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		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	libev - a high performance full-featured event loop written in C	5	libev - a high performance full-featured event loop written in C
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
…		…
9	=head2 EXAMPLE PROGRAM	11	=head2 EXAMPLE PROGRAM
10		12
11	// a single header file is required	13	// a single header file is required
12	#include <ev.h>	14	#include <ev.h>
13		15
		16	#include <stdio.h> // for puts
		17
14	// every watcher type has its own typedef'd struct	18	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	19	// with the name ev_TYPE
16	ev_io stdin_watcher;	20	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	21	ev_timer timeout_watcher;
18		22
19	// all watcher callbacks have a similar signature	23	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	24	// this callback is called when data is readable on stdin
21	static void	25	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	26	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	27	{
24	puts ("stdin ready");	28	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	29	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	30	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	31	ev_io_stop (EV_A_ w);
28		32
29	// this causes all nested ev_loop's to stop iterating	33	// this causes all nested ev_run's to stop iterating
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	34	ev_break (EV_A_ EVBREAK_ALL);
31	}	35	}
32		36
33	// another callback, this time for a time-out	37	// another callback, this time for a time-out
34	static void	38	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	39	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	40	{
37	puts ("timeout");	41	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	42	// this causes the innermost ev_run to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	43	ev_break (EV_A_ EVBREAK_ONE);
40	}	44	}
41		45
42	int	46	int
43	main (void)	47	main (void)
44	{	48	{
45	// use the default event loop unless you have special needs	49	// use the default event loop unless you have special needs
46	struct ev_loop *loop = ev_default_loop (0);	50	struct ev_loop *loop = EV_DEFAULT;
47		51
48	// initialise an io watcher, then start it	52	// initialise an io watcher, then start it
49	// this one will watch for stdin to become readable	53	// this one will watch for stdin to become readable
50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	54	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
51	ev_io_start (loop, &stdin_watcher);	55	ev_io_start (loop, &stdin_watcher);
…		…
54	// simple non-repeating 5.5 second timeout	58	// simple non-repeating 5.5 second timeout
55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	59	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
56	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
57		61
58	// now wait for events to arrive	62	// now wait for events to arrive
59	ev_loop (loop, 0);	63	ev_run (loop, 0);
60		64
61	// unloop was called, so exit	65	// break was called, so exit
62	return 0;	66	return 0;
63	}	67	}
64		68
65	=head1 DESCRIPTION	69	=head1 ABOUT THIS DOCUMENT
		70
		71	This document documents the libev software package.
66		72
67	The newest version of this document is also available as an html-formatted	73	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	74	web page you might find easier to navigate when reading it for the first
69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.	75	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		76
		77	While this document tries to be as complete as possible in documenting
		78	libev, its usage and the rationale behind its design, it is not a tutorial
		79	on event-based programming, nor will it introduce event-based programming
		80	with libev.
		81
		82	Familiarity with event based programming techniques in general is assumed
		83	throughout this document.
		84
		85	=head1 WHAT TO READ WHEN IN A HURRY
		86
		87	This manual tries to be very detailed, but unfortunately, this also makes
		88	it very long. If you just want to know the basics of libev, I suggest
		89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
		90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
		91	C<ev_timer> sections in L</WATCHER TYPES>.
		92
		93	=head1 ABOUT LIBEV
70		94
71	Libev is an event loop: you register interest in certain events (such as a	95	Libev is an event loop: you register interest in certain events (such as a
72	file descriptor being readable or a timeout occurring), and it will manage	96	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	97	these event sources and provide your program with events.
74		98
…		…
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 C<epoll>, the
87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	112	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	113	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
90	with customised rescheduling (C<ev_periodic>), synchronous signals	114	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
91	(C<ev_signal>), process status change events (C<ev_child>), and event	115	timers (C<ev_timer>), absolute timers with customised rescheduling
92	watchers dealing with the event loop mechanism itself (C<ev_idle>,	116	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	117	change events (C<ev_child>), and event watchers dealing with the event
94	file watchers (C<ev_stat>) and even limited support for fork events	118	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
95	(C<ev_fork>).	119	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		120	limited support for fork events (C<ev_fork>).
96		121
97	It also is quite fast (see this	122	It also is quite fast (see this
98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	123	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
99	for example).	124	for example).
100		125
…		…
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	133	name C<loop> (which is always of type C<struct ev_loop *>) will not have
109	this argument.	134	this argument.
110		135
111	=head2 TIME REPRESENTATION	136	=head2 TIME REPRESENTATION
112		137
113	Libev represents time as a single floating point number, representing the	138	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	139	the (fractional) number of seconds since the (POSIX) epoch (in practice
115	the beginning of 1970, details are complicated, don't ask). This type is	140	somewhere near the beginning of 1970, details are complicated, don't
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	141	ask). This type is called C<ev_tstamp>, which is what you should use
117	to the C<double> type in C, and when you need to do any calculations on	142	too. It usually aliases to the C<double> type in C. When you need to do
118	it, you should treat it as some floating point value. Unlike the name	143	any calculations on it, you should treat it as some floating point value.
		144
119	component C<stamp> might indicate, it is also used for time differences	145	Unlike the name component C<stamp> might indicate, it is also used for
120	throughout libev.	146	time differences (e.g. delays) throughout libev.
121		147
122	=head1 ERROR HANDLING	148	=head1 ERROR HANDLING
123		149
124	Libev knows three classes of errors: operating system errors, usage errors	150	Libev knows three classes of errors: operating system errors, usage errors
125	and internal errors (bugs).	151	and internal errors (bugs).
…		…
149		175
150	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
151		177
152	Returns the current time as libev would use it. Please note that the	178	Returns the current time as libev would use it. Please note that the
153	C<ev_now> function is usually faster and also often returns the timestamp	179	C<ev_now> function is usually faster and also often returns the timestamp
154	you actually want to know.	180	you actually want to know. Also interesting is the combination of
		181	C<ev_now_update> and C<ev_now>.
155		182
156	=item ev_sleep (ev_tstamp interval)	183	=item ev_sleep (ev_tstamp interval)
157		184
158	Sleep for the given interval: The current thread will be blocked until	185	Sleep for the given interval: The current thread will be blocked
159	either it is interrupted or the given time interval has passed. Basically	186	until either it is interrupted or the given time interval has
		187	passed (approximately - it might return a bit earlier even if not
		188	interrupted). Returns immediately if C<< interval <= 0 >>.
		189
160	this is a sub-second-resolution C<sleep ()>.	190	Basically this is a sub-second-resolution C<sleep ()>.
		191
		192	The range of the C<interval> is limited - libev only guarantees to work
		193	with sleep times of up to one day (C<< interval <= 86400 >>).
161		194
162	=item int ev_version_major ()	195	=item int ev_version_major ()
163		196
164	=item int ev_version_minor ()	197	=item int ev_version_minor ()
165		198
…		…
176	as this indicates an incompatible change. Minor versions are usually	209	as this indicates an incompatible change. Minor versions are usually
177	compatible to older versions, so a larger minor version alone is usually	210	compatible to older versions, so a larger minor version alone is usually
178	not a problem.	211	not a problem.
179		212
180	Example: Make sure we haven't accidentally been linked against the wrong	213	Example: Make sure we haven't accidentally been linked against the wrong
181	version.	214	version (note, however, that this will not detect other ABI mismatches,
		215	such as LFS or reentrancy).
182		216
183	assert (("libev version mismatch",	217	assert (("libev version mismatch",
184	ev_version_major () == EV_VERSION_MAJOR	218	ev_version_major () == EV_VERSION_MAJOR
185	&& ev_version_minor () >= EV_VERSION_MINOR));	219	&& ev_version_minor () >= EV_VERSION_MINOR));
186		220
…		…
197	assert (("sorry, no epoll, no sex",	231	assert (("sorry, no epoll, no sex",
198	ev_supported_backends () & EVBACKEND_EPOLL));	232	ev_supported_backends () & EVBACKEND_EPOLL));
199		233
200	=item unsigned int ev_recommended_backends ()	234	=item unsigned int ev_recommended_backends ()
201		235
202	Return the set of all backends compiled into this binary of libev and also	236	Return the set of all backends compiled into this binary of libev and
203	recommended for this platform. This set is often smaller than the one	237	also recommended for this platform, meaning it will work for most file
		238	descriptor types. This set is often smaller than the one returned by
204	returned by C<ev_supported_backends>, as for example kqueue is broken on	239	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
205	most BSDs and will not be auto-detected unless you explicitly request it	240	and will not be auto-detected unless you explicitly request it (assuming
206	(assuming you know what you are doing). This is the set of backends that	241	you know what you are doing). This is the set of backends that libev will
207	libev will probe for if you specify no backends explicitly.	242	probe for if you specify no backends explicitly.
208		243
209	=item unsigned int ev_embeddable_backends ()	244	=item unsigned int ev_embeddable_backends ()
210		245
211	Returns the set of backends that are embeddable in other event loops. This	246	Returns the set of backends that are embeddable in other event loops. This
212	is the theoretical, all-platform, value. To find which backends	247	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	248	current system. To find which embeddable backends might be supported on
214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	249	the current system, you would need to look at C<ev_embeddable_backends ()
215	recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
216		251
217	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
218		253
219	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
220		255
221	Sets the allocation function to use (the prototype is similar - the	256	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	257	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	258	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	259	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
250	}	285	}
251		286
252	...	287	...
253	ev_set_allocator (persistent_realloc);	288	ev_set_allocator (persistent_realloc);
254		289
255	=item ev_set_syserr_cb (void (*cb)(const char *msg));	290	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
256		291
257	Set the callback function to call on a retryable system call error (such	292	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	293	as failed select, poll, epoll_wait). The message is a printable string
259	indicating the system call or subsystem causing the problem. If this	294	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	295	callback is set, then libev will expect it to remedy the situation, no
…		…
272	}	307	}
273		308
274	...	309	...
275	ev_set_syserr_cb (fatal_error);	310	ev_set_syserr_cb (fatal_error);
276		311
		312	=item ev_feed_signal (int signum)
		313
		314	This function can be used to "simulate" a signal receive. It is completely
		315	safe to call this function at any time, from any context, including signal
		316	handlers or random threads.
		317
		318	Its main use is to customise signal handling in your process, especially
		319	in the presence of threads. For example, you could block signals
		320	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		321	creating any loops), and in one thread, use C<sigwait> or any other
		322	mechanism to wait for signals, then "deliver" them to libev by calling
		323	C<ev_feed_signal>.
		324
277	=back	325	=back
278		326
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	327	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
280		328
281	An event loop is described by a C<struct ev_loop *>. The library knows two	329	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	330	I<not> optional in this case unless libev 3 compatibility is disabled, as
283	events, and dynamically created loops which do not.	331	libev 3 had an C<ev_loop> function colliding with the struct name).
		332
		333	The library knows two types of such loops, the I<default> loop, which
		334	supports child process events, and dynamically created event loops which
		335	do not.
284		336
285	=over 4	337	=over 4
286		338
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	339	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		340
289	This will initialise the default event loop if it hasn't been initialised	341	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	342	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	343	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).	344	C<ev_loop_new>.
		345
		346	If the default loop is already initialised then this function simply
		347	returns it (and ignores the flags. If that is troubling you, check
		348	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		349	flags, which should almost always be C<0>, unless the caller is also the
		350	one calling C<ev_run> or otherwise qualifies as "the main program".
293		351
294	If you don't know what event loop to use, use the one returned from this	352	If you don't know what event loop to use, use the one returned from this
295	function.	353	function (or via the C<EV_DEFAULT> macro).
296		354
297	Note that this function is I<not> thread-safe, so if you want to use it	355	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,	356	from multiple threads, you have to employ some kind of mutex (note also
299	as loops cannot bes hared easily between threads anyway).	357	that this case is unlikely, as loops cannot be shared easily between
		358	threads anyway).
300		359
301	The default loop is the only loop that can handle C<ev_signal> and	360	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	361	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	362	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	363	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	364	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
306	C<ev_default_init>.	365
		366	Example: This is the most typical usage.
		367
		368	if (!ev_default_loop (0))
		369	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		370
		371	Example: Restrict libev to the select and poll backends, and do not allow
		372	environment settings to be taken into account:
		373
		374	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		375
		376	=item struct ev_loop *ev_loop_new (unsigned int flags)
		377
		378	This will create and initialise a new event loop object. If the loop
		379	could not be initialised, returns false.
		380
		381	This function is thread-safe, and one common way to use libev with
		382	threads is indeed to create one loop per thread, and using the default
		383	loop in the "main" or "initial" thread.
307		384
308	The flags argument can be used to specify special behaviour or specific	385	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>).	386	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
310		387
311	The following flags are supported:	388	The following flags are supported:
…		…
321		398
322	If this flag bit is or'ed into the flag value (or the program runs setuid	399	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	400	or setgid) then libev will I<not> look at the environment variable
324	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	401	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
325	override the flags completely if it is found in the environment. This is	402	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	403	useful to try out specific backends to test their performance, to work
327	around bugs.	404	around bugs, or to make libev threadsafe (accessing environment variables
		405	cannot be done in a threadsafe way, but usually it works if no other
		406	thread modifies them).
328		407
329	=item C<EVFLAG_FORKCHECK>	408	=item C<EVFLAG_FORKCHECK>
330		409
331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	410	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	411	make libev check for a fork in each iteration by enabling this flag.
333	enabling this flag.
334		412
335	This works by calling C<getpid ()> on every iteration of the loop,	413	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	414	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	415	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	416	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	417	sequence without a system call and thus I<very> fast, but my GNU/Linux
340	C<pthread_atfork> which is even faster).	418	system also has C<pthread_atfork> which is even faster). (Update: glibc
		419	versions 2.25 apparently removed the C<getpid> optimisation again).
341		420
342	The big advantage of this flag is that you can forget about fork (and	421	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	422	forget about forgetting to tell libev about forking, although you still
344	flag.	423	have to ignore C<SIGPIPE>) when you use this flag.
345		424
346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	425	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
347	environment variable.	426	environment variable.
		427
		428	=item C<EVFLAG_NOINOTIFY>
		429
		430	When this flag is specified, then libev will not attempt to use the
		431	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		432	testing, this flag can be useful to conserve inotify file descriptors, as
		433	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		434
		435	=item C<EVFLAG_SIGNALFD>
		436
		437	When this flag is specified, then libev will attempt to use the
		438	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		439	delivers signals synchronously, which makes it both faster and might make
		440	it possible to get the queued signal data. It can also simplify signal
		441	handling with threads, as long as you properly block signals in your
		442	threads that are not interested in handling them.
		443
		444	Signalfd will not be used by default as this changes your signal mask, and
		445	there are a lot of shoddy libraries and programs (glib's threadpool for
		446	example) that can't properly initialise their signal masks.
		447
		448	=item C<EVFLAG_NOSIGMASK>
		449
		450	When this flag is specified, then libev will avoid to modify the signal
		451	mask. Specifically, this means you have to make sure signals are unblocked
		452	when you want to receive them.
		453
		454	This behaviour is useful when you want to do your own signal handling, or
		455	want to handle signals only in specific threads and want to avoid libev
		456	unblocking the signals.
		457
		458	It's also required by POSIX in a threaded program, as libev calls
		459	C<sigprocmask>, whose behaviour is officially unspecified.
		460
		461	This flag's behaviour will become the default in future versions of libev.
348		462
349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	463	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
350		464
351	This is your standard select(2) backend. Not I<completely> standard, as	465	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,	466	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
359	writing a server, you should C<accept ()> in a loop to accept as many	473	writing a server, you should C<accept ()> in a loop to accept as many
360	connections as possible during one iteration. You might also want to have	474	connections as possible during one iteration. You might also want to have
361	a look at C<ev_set_io_collect_interval ()> to increase the amount of	475	a look at C<ev_set_io_collect_interval ()> to increase the amount of
362	readiness notifications you get per iteration.	476	readiness notifications you get per iteration.
363		477
		478	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		479	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		480	C<exceptfds> set on that platform).
		481
364	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	482	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
365		483
366	And this is your standard poll(2) backend. It's more complicated	484	And this is your standard poll(2) backend. It's more complicated
367	than select, but handles sparse fds better and has no artificial	485	than select, but handles sparse fds better and has no artificial
368	limit on the number of fds you can use (except it will slow down	486	limit on the number of fds you can use (except it will slow down
369	considerably with a lot of inactive fds). It scales similarly to select,	487	considerably with a lot of inactive fds). It scales similarly to select,
370	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	488	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
371	performance tips.	489	performance tips.
372		490
		491	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		492	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		493
373	=item C<EVBACKEND_EPOLL> (value 4, Linux)	494	=item C<EVBACKEND_EPOLL> (value 4, Linux)
374		495
		496	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		497	kernels).
		498
375	For few fds, this backend is a bit little slower than poll and select,	499	For few fds, this backend is a bit little slower than poll and select, but
376	but it scales phenomenally better. While poll and select usually scale	500	it scales phenomenally better. While poll and select usually scale like
377	like O(total_fds) where n is the total number of fds (or the highest fd),	501	O(total_fds) where total_fds is the total number of fds (or the highest
378	epoll scales either O(1) or O(active_fds). The epoll design has a number	502	fd), epoll scales either O(1) or O(active_fds).
379	of shortcomings, such as silently dropping events in some hard-to-detect	503
380	cases and requiring a system call per fd change, no fork support and bad	504	The epoll mechanism deserves honorable mention as the most misdesigned
381	support for dup.	505	of the more advanced event mechanisms: mere annoyances include silently
		506	dropping file descriptors, requiring a system call per change per file
		507	descriptor (and unnecessary guessing of parameters), problems with dup,
		508	returning before the timeout value, resulting in additional iterations
		509	(and only giving 5ms accuracy while select on the same platform gives
		510	0.1ms) and so on. The biggest issue is fork races, however - if a program
		511	forks then I<both> parent and child process have to recreate the epoll
		512	set, which can take considerable time (one syscall per file descriptor)
		513	and is of course hard to detect.
		514
		515	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		516	but of course I<doesn't>, and epoll just loves to report events for
		517	totally I<different> file descriptors (even already closed ones, so
		518	one cannot even remove them from the set) than registered in the set
		519	(especially on SMP systems). Libev tries to counter these spurious
		520	notifications by employing an additional generation counter and comparing
		521	that against the events to filter out spurious ones, recreating the set
		522	when required. Epoll also erroneously rounds down timeouts, but gives you
		523	no way to know when and by how much, so sometimes you have to busy-wait
		524	because epoll returns immediately despite a nonzero timeout. And last
		525	not least, it also refuses to work with some file descriptors which work
		526	perfectly fine with C<select> (files, many character devices...).
		527
		528	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		529	cobbled together in a hurry, no thought to design or interaction with
		530	others. Oh, the pain, will it ever stop...
382		531
383	While stopping, setting and starting an I/O watcher in the same iteration	532	While stopping, setting and starting an I/O watcher in the same iteration
384	will result in some caching, there is still a system call per such incident	533	will result in some caching, there is still a system call per such
385	(because the fd could point to a different file description now), so its	534	incident (because the same I<file descriptor> could point to a different
386	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	535	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
387	very well if you register events for both fds.	536	file descriptors might not work very well if you register events for both
388		537	file descriptors.
389	Please note that epoll sometimes generates spurious notifications, so you
390	need to use non-blocking I/O or other means to avoid blocking when no data
391	(or space) is available.
392		538
393	Best performance from this backend is achieved by not unregistering all	539	Best performance from this backend is achieved by not unregistering all
394	watchers for a file descriptor until it has been closed, if possible, i.e.	540	watchers for a file descriptor until it has been closed, if possible,
395	keep at least one watcher active per fd at all times.	541	i.e. keep at least one watcher active per fd at all times. Stopping and
		542	starting a watcher (without re-setting it) also usually doesn't cause
		543	extra overhead. A fork can both result in spurious notifications as well
		544	as in libev having to destroy and recreate the epoll object, which can
		545	take considerable time and thus should be avoided.
		546
		547	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		548	faster than epoll for maybe up to a hundred file descriptors, depending on
		549	the usage. So sad.
396		550
397	While nominally embeddable in other event loops, this feature is broken in	551	While nominally embeddable in other event loops, this feature is broken in
398	all kernel versions tested so far.	552	all kernel versions tested so far.
		553
		554	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		555	C<EVBACKEND_POLL>.
399		556
400	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	557	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
401		558
402	Kqueue deserves special mention, as at the time of this writing, it	559	Kqueue deserves special mention, as at the time of this writing, it
403	was broken on all BSDs except NetBSD (usually it doesn't work reliably	560	was broken on all BSDs except NetBSD (usually it doesn't work reliably
404	with anything but sockets and pipes, except on Darwin, where of course	561	with anything but sockets and pipes, except on Darwin, where of course
405	it's completely useless). For this reason it's not being "auto-detected"	562	it's completely useless). Unlike epoll, however, whose brokenness
		563	is by design, these kqueue bugs can (and eventually will) be fixed
		564	without API changes to existing programs. For this reason it's not being
406	unless you explicitly specify it explicitly in the flags (i.e. using	565	"auto-detected" unless you explicitly specify it in the flags (i.e. using
407	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	566	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
408	system like NetBSD.	567	system like NetBSD.
409		568
410	You still can embed kqueue into a normal poll or select backend and use it	569	You still can embed kqueue into a normal poll or select backend and use it
411	only for sockets (after having made sure that sockets work with kqueue on	570	only for sockets (after having made sure that sockets work with kqueue on
…		…
413		572
414	It scales in the same way as the epoll backend, but the interface to the	573	It scales in the same way as the epoll backend, but the interface to the
415	kernel is more efficient (which says nothing about its actual speed, of	574	kernel is more efficient (which says nothing about its actual speed, of
416	course). While stopping, setting and starting an I/O watcher does never	575	course). While stopping, setting and starting an I/O watcher does never
417	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	576	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
418	two event changes per incident, support for C<fork ()> is very bad and it	577	two event changes per incident. Support for C<fork ()> is very bad (you
		578	might have to leak fd's on fork, but it's more sane than epoll) and it
419	drops fds silently in similarly hard-to-detect cases.	579	drops fds silently in similarly hard-to-detect cases.
420		580
421	This backend usually performs well under most conditions.	581	This backend usually performs well under most conditions.
422		582
423	While nominally embeddable in other event loops, this doesn't work	583	While nominally embeddable in other event loops, this doesn't work
424	everywhere, so you might need to test for this. And since it is broken	584	everywhere, so you might need to test for this. And since it is broken
425	almost everywhere, you should only use it when you have a lot of sockets	585	almost everywhere, you should only use it when you have a lot of sockets
426	(for which it usually works), by embedding it into another event loop	586	(for which it usually works), by embedding it into another event loop
427	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	587	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
428	sockets.	588	also broken on OS X)) and, did I mention it, using it only for sockets.
		589
		590	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		591	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		592	C<NOTE_EOF>.
429		593
430	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	594	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
431		595
432	This is not implemented yet (and might never be, unless you send me an	596	This is not implemented yet (and might never be, unless you send me an
433	implementation). According to reports, C</dev/poll> only supports sockets	597	implementation). According to reports, C</dev/poll> only supports sockets
…		…
437	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	601	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
438		602
439	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	603	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
440	it's really slow, but it still scales very well (O(active_fds)).	604	it's really slow, but it still scales very well (O(active_fds)).
441		605
442	Please note that Solaris event ports can deliver a lot of spurious
443	notifications, so you need to use non-blocking I/O or other means to avoid
444	blocking when no data (or space) is available.
445
446	While this backend scales well, it requires one system call per active	606	While this backend scales well, it requires one system call per active
447	file descriptor per loop iteration. For small and medium numbers of file	607	file descriptor per loop iteration. For small and medium numbers of file
448	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	608	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
449	might perform better.	609	might perform better.
450		610
451	On the positive side, ignoring the spurious readiness notifications, this	611	On the positive side, this backend actually performed fully to
452	backend actually performed to specification in all tests and is fully	612	specification in all tests and is fully embeddable, which is a rare feat
453	embeddable, which is a rare feat among the OS-specific backends.	613	among the OS-specific backends (I vastly prefer correctness over speed
		614	hacks).
		615
		616	On the negative side, the interface is I<bizarre> - so bizarre that
		617	even sun itself gets it wrong in their code examples: The event polling
		618	function sometimes returns events to the caller even though an error
		619	occurred, but with no indication whether it has done so or not (yes, it's
		620	even documented that way) - deadly for edge-triggered interfaces where you
		621	absolutely have to know whether an event occurred or not because you have
		622	to re-arm the watcher.
		623
		624	Fortunately libev seems to be able to work around these idiocies.
		625
		626	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		627	C<EVBACKEND_POLL>.
454		628
455	=item C<EVBACKEND_ALL>	629	=item C<EVBACKEND_ALL>
456		630
457	Try all backends (even potentially broken ones that wouldn't be tried	631	Try all backends (even potentially broken ones that wouldn't be tried
458	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	632	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
459	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	633	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
460		634
461	It is definitely not recommended to use this flag.	635	It is definitely not recommended to use this flag, use whatever
		636	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		637	at all.
		638
		639	=item C<EVBACKEND_MASK>
		640
		641	Not a backend at all, but a mask to select all backend bits from a
		642	C<flags> value, in case you want to mask out any backends from a flags
		643	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
462		644
463	=back	645	=back
464		646
465	If one or more of these are or'ed into the flags value, then only these	647	If one or more of the backend flags are or'ed into the flags value,
466	backends will be tried (in the reverse order as listed here). If none are	648	then only these backends will be tried (in the reverse order as listed
467	specified, all backends in C<ev_recommended_backends ()> will be tried.	649	here). If none are specified, all backends in C<ev_recommended_backends
468		650	()> will be tried.
469	The most typical usage is like this:
470
471	if (!ev_default_loop (0))
472	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
473
474	Restrict libev to the select and poll backends, and do not allow
475	environment settings to be taken into account:
476
477	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
478
479	Use whatever libev has to offer, but make sure that kqueue is used if
480	available (warning, breaks stuff, best use only with your own private
481	event loop and only if you know the OS supports your types of fds):
482
483	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
484
485	=item struct ev_loop *ev_loop_new (unsigned int flags)
486
487	Similar to C<ev_default_loop>, but always creates a new event loop that is
488	always distinct from the default loop. Unlike the default loop, it cannot
489	handle signal and child watchers, and attempts to do so will be greeted by
490	undefined behaviour (or a failed assertion if assertions are enabled).
491
492	Note that this function I<is> thread-safe, and the recommended way to use
493	libev with threads is indeed to create one loop per thread, and using the
494	default loop in the "main" or "initial" thread.
495		651
496	Example: Try to create a event loop that uses epoll and nothing else.	652	Example: Try to create a event loop that uses epoll and nothing else.
497		653
498	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	654	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
499	if (!epoller)	655	if (!epoller)
500	fatal ("no epoll found here, maybe it hides under your chair");	656	fatal ("no epoll found here, maybe it hides under your chair");
501		657
		658	Example: Use whatever libev has to offer, but make sure that kqueue is
		659	used if available.
		660
		661	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		662
502	=item ev_default_destroy ()	663	=item ev_loop_destroy (loop)
503		664
504	Destroys the default loop again (frees all memory and kernel state	665	Destroys an event loop object (frees all memory and kernel state
505	etc.). None of the active event watchers will be stopped in the normal	666	etc.). None of the active event watchers will be stopped in the normal
506	sense, so e.g. C<ev_is_active> might still return true. It is your	667	sense, so e.g. C<ev_is_active> might still return true. It is your
507	responsibility to either stop all watchers cleanly yourself I<before>	668	responsibility to either stop all watchers cleanly yourself I<before>
508	calling this function, or cope with the fact afterwards (which is usually	669	calling this function, or cope with the fact afterwards (which is usually
509	the easiest thing, you can just ignore the watchers and/or C<free ()> them	670	the easiest thing, you can just ignore the watchers and/or C<free ()> them
510	for example).	671	for example).
511		672
512	Note that certain global state, such as signal state, will not be freed by	673	Note that certain global state, such as signal state (and installed signal
513	this function, and related watchers (such as signal and child watchers)	674	handlers), will not be freed by this function, and related watchers (such
514	would need to be stopped manually.	675	as signal and child watchers) would need to be stopped manually.
515		676
516	In general it is not advisable to call this function except in the	677	This function is normally used on loop objects allocated by
517	rare occasion where you really need to free e.g. the signal handling	678	C<ev_loop_new>, but it can also be used on the default loop returned by
		679	C<ev_default_loop>, in which case it is not thread-safe.
		680
		681	Note that it is not advisable to call this function on the default loop
		682	except in the rare occasion where you really need to free its resources.
518	pipe fds. If you need dynamically allocated loops it is better to use	683	If you need dynamically allocated loops it is better to use C<ev_loop_new>
519	C<ev_loop_new> and C<ev_loop_destroy>).	684	and C<ev_loop_destroy>.
520		685
521	=item ev_loop_destroy (loop)	686	=item ev_loop_fork (loop)
522		687
523	Like C<ev_default_destroy>, but destroys an event loop created by an
524	earlier call to C<ev_loop_new>.
525
526	=item ev_default_fork ()
527
528	This function sets a flag that causes subsequent C<ev_loop> iterations	688	This function sets a flag that causes subsequent C<ev_run> iterations
529	to reinitialise the kernel state for backends that have one. Despite the	689	to reinitialise the kernel state for backends that have one. Despite
530	name, you can call it anytime, but it makes most sense after forking, in	690	the name, you can call it anytime you are allowed to start or stop
531	the child process (or both child and parent, but that again makes little	691	watchers (except inside an C<ev_prepare> callback), but it makes most
532	sense). You I<must> call it in the child before using any of the libev	692	sense after forking, in the child process. You I<must> call it (or use
533	functions, and it will only take effect at the next C<ev_loop> iteration.	693	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
		694
		695	In addition, if you want to reuse a loop (via this function or
		696	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		697
		698	Again, you I<have> to call it on I<any> loop that you want to re-use after
		699	a fork, I<even if you do not plan to use the loop in the parent>. This is
		700	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		701	during fork.
534		702
535	On the other hand, you only need to call this function in the child	703	On the other hand, you only need to call this function in the child
536	process if and only if you want to use the event library in the child. If	704	process if and only if you want to use the event loop in the child. If
537	you just fork+exec, you don't have to call it at all.	705	you just fork+exec or create a new loop in the child, you don't have to
		706	call it at all (in fact, C<epoll> is so badly broken that it makes a
		707	difference, but libev will usually detect this case on its own and do a
		708	costly reset of the backend).
538		709
539	The function itself is quite fast and it's usually not a problem to call	710	The function itself is quite fast and it's usually not a problem to call
540	it just in case after a fork. To make this easy, the function will fit in	711	it just in case after a fork.
541	quite nicely into a call to C<pthread_atfork>:
542		712
		713	Example: Automate calling C<ev_loop_fork> on the default loop when
		714	using pthreads.
		715
		716	static void
		717	post_fork_child (void)
		718	{
		719	ev_loop_fork (EV_DEFAULT);
		720	}
		721
		722	...
543	pthread_atfork (0, 0, ev_default_fork);	723	pthread_atfork (0, 0, post_fork_child);
544
545	=item ev_loop_fork (loop)
546
547	Like C<ev_default_fork>, but acts on an event loop created by
548	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
549	after fork, and how you do this is entirely your own problem.
550		724
551	=item int ev_is_default_loop (loop)	725	=item int ev_is_default_loop (loop)
552		726
553	Returns true when the given loop actually is the default loop, false otherwise.	727	Returns true when the given loop is, in fact, the default loop, and false
		728	otherwise.
554		729
555	=item unsigned int ev_loop_count (loop)	730	=item unsigned int ev_iteration (loop)
556		731
557	Returns the count of loop iterations for the loop, which is identical to	732	Returns the current iteration count for the event loop, which is identical
558	the number of times libev did poll for new events. It starts at C<0> and	733	to the number of times libev did poll for new events. It starts at C<0>
559	happily wraps around with enough iterations.	734	and happily wraps around with enough iterations.
560		735
561	This value can sometimes be useful as a generation counter of sorts (it	736	This value can sometimes be useful as a generation counter of sorts (it
562	"ticks" the number of loop iterations), as it roughly corresponds with	737	"ticks" the number of loop iterations), as it roughly corresponds with
563	C<ev_prepare> and C<ev_check> calls.	738	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		739	prepare and check phases.
		740
		741	=item unsigned int ev_depth (loop)
		742
		743	Returns the number of times C<ev_run> was entered minus the number of
		744	times C<ev_run> was exited normally, in other words, the recursion depth.
		745
		746	Outside C<ev_run>, this number is zero. In a callback, this number is
		747	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		748	in which case it is higher.
		749
		750	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		751	throwing an exception etc.), doesn't count as "exit" - consider this
		752	as a hint to avoid such ungentleman-like behaviour unless it's really
		753	convenient, in which case it is fully supported.
564		754
565	=item unsigned int ev_backend (loop)	755	=item unsigned int ev_backend (loop)
566		756
567	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	757	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
568	use.	758	use.
…		…
577		767
578	=item ev_now_update (loop)	768	=item ev_now_update (loop)
579		769
580	Establishes the current time by querying the kernel, updating the time	770	Establishes the current time by querying the kernel, updating the time
581	returned by C<ev_now ()> in the progress. This is a costly operation and	771	returned by C<ev_now ()> in the progress. This is a costly operation and
582	is usually done automatically within C<ev_loop ()>.	772	is usually done automatically within C<ev_run ()>.
583		773
584	This function is rarely useful, but when some event callback runs for a	774	This function is rarely useful, but when some event callback runs for a
585	very long time without entering the event loop, updating libev's idea of	775	very long time without entering the event loop, updating libev's idea of
586	the current time is a good idea.	776	the current time is a good idea.
587		777
588	See also "The special problem of time updates" in the C<ev_timer> section.	778	See also L</The special problem of time updates> in the C<ev_timer> section.
589		779
		780	=item ev_suspend (loop)
		781
		782	=item ev_resume (loop)
		783
		784	These two functions suspend and resume an event loop, for use when the
		785	loop is not used for a while and timeouts should not be processed.
		786
		787	A typical use case would be an interactive program such as a game: When
		788	the user presses C<^Z> to suspend the game and resumes it an hour later it
		789	would be best to handle timeouts as if no time had actually passed while
		790	the program was suspended. This can be achieved by calling C<ev_suspend>
		791	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		792	C<ev_resume> directly afterwards to resume timer processing.
		793
		794	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		795	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		796	will be rescheduled (that is, they will lose any events that would have
		797	occurred while suspended).
		798
		799	After calling C<ev_suspend> you B<must not> call I<any> function on the
		800	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		801	without a previous call to C<ev_suspend>.
		802
		803	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		804	event loop time (see C<ev_now_update>).
		805
590	=item ev_loop (loop, int flags)	806	=item bool ev_run (loop, int flags)
591		807
592	Finally, this is it, the event handler. This function usually is called	808	Finally, this is it, the event handler. This function usually is called
593	after you initialised all your watchers and you want to start handling	809	after you have initialised all your watchers and you want to start
594	events.	810	handling events. It will ask the operating system for any new events, call
		811	the watcher callbacks, and then repeat the whole process indefinitely: This
		812	is why event loops are called I<loops>.
595		813
596	If the flags argument is specified as C<0>, it will not return until	814	If the flags argument is specified as C<0>, it will keep handling events
597	either no event watchers are active anymore or C<ev_unloop> was called.	815	until either no event watchers are active anymore or C<ev_break> was
		816	called.
598		817
		818	The return value is false if there are no more active watchers (which
		819	usually means "all jobs done" or "deadlock"), and true in all other cases
		820	(which usually means " you should call C<ev_run> again").
		821
599	Please note that an explicit C<ev_unloop> is usually better than	822	Please note that an explicit C<ev_break> is usually better than
600	relying on all watchers to be stopped when deciding when a program has	823	relying on all watchers to be stopped when deciding when a program has
601	finished (especially in interactive programs), but having a program that	824	finished (especially in interactive programs), but having a program
602	automatically loops as long as it has to and no longer by virtue of	825	that automatically loops as long as it has to and no longer by virtue
603	relying on its watchers stopping correctly is a thing of beauty.	826	of relying on its watchers stopping correctly, that is truly a thing of
		827	beauty.
604		828
		829	This function is I<mostly> exception-safe - you can break out of a
		830	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		831	exception and so on. This does not decrement the C<ev_depth> value, nor
		832	will it clear any outstanding C<EVBREAK_ONE> breaks.
		833
605	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	834	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
606	those events and any outstanding ones, but will not block your process in	835	those events and any already outstanding ones, but will not wait and
607	case there are no events and will return after one iteration of the loop.	836	block your process in case there are no events and will return after one
		837	iteration of the loop. This is sometimes useful to poll and handle new
		838	events while doing lengthy calculations, to keep the program responsive.
608		839
609	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	840	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
610	necessary) and will handle those and any outstanding ones. It will block	841	necessary) and will handle those and any already outstanding ones. It
611	your process until at least one new event arrives, and will return after	842	will block your process until at least one new event arrives (which could
612	one iteration of the loop. This is useful if you are waiting for some	843	be an event internal to libev itself, so there is no guarantee that a
613	external event in conjunction with something not expressible using other	844	user-registered callback will be called), and will return after one
		845	iteration of the loop.
		846
		847	This is useful if you are waiting for some external event in conjunction
		848	with something not expressible using other libev watchers (i.e. "roll your
614	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	849	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
615	usually a better approach for this kind of thing.	850	usually a better approach for this kind of thing.
616		851
617	Here are the gory details of what C<ev_loop> does:	852	Here are the gory details of what C<ev_run> does (this is for your
		853	understanding, not a guarantee that things will work exactly like this in
		854	future versions):
618		855
		856	- Increment loop depth.
		857	- Reset the ev_break status.
619	- Before the first iteration, call any pending watchers.	858	- Before the first iteration, call any pending watchers.
		859	LOOP:
620	* If EVFLAG_FORKCHECK was used, check for a fork.	860	- If EVFLAG_FORKCHECK was used, check for a fork.
621	- If a fork was detected (by any means), queue and call all fork watchers.	861	- If a fork was detected (by any means), queue and call all fork watchers.
622	- Queue and call all prepare watchers.	862	- Queue and call all prepare watchers.
		863	- If ev_break was called, goto FINISH.
623	- If we have been forked, detach and recreate the kernel state	864	- If we have been forked, detach and recreate the kernel state
624	as to not disturb the other process.	865	as to not disturb the other process.
625	- Update the kernel state with all outstanding changes.	866	- Update the kernel state with all outstanding changes.
626	- Update the "event loop time" (ev_now ()).	867	- Update the "event loop time" (ev_now ()).
627	- Calculate for how long to sleep or block, if at all	868	- Calculate for how long to sleep or block, if at all
628	(active idle watchers, EVLOOP_NONBLOCK or not having	869	(active idle watchers, EVRUN_NOWAIT or not having
629	any active watchers at all will result in not sleeping).	870	any active watchers at all will result in not sleeping).
630	- Sleep if the I/O and timer collect interval say so.	871	- Sleep if the I/O and timer collect interval say so.
		872	- Increment loop iteration counter.
631	- Block the process, waiting for any events.	873	- Block the process, waiting for any events.
632	- Queue all outstanding I/O (fd) events.	874	- Queue all outstanding I/O (fd) events.
633	- Update the "event loop time" (ev_now ()), and do time jump adjustments.	875	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
634	- Queue all outstanding timers.	876	- Queue all expired timers.
635	- Queue all outstanding periodics.	877	- Queue all expired periodics.
636	- Unless any events are pending now, queue all idle watchers.	878	- Queue all idle watchers with priority higher than that of pending events.
637	- Queue all check watchers.	879	- Queue all check watchers.
638	- Call all queued watchers in reverse order (i.e. check watchers first).	880	- Call all queued watchers in reverse order (i.e. check watchers first).
639	Signals and child watchers are implemented as I/O watchers, and will	881	Signals and child watchers are implemented as I/O watchers, and will
640	be handled here by queueing them when their watcher gets executed.	882	be handled here by queueing them when their watcher gets executed.
641	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	883	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
642	were used, or there are no active watchers, return, otherwise	884	were used, or there are no active watchers, goto FINISH, otherwise
643	continue with step *.	885	continue with step LOOP.
		886	FINISH:
		887	- Reset the ev_break status iff it was EVBREAK_ONE.
		888	- Decrement the loop depth.
		889	- Return.
644		890
645	Example: Queue some jobs and then loop until no events are outstanding	891	Example: Queue some jobs and then loop until no events are outstanding
646	anymore.	892	anymore.
647		893
648	... queue jobs here, make sure they register event watchers as long	894	... queue jobs here, make sure they register event watchers as long
649	... as they still have work to do (even an idle watcher will do..)	895	... as they still have work to do (even an idle watcher will do..)
650	ev_loop (my_loop, 0);	896	ev_run (my_loop, 0);
651	... jobs done or somebody called unloop. yeah!	897	... jobs done or somebody called break. yeah!
652		898
653	=item ev_unloop (loop, how)	899	=item ev_break (loop, how)
654		900
655	Can be used to make a call to C<ev_loop> return early (but only after it	901	Can be used to make a call to C<ev_run> return early (but only after it
656	has processed all outstanding events). The C<how> argument must be either	902	has processed all outstanding events). The C<how> argument must be either
657	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	903	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
658	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	904	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
659		905
660	This "unloop state" will be cleared when entering C<ev_loop> again.	906	This "break state" will be cleared on the next call to C<ev_run>.
		907
		908	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		909	which case it will have no effect.
661		910
662	=item ev_ref (loop)	911	=item ev_ref (loop)
663		912
664	=item ev_unref (loop)	913	=item ev_unref (loop)
665		914
666	Ref/unref can be used to add or remove a reference count on the event	915	Ref/unref can be used to add or remove a reference count on the event
667	loop: Every watcher keeps one reference, and as long as the reference	916	loop: Every watcher keeps one reference, and as long as the reference
668	count is nonzero, C<ev_loop> will not return on its own. If you have	917	count is nonzero, C<ev_run> will not return on its own.
669	a watcher you never unregister that should not keep C<ev_loop> from	918
670	returning, ev_unref() after starting, and ev_ref() before stopping it. For	919	This is useful when you have a watcher that you never intend to
		920	unregister, but that nevertheless should not keep C<ev_run> from
		921	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		922	before stopping it.
		923
671	example, libev itself uses this for its internal signal pipe: It is not	924	As an example, libev itself uses this for its internal signal pipe: It
672	visible to the libev user and should not keep C<ev_loop> from exiting if	925	is not visible to the libev user and should not keep C<ev_run> from
673	no event watchers registered by it are active. It is also an excellent	926	exiting if no event watchers registered by it are active. It is also an
674	way to do this for generic recurring timers or from within third-party	927	excellent way to do this for generic recurring timers or from within
675	libraries. Just remember to I<unref after start> and I<ref before stop>	928	third-party libraries. Just remember to I<unref after start> and I<ref
676	(but only if the watcher wasn't active before, or was active before,	929	before stop> (but only if the watcher wasn't active before, or was active
677	respectively).	930	before, respectively. Note also that libev might stop watchers itself
		931	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		932	in the callback).
678		933
679	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	934	Example: Create a signal watcher, but keep it from keeping C<ev_run>
680	running when nothing else is active.	935	running when nothing else is active.
681		936
682	struct ev_signal exitsig;	937	ev_signal exitsig;
683	ev_signal_init (&exitsig, sig_cb, SIGINT);	938	ev_signal_init (&exitsig, sig_cb, SIGINT);
684	ev_signal_start (loop, &exitsig);	939	ev_signal_start (loop, &exitsig);
685	evf_unref (loop);	940	ev_unref (loop);
686		941
687	Example: For some weird reason, unregister the above signal handler again.	942	Example: For some weird reason, unregister the above signal handler again.
688		943
689	ev_ref (loop);	944	ev_ref (loop);
690	ev_signal_stop (loop, &exitsig);	945	ev_signal_stop (loop, &exitsig);
…		…
701	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	956	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
702	allows libev to delay invocation of I/O and timer/periodic callbacks	957	allows libev to delay invocation of I/O and timer/periodic callbacks
703	to increase efficiency of loop iterations (or to increase power-saving	958	to increase efficiency of loop iterations (or to increase power-saving
704	opportunities).	959	opportunities).
705		960
706	The background is that sometimes your program runs just fast enough to	961	The idea is that sometimes your program runs just fast enough to handle
707	handle one (or very few) event(s) per loop iteration. While this makes	962	one (or very few) event(s) per loop iteration. While this makes the
708	the program responsive, it also wastes a lot of CPU time to poll for new	963	program responsive, it also wastes a lot of CPU time to poll for new
709	events, especially with backends like C<select ()> which have a high	964	events, especially with backends like C<select ()> which have a high
710	overhead for the actual polling but can deliver many events at once.	965	overhead for the actual polling but can deliver many events at once.
711		966
712	By setting a higher I<io collect interval> you allow libev to spend more	967	By setting a higher I<io collect interval> you allow libev to spend more
713	time collecting I/O events, so you can handle more events per iteration,	968	time collecting I/O events, so you can handle more events per iteration,
714	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	969	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
715	C<ev_timer>) will be not affected. Setting this to a non-null value will	970	C<ev_timer>) will not be affected. Setting this to a non-null value will
716	introduce an additional C<ev_sleep ()> call into most loop iterations.	971	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		972	sleep time ensures that libev will not poll for I/O events more often then
		973	once per this interval, on average (as long as the host time resolution is
		974	good enough).
717		975
718	Likewise, by setting a higher I<timeout collect interval> you allow libev	976	Likewise, by setting a higher I<timeout collect interval> you allow libev
719	to spend more time collecting timeouts, at the expense of increased	977	to spend more time collecting timeouts, at the expense of increased
720	latency (the watcher callback will be called later). C<ev_io> watchers	978	latency/jitter/inexactness (the watcher callback will be called
721	will not be affected. Setting this to a non-null value will not introduce	979	later). C<ev_io> watchers will not be affected. Setting this to a non-null
722	any overhead in libev.	980	value will not introduce any overhead in libev.
723		981
724	Many (busy) programs can usually benefit by setting the I/O collect	982	Many (busy) programs can usually benefit by setting the I/O collect
725	interval to a value near C<0.1> or so, which is often enough for	983	interval to a value near C<0.1> or so, which is often enough for
726	interactive servers (of course not for games), likewise for timeouts. It	984	interactive servers (of course not for games), likewise for timeouts. It
727	usually doesn't make much sense to set it to a lower value than C<0.01>,	985	usually doesn't make much sense to set it to a lower value than C<0.01>,
728	as this approaches the timing granularity of most systems.	986	as this approaches the timing granularity of most systems. Note that if
		987	you do transactions with the outside world and you can't increase the
		988	parallelity, then this setting will limit your transaction rate (if you
		989	need to poll once per transaction and the I/O collect interval is 0.01,
		990	then you can't do more than 100 transactions per second).
729		991
730	Setting the I<timeout collect interval> can improve the opportunity for	992	Setting the I<timeout collect interval> can improve the opportunity for
731	saving power, as the program will "bundle" timer callback invocations that	993	saving power, as the program will "bundle" timer callback invocations that
732	are "near" in time together, by delaying some, thus reducing the number of	994	are "near" in time together, by delaying some, thus reducing the number of
733	times the process sleeps and wakes up again. Another useful technique to	995	times the process sleeps and wakes up again. Another useful technique to
734	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	996	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
735	they fire on, say, one-second boundaries only.	997	they fire on, say, one-second boundaries only.
736		998
		999	Example: we only need 0.1s timeout granularity, and we wish not to poll
		1000	more often than 100 times per second:
		1001
		1002	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		1003	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		1004
		1005	=item ev_invoke_pending (loop)
		1006
		1007	This call will simply invoke all pending watchers while resetting their
		1008	pending state. Normally, C<ev_run> does this automatically when required,
		1009	but when overriding the invoke callback this call comes handy. This
		1010	function can be invoked from a watcher - this can be useful for example
		1011	when you want to do some lengthy calculation and want to pass further
		1012	event handling to another thread (you still have to make sure only one
		1013	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1014
		1015	=item int ev_pending_count (loop)
		1016
		1017	Returns the number of pending watchers - zero indicates that no watchers
		1018	are pending.
		1019
		1020	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1021
		1022	This overrides the invoke pending functionality of the loop: Instead of
		1023	invoking all pending watchers when there are any, C<ev_run> will call
		1024	this callback instead. This is useful, for example, when you want to
		1025	invoke the actual watchers inside another context (another thread etc.).
		1026
		1027	If you want to reset the callback, use C<ev_invoke_pending> as new
		1028	callback.
		1029
		1030	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1031
		1032	Sometimes you want to share the same loop between multiple threads. This
		1033	can be done relatively simply by putting mutex_lock/unlock calls around
		1034	each call to a libev function.
		1035
		1036	However, C<ev_run> can run an indefinite time, so it is not feasible
		1037	to wait for it to return. One way around this is to wake up the event
		1038	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1039	I<release> and I<acquire> callbacks on the loop.
		1040
		1041	When set, then C<release> will be called just before the thread is
		1042	suspended waiting for new events, and C<acquire> is called just
		1043	afterwards.
		1044
		1045	Ideally, C<release> will just call your mutex_unlock function, and
		1046	C<acquire> will just call the mutex_lock function again.
		1047
		1048	While event loop modifications are allowed between invocations of
		1049	C<release> and C<acquire> (that's their only purpose after all), no
		1050	modifications done will affect the event loop, i.e. adding watchers will
		1051	have no effect on the set of file descriptors being watched, or the time
		1052	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1053	to take note of any changes you made.
		1054
		1055	In theory, threads executing C<ev_run> will be async-cancel safe between
		1056	invocations of C<release> and C<acquire>.
		1057
		1058	See also the locking example in the C<THREADS> section later in this
		1059	document.
		1060
		1061	=item ev_set_userdata (loop, void *data)
		1062
		1063	=item void *ev_userdata (loop)
		1064
		1065	Set and retrieve a single C<void *> associated with a loop. When
		1066	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1067	C<0>.
		1068
		1069	These two functions can be used to associate arbitrary data with a loop,
		1070	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1071	C<acquire> callbacks described above, but of course can be (ab-)used for
		1072	any other purpose as well.
		1073
737	=item ev_loop_verify (loop)	1074	=item ev_verify (loop)
738		1075
739	This function only does something when C<EV_VERIFY> support has been	1076	This function only does something when C<EV_VERIFY> support has been
740	compiled in. It tries to go through all internal structures and checks	1077	compiled in, which is the default for non-minimal builds. It tries to go
741	them for validity. If anything is found to be inconsistent, it will print	1078	through all internal structures and checks them for validity. If anything
742	an error message to standard error and call C<abort ()>.	1079	is found to be inconsistent, it will print an error message to standard
		1080	error and call C<abort ()>.
743		1081
744	This can be used to catch bugs inside libev itself: under normal	1082	This can be used to catch bugs inside libev itself: under normal
745	circumstances, this function will never abort as of course libev keeps its	1083	circumstances, this function will never abort as of course libev keeps its
746	data structures consistent.	1084	data structures consistent.
747		1085
748	=back	1086	=back
749		1087
750		1088
751	=head1 ANATOMY OF A WATCHER	1089	=head1 ANATOMY OF A WATCHER
752		1090
		1091	In the following description, uppercase C<TYPE> in names stands for the
		1092	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1093	watchers and C<ev_io_start> for I/O watchers.
		1094
753	A watcher is a structure that you create and register to record your	1095	A watcher is an opaque structure that you allocate and register to record
754	interest in some event. For instance, if you want to wait for STDIN to	1096	your interest in some event. To make a concrete example, imagine you want
755	become readable, you would create an C<ev_io> watcher for that:	1097	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1098	for that:
756		1099
757	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1100	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
758	{	1101	{
759	ev_io_stop (w);	1102	ev_io_stop (w);
760	ev_unloop (loop, EVUNLOOP_ALL);	1103	ev_break (loop, EVBREAK_ALL);
761	}	1104	}
762		1105
763	struct ev_loop *loop = ev_default_loop (0);	1106	struct ev_loop *loop = ev_default_loop (0);
		1107
764	struct ev_io stdin_watcher;	1108	ev_io stdin_watcher;
		1109
765	ev_init (&stdin_watcher, my_cb);	1110	ev_init (&stdin_watcher, my_cb);
766	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1111	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
767	ev_io_start (loop, &stdin_watcher);	1112	ev_io_start (loop, &stdin_watcher);
		1113
768	ev_loop (loop, 0);	1114	ev_run (loop, 0);
769		1115
770	As you can see, you are responsible for allocating the memory for your	1116	As you can see, you are responsible for allocating the memory for your
771	watcher structures (and it is usually a bad idea to do this on the stack,	1117	watcher structures (and it is I<usually> a bad idea to do this on the
772	although this can sometimes be quite valid).	1118	stack).
773		1119
		1120	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1121	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1122
774	Each watcher structure must be initialised by a call to C<ev_init	1123	Each watcher structure must be initialised by a call to C<ev_init (watcher
775	(watcher *, callback)>, which expects a callback to be provided. This	1124	*, callback)>, which expects a callback to be provided. This callback is
776	callback gets invoked each time the event occurs (or, in the case of I/O	1125	invoked each time the event occurs (or, in the case of I/O watchers, each
777	watchers, each time the event loop detects that the file descriptor given	1126	time the event loop detects that the file descriptor given is readable
778	is readable and/or writable).	1127	and/or writable).
779		1128
780	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1129	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
781	with arguments specific to this watcher type. There is also a macro	1130	macro to configure it, with arguments specific to the watcher type. There
782	to combine initialisation and setting in one call: C<< ev_<type>_init	1131	is also a macro to combine initialisation and setting in one call: C<<
783	(watcher *, callback, ...) >>.	1132	ev_TYPE_init (watcher *, callback, ...) >>.
784		1133
785	To make the watcher actually watch out for events, you have to start it	1134	To make the watcher actually watch out for events, you have to start it
786	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1135	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
787	*) >>), and you can stop watching for events at any time by calling the	1136	*) >>), and you can stop watching for events at any time by calling the
788	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1137	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
789		1138
790	As long as your watcher is active (has been started but not stopped) you	1139	As long as your watcher is active (has been started but not stopped) you
791	must not touch the values stored in it. Most specifically you must never	1140	must not touch the values stored in it. Most specifically you must never
792	reinitialise it or call its C<set> macro.	1141	reinitialise it or call its C<ev_TYPE_set> macro.
793		1142
794	Each and every callback receives the event loop pointer as first, the	1143	Each and every callback receives the event loop pointer as first, the
795	registered watcher structure as second, and a bitset of received events as	1144	registered watcher structure as second, and a bitset of received events as
796	third argument.	1145	third argument.
797		1146
…		…
806	=item C<EV_WRITE>	1155	=item C<EV_WRITE>
807		1156
808	The file descriptor in the C<ev_io> watcher has become readable and/or	1157	The file descriptor in the C<ev_io> watcher has become readable and/or
809	writable.	1158	writable.
810		1159
811	=item C<EV_TIMEOUT>	1160	=item C<EV_TIMER>
812		1161
813	The C<ev_timer> watcher has timed out.	1162	The C<ev_timer> watcher has timed out.
814		1163
815	=item C<EV_PERIODIC>	1164	=item C<EV_PERIODIC>
816		1165
…		…
834		1183
835	=item C<EV_PREPARE>	1184	=item C<EV_PREPARE>
836		1185
837	=item C<EV_CHECK>	1186	=item C<EV_CHECK>
838		1187
839	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1188	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
840	to gather new events, and all C<ev_check> watchers are invoked just after	1189	gather new events, and all C<ev_check> watchers are queued (not invoked)
841	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1190	just after C<ev_run> has gathered them, but before it queues any callbacks
		1191	for any received events. That means C<ev_prepare> watchers are the last
		1192	watchers invoked before the event loop sleeps or polls for new events, and
		1193	C<ev_check> watchers will be invoked before any other watchers of the same
		1194	or lower priority within an event loop iteration.
		1195
842	received events. Callbacks of both watcher types can start and stop as	1196	Callbacks of both watcher types can start and stop as many watchers as
843	many watchers as they want, and all of them will be taken into account	1197	they want, and all of them will be taken into account (for example, a
844	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1198	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
845	C<ev_loop> from blocking).	1199	blocking).
846		1200
847	=item C<EV_EMBED>	1201	=item C<EV_EMBED>
848		1202
849	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1203	The embedded event loop specified in the C<ev_embed> watcher needs attention.
850		1204
851	=item C<EV_FORK>	1205	=item C<EV_FORK>
852		1206
853	The event loop has been resumed in the child process after fork (see	1207	The event loop has been resumed in the child process after fork (see
854	C<ev_fork>).	1208	C<ev_fork>).
855		1209
		1210	=item C<EV_CLEANUP>
		1211
		1212	The event loop is about to be destroyed (see C<ev_cleanup>).
		1213
856	=item C<EV_ASYNC>	1214	=item C<EV_ASYNC>
857		1215
858	The given async watcher has been asynchronously notified (see C<ev_async>).	1216	The given async watcher has been asynchronously notified (see C<ev_async>).
		1217
		1218	=item C<EV_CUSTOM>
		1219
		1220	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1221	by libev users to signal watchers (e.g. via C<ev_feed_event>).
859		1222
860	=item C<EV_ERROR>	1223	=item C<EV_ERROR>
861		1224
862	An unspecified error has occurred, the watcher has been stopped. This might	1225	An unspecified error has occurred, the watcher has been stopped. This might
863	happen because the watcher could not be properly started because libev	1226	happen because the watcher could not be properly started because libev
864	ran out of memory, a file descriptor was found to be closed or any other	1227	ran out of memory, a file descriptor was found to be closed or any other
		1228	problem. Libev considers these application bugs.
		1229
865	problem. You best act on it by reporting the problem and somehow coping	1230	You best act on it by reporting the problem and somehow coping with the
866	with the watcher being stopped.	1231	watcher being stopped. Note that well-written programs should not receive
		1232	an error ever, so when your watcher receives it, this usually indicates a
		1233	bug in your program.
867		1234
868	Libev will usually signal a few "dummy" events together with an error,	1235	Libev will usually signal a few "dummy" events together with an error, for
869	for example it might indicate that a fd is readable or writable, and if	1236	example it might indicate that a fd is readable or writable, and if your
870	your callbacks is well-written it can just attempt the operation and cope	1237	callbacks is well-written it can just attempt the operation and cope with
871	with the error from read() or write(). This will not work in multi-threaded	1238	the error from read() or write(). This will not work in multi-threaded
872	programs, though, so beware.	1239	programs, though, as the fd could already be closed and reused for another
		1240	thing, so beware.
873		1241
874	=back	1242	=back
875		1243
876	=head2 GENERIC WATCHER FUNCTIONS	1244	=head2 GENERIC WATCHER FUNCTIONS
877
878	In the following description, C<TYPE> stands for the watcher type,
879	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
880		1245
881	=over 4	1246	=over 4
882		1247
883	=item C<ev_init> (ev_TYPE *watcher, callback)	1248	=item C<ev_init> (ev_TYPE *watcher, callback)
884		1249
…		…
890	which rolls both calls into one.	1255	which rolls both calls into one.
891		1256
892	You can reinitialise a watcher at any time as long as it has been stopped	1257	You can reinitialise a watcher at any time as long as it has been stopped
893	(or never started) and there are no pending events outstanding.	1258	(or never started) and there are no pending events outstanding.
894		1259
895	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1260	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
896	int revents)>.	1261	int revents)>.
897		1262
		1263	Example: Initialise an C<ev_io> watcher in two steps.
		1264
		1265	ev_io w;
		1266	ev_init (&w, my_cb);
		1267	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1268
898	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1269	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
899		1270
900	This macro initialises the type-specific parts of a watcher. You need to	1271	This macro initialises the type-specific parts of a watcher. You need to
901	call C<ev_init> at least once before you call this macro, but you can	1272	call C<ev_init> at least once before you call this macro, but you can
902	call C<ev_TYPE_set> any number of times. You must not, however, call this	1273	call C<ev_TYPE_set> any number of times. You must not, however, call this
903	macro on a watcher that is active (it can be pending, however, which is a	1274	macro on a watcher that is active (it can be pending, however, which is a
904	difference to the C<ev_init> macro).	1275	difference to the C<ev_init> macro).
905		1276
906	Although some watcher types do not have type-specific arguments	1277	Although some watcher types do not have type-specific arguments
907	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1278	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
908		1279
		1280	See C<ev_init>, above, for an example.
		1281
909	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1282	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
910		1283
911	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1284	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
912	calls into a single call. This is the most convenient method to initialise	1285	calls into a single call. This is the most convenient method to initialise
913	a watcher. The same limitations apply, of course.	1286	a watcher. The same limitations apply, of course.
914		1287
		1288	Example: Initialise and set an C<ev_io> watcher in one step.
		1289
		1290	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1291
915	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1292	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
916		1293
917	Starts (activates) the given watcher. Only active watchers will receive	1294	Starts (activates) the given watcher. Only active watchers will receive
918	events. If the watcher is already active nothing will happen.	1295	events. If the watcher is already active nothing will happen.
919		1296
		1297	Example: Start the C<ev_io> watcher that is being abused as example in this
		1298	whole section.
		1299
		1300	ev_io_start (EV_DEFAULT_UC, &w);
		1301
920	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1302	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
921		1303
922	Stops the given watcher again (if active) and clears the pending	1304	Stops the given watcher if active, and clears the pending status (whether
		1305	the watcher was active or not).
		1306
923	status. It is possible that stopped watchers are pending (for example,	1307	It is possible that stopped watchers are pending - for example,
924	non-repeating timers are being stopped when they become pending), but	1308	non-repeating timers are being stopped when they become pending - but
925	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1309	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
926	you want to free or reuse the memory used by the watcher it is therefore a	1310	pending. If you want to free or reuse the memory used by the watcher it is
927	good idea to always call its C<ev_TYPE_stop> function.	1311	therefore a good idea to always call its C<ev_TYPE_stop> function.
928		1312
929	=item bool ev_is_active (ev_TYPE *watcher)	1313	=item bool ev_is_active (ev_TYPE *watcher)
930		1314
931	Returns a true value iff the watcher is active (i.e. it has been started	1315	Returns a true value iff the watcher is active (i.e. it has been started
932	and not yet been stopped). As long as a watcher is active you must not modify	1316	and not yet been stopped). As long as a watcher is active you must not modify
…		…
943		1327
944	=item callback ev_cb (ev_TYPE *watcher)	1328	=item callback ev_cb (ev_TYPE *watcher)
945		1329
946	Returns the callback currently set on the watcher.	1330	Returns the callback currently set on the watcher.
947		1331
948	=item ev_cb_set (ev_TYPE *watcher, callback)	1332	=item ev_set_cb (ev_TYPE *watcher, callback)
949		1333
950	Change the callback. You can change the callback at virtually any time	1334	Change the callback. You can change the callback at virtually any time
951	(modulo threads).	1335	(modulo threads).
952		1336
953	=item ev_set_priority (ev_TYPE *watcher, priority)	1337	=item ev_set_priority (ev_TYPE *watcher, int priority)
954		1338
955	=item int ev_priority (ev_TYPE *watcher)	1339	=item int ev_priority (ev_TYPE *watcher)
956		1340
957	Set and query the priority of the watcher. The priority is a small	1341	Set and query the priority of the watcher. The priority is a small
958	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1342	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
959	(default: C<-2>). Pending watchers with higher priority will be invoked	1343	(default: C<-2>). Pending watchers with higher priority will be invoked
960	before watchers with lower priority, but priority will not keep watchers	1344	before watchers with lower priority, but priority will not keep watchers
961	from being executed (except for C<ev_idle> watchers).	1345	from being executed (except for C<ev_idle> watchers).
962		1346
963	This means that priorities are I<only> used for ordering callback
964	invocation after new events have been received. This is useful, for
965	example, to reduce latency after idling, or more often, to bind two
966	watchers on the same event and make sure one is called first.
967
968	If you need to suppress invocation when higher priority events are pending	1347	If you need to suppress invocation when higher priority events are pending
969	you need to look at C<ev_idle> watchers, which provide this functionality.	1348	you need to look at C<ev_idle> watchers, which provide this functionality.
970		1349
971	You I<must not> change the priority of a watcher as long as it is active or	1350	You I<must not> change the priority of a watcher as long as it is active or
972	pending.	1351	pending.
973		1352
		1353	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1354	fine, as long as you do not mind that the priority value you query might
		1355	or might not have been clamped to the valid range.
		1356
974	The default priority used by watchers when no priority has been set is	1357	The default priority used by watchers when no priority has been set is
975	always C<0>, which is supposed to not be too high and not be too low :).	1358	always C<0>, which is supposed to not be too high and not be too low :).
976		1359
977	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1360	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
978	fine, as long as you do not mind that the priority value you query might	1361	priorities.
979	or might not have been adjusted to be within valid range.
980		1362
981	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1363	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
982		1364
983	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1365	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
984	C<loop> nor C<revents> need to be valid as long as the watcher callback	1366	C<loop> nor C<revents> need to be valid as long as the watcher callback
985	can deal with that fact.	1367	can deal with that fact, as both are simply passed through to the
		1368	callback.
986		1369
987	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1370	=item int ev_clear_pending (loop, ev_TYPE *watcher)
988		1371
989	If the watcher is pending, this function returns clears its pending status	1372	If the watcher is pending, this function clears its pending status and
990	and returns its C<revents> bitset (as if its callback was invoked). If the	1373	returns its C<revents> bitset (as if its callback was invoked). If the
991	watcher isn't pending it does nothing and returns C<0>.	1374	watcher isn't pending it does nothing and returns C<0>.
992		1375
		1376	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1377	callback to be invoked, which can be accomplished with this function.
		1378
		1379	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1380
		1381	Feeds the given event set into the event loop, as if the specified event
		1382	had happened for the specified watcher (which must be a pointer to an
		1383	initialised but not necessarily started event watcher). Obviously you must
		1384	not free the watcher as long as it has pending events.
		1385
		1386	Stopping the watcher, letting libev invoke it, or calling
		1387	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1388	not started in the first place.
		1389
		1390	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1391	functions that do not need a watcher.
		1392
993	=back	1393	=back
994		1394
		1395	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1396	OWN COMPOSITE WATCHERS> idioms.
995		1397
996	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1398	=head2 WATCHER STATES
997		1399
998	Each watcher has, by default, a member C<void *data> that you can change	1400	There are various watcher states mentioned throughout this manual -
999	and read at any time, libev will completely ignore it. This can be used	1401	active, pending and so on. In this section these states and the rules to
1000	to associate arbitrary data with your watcher. If you need more data and	1402	transition between them will be described in more detail - and while these
1001	don't want to allocate memory and store a pointer to it in that data	1403	rules might look complicated, they usually do "the right thing".
1002	member, you can also "subclass" the watcher type and provide your own
1003	data:
1004		1404
1005	struct my_io	1405	=over 4
		1406
		1407	=item initialised
		1408
		1409	Before a watcher can be registered with the event loop it has to be
		1410	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1411	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1412
		1413	In this state it is simply some block of memory that is suitable for
		1414	use in an event loop. It can be moved around, freed, reused etc. at
		1415	will - as long as you either keep the memory contents intact, or call
		1416	C<ev_TYPE_init> again.
		1417
		1418	=item started/running/active
		1419
		1420	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1421	property of the event loop, and is actively waiting for events. While in
		1422	this state it cannot be accessed (except in a few documented ways), moved,
		1423	freed or anything else - the only legal thing is to keep a pointer to it,
		1424	and call libev functions on it that are documented to work on active watchers.
		1425
		1426	=item pending
		1427
		1428	If a watcher is active and libev determines that an event it is interested
		1429	in has occurred (such as a timer expiring), it will become pending. It will
		1430	stay in this pending state until either it is stopped or its callback is
		1431	about to be invoked, so it is not normally pending inside the watcher
		1432	callback.
		1433
		1434	The watcher might or might not be active while it is pending (for example,
		1435	an expired non-repeating timer can be pending but no longer active). If it
		1436	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1437	but it is still property of the event loop at this time, so cannot be
		1438	moved, freed or reused. And if it is active the rules described in the
		1439	previous item still apply.
		1440
		1441	It is also possible to feed an event on a watcher that is not active (e.g.
		1442	via C<ev_feed_event>), in which case it becomes pending without being
		1443	active.
		1444
		1445	=item stopped
		1446
		1447	A watcher can be stopped implicitly by libev (in which case it might still
		1448	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1449	latter will clear any pending state the watcher might be in, regardless
		1450	of whether it was active or not, so stopping a watcher explicitly before
		1451	freeing it is often a good idea.
		1452
		1453	While stopped (and not pending) the watcher is essentially in the
		1454	initialised state, that is, it can be reused, moved, modified in any way
		1455	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1456	it again).
		1457
		1458	=back
		1459
		1460	=head2 WATCHER PRIORITY MODELS
		1461
		1462	Many event loops support I<watcher priorities>, which are usually small
		1463	integers that influence the ordering of event callback invocation
		1464	between watchers in some way, all else being equal.
		1465
		1466	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1467	description for the more technical details such as the actual priority
		1468	range.
		1469
		1470	There are two common ways how these these priorities are being interpreted
		1471	by event loops:
		1472
		1473	In the more common lock-out model, higher priorities "lock out" invocation
		1474	of lower priority watchers, which means as long as higher priority
		1475	watchers receive events, lower priority watchers are not being invoked.
		1476
		1477	The less common only-for-ordering model uses priorities solely to order
		1478	callback invocation within a single event loop iteration: Higher priority
		1479	watchers are invoked before lower priority ones, but they all get invoked
		1480	before polling for new events.
		1481
		1482	Libev uses the second (only-for-ordering) model for all its watchers
		1483	except for idle watchers (which use the lock-out model).
		1484
		1485	The rationale behind this is that implementing the lock-out model for
		1486	watchers is not well supported by most kernel interfaces, and most event
		1487	libraries will just poll for the same events again and again as long as
		1488	their callbacks have not been executed, which is very inefficient in the
		1489	common case of one high-priority watcher locking out a mass of lower
		1490	priority ones.
		1491
		1492	Static (ordering) priorities are most useful when you have two or more
		1493	watchers handling the same resource: a typical usage example is having an
		1494	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1495	timeouts. Under load, data might be received while the program handles
		1496	other jobs, but since timers normally get invoked first, the timeout
		1497	handler will be executed before checking for data. In that case, giving
		1498	the timer a lower priority than the I/O watcher ensures that I/O will be
		1499	handled first even under adverse conditions (which is usually, but not
		1500	always, what you want).
		1501
		1502	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1503	will only be executed when no same or higher priority watchers have
		1504	received events, they can be used to implement the "lock-out" model when
		1505	required.
		1506
		1507	For example, to emulate how many other event libraries handle priorities,
		1508	you can associate an C<ev_idle> watcher to each such watcher, and in
		1509	the normal watcher callback, you just start the idle watcher. The real
		1510	processing is done in the idle watcher callback. This causes libev to
		1511	continuously poll and process kernel event data for the watcher, but when
		1512	the lock-out case is known to be rare (which in turn is rare :), this is
		1513	workable.
		1514
		1515	Usually, however, the lock-out model implemented that way will perform
		1516	miserably under the type of load it was designed to handle. In that case,
		1517	it might be preferable to stop the real watcher before starting the
		1518	idle watcher, so the kernel will not have to process the event in case
		1519	the actual processing will be delayed for considerable time.
		1520
		1521	Here is an example of an I/O watcher that should run at a strictly lower
		1522	priority than the default, and which should only process data when no
		1523	other events are pending:
		1524
		1525	ev_idle idle; // actual processing watcher
		1526	ev_io io; // actual event watcher
		1527
		1528	static void
		1529	io_cb (EV_P_ ev_io *w, int revents)
1006	{	1530	{
1007	struct ev_io io;	1531	// stop the I/O watcher, we received the event, but
1008	int otherfd;	1532	// are not yet ready to handle it.
1009	void *somedata;	1533	ev_io_stop (EV_A_ w);
1010	struct whatever *mostinteresting;	1534
		1535	// start the idle watcher to handle the actual event.
		1536	// it will not be executed as long as other watchers
		1537	// with the default priority are receiving events.
		1538	ev_idle_start (EV_A_ &idle);
1011	}	1539	}
1012		1540
1013	And since your callback will be called with a pointer to the watcher, you	1541	static void
1014	can cast it back to your own type:	1542	idle_cb (EV_P_ ev_idle *w, int revents)
1015
1016	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
1017	{	1543	{
1018	struct my_io *w = (struct my_io *)w_;	1544	// actual processing
1019	...	1545	read (STDIN_FILENO, ...);
		1546
		1547	// have to start the I/O watcher again, as
		1548	// we have handled the event
		1549	ev_io_start (EV_P_ &io);
1020	}	1550	}
1021		1551
1022	More interesting and less C-conformant ways of casting your callback type	1552	// initialisation
1023	instead have been omitted.	1553	ev_idle_init (&idle, idle_cb);
		1554	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1555	ev_io_start (EV_DEFAULT_ &io);
1024		1556
1025	Another common scenario is having some data structure with multiple	1557	In the "real" world, it might also be beneficial to start a timer, so that
1026	watchers:	1558	low-priority connections can not be locked out forever under load. This
1027		1559	enables your program to keep a lower latency for important connections
1028	struct my_biggy	1560	during short periods of high load, while not completely locking out less
1029	{	1561	important ones.
1030	int some_data;
1031	ev_timer t1;
1032	ev_timer t2;
1033	}
1034
1035	In this case getting the pointer to C<my_biggy> is a bit more complicated,
1036	you need to use C<offsetof>:
1037
1038	#include <stddef.h>
1039
1040	static void
1041	t1_cb (EV_P_ struct ev_timer *w, int revents)
1042	{
1043	struct my_biggy big = (struct my_biggy *
1044	(((char *)w) - offsetof (struct my_biggy, t1));
1045	}
1046
1047	static void
1048	t2_cb (EV_P_ struct ev_timer *w, int revents)
1049	{
1050	struct my_biggy big = (struct my_biggy *
1051	(((char *)w) - offsetof (struct my_biggy, t2));
1052	}
1053		1562
1054		1563
1055	=head1 WATCHER TYPES	1564	=head1 WATCHER TYPES
1056		1565
1057	This section describes each watcher in detail, but will not repeat	1566	This section describes each watcher in detail, but will not repeat
…		…
1081	In general you can register as many read and/or write event watchers per	1590	In general you can register as many read and/or write event watchers per
1082	fd as you want (as long as you don't confuse yourself). Setting all file	1591	fd as you want (as long as you don't confuse yourself). Setting all file
1083	descriptors to non-blocking mode is also usually a good idea (but not	1592	descriptors to non-blocking mode is also usually a good idea (but not
1084	required if you know what you are doing).	1593	required if you know what you are doing).
1085		1594
1086	If you must do this, then force the use of a known-to-be-good backend
1087	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1088	C<EVBACKEND_POLL>).
1089
1090	Another thing you have to watch out for is that it is quite easy to	1595	Another thing you have to watch out for is that it is quite easy to
1091	receive "spurious" readiness notifications, that is your callback might	1596	receive "spurious" readiness notifications, that is, your callback might
1092	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1597	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1093	because there is no data. Not only are some backends known to create a	1598	because there is no data. It is very easy to get into this situation even
1094	lot of those (for example Solaris ports), it is very easy to get into	1599	with a relatively standard program structure. Thus it is best to always
1095	this situation even with a relatively standard program structure. Thus	1600	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1096	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1097	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1601	preferable to a program hanging until some data arrives.
1098		1602
1099	If you cannot run the fd in non-blocking mode (for example you should not	1603	If you cannot run the fd in non-blocking mode (for example you should
1100	play around with an Xlib connection), then you have to separately re-test	1604	not play around with an Xlib connection), then you have to separately
1101	whether a file descriptor is really ready with a known-to-be good interface	1605	re-test whether a file descriptor is really ready with a known-to-be good
1102	such as poll (fortunately in our Xlib example, Xlib already does this on	1606	interface such as poll (fortunately in the case of Xlib, it already does
1103	its own, so its quite safe to use).	1607	this on its own, so its quite safe to use). Some people additionally
		1608	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1609	indefinitely.
		1610
		1611	But really, best use non-blocking mode.
1104		1612
1105	=head3 The special problem of disappearing file descriptors	1613	=head3 The special problem of disappearing file descriptors
1106		1614
1107	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1615	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1108	descriptor (either by calling C<close> explicitly or by any other means,	1616	descriptor (either due to calling C<close> explicitly or any other means,
1109	such as C<dup>). The reason is that you register interest in some file	1617	such as C<dup2>). The reason is that you register interest in some file
1110	descriptor, but when it goes away, the operating system will silently drop	1618	descriptor, but when it goes away, the operating system will silently drop
1111	this interest. If another file descriptor with the same number then is	1619	this interest. If another file descriptor with the same number then is
1112	registered with libev, there is no efficient way to see that this is, in	1620	registered with libev, there is no efficient way to see that this is, in
1113	fact, a different file descriptor.	1621	fact, a different file descriptor.
1114		1622
…		…
1132		1640
1133	There is no workaround possible except not registering events	1641	There is no workaround possible except not registering events
1134	for potentially C<dup ()>'ed file descriptors, or to resort to	1642	for potentially C<dup ()>'ed file descriptors, or to resort to
1135	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1643	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1136		1644
		1645	=head3 The special problem of files
		1646
		1647	Many people try to use C<select> (or libev) on file descriptors
		1648	representing files, and expect it to become ready when their program
		1649	doesn't block on disk accesses (which can take a long time on their own).
		1650
		1651	However, this cannot ever work in the "expected" way - you get a readiness
		1652	notification as soon as the kernel knows whether and how much data is
		1653	there, and in the case of open files, that's always the case, so you
		1654	always get a readiness notification instantly, and your read (or possibly
		1655	write) will still block on the disk I/O.
		1656
		1657	Another way to view it is that in the case of sockets, pipes, character
		1658	devices and so on, there is another party (the sender) that delivers data
		1659	on its own, but in the case of files, there is no such thing: the disk
		1660	will not send data on its own, simply because it doesn't know what you
		1661	wish to read - you would first have to request some data.
		1662
		1663	Since files are typically not-so-well supported by advanced notification
		1664	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1665	to files, even though you should not use it. The reason for this is
		1666	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1667	usually a tty, often a pipe, but also sometimes files or special devices
		1668	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1669	F</dev/urandom>), and even though the file might better be served with
		1670	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1671	it "just works" instead of freezing.
		1672
		1673	So avoid file descriptors pointing to files when you know it (e.g. use
		1674	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1675	when you rarely read from a file instead of from a socket, and want to
		1676	reuse the same code path.
		1677
1137	=head3 The special problem of fork	1678	=head3 The special problem of fork
1138		1679
1139	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1680	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1140	useless behaviour. Libev fully supports fork, but needs to be told about	1681	useless behaviour. Libev fully supports fork, but needs to be told about
1141	it in the child.	1682	it in the child if you want to continue to use it in the child.
1142		1683
1143	To support fork in your programs, you either have to call	1684	To support fork in your child processes, you have to call C<ev_loop_fork
1144	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1685	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1145	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1686	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1146	C<EVBACKEND_POLL>.
1147		1687
1148	=head3 The special problem of SIGPIPE	1688	=head3 The special problem of SIGPIPE
1149		1689
1150	While not really specific to libev, it is easy to forget about SIGPIPE:	1690	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1151	when writing to a pipe whose other end has been closed, your program gets	1691	when writing to a pipe whose other end has been closed, your program gets
1152	send a SIGPIPE, which, by default, aborts your program. For most programs	1692	sent a SIGPIPE, which, by default, aborts your program. For most programs
1153	this is sensible behaviour, for daemons, this is usually undesirable.	1693	this is sensible behaviour, for daemons, this is usually undesirable.
1154		1694
1155	So when you encounter spurious, unexplained daemon exits, make sure you	1695	So when you encounter spurious, unexplained daemon exits, make sure you
1156	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1696	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1157	somewhere, as that would have given you a big clue).	1697	somewhere, as that would have given you a big clue).
1158		1698
		1699	=head3 The special problem of accept()ing when you can't
		1700
		1701	Many implementations of the POSIX C<accept> function (for example,
		1702	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1703	connection from the pending queue in all error cases.
		1704
		1705	For example, larger servers often run out of file descriptors (because
		1706	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1707	rejecting the connection, leading to libev signalling readiness on
		1708	the next iteration again (the connection still exists after all), and
		1709	typically causing the program to loop at 100% CPU usage.
		1710
		1711	Unfortunately, the set of errors that cause this issue differs between
		1712	operating systems, there is usually little the app can do to remedy the
		1713	situation, and no known thread-safe method of removing the connection to
		1714	cope with overload is known (to me).
		1715
		1716	One of the easiest ways to handle this situation is to just ignore it
		1717	- when the program encounters an overload, it will just loop until the
		1718	situation is over. While this is a form of busy waiting, no OS offers an
		1719	event-based way to handle this situation, so it's the best one can do.
		1720
		1721	A better way to handle the situation is to log any errors other than
		1722	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1723	messages, and continue as usual, which at least gives the user an idea of
		1724	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1725	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1726	usage.
		1727
		1728	If your program is single-threaded, then you could also keep a dummy file
		1729	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1730	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1731	close that fd, and create a new dummy fd. This will gracefully refuse
		1732	clients under typical overload conditions.
		1733
		1734	The last way to handle it is to simply log the error and C<exit>, as
		1735	is often done with C<malloc> failures, but this results in an easy
		1736	opportunity for a DoS attack.
1159		1737
1160	=head3 Watcher-Specific Functions	1738	=head3 Watcher-Specific Functions
1161		1739
1162	=over 4	1740	=over 4
1163		1741
1164	=item ev_io_init (ev_io *, callback, int fd, int events)	1742	=item ev_io_init (ev_io *, callback, int fd, int events)
1165		1743
1166	=item ev_io_set (ev_io *, int fd, int events)	1744	=item ev_io_set (ev_io *, int fd, int events)
1167		1745
1168	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1746	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1169	receive events for and events is either C<EV_READ>, C<EV_WRITE> or	1747	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1170	C<EV_READ | EV_WRITE> to receive the given events.	1748	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1171		1749
1172	=item int fd [read-only]	1750	=item int fd [read-only]
1173		1751
1174	The file descriptor being watched.	1752	The file descriptor being watched.
1175		1753
…		…
1184	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1762	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1185	readable, but only once. Since it is likely line-buffered, you could	1763	readable, but only once. Since it is likely line-buffered, you could
1186	attempt to read a whole line in the callback.	1764	attempt to read a whole line in the callback.
1187		1765
1188	static void	1766	static void
1189	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1767	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1190	{	1768	{
1191	ev_io_stop (loop, w);	1769	ev_io_stop (loop, w);
1192	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1770	.. read from stdin here (or from w->fd) and handle any I/O errors
1193	}	1771	}
1194		1772
1195	...	1773	...
1196	struct ev_loop *loop = ev_default_init (0);	1774	struct ev_loop *loop = ev_default_init (0);
1197	struct ev_io stdin_readable;	1775	ev_io stdin_readable;
1198	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1776	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1199	ev_io_start (loop, &stdin_readable);	1777	ev_io_start (loop, &stdin_readable);
1200	ev_loop (loop, 0);	1778	ev_run (loop, 0);
1201		1779
1202		1780
1203	=head2 C<ev_timer> - relative and optionally repeating timeouts	1781	=head2 C<ev_timer> - relative and optionally repeating timeouts
1204		1782
1205	Timer watchers are simple relative timers that generate an event after a	1783	Timer watchers are simple relative timers that generate an event after a
1206	given time, and optionally repeating in regular intervals after that.	1784	given time, and optionally repeating in regular intervals after that.
1207		1785
1208	The timers are based on real time, that is, if you register an event that	1786	The timers are based on real time, that is, if you register an event that
1209	times out after an hour and you reset your system clock to January last	1787	times out after an hour and you reset your system clock to January last
1210	year, it will still time out after (roughly) and hour. "Roughly" because	1788	year, it will still time out after (roughly) one hour. "Roughly" because
1211	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1789	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1212	monotonic clock option helps a lot here).	1790	monotonic clock option helps a lot here).
1213		1791
1214	The callback is guaranteed to be invoked only after its timeout has passed,	1792	The callback is guaranteed to be invoked only I<after> its timeout has
1215	but if multiple timers become ready during the same loop iteration then	1793	passed (not I<at>, so on systems with very low-resolution clocks this
1216	order of execution is undefined.	1794	might introduce a small delay, see "the special problem of being too
		1795	early", below). If multiple timers become ready during the same loop
		1796	iteration then the ones with earlier time-out values are invoked before
		1797	ones of the same priority with later time-out values (but this is no
		1798	longer true when a callback calls C<ev_run> recursively).
		1799
		1800	=head3 Be smart about timeouts
		1801
		1802	Many real-world problems involve some kind of timeout, usually for error
		1803	recovery. A typical example is an HTTP request - if the other side hangs,
		1804	you want to raise some error after a while.
		1805
		1806	What follows are some ways to handle this problem, from obvious and
		1807	inefficient to smart and efficient.
		1808
		1809	In the following, a 60 second activity timeout is assumed - a timeout that
		1810	gets reset to 60 seconds each time there is activity (e.g. each time some
		1811	data or other life sign was received).
		1812
		1813	=over 4
		1814
		1815	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1816
		1817	This is the most obvious, but not the most simple way: In the beginning,
		1818	start the watcher:
		1819
		1820	ev_timer_init (timer, callback, 60., 0.);
		1821	ev_timer_start (loop, timer);
		1822
		1823	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1824	and start it again:
		1825
		1826	ev_timer_stop (loop, timer);
		1827	ev_timer_set (timer, 60., 0.);
		1828	ev_timer_start (loop, timer);
		1829
		1830	This is relatively simple to implement, but means that each time there is
		1831	some activity, libev will first have to remove the timer from its internal
		1832	data structure and then add it again. Libev tries to be fast, but it's
		1833	still not a constant-time operation.
		1834
		1835	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1836
		1837	This is the easiest way, and involves using C<ev_timer_again> instead of
		1838	C<ev_timer_start>.
		1839
		1840	To implement this, configure an C<ev_timer> with a C<repeat> value
		1841	of C<60> and then call C<ev_timer_again> at start and each time you
		1842	successfully read or write some data. If you go into an idle state where
		1843	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1844	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1845
		1846	That means you can ignore both the C<ev_timer_start> function and the
		1847	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1848	member and C<ev_timer_again>.
		1849
		1850	At start:
		1851
		1852	ev_init (timer, callback);
		1853	timer->repeat = 60.;
		1854	ev_timer_again (loop, timer);
		1855
		1856	Each time there is some activity:
		1857
		1858	ev_timer_again (loop, timer);
		1859
		1860	It is even possible to change the time-out on the fly, regardless of
		1861	whether the watcher is active or not:
		1862
		1863	timer->repeat = 30.;
		1864	ev_timer_again (loop, timer);
		1865
		1866	This is slightly more efficient then stopping/starting the timer each time
		1867	you want to modify its timeout value, as libev does not have to completely
		1868	remove and re-insert the timer from/into its internal data structure.
		1869
		1870	It is, however, even simpler than the "obvious" way to do it.
		1871
		1872	=item 3. Let the timer time out, but then re-arm it as required.
		1873
		1874	This method is more tricky, but usually most efficient: Most timeouts are
		1875	relatively long compared to the intervals between other activity - in
		1876	our example, within 60 seconds, there are usually many I/O events with
		1877	associated activity resets.
		1878
		1879	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1880	but remember the time of last activity, and check for a real timeout only
		1881	within the callback:
		1882
		1883	ev_tstamp timeout = 60.;
		1884	ev_tstamp last_activity; // time of last activity
		1885	ev_timer timer;
		1886
		1887	static void
		1888	callback (EV_P_ ev_timer *w, int revents)
		1889	{
		1890	// calculate when the timeout would happen
		1891	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1892
		1893	// if negative, it means we the timeout already occurred
		1894	if (after < 0.)
		1895	{
		1896	// timeout occurred, take action
		1897	}
		1898	else
		1899	{
		1900	// callback was invoked, but there was some recent
		1901	// activity. simply restart the timer to time out
		1902	// after "after" seconds, which is the earliest time
		1903	// the timeout can occur.
		1904	ev_timer_set (w, after, 0.);
		1905	ev_timer_start (EV_A_ w);
		1906	}
		1907	}
		1908
		1909	To summarise the callback: first calculate in how many seconds the
		1910	timeout will occur (by calculating the absolute time when it would occur,
		1911	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1912	(EV_A)> from that).
		1913
		1914	If this value is negative, then we are already past the timeout, i.e. we
		1915	timed out, and need to do whatever is needed in this case.
		1916
		1917	Otherwise, we now the earliest time at which the timeout would trigger,
		1918	and simply start the timer with this timeout value.
		1919
		1920	In other words, each time the callback is invoked it will check whether
		1921	the timeout occurred. If not, it will simply reschedule itself to check
		1922	again at the earliest time it could time out. Rinse. Repeat.
		1923
		1924	This scheme causes more callback invocations (about one every 60 seconds
		1925	minus half the average time between activity), but virtually no calls to
		1926	libev to change the timeout.
		1927
		1928	To start the machinery, simply initialise the watcher and set
		1929	C<last_activity> to the current time (meaning there was some activity just
		1930	now), then call the callback, which will "do the right thing" and start
		1931	the timer:
		1932
		1933	last_activity = ev_now (EV_A);
		1934	ev_init (&timer, callback);
		1935	callback (EV_A_ &timer, 0);
		1936
		1937	When there is some activity, simply store the current time in
		1938	C<last_activity>, no libev calls at all:
		1939
		1940	if (activity detected)
		1941	last_activity = ev_now (EV_A);
		1942
		1943	When your timeout value changes, then the timeout can be changed by simply
		1944	providing a new value, stopping the timer and calling the callback, which
		1945	will again do the right thing (for example, time out immediately :).
		1946
		1947	timeout = new_value;
		1948	ev_timer_stop (EV_A_ &timer);
		1949	callback (EV_A_ &timer, 0);
		1950
		1951	This technique is slightly more complex, but in most cases where the
		1952	time-out is unlikely to be triggered, much more efficient.
		1953
		1954	=item 4. Wee, just use a double-linked list for your timeouts.
		1955
		1956	If there is not one request, but many thousands (millions...), all
		1957	employing some kind of timeout with the same timeout value, then one can
		1958	do even better:
		1959
		1960	When starting the timeout, calculate the timeout value and put the timeout
		1961	at the I<end> of the list.
		1962
		1963	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1964	the list is expected to fire (for example, using the technique #3).
		1965
		1966	When there is some activity, remove the timer from the list, recalculate
		1967	the timeout, append it to the end of the list again, and make sure to
		1968	update the C<ev_timer> if it was taken from the beginning of the list.
		1969
		1970	This way, one can manage an unlimited number of timeouts in O(1) time for
		1971	starting, stopping and updating the timers, at the expense of a major
		1972	complication, and having to use a constant timeout. The constant timeout
		1973	ensures that the list stays sorted.
		1974
		1975	=back
		1976
		1977	So which method the best?
		1978
		1979	Method #2 is a simple no-brain-required solution that is adequate in most
		1980	situations. Method #3 requires a bit more thinking, but handles many cases
		1981	better, and isn't very complicated either. In most case, choosing either
		1982	one is fine, with #3 being better in typical situations.
		1983
		1984	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1985	rather complicated, but extremely efficient, something that really pays
		1986	off after the first million or so of active timers, i.e. it's usually
		1987	overkill :)
		1988
		1989	=head3 The special problem of being too early
		1990
		1991	If you ask a timer to call your callback after three seconds, then
		1992	you expect it to be invoked after three seconds - but of course, this
		1993	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1994	guaranteed to any precision by libev - imagine somebody suspending the
		1995	process with a STOP signal for a few hours for example.
		1996
		1997	So, libev tries to invoke your callback as soon as possible I<after> the
		1998	delay has occurred, but cannot guarantee this.
		1999
		2000	A less obvious failure mode is calling your callback too early: many event
		2001	loops compare timestamps with a "elapsed delay >= requested delay", but
		2002	this can cause your callback to be invoked much earlier than you would
		2003	expect.
		2004
		2005	To see why, imagine a system with a clock that only offers full second
		2006	resolution (think windows if you can't come up with a broken enough OS
		2007	yourself). If you schedule a one-second timer at the time 500.9, then the
		2008	event loop will schedule your timeout to elapse at a system time of 500
		2009	(500.9 truncated to the resolution) + 1, or 501.
		2010
		2011	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2012	501" and invoke the callback 0.1s after it was started, even though a
		2013	one-second delay was requested - this is being "too early", despite best
		2014	intentions.
		2015
		2016	This is the reason why libev will never invoke the callback if the elapsed
		2017	delay equals the requested delay, but only when the elapsed delay is
		2018	larger than the requested delay. In the example above, libev would only invoke
		2019	the callback at system time 502, or 1.1s after the timer was started.
		2020
		2021	So, while libev cannot guarantee that your callback will be invoked
		2022	exactly when requested, it I<can> and I<does> guarantee that the requested
		2023	delay has actually elapsed, or in other words, it always errs on the "too
		2024	late" side of things.
1217		2025
1218	=head3 The special problem of time updates	2026	=head3 The special problem of time updates
1219		2027
1220	Establishing the current time is a costly operation (it usually takes at	2028	Establishing the current time is a costly operation (it usually takes
1221	least two system calls): EV therefore updates its idea of the current	2029	at least one system call): EV therefore updates its idea of the current
1222	time only before and after C<ev_loop> polls for new events, which causes	2030	time only before and after C<ev_run> collects new events, which causes a
1223	a growing difference between C<ev_now ()> and C<ev_time ()> when handling	2031	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1224	lots of events.	2032	lots of events in one iteration.
1225		2033
1226	The relative timeouts are calculated relative to the C<ev_now ()>	2034	The relative timeouts are calculated relative to the C<ev_now ()>
1227	time. This is usually the right thing as this timestamp refers to the time	2035	time. This is usually the right thing as this timestamp refers to the time
1228	of the event triggering whatever timeout you are modifying/starting. If	2036	of the event triggering whatever timeout you are modifying/starting. If
1229	you suspect event processing to be delayed and you I<need> to base the	2037	you suspect event processing to be delayed and you I<need> to base the
1230	timeout on the current time, use something like this to adjust for this:	2038	timeout on the current time, use something like the following to adjust
		2039	for it:
1231		2040
1232	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2041	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1233		2042
1234	If the event loop is suspended for a long time, one can also force an	2043	If the event loop is suspended for a long time, you can also force an
1235	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2044	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1236	()>.	2045	()>, although that will push the event time of all outstanding events
		2046	further into the future.
		2047
		2048	=head3 The special problem of unsynchronised clocks
		2049
		2050	Modern systems have a variety of clocks - libev itself uses the normal
		2051	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2052	jumps).
		2053
		2054	Neither of these clocks is synchronised with each other or any other clock
		2055	on the system, so C<ev_time ()> might return a considerably different time
		2056	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2057	a call to C<gettimeofday> might return a second count that is one higher
		2058	than a directly following call to C<time>.
		2059
		2060	The moral of this is to only compare libev-related timestamps with
		2061	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2062	a second or so.
		2063
		2064	One more problem arises due to this lack of synchronisation: if libev uses
		2065	the system monotonic clock and you compare timestamps from C<ev_time>
		2066	or C<ev_now> from when you started your timer and when your callback is
		2067	invoked, you will find that sometimes the callback is a bit "early".
		2068
		2069	This is because C<ev_timer>s work in real time, not wall clock time, so
		2070	libev makes sure your callback is not invoked before the delay happened,
		2071	I<measured according to the real time>, not the system clock.
		2072
		2073	If your timeouts are based on a physical timescale (e.g. "time out this
		2074	connection after 100 seconds") then this shouldn't bother you as it is
		2075	exactly the right behaviour.
		2076
		2077	If you want to compare wall clock/system timestamps to your timers, then
		2078	you need to use C<ev_periodic>s, as these are based on the wall clock
		2079	time, where your comparisons will always generate correct results.
		2080
		2081	=head3 The special problems of suspended animation
		2082
		2083	When you leave the server world it is quite customary to hit machines that
		2084	can suspend/hibernate - what happens to the clocks during such a suspend?
		2085
		2086	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2087	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2088	to run until the system is suspended, but they will not advance while the
		2089	system is suspended. That means, on resume, it will be as if the program
		2090	was frozen for a few seconds, but the suspend time will not be counted
		2091	towards C<ev_timer> when a monotonic clock source is used. The real time
		2092	clock advanced as expected, but if it is used as sole clocksource, then a
		2093	long suspend would be detected as a time jump by libev, and timers would
		2094	be adjusted accordingly.
		2095
		2096	I would not be surprised to see different behaviour in different between
		2097	operating systems, OS versions or even different hardware.
		2098
		2099	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2100	time jump in the monotonic clocks and the realtime clock. If the program
		2101	is suspended for a very long time, and monotonic clock sources are in use,
		2102	then you can expect C<ev_timer>s to expire as the full suspension time
		2103	will be counted towards the timers. When no monotonic clock source is in
		2104	use, then libev will again assume a timejump and adjust accordingly.
		2105
		2106	It might be beneficial for this latter case to call C<ev_suspend>
		2107	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2108	deterministic behaviour in this case (you can do nothing against
		2109	C<SIGSTOP>).
1237		2110
1238	=head3 Watcher-Specific Functions and Data Members	2111	=head3 Watcher-Specific Functions and Data Members
1239		2112
1240	=over 4	2113	=over 4
1241		2114
1242	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2115	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1243		2116
1244	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2117	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1245		2118
1246	Configure the timer to trigger after C<after> seconds. If C<repeat>	2119	Configure the timer to trigger after C<after> seconds (fractional and
1247	is C<0.>, then it will automatically be stopped once the timeout is	2120	negative values are supported). If C<repeat> is C<0.>, then it will
1248	reached. If it is positive, then the timer will automatically be	2121	automatically be stopped once the timeout is reached. If it is positive,
1249	configured to trigger again C<repeat> seconds later, again, and again,	2122	then the timer will automatically be configured to trigger again C<repeat>
1250	until stopped manually.	2123	seconds later, again, and again, until stopped manually.
1251		2124
1252	The timer itself will do a best-effort at avoiding drift, that is, if	2125	The timer itself will do a best-effort at avoiding drift, that is, if
1253	you configure a timer to trigger every 10 seconds, then it will normally	2126	you configure a timer to trigger every 10 seconds, then it will normally
1254	trigger at exactly 10 second intervals. If, however, your program cannot	2127	trigger at exactly 10 second intervals. If, however, your program cannot
1255	keep up with the timer (because it takes longer than those 10 seconds to	2128	keep up with the timer (because it takes longer than those 10 seconds to
1256	do stuff) the timer will not fire more than once per event loop iteration.	2129	do stuff) the timer will not fire more than once per event loop iteration.
1257		2130
1258	=item ev_timer_again (loop, ev_timer *)	2131	=item ev_timer_again (loop, ev_timer *)
1259		2132
1260	This will act as if the timer timed out and restart it again if it is	2133	This will act as if the timer timed out, and restarts it again if it is
1261	repeating. The exact semantics are:	2134	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2135	timeout to the C<repeat> value and calling C<ev_timer_start>.
1262		2136
		2137	The exact semantics are as in the following rules, all of which will be
		2138	applied to the watcher:
		2139
		2140	=over 4
		2141
1263	If the timer is pending, its pending status is cleared.	2142	=item If the timer is pending, the pending status is always cleared.
1264		2143
1265	If the timer is started but non-repeating, stop it (as if it timed out).	2144	=item If the timer is started but non-repeating, stop it (as if it timed
		2145	out, without invoking it).
1266		2146
1267	If the timer is repeating, either start it if necessary (with the	2147	=item If the timer is repeating, make the C<repeat> value the new timeout
1268	C<repeat> value), or reset the running timer to the C<repeat> value.	2148	and start the timer, if necessary.
1269		2149
1270	This sounds a bit complicated, but here is a useful and typical	2150	=back
1271	example: Imagine you have a TCP connection and you want a so-called idle
1272	timeout, that is, you want to be called when there have been, say, 60
1273	seconds of inactivity on the socket. The easiest way to do this is to
1274	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1275	C<ev_timer_again> each time you successfully read or write some data. If
1276	you go into an idle state where you do not expect data to travel on the
1277	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1278	automatically restart it if need be.
1279		2151
1280	That means you can ignore the C<after> value and C<ev_timer_start>	2152	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1281	altogether and only ever use the C<repeat> value and C<ev_timer_again>:	2153	usage example.
1282		2154
1283	ev_timer_init (timer, callback, 0., 5.);	2155	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1284	ev_timer_again (loop, timer);
1285	...
1286	timer->again = 17.;
1287	ev_timer_again (loop, timer);
1288	...
1289	timer->again = 10.;
1290	ev_timer_again (loop, timer);
1291		2156
1292	This is more slightly efficient then stopping/starting the timer each time	2157	Returns the remaining time until a timer fires. If the timer is active,
1293	you want to modify its timeout value.	2158	then this time is relative to the current event loop time, otherwise it's
		2159	the timeout value currently configured.
		2160
		2161	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2162	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2163	will return C<4>. When the timer expires and is restarted, it will return
		2164	roughly C<7> (likely slightly less as callback invocation takes some time,
		2165	too), and so on.
1294		2166
1295	=item ev_tstamp repeat [read-write]	2167	=item ev_tstamp repeat [read-write]
1296		2168
1297	The current C<repeat> value. Will be used each time the watcher times out	2169	The current C<repeat> value. Will be used each time the watcher times out
1298	or C<ev_timer_again> is called and determines the next timeout (if any),	2170	or C<ev_timer_again> is called, and determines the next timeout (if any),
1299	which is also when any modifications are taken into account.	2171	which is also when any modifications are taken into account.
1300		2172
1301	=back	2173	=back
1302		2174
1303	=head3 Examples	2175	=head3 Examples
1304		2176
1305	Example: Create a timer that fires after 60 seconds.	2177	Example: Create a timer that fires after 60 seconds.
1306		2178
1307	static void	2179	static void
1308	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2180	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1309	{	2181	{
1310	.. one minute over, w is actually stopped right here	2182	.. one minute over, w is actually stopped right here
1311	}	2183	}
1312		2184
1313	struct ev_timer mytimer;	2185	ev_timer mytimer;
1314	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2186	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1315	ev_timer_start (loop, &mytimer);	2187	ev_timer_start (loop, &mytimer);
1316		2188
1317	Example: Create a timeout timer that times out after 10 seconds of	2189	Example: Create a timeout timer that times out after 10 seconds of
1318	inactivity.	2190	inactivity.
1319		2191
1320	static void	2192	static void
1321	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2193	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1322	{	2194	{
1323	.. ten seconds without any activity	2195	.. ten seconds without any activity
1324	}	2196	}
1325		2197
1326	struct ev_timer mytimer;	2198	ev_timer mytimer;
1327	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2199	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1328	ev_timer_again (&mytimer); /* start timer */	2200	ev_timer_again (&mytimer); /* start timer */
1329	ev_loop (loop, 0);	2201	ev_run (loop, 0);
1330		2202
1331	// and in some piece of code that gets executed on any "activity":	2203	// and in some piece of code that gets executed on any "activity":
1332	// reset the timeout to start ticking again at 10 seconds	2204	// reset the timeout to start ticking again at 10 seconds
1333	ev_timer_again (&mytimer);	2205	ev_timer_again (&mytimer);
1334		2206
…		…
1336	=head2 C<ev_periodic> - to cron or not to cron?	2208	=head2 C<ev_periodic> - to cron or not to cron?
1337		2209
1338	Periodic watchers are also timers of a kind, but they are very versatile	2210	Periodic watchers are also timers of a kind, but they are very versatile
1339	(and unfortunately a bit complex).	2211	(and unfortunately a bit complex).
1340		2212
1341	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2213	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1342	but on wall clock time (absolute time). You can tell a periodic watcher	2214	relative time, the physical time that passes) but on wall clock time
1343	to trigger after some specific point in time. For example, if you tell a	2215	(absolute time, the thing you can read on your calendar or clock). The
1344	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	2216	difference is that wall clock time can run faster or slower than real
1345	+ 10.>, that is, an absolute time not a delay) and then reset your system	2217	time, and time jumps are not uncommon (e.g. when you adjust your
1346	clock to January of the previous year, then it will take more than year	2218	wrist-watch).
1347	to trigger the event (unlike an C<ev_timer>, which would still trigger
1348	roughly 10 seconds later as it uses a relative timeout).
1349		2219
		2220	You can tell a periodic watcher to trigger after some specific point
		2221	in time: for example, if you tell a periodic watcher to trigger "in 10
		2222	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2223	not a delay) and then reset your system clock to January of the previous
		2224	year, then it will take a year or more to trigger the event (unlike an
		2225	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2226	it, as it uses a relative timeout).
		2227
1350	C<ev_periodic>s can also be used to implement vastly more complex timers,	2228	C<ev_periodic> watchers can also be used to implement vastly more complex
1351	such as triggering an event on each "midnight, local time", or other	2229	timers, such as triggering an event on each "midnight, local time", or
1352	complicated, rules.	2230	other complicated rules. This cannot easily be done with C<ev_timer>
		2231	watchers, as those cannot react to time jumps.
1353		2232
1354	As with timers, the callback is guaranteed to be invoked only when the	2233	As with timers, the callback is guaranteed to be invoked only when the
1355	time (C<at>) has passed, but if multiple periodic timers become ready	2234	point in time where it is supposed to trigger has passed. If multiple
1356	during the same loop iteration then order of execution is undefined.	2235	timers become ready during the same loop iteration then the ones with
		2236	earlier time-out values are invoked before ones with later time-out values
		2237	(but this is no longer true when a callback calls C<ev_run> recursively).
1357		2238
1358	=head3 Watcher-Specific Functions and Data Members	2239	=head3 Watcher-Specific Functions and Data Members
1359		2240
1360	=over 4	2241	=over 4
1361		2242
1362	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2243	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1363		2244
1364	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2245	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1365		2246
1366	Lots of arguments, lets sort it out... There are basically three modes of	2247	Lots of arguments, let's sort it out... There are basically three modes of
1367	operation, and we will explain them from simplest to complex:	2248	operation, and we will explain them from simplest to most complex:
1368		2249
1369	=over 4	2250	=over 4
1370		2251
1371	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2252	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1372		2253
1373	In this configuration the watcher triggers an event after the wall clock	2254	In this configuration the watcher triggers an event after the wall clock
1374	time C<at> has passed and doesn't repeat. It will not adjust when a time	2255	time C<offset> has passed. It will not repeat and will not adjust when a
1375	jump occurs, that is, if it is to be run at January 1st 2011 then it will	2256	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1376	run when the system time reaches or surpasses this time.	2257	will be stopped and invoked when the system clock reaches or surpasses
		2258	this point in time.
1377		2259
1378	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2260	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1379		2261
1380	In this mode the watcher will always be scheduled to time out at the next	2262	In this mode the watcher will always be scheduled to time out at the next
1381	C<at + N * interval> time (for some integer N, which can also be negative)	2263	C<offset + N * interval> time (for some integer N, which can also be
1382	and then repeat, regardless of any time jumps.	2264	negative) and then repeat, regardless of any time jumps. The C<offset>
		2265	argument is merely an offset into the C<interval> periods.
1383		2266
1384	This can be used to create timers that do not drift with respect to system	2267	This can be used to create timers that do not drift with respect to the
1385	time, for example, here is a C<ev_periodic> that triggers each hour, on	2268	system clock, for example, here is an C<ev_periodic> that triggers each
1386	the hour:	2269	hour, on the hour (with respect to UTC):
1387		2270
1388	ev_periodic_set (&periodic, 0., 3600., 0);	2271	ev_periodic_set (&periodic, 0., 3600., 0);
1389		2272
1390	This doesn't mean there will always be 3600 seconds in between triggers,	2273	This doesn't mean there will always be 3600 seconds in between triggers,
1391	but only that the callback will be called when the system time shows a	2274	but only that the callback will be called when the system time shows a
1392	full hour (UTC), or more correctly, when the system time is evenly divisible	2275	full hour (UTC), or more correctly, when the system time is evenly divisible
1393	by 3600.	2276	by 3600.
1394		2277
1395	Another way to think about it (for the mathematically inclined) is that	2278	Another way to think about it (for the mathematically inclined) is that
1396	C<ev_periodic> will try to run the callback in this mode at the next possible	2279	C<ev_periodic> will try to run the callback in this mode at the next possible
1397	time where C<time = at (mod interval)>, regardless of any time jumps.	2280	time where C<time = offset (mod interval)>, regardless of any time jumps.
1398		2281
1399	For numerical stability it is preferable that the C<at> value is near	2282	The C<interval> I<MUST> be positive, and for numerical stability, the
1400	C<ev_now ()> (the current time), but there is no range requirement for	2283	interval value should be higher than C<1/8192> (which is around 100
1401	this value, and in fact is often specified as zero.	2284	microseconds) and C<offset> should be higher than C<0> and should have
		2285	at most a similar magnitude as the current time (say, within a factor of
		2286	ten). Typical values for offset are, in fact, C<0> or something between
		2287	C<0> and C<interval>, which is also the recommended range.
1402		2288
1403	Note also that there is an upper limit to how often a timer can fire (CPU	2289	Note also that there is an upper limit to how often a timer can fire (CPU
1404	speed for example), so if C<interval> is very small then timing stability	2290	speed for example), so if C<interval> is very small then timing stability
1405	will of course deteriorate. Libev itself tries to be exact to be about one	2291	will of course deteriorate. Libev itself tries to be exact to be about one
1406	millisecond (if the OS supports it and the machine is fast enough).	2292	millisecond (if the OS supports it and the machine is fast enough).
1407		2293
1408	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2294	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1409		2295
1410	In this mode the values for C<interval> and C<at> are both being	2296	In this mode the values for C<interval> and C<offset> are both being
1411	ignored. Instead, each time the periodic watcher gets scheduled, the	2297	ignored. Instead, each time the periodic watcher gets scheduled, the
1412	reschedule callback will be called with the watcher as first, and the	2298	reschedule callback will be called with the watcher as first, and the
1413	current time as second argument.	2299	current time as second argument.
1414		2300
1415	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2301	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1416	ever, or make ANY event loop modifications whatsoever>.	2302	or make ANY other event loop modifications whatsoever, unless explicitly
		2303	allowed by documentation here>.
1417		2304
1418	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2305	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1419	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	2306	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1420	only event loop modification you are allowed to do).	2307	only event loop modification you are allowed to do).
1421		2308
1422	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	2309	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1423	*w, ev_tstamp now)>, e.g.:	2310	*w, ev_tstamp now)>, e.g.:
1424		2311
		2312	static ev_tstamp
1425	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2313	my_rescheduler (ev_periodic *w, ev_tstamp now)
1426	{	2314	{
1427	return now + 60.;	2315	return now + 60.;
1428	}	2316	}
1429		2317
1430	It must return the next time to trigger, based on the passed time value	2318	It must return the next time to trigger, based on the passed time value
…		…
1434		2322
1435	NOTE: I<< This callback must always return a time that is higher than or	2323	NOTE: I<< This callback must always return a time that is higher than or
1436	equal to the passed C<now> value >>.	2324	equal to the passed C<now> value >>.
1437		2325
1438	This can be used to create very complex timers, such as a timer that	2326	This can be used to create very complex timers, such as a timer that
1439	triggers on "next midnight, local time". To do this, you would calculate the	2327	triggers on "next midnight, local time". To do this, you would calculate
1440	next midnight after C<now> and return the timestamp value for this. How	2328	the next midnight after C<now> and return the timestamp value for
1441	you do this is, again, up to you (but it is not trivial, which is the main	2329	this. Here is a (completely untested, no error checking) example on how to
1442	reason I omitted it as an example).	2330	do this:
		2331
		2332	#include <time.h>
		2333
		2334	static ev_tstamp
		2335	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2336	{
		2337	time_t tnow = (time_t)now;
		2338	struct tm tm;
		2339	localtime_r (&tnow, &tm);
		2340
		2341	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2342	++tm.tm_mday; // midnight next day
		2343
		2344	return mktime (&tm);
		2345	}
		2346
		2347	Note: this code might run into trouble on days that have more then two
		2348	midnights (beginning and end).
1443		2349
1444	=back	2350	=back
1445		2351
1446	=item ev_periodic_again (loop, ev_periodic *)	2352	=item ev_periodic_again (loop, ev_periodic *)
1447		2353
…		…
1450	a different time than the last time it was called (e.g. in a crond like	2356	a different time than the last time it was called (e.g. in a crond like
1451	program when the crontabs have changed).	2357	program when the crontabs have changed).
1452		2358
1453	=item ev_tstamp ev_periodic_at (ev_periodic *)	2359	=item ev_tstamp ev_periodic_at (ev_periodic *)
1454		2360
1455	When active, returns the absolute time that the watcher is supposed to	2361	When active, returns the absolute time that the watcher is supposed
1456	trigger next.	2362	to trigger next. This is not the same as the C<offset> argument to
		2363	C<ev_periodic_set>, but indeed works even in interval and manual
		2364	rescheduling modes.
1457		2365
1458	=item ev_tstamp offset [read-write]	2366	=item ev_tstamp offset [read-write]
1459		2367
1460	When repeating, this contains the offset value, otherwise this is the	2368	When repeating, this contains the offset value, otherwise this is the
1461	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2369	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2370	although libev might modify this value for better numerical stability).
1462		2371
1463	Can be modified any time, but changes only take effect when the periodic	2372	Can be modified any time, but changes only take effect when the periodic
1464	timer fires or C<ev_periodic_again> is being called.	2373	timer fires or C<ev_periodic_again> is being called.
1465		2374
1466	=item ev_tstamp interval [read-write]	2375	=item ev_tstamp interval [read-write]
1467		2376
1468	The current interval value. Can be modified any time, but changes only	2377	The current interval value. Can be modified any time, but changes only
1469	take effect when the periodic timer fires or C<ev_periodic_again> is being	2378	take effect when the periodic timer fires or C<ev_periodic_again> is being
1470	called.	2379	called.
1471		2380
1472	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2381	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1473		2382
1474	The current reschedule callback, or C<0>, if this functionality is	2383	The current reschedule callback, or C<0>, if this functionality is
1475	switched off. Can be changed any time, but changes only take effect when	2384	switched off. Can be changed any time, but changes only take effect when
1476	the periodic timer fires or C<ev_periodic_again> is being called.	2385	the periodic timer fires or C<ev_periodic_again> is being called.
1477		2386
1478	=back	2387	=back
1479		2388
1480	=head3 Examples	2389	=head3 Examples
1481		2390
1482	Example: Call a callback every hour, or, more precisely, whenever the	2391	Example: Call a callback every hour, or, more precisely, whenever the
1483	system clock is divisible by 3600. The callback invocation times have	2392	system time is divisible by 3600. The callback invocation times have
1484	potentially a lot of jitter, but good long-term stability.	2393	potentially a lot of jitter, but good long-term stability.
1485		2394
1486	static void	2395	static void
1487	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2396	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1488	{	2397	{
1489	... its now a full hour (UTC, or TAI or whatever your clock follows)	2398	... its now a full hour (UTC, or TAI or whatever your clock follows)
1490	}	2399	}
1491		2400
1492	struct ev_periodic hourly_tick;	2401	ev_periodic hourly_tick;
1493	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2402	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1494	ev_periodic_start (loop, &hourly_tick);	2403	ev_periodic_start (loop, &hourly_tick);
1495		2404
1496	Example: The same as above, but use a reschedule callback to do it:	2405	Example: The same as above, but use a reschedule callback to do it:
1497		2406
1498	#include <math.h>	2407	#include <math.h>
1499		2408
1500	static ev_tstamp	2409	static ev_tstamp
1501	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2410	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1502	{	2411	{
1503	return fmod (now, 3600.) + 3600.;	2412	return now + (3600. - fmod (now, 3600.));
1504	}	2413	}
1505		2414
1506	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2415	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1507		2416
1508	Example: Call a callback every hour, starting now:	2417	Example: Call a callback every hour, starting now:
1509		2418
1510	struct ev_periodic hourly_tick;	2419	ev_periodic hourly_tick;
1511	ev_periodic_init (&hourly_tick, clock_cb,	2420	ev_periodic_init (&hourly_tick, clock_cb,
1512	fmod (ev_now (loop), 3600.), 3600., 0);	2421	fmod (ev_now (loop), 3600.), 3600., 0);
1513	ev_periodic_start (loop, &hourly_tick);	2422	ev_periodic_start (loop, &hourly_tick);
1514		2423
1515		2424
1516	=head2 C<ev_signal> - signal me when a signal gets signalled!	2425	=head2 C<ev_signal> - signal me when a signal gets signalled!
1517		2426
1518	Signal watchers will trigger an event when the process receives a specific	2427	Signal watchers will trigger an event when the process receives a specific
1519	signal one or more times. Even though signals are very asynchronous, libev	2428	signal one or more times. Even though signals are very asynchronous, libev
1520	will try it's best to deliver signals synchronously, i.e. as part of the	2429	will try its best to deliver signals synchronously, i.e. as part of the
1521	normal event processing, like any other event.	2430	normal event processing, like any other event.
1522		2431
		2432	If you want signals to be delivered truly asynchronously, just use
		2433	C<sigaction> as you would do without libev and forget about sharing
		2434	the signal. You can even use C<ev_async> from a signal handler to
		2435	synchronously wake up an event loop.
		2436
1523	You can configure as many watchers as you like per signal. Only when the	2437	You can configure as many watchers as you like for the same signal, but
1524	first watcher gets started will libev actually register a signal watcher	2438	only within the same loop, i.e. you can watch for C<SIGINT> in your
1525	with the kernel (thus it coexists with your own signal handlers as long	2439	default loop and for C<SIGIO> in another loop, but you cannot watch for
1526	as you don't register any with libev). Similarly, when the last signal	2440	C<SIGINT> in both the default loop and another loop at the same time. At
1527	watcher for a signal is stopped libev will reset the signal handler to	2441	the moment, C<SIGCHLD> is permanently tied to the default loop.
1528	SIG_DFL (regardless of what it was set to before).	2442
		2443	Only after the first watcher for a signal is started will libev actually
		2444	register something with the kernel. It thus coexists with your own signal
		2445	handlers as long as you don't register any with libev for the same signal.
1529		2446
1530	If possible and supported, libev will install its handlers with	2447	If possible and supported, libev will install its handlers with
1531	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2448	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1532	interrupted. If you have a problem with system calls getting interrupted by	2449	not be unduly interrupted. If you have a problem with system calls getting
1533	signals you can block all signals in an C<ev_check> watcher and unblock	2450	interrupted by signals you can block all signals in an C<ev_check> watcher
1534	them in an C<ev_prepare> watcher.	2451	and unblock them in an C<ev_prepare> watcher.
		2452
		2453	=head3 The special problem of inheritance over fork/execve/pthread_create
		2454
		2455	Both the signal mask (C<sigprocmask>) and the signal disposition
		2456	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2457	stopping it again), that is, libev might or might not block the signal,
		2458	and might or might not set or restore the installed signal handler (but
		2459	see C<EVFLAG_NOSIGMASK>).
		2460
		2461	While this does not matter for the signal disposition (libev never
		2462	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2463	C<execve>), this matters for the signal mask: many programs do not expect
		2464	certain signals to be blocked.
		2465
		2466	This means that before calling C<exec> (from the child) you should reset
		2467	the signal mask to whatever "default" you expect (all clear is a good
		2468	choice usually).
		2469
		2470	The simplest way to ensure that the signal mask is reset in the child is
		2471	to install a fork handler with C<pthread_atfork> that resets it. That will
		2472	catch fork calls done by libraries (such as the libc) as well.
		2473
		2474	In current versions of libev, the signal will not be blocked indefinitely
		2475	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2476	the window of opportunity for problems, it will not go away, as libev
		2477	I<has> to modify the signal mask, at least temporarily.
		2478
		2479	So I can't stress this enough: I<If you do not reset your signal mask when
		2480	you expect it to be empty, you have a race condition in your code>. This
		2481	is not a libev-specific thing, this is true for most event libraries.
		2482
		2483	=head3 The special problem of threads signal handling
		2484
		2485	POSIX threads has problematic signal handling semantics, specifically,
		2486	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2487	threads in a process block signals, which is hard to achieve.
		2488
		2489	When you want to use sigwait (or mix libev signal handling with your own
		2490	for the same signals), you can tackle this problem by globally blocking
		2491	all signals before creating any threads (or creating them with a fully set
		2492	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2493	loops. Then designate one thread as "signal receiver thread" which handles
		2494	these signals. You can pass on any signals that libev might be interested
		2495	in by calling C<ev_feed_signal>.
1535		2496
1536	=head3 Watcher-Specific Functions and Data Members	2497	=head3 Watcher-Specific Functions and Data Members
1537		2498
1538	=over 4	2499	=over 4
1539		2500
…		…
1550		2511
1551	=back	2512	=back
1552		2513
1553	=head3 Examples	2514	=head3 Examples
1554		2515
1555	Example: Try to exit cleanly on SIGINT and SIGTERM.	2516	Example: Try to exit cleanly on SIGINT.
1556		2517
1557	static void	2518	static void
1558	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2519	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1559	{	2520	{
1560	ev_unloop (loop, EVUNLOOP_ALL);	2521	ev_break (loop, EVBREAK_ALL);
1561	}	2522	}
1562		2523
1563	struct ev_signal signal_watcher;	2524	ev_signal signal_watcher;
1564	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2525	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1565	ev_signal_start (loop, &sigint_cb);	2526	ev_signal_start (loop, &signal_watcher);
1566		2527
1567		2528
1568	=head2 C<ev_child> - watch out for process status changes	2529	=head2 C<ev_child> - watch out for process status changes
1569		2530
1570	Child watchers trigger when your process receives a SIGCHLD in response to	2531	Child watchers trigger when your process receives a SIGCHLD in response to
1571	some child status changes (most typically when a child of yours dies). It	2532	some child status changes (most typically when a child of yours dies or
1572	is permissible to install a child watcher I<after> the child has been	2533	exits). It is permissible to install a child watcher I<after> the child
1573	forked (which implies it might have already exited), as long as the event	2534	has been forked (which implies it might have already exited), as long
1574	loop isn't entered (or is continued from a watcher).	2535	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2536	forking and then immediately registering a watcher for the child is fine,
		2537	but forking and registering a watcher a few event loop iterations later or
		2538	in the next callback invocation is not.
1575		2539
1576	Only the default event loop is capable of handling signals, and therefore	2540	Only the default event loop is capable of handling signals, and therefore
1577	you can only register child watchers in the default event loop.	2541	you can only register child watchers in the default event loop.
1578		2542
		2543	Due to some design glitches inside libev, child watchers will always be
		2544	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2545	libev)
		2546
1579	=head3 Process Interaction	2547	=head3 Process Interaction
1580		2548
1581	Libev grabs C<SIGCHLD> as soon as the default event loop is	2549	Libev grabs C<SIGCHLD> as soon as the default event loop is
1582	initialised. This is necessary to guarantee proper behaviour even if	2550	initialised. This is necessary to guarantee proper behaviour even if the
1583	the first child watcher is started after the child exits. The occurrence	2551	first child watcher is started after the child exits. The occurrence
1584	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2552	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1585	synchronously as part of the event loop processing. Libev always reaps all	2553	synchronously as part of the event loop processing. Libev always reaps all
1586	children, even ones not watched.	2554	children, even ones not watched.
1587		2555
1588	=head3 Overriding the Built-In Processing	2556	=head3 Overriding the Built-In Processing
…		…
1598	=head3 Stopping the Child Watcher	2566	=head3 Stopping the Child Watcher
1599		2567
1600	Currently, the child watcher never gets stopped, even when the	2568	Currently, the child watcher never gets stopped, even when the
1601	child terminates, so normally one needs to stop the watcher in the	2569	child terminates, so normally one needs to stop the watcher in the
1602	callback. Future versions of libev might stop the watcher automatically	2570	callback. Future versions of libev might stop the watcher automatically
1603	when a child exit is detected.	2571	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2572	problem).
1604		2573
1605	=head3 Watcher-Specific Functions and Data Members	2574	=head3 Watcher-Specific Functions and Data Members
1606		2575
1607	=over 4	2576	=over 4
1608		2577
…		…
1640	its completion.	2609	its completion.
1641		2610
1642	ev_child cw;	2611	ev_child cw;
1643		2612
1644	static void	2613	static void
1645	child_cb (EV_P_ struct ev_child *w, int revents)	2614	child_cb (EV_P_ ev_child *w, int revents)
1646	{	2615	{
1647	ev_child_stop (EV_A_ w);	2616	ev_child_stop (EV_A_ w);
1648	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2617	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1649	}	2618	}
1650		2619
…		…
1665		2634
1666		2635
1667	=head2 C<ev_stat> - did the file attributes just change?	2636	=head2 C<ev_stat> - did the file attributes just change?
1668		2637
1669	This watches a file system path for attribute changes. That is, it calls	2638	This watches a file system path for attribute changes. That is, it calls
1670	C<stat> regularly (or when the OS says it changed) and sees if it changed	2639	C<stat> on that path in regular intervals (or when the OS says it changed)
1671	compared to the last time, invoking the callback if it did.	2640	and sees if it changed compared to the last time, invoking the callback
		2641	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2642	happen after the watcher has been started will be reported.
1672		2643
1673	The path does not need to exist: changing from "path exists" to "path does	2644	The path does not need to exist: changing from "path exists" to "path does
1674	not exist" is a status change like any other. The condition "path does	2645	not exist" is a status change like any other. The condition "path does not
1675	not exist" is signified by the C<st_nlink> field being zero (which is	2646	exist" (or more correctly "path cannot be stat'ed") is signified by the
1676	otherwise always forced to be at least one) and all the other fields of	2647	C<st_nlink> field being zero (which is otherwise always forced to be at
1677	the stat buffer having unspecified contents.	2648	least one) and all the other fields of the stat buffer having unspecified
		2649	contents.
1678		2650
1679	The path I<should> be absolute and I<must not> end in a slash. If it is	2651	The path I<must not> end in a slash or contain special components such as
		2652	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1680	relative and your working directory changes, the behaviour is undefined.	2653	your working directory changes, then the behaviour is undefined.
1681		2654
1682	Since there is no standard to do this, the portable implementation simply	2655	Since there is no portable change notification interface available, the
1683	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2656	portable implementation simply calls C<stat(2)> regularly on the path
1684	can specify a recommended polling interval for this case. If you specify	2657	to see if it changed somehow. You can specify a recommended polling
1685	a polling interval of C<0> (highly recommended!) then a I<suitable,	2658	interval for this case. If you specify a polling interval of C<0> (highly
1686	unspecified default> value will be used (which you can expect to be around	2659	recommended!) then a I<suitable, unspecified default> value will be used
1687	five seconds, although this might change dynamically). Libev will also	2660	(which you can expect to be around five seconds, although this might
1688	impose a minimum interval which is currently around C<0.1>, but thats	2661	change dynamically). Libev will also impose a minimum interval which is
1689	usually overkill.	2662	currently around C<0.1>, but that's usually overkill.
1690		2663
1691	This watcher type is not meant for massive numbers of stat watchers,	2664	This watcher type is not meant for massive numbers of stat watchers,
1692	as even with OS-supported change notifications, this can be	2665	as even with OS-supported change notifications, this can be
1693	resource-intensive.	2666	resource-intensive.
1694		2667
1695	At the time of this writing, only the Linux inotify interface is	2668	At the time of this writing, the only OS-specific interface implemented
1696	implemented (implementing kqueue support is left as an exercise for the	2669	is the Linux inotify interface (implementing kqueue support is left as an
1697	reader, note, however, that the author sees no way of implementing ev_stat	2670	exercise for the reader. Note, however, that the author sees no way of
1698	semantics with kqueue). Inotify will be used to give hints only and should	2671	implementing C<ev_stat> semantics with kqueue, except as a hint).
1699	not change the semantics of C<ev_stat> watchers, which means that libev
1700	sometimes needs to fall back to regular polling again even with inotify,
1701	but changes are usually detected immediately, and if the file exists there
1702	will be no polling.
1703		2672
1704	=head3 ABI Issues (Largefile Support)	2673	=head3 ABI Issues (Largefile Support)
1705		2674
1706	Libev by default (unless the user overrides this) uses the default	2675	Libev by default (unless the user overrides this) uses the default
1707	compilation environment, which means that on systems with large file	2676	compilation environment, which means that on systems with large file
1708	support disabled by default, you get the 32 bit version of the stat	2677	support disabled by default, you get the 32 bit version of the stat
1709	structure. When using the library from programs that change the ABI to	2678	structure. When using the library from programs that change the ABI to
1710	use 64 bit file offsets the programs will fail. In that case you have to	2679	use 64 bit file offsets the programs will fail. In that case you have to
1711	compile libev with the same flags to get binary compatibility. This is	2680	compile libev with the same flags to get binary compatibility. This is
1712	obviously the case with any flags that change the ABI, but the problem is	2681	obviously the case with any flags that change the ABI, but the problem is
1713	most noticeably disabled with ev_stat and large file support.	2682	most noticeably displayed with ev_stat and large file support.
1714		2683
1715	The solution for this is to lobby your distribution maker to make large	2684	The solution for this is to lobby your distribution maker to make large
1716	file interfaces available by default (as e.g. FreeBSD does) and not	2685	file interfaces available by default (as e.g. FreeBSD does) and not
1717	optional. Libev cannot simply switch on large file support because it has	2686	optional. Libev cannot simply switch on large file support because it has
1718	to exchange stat structures with application programs compiled using the	2687	to exchange stat structures with application programs compiled using the
1719	default compilation environment.	2688	default compilation environment.
1720		2689
1721	=head3 Inotify	2690	=head3 Inotify and Kqueue
1722		2691
1723	When C<inotify (7)> support has been compiled into libev (generally only	2692	When C<inotify (7)> support has been compiled into libev and present at
1724	available on Linux) and present at runtime, it will be used to speed up	2693	runtime, it will be used to speed up change detection where possible. The
1725	change detection where possible. The inotify descriptor will be created lazily	2694	inotify descriptor will be created lazily when the first C<ev_stat>
1726	when the first C<ev_stat> watcher is being started.	2695	watcher is being started.
1727		2696
1728	Inotify presence does not change the semantics of C<ev_stat> watchers	2697	Inotify presence does not change the semantics of C<ev_stat> watchers
1729	except that changes might be detected earlier, and in some cases, to avoid	2698	except that changes might be detected earlier, and in some cases, to avoid
1730	making regular C<stat> calls. Even in the presence of inotify support	2699	making regular C<stat> calls. Even in the presence of inotify support
1731	there are many cases where libev has to resort to regular C<stat> polling.	2700	there are many cases where libev has to resort to regular C<stat> polling,
		2701	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2702	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2703	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2704	xfs are fully working) libev usually gets away without polling.
1732		2705
1733	(There is no support for kqueue, as apparently it cannot be used to	2706	There is no support for kqueue, as apparently it cannot be used to
1734	implement this functionality, due to the requirement of having a file	2707	implement this functionality, due to the requirement of having a file
1735	descriptor open on the object at all times).	2708	descriptor open on the object at all times, and detecting renames, unlinks
		2709	etc. is difficult.
		2710
		2711	=head3 C<stat ()> is a synchronous operation
		2712
		2713	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2714	the process. The exception are C<ev_stat> watchers - those call C<stat
		2715	()>, which is a synchronous operation.
		2716
		2717	For local paths, this usually doesn't matter: unless the system is very
		2718	busy or the intervals between stat's are large, a stat call will be fast,
		2719	as the path data is usually in memory already (except when starting the
		2720	watcher).
		2721
		2722	For networked file systems, calling C<stat ()> can block an indefinite
		2723	time due to network issues, and even under good conditions, a stat call
		2724	often takes multiple milliseconds.
		2725
		2726	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2727	paths, although this is fully supported by libev.
1736		2728
1737	=head3 The special problem of stat time resolution	2729	=head3 The special problem of stat time resolution
1738		2730
1739	The C<stat ()> system call only supports full-second resolution portably, and	2731	The C<stat ()> system call only supports full-second resolution portably,
1740	even on systems where the resolution is higher, many file systems still	2732	and even on systems where the resolution is higher, most file systems
1741	only support whole seconds.	2733	still only support whole seconds.
1742		2734
1743	That means that, if the time is the only thing that changes, you can	2735	That means that, if the time is the only thing that changes, you can
1744	easily miss updates: on the first update, C<ev_stat> detects a change and	2736	easily miss updates: on the first update, C<ev_stat> detects a change and
1745	calls your callback, which does something. When there is another update	2737	calls your callback, which does something. When there is another update
1746	within the same second, C<ev_stat> will be unable to detect it as the stat	2738	within the same second, C<ev_stat> will be unable to detect unless the
1747	data does not change.	2739	stat data does change in other ways (e.g. file size).
1748		2740
1749	The solution to this is to delay acting on a change for slightly more	2741	The solution to this is to delay acting on a change for slightly more
1750	than a second (or till slightly after the next full second boundary), using	2742	than a second (or till slightly after the next full second boundary), using
1751	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);	2743	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1752	ev_timer_again (loop, w)>).	2744	ev_timer_again (loop, w)>).
…		…
1772	C<path>. The C<interval> is a hint on how quickly a change is expected to	2764	C<path>. The C<interval> is a hint on how quickly a change is expected to
1773	be detected and should normally be specified as C<0> to let libev choose	2765	be detected and should normally be specified as C<0> to let libev choose
1774	a suitable value. The memory pointed to by C<path> must point to the same	2766	a suitable value. The memory pointed to by C<path> must point to the same
1775	path for as long as the watcher is active.	2767	path for as long as the watcher is active.
1776		2768
1777	The callback will receive C<EV_STAT> when a change was detected, relative	2769	The callback will receive an C<EV_STAT> event when a change was detected,
1778	to the attributes at the time the watcher was started (or the last change	2770	relative to the attributes at the time the watcher was started (or the
1779	was detected).	2771	last change was detected).
1780		2772
1781	=item ev_stat_stat (loop, ev_stat *)	2773	=item ev_stat_stat (loop, ev_stat *)
1782		2774
1783	Updates the stat buffer immediately with new values. If you change the	2775	Updates the stat buffer immediately with new values. If you change the
1784	watched path in your callback, you could call this function to avoid	2776	watched path in your callback, you could call this function to avoid
…		…
1867		2859
1868		2860
1869	=head2 C<ev_idle> - when you've got nothing better to do...	2861	=head2 C<ev_idle> - when you've got nothing better to do...
1870		2862
1871	Idle watchers trigger events when no other events of the same or higher	2863	Idle watchers trigger events when no other events of the same or higher
1872	priority are pending (prepare, check and other idle watchers do not	2864	priority are pending (prepare, check and other idle watchers do not count
1873	count).	2865	as receiving "events").
1874		2866
1875	That is, as long as your process is busy handling sockets or timeouts	2867	That is, as long as your process is busy handling sockets or timeouts
1876	(or even signals, imagine) of the same or higher priority it will not be	2868	(or even signals, imagine) of the same or higher priority it will not be
1877	triggered. But when your process is idle (or only lower-priority watchers	2869	triggered. But when your process is idle (or only lower-priority watchers
1878	are pending), the idle watchers are being called once per event loop	2870	are pending), the idle watchers are being called once per event loop
…		…
1885	Apart from keeping your process non-blocking (which is a useful	2877	Apart from keeping your process non-blocking (which is a useful
1886	effect on its own sometimes), idle watchers are a good place to do	2878	effect on its own sometimes), idle watchers are a good place to do
1887	"pseudo-background processing", or delay processing stuff to after the	2879	"pseudo-background processing", or delay processing stuff to after the
1888	event loop has handled all outstanding events.	2880	event loop has handled all outstanding events.
1889		2881
		2882	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2883
		2884	As long as there is at least one active idle watcher, libev will never
		2885	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2886	For this to work, the idle watcher doesn't need to be invoked at all - the
		2887	lowest priority will do.
		2888
		2889	This mode of operation can be useful together with an C<ev_check> watcher,
		2890	to do something on each event loop iteration - for example to balance load
		2891	between different connections.
		2892
		2893	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2894	example.
		2895
1890	=head3 Watcher-Specific Functions and Data Members	2896	=head3 Watcher-Specific Functions and Data Members
1891		2897
1892	=over 4	2898	=over 4
1893		2899
1894	=item ev_idle_init (ev_signal *, callback)	2900	=item ev_idle_init (ev_idle *, callback)
1895		2901
1896	Initialises and configures the idle watcher - it has no parameters of any	2902	Initialises and configures the idle watcher - it has no parameters of any
1897	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2903	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1898	believe me.	2904	believe me.
1899		2905
…		…
1903		2909
1904	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2910	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1905	callback, free it. Also, use no error checking, as usual.	2911	callback, free it. Also, use no error checking, as usual.
1906		2912
1907	static void	2913	static void
1908	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2914	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1909	{	2915	{
		2916	// stop the watcher
		2917	ev_idle_stop (loop, w);
		2918
		2919	// now we can free it
1910	free (w);	2920	free (w);
		2921
1911	// now do something you wanted to do when the program has	2922	// now do something you wanted to do when the program has
1912	// no longer anything immediate to do.	2923	// no longer anything immediate to do.
1913	}	2924	}
1914		2925
1915	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2926	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1916	ev_idle_init (idle_watcher, idle_cb);	2927	ev_idle_init (idle_watcher, idle_cb);
1917	ev_idle_start (loop, idle_cb);	2928	ev_idle_start (loop, idle_watcher);
1918		2929
1919		2930
1920	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2931	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1921		2932
1922	Prepare and check watchers are usually (but not always) used in tandem:	2933	Prepare and check watchers are often (but not always) used in pairs:
1923	prepare watchers get invoked before the process blocks and check watchers	2934	prepare watchers get invoked before the process blocks and check watchers
1924	afterwards.	2935	afterwards.
1925		2936
1926	You I<must not> call C<ev_loop> or similar functions that enter	2937	You I<must not> call C<ev_run> (or similar functions that enter the
1927	the current event loop from either C<ev_prepare> or C<ev_check>	2938	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
1928	watchers. Other loops than the current one are fine, however. The	2939	C<ev_check> watchers. Other loops than the current one are fine,
1929	rationale behind this is that you do not need to check for recursion in	2940	however. The rationale behind this is that you do not need to check
1930	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2941	for recursion in those watchers, i.e. the sequence will always be
1931	C<ev_check> so if you have one watcher of each kind they will always be	2942	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
1932	called in pairs bracketing the blocking call.	2943	kind they will always be called in pairs bracketing the blocking call.
1933		2944
1934	Their main purpose is to integrate other event mechanisms into libev and	2945	Their main purpose is to integrate other event mechanisms into libev and
1935	their use is somewhat advanced. This could be used, for example, to track	2946	their use is somewhat advanced. They could be used, for example, to track
1936	variable changes, implement your own watchers, integrate net-snmp or a	2947	variable changes, implement your own watchers, integrate net-snmp or a
1937	coroutine library and lots more. They are also occasionally useful if	2948	coroutine library and lots more. They are also occasionally useful if
1938	you cache some data and want to flush it before blocking (for example,	2949	you cache some data and want to flush it before blocking (for example,
1939	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2950	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1940	watcher).	2951	watcher).
1941		2952
1942	This is done by examining in each prepare call which file descriptors need	2953	This is done by examining in each prepare call which file descriptors
1943	to be watched by the other library, registering C<ev_io> watchers for	2954	need to be watched by the other library, registering C<ev_io> watchers
1944	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2955	for them and starting an C<ev_timer> watcher for any timeouts (many
1945	provide just this functionality). Then, in the check watcher you check for	2956	libraries provide exactly this functionality). Then, in the check watcher,
1946	any events that occurred (by checking the pending status of all watchers	2957	you check for any events that occurred (by checking the pending status
1947	and stopping them) and call back into the library. The I/O and timer	2958	of all watchers and stopping them) and call back into the library. The
1948	callbacks will never actually be called (but must be valid nevertheless,	2959	I/O and timer callbacks will never actually be called (but must be valid
1949	because you never know, you know?).	2960	nevertheless, because you never know, you know?).
1950		2961
1951	As another example, the Perl Coro module uses these hooks to integrate	2962	As another example, the Perl Coro module uses these hooks to integrate
1952	coroutines into libev programs, by yielding to other active coroutines	2963	coroutines into libev programs, by yielding to other active coroutines
1953	during each prepare and only letting the process block if no coroutines	2964	during each prepare and only letting the process block if no coroutines
1954	are ready to run (it's actually more complicated: it only runs coroutines	2965	are ready to run (it's actually more complicated: it only runs coroutines
1955	with priority higher than or equal to the event loop and one coroutine	2966	with priority higher than or equal to the event loop and one coroutine
1956	of lower priority, but only once, using idle watchers to keep the event	2967	of lower priority, but only once, using idle watchers to keep the event
1957	loop from blocking if lower-priority coroutines are active, thus mapping	2968	loop from blocking if lower-priority coroutines are active, thus mapping
1958	low-priority coroutines to idle/background tasks).	2969	low-priority coroutines to idle/background tasks).
1959		2970
1960	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2971	When used for this purpose, it is recommended to give C<ev_check> watchers
1961	priority, to ensure that they are being run before any other watchers	2972	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
		2973	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2974	watchers).
		2975
1962	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2976	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1963	too) should not activate ("feed") events into libev. While libev fully	2977	activate ("feed") events into libev. While libev fully supports this, they
1964	supports this, they might get executed before other C<ev_check> watchers	2978	might get executed before other C<ev_check> watchers did their job. As
1965	did their job. As C<ev_check> watchers are often used to embed other	2979	C<ev_check> watchers are often used to embed other (non-libev) event
1966	(non-libev) event loops those other event loops might be in an unusable	2980	loops those other event loops might be in an unusable state until their
1967	state until their C<ev_check> watcher ran (always remind yourself to	2981	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1968	coexist peacefully with others).	2982	others).
		2983
		2984	=head3 Abusing an C<ev_check> watcher for its side-effect
		2985
		2986	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2987	useful because they are called once per event loop iteration. For
		2988	example, if you want to handle a large number of connections fairly, you
		2989	normally only do a bit of work for each active connection, and if there
		2990	is more work to do, you wait for the next event loop iteration, so other
		2991	connections have a chance of making progress.
		2992
		2993	Using an C<ev_check> watcher is almost enough: it will be called on the
		2994	next event loop iteration. However, that isn't as soon as possible -
		2995	without external events, your C<ev_check> watcher will not be invoked.
		2996
		2997	This is where C<ev_idle> watchers come in handy - all you need is a
		2998	single global idle watcher that is active as long as you have one active
		2999	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3000	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3001	invoked. Neither watcher alone can do that.
1969		3002
1970	=head3 Watcher-Specific Functions and Data Members	3003	=head3 Watcher-Specific Functions and Data Members
1971		3004
1972	=over 4	3005	=over 4
1973		3006
…		…
1975		3008
1976	=item ev_check_init (ev_check *, callback)	3009	=item ev_check_init (ev_check *, callback)
1977		3010
1978	Initialises and configures the prepare or check watcher - they have no	3011	Initialises and configures the prepare or check watcher - they have no
1979	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	3012	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1980	macros, but using them is utterly, utterly and completely pointless.	3013	macros, but using them is utterly, utterly, utterly and completely
		3014	pointless.
1981		3015
1982	=back	3016	=back
1983		3017
1984	=head3 Examples	3018	=head3 Examples
1985		3019
…		…
1998		3032
1999	static ev_io iow [nfd];	3033	static ev_io iow [nfd];
2000	static ev_timer tw;	3034	static ev_timer tw;
2001		3035
2002	static void	3036	static void
2003	io_cb (ev_loop *loop, ev_io *w, int revents)	3037	io_cb (struct ev_loop *loop, ev_io *w, int revents)
2004	{	3038	{
2005	}	3039	}
2006		3040
2007	// create io watchers for each fd and a timer before blocking	3041	// create io watchers for each fd and a timer before blocking
2008	static void	3042	static void
2009	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	3043	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2010	{	3044	{
2011	int timeout = 3600000;	3045	int timeout = 3600000;
2012	struct pollfd fds [nfd];	3046	struct pollfd fds [nfd];
2013	// actual code will need to loop here and realloc etc.	3047	// actual code will need to loop here and realloc etc.
2014	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	3048	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2015		3049
2016	/* the callback is illegal, but won't be called as we stop during check */	3050	/* the callback is illegal, but won't be called as we stop during check */
2017	ev_timer_init (&tw, 0, timeout * 1e-3);	3051	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2018	ev_timer_start (loop, &tw);	3052	ev_timer_start (loop, &tw);
2019		3053
2020	// create one ev_io per pollfd	3054	// create one ev_io per pollfd
2021	for (int i = 0; i < nfd; ++i)	3055	for (int i = 0; i < nfd; ++i)
2022	{	3056	{
…		…
2029	}	3063	}
2030	}	3064	}
2031		3065
2032	// stop all watchers after blocking	3066	// stop all watchers after blocking
2033	static void	3067	static void
2034	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	3068	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2035	{	3069	{
2036	ev_timer_stop (loop, &tw);	3070	ev_timer_stop (loop, &tw);
2037		3071
2038	for (int i = 0; i < nfd; ++i)	3072	for (int i = 0; i < nfd; ++i)
2039	{	3073	{
…		…
2078	}	3112	}
2079		3113
2080	// do not ever call adns_afterpoll	3114	// do not ever call adns_afterpoll
2081		3115
2082	Method 4: Do not use a prepare or check watcher because the module you	3116	Method 4: Do not use a prepare or check watcher because the module you
2083	want to embed is too inflexible to support it. Instead, you can override	3117	want to embed is not flexible enough to support it. Instead, you can
2084	their poll function. The drawback with this solution is that the main	3118	override their poll function. The drawback with this solution is that the
2085	loop is now no longer controllable by EV. The C<Glib::EV> module does	3119	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
2086	this.	3120	this approach, effectively embedding EV as a client into the horrible
		3121	libglib event loop.
2087		3122
2088	static gint	3123	static gint
2089	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	3124	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2090	{	3125	{
2091	int got_events = 0;	3126	int got_events = 0;
…		…
2095		3130
2096	if (timeout >= 0)	3131	if (timeout >= 0)
2097	// create/start timer	3132	// create/start timer
2098		3133
2099	// poll	3134	// poll
2100	ev_loop (EV_A_ 0);	3135	ev_run (EV_A_ 0);
2101		3136
2102	// stop timer again	3137	// stop timer again
2103	if (timeout >= 0)	3138	if (timeout >= 0)
2104	ev_timer_stop (EV_A_ &to);	3139	ev_timer_stop (EV_A_ &to);
2105		3140
…		…
2122	prioritise I/O.	3157	prioritise I/O.
2123		3158
2124	As an example for a bug workaround, the kqueue backend might only support	3159	As an example for a bug workaround, the kqueue backend might only support
2125	sockets on some platform, so it is unusable as generic backend, but you	3160	sockets on some platform, so it is unusable as generic backend, but you
2126	still want to make use of it because you have many sockets and it scales	3161	still want to make use of it because you have many sockets and it scales
2127	so nicely. In this case, you would create a kqueue-based loop and embed it	3162	so nicely. In this case, you would create a kqueue-based loop and embed
2128	into your default loop (which might use e.g. poll). Overall operation will	3163	it into your default loop (which might use e.g. poll). Overall operation
2129	be a bit slower because first libev has to poll and then call kevent, but	3164	will be a bit slower because first libev has to call C<poll> and then
2130	at least you can use both at what they are best.	3165	C<kevent>, but at least you can use both mechanisms for what they are
		3166	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2131		3167
2132	As for prioritising I/O: rarely you have the case where some fds have	3168	As for prioritising I/O: under rare circumstances you have the case where
2133	to be watched and handled very quickly (with low latency), and even	3169	some fds have to be watched and handled very quickly (with low latency),
2134	priorities and idle watchers might have too much overhead. In this case	3170	and even priorities and idle watchers might have too much overhead. In
2135	you would put all the high priority stuff in one loop and all the rest in	3171	this case you would put all the high priority stuff in one loop and all
2136	a second one, and embed the second one in the first.	3172	the rest in a second one, and embed the second one in the first.
2137		3173
2138	As long as the watcher is active, the callback will be invoked every time	3174	As long as the watcher is active, the callback will be invoked every
2139	there might be events pending in the embedded loop. The callback must then	3175	time there might be events pending in the embedded loop. The callback
2140	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3176	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2141	their callbacks (you could also start an idle watcher to give the embedded	3177	sweep and invoke their callbacks (the callback doesn't need to invoke the
2142	loop strictly lower priority for example). You can also set the callback	3178	C<ev_embed_sweep> function directly, it could also start an idle watcher
2143	to C<0>, in which case the embed watcher will automatically execute the	3179	to give the embedded loop strictly lower priority for example).
2144	embedded loop sweep.
2145		3180
2146	As long as the watcher is started it will automatically handle events. The	3181	You can also set the callback to C<0>, in which case the embed watcher
2147	callback will be invoked whenever some events have been handled. You can	3182	will automatically execute the embedded loop sweep whenever necessary.
2148	set the callback to C<0> to avoid having to specify one if you are not
2149	interested in that.
2150		3183
2151	Also, there have not currently been made special provisions for forking:	3184	Fork detection will be handled transparently while the C<ev_embed> watcher
2152	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3185	is active, i.e., the embedded loop will automatically be forked when the
2153	but you will also have to stop and restart any C<ev_embed> watchers	3186	embedding loop forks. In other cases, the user is responsible for calling
2154	yourself.	3187	C<ev_loop_fork> on the embedded loop.
2155		3188
2156	Unfortunately, not all backends are embeddable, only the ones returned by	3189	Unfortunately, not all backends are embeddable: only the ones returned by
2157	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3190	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2158	portable one.	3191	portable one.
2159		3192
2160	So when you want to use this feature you will always have to be prepared	3193	So when you want to use this feature you will always have to be prepared
2161	that you cannot get an embeddable loop. The recommended way to get around	3194	that you cannot get an embeddable loop. The recommended way to get around
2162	this is to have a separate variables for your embeddable loop, try to	3195	this is to have a separate variables for your embeddable loop, try to
2163	create it, and if that fails, use the normal loop for everything.	3196	create it, and if that fails, use the normal loop for everything.
2164		3197
		3198	=head3 C<ev_embed> and fork
		3199
		3200	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3201	automatically be applied to the embedded loop as well, so no special
		3202	fork handling is required in that case. When the watcher is not running,
		3203	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3204	as applicable.
		3205
2165	=head3 Watcher-Specific Functions and Data Members	3206	=head3 Watcher-Specific Functions and Data Members
2166		3207
2167	=over 4	3208	=over 4
2168		3209
2169	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3210	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2170		3211
2171	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3212	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2172		3213
2173	Configures the watcher to embed the given loop, which must be	3214	Configures the watcher to embed the given loop, which must be
2174	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3215	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2175	invoked automatically, otherwise it is the responsibility of the callback	3216	invoked automatically, otherwise it is the responsibility of the callback
2176	to invoke it (it will continue to be called until the sweep has been done,	3217	to invoke it (it will continue to be called until the sweep has been done,
2177	if you do not want that, you need to temporarily stop the embed watcher).	3218	if you do not want that, you need to temporarily stop the embed watcher).
2178		3219
2179	=item ev_embed_sweep (loop, ev_embed *)	3220	=item ev_embed_sweep (loop, ev_embed *)
2180		3221
2181	Make a single, non-blocking sweep over the embedded loop. This works	3222	Make a single, non-blocking sweep over the embedded loop. This works
2182	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3223	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
2183	appropriate way for embedded loops.	3224	appropriate way for embedded loops.
2184		3225
2185	=item struct ev_loop *other [read-only]	3226	=item struct ev_loop *other [read-only]
2186		3227
2187	The embedded event loop.	3228	The embedded event loop.
…		…
2196	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	3237	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2197	used).	3238	used).
2198		3239
2199	struct ev_loop *loop_hi = ev_default_init (0);	3240	struct ev_loop *loop_hi = ev_default_init (0);
2200	struct ev_loop *loop_lo = 0;	3241	struct ev_loop *loop_lo = 0;
2201	struct ev_embed embed;	3242	ev_embed embed;
2202		3243
2203	// see if there is a chance of getting one that works	3244	// see if there is a chance of getting one that works
2204	// (remember that a flags value of 0 means autodetection)	3245	// (remember that a flags value of 0 means autodetection)
2205	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3246	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2206	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3247	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2207	: 0;	3248	: 0;
…		…
2220	kqueue implementation). Store the kqueue/socket-only event loop in	3261	kqueue implementation). Store the kqueue/socket-only event loop in
2221	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3262	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2222		3263
2223	struct ev_loop *loop = ev_default_init (0);	3264	struct ev_loop *loop = ev_default_init (0);
2224	struct ev_loop *loop_socket = 0;	3265	struct ev_loop *loop_socket = 0;
2225	struct ev_embed embed;	3266	ev_embed embed;
2226		3267
2227	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3268	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2228	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3269	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2229	{	3270	{
2230	ev_embed_init (&embed, 0, loop_socket);	3271	ev_embed_init (&embed, 0, loop_socket);
2231	ev_embed_start (loop, &embed);	3272	ev_embed_start (loop, &embed);
…		…
2239		3280
2240	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3281	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2241		3282
2242	Fork watchers are called when a C<fork ()> was detected (usually because	3283	Fork watchers are called when a C<fork ()> was detected (usually because
2243	whoever is a good citizen cared to tell libev about it by calling	3284	whoever is a good citizen cared to tell libev about it by calling
2244	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3285	C<ev_loop_fork>). The invocation is done before the event loop blocks next
2245	event loop blocks next and before C<ev_check> watchers are being called,	3286	and before C<ev_check> watchers are being called, and only in the child
2246	and only in the child after the fork. If whoever good citizen calling	3287	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
2247	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3288	and calls it in the wrong process, the fork handlers will be invoked, too,
2248	handlers will be invoked, too, of course.	3289	of course.
		3290
		3291	=head3 The special problem of life after fork - how is it possible?
		3292
		3293	Most uses of C<fork ()> consist of forking, then some simple calls to set
		3294	up/change the process environment, followed by a call to C<exec()>. This
		3295	sequence should be handled by libev without any problems.
		3296
		3297	This changes when the application actually wants to do event handling
		3298	in the child, or both parent in child, in effect "continuing" after the
		3299	fork.
		3300
		3301	The default mode of operation (for libev, with application help to detect
		3302	forks) is to duplicate all the state in the child, as would be expected
		3303	when I<either> the parent I<or> the child process continues.
		3304
		3305	When both processes want to continue using libev, then this is usually the
		3306	wrong result. In that case, usually one process (typically the parent) is
		3307	supposed to continue with all watchers in place as before, while the other
		3308	process typically wants to start fresh, i.e. without any active watchers.
		3309
		3310	The cleanest and most efficient way to achieve that with libev is to
		3311	simply create a new event loop, which of course will be "empty", and
		3312	use that for new watchers. This has the advantage of not touching more
		3313	memory than necessary, and thus avoiding the copy-on-write, and the
		3314	disadvantage of having to use multiple event loops (which do not support
		3315	signal watchers).
		3316
		3317	When this is not possible, or you want to use the default loop for
		3318	other reasons, then in the process that wants to start "fresh", call
		3319	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3320	Destroying the default loop will "orphan" (not stop) all registered
		3321	watchers, so you have to be careful not to execute code that modifies
		3322	those watchers. Note also that in that case, you have to re-register any
		3323	signal watchers.
2249		3324
2250	=head3 Watcher-Specific Functions and Data Members	3325	=head3 Watcher-Specific Functions and Data Members
2251		3326
2252	=over 4	3327	=over 4
2253		3328
2254	=item ev_fork_init (ev_signal *, callback)	3329	=item ev_fork_init (ev_fork *, callback)
2255		3330
2256	Initialises and configures the fork watcher - it has no parameters of any	3331	Initialises and configures the fork watcher - it has no parameters of any
2257	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3332	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2258	believe me.	3333	really.
2259		3334
2260	=back	3335	=back
2261		3336
2262		3337
		3338	=head2 C<ev_cleanup> - even the best things end
		3339
		3340	Cleanup watchers are called just before the event loop is being destroyed
		3341	by a call to C<ev_loop_destroy>.
		3342
		3343	While there is no guarantee that the event loop gets destroyed, cleanup
		3344	watchers provide a convenient method to install cleanup hooks for your
		3345	program, worker threads and so on - you just to make sure to destroy the
		3346	loop when you want them to be invoked.
		3347
		3348	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3349	all other watchers, they do not keep a reference to the event loop (which
		3350	makes a lot of sense if you think about it). Like all other watchers, you
		3351	can call libev functions in the callback, except C<ev_cleanup_start>.
		3352
		3353	=head3 Watcher-Specific Functions and Data Members
		3354
		3355	=over 4
		3356
		3357	=item ev_cleanup_init (ev_cleanup *, callback)
		3358
		3359	Initialises and configures the cleanup watcher - it has no parameters of
		3360	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3361	pointless, I assure you.
		3362
		3363	=back
		3364
		3365	Example: Register an atexit handler to destroy the default loop, so any
		3366	cleanup functions are called.
		3367
		3368	static void
		3369	program_exits (void)
		3370	{
		3371	ev_loop_destroy (EV_DEFAULT_UC);
		3372	}
		3373
		3374	...
		3375	atexit (program_exits);
		3376
		3377
2263	=head2 C<ev_async> - how to wake up another event loop	3378	=head2 C<ev_async> - how to wake up an event loop
2264		3379
2265	In general, you cannot use an C<ev_loop> from multiple threads or other	3380	In general, you cannot use an C<ev_loop> from multiple threads or other
2266	asynchronous sources such as signal handlers (as opposed to multiple event	3381	asynchronous sources such as signal handlers (as opposed to multiple event
2267	loops - those are of course safe to use in different threads).	3382	loops - those are of course safe to use in different threads).
2268		3383
2269	Sometimes, however, you need to wake up another event loop you do not	3384	Sometimes, however, you need to wake up an event loop you do not control,
2270	control, for example because it belongs to another thread. This is what	3385	for example because it belongs to another thread. This is what C<ev_async>
2271	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3386	watchers do: as long as the C<ev_async> watcher is active, you can signal
2272	can signal it by calling C<ev_async_send>, which is thread- and signal	3387	it by calling C<ev_async_send>, which is thread- and signal safe.
2273	safe.
2274		3388
2275	This functionality is very similar to C<ev_signal> watchers, as signals,	3389	This functionality is very similar to C<ev_signal> watchers, as signals,
2276	too, are asynchronous in nature, and signals, too, will be compressed	3390	too, are asynchronous in nature, and signals, too, will be compressed
2277	(i.e. the number of callback invocations may be less than the number of	3391	(i.e. the number of callback invocations may be less than the number of
2278	C<ev_async_sent> calls).	3392	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
2279		3393	of "global async watchers" by using a watcher on an otherwise unused
2280	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3394	signal, and C<ev_feed_signal> to signal this watcher from another thread,
2281	just the default loop.	3395	even without knowing which loop owns the signal.
2282		3396
2283	=head3 Queueing	3397	=head3 Queueing
2284		3398
2285	C<ev_async> does not support queueing of data in any way. The reason	3399	C<ev_async> does not support queueing of data in any way. The reason
2286	is that the author does not know of a simple (or any) algorithm for a	3400	is that the author does not know of a simple (or any) algorithm for a
2287	multiple-writer-single-reader queue that works in all cases and doesn't	3401	multiple-writer-single-reader queue that works in all cases and doesn't
2288	need elaborate support such as pthreads.	3402	need elaborate support such as pthreads or unportable memory access
		3403	semantics.
2289		3404
2290	That means that if you want to queue data, you have to provide your own	3405	That means that if you want to queue data, you have to provide your own
2291	queue. But at least I can tell you would implement locking around your	3406	queue. But at least I can tell you how to implement locking around your
2292	queue:	3407	queue:
2293		3408
2294	=over 4	3409	=over 4
2295		3410
2296	=item queueing from a signal handler context	3411	=item queueing from a signal handler context
2297		3412
2298	To implement race-free queueing, you simply add to the queue in the signal	3413	To implement race-free queueing, you simply add to the queue in the signal
2299	handler but you block the signal handler in the watcher callback. Here is an example that does that for	3414	handler but you block the signal handler in the watcher callback. Here is
2300	some fictitious SIGUSR1 handler:	3415	an example that does that for some fictitious SIGUSR1 handler:
2301		3416
2302	static ev_async mysig;	3417	static ev_async mysig;
2303		3418
2304	static void	3419	static void
2305	sigusr1_handler (void)	3420	sigusr1_handler (void)
…		…
2371	=over 4	3486	=over 4
2372		3487
2373	=item ev_async_init (ev_async *, callback)	3488	=item ev_async_init (ev_async *, callback)
2374		3489
2375	Initialises and configures the async watcher - it has no parameters of any	3490	Initialises and configures the async watcher - it has no parameters of any
2376	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3491	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2377	believe me.	3492	trust me.
2378		3493
2379	=item ev_async_send (loop, ev_async *)	3494	=item ev_async_send (loop, ev_async *)
2380		3495
2381	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3496	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2382	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3497	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3498	returns.
		3499
2383	C<ev_feed_event>, this call is safe to do in other threads, signal or	3500	Unlike C<ev_feed_event>, this call is safe to do from other threads,
2384	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3501	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
2385	section below on what exactly this means).	3502	embedding section below on what exactly this means).
2386		3503
2387	This call incurs the overhead of a system call only once per loop iteration,	3504	Note that, as with other watchers in libev, multiple events might get
2388	so while the overhead might be noticeable, it doesn't apply to repeated	3505	compressed into a single callback invocation (another way to look at
2389	calls to C<ev_async_send>.	3506	this is that C<ev_async> watchers are level-triggered: they are set on
		3507	C<ev_async_send>, reset when the event loop detects that).
		3508
		3509	This call incurs the overhead of at most one extra system call per event
		3510	loop iteration, if the event loop is blocked, and no syscall at all if
		3511	the event loop (or your program) is processing events. That means that
		3512	repeated calls are basically free (there is no need to avoid calls for
		3513	performance reasons) and that the overhead becomes smaller (typically
		3514	zero) under load.
2390		3515
2391	=item bool = ev_async_pending (ev_async *)	3516	=item bool = ev_async_pending (ev_async *)
2392		3517
2393	Returns a non-zero value when C<ev_async_send> has been called on the	3518	Returns a non-zero value when C<ev_async_send> has been called on the
2394	watcher but the event has not yet been processed (or even noted) by the	3519	watcher but the event has not yet been processed (or even noted) by the
…		…
2397	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3522	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2398	the loop iterates next and checks for the watcher to have become active,	3523	the loop iterates next and checks for the watcher to have become active,
2399	it will reset the flag again. C<ev_async_pending> can be used to very	3524	it will reset the flag again. C<ev_async_pending> can be used to very
2400	quickly check whether invoking the loop might be a good idea.	3525	quickly check whether invoking the loop might be a good idea.
2401		3526
2402	Not that this does I<not> check whether the watcher itself is pending, only	3527	Not that this does I<not> check whether the watcher itself is pending,
2403	whether it has been requested to make this watcher pending.	3528	only whether it has been requested to make this watcher pending: there
		3529	is a time window between the event loop checking and resetting the async
		3530	notification, and the callback being invoked.
2404		3531
2405	=back	3532	=back
2406		3533
2407		3534
2408	=head1 OTHER FUNCTIONS	3535	=head1 OTHER FUNCTIONS
2409		3536
2410	There are some other functions of possible interest. Described. Here. Now.	3537	There are some other functions of possible interest. Described. Here. Now.
2411		3538
2412	=over 4	3539	=over 4
2413		3540
2414	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3541	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
2415		3542
2416	This function combines a simple timer and an I/O watcher, calls your	3543	This function combines a simple timer and an I/O watcher, calls your
2417	callback on whichever event happens first and automatically stop both	3544	callback on whichever event happens first and automatically stops both
2418	watchers. This is useful if you want to wait for a single event on an fd	3545	watchers. This is useful if you want to wait for a single event on an fd
2419	or timeout without having to allocate/configure/start/stop/free one or	3546	or timeout without having to allocate/configure/start/stop/free one or
2420	more watchers yourself.	3547	more watchers yourself.
2421		3548
2422	If C<fd> is less than 0, then no I/O watcher will be started and events	3549	If C<fd> is less than 0, then no I/O watcher will be started and the
2423	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3550	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2424	C<events> set will be created and started.	3551	the given C<fd> and C<events> set will be created and started.
2425		3552
2426	If C<timeout> is less than 0, then no timeout watcher will be	3553	If C<timeout> is less than 0, then no timeout watcher will be
2427	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3554	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2428	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3555	repeat = 0) will be started. C<0> is a valid timeout.
2429	dubious value.
2430		3556
2431	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3557	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2432	passed an C<revents> set like normal event callbacks (a combination of	3558	passed an C<revents> set like normal event callbacks (a combination of
2433	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3559	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2434	value passed to C<ev_once>:	3560	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3561	a timeout and an io event at the same time - you probably should give io
		3562	events precedence.
		3563
		3564	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2435		3565
2436	static void stdin_ready (int revents, void *arg)	3566	static void stdin_ready (int revents, void *arg)
2437	{	3567	{
		3568	if (revents & EV_READ)
		3569	/* stdin might have data for us, joy! */;
2438	if (revents & EV_TIMEOUT)	3570	else if (revents & EV_TIMER)
2439	/* doh, nothing entered */;	3571	/* doh, nothing entered */;
2440	else if (revents & EV_READ)
2441	/* stdin might have data for us, joy! */;
2442	}	3572	}
2443		3573
2444	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3574	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2445		3575
2446	=item ev_feed_event (ev_loop *, watcher *, int revents)
2447
2448	Feeds the given event set into the event loop, as if the specified event
2449	had happened for the specified watcher (which must be a pointer to an
2450	initialised but not necessarily started event watcher).
2451
2452	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3576	=item ev_feed_fd_event (loop, int fd, int revents)
2453		3577
2454	Feed an event on the given fd, as if a file descriptor backend detected	3578	Feed an event on the given fd, as if a file descriptor backend detected
2455	the given events it.	3579	the given events.
2456		3580
2457	=item ev_feed_signal_event (ev_loop *loop, int signum)	3581	=item ev_feed_signal_event (loop, int signum)
2458		3582
2459	Feed an event as if the given signal occurred (C<loop> must be the default	3583	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
2460	loop!).	3584	which is async-safe.
2461		3585
2462	=back	3586	=back
		3587
		3588
		3589	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3590
		3591	This section explains some common idioms that are not immediately
		3592	obvious. Note that examples are sprinkled over the whole manual, and this
		3593	section only contains stuff that wouldn't fit anywhere else.
		3594
		3595	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3596
		3597	Each watcher has, by default, a C<void *data> member that you can read
		3598	or modify at any time: libev will completely ignore it. This can be used
		3599	to associate arbitrary data with your watcher. If you need more data and
		3600	don't want to allocate memory separately and store a pointer to it in that
		3601	data member, you can also "subclass" the watcher type and provide your own
		3602	data:
		3603
		3604	struct my_io
		3605	{
		3606	ev_io io;
		3607	int otherfd;
		3608	void *somedata;
		3609	struct whatever *mostinteresting;
		3610	};
		3611
		3612	...
		3613	struct my_io w;
		3614	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3615
		3616	And since your callback will be called with a pointer to the watcher, you
		3617	can cast it back to your own type:
		3618
		3619	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3620	{
		3621	struct my_io *w = (struct my_io *)w_;
		3622	...
		3623	}
		3624
		3625	More interesting and less C-conformant ways of casting your callback
		3626	function type instead have been omitted.
		3627
		3628	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3629
		3630	Another common scenario is to use some data structure with multiple
		3631	embedded watchers, in effect creating your own watcher that combines
		3632	multiple libev event sources into one "super-watcher":
		3633
		3634	struct my_biggy
		3635	{
		3636	int some_data;
		3637	ev_timer t1;
		3638	ev_timer t2;
		3639	}
		3640
		3641	In this case getting the pointer to C<my_biggy> is a bit more
		3642	complicated: Either you store the address of your C<my_biggy> struct in
		3643	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3644	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3645	real programmers):
		3646
		3647	#include <stddef.h>
		3648
		3649	static void
		3650	t1_cb (EV_P_ ev_timer *w, int revents)
		3651	{
		3652	struct my_biggy big = (struct my_biggy *)
		3653	(((char *)w) - offsetof (struct my_biggy, t1));
		3654	}
		3655
		3656	static void
		3657	t2_cb (EV_P_ ev_timer *w, int revents)
		3658	{
		3659	struct my_biggy big = (struct my_biggy *)
		3660	(((char *)w) - offsetof (struct my_biggy, t2));
		3661	}
		3662
		3663	=head2 AVOIDING FINISHING BEFORE RETURNING
		3664
		3665	Often you have structures like this in event-based programs:
		3666
		3667	callback ()
		3668	{
		3669	free (request);
		3670	}
		3671
		3672	request = start_new_request (..., callback);
		3673
		3674	The intent is to start some "lengthy" operation. The C<request> could be
		3675	used to cancel the operation, or do other things with it.
		3676
		3677	It's not uncommon to have code paths in C<start_new_request> that
		3678	immediately invoke the callback, for example, to report errors. Or you add
		3679	some caching layer that finds that it can skip the lengthy aspects of the
		3680	operation and simply invoke the callback with the result.
		3681
		3682	The problem here is that this will happen I<before> C<start_new_request>
		3683	has returned, so C<request> is not set.
		3684
		3685	Even if you pass the request by some safer means to the callback, you
		3686	might want to do something to the request after starting it, such as
		3687	canceling it, which probably isn't working so well when the callback has
		3688	already been invoked.
		3689
		3690	A common way around all these issues is to make sure that
		3691	C<start_new_request> I<always> returns before the callback is invoked. If
		3692	C<start_new_request> immediately knows the result, it can artificially
		3693	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3694	example, or more sneakily, by reusing an existing (stopped) watcher and
		3695	pushing it into the pending queue:
		3696
		3697	ev_set_cb (watcher, callback);
		3698	ev_feed_event (EV_A_ watcher, 0);
		3699
		3700	This way, C<start_new_request> can safely return before the callback is
		3701	invoked, while not delaying callback invocation too much.
		3702
		3703	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3704
		3705	Often (especially in GUI toolkits) there are places where you have
		3706	I<modal> interaction, which is most easily implemented by recursively
		3707	invoking C<ev_run>.
		3708
		3709	This brings the problem of exiting - a callback might want to finish the
		3710	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3711	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3712	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3713	other combination: In these cases, a simple C<ev_break> will not work.
		3714
		3715	The solution is to maintain "break this loop" variable for each C<ev_run>
		3716	invocation, and use a loop around C<ev_run> until the condition is
		3717	triggered, using C<EVRUN_ONCE>:
		3718
		3719	// main loop
		3720	int exit_main_loop = 0;
		3721
		3722	while (!exit_main_loop)
		3723	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3724
		3725	// in a modal watcher
		3726	int exit_nested_loop = 0;
		3727
		3728	while (!exit_nested_loop)
		3729	ev_run (EV_A_ EVRUN_ONCE);
		3730
		3731	To exit from any of these loops, just set the corresponding exit variable:
		3732
		3733	// exit modal loop
		3734	exit_nested_loop = 1;
		3735
		3736	// exit main program, after modal loop is finished
		3737	exit_main_loop = 1;
		3738
		3739	// exit both
		3740	exit_main_loop = exit_nested_loop = 1;
		3741
		3742	=head2 THREAD LOCKING EXAMPLE
		3743
		3744	Here is a fictitious example of how to run an event loop in a different
		3745	thread from where callbacks are being invoked and watchers are
		3746	created/added/removed.
		3747
		3748	For a real-world example, see the C<EV::Loop::Async> perl module,
		3749	which uses exactly this technique (which is suited for many high-level
		3750	languages).
		3751
		3752	The example uses a pthread mutex to protect the loop data, a condition
		3753	variable to wait for callback invocations, an async watcher to notify the
		3754	event loop thread and an unspecified mechanism to wake up the main thread.
		3755
		3756	First, you need to associate some data with the event loop:
		3757
		3758	typedef struct {
		3759	mutex_t lock; /* global loop lock */
		3760	ev_async async_w;
		3761	thread_t tid;
		3762	cond_t invoke_cv;
		3763	} userdata;
		3764
		3765	void prepare_loop (EV_P)
		3766	{
		3767	// for simplicity, we use a static userdata struct.
		3768	static userdata u;
		3769
		3770	ev_async_init (&u->async_w, async_cb);
		3771	ev_async_start (EV_A_ &u->async_w);
		3772
		3773	pthread_mutex_init (&u->lock, 0);
		3774	pthread_cond_init (&u->invoke_cv, 0);
		3775
		3776	// now associate this with the loop
		3777	ev_set_userdata (EV_A_ u);
		3778	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3779	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3780
		3781	// then create the thread running ev_run
		3782	pthread_create (&u->tid, 0, l_run, EV_A);
		3783	}
		3784
		3785	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3786	solely to wake up the event loop so it takes notice of any new watchers
		3787	that might have been added:
		3788
		3789	static void
		3790	async_cb (EV_P_ ev_async *w, int revents)
		3791	{
		3792	// just used for the side effects
		3793	}
		3794
		3795	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3796	protecting the loop data, respectively.
		3797
		3798	static void
		3799	l_release (EV_P)
		3800	{
		3801	userdata *u = ev_userdata (EV_A);
		3802	pthread_mutex_unlock (&u->lock);
		3803	}
		3804
		3805	static void
		3806	l_acquire (EV_P)
		3807	{
		3808	userdata *u = ev_userdata (EV_A);
		3809	pthread_mutex_lock (&u->lock);
		3810	}
		3811
		3812	The event loop thread first acquires the mutex, and then jumps straight
		3813	into C<ev_run>:
		3814
		3815	void *
		3816	l_run (void *thr_arg)
		3817	{
		3818	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3819
		3820	l_acquire (EV_A);
		3821	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3822	ev_run (EV_A_ 0);
		3823	l_release (EV_A);
		3824
		3825	return 0;
		3826	}
		3827
		3828	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3829	signal the main thread via some unspecified mechanism (signals? pipe
		3830	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3831	have been called (in a while loop because a) spurious wakeups are possible
		3832	and b) skipping inter-thread-communication when there are no pending
		3833	watchers is very beneficial):
		3834
		3835	static void
		3836	l_invoke (EV_P)
		3837	{
		3838	userdata *u = ev_userdata (EV_A);
		3839
		3840	while (ev_pending_count (EV_A))
		3841	{
		3842	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3843	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3844	}
		3845	}
		3846
		3847	Now, whenever the main thread gets told to invoke pending watchers, it
		3848	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3849	thread to continue:
		3850
		3851	static void
		3852	real_invoke_pending (EV_P)
		3853	{
		3854	userdata *u = ev_userdata (EV_A);
		3855
		3856	pthread_mutex_lock (&u->lock);
		3857	ev_invoke_pending (EV_A);
		3858	pthread_cond_signal (&u->invoke_cv);
		3859	pthread_mutex_unlock (&u->lock);
		3860	}
		3861
		3862	Whenever you want to start/stop a watcher or do other modifications to an
		3863	event loop, you will now have to lock:
		3864
		3865	ev_timer timeout_watcher;
		3866	userdata *u = ev_userdata (EV_A);
		3867
		3868	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3869
		3870	pthread_mutex_lock (&u->lock);
		3871	ev_timer_start (EV_A_ &timeout_watcher);
		3872	ev_async_send (EV_A_ &u->async_w);
		3873	pthread_mutex_unlock (&u->lock);
		3874
		3875	Note that sending the C<ev_async> watcher is required because otherwise
		3876	an event loop currently blocking in the kernel will have no knowledge
		3877	about the newly added timer. By waking up the loop it will pick up any new
		3878	watchers in the next event loop iteration.
		3879
		3880	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3881
		3882	While the overhead of a callback that e.g. schedules a thread is small, it
		3883	is still an overhead. If you embed libev, and your main usage is with some
		3884	kind of threads or coroutines, you might want to customise libev so that
		3885	doesn't need callbacks anymore.
		3886
		3887	Imagine you have coroutines that you can switch to using a function
		3888	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3889	and that due to some magic, the currently active coroutine is stored in a
		3890	global called C<current_coro>. Then you can build your own "wait for libev
		3891	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3892	the differing C<;> conventions):
		3893
		3894	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3895	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3896
		3897	That means instead of having a C callback function, you store the
		3898	coroutine to switch to in each watcher, and instead of having libev call
		3899	your callback, you instead have it switch to that coroutine.
		3900
		3901	A coroutine might now wait for an event with a function called
		3902	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3903	matter when, or whether the watcher is active or not when this function is
		3904	called):
		3905
		3906	void
		3907	wait_for_event (ev_watcher *w)
		3908	{
		3909	ev_set_cb (w, current_coro);
		3910	switch_to (libev_coro);
		3911	}
		3912
		3913	That basically suspends the coroutine inside C<wait_for_event> and
		3914	continues the libev coroutine, which, when appropriate, switches back to
		3915	this or any other coroutine.
		3916
		3917	You can do similar tricks if you have, say, threads with an event queue -
		3918	instead of storing a coroutine, you store the queue object and instead of
		3919	switching to a coroutine, you push the watcher onto the queue and notify
		3920	any waiters.
		3921
		3922	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3923	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3924
		3925	// my_ev.h
		3926	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3927	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3928	#include "../libev/ev.h"
		3929
		3930	// my_ev.c
		3931	#define EV_H "my_ev.h"
		3932	#include "../libev/ev.c"
		3933
		3934	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3935	F<my_ev.c> into your project. When properly specifying include paths, you
		3936	can even use F<ev.h> as header file name directly.
2463		3937
2464		3938
2465	=head1 LIBEVENT EMULATION	3939	=head1 LIBEVENT EMULATION
2466		3940
2467	Libev offers a compatibility emulation layer for libevent. It cannot	3941	Libev offers a compatibility emulation layer for libevent. It cannot
2468	emulate the internals of libevent, so here are some usage hints:	3942	emulate the internals of libevent, so here are some usage hints:
2469		3943
2470	=over 4	3944	=over 4
		3945
		3946	=item * Only the libevent-1.4.1-beta API is being emulated.
		3947
		3948	This was the newest libevent version available when libev was implemented,
		3949	and is still mostly unchanged in 2010.
2471		3950
2472	=item * Use it by including <event.h>, as usual.	3951	=item * Use it by including <event.h>, as usual.
2473		3952
2474	=item * The following members are fully supported: ev_base, ev_callback,	3953	=item * The following members are fully supported: ev_base, ev_callback,
2475	ev_arg, ev_fd, ev_res, ev_events.	3954	ev_arg, ev_fd, ev_res, ev_events.
…		…
2481	=item * Priorities are not currently supported. Initialising priorities	3960	=item * Priorities are not currently supported. Initialising priorities
2482	will fail and all watchers will have the same priority, even though there	3961	will fail and all watchers will have the same priority, even though there
2483	is an ev_pri field.	3962	is an ev_pri field.
2484		3963
2485	=item * In libevent, the last base created gets the signals, in libev, the	3964	=item * In libevent, the last base created gets the signals, in libev, the
2486	first base created (== the default loop) gets the signals.	3965	base that registered the signal gets the signals.
2487		3966
2488	=item * Other members are not supported.	3967	=item * Other members are not supported.
2489		3968
2490	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3969	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2491	to use the libev header file and library.	3970	to use the libev header file and library.
2492		3971
2493	=back	3972	=back
2494		3973
2495	=head1 C++ SUPPORT	3974	=head1 C++ SUPPORT
		3975
		3976	=head2 C API
		3977
		3978	The normal C API should work fine when used from C++: both ev.h and the
		3979	libev sources can be compiled as C++. Therefore, code that uses the C API
		3980	will work fine.
		3981
		3982	Proper exception specifications might have to be added to callbacks passed
		3983	to libev: exceptions may be thrown only from watcher callbacks, all
		3984	other callbacks (allocator, syserr, loop acquire/release and periodic
		3985	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3986	()> specification. If you have code that needs to be compiled as both C
		3987	and C++ you can use the C<EV_THROW> macro for this:
		3988
		3989	static void
		3990	fatal_error (const char *msg) EV_THROW
		3991	{
		3992	perror (msg);
		3993	abort ();
		3994	}
		3995
		3996	...
		3997	ev_set_syserr_cb (fatal_error);
		3998
		3999	The only API functions that can currently throw exceptions are C<ev_run>,
		4000	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4001	because it runs cleanup watchers).
		4002
		4003	Throwing exceptions in watcher callbacks is only supported if libev itself
		4004	is compiled with a C++ compiler or your C and C++ environments allow
		4005	throwing exceptions through C libraries (most do).
		4006
		4007	=head2 C++ API
2496		4008
2497	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4009	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2498	you to use some convenience methods to start/stop watchers and also change	4010	you to use some convenience methods to start/stop watchers and also change
2499	the callback model to a model using method callbacks on objects.	4011	the callback model to a model using method callbacks on objects.
2500		4012
2501	To use it,	4013	To use it,
2502		4014
2503	#include <ev++.h>	4015	#include <ev++.h>
2504		4016
2505	This automatically includes F<ev.h> and puts all of its definitions (many	4017	This automatically includes F<ev.h> and puts all of its definitions (many
2506	of them macros) into the global namespace. All C++ specific things are	4018	of them macros) into the global namespace. All C++ specific things are
2507	put into the C<ev> namespace. It should support all the same embedding	4019	put into the C<ev> namespace. It should support all the same embedding
…		…
2510	Care has been taken to keep the overhead low. The only data member the C++	4022	Care has been taken to keep the overhead low. The only data member the C++
2511	classes add (compared to plain C-style watchers) is the event loop pointer	4023	classes add (compared to plain C-style watchers) is the event loop pointer
2512	that the watcher is associated with (or no additional members at all if	4024	that the watcher is associated with (or no additional members at all if
2513	you disable C<EV_MULTIPLICITY> when embedding libev).	4025	you disable C<EV_MULTIPLICITY> when embedding libev).
2514		4026
2515	Currently, functions, and static and non-static member functions can be	4027	Currently, functions, static and non-static member functions and classes
2516	used as callbacks. Other types should be easy to add as long as they only	4028	with C<operator ()> can be used as callbacks. Other types should be easy
2517	need one additional pointer for context. If you need support for other	4029	to add as long as they only need one additional pointer for context. If
2518	types of functors please contact the author (preferably after implementing	4030	you need support for other types of functors please contact the author
2519	it).	4031	(preferably after implementing it).
		4032
		4033	For all this to work, your C++ compiler either has to use the same calling
		4034	conventions as your C compiler (for static member functions), or you have
		4035	to embed libev and compile libev itself as C++.
2520		4036
2521	Here is a list of things available in the C<ev> namespace:	4037	Here is a list of things available in the C<ev> namespace:
2522		4038
2523	=over 4	4039	=over 4
2524		4040
…		…
2534	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4050	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
2535		4051
2536	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4052	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
2537	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4053	the same name in the C<ev> namespace, with the exception of C<ev_signal>
2538	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4054	which is called C<ev::sig> to avoid clashes with the C<signal> macro
2539	defines by many implementations.	4055	defined by many implementations.
2540		4056
2541	All of those classes have these methods:	4057	All of those classes have these methods:
2542		4058
2543	=over 4	4059	=over 4
2544		4060
2545	=item ev::TYPE::TYPE ()	4061	=item ev::TYPE::TYPE ()
2546		4062
2547	=item ev::TYPE::TYPE (struct ev_loop *)	4063	=item ev::TYPE::TYPE (loop)
2548		4064
2549	=item ev::TYPE::~TYPE	4065	=item ev::TYPE::~TYPE
2550		4066
2551	The constructor (optionally) takes an event loop to associate the watcher	4067	The constructor (optionally) takes an event loop to associate the watcher
2552	with. If it is omitted, it will use C<EV_DEFAULT>.	4068	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2584		4100
2585	myclass obj;	4101	myclass obj;
2586	ev::io iow;	4102	ev::io iow;
2587	iow.set <myclass, &myclass::io_cb> (&obj);	4103	iow.set <myclass, &myclass::io_cb> (&obj);
2588		4104
		4105	=item w->set (object *)
		4106
		4107	This is a variation of a method callback - leaving out the method to call
		4108	will default the method to C<operator ()>, which makes it possible to use
		4109	functor objects without having to manually specify the C<operator ()> all
		4110	the time. Incidentally, you can then also leave out the template argument
		4111	list.
		4112
		4113	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4114	int revents)>.
		4115
		4116	See the method-C<set> above for more details.
		4117
		4118	Example: use a functor object as callback.
		4119
		4120	struct myfunctor
		4121	{
		4122	void operator() (ev::io &w, int revents)
		4123	{
		4124	...
		4125	}
		4126	}
		4127
		4128	myfunctor f;
		4129
		4130	ev::io w;
		4131	w.set (&f);
		4132
2589	=item w->set<function> (void *data = 0)	4133	=item w->set<function> (void *data = 0)
2590		4134
2591	Also sets a callback, but uses a static method or plain function as	4135	Also sets a callback, but uses a static method or plain function as
2592	callback. The optional C<data> argument will be stored in the watcher's	4136	callback. The optional C<data> argument will be stored in the watcher's
2593	C<data> member and is free for you to use.	4137	C<data> member and is free for you to use.
2594		4138
2595	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	4139	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2596		4140
2597	See the method-C<set> above for more details.	4141	See the method-C<set> above for more details.
2598		4142
2599	Example:	4143	Example: Use a plain function as callback.
2600		4144
2601	static void io_cb (ev::io &w, int revents) { }	4145	static void io_cb (ev::io &w, int revents) { }
2602	iow.set <io_cb> ();	4146	iow.set <io_cb> ();
2603		4147
2604	=item w->set (struct ev_loop *)	4148	=item w->set (loop)
2605		4149
2606	Associates a different C<struct ev_loop> with this watcher. You can only	4150	Associates a different C<struct ev_loop> with this watcher. You can only
2607	do this when the watcher is inactive (and not pending either).	4151	do this when the watcher is inactive (and not pending either).
2608		4152
2609	=item w->set ([arguments])	4153	=item w->set ([arguments])
2610		4154
2611	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be	4155	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4156	with the same arguments. Either this method or a suitable start method
2612	called at least once. Unlike the C counterpart, an active watcher gets	4157	must be called at least once. Unlike the C counterpart, an active watcher
2613	automatically stopped and restarted when reconfiguring it with this	4158	gets automatically stopped and restarted when reconfiguring it with this
2614	method.	4159	method.
		4160
		4161	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4162	clashing with the C<set (loop)> method.
2615		4163
2616	=item w->start ()	4164	=item w->start ()
2617		4165
2618	Starts the watcher. Note that there is no C<loop> argument, as the	4166	Starts the watcher. Note that there is no C<loop> argument, as the
2619	constructor already stores the event loop.	4167	constructor already stores the event loop.
2620		4168
		4169	=item w->start ([arguments])
		4170
		4171	Instead of calling C<set> and C<start> methods separately, it is often
		4172	convenient to wrap them in one call. Uses the same type of arguments as
		4173	the configure C<set> method of the watcher.
		4174
2621	=item w->stop ()	4175	=item w->stop ()
2622		4176
2623	Stops the watcher if it is active. Again, no C<loop> argument.	4177	Stops the watcher if it is active. Again, no C<loop> argument.
2624		4178
2625	=item w->again () (C<ev::timer>, C<ev::periodic> only)	4179	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2637		4191
2638	=back	4192	=back
2639		4193
2640	=back	4194	=back
2641		4195
2642	Example: Define a class with an IO and idle watcher, start one of them in	4196	Example: Define a class with two I/O and idle watchers, start the I/O
2643	the constructor.	4197	watchers in the constructor.
2644		4198
2645	class myclass	4199	class myclass
2646	{	4200	{
2647	ev::io io; void io_cb (ev::io &w, int revents);	4201	ev::io io ; void io_cb (ev::io &w, int revents);
		4202	ev::io io2 ; void io2_cb (ev::io &w, int revents);
2648	ev:idle idle void idle_cb (ev::idle &w, int revents);	4203	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2649		4204
2650	myclass (int fd)	4205	myclass (int fd)
2651	{	4206	{
2652	io .set <myclass, &myclass::io_cb > (this);	4207	io .set <myclass, &myclass::io_cb > (this);
		4208	io2 .set <myclass, &myclass::io2_cb > (this);
2653	idle.set <myclass, &myclass::idle_cb> (this);	4209	idle.set <myclass, &myclass::idle_cb> (this);
2654		4210
2655	io.start (fd, ev::READ);	4211	io.set (fd, ev::WRITE); // configure the watcher
		4212	io.start (); // start it whenever convenient
		4213
		4214	io2.start (fd, ev::READ); // set + start in one call
2656	}	4215	}
2657	};	4216	};
2658		4217
2659		4218
2660	=head1 OTHER LANGUAGE BINDINGS	4219	=head1 OTHER LANGUAGE BINDINGS
…		…
2669	=item Perl	4228	=item Perl
2670		4229
2671	The EV module implements the full libev API and is actually used to test	4230	The EV module implements the full libev API and is actually used to test
2672	libev. EV is developed together with libev. Apart from the EV core module,	4231	libev. EV is developed together with libev. Apart from the EV core module,
2673	there are additional modules that implement libev-compatible interfaces	4232	there are additional modules that implement libev-compatible interfaces
2674	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	4233	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2675	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	4234	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4235	and C<EV::Glib>).
2676		4236
2677	It can be found and installed via CPAN, its homepage is at	4237	It can be found and installed via CPAN, its homepage is at
2678	L<http://software.schmorp.de/pkg/EV>.	4238	L<http://software.schmorp.de/pkg/EV>.
2679		4239
2680	=item Python	4240	=item Python
2681		4241
2682	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	4242	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2683	seems to be quite complete and well-documented. Note, however, that the	4243	seems to be quite complete and well-documented.
2684	patch they require for libev is outright dangerous as it breaks the ABI
2685	for everybody else, and therefore, should never be applied in an installed
2686	libev (if python requires an incompatible ABI then it needs to embed
2687	libev).
2688		4244
2689	=item Ruby	4245	=item Ruby
2690		4246
2691	Tony Arcieri has written a ruby extension that offers access to a subset	4247	Tony Arcieri has written a ruby extension that offers access to a subset
2692	of the libev API and adds file handle abstractions, asynchronous DNS and	4248	of the libev API and adds file handle abstractions, asynchronous DNS and
2693	more on top of it. It can be found via gem servers. Its homepage is at	4249	more on top of it. It can be found via gem servers. Its homepage is at
2694	L<http://rev.rubyforge.org/>.	4250	L<http://rev.rubyforge.org/>.
2695		4251
		4252	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4253	makes rev work even on mingw.
		4254
		4255	=item Haskell
		4256
		4257	A haskell binding to libev is available at
		4258	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4259
2696	=item D	4260	=item D
2697		4261
2698	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4262	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2699	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4263	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4264
		4265	=item Ocaml
		4266
		4267	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4268	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4269
		4270	=item Lua
		4271
		4272	Brian Maher has written a partial interface to libev for lua (at the
		4273	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4274	L<http://github.com/brimworks/lua-ev>.
		4275
		4276	=item Javascript
		4277
		4278	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4279
		4280	=item Others
		4281
		4282	There are others, and I stopped counting.
2700		4283
2701	=back	4284	=back
2702		4285
2703		4286
2704	=head1 MACRO MAGIC	4287	=head1 MACRO MAGIC
…		…
2718	loop argument"). The C<EV_A> form is used when this is the sole argument,	4301	loop argument"). The C<EV_A> form is used when this is the sole argument,
2719	C<EV_A_> is used when other arguments are following. Example:	4302	C<EV_A_> is used when other arguments are following. Example:
2720		4303
2721	ev_unref (EV_A);	4304	ev_unref (EV_A);
2722	ev_timer_add (EV_A_ watcher);	4305	ev_timer_add (EV_A_ watcher);
2723	ev_loop (EV_A_ 0);	4306	ev_run (EV_A_ 0);
2724		4307
2725	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4308	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2726	which is often provided by the following macro.	4309	which is often provided by the following macro.
2727		4310
2728	=item C<EV_P>, C<EV_P_>	4311	=item C<EV_P>, C<EV_P_>
…		…
2741	suitable for use with C<EV_A>.	4324	suitable for use with C<EV_A>.
2742		4325
2743	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4326	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2744		4327
2745	Similar to the other two macros, this gives you the value of the default	4328	Similar to the other two macros, this gives you the value of the default
2746	loop, if multiple loops are supported ("ev loop default").	4329	loop, if multiple loops are supported ("ev loop default"). The default loop
		4330	will be initialised if it isn't already initialised.
		4331
		4332	For non-multiplicity builds, these macros do nothing, so you always have
		4333	to initialise the loop somewhere.
2747		4334
2748	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4335	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
2749		4336
2750	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4337	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
2751	default loop has been initialised (C<UC> == unchecked). Their behaviour	4338	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
2768	}	4355	}
2769		4356
2770	ev_check check;	4357	ev_check check;
2771	ev_check_init (&check, check_cb);	4358	ev_check_init (&check, check_cb);
2772	ev_check_start (EV_DEFAULT_ &check);	4359	ev_check_start (EV_DEFAULT_ &check);
2773	ev_loop (EV_DEFAULT_ 0);	4360	ev_run (EV_DEFAULT_ 0);
2774		4361
2775	=head1 EMBEDDING	4362	=head1 EMBEDDING
2776		4363
2777	Libev can (and often is) directly embedded into host	4364	Libev can (and often is) directly embedded into host
2778	applications. Examples of applications that embed it include the Deliantra	4365	applications. Examples of applications that embed it include the Deliantra
…		…
2805		4392
2806	#define EV_STANDALONE 1	4393	#define EV_STANDALONE 1
2807	#include "ev.h"	4394	#include "ev.h"
2808		4395
2809	Both header files and implementation files can be compiled with a C++	4396	Both header files and implementation files can be compiled with a C++
2810	compiler (at least, thats a stated goal, and breakage will be treated	4397	compiler (at least, that's a stated goal, and breakage will be treated
2811	as a bug).	4398	as a bug).
2812		4399
2813	You need the following files in your source tree, or in a directory	4400	You need the following files in your source tree, or in a directory
2814	in your include path (e.g. in libev/ when using -Ilibev):	4401	in your include path (e.g. in libev/ when using -Ilibev):
2815		4402
…		…
2818	ev_vars.h	4405	ev_vars.h
2819	ev_wrap.h	4406	ev_wrap.h
2820		4407
2821	ev_win32.c required on win32 platforms only	4408	ev_win32.c required on win32 platforms only
2822		4409
2823	ev_select.c only when select backend is enabled (which is enabled by default)	4410	ev_select.c only when select backend is enabled
2824	ev_poll.c only when poll backend is enabled (disabled by default)	4411	ev_poll.c only when poll backend is enabled
2825	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4412	ev_epoll.c only when the epoll backend is enabled
2826	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4413	ev_kqueue.c only when the kqueue backend is enabled
2827	ev_port.c only when the solaris port backend is enabled (disabled by default)	4414	ev_port.c only when the solaris port backend is enabled
2828		4415
2829	F<ev.c> includes the backend files directly when enabled, so you only need	4416	F<ev.c> includes the backend files directly when enabled, so you only need
2830	to compile this single file.	4417	to compile this single file.
2831		4418
2832	=head3 LIBEVENT COMPATIBILITY API	4419	=head3 LIBEVENT COMPATIBILITY API
…		…
2858	libev.m4	4445	libev.m4
2859		4446
2860	=head2 PREPROCESSOR SYMBOLS/MACROS	4447	=head2 PREPROCESSOR SYMBOLS/MACROS
2861		4448
2862	Libev can be configured via a variety of preprocessor symbols you have to	4449	Libev can be configured via a variety of preprocessor symbols you have to
2863	define before including any of its files. The default in the absence of	4450	define before including (or compiling) any of its files. The default in
2864	autoconf is noted for every option.	4451	the absence of autoconf is documented for every option.
		4452
		4453	Symbols marked with "(h)" do not change the ABI, and can have different
		4454	values when compiling libev vs. including F<ev.h>, so it is permissible
		4455	to redefine them before including F<ev.h> without breaking compatibility
		4456	to a compiled library. All other symbols change the ABI, which means all
		4457	users of libev and the libev code itself must be compiled with compatible
		4458	settings.
2865		4459
2866	=over 4	4460	=over 4
2867		4461
		4462	=item EV_COMPAT3 (h)
		4463
		4464	Backwards compatibility is a major concern for libev. This is why this
		4465	release of libev comes with wrappers for the functions and symbols that
		4466	have been renamed between libev version 3 and 4.
		4467
		4468	You can disable these wrappers (to test compatibility with future
		4469	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4470	sources. This has the additional advantage that you can drop the C<struct>
		4471	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4472	typedef in that case.
		4473
		4474	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4475	and in some even more future version the compatibility code will be
		4476	removed completely.
		4477
2868	=item EV_STANDALONE	4478	=item EV_STANDALONE (h)
2869		4479
2870	Must always be C<1> if you do not use autoconf configuration, which	4480	Must always be C<1> if you do not use autoconf configuration, which
2871	keeps libev from including F<config.h>, and it also defines dummy	4481	keeps libev from including F<config.h>, and it also defines dummy
2872	implementations for some libevent functions (such as logging, which is not	4482	implementations for some libevent functions (such as logging, which is not
2873	supported). It will also not define any of the structs usually found in	4483	supported). It will also not define any of the structs usually found in
2874	F<event.h> that are not directly supported by the libev core alone.	4484	F<event.h> that are not directly supported by the libev core alone.
2875		4485
		4486	In standalone mode, libev will still try to automatically deduce the
		4487	configuration, but has to be more conservative.
		4488
		4489	=item EV_USE_FLOOR
		4490
		4491	If defined to be C<1>, libev will use the C<floor ()> function for its
		4492	periodic reschedule calculations, otherwise libev will fall back on a
		4493	portable (slower) implementation. If you enable this, you usually have to
		4494	link against libm or something equivalent. Enabling this when the C<floor>
		4495	function is not available will fail, so the safe default is to not enable
		4496	this.
		4497
2876	=item EV_USE_MONOTONIC	4498	=item EV_USE_MONOTONIC
2877		4499
2878	If defined to be C<1>, libev will try to detect the availability of the	4500	If defined to be C<1>, libev will try to detect the availability of the
2879	monotonic clock option at both compile time and runtime. Otherwise no use	4501	monotonic clock option at both compile time and runtime. Otherwise no
2880	of the monotonic clock option will be attempted. If you enable this, you	4502	use of the monotonic clock option will be attempted. If you enable this,
2881	usually have to link against librt or something similar. Enabling it when	4503	you usually have to link against librt or something similar. Enabling it
2882	the functionality isn't available is safe, though, although you have	4504	when the functionality isn't available is safe, though, although you have
2883	to make sure you link against any libraries where the C<clock_gettime>	4505	to make sure you link against any libraries where the C<clock_gettime>
2884	function is hiding in (often F<-lrt>).	4506	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2885		4507
2886	=item EV_USE_REALTIME	4508	=item EV_USE_REALTIME
2887		4509
2888	If defined to be C<1>, libev will try to detect the availability of the	4510	If defined to be C<1>, libev will try to detect the availability of the
2889	real-time clock option at compile time (and assume its availability at	4511	real-time clock option at compile time (and assume its availability
2890	runtime if successful). Otherwise no use of the real-time clock option will	4512	at runtime if successful). Otherwise no use of the real-time clock
2891	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4513	option will be attempted. This effectively replaces C<gettimeofday>
2892	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4514	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2893	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4515	correctness. See the note about libraries in the description of
		4516	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4517	C<EV_USE_CLOCK_SYSCALL>.
		4518
		4519	=item EV_USE_CLOCK_SYSCALL
		4520
		4521	If defined to be C<1>, libev will try to use a direct syscall instead
		4522	of calling the system-provided C<clock_gettime> function. This option
		4523	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4524	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4525	programs needlessly. Using a direct syscall is slightly slower (in
		4526	theory), because no optimised vdso implementation can be used, but avoids
		4527	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4528	higher, as it simplifies linking (no need for C<-lrt>).
2894		4529
2895	=item EV_USE_NANOSLEEP	4530	=item EV_USE_NANOSLEEP
2896		4531
2897	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4532	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2898	and will use it for delays. Otherwise it will use C<select ()>.	4533	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2914		4549
2915	=item EV_SELECT_USE_FD_SET	4550	=item EV_SELECT_USE_FD_SET
2916		4551
2917	If defined to C<1>, then the select backend will use the system C<fd_set>	4552	If defined to C<1>, then the select backend will use the system C<fd_set>
2918	structure. This is useful if libev doesn't compile due to a missing	4553	structure. This is useful if libev doesn't compile due to a missing
2919	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	4554	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2920	exotic systems. This usually limits the range of file descriptors to some	4555	on exotic systems. This usually limits the range of file descriptors to
2921	low limit such as 1024 or might have other limitations (winsocket only	4556	some low limit such as 1024 or might have other limitations (winsocket
2922	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4557	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2923	influence the size of the C<fd_set> used.	4558	configures the maximum size of the C<fd_set>.
2924		4559
2925	=item EV_SELECT_IS_WINSOCKET	4560	=item EV_SELECT_IS_WINSOCKET
2926		4561
2927	When defined to C<1>, the select backend will assume that	4562	When defined to C<1>, the select backend will assume that
2928	select/socket/connect etc. don't understand file descriptors but	4563	select/socket/connect etc. don't understand file descriptors but
…		…
2930	be used is the winsock select). This means that it will call	4565	be used is the winsock select). This means that it will call
2931	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4566	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2932	it is assumed that all these functions actually work on fds, even	4567	it is assumed that all these functions actually work on fds, even
2933	on win32. Should not be defined on non-win32 platforms.	4568	on win32. Should not be defined on non-win32 platforms.
2934		4569
2935	=item EV_FD_TO_WIN32_HANDLE	4570	=item EV_FD_TO_WIN32_HANDLE(fd)
2936		4571
2937	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4572	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2938	file descriptors to socket handles. When not defining this symbol (the	4573	file descriptors to socket handles. When not defining this symbol (the
2939	default), then libev will call C<_get_osfhandle>, which is usually	4574	default), then libev will call C<_get_osfhandle>, which is usually
2940	correct. In some cases, programs use their own file descriptor management,	4575	correct. In some cases, programs use their own file descriptor management,
2941	in which case they can provide this function to map fds to socket handles.	4576	in which case they can provide this function to map fds to socket handles.
		4577
		4578	=item EV_WIN32_HANDLE_TO_FD(handle)
		4579
		4580	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4581	using the standard C<_open_osfhandle> function. For programs implementing
		4582	their own fd to handle mapping, overwriting this function makes it easier
		4583	to do so. This can be done by defining this macro to an appropriate value.
		4584
		4585	=item EV_WIN32_CLOSE_FD(fd)
		4586
		4587	If programs implement their own fd to handle mapping on win32, then this
		4588	macro can be used to override the C<close> function, useful to unregister
		4589	file descriptors again. Note that the replacement function has to close
		4590	the underlying OS handle.
		4591
		4592	=item EV_USE_WSASOCKET
		4593
		4594	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4595	communication socket, which works better in some environments. Otherwise,
		4596	the normal C<socket> function will be used, which works better in other
		4597	environments.
2942		4598
2943	=item EV_USE_POLL	4599	=item EV_USE_POLL
2944		4600
2945	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4601	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2946	backend. Otherwise it will be enabled on non-win32 platforms. It	4602	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
2982	If defined to be C<1>, libev will compile in support for the Linux inotify	4638	If defined to be C<1>, libev will compile in support for the Linux inotify
2983	interface to speed up C<ev_stat> watchers. Its actual availability will	4639	interface to speed up C<ev_stat> watchers. Its actual availability will
2984	be detected at runtime. If undefined, it will be enabled if the headers	4640	be detected at runtime. If undefined, it will be enabled if the headers
2985	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4641	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2986		4642
		4643	=item EV_NO_SMP
		4644
		4645	If defined to be C<1>, libev will assume that memory is always coherent
		4646	between threads, that is, threads can be used, but threads never run on
		4647	different cpus (or different cpu cores). This reduces dependencies
		4648	and makes libev faster.
		4649
		4650	=item EV_NO_THREADS
		4651
		4652	If defined to be C<1>, libev will assume that it will never be called from
		4653	different threads (that includes signal handlers), which is a stronger
		4654	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4655	libev faster.
		4656
2987	=item EV_ATOMIC_T	4657	=item EV_ATOMIC_T
2988		4658
2989	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4659	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2990	access is atomic with respect to other threads or signal contexts. No such	4660	access is atomic with respect to other threads or signal contexts. No
2991	type is easily found in the C language, so you can provide your own type	4661	such type is easily found in the C language, so you can provide your own
2992	that you know is safe for your purposes. It is used both for signal handler "locking"	4662	type that you know is safe for your purposes. It is used both for signal
2993	as well as for signal and thread safety in C<ev_async> watchers.	4663	handler "locking" as well as for signal and thread safety in C<ev_async>
		4664	watchers.
2994		4665
2995	In the absence of this define, libev will use C<sig_atomic_t volatile>	4666	In the absence of this define, libev will use C<sig_atomic_t volatile>
2996	(from F<signal.h>), which is usually good enough on most platforms.	4667	(from F<signal.h>), which is usually good enough on most platforms.
2997		4668
2998	=item EV_H	4669	=item EV_H (h)
2999		4670
3000	The name of the F<ev.h> header file used to include it. The default if	4671	The name of the F<ev.h> header file used to include it. The default if
3001	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4672	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
3002	used to virtually rename the F<ev.h> header file in case of conflicts.	4673	used to virtually rename the F<ev.h> header file in case of conflicts.
3003		4674
3004	=item EV_CONFIG_H	4675	=item EV_CONFIG_H (h)
3005		4676
3006	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4677	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
3007	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4678	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
3008	C<EV_H>, above.	4679	C<EV_H>, above.
3009		4680
3010	=item EV_EVENT_H	4681	=item EV_EVENT_H (h)
3011		4682
3012	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4683	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
3013	of how the F<event.h> header can be found, the default is C<"event.h">.	4684	of how the F<event.h> header can be found, the default is C<"event.h">.
3014		4685
3015	=item EV_PROTOTYPES	4686	=item EV_PROTOTYPES (h)
3016		4687
3017	If defined to be C<0>, then F<ev.h> will not define any function	4688	If defined to be C<0>, then F<ev.h> will not define any function
3018	prototypes, but still define all the structs and other symbols. This is	4689	prototypes, but still define all the structs and other symbols. This is
3019	occasionally useful if you want to provide your own wrapper functions	4690	occasionally useful if you want to provide your own wrapper functions
3020	around libev functions.	4691	around libev functions.
…		…
3025	will have the C<struct ev_loop *> as first argument, and you can create	4696	will have the C<struct ev_loop *> as first argument, and you can create
3026	additional independent event loops. Otherwise there will be no support	4697	additional independent event loops. Otherwise there will be no support
3027	for multiple event loops and there is no first event loop pointer	4698	for multiple event loops and there is no first event loop pointer
3028	argument. Instead, all functions act on the single default loop.	4699	argument. Instead, all functions act on the single default loop.
3029		4700
		4701	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4702	default loop when multiplicity is switched off - you always have to
		4703	initialise the loop manually in this case.
		4704
3030	=item EV_MINPRI	4705	=item EV_MINPRI
3031		4706
3032	=item EV_MAXPRI	4707	=item EV_MAXPRI
3033		4708
3034	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4709	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
3039	When doing priority-based operations, libev usually has to linearly search	4714	When doing priority-based operations, libev usually has to linearly search
3040	all the priorities, so having many of them (hundreds) uses a lot of space	4715	all the priorities, so having many of them (hundreds) uses a lot of space
3041	and time, so using the defaults of five priorities (-2 .. +2) is usually	4716	and time, so using the defaults of five priorities (-2 .. +2) is usually
3042	fine.	4717	fine.
3043		4718
3044	If your embedding application does not need any priorities, defining these both to	4719	If your embedding application does not need any priorities, defining these
3045	C<0> will save some memory and CPU.	4720	both to C<0> will save some memory and CPU.
3046		4721
3047	=item EV_PERIODIC_ENABLE	4722	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4723	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4724	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
3048		4725
3049	If undefined or defined to be C<1>, then periodic timers are supported. If	4726	If undefined or defined to be C<1> (and the platform supports it), then
3050	defined to be C<0>, then they are not. Disabling them saves a few kB of	4727	the respective watcher type is supported. If defined to be C<0>, then it
3051	code.	4728	is not. Disabling watcher types mainly saves code size.
3052		4729
3053	=item EV_IDLE_ENABLE	4730	=item EV_FEATURES
3054
3055	If undefined or defined to be C<1>, then idle watchers are supported. If
3056	defined to be C<0>, then they are not. Disabling them saves a few kB of
3057	code.
3058
3059	=item EV_EMBED_ENABLE
3060
3061	If undefined or defined to be C<1>, then embed watchers are supported. If
3062	defined to be C<0>, then they are not.
3063
3064	=item EV_STAT_ENABLE
3065
3066	If undefined or defined to be C<1>, then stat watchers are supported. If
3067	defined to be C<0>, then they are not.
3068
3069	=item EV_FORK_ENABLE
3070
3071	If undefined or defined to be C<1>, then fork watchers are supported. If
3072	defined to be C<0>, then they are not.
3073
3074	=item EV_ASYNC_ENABLE
3075
3076	If undefined or defined to be C<1>, then async watchers are supported. If
3077	defined to be C<0>, then they are not.
3078
3079	=item EV_MINIMAL
3080		4731
3081	If you need to shave off some kilobytes of code at the expense of some	4732	If you need to shave off some kilobytes of code at the expense of some
3082	speed, define this symbol to C<1>. Currently this is used to override some	4733	speed (but with the full API), you can define this symbol to request
3083	inlining decisions, saves roughly 30% code size on amd64. It also selects a	4734	certain subsets of functionality. The default is to enable all features
3084	much smaller 2-heap for timer management over the default 4-heap.	4735	that can be enabled on the platform.
		4736
		4737	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4738	with some broad features you want) and then selectively re-enable
		4739	additional parts you want, for example if you want everything minimal,
		4740	but multiple event loop support, async and child watchers and the poll
		4741	backend, use this:
		4742
		4743	#define EV_FEATURES 0
		4744	#define EV_MULTIPLICITY 1
		4745	#define EV_USE_POLL 1
		4746	#define EV_CHILD_ENABLE 1
		4747	#define EV_ASYNC_ENABLE 1
		4748
		4749	The actual value is a bitset, it can be a combination of the following
		4750	values (by default, all of these are enabled):
		4751
		4752	=over 4
		4753
		4754	=item C<1> - faster/larger code
		4755
		4756	Use larger code to speed up some operations.
		4757
		4758	Currently this is used to override some inlining decisions (enlarging the
		4759	code size by roughly 30% on amd64).
		4760
		4761	When optimising for size, use of compiler flags such as C<-Os> with
		4762	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4763	assertions.
		4764
		4765	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4766	(e.g. gcc with C<-Os>).
		4767
		4768	=item C<2> - faster/larger data structures
		4769
		4770	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4771	hash table sizes and so on. This will usually further increase code size
		4772	and can additionally have an effect on the size of data structures at
		4773	runtime.
		4774
		4775	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4776	(e.g. gcc with C<-Os>).
		4777
		4778	=item C<4> - full API configuration
		4779
		4780	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4781	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4782
		4783	=item C<8> - full API
		4784
		4785	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4786	details on which parts of the API are still available without this
		4787	feature, and do not complain if this subset changes over time.
		4788
		4789	=item C<16> - enable all optional watcher types
		4790
		4791	Enables all optional watcher types. If you want to selectively enable
		4792	only some watcher types other than I/O and timers (e.g. prepare,
		4793	embed, async, child...) you can enable them manually by defining
		4794	C<EV_watchertype_ENABLE> to C<1> instead.
		4795
		4796	=item C<32> - enable all backends
		4797
		4798	This enables all backends - without this feature, you need to enable at
		4799	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4800
		4801	=item C<64> - enable OS-specific "helper" APIs
		4802
		4803	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4804	default.
		4805
		4806	=back
		4807
		4808	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4809	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4810	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4811	watchers, timers and monotonic clock support.
		4812
		4813	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4814	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4815	your program might be left out as well - a binary starting a timer and an
		4816	I/O watcher then might come out at only 5Kb.
		4817
		4818	=item EV_API_STATIC
		4819
		4820	If this symbol is defined (by default it is not), then all identifiers
		4821	will have static linkage. This means that libev will not export any
		4822	identifiers, and you cannot link against libev anymore. This can be useful
		4823	when you embed libev, only want to use libev functions in a single file,
		4824	and do not want its identifiers to be visible.
		4825
		4826	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4827	wants to use libev.
		4828
		4829	This option only works when libev is compiled with a C compiler, as C++
		4830	doesn't support the required declaration syntax.
		4831
		4832	=item EV_AVOID_STDIO
		4833
		4834	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4835	functions (printf, scanf, perror etc.). This will increase the code size
		4836	somewhat, but if your program doesn't otherwise depend on stdio and your
		4837	libc allows it, this avoids linking in the stdio library which is quite
		4838	big.
		4839
		4840	Note that error messages might become less precise when this option is
		4841	enabled.
		4842
		4843	=item EV_NSIG
		4844
		4845	The highest supported signal number, +1 (or, the number of
		4846	signals): Normally, libev tries to deduce the maximum number of signals
		4847	automatically, but sometimes this fails, in which case it can be
		4848	specified. Also, using a lower number than detected (C<32> should be
		4849	good for about any system in existence) can save some memory, as libev
		4850	statically allocates some 12-24 bytes per signal number.
3085		4851
3086	=item EV_PID_HASHSIZE	4852	=item EV_PID_HASHSIZE
3087		4853
3088	C<ev_child> watchers use a small hash table to distribute workload by	4854	C<ev_child> watchers use a small hash table to distribute workload by
3089	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4855	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
3090	than enough. If you need to manage thousands of children you might want to	4856	usually more than enough. If you need to manage thousands of children you
3091	increase this value (I<must> be a power of two).	4857	might want to increase this value (I<must> be a power of two).
3092		4858
3093	=item EV_INOTIFY_HASHSIZE	4859	=item EV_INOTIFY_HASHSIZE
3094		4860
3095	C<ev_stat> watchers use a small hash table to distribute workload by	4861	C<ev_stat> watchers use a small hash table to distribute workload by
3096	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4862	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
3097	usually more than enough. If you need to manage thousands of C<ev_stat>	4863	disabled), usually more than enough. If you need to manage thousands of
3098	watchers you might want to increase this value (I<must> be a power of	4864	C<ev_stat> watchers you might want to increase this value (I<must> be a
3099	two).	4865	power of two).
3100		4866
3101	=item EV_USE_4HEAP	4867	=item EV_USE_4HEAP
3102		4868
3103	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4869	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3104	timer and periodics heap, libev uses a 4-heap when this symbol is defined	4870	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3105	to C<1>. The 4-heap uses more complicated (longer) code but has	4871	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3106	noticeably faster performance with many (thousands) of watchers.	4872	faster performance with many (thousands) of watchers.
3107		4873
3108	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4874	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3109	(disabled).	4875	will be C<0>.
3110		4876
3111	=item EV_HEAP_CACHE_AT	4877	=item EV_HEAP_CACHE_AT
3112		4878
3113	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4879	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3114	timer and periodics heap, libev can cache the timestamp (I<at>) within	4880	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3115	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	4881	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3116	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	4882	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3117	but avoids random read accesses on heap changes. This improves performance	4883	but avoids random read accesses on heap changes. This improves performance
3118	noticeably with with many (hundreds) of watchers.	4884	noticeably with many (hundreds) of watchers.
3119		4885
3120	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4886	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3121	(disabled).	4887	will be C<0>.
3122		4888
3123	=item EV_VERIFY	4889	=item EV_VERIFY
3124		4890
3125	Controls how much internal verification (see C<ev_loop_verify ()>) will	4891	Controls how much internal verification (see C<ev_verify ()>) will
3126	be done: If set to C<0>, no internal verification code will be compiled	4892	be done: If set to C<0>, no internal verification code will be compiled
3127	in. If set to C<1>, then verification code will be compiled in, but not	4893	in. If set to C<1>, then verification code will be compiled in, but not
3128	called. If set to C<2>, then the internal verification code will be	4894	called. If set to C<2>, then the internal verification code will be
3129	called once per loop, which can slow down libev. If set to C<3>, then the	4895	called once per loop, which can slow down libev. If set to C<3>, then the
3130	verification code will be called very frequently, which will slow down	4896	verification code will be called very frequently, which will slow down
3131	libev considerably.	4897	libev considerably.
3132		4898
3133	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	4899	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3134	C<0.>	4900	will be C<0>.
3135		4901
3136	=item EV_COMMON	4902	=item EV_COMMON
3137		4903
3138	By default, all watchers have a C<void *data> member. By redefining	4904	By default, all watchers have a C<void *data> member. By redefining
3139	this macro to a something else you can include more and other types of	4905	this macro to something else you can include more and other types of
3140	members. You have to define it each time you include one of the files,	4906	members. You have to define it each time you include one of the files,
3141	though, and it must be identical each time.	4907	though, and it must be identical each time.
3142		4908
3143	For example, the perl EV module uses something like this:	4909	For example, the perl EV module uses something like this:
3144		4910
…		…
3156	and the way callbacks are invoked and set. Must expand to a struct member	4922	and the way callbacks are invoked and set. Must expand to a struct member
3157	definition and a statement, respectively. See the F<ev.h> header file for	4923	definition and a statement, respectively. See the F<ev.h> header file for
3158	their default definitions. One possible use for overriding these is to	4924	their default definitions. One possible use for overriding these is to
3159	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4925	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3160	method calls instead of plain function calls in C++.	4926	method calls instead of plain function calls in C++.
		4927
		4928	=back
3161		4929
3162	=head2 EXPORTED API SYMBOLS	4930	=head2 EXPORTED API SYMBOLS
3163		4931
3164	If you need to re-export the API (e.g. via a DLL) and you need a list of	4932	If you need to re-export the API (e.g. via a DLL) and you need a list of
3165	exported symbols, you can use the provided F<Symbol.*> files which list	4933	exported symbols, you can use the provided F<Symbol.*> files which list
…		…
3195	file.	4963	file.
3196		4964
3197	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4965	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
3198	that everybody includes and which overrides some configure choices:	4966	that everybody includes and which overrides some configure choices:
3199		4967
3200	#define EV_MINIMAL 1	4968	#define EV_FEATURES 8
3201	#define EV_USE_POLL 0	4969	#define EV_USE_SELECT 1
3202	#define EV_MULTIPLICITY 0
3203	#define EV_PERIODIC_ENABLE 0	4970	#define EV_PREPARE_ENABLE 1
		4971	#define EV_IDLE_ENABLE 1
3204	#define EV_STAT_ENABLE 0	4972	#define EV_SIGNAL_ENABLE 1
3205	#define EV_FORK_ENABLE 0	4973	#define EV_CHILD_ENABLE 1
		4974	#define EV_USE_STDEXCEPT 0
3206	#define EV_CONFIG_H <config.h>	4975	#define EV_CONFIG_H <config.h>
3207	#define EV_MINPRI 0
3208	#define EV_MAXPRI 0
3209		4976
3210	#include "ev++.h"	4977	#include "ev++.h"
3211		4978
3212	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4979	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3213		4980
3214	#include "ev_cpp.h"	4981	#include "ev_cpp.h"
3215	#include "ev.c"	4982	#include "ev.c"
3216		4983
		4984	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
3217		4985
3218	=head1 THREADS AND COROUTINES	4986	=head2 THREADS AND COROUTINES
3219		4987
3220	=head2 THREADS	4988	=head3 THREADS
3221		4989
3222	Libev itself is completely thread-safe, but it uses no locking. This	4990	All libev functions are reentrant and thread-safe unless explicitly
		4991	documented otherwise, but libev implements no locking itself. This means
3223	means that you can use as many loops as you want in parallel, as long as	4992	that you can use as many loops as you want in parallel, as long as there
3224	only one thread ever calls into one libev function with the same loop	4993	are no concurrent calls into any libev function with the same loop
3225	parameter.	4994	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4995	of course): libev guarantees that different event loops share no data
		4996	structures that need any locking.
3226		4997
3227	Or put differently: calls with different loop parameters can be done in	4998	Or to put it differently: calls with different loop parameters can be done
3228	parallel from multiple threads, calls with the same loop parameter must be	4999	concurrently from multiple threads, calls with the same loop parameter
3229	done serially (but can be done from different threads, as long as only one	5000	must be done serially (but can be done from different threads, as long as
3230	thread ever is inside a call at any point in time, e.g. by using a mutex	5001	only one thread ever is inside a call at any point in time, e.g. by using
3231	per loop).	5002	a mutex per loop).
		5003
		5004	Specifically to support threads (and signal handlers), libev implements
		5005	so-called C<ev_async> watchers, which allow some limited form of
		5006	concurrency on the same event loop, namely waking it up "from the
		5007	outside".
3232		5008
3233	If you want to know which design (one loop, locking, or multiple loops	5009	If you want to know which design (one loop, locking, or multiple loops
3234	without or something else still) is best for your problem, then I cannot	5010	without or something else still) is best for your problem, then I cannot
3235	help you. I can give some generic advice however:	5011	help you, but here is some generic advice:
3236		5012
3237	=over 4	5013	=over 4
3238		5014
3239	=item * most applications have a main thread: use the default libev loop	5015	=item * most applications have a main thread: use the default libev loop
3240	in that thread, or create a separate thread running only the default loop.	5016	in that thread, or create a separate thread running only the default loop.
…		…
3252		5028
3253	Choosing a model is hard - look around, learn, know that usually you can do	5029	Choosing a model is hard - look around, learn, know that usually you can do
3254	better than you currently do :-)	5030	better than you currently do :-)
3255		5031
3256	=item * often you need to talk to some other thread which blocks in the	5032	=item * often you need to talk to some other thread which blocks in the
		5033	event loop.
		5034
3257	event loop - C<ev_async> watchers can be used to wake them up from other	5035	C<ev_async> watchers can be used to wake them up from other threads safely
3258	threads safely (or from signal contexts...).	5036	(or from signal contexts...).
		5037
		5038	An example use would be to communicate signals or other events that only
		5039	work in the default loop by registering the signal watcher with the
		5040	default loop and triggering an C<ev_async> watcher from the default loop
		5041	watcher callback into the event loop interested in the signal.
3259		5042
3260	=back	5043	=back
3261		5044
		5045	See also L</THREAD LOCKING EXAMPLE>.
		5046
3262	=head2 COROUTINES	5047	=head3 COROUTINES
3263		5048
3264	Libev is much more accommodating to coroutines ("cooperative threads"):	5049	Libev is very accommodating to coroutines ("cooperative threads"):
3265	libev fully supports nesting calls to it's functions from different	5050	libev fully supports nesting calls to its functions from different
3266	coroutines (e.g. you can call C<ev_loop> on the same loop from two	5051	coroutines (e.g. you can call C<ev_run> on the same loop from two
3267	different coroutines and switch freely between both coroutines running the	5052	different coroutines, and switch freely between both coroutines running
3268	loop, as long as you don't confuse yourself). The only exception is that	5053	the loop, as long as you don't confuse yourself). The only exception is
3269	you must not do this from C<ev_periodic> reschedule callbacks.	5054	that you must not do this from C<ev_periodic> reschedule callbacks.
3270		5055
3271	Care has been invested into making sure that libev does not keep local	5056	Care has been taken to ensure that libev does not keep local state inside
3272	state inside C<ev_loop>, and other calls do not usually allow coroutine	5057	C<ev_run>, and other calls do not usually allow for coroutine switches as
3273	switches.	5058	they do not call any callbacks.
3274		5059
		5060	=head2 COMPILER WARNINGS
3275		5061
3276	=head1 COMPLEXITIES	5062	Depending on your compiler and compiler settings, you might get no or a
		5063	lot of warnings when compiling libev code. Some people are apparently
		5064	scared by this.
3277		5065
3278	In this section the complexities of (many of) the algorithms used inside	5066	However, these are unavoidable for many reasons. For one, each compiler
3279	libev will be explained. For complexity discussions about backends see the	5067	has different warnings, and each user has different tastes regarding
3280	documentation for C<ev_default_init>.	5068	warning options. "Warn-free" code therefore cannot be a goal except when
		5069	targeting a specific compiler and compiler-version.
3281		5070
3282	All of the following are about amortised time: If an array needs to be	5071	Another reason is that some compiler warnings require elaborate
3283	extended, libev needs to realloc and move the whole array, but this	5072	workarounds, or other changes to the code that make it less clear and less
3284	happens asymptotically never with higher number of elements, so O(1) might	5073	maintainable.
3285	mean it might do a lengthy realloc operation in rare cases, but on average
3286	it is much faster and asymptotically approaches constant time.
3287		5074
3288	=over 4	5075	And of course, some compiler warnings are just plain stupid, or simply
		5076	wrong (because they don't actually warn about the condition their message
		5077	seems to warn about). For example, certain older gcc versions had some
		5078	warnings that resulted in an extreme number of false positives. These have
		5079	been fixed, but some people still insist on making code warn-free with
		5080	such buggy versions.
3289		5081
3290	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	5082	While libev is written to generate as few warnings as possible,
		5083	"warn-free" code is not a goal, and it is recommended not to build libev
		5084	with any compiler warnings enabled unless you are prepared to cope with
		5085	them (e.g. by ignoring them). Remember that warnings are just that:
		5086	warnings, not errors, or proof of bugs.
3291		5087
3292	This means that, when you have a watcher that triggers in one hour and
3293	there are 100 watchers that would trigger before that then inserting will
3294	have to skip roughly seven (C<ld 100>) of these watchers.
3295		5088
3296	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	5089	=head2 VALGRIND
3297		5090
3298	That means that changing a timer costs less than removing/adding them	5091	Valgrind has a special section here because it is a popular tool that is
3299	as only the relative motion in the event queue has to be paid for.	5092	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3300		5093
3301	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	5094	If you think you found a bug (memory leak, uninitialised data access etc.)
		5095	in libev, then check twice: If valgrind reports something like:
3302		5096
3303	These just add the watcher into an array or at the head of a list.	5097	==2274== definitely lost: 0 bytes in 0 blocks.
		5098	==2274== possibly lost: 0 bytes in 0 blocks.
		5099	==2274== still reachable: 256 bytes in 1 blocks.
3304		5100
3305	=item Stopping check/prepare/idle/fork/async watchers: O(1)	5101	Then there is no memory leak, just as memory accounted to global variables
		5102	is not a memleak - the memory is still being referenced, and didn't leak.
3306		5103
3307	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	5104	Similarly, under some circumstances, valgrind might report kernel bugs
		5105	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5106	although an acceptable workaround has been found here), or it might be
		5107	confused.
3308		5108
3309	These watchers are stored in lists then need to be walked to find the	5109	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3310	correct watcher to remove. The lists are usually short (you don't usually	5110	make it into some kind of religion.
3311	have many watchers waiting for the same fd or signal).
3312		5111
3313	=item Finding the next timer in each loop iteration: O(1)	5112	If you are unsure about something, feel free to contact the mailing list
		5113	with the full valgrind report and an explanation on why you think this
		5114	is a bug in libev (best check the archives, too :). However, don't be
		5115	annoyed when you get a brisk "this is no bug" answer and take the chance
		5116	of learning how to interpret valgrind properly.
3314		5117
3315	By virtue of using a binary or 4-heap, the next timer is always found at a	5118	If you need, for some reason, empty reports from valgrind for your project
3316	fixed position in the storage array.	5119	I suggest using suppression lists.
3317		5120
3318	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3319		5121
3320	A change means an I/O watcher gets started or stopped, which requires	5122	=head1 PORTABILITY NOTES
3321	libev to recalculate its status (and possibly tell the kernel, depending
3322	on backend and whether C<ev_io_set> was used).
3323		5123
3324	=item Activating one watcher (putting it into the pending state): O(1)	5124	=head2 GNU/LINUX 32 BIT LIMITATIONS
3325		5125
3326	=item Priority handling: O(number_of_priorities)	5126	GNU/Linux is the only common platform that supports 64 bit file/large file
		5127	interfaces but I<disables> them by default.
3327		5128
3328	Priorities are implemented by allocating some space for each	5129	That means that libev compiled in the default environment doesn't support
3329	priority. When doing priority-based operations, libev usually has to	5130	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
3330	linearly search all the priorities, but starting/stopping and activating
3331	watchers becomes O(1) w.r.t. priority handling.
3332		5131
3333	=item Sending an ev_async: O(1)	5132	Unfortunately, many programs try to work around this GNU/Linux issue
		5133	by enabling the large file API, which makes them incompatible with the
		5134	standard libev compiled for their system.
3334		5135
3335	=item Processing ev_async_send: O(number_of_async_watchers)	5136	Likewise, libev cannot enable the large file API itself as this would
		5137	suddenly make it incompatible to the default compile time environment,
		5138	i.e. all programs not using special compile switches.
3336		5139
3337	=item Processing signals: O(max_signal_number)	5140	=head2 OS/X AND DARWIN BUGS
3338		5141
3339	Sending involves a system call I<iff> there were no other C<ev_async_send>	5142	The whole thing is a bug if you ask me - basically any system interface
3340	calls in the current loop iteration. Checking for async and signal events	5143	you touch is broken, whether it is locales, poll, kqueue or even the
3341	involves iterating over all running async watchers or all signal numbers.	5144	OpenGL drivers.
3342		5145
3343	=back	5146	=head3 C<kqueue> is buggy
3344		5147
		5148	The kqueue syscall is broken in all known versions - most versions support
		5149	only sockets, many support pipes.
3345		5150
		5151	Libev tries to work around this by not using C<kqueue> by default on this
		5152	rotten platform, but of course you can still ask for it when creating a
		5153	loop - embedding a socket-only kqueue loop into a select-based one is
		5154	probably going to work well.
		5155
		5156	=head3 C<poll> is buggy
		5157
		5158	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5159	implementation by something calling C<kqueue> internally around the 10.5.6
		5160	release, so now C<kqueue> I<and> C<poll> are broken.
		5161
		5162	Libev tries to work around this by not using C<poll> by default on
		5163	this rotten platform, but of course you can still ask for it when creating
		5164	a loop.
		5165
		5166	=head3 C<select> is buggy
		5167
		5168	All that's left is C<select>, and of course Apple found a way to fuck this
		5169	one up as well: On OS/X, C<select> actively limits the number of file
		5170	descriptors you can pass in to 1024 - your program suddenly crashes when
		5171	you use more.
		5172
		5173	There is an undocumented "workaround" for this - defining
		5174	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5175	work on OS/X.
		5176
		5177	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5178
		5179	=head3 C<errno> reentrancy
		5180
		5181	The default compile environment on Solaris is unfortunately so
		5182	thread-unsafe that you can't even use components/libraries compiled
		5183	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5184	defined by default. A valid, if stupid, implementation choice.
		5185
		5186	If you want to use libev in threaded environments you have to make sure
		5187	it's compiled with C<_REENTRANT> defined.
		5188
		5189	=head3 Event port backend
		5190
		5191	The scalable event interface for Solaris is called "event
		5192	ports". Unfortunately, this mechanism is very buggy in all major
		5193	releases. If you run into high CPU usage, your program freezes or you get
		5194	a large number of spurious wakeups, make sure you have all the relevant
		5195	and latest kernel patches applied. No, I don't know which ones, but there
		5196	are multiple ones to apply, and afterwards, event ports actually work
		5197	great.
		5198
		5199	If you can't get it to work, you can try running the program by setting
		5200	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5201	C<select> backends.
		5202
		5203	=head2 AIX POLL BUG
		5204
		5205	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5206	this by trying to avoid the poll backend altogether (i.e. it's not even
		5207	compiled in), which normally isn't a big problem as C<select> works fine
		5208	with large bitsets on AIX, and AIX is dead anyway.
		5209
3346	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	5210	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5211
		5212	=head3 General issues
3347		5213
3348	Win32 doesn't support any of the standards (e.g. POSIX) that libev	5214	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3349	requires, and its I/O model is fundamentally incompatible with the POSIX	5215	requires, and its I/O model is fundamentally incompatible with the POSIX
3350	model. Libev still offers limited functionality on this platform in	5216	model. Libev still offers limited functionality on this platform in
3351	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5217	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3352	descriptors. This only applies when using Win32 natively, not when using	5218	descriptors. This only applies when using Win32 natively, not when using
3353	e.g. cygwin.	5219	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5220	as every compiler comes with a slightly differently broken/incompatible
		5221	environment.
3354		5222
3355	Lifting these limitations would basically require the full	5223	Lifting these limitations would basically require the full
3356	re-implementation of the I/O system. If you are into these kinds of	5224	re-implementation of the I/O system. If you are into this kind of thing,
3357	things, then note that glib does exactly that for you in a very portable	5225	then note that glib does exactly that for you in a very portable way (note
3358	way (note also that glib is the slowest event library known to man).	5226	also that glib is the slowest event library known to man).
3359		5227
3360	There is no supported compilation method available on windows except	5228	There is no supported compilation method available on windows except
3361	embedding it into other applications.	5229	embedding it into other applications.
		5230
		5231	Sensible signal handling is officially unsupported by Microsoft - libev
		5232	tries its best, but under most conditions, signals will simply not work.
3362		5233
3363	Not a libev limitation but worth mentioning: windows apparently doesn't	5234	Not a libev limitation but worth mentioning: windows apparently doesn't
3364	accept large writes: instead of resulting in a partial write, windows will	5235	accept large writes: instead of resulting in a partial write, windows will
3365	either accept everything or return C<ENOBUFS> if the buffer is too large,	5236	either accept everything or return C<ENOBUFS> if the buffer is too large,
3366	so make sure you only write small amounts into your sockets (less than a	5237	so make sure you only write small amounts into your sockets (less than a
3367	megabyte seems safe, but thsi apparently depends on the amount of memory	5238	megabyte seems safe, but this apparently depends on the amount of memory
3368	available).	5239	available).
3369		5240
3370	Due to the many, low, and arbitrary limits on the win32 platform and	5241	Due to the many, low, and arbitrary limits on the win32 platform and
3371	the abysmal performance of winsockets, using a large number of sockets	5242	the abysmal performance of winsockets, using a large number of sockets
3372	is not recommended (and not reasonable). If your program needs to use	5243	is not recommended (and not reasonable). If your program needs to use
3373	more than a hundred or so sockets, then likely it needs to use a totally	5244	more than a hundred or so sockets, then likely it needs to use a totally
3374	different implementation for windows, as libev offers the POSIX readiness	5245	different implementation for windows, as libev offers the POSIX readiness
3375	notification model, which cannot be implemented efficiently on windows	5246	notification model, which cannot be implemented efficiently on windows
3376	(Microsoft monopoly games).	5247	(due to Microsoft monopoly games).
3377		5248
3378	A typical way to use libev under windows is to embed it (see the embedding	5249	A typical way to use libev under windows is to embed it (see the embedding
3379	section for details) and use the following F<evwrap.h> header file instead	5250	section for details) and use the following F<evwrap.h> header file instead
3380	of F<ev.h>:	5251	of F<ev.h>:
3381		5252
…		…
3383	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */	5254	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
3384		5255
3385	#include "ev.h"	5256	#include "ev.h"
3386		5257
3387	And compile the following F<evwrap.c> file into your project (make sure	5258	And compile the following F<evwrap.c> file into your project (make sure
3388	you do I<not> compile the F<ev.c> or any other embedded soruce files!):	5259	you do I<not> compile the F<ev.c> or any other embedded source files!):
3389		5260
3390	#include "evwrap.h"	5261	#include "evwrap.h"
3391	#include "ev.c"	5262	#include "ev.c"
3392		5263
3393	=over 4
3394
3395	=item The winsocket select function	5264	=head3 The winsocket C<select> function
3396		5265
3397	The winsocket C<select> function doesn't follow POSIX in that it	5266	The winsocket C<select> function doesn't follow POSIX in that it
3398	requires socket I<handles> and not socket I<file descriptors> (it is	5267	requires socket I<handles> and not socket I<file descriptors> (it is
3399	also extremely buggy). This makes select very inefficient, and also	5268	also extremely buggy). This makes select very inefficient, and also
3400	requires a mapping from file descriptors to socket handles (the Microsoft	5269	requires a mapping from file descriptors to socket handles (the Microsoft
…		…
3409	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	5278	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3410		5279
3411	Note that winsockets handling of fd sets is O(n), so you can easily get a	5280	Note that winsockets handling of fd sets is O(n), so you can easily get a
3412	complexity in the O(n²) range when using win32.	5281	complexity in the O(n²) range when using win32.
3413		5282
3414	=item Limited number of file descriptors	5283	=head3 Limited number of file descriptors
3415		5284
3416	Windows has numerous arbitrary (and low) limits on things.	5285	Windows has numerous arbitrary (and low) limits on things.
3417		5286
3418	Early versions of winsocket's select only supported waiting for a maximum	5287	Early versions of winsocket's select only supported waiting for a maximum
3419	of C<64> handles (probably owning to the fact that all windows kernels	5288	of C<64> handles (probably owning to the fact that all windows kernels
3420	can only wait for C<64> things at the same time internally; Microsoft	5289	can only wait for C<64> things at the same time internally; Microsoft
3421	recommends spawning a chain of threads and wait for 63 handles and the	5290	recommends spawning a chain of threads and wait for 63 handles and the
3422	previous thread in each. Great).	5291	previous thread in each. Sounds great!).
3423		5292
3424	Newer versions support more handles, but you need to define C<FD_SETSIZE>	5293	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3425	to some high number (e.g. C<2048>) before compiling the winsocket select	5294	to some high number (e.g. C<2048>) before compiling the winsocket select
3426	call (which might be in libev or elsewhere, for example, perl does its own	5295	call (which might be in libev or elsewhere, for example, perl and many
3427	select emulation on windows).	5296	other interpreters do their own select emulation on windows).
3428		5297
3429	Another limit is the number of file descriptors in the Microsoft runtime	5298	Another limit is the number of file descriptors in the Microsoft runtime
3430	libraries, which by default is C<64> (there must be a hidden I<64> fetish	5299	libraries, which by default is C<64> (there must be a hidden I<64>
3431	or something like this inside Microsoft). You can increase this by calling	5300	fetish or something like this inside Microsoft). You can increase this
3432	C<_setmaxstdio>, which can increase this limit to C<2048> (another	5301	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3433	arbitrary limit), but is broken in many versions of the Microsoft runtime	5302	(another arbitrary limit), but is broken in many versions of the Microsoft
3434	libraries.
3435
3436	This might get you to about C<512> or C<2048> sockets (depending on	5303	runtime libraries. This might get you to about C<512> or C<2048> sockets
3437	windows version and/or the phase of the moon). To get more, you need to	5304	(depending on windows version and/or the phase of the moon). To get more,
3438	wrap all I/O functions and provide your own fd management, but the cost of	5305	you need to wrap all I/O functions and provide your own fd management, but
3439	calling select (O(n²)) will likely make this unworkable.	5306	the cost of calling select (O(n²)) will likely make this unworkable.
3440		5307
3441	=back
3442
3443
3444	=head1 PORTABILITY REQUIREMENTS	5308	=head2 PORTABILITY REQUIREMENTS
3445		5309
3446	In addition to a working ISO-C implementation, libev relies on a few	5310	In addition to a working ISO-C implementation and of course the
3447	additional extensions:	5311	backend-specific APIs, libev relies on a few additional extensions:
3448		5312
3449	=over 4	5313	=over 4
3450		5314
3451	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible	5315	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
3452	calling conventions regardless of C<ev_watcher_type *>.	5316	calling conventions regardless of C<ev_watcher_type *>.
…		…
3455	structure (guaranteed by POSIX but not by ISO C for example), but it also	5319	structure (guaranteed by POSIX but not by ISO C for example), but it also
3456	assumes that the same (machine) code can be used to call any watcher	5320	assumes that the same (machine) code can be used to call any watcher
3457	callback: The watcher callbacks have different type signatures, but libev	5321	callback: The watcher callbacks have different type signatures, but libev
3458	calls them using an C<ev_watcher *> internally.	5322	calls them using an C<ev_watcher *> internally.
3459		5323
		5324	=item null pointers and integer zero are represented by 0 bytes
		5325
		5326	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5327	relies on this setting pointers and integers to null.
		5328
		5329	=item pointer accesses must be thread-atomic
		5330
		5331	Accessing a pointer value must be atomic, it must both be readable and
		5332	writable in one piece - this is the case on all current architectures.
		5333
3460	=item C<sig_atomic_t volatile> must be thread-atomic as well	5334	=item C<sig_atomic_t volatile> must be thread-atomic as well
3461		5335
3462	The type C<sig_atomic_t volatile> (or whatever is defined as	5336	The type C<sig_atomic_t volatile> (or whatever is defined as
3463	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	5337	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3464	threads. This is not part of the specification for C<sig_atomic_t>, but is	5338	threads. This is not part of the specification for C<sig_atomic_t>, but is
3465	believed to be sufficiently portable.	5339	believed to be sufficiently portable.
3466		5340
3467	=item C<sigprocmask> must work in a threaded environment	5341	=item C<sigprocmask> must work in a threaded environment
3468		5342
…		…
3472	thread" or will block signals process-wide, both behaviours would	5346	thread" or will block signals process-wide, both behaviours would
3473	be compatible with libev. Interaction between C<sigprocmask> and	5347	be compatible with libev. Interaction between C<sigprocmask> and
3474	C<pthread_sigmask> could complicate things, however.	5348	C<pthread_sigmask> could complicate things, however.
3475		5349
3476	The most portable way to handle signals is to block signals in all threads	5350	The most portable way to handle signals is to block signals in all threads
3477	except the initial one, and run the default loop in the initial thread as	5351	except the initial one, and run the signal handling loop in the initial
3478	well.	5352	thread as well.
3479		5353
3480	=item C<long> must be large enough for common memory allocation sizes	5354	=item C<long> must be large enough for common memory allocation sizes
3481		5355
3482	To improve portability and simplify using libev, libev uses C<long>	5356	To improve portability and simplify its API, libev uses C<long> internally
3483	internally instead of C<size_t> when allocating its data structures. On	5357	instead of C<size_t> when allocating its data structures. On non-POSIX
3484	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	5358	systems (Microsoft...) this might be unexpectedly low, but is still at
3485	is still at least 31 bits everywhere, which is enough for hundreds of	5359	least 31 bits everywhere, which is enough for hundreds of millions of
3486	millions of watchers.	5360	watchers.
3487		5361
3488	=item C<double> must hold a time value in seconds with enough accuracy	5362	=item C<double> must hold a time value in seconds with enough accuracy
3489		5363
3490	The type C<double> is used to represent timestamps. It is required to	5364	The type C<double> is used to represent timestamps. It is required to
3491	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	5365	have at least 51 bits of mantissa (and 9 bits of exponent), which is
3492	enough for at least into the year 4000. This requirement is fulfilled by	5366	good enough for at least into the year 4000 with millisecond accuracy
		5367	(the design goal for libev). This requirement is overfulfilled by
3493	implementations implementing IEEE 754 (basically all existing ones).	5368	implementations using IEEE 754, which is basically all existing ones.
		5369
		5370	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5371	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5372	is either obsolete or somebody patched it to use C<long double> or
		5373	something like that, just kidding).
3494		5374
3495	=back	5375	=back
3496		5376
3497	If you know of other additional requirements drop me a note.	5377	If you know of other additional requirements drop me a note.
3498		5378
3499		5379
3500	=head1 COMPILER WARNINGS	5380	=head1 ALGORITHMIC COMPLEXITIES
3501		5381
3502	Depending on your compiler and compiler settings, you might get no or a	5382	In this section the complexities of (many of) the algorithms used inside
3503	lot of warnings when compiling libev code. Some people are apparently	5383	libev will be documented. For complexity discussions about backends see
3504	scared by this.	5384	the documentation for C<ev_default_init>.
3505		5385
3506	However, these are unavoidable for many reasons. For one, each compiler	5386	All of the following are about amortised time: If an array needs to be
3507	has different warnings, and each user has different tastes regarding	5387	extended, libev needs to realloc and move the whole array, but this
3508	warning options. "Warn-free" code therefore cannot be a goal except when	5388	happens asymptotically rarer with higher number of elements, so O(1) might
3509	targeting a specific compiler and compiler-version.	5389	mean that libev does a lengthy realloc operation in rare cases, but on
		5390	average it is much faster and asymptotically approaches constant time.
3510		5391
3511	Another reason is that some compiler warnings require elaborate	5392	=over 4
3512	workarounds, or other changes to the code that make it less clear and less
3513	maintainable.
3514		5393
3515	And of course, some compiler warnings are just plain stupid, or simply	5394	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3516	wrong (because they don't actually warn about the condition their message
3517	seems to warn about).
3518		5395
3519	While libev is written to generate as few warnings as possible,	5396	This means that, when you have a watcher that triggers in one hour and
3520	"warn-free" code is not a goal, and it is recommended not to build libev	5397	there are 100 watchers that would trigger before that, then inserting will
3521	with any compiler warnings enabled unless you are prepared to cope with	5398	have to skip roughly seven (C<ld 100>) of these watchers.
3522	them (e.g. by ignoring them). Remember that warnings are just that:
3523	warnings, not errors, or proof of bugs.
3524		5399
		5400	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3525		5401
3526	=head1 VALGRIND	5402	That means that changing a timer costs less than removing/adding them,
		5403	as only the relative motion in the event queue has to be paid for.
3527		5404
3528	Valgrind has a special section here because it is a popular tool that is	5405	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3529	highly useful, but valgrind reports are very hard to interpret.
3530		5406
3531	If you think you found a bug (memory leak, uninitialised data access etc.)	5407	These just add the watcher into an array or at the head of a list.
3532	in libev, then check twice: If valgrind reports something like:
3533		5408
3534	==2274== definitely lost: 0 bytes in 0 blocks.	5409	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3535	==2274== possibly lost: 0 bytes in 0 blocks.
3536	==2274== still reachable: 256 bytes in 1 blocks.
3537		5410
3538	Then there is no memory leak. Similarly, under some circumstances,	5411	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3539	valgrind might report kernel bugs as if it were a bug in libev, or it
3540	might be confused (it is a very good tool, but only a tool).
3541		5412
3542	If you are unsure about something, feel free to contact the mailing list	5413	These watchers are stored in lists, so they need to be walked to find the
3543	with the full valgrind report and an explanation on why you think this is	5414	correct watcher to remove. The lists are usually short (you don't usually
3544	a bug in libev. However, don't be annoyed when you get a brisk "this is	5415	have many watchers waiting for the same fd or signal: one is typical, two
3545	no bug" answer and take the chance of learning how to interpret valgrind	5416	is rare).
3546	properly.
3547		5417
3548	If you need, for some reason, empty reports from valgrind for your project	5418	=item Finding the next timer in each loop iteration: O(1)
3549	I suggest using suppression lists.
3550		5419
		5420	By virtue of using a binary or 4-heap, the next timer is always found at a
		5421	fixed position in the storage array.
		5422
		5423	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5424
		5425	A change means an I/O watcher gets started or stopped, which requires
		5426	libev to recalculate its status (and possibly tell the kernel, depending
		5427	on backend and whether C<ev_io_set> was used).
		5428
		5429	=item Activating one watcher (putting it into the pending state): O(1)
		5430
		5431	=item Priority handling: O(number_of_priorities)
		5432
		5433	Priorities are implemented by allocating some space for each
		5434	priority. When doing priority-based operations, libev usually has to
		5435	linearly search all the priorities, but starting/stopping and activating
		5436	watchers becomes O(1) with respect to priority handling.
		5437
		5438	=item Sending an ev_async: O(1)
		5439
		5440	=item Processing ev_async_send: O(number_of_async_watchers)
		5441
		5442	=item Processing signals: O(max_signal_number)
		5443
		5444	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5445	calls in the current loop iteration and the loop is currently
		5446	blocked. Checking for async and signal events involves iterating over all
		5447	running async watchers or all signal numbers.
		5448
		5449	=back
		5450
		5451
		5452	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5453
		5454	The major version 4 introduced some incompatible changes to the API.
		5455
		5456	At the moment, the C<ev.h> header file provides compatibility definitions
		5457	for all changes, so most programs should still compile. The compatibility
		5458	layer might be removed in later versions of libev, so better update to the
		5459	new API early than late.
		5460
		5461	=over 4
		5462
		5463	=item C<EV_COMPAT3> backwards compatibility mechanism
		5464
		5465	The backward compatibility mechanism can be controlled by
		5466	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5467	section.
		5468
		5469	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5470
		5471	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5472
		5473	ev_loop_destroy (EV_DEFAULT_UC);
		5474	ev_loop_fork (EV_DEFAULT);
		5475
		5476	=item function/symbol renames
		5477
		5478	A number of functions and symbols have been renamed:
		5479
		5480	ev_loop => ev_run
		5481	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5482	EVLOOP_ONESHOT => EVRUN_ONCE
		5483
		5484	ev_unloop => ev_break
		5485	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5486	EVUNLOOP_ONE => EVBREAK_ONE
		5487	EVUNLOOP_ALL => EVBREAK_ALL
		5488
		5489	EV_TIMEOUT => EV_TIMER
		5490
		5491	ev_loop_count => ev_iteration
		5492	ev_loop_depth => ev_depth
		5493	ev_loop_verify => ev_verify
		5494
		5495	Most functions working on C<struct ev_loop> objects don't have an
		5496	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5497	associated constants have been renamed to not collide with the C<struct
		5498	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5499	as all other watcher types. Note that C<ev_loop_fork> is still called
		5500	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5501	typedef.
		5502
		5503	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5504
		5505	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5506	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5507	and work, but the library code will of course be larger.
		5508
		5509	=back
		5510
		5511
		5512	=head1 GLOSSARY
		5513
		5514	=over 4
		5515
		5516	=item active
		5517
		5518	A watcher is active as long as it has been started and not yet stopped.
		5519	See L</WATCHER STATES> for details.
		5520
		5521	=item application
		5522
		5523	In this document, an application is whatever is using libev.
		5524
		5525	=item backend
		5526
		5527	The part of the code dealing with the operating system interfaces.
		5528
		5529	=item callback
		5530
		5531	The address of a function that is called when some event has been
		5532	detected. Callbacks are being passed the event loop, the watcher that
		5533	received the event, and the actual event bitset.
		5534
		5535	=item callback/watcher invocation
		5536
		5537	The act of calling the callback associated with a watcher.
		5538
		5539	=item event
		5540
		5541	A change of state of some external event, such as data now being available
		5542	for reading on a file descriptor, time having passed or simply not having
		5543	any other events happening anymore.
		5544
		5545	In libev, events are represented as single bits (such as C<EV_READ> or
		5546	C<EV_TIMER>).
		5547
		5548	=item event library
		5549
		5550	A software package implementing an event model and loop.
		5551
		5552	=item event loop
		5553
		5554	An entity that handles and processes external events and converts them
		5555	into callback invocations.
		5556
		5557	=item event model
		5558
		5559	The model used to describe how an event loop handles and processes
		5560	watchers and events.
		5561
		5562	=item pending
		5563
		5564	A watcher is pending as soon as the corresponding event has been
		5565	detected. See L</WATCHER STATES> for details.
		5566
		5567	=item real time
		5568
		5569	The physical time that is observed. It is apparently strictly monotonic :)
		5570
		5571	=item wall-clock time
		5572
		5573	The time and date as shown on clocks. Unlike real time, it can actually
		5574	be wrong and jump forwards and backwards, e.g. when you adjust your
		5575	clock.
		5576
		5577	=item watcher
		5578
		5579	A data structure that describes interest in certain events. Watchers need
		5580	to be started (attached to an event loop) before they can receive events.
		5581
		5582	=back
3551		5583
3552	=head1 AUTHOR	5584	=head1 AUTHOR
3553		5585
3554	Marc Lehmann <libev@schmorp.de>.	5586	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5587	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
3555		5588

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