (you still have to make sure only one
		1096	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1097
		1098	=item int ev_pending_count (loop)
		1099
		1100	Returns the number of pending watchers - zero indicates that no watchers
		1101	are pending.
		1102
		1103	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1104
		1105	This overrides the invoke pending functionality of the loop: Instead of
		1106	invoking all pending watchers when there are any, C<ev_run> will call
		1107	this callback instead. This is useful, for example, when you want to
		1108	invoke the actual watchers inside another context (another thread etc.).
		1109
		1110	If you want to reset the callback, use C<ev_invoke_pending> as new
		1111	callback.
		1112
		1113	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1114
		1115	Sometimes you want to share the same loop between multiple threads. This
		1116	can be done relatively simply by putting mutex_lock/unlock calls around
		1117	each call to a libev function.
		1118
		1119	However, C<ev_run> can run an indefinite time, so it is not feasible
		1120	to wait for it to return. One way around this is to wake up the event
		1121	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1122	I<release> and I<acquire> callbacks on the loop.
		1123
		1124	When set, then C<release> will be called just before the thread is
		1125	suspended waiting for new events, and C<acquire> is called just
		1126	afterwards.
		1127
		1128	Ideally, C<release> will just call your mutex_unlock function, and
		1129	C<acquire> will just call the mutex_lock function again.
		1130
		1131	While event loop modifications are allowed between invocations of
		1132	C<release> and C<acquire> (that's their only purpose after all), no
		1133	modifications done will affect the event loop, i.e. adding watchers will
		1134	have no effect on the set of file descriptors being watched, or the time
		1135	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1136	to take note of any changes you made.
		1137
		1138	In theory, threads executing C<ev_run> will be async-cancel safe between
		1139	invocations of C<release> and C<acquire>.
		1140
		1141	See also the locking example in the C<THREADS> section later in this
		1142	document.
		1143
		1144	=item ev_set_userdata (loop, void *data)
		1145
		1146	=item void *ev_userdata (loop)
		1147
		1148	Set and retrieve a single C<void *> associated with a loop. When
		1149	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1150	C<0>.
		1151
		1152	These two functions can be used to associate arbitrary data with a loop,
		1153	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1154	C<acquire> callbacks described above, but of course can be (ab-)used for
		1155	any other purpose as well.
		1156
770	=item ev_loop_verify (loop)	1157	=item ev_verify (loop)
771		1158
772	This function only does something when C<EV_VERIFY> support has been	1159	This function only does something when C<EV_VERIFY> support has been
773	compiled in. which is the default for non-minimal builds. It tries to go	1160	compiled in, which is the default for non-minimal builds. It tries to go
774	through all internal structures and checks them for validity. If anything	1161	through all internal structures and checks them for validity. If anything
775	is found to be inconsistent, it will print an error message to standard	1162	is found to be inconsistent, it will print an error message to standard
776	error and call C<abort ()>.	1163	error and call C<abort ()>.
777		1164
778	This can be used to catch bugs inside libev itself: under normal	1165	This can be used to catch bugs inside libev itself: under normal
…		…
782	=back	1169	=back
783		1170
784		1171
785	=head1 ANATOMY OF A WATCHER	1172	=head1 ANATOMY OF A WATCHER
786		1173
		1174	In the following description, uppercase C<TYPE> in names stands for the
		1175	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1176	watchers and C<ev_io_start> for I/O watchers.
		1177
787	A watcher is a structure that you create and register to record your	1178	A watcher is an opaque structure that you allocate and register to record
788	interest in some event. For instance, if you want to wait for STDIN to	1179	your interest in some event. To make a concrete example, imagine you want
789	become readable, you would create an C<ev_io> watcher for that:	1180	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1181	for that:
790		1182
791	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)	1183	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
792	{	1184	{
793	ev_io_stop (w);	1185	ev_io_stop (w);
794	ev_unloop (loop, EVUNLOOP_ALL);	1186	ev_break (loop, EVBREAK_ALL);
795	}	1187	}
796		1188
797	struct ev_loop *loop = ev_default_loop (0);	1189	struct ev_loop *loop = ev_default_loop (0);
		1190
798	ev_io stdin_watcher;	1191	ev_io stdin_watcher;
		1192
799	ev_init (&stdin_watcher, my_cb);	1193	ev_init (&stdin_watcher, my_cb);
800	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1194	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
801	ev_io_start (loop, &stdin_watcher);	1195	ev_io_start (loop, &stdin_watcher);
		1196
802	ev_loop (loop, 0);	1197	ev_run (loop, 0);
803		1198
804	As you can see, you are responsible for allocating the memory for your	1199	As you can see, you are responsible for allocating the memory for your
805	watcher structures (and it is usually a bad idea to do this on the stack,	1200	watcher structures (and it is I<usually> a bad idea to do this on the
806	although this can sometimes be quite valid).	1201	stack).
807		1202
		1203	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1204	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1205
808	Each watcher structure must be initialised by a call to C<ev_init	1206	Each watcher structure must be initialised by a call to C<ev_init (watcher
809	(watcher *, callback)>, which expects a callback to be provided. This	1207	*, callback)>, which expects a callback to be provided. This callback is
810	callback gets invoked each time the event occurs (or, in the case of I/O	1208	invoked each time the event occurs (or, in the case of I/O watchers, each
811	watchers, each time the event loop detects that the file descriptor given	1209	time the event loop detects that the file descriptor given is readable
812	is readable and/or writable).	1210	and/or writable).
813		1211
814	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1212	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
815	with arguments specific to this watcher type. There is also a macro	1213	macro to configure it, with arguments specific to the watcher type. There
816	to combine initialisation and setting in one call: C<< ev_<type>_init	1214	is also a macro to combine initialisation and setting in one call: C<<
817	(watcher *, callback, ...) >>.	1215	ev_TYPE_init (watcher *, callback, ...) >>.
818		1216
819	To make the watcher actually watch out for events, you have to start it	1217	To make the watcher actually watch out for events, you have to start it
820	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1218	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
821	*) >>), and you can stop watching for events at any time by calling the	1219	*) >>), and you can stop watching for events at any time by calling the
822	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1220	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
823		1221
824	As long as your watcher is active (has been started but not stopped) you	1222	As long as your watcher is active (has been started but not stopped) you
825	must not touch the values stored in it. Most specifically you must never	1223	must not touch the values stored in it except when explicitly documented
826	reinitialise it or call its C<set> macro.	1224	otherwise. Most specifically you must never reinitialise it or call its
		1225	C<ev_TYPE_set> macro.
827		1226
828	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
829	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
830	third argument.	1229	third argument.
831		1230
…		…
840	=item C<EV_WRITE>	1239	=item C<EV_WRITE>
841		1240
842	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
843	writable.	1242	writable.
844		1243
845	=item C<EV_TIMEOUT>	1244	=item C<EV_TIMER>
846		1245
847	The C<ev_timer> watcher has timed out.	1246	The C<ev_timer> watcher has timed out.
848		1247
849	=item C<EV_PERIODIC>	1248	=item C<EV_PERIODIC>
850		1249
…		…
868		1267
869	=item C<EV_PREPARE>	1268	=item C<EV_PREPARE>
870		1269
871	=item C<EV_CHECK>	1270	=item C<EV_CHECK>
872		1271
873	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
874	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)
875	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
876	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
877	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
878	(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
879	C<ev_loop> from blocking).	1283	blocking).
880		1284
881	=item C<EV_EMBED>	1285	=item C<EV_EMBED>
882		1286
883	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.
884		1288
885	=item C<EV_FORK>	1289	=item C<EV_FORK>
886		1290
887	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
888	C<ev_fork>).	1292	C<ev_fork>).
889		1293
		1294	=item C<EV_CLEANUP>
		1295
		1296	The event loop is about to be destroyed (see C<ev_cleanup>).
		1297
890	=item C<EV_ASYNC>	1298	=item C<EV_ASYNC>
891		1299
892	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>).
893		1306
894	=item C<EV_ERROR>	1307	=item C<EV_ERROR>
895		1308
896	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
897	happen because the watcher could not be properly started because libev	1310	happen because the watcher could not be properly started because libev
…		…
912		1325
913	=back	1326	=back
914		1327
915	=head2 GENERIC WATCHER FUNCTIONS	1328	=head2 GENERIC WATCHER FUNCTIONS
916		1329
917	In the following description, C<TYPE> stands for the watcher type,
918	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
919
920	=over 4	1330	=over 4
921		1331
922	=item C<ev_init> (ev_TYPE *watcher, callback)	1332	=item C<ev_init> (ev_TYPE *watcher, callback)
923		1333
924	This macro initialises the generic portion of a watcher. The contents	1334	This macro initialises the generic portion of a watcher. The contents
…		…
938		1348
939	ev_io w;	1349	ev_io w;
940	ev_init (&w, my_cb);	1350	ev_init (&w, my_cb);
941	ev_io_set (&w, STDIN_FILENO, EV_READ);	1351	ev_io_set (&w, STDIN_FILENO, EV_READ);
942		1352
943	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1353	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
944		1354
945	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
946	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
947	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
948	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
…		…
961		1371
962	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.
963		1373
964	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);	1374	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
965		1375
966	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1376	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
967		1377
968	Starts (activates) the given watcher. Only active watchers will receive	1378	Starts (activates) the given watcher. Only active watchers will receive
969	events. If the watcher is already active nothing will happen.	1379	events. If the watcher is already active nothing will happen.
970		1380
971	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
972	whole section.	1382	whole section.
973		1383
974	ev_io_start (EV_DEFAULT_UC, &w);	1384	ev_io_start (EV_DEFAULT_UC, &w);
975		1385
976	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1386	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
977		1387
978	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
979	the watcher was active or not).	1389	the watcher was active or not).
980		1390
981	It is possible that stopped watchers are pending - for example,	1391	It is possible that stopped watchers are pending - for example,
…		…
1001		1411
1002	=item callback ev_cb (ev_TYPE *watcher)	1412	=item callback ev_cb (ev_TYPE *watcher)
1003		1413
1004	Returns the callback currently set on the watcher.	1414	Returns the callback currently set on the watcher.
1005		1415
1006	=item ev_cb_set (ev_TYPE *watcher, callback)	1416	=item ev_set_cb (ev_TYPE *watcher, callback)
1007		1417
1008	Change the callback. You can change the callback at virtually any time	1418	Change the callback. You can change the callback at virtually any time
1009	(modulo threads).	1419	(modulo threads).
1010		1420
1011	=item ev_set_priority (ev_TYPE *watcher, priority)	1421	=item ev_set_priority (ev_TYPE *watcher, int priority)
1012		1422
1013	=item int ev_priority (ev_TYPE *watcher)	1423	=item int ev_priority (ev_TYPE *watcher)
1014		1424
1015	Set and query the priority of the watcher. The priority is a small	1425	Set and query the priority of the watcher. The priority is a small
1016	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1426	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1017	(default: C<-2>). Pending watchers with higher priority will be invoked	1427	(default: C<-2>). Pending watchers with higher priority will be invoked
1018	before watchers with lower priority, but priority will not keep watchers	1428	before watchers with lower priority, but priority will not keep watchers
1019	from being executed (except for C<ev_idle> watchers).	1429	from being executed (except for C<ev_idle> watchers).
1020		1430
1021	This means that priorities are I<only> used for ordering callback
1022	invocation after new events have been received. This is useful, for
1023	example, to reduce latency after idling, or more often, to bind two
1024	watchers on the same event and make sure one is called first.
1025
1026	If you need to suppress invocation when higher priority events are pending	1431	If you need to suppress invocation when higher priority events are pending
1027	you need to look at C<ev_idle> watchers, which provide this functionality.	1432	you need to look at C<ev_idle> watchers, which provide this functionality.
1028		1433
1029	You I<must not> change the priority of a watcher as long as it is active or	1434	You I<must not> change the priority of a watcher as long as it is active or
1030	pending.	1435	pending.
1031		1436
		1437	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1438	fine, as long as you do not mind that the priority value you query might
		1439	or might not have been clamped to the valid range.
		1440
1032	The default priority used by watchers when no priority has been set is	1441	The default priority used by watchers when no priority has been set is
1033	always C<0>, which is supposed to not be too high and not be too low :).	1442	always C<0>, which is supposed to not be too high and not be too low :).
1034		1443
1035	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1444	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1036	fine, as long as you do not mind that the priority value you query might	1445	priorities.
1037	or might not have been adjusted to be within valid range.
1038		1446
1039	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1447	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1040		1448
1041	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1449	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1042	C<loop> nor C<revents> need to be valid as long as the watcher callback	1450	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1050	watcher isn't pending it does nothing and returns C<0>.	1458	watcher isn't pending it does nothing and returns C<0>.
1051		1459
1052	Sometimes it can be useful to "poll" a watcher instead of waiting for its	1460	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1053	callback to be invoked, which can be accomplished with this function.	1461	callback to be invoked, which can be accomplished with this function.
1054		1462
		1463	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1464
		1465	Feeds the given event set into the event loop, as if the specified event
		1466	had happened for the specified watcher (which must be a pointer to an
		1467	initialised but not necessarily started event watcher). Obviously you must
		1468	not free the watcher as long as it has pending events.
		1469
		1470	Stopping the watcher, letting libev invoke it, or calling
		1471	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1472	not started in the first place.
		1473
		1474	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1475	functions that do not need a watcher.
		1476
1055	=back	1477	=back
1056		1478
		1479	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1480	OWN COMPOSITE WATCHERS> idioms.
1057		1481
1058	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1482	=head2 WATCHER STATES
1059		1483
1060	Each watcher has, by default, a member C<void *data> that you can change	1484	There are various watcher states mentioned throughout this manual -
1061	and read at any time: libev will completely ignore it. This can be used	1485	active, pending and so on. In this section these states and the rules to
1062	to associate arbitrary data with your watcher. If you need more data and	1486	transition between them will be described in more detail - and while these
1063	don't want to allocate memory and store a pointer to it in that data	1487	rules might look complicated, they usually do "the right thing".
1064	member, you can also "subclass" the watcher type and provide your own
1065	data:
1066		1488
1067	struct my_io	1489	=over 4
		1490
		1491	=item initialised
		1492
		1493	Before a watcher can be registered with the event loop it has to be
		1494	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1495	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1496
		1497	In this state it is simply some block of memory that is suitable for
		1498	use in an event loop. It can be moved around, freed, reused etc. at
		1499	will - as long as you either keep the memory contents intact, or call
		1500	C<ev_TYPE_init> again.
		1501
		1502	=item started/running/active
		1503
		1504	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1505	property of the event loop, and is actively waiting for events. While in
		1506	this state it cannot be accessed (except in a few documented ways), moved,
		1507	freed or anything else - the only legal thing is to keep a pointer to it,
		1508	and call libev functions on it that are documented to work on active watchers.
		1509
		1510	=item pending
		1511
		1512	If a watcher is active and libev determines that an event it is interested
		1513	in has occurred (such as a timer expiring), it will become pending. It will
		1514	stay in this pending state until either it is stopped or its callback is
		1515	about to be invoked, so it is not normally pending inside the watcher
		1516	callback.
		1517
		1518	The watcher might or might not be active while it is pending (for example,
		1519	an expired non-repeating timer can be pending but no longer active). If it
		1520	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1521	but it is still property of the event loop at this time, so cannot be
		1522	moved, freed or reused. And if it is active the rules described in the
		1523	previous item still apply.
		1524
		1525	It is also possible to feed an event on a watcher that is not active (e.g.
		1526	via C<ev_feed_event>), in which case it becomes pending without being
		1527	active.
		1528
		1529	=item stopped
		1530
		1531	A watcher can be stopped implicitly by libev (in which case it might still
		1532	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1533	latter will clear any pending state the watcher might be in, regardless
		1534	of whether it was active or not, so stopping a watcher explicitly before
		1535	freeing it is often a good idea.
		1536
		1537	While stopped (and not pending) the watcher is essentially in the
		1538	initialised state, that is, it can be reused, moved, modified in any way
		1539	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1540	it again).
		1541
		1542	=back
		1543
		1544	=head2 WATCHER PRIORITY MODELS
		1545
		1546	Many event loops support I<watcher priorities>, which are usually small
		1547	integers that influence the ordering of event callback invocation
		1548	between watchers in some way, all else being equal.
		1549
		1550	In libev, watcher priorities can be set using C<ev_set_priority>. See its
		1551	description for the more technical details such as the actual priority
		1552	range.
		1553
		1554	There are two common ways how these these priorities are being interpreted
		1555	by event loops:
		1556
		1557	In the more common lock-out model, higher priorities "lock out" invocation
		1558	of lower priority watchers, which means as long as higher priority
		1559	watchers receive events, lower priority watchers are not being invoked.
		1560
		1561	The less common only-for-ordering model uses priorities solely to order
		1562	callback invocation within a single event loop iteration: Higher priority
		1563	watchers are invoked before lower priority ones, but they all get invoked
		1564	before polling for new events.
		1565
		1566	Libev uses the second (only-for-ordering) model for all its watchers
		1567	except for idle watchers (which use the lock-out model).
		1568
		1569	The rationale behind this is that implementing the lock-out model for
		1570	watchers is not well supported by most kernel interfaces, and most event
		1571	libraries will just poll for the same events again and again as long as
		1572	their callbacks have not been executed, which is very inefficient in the
		1573	common case of one high-priority watcher locking out a mass of lower
		1574	priority ones.
		1575
		1576	Static (ordering) priorities are most useful when you have two or more
		1577	watchers handling the same resource: a typical usage example is having an
		1578	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1579	timeouts. Under load, data might be received while the program handles
		1580	other jobs, but since timers normally get invoked first, the timeout
		1581	handler will be executed before checking for data. In that case, giving
		1582	the timer a lower priority than the I/O watcher ensures that I/O will be
		1583	handled first even under adverse conditions (which is usually, but not
		1584	always, what you want).
		1585
		1586	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1587	will only be executed when no same or higher priority watchers have
		1588	received events, they can be used to implement the "lock-out" model when
		1589	required.
		1590
		1591	For example, to emulate how many other event libraries handle priorities,
		1592	you can associate an C<ev_idle> watcher to each such watcher, and in
		1593	the normal watcher callback, you just start the idle watcher. The real
		1594	processing is done in the idle watcher callback. This causes libev to
		1595	continuously poll and process kernel event data for the watcher, but when
		1596	the lock-out case is known to be rare (which in turn is rare :), this is
		1597	workable.
		1598
		1599	Usually, however, the lock-out model implemented that way will perform
		1600	miserably under the type of load it was designed to handle. In that case,
		1601	it might be preferable to stop the real watcher before starting the
		1602	idle watcher, so the kernel will not have to process the event in case
		1603	the actual processing will be delayed for considerable time.
		1604
		1605	Here is an example of an I/O watcher that should run at a strictly lower
		1606	priority than the default, and which should only process data when no
		1607	other events are pending:
		1608
		1609	ev_idle idle; // actual processing watcher
		1610	ev_io io; // actual event watcher
		1611
		1612	static void
		1613	io_cb (EV_P_ ev_io *w, int revents)
1068	{	1614	{
1069	ev_io io;	1615	// stop the I/O watcher, we received the event, but
1070	int otherfd;	1616	// are not yet ready to handle it.
1071	void *somedata;	1617	ev_io_stop (EV_A_ w);
1072	struct whatever *mostinteresting;	1618
		1619	// start the idle watcher to handle the actual event.
		1620	// it will not be executed as long as other watchers
		1621	// with the default priority are receiving events.
		1622	ev_idle_start (EV_A_ &idle);
1073	};	1623	}
1074		1624
1075	...	1625	static void
1076	struct my_io w;	1626	idle_cb (EV_P_ ev_idle *w, int revents)
1077	ev_io_init (&w.io, my_cb, fd, EV_READ);
1078
1079	And since your callback will be called with a pointer to the watcher, you
1080	can cast it back to your own type:
1081
1082	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1083	{	1627	{
1084	struct my_io *w = (struct my_io *)w_;	1628	// actual processing
1085	...	1629	read (STDIN_FILENO, ...);
		1630
		1631	// have to start the I/O watcher again, as
		1632	// we have handled the event
		1633	ev_io_start (EV_P_ &io);
1086	}	1634	}
1087		1635
1088	More interesting and less C-conformant ways of casting your callback type	1636	// initialisation
1089	instead have been omitted.	1637	ev_idle_init (&idle, idle_cb);
		1638	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1639	ev_io_start (EV_DEFAULT_ &io);
1090		1640
1091	Another common scenario is to use some data structure with multiple	1641	In the "real" world, it might also be beneficial to start a timer, so that
1092	embedded watchers:	1642	low-priority connections can not be locked out forever under load. This
1093		1643	enables your program to keep a lower latency for important connections
1094	struct my_biggy	1644	during short periods of high load, while not completely locking out less
1095	{	1645	important ones.
1096	int some_data;
1097	ev_timer t1;
1098	ev_timer t2;
1099	}
1100
1101	In this case getting the pointer to C<my_biggy> is a bit more
1102	complicated: Either you store the address of your C<my_biggy> struct
1103	in the C<data> member of the watcher (for woozies), or you need to use
1104	some pointer arithmetic using C<offsetof> inside your watchers (for real
1105	programmers):
1106
1107	#include <stddef.h>
1108
1109	static void
1110	t1_cb (EV_P_ ev_timer *w, int revents)
1111	{
1112	struct my_biggy big = (struct my_biggy *
1113	(((char *)w) - offsetof (struct my_biggy, t1));
1114	}
1115
1116	static void
1117	t2_cb (EV_P_ ev_timer *w, int revents)
1118	{
1119	struct my_biggy big = (struct my_biggy *
1120	(((char *)w) - offsetof (struct my_biggy, t2));
1121	}
1122		1646
1123		1647
1124	=head1 WATCHER TYPES	1648	=head1 WATCHER TYPES
1125		1649
1126	This section describes each watcher in detail, but will not repeat	1650	This section describes each watcher in detail, but will not repeat
1127	information given in the last section. Any initialisation/set macros,	1651	information given in the last section. Any initialisation/set macros,
1128	functions and members specific to the watcher type are explained.	1652	functions and members specific to the watcher type are explained.
1129		1653
1130	Members are additionally marked with either I<[read-only]>, meaning that,	1654	Most members are additionally marked with either I<[read-only]>, meaning
1131	while the watcher is active, you can look at the member and expect some	1655	that, while the watcher is active, you can look at the member and expect
1132	sensible content, but you must not modify it (you can modify it while the	1656	some sensible content, but you must not modify it (you can modify it while
1133	watcher is stopped to your hearts content), or I<[read-write]>, which	1657	the watcher is stopped to your hearts content), or I<[read-write]>, which
1134	means you can expect it to have some sensible content while the watcher	1658	means you can expect it to have some sensible content while the watcher
1135	is active, but you can also modify it. Modifying it may not do something	1659	is active, but you can also modify it. Modifying it may not do something
1136	sensible or take immediate effect (or do anything at all), but libev will	1660	sensible or take immediate effect (or do anything at all), but libev will
1137	not crash or malfunction in any way.	1661	not crash or malfunction in any way.
1138		1662
		1663	In any case, the documentation for each member will explain what the
		1664	effects are, and if there are any additional access restrictions.
1139		1665
1140	=head2 C<ev_io> - is this file descriptor readable or writable?	1666	=head2 C<ev_io> - is this file descriptor readable or writable?
1141		1667
1142	I/O watchers check whether a file descriptor is readable or writable	1668	I/O watchers check whether a file descriptor is readable or writable
1143	in each iteration of the event loop, or, more precisely, when reading	1669	in each iteration of the event loop, or, more precisely, when reading
…		…
1150	In general you can register as many read and/or write event watchers per	1676	In general you can register as many read and/or write event watchers per
1151	fd as you want (as long as you don't confuse yourself). Setting all file	1677	fd as you want (as long as you don't confuse yourself). Setting all file
1152	descriptors to non-blocking mode is also usually a good idea (but not	1678	descriptors to non-blocking mode is also usually a good idea (but not
1153	required if you know what you are doing).	1679	required if you know what you are doing).
1154		1680
1155	If you cannot use non-blocking mode, then force the use of a
1156	known-to-be-good backend (at the time of this writing, this includes only
1157	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
1158
1159	Another thing you have to watch out for is that it is quite easy to	1681	Another thing you have to watch out for is that it is quite easy to
1160	receive "spurious" readiness notifications, that is your callback might	1682	receive "spurious" readiness notifications, that is, your callback might
1161	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1683	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1162	because there is no data. Not only are some backends known to create a	1684	because there is no data. It is very easy to get into this situation even
1163	lot of those (for example Solaris ports), it is very easy to get into	1685	with a relatively standard program structure. Thus it is best to always
1164	this situation even with a relatively standard program structure. Thus	1686	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1165	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1166	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1687	preferable to a program hanging until some data arrives.
1167		1688
1168	If you cannot run the fd in non-blocking mode (for example you should	1689	If you cannot run the fd in non-blocking mode (for example you should
1169	not play around with an Xlib connection), then you have to separately	1690	not play around with an Xlib connection), then you have to separately
1170	re-test whether a file descriptor is really ready with a known-to-be good	1691	re-test whether a file descriptor is really ready with a known-to-be good
1171	interface such as poll (fortunately in our Xlib example, Xlib already	1692	interface such as poll (fortunately in the case of Xlib, it already does
1172	does this on its own, so its quite safe to use). Some people additionally	1693	this on its own, so its quite safe to use). Some people additionally
1173	use C<SIGALRM> and an interval timer, just to be sure you won't block	1694	use C<SIGALRM> and an interval timer, just to be sure you won't block
1174	indefinitely.	1695	indefinitely.
1175		1696
1176	But really, best use non-blocking mode.	1697	But really, best use non-blocking mode.
1177		1698
1178	=head3 The special problem of disappearing file descriptors	1699	=head3 The special problem of disappearing file descriptors
1179		1700
1180	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1701	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1181	descriptor (either due to calling C<close> explicitly or any other means,	1702	a file descriptor (either due to calling C<close> explicitly or any other
1182	such as C<dup2>). The reason is that you register interest in some file	1703	means, such as C<dup2>). The reason is that you register interest in some
1183	descriptor, but when it goes away, the operating system will silently drop	1704	file descriptor, but when it goes away, the operating system will silently
1184	this interest. If another file descriptor with the same number then is	1705	drop this interest. If another file descriptor with the same number then
1185	registered with libev, there is no efficient way to see that this is, in	1706	is registered with libev, there is no efficient way to see that this is,
1186	fact, a different file descriptor.	1707	in fact, a different file descriptor.
1187		1708
1188	To avoid having to explicitly tell libev about such cases, libev follows	1709	To avoid having to explicitly tell libev about such cases, libev follows
1189	the following policy: Each time C<ev_io_set> is being called, libev	1710	the following policy: Each time C<ev_io_set> is being called, libev
1190	will assume that this is potentially a new file descriptor, otherwise	1711	will assume that this is potentially a new file descriptor, otherwise
1191	it is assumed that the file descriptor stays the same. That means that	1712	it is assumed that the file descriptor stays the same. That means that
…		…
1205		1726
1206	There is no workaround possible except not registering events	1727	There is no workaround possible except not registering events
1207	for potentially C<dup ()>'ed file descriptors, or to resort to	1728	for potentially C<dup ()>'ed file descriptors, or to resort to
1208	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1729	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1209		1730
		1731	=head3 The special problem of files
		1732
		1733	Many people try to use C<select> (or libev) on file descriptors
		1734	representing files, and expect it to become ready when their program
		1735	doesn't block on disk accesses (which can take a long time on their own).
		1736
		1737	However, this cannot ever work in the "expected" way - you get a readiness
		1738	notification as soon as the kernel knows whether and how much data is
		1739	there, and in the case of open files, that's always the case, so you
		1740	always get a readiness notification instantly, and your read (or possibly
		1741	write) will still block on the disk I/O.
		1742
		1743	Another way to view it is that in the case of sockets, pipes, character
		1744	devices and so on, there is another party (the sender) that delivers data
		1745	on its own, but in the case of files, there is no such thing: the disk
		1746	will not send data on its own, simply because it doesn't know what you
		1747	wish to read - you would first have to request some data.
		1748
		1749	Since files are typically not-so-well supported by advanced notification
		1750	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1751	to files, even though you should not use it. The reason for this is
		1752	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1753	usually a tty, often a pipe, but also sometimes files or special devices
		1754	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1755	F</dev/urandom>), and even though the file might better be served with
		1756	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1757	it "just works" instead of freezing.
		1758
		1759	So avoid file descriptors pointing to files when you know it (e.g. use
		1760	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1761	when you rarely read from a file instead of from a socket, and want to
		1762	reuse the same code path.
		1763
1210	=head3 The special problem of fork	1764	=head3 The special problem of fork
1211		1765
1212	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1766	Some backends (epoll, kqueue, linuxaio, iouring) do not support C<fork ()>
1213	useless behaviour. Libev fully supports fork, but needs to be told about	1767	at all or exhibit useless behaviour. Libev fully supports fork, but needs
1214	it in the child.	1768	to be told about it in the child if you want to continue to use it in the
		1769	child.
1215		1770
1216	To support fork in your programs, you either have to call	1771	To support fork in your child processes, you have to call C<ev_loop_fork
1217	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1772	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1218	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1773	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1219	C<EVBACKEND_POLL>.
1220		1774
1221	=head3 The special problem of SIGPIPE	1775	=head3 The special problem of SIGPIPE
1222		1776
1223	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1777	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1224	when writing to a pipe whose other end has been closed, your program gets	1778	when writing to a pipe whose other end has been closed, your program gets
…		…
1227		1781
1228	So when you encounter spurious, unexplained daemon exits, make sure you	1782	So when you encounter spurious, unexplained daemon exits, make sure you
1229	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1783	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1230	somewhere, as that would have given you a big clue).	1784	somewhere, as that would have given you a big clue).
1231		1785
		1786	=head3 The special problem of accept()ing when you can't
		1787
		1788	Many implementations of the POSIX C<accept> function (for example,
		1789	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1790	connection from the pending queue in all error cases.
		1791
		1792	For example, larger servers often run out of file descriptors (because
		1793	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1794	rejecting the connection, leading to libev signalling readiness on
		1795	the next iteration again (the connection still exists after all), and
		1796	typically causing the program to loop at 100% CPU usage.
		1797
		1798	Unfortunately, the set of errors that cause this issue differs between
		1799	operating systems, there is usually little the app can do to remedy the
		1800	situation, and no known thread-safe method of removing the connection to
		1801	cope with overload is known (to me).
		1802
		1803	One of the easiest ways to handle this situation is to just ignore it
		1804	- when the program encounters an overload, it will just loop until the
		1805	situation is over. While this is a form of busy waiting, no OS offers an
		1806	event-based way to handle this situation, so it's the best one can do.
		1807
		1808	A better way to handle the situation is to log any errors other than
		1809	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1810	messages, and continue as usual, which at least gives the user an idea of
		1811	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1812	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1813	usage.
		1814
		1815	If your program is single-threaded, then you could also keep a dummy file
		1816	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1817	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1818	close that fd, and create a new dummy fd. This will gracefully refuse
		1819	clients under typical overload conditions.
		1820
		1821	The last way to handle it is to simply log the error and C<exit>, as
		1822	is often done with C<malloc> failures, but this results in an easy
		1823	opportunity for a DoS attack.
1232		1824
1233	=head3 Watcher-Specific Functions	1825	=head3 Watcher-Specific Functions
1234		1826
1235	=over 4	1827	=over 4
1236		1828
…		…
1240		1832
1241	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1833	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1242	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or	1834	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1243	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.	1835	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1244		1836
1245	=item int fd [read-only]	1837	=item ev_io_modify (ev_io *, int events)
1246		1838
1247	The file descriptor being watched.	1839	Similar to C<ev_io_set>, but only changes the event mask. Using this might
		1840	be faster with some backends, as libev can assume that the C<fd> still
		1841	refers to the same underlying file description, something it cannot do
		1842	when using C<ev_io_set>.
1248		1843
		1844	=item int fd [no-modify]
		1845
		1846	The file descriptor being watched. While it can be read at any time, you
		1847	must not modify this member even when the watcher is stopped - always use
		1848	C<ev_io_set> for that.
		1849
1249	=item int events [read-only]	1850	=item int events [no-modify]
1250		1851
1251	The events being watched.	1852	The set of events the fd is being watched for, among other flags. Remember
		1853	that this is a bit set - to test for C<EV_READ>, use C<< w->events &
		1854	EV_READ >>, and similarly for C<EV_WRITE>.
		1855
		1856	As with C<fd>, you must not modify this member even when the watcher is
		1857	stopped, always use C<ev_io_set> or C<ev_io_modify> for that.
1252		1858
1253	=back	1859	=back
1254		1860
1255	=head3 Examples	1861	=head3 Examples
1256		1862
…		…
1268	...	1874	...
1269	struct ev_loop *loop = ev_default_init (0);	1875	struct ev_loop *loop = ev_default_init (0);
1270	ev_io stdin_readable;	1876	ev_io stdin_readable;
1271	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1877	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1272	ev_io_start (loop, &stdin_readable);	1878	ev_io_start (loop, &stdin_readable);
1273	ev_loop (loop, 0);	1879	ev_run (loop, 0);
1274		1880
1275		1881
1276	=head2 C<ev_timer> - relative and optionally repeating timeouts	1882	=head2 C<ev_timer> - relative and optionally repeating timeouts
1277		1883
1278	Timer watchers are simple relative timers that generate an event after a	1884	Timer watchers are simple relative timers that generate an event after a
…		…
1283	year, it will still time out after (roughly) one hour. "Roughly" because	1889	year, it will still time out after (roughly) one hour. "Roughly" because
1284	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1890	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1285	monotonic clock option helps a lot here).	1891	monotonic clock option helps a lot here).
1286		1892
1287	The callback is guaranteed to be invoked only I<after> its timeout has	1893	The callback is guaranteed to be invoked only I<after> its timeout has
1288	passed, but if multiple timers become ready during the same loop iteration	1894	passed (not I<at>, so on systems with very low-resolution clocks this
1289	then order of execution is undefined.	1895	might introduce a small delay, see "the special problem of being too
		1896	early", below). If multiple timers become ready during the same loop
		1897	iteration then the ones with earlier time-out values are invoked before
		1898	ones of the same priority with later time-out values (but this is no
		1899	longer true when a callback calls C<ev_run> recursively).
1290		1900
1291	=head3 Be smart about timeouts	1901	=head3 Be smart about timeouts
1292		1902
1293	Many real-world problems invole some kind of time-out, usually for error	1903	Many real-world problems involve some kind of timeout, usually for error
1294	recovery. A typical example is an HTTP request - if the other side hangs,	1904	recovery. A typical example is an HTTP request - if the other side hangs,
1295	you want to raise some error after a while.	1905	you want to raise some error after a while.
1296		1906
1297	Here are some ways on how to handle this problem, from simple and	1907	What follows are some ways to handle this problem, from obvious and
1298	inefficient to very efficient.	1908	inefficient to smart and efficient.
1299		1909
1300	In the following examples a 60 second activity timeout is assumed - a	1910	In the following, a 60 second activity timeout is assumed - a timeout that
1301	timeout that gets reset to 60 seconds each time some data ("a lifesign")	1911	gets reset to 60 seconds each time there is activity (e.g. each time some
1302	was received.	1912	data or other life sign was received).
1303		1913
1304	=over 4	1914	=over 4
1305		1915
1306	=item 1. Use a timer and stop, reinitialise, start it on activity.	1916	=item 1. Use a timer and stop, reinitialise and start it on activity.
1307		1917
1308	This is the most obvious, but not the most simple way: In the beginning,	1918	This is the most obvious, but not the most simple way: In the beginning,
1309	start the watcher:	1919	start the watcher:
1310		1920
1311	ev_timer_init (timer, callback, 60., 0.);	1921	ev_timer_init (timer, callback, 60., 0.);
1312	ev_timer_start (loop, timer);	1922	ev_timer_start (loop, timer);
1313		1923
1314	Then, each time there is some activity, C<ev_timer_stop> the timer,	1924	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
1315	initialise it again, and start it:	1925	and start it again:
1316		1926
1317	ev_timer_stop (loop, timer);	1927	ev_timer_stop (loop, timer);
1318	ev_timer_set (timer, 60., 0.);	1928	ev_timer_set (timer, 60., 0.);
1319	ev_timer_start (loop, timer);	1929	ev_timer_start (loop, timer);
1320		1930
1321	This is relatively simple to implement, but means that each time there	1931	This is relatively simple to implement, but means that each time there is
1322	is some activity, libev will first have to remove the timer from it's	1932	some activity, libev will first have to remove the timer from its internal
1323	internal data strcuture and then add it again.	1933	data structure and then add it again. Libev tries to be fast, but it's
		1934	still not a constant-time operation.
1324		1935
1325	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.	1936	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
1326		1937
1327	This is the easiest way, and involves using C<ev_timer_again> instead of	1938	This is the easiest way, and involves using C<ev_timer_again> instead of
1328	C<ev_timer_start>.	1939	C<ev_timer_start>.
1329		1940
1330	For this, configure an C<ev_timer> with a C<repeat> value of C<60> and	1941	To implement this, configure an C<ev_timer> with a C<repeat> value
1331	then call C<ev_timer_again> at start and each time you successfully read	1942	of C<60> and then call C<ev_timer_again> at start and each time you
1332	or write some data. If you go into an idle state where you do not expect	1943	successfully read or write some data. If you go into an idle state where
1333	data to travel on the socket, you can C<ev_timer_stop> the timer, and	1944	you do not expect data to travel on the socket, you can C<ev_timer_stop>
1334	C<ev_timer_again> will automatically restart it if need be.	1945	the timer, and C<ev_timer_again> will automatically restart it if need be.
1335		1946
1336	That means you can ignore the C<after> value and C<ev_timer_start>	1947	That means you can ignore both the C<ev_timer_start> function and the
1337	altogether and only ever use the C<repeat> value and C<ev_timer_again>.	1948	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1949	member and C<ev_timer_again>.
1338		1950
1339	At start:	1951	At start:
1340		1952
1341	ev_timer_init (timer, callback, 0., 60.);	1953	ev_init (timer, callback);
		1954	timer->repeat = 60.;
1342	ev_timer_again (loop, timer);	1955	ev_timer_again (loop, timer);
1343		1956
1344	Each time you receive some data:	1957	Each time there is some activity:
1345		1958
1346	ev_timer_again (loop, timer);	1959	ev_timer_again (loop, timer);
1347		1960
1348	It is even possible to change the time-out on the fly:	1961	It is even possible to change the time-out on the fly, regardless of
		1962	whether the watcher is active or not:
1349		1963
1350	timer->repeat = 30.;	1964	timer->repeat = 30.;
1351	ev_timer_again (loop, timer);	1965	ev_timer_again (loop, timer);
1352		1966
1353	This is slightly more efficient then stopping/starting the timer each time	1967	This is slightly more efficient then stopping/starting the timer each time
1354	you want to modify its timeout value, as libev does not have to completely	1968	you want to modify its timeout value, as libev does not have to completely
1355	remove and re-insert the timer from/into it's internal data structure.	1969	remove and re-insert the timer from/into its internal data structure.
		1970
		1971	It is, however, even simpler than the "obvious" way to do it.
1356		1972
1357	=item 3. Let the timer time out, but then re-arm it as required.	1973	=item 3. Let the timer time out, but then re-arm it as required.
1358		1974
1359	This method is more tricky, but usually most efficient: Most timeouts are	1975	This method is more tricky, but usually most efficient: Most timeouts are
1360	relatively long compared to the loop iteration time - in our example,	1976	relatively long compared to the intervals between other activity - in
1361	within 60 seconds, there are usually many I/O events with associated	1977	our example, within 60 seconds, there are usually many I/O events with
1362	activity resets.	1978	associated activity resets.
1363		1979
1364	In this case, it would be more efficient to leave the C<ev_timer> alone,	1980	In this case, it would be more efficient to leave the C<ev_timer> alone,
1365	but remember the time of last activity, and check for a real timeout only	1981	but remember the time of last activity, and check for a real timeout only
1366	within the callback:	1982	within the callback:
1367		1983
		1984	ev_tstamp timeout = 60.;
1368	ev_tstamp last_activity; // time of last activity	1985	ev_tstamp last_activity; // time of last activity
		1986	ev_timer timer;
1369		1987
1370	static void	1988	static void
1371	callback (EV_P_ ev_timer *w, int revents)	1989	callback (EV_P_ ev_timer *w, int revents)
1372	{	1990	{
1373	ev_tstamp now = ev_now (EV_A);	1991	// calculate when the timeout would happen
1374	ev_tstamp timeout = last_activity + 60.;	1992	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1375		1993
1376	// if last_activity is older than now - timeout, we did time out	1994	// if negative, it means we the timeout already occurred
1377	if (timeout < now)	1995	if (after < 0.)
1378	{	1996	{
1379	// timeout occured, take action	1997	// timeout occurred, take action
1380	}	1998	}
1381	else	1999	else
1382	{	2000	{
1383	// callback was invoked, but there was some activity, re-arm	2001	// callback was invoked, but there was some recent
1384	// to fire in last_activity + 60.	2002	// activity. simply restart the timer to time out
1385	w->again = timeout - now;	2003	// after "after" seconds, which is the earliest time
		2004	// the timeout can occur.
		2005	ev_timer_set (w, after, 0.);
1386	ev_timer_again (EV_A_ w);	2006	ev_timer_start (EV_A_ w);
1387	}	2007	}
1388	}	2008	}
1389		2009
1390	To summarise the callback: first calculate the real time-out (defined as	2010	To summarise the callback: first calculate in how many seconds the
1391	"60 seconds after the last activity"), then check if that time has been	2011	timeout will occur (by calculating the absolute time when it would occur,
1392	reached, which means there was a real timeout. Otherwise the callback was	2012	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1393	invoked too early (timeout is in the future), so re-schedule the timer to	2013	(EV_A)> from that).
1394	fire at that future time.
1395		2014
1396	Note how C<ev_timer_again> is used, taking advantage of the	2015	If this value is negative, then we are already past the timeout, i.e. we
1397	C<ev_timer_again> optimisation when the timer is already running.	2016	timed out, and need to do whatever is needed in this case.
1398		2017
		2018	Otherwise, we now the earliest time at which the timeout would trigger,
		2019	and simply start the timer with this timeout value.
		2020
		2021	In other words, each time the callback is invoked it will check whether
		2022	the timeout occurred. If not, it will simply reschedule itself to check
		2023	again at the earliest time it could time out. Rinse. Repeat.
		2024
1399	This scheme causes more callback invocations (about one every 60 seconds),	2025	This scheme causes more callback invocations (about one every 60 seconds
1400	but virtually no calls to libev to change the timeout.	2026	minus half the average time between activity), but virtually no calls to
		2027	libev to change the timeout.
1401		2028
1402	To start the timer, simply intiialise the watcher and C<last_activity>,	2029	To start the machinery, simply initialise the watcher and set
1403	then call the callback:	2030	C<last_activity> to the current time (meaning there was some activity just
		2031	now), then call the callback, which will "do the right thing" and start
		2032	the timer:
1404		2033
		2034	last_activity = ev_now (EV_A);
1405	ev_timer_init (timer, callback);	2035	ev_init (&timer, callback);
		2036	callback (EV_A_ &timer, 0);
		2037
		2038	When there is some activity, simply store the current time in
		2039	C<last_activity>, no libev calls at all:
		2040
		2041	if (activity detected)
1406	last_activity = ev_now (loop);	2042	last_activity = ev_now (EV_A);
1407	callback (loop, timer, EV_TIMEOUT);
1408		2043
1409	And when there is some activity, simply remember the time in	2044	When your timeout value changes, then the timeout can be changed by simply
1410	C<last_activity>:	2045	providing a new value, stopping the timer and calling the callback, which
		2046	will again do the right thing (for example, time out immediately :).
1411		2047
1412	last_actiivty = ev_now (loop);	2048	timeout = new_value;
		2049	ev_timer_stop (EV_A_ &timer);
		2050	callback (EV_A_ &timer, 0);
1413		2051
1414	This technique is slightly more complex, but in most cases where the	2052	This technique is slightly more complex, but in most cases where the
1415	time-out is unlikely to be triggered, much more efficient.	2053	time-out is unlikely to be triggered, much more efficient.
1416		2054
		2055	=item 4. Wee, just use a double-linked list for your timeouts.
		2056
		2057	If there is not one request, but many thousands (millions...), all
		2058	employing some kind of timeout with the same timeout value, then one can
		2059	do even better:
		2060
		2061	When starting the timeout, calculate the timeout value and put the timeout
		2062	at the I<end> of the list.
		2063
		2064	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		2065	the list is expected to fire (for example, using the technique #3).
		2066
		2067	When there is some activity, remove the timer from the list, recalculate
		2068	the timeout, append it to the end of the list again, and make sure to
		2069	update the C<ev_timer> if it was taken from the beginning of the list.
		2070
		2071	This way, one can manage an unlimited number of timeouts in O(1) time for
		2072	starting, stopping and updating the timers, at the expense of a major
		2073	complication, and having to use a constant timeout. The constant timeout
		2074	ensures that the list stays sorted.
		2075
1417	=back	2076	=back
1418		2077
		2078	So which method the best?
		2079
		2080	Method #2 is a simple no-brain-required solution that is adequate in most
		2081	situations. Method #3 requires a bit more thinking, but handles many cases
		2082	better, and isn't very complicated either. In most case, choosing either
		2083	one is fine, with #3 being better in typical situations.
		2084
		2085	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		2086	rather complicated, but extremely efficient, something that really pays
		2087	off after the first million or so of active timers, i.e. it's usually
		2088	overkill :)
		2089
		2090	=head3 The special problem of being too early
		2091
		2092	If you ask a timer to call your callback after three seconds, then
		2093	you expect it to be invoked after three seconds - but of course, this
		2094	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2095	guaranteed to any precision by libev - imagine somebody suspending the
		2096	process with a STOP signal for a few hours for example.
		2097
		2098	So, libev tries to invoke your callback as soon as possible I<after> the
		2099	delay has occurred, but cannot guarantee this.
		2100
		2101	A less obvious failure mode is calling your callback too early: many event
		2102	loops compare timestamps with a "elapsed delay >= requested delay", but
		2103	this can cause your callback to be invoked much earlier than you would
		2104	expect.
		2105
		2106	To see why, imagine a system with a clock that only offers full second
		2107	resolution (think windows if you can't come up with a broken enough OS
		2108	yourself). If you schedule a one-second timer at the time 500.9, then the
		2109	event loop will schedule your timeout to elapse at a system time of 500
		2110	(500.9 truncated to the resolution) + 1, or 501.
		2111
		2112	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2113	501" and invoke the callback 0.1s after it was started, even though a
		2114	one-second delay was requested - this is being "too early", despite best
		2115	intentions.
		2116
		2117	This is the reason why libev will never invoke the callback if the elapsed
		2118	delay equals the requested delay, but only when the elapsed delay is
		2119	larger than the requested delay. In the example above, libev would only invoke
		2120	the callback at system time 502, or 1.1s after the timer was started.
		2121
		2122	So, while libev cannot guarantee that your callback will be invoked
		2123	exactly when requested, it I<can> and I<does> guarantee that the requested
		2124	delay has actually elapsed, or in other words, it always errs on the "too
		2125	late" side of things.
		2126
1419	=head3 The special problem of time updates	2127	=head3 The special problem of time updates
1420		2128
1421	Establishing the current time is a costly operation (it usually takes at	2129	Establishing the current time is a costly operation (it usually takes
1422	least two system calls): EV therefore updates its idea of the current	2130	at least one system call): EV therefore updates its idea of the current
1423	time only before and after C<ev_loop> collects new events, which causes a	2131	time only before and after C<ev_run> collects new events, which causes a
1424	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2132	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1425	lots of events in one iteration.	2133	lots of events in one iteration.
1426		2134
1427	The relative timeouts are calculated relative to the C<ev_now ()>	2135	The relative timeouts are calculated relative to the C<ev_now ()>
1428	time. This is usually the right thing as this timestamp refers to the time	2136	time. This is usually the right thing as this timestamp refers to the time
1429	of the event triggering whatever timeout you are modifying/starting. If	2137	of the event triggering whatever timeout you are modifying/starting. If
1430	you suspect event processing to be delayed and you I<need> to base the	2138	you suspect event processing to be delayed and you I<need> to base the
1431	timeout on the current time, use something like this to adjust for this:	2139	timeout on the current time, use something like the following to adjust
		2140	for it:
1432		2141
1433	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2142	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1434		2143
1435	If the event loop is suspended for a long time, you can also force an	2144	If the event loop is suspended for a long time, you can also force an
1436	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2145	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1437	()>.	2146	()>, although that will push the event time of all outstanding events
		2147	further into the future.
		2148
		2149	=head3 The special problem of unsynchronised clocks
		2150
		2151	Modern systems have a variety of clocks - libev itself uses the normal
		2152	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2153	jumps).
		2154
		2155	Neither of these clocks is synchronised with each other or any other clock
		2156	on the system, so C<ev_time ()> might return a considerably different time
		2157	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2158	a call to C<gettimeofday> might return a second count that is one higher
		2159	than a directly following call to C<time>.
		2160
		2161	The moral of this is to only compare libev-related timestamps with
		2162	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2163	a second or so.
		2164
		2165	One more problem arises due to this lack of synchronisation: if libev uses
		2166	the system monotonic clock and you compare timestamps from C<ev_time>
		2167	or C<ev_now> from when you started your timer and when your callback is
		2168	invoked, you will find that sometimes the callback is a bit "early".
		2169
		2170	This is because C<ev_timer>s work in real time, not wall clock time, so
		2171	libev makes sure your callback is not invoked before the delay happened,
		2172	I<measured according to the real time>, not the system clock.
		2173
		2174	If your timeouts are based on a physical timescale (e.g. "time out this
		2175	connection after 100 seconds") then this shouldn't bother you as it is
		2176	exactly the right behaviour.
		2177
		2178	If you want to compare wall clock/system timestamps to your timers, then
		2179	you need to use C<ev_periodic>s, as these are based on the wall clock
		2180	time, where your comparisons will always generate correct results.
		2181
		2182	=head3 The special problems of suspended animation
		2183
		2184	When you leave the server world it is quite customary to hit machines that
		2185	can suspend/hibernate - what happens to the clocks during such a suspend?
		2186
		2187	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2188	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2189	to run until the system is suspended, but they will not advance while the
		2190	system is suspended. That means, on resume, it will be as if the program
		2191	was frozen for a few seconds, but the suspend time will not be counted
		2192	towards C<ev_timer> when a monotonic clock source is used. The real time
		2193	clock advanced as expected, but if it is used as sole clocksource, then a
		2194	long suspend would be detected as a time jump by libev, and timers would
		2195	be adjusted accordingly.
		2196
		2197	I would not be surprised to see different behaviour in different between
		2198	operating systems, OS versions or even different hardware.
		2199
		2200	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2201	time jump in the monotonic clocks and the realtime clock. If the program
		2202	is suspended for a very long time, and monotonic clock sources are in use,
		2203	then you can expect C<ev_timer>s to expire as the full suspension time
		2204	will be counted towards the timers. When no monotonic clock source is in
		2205	use, then libev will again assume a timejump and adjust accordingly.
		2206
		2207	It might be beneficial for this latter case to call C<ev_suspend>
		2208	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2209	deterministic behaviour in this case (you can do nothing against
		2210	C<SIGSTOP>).
1438		2211
1439	=head3 Watcher-Specific Functions and Data Members	2212	=head3 Watcher-Specific Functions and Data Members
1440		2213
1441	=over 4	2214	=over 4
1442		2215
1443	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2216	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1444		2217
1445	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2218	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1446		2219
1447	Configure the timer to trigger after C<after> seconds. If C<repeat>	2220	Configure the timer to trigger after C<after> seconds (fractional and
1448	is C<0.>, then it will automatically be stopped once the timeout is	2221	negative values are supported). If C<repeat> is C<0.>, then it will
1449	reached. If it is positive, then the timer will automatically be	2222	automatically be stopped once the timeout is reached. If it is positive,
1450	configured to trigger again C<repeat> seconds later, again, and again,	2223	then the timer will automatically be configured to trigger again C<repeat>
1451	until stopped manually.	2224	seconds later, again, and again, until stopped manually.
1452		2225
1453	The timer itself will do a best-effort at avoiding drift, that is, if	2226	The timer itself will do a best-effort at avoiding drift, that is, if
1454	you configure a timer to trigger every 10 seconds, then it will normally	2227	you configure a timer to trigger every 10 seconds, then it will normally
1455	trigger at exactly 10 second intervals. If, however, your program cannot	2228	trigger at exactly 10 second intervals. If, however, your program cannot
1456	keep up with the timer (because it takes longer than those 10 seconds to	2229	keep up with the timer (because it takes longer than those 10 seconds to
1457	do stuff) the timer will not fire more than once per event loop iteration.	2230	do stuff) the timer will not fire more than once per event loop iteration.
1458		2231
1459	=item ev_timer_again (loop, ev_timer *)	2232	=item ev_timer_again (loop, ev_timer *)
1460		2233
1461	This will act as if the timer timed out and restart it again if it is	2234	This will act as if the timer timed out, and restarts it again if it is
1462	repeating. The exact semantics are:	2235	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2236	timeout to the C<repeat> value and calling C<ev_timer_start>.
1463		2237
		2238	The exact semantics are as in the following rules, all of which will be
		2239	applied to the watcher:
		2240
		2241	=over 4
		2242
1464	If the timer is pending, its pending status is cleared.	2243	=item If the timer is pending, the pending status is always cleared.
1465		2244
1466	If the timer is started but non-repeating, stop it (as if it timed out).	2245	=item If the timer is started but non-repeating, stop it (as if it timed
		2246	out, without invoking it).
1467		2247
1468	If the timer is repeating, either start it if necessary (with the	2248	=item If the timer is repeating, make the C<repeat> value the new timeout
1469	C<repeat> value), or reset the running timer to the C<repeat> value.	2249	and start the timer, if necessary.
1470		2250
		2251	=back
		2252
1471	This sounds a bit complicated, see "Be smart about timeouts", above, for a	2253	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1472	usage example.	2254	usage example.
		2255
		2256	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
		2257
		2258	Returns the remaining time until a timer fires. If the timer is active,
		2259	then this time is relative to the current event loop time, otherwise it's
		2260	the timeout value currently configured.
		2261
		2262	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2263	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2264	will return C<4>. When the timer expires and is restarted, it will return
		2265	roughly C<7> (likely slightly less as callback invocation takes some time,
		2266	too), and so on.
1473		2267
1474	=item ev_tstamp repeat [read-write]	2268	=item ev_tstamp repeat [read-write]
1475		2269
1476	The current C<repeat> value. Will be used each time the watcher times out	2270	The current C<repeat> value. Will be used each time the watcher times out
1477	or C<ev_timer_again> is called, and determines the next timeout (if any),	2271	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1503	}	2297	}
1504		2298
1505	ev_timer mytimer;	2299	ev_timer mytimer;
1506	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2300	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1507	ev_timer_again (&mytimer); /* start timer */	2301	ev_timer_again (&mytimer); /* start timer */
1508	ev_loop (loop, 0);	2302	ev_run (loop, 0);
1509		2303
1510	// and in some piece of code that gets executed on any "activity":	2304	// and in some piece of code that gets executed on any "activity":
1511	// reset the timeout to start ticking again at 10 seconds	2305	// reset the timeout to start ticking again at 10 seconds
1512	ev_timer_again (&mytimer);	2306	ev_timer_again (&mytimer);
1513		2307
…		…
1515	=head2 C<ev_periodic> - to cron or not to cron?	2309	=head2 C<ev_periodic> - to cron or not to cron?
1516		2310
1517	Periodic watchers are also timers of a kind, but they are very versatile	2311	Periodic watchers are also timers of a kind, but they are very versatile
1518	(and unfortunately a bit complex).	2312	(and unfortunately a bit complex).
1519		2313
1520	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2314	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1521	but on wall clock time (absolute time). You can tell a periodic watcher	2315	relative time, the physical time that passes) but on wall clock time
1522	to trigger after some specific point in time. For example, if you tell a	2316	(absolute time, the thing you can read on your calendar or clock). The
1523	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	2317	difference is that wall clock time can run faster or slower than real
1524	+ 10.>, that is, an absolute time not a delay) and then reset your system	2318	time, and time jumps are not uncommon (e.g. when you adjust your
1525	clock to January of the previous year, then it will take more than year	2319	wrist-watch).
1526	to trigger the event (unlike an C<ev_timer>, which would still trigger
1527	roughly 10 seconds later as it uses a relative timeout).
1528		2320
		2321	You can tell a periodic watcher to trigger after some specific point
		2322	in time: for example, if you tell a periodic watcher to trigger "in 10
		2323	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2324	not a delay) and then reset your system clock to January of the previous
		2325	year, then it will take a year or more to trigger the event (unlike an
		2326	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2327	it, as it uses a relative timeout).
		2328
1529	C<ev_periodic>s can also be used to implement vastly more complex timers,	2329	C<ev_periodic> watchers can also be used to implement vastly more complex
1530	such as triggering an event on each "midnight, local time", or other	2330	timers, such as triggering an event on each "midnight, local time", or
1531	complicated rules.	2331	other complicated rules. This cannot easily be done with C<ev_timer>
		2332	watchers, as those cannot react to time jumps.
1532		2333
1533	As with timers, the callback is guaranteed to be invoked only when the	2334	As with timers, the callback is guaranteed to be invoked only when the
1534	time (C<at>) has passed, but if multiple periodic timers become ready	2335	point in time where it is supposed to trigger has passed. If multiple
1535	during the same loop iteration, then order of execution is undefined.	2336	timers become ready during the same loop iteration then the ones with
		2337	earlier time-out values are invoked before ones with later time-out values
		2338	(but this is no longer true when a callback calls C<ev_run> recursively).
1536		2339
1537	=head3 Watcher-Specific Functions and Data Members	2340	=head3 Watcher-Specific Functions and Data Members
1538		2341
1539	=over 4	2342	=over 4
1540		2343
1541	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2344	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1542		2345
1543	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2346	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1544		2347
1545	Lots of arguments, lets sort it out... There are basically three modes of	2348	Lots of arguments, let's sort it out... There are basically three modes of
1546	operation, and we will explain them from simplest to most complex:	2349	operation, and we will explain them from simplest to most complex:
1547		2350
1548	=over 4	2351	=over 4
1549		2352
1550	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2353	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1551		2354
1552	In this configuration the watcher triggers an event after the wall clock	2355	In this configuration the watcher triggers an event after the wall clock
1553	time C<at> has passed. It will not repeat and will not adjust when a time	2356	time C<offset> has passed. It will not repeat and will not adjust when a
1554	jump occurs, that is, if it is to be run at January 1st 2011 then it will	2357	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1555	only run when the system clock reaches or surpasses this time.	2358	will be stopped and invoked when the system clock reaches or surpasses
		2359	this point in time.
1556		2360
1557	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2361	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1558		2362
1559	In this mode the watcher will always be scheduled to time out at the next	2363	In this mode the watcher will always be scheduled to time out at the next
1560	C<at + N * interval> time (for some integer N, which can also be negative)	2364	C<offset + N * interval> time (for some integer N, which can also be
1561	and then repeat, regardless of any time jumps.	2365	negative) and then repeat, regardless of any time jumps. The C<offset>
		2366	argument is merely an offset into the C<interval> periods.
1562		2367
1563	This can be used to create timers that do not drift with respect to the	2368	This can be used to create timers that do not drift with respect to the
1564	system clock, for example, here is a C<ev_periodic> that triggers each	2369	system clock, for example, here is an C<ev_periodic> that triggers each
1565	hour, on the hour:	2370	hour, on the hour (with respect to UTC):
1566		2371
1567	ev_periodic_set (&periodic, 0., 3600., 0);	2372	ev_periodic_set (&periodic, 0., 3600., 0);
1568		2373
1569	This doesn't mean there will always be 3600 seconds in between triggers,	2374	This doesn't mean there will always be 3600 seconds in between triggers,
1570	but only that the callback will be called when the system time shows a	2375	but only that the callback will be called when the system time shows a
1571	full hour (UTC), or more correctly, when the system time is evenly divisible	2376	full hour (UTC), or more correctly, when the system time is evenly divisible
1572	by 3600.	2377	by 3600.
1573		2378
1574	Another way to think about it (for the mathematically inclined) is that	2379	Another way to think about it (for the mathematically inclined) is that
1575	C<ev_periodic> will try to run the callback in this mode at the next possible	2380	C<ev_periodic> will try to run the callback in this mode at the next possible
1576	time where C<time = at (mod interval)>, regardless of any time jumps.	2381	time where C<time = offset (mod interval)>, regardless of any time jumps.
1577		2382
1578	For numerical stability it is preferable that the C<at> value is near	2383	The C<interval> I<MUST> be positive, and for numerical stability, the
1579	C<ev_now ()> (the current time), but there is no range requirement for	2384	interval value should be higher than C<1/8192> (which is around 100
1580	this value, and in fact is often specified as zero.	2385	microseconds) and C<offset> should be higher than C<0> and should have
		2386	at most a similar magnitude as the current time (say, within a factor of
		2387	ten). Typical values for offset are, in fact, C<0> or something between
		2388	C<0> and C<interval>, which is also the recommended range.
1581		2389
1582	Note also that there is an upper limit to how often a timer can fire (CPU	2390	Note also that there is an upper limit to how often a timer can fire (CPU
1583	speed for example), so if C<interval> is very small then timing stability	2391	speed for example), so if C<interval> is very small then timing stability
1584	will of course deteriorate. Libev itself tries to be exact to be about one	2392	will of course deteriorate. Libev itself tries to be exact to be about one
1585	millisecond (if the OS supports it and the machine is fast enough).	2393	millisecond (if the OS supports it and the machine is fast enough).
1586		2394
1587	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2395	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1588		2396
1589	In this mode the values for C<interval> and C<at> are both being	2397	In this mode the values for C<interval> and C<offset> are both being
1590	ignored. Instead, each time the periodic watcher gets scheduled, the	2398	ignored. Instead, each time the periodic watcher gets scheduled, the
1591	reschedule callback will be called with the watcher as first, and the	2399	reschedule callback will be called with the watcher as first, and the
1592	current time as second argument.	2400	current time as second argument.
1593		2401
1594	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2402	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1595	ever, or make ANY event loop modifications whatsoever>.	2403	or make ANY other event loop modifications whatsoever, unless explicitly
		2404	allowed by documentation here>.
1596		2405
1597	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2406	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1598	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	2407	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1599	only event loop modification you are allowed to do).	2408	only event loop modification you are allowed to do).
1600		2409
…		…
1614		2423
1615	NOTE: I<< This callback must always return a time that is higher than or	2424	NOTE: I<< This callback must always return a time that is higher than or
1616	equal to the passed C<now> value >>.	2425	equal to the passed C<now> value >>.
1617		2426
1618	This can be used to create very complex timers, such as a timer that	2427	This can be used to create very complex timers, such as a timer that
1619	triggers on "next midnight, local time". To do this, you would calculate the	2428	triggers on "next midnight, local time". To do this, you would calculate
1620	next midnight after C<now> and return the timestamp value for this. How	2429	the next midnight after C<now> and return the timestamp value for
1621	you do this is, again, up to you (but it is not trivial, which is the main	2430	this. Here is a (completely untested, no error checking) example on how to
1622	reason I omitted it as an example).	2431	do this:
		2432
		2433	#include <time.h>
		2434
		2435	static ev_tstamp
		2436	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2437	{
		2438	time_t tnow = (time_t)now;
		2439	struct tm tm;
		2440	localtime_r (&tnow, &tm);
		2441
		2442	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2443	++tm.tm_mday; // midnight next day
		2444
		2445	return mktime (&tm);
		2446	}
		2447
		2448	Note: this code might run into trouble on days that have more then two
		2449	midnights (beginning and end).
1623		2450
1624	=back	2451	=back
1625		2452
1626	=item ev_periodic_again (loop, ev_periodic *)	2453	=item ev_periodic_again (loop, ev_periodic *)
1627		2454
…		…
1630	a different time than the last time it was called (e.g. in a crond like	2457	a different time than the last time it was called (e.g. in a crond like
1631	program when the crontabs have changed).	2458	program when the crontabs have changed).
1632		2459
1633	=item ev_tstamp ev_periodic_at (ev_periodic *)	2460	=item ev_tstamp ev_periodic_at (ev_periodic *)
1634		2461
1635	When active, returns the absolute time that the watcher is supposed to	2462	When active, returns the absolute time that the watcher is supposed
1636	trigger next.	2463	to trigger next. This is not the same as the C<offset> argument to
		2464	C<ev_periodic_set>, but indeed works even in interval and manual
		2465	rescheduling modes.
1637		2466
1638	=item ev_tstamp offset [read-write]	2467	=item ev_tstamp offset [read-write]
1639		2468
1640	When repeating, this contains the offset value, otherwise this is the	2469	When repeating, this contains the offset value, otherwise this is the
1641	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2470	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2471	although libev might modify this value for better numerical stability).
1642		2472
1643	Can be modified any time, but changes only take effect when the periodic	2473	Can be modified any time, but changes only take effect when the periodic
1644	timer fires or C<ev_periodic_again> is being called.	2474	timer fires or C<ev_periodic_again> is being called.
1645		2475
1646	=item ev_tstamp interval [read-write]	2476	=item ev_tstamp interval [read-write]
…		…
1662	Example: Call a callback every hour, or, more precisely, whenever the	2492	Example: Call a callback every hour, or, more precisely, whenever the
1663	system time is divisible by 3600. The callback invocation times have	2493	system time is divisible by 3600. The callback invocation times have
1664	potentially a lot of jitter, but good long-term stability.	2494	potentially a lot of jitter, but good long-term stability.
1665		2495
1666	static void	2496	static void
1667	clock_cb (struct ev_loop *loop, ev_io *w, int revents)	2497	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1668	{	2498	{
1669	... its now a full hour (UTC, or TAI or whatever your clock follows)	2499	... its now a full hour (UTC, or TAI or whatever your clock follows)
1670	}	2500	}
1671		2501
1672	ev_periodic hourly_tick;	2502	ev_periodic hourly_tick;
…		…
1689		2519
1690	ev_periodic hourly_tick;	2520	ev_periodic hourly_tick;
1691	ev_periodic_init (&hourly_tick, clock_cb,	2521	ev_periodic_init (&hourly_tick, clock_cb,
1692	fmod (ev_now (loop), 3600.), 3600., 0);	2522	fmod (ev_now (loop), 3600.), 3600., 0);
1693	ev_periodic_start (loop, &hourly_tick);	2523	ev_periodic_start (loop, &hourly_tick);
1694		2524
1695		2525
1696	=head2 C<ev_signal> - signal me when a signal gets signalled!	2526	=head2 C<ev_signal> - signal me when a signal gets signalled!
1697		2527
1698	Signal watchers will trigger an event when the process receives a specific	2528	Signal watchers will trigger an event when the process receives a specific
1699	signal one or more times. Even though signals are very asynchronous, libev	2529	signal one or more times. Even though signals are very asynchronous, libev
1700	will try it's best to deliver signals synchronously, i.e. as part of the	2530	will try its best to deliver signals synchronously, i.e. as part of the
1701	normal event processing, like any other event.	2531	normal event processing, like any other event.
1702		2532
1703	If you want signals asynchronously, just use C<sigaction> as you would	2533	If you want signals to be delivered truly asynchronously, just use
1704	do without libev and forget about sharing the signal. You can even use	2534	C<sigaction> as you would do without libev and forget about sharing
1705	C<ev_async> from a signal handler to synchronously wake up an event loop.	2535	the signal. You can even use C<ev_async> from a signal handler to
		2536	synchronously wake up an event loop.
1706		2537
1707	You can configure as many watchers as you like per signal. Only when the	2538	You can configure as many watchers as you like for the same signal, but
1708	first watcher gets started will libev actually register a signal handler	2539	only within the same loop, i.e. you can watch for C<SIGINT> in your
1709	with the kernel (thus it coexists with your own signal handlers as long as	2540	default loop and for C<SIGIO> in another loop, but you cannot watch for
1710	you don't register any with libev for the same signal). Similarly, when	2541	C<SIGINT> in both the default loop and another loop at the same time. At
1711	the last signal watcher for a signal is stopped, libev will reset the	2542	the moment, C<SIGCHLD> is permanently tied to the default loop.
1712	signal handler to SIG_DFL (regardless of what it was set to before).	2543
		2544	Only after the first watcher for a signal is started will libev actually
		2545	register something with the kernel. It thus coexists with your own signal
		2546	handlers as long as you don't register any with libev for the same signal.
1713		2547
1714	If possible and supported, libev will install its handlers with	2548	If possible and supported, libev will install its handlers with
1715	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2549	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1716	interrupted. If you have a problem with system calls getting interrupted by	2550	not be unduly interrupted. If you have a problem with system calls getting
1717	signals you can block all signals in an C<ev_check> watcher and unblock	2551	interrupted by signals you can block all signals in an C<ev_check> watcher
1718	them in an C<ev_prepare> watcher.	2552	and unblock them in an C<ev_prepare> watcher.
		2553
		2554	=head3 The special problem of inheritance over fork/execve/pthread_create
		2555
		2556	Both the signal mask (C<sigprocmask>) and the signal disposition
		2557	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2558	stopping it again), that is, libev might or might not block the signal,
		2559	and might or might not set or restore the installed signal handler (but
		2560	see C<EVFLAG_NOSIGMASK>).
		2561
		2562	While this does not matter for the signal disposition (libev never
		2563	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2564	C<execve>), this matters for the signal mask: many programs do not expect
		2565	certain signals to be blocked.
		2566
		2567	This means that before calling C<exec> (from the child) you should reset
		2568	the signal mask to whatever "default" you expect (all clear is a good
		2569	choice usually).
		2570
		2571	The simplest way to ensure that the signal mask is reset in the child is
		2572	to install a fork handler with C<pthread_atfork> that resets it. That will
		2573	catch fork calls done by libraries (such as the libc) as well.
		2574
		2575	In current versions of libev, the signal will not be blocked indefinitely
		2576	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2577	the window of opportunity for problems, it will not go away, as libev
		2578	I<has> to modify the signal mask, at least temporarily.
		2579
		2580	So I can't stress this enough: I<If you do not reset your signal mask when
		2581	you expect it to be empty, you have a race condition in your code>. This
		2582	is not a libev-specific thing, this is true for most event libraries.
		2583
		2584	=head3 The special problem of threads signal handling
		2585
		2586	POSIX threads has problematic signal handling semantics, specifically,
		2587	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2588	threads in a process block signals, which is hard to achieve.
		2589
		2590	When you want to use sigwait (or mix libev signal handling with your own
		2591	for the same signals), you can tackle this problem by globally blocking
		2592	all signals before creating any threads (or creating them with a fully set
		2593	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2594	loops. Then designate one thread as "signal receiver thread" which handles
		2595	these signals. You can pass on any signals that libev might be interested
		2596	in by calling C<ev_feed_signal>.
1719		2597
1720	=head3 Watcher-Specific Functions and Data Members	2598	=head3 Watcher-Specific Functions and Data Members
1721		2599
1722	=over 4	2600	=over 4
1723		2601
…		…
1739	Example: Try to exit cleanly on SIGINT.	2617	Example: Try to exit cleanly on SIGINT.
1740		2618
1741	static void	2619	static void
1742	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)	2620	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1743	{	2621	{
1744	ev_unloop (loop, EVUNLOOP_ALL);	2622	ev_break (loop, EVBREAK_ALL);
1745	}	2623	}
1746		2624
1747	ev_signal signal_watcher;	2625	ev_signal signal_watcher;
1748	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2626	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1749	ev_signal_start (loop, &signal_watcher);	2627	ev_signal_start (loop, &signal_watcher);
…		…
1755	some child status changes (most typically when a child of yours dies or	2633	some child status changes (most typically when a child of yours dies or
1756	exits). It is permissible to install a child watcher I<after> the child	2634	exits). It is permissible to install a child watcher I<after> the child
1757	has been forked (which implies it might have already exited), as long	2635	has been forked (which implies it might have already exited), as long
1758	as the event loop isn't entered (or is continued from a watcher), i.e.,	2636	as the event loop isn't entered (or is continued from a watcher), i.e.,
1759	forking and then immediately registering a watcher for the child is fine,	2637	forking and then immediately registering a watcher for the child is fine,
1760	but forking and registering a watcher a few event loop iterations later is	2638	but forking and registering a watcher a few event loop iterations later or
1761	not.	2639	in the next callback invocation is not.
1762		2640
1763	Only the default event loop is capable of handling signals, and therefore	2641	Only the default event loop is capable of handling signals, and therefore
1764	you can only register child watchers in the default event loop.	2642	you can only register child watchers in the default event loop.
1765		2643
		2644	Due to some design glitches inside libev, child watchers will always be
		2645	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2646	libev)
		2647
1766	=head3 Process Interaction	2648	=head3 Process Interaction
1767		2649
1768	Libev grabs C<SIGCHLD> as soon as the default event loop is	2650	Libev grabs C<SIGCHLD> as soon as the default event loop is
1769	initialised. This is necessary to guarantee proper behaviour even if	2651	initialised. This is necessary to guarantee proper behaviour even if the
1770	the first child watcher is started after the child exits. The occurrence	2652	first child watcher is started after the child exits. The occurrence
1771	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2653	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1772	synchronously as part of the event loop processing. Libev always reaps all	2654	synchronously as part of the event loop processing. Libev always reaps all
1773	children, even ones not watched.	2655	children, even ones not watched.
1774		2656
1775	=head3 Overriding the Built-In Processing	2657	=head3 Overriding the Built-In Processing
…		…
1785	=head3 Stopping the Child Watcher	2667	=head3 Stopping the Child Watcher
1786		2668
1787	Currently, the child watcher never gets stopped, even when the	2669	Currently, the child watcher never gets stopped, even when the
1788	child terminates, so normally one needs to stop the watcher in the	2670	child terminates, so normally one needs to stop the watcher in the
1789	callback. Future versions of libev might stop the watcher automatically	2671	callback. Future versions of libev might stop the watcher automatically
1790	when a child exit is detected.	2672	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2673	problem).
1791		2674
1792	=head3 Watcher-Specific Functions and Data Members	2675	=head3 Watcher-Specific Functions and Data Members
1793		2676
1794	=over 4	2677	=over 4
1795		2678
…		…
1852		2735
1853		2736
1854	=head2 C<ev_stat> - did the file attributes just change?	2737	=head2 C<ev_stat> - did the file attributes just change?
1855		2738
1856	This watches a file system path for attribute changes. That is, it calls	2739	This watches a file system path for attribute changes. That is, it calls
1857	C<stat> regularly (or when the OS says it changed) and sees if it changed	2740	C<stat> on that path in regular intervals (or when the OS says it changed)
1858	compared to the last time, invoking the callback if it did.	2741	and sees if it changed compared to the last time, invoking the callback
		2742	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2743	happen after the watcher has been started will be reported.
1859		2744
1860	The path does not need to exist: changing from "path exists" to "path does	2745	The path does not need to exist: changing from "path exists" to "path does
1861	not exist" is a status change like any other. The condition "path does	2746	not exist" is a status change like any other. The condition "path does not
1862	not exist" is signified by the C<st_nlink> field being zero (which is	2747	exist" (or more correctly "path cannot be stat'ed") is signified by the
1863	otherwise always forced to be at least one) and all the other fields of	2748	C<st_nlink> field being zero (which is otherwise always forced to be at
1864	the stat buffer having unspecified contents.	2749	least one) and all the other fields of the stat buffer having unspecified
		2750	contents.
1865		2751
1866	The path I<should> be absolute and I<must not> end in a slash. If it is	2752	The path I<must not> end in a slash or contain special components such as
		2753	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1867	relative and your working directory changes, the behaviour is undefined.	2754	your working directory changes, then the behaviour is undefined.
1868		2755
1869	Since there is no standard kernel interface to do this, the portable	2756	Since there is no portable change notification interface available, the
1870	implementation simply calls C<stat (2)> regularly on the path to see if	2757	portable implementation simply calls C<stat(2)> regularly on the path
1871	it changed somehow. You can specify a recommended polling interval for	2758	to see if it changed somehow. You can specify a recommended polling
1872	this case. If you specify a polling interval of C<0> (highly recommended!)	2759	interval for this case. If you specify a polling interval of C<0> (highly
1873	then a I<suitable, unspecified default> value will be used (which	2760	recommended!) then a I<suitable, unspecified default> value will be used
1874	you can expect to be around five seconds, although this might change	2761	(which you can expect to be around five seconds, although this might
1875	dynamically). Libev will also impose a minimum interval which is currently	2762	change dynamically). Libev will also impose a minimum interval which is
1876	around C<0.1>, but thats usually overkill.	2763	currently around C<0.1>, but that's usually overkill.
1877		2764
1878	This watcher type is not meant for massive numbers of stat watchers,	2765	This watcher type is not meant for massive numbers of stat watchers,
1879	as even with OS-supported change notifications, this can be	2766	as even with OS-supported change notifications, this can be
1880	resource-intensive.	2767	resource-intensive.
1881		2768
1882	At the time of this writing, the only OS-specific interface implemented	2769	At the time of this writing, the only OS-specific interface implemented
1883	is the Linux inotify interface (implementing kqueue support is left as	2770	is the Linux inotify interface (implementing kqueue support is left as an
1884	an exercise for the reader. Note, however, that the author sees no way	2771	exercise for the reader. Note, however, that the author sees no way of
1885	of implementing C<ev_stat> semantics with kqueue).	2772	implementing C<ev_stat> semantics with kqueue, except as a hint).
1886		2773
1887	=head3 ABI Issues (Largefile Support)	2774	=head3 ABI Issues (Largefile Support)
1888		2775
1889	Libev by default (unless the user overrides this) uses the default	2776	Libev by default (unless the user overrides this) uses the default
1890	compilation environment, which means that on systems with large file	2777	compilation environment, which means that on systems with large file
1891	support disabled by default, you get the 32 bit version of the stat	2778	support disabled by default, you get the 32 bit version of the stat
1892	structure. When using the library from programs that change the ABI to	2779	structure. When using the library from programs that change the ABI to
1893	use 64 bit file offsets the programs will fail. In that case you have to	2780	use 64 bit file offsets the programs will fail. In that case you have to
1894	compile libev with the same flags to get binary compatibility. This is	2781	compile libev with the same flags to get binary compatibility. This is
1895	obviously the case with any flags that change the ABI, but the problem is	2782	obviously the case with any flags that change the ABI, but the problem is
1896	most noticeably disabled with ev_stat and large file support.	2783	most noticeably displayed with ev_stat and large file support.
1897		2784
1898	The solution for this is to lobby your distribution maker to make large	2785	The solution for this is to lobby your distribution maker to make large
1899	file interfaces available by default (as e.g. FreeBSD does) and not	2786	file interfaces available by default (as e.g. FreeBSD does) and not
1900	optional. Libev cannot simply switch on large file support because it has	2787	optional. Libev cannot simply switch on large file support because it has
1901	to exchange stat structures with application programs compiled using the	2788	to exchange stat structures with application programs compiled using the
1902	default compilation environment.	2789	default compilation environment.
1903		2790
1904	=head3 Inotify and Kqueue	2791	=head3 Inotify and Kqueue
1905		2792
1906	When C<inotify (7)> support has been compiled into libev (generally	2793	When C<inotify (7)> support has been compiled into libev and present at
1907	only available with Linux 2.6.25 or above due to bugs in earlier	2794	runtime, it will be used to speed up change detection where possible. The
1908	implementations) and present at runtime, it will be used to speed up	2795	inotify descriptor will be created lazily when the first C<ev_stat>
1909	change detection where possible. The inotify descriptor will be created	2796	watcher is being started.
1910	lazily when the first C<ev_stat> watcher is being started.
1911		2797
1912	Inotify presence does not change the semantics of C<ev_stat> watchers	2798	Inotify presence does not change the semantics of C<ev_stat> watchers
1913	except that changes might be detected earlier, and in some cases, to avoid	2799	except that changes might be detected earlier, and in some cases, to avoid
1914	making regular C<stat> calls. Even in the presence of inotify support	2800	making regular C<stat> calls. Even in the presence of inotify support
1915	there are many cases where libev has to resort to regular C<stat> polling,	2801	there are many cases where libev has to resort to regular C<stat> polling,
1916	but as long as the path exists, libev usually gets away without polling.	2802	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2803	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2804	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2805	xfs are fully working) libev usually gets away without polling.
1917		2806
1918	There is no support for kqueue, as apparently it cannot be used to	2807	There is no support for kqueue, as apparently it cannot be used to
1919	implement this functionality, due to the requirement of having a file	2808	implement this functionality, due to the requirement of having a file
1920	descriptor open on the object at all times, and detecting renames, unlinks	2809	descriptor open on the object at all times, and detecting renames, unlinks
1921	etc. is difficult.	2810	etc. is difficult.
1922		2811
		2812	=head3 C<stat ()> is a synchronous operation
		2813
		2814	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2815	the process. The exception are C<ev_stat> watchers - those call C<stat
		2816	()>, which is a synchronous operation.
		2817
		2818	For local paths, this usually doesn't matter: unless the system is very
		2819	busy or the intervals between stat's are large, a stat call will be fast,
		2820	as the path data is usually in memory already (except when starting the
		2821	watcher).
		2822
		2823	For networked file systems, calling C<stat ()> can block an indefinite
		2824	time due to network issues, and even under good conditions, a stat call
		2825	often takes multiple milliseconds.
		2826
		2827	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2828	paths, although this is fully supported by libev.
		2829
1923	=head3 The special problem of stat time resolution	2830	=head3 The special problem of stat time resolution
1924		2831
1925	The C<stat ()> system call only supports full-second resolution portably, and	2832	The C<stat ()> system call only supports full-second resolution portably,
1926	even on systems where the resolution is higher, most file systems still	2833	and even on systems where the resolution is higher, most file systems
1927	only support whole seconds.	2834	still only support whole seconds.
1928		2835
1929	That means that, if the time is the only thing that changes, you can	2836	That means that, if the time is the only thing that changes, you can
1930	easily miss updates: on the first update, C<ev_stat> detects a change and	2837	easily miss updates: on the first update, C<ev_stat> detects a change and
1931	calls your callback, which does something. When there is another update	2838	calls your callback, which does something. When there is another update
1932	within the same second, C<ev_stat> will be unable to detect unless the	2839	within the same second, C<ev_stat> will be unable to detect unless the
…		…
2071	Apart from keeping your process non-blocking (which is a useful	2978	Apart from keeping your process non-blocking (which is a useful
2072	effect on its own sometimes), idle watchers are a good place to do	2979	effect on its own sometimes), idle watchers are a good place to do
2073	"pseudo-background processing", or delay processing stuff to after the	2980	"pseudo-background processing", or delay processing stuff to after the
2074	event loop has handled all outstanding events.	2981	event loop has handled all outstanding events.
2075		2982
		2983	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2984
		2985	As long as there is at least one active idle watcher, libev will never
		2986	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2987	For this to work, the idle watcher doesn't need to be invoked at all - the
		2988	lowest priority will do.
		2989
		2990	This mode of operation can be useful together with an C<ev_check> watcher,
		2991	to do something on each event loop iteration - for example to balance load
		2992	between different connections.
		2993
		2994	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2995	example.
		2996
2076	=head3 Watcher-Specific Functions and Data Members	2997	=head3 Watcher-Specific Functions and Data Members
2077		2998
2078	=over 4	2999	=over 4
2079		3000
2080	=item ev_idle_init (ev_signal *, callback)	3001	=item ev_idle_init (ev_idle *, callback)
2081		3002
2082	Initialises and configures the idle watcher - it has no parameters of any	3003	Initialises and configures the idle watcher - it has no parameters of any
2083	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	3004	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
2084	believe me.	3005	believe me.
2085		3006
…		…
2091	callback, free it. Also, use no error checking, as usual.	3012	callback, free it. Also, use no error checking, as usual.
2092		3013
2093	static void	3014	static void
2094	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	3015	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2095	{	3016	{
		3017	// stop the watcher
		3018	ev_idle_stop (loop, w);
		3019
		3020	// now we can free it
2096	free (w);	3021	free (w);
		3022
2097	// now do something you wanted to do when the program has	3023	// now do something you wanted to do when the program has
2098	// no longer anything immediate to do.	3024	// no longer anything immediate to do.
2099	}	3025	}
2100		3026
2101	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	3027	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2102	ev_idle_init (idle_watcher, idle_cb);	3028	ev_idle_init (idle_watcher, idle_cb);
2103	ev_idle_start (loop, idle_cb);	3029	ev_idle_start (loop, idle_watcher);
2104		3030
2105		3031
2106	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3032	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2107		3033
2108	Prepare and check watchers are usually (but not always) used in pairs:	3034	Prepare and check watchers are often (but not always) used in pairs:
2109	prepare watchers get invoked before the process blocks and check watchers	3035	prepare watchers get invoked before the process blocks and check watchers
2110	afterwards.	3036	afterwards.
2111		3037
2112	You I<must not> call C<ev_loop> or similar functions that enter	3038	You I<must not> call C<ev_run> (or similar functions that enter the
2113	the current event loop from either C<ev_prepare> or C<ev_check>	3039	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2114	watchers. Other loops than the current one are fine, however. The	3040	C<ev_check> watchers. Other loops than the current one are fine,
2115	rationale behind this is that you do not need to check for recursion in	3041	however. The rationale behind this is that you do not need to check
2116	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3042	for recursion in those watchers, i.e. the sequence will always be
2117	C<ev_check> so if you have one watcher of each kind they will always be	3043	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2118	called in pairs bracketing the blocking call.	3044	kind they will always be called in pairs bracketing the blocking call.
2119		3045
2120	Their main purpose is to integrate other event mechanisms into libev and	3046	Their main purpose is to integrate other event mechanisms into libev and
2121	their use is somewhat advanced. They could be used, for example, to track	3047	their use is somewhat advanced. They could be used, for example, to track
2122	variable changes, implement your own watchers, integrate net-snmp or a	3048	variable changes, implement your own watchers, integrate net-snmp or a
2123	coroutine library and lots more. They are also occasionally useful if	3049	coroutine library and lots more. They are also occasionally useful if
…		…
2141	with priority higher than or equal to the event loop and one coroutine	3067	with priority higher than or equal to the event loop and one coroutine
2142	of lower priority, but only once, using idle watchers to keep the event	3068	of lower priority, but only once, using idle watchers to keep the event
2143	loop from blocking if lower-priority coroutines are active, thus mapping	3069	loop from blocking if lower-priority coroutines are active, thus mapping
2144	low-priority coroutines to idle/background tasks).	3070	low-priority coroutines to idle/background tasks).
2145		3071
2146	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3072	When used for this purpose, it is recommended to give C<ev_check> watchers
2147	priority, to ensure that they are being run before any other watchers	3073	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2148	after the poll (this doesn't matter for C<ev_prepare> watchers).	3074	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3075	watchers).
2149		3076
2150	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	3077	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2151	activate ("feed") events into libev. While libev fully supports this, they	3078	activate ("feed") events into libev. While libev fully supports this, they
2152	might get executed before other C<ev_check> watchers did their job. As	3079	might get executed before other C<ev_check> watchers did their job. As
2153	C<ev_check> watchers are often used to embed other (non-libev) event	3080	C<ev_check> watchers are often used to embed other (non-libev) event
2154	loops those other event loops might be in an unusable state until their	3081	loops those other event loops might be in an unusable state until their
2155	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3082	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2156	others).	3083	others).
		3084
		3085	=head3 Abusing an C<ev_check> watcher for its side-effect
		3086
		3087	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3088	useful because they are called once per event loop iteration. For
		3089	example, if you want to handle a large number of connections fairly, you
		3090	normally only do a bit of work for each active connection, and if there
		3091	is more work to do, you wait for the next event loop iteration, so other
		3092	connections have a chance of making progress.
		3093
		3094	Using an C<ev_check> watcher is almost enough: it will be called on the
		3095	next event loop iteration. However, that isn't as soon as possible -
		3096	without external events, your C<ev_check> watcher will not be invoked.
		3097
		3098	This is where C<ev_idle> watchers come in handy - all you need is a
		3099	single global idle watcher that is active as long as you have one active
		3100	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3101	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3102	invoked. Neither watcher alone can do that.
2157		3103
2158	=head3 Watcher-Specific Functions and Data Members	3104	=head3 Watcher-Specific Functions and Data Members
2159		3105
2160	=over 4	3106	=over 4
2161		3107
…		…
2201	struct pollfd fds [nfd];	3147	struct pollfd fds [nfd];
2202	// actual code will need to loop here and realloc etc.	3148	// actual code will need to loop here and realloc etc.
2203	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	3149	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2204		3150
2205	/* the callback is illegal, but won't be called as we stop during check */	3151	/* the callback is illegal, but won't be called as we stop during check */
2206	ev_timer_init (&tw, 0, timeout * 1e-3);	3152	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2207	ev_timer_start (loop, &tw);	3153	ev_timer_start (loop, &tw);
2208		3154
2209	// create one ev_io per pollfd	3155	// create one ev_io per pollfd
2210	for (int i = 0; i < nfd; ++i)	3156	for (int i = 0; i < nfd; ++i)
2211	{	3157	{
…		…
2285		3231
2286	if (timeout >= 0)	3232	if (timeout >= 0)
2287	// create/start timer	3233	// create/start timer
2288		3234
2289	// poll	3235	// poll
2290	ev_loop (EV_A_ 0);	3236	ev_run (EV_A_ 0);
2291		3237
2292	// stop timer again	3238	// stop timer again
2293	if (timeout >= 0)	3239	if (timeout >= 0)
2294	ev_timer_stop (EV_A_ &to);	3240	ev_timer_stop (EV_A_ &to);
2295		3241
…		…
2324	some fds have to be watched and handled very quickly (with low latency),	3270	some fds have to be watched and handled very quickly (with low latency),
2325	and even priorities and idle watchers might have too much overhead. In	3271	and even priorities and idle watchers might have too much overhead. In
2326	this case you would put all the high priority stuff in one loop and all	3272	this case you would put all the high priority stuff in one loop and all
2327	the rest in a second one, and embed the second one in the first.	3273	the rest in a second one, and embed the second one in the first.
2328		3274
2329	As long as the watcher is active, the callback will be invoked every time	3275	As long as the watcher is active, the callback will be invoked every
2330	there might be events pending in the embedded loop. The callback must then	3276	time there might be events pending in the embedded loop. The callback
2331	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3277	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2332	their callbacks (you could also start an idle watcher to give the embedded	3278	sweep and invoke their callbacks (the callback doesn't need to invoke the
2333	loop strictly lower priority for example). You can also set the callback	3279	C<ev_embed_sweep> function directly, it could also start an idle watcher
2334	to C<0>, in which case the embed watcher will automatically execute the	3280	to give the embedded loop strictly lower priority for example).
2335	embedded loop sweep.
2336		3281
2337	As long as the watcher is started it will automatically handle events. The	3282	You can also set the callback to C<0>, in which case the embed watcher
2338	callback will be invoked whenever some events have been handled. You can	3283	will automatically execute the embedded loop sweep whenever necessary.
2339	set the callback to C<0> to avoid having to specify one if you are not
2340	interested in that.
2341		3284
2342	Also, there have not currently been made special provisions for forking:	3285	Fork detection will be handled transparently while the C<ev_embed> watcher
2343	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3286	is active, i.e., the embedded loop will automatically be forked when the
2344	but you will also have to stop and restart any C<ev_embed> watchers	3287	embedding loop forks. In other cases, the user is responsible for calling
2345	yourself - but you can use a fork watcher to handle this automatically,	3288	C<ev_loop_fork> on the embedded loop.
2346	and future versions of libev might do just that.
2347		3289
2348	Unfortunately, not all backends are embeddable: only the ones returned by	3290	Unfortunately, not all backends are embeddable: only the ones returned by
2349	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3291	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2350	portable one.	3292	portable one.
2351		3293
…		…
2366		3308
2367	=over 4	3309	=over 4
2368		3310
2369	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3311	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2370		3312
2371	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3313	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2372		3314
2373	Configures the watcher to embed the given loop, which must be	3315	Configures the watcher to embed the given loop, which must be
2374	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3316	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2375	invoked automatically, otherwise it is the responsibility of the callback	3317	invoked automatically, otherwise it is the responsibility of the callback
2376	to invoke it (it will continue to be called until the sweep has been done,	3318	to invoke it (it will continue to be called until the sweep has been done,
2377	if you do not want that, you need to temporarily stop the embed watcher).	3319	if you do not want that, you need to temporarily stop the embed watcher).
2378		3320
2379	=item ev_embed_sweep (loop, ev_embed *)	3321	=item ev_embed_sweep (loop, ev_embed *)
2380		3322
2381	Make a single, non-blocking sweep over the embedded loop. This works	3323	Make a single, non-blocking sweep over the embedded loop. This works
2382	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3324	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
2383	appropriate way for embedded loops.	3325	appropriate way for embedded loops.
2384		3326
2385	=item struct ev_loop *other [read-only]	3327	=item struct ev_loop *other [read-only]
2386		3328
2387	The embedded event loop.	3329	The embedded event loop.
…		…
2397	used).	3339	used).
2398		3340
2399	struct ev_loop *loop_hi = ev_default_init (0);	3341	struct ev_loop *loop_hi = ev_default_init (0);
2400	struct ev_loop *loop_lo = 0;	3342	struct ev_loop *loop_lo = 0;
2401	ev_embed embed;	3343	ev_embed embed;
2402		3344
2403	// see if there is a chance of getting one that works	3345	// see if there is a chance of getting one that works
2404	// (remember that a flags value of 0 means autodetection)	3346	// (remember that a flags value of 0 means autodetection)
2405	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3347	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2406	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3348	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2407	: 0;	3349	: 0;
…		…
2421	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3363	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2422		3364
2423	struct ev_loop *loop = ev_default_init (0);	3365	struct ev_loop *loop = ev_default_init (0);
2424	struct ev_loop *loop_socket = 0;	3366	struct ev_loop *loop_socket = 0;
2425	ev_embed embed;	3367	ev_embed embed;
2426		3368
2427	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3369	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2428	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3370	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2429	{	3371	{
2430	ev_embed_init (&embed, 0, loop_socket);	3372	ev_embed_init (&embed, 0, loop_socket);
2431	ev_embed_start (loop, &embed);	3373	ev_embed_start (loop, &embed);
…		…
2439		3381
2440	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3382	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2441		3383
2442	Fork watchers are called when a C<fork ()> was detected (usually because	3384	Fork watchers are called when a C<fork ()> was detected (usually because
2443	whoever is a good citizen cared to tell libev about it by calling	3385	whoever is a good citizen cared to tell libev about it by calling
2444	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3386	C<ev_loop_fork>). The invocation is done before the event loop blocks next
2445	event loop blocks next and before C<ev_check> watchers are being called,	3387	and before C<ev_check> watchers are being called, and only in the child
2446	and only in the child after the fork. If whoever good citizen calling	3388	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
2447	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3389	and calls it in the wrong process, the fork handlers will be invoked, too,
2448	handlers will be invoked, too, of course.	3390	of course.
		3391
		3392	=head3 The special problem of life after fork - how is it possible?
		3393
		3394	Most uses of C<fork ()> consist of forking, then some simple calls to set
		3395	up/change the process environment, followed by a call to C<exec()>. This
		3396	sequence should be handled by libev without any problems.
		3397
		3398	This changes when the application actually wants to do event handling
		3399	in the child, or both parent in child, in effect "continuing" after the
		3400	fork.
		3401
		3402	The default mode of operation (for libev, with application help to detect
		3403	forks) is to duplicate all the state in the child, as would be expected
		3404	when I<either> the parent I<or> the child process continues.
		3405
		3406	When both processes want to continue using libev, then this is usually the
		3407	wrong result. In that case, usually one process (typically the parent) is
		3408	supposed to continue with all watchers in place as before, while the other
		3409	process typically wants to start fresh, i.e. without any active watchers.
		3410
		3411	The cleanest and most efficient way to achieve that with libev is to
		3412	simply create a new event loop, which of course will be "empty", and
		3413	use that for new watchers. This has the advantage of not touching more
		3414	memory than necessary, and thus avoiding the copy-on-write, and the
		3415	disadvantage of having to use multiple event loops (which do not support
		3416	signal watchers).
		3417
		3418	When this is not possible, or you want to use the default loop for
		3419	other reasons, then in the process that wants to start "fresh", call
		3420	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3421	Destroying the default loop will "orphan" (not stop) all registered
		3422	watchers, so you have to be careful not to execute code that modifies
		3423	those watchers. Note also that in that case, you have to re-register any
		3424	signal watchers.
2449		3425
2450	=head3 Watcher-Specific Functions and Data Members	3426	=head3 Watcher-Specific Functions and Data Members
2451		3427
2452	=over 4	3428	=over 4
2453		3429
2454	=item ev_fork_init (ev_signal *, callback)	3430	=item ev_fork_init (ev_fork *, callback)
2455		3431
2456	Initialises and configures the fork watcher - it has no parameters of any	3432	Initialises and configures the fork watcher - it has no parameters of any
2457	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3433	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2458	believe me.	3434	really.
2459		3435
2460	=back	3436	=back
2461		3437
2462		3438
		3439	=head2 C<ev_cleanup> - even the best things end
		3440
		3441	Cleanup watchers are called just before the event loop is being destroyed
		3442	by a call to C<ev_loop_destroy>.
		3443
		3444	While there is no guarantee that the event loop gets destroyed, cleanup
		3445	watchers provide a convenient method to install cleanup hooks for your
		3446	program, worker threads and so on - you just to make sure to destroy the
		3447	loop when you want them to be invoked.
		3448
		3449	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3450	all other watchers, they do not keep a reference to the event loop (which
		3451	makes a lot of sense if you think about it). Like all other watchers, you
		3452	can call libev functions in the callback, except C<ev_cleanup_start>.
		3453
		3454	=head3 Watcher-Specific Functions and Data Members
		3455
		3456	=over 4
		3457
		3458	=item ev_cleanup_init (ev_cleanup *, callback)
		3459
		3460	Initialises and configures the cleanup watcher - it has no parameters of
		3461	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3462	pointless, I assure you.
		3463
		3464	=back
		3465
		3466	Example: Register an atexit handler to destroy the default loop, so any
		3467	cleanup functions are called.
		3468
		3469	static void
		3470	program_exits (void)
		3471	{
		3472	ev_loop_destroy (EV_DEFAULT_UC);
		3473	}
		3474
		3475	...
		3476	atexit (program_exits);
		3477
		3478
2463	=head2 C<ev_async> - how to wake up another event loop	3479	=head2 C<ev_async> - how to wake up an event loop
2464		3480
2465	In general, you cannot use an C<ev_loop> from multiple threads or other	3481	In general, you cannot use an C<ev_loop> from multiple threads or other
2466	asynchronous sources such as signal handlers (as opposed to multiple event	3482	asynchronous sources such as signal handlers (as opposed to multiple event
2467	loops - those are of course safe to use in different threads).	3483	loops - those are of course safe to use in different threads).
2468		3484
2469	Sometimes, however, you need to wake up another event loop you do not	3485	Sometimes, however, you need to wake up an event loop you do not control,
2470	control, for example because it belongs to another thread. This is what	3486	for example because it belongs to another thread. This is what C<ev_async>
2471	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3487	watchers do: as long as the C<ev_async> watcher is active, you can signal
2472	can signal it by calling C<ev_async_send>, which is thread- and signal	3488	it by calling C<ev_async_send>, which is thread- and signal safe.
2473	safe.
2474		3489
2475	This functionality is very similar to C<ev_signal> watchers, as signals,	3490	This functionality is very similar to C<ev_signal> watchers, as signals,
2476	too, are asynchronous in nature, and signals, too, will be compressed	3491	too, are asynchronous in nature, and signals, too, will be compressed
2477	(i.e. the number of callback invocations may be less than the number of	3492	(i.e. the number of callback invocations may be less than the number of
2478	C<ev_async_sent> calls).	3493	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
2479		3494	of "global async watchers" by using a watcher on an otherwise unused
2480	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3495	signal, and C<ev_feed_signal> to signal this watcher from another thread,
2481	just the default loop.	3496	even without knowing which loop owns the signal.
2482		3497
2483	=head3 Queueing	3498	=head3 Queueing
2484		3499
2485	C<ev_async> does not support queueing of data in any way. The reason	3500	C<ev_async> does not support queueing of data in any way. The reason
2486	is that the author does not know of a simple (or any) algorithm for a	3501	is that the author does not know of a simple (or any) algorithm for a
2487	multiple-writer-single-reader queue that works in all cases and doesn't	3502	multiple-writer-single-reader queue that works in all cases and doesn't
2488	need elaborate support such as pthreads.	3503	need elaborate support such as pthreads or unportable memory access
		3504	semantics.
2489		3505
2490	That means that if you want to queue data, you have to provide your own	3506	That means that if you want to queue data, you have to provide your own
2491	queue. But at least I can tell you how to implement locking around your	3507	queue. But at least I can tell you how to implement locking around your
2492	queue:	3508	queue:
2493		3509
…		…
2571	=over 4	3587	=over 4
2572		3588
2573	=item ev_async_init (ev_async *, callback)	3589	=item ev_async_init (ev_async *, callback)
2574		3590
2575	Initialises and configures the async watcher - it has no parameters of any	3591	Initialises and configures the async watcher - it has no parameters of any
2576	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3592	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2577	trust me.	3593	trust me.
2578		3594
2579	=item ev_async_send (loop, ev_async *)	3595	=item ev_async_send (loop, ev_async *)
2580		3596
2581	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3597	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2582	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3598	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3599	returns.
		3600
2583	C<ev_feed_event>, this call is safe to do from other threads, signal or	3601	Unlike C<ev_feed_event>, this call is safe to do from other threads,
2584	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3602	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
2585	section below on what exactly this means).	3603	embedding section below on what exactly this means).
2586		3604
2587	This call incurs the overhead of a system call only once per loop iteration,	3605	Note that, as with other watchers in libev, multiple events might get
2588	so while the overhead might be noticeable, it doesn't apply to repeated	3606	compressed into a single callback invocation (another way to look at
2589	calls to C<ev_async_send>.	3607	this is that C<ev_async> watchers are level-triggered: they are set on
		3608	C<ev_async_send>, reset when the event loop detects that).
		3609
		3610	This call incurs the overhead of at most one extra system call per event
		3611	loop iteration, if the event loop is blocked, and no syscall at all if
		3612	the event loop (or your program) is processing events. That means that
		3613	repeated calls are basically free (there is no need to avoid calls for
		3614	performance reasons) and that the overhead becomes smaller (typically
		3615	zero) under load.
2590		3616
2591	=item bool = ev_async_pending (ev_async *)	3617	=item bool = ev_async_pending (ev_async *)
2592		3618
2593	Returns a non-zero value when C<ev_async_send> has been called on the	3619	Returns a non-zero value when C<ev_async_send> has been called on the
2594	watcher but the event has not yet been processed (or even noted) by the	3620	watcher but the event has not yet been processed (or even noted) by the
…		…
2597	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3623	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2598	the loop iterates next and checks for the watcher to have become active,	3624	the loop iterates next and checks for the watcher to have become active,
2599	it will reset the flag again. C<ev_async_pending> can be used to very	3625	it will reset the flag again. C<ev_async_pending> can be used to very
2600	quickly check whether invoking the loop might be a good idea.	3626	quickly check whether invoking the loop might be a good idea.
2601		3627
2602	Not that this does I<not> check whether the watcher itself is pending, only	3628	Not that this does I<not> check whether the watcher itself is pending,
2603	whether it has been requested to make this watcher pending.	3629	only whether it has been requested to make this watcher pending: there
		3630	is a time window between the event loop checking and resetting the async
		3631	notification, and the callback being invoked.
2604		3632
2605	=back	3633	=back
2606		3634
2607		3635
2608	=head1 OTHER FUNCTIONS	3636	=head1 OTHER FUNCTIONS
2609		3637
2610	There are some other functions of possible interest. Described. Here. Now.	3638	There are some other functions of possible interest. Described. Here. Now.
2611		3639
2612	=over 4	3640	=over 4
2613		3641
2614	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3642	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
2615		3643
2616	This function combines a simple timer and an I/O watcher, calls your	3644	This function combines a simple timer and an I/O watcher, calls your
2617	callback on whichever event happens first and automatically stops both	3645	callback on whichever event happens first and automatically stops both
2618	watchers. This is useful if you want to wait for a single event on an fd	3646	watchers. This is useful if you want to wait for a single event on an fd
2619	or timeout without having to allocate/configure/start/stop/free one or	3647	or timeout without having to allocate/configure/start/stop/free one or
…		…
2625		3653
2626	If C<timeout> is less than 0, then no timeout watcher will be	3654	If C<timeout> is less than 0, then no timeout watcher will be
2627	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3655	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2628	repeat = 0) will be started. C<0> is a valid timeout.	3656	repeat = 0) will be started. C<0> is a valid timeout.
2629		3657
2630	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3658	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2631	passed an C<revents> set like normal event callbacks (a combination of	3659	passed an C<revents> set like normal event callbacks (a combination of
2632	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3660	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2633	value passed to C<ev_once>. Note that it is possible to receive I<both>	3661	value passed to C<ev_once>. Note that it is possible to receive I<both>
2634	a timeout and an io event at the same time - you probably should give io	3662	a timeout and an io event at the same time - you probably should give io
2635	events precedence.	3663	events precedence.
2636		3664
2637	Example: wait up to ten seconds for data to appear on STDIN_FILENO.	3665	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2638		3666
2639	static void stdin_ready (int revents, void *arg)	3667	static void stdin_ready (int revents, void *arg)
2640	{	3668	{
2641	if (revents & EV_READ)	3669	if (revents & EV_READ)
2642	/* stdin might have data for us, joy! */;	3670	/* stdin might have data for us, joy! */;
2643	else if (revents & EV_TIMEOUT)	3671	else if (revents & EV_TIMER)
2644	/* doh, nothing entered */;	3672	/* doh, nothing entered */;
2645	}	3673	}
2646		3674
2647	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3675	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2648		3676
2649	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
2650
2651	Feeds the given event set into the event loop, as if the specified event
2652	had happened for the specified watcher (which must be a pointer to an
2653	initialised but not necessarily started event watcher).
2654
2655	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)	3677	=item ev_feed_fd_event (loop, int fd, int revents)
2656		3678
2657	Feed an event on the given fd, as if a file descriptor backend detected	3679	Feed an event on the given fd, as if a file descriptor backend detected
2658	the given events it.	3680	the given events.
2659		3681
2660	=item ev_feed_signal_event (struct ev_loop *loop, int signum)	3682	=item ev_feed_signal_event (loop, int signum)
2661		3683
2662	Feed an event as if the given signal occurred (C<loop> must be the default	3684	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
2663	loop!).	3685	which is async-safe.
2664		3686
2665	=back	3687	=back
		3688
		3689
		3690	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3691
		3692	This section explains some common idioms that are not immediately
		3693	obvious. Note that examples are sprinkled over the whole manual, and this
		3694	section only contains stuff that wouldn't fit anywhere else.
		3695
		3696	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3697
		3698	Each watcher has, by default, a C<void *data> member that you can read
		3699	or modify at any time: libev will completely ignore it. This can be used
		3700	to associate arbitrary data with your watcher. If you need more data and
		3701	don't want to allocate memory separately and store a pointer to it in that
		3702	data member, you can also "subclass" the watcher type and provide your own
		3703	data:
		3704
		3705	struct my_io
		3706	{
		3707	ev_io io;
		3708	int otherfd;
		3709	void *somedata;
		3710	struct whatever *mostinteresting;
		3711	};
		3712
		3713	...
		3714	struct my_io w;
		3715	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3716
		3717	And since your callback will be called with a pointer to the watcher, you
		3718	can cast it back to your own type:
		3719
		3720	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3721	{
		3722	struct my_io *w = (struct my_io *)w_;
		3723	...
		3724	}
		3725
		3726	More interesting and less C-conformant ways of casting your callback
		3727	function type instead have been omitted.
		3728
		3729	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3730
		3731	Another common scenario is to use some data structure with multiple
		3732	embedded watchers, in effect creating your own watcher that combines
		3733	multiple libev event sources into one "super-watcher":
		3734
		3735	struct my_biggy
		3736	{
		3737	int some_data;
		3738	ev_timer t1;
		3739	ev_timer t2;
		3740	}
		3741
		3742	In this case getting the pointer to C<my_biggy> is a bit more
		3743	complicated: Either you store the address of your C<my_biggy> struct in
		3744	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3745	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3746	real programmers):
		3747
		3748	#include <stddef.h>
		3749
		3750	static void
		3751	t1_cb (EV_P_ ev_timer *w, int revents)
		3752	{
		3753	struct my_biggy big = (struct my_biggy *)
		3754	(((char *)w) - offsetof (struct my_biggy, t1));
		3755	}
		3756
		3757	static void
		3758	t2_cb (EV_P_ ev_timer *w, int revents)
		3759	{
		3760	struct my_biggy big = (struct my_biggy *)
		3761	(((char *)w) - offsetof (struct my_biggy, t2));
		3762	}
		3763
		3764	=head2 AVOIDING FINISHING BEFORE RETURNING
		3765
		3766	Often you have structures like this in event-based programs:
		3767
		3768	callback ()
		3769	{
		3770	free (request);
		3771	}
		3772
		3773	request = start_new_request (..., callback);
		3774
		3775	The intent is to start some "lengthy" operation. The C<request> could be
		3776	used to cancel the operation, or do other things with it.
		3777
		3778	It's not uncommon to have code paths in C<start_new_request> that
		3779	immediately invoke the callback, for example, to report errors. Or you add
		3780	some caching layer that finds that it can skip the lengthy aspects of the
		3781	operation and simply invoke the callback with the result.
		3782
		3783	The problem here is that this will happen I<before> C<start_new_request>
		3784	has returned, so C<request> is not set.
		3785
		3786	Even if you pass the request by some safer means to the callback, you
		3787	might want to do something to the request after starting it, such as
		3788	canceling it, which probably isn't working so well when the callback has
		3789	already been invoked.
		3790
		3791	A common way around all these issues is to make sure that
		3792	C<start_new_request> I<always> returns before the callback is invoked. If
		3793	C<start_new_request> immediately knows the result, it can artificially
		3794	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3795	example, or more sneakily, by reusing an existing (stopped) watcher and
		3796	pushing it into the pending queue:
		3797
		3798	ev_set_cb (watcher, callback);
		3799	ev_feed_event (EV_A_ watcher, 0);
		3800
		3801	This way, C<start_new_request> can safely return before the callback is
		3802	invoked, while not delaying callback invocation too much.
		3803
		3804	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3805
		3806	Often (especially in GUI toolkits) there are places where you have
		3807	I<modal> interaction, which is most easily implemented by recursively
		3808	invoking C<ev_run>.
		3809
		3810	This brings the problem of exiting - a callback might want to finish the
		3811	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3812	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3813	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3814	other combination: In these cases, a simple C<ev_break> will not work.
		3815
		3816	The solution is to maintain "break this loop" variable for each C<ev_run>
		3817	invocation, and use a loop around C<ev_run> until the condition is
		3818	triggered, using C<EVRUN_ONCE>:
		3819
		3820	// main loop
		3821	int exit_main_loop = 0;
		3822
		3823	while (!exit_main_loop)
		3824	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3825
		3826	// in a modal watcher
		3827	int exit_nested_loop = 0;
		3828
		3829	while (!exit_nested_loop)
		3830	ev_run (EV_A_ EVRUN_ONCE);
		3831
		3832	To exit from any of these loops, just set the corresponding exit variable:
		3833
		3834	// exit modal loop
		3835	exit_nested_loop = 1;
		3836
		3837	// exit main program, after modal loop is finished
		3838	exit_main_loop = 1;
		3839
		3840	// exit both
		3841	exit_main_loop = exit_nested_loop = 1;
		3842
		3843	=head2 THREAD LOCKING EXAMPLE
		3844
		3845	Here is a fictitious example of how to run an event loop in a different
		3846	thread from where callbacks are being invoked and watchers are
		3847	created/added/removed.
		3848
		3849	For a real-world example, see the C<EV::Loop::Async> perl module,
		3850	which uses exactly this technique (which is suited for many high-level
		3851	languages).
		3852
		3853	The example uses a pthread mutex to protect the loop data, a condition
		3854	variable to wait for callback invocations, an async watcher to notify the
		3855	event loop thread and an unspecified mechanism to wake up the main thread.
		3856
		3857	First, you need to associate some data with the event loop:
		3858
		3859	typedef struct {
		3860	mutex_t lock; /* global loop lock */
		3861	ev_async async_w;
		3862	thread_t tid;
		3863	cond_t invoke_cv;
		3864	} userdata;
		3865
		3866	void prepare_loop (EV_P)
		3867	{
		3868	// for simplicity, we use a static userdata struct.
		3869	static userdata u;
		3870
		3871	ev_async_init (&u->async_w, async_cb);
		3872	ev_async_start (EV_A_ &u->async_w);
		3873
		3874	pthread_mutex_init (&u->lock, 0);
		3875	pthread_cond_init (&u->invoke_cv, 0);
		3876
		3877	// now associate this with the loop
		3878	ev_set_userdata (EV_A_ u);
		3879	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3880	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3881
		3882	// then create the thread running ev_run
		3883	pthread_create (&u->tid, 0, l_run, EV_A);
		3884	}
		3885
		3886	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3887	solely to wake up the event loop so it takes notice of any new watchers
		3888	that might have been added:
		3889
		3890	static void
		3891	async_cb (EV_P_ ev_async *w, int revents)
		3892	{
		3893	// just used for the side effects
		3894	}
		3895
		3896	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3897	protecting the loop data, respectively.
		3898
		3899	static void
		3900	l_release (EV_P)
		3901	{
		3902	userdata *u = ev_userdata (EV_A);
		3903	pthread_mutex_unlock (&u->lock);
		3904	}
		3905
		3906	static void
		3907	l_acquire (EV_P)
		3908	{
		3909	userdata *u = ev_userdata (EV_A);
		3910	pthread_mutex_lock (&u->lock);
		3911	}
		3912
		3913	The event loop thread first acquires the mutex, and then jumps straight
		3914	into C<ev_run>:
		3915
		3916	void *
		3917	l_run (void *thr_arg)
		3918	{
		3919	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3920
		3921	l_acquire (EV_A);
		3922	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3923	ev_run (EV_A_ 0);
		3924	l_release (EV_A);
		3925
		3926	return 0;
		3927	}
		3928
		3929	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3930	signal the main thread via some unspecified mechanism (signals? pipe
		3931	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3932	have been called (in a while loop because a) spurious wakeups are possible
		3933	and b) skipping inter-thread-communication when there are no pending
		3934	watchers is very beneficial):
		3935
		3936	static void
		3937	l_invoke (EV_P)
		3938	{
		3939	userdata *u = ev_userdata (EV_A);
		3940
		3941	while (ev_pending_count (EV_A))
		3942	{
		3943	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3944	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3945	}
		3946	}
		3947
		3948	Now, whenever the main thread gets told to invoke pending watchers, it
		3949	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3950	thread to continue:
		3951
		3952	static void
		3953	real_invoke_pending (EV_P)
		3954	{
		3955	userdata *u = ev_userdata (EV_A);
		3956
		3957	pthread_mutex_lock (&u->lock);
		3958	ev_invoke_pending (EV_A);
		3959	pthread_cond_signal (&u->invoke_cv);
		3960	pthread_mutex_unlock (&u->lock);
		3961	}
		3962
		3963	Whenever you want to start/stop a watcher or do other modifications to an
		3964	event loop, you will now have to lock:
		3965
		3966	ev_timer timeout_watcher;
		3967	userdata *u = ev_userdata (EV_A);
		3968
		3969	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3970
		3971	pthread_mutex_lock (&u->lock);
		3972	ev_timer_start (EV_A_ &timeout_watcher);
		3973	ev_async_send (EV_A_ &u->async_w);
		3974	pthread_mutex_unlock (&u->lock);
		3975
		3976	Note that sending the C<ev_async> watcher is required because otherwise
		3977	an event loop currently blocking in the kernel will have no knowledge
		3978	about the newly added timer. By waking up the loop it will pick up any new
		3979	watchers in the next event loop iteration.
		3980
		3981	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3982
		3983	While the overhead of a callback that e.g. schedules a thread is small, it
		3984	is still an overhead. If you embed libev, and your main usage is with some
		3985	kind of threads or coroutines, you might want to customise libev so that
		3986	doesn't need callbacks anymore.
		3987
		3988	Imagine you have coroutines that you can switch to using a function
		3989	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3990	and that due to some magic, the currently active coroutine is stored in a
		3991	global called C<current_coro>. Then you can build your own "wait for libev
		3992	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3993	the differing C<;> conventions):
		3994
		3995	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3996	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3997
		3998	That means instead of having a C callback function, you store the
		3999	coroutine to switch to in each watcher, and instead of having libev call
		4000	your callback, you instead have it switch to that coroutine.
		4001
		4002	A coroutine might now wait for an event with a function called
		4003	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		4004	matter when, or whether the watcher is active or not when this function is
		4005	called):
		4006
		4007	void
		4008	wait_for_event (ev_watcher *w)
		4009	{
		4010	ev_set_cb (w, current_coro);
		4011	switch_to (libev_coro);
		4012	}
		4013
		4014	That basically suspends the coroutine inside C<wait_for_event> and
		4015	continues the libev coroutine, which, when appropriate, switches back to
		4016	this or any other coroutine.
		4017
		4018	You can do similar tricks if you have, say, threads with an event queue -
		4019	instead of storing a coroutine, you store the queue object and instead of
		4020	switching to a coroutine, you push the watcher onto the queue and notify
		4021	any waiters.
		4022
		4023	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		4024	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		4025
		4026	// my_ev.h
		4027	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4028	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4029	#include "../libev/ev.h"
		4030
		4031	// my_ev.c
		4032	#define EV_H "my_ev.h"
		4033	#include "../libev/ev.c"
		4034
		4035	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4036	F<my_ev.c> into your project. When properly specifying include paths, you
		4037	can even use F<ev.h> as header file name directly.
2666		4038
2667		4039
2668	=head1 LIBEVENT EMULATION	4040	=head1 LIBEVENT EMULATION
2669		4041
2670	Libev offers a compatibility emulation layer for libevent. It cannot	4042	Libev offers a compatibility emulation layer for libevent. It cannot
2671	emulate the internals of libevent, so here are some usage hints:	4043	emulate the internals of libevent, so here are some usage hints:
2672		4044
2673	=over 4	4045	=over 4
		4046
		4047	=item * Only the libevent-1.4.1-beta API is being emulated.
		4048
		4049	This was the newest libevent version available when libev was implemented,
		4050	and is still mostly unchanged in 2010.
2674		4051
2675	=item * Use it by including <event.h>, as usual.	4052	=item * Use it by including <event.h>, as usual.
2676		4053
2677	=item * The following members are fully supported: ev_base, ev_callback,	4054	=item * The following members are fully supported: ev_base, ev_callback,
2678	ev_arg, ev_fd, ev_res, ev_events.	4055	ev_arg, ev_fd, ev_res, ev_events.
…		…
2684	=item * Priorities are not currently supported. Initialising priorities	4061	=item * Priorities are not currently supported. Initialising priorities
2685	will fail and all watchers will have the same priority, even though there	4062	will fail and all watchers will have the same priority, even though there
2686	is an ev_pri field.	4063	is an ev_pri field.
2687		4064
2688	=item * In libevent, the last base created gets the signals, in libev, the	4065	=item * In libevent, the last base created gets the signals, in libev, the
2689	first base created (== the default loop) gets the signals.	4066	base that registered the signal gets the signals.
2690		4067
2691	=item * Other members are not supported.	4068	=item * Other members are not supported.
2692		4069
2693	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4070	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2694	to use the libev header file and library.	4071	to use the libev header file and library.
2695		4072
2696	=back	4073	=back
2697		4074
2698	=head1 C++ SUPPORT	4075	=head1 C++ SUPPORT
		4076
		4077	=head2 C API
		4078
		4079	The normal C API should work fine when used from C++: both ev.h and the
		4080	libev sources can be compiled as C++. Therefore, code that uses the C API
		4081	will work fine.
		4082
		4083	Proper exception specifications might have to be added to callbacks passed
		4084	to libev: exceptions may be thrown only from watcher callbacks, all other
		4085	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4086	callbacks) must not throw exceptions, and might need a C<noexcept>
		4087	specification. If you have code that needs to be compiled as both C and
		4088	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4089
		4090	static void
		4091	fatal_error (const char *msg) EV_NOEXCEPT
		4092	{
		4093	perror (msg);
		4094	abort ();
		4095	}
		4096
		4097	...
		4098	ev_set_syserr_cb (fatal_error);
		4099
		4100	The only API functions that can currently throw exceptions are C<ev_run>,
		4101	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4102	because it runs cleanup watchers).
		4103
		4104	Throwing exceptions in watcher callbacks is only supported if libev itself
		4105	is compiled with a C++ compiler or your C and C++ environments allow
		4106	throwing exceptions through C libraries (most do).
		4107
		4108	=head2 C++ API
2699		4109
2700	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4110	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2701	you to use some convenience methods to start/stop watchers and also change	4111	you to use some convenience methods to start/stop watchers and also change
2702	the callback model to a model using method callbacks on objects.	4112	the callback model to a model using method callbacks on objects.
2703		4113
2704	To use it,	4114	To use it,
2705		4115
2706	#include <ev++.h>	4116	#include <ev++.h>
2707		4117
2708	This automatically includes F<ev.h> and puts all of its definitions (many	4118	This automatically includes F<ev.h> and puts all of its definitions (many
2709	of them macros) into the global namespace. All C++ specific things are	4119	of them macros) into the global namespace. All C++ specific things are
2710	put into the C<ev> namespace. It should support all the same embedding	4120	put into the C<ev> namespace. It should support all the same embedding
…		…
2713	Care has been taken to keep the overhead low. The only data member the C++	4123	Care has been taken to keep the overhead low. The only data member the C++
2714	classes add (compared to plain C-style watchers) is the event loop pointer	4124	classes add (compared to plain C-style watchers) is the event loop pointer
2715	that the watcher is associated with (or no additional members at all if	4125	that the watcher is associated with (or no additional members at all if
2716	you disable C<EV_MULTIPLICITY> when embedding libev).	4126	you disable C<EV_MULTIPLICITY> when embedding libev).
2717		4127
2718	Currently, functions, and static and non-static member functions can be	4128	Currently, functions, static and non-static member functions and classes
2719	used as callbacks. Other types should be easy to add as long as they only	4129	with C<operator ()> can be used as callbacks. Other types should be easy
2720	need one additional pointer for context. If you need support for other	4130	to add as long as they only need one additional pointer for context. If
2721	types of functors please contact the author (preferably after implementing	4131	you need support for other types of functors please contact the author
2722	it).	4132	(preferably after implementing it).
		4133
		4134	For all this to work, your C++ compiler either has to use the same calling
		4135	conventions as your C compiler (for static member functions), or you have
		4136	to embed libev and compile libev itself as C++.
2723		4137
2724	Here is a list of things available in the C<ev> namespace:	4138	Here is a list of things available in the C<ev> namespace:
2725		4139
2726	=over 4	4140	=over 4
2727		4141
…		…
2737	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4151	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
2738		4152
2739	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4153	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
2740	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4154	the same name in the C<ev> namespace, with the exception of C<ev_signal>
2741	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4155	which is called C<ev::sig> to avoid clashes with the C<signal> macro
2742	defines by many implementations.	4156	defined by many implementations.
2743		4157
2744	All of those classes have these methods:	4158	All of those classes have these methods:
2745		4159
2746	=over 4	4160	=over 4
2747		4161
2748	=item ev::TYPE::TYPE ()	4162	=item ev::TYPE::TYPE ()
2749		4163
2750	=item ev::TYPE::TYPE (struct ev_loop *)	4164	=item ev::TYPE::TYPE (loop)
2751		4165
2752	=item ev::TYPE::~TYPE	4166	=item ev::TYPE::~TYPE
2753		4167
2754	The constructor (optionally) takes an event loop to associate the watcher	4168	The constructor (optionally) takes an event loop to associate the watcher
2755	with. If it is omitted, it will use C<EV_DEFAULT>.	4169	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2787		4201
2788	myclass obj;	4202	myclass obj;
2789	ev::io iow;	4203	ev::io iow;
2790	iow.set <myclass, &myclass::io_cb> (&obj);	4204	iow.set <myclass, &myclass::io_cb> (&obj);
2791		4205
		4206	=item w->set (object *)
		4207
		4208	This is a variation of a method callback - leaving out the method to call
		4209	will default the method to C<operator ()>, which makes it possible to use
		4210	functor objects without having to manually specify the C<operator ()> all
		4211	the time. Incidentally, you can then also leave out the template argument
		4212	list.
		4213
		4214	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4215	int revents)>.
		4216
		4217	See the method-C<set> above for more details.
		4218
		4219	Example: use a functor object as callback.
		4220
		4221	struct myfunctor
		4222	{
		4223	void operator() (ev::io &w, int revents)
		4224	{
		4225	...
		4226	}
		4227	}
		4228
		4229	myfunctor f;
		4230
		4231	ev::io w;
		4232	w.set (&f);
		4233
2792	=item w->set<function> (void *data = 0)	4234	=item w->set<function> (void *data = 0)
2793		4235
2794	Also sets a callback, but uses a static method or plain function as	4236	Also sets a callback, but uses a static method or plain function as
2795	callback. The optional C<data> argument will be stored in the watcher's	4237	callback. The optional C<data> argument will be stored in the watcher's
2796	C<data> member and is free for you to use.	4238	C<data> member and is free for you to use.
…		…
2802	Example: Use a plain function as callback.	4244	Example: Use a plain function as callback.
2803		4245
2804	static void io_cb (ev::io &w, int revents) { }	4246	static void io_cb (ev::io &w, int revents) { }
2805	iow.set <io_cb> ();	4247	iow.set <io_cb> ();
2806		4248
2807	=item w->set (struct ev_loop *)	4249	=item w->set (loop)
2808		4250
2809	Associates a different C<struct ev_loop> with this watcher. You can only	4251	Associates a different C<struct ev_loop> with this watcher. You can only
2810	do this when the watcher is inactive (and not pending either).	4252	do this when the watcher is inactive (and not pending either).
2811		4253
2812	=item w->set ([arguments])	4254	=item w->set ([arguments])
2813		4255
2814	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be	4256	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4257	with the same arguments. Either this method or a suitable start method
2815	called at least once. Unlike the C counterpart, an active watcher gets	4258	must be called at least once. Unlike the C counterpart, an active watcher
2816	automatically stopped and restarted when reconfiguring it with this	4259	gets automatically stopped and restarted when reconfiguring it with this
2817	method.	4260	method.
		4261
		4262	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4263	clashing with the C<set (loop)> method.
		4264
		4265	For C<ev::io> watchers there is an additional C<set> method that acepts a
		4266	new event mask only, and internally calls C<ev_io_modfify>.
2818		4267
2819	=item w->start ()	4268	=item w->start ()
2820		4269
2821	Starts the watcher. Note that there is no C<loop> argument, as the	4270	Starts the watcher. Note that there is no C<loop> argument, as the
2822	constructor already stores the event loop.	4271	constructor already stores the event loop.
2823		4272
		4273	=item w->start ([arguments])
		4274
		4275	Instead of calling C<set> and C<start> methods separately, it is often
		4276	convenient to wrap them in one call. Uses the same type of arguments as
		4277	the configure C<set> method of the watcher.
		4278
2824	=item w->stop ()	4279	=item w->stop ()
2825		4280
2826	Stops the watcher if it is active. Again, no C<loop> argument.	4281	Stops the watcher if it is active. Again, no C<loop> argument.
2827		4282
2828	=item w->again () (C<ev::timer>, C<ev::periodic> only)	4283	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2840		4295
2841	=back	4296	=back
2842		4297
2843	=back	4298	=back
2844		4299
2845	Example: Define a class with an IO and idle watcher, start one of them in	4300	Example: Define a class with two I/O and idle watchers, start the I/O
2846	the constructor.	4301	watchers in the constructor.
2847		4302
2848	class myclass	4303	class myclass
2849	{	4304	{
2850	ev::io io ; void io_cb (ev::io &w, int revents);	4305	ev::io io ; void io_cb (ev::io &w, int revents);
		4306	ev::io io2 ; void io2_cb (ev::io &w, int revents);
2851	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4307	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2852		4308
2853	myclass (int fd)	4309	myclass (int fd)
2854	{	4310	{
2855	io .set <myclass, &myclass::io_cb > (this);	4311	io .set <myclass, &myclass::io_cb > (this);
		4312	io2 .set <myclass, &myclass::io2_cb > (this);
2856	idle.set <myclass, &myclass::idle_cb> (this);	4313	idle.set <myclass, &myclass::idle_cb> (this);
2857		4314
2858	io.start (fd, ev::READ);	4315	io.set (fd, ev::WRITE); // configure the watcher
		4316	io.start (); // start it whenever convenient
		4317
		4318	io2.start (fd, ev::READ); // set + start in one call
2859	}	4319	}
2860	};	4320	};
2861		4321
2862		4322
2863	=head1 OTHER LANGUAGE BINDINGS	4323	=head1 OTHER LANGUAGE BINDINGS
…		…
2882	L<http://software.schmorp.de/pkg/EV>.	4342	L<http://software.schmorp.de/pkg/EV>.
2883		4343
2884	=item Python	4344	=item Python
2885		4345
2886	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	4346	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2887	seems to be quite complete and well-documented. Note, however, that the	4347	seems to be quite complete and well-documented.
2888	patch they require for libev is outright dangerous as it breaks the ABI
2889	for everybody else, and therefore, should never be applied in an installed
2890	libev (if python requires an incompatible ABI then it needs to embed
2891	libev).
2892		4348
2893	=item Ruby	4349	=item Ruby
2894		4350
2895	Tony Arcieri has written a ruby extension that offers access to a subset	4351	Tony Arcieri has written a ruby extension that offers access to a subset
2896	of the libev API and adds file handle abstractions, asynchronous DNS and	4352	of the libev API and adds file handle abstractions, asynchronous DNS and
2897	more on top of it. It can be found via gem servers. Its homepage is at	4353	more on top of it. It can be found via gem servers. Its homepage is at
2898	L<http://rev.rubyforge.org/>.	4354	L<http://rev.rubyforge.org/>.
2899		4355
		4356	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4357	makes rev work even on mingw.
		4358
		4359	=item Haskell
		4360
		4361	A haskell binding to libev is available at
		4362	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4363
2900	=item D	4364	=item D
2901		4365
2902	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4366	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2903	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4367	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4368
		4369	=item Ocaml
		4370
		4371	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4372	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4373
		4374	=item Lua
		4375
		4376	Brian Maher has written a partial interface to libev for lua (at the
		4377	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4378	L<http://github.com/brimworks/lua-ev>.
		4379
		4380	=item Javascript
		4381
		4382	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4383
		4384	=item Others
		4385
		4386	There are others, and I stopped counting.
2904		4387
2905	=back	4388	=back
2906		4389
2907		4390
2908	=head1 MACRO MAGIC	4391	=head1 MACRO MAGIC
…		…
2922	loop argument"). The C<EV_A> form is used when this is the sole argument,	4405	loop argument"). The C<EV_A> form is used when this is the sole argument,
2923	C<EV_A_> is used when other arguments are following. Example:	4406	C<EV_A_> is used when other arguments are following. Example:
2924		4407
2925	ev_unref (EV_A);	4408	ev_unref (EV_A);
2926	ev_timer_add (EV_A_ watcher);	4409	ev_timer_add (EV_A_ watcher);
2927	ev_loop (EV_A_ 0);	4410	ev_run (EV_A_ 0);
2928		4411
2929	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4412	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2930	which is often provided by the following macro.	4413	which is often provided by the following macro.
2931		4414
2932	=item C<EV_P>, C<EV_P_>	4415	=item C<EV_P>, C<EV_P_>
…		…
2945	suitable for use with C<EV_A>.	4428	suitable for use with C<EV_A>.
2946		4429
2947	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4430	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2948		4431
2949	Similar to the other two macros, this gives you the value of the default	4432	Similar to the other two macros, this gives you the value of the default
2950	loop, if multiple loops are supported ("ev loop default").	4433	loop, if multiple loops are supported ("ev loop default"). The default loop
		4434	will be initialised if it isn't already initialised.
		4435
		4436	For non-multiplicity builds, these macros do nothing, so you always have
		4437	to initialise the loop somewhere.
2951		4438
2952	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4439	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
2953		4440
2954	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4441	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
2955	default loop has been initialised (C<UC> == unchecked). Their behaviour	4442	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
2972	}	4459	}
2973		4460
2974	ev_check check;	4461	ev_check check;
2975	ev_check_init (&check, check_cb);	4462	ev_check_init (&check, check_cb);
2976	ev_check_start (EV_DEFAULT_ &check);	4463	ev_check_start (EV_DEFAULT_ &check);
2977	ev_loop (EV_DEFAULT_ 0);	4464	ev_run (EV_DEFAULT_ 0);
2978		4465
2979	=head1 EMBEDDING	4466	=head1 EMBEDDING
2980		4467
2981	Libev can (and often is) directly embedded into host	4468	Libev can (and often is) directly embedded into host
2982	applications. Examples of applications that embed it include the Deliantra	4469	applications. Examples of applications that embed it include the Deliantra
…		…
3009		4496
3010	#define EV_STANDALONE 1	4497	#define EV_STANDALONE 1
3011	#include "ev.h"	4498	#include "ev.h"
3012		4499
3013	Both header files and implementation files can be compiled with a C++	4500	Both header files and implementation files can be compiled with a C++
3014	compiler (at least, thats a stated goal, and breakage will be treated	4501	compiler (at least, that's a stated goal, and breakage will be treated
3015	as a bug).	4502	as a bug).
3016		4503
3017	You need the following files in your source tree, or in a directory	4504	You need the following files in your source tree, or in a directory
3018	in your include path (e.g. in libev/ when using -Ilibev):	4505	in your include path (e.g. in libev/ when using -Ilibev):
3019		4506
…		…
3022	ev_vars.h	4509	ev_vars.h
3023	ev_wrap.h	4510	ev_wrap.h
3024		4511
3025	ev_win32.c required on win32 platforms only	4512	ev_win32.c required on win32 platforms only
3026		4513
3027	ev_select.c only when select backend is enabled (which is enabled by default)	4514	ev_select.c only when select backend is enabled
3028	ev_poll.c only when poll backend is enabled (disabled by default)	4515	ev_poll.c only when poll backend is enabled
3029	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4516	ev_epoll.c only when the epoll backend is enabled
		4517	ev_linuxaio.c only when the linux aio backend is enabled
		4518	ev_iouring.c only when the linux io_uring backend is enabled
3030	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4519	ev_kqueue.c only when the kqueue backend is enabled
3031	ev_port.c only when the solaris port backend is enabled (disabled by default)	4520	ev_port.c only when the solaris port backend is enabled
3032		4521
3033	F<ev.c> includes the backend files directly when enabled, so you only need	4522	F<ev.c> includes the backend files directly when enabled, so you only need
3034	to compile this single file.	4523	to compile this single file.
3035		4524
3036	=head3 LIBEVENT COMPATIBILITY API	4525	=head3 LIBEVENT COMPATIBILITY API
…		…
3062	libev.m4	4551	libev.m4
3063		4552
3064	=head2 PREPROCESSOR SYMBOLS/MACROS	4553	=head2 PREPROCESSOR SYMBOLS/MACROS
3065		4554
3066	Libev can be configured via a variety of preprocessor symbols you have to	4555	Libev can be configured via a variety of preprocessor symbols you have to
3067	define before including any of its files. The default in the absence of	4556	define before including (or compiling) any of its files. The default in
3068	autoconf is documented for every option.	4557	the absence of autoconf is documented for every option.
		4558
		4559	Symbols marked with "(h)" do not change the ABI, and can have different
		4560	values when compiling libev vs. including F<ev.h>, so it is permissible
		4561	to redefine them before including F<ev.h> without breaking compatibility
		4562	to a compiled library. All other symbols change the ABI, which means all
		4563	users of libev and the libev code itself must be compiled with compatible
		4564	settings.
3069		4565
3070	=over 4	4566	=over 4
3071		4567
		4568	=item EV_COMPAT3 (h)
		4569
		4570	Backwards compatibility is a major concern for libev. This is why this
		4571	release of libev comes with wrappers for the functions and symbols that
		4572	have been renamed between libev version 3 and 4.
		4573
		4574	You can disable these wrappers (to test compatibility with future
		4575	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4576	sources. This has the additional advantage that you can drop the C<struct>
		4577	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4578	typedef in that case.
		4579
		4580	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4581	and in some even more future version the compatibility code will be
		4582	removed completely.
		4583
3072	=item EV_STANDALONE	4584	=item EV_STANDALONE (h)
3073		4585
3074	Must always be C<1> if you do not use autoconf configuration, which	4586	Must always be C<1> if you do not use autoconf configuration, which
3075	keeps libev from including F<config.h>, and it also defines dummy	4587	keeps libev from including F<config.h>, and it also defines dummy
3076	implementations for some libevent functions (such as logging, which is not	4588	implementations for some libevent functions (such as logging, which is not
3077	supported). It will also not define any of the structs usually found in	4589	supported). It will also not define any of the structs usually found in
3078	F<event.h> that are not directly supported by the libev core alone.	4590	F<event.h> that are not directly supported by the libev core alone.
3079		4591
		4592	In standalone mode, libev will still try to automatically deduce the
		4593	configuration, but has to be more conservative.
		4594
		4595	=item EV_USE_FLOOR
		4596
		4597	If defined to be C<1>, libev will use the C<floor ()> function for its
		4598	periodic reschedule calculations, otherwise libev will fall back on a
		4599	portable (slower) implementation. If you enable this, you usually have to
		4600	link against libm or something equivalent. Enabling this when the C<floor>
		4601	function is not available will fail, so the safe default is to not enable
		4602	this.
		4603
3080	=item EV_USE_MONOTONIC	4604	=item EV_USE_MONOTONIC
3081		4605
3082	If defined to be C<1>, libev will try to detect the availability of the	4606	If defined to be C<1>, libev will try to detect the availability of the
3083	monotonic clock option at both compile time and runtime. Otherwise no use	4607	monotonic clock option at both compile time and runtime. Otherwise no
3084	of the monotonic clock option will be attempted. If you enable this, you	4608	use of the monotonic clock option will be attempted. If you enable this,
3085	usually have to link against librt or something similar. Enabling it when	4609	you usually have to link against librt or something similar. Enabling it
3086	the functionality isn't available is safe, though, although you have	4610	when the functionality isn't available is safe, though, although you have
3087	to make sure you link against any libraries where the C<clock_gettime>	4611	to make sure you link against any libraries where the C<clock_gettime>
3088	function is hiding in (often F<-lrt>).	4612	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
3089		4613
3090	=item EV_USE_REALTIME	4614	=item EV_USE_REALTIME
3091		4615
3092	If defined to be C<1>, libev will try to detect the availability of the	4616	If defined to be C<1>, libev will try to detect the availability of the
3093	real-time clock option at compile time (and assume its availability at	4617	real-time clock option at compile time (and assume its availability
3094	runtime if successful). Otherwise no use of the real-time clock option will	4618	at runtime if successful). Otherwise no use of the real-time clock
3095	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4619	option will be attempted. This effectively replaces C<gettimeofday>
3096	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4620	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
3097	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4621	correctness. See the note about libraries in the description of
		4622	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4623	C<EV_USE_CLOCK_SYSCALL>.
		4624
		4625	=item EV_USE_CLOCK_SYSCALL
		4626
		4627	If defined to be C<1>, libev will try to use a direct syscall instead
		4628	of calling the system-provided C<clock_gettime> function. This option
		4629	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4630	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4631	programs needlessly. Using a direct syscall is slightly slower (in
		4632	theory), because no optimised vdso implementation can be used, but avoids
		4633	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4634	higher, as it simplifies linking (no need for C<-lrt>).
3098		4635
3099	=item EV_USE_NANOSLEEP	4636	=item EV_USE_NANOSLEEP
3100		4637
3101	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4638	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
3102	and will use it for delays. Otherwise it will use C<select ()>.	4639	and will use it for delays. Otherwise it will use C<select ()>.
…		…
3107	available and will probe for kernel support at runtime. This will improve	4644	available and will probe for kernel support at runtime. This will improve
3108	C<ev_signal> and C<ev_async> performance and reduce resource consumption.	4645	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
3109	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc	4646	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
3110	2.7 or newer, otherwise disabled.	4647	2.7 or newer, otherwise disabled.
3111		4648
		4649	=item EV_USE_SIGNALFD
		4650
		4651	If defined to be C<1>, then libev will assume that C<signalfd ()> is
		4652	available and will probe for kernel support at runtime. This enables
		4653	the use of EVFLAG_SIGNALFD for faster and simpler signal handling. If
		4654	undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4655	2.7 or newer, otherwise disabled.
		4656
		4657	=item EV_USE_TIMERFD
		4658
		4659	If defined to be C<1>, then libev will assume that C<timerfd ()> is
		4660	available and will probe for kernel support at runtime. This allows
		4661	libev to detect time jumps accurately. If undefined, it will be enabled
		4662	if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
		4663	C<TFD_TIMER_CANCEL_ON_SET>, otherwise disabled.
		4664
		4665	=item EV_USE_EVENTFD
		4666
		4667	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4668	available and will probe for kernel support at runtime. This will improve
		4669	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4670	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4671	2.7 or newer, otherwise disabled.
		4672
3112	=item EV_USE_SELECT	4673	=item EV_USE_SELECT
3113		4674
3114	If undefined or defined to be C<1>, libev will compile in support for the	4675	If undefined or defined to be C<1>, libev will compile in support for the
3115	C<select>(2) backend. No attempt at auto-detection will be done: if no	4676	C<select>(2) backend. No attempt at auto-detection will be done: if no
3116	other method takes over, select will be it. Otherwise the select backend	4677	other method takes over, select will be it. Otherwise the select backend
…		…
3118		4679
3119	=item EV_SELECT_USE_FD_SET	4680	=item EV_SELECT_USE_FD_SET
3120		4681
3121	If defined to C<1>, then the select backend will use the system C<fd_set>	4682	If defined to C<1>, then the select backend will use the system C<fd_set>
3122	structure. This is useful if libev doesn't compile due to a missing	4683	structure. This is useful if libev doesn't compile due to a missing
3123	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	4684	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
3124	exotic systems. This usually limits the range of file descriptors to some	4685	on exotic systems. This usually limits the range of file descriptors to
3125	low limit such as 1024 or might have other limitations (winsocket only	4686	some low limit such as 1024 or might have other limitations (winsocket
3126	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4687	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
3127	influence the size of the C<fd_set> used.	4688	configures the maximum size of the C<fd_set>.
3128		4689
3129	=item EV_SELECT_IS_WINSOCKET	4690	=item EV_SELECT_IS_WINSOCKET
3130		4691
3131	When defined to C<1>, the select backend will assume that	4692	When defined to C<1>, the select backend will assume that
3132	select/socket/connect etc. don't understand file descriptors but	4693	select/socket/connect etc. don't understand file descriptors but
…		…
3134	be used is the winsock select). This means that it will call	4695	be used is the winsock select). This means that it will call
3135	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4696	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
3136	it is assumed that all these functions actually work on fds, even	4697	it is assumed that all these functions actually work on fds, even
3137	on win32. Should not be defined on non-win32 platforms.	4698	on win32. Should not be defined on non-win32 platforms.
3138		4699
3139	=item EV_FD_TO_WIN32_HANDLE	4700	=item EV_FD_TO_WIN32_HANDLE(fd)
3140		4701
3141	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4702	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
3142	file descriptors to socket handles. When not defining this symbol (the	4703	file descriptors to socket handles. When not defining this symbol (the
3143	default), then libev will call C<_get_osfhandle>, which is usually	4704	default), then libev will call C<_get_osfhandle>, which is usually
3144	correct. In some cases, programs use their own file descriptor management,	4705	correct. In some cases, programs use their own file descriptor management,
3145	in which case they can provide this function to map fds to socket handles.	4706	in which case they can provide this function to map fds to socket handles.
3146		4707
		4708	=item EV_WIN32_HANDLE_TO_FD(handle)
		4709
		4710	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4711	using the standard C<_open_osfhandle> function. For programs implementing
		4712	their own fd to handle mapping, overwriting this function makes it easier
		4713	to do so. This can be done by defining this macro to an appropriate value.
		4714
		4715	=item EV_WIN32_CLOSE_FD(fd)
		4716
		4717	If programs implement their own fd to handle mapping on win32, then this
		4718	macro can be used to override the C<close> function, useful to unregister
		4719	file descriptors again. Note that the replacement function has to close
		4720	the underlying OS handle.
		4721
		4722	=item EV_USE_WSASOCKET
		4723
		4724	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4725	communication socket, which works better in some environments. Otherwise,
		4726	the normal C<socket> function will be used, which works better in other
		4727	environments.
		4728
3147	=item EV_USE_POLL	4729	=item EV_USE_POLL
3148		4730
3149	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4731	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3150	backend. Otherwise it will be enabled on non-win32 platforms. It	4732	backend. Otherwise it will be enabled on non-win32 platforms. It
3151	takes precedence over select.	4733	takes precedence over select.
…		…
3155	If defined to be C<1>, libev will compile in support for the Linux	4737	If defined to be C<1>, libev will compile in support for the Linux
3156	C<epoll>(7) backend. Its availability will be detected at runtime,	4738	C<epoll>(7) backend. Its availability will be detected at runtime,
3157	otherwise another method will be used as fallback. This is the preferred	4739	otherwise another method will be used as fallback. This is the preferred
3158	backend for GNU/Linux systems. If undefined, it will be enabled if the	4740	backend for GNU/Linux systems. If undefined, it will be enabled if the
3159	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4741	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4742
		4743	=item EV_USE_LINUXAIO
		4744
		4745	If defined to be C<1>, libev will compile in support for the Linux aio
		4746	backend (C<EV_USE_EPOLL> must also be enabled). If undefined, it will be
		4747	enabled on linux, otherwise disabled.
		4748
		4749	=item EV_USE_IOURING
		4750
		4751	If defined to be C<1>, libev will compile in support for the Linux
		4752	io_uring backend (C<EV_USE_EPOLL> must also be enabled). Due to it's
		4753	current limitations it has to be requested explicitly. If undefined, it
		4754	will be enabled on linux, otherwise disabled.
3160		4755
3161	=item EV_USE_KQUEUE	4756	=item EV_USE_KQUEUE
3162		4757
3163	If defined to be C<1>, libev will compile in support for the BSD style	4758	If defined to be C<1>, libev will compile in support for the BSD style
3164	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4759	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
3186	If defined to be C<1>, libev will compile in support for the Linux inotify	4781	If defined to be C<1>, libev will compile in support for the Linux inotify
3187	interface to speed up C<ev_stat> watchers. Its actual availability will	4782	interface to speed up C<ev_stat> watchers. Its actual availability will
3188	be detected at runtime. If undefined, it will be enabled if the headers	4783	be detected at runtime. If undefined, it will be enabled if the headers
3189	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4784	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3190		4785
		4786	=item EV_NO_SMP
		4787
		4788	If defined to be C<1>, libev will assume that memory is always coherent
		4789	between threads, that is, threads can be used, but threads never run on
		4790	different cpus (or different cpu cores). This reduces dependencies
		4791	and makes libev faster.
		4792
		4793	=item EV_NO_THREADS
		4794
		4795	If defined to be C<1>, libev will assume that it will never be called from
		4796	different threads (that includes signal handlers), which is a stronger
		4797	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4798	libev faster.
		4799
3191	=item EV_ATOMIC_T	4800	=item EV_ATOMIC_T
3192		4801
3193	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4802	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3194	access is atomic with respect to other threads or signal contexts. No such	4803	access is atomic with respect to other threads or signal contexts. No
3195	type is easily found in the C language, so you can provide your own type	4804	such type is easily found in the C language, so you can provide your own
3196	that you know is safe for your purposes. It is used both for signal handler "locking"	4805	type that you know is safe for your purposes. It is used both for signal
3197	as well as for signal and thread safety in C<ev_async> watchers.	4806	handler "locking" as well as for signal and thread safety in C<ev_async>
		4807	watchers.
3198		4808
3199	In the absence of this define, libev will use C<sig_atomic_t volatile>	4809	In the absence of this define, libev will use C<sig_atomic_t volatile>
3200	(from F<signal.h>), which is usually good enough on most platforms.	4810	(from F<signal.h>), which is usually good enough on most platforms.
3201		4811
3202	=item EV_H	4812	=item EV_H (h)
3203		4813
3204	The name of the F<ev.h> header file used to include it. The default if	4814	The name of the F<ev.h> header file used to include it. The default if
3205	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4815	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
3206	used to virtually rename the F<ev.h> header file in case of conflicts.	4816	used to virtually rename the F<ev.h> header file in case of conflicts.
3207		4817
3208	=item EV_CONFIG_H	4818	=item EV_CONFIG_H (h)
3209		4819
3210	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4820	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
3211	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4821	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
3212	C<EV_H>, above.	4822	C<EV_H>, above.
3213		4823
3214	=item EV_EVENT_H	4824	=item EV_EVENT_H (h)
3215		4825
3216	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4826	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
3217	of how the F<event.h> header can be found, the default is C<"event.h">.	4827	of how the F<event.h> header can be found, the default is C<"event.h">.
3218		4828
3219	=item EV_PROTOTYPES	4829	=item EV_PROTOTYPES (h)
3220		4830
3221	If defined to be C<0>, then F<ev.h> will not define any function	4831	If defined to be C<0>, then F<ev.h> will not define any function
3222	prototypes, but still define all the structs and other symbols. This is	4832	prototypes, but still define all the structs and other symbols. This is
3223	occasionally useful if you want to provide your own wrapper functions	4833	occasionally useful if you want to provide your own wrapper functions
3224	around libev functions.	4834	around libev functions.
…		…
3229	will have the C<struct ev_loop *> as first argument, and you can create	4839	will have the C<struct ev_loop *> as first argument, and you can create
3230	additional independent event loops. Otherwise there will be no support	4840	additional independent event loops. Otherwise there will be no support
3231	for multiple event loops and there is no first event loop pointer	4841	for multiple event loops and there is no first event loop pointer
3232	argument. Instead, all functions act on the single default loop.	4842	argument. Instead, all functions act on the single default loop.
3233		4843
		4844	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4845	default loop when multiplicity is switched off - you always have to
		4846	initialise the loop manually in this case.
		4847
3234	=item EV_MINPRI	4848	=item EV_MINPRI
3235		4849
3236	=item EV_MAXPRI	4850	=item EV_MAXPRI
3237		4851
3238	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4852	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
3246	fine.	4860	fine.
3247		4861
3248	If your embedding application does not need any priorities, defining these	4862	If your embedding application does not need any priorities, defining these
3249	both to C<0> will save some memory and CPU.	4863	both to C<0> will save some memory and CPU.
3250		4864
3251	=item EV_PERIODIC_ENABLE	4865	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4866	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4867	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
3252		4868
3253	If undefined or defined to be C<1>, then periodic timers are supported. If	4869	If undefined or defined to be C<1> (and the platform supports it), then
3254	defined to be C<0>, then they are not. Disabling them saves a few kB of	4870	the respective watcher type is supported. If defined to be C<0>, then it
3255	code.	4871	is not. Disabling watcher types mainly saves code size.
3256		4872
3257	=item EV_IDLE_ENABLE	4873	=item EV_FEATURES
3258
3259	If undefined or defined to be C<1>, then idle watchers are supported. If
3260	defined to be C<0>, then they are not. Disabling them saves a few kB of
3261	code.
3262
3263	=item EV_EMBED_ENABLE
3264
3265	If undefined or defined to be C<1>, then embed watchers are supported. If
3266	defined to be C<0>, then they are not. Embed watchers rely on most other
3267	watcher types, which therefore must not be disabled.
3268
3269	=item EV_STAT_ENABLE
3270
3271	If undefined or defined to be C<1>, then stat watchers are supported. If
3272	defined to be C<0>, then they are not.
3273
3274	=item EV_FORK_ENABLE
3275
3276	If undefined or defined to be C<1>, then fork watchers are supported. If
3277	defined to be C<0>, then they are not.
3278
3279	=item EV_ASYNC_ENABLE
3280
3281	If undefined or defined to be C<1>, then async watchers are supported. If
3282	defined to be C<0>, then they are not.
3283
3284	=item EV_MINIMAL
3285		4874
3286	If you need to shave off some kilobytes of code at the expense of some	4875	If you need to shave off some kilobytes of code at the expense of some
3287	speed, define this symbol to C<1>. Currently this is used to override some	4876	speed (but with the full API), you can define this symbol to request
3288	inlining decisions, saves roughly 30% code size on amd64. It also selects a	4877	certain subsets of functionality. The default is to enable all features
3289	much smaller 2-heap for timer management over the default 4-heap.	4878	that can be enabled on the platform.
		4879
		4880	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4881	with some broad features you want) and then selectively re-enable
		4882	additional parts you want, for example if you want everything minimal,
		4883	but multiple event loop support, async and child watchers and the poll
		4884	backend, use this:
		4885
		4886	#define EV_FEATURES 0
		4887	#define EV_MULTIPLICITY 1
		4888	#define EV_USE_POLL 1
		4889	#define EV_CHILD_ENABLE 1
		4890	#define EV_ASYNC_ENABLE 1
		4891
		4892	The actual value is a bitset, it can be a combination of the following
		4893	values (by default, all of these are enabled):
		4894
		4895	=over 4
		4896
		4897	=item C<1> - faster/larger code
		4898
		4899	Use larger code to speed up some operations.
		4900
		4901	Currently this is used to override some inlining decisions (enlarging the
		4902	code size by roughly 30% on amd64).
		4903
		4904	When optimising for size, use of compiler flags such as C<-Os> with
		4905	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4906	assertions.
		4907
		4908	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4909	(e.g. gcc with C<-Os>).
		4910
		4911	=item C<2> - faster/larger data structures
		4912
		4913	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4914	hash table sizes and so on. This will usually further increase code size
		4915	and can additionally have an effect on the size of data structures at
		4916	runtime.
		4917
		4918	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4919	(e.g. gcc with C<-Os>).
		4920
		4921	=item C<4> - full API configuration
		4922
		4923	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4924	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4925
		4926	=item C<8> - full API
		4927
		4928	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4929	details on which parts of the API are still available without this
		4930	feature, and do not complain if this subset changes over time.
		4931
		4932	=item C<16> - enable all optional watcher types
		4933
		4934	Enables all optional watcher types. If you want to selectively enable
		4935	only some watcher types other than I/O and timers (e.g. prepare,
		4936	embed, async, child...) you can enable them manually by defining
		4937	C<EV_watchertype_ENABLE> to C<1> instead.
		4938
		4939	=item C<32> - enable all backends
		4940
		4941	This enables all backends - without this feature, you need to enable at
		4942	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4943
		4944	=item C<64> - enable OS-specific "helper" APIs
		4945
		4946	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4947	default.
		4948
		4949	=back
		4950
		4951	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4952	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4953	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4954	watchers, timers and monotonic clock support.
		4955
		4956	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4957	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4958	your program might be left out as well - a binary starting a timer and an
		4959	I/O watcher then might come out at only 5Kb.
		4960
		4961	=item EV_API_STATIC
		4962
		4963	If this symbol is defined (by default it is not), then all identifiers
		4964	will have static linkage. This means that libev will not export any
		4965	identifiers, and you cannot link against libev anymore. This can be useful
		4966	when you embed libev, only want to use libev functions in a single file,
		4967	and do not want its identifiers to be visible.
		4968
		4969	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4970	wants to use libev.
		4971
		4972	This option only works when libev is compiled with a C compiler, as C++
		4973	doesn't support the required declaration syntax.
		4974
		4975	=item EV_AVOID_STDIO
		4976
		4977	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4978	functions (printf, scanf, perror etc.). This will increase the code size
		4979	somewhat, but if your program doesn't otherwise depend on stdio and your
		4980	libc allows it, this avoids linking in the stdio library which is quite
		4981	big.
		4982
		4983	Note that error messages might become less precise when this option is
		4984	enabled.
		4985
		4986	=item EV_NSIG
		4987
		4988	The highest supported signal number, +1 (or, the number of
		4989	signals): Normally, libev tries to deduce the maximum number of signals
		4990	automatically, but sometimes this fails, in which case it can be
		4991	specified. Also, using a lower number than detected (C<32> should be
		4992	good for about any system in existence) can save some memory, as libev
		4993	statically allocates some 12-24 bytes per signal number.
3290		4994
3291	=item EV_PID_HASHSIZE	4995	=item EV_PID_HASHSIZE
3292		4996
3293	C<ev_child> watchers use a small hash table to distribute workload by	4997	C<ev_child> watchers use a small hash table to distribute workload by
3294	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4998	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
3295	than enough. If you need to manage thousands of children you might want to	4999	usually more than enough. If you need to manage thousands of children you
3296	increase this value (I<must> be a power of two).	5000	might want to increase this value (I<must> be a power of two).
3297		5001
3298	=item EV_INOTIFY_HASHSIZE	5002	=item EV_INOTIFY_HASHSIZE
3299		5003
3300	C<ev_stat> watchers use a small hash table to distribute workload by	5004	C<ev_stat> watchers use a small hash table to distribute workload by
3301	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	5005	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
3302	usually more than enough. If you need to manage thousands of C<ev_stat>	5006	disabled), usually more than enough. If you need to manage thousands of
3303	watchers you might want to increase this value (I<must> be a power of	5007	C<ev_stat> watchers you might want to increase this value (I<must> be a
3304	two).	5008	power of two).
3305		5009
3306	=item EV_USE_4HEAP	5010	=item EV_USE_4HEAP
3307		5011
3308	Heaps are not very cache-efficient. To improve the cache-efficiency of the	5012	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3309	timer and periodics heaps, libev uses a 4-heap when this symbol is defined	5013	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3310	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably	5014	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3311	faster performance with many (thousands) of watchers.	5015	faster performance with many (thousands) of watchers.
3312		5016
3313	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	5017	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3314	(disabled).	5018	will be C<0>.
3315		5019
3316	=item EV_HEAP_CACHE_AT	5020	=item EV_HEAP_CACHE_AT
3317		5021
3318	Heaps are not very cache-efficient. To improve the cache-efficiency of the	5022	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3319	timer and periodics heaps, libev can cache the timestamp (I<at>) within	5023	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3320	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	5024	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3321	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	5025	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3322	but avoids random read accesses on heap changes. This improves performance	5026	but avoids random read accesses on heap changes. This improves performance
3323	noticeably with many (hundreds) of watchers.	5027	noticeably with many (hundreds) of watchers.
3324		5028
3325	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	5029	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3326	(disabled).	5030	will be C<0>.
3327		5031
3328	=item EV_VERIFY	5032	=item EV_VERIFY
3329		5033
3330	Controls how much internal verification (see C<ev_loop_verify ()>) will	5034	Controls how much internal verification (see C<ev_verify ()>) will
3331	be done: If set to C<0>, no internal verification code will be compiled	5035	be done: If set to C<0>, no internal verification code will be compiled
3332	in. If set to C<1>, then verification code will be compiled in, but not	5036	in. If set to C<1>, then verification code will be compiled in, but not
3333	called. If set to C<2>, then the internal verification code will be	5037	called. If set to C<2>, then the internal verification code will be
3334	called once per loop, which can slow down libev. If set to C<3>, then the	5038	called once per loop, which can slow down libev. If set to C<3>, then the
3335	verification code will be called very frequently, which will slow down	5039	verification code will be called very frequently, which will slow down
3336	libev considerably.	5040	libev considerably.
3337		5041
		5042	Verification errors are reported via C's C<assert> mechanism, so if you
		5043	disable that (e.g. by defining C<NDEBUG>) then no errors will be reported.
		5044
3338	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	5045	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3339	C<0>.	5046	will be C<0>.
3340		5047
3341	=item EV_COMMON	5048	=item EV_COMMON
3342		5049
3343	By default, all watchers have a C<void *data> member. By redefining	5050	By default, all watchers have a C<void *data> member. By redefining
3344	this macro to a something else you can include more and other types of	5051	this macro to something else you can include more and other types of
3345	members. You have to define it each time you include one of the files,	5052	members. You have to define it each time you include one of the files,
3346	though, and it must be identical each time.	5053	though, and it must be identical each time.
3347		5054
3348	For example, the perl EV module uses something like this:	5055	For example, the perl EV module uses something like this:
3349		5056
…		…
3402	file.	5109	file.
3403		5110
3404	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	5111	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
3405	that everybody includes and which overrides some configure choices:	5112	that everybody includes and which overrides some configure choices:
3406		5113
3407	#define EV_MINIMAL 1	5114	#define EV_FEATURES 8
3408	#define EV_USE_POLL 0	5115	#define EV_USE_SELECT 1
3409	#define EV_MULTIPLICITY 0
3410	#define EV_PERIODIC_ENABLE 0	5116	#define EV_PREPARE_ENABLE 1
		5117	#define EV_IDLE_ENABLE 1
3411	#define EV_STAT_ENABLE 0	5118	#define EV_SIGNAL_ENABLE 1
3412	#define EV_FORK_ENABLE 0	5119	#define EV_CHILD_ENABLE 1
		5120	#define EV_USE_STDEXCEPT 0
3413	#define EV_CONFIG_H <config.h>	5121	#define EV_CONFIG_H <config.h>
3414	#define EV_MINPRI 0
3415	#define EV_MAXPRI 0
3416		5122
3417	#include "ev++.h"	5123	#include "ev++.h"
3418		5124
3419	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5125	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3420		5126
3421	#include "ev_cpp.h"	5127	#include "ev_cpp.h"
3422	#include "ev.c"	5128	#include "ev.c"
3423		5129
3424	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5130	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
3425		5131
3426	=head2 THREADS AND COROUTINES	5132	=head2 THREADS AND COROUTINES
3427		5133
3428	=head3 THREADS	5134	=head3 THREADS
3429		5135
…		…
3480	default loop and triggering an C<ev_async> watcher from the default loop	5186	default loop and triggering an C<ev_async> watcher from the default loop
3481	watcher callback into the event loop interested in the signal.	5187	watcher callback into the event loop interested in the signal.
3482		5188
3483	=back	5189	=back
3484		5190
		5191	See also L</THREAD LOCKING EXAMPLE>.
		5192
3485	=head3 COROUTINES	5193	=head3 COROUTINES
3486		5194
3487	Libev is very accommodating to coroutines ("cooperative threads"):	5195	Libev is very accommodating to coroutines ("cooperative threads"):
3488	libev fully supports nesting calls to its functions from different	5196	libev fully supports nesting calls to its functions from different
3489	coroutines (e.g. you can call C<ev_loop> on the same loop from two	5197	coroutines (e.g. you can call C<ev_run> on the same loop from two
3490	different coroutines, and switch freely between both coroutines running the	5198	different coroutines, and switch freely between both coroutines running
3491	loop, as long as you don't confuse yourself). The only exception is that	5199	the loop, as long as you don't confuse yourself). The only exception is
3492	you must not do this from C<ev_periodic> reschedule callbacks.	5200	that you must not do this from C<ev_periodic> reschedule callbacks.
3493		5201
3494	Care has been taken to ensure that libev does not keep local state inside	5202	Care has been taken to ensure that libev does not keep local state inside
3495	C<ev_loop>, and other calls do not usually allow for coroutine switches as	5203	C<ev_run>, and other calls do not usually allow for coroutine switches as
3496	they do not clal any callbacks.	5204	they do not call any callbacks.
3497		5205
3498	=head2 COMPILER WARNINGS	5206	=head2 COMPILER WARNINGS
3499		5207
3500	Depending on your compiler and compiler settings, you might get no or a	5208	Depending on your compiler and compiler settings, you might get no or a
3501	lot of warnings when compiling libev code. Some people are apparently	5209	lot of warnings when compiling libev code. Some people are apparently
…		…
3511	maintainable.	5219	maintainable.
3512		5220
3513	And of course, some compiler warnings are just plain stupid, or simply	5221	And of course, some compiler warnings are just plain stupid, or simply
3514	wrong (because they don't actually warn about the condition their message	5222	wrong (because they don't actually warn about the condition their message
3515	seems to warn about). For example, certain older gcc versions had some	5223	seems to warn about). For example, certain older gcc versions had some
3516	warnings that resulted an extreme number of false positives. These have	5224	warnings that resulted in an extreme number of false positives. These have
3517	been fixed, but some people still insist on making code warn-free with	5225	been fixed, but some people still insist on making code warn-free with
3518	such buggy versions.	5226	such buggy versions.
3519		5227
3520	While libev is written to generate as few warnings as possible,	5228	While libev is written to generate as few warnings as possible,
3521	"warn-free" code is not a goal, and it is recommended not to build libev	5229	"warn-free" code is not a goal, and it is recommended not to build libev
…		…
3535	==2274== definitely lost: 0 bytes in 0 blocks.	5243	==2274== definitely lost: 0 bytes in 0 blocks.
3536	==2274== possibly lost: 0 bytes in 0 blocks.	5244	==2274== possibly lost: 0 bytes in 0 blocks.
3537	==2274== still reachable: 256 bytes in 1 blocks.	5245	==2274== still reachable: 256 bytes in 1 blocks.
3538		5246
3539	Then there is no memory leak, just as memory accounted to global variables	5247	Then there is no memory leak, just as memory accounted to global variables
3540	is not a memleak - the memory is still being refernced, and didn't leak.	5248	is not a memleak - the memory is still being referenced, and didn't leak.
3541		5249
3542	Similarly, under some circumstances, valgrind might report kernel bugs	5250	Similarly, under some circumstances, valgrind might report kernel bugs
3543	as if it were a bug in libev (e.g. in realloc or in the poll backend,	5251	as if it were a bug in libev (e.g. in realloc or in the poll backend,
3544	although an acceptable workaround has been found here), or it might be	5252	although an acceptable workaround has been found here), or it might be
3545	confused.	5253	confused.
…		…
3557	I suggest using suppression lists.	5265	I suggest using suppression lists.
3558		5266
3559		5267
3560	=head1 PORTABILITY NOTES	5268	=head1 PORTABILITY NOTES
3561		5269
		5270	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5271
		5272	GNU/Linux is the only common platform that supports 64 bit file/large file
		5273	interfaces but I<disables> them by default.
		5274
		5275	That means that libev compiled in the default environment doesn't support
		5276	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5277
		5278	Unfortunately, many programs try to work around this GNU/Linux issue
		5279	by enabling the large file API, which makes them incompatible with the
		5280	standard libev compiled for their system.
		5281
		5282	Likewise, libev cannot enable the large file API itself as this would
		5283	suddenly make it incompatible to the default compile time environment,
		5284	i.e. all programs not using special compile switches.
		5285
		5286	=head2 OS/X AND DARWIN BUGS
		5287
		5288	The whole thing is a bug if you ask me - basically any system interface
		5289	you touch is broken, whether it is locales, poll, kqueue or even the
		5290	OpenGL drivers.
		5291
		5292	=head3 C<kqueue> is buggy
		5293
		5294	The kqueue syscall is broken in all known versions - most versions support
		5295	only sockets, many support pipes.
		5296
		5297	Libev tries to work around this by not using C<kqueue> by default on this
		5298	rotten platform, but of course you can still ask for it when creating a
		5299	loop - embedding a socket-only kqueue loop into a select-based one is
		5300	probably going to work well.
		5301
		5302	=head3 C<poll> is buggy
		5303
		5304	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5305	implementation by something calling C<kqueue> internally around the 10.5.6
		5306	release, so now C<kqueue> I<and> C<poll> are broken.
		5307
		5308	Libev tries to work around this by not using C<poll> by default on
		5309	this rotten platform, but of course you can still ask for it when creating
		5310	a loop.
		5311
		5312	=head3 C<select> is buggy
		5313
		5314	All that's left is C<select>, and of course Apple found a way to fuck this
		5315	one up as well: On OS/X, C<select> actively limits the number of file
		5316	descriptors you can pass in to 1024 - your program suddenly crashes when
		5317	you use more.
		5318
		5319	There is an undocumented "workaround" for this - defining
		5320	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5321	work on OS/X.
		5322
		5323	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5324
		5325	=head3 C<errno> reentrancy
		5326
		5327	The default compile environment on Solaris is unfortunately so
		5328	thread-unsafe that you can't even use components/libraries compiled
		5329	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5330	defined by default. A valid, if stupid, implementation choice.
		5331
		5332	If you want to use libev in threaded environments you have to make sure
		5333	it's compiled with C<_REENTRANT> defined.
		5334
		5335	=head3 Event port backend
		5336
		5337	The scalable event interface for Solaris is called "event
		5338	ports". Unfortunately, this mechanism is very buggy in all major
		5339	releases. If you run into high CPU usage, your program freezes or you get
		5340	a large number of spurious wakeups, make sure you have all the relevant
		5341	and latest kernel patches applied. No, I don't know which ones, but there
		5342	are multiple ones to apply, and afterwards, event ports actually work
		5343	great.
		5344
		5345	If you can't get it to work, you can try running the program by setting
		5346	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5347	C<select> backends.
		5348
		5349	=head2 AIX POLL BUG
		5350
		5351	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5352	this by trying to avoid the poll backend altogether (i.e. it's not even
		5353	compiled in), which normally isn't a big problem as C<select> works fine
		5354	with large bitsets on AIX, and AIX is dead anyway.
		5355
3562	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	5356	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5357
		5358	=head3 General issues
3563		5359
3564	Win32 doesn't support any of the standards (e.g. POSIX) that libev	5360	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3565	requires, and its I/O model is fundamentally incompatible with the POSIX	5361	requires, and its I/O model is fundamentally incompatible with the POSIX
3566	model. Libev still offers limited functionality on this platform in	5362	model. Libev still offers limited functionality on this platform in
3567	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5363	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3568	descriptors. This only applies when using Win32 natively, not when using	5364	descriptors. This only applies when using Win32 natively, not when using
3569	e.g. cygwin.	5365	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5366	as every compiler comes with a slightly differently broken/incompatible
		5367	environment.
3570		5368
3571	Lifting these limitations would basically require the full	5369	Lifting these limitations would basically require the full
3572	re-implementation of the I/O system. If you are into these kinds of	5370	re-implementation of the I/O system. If you are into this kind of thing,
3573	things, then note that glib does exactly that for you in a very portable	5371	then note that glib does exactly that for you in a very portable way (note
3574	way (note also that glib is the slowest event library known to man).	5372	also that glib is the slowest event library known to man).
3575		5373
3576	There is no supported compilation method available on windows except	5374	There is no supported compilation method available on windows except
3577	embedding it into other applications.	5375	embedding it into other applications.
		5376
		5377	Sensible signal handling is officially unsupported by Microsoft - libev
		5378	tries its best, but under most conditions, signals will simply not work.
3578		5379
3579	Not a libev limitation but worth mentioning: windows apparently doesn't	5380	Not a libev limitation but worth mentioning: windows apparently doesn't
3580	accept large writes: instead of resulting in a partial write, windows will	5381	accept large writes: instead of resulting in a partial write, windows will
3581	either accept everything or return C<ENOBUFS> if the buffer is too large,	5382	either accept everything or return C<ENOBUFS> if the buffer is too large,
3582	so make sure you only write small amounts into your sockets (less than a	5383	so make sure you only write small amounts into your sockets (less than a
…		…
3587	the abysmal performance of winsockets, using a large number of sockets	5388	the abysmal performance of winsockets, using a large number of sockets
3588	is not recommended (and not reasonable). If your program needs to use	5389	is not recommended (and not reasonable). If your program needs to use
3589	more than a hundred or so sockets, then likely it needs to use a totally	5390	more than a hundred or so sockets, then likely it needs to use a totally
3590	different implementation for windows, as libev offers the POSIX readiness	5391	different implementation for windows, as libev offers the POSIX readiness
3591	notification model, which cannot be implemented efficiently on windows	5392	notification model, which cannot be implemented efficiently on windows
3592	(Microsoft monopoly games).	5393	(due to Microsoft monopoly games).
3593		5394
3594	A typical way to use libev under windows is to embed it (see the embedding	5395	A typical way to use libev under windows is to embed it (see the embedding
3595	section for details) and use the following F<evwrap.h> header file instead	5396	section for details) and use the following F<evwrap.h> header file instead
3596	of F<ev.h>:	5397	of F<ev.h>:
3597		5398
…		…
3604	you do I<not> compile the F<ev.c> or any other embedded source files!):	5405	you do I<not> compile the F<ev.c> or any other embedded source files!):
3605		5406
3606	#include "evwrap.h"	5407	#include "evwrap.h"
3607	#include "ev.c"	5408	#include "ev.c"
3608		5409
3609	=over 4
3610
3611	=item The winsocket select function	5410	=head3 The winsocket C<select> function
3612		5411
3613	The winsocket C<select> function doesn't follow POSIX in that it	5412	The winsocket C<select> function doesn't follow POSIX in that it
3614	requires socket I<handles> and not socket I<file descriptors> (it is	5413	requires socket I<handles> and not socket I<file descriptors> (it is
3615	also extremely buggy). This makes select very inefficient, and also	5414	also extremely buggy). This makes select very inefficient, and also
3616	requires a mapping from file descriptors to socket handles (the Microsoft	5415	requires a mapping from file descriptors to socket handles (the Microsoft
…		…
3625	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	5424	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3626		5425
3627	Note that winsockets handling of fd sets is O(n), so you can easily get a	5426	Note that winsockets handling of fd sets is O(n), so you can easily get a
3628	complexity in the O(n²) range when using win32.	5427	complexity in the O(n²) range when using win32.
3629		5428
3630	=item Limited number of file descriptors	5429	=head3 Limited number of file descriptors
3631		5430
3632	Windows has numerous arbitrary (and low) limits on things.	5431	Windows has numerous arbitrary (and low) limits on things.
3633		5432
3634	Early versions of winsocket's select only supported waiting for a maximum	5433	Early versions of winsocket's select only supported waiting for a maximum
3635	of C<64> handles (probably owning to the fact that all windows kernels	5434	of C<64> handles (probably owning to the fact that all windows kernels
3636	can only wait for C<64> things at the same time internally; Microsoft	5435	can only wait for C<64> things at the same time internally; Microsoft
3637	recommends spawning a chain of threads and wait for 63 handles and the	5436	recommends spawning a chain of threads and wait for 63 handles and the
3638	previous thread in each. Great).	5437	previous thread in each. Sounds great!).
3639		5438
3640	Newer versions support more handles, but you need to define C<FD_SETSIZE>	5439	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3641	to some high number (e.g. C<2048>) before compiling the winsocket select	5440	to some high number (e.g. C<2048>) before compiling the winsocket select
3642	call (which might be in libev or elsewhere, for example, perl does its own	5441	call (which might be in libev or elsewhere, for example, perl and many
3643	select emulation on windows).	5442	other interpreters do their own select emulation on windows).
3644		5443
3645	Another limit is the number of file descriptors in the Microsoft runtime	5444	Another limit is the number of file descriptors in the Microsoft runtime
3646	libraries, which by default is C<64> (there must be a hidden I<64> fetish	5445	libraries, which by default is C<64> (there must be a hidden I<64>
3647	or something like this inside Microsoft). You can increase this by calling	5446	fetish or something like this inside Microsoft). You can increase this
3648	C<_setmaxstdio>, which can increase this limit to C<2048> (another	5447	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3649	arbitrary limit), but is broken in many versions of the Microsoft runtime	5448	(another arbitrary limit), but is broken in many versions of the Microsoft
3650	libraries.
3651
3652	This might get you to about C<512> or C<2048> sockets (depending on	5449	runtime libraries. This might get you to about C<512> or C<2048> sockets
3653	windows version and/or the phase of the moon). To get more, you need to	5450	(depending on windows version and/or the phase of the moon). To get more,
3654	wrap all I/O functions and provide your own fd management, but the cost of	5451	you need to wrap all I/O functions and provide your own fd management, but
3655	calling select (O(n²)) will likely make this unworkable.	5452	the cost of calling select (O(n²)) will likely make this unworkable.
3656
3657	=back
3658		5453
3659	=head2 PORTABILITY REQUIREMENTS	5454	=head2 PORTABILITY REQUIREMENTS
3660		5455
3661	In addition to a working ISO-C implementation and of course the	5456	In addition to a working ISO-C implementation and of course the
3662	backend-specific APIs, libev relies on a few additional extensions:	5457	backend-specific APIs, libev relies on a few additional extensions:
…		…
3669	Libev assumes not only that all watcher pointers have the same internal	5464	Libev assumes not only that all watcher pointers have the same internal
3670	structure (guaranteed by POSIX but not by ISO C for example), but it also	5465	structure (guaranteed by POSIX but not by ISO C for example), but it also
3671	assumes that the same (machine) code can be used to call any watcher	5466	assumes that the same (machine) code can be used to call any watcher
3672	callback: The watcher callbacks have different type signatures, but libev	5467	callback: The watcher callbacks have different type signatures, but libev
3673	calls them using an C<ev_watcher *> internally.	5468	calls them using an C<ev_watcher *> internally.
		5469
		5470	=item null pointers and integer zero are represented by 0 bytes
		5471
		5472	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5473	relies on this setting pointers and integers to null.
		5474
		5475	=item pointer accesses must be thread-atomic
		5476
		5477	Accessing a pointer value must be atomic, it must both be readable and
		5478	writable in one piece - this is the case on all current architectures.
3674		5479
3675	=item C<sig_atomic_t volatile> must be thread-atomic as well	5480	=item C<sig_atomic_t volatile> must be thread-atomic as well
3676		5481
3677	The type C<sig_atomic_t volatile> (or whatever is defined as	5482	The type C<sig_atomic_t volatile> (or whatever is defined as
3678	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5483	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
…		…
3687	thread" or will block signals process-wide, both behaviours would	5492	thread" or will block signals process-wide, both behaviours would
3688	be compatible with libev. Interaction between C<sigprocmask> and	5493	be compatible with libev. Interaction between C<sigprocmask> and
3689	C<pthread_sigmask> could complicate things, however.	5494	C<pthread_sigmask> could complicate things, however.
3690		5495
3691	The most portable way to handle signals is to block signals in all threads	5496	The most portable way to handle signals is to block signals in all threads
3692	except the initial one, and run the default loop in the initial thread as	5497	except the initial one, and run the signal handling loop in the initial
3693	well.	5498	thread as well.
3694		5499
3695	=item C<long> must be large enough for common memory allocation sizes	5500	=item C<long> must be large enough for common memory allocation sizes
3696		5501
3697	To improve portability and simplify its API, libev uses C<long> internally	5502	To improve portability and simplify its API, libev uses C<long> internally
3698	instead of C<size_t> when allocating its data structures. On non-POSIX	5503	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
3701	watchers.	5506	watchers.
3702		5507
3703	=item C<double> must hold a time value in seconds with enough accuracy	5508	=item C<double> must hold a time value in seconds with enough accuracy
3704		5509
3705	The type C<double> is used to represent timestamps. It is required to	5510	The type C<double> is used to represent timestamps. It is required to
3706	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	5511	have at least 51 bits of mantissa (and 9 bits of exponent), which is
3707	enough for at least into the year 4000. This requirement is fulfilled by	5512	good enough for at least into the year 4000 with millisecond accuracy
		5513	(the design goal for libev). This requirement is overfulfilled by
3708	implementations implementing IEEE 754 (basically all existing ones).	5514	implementations using IEEE 754, which is basically all existing ones.
		5515
		5516	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5517	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5518	is either obsolete or somebody patched it to use C<long double> or
		5519	something like that, just kidding).
3709		5520
3710	=back	5521	=back
3711		5522
3712	If you know of other additional requirements drop me a note.	5523	If you know of other additional requirements drop me a note.
3713		5524
…		…
3775	=item Processing ev_async_send: O(number_of_async_watchers)	5586	=item Processing ev_async_send: O(number_of_async_watchers)
3776		5587
3777	=item Processing signals: O(max_signal_number)	5588	=item Processing signals: O(max_signal_number)
3778		5589
3779	Sending involves a system call I<iff> there were no other C<ev_async_send>	5590	Sending involves a system call I<iff> there were no other C<ev_async_send>
3780	calls in the current loop iteration. Checking for async and signal events	5591	calls in the current loop iteration and the loop is currently
		5592	blocked. Checking for async and signal events involves iterating over all
3781	involves iterating over all running async watchers or all signal numbers.	5593	running async watchers or all signal numbers.
3782		5594
3783	=back	5595	=back
3784		5596
3785		5597
		5598	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5599
		5600	The major version 4 introduced some incompatible changes to the API.
		5601
		5602	At the moment, the C<ev.h> header file provides compatibility definitions
		5603	for all changes, so most programs should still compile. The compatibility
		5604	layer might be removed in later versions of libev, so better update to the
		5605	new API early than late.
		5606
		5607	=over 4
		5608
		5609	=item C<EV_COMPAT3> backwards compatibility mechanism
		5610
		5611	The backward compatibility mechanism can be controlled by
		5612	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5613	section.
		5614
		5615	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5616
		5617	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5618
		5619	ev_loop_destroy (EV_DEFAULT_UC);
		5620	ev_loop_fork (EV_DEFAULT);
		5621
		5622	=item function/symbol renames
		5623
		5624	A number of functions and symbols have been renamed:
		5625
		5626	ev_loop => ev_run
		5627	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5628	EVLOOP_ONESHOT => EVRUN_ONCE
		5629
		5630	ev_unloop => ev_break
		5631	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5632	EVUNLOOP_ONE => EVBREAK_ONE
		5633	EVUNLOOP_ALL => EVBREAK_ALL
		5634
		5635	EV_TIMEOUT => EV_TIMER
		5636
		5637	ev_loop_count => ev_iteration
		5638	ev_loop_depth => ev_depth
		5639	ev_loop_verify => ev_verify
		5640
		5641	Most functions working on C<struct ev_loop> objects don't have an
		5642	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5643	associated constants have been renamed to not collide with the C<struct
		5644	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5645	as all other watcher types. Note that C<ev_loop_fork> is still called
		5646	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5647	typedef.
		5648
		5649	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5650
		5651	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5652	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5653	and work, but the library code will of course be larger.
		5654
		5655	=back
		5656
		5657
		5658	=head1 GLOSSARY
		5659
		5660	=over 4
		5661
		5662	=item active
		5663
		5664	A watcher is active as long as it has been started and not yet stopped.
		5665	See L</WATCHER STATES> for details.
		5666
		5667	=item application
		5668
		5669	In this document, an application is whatever is using libev.
		5670
		5671	=item backend
		5672
		5673	The part of the code dealing with the operating system interfaces.
		5674
		5675	=item callback
		5676
		5677	The address of a function that is called when some event has been
		5678	detected. Callbacks are being passed the event loop, the watcher that
		5679	received the event, and the actual event bitset.
		5680
		5681	=item callback/watcher invocation
		5682
		5683	The act of calling the callback associated with a watcher.
		5684
		5685	=item event
		5686
		5687	A change of state of some external event, such as data now being available
		5688	for reading on a file descriptor, time having passed or simply not having
		5689	any other events happening anymore.
		5690
		5691	In libev, events are represented as single bits (such as C<EV_READ> or
		5692	C<EV_TIMER>).
		5693
		5694	=item event library
		5695
		5696	A software package implementing an event model and loop.
		5697
		5698	=item event loop
		5699
		5700	An entity that handles and processes external events and converts them
		5701	into callback invocations.
		5702
		5703	=item event model
		5704
		5705	The model used to describe how an event loop handles and processes
		5706	watchers and events.
		5707
		5708	=item pending
		5709
		5710	A watcher is pending as soon as the corresponding event has been
		5711	detected. See L</WATCHER STATES> for details.
		5712
		5713	=item real time
		5714
		5715	The physical time that is observed. It is apparently strictly monotonic :)
		5716
		5717	=item wall-clock time
		5718
		5719	The time and date as shown on clocks. Unlike real time, it can actually
		5720	be wrong and jump forwards and backwards, e.g. when you adjust your
		5721	clock.
		5722
		5723	=item watcher
		5724
		5725	A data structure that describes interest in certain events. Watchers need
		5726	to be started (attached to an event loop) before they can receive events.
		5727
		5728	=back
		5729
3786	=head1 AUTHOR	5730	=head1 AUTHOR
3787		5731
3788	Marc Lehmann <libev@schmorp.de>.	5732	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5733	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
3789		5734

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