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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
6		8
7	#include <ev.h>	9	#include <ev.h>
8		10
9	=head1 EXAMPLE PROGRAM	11	=head2 EXAMPLE PROGRAM
10		12
		13	// a single header file is required
11	#include <ev.h>	14	#include <ev.h>
12		15
		16	#include <stdio.h> // for puts
		17
		18	// every watcher type has its own typedef'd struct
		19	// with the name ev_TYPE
13	ev_io stdin_watcher;	20	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	21	ev_timer timeout_watcher;
15		22
16	/* called when data readable on stdin */	23	// all watcher callbacks have a similar signature
		24	// this callback is called when data is readable on stdin
17	static void	25	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	26	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	27	{
20	/* puts ("stdin ready"); */	28	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	29	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	30	// with its corresponding stop function.
		31	ev_io_stop (EV_A_ w);
		32
		33	// this causes all nested ev_run's to stop iterating
		34	ev_break (EV_A_ EVBREAK_ALL);
23	}	35	}
24		36
		37	// another callback, this time for a time-out
25	static void	38	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	39	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	40	{
28	/* puts ("timeout"); */	41	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	42	// this causes the innermost ev_run to stop iterating
		43	ev_break (EV_A_ EVBREAK_ONE);
30	}	44	}
31		45
32	int	46	int
33	main (void)	47	main (void)
34	{	48	{
35	struct ev_loop *loop = ev_default_loop (0);	49	// use the default event loop unless you have special needs
		50	struct ev_loop *loop = EV_DEFAULT;
36		51
37	/* initialise an io watcher, then start it */	52	// initialise an io watcher, then start it
		53	// this one will watch for stdin to become readable
38	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);
39	ev_io_start (loop, &stdin_watcher);	55	ev_io_start (loop, &stdin_watcher);
40		56
		57	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	58	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	59	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
44		61
45	/* loop till timeout or data ready */	62	// now wait for events to arrive
46	ev_loop (loop, 0);	63	ev_run (loop, 0);
47		64
		65	// break was called, so exit
48	return 0;	66	return 0;
49	}	67	}
50		68
51	=head1 DESCRIPTION	69	=head1 ABOUT THIS DOCUMENT
52		70
		71	This document documents the libev software package.
		72
53	The newest version of this document is also available as a html-formatted	73	The newest version of this document is also available as an html-formatted
54	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
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	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
56		94
57	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
58	file descriptor being readable or a timeout occuring), and it will manage	96	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	97	these event sources and provide your program with events.
60		98
61	To do this, it must take more or less complete control over your process	99	To do this, it must take more or less complete control over your process
62	(or thread) by executing the I<event loop> handler, and will then	100	(or thread) by executing the I<event loop> handler, and will then
63	communicate events via a callback mechanism.	101	communicate events via a callback mechanism.
…		…
65	You register interest in certain events by registering so-called I<event	103	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	104	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	105	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	106	watcher.
69		107
70	=head1 FEATURES	108	=head2 FEATURES
71		109
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	110	Libev supports C<select>, C<poll>, the Linux-specific aio and C<epoll>
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	112	mechanisms for file descriptor events (C<ev_io>), the Linux C<inotify>
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	113	interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
76	with customised rescheduling (C<ev_periodic>), synchronous signals	114	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
77	(C<ev_signal>), process status change events (C<ev_child>), and event	115	timers (C<ev_timer>), absolute timers with customised rescheduling
78	watchers dealing with the event loop mechanism itself (C<ev_idle>,	116	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
79	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
80	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
81	(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>).
82		121
83	It also is quite fast (see this	122	It also is quite fast (see this
84	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
85	for example).	124	for example).
86		125
87	=head1 CONVENTIONS	126	=head2 CONVENTIONS
88		127
89	Libev is very configurable. In this manual the default configuration will	128	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	129	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	130	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	131	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	132	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	133	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		134	this argument.
95		135
96	=head1 TIME REPRESENTATION	136	=head2 TIME REPRESENTATION
97		137
98	Libev represents time as a single floating point number, representing the	138	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	139	the (fractional) number of seconds since the (POSIX) epoch (in practice
100	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
101	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
102	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
103	it, you should treat it as such.	143	any calculations on it, you should treat it as some floating point value.
		144
		145	Unlike the name component C<stamp> might indicate, it is also used for
		146	time differences (e.g. delays) throughout libev.
		147
		148	=head1 ERROR HANDLING
		149
		150	Libev knows three classes of errors: operating system errors, usage errors
		151	and internal errors (bugs).
		152
		153	When libev catches an operating system error it cannot handle (for example
		154	a system call indicating a condition libev cannot fix), it calls the callback
		155	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		156	abort. The default is to print a diagnostic message and to call C<abort
		157	()>.
		158
		159	When libev detects a usage error such as a negative timer interval, then
		160	it will print a diagnostic message and abort (via the C<assert> mechanism,
		161	so C<NDEBUG> will disable this checking): these are programming errors in
		162	the libev caller and need to be fixed there.
		163
		164	Via the C<EV_FREQUENT> macro you can compile in and/or enable extensive
		165	consistency checking code inside libev that can be used to check for
		166	internal inconsistencies, suually caused by application bugs.
		167
		168	Libev also has a few internal error-checking C<assert>ions. These do not
		169	trigger under normal circumstances, as they indicate either a bug in libev
		170	or worse.
		171
104		172
105	=head1 GLOBAL FUNCTIONS	173	=head1 GLOBAL FUNCTIONS
106		174
107	These functions can be called anytime, even before initialising the	175	These functions can be called anytime, even before initialising the
108	library in any way.	176	library in any way.
…		…
111		179
112	=item ev_tstamp ev_time ()	180	=item ev_tstamp ev_time ()
113		181
114	Returns the current time as libev would use it. Please note that the	182	Returns the current time as libev would use it. Please note that the
115	C<ev_now> function is usually faster and also often returns the timestamp	183	C<ev_now> function is usually faster and also often returns the timestamp
116	you actually want to know.	184	you actually want to know. Also interesting is the combination of
		185	C<ev_now_update> and C<ev_now>.
		186
		187	=item ev_sleep (ev_tstamp interval)
		188
		189	Sleep for the given interval: The current thread will be blocked
		190	until either it is interrupted or the given time interval has
		191	passed (approximately - it might return a bit earlier even if not
		192	interrupted). Returns immediately if C<< interval <= 0 >>.
		193
		194	Basically this is a sub-second-resolution C<sleep ()>.
		195
		196	The range of the C<interval> is limited - libev only guarantees to work
		197	with sleep times of up to one day (C<< interval <= 86400 >>).
117		198
118	=item int ev_version_major ()	199	=item int ev_version_major ()
119		200
120	=item int ev_version_minor ()	201	=item int ev_version_minor ()
121		202
…		…
132	as this indicates an incompatible change. Minor versions are usually	213	as this indicates an incompatible change. Minor versions are usually
133	compatible to older versions, so a larger minor version alone is usually	214	compatible to older versions, so a larger minor version alone is usually
134	not a problem.	215	not a problem.
135		216
136	Example: Make sure we haven't accidentally been linked against the wrong	217	Example: Make sure we haven't accidentally been linked against the wrong
137	version.	218	version (note, however, that this will not detect other ABI mismatches,
		219	such as LFS or reentrancy).
138		220
139	assert (("libev version mismatch",	221	assert (("libev version mismatch",
140	ev_version_major () == EV_VERSION_MAJOR	222	ev_version_major () == EV_VERSION_MAJOR
141	&& ev_version_minor () >= EV_VERSION_MINOR));	223	&& ev_version_minor () >= EV_VERSION_MINOR));
142		224
143	=item unsigned int ev_supported_backends ()	225	=item unsigned int ev_supported_backends ()
144		226
145	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	227	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
146	value) compiled into this binary of libev (independent of their	228	value) compiled into this binary of libev (independent of their
…		…
148	a description of the set values.	230	a description of the set values.
149		231
150	Example: make sure we have the epoll method, because yeah this is cool and	232	Example: make sure we have the epoll method, because yeah this is cool and
151	a must have and can we have a torrent of it please!!!11	233	a must have and can we have a torrent of it please!!!11
152		234
153	assert (("sorry, no epoll, no sex",	235	assert (("sorry, no epoll, no sex",
154	ev_supported_backends () & EVBACKEND_EPOLL));	236	ev_supported_backends () & EVBACKEND_EPOLL));
155		237
156	=item unsigned int ev_recommended_backends ()	238	=item unsigned int ev_recommended_backends ()
157		239
158	Return the set of all backends compiled into this binary of libev and also	240	Return the set of all backends compiled into this binary of libev and
159	recommended for this platform. This set is often smaller than the one	241	also recommended for this platform, meaning it will work for most file
		242	descriptor types. This set is often smaller than the one returned by
160	returned by C<ev_supported_backends>, as for example kqueue is broken on	243	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
161	most BSDs and will not be autodetected unless you explicitly request it	244	and will not be auto-detected unless you explicitly request it (assuming
162	(assuming you know what you are doing). This is the set of backends that	245	you know what you are doing). This is the set of backends that libev will
163	libev will probe for if you specify no backends explicitly.	246	probe for if you specify no backends explicitly.
164		247
165	=item unsigned int ev_embeddable_backends ()	248	=item unsigned int ev_embeddable_backends ()
166		249
167	Returns the set of backends that are embeddable in other event loops. This	250	Returns the set of backends that are embeddable in other event loops. This
168	is the theoretical, all-platform, value. To find which backends	251	value is platform-specific but can include backends not available on the
169	might be supported on the current system, you would need to look at	252	current system. To find which embeddable backends might be supported on
170	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	253	the current system, you would need to look at C<ev_embeddable_backends ()
171	recommended ones.	254	& ev_supported_backends ()>, likewise for recommended ones.
172		255
173	See the description of C<ev_embed> watchers for more info.	256	See the description of C<ev_embed> watchers for more info.
174		257
175	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	258	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
176		259
177	Sets the allocation function to use (the prototype is similar - the	260	Sets the allocation function to use (the prototype is similar - the
178	semantics is identical - to the realloc C function). It is used to	261	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
179	allocate and free memory (no surprises here). If it returns zero when	262	used to allocate and free memory (no surprises here). If it returns zero
180	memory needs to be allocated, the library might abort or take some	263	when memory needs to be allocated (C<size != 0>), the library might abort
181	potentially destructive action. The default is your system realloc	264	or take some potentially destructive action.
182	function.	265
		266	Since some systems (at least OpenBSD and Darwin) fail to implement
		267	correct C<realloc> semantics, libev will use a wrapper around the system
		268	C<realloc> and C<free> functions by default.
183		269
184	You could override this function in high-availability programs to, say,	270	You could override this function in high-availability programs to, say,
185	free some memory if it cannot allocate memory, to use a special allocator,	271	free some memory if it cannot allocate memory, to use a special allocator,
186	or even to sleep a while and retry until some memory is available.	272	or even to sleep a while and retry until some memory is available.
187		273
		274	Example: The following is the C<realloc> function that libev itself uses
		275	which should work with C<realloc> and C<free> functions of all kinds and
		276	is probably a good basis for your own implementation.
		277
		278	static void *
		279	ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
		280	{
		281	if (size)
		282	return realloc (ptr, size);
		283
		284	free (ptr);
		285	return 0;
		286	}
		287
188	Example: Replace the libev allocator with one that waits a bit and then	288	Example: Replace the libev allocator with one that waits a bit and then
189	retries).	289	retries.
190		290
191	static void *	291	static void *
192	persistent_realloc (void *ptr, size_t size)	292	persistent_realloc (void *ptr, size_t size)
193	{	293	{
		294	if (!size)
		295	{
		296	free (ptr);
		297	return 0;
		298	}
		299
194	for (;;)	300	for (;;)
195	{	301	{
196	void *newptr = realloc (ptr, size);	302	void *newptr = realloc (ptr, size);
197		303
198	if (newptr)	304	if (newptr)
…		…
203	}	309	}
204		310
205	...	311	...
206	ev_set_allocator (persistent_realloc);	312	ev_set_allocator (persistent_realloc);
207		313
208	=item ev_set_syserr_cb (void (*cb)(const char *msg));	314	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
209		315
210	Set the callback function to call on a retryable syscall error (such	316	Set the callback function to call on a retryable system call error (such
211	as failed select, poll, epoll_wait). The message is a printable string	317	as failed select, poll, epoll_wait). The message is a printable string
212	indicating the system call or subsystem causing the problem. If this	318	indicating the system call or subsystem causing the problem. If this
213	callback is set, then libev will expect it to remedy the sitution, no	319	callback is set, then libev will expect it to remedy the situation, no
214	matter what, when it returns. That is, libev will generally retry the	320	matter what, when it returns. That is, libev will generally retry the
215	requested operation, or, if the condition doesn't go away, do bad stuff	321	requested operation, or, if the condition doesn't go away, do bad stuff
216	(such as abort).	322	(such as abort).
217		323
218	Example: This is basically the same thing that libev does internally, too.	324	Example: This is basically the same thing that libev does internally, too.
…		…
225	}	331	}
226		332
227	...	333	...
228	ev_set_syserr_cb (fatal_error);	334	ev_set_syserr_cb (fatal_error);
229		335
		336	=item ev_feed_signal (int signum)
		337
		338	This function can be used to "simulate" a signal receive. It is completely
		339	safe to call this function at any time, from any context, including signal
		340	handlers or random threads.
		341
		342	Its main use is to customise signal handling in your process, especially
		343	in the presence of threads. For example, you could block signals
		344	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		345	creating any loops), and in one thread, use C<sigwait> or any other
		346	mechanism to wait for signals, then "deliver" them to libev by calling
		347	C<ev_feed_signal>.
		348
230	=back	349	=back
231		350
232	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	351	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
233		352
234	An event loop is described by a C<struct ev_loop *>. The library knows two	353	An event loop is described by a C<struct ev_loop *> (the C<struct> is
235	types of such loops, the I<default> loop, which supports signals and child	354	I<not> optional in this case unless libev 3 compatibility is disabled, as
236	events, and dynamically created loops which do not.	355	libev 3 had an C<ev_loop> function colliding with the struct name).
237		356
238	If you use threads, a common model is to run the default event loop	357	The library knows two types of such loops, the I<default> loop, which
239	in your main thread (or in a separate thread) and for each thread you	358	supports child process events, and dynamically created event loops which
240	create, you also create another event loop. Libev itself does no locking	359	do not.
241	whatsoever, so if you mix calls to the same event loop in different
242	threads, make sure you lock (this is usually a bad idea, though, even if
243	done correctly, because it's hideous and inefficient).
244		360
245	=over 4	361	=over 4
246		362
247	=item struct ev_loop *ev_default_loop (unsigned int flags)	363	=item struct ev_loop *ev_default_loop (unsigned int flags)
248		364
249	This will initialise the default event loop if it hasn't been initialised	365	This returns the "default" event loop object, which is what you should
250	yet and return it. If the default loop could not be initialised, returns	366	normally use when you just need "the event loop". Event loop objects and
251	false. If it already was initialised it simply returns it (and ignores the	367	the C<flags> parameter are described in more detail in the entry for
252	flags. If that is troubling you, check C<ev_backend ()> afterwards).	368	C<ev_loop_new>.
		369
		370	If the default loop is already initialised then this function simply
		371	returns it (and ignores the flags. If that is troubling you, check
		372	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		373	flags, which should almost always be C<0>, unless the caller is also the
		374	one calling C<ev_run> or otherwise qualifies as "the main program".
253		375
254	If you don't know what event loop to use, use the one returned from this	376	If you don't know what event loop to use, use the one returned from this
255	function.	377	function (or via the C<EV_DEFAULT> macro).
		378
		379	Note that this function is I<not> thread-safe, so if you want to use it
		380	from multiple threads, you have to employ some kind of mutex (note also
		381	that this case is unlikely, as loops cannot be shared easily between
		382	threads anyway).
		383
		384	The default loop is the only loop that can handle C<ev_child> watchers,
		385	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		386	a problem for your application you can either create a dynamic loop with
		387	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		388	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
		389
		390	Example: This is the most typical usage.
		391
		392	if (!ev_default_loop (0))
		393	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		394
		395	Example: Restrict libev to the select and poll backends, and do not allow
		396	environment settings to be taken into account:
		397
		398	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		399
		400	=item struct ev_loop *ev_loop_new (unsigned int flags)
		401
		402	This will create and initialise a new event loop object. If the loop
		403	could not be initialised, returns false.
		404
		405	This function is thread-safe, and one common way to use libev with
		406	threads is indeed to create one loop per thread, and using the default
		407	loop in the "main" or "initial" thread.
256		408
257	The flags argument can be used to specify special behaviour or specific	409	The flags argument can be used to specify special behaviour or specific
258	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	410	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
259		411
260	The following flags are supported:	412	The following flags are supported:
…		…
266	The default flags value. Use this if you have no clue (it's the right	418	The default flags value. Use this if you have no clue (it's the right
267	thing, believe me).	419	thing, believe me).
268		420
269	=item C<EVFLAG_NOENV>	421	=item C<EVFLAG_NOENV>
270		422
271	If this flag bit is ored into the flag value (or the program runs setuid	423	If this flag bit is or'ed into the flag value (or the program runs setuid
272	or setgid) then libev will I<not> look at the environment variable	424	or setgid) then libev will I<not> look at the environment variable
273	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	425	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
274	override the flags completely if it is found in the environment. This is	426	override the flags completely if it is found in the environment. This is
275	useful to try out specific backends to test their performance, or to work	427	useful to try out specific backends to test their performance, to work
276	around bugs.	428	around bugs, or to make libev threadsafe (accessing environment variables
		429	cannot be done in a threadsafe way, but usually it works if no other
		430	thread modifies them).
277		431
278	=item C<EVFLAG_FORKCHECK>	432	=item C<EVFLAG_FORKCHECK>
279		433
280	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	434	Instead of calling C<ev_loop_fork> manually after a fork, you can also
281	a fork, you can also make libev check for a fork in each iteration by	435	make libev check for a fork in each iteration by enabling this flag.
282	enabling this flag.
283		436
284	This works by calling C<getpid ()> on every iteration of the loop,	437	This works by calling C<getpid ()> on every iteration of the loop,
285	and thus this might slow down your event loop if you do a lot of loop	438	and thus this might slow down your event loop if you do a lot of loop
286	iterations and little real work, but is usually not noticeable (on my	439	iterations and little real work, but is usually not noticeable (on my
287	Linux system for example, C<getpid> is actually a simple 5-insn sequence	440	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
288	without a syscall and thus I<very> fast, but my Linux system also has	441	sequence without a system call and thus I<very> fast, but my GNU/Linux
289	C<pthread_atfork> which is even faster).	442	system also has C<pthread_atfork> which is even faster). (Update: glibc
		443	versions 2.25 apparently removed the C<getpid> optimisation again).
290		444
291	The big advantage of this flag is that you can forget about fork (and	445	The big advantage of this flag is that you can forget about fork (and
292	forget about forgetting to tell libev about forking) when you use this	446	forget about forgetting to tell libev about forking, although you still
293	flag.	447	have to ignore C<SIGPIPE>) when you use this flag.
294		448
295	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	449	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
296	environment variable.	450	environment variable.
		451
		452	=item C<EVFLAG_NOINOTIFY>
		453
		454	When this flag is specified, then libev will not attempt to use the
		455	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		456	testing, this flag can be useful to conserve inotify file descriptors, as
		457	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		458
		459	=item C<EVFLAG_SIGNALFD>
		460
		461	When this flag is specified, then libev will attempt to use the
		462	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		463	delivers signals synchronously, which makes it both faster and might make
		464	it possible to get the queued signal data. It can also simplify signal
		465	handling with threads, as long as you properly block signals in your
		466	threads that are not interested in handling them.
		467
		468	Signalfd will not be used by default as this changes your signal mask, and
		469	there are a lot of shoddy libraries and programs (glib's threadpool for
		470	example) that can't properly initialise their signal masks.
		471
		472	=item C<EVFLAG_NOSIGMASK>
		473
		474	When this flag is specified, then libev will avoid to modify the signal
		475	mask. Specifically, this means you have to make sure signals are unblocked
		476	when you want to receive them.
		477
		478	This behaviour is useful when you want to do your own signal handling, or
		479	want to handle signals only in specific threads and want to avoid libev
		480	unblocking the signals.
		481
		482	It's also required by POSIX in a threaded program, as libev calls
		483	C<sigprocmask>, whose behaviour is officially unspecified.
		484
		485	This flag's behaviour will become the default in future versions of libev.
297		486
298	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	487	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
299		488
300	This is your standard select(2) backend. Not I<completely> standard, as	489	This is your standard select(2) backend. Not I<completely> standard, as
301	libev tries to roll its own fd_set with no limits on the number of fds,	490	libev tries to roll its own fd_set with no limits on the number of fds,
302	but if that fails, expect a fairly low limit on the number of fds when	491	but if that fails, expect a fairly low limit on the number of fds when
303	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	492	using this backend. It doesn't scale too well (O(highest_fd)), but its
304	the fastest backend for a low number of fds.	493	usually the fastest backend for a low number of (low-numbered :) fds.
		494
		495	To get good performance out of this backend you need a high amount of
		496	parallelism (most of the file descriptors should be busy). If you are
		497	writing a server, you should C<accept ()> in a loop to accept as many
		498	connections as possible during one iteration. You might also want to have
		499	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		500	readiness notifications you get per iteration.
		501
		502	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		503	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		504	C<exceptfds> set on that platform).
305		505
306	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	506	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
307		507
308	And this is your standard poll(2) backend. It's more complicated than	508	And this is your standard poll(2) backend. It's more complicated
309	select, but handles sparse fds better and has no artificial limit on the	509	than select, but handles sparse fds better and has no artificial
310	number of fds you can use (except it will slow down considerably with a	510	limit on the number of fds you can use (except it will slow down
311	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	511	considerably with a lot of inactive fds). It scales similarly to select,
		512	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		513	performance tips.
		514
		515	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		516	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
312		517
313	=item C<EVBACKEND_EPOLL> (value 4, Linux)	518	=item C<EVBACKEND_EPOLL> (value 4, Linux)
314		519
		520	Use the Linux-specific epoll(7) interface (for both pre- and post-2.6.9
		521	kernels).
		522
315	For few fds, this backend is a bit little slower than poll and select,	523	For few fds, this backend is a bit little slower than poll and select, but
316	but it scales phenomenally better. While poll and select usually scale like	524	it scales phenomenally better. While poll and select usually scale like
317	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	525	O(total_fds) where total_fds is the total number of fds (or the highest
318	either O(1) or O(active_fds).	526	fd), epoll scales either O(1) or O(active_fds).
319		527
		528	The epoll mechanism deserves honorable mention as the most misdesigned
		529	of the more advanced event mechanisms: mere annoyances include silently
		530	dropping file descriptors, requiring a system call per change per file
		531	descriptor (and unnecessary guessing of parameters), problems with dup,
		532	returning before the timeout value, resulting in additional iterations
		533	(and only giving 5ms accuracy while select on the same platform gives
		534	0.1ms) and so on. The biggest issue is fork races, however - if a program
		535	forks then I<both> parent and child process have to recreate the epoll
		536	set, which can take considerable time (one syscall per file descriptor)
		537	and is of course hard to detect.
		538
		539	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		540	but of course I<doesn't>, and epoll just loves to report events for
		541	totally I<different> file descriptors (even already closed ones, so
		542	one cannot even remove them from the set) than registered in the set
		543	(especially on SMP systems). Libev tries to counter these spurious
		544	notifications by employing an additional generation counter and comparing
		545	that against the events to filter out spurious ones, recreating the set
		546	when required. Epoll also erroneously rounds down timeouts, but gives you
		547	no way to know when and by how much, so sometimes you have to busy-wait
		548	because epoll returns immediately despite a nonzero timeout. And last
		549	not least, it also refuses to work with some file descriptors which work
		550	perfectly fine with C<select> (files, many character devices...).
		551
		552	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		553	cobbled together in a hurry, no thought to design or interaction with
		554	others. Oh, the pain, will it ever stop...
		555
320	While stopping and starting an I/O watcher in the same iteration will	556	While stopping, setting and starting an I/O watcher in the same iteration
321	result in some caching, there is still a syscall per such incident	557	will result in some caching, there is still a system call per such
322	(because the fd could point to a different file description now), so its	558	incident (because the same I<file descriptor> could point to a different
323	best to avoid that. Also, dup()ed file descriptors might not work very	559	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
324	well if you register events for both fds.	560	file descriptors might not work very well if you register events for both
		561	file descriptors.
325		562
326	Please note that epoll sometimes generates spurious notifications, so you	563	Best performance from this backend is achieved by not unregistering all
327	need to use non-blocking I/O or other means to avoid blocking when no data	564	watchers for a file descriptor until it has been closed, if possible,
328	(or space) is available.	565	i.e. keep at least one watcher active per fd at all times. Stopping and
		566	starting a watcher (without re-setting it) also usually doesn't cause
		567	extra overhead. A fork can both result in spurious notifications as well
		568	as in libev having to destroy and recreate the epoll object, which can
		569	take considerable time and thus should be avoided.
		570
		571	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		572	faster than epoll for maybe up to a hundred file descriptors, depending on
		573	the usage. So sad.
		574
		575	While nominally embeddable in other event loops, this feature is broken in
		576	a lot of kernel revisions, but probably(!) works in current versions.
		577
		578	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		579	C<EVBACKEND_POLL>.
		580
		581	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		582
		583	Use the Linux-specific Linux AIO (I<not> C<< aio(7) >> but C<<
		584	io_submit(2) >>) event interface available in post-4.18 kernels (but libev
		585	only tries to use it in 4.19+).
		586
		587	This is another Linux train wreck of an event interface.
		588
		589	If this backend works for you (as of this writing, it was very
		590	experimental), it is the best event interface available on Linux and might
		591	be well worth enabling it - if it isn't available in your kernel this will
		592	be detected and this backend will be skipped.
		593
		594	This backend can batch oneshot requests and supports a user-space ring
		595	buffer to receive events. It also doesn't suffer from most of the design
		596	problems of epoll (such as not being able to remove event sources from
		597	the epoll set), and generally sounds too good to be true. Because, this
		598	being the Linux kernel, of course it suffers from a whole new set of
		599	limitations, forcing you to fall back to epoll, inheriting all its design
		600	issues.
		601
		602	For one, it is not easily embeddable (but probably could be done using
		603	an event fd at some extra overhead). It also is subject to a system wide
		604	limit that can be configured in F</proc/sys/fs/aio-max-nr>. If no AIO
		605	requests are left, this backend will be skipped during initialisation, and
		606	will switch to epoll when the loop is active.
		607
		608	Most problematic in practice, however, is that not all file descriptors
		609	work with it. For example, in Linux 5.1, TCP sockets, pipes, event fds,
		610	files, F</dev/null> and many others are supported, but ttys do not work
		611	properly (a known bug that the kernel developers don't care about, see
		612	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		613	(yet?) a generic event polling interface.
		614
		615	Overall, it seems the Linux developers just don't want it to have a
		616	generic event handling mechanism other than C<select> or C<poll>.
		617
		618	To work around all these problem, the current version of libev uses its
		619	epoll backend as a fallback for file descriptor types that do not work. Or
		620	falls back completely to epoll if the kernel acts up.
		621
		622	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		623	C<EVBACKEND_POLL>.
329		624
330	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	625	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
331		626
332	Kqueue deserves special mention, as at the time of this writing, it	627	Kqueue deserves special mention, as at the time this backend was
333	was broken on all BSDs except NetBSD (usually it doesn't work with	628	implemented, it was broken on all BSDs except NetBSD (usually it doesn't
334	anything but sockets and pipes, except on Darwin, where of course its	629	work reliably with anything but sockets and pipes, except on Darwin,
335	completely useless). For this reason its not being "autodetected"	630	where of course it's completely useless). Unlike epoll, however, whose
336	unless you explicitly specify it explicitly in the flags (i.e. using	631	brokenness is by design, these kqueue bugs can be (and mostly have been)
337	C<EVBACKEND_KQUEUE>).	632	fixed without API changes to existing programs. For this reason it's not
		633	being "auto-detected" on all platforms unless you explicitly specify it
		634	in the flags (i.e. using C<EVBACKEND_KQUEUE>) or libev was compiled on a
		635	known-to-be-good (-enough) system like NetBSD.
		636
		637	You still can embed kqueue into a normal poll or select backend and use it
		638	only for sockets (after having made sure that sockets work with kqueue on
		639	the target platform). See C<ev_embed> watchers for more info.
338		640
339	It scales in the same way as the epoll backend, but the interface to the	641	It scales in the same way as the epoll backend, but the interface to the
340	kernel is more efficient (which says nothing about its actual speed, of	642	kernel is more efficient (which says nothing about its actual speed, of
341	course). While starting and stopping an I/O watcher does not cause an	643	course). While stopping, setting and starting an I/O watcher does never
342	extra syscall as with epoll, it still adds up to four event changes per	644	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
343	incident, so its best to avoid that.	645	two event changes per incident. Support for C<fork ()> is very bad (you
		646	might have to leak fds on fork, but it's more sane than epoll) and it
		647	drops fds silently in similarly hard-to-detect cases.
		648
		649	This backend usually performs well under most conditions.
		650
		651	While nominally embeddable in other event loops, this doesn't work
		652	everywhere, so you might need to test for this. And since it is broken
		653	almost everywhere, you should only use it when you have a lot of sockets
		654	(for which it usually works), by embedding it into another event loop
		655	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		656	also broken on OS X)) and, did I mention it, using it only for sockets.
		657
		658	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		659	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		660	C<NOTE_EOF>.
344		661
345	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	662	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
346		663
347	This is not implemented yet (and might never be).	664	This is not implemented yet (and might never be, unless you send me an
		665	implementation). According to reports, C</dev/poll> only supports sockets
		666	and is not embeddable, which would limit the usefulness of this backend
		667	immensely.
348		668
349	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	669	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
350		670
351	This uses the Solaris 10 port mechanism. As with everything on Solaris,	671	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
352	it's really slow, but it still scales very well (O(active_fds)).	672	it's really slow, but it still scales very well (O(active_fds)).
353		673
354	Please note that solaris ports can result in a lot of spurious	674	While this backend scales well, it requires one system call per active
355	notifications, so you need to use non-blocking I/O or other means to avoid	675	file descriptor per loop iteration. For small and medium numbers of file
356	blocking when no data (or space) is available.	676	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		677	might perform better.
		678
		679	On the positive side, this backend actually performed fully to
		680	specification in all tests and is fully embeddable, which is a rare feat
		681	among the OS-specific backends (I vastly prefer correctness over speed
		682	hacks).
		683
		684	On the negative side, the interface is I<bizarre> - so bizarre that
		685	even sun itself gets it wrong in their code examples: The event polling
		686	function sometimes returns events to the caller even though an error
		687	occurred, but with no indication whether it has done so or not (yes, it's
		688	even documented that way) - deadly for edge-triggered interfaces where you
		689	absolutely have to know whether an event occurred or not because you have
		690	to re-arm the watcher.
		691
		692	Fortunately libev seems to be able to work around these idiocies.
		693
		694	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		695	C<EVBACKEND_POLL>.
357		696
358	=item C<EVBACKEND_ALL>	697	=item C<EVBACKEND_ALL>
359		698
360	Try all backends (even potentially broken ones that wouldn't be tried	699	Try all backends (even potentially broken ones that wouldn't be tried
361	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	700	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
362	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	701	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
363		702
		703	It is definitely not recommended to use this flag, use whatever
		704	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		705	at all.
		706
		707	=item C<EVBACKEND_MASK>
		708
		709	Not a backend at all, but a mask to select all backend bits from a
		710	C<flags> value, in case you want to mask out any backends from a flags
		711	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
		712
364	=back	713	=back
365		714
366	If one or more of these are ored into the flags value, then only these	715	If one or more of the backend flags are or'ed into the flags value,
367	backends will be tried (in the reverse order as given here). If none are	716	then only these backends will be tried (in the reverse order as listed
368	specified, most compiled-in backend will be tried, usually in reverse	717	here). If none are specified, all backends in C<ev_recommended_backends
369	order of their flag values :)	718	()> will be tried.
370
371	The most typical usage is like this:
372
373	if (!ev_default_loop (0))
374	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
375
376	Restrict libev to the select and poll backends, and do not allow
377	environment settings to be taken into account:
378
379	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
380
381	Use whatever libev has to offer, but make sure that kqueue is used if
382	available (warning, breaks stuff, best use only with your own private
383	event loop and only if you know the OS supports your types of fds):
384
385	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
386
387	=item struct ev_loop *ev_loop_new (unsigned int flags)
388
389	Similar to C<ev_default_loop>, but always creates a new event loop that is
390	always distinct from the default loop. Unlike the default loop, it cannot
391	handle signal and child watchers, and attempts to do so will be greeted by
392	undefined behaviour (or a failed assertion if assertions are enabled).
393		719
394	Example: Try to create a event loop that uses epoll and nothing else.	720	Example: Try to create a event loop that uses epoll and nothing else.
395		721
396	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	722	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
397	if (!epoller)	723	if (!epoller)
398	fatal ("no epoll found here, maybe it hides under your chair");	724	fatal ("no epoll found here, maybe it hides under your chair");
399		725
		726	Example: Use whatever libev has to offer, but make sure that kqueue is
		727	used if available.
		728
		729	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		730
		731	Example: Similarly, on linux, you mgiht want to take advantage of the
		732	linux aio backend if possible, but fall back to something else if that
		733	isn't available.
		734
		735	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
		736
400	=item ev_default_destroy ()	737	=item ev_loop_destroy (loop)
401		738
402	Destroys the default loop again (frees all memory and kernel state	739	Destroys an event loop object (frees all memory and kernel state
403	etc.). None of the active event watchers will be stopped in the normal	740	etc.). None of the active event watchers will be stopped in the normal
404	sense, so e.g. C<ev_is_active> might still return true. It is your	741	sense, so e.g. C<ev_is_active> might still return true. It is your
405	responsibility to either stop all watchers cleanly yoursef I<before>	742	responsibility to either stop all watchers cleanly yourself I<before>
406	calling this function, or cope with the fact afterwards (which is usually	743	calling this function, or cope with the fact afterwards (which is usually
407	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	744	the easiest thing, you can just ignore the watchers and/or C<free ()> them
408	for example).	745	for example).
409		746
		747	Note that certain global state, such as signal state (and installed signal
		748	handlers), will not be freed by this function, and related watchers (such
		749	as signal and child watchers) would need to be stopped manually.
		750
		751	This function is normally used on loop objects allocated by
		752	C<ev_loop_new>, but it can also be used on the default loop returned by
		753	C<ev_default_loop>, in which case it is not thread-safe.
		754
		755	Note that it is not advisable to call this function on the default loop
		756	except in the rare occasion where you really need to free its resources.
		757	If you need dynamically allocated loops it is better to use C<ev_loop_new>
		758	and C<ev_loop_destroy>.
		759
410	=item ev_loop_destroy (loop)	760	=item ev_loop_fork (loop)
411		761
412	Like C<ev_default_destroy>, but destroys an event loop created by an	762	This function sets a flag that causes subsequent C<ev_run> iterations
413	earlier call to C<ev_loop_new>.
414
415	=item ev_default_fork ()
416
417	This function reinitialises the kernel state for backends that have	763	to reinitialise the kernel state for backends that have one. Despite
418	one. Despite the name, you can call it anytime, but it makes most sense	764	the name, you can call it anytime you are allowed to start or stop
419	after forking, in either the parent or child process (or both, but that	765	watchers (except inside an C<ev_prepare> callback), but it makes most
420	again makes little sense).	766	sense after forking, in the child process. You I<must> call it (or use
		767	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
421		768
422	You I<must> call this function in the child process after forking if and	769	In addition, if you want to reuse a loop (via this function or
423	only if you want to use the event library in both processes. If you just	770	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
424	fork+exec, you don't have to call it.	771
		772	Again, you I<have> to call it on I<any> loop that you want to re-use after
		773	a fork, I<even if you do not plan to use the loop in the parent>. This is
		774	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		775	during fork.
		776
		777	On the other hand, you only need to call this function in the child
		778	process if and only if you want to use the event loop in the child. If
		779	you just fork+exec or create a new loop in the child, you don't have to
		780	call it at all (in fact, C<epoll> is so badly broken that it makes a
		781	difference, but libev will usually detect this case on its own and do a
		782	costly reset of the backend).
425		783
426	The function itself is quite fast and it's usually not a problem to call	784	The function itself is quite fast and it's usually not a problem to call
427	it just in case after a fork. To make this easy, the function will fit in	785	it just in case after a fork.
428	quite nicely into a call to C<pthread_atfork>:
429		786
		787	Example: Automate calling C<ev_loop_fork> on the default loop when
		788	using pthreads.
		789
		790	static void
		791	post_fork_child (void)
		792	{
		793	ev_loop_fork (EV_DEFAULT);
		794	}
		795
		796	...
430	pthread_atfork (0, 0, ev_default_fork);	797	pthread_atfork (0, 0, post_fork_child);
431		798
432	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	799	=item int ev_is_default_loop (loop)
433	without calling this function, so if you force one of those backends you
434	do not need to care.
435		800
436	=item ev_loop_fork (loop)	801	Returns true when the given loop is, in fact, the default loop, and false
		802	otherwise.
437		803
438	Like C<ev_default_fork>, but acts on an event loop created by
439	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
440	after fork, and how you do this is entirely your own problem.
441
442	=item unsigned int ev_loop_count (loop)	804	=item unsigned int ev_iteration (loop)
443		805
444	Returns the count of loop iterations for the loop, which is identical to	806	Returns the current iteration count for the event loop, which is identical
445	the number of times libev did poll for new events. It starts at C<0> and	807	to the number of times libev did poll for new events. It starts at C<0>
446	happily wraps around with enough iterations.	808	and happily wraps around with enough iterations.
447		809
448	This value can sometimes be useful as a generation counter of sorts (it	810	This value can sometimes be useful as a generation counter of sorts (it
449	"ticks" the number of loop iterations), as it roughly corresponds with	811	"ticks" the number of loop iterations), as it roughly corresponds with
450	C<ev_prepare> and C<ev_check> calls.	812	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		813	prepare and check phases.
		814
		815	=item unsigned int ev_depth (loop)
		816
		817	Returns the number of times C<ev_run> was entered minus the number of
		818	times C<ev_run> was exited normally, in other words, the recursion depth.
		819
		820	Outside C<ev_run>, this number is zero. In a callback, this number is
		821	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		822	in which case it is higher.
		823
		824	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		825	throwing an exception etc.), doesn't count as "exit" - consider this
		826	as a hint to avoid such ungentleman-like behaviour unless it's really
		827	convenient, in which case it is fully supported.
451		828
452	=item unsigned int ev_backend (loop)	829	=item unsigned int ev_backend (loop)
453		830
454	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	831	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
455	use.	832	use.
…		…
458		835
459	Returns the current "event loop time", which is the time the event loop	836	Returns the current "event loop time", which is the time the event loop
460	received events and started processing them. This timestamp does not	837	received events and started processing them. This timestamp does not
461	change as long as callbacks are being processed, and this is also the base	838	change as long as callbacks are being processed, and this is also the base
462	time used for relative timers. You can treat it as the timestamp of the	839	time used for relative timers. You can treat it as the timestamp of the
463	event occuring (or more correctly, libev finding out about it).	840	event occurring (or more correctly, libev finding out about it).
464		841
		842	=item ev_now_update (loop)
		843
		844	Establishes the current time by querying the kernel, updating the time
		845	returned by C<ev_now ()> in the progress. This is a costly operation and
		846	is usually done automatically within C<ev_run ()>.
		847
		848	This function is rarely useful, but when some event callback runs for a
		849	very long time without entering the event loop, updating libev's idea of
		850	the current time is a good idea.
		851
		852	See also L</The special problem of time updates> in the C<ev_timer> section.
		853
		854	=item ev_suspend (loop)
		855
		856	=item ev_resume (loop)
		857
		858	These two functions suspend and resume an event loop, for use when the
		859	loop is not used for a while and timeouts should not be processed.
		860
		861	A typical use case would be an interactive program such as a game: When
		862	the user presses C<^Z> to suspend the game and resumes it an hour later it
		863	would be best to handle timeouts as if no time had actually passed while
		864	the program was suspended. This can be achieved by calling C<ev_suspend>
		865	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		866	C<ev_resume> directly afterwards to resume timer processing.
		867
		868	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		869	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		870	will be rescheduled (that is, they will lose any events that would have
		871	occurred while suspended).
		872
		873	After calling C<ev_suspend> you B<must not> call I<any> function on the
		874	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		875	without a previous call to C<ev_suspend>.
		876
		877	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		878	event loop time (see C<ev_now_update>).
		879
465	=item ev_loop (loop, int flags)	880	=item bool ev_run (loop, int flags)
466		881
467	Finally, this is it, the event handler. This function usually is called	882	Finally, this is it, the event handler. This function usually is called
468	after you initialised all your watchers and you want to start handling	883	after you have initialised all your watchers and you want to start
469	events.	884	handling events. It will ask the operating system for any new events, call
		885	the watcher callbacks, and then repeat the whole process indefinitely: This
		886	is why event loops are called I<loops>.
470		887
471	If the flags argument is specified as C<0>, it will not return until	888	If the flags argument is specified as C<0>, it will keep handling events
472	either no event watchers are active anymore or C<ev_unloop> was called.	889	until either no event watchers are active anymore or C<ev_break> was
		890	called.
473		891
		892	The return value is false if there are no more active watchers (which
		893	usually means "all jobs done" or "deadlock"), and true in all other cases
		894	(which usually means " you should call C<ev_run> again").
		895
474	Please note that an explicit C<ev_unloop> is usually better than	896	Please note that an explicit C<ev_break> is usually better than
475	relying on all watchers to be stopped when deciding when a program has	897	relying on all watchers to be stopped when deciding when a program has
476	finished (especially in interactive programs), but having a program that	898	finished (especially in interactive programs), but having a program
477	automatically loops as long as it has to and no longer by virtue of	899	that automatically loops as long as it has to and no longer by virtue
478	relying on its watchers stopping correctly is a thing of beauty.	900	of relying on its watchers stopping correctly, that is truly a thing of
		901	beauty.
479		902
		903	This function is I<mostly> exception-safe - you can break out of a
		904	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		905	exception and so on. This does not decrement the C<ev_depth> value, nor
		906	will it clear any outstanding C<EVBREAK_ONE> breaks.
		907
480	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	908	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
481	those events and any outstanding ones, but will not block your process in	909	those events and any already outstanding ones, but will not wait and
482	case there are no events and will return after one iteration of the loop.	910	block your process in case there are no events and will return after one
		911	iteration of the loop. This is sometimes useful to poll and handle new
		912	events while doing lengthy calculations, to keep the program responsive.
483		913
484	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	914	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
485	neccessary) and will handle those and any outstanding ones. It will block	915	necessary) and will handle those and any already outstanding ones. It
486	your process until at least one new event arrives, and will return after	916	will block your process until at least one new event arrives (which could
487	one iteration of the loop. This is useful if you are waiting for some	917	be an event internal to libev itself, so there is no guarantee that a
488	external event in conjunction with something not expressible using other	918	user-registered callback will be called), and will return after one
		919	iteration of the loop.
		920
		921	This is useful if you are waiting for some external event in conjunction
		922	with something not expressible using other libev watchers (i.e. "roll your
489	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	923	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
490	usually a better approach for this kind of thing.	924	usually a better approach for this kind of thing.
491		925
492	Here are the gory details of what C<ev_loop> does:	926	Here are the gory details of what C<ev_run> does (this is for your
		927	understanding, not a guarantee that things will work exactly like this in
		928	future versions):
493		929
		930	- Increment loop depth.
		931	- Reset the ev_break status.
494	- Before the first iteration, call any pending watchers.	932	- Before the first iteration, call any pending watchers.
495	* If there are no active watchers (reference count is zero), return.	933	LOOP:
496	- Queue all prepare watchers and then call all outstanding watchers.	934	- If EVFLAG_FORKCHECK was used, check for a fork.
		935	- If a fork was detected (by any means), queue and call all fork watchers.
		936	- Queue and call all prepare watchers.
		937	- If ev_break was called, goto FINISH.
497	- If we have been forked, recreate the kernel state.	938	- If we have been forked, detach and recreate the kernel state
		939	as to not disturb the other process.
498	- Update the kernel state with all outstanding changes.	940	- Update the kernel state with all outstanding changes.
499	- Update the "event loop time".	941	- Update the "event loop time" (ev_now ()).
500	- Calculate for how long to block.	942	- Calculate for how long to sleep or block, if at all
		943	(active idle watchers, EVRUN_NOWAIT or not having
		944	any active watchers at all will result in not sleeping).
		945	- Sleep if the I/O and timer collect interval say so.
		946	- Increment loop iteration counter.
501	- Block the process, waiting for any events.	947	- Block the process, waiting for any events.
502	- Queue all outstanding I/O (fd) events.	948	- Queue all outstanding I/O (fd) events.
503	- Update the "event loop time" and do time jump handling.	949	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
504	- Queue all outstanding timers.	950	- Queue all expired timers.
505	- Queue all outstanding periodics.	951	- Queue all expired periodics.
506	- If no events are pending now, queue all idle watchers.	952	- Queue all idle watchers with priority higher than that of pending events.
507	- Queue all check watchers.	953	- Queue all check watchers.
508	- Call all queued watchers in reverse order (i.e. check watchers first).	954	- Call all queued watchers in reverse order (i.e. check watchers first).
509	Signals and child watchers are implemented as I/O watchers, and will	955	Signals and child watchers are implemented as I/O watchers, and will
510	be handled here by queueing them when their watcher gets executed.	956	be handled here by queueing them when their watcher gets executed.
511	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	957	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
512	were used, return, otherwise continue with step *.	958	were used, or there are no active watchers, goto FINISH, otherwise
		959	continue with step LOOP.
		960	FINISH:
		961	- Reset the ev_break status iff it was EVBREAK_ONE.
		962	- Decrement the loop depth.
		963	- Return.
513		964
514	Example: Queue some jobs and then loop until no events are outsanding	965	Example: Queue some jobs and then loop until no events are outstanding
515	anymore.	966	anymore.
516		967
517	... queue jobs here, make sure they register event watchers as long	968	... queue jobs here, make sure they register event watchers as long
518	... as they still have work to do (even an idle watcher will do..)	969	... as they still have work to do (even an idle watcher will do..)
519	ev_loop (my_loop, 0);	970	ev_run (my_loop, 0);
520	... jobs done. yeah!	971	... jobs done or somebody called break. yeah!
521		972
522	=item ev_unloop (loop, how)	973	=item ev_break (loop, how)
523		974
524	Can be used to make a call to C<ev_loop> return early (but only after it	975	Can be used to make a call to C<ev_run> return early (but only after it
525	has processed all outstanding events). The C<how> argument must be either	976	has processed all outstanding events). The C<how> argument must be either
526	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	977	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
527	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	978	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		979
		980	This "break state" will be cleared on the next call to C<ev_run>.
		981
		982	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		983	which case it will have no effect.
528		984
529	=item ev_ref (loop)	985	=item ev_ref (loop)
530		986
531	=item ev_unref (loop)	987	=item ev_unref (loop)
532		988
533	Ref/unref can be used to add or remove a reference count on the event	989	Ref/unref can be used to add or remove a reference count on the event
534	loop: Every watcher keeps one reference, and as long as the reference	990	loop: Every watcher keeps one reference, and as long as the reference
535	count is nonzero, C<ev_loop> will not return on its own. If you have	991	count is nonzero, C<ev_run> will not return on its own.
536	a watcher you never unregister that should not keep C<ev_loop> from	992
537	returning, ev_unref() after starting, and ev_ref() before stopping it. For	993	This is useful when you have a watcher that you never intend to
		994	unregister, but that nevertheless should not keep C<ev_run> from
		995	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		996	before stopping it.
		997
538	example, libev itself uses this for its internal signal pipe: It is not	998	As an example, libev itself uses this for its internal signal pipe: It
539	visible to the libev user and should not keep C<ev_loop> from exiting if	999	is not visible to the libev user and should not keep C<ev_run> from
540	no event watchers registered by it are active. It is also an excellent	1000	exiting if no event watchers registered by it are active. It is also an
541	way to do this for generic recurring timers or from within third-party	1001	excellent way to do this for generic recurring timers or from within
542	libraries. Just remember to I<unref after start> and I<ref before stop>.	1002	third-party libraries. Just remember to I<unref after start> and I<ref
		1003	before stop> (but only if the watcher wasn't active before, or was active
		1004	before, respectively. Note also that libev might stop watchers itself
		1005	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		1006	in the callback).
543		1007
544	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	1008	Example: Create a signal watcher, but keep it from keeping C<ev_run>
545	running when nothing else is active.	1009	running when nothing else is active.
546		1010
547	struct ev_signal exitsig;	1011	ev_signal exitsig;
548	ev_signal_init (&exitsig, sig_cb, SIGINT);	1012	ev_signal_init (&exitsig, sig_cb, SIGINT);
549	ev_signal_start (loop, &exitsig);	1013	ev_signal_start (loop, &exitsig);
550	evf_unref (loop);	1014	ev_unref (loop);
551		1015
552	Example: For some weird reason, unregister the above signal handler again.	1016	Example: For some weird reason, unregister the above signal handler again.
553		1017
554	ev_ref (loop);	1018	ev_ref (loop);
555	ev_signal_stop (loop, &exitsig);	1019	ev_signal_stop (loop, &exitsig);
		1020
		1021	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		1022
		1023	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		1024
		1025	These advanced functions influence the time that libev will spend waiting
		1026	for events. Both time intervals are by default C<0>, meaning that libev
		1027	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		1028	latency.
		1029
		1030	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		1031	allows libev to delay invocation of I/O and timer/periodic callbacks
		1032	to increase efficiency of loop iterations (or to increase power-saving
		1033	opportunities).
		1034
		1035	The idea is that sometimes your program runs just fast enough to handle
		1036	one (or very few) event(s) per loop iteration. While this makes the
		1037	program responsive, it also wastes a lot of CPU time to poll for new
		1038	events, especially with backends like C<select ()> which have a high
		1039	overhead for the actual polling but can deliver many events at once.
		1040
		1041	By setting a higher I<io collect interval> you allow libev to spend more
		1042	time collecting I/O events, so you can handle more events per iteration,
		1043	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		1044	C<ev_timer>) will not be affected. Setting this to a non-null value will
		1045	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		1046	sleep time ensures that libev will not poll for I/O events more often then
		1047	once per this interval, on average (as long as the host time resolution is
		1048	good enough).
		1049
		1050	Likewise, by setting a higher I<timeout collect interval> you allow libev
		1051	to spend more time collecting timeouts, at the expense of increased
		1052	latency/jitter/inexactness (the watcher callback will be called
		1053	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		1054	value will not introduce any overhead in libev.
		1055
		1056	Many (busy) programs can usually benefit by setting the I/O collect
		1057	interval to a value near C<0.1> or so, which is often enough for
		1058	interactive servers (of course not for games), likewise for timeouts. It
		1059	usually doesn't make much sense to set it to a lower value than C<0.01>,
		1060	as this approaches the timing granularity of most systems. Note that if
		1061	you do transactions with the outside world and you can't increase the
		1062	parallelity, then this setting will limit your transaction rate (if you
		1063	need to poll once per transaction and the I/O collect interval is 0.01,
		1064	then you can't do more than 100 transactions per second).
		1065
		1066	Setting the I<timeout collect interval> can improve the opportunity for
		1067	saving power, as the program will "bundle" timer callback invocations that
		1068	are "near" in time together, by delaying some, thus reducing the number of
		1069	times the process sleeps and wakes up again. Another useful technique to
		1070	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		1071	they fire on, say, one-second boundaries only.
		1072
		1073	Example: we only need 0.1s timeout granularity, and we wish not to poll
		1074	more often than 100 times per second:
		1075
		1076	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		1077	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		1078
		1079	=item ev_invoke_pending (loop)
		1080
		1081	This call will simply invoke all pending watchers while resetting their
		1082	pending state. Normally, C<ev_run> does this automatically when required,
		1083	but when overriding the invoke callback this call comes handy. This
		1084	function can be invoked from a watcher - this can be useful for example
		1085	when you want to do some lengthy calculation and want to pass further
		1086	event handling to another thread (you still have to make sure only one
		1087	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1088
		1089	=item int ev_pending_count (loop)
		1090
		1091	Returns the number of pending watchers - zero indicates that no watchers
		1092	are pending.
		1093
		1094	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1095
		1096	This overrides the invoke pending functionality of the loop: Instead of
		1097	invoking all pending watchers when there are any, C<ev_run> will call
		1098	this callback instead. This is useful, for example, when you want to
		1099	invoke the actual watchers inside another context (another thread etc.).
		1100
		1101	If you want to reset the callback, use C<ev_invoke_pending> as new
		1102	callback.
		1103
		1104	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1105
		1106	Sometimes you want to share the same loop between multiple threads. This
		1107	can be done relatively simply by putting mutex_lock/unlock calls around
		1108	each call to a libev function.
		1109
		1110	However, C<ev_run> can run an indefinite time, so it is not feasible
		1111	to wait for it to return. One way around this is to wake up the event
		1112	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1113	I<release> and I<acquire> callbacks on the loop.
		1114
		1115	When set, then C<release> will be called just before the thread is
		1116	suspended waiting for new events, and C<acquire> is called just
		1117	afterwards.
		1118
		1119	Ideally, C<release> will just call your mutex_unlock function, and
		1120	C<acquire> will just call the mutex_lock function again.
		1121
		1122	While event loop modifications are allowed between invocations of
		1123	C<release> and C<acquire> (that's their only purpose after all), no
		1124	modifications done will affect the event loop, i.e. adding watchers will
		1125	have no effect on the set of file descriptors being watched, or the time
		1126	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1127	to take note of any changes you made.
		1128
		1129	In theory, threads executing C<ev_run> will be async-cancel safe between
		1130	invocations of C<release> and C<acquire>.
		1131
		1132	See also the locking example in the C<THREADS> section later in this
		1133	document.
		1134
		1135	=item ev_set_userdata (loop, void *data)
		1136
		1137	=item void *ev_userdata (loop)
		1138
		1139	Set and retrieve a single C<void *> associated with a loop. When
		1140	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1141	C<0>.
		1142
		1143	These two functions can be used to associate arbitrary data with a loop,
		1144	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1145	C<acquire> callbacks described above, but of course can be (ab-)used for
		1146	any other purpose as well.
		1147
		1148	=item ev_verify (loop)
		1149
		1150	This function only does something when C<EV_VERIFY> support has been
		1151	compiled in, which is the default for non-minimal builds. It tries to go
		1152	through all internal structures and checks them for validity. If anything
		1153	is found to be inconsistent, it will print an error message to standard
		1154	error and call C<abort ()>.
		1155
		1156	This can be used to catch bugs inside libev itself: under normal
		1157	circumstances, this function will never abort as of course libev keeps its
		1158	data structures consistent.
556		1159
557	=back	1160	=back
558		1161
559		1162
560	=head1 ANATOMY OF A WATCHER	1163	=head1 ANATOMY OF A WATCHER
561		1164
		1165	In the following description, uppercase C<TYPE> in names stands for the
		1166	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1167	watchers and C<ev_io_start> for I/O watchers.
		1168
562	A watcher is a structure that you create and register to record your	1169	A watcher is an opaque structure that you allocate and register to record
563	interest in some event. For instance, if you want to wait for STDIN to	1170	your interest in some event. To make a concrete example, imagine you want
564	become readable, you would create an C<ev_io> watcher for that:	1171	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1172	for that:
565		1173
566	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1174	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
567	{	1175	{
568	ev_io_stop (w);	1176	ev_io_stop (w);
569	ev_unloop (loop, EVUNLOOP_ALL);	1177	ev_break (loop, EVBREAK_ALL);
570	}	1178	}
571		1179
572	struct ev_loop *loop = ev_default_loop (0);	1180	struct ev_loop *loop = ev_default_loop (0);
		1181
573	struct ev_io stdin_watcher;	1182	ev_io stdin_watcher;
		1183
574	ev_init (&stdin_watcher, my_cb);	1184	ev_init (&stdin_watcher, my_cb);
575	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1185	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
576	ev_io_start (loop, &stdin_watcher);	1186	ev_io_start (loop, &stdin_watcher);
		1187
577	ev_loop (loop, 0);	1188	ev_run (loop, 0);
578		1189
579	As you can see, you are responsible for allocating the memory for your	1190	As you can see, you are responsible for allocating the memory for your
580	watcher structures (and it is usually a bad idea to do this on the stack,	1191	watcher structures (and it is I<usually> a bad idea to do this on the
581	although this can sometimes be quite valid).	1192	stack).
582		1193
		1194	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1195	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1196
583	Each watcher structure must be initialised by a call to C<ev_init	1197	Each watcher structure must be initialised by a call to C<ev_init (watcher
584	(watcher *, callback)>, which expects a callback to be provided. This	1198	*, callback)>, which expects a callback to be provided. This callback is
585	callback gets invoked each time the event occurs (or, in the case of io	1199	invoked each time the event occurs (or, in the case of I/O watchers, each
586	watchers, each time the event loop detects that the file descriptor given	1200	time the event loop detects that the file descriptor given is readable
587	is readable and/or writable).	1201	and/or writable).
588		1202
589	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1203	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
590	with arguments specific to this watcher type. There is also a macro	1204	macro to configure it, with arguments specific to the watcher type. There
591	to combine initialisation and setting in one call: C<< ev_<type>_init	1205	is also a macro to combine initialisation and setting in one call: C<<
592	(watcher *, callback, ...) >>.	1206	ev_TYPE_init (watcher *, callback, ...) >>.
593		1207
594	To make the watcher actually watch out for events, you have to start it	1208	To make the watcher actually watch out for events, you have to start it
595	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1209	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
596	*) >>), and you can stop watching for events at any time by calling the	1210	*) >>), and you can stop watching for events at any time by calling the
597	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1211	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
598		1212
599	As long as your watcher is active (has been started but not stopped) you	1213	As long as your watcher is active (has been started but not stopped) you
600	must not touch the values stored in it. Most specifically you must never	1214	must not touch the values stored in it. Most specifically you must never
601	reinitialise it or call its C<set> macro.	1215	reinitialise it or call its C<ev_TYPE_set> macro.
602		1216
603	Each and every callback receives the event loop pointer as first, the	1217	Each and every callback receives the event loop pointer as first, the
604	registered watcher structure as second, and a bitset of received events as	1218	registered watcher structure as second, and a bitset of received events as
605	third argument.	1219	third argument.
606		1220
…		…
615	=item C<EV_WRITE>	1229	=item C<EV_WRITE>
616		1230
617	The file descriptor in the C<ev_io> watcher has become readable and/or	1231	The file descriptor in the C<ev_io> watcher has become readable and/or
618	writable.	1232	writable.
619		1233
620	=item C<EV_TIMEOUT>	1234	=item C<EV_TIMER>
621		1235
622	The C<ev_timer> watcher has timed out.	1236	The C<ev_timer> watcher has timed out.
623		1237
624	=item C<EV_PERIODIC>	1238	=item C<EV_PERIODIC>
625		1239
…		…
643		1257
644	=item C<EV_PREPARE>	1258	=item C<EV_PREPARE>
645		1259
646	=item C<EV_CHECK>	1260	=item C<EV_CHECK>
647		1261
648	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1262	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
649	to gather new events, and all C<ev_check> watchers are invoked just after	1263	gather new events, and all C<ev_check> watchers are queued (not invoked)
650	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1264	just after C<ev_run> has gathered them, but before it queues any callbacks
		1265	for any received events. That means C<ev_prepare> watchers are the last
		1266	watchers invoked before the event loop sleeps or polls for new events, and
		1267	C<ev_check> watchers will be invoked before any other watchers of the same
		1268	or lower priority within an event loop iteration.
		1269
651	received events. Callbacks of both watcher types can start and stop as	1270	Callbacks of both watcher types can start and stop as many watchers as
652	many watchers as they want, and all of them will be taken into account	1271	they want, and all of them will be taken into account (for example, a
653	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1272	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
654	C<ev_loop> from blocking).	1273	blocking).
655		1274
656	=item C<EV_EMBED>	1275	=item C<EV_EMBED>
657		1276
658	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1277	The embedded event loop specified in the C<ev_embed> watcher needs attention.
659		1278
660	=item C<EV_FORK>	1279	=item C<EV_FORK>
661		1280
662	The event loop has been resumed in the child process after fork (see	1281	The event loop has been resumed in the child process after fork (see
663	C<ev_fork>).	1282	C<ev_fork>).
664		1283
		1284	=item C<EV_CLEANUP>
		1285
		1286	The event loop is about to be destroyed (see C<ev_cleanup>).
		1287
		1288	=item C<EV_ASYNC>
		1289
		1290	The given async watcher has been asynchronously notified (see C<ev_async>).
		1291
		1292	=item C<EV_CUSTOM>
		1293
		1294	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1295	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1296
665	=item C<EV_ERROR>	1297	=item C<EV_ERROR>
666		1298
667	An unspecified error has occured, the watcher has been stopped. This might	1299	An unspecified error has occurred, the watcher has been stopped. This might
668	happen because the watcher could not be properly started because libev	1300	happen because the watcher could not be properly started because libev
669	ran out of memory, a file descriptor was found to be closed or any other	1301	ran out of memory, a file descriptor was found to be closed or any other
		1302	problem. Libev considers these application bugs.
		1303
670	problem. You best act on it by reporting the problem and somehow coping	1304	You best act on it by reporting the problem and somehow coping with the
671	with the watcher being stopped.	1305	watcher being stopped. Note that well-written programs should not receive
		1306	an error ever, so when your watcher receives it, this usually indicates a
		1307	bug in your program.
672		1308
673	Libev will usually signal a few "dummy" events together with an error,	1309	Libev will usually signal a few "dummy" events together with an error, for
674	for example it might indicate that a fd is readable or writable, and if	1310	example it might indicate that a fd is readable or writable, and if your
675	your callbacks is well-written it can just attempt the operation and cope	1311	callbacks is well-written it can just attempt the operation and cope with
676	with the error from read() or write(). This will not work in multithreaded	1312	the error from read() or write(). This will not work in multi-threaded
677	programs, though, so beware.	1313	programs, though, as the fd could already be closed and reused for another
		1314	thing, so beware.
678		1315
679	=back	1316	=back
680		1317
681	=head2 GENERIC WATCHER FUNCTIONS	1318	=head2 GENERIC WATCHER FUNCTIONS
682
683	In the following description, C<TYPE> stands for the watcher type,
684	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
685		1319
686	=over 4	1320	=over 4
687		1321
688	=item C<ev_init> (ev_TYPE *watcher, callback)	1322	=item C<ev_init> (ev_TYPE *watcher, callback)
689		1323
…		…
695	which rolls both calls into one.	1329	which rolls both calls into one.
696		1330
697	You can reinitialise a watcher at any time as long as it has been stopped	1331	You can reinitialise a watcher at any time as long as it has been stopped
698	(or never started) and there are no pending events outstanding.	1332	(or never started) and there are no pending events outstanding.
699		1333
700	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1334	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
701	int revents)>.	1335	int revents)>.
702		1336
		1337	Example: Initialise an C<ev_io> watcher in two steps.
		1338
		1339	ev_io w;
		1340	ev_init (&w, my_cb);
		1341	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1342
703	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1343	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
704		1344
705	This macro initialises the type-specific parts of a watcher. You need to	1345	This macro initialises the type-specific parts of a watcher. You need to
706	call C<ev_init> at least once before you call this macro, but you can	1346	call C<ev_init> at least once before you call this macro, but you can
707	call C<ev_TYPE_set> any number of times. You must not, however, call this	1347	call C<ev_TYPE_set> any number of times. You must not, however, call this
708	macro on a watcher that is active (it can be pending, however, which is a	1348	macro on a watcher that is active (it can be pending, however, which is a
709	difference to the C<ev_init> macro).	1349	difference to the C<ev_init> macro).
710		1350
711	Although some watcher types do not have type-specific arguments	1351	Although some watcher types do not have type-specific arguments
712	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1352	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
713		1353
		1354	See C<ev_init>, above, for an example.
		1355
714	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1356	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
715		1357
716	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1358	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
717	calls into a single call. This is the most convinient method to initialise	1359	calls into a single call. This is the most convenient method to initialise
718	a watcher. The same limitations apply, of course.	1360	a watcher. The same limitations apply, of course.
719		1361
		1362	Example: Initialise and set an C<ev_io> watcher in one step.
		1363
		1364	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1365
720	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1366	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
721		1367
722	Starts (activates) the given watcher. Only active watchers will receive	1368	Starts (activates) the given watcher. Only active watchers will receive
723	events. If the watcher is already active nothing will happen.	1369	events. If the watcher is already active nothing will happen.
724		1370
		1371	Example: Start the C<ev_io> watcher that is being abused as example in this
		1372	whole section.
		1373
		1374	ev_io_start (EV_DEFAULT_UC, &w);
		1375
725	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1376	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
726		1377
727	Stops the given watcher again (if active) and clears the pending	1378	Stops the given watcher if active, and clears the pending status (whether
		1379	the watcher was active or not).
		1380
728	status. It is possible that stopped watchers are pending (for example,	1381	It is possible that stopped watchers are pending - for example,
729	non-repeating timers are being stopped when they become pending), but	1382	non-repeating timers are being stopped when they become pending - but
730	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1383	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
731	you want to free or reuse the memory used by the watcher it is therefore a	1384	pending. If you want to free or reuse the memory used by the watcher it is
732	good idea to always call its C<ev_TYPE_stop> function.	1385	therefore a good idea to always call its C<ev_TYPE_stop> function.
733		1386
734	=item bool ev_is_active (ev_TYPE *watcher)	1387	=item bool ev_is_active (ev_TYPE *watcher)
735		1388
736	Returns a true value iff the watcher is active (i.e. it has been started	1389	Returns a true value iff the watcher is active (i.e. it has been started
737	and not yet been stopped). As long as a watcher is active you must not modify	1390	and not yet been stopped). As long as a watcher is active you must not modify
…		…
748		1401
749	=item callback ev_cb (ev_TYPE *watcher)	1402	=item callback ev_cb (ev_TYPE *watcher)
750		1403
751	Returns the callback currently set on the watcher.	1404	Returns the callback currently set on the watcher.
752		1405
753	=item ev_cb_set (ev_TYPE *watcher, callback)	1406	=item ev_set_cb (ev_TYPE *watcher, callback)
754		1407
755	Change the callback. You can change the callback at virtually any time	1408	Change the callback. You can change the callback at virtually any time
756	(modulo threads).	1409	(modulo threads).
757		1410
758	=item ev_set_priority (ev_TYPE *watcher, priority)	1411	=item ev_set_priority (ev_TYPE *watcher, int priority)
759		1412
760	=item int ev_priority (ev_TYPE *watcher)	1413	=item int ev_priority (ev_TYPE *watcher)
761		1414
762	Set and query the priority of the watcher. The priority is a small	1415	Set and query the priority of the watcher. The priority is a small
763	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1416	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
764	(default: C<-2>). Pending watchers with higher priority will be invoked	1417	(default: C<-2>). Pending watchers with higher priority will be invoked
765	before watchers with lower priority, but priority will not keep watchers	1418	before watchers with lower priority, but priority will not keep watchers
766	from being executed (except for C<ev_idle> watchers).	1419	from being executed (except for C<ev_idle> watchers).
767		1420
768	This means that priorities are I<only> used for ordering callback
769	invocation after new events have been received. This is useful, for
770	example, to reduce latency after idling, or more often, to bind two
771	watchers on the same event and make sure one is called first.
772
773	If you need to suppress invocation when higher priority events are pending	1421	If you need to suppress invocation when higher priority events are pending
774	you need to look at C<ev_idle> watchers, which provide this functionality.	1422	you need to look at C<ev_idle> watchers, which provide this functionality.
775		1423
776	You I<must not> change the priority of a watcher as long as it is active or	1424	You I<must not> change the priority of a watcher as long as it is active or
777	pending.	1425	pending.
778		1426
		1427	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1428	fine, as long as you do not mind that the priority value you query might
		1429	or might not have been clamped to the valid range.
		1430
779	The default priority used by watchers when no priority has been set is	1431	The default priority used by watchers when no priority has been set is
780	always C<0>, which is supposed to not be too high and not be too low :).	1432	always C<0>, which is supposed to not be too high and not be too low :).
781		1433
782	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1434	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
783	fine, as long as you do not mind that the priority value you query might	1435	priorities.
784	or might not have been adjusted to be within valid range.
785		1436
786	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1437	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
787		1438
788	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1439	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
789	C<loop> nor C<revents> need to be valid as long as the watcher callback	1440	C<loop> nor C<revents> need to be valid as long as the watcher callback
790	can deal with that fact.	1441	can deal with that fact, as both are simply passed through to the
		1442	callback.
791		1443
792	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1444	=item int ev_clear_pending (loop, ev_TYPE *watcher)
793		1445
794	If the watcher is pending, this function returns clears its pending status	1446	If the watcher is pending, this function clears its pending status and
795	and returns its C<revents> bitset (as if its callback was invoked). If the	1447	returns its C<revents> bitset (as if its callback was invoked). If the
796	watcher isn't pending it does nothing and returns C<0>.	1448	watcher isn't pending it does nothing and returns C<0>.
797		1449
		1450	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1451	callback to be invoked, which can be accomplished with this function.
		1452
		1453	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1454
		1455	Feeds the given event set into the event loop, as if the specified event
		1456	had happened for the specified watcher (which must be a pointer to an
		1457	initialised but not necessarily started event watcher). Obviously you must
		1458	not free the watcher as long as it has pending events.
		1459
		1460	Stopping the watcher, letting libev invoke it, or calling
		1461	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1462	not started in the first place.
		1463
		1464	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1465	functions that do not need a watcher.
		1466
798	=back	1467	=back
799		1468
		1469	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1470	OWN COMPOSITE WATCHERS> idioms.
800		1471
801	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1472	=head2 WATCHER STATES
802		1473
803	Each watcher has, by default, a member C<void *data> that you can change	1474	There are various watcher states mentioned throughout this manual -
804	and read at any time, libev will completely ignore it. This can be used	1475	active, pending and so on. In this section these states and the rules to
805	to associate arbitrary data with your watcher. If you need more data and	1476	transition between them will be described in more detail - and while these
806	don't want to allocate memory and store a pointer to it in that data	1477	rules might look complicated, they usually do "the right thing".
807	member, you can also "subclass" the watcher type and provide your own
808	data:
809		1478
810	struct my_io	1479	=over 4
811	{
812	struct ev_io io;
813	int otherfd;
814	void *somedata;
815	struct whatever *mostinteresting;
816	}
817		1480
818	And since your callback will be called with a pointer to the watcher, you	1481	=item initialised
819	can cast it back to your own type:
820		1482
821	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1483	Before a watcher can be registered with the event loop it has to be
822	{	1484	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
823	struct my_io *w = (struct my_io *)w_;	1485	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
824	...
825	}
826		1486
827	More interesting and less C-conformant ways of casting your callback type	1487	In this state it is simply some block of memory that is suitable for
828	instead have been omitted.	1488	use in an event loop. It can be moved around, freed, reused etc. at
		1489	will - as long as you either keep the memory contents intact, or call
		1490	C<ev_TYPE_init> again.
829		1491
830	Another common scenario is having some data structure with multiple	1492	=item started/running/active
831	watchers:
832		1493
833	struct my_biggy	1494	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
834	{	1495	property of the event loop, and is actively waiting for events. While in
835	int some_data;	1496	this state it cannot be accessed (except in a few documented ways), moved,
836	ev_timer t1;	1497	freed or anything else - the only legal thing is to keep a pointer to it,
837	ev_timer t2;	1498	and call libev functions on it that are documented to work on active watchers.
838	}
839		1499
840	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1500	=item pending
841	you need to use C<offsetof>:
842		1501
843	#include <stddef.h>	1502	If a watcher is active and libev determines that an event it is interested
		1503	in has occurred (such as a timer expiring), it will become pending. It will
		1504	stay in this pending state until either it is stopped or its callback is
		1505	about to be invoked, so it is not normally pending inside the watcher
		1506	callback.
844		1507
		1508	The watcher might or might not be active while it is pending (for example,
		1509	an expired non-repeating timer can be pending but no longer active). If it
		1510	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1511	but it is still property of the event loop at this time, so cannot be
		1512	moved, freed or reused. And if it is active the rules described in the
		1513	previous item still apply.
		1514
		1515	It is also possible to feed an event on a watcher that is not active (e.g.
		1516	via C<ev_feed_event>), in which case it becomes pending without being
		1517	active.
		1518
		1519	=item stopped
		1520
		1521	A watcher can be stopped implicitly by libev (in which case it might still
		1522	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1523	latter will clear any pending state the watcher might be in, regardless
		1524	of whether it was active or not, so stopping a watcher explicitly before
		1525	freeing it is often a good idea.
		1526
		1527	While stopped (and not pending) the watcher is essentially in the
		1528	initialised state, that is, it can be reused, moved, modified in any way
		1529	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1530	it again).
		1531
		1532	=back
		1533
		1534	=head2 WATCHER PRIORITY MODELS
		1535
		1536	Many event loops support I<watcher priorities>, which are usually small
		1537	integers that influence the ordering of event callback invocation
		1538	between watchers in some way, all else being equal.
		1539
		1540	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1541	description for the more technical details such as the actual priority
		1542	range.
		1543
		1544	There are two common ways how these these priorities are being interpreted
		1545	by event loops:
		1546
		1547	In the more common lock-out model, higher priorities "lock out" invocation
		1548	of lower priority watchers, which means as long as higher priority
		1549	watchers receive events, lower priority watchers are not being invoked.
		1550
		1551	The less common only-for-ordering model uses priorities solely to order
		1552	callback invocation within a single event loop iteration: Higher priority
		1553	watchers are invoked before lower priority ones, but they all get invoked
		1554	before polling for new events.
		1555
		1556	Libev uses the second (only-for-ordering) model for all its watchers
		1557	except for idle watchers (which use the lock-out model).
		1558
		1559	The rationale behind this is that implementing the lock-out model for
		1560	watchers is not well supported by most kernel interfaces, and most event
		1561	libraries will just poll for the same events again and again as long as
		1562	their callbacks have not been executed, which is very inefficient in the
		1563	common case of one high-priority watcher locking out a mass of lower
		1564	priority ones.
		1565
		1566	Static (ordering) priorities are most useful when you have two or more
		1567	watchers handling the same resource: a typical usage example is having an
		1568	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1569	timeouts. Under load, data might be received while the program handles
		1570	other jobs, but since timers normally get invoked first, the timeout
		1571	handler will be executed before checking for data. In that case, giving
		1572	the timer a lower priority than the I/O watcher ensures that I/O will be
		1573	handled first even under adverse conditions (which is usually, but not
		1574	always, what you want).
		1575
		1576	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1577	will only be executed when no same or higher priority watchers have
		1578	received events, they can be used to implement the "lock-out" model when
		1579	required.
		1580
		1581	For example, to emulate how many other event libraries handle priorities,
		1582	you can associate an C<ev_idle> watcher to each such watcher, and in
		1583	the normal watcher callback, you just start the idle watcher. The real
		1584	processing is done in the idle watcher callback. This causes libev to
		1585	continuously poll and process kernel event data for the watcher, but when
		1586	the lock-out case is known to be rare (which in turn is rare :), this is
		1587	workable.
		1588
		1589	Usually, however, the lock-out model implemented that way will perform
		1590	miserably under the type of load it was designed to handle. In that case,
		1591	it might be preferable to stop the real watcher before starting the
		1592	idle watcher, so the kernel will not have to process the event in case
		1593	the actual processing will be delayed for considerable time.
		1594
		1595	Here is an example of an I/O watcher that should run at a strictly lower
		1596	priority than the default, and which should only process data when no
		1597	other events are pending:
		1598
		1599	ev_idle idle; // actual processing watcher
		1600	ev_io io; // actual event watcher
		1601
845	static void	1602	static void
846	t1_cb (EV_P_ struct ev_timer *w, int revents)	1603	io_cb (EV_P_ ev_io *w, int revents)
847	{	1604	{
848	struct my_biggy big = (struct my_biggy *	1605	// stop the I/O watcher, we received the event, but
849	(((char *)w) - offsetof (struct my_biggy, t1));	1606	// are not yet ready to handle it.
		1607	ev_io_stop (EV_A_ w);
		1608
		1609	// start the idle watcher to handle the actual event.
		1610	// it will not be executed as long as other watchers
		1611	// with the default priority are receiving events.
		1612	ev_idle_start (EV_A_ &idle);
850	}	1613	}
851		1614
852	static void	1615	static void
853	t2_cb (EV_P_ struct ev_timer *w, int revents)	1616	idle_cb (EV_P_ ev_idle *w, int revents)
854	{	1617	{
855	struct my_biggy big = (struct my_biggy *	1618	// actual processing
856	(((char *)w) - offsetof (struct my_biggy, t2));	1619	read (STDIN_FILENO, ...);
		1620
		1621	// have to start the I/O watcher again, as
		1622	// we have handled the event
		1623	ev_io_start (EV_P_ &io);
857	}	1624	}
		1625
		1626	// initialisation
		1627	ev_idle_init (&idle, idle_cb);
		1628	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1629	ev_io_start (EV_DEFAULT_ &io);
		1630
		1631	In the "real" world, it might also be beneficial to start a timer, so that
		1632	low-priority connections can not be locked out forever under load. This
		1633	enables your program to keep a lower latency for important connections
		1634	during short periods of high load, while not completely locking out less
		1635	important ones.
858		1636
859		1637
860	=head1 WATCHER TYPES	1638	=head1 WATCHER TYPES
861		1639
862	This section describes each watcher in detail, but will not repeat	1640	This section describes each watcher in detail, but will not repeat
…		…
886	In general you can register as many read and/or write event watchers per	1664	In general you can register as many read and/or write event watchers per
887	fd as you want (as long as you don't confuse yourself). Setting all file	1665	fd as you want (as long as you don't confuse yourself). Setting all file
888	descriptors to non-blocking mode is also usually a good idea (but not	1666	descriptors to non-blocking mode is also usually a good idea (but not
889	required if you know what you are doing).	1667	required if you know what you are doing).
890		1668
891	You have to be careful with dup'ed file descriptors, though. Some backends
892	(the linux epoll backend is a notable example) cannot handle dup'ed file
893	descriptors correctly if you register interest in two or more fds pointing
894	to the same underlying file/socket/etc. description (that is, they share
895	the same underlying "file open").
896
897	If you must do this, then force the use of a known-to-be-good backend
898	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
899	C<EVBACKEND_POLL>).
900
901	Another thing you have to watch out for is that it is quite easy to	1669	Another thing you have to watch out for is that it is quite easy to
902	receive "spurious" readyness notifications, that is your callback might	1670	receive "spurious" readiness notifications, that is, your callback might
903	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1671	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
904	because there is no data. Not only are some backends known to create a	1672	because there is no data. It is very easy to get into this situation even
905	lot of those (for example solaris ports), it is very easy to get into	1673	with a relatively standard program structure. Thus it is best to always
906	this situation even with a relatively standard program structure. Thus	1674	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
907	it is best to always use non-blocking I/O: An extra C<read>(2) returning
908	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1675	preferable to a program hanging until some data arrives.
909		1676
910	If you cannot run the fd in non-blocking mode (for example you should not	1677	If you cannot run the fd in non-blocking mode (for example you should
911	play around with an Xlib connection), then you have to seperately re-test	1678	not play around with an Xlib connection), then you have to separately
912	whether a file descriptor is really ready with a known-to-be good interface	1679	re-test whether a file descriptor is really ready with a known-to-be good
913	such as poll (fortunately in our Xlib example, Xlib already does this on	1680	interface such as poll (fortunately in the case of Xlib, it already does
914	its own, so its quite safe to use).	1681	this on its own, so its quite safe to use). Some people additionally
		1682	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1683	indefinitely.
		1684
		1685	But really, best use non-blocking mode.
915		1686
916	=head3 The special problem of disappearing file descriptors	1687	=head3 The special problem of disappearing file descriptors
917		1688
918	Some backends (e.g kqueue, epoll) need to be told about closing a file	1689	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
919	descriptor (either by calling C<close> explicitly or by any other means,	1690	a file descriptor (either due to calling C<close> explicitly or any other
920	such as C<dup>). The reason is that you register interest in some file	1691	means, such as C<dup2>). The reason is that you register interest in some
921	descriptor, but when it goes away, the operating system will silently drop	1692	file descriptor, but when it goes away, the operating system will silently
922	this interest. If another file descriptor with the same number then is	1693	drop this interest. If another file descriptor with the same number then
923	registered with libev, there is no efficient way to see that this is, in	1694	is registered with libev, there is no efficient way to see that this is,
924	fact, a different file descriptor.	1695	in fact, a different file descriptor.
925		1696
926	To avoid having to explicitly tell libev about such cases, libev follows	1697	To avoid having to explicitly tell libev about such cases, libev follows
927	the following policy: Each time C<ev_io_set> is being called, libev	1698	the following policy: Each time C<ev_io_set> is being called, libev
928	will assume that this is potentially a new file descriptor, otherwise	1699	will assume that this is potentially a new file descriptor, otherwise
929	it is assumed that the file descriptor stays the same. That means that	1700	it is assumed that the file descriptor stays the same. That means that
…		…
932		1703
933	This is how one would do it normally anyway, the important point is that	1704	This is how one would do it normally anyway, the important point is that
934	the libev application should not optimise around libev but should leave	1705	the libev application should not optimise around libev but should leave
935	optimisations to libev.	1706	optimisations to libev.
936		1707
		1708	=head3 The special problem of dup'ed file descriptors
		1709
		1710	Some backends (e.g. epoll), cannot register events for file descriptors,
		1711	but only events for the underlying file descriptions. That means when you
		1712	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1713	events for them, only one file descriptor might actually receive events.
		1714
		1715	There is no workaround possible except not registering events
		1716	for potentially C<dup ()>'ed file descriptors, or to resort to
		1717	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1718
		1719	=head3 The special problem of files
		1720
		1721	Many people try to use C<select> (or libev) on file descriptors
		1722	representing files, and expect it to become ready when their program
		1723	doesn't block on disk accesses (which can take a long time on their own).
		1724
		1725	However, this cannot ever work in the "expected" way - you get a readiness
		1726	notification as soon as the kernel knows whether and how much data is
		1727	there, and in the case of open files, that's always the case, so you
		1728	always get a readiness notification instantly, and your read (or possibly
		1729	write) will still block on the disk I/O.
		1730
		1731	Another way to view it is that in the case of sockets, pipes, character
		1732	devices and so on, there is another party (the sender) that delivers data
		1733	on its own, but in the case of files, there is no such thing: the disk
		1734	will not send data on its own, simply because it doesn't know what you
		1735	wish to read - you would first have to request some data.
		1736
		1737	Since files are typically not-so-well supported by advanced notification
		1738	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1739	to files, even though you should not use it. The reason for this is
		1740	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1741	usually a tty, often a pipe, but also sometimes files or special devices
		1742	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1743	F</dev/urandom>), and even though the file might better be served with
		1744	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1745	it "just works" instead of freezing.
		1746
		1747	So avoid file descriptors pointing to files when you know it (e.g. use
		1748	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1749	when you rarely read from a file instead of from a socket, and want to
		1750	reuse the same code path.
		1751
		1752	=head3 The special problem of fork
		1753
		1754	Some backends (epoll, kqueue, linuxaio, iouring) do not support C<fork ()>
		1755	at all or exhibit useless behaviour. Libev fully supports fork, but needs
		1756	to be told about it in the child if you want to continue to use it in the
		1757	child.
		1758
		1759	To support fork in your child processes, you have to call C<ev_loop_fork
		1760	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
		1761	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1762
		1763	=head3 The special problem of SIGPIPE
		1764
		1765	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1766	when writing to a pipe whose other end has been closed, your program gets
		1767	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1768	this is sensible behaviour, for daemons, this is usually undesirable.
		1769
		1770	So when you encounter spurious, unexplained daemon exits, make sure you
		1771	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1772	somewhere, as that would have given you a big clue).
		1773
		1774	=head3 The special problem of accept()ing when you can't
		1775
		1776	Many implementations of the POSIX C<accept> function (for example,
		1777	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1778	connection from the pending queue in all error cases.
		1779
		1780	For example, larger servers often run out of file descriptors (because
		1781	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1782	rejecting the connection, leading to libev signalling readiness on
		1783	the next iteration again (the connection still exists after all), and
		1784	typically causing the program to loop at 100% CPU usage.
		1785
		1786	Unfortunately, the set of errors that cause this issue differs between
		1787	operating systems, there is usually little the app can do to remedy the
		1788	situation, and no known thread-safe method of removing the connection to
		1789	cope with overload is known (to me).
		1790
		1791	One of the easiest ways to handle this situation is to just ignore it
		1792	- when the program encounters an overload, it will just loop until the
		1793	situation is over. While this is a form of busy waiting, no OS offers an
		1794	event-based way to handle this situation, so it's the best one can do.
		1795
		1796	A better way to handle the situation is to log any errors other than
		1797	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1798	messages, and continue as usual, which at least gives the user an idea of
		1799	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1800	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1801	usage.
		1802
		1803	If your program is single-threaded, then you could also keep a dummy file
		1804	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1805	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1806	close that fd, and create a new dummy fd. This will gracefully refuse
		1807	clients under typical overload conditions.
		1808
		1809	The last way to handle it is to simply log the error and C<exit>, as
		1810	is often done with C<malloc> failures, but this results in an easy
		1811	opportunity for a DoS attack.
937		1812
938	=head3 Watcher-Specific Functions	1813	=head3 Watcher-Specific Functions
939		1814
940	=over 4	1815	=over 4
941		1816
942	=item ev_io_init (ev_io *, callback, int fd, int events)	1817	=item ev_io_init (ev_io *, callback, int fd, int events)
943		1818
944	=item ev_io_set (ev_io *, int fd, int events)	1819	=item ev_io_set (ev_io *, int fd, int events)
945		1820
946	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1821	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
947	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1822	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
948	C<EV_READ | EV_WRITE> to receive the given events.	1823	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
949		1824
950	=item int fd [read-only]	1825	=item int fd [read-only]
951		1826
952	The file descriptor being watched.	1827	The file descriptor being watched.
953		1828
954	=item int events [read-only]	1829	=item int events [read-only]
955		1830
956	The events being watched.	1831	The events being watched.
957		1832
958	=back	1833	=back
		1834
		1835	=head3 Examples
959		1836
960	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1837	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
961	readable, but only once. Since it is likely line-buffered, you could	1838	readable, but only once. Since it is likely line-buffered, you could
962	attempt to read a whole line in the callback.	1839	attempt to read a whole line in the callback.
963		1840
964	static void	1841	static void
965	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1842	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
966	{	1843	{
967	ev_io_stop (loop, w);	1844	ev_io_stop (loop, w);
968	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1845	.. read from stdin here (or from w->fd) and handle any I/O errors
969	}	1846	}
970		1847
971	...	1848	...
972	struct ev_loop *loop = ev_default_init (0);	1849	struct ev_loop *loop = ev_default_init (0);
973	struct ev_io stdin_readable;	1850	ev_io stdin_readable;
974	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1851	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
975	ev_io_start (loop, &stdin_readable);	1852	ev_io_start (loop, &stdin_readable);
976	ev_loop (loop, 0);	1853	ev_run (loop, 0);
977		1854
978		1855
979	=head2 C<ev_timer> - relative and optionally repeating timeouts	1856	=head2 C<ev_timer> - relative and optionally repeating timeouts
980		1857
981	Timer watchers are simple relative timers that generate an event after a	1858	Timer watchers are simple relative timers that generate an event after a
982	given time, and optionally repeating in regular intervals after that.	1859	given time, and optionally repeating in regular intervals after that.
983		1860
984	The timers are based on real time, that is, if you register an event that	1861	The timers are based on real time, that is, if you register an event that
985	times out after an hour and you reset your system clock to last years	1862	times out after an hour and you reset your system clock to January last
986	time, it will still time out after (roughly) and hour. "Roughly" because	1863	year, it will still time out after (roughly) one hour. "Roughly" because
987	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1864	detecting time jumps is hard, and some inaccuracies are unavoidable (the
988	monotonic clock option helps a lot here).	1865	monotonic clock option helps a lot here).
		1866
		1867	The callback is guaranteed to be invoked only I<after> its timeout has
		1868	passed (not I<at>, so on systems with very low-resolution clocks this
		1869	might introduce a small delay, see "the special problem of being too
		1870	early", below). If multiple timers become ready during the same loop
		1871	iteration then the ones with earlier time-out values are invoked before
		1872	ones of the same priority with later time-out values (but this is no
		1873	longer true when a callback calls C<ev_run> recursively).
		1874
		1875	=head3 Be smart about timeouts
		1876
		1877	Many real-world problems involve some kind of timeout, usually for error
		1878	recovery. A typical example is an HTTP request - if the other side hangs,
		1879	you want to raise some error after a while.
		1880
		1881	What follows are some ways to handle this problem, from obvious and
		1882	inefficient to smart and efficient.
		1883
		1884	In the following, a 60 second activity timeout is assumed - a timeout that
		1885	gets reset to 60 seconds each time there is activity (e.g. each time some
		1886	data or other life sign was received).
		1887
		1888	=over 4
		1889
		1890	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1891
		1892	This is the most obvious, but not the most simple way: In the beginning,
		1893	start the watcher:
		1894
		1895	ev_timer_init (timer, callback, 60., 0.);
		1896	ev_timer_start (loop, timer);
		1897
		1898	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1899	and start it again:
		1900
		1901	ev_timer_stop (loop, timer);
		1902	ev_timer_set (timer, 60., 0.);
		1903	ev_timer_start (loop, timer);
		1904
		1905	This is relatively simple to implement, but means that each time there is
		1906	some activity, libev will first have to remove the timer from its internal
		1907	data structure and then add it again. Libev tries to be fast, but it's
		1908	still not a constant-time operation.
		1909
		1910	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1911
		1912	This is the easiest way, and involves using C<ev_timer_again> instead of
		1913	C<ev_timer_start>.
		1914
		1915	To implement this, configure an C<ev_timer> with a C<repeat> value
		1916	of C<60> and then call C<ev_timer_again> at start and each time you
		1917	successfully read or write some data. If you go into an idle state where
		1918	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1919	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1920
		1921	That means you can ignore both the C<ev_timer_start> function and the
		1922	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1923	member and C<ev_timer_again>.
		1924
		1925	At start:
		1926
		1927	ev_init (timer, callback);
		1928	timer->repeat = 60.;
		1929	ev_timer_again (loop, timer);
		1930
		1931	Each time there is some activity:
		1932
		1933	ev_timer_again (loop, timer);
		1934
		1935	It is even possible to change the time-out on the fly, regardless of
		1936	whether the watcher is active or not:
		1937
		1938	timer->repeat = 30.;
		1939	ev_timer_again (loop, timer);
		1940
		1941	This is slightly more efficient then stopping/starting the timer each time
		1942	you want to modify its timeout value, as libev does not have to completely
		1943	remove and re-insert the timer from/into its internal data structure.
		1944
		1945	It is, however, even simpler than the "obvious" way to do it.
		1946
		1947	=item 3. Let the timer time out, but then re-arm it as required.
		1948
		1949	This method is more tricky, but usually most efficient: Most timeouts are
		1950	relatively long compared to the intervals between other activity - in
		1951	our example, within 60 seconds, there are usually many I/O events with
		1952	associated activity resets.
		1953
		1954	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1955	but remember the time of last activity, and check for a real timeout only
		1956	within the callback:
		1957
		1958	ev_tstamp timeout = 60.;
		1959	ev_tstamp last_activity; // time of last activity
		1960	ev_timer timer;
		1961
		1962	static void
		1963	callback (EV_P_ ev_timer *w, int revents)
		1964	{
		1965	// calculate when the timeout would happen
		1966	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1967
		1968	// if negative, it means we the timeout already occurred
		1969	if (after < 0.)
		1970	{
		1971	// timeout occurred, take action
		1972	}
		1973	else
		1974	{
		1975	// callback was invoked, but there was some recent
		1976	// activity. simply restart the timer to time out
		1977	// after "after" seconds, which is the earliest time
		1978	// the timeout can occur.
		1979	ev_timer_set (w, after, 0.);
		1980	ev_timer_start (EV_A_ w);
		1981	}
		1982	}
		1983
		1984	To summarise the callback: first calculate in how many seconds the
		1985	timeout will occur (by calculating the absolute time when it would occur,
		1986	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1987	(EV_A)> from that).
		1988
		1989	If this value is negative, then we are already past the timeout, i.e. we
		1990	timed out, and need to do whatever is needed in this case.
		1991
		1992	Otherwise, we now the earliest time at which the timeout would trigger,
		1993	and simply start the timer with this timeout value.
		1994
		1995	In other words, each time the callback is invoked it will check whether
		1996	the timeout occurred. If not, it will simply reschedule itself to check
		1997	again at the earliest time it could time out. Rinse. Repeat.
		1998
		1999	This scheme causes more callback invocations (about one every 60 seconds
		2000	minus half the average time between activity), but virtually no calls to
		2001	libev to change the timeout.
		2002
		2003	To start the machinery, simply initialise the watcher and set
		2004	C<last_activity> to the current time (meaning there was some activity just
		2005	now), then call the callback, which will "do the right thing" and start
		2006	the timer:
		2007
		2008	last_activity = ev_now (EV_A);
		2009	ev_init (&timer, callback);
		2010	callback (EV_A_ &timer, 0);
		2011
		2012	When there is some activity, simply store the current time in
		2013	C<last_activity>, no libev calls at all:
		2014
		2015	if (activity detected)
		2016	last_activity = ev_now (EV_A);
		2017
		2018	When your timeout value changes, then the timeout can be changed by simply
		2019	providing a new value, stopping the timer and calling the callback, which
		2020	will again do the right thing (for example, time out immediately :).
		2021
		2022	timeout = new_value;
		2023	ev_timer_stop (EV_A_ &timer);
		2024	callback (EV_A_ &timer, 0);
		2025
		2026	This technique is slightly more complex, but in most cases where the
		2027	time-out is unlikely to be triggered, much more efficient.
		2028
		2029	=item 4. Wee, just use a double-linked list for your timeouts.
		2030
		2031	If there is not one request, but many thousands (millions...), all
		2032	employing some kind of timeout with the same timeout value, then one can
		2033	do even better:
		2034
		2035	When starting the timeout, calculate the timeout value and put the timeout
		2036	at the I<end> of the list.
		2037
		2038	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		2039	the list is expected to fire (for example, using the technique #3).
		2040
		2041	When there is some activity, remove the timer from the list, recalculate
		2042	the timeout, append it to the end of the list again, and make sure to
		2043	update the C<ev_timer> if it was taken from the beginning of the list.
		2044
		2045	This way, one can manage an unlimited number of timeouts in O(1) time for
		2046	starting, stopping and updating the timers, at the expense of a major
		2047	complication, and having to use a constant timeout. The constant timeout
		2048	ensures that the list stays sorted.
		2049
		2050	=back
		2051
		2052	So which method the best?
		2053
		2054	Method #2 is a simple no-brain-required solution that is adequate in most
		2055	situations. Method #3 requires a bit more thinking, but handles many cases
		2056	better, and isn't very complicated either. In most case, choosing either
		2057	one is fine, with #3 being better in typical situations.
		2058
		2059	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		2060	rather complicated, but extremely efficient, something that really pays
		2061	off after the first million or so of active timers, i.e. it's usually
		2062	overkill :)
		2063
		2064	=head3 The special problem of being too early
		2065
		2066	If you ask a timer to call your callback after three seconds, then
		2067	you expect it to be invoked after three seconds - but of course, this
		2068	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2069	guaranteed to any precision by libev - imagine somebody suspending the
		2070	process with a STOP signal for a few hours for example.
		2071
		2072	So, libev tries to invoke your callback as soon as possible I<after> the
		2073	delay has occurred, but cannot guarantee this.
		2074
		2075	A less obvious failure mode is calling your callback too early: many event
		2076	loops compare timestamps with a "elapsed delay >= requested delay", but
		2077	this can cause your callback to be invoked much earlier than you would
		2078	expect.
		2079
		2080	To see why, imagine a system with a clock that only offers full second
		2081	resolution (think windows if you can't come up with a broken enough OS
		2082	yourself). If you schedule a one-second timer at the time 500.9, then the
		2083	event loop will schedule your timeout to elapse at a system time of 500
		2084	(500.9 truncated to the resolution) + 1, or 501.
		2085
		2086	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2087	501" and invoke the callback 0.1s after it was started, even though a
		2088	one-second delay was requested - this is being "too early", despite best
		2089	intentions.
		2090
		2091	This is the reason why libev will never invoke the callback if the elapsed
		2092	delay equals the requested delay, but only when the elapsed delay is
		2093	larger than the requested delay. In the example above, libev would only invoke
		2094	the callback at system time 502, or 1.1s after the timer was started.
		2095
		2096	So, while libev cannot guarantee that your callback will be invoked
		2097	exactly when requested, it I<can> and I<does> guarantee that the requested
		2098	delay has actually elapsed, or in other words, it always errs on the "too
		2099	late" side of things.
		2100
		2101	=head3 The special problem of time updates
		2102
		2103	Establishing the current time is a costly operation (it usually takes
		2104	at least one system call): EV therefore updates its idea of the current
		2105	time only before and after C<ev_run> collects new events, which causes a
		2106	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2107	lots of events in one iteration.
989		2108
990	The relative timeouts are calculated relative to the C<ev_now ()>	2109	The relative timeouts are calculated relative to the C<ev_now ()>
991	time. This is usually the right thing as this timestamp refers to the time	2110	time. This is usually the right thing as this timestamp refers to the time
992	of the event triggering whatever timeout you are modifying/starting. If	2111	of the event triggering whatever timeout you are modifying/starting. If
993	you suspect event processing to be delayed and you I<need> to base the timeout	2112	you suspect event processing to be delayed and you I<need> to base the
994	on the current time, use something like this to adjust for this:	2113	timeout on the current time, use something like the following to adjust
		2114	for it:
995		2115
996	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2116	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
997		2117
998	The callback is guarenteed to be invoked only when its timeout has passed,	2118	If the event loop is suspended for a long time, you can also force an
999	but if multiple timers become ready during the same loop iteration then	2119	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1000	order of execution is undefined.	2120	()>, although that will push the event time of all outstanding events
		2121	further into the future.
		2122
		2123	=head3 The special problem of unsynchronised clocks
		2124
		2125	Modern systems have a variety of clocks - libev itself uses the normal
		2126	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2127	jumps).
		2128
		2129	Neither of these clocks is synchronised with each other or any other clock
		2130	on the system, so C<ev_time ()> might return a considerably different time
		2131	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2132	a call to C<gettimeofday> might return a second count that is one higher
		2133	than a directly following call to C<time>.
		2134
		2135	The moral of this is to only compare libev-related timestamps with
		2136	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2137	a second or so.
		2138
		2139	One more problem arises due to this lack of synchronisation: if libev uses
		2140	the system monotonic clock and you compare timestamps from C<ev_time>
		2141	or C<ev_now> from when you started your timer and when your callback is
		2142	invoked, you will find that sometimes the callback is a bit "early".
		2143
		2144	This is because C<ev_timer>s work in real time, not wall clock time, so
		2145	libev makes sure your callback is not invoked before the delay happened,
		2146	I<measured according to the real time>, not the system clock.
		2147
		2148	If your timeouts are based on a physical timescale (e.g. "time out this
		2149	connection after 100 seconds") then this shouldn't bother you as it is
		2150	exactly the right behaviour.
		2151
		2152	If you want to compare wall clock/system timestamps to your timers, then
		2153	you need to use C<ev_periodic>s, as these are based on the wall clock
		2154	time, where your comparisons will always generate correct results.
		2155
		2156	=head3 The special problems of suspended animation
		2157
		2158	When you leave the server world it is quite customary to hit machines that
		2159	can suspend/hibernate - what happens to the clocks during such a suspend?
		2160
		2161	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2162	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2163	to run until the system is suspended, but they will not advance while the
		2164	system is suspended. That means, on resume, it will be as if the program
		2165	was frozen for a few seconds, but the suspend time will not be counted
		2166	towards C<ev_timer> when a monotonic clock source is used. The real time
		2167	clock advanced as expected, but if it is used as sole clocksource, then a
		2168	long suspend would be detected as a time jump by libev, and timers would
		2169	be adjusted accordingly.
		2170
		2171	I would not be surprised to see different behaviour in different between
		2172	operating systems, OS versions or even different hardware.
		2173
		2174	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2175	time jump in the monotonic clocks and the realtime clock. If the program
		2176	is suspended for a very long time, and monotonic clock sources are in use,
		2177	then you can expect C<ev_timer>s to expire as the full suspension time
		2178	will be counted towards the timers. When no monotonic clock source is in
		2179	use, then libev will again assume a timejump and adjust accordingly.
		2180
		2181	It might be beneficial for this latter case to call C<ev_suspend>
		2182	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2183	deterministic behaviour in this case (you can do nothing against
		2184	C<SIGSTOP>).
1001		2185
1002	=head3 Watcher-Specific Functions and Data Members	2186	=head3 Watcher-Specific Functions and Data Members
1003		2187
1004	=over 4	2188	=over 4
1005		2189
1006	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2190	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1007		2191
1008	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2192	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1009		2193
1010	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2194	Configure the timer to trigger after C<after> seconds (fractional and
1011	C<0.>, then it will automatically be stopped. If it is positive, then the	2195	negative values are supported). If C<repeat> is C<0.>, then it will
		2196	automatically be stopped once the timeout is reached. If it is positive,
1012	timer will automatically be configured to trigger again C<repeat> seconds	2197	then the timer will automatically be configured to trigger again C<repeat>
1013	later, again, and again, until stopped manually.	2198	seconds later, again, and again, until stopped manually.
1014		2199
1015	The timer itself will do a best-effort at avoiding drift, that is, if you	2200	The timer itself will do a best-effort at avoiding drift, that is, if
1016	configure a timer to trigger every 10 seconds, then it will trigger at	2201	you configure a timer to trigger every 10 seconds, then it will normally
1017	exactly 10 second intervals. If, however, your program cannot keep up with	2202	trigger at exactly 10 second intervals. If, however, your program cannot
1018	the timer (because it takes longer than those 10 seconds to do stuff) the	2203	keep up with the timer (because it takes longer than those 10 seconds to
1019	timer will not fire more than once per event loop iteration.	2204	do stuff) the timer will not fire more than once per event loop iteration.
1020		2205
1021	=item ev_timer_again (loop)	2206	=item ev_timer_again (loop, ev_timer *)
1022		2207
1023	This will act as if the timer timed out and restart it again if it is	2208	This will act as if the timer timed out, and restarts it again if it is
1024	repeating. The exact semantics are:	2209	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2210	timeout to the C<repeat> value and calling C<ev_timer_start>.
1025		2211
		2212	The exact semantics are as in the following rules, all of which will be
		2213	applied to the watcher:
		2214
		2215	=over 4
		2216
1026	If the timer is pending, its pending status is cleared.	2217	=item If the timer is pending, the pending status is always cleared.
1027		2218
1028	If the timer is started but nonrepeating, stop it (as if it timed out).	2219	=item If the timer is started but non-repeating, stop it (as if it timed
		2220	out, without invoking it).
1029		2221
1030	If the timer is repeating, either start it if necessary (with the	2222	=item If the timer is repeating, make the C<repeat> value the new timeout
1031	C<repeat> value), or reset the running timer to the C<repeat> value.	2223	and start the timer, if necessary.
1032		2224
1033	This sounds a bit complicated, but here is a useful and typical	2225	=back
1034	example: Imagine you have a tcp connection and you want a so-called idle
1035	timeout, that is, you want to be called when there have been, say, 60
1036	seconds of inactivity on the socket. The easiest way to do this is to
1037	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1038	C<ev_timer_again> each time you successfully read or write some data. If
1039	you go into an idle state where you do not expect data to travel on the
1040	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1041	automatically restart it if need be.
1042		2226
1043	That means you can ignore the C<after> value and C<ev_timer_start>	2227	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1044	altogether and only ever use the C<repeat> value and C<ev_timer_again>:	2228	usage example.
1045		2229
1046	ev_timer_init (timer, callback, 0., 5.);	2230	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1047	ev_timer_again (loop, timer);
1048	...
1049	timer->again = 17.;
1050	ev_timer_again (loop, timer);
1051	...
1052	timer->again = 10.;
1053	ev_timer_again (loop, timer);
1054		2231
1055	This is more slightly efficient then stopping/starting the timer each time	2232	Returns the remaining time until a timer fires. If the timer is active,
1056	you want to modify its timeout value.	2233	then this time is relative to the current event loop time, otherwise it's
		2234	the timeout value currently configured.
		2235
		2236	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2237	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2238	will return C<4>. When the timer expires and is restarted, it will return
		2239	roughly C<7> (likely slightly less as callback invocation takes some time,
		2240	too), and so on.
1057		2241
1058	=item ev_tstamp repeat [read-write]	2242	=item ev_tstamp repeat [read-write]
1059		2243
1060	The current C<repeat> value. Will be used each time the watcher times out	2244	The current C<repeat> value. Will be used each time the watcher times out
1061	or C<ev_timer_again> is called and determines the next timeout (if any),	2245	or C<ev_timer_again> is called, and determines the next timeout (if any),
1062	which is also when any modifications are taken into account.	2246	which is also when any modifications are taken into account.
1063		2247
1064	=back	2248	=back
1065		2249
		2250	=head3 Examples
		2251
1066	Example: Create a timer that fires after 60 seconds.	2252	Example: Create a timer that fires after 60 seconds.
1067		2253
1068	static void	2254	static void
1069	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2255	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1070	{	2256	{
1071	.. one minute over, w is actually stopped right here	2257	.. one minute over, w is actually stopped right here
1072	}	2258	}
1073		2259
1074	struct ev_timer mytimer;	2260	ev_timer mytimer;
1075	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2261	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1076	ev_timer_start (loop, &mytimer);	2262	ev_timer_start (loop, &mytimer);
1077		2263
1078	Example: Create a timeout timer that times out after 10 seconds of	2264	Example: Create a timeout timer that times out after 10 seconds of
1079	inactivity.	2265	inactivity.
1080		2266
1081	static void	2267	static void
1082	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2268	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1083	{	2269	{
1084	.. ten seconds without any activity	2270	.. ten seconds without any activity
1085	}	2271	}
1086		2272
1087	struct ev_timer mytimer;	2273	ev_timer mytimer;
1088	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2274	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1089	ev_timer_again (&mytimer); /* start timer */	2275	ev_timer_again (&mytimer); /* start timer */
1090	ev_loop (loop, 0);	2276	ev_run (loop, 0);
1091		2277
1092	// and in some piece of code that gets executed on any "activity":	2278	// and in some piece of code that gets executed on any "activity":
1093	// reset the timeout to start ticking again at 10 seconds	2279	// reset the timeout to start ticking again at 10 seconds
1094	ev_timer_again (&mytimer);	2280	ev_timer_again (&mytimer);
1095		2281
1096		2282
1097	=head2 C<ev_periodic> - to cron or not to cron?	2283	=head2 C<ev_periodic> - to cron or not to cron?
1098		2284
1099	Periodic watchers are also timers of a kind, but they are very versatile	2285	Periodic watchers are also timers of a kind, but they are very versatile
1100	(and unfortunately a bit complex).	2286	(and unfortunately a bit complex).
1101		2287
1102	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2288	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1103	but on wallclock time (absolute time). You can tell a periodic watcher	2289	relative time, the physical time that passes) but on wall clock time
1104	to trigger "at" some specific point in time. For example, if you tell a	2290	(absolute time, the thing you can read on your calendar or clock). The
1105	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2291	difference is that wall clock time can run faster or slower than real
1106	+ 10.>) and then reset your system clock to the last year, then it will	2292	time, and time jumps are not uncommon (e.g. when you adjust your
1107	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2293	wrist-watch).
1108	roughly 10 seconds later).
1109		2294
1110	They can also be used to implement vastly more complex timers, such as	2295	You can tell a periodic watcher to trigger after some specific point
1111	triggering an event on each midnight, local time or other, complicated,	2296	in time: for example, if you tell a periodic watcher to trigger "in 10
1112	rules.	2297	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2298	not a delay) and then reset your system clock to January of the previous
		2299	year, then it will take a year or more to trigger the event (unlike an
		2300	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2301	it, as it uses a relative timeout).
1113		2302
		2303	C<ev_periodic> watchers can also be used to implement vastly more complex
		2304	timers, such as triggering an event on each "midnight, local time", or
		2305	other complicated rules. This cannot easily be done with C<ev_timer>
		2306	watchers, as those cannot react to time jumps.
		2307
1114	As with timers, the callback is guarenteed to be invoked only when the	2308	As with timers, the callback is guaranteed to be invoked only when the
1115	time (C<at>) has been passed, but if multiple periodic timers become ready	2309	point in time where it is supposed to trigger has passed. If multiple
1116	during the same loop iteration then order of execution is undefined.	2310	timers become ready during the same loop iteration then the ones with
		2311	earlier time-out values are invoked before ones with later time-out values
		2312	(but this is no longer true when a callback calls C<ev_run> recursively).
1117		2313
1118	=head3 Watcher-Specific Functions and Data Members	2314	=head3 Watcher-Specific Functions and Data Members
1119		2315
1120	=over 4	2316	=over 4
1121		2317
1122	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2318	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1123		2319
1124	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2320	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1125		2321
1126	Lots of arguments, lets sort it out... There are basically three modes of	2322	Lots of arguments, let's sort it out... There are basically three modes of
1127	operation, and we will explain them from simplest to complex:	2323	operation, and we will explain them from simplest to most complex:
1128		2324
1129	=over 4	2325	=over 4
1130		2326
1131	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2327	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1132		2328
1133	In this configuration the watcher triggers an event at the wallclock time	2329	In this configuration the watcher triggers an event after the wall clock
1134	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2330	time C<offset> has passed. It will not repeat and will not adjust when a
1135	that is, if it is to be run at January 1st 2011 then it will run when the	2331	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1136	system time reaches or surpasses this time.	2332	will be stopped and invoked when the system clock reaches or surpasses
		2333	this point in time.
1137		2334
1138	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2335	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1139		2336
1140	In this mode the watcher will always be scheduled to time out at the next	2337	In this mode the watcher will always be scheduled to time out at the next
1141	C<at + N * interval> time (for some integer N, which can also be negative)	2338	C<offset + N * interval> time (for some integer N, which can also be
1142	and then repeat, regardless of any time jumps.	2339	negative) and then repeat, regardless of any time jumps. The C<offset>
		2340	argument is merely an offset into the C<interval> periods.
1143		2341
1144	This can be used to create timers that do not drift with respect to system	2342	This can be used to create timers that do not drift with respect to the
1145	time:	2343	system clock, for example, here is an C<ev_periodic> that triggers each
		2344	hour, on the hour (with respect to UTC):
1146		2345
1147	ev_periodic_set (&periodic, 0., 3600., 0);	2346	ev_periodic_set (&periodic, 0., 3600., 0);
1148		2347
1149	This doesn't mean there will always be 3600 seconds in between triggers,	2348	This doesn't mean there will always be 3600 seconds in between triggers,
1150	but only that the the callback will be called when the system time shows a	2349	but only that the callback will be called when the system time shows a
1151	full hour (UTC), or more correctly, when the system time is evenly divisible	2350	full hour (UTC), or more correctly, when the system time is evenly divisible
1152	by 3600.	2351	by 3600.
1153		2352
1154	Another way to think about it (for the mathematically inclined) is that	2353	Another way to think about it (for the mathematically inclined) is that
1155	C<ev_periodic> will try to run the callback in this mode at the next possible	2354	C<ev_periodic> will try to run the callback in this mode at the next possible
1156	time where C<time = at (mod interval)>, regardless of any time jumps.	2355	time where C<time = offset (mod interval)>, regardless of any time jumps.
1157		2356
1158	For numerical stability it is preferable that the C<at> value is near	2357	The C<interval> I<MUST> be positive, and for numerical stability, the
1159	C<ev_now ()> (the current time), but there is no range requirement for	2358	interval value should be higher than C<1/8192> (which is around 100
1160	this value.	2359	microseconds) and C<offset> should be higher than C<0> and should have
		2360	at most a similar magnitude as the current time (say, within a factor of
		2361	ten). Typical values for offset are, in fact, C<0> or something between
		2362	C<0> and C<interval>, which is also the recommended range.
1161		2363
		2364	Note also that there is an upper limit to how often a timer can fire (CPU
		2365	speed for example), so if C<interval> is very small then timing stability
		2366	will of course deteriorate. Libev itself tries to be exact to be about one
		2367	millisecond (if the OS supports it and the machine is fast enough).
		2368
1162	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2369	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1163		2370
1164	In this mode the values for C<interval> and C<at> are both being	2371	In this mode the values for C<interval> and C<offset> are both being
1165	ignored. Instead, each time the periodic watcher gets scheduled, the	2372	ignored. Instead, each time the periodic watcher gets scheduled, the
1166	reschedule callback will be called with the watcher as first, and the	2373	reschedule callback will be called with the watcher as first, and the
1167	current time as second argument.	2374	current time as second argument.
1168		2375
1169	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2376	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1170	ever, or make any event loop modifications>. If you need to stop it,	2377	or make ANY other event loop modifications whatsoever, unless explicitly
1171	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2378	allowed by documentation here>.
1172	starting an C<ev_prepare> watcher, which is legal).
1173		2379
		2380	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2381	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2382	only event loop modification you are allowed to do).
		2383
1174	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2384	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1175	ev_tstamp now)>, e.g.:	2385	*w, ev_tstamp now)>, e.g.:
1176		2386
		2387	static ev_tstamp
1177	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2388	my_rescheduler (ev_periodic *w, ev_tstamp now)
1178	{	2389	{
1179	return now + 60.;	2390	return now + 60.;
1180	}	2391	}
1181		2392
1182	It must return the next time to trigger, based on the passed time value	2393	It must return the next time to trigger, based on the passed time value
1183	(that is, the lowest time value larger than to the second argument). It	2394	(that is, the lowest time value larger than to the second argument). It
1184	will usually be called just before the callback will be triggered, but	2395	will usually be called just before the callback will be triggered, but
1185	might be called at other times, too.	2396	might be called at other times, too.
1186		2397
1187	NOTE: I<< This callback must always return a time that is later than the	2398	NOTE: I<< This callback must always return a time that is higher than or
1188	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2399	equal to the passed C<now> value >>.
1189		2400
1190	This can be used to create very complex timers, such as a timer that	2401	This can be used to create very complex timers, such as a timer that
1191	triggers on each midnight, local time. To do this, you would calculate the	2402	triggers on "next midnight, local time". To do this, you would calculate
1192	next midnight after C<now> and return the timestamp value for this. How	2403	the next midnight after C<now> and return the timestamp value for
1193	you do this is, again, up to you (but it is not trivial, which is the main	2404	this. Here is a (completely untested, no error checking) example on how to
1194	reason I omitted it as an example).	2405	do this:
		2406
		2407	#include <time.h>
		2408
		2409	static ev_tstamp
		2410	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2411	{
		2412	time_t tnow = (time_t)now;
		2413	struct tm tm;
		2414	localtime_r (&tnow, &tm);
		2415
		2416	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2417	++tm.tm_mday; // midnight next day
		2418
		2419	return mktime (&tm);
		2420	}
		2421
		2422	Note: this code might run into trouble on days that have more then two
		2423	midnights (beginning and end).
1195		2424
1196	=back	2425	=back
1197		2426
1198	=item ev_periodic_again (loop, ev_periodic *)	2427	=item ev_periodic_again (loop, ev_periodic *)
1199		2428
1200	Simply stops and restarts the periodic watcher again. This is only useful	2429	Simply stops and restarts the periodic watcher again. This is only useful
1201	when you changed some parameters or the reschedule callback would return	2430	when you changed some parameters or the reschedule callback would return
1202	a different time than the last time it was called (e.g. in a crond like	2431	a different time than the last time it was called (e.g. in a crond like
1203	program when the crontabs have changed).	2432	program when the crontabs have changed).
1204		2433
		2434	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2435
		2436	When active, returns the absolute time that the watcher is supposed
		2437	to trigger next. This is not the same as the C<offset> argument to
		2438	C<ev_periodic_set>, but indeed works even in interval and manual
		2439	rescheduling modes.
		2440
1205	=item ev_tstamp offset [read-write]	2441	=item ev_tstamp offset [read-write]
1206		2442
1207	When repeating, this contains the offset value, otherwise this is the	2443	When repeating, this contains the offset value, otherwise this is the
1208	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2444	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2445	although libev might modify this value for better numerical stability).
1209		2446
1210	Can be modified any time, but changes only take effect when the periodic	2447	Can be modified any time, but changes only take effect when the periodic
1211	timer fires or C<ev_periodic_again> is being called.	2448	timer fires or C<ev_periodic_again> is being called.
1212		2449
1213	=item ev_tstamp interval [read-write]	2450	=item ev_tstamp interval [read-write]
1214		2451
1215	The current interval value. Can be modified any time, but changes only	2452	The current interval value. Can be modified any time, but changes only
1216	take effect when the periodic timer fires or C<ev_periodic_again> is being	2453	take effect when the periodic timer fires or C<ev_periodic_again> is being
1217	called.	2454	called.
1218		2455
1219	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2456	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1220		2457
1221	The current reschedule callback, or C<0>, if this functionality is	2458	The current reschedule callback, or C<0>, if this functionality is
1222	switched off. Can be changed any time, but changes only take effect when	2459	switched off. Can be changed any time, but changes only take effect when
1223	the periodic timer fires or C<ev_periodic_again> is being called.	2460	the periodic timer fires or C<ev_periodic_again> is being called.
1224		2461
1225	=back	2462	=back
1226		2463
		2464	=head3 Examples
		2465
1227	Example: Call a callback every hour, or, more precisely, whenever the	2466	Example: Call a callback every hour, or, more precisely, whenever the
1228	system clock is divisible by 3600. The callback invocation times have	2467	system time is divisible by 3600. The callback invocation times have
1229	potentially a lot of jittering, but good long-term stability.	2468	potentially a lot of jitter, but good long-term stability.
1230		2469
1231	static void	2470	static void
1232	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2471	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1233	{	2472	{
1234	... its now a full hour (UTC, or TAI or whatever your clock follows)	2473	... its now a full hour (UTC, or TAI or whatever your clock follows)
1235	}	2474	}
1236		2475
1237	struct ev_periodic hourly_tick;	2476	ev_periodic hourly_tick;
1238	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2477	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1239	ev_periodic_start (loop, &hourly_tick);	2478	ev_periodic_start (loop, &hourly_tick);
1240		2479
1241	Example: The same as above, but use a reschedule callback to do it:	2480	Example: The same as above, but use a reschedule callback to do it:
1242		2481
1243	#include <math.h>	2482	#include <math.h>
1244		2483
1245	static ev_tstamp	2484	static ev_tstamp
1246	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2485	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1247	{	2486	{
1248	return fmod (now, 3600.) + 3600.;	2487	return now + (3600. - fmod (now, 3600.));
1249	}	2488	}
1250		2489
1251	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2490	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1252		2491
1253	Example: Call a callback every hour, starting now:	2492	Example: Call a callback every hour, starting now:
1254		2493
1255	struct ev_periodic hourly_tick;	2494	ev_periodic hourly_tick;
1256	ev_periodic_init (&hourly_tick, clock_cb,	2495	ev_periodic_init (&hourly_tick, clock_cb,
1257	fmod (ev_now (loop), 3600.), 3600., 0);	2496	fmod (ev_now (loop), 3600.), 3600., 0);
1258	ev_periodic_start (loop, &hourly_tick);	2497	ev_periodic_start (loop, &hourly_tick);
1259		2498
1260		2499
1261	=head2 C<ev_signal> - signal me when a signal gets signalled!	2500	=head2 C<ev_signal> - signal me when a signal gets signalled!
1262		2501
1263	Signal watchers will trigger an event when the process receives a specific	2502	Signal watchers will trigger an event when the process receives a specific
1264	signal one or more times. Even though signals are very asynchronous, libev	2503	signal one or more times. Even though signals are very asynchronous, libev
1265	will try it's best to deliver signals synchronously, i.e. as part of the	2504	will try its best to deliver signals synchronously, i.e. as part of the
1266	normal event processing, like any other event.	2505	normal event processing, like any other event.
1267		2506
		2507	If you want signals to be delivered truly asynchronously, just use
		2508	C<sigaction> as you would do without libev and forget about sharing
		2509	the signal. You can even use C<ev_async> from a signal handler to
		2510	synchronously wake up an event loop.
		2511
1268	You can configure as many watchers as you like per signal. Only when the	2512	You can configure as many watchers as you like for the same signal, but
1269	first watcher gets started will libev actually register a signal watcher	2513	only within the same loop, i.e. you can watch for C<SIGINT> in your
1270	with the kernel (thus it coexists with your own signal handlers as long	2514	default loop and for C<SIGIO> in another loop, but you cannot watch for
1271	as you don't register any with libev). Similarly, when the last signal	2515	C<SIGINT> in both the default loop and another loop at the same time. At
1272	watcher for a signal is stopped libev will reset the signal handler to	2516	the moment, C<SIGCHLD> is permanently tied to the default loop.
1273	SIG_DFL (regardless of what it was set to before).	2517
		2518	Only after the first watcher for a signal is started will libev actually
		2519	register something with the kernel. It thus coexists with your own signal
		2520	handlers as long as you don't register any with libev for the same signal.
		2521
		2522	If possible and supported, libev will install its handlers with
		2523	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2524	not be unduly interrupted. If you have a problem with system calls getting
		2525	interrupted by signals you can block all signals in an C<ev_check> watcher
		2526	and unblock them in an C<ev_prepare> watcher.
		2527
		2528	=head3 The special problem of inheritance over fork/execve/pthread_create
		2529
		2530	Both the signal mask (C<sigprocmask>) and the signal disposition
		2531	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2532	stopping it again), that is, libev might or might not block the signal,
		2533	and might or might not set or restore the installed signal handler (but
		2534	see C<EVFLAG_NOSIGMASK>).
		2535
		2536	While this does not matter for the signal disposition (libev never
		2537	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2538	C<execve>), this matters for the signal mask: many programs do not expect
		2539	certain signals to be blocked.
		2540
		2541	This means that before calling C<exec> (from the child) you should reset
		2542	the signal mask to whatever "default" you expect (all clear is a good
		2543	choice usually).
		2544
		2545	The simplest way to ensure that the signal mask is reset in the child is
		2546	to install a fork handler with C<pthread_atfork> that resets it. That will
		2547	catch fork calls done by libraries (such as the libc) as well.
		2548
		2549	In current versions of libev, the signal will not be blocked indefinitely
		2550	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2551	the window of opportunity for problems, it will not go away, as libev
		2552	I<has> to modify the signal mask, at least temporarily.
		2553
		2554	So I can't stress this enough: I<If you do not reset your signal mask when
		2555	you expect it to be empty, you have a race condition in your code>. This
		2556	is not a libev-specific thing, this is true for most event libraries.
		2557
		2558	=head3 The special problem of threads signal handling
		2559
		2560	POSIX threads has problematic signal handling semantics, specifically,
		2561	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2562	threads in a process block signals, which is hard to achieve.
		2563
		2564	When you want to use sigwait (or mix libev signal handling with your own
		2565	for the same signals), you can tackle this problem by globally blocking
		2566	all signals before creating any threads (or creating them with a fully set
		2567	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2568	loops. Then designate one thread as "signal receiver thread" which handles
		2569	these signals. You can pass on any signals that libev might be interested
		2570	in by calling C<ev_feed_signal>.
1274		2571
1275	=head3 Watcher-Specific Functions and Data Members	2572	=head3 Watcher-Specific Functions and Data Members
1276		2573
1277	=over 4	2574	=over 4
1278		2575
…		…
1287		2584
1288	The signal the watcher watches out for.	2585	The signal the watcher watches out for.
1289		2586
1290	=back	2587	=back
1291		2588
		2589	=head3 Examples
		2590
		2591	Example: Try to exit cleanly on SIGINT.
		2592
		2593	static void
		2594	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2595	{
		2596	ev_break (loop, EVBREAK_ALL);
		2597	}
		2598
		2599	ev_signal signal_watcher;
		2600	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2601	ev_signal_start (loop, &signal_watcher);
		2602
1292		2603
1293	=head2 C<ev_child> - watch out for process status changes	2604	=head2 C<ev_child> - watch out for process status changes
1294		2605
1295	Child watchers trigger when your process receives a SIGCHLD in response to	2606	Child watchers trigger when your process receives a SIGCHLD in response to
1296	some child status changes (most typically when a child of yours dies).	2607	some child status changes (most typically when a child of yours dies or
		2608	exits). It is permissible to install a child watcher I<after> the child
		2609	has been forked (which implies it might have already exited), as long
		2610	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2611	forking and then immediately registering a watcher for the child is fine,
		2612	but forking and registering a watcher a few event loop iterations later or
		2613	in the next callback invocation is not.
		2614
		2615	Only the default event loop is capable of handling signals, and therefore
		2616	you can only register child watchers in the default event loop.
		2617
		2618	Due to some design glitches inside libev, child watchers will always be
		2619	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2620	libev)
		2621
		2622	=head3 Process Interaction
		2623
		2624	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2625	initialised. This is necessary to guarantee proper behaviour even if the
		2626	first child watcher is started after the child exits. The occurrence
		2627	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2628	synchronously as part of the event loop processing. Libev always reaps all
		2629	children, even ones not watched.
		2630
		2631	=head3 Overriding the Built-In Processing
		2632
		2633	Libev offers no special support for overriding the built-in child
		2634	processing, but if your application collides with libev's default child
		2635	handler, you can override it easily by installing your own handler for
		2636	C<SIGCHLD> after initialising the default loop, and making sure the
		2637	default loop never gets destroyed. You are encouraged, however, to use an
		2638	event-based approach to child reaping and thus use libev's support for
		2639	that, so other libev users can use C<ev_child> watchers freely.
		2640
		2641	=head3 Stopping the Child Watcher
		2642
		2643	Currently, the child watcher never gets stopped, even when the
		2644	child terminates, so normally one needs to stop the watcher in the
		2645	callback. Future versions of libev might stop the watcher automatically
		2646	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2647	problem).
1297		2648
1298	=head3 Watcher-Specific Functions and Data Members	2649	=head3 Watcher-Specific Functions and Data Members
1299		2650
1300	=over 4	2651	=over 4
1301		2652
1302	=item ev_child_init (ev_child *, callback, int pid)	2653	=item ev_child_init (ev_child *, callback, int pid, int trace)
1303		2654
1304	=item ev_child_set (ev_child *, int pid)	2655	=item ev_child_set (ev_child *, int pid, int trace)
1305		2656
1306	Configures the watcher to wait for status changes of process C<pid> (or	2657	Configures the watcher to wait for status changes of process C<pid> (or
1307	I<any> process if C<pid> is specified as C<0>). The callback can look	2658	I<any> process if C<pid> is specified as C<0>). The callback can look
1308	at the C<rstatus> member of the C<ev_child> watcher structure to see	2659	at the C<rstatus> member of the C<ev_child> watcher structure to see
1309	the status word (use the macros from C<sys/wait.h> and see your systems	2660	the status word (use the macros from C<sys/wait.h> and see your systems
1310	C<waitpid> documentation). The C<rpid> member contains the pid of the	2661	C<waitpid> documentation). The C<rpid> member contains the pid of the
1311	process causing the status change.	2662	process causing the status change. C<trace> must be either C<0> (only
		2663	activate the watcher when the process terminates) or C<1> (additionally
		2664	activate the watcher when the process is stopped or continued).
1312		2665
1313	=item int pid [read-only]	2666	=item int pid [read-only]
1314		2667
1315	The process id this watcher watches out for, or C<0>, meaning any process id.	2668	The process id this watcher watches out for, or C<0>, meaning any process id.
1316		2669
…		…
1323	The process exit/trace status caused by C<rpid> (see your systems	2676	The process exit/trace status caused by C<rpid> (see your systems
1324	C<waitpid> and C<sys/wait.h> documentation for details).	2677	C<waitpid> and C<sys/wait.h> documentation for details).
1325		2678
1326	=back	2679	=back
1327		2680
1328	Example: Try to exit cleanly on SIGINT and SIGTERM.	2681	=head3 Examples
1329		2682
		2683	Example: C<fork()> a new process and install a child handler to wait for
		2684	its completion.
		2685
		2686	ev_child cw;
		2687
1330	static void	2688	static void
1331	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2689	child_cb (EV_P_ ev_child *w, int revents)
1332	{	2690	{
1333	ev_unloop (loop, EVUNLOOP_ALL);	2691	ev_child_stop (EV_A_ w);
		2692	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1334	}	2693	}
1335		2694
1336	struct ev_signal signal_watcher;	2695	pid_t pid = fork ();
1337	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2696
1338	ev_signal_start (loop, &sigint_cb);	2697	if (pid < 0)
		2698	// error
		2699	else if (pid == 0)
		2700	{
		2701	// the forked child executes here
		2702	exit (1);
		2703	}
		2704	else
		2705	{
		2706	ev_child_init (&cw, child_cb, pid, 0);
		2707	ev_child_start (EV_DEFAULT_ &cw);
		2708	}
1339		2709
1340		2710
1341	=head2 C<ev_stat> - did the file attributes just change?	2711	=head2 C<ev_stat> - did the file attributes just change?
1342		2712
1343	This watches a filesystem path for attribute changes. That is, it calls	2713	This watches a file system path for attribute changes. That is, it calls
1344	C<stat> regularly (or when the OS says it changed) and sees if it changed	2714	C<stat> on that path in regular intervals (or when the OS says it changed)
1345	compared to the last time, invoking the callback if it did.	2715	and sees if it changed compared to the last time, invoking the callback
		2716	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2717	happen after the watcher has been started will be reported.
1346		2718
1347	The path does not need to exist: changing from "path exists" to "path does	2719	The path does not need to exist: changing from "path exists" to "path does
1348	not exist" is a status change like any other. The condition "path does	2720	not exist" is a status change like any other. The condition "path does not
1349	not exist" is signified by the C<st_nlink> field being zero (which is	2721	exist" (or more correctly "path cannot be stat'ed") is signified by the
1350	otherwise always forced to be at least one) and all the other fields of	2722	C<st_nlink> field being zero (which is otherwise always forced to be at
1351	the stat buffer having unspecified contents.	2723	least one) and all the other fields of the stat buffer having unspecified
		2724	contents.
1352		2725
1353	The path I<should> be absolute and I<must not> end in a slash. If it is	2726	The path I<must not> end in a slash or contain special components such as
		2727	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1354	relative and your working directory changes, the behaviour is undefined.	2728	your working directory changes, then the behaviour is undefined.
1355		2729
1356	Since there is no standard to do this, the portable implementation simply	2730	Since there is no portable change notification interface available, the
1357	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2731	portable implementation simply calls C<stat(2)> regularly on the path
1358	can specify a recommended polling interval for this case. If you specify	2732	to see if it changed somehow. You can specify a recommended polling
1359	a polling interval of C<0> (highly recommended!) then a I<suitable,	2733	interval for this case. If you specify a polling interval of C<0> (highly
1360	unspecified default> value will be used (which you can expect to be around	2734	recommended!) then a I<suitable, unspecified default> value will be used
1361	five seconds, although this might change dynamically). Libev will also	2735	(which you can expect to be around five seconds, although this might
1362	impose a minimum interval which is currently around C<0.1>, but thats	2736	change dynamically). Libev will also impose a minimum interval which is
1363	usually overkill.	2737	currently around C<0.1>, but that's usually overkill.
1364		2738
1365	This watcher type is not meant for massive numbers of stat watchers,	2739	This watcher type is not meant for massive numbers of stat watchers,
1366	as even with OS-supported change notifications, this can be	2740	as even with OS-supported change notifications, this can be
1367	resource-intensive.	2741	resource-intensive.
1368		2742
1369	At the time of this writing, only the Linux inotify interface is	2743	At the time of this writing, the only OS-specific interface implemented
1370	implemented (implementing kqueue support is left as an exercise for the	2744	is the Linux inotify interface (implementing kqueue support is left as an
1371	reader). Inotify will be used to give hints only and should not change the	2745	exercise for the reader. Note, however, that the author sees no way of
1372	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2746	implementing C<ev_stat> semantics with kqueue, except as a hint).
1373	to fall back to regular polling again even with inotify, but changes are	2747
1374	usually detected immediately, and if the file exists there will be no	2748	=head3 ABI Issues (Largefile Support)
1375	polling.	2749
		2750	Libev by default (unless the user overrides this) uses the default
		2751	compilation environment, which means that on systems with large file
		2752	support disabled by default, you get the 32 bit version of the stat
		2753	structure. When using the library from programs that change the ABI to
		2754	use 64 bit file offsets the programs will fail. In that case you have to
		2755	compile libev with the same flags to get binary compatibility. This is
		2756	obviously the case with any flags that change the ABI, but the problem is
		2757	most noticeably displayed with ev_stat and large file support.
		2758
		2759	The solution for this is to lobby your distribution maker to make large
		2760	file interfaces available by default (as e.g. FreeBSD does) and not
		2761	optional. Libev cannot simply switch on large file support because it has
		2762	to exchange stat structures with application programs compiled using the
		2763	default compilation environment.
		2764
		2765	=head3 Inotify and Kqueue
		2766
		2767	When C<inotify (7)> support has been compiled into libev and present at
		2768	runtime, it will be used to speed up change detection where possible. The
		2769	inotify descriptor will be created lazily when the first C<ev_stat>
		2770	watcher is being started.
		2771
		2772	Inotify presence does not change the semantics of C<ev_stat> watchers
		2773	except that changes might be detected earlier, and in some cases, to avoid
		2774	making regular C<stat> calls. Even in the presence of inotify support
		2775	there are many cases where libev has to resort to regular C<stat> polling,
		2776	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2777	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2778	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2779	xfs are fully working) libev usually gets away without polling.
		2780
		2781	There is no support for kqueue, as apparently it cannot be used to
		2782	implement this functionality, due to the requirement of having a file
		2783	descriptor open on the object at all times, and detecting renames, unlinks
		2784	etc. is difficult.
		2785
		2786	=head3 C<stat ()> is a synchronous operation
		2787
		2788	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2789	the process. The exception are C<ev_stat> watchers - those call C<stat
		2790	()>, which is a synchronous operation.
		2791
		2792	For local paths, this usually doesn't matter: unless the system is very
		2793	busy or the intervals between stat's are large, a stat call will be fast,
		2794	as the path data is usually in memory already (except when starting the
		2795	watcher).
		2796
		2797	For networked file systems, calling C<stat ()> can block an indefinite
		2798	time due to network issues, and even under good conditions, a stat call
		2799	often takes multiple milliseconds.
		2800
		2801	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2802	paths, although this is fully supported by libev.
		2803
		2804	=head3 The special problem of stat time resolution
		2805
		2806	The C<stat ()> system call only supports full-second resolution portably,
		2807	and even on systems where the resolution is higher, most file systems
		2808	still only support whole seconds.
		2809
		2810	That means that, if the time is the only thing that changes, you can
		2811	easily miss updates: on the first update, C<ev_stat> detects a change and
		2812	calls your callback, which does something. When there is another update
		2813	within the same second, C<ev_stat> will be unable to detect unless the
		2814	stat data does change in other ways (e.g. file size).
		2815
		2816	The solution to this is to delay acting on a change for slightly more
		2817	than a second (or till slightly after the next full second boundary), using
		2818	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2819	ev_timer_again (loop, w)>).
		2820
		2821	The C<.02> offset is added to work around small timing inconsistencies
		2822	of some operating systems (where the second counter of the current time
		2823	might be be delayed. One such system is the Linux kernel, where a call to
		2824	C<gettimeofday> might return a timestamp with a full second later than
		2825	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2826	update file times then there will be a small window where the kernel uses
		2827	the previous second to update file times but libev might already execute
		2828	the timer callback).
1376		2829
1377	=head3 Watcher-Specific Functions and Data Members	2830	=head3 Watcher-Specific Functions and Data Members
1378		2831
1379	=over 4	2832	=over 4
1380		2833
…		…
1386	C<path>. The C<interval> is a hint on how quickly a change is expected to	2839	C<path>. The C<interval> is a hint on how quickly a change is expected to
1387	be detected and should normally be specified as C<0> to let libev choose	2840	be detected and should normally be specified as C<0> to let libev choose
1388	a suitable value. The memory pointed to by C<path> must point to the same	2841	a suitable value. The memory pointed to by C<path> must point to the same
1389	path for as long as the watcher is active.	2842	path for as long as the watcher is active.
1390		2843
1391	The callback will be receive C<EV_STAT> when a change was detected,	2844	The callback will receive an C<EV_STAT> event when a change was detected,
1392	relative to the attributes at the time the watcher was started (or the	2845	relative to the attributes at the time the watcher was started (or the
1393	last change was detected).	2846	last change was detected).
1394		2847
1395	=item ev_stat_stat (ev_stat *)	2848	=item ev_stat_stat (loop, ev_stat *)
1396		2849
1397	Updates the stat buffer immediately with new values. If you change the	2850	Updates the stat buffer immediately with new values. If you change the
1398	watched path in your callback, you could call this fucntion to avoid	2851	watched path in your callback, you could call this function to avoid
1399	detecting this change (while introducing a race condition). Can also be	2852	detecting this change (while introducing a race condition if you are not
1400	useful simply to find out the new values.	2853	the only one changing the path). Can also be useful simply to find out the
		2854	new values.
1401		2855
1402	=item ev_statdata attr [read-only]	2856	=item ev_statdata attr [read-only]
1403		2857
1404	The most-recently detected attributes of the file. Although the type is of	2858	The most-recently detected attributes of the file. Although the type is
1405	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2859	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1406	suitable for your system. If the C<st_nlink> member is C<0>, then there	2860	suitable for your system, but you can only rely on the POSIX-standardised
		2861	members to be present. If the C<st_nlink> member is C<0>, then there was
1407	was some error while C<stat>ing the file.	2862	some error while C<stat>ing the file.
1408		2863
1409	=item ev_statdata prev [read-only]	2864	=item ev_statdata prev [read-only]
1410		2865
1411	The previous attributes of the file. The callback gets invoked whenever	2866	The previous attributes of the file. The callback gets invoked whenever
1412	C<prev> != C<attr>.	2867	C<prev> != C<attr>, or, more precisely, one or more of these members
		2868	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2869	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1413		2870
1414	=item ev_tstamp interval [read-only]	2871	=item ev_tstamp interval [read-only]
1415		2872
1416	The specified interval.	2873	The specified interval.
1417		2874
1418	=item const char *path [read-only]	2875	=item const char *path [read-only]
1419		2876
1420	The filesystem path that is being watched.	2877	The file system path that is being watched.
1421		2878
1422	=back	2879	=back
1423		2880
		2881	=head3 Examples
		2882
1424	Example: Watch C</etc/passwd> for attribute changes.	2883	Example: Watch C</etc/passwd> for attribute changes.
1425		2884
1426	static void	2885	static void
1427	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2886	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1428	{	2887	{
1429	/* /etc/passwd changed in some way */	2888	/* /etc/passwd changed in some way */
1430	if (w->attr.st_nlink)	2889	if (w->attr.st_nlink)
1431	{	2890	{
1432	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2891	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1433	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2892	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1434	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2893	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1435	}	2894	}
1436	else	2895	else
1437	/* you shalt not abuse printf for puts */	2896	/* you shalt not abuse printf for puts */
1438	puts ("wow, /etc/passwd is not there, expect problems. "	2897	puts ("wow, /etc/passwd is not there, expect problems. "
1439	"if this is windows, they already arrived\n");	2898	"if this is windows, they already arrived\n");
1440	}	2899	}
1441		2900
1442	...	2901	...
1443	ev_stat passwd;	2902	ev_stat passwd;
1444		2903
1445	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2904	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1446	ev_stat_start (loop, &passwd);	2905	ev_stat_start (loop, &passwd);
		2906
		2907	Example: Like above, but additionally use a one-second delay so we do not
		2908	miss updates (however, frequent updates will delay processing, too, so
		2909	one might do the work both on C<ev_stat> callback invocation I<and> on
		2910	C<ev_timer> callback invocation).
		2911
		2912	static ev_stat passwd;
		2913	static ev_timer timer;
		2914
		2915	static void
		2916	timer_cb (EV_P_ ev_timer *w, int revents)
		2917	{
		2918	ev_timer_stop (EV_A_ w);
		2919
		2920	/* now it's one second after the most recent passwd change */
		2921	}
		2922
		2923	static void
		2924	stat_cb (EV_P_ ev_stat *w, int revents)
		2925	{
		2926	/* reset the one-second timer */
		2927	ev_timer_again (EV_A_ &timer);
		2928	}
		2929
		2930	...
		2931	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2932	ev_stat_start (loop, &passwd);
		2933	ev_timer_init (&timer, timer_cb, 0., 1.02);
1447		2934
1448		2935
1449	=head2 C<ev_idle> - when you've got nothing better to do...	2936	=head2 C<ev_idle> - when you've got nothing better to do...
1450		2937
1451	Idle watchers trigger events when no other events of the same or higher	2938	Idle watchers trigger events when no other events of the same or higher
1452	priority are pending (prepare, check and other idle watchers do not	2939	priority are pending (prepare, check and other idle watchers do not count
1453	count).	2940	as receiving "events").
1454		2941
1455	That is, as long as your process is busy handling sockets or timeouts	2942	That is, as long as your process is busy handling sockets or timeouts
1456	(or even signals, imagine) of the same or higher priority it will not be	2943	(or even signals, imagine) of the same or higher priority it will not be
1457	triggered. But when your process is idle (or only lower-priority watchers	2944	triggered. But when your process is idle (or only lower-priority watchers
1458	are pending), the idle watchers are being called once per event loop	2945	are pending), the idle watchers are being called once per event loop
…		…
1465	Apart from keeping your process non-blocking (which is a useful	2952	Apart from keeping your process non-blocking (which is a useful
1466	effect on its own sometimes), idle watchers are a good place to do	2953	effect on its own sometimes), idle watchers are a good place to do
1467	"pseudo-background processing", or delay processing stuff to after the	2954	"pseudo-background processing", or delay processing stuff to after the
1468	event loop has handled all outstanding events.	2955	event loop has handled all outstanding events.
1469		2956
		2957	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2958
		2959	As long as there is at least one active idle watcher, libev will never
		2960	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2961	For this to work, the idle watcher doesn't need to be invoked at all - the
		2962	lowest priority will do.
		2963
		2964	This mode of operation can be useful together with an C<ev_check> watcher,
		2965	to do something on each event loop iteration - for example to balance load
		2966	between different connections.
		2967
		2968	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2969	example.
		2970
1470	=head3 Watcher-Specific Functions and Data Members	2971	=head3 Watcher-Specific Functions and Data Members
1471		2972
1472	=over 4	2973	=over 4
1473		2974
1474	=item ev_idle_init (ev_signal *, callback)	2975	=item ev_idle_init (ev_idle *, callback)
1475		2976
1476	Initialises and configures the idle watcher - it has no parameters of any	2977	Initialises and configures the idle watcher - it has no parameters of any
1477	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2978	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1478	believe me.	2979	believe me.
1479		2980
1480	=back	2981	=back
1481		2982
		2983	=head3 Examples
		2984
1482	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2985	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1483	callback, free it. Also, use no error checking, as usual.	2986	callback, free it. Also, use no error checking, as usual.
1484		2987
1485	static void	2988	static void
1486	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2989	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1487	{	2990	{
		2991	// stop the watcher
		2992	ev_idle_stop (loop, w);
		2993
		2994	// now we can free it
1488	free (w);	2995	free (w);
		2996
1489	// now do something you wanted to do when the program has	2997	// now do something you wanted to do when the program has
1490	// no longer asnything immediate to do.	2998	// no longer anything immediate to do.
1491	}	2999	}
1492		3000
1493	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	3001	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1494	ev_idle_init (idle_watcher, idle_cb);	3002	ev_idle_init (idle_watcher, idle_cb);
1495	ev_idle_start (loop, idle_cb);	3003	ev_idle_start (loop, idle_watcher);
1496		3004
1497		3005
1498	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	3006	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1499		3007
1500	Prepare and check watchers are usually (but not always) used in tandem:	3008	Prepare and check watchers are often (but not always) used in pairs:
1501	prepare watchers get invoked before the process blocks and check watchers	3009	prepare watchers get invoked before the process blocks and check watchers
1502	afterwards.	3010	afterwards.
1503		3011
1504	You I<must not> call C<ev_loop> or similar functions that enter	3012	You I<must not> call C<ev_run> (or similar functions that enter the
1505	the current event loop from either C<ev_prepare> or C<ev_check>	3013	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
1506	watchers. Other loops than the current one are fine, however. The	3014	C<ev_check> watchers. Other loops than the current one are fine,
1507	rationale behind this is that you do not need to check for recursion in	3015	however. The rationale behind this is that you do not need to check
1508	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3016	for recursion in those watchers, i.e. the sequence will always be
1509	C<ev_check> so if you have one watcher of each kind they will always be	3017	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
1510	called in pairs bracketing the blocking call.	3018	kind they will always be called in pairs bracketing the blocking call.
1511		3019
1512	Their main purpose is to integrate other event mechanisms into libev and	3020	Their main purpose is to integrate other event mechanisms into libev and
1513	their use is somewhat advanced. This could be used, for example, to track	3021	their use is somewhat advanced. They could be used, for example, to track
1514	variable changes, implement your own watchers, integrate net-snmp or a	3022	variable changes, implement your own watchers, integrate net-snmp or a
1515	coroutine library and lots more. They are also occasionally useful if	3023	coroutine library and lots more. They are also occasionally useful if
1516	you cache some data and want to flush it before blocking (for example,	3024	you cache some data and want to flush it before blocking (for example,
1517	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	3025	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1518	watcher).	3026	watcher).
1519		3027
1520	This is done by examining in each prepare call which file descriptors need	3028	This is done by examining in each prepare call which file descriptors
1521	to be watched by the other library, registering C<ev_io> watchers for	3029	need to be watched by the other library, registering C<ev_io> watchers
1522	them and starting an C<ev_timer> watcher for any timeouts (many libraries	3030	for them and starting an C<ev_timer> watcher for any timeouts (many
1523	provide just this functionality). Then, in the check watcher you check for	3031	libraries provide exactly this functionality). Then, in the check watcher,
1524	any events that occured (by checking the pending status of all watchers	3032	you check for any events that occurred (by checking the pending status
1525	and stopping them) and call back into the library. The I/O and timer	3033	of all watchers and stopping them) and call back into the library. The
1526	callbacks will never actually be called (but must be valid nevertheless,	3034	I/O and timer callbacks will never actually be called (but must be valid
1527	because you never know, you know?).	3035	nevertheless, because you never know, you know?).
1528		3036
1529	As another example, the Perl Coro module uses these hooks to integrate	3037	As another example, the Perl Coro module uses these hooks to integrate
1530	coroutines into libev programs, by yielding to other active coroutines	3038	coroutines into libev programs, by yielding to other active coroutines
1531	during each prepare and only letting the process block if no coroutines	3039	during each prepare and only letting the process block if no coroutines
1532	are ready to run (it's actually more complicated: it only runs coroutines	3040	are ready to run (it's actually more complicated: it only runs coroutines
1533	with priority higher than or equal to the event loop and one coroutine	3041	with priority higher than or equal to the event loop and one coroutine
1534	of lower priority, but only once, using idle watchers to keep the event	3042	of lower priority, but only once, using idle watchers to keep the event
1535	loop from blocking if lower-priority coroutines are active, thus mapping	3043	loop from blocking if lower-priority coroutines are active, thus mapping
1536	low-priority coroutines to idle/background tasks).	3044	low-priority coroutines to idle/background tasks).
1537		3045
1538	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	3046	When used for this purpose, it is recommended to give C<ev_check> watchers
1539	priority, to ensure that they are being run before any other watchers	3047	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
		3048	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3049	watchers).
		3050
1540	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	3051	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1541	too) should not activate ("feed") events into libev. While libev fully	3052	activate ("feed") events into libev. While libev fully supports this, they
1542	supports this, they will be called before other C<ev_check> watchers did	3053	might get executed before other C<ev_check> watchers did their job. As
1543	their job. As C<ev_check> watchers are often used to embed other event	3054	C<ev_check> watchers are often used to embed other (non-libev) event
1544	loops those other event loops might be in an unusable state until their	3055	loops those other event loops might be in an unusable state until their
1545	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3056	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1546	others).	3057	others).
1547		3058
		3059	=head3 Abusing an C<ev_check> watcher for its side-effect
		3060
		3061	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3062	useful because they are called once per event loop iteration. For
		3063	example, if you want to handle a large number of connections fairly, you
		3064	normally only do a bit of work for each active connection, and if there
		3065	is more work to do, you wait for the next event loop iteration, so other
		3066	connections have a chance of making progress.
		3067
		3068	Using an C<ev_check> watcher is almost enough: it will be called on the
		3069	next event loop iteration. However, that isn't as soon as possible -
		3070	without external events, your C<ev_check> watcher will not be invoked.
		3071
		3072	This is where C<ev_idle> watchers come in handy - all you need is a
		3073	single global idle watcher that is active as long as you have one active
		3074	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3075	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3076	invoked. Neither watcher alone can do that.
		3077
1548	=head3 Watcher-Specific Functions and Data Members	3078	=head3 Watcher-Specific Functions and Data Members
1549		3079
1550	=over 4	3080	=over 4
1551		3081
1552	=item ev_prepare_init (ev_prepare *, callback)	3082	=item ev_prepare_init (ev_prepare *, callback)
1553		3083
1554	=item ev_check_init (ev_check *, callback)	3084	=item ev_check_init (ev_check *, callback)
1555		3085
1556	Initialises and configures the prepare or check watcher - they have no	3086	Initialises and configures the prepare or check watcher - they have no
1557	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	3087	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1558	macros, but using them is utterly, utterly and completely pointless.	3088	macros, but using them is utterly, utterly, utterly and completely
		3089	pointless.
1559		3090
1560	=back	3091	=back
		3092
		3093	=head3 Examples
1561		3094
1562	There are a number of principal ways to embed other event loops or modules	3095	There are a number of principal ways to embed other event loops or modules
1563	into libev. Here are some ideas on how to include libadns into libev	3096	into libev. Here are some ideas on how to include libadns into libev
1564	(there is a Perl module named C<EV::ADNS> that does this, which you could	3097	(there is a Perl module named C<EV::ADNS> that does this, which you could
1565	use for an actually working example. Another Perl module named C<EV::Glib>	3098	use as a working example. Another Perl module named C<EV::Glib> embeds a
1566	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	3099	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1567	into the Glib event loop).	3100	Glib event loop).
1568		3101
1569	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	3102	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1570	and in a check watcher, destroy them and call into libadns. What follows	3103	and in a check watcher, destroy them and call into libadns. What follows
1571	is pseudo-code only of course. This requires you to either use a low	3104	is pseudo-code only of course. This requires you to either use a low
1572	priority for the check watcher or use C<ev_clear_pending> explicitly, as	3105	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1573	the callbacks for the IO/timeout watchers might not have been called yet.	3106	the callbacks for the IO/timeout watchers might not have been called yet.
1574		3107
1575	static ev_io iow [nfd];	3108	static ev_io iow [nfd];
1576	static ev_timer tw;	3109	static ev_timer tw;
1577		3110
1578	static void	3111	static void
1579	io_cb (ev_loop *loop, ev_io *w, int revents)	3112	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1580	{	3113	{
1581	}	3114	}
1582		3115
1583	// create io watchers for each fd and a timer before blocking	3116	// create io watchers for each fd and a timer before blocking
1584	static void	3117	static void
1585	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	3118	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1586	{	3119	{
1587	int timeout = 3600000;	3120	int timeout = 3600000;
1588	struct pollfd fds [nfd];	3121	struct pollfd fds [nfd];
1589	// actual code will need to loop here and realloc etc.	3122	// actual code will need to loop here and realloc etc.
1590	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	3123	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1591		3124
1592	/* the callback is illegal, but won't be called as we stop during check */	3125	/* the callback is illegal, but won't be called as we stop during check */
1593	ev_timer_init (&tw, 0, timeout * 1e-3);	3126	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1594	ev_timer_start (loop, &tw);	3127	ev_timer_start (loop, &tw);
1595		3128
1596	// create one ev_io per pollfd	3129	// create one ev_io per pollfd
1597	for (int i = 0; i < nfd; ++i)	3130	for (int i = 0; i < nfd; ++i)
1598	{	3131	{
1599	ev_io_init (iow + i, io_cb, fds [i].fd,	3132	ev_io_init (iow + i, io_cb, fds [i].fd,
1600	((fds [i].events & POLLIN ? EV_READ : 0)	3133	((fds [i].events & POLLIN ? EV_READ : 0)
1601	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	3134	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1602		3135
1603	fds [i].revents = 0;	3136	fds [i].revents = 0;
1604	ev_io_start (loop, iow + i);	3137	ev_io_start (loop, iow + i);
1605	}	3138	}
1606	}	3139	}
1607		3140
1608	// stop all watchers after blocking	3141	// stop all watchers after blocking
1609	static void	3142	static void
1610	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	3143	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1611	{	3144	{
1612	ev_timer_stop (loop, &tw);	3145	ev_timer_stop (loop, &tw);
1613		3146
1614	for (int i = 0; i < nfd; ++i)	3147	for (int i = 0; i < nfd; ++i)
1615	{	3148	{
1616	// set the relevant poll flags	3149	// set the relevant poll flags
1617	// could also call adns_processreadable etc. here	3150	// could also call adns_processreadable etc. here
1618	struct pollfd *fd = fds + i;	3151	struct pollfd *fd = fds + i;
1619	int revents = ev_clear_pending (iow + i);	3152	int revents = ev_clear_pending (iow + i);
1620	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	3153	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1621	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	3154	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1622		3155
1623	// now stop the watcher	3156	// now stop the watcher
1624	ev_io_stop (loop, iow + i);	3157	ev_io_stop (loop, iow + i);
1625	}	3158	}
1626		3159
1627	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	3160	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1628	}	3161	}
1629		3162
1630	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	3163	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1631	in the prepare watcher and would dispose of the check watcher.	3164	in the prepare watcher and would dispose of the check watcher.
1632		3165
1633	Method 3: If the module to be embedded supports explicit event	3166	Method 3: If the module to be embedded supports explicit event
1634	notification (adns does), you can also make use of the actual watcher	3167	notification (libadns does), you can also make use of the actual watcher
1635	callbacks, and only destroy/create the watchers in the prepare watcher.	3168	callbacks, and only destroy/create the watchers in the prepare watcher.
1636		3169
1637	static void	3170	static void
1638	timer_cb (EV_P_ ev_timer *w, int revents)	3171	timer_cb (EV_P_ ev_timer *w, int revents)
1639	{	3172	{
1640	adns_state ads = (adns_state)w->data;	3173	adns_state ads = (adns_state)w->data;
1641	update_now (EV_A);	3174	update_now (EV_A);
1642		3175
1643	adns_processtimeouts (ads, &tv_now);	3176	adns_processtimeouts (ads, &tv_now);
1644	}	3177	}
1645		3178
1646	static void	3179	static void
1647	io_cb (EV_P_ ev_io *w, int revents)	3180	io_cb (EV_P_ ev_io *w, int revents)
1648	{	3181	{
1649	adns_state ads = (adns_state)w->data;	3182	adns_state ads = (adns_state)w->data;
1650	update_now (EV_A);	3183	update_now (EV_A);
1651		3184
1652	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	3185	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1653	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	3186	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1654	}	3187	}
1655		3188
1656	// do not ever call adns_afterpoll	3189	// do not ever call adns_afterpoll
1657		3190
1658	Method 4: Do not use a prepare or check watcher because the module you	3191	Method 4: Do not use a prepare or check watcher because the module you
1659	want to embed is too inflexible to support it. Instead, youc na override	3192	want to embed is not flexible enough to support it. Instead, you can
1660	their poll function. The drawback with this solution is that the main	3193	override their poll function. The drawback with this solution is that the
1661	loop is now no longer controllable by EV. The C<Glib::EV> module does	3194	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1662	this.	3195	this approach, effectively embedding EV as a client into the horrible
		3196	libglib event loop.
1663		3197
1664	static gint	3198	static gint
1665	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	3199	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1666	{	3200	{
1667	int got_events = 0;	3201	int got_events = 0;
1668		3202
1669	for (n = 0; n < nfds; ++n)	3203	for (n = 0; n < nfds; ++n)
1670	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	3204	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1671		3205
1672	if (timeout >= 0)	3206	if (timeout >= 0)
1673	// create/start timer	3207	// create/start timer
1674		3208
1675	// poll	3209	// poll
1676	ev_loop (EV_A_ 0);	3210	ev_run (EV_A_ 0);
1677		3211
1678	// stop timer again	3212	// stop timer again
1679	if (timeout >= 0)	3213	if (timeout >= 0)
1680	ev_timer_stop (EV_A_ &to);	3214	ev_timer_stop (EV_A_ &to);
1681		3215
1682	// stop io watchers again - their callbacks should have set	3216	// stop io watchers again - their callbacks should have set
1683	for (n = 0; n < nfds; ++n)	3217	for (n = 0; n < nfds; ++n)
1684	ev_io_stop (EV_A_ iow [n]);	3218	ev_io_stop (EV_A_ iow [n]);
1685		3219
1686	return got_events;	3220	return got_events;
1687	}	3221	}
1688		3222
1689		3223
1690	=head2 C<ev_embed> - when one backend isn't enough...	3224	=head2 C<ev_embed> - when one backend isn't enough...
1691		3225
1692	This is a rather advanced watcher type that lets you embed one event loop	3226	This is a rather advanced watcher type that lets you embed one event loop
…		…
1698	prioritise I/O.	3232	prioritise I/O.
1699		3233
1700	As an example for a bug workaround, the kqueue backend might only support	3234	As an example for a bug workaround, the kqueue backend might only support
1701	sockets on some platform, so it is unusable as generic backend, but you	3235	sockets on some platform, so it is unusable as generic backend, but you
1702	still want to make use of it because you have many sockets and it scales	3236	still want to make use of it because you have many sockets and it scales
1703	so nicely. In this case, you would create a kqueue-based loop and embed it	3237	so nicely. In this case, you would create a kqueue-based loop and embed
1704	into your default loop (which might use e.g. poll). Overall operation will	3238	it into your default loop (which might use e.g. poll). Overall operation
1705	be a bit slower because first libev has to poll and then call kevent, but	3239	will be a bit slower because first libev has to call C<poll> and then
1706	at least you can use both at what they are best.	3240	C<kevent>, but at least you can use both mechanisms for what they are
		3241	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1707		3242
1708	As for prioritising I/O: rarely you have the case where some fds have	3243	As for prioritising I/O: under rare circumstances you have the case where
1709	to be watched and handled very quickly (with low latency), and even	3244	some fds have to be watched and handled very quickly (with low latency),
1710	priorities and idle watchers might have too much overhead. In this case	3245	and even priorities and idle watchers might have too much overhead. In
1711	you would put all the high priority stuff in one loop and all the rest in	3246	this case you would put all the high priority stuff in one loop and all
1712	a second one, and embed the second one in the first.	3247	the rest in a second one, and embed the second one in the first.
1713		3248
1714	As long as the watcher is active, the callback will be invoked every time	3249	As long as the watcher is active, the callback will be invoked every
1715	there might be events pending in the embedded loop. The callback must then	3250	time there might be events pending in the embedded loop. The callback
1716	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3251	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1717	their callbacks (you could also start an idle watcher to give the embedded	3252	sweep and invoke their callbacks (the callback doesn't need to invoke the
1718	loop strictly lower priority for example). You can also set the callback	3253	C<ev_embed_sweep> function directly, it could also start an idle watcher
1719	to C<0>, in which case the embed watcher will automatically execute the	3254	to give the embedded loop strictly lower priority for example).
1720	embedded loop sweep.
1721		3255
1722	As long as the watcher is started it will automatically handle events. The	3256	You can also set the callback to C<0>, in which case the embed watcher
1723	callback will be invoked whenever some events have been handled. You can	3257	will automatically execute the embedded loop sweep whenever necessary.
1724	set the callback to C<0> to avoid having to specify one if you are not
1725	interested in that.
1726		3258
1727	Also, there have not currently been made special provisions for forking:	3259	Fork detection will be handled transparently while the C<ev_embed> watcher
1728	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3260	is active, i.e., the embedded loop will automatically be forked when the
1729	but you will also have to stop and restart any C<ev_embed> watchers	3261	embedding loop forks. In other cases, the user is responsible for calling
1730	yourself.	3262	C<ev_loop_fork> on the embedded loop.
1731		3263
1732	Unfortunately, not all backends are embeddable, only the ones returned by	3264	Unfortunately, not all backends are embeddable: only the ones returned by
1733	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3265	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1734	portable one.	3266	portable one.
1735		3267
1736	So when you want to use this feature you will always have to be prepared	3268	So when you want to use this feature you will always have to be prepared
1737	that you cannot get an embeddable loop. The recommended way to get around	3269	that you cannot get an embeddable loop. The recommended way to get around
1738	this is to have a separate variables for your embeddable loop, try to	3270	this is to have a separate variables for your embeddable loop, try to
1739	create it, and if that fails, use the normal loop for everything:	3271	create it, and if that fails, use the normal loop for everything.
1740		3272
1741	struct ev_loop *loop_hi = ev_default_init (0);	3273	=head3 C<ev_embed> and fork
1742	struct ev_loop *loop_lo = 0;
1743	struct ev_embed embed;
1744
1745	// see if there is a chance of getting one that works
1746	// (remember that a flags value of 0 means autodetection)
1747	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1748	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1749	: 0;
1750		3274
1751	// if we got one, then embed it, otherwise default to loop_hi	3275	While the C<ev_embed> watcher is running, forks in the embedding loop will
1752	if (loop_lo)	3276	automatically be applied to the embedded loop as well, so no special
1753	{	3277	fork handling is required in that case. When the watcher is not running,
1754	ev_embed_init (&embed, 0, loop_lo);	3278	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1755	ev_embed_start (loop_hi, &embed);	3279	as applicable.
1756	}
1757	else
1758	loop_lo = loop_hi;
1759		3280
1760	=head3 Watcher-Specific Functions and Data Members	3281	=head3 Watcher-Specific Functions and Data Members
1761		3282
1762	=over 4	3283	=over 4
1763		3284
1764	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3285	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1765		3286
1766	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3287	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
1767		3288
1768	Configures the watcher to embed the given loop, which must be	3289	Configures the watcher to embed the given loop, which must be
1769	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3290	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1770	invoked automatically, otherwise it is the responsibility of the callback	3291	invoked automatically, otherwise it is the responsibility of the callback
1771	to invoke it (it will continue to be called until the sweep has been done,	3292	to invoke it (it will continue to be called until the sweep has been done,
1772	if you do not want thta, you need to temporarily stop the embed watcher).	3293	if you do not want that, you need to temporarily stop the embed watcher).
1773		3294
1774	=item ev_embed_sweep (loop, ev_embed *)	3295	=item ev_embed_sweep (loop, ev_embed *)
1775		3296
1776	Make a single, non-blocking sweep over the embedded loop. This works	3297	Make a single, non-blocking sweep over the embedded loop. This works
1777	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3298	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1778	apropriate way for embedded loops.	3299	appropriate way for embedded loops.
1779		3300
1780	=item struct ev_loop *loop [read-only]	3301	=item struct ev_loop *other [read-only]
1781		3302
1782	The embedded event loop.	3303	The embedded event loop.
1783		3304
1784	=back	3305	=back
		3306
		3307	=head3 Examples
		3308
		3309	Example: Try to get an embeddable event loop and embed it into the default
		3310	event loop. If that is not possible, use the default loop. The default
		3311	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3312	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3313	used).
		3314
		3315	struct ev_loop *loop_hi = ev_default_init (0);
		3316	struct ev_loop *loop_lo = 0;
		3317	ev_embed embed;
		3318
		3319	// see if there is a chance of getting one that works
		3320	// (remember that a flags value of 0 means autodetection)
		3321	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3322	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3323	: 0;
		3324
		3325	// if we got one, then embed it, otherwise default to loop_hi
		3326	if (loop_lo)
		3327	{
		3328	ev_embed_init (&embed, 0, loop_lo);
		3329	ev_embed_start (loop_hi, &embed);
		3330	}
		3331	else
		3332	loop_lo = loop_hi;
		3333
		3334	Example: Check if kqueue is available but not recommended and create
		3335	a kqueue backend for use with sockets (which usually work with any
		3336	kqueue implementation). Store the kqueue/socket-only event loop in
		3337	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3338
		3339	struct ev_loop *loop = ev_default_init (0);
		3340	struct ev_loop *loop_socket = 0;
		3341	ev_embed embed;
		3342
		3343	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3344	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3345	{
		3346	ev_embed_init (&embed, 0, loop_socket);
		3347	ev_embed_start (loop, &embed);
		3348	}
		3349
		3350	if (!loop_socket)
		3351	loop_socket = loop;
		3352
		3353	// now use loop_socket for all sockets, and loop for everything else
1785		3354
1786		3355
1787	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3356	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1788		3357
1789	Fork watchers are called when a C<fork ()> was detected (usually because	3358	Fork watchers are called when a C<fork ()> was detected (usually because
1790	whoever is a good citizen cared to tell libev about it by calling	3359	whoever is a good citizen cared to tell libev about it by calling
1791	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3360	C<ev_loop_fork>). The invocation is done before the event loop blocks next
1792	event loop blocks next and before C<ev_check> watchers are being called,	3361	and before C<ev_check> watchers are being called, and only in the child
1793	and only in the child after the fork. If whoever good citizen calling	3362	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
1794	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3363	and calls it in the wrong process, the fork handlers will be invoked, too,
1795	handlers will be invoked, too, of course.	3364	of course.
		3365
		3366	=head3 The special problem of life after fork - how is it possible?
		3367
		3368	Most uses of C<fork ()> consist of forking, then some simple calls to set
		3369	up/change the process environment, followed by a call to C<exec()>. This
		3370	sequence should be handled by libev without any problems.
		3371
		3372	This changes when the application actually wants to do event handling
		3373	in the child, or both parent in child, in effect "continuing" after the
		3374	fork.
		3375
		3376	The default mode of operation (for libev, with application help to detect
		3377	forks) is to duplicate all the state in the child, as would be expected
		3378	when I<either> the parent I<or> the child process continues.
		3379
		3380	When both processes want to continue using libev, then this is usually the
		3381	wrong result. In that case, usually one process (typically the parent) is
		3382	supposed to continue with all watchers in place as before, while the other
		3383	process typically wants to start fresh, i.e. without any active watchers.
		3384
		3385	The cleanest and most efficient way to achieve that with libev is to
		3386	simply create a new event loop, which of course will be "empty", and
		3387	use that for new watchers. This has the advantage of not touching more
		3388	memory than necessary, and thus avoiding the copy-on-write, and the
		3389	disadvantage of having to use multiple event loops (which do not support
		3390	signal watchers).
		3391
		3392	When this is not possible, or you want to use the default loop for
		3393	other reasons, then in the process that wants to start "fresh", call
		3394	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3395	Destroying the default loop will "orphan" (not stop) all registered
		3396	watchers, so you have to be careful not to execute code that modifies
		3397	those watchers. Note also that in that case, you have to re-register any
		3398	signal watchers.
1796		3399
1797	=head3 Watcher-Specific Functions and Data Members	3400	=head3 Watcher-Specific Functions and Data Members
1798		3401
1799	=over 4	3402	=over 4
1800		3403
1801	=item ev_fork_init (ev_signal *, callback)	3404	=item ev_fork_init (ev_fork *, callback)
1802		3405
1803	Initialises and configures the fork watcher - it has no parameters of any	3406	Initialises and configures the fork watcher - it has no parameters of any
1804	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3407	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
1805	believe me.	3408	really.
1806		3409
1807	=back	3410	=back
1808		3411
1809		3412
		3413	=head2 C<ev_cleanup> - even the best things end
		3414
		3415	Cleanup watchers are called just before the event loop is being destroyed
		3416	by a call to C<ev_loop_destroy>.
		3417
		3418	While there is no guarantee that the event loop gets destroyed, cleanup
		3419	watchers provide a convenient method to install cleanup hooks for your
		3420	program, worker threads and so on - you just to make sure to destroy the
		3421	loop when you want them to be invoked.
		3422
		3423	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3424	all other watchers, they do not keep a reference to the event loop (which
		3425	makes a lot of sense if you think about it). Like all other watchers, you
		3426	can call libev functions in the callback, except C<ev_cleanup_start>.
		3427
		3428	=head3 Watcher-Specific Functions and Data Members
		3429
		3430	=over 4
		3431
		3432	=item ev_cleanup_init (ev_cleanup *, callback)
		3433
		3434	Initialises and configures the cleanup watcher - it has no parameters of
		3435	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3436	pointless, I assure you.
		3437
		3438	=back
		3439
		3440	Example: Register an atexit handler to destroy the default loop, so any
		3441	cleanup functions are called.
		3442
		3443	static void
		3444	program_exits (void)
		3445	{
		3446	ev_loop_destroy (EV_DEFAULT_UC);
		3447	}
		3448
		3449	...
		3450	atexit (program_exits);
		3451
		3452
		3453	=head2 C<ev_async> - how to wake up an event loop
		3454
		3455	In general, you cannot use an C<ev_loop> from multiple threads or other
		3456	asynchronous sources such as signal handlers (as opposed to multiple event
		3457	loops - those are of course safe to use in different threads).
		3458
		3459	Sometimes, however, you need to wake up an event loop you do not control,
		3460	for example because it belongs to another thread. This is what C<ev_async>
		3461	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3462	it by calling C<ev_async_send>, which is thread- and signal safe.
		3463
		3464	This functionality is very similar to C<ev_signal> watchers, as signals,
		3465	too, are asynchronous in nature, and signals, too, will be compressed
		3466	(i.e. the number of callback invocations may be less than the number of
		3467	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
		3468	of "global async watchers" by using a watcher on an otherwise unused
		3469	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3470	even without knowing which loop owns the signal.
		3471
		3472	=head3 Queueing
		3473
		3474	C<ev_async> does not support queueing of data in any way. The reason
		3475	is that the author does not know of a simple (or any) algorithm for a
		3476	multiple-writer-single-reader queue that works in all cases and doesn't
		3477	need elaborate support such as pthreads or unportable memory access
		3478	semantics.
		3479
		3480	That means that if you want to queue data, you have to provide your own
		3481	queue. But at least I can tell you how to implement locking around your
		3482	queue:
		3483
		3484	=over 4
		3485
		3486	=item queueing from a signal handler context
		3487
		3488	To implement race-free queueing, you simply add to the queue in the signal
		3489	handler but you block the signal handler in the watcher callback. Here is
		3490	an example that does that for some fictitious SIGUSR1 handler:
		3491
		3492	static ev_async mysig;
		3493
		3494	static void
		3495	sigusr1_handler (void)
		3496	{
		3497	sometype data;
		3498
		3499	// no locking etc.
		3500	queue_put (data);
		3501	ev_async_send (EV_DEFAULT_ &mysig);
		3502	}
		3503
		3504	static void
		3505	mysig_cb (EV_P_ ev_async *w, int revents)
		3506	{
		3507	sometype data;
		3508	sigset_t block, prev;
		3509
		3510	sigemptyset (&block);
		3511	sigaddset (&block, SIGUSR1);
		3512	sigprocmask (SIG_BLOCK, &block, &prev);
		3513
		3514	while (queue_get (&data))
		3515	process (data);
		3516
		3517	if (sigismember (&prev, SIGUSR1)
		3518	sigprocmask (SIG_UNBLOCK, &block, 0);
		3519	}
		3520
		3521	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3522	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3523	either...).
		3524
		3525	=item queueing from a thread context
		3526
		3527	The strategy for threads is different, as you cannot (easily) block
		3528	threads but you can easily preempt them, so to queue safely you need to
		3529	employ a traditional mutex lock, such as in this pthread example:
		3530
		3531	static ev_async mysig;
		3532	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3533
		3534	static void
		3535	otherthread (void)
		3536	{
		3537	// only need to lock the actual queueing operation
		3538	pthread_mutex_lock (&mymutex);
		3539	queue_put (data);
		3540	pthread_mutex_unlock (&mymutex);
		3541
		3542	ev_async_send (EV_DEFAULT_ &mysig);
		3543	}
		3544
		3545	static void
		3546	mysig_cb (EV_P_ ev_async *w, int revents)
		3547	{
		3548	pthread_mutex_lock (&mymutex);
		3549
		3550	while (queue_get (&data))
		3551	process (data);
		3552
		3553	pthread_mutex_unlock (&mymutex);
		3554	}
		3555
		3556	=back
		3557
		3558
		3559	=head3 Watcher-Specific Functions and Data Members
		3560
		3561	=over 4
		3562
		3563	=item ev_async_init (ev_async *, callback)
		3564
		3565	Initialises and configures the async watcher - it has no parameters of any
		3566	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3567	trust me.
		3568
		3569	=item ev_async_send (loop, ev_async *)
		3570
		3571	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3572	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3573	returns.
		3574
		3575	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3576	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3577	embedding section below on what exactly this means).
		3578
		3579	Note that, as with other watchers in libev, multiple events might get
		3580	compressed into a single callback invocation (another way to look at
		3581	this is that C<ev_async> watchers are level-triggered: they are set on
		3582	C<ev_async_send>, reset when the event loop detects that).
		3583
		3584	This call incurs the overhead of at most one extra system call per event
		3585	loop iteration, if the event loop is blocked, and no syscall at all if
		3586	the event loop (or your program) is processing events. That means that
		3587	repeated calls are basically free (there is no need to avoid calls for
		3588	performance reasons) and that the overhead becomes smaller (typically
		3589	zero) under load.
		3590
		3591	=item bool = ev_async_pending (ev_async *)
		3592
		3593	Returns a non-zero value when C<ev_async_send> has been called on the
		3594	watcher but the event has not yet been processed (or even noted) by the
		3595	event loop.
		3596
		3597	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3598	the loop iterates next and checks for the watcher to have become active,
		3599	it will reset the flag again. C<ev_async_pending> can be used to very
		3600	quickly check whether invoking the loop might be a good idea.
		3601
		3602	Not that this does I<not> check whether the watcher itself is pending,
		3603	only whether it has been requested to make this watcher pending: there
		3604	is a time window between the event loop checking and resetting the async
		3605	notification, and the callback being invoked.
		3606
		3607	=back
		3608
		3609
1810	=head1 OTHER FUNCTIONS	3610	=head1 OTHER FUNCTIONS
1811		3611
1812	There are some other functions of possible interest. Described. Here. Now.	3612	There are some other functions of possible interest. Described. Here. Now.
1813		3613
1814	=over 4	3614	=over 4
1815		3615
1816	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3616	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
1817		3617
1818	This function combines a simple timer and an I/O watcher, calls your	3618	This function combines a simple timer and an I/O watcher, calls your
1819	callback on whichever event happens first and automatically stop both	3619	callback on whichever event happens first and automatically stops both
1820	watchers. This is useful if you want to wait for a single event on an fd	3620	watchers. This is useful if you want to wait for a single event on an fd
1821	or timeout without having to allocate/configure/start/stop/free one or	3621	or timeout without having to allocate/configure/start/stop/free one or
1822	more watchers yourself.	3622	more watchers yourself.
1823		3623
1824	If C<fd> is less than 0, then no I/O watcher will be started and events	3624	If C<fd> is less than 0, then no I/O watcher will be started and the
1825	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3625	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1826	C<events> set will be craeted and started.	3626	the given C<fd> and C<events> set will be created and started.
1827		3627
1828	If C<timeout> is less than 0, then no timeout watcher will be	3628	If C<timeout> is less than 0, then no timeout watcher will be
1829	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3629	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1830	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3630	repeat = 0) will be started. C<0> is a valid timeout.
1831	dubious value.
1832		3631
1833	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3632	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1834	passed an C<revents> set like normal event callbacks (a combination of	3633	passed an C<revents> set like normal event callbacks (a combination of
1835	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3634	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1836	value passed to C<ev_once>:	3635	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3636	a timeout and an io event at the same time - you probably should give io
		3637	events precedence.
1837		3638
		3639	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3640
1838	static void stdin_ready (int revents, void *arg)	3641	static void stdin_ready (int revents, void *arg)
		3642	{
		3643	if (revents & EV_READ)
		3644	/* stdin might have data for us, joy! */;
		3645	else if (revents & EV_TIMER)
		3646	/* doh, nothing entered */;
		3647	}
		3648
		3649	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3650
		3651	=item ev_feed_fd_event (loop, int fd, int revents)
		3652
		3653	Feed an event on the given fd, as if a file descriptor backend detected
		3654	the given events.
		3655
		3656	=item ev_feed_signal_event (loop, int signum)
		3657
		3658	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3659	which is async-safe.
		3660
		3661	=back
		3662
		3663
		3664	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3665
		3666	This section explains some common idioms that are not immediately
		3667	obvious. Note that examples are sprinkled over the whole manual, and this
		3668	section only contains stuff that wouldn't fit anywhere else.
		3669
		3670	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3671
		3672	Each watcher has, by default, a C<void *data> member that you can read
		3673	or modify at any time: libev will completely ignore it. This can be used
		3674	to associate arbitrary data with your watcher. If you need more data and
		3675	don't want to allocate memory separately and store a pointer to it in that
		3676	data member, you can also "subclass" the watcher type and provide your own
		3677	data:
		3678
		3679	struct my_io
		3680	{
		3681	ev_io io;
		3682	int otherfd;
		3683	void *somedata;
		3684	struct whatever *mostinteresting;
		3685	};
		3686
		3687	...
		3688	struct my_io w;
		3689	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3690
		3691	And since your callback will be called with a pointer to the watcher, you
		3692	can cast it back to your own type:
		3693
		3694	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3695	{
		3696	struct my_io *w = (struct my_io *)w_;
		3697	...
		3698	}
		3699
		3700	More interesting and less C-conformant ways of casting your callback
		3701	function type instead have been omitted.
		3702
		3703	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3704
		3705	Another common scenario is to use some data structure with multiple
		3706	embedded watchers, in effect creating your own watcher that combines
		3707	multiple libev event sources into one "super-watcher":
		3708
		3709	struct my_biggy
		3710	{
		3711	int some_data;
		3712	ev_timer t1;
		3713	ev_timer t2;
		3714	}
		3715
		3716	In this case getting the pointer to C<my_biggy> is a bit more
		3717	complicated: Either you store the address of your C<my_biggy> struct in
		3718	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3719	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3720	real programmers):
		3721
		3722	#include <stddef.h>
		3723
		3724	static void
		3725	t1_cb (EV_P_ ev_timer *w, int revents)
		3726	{
		3727	struct my_biggy big = (struct my_biggy *)
		3728	(((char *)w) - offsetof (struct my_biggy, t1));
		3729	}
		3730
		3731	static void
		3732	t2_cb (EV_P_ ev_timer *w, int revents)
		3733	{
		3734	struct my_biggy big = (struct my_biggy *)
		3735	(((char *)w) - offsetof (struct my_biggy, t2));
		3736	}
		3737
		3738	=head2 AVOIDING FINISHING BEFORE RETURNING
		3739
		3740	Often you have structures like this in event-based programs:
		3741
		3742	callback ()
1839	{	3743	{
1840	if (revents & EV_TIMEOUT)	3744	free (request);
1841	/* doh, nothing entered */;
1842	else if (revents & EV_READ)
1843	/* stdin might have data for us, joy! */;
1844	}	3745	}
1845		3746
1846	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3747	request = start_new_request (..., callback);
1847		3748
1848	=item ev_feed_event (ev_loop *, watcher *, int revents)	3749	The intent is to start some "lengthy" operation. The C<request> could be
		3750	used to cancel the operation, or do other things with it.
1849		3751
1850	Feeds the given event set into the event loop, as if the specified event	3752	It's not uncommon to have code paths in C<start_new_request> that
1851	had happened for the specified watcher (which must be a pointer to an	3753	immediately invoke the callback, for example, to report errors. Or you add
1852	initialised but not necessarily started event watcher).	3754	some caching layer that finds that it can skip the lengthy aspects of the
		3755	operation and simply invoke the callback with the result.
1853		3756
1854	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3757	The problem here is that this will happen I<before> C<start_new_request>
		3758	has returned, so C<request> is not set.
1855		3759
1856	Feed an event on the given fd, as if a file descriptor backend detected	3760	Even if you pass the request by some safer means to the callback, you
1857	the given events it.	3761	might want to do something to the request after starting it, such as
		3762	canceling it, which probably isn't working so well when the callback has
		3763	already been invoked.
1858		3764
1859	=item ev_feed_signal_event (ev_loop *loop, int signum)	3765	A common way around all these issues is to make sure that
		3766	C<start_new_request> I<always> returns before the callback is invoked. If
		3767	C<start_new_request> immediately knows the result, it can artificially
		3768	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3769	example, or more sneakily, by reusing an existing (stopped) watcher and
		3770	pushing it into the pending queue:
1860		3771
1861	Feed an event as if the given signal occured (C<loop> must be the default	3772	ev_set_cb (watcher, callback);
1862	loop!).	3773	ev_feed_event (EV_A_ watcher, 0);
1863		3774
1864	=back	3775	This way, C<start_new_request> can safely return before the callback is
		3776	invoked, while not delaying callback invocation too much.
		3777
		3778	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3779
		3780	Often (especially in GUI toolkits) there are places where you have
		3781	I<modal> interaction, which is most easily implemented by recursively
		3782	invoking C<ev_run>.
		3783
		3784	This brings the problem of exiting - a callback might want to finish the
		3785	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3786	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3787	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3788	other combination: In these cases, a simple C<ev_break> will not work.
		3789
		3790	The solution is to maintain "break this loop" variable for each C<ev_run>
		3791	invocation, and use a loop around C<ev_run> until the condition is
		3792	triggered, using C<EVRUN_ONCE>:
		3793
		3794	// main loop
		3795	int exit_main_loop = 0;
		3796
		3797	while (!exit_main_loop)
		3798	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3799
		3800	// in a modal watcher
		3801	int exit_nested_loop = 0;
		3802
		3803	while (!exit_nested_loop)
		3804	ev_run (EV_A_ EVRUN_ONCE);
		3805
		3806	To exit from any of these loops, just set the corresponding exit variable:
		3807
		3808	// exit modal loop
		3809	exit_nested_loop = 1;
		3810
		3811	// exit main program, after modal loop is finished
		3812	exit_main_loop = 1;
		3813
		3814	// exit both
		3815	exit_main_loop = exit_nested_loop = 1;
		3816
		3817	=head2 THREAD LOCKING EXAMPLE
		3818
		3819	Here is a fictitious example of how to run an event loop in a different
		3820	thread from where callbacks are being invoked and watchers are
		3821	created/added/removed.
		3822
		3823	For a real-world example, see the C<EV::Loop::Async> perl module,
		3824	which uses exactly this technique (which is suited for many high-level
		3825	languages).
		3826
		3827	The example uses a pthread mutex to protect the loop data, a condition
		3828	variable to wait for callback invocations, an async watcher to notify the
		3829	event loop thread and an unspecified mechanism to wake up the main thread.
		3830
		3831	First, you need to associate some data with the event loop:
		3832
		3833	typedef struct {
		3834	mutex_t lock; /* global loop lock */
		3835	ev_async async_w;
		3836	thread_t tid;
		3837	cond_t invoke_cv;
		3838	} userdata;
		3839
		3840	void prepare_loop (EV_P)
		3841	{
		3842	// for simplicity, we use a static userdata struct.
		3843	static userdata u;
		3844
		3845	ev_async_init (&u->async_w, async_cb);
		3846	ev_async_start (EV_A_ &u->async_w);
		3847
		3848	pthread_mutex_init (&u->lock, 0);
		3849	pthread_cond_init (&u->invoke_cv, 0);
		3850
		3851	// now associate this with the loop
		3852	ev_set_userdata (EV_A_ u);
		3853	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3854	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3855
		3856	// then create the thread running ev_run
		3857	pthread_create (&u->tid, 0, l_run, EV_A);
		3858	}
		3859
		3860	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3861	solely to wake up the event loop so it takes notice of any new watchers
		3862	that might have been added:
		3863
		3864	static void
		3865	async_cb (EV_P_ ev_async *w, int revents)
		3866	{
		3867	// just used for the side effects
		3868	}
		3869
		3870	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3871	protecting the loop data, respectively.
		3872
		3873	static void
		3874	l_release (EV_P)
		3875	{
		3876	userdata *u = ev_userdata (EV_A);
		3877	pthread_mutex_unlock (&u->lock);
		3878	}
		3879
		3880	static void
		3881	l_acquire (EV_P)
		3882	{
		3883	userdata *u = ev_userdata (EV_A);
		3884	pthread_mutex_lock (&u->lock);
		3885	}
		3886
		3887	The event loop thread first acquires the mutex, and then jumps straight
		3888	into C<ev_run>:
		3889
		3890	void *
		3891	l_run (void *thr_arg)
		3892	{
		3893	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3894
		3895	l_acquire (EV_A);
		3896	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3897	ev_run (EV_A_ 0);
		3898	l_release (EV_A);
		3899
		3900	return 0;
		3901	}
		3902
		3903	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3904	signal the main thread via some unspecified mechanism (signals? pipe
		3905	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3906	have been called (in a while loop because a) spurious wakeups are possible
		3907	and b) skipping inter-thread-communication when there are no pending
		3908	watchers is very beneficial):
		3909
		3910	static void
		3911	l_invoke (EV_P)
		3912	{
		3913	userdata *u = ev_userdata (EV_A);
		3914
		3915	while (ev_pending_count (EV_A))
		3916	{
		3917	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3918	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3919	}
		3920	}
		3921
		3922	Now, whenever the main thread gets told to invoke pending watchers, it
		3923	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3924	thread to continue:
		3925
		3926	static void
		3927	real_invoke_pending (EV_P)
		3928	{
		3929	userdata *u = ev_userdata (EV_A);
		3930
		3931	pthread_mutex_lock (&u->lock);
		3932	ev_invoke_pending (EV_A);
		3933	pthread_cond_signal (&u->invoke_cv);
		3934	pthread_mutex_unlock (&u->lock);
		3935	}
		3936
		3937	Whenever you want to start/stop a watcher or do other modifications to an
		3938	event loop, you will now have to lock:
		3939
		3940	ev_timer timeout_watcher;
		3941	userdata *u = ev_userdata (EV_A);
		3942
		3943	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3944
		3945	pthread_mutex_lock (&u->lock);
		3946	ev_timer_start (EV_A_ &timeout_watcher);
		3947	ev_async_send (EV_A_ &u->async_w);
		3948	pthread_mutex_unlock (&u->lock);
		3949
		3950	Note that sending the C<ev_async> watcher is required because otherwise
		3951	an event loop currently blocking in the kernel will have no knowledge
		3952	about the newly added timer. By waking up the loop it will pick up any new
		3953	watchers in the next event loop iteration.
		3954
		3955	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3956
		3957	While the overhead of a callback that e.g. schedules a thread is small, it
		3958	is still an overhead. If you embed libev, and your main usage is with some
		3959	kind of threads or coroutines, you might want to customise libev so that
		3960	doesn't need callbacks anymore.
		3961
		3962	Imagine you have coroutines that you can switch to using a function
		3963	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3964	and that due to some magic, the currently active coroutine is stored in a
		3965	global called C<current_coro>. Then you can build your own "wait for libev
		3966	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3967	the differing C<;> conventions):
		3968
		3969	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3970	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3971
		3972	That means instead of having a C callback function, you store the
		3973	coroutine to switch to in each watcher, and instead of having libev call
		3974	your callback, you instead have it switch to that coroutine.
		3975
		3976	A coroutine might now wait for an event with a function called
		3977	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3978	matter when, or whether the watcher is active or not when this function is
		3979	called):
		3980
		3981	void
		3982	wait_for_event (ev_watcher *w)
		3983	{
		3984	ev_set_cb (w, current_coro);
		3985	switch_to (libev_coro);
		3986	}
		3987
		3988	That basically suspends the coroutine inside C<wait_for_event> and
		3989	continues the libev coroutine, which, when appropriate, switches back to
		3990	this or any other coroutine.
		3991
		3992	You can do similar tricks if you have, say, threads with an event queue -
		3993	instead of storing a coroutine, you store the queue object and instead of
		3994	switching to a coroutine, you push the watcher onto the queue and notify
		3995	any waiters.
		3996
		3997	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3998	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3999
		4000	// my_ev.h
		4001	#define EV_CB_DECLARE(type) struct my_coro *cb;
		4002	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		4003	#include "../libev/ev.h"
		4004
		4005	// my_ev.c
		4006	#define EV_H "my_ev.h"
		4007	#include "../libev/ev.c"
		4008
		4009	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4010	F<my_ev.c> into your project. When properly specifying include paths, you
		4011	can even use F<ev.h> as header file name directly.
1865		4012
1866		4013
1867	=head1 LIBEVENT EMULATION	4014	=head1 LIBEVENT EMULATION
1868		4015
1869	Libev offers a compatibility emulation layer for libevent. It cannot	4016	Libev offers a compatibility emulation layer for libevent. It cannot
1870	emulate the internals of libevent, so here are some usage hints:	4017	emulate the internals of libevent, so here are some usage hints:
1871		4018
1872	=over 4	4019	=over 4
		4020
		4021	=item * Only the libevent-1.4.1-beta API is being emulated.
		4022
		4023	This was the newest libevent version available when libev was implemented,
		4024	and is still mostly unchanged in 2010.
1873		4025
1874	=item * Use it by including <event.h>, as usual.	4026	=item * Use it by including <event.h>, as usual.
1875		4027
1876	=item * The following members are fully supported: ev_base, ev_callback,	4028	=item * The following members are fully supported: ev_base, ev_callback,
1877	ev_arg, ev_fd, ev_res, ev_events.	4029	ev_arg, ev_fd, ev_res, ev_events.
…		…
1882		4034
1883	=item * Priorities are not currently supported. Initialising priorities	4035	=item * Priorities are not currently supported. Initialising priorities
1884	will fail and all watchers will have the same priority, even though there	4036	will fail and all watchers will have the same priority, even though there
1885	is an ev_pri field.	4037	is an ev_pri field.
1886		4038
		4039	=item * In libevent, the last base created gets the signals, in libev, the
		4040	base that registered the signal gets the signals.
		4041
1887	=item * Other members are not supported.	4042	=item * Other members are not supported.
1888		4043
1889	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4044	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1890	to use the libev header file and library.	4045	to use the libev header file and library.
1891		4046
1892	=back	4047	=back
1893		4048
1894	=head1 C++ SUPPORT	4049	=head1 C++ SUPPORT
1895		4050
		4051	=head2 C API
		4052
		4053	The normal C API should work fine when used from C++: both ev.h and the
		4054	libev sources can be compiled as C++. Therefore, code that uses the C API
		4055	will work fine.
		4056
		4057	Proper exception specifications might have to be added to callbacks passed
		4058	to libev: exceptions may be thrown only from watcher callbacks, all other
		4059	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4060	callbacks) must not throw exceptions, and might need a C<noexcept>
		4061	specification. If you have code that needs to be compiled as both C and
		4062	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4063
		4064	static void
		4065	fatal_error (const char *msg) EV_NOEXCEPT
		4066	{
		4067	perror (msg);
		4068	abort ();
		4069	}
		4070
		4071	...
		4072	ev_set_syserr_cb (fatal_error);
		4073
		4074	The only API functions that can currently throw exceptions are C<ev_run>,
		4075	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4076	because it runs cleanup watchers).
		4077
		4078	Throwing exceptions in watcher callbacks is only supported if libev itself
		4079	is compiled with a C++ compiler or your C and C++ environments allow
		4080	throwing exceptions through C libraries (most do).
		4081
		4082	=head2 C++ API
		4083
1896	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4084	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1897	you to use some convinience methods to start/stop watchers and also change	4085	you to use some convenience methods to start/stop watchers and also change
1898	the callback model to a model using method callbacks on objects.	4086	the callback model to a model using method callbacks on objects.
1899		4087
1900	To use it,	4088	To use it,
1901		4089
1902	#include <ev++.h>	4090	#include <ev++.h>
1903		4091
1904	This automatically includes F<ev.h> and puts all of its definitions (many	4092	This automatically includes F<ev.h> and puts all of its definitions (many
1905	of them macros) into the global namespace. All C++ specific things are	4093	of them macros) into the global namespace. All C++ specific things are
1906	put into the C<ev> namespace. It should support all the same embedding	4094	put into the C<ev> namespace. It should support all the same embedding
1907	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	4095	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1909	Care has been taken to keep the overhead low. The only data member the C++	4097	Care has been taken to keep the overhead low. The only data member the C++
1910	classes add (compared to plain C-style watchers) is the event loop pointer	4098	classes add (compared to plain C-style watchers) is the event loop pointer
1911	that the watcher is associated with (or no additional members at all if	4099	that the watcher is associated with (or no additional members at all if
1912	you disable C<EV_MULTIPLICITY> when embedding libev).	4100	you disable C<EV_MULTIPLICITY> when embedding libev).
1913		4101
1914	Currently, functions, and static and non-static member functions can be	4102	Currently, functions, static and non-static member functions and classes
1915	used as callbacks. Other types should be easy to add as long as they only	4103	with C<operator ()> can be used as callbacks. Other types should be easy
1916	need one additional pointer for context. If you need support for other	4104	to add as long as they only need one additional pointer for context. If
1917	types of functors please contact the author (preferably after implementing	4105	you need support for other types of functors please contact the author
1918	it).	4106	(preferably after implementing it).
		4107
		4108	For all this to work, your C++ compiler either has to use the same calling
		4109	conventions as your C compiler (for static member functions), or you have
		4110	to embed libev and compile libev itself as C++.
1919		4111
1920	Here is a list of things available in the C<ev> namespace:	4112	Here is a list of things available in the C<ev> namespace:
1921		4113
1922	=over 4	4114	=over 4
1923		4115
…		…
1933	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4125	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
1934		4126
1935	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4127	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
1936	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4128	the same name in the C<ev> namespace, with the exception of C<ev_signal>
1937	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4129	which is called C<ev::sig> to avoid clashes with the C<signal> macro
1938	defines by many implementations.	4130	defined by many implementations.
1939		4131
1940	All of those classes have these methods:	4132	All of those classes have these methods:
1941		4133
1942	=over 4	4134	=over 4
1943		4135
1944	=item ev::TYPE::TYPE ()	4136	=item ev::TYPE::TYPE ()
1945		4137
1946	=item ev::TYPE::TYPE (struct ev_loop *)	4138	=item ev::TYPE::TYPE (loop)
1947		4139
1948	=item ev::TYPE::~TYPE	4140	=item ev::TYPE::~TYPE
1949		4141
1950	The constructor (optionally) takes an event loop to associate the watcher	4142	The constructor (optionally) takes an event loop to associate the watcher
1951	with. If it is omitted, it will use C<EV_DEFAULT>.	4143	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
1974	your compiler is good :), then the method will be fully inlined into the	4166	your compiler is good :), then the method will be fully inlined into the
1975	thunking function, making it as fast as a direct C callback.	4167	thunking function, making it as fast as a direct C callback.
1976		4168
1977	Example: simple class declaration and watcher initialisation	4169	Example: simple class declaration and watcher initialisation
1978		4170
1979	struct myclass	4171	struct myclass
1980	{	4172	{
1981	void io_cb (ev::io &w, int revents) { }	4173	void io_cb (ev::io &w, int revents) { }
1982	}	4174	}
1983		4175
1984	myclass obj;	4176	myclass obj;
1985	ev::io iow;	4177	ev::io iow;
1986	iow.set <myclass, &myclass::io_cb> (&obj);	4178	iow.set <myclass, &myclass::io_cb> (&obj);
		4179
		4180	=item w->set (object *)
		4181
		4182	This is a variation of a method callback - leaving out the method to call
		4183	will default the method to C<operator ()>, which makes it possible to use
		4184	functor objects without having to manually specify the C<operator ()> all
		4185	the time. Incidentally, you can then also leave out the template argument
		4186	list.
		4187
		4188	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4189	int revents)>.
		4190
		4191	See the method-C<set> above for more details.
		4192
		4193	Example: use a functor object as callback.
		4194
		4195	struct myfunctor
		4196	{
		4197	void operator() (ev::io &w, int revents)
		4198	{
		4199	...
		4200	}
		4201	}
		4202
		4203	myfunctor f;
		4204
		4205	ev::io w;
		4206	w.set (&f);
1987		4207
1988	=item w->set<function> (void *data = 0)	4208	=item w->set<function> (void *data = 0)
1989		4209
1990	Also sets a callback, but uses a static method or plain function as	4210	Also sets a callback, but uses a static method or plain function as
1991	callback. The optional C<data> argument will be stored in the watcher's	4211	callback. The optional C<data> argument will be stored in the watcher's
…		…
1993		4213
1994	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	4214	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
1995		4215
1996	See the method-C<set> above for more details.	4216	See the method-C<set> above for more details.
1997		4217
1998	Example:	4218	Example: Use a plain function as callback.
1999		4219
2000	static void io_cb (ev::io &w, int revents) { }	4220	static void io_cb (ev::io &w, int revents) { }
2001	iow.set <io_cb> ();	4221	iow.set <io_cb> ();
2002		4222
2003	=item w->set (struct ev_loop *)	4223	=item w->set (loop)
2004		4224
2005	Associates a different C<struct ev_loop> with this watcher. You can only	4225	Associates a different C<struct ev_loop> with this watcher. You can only
2006	do this when the watcher is inactive (and not pending either).	4226	do this when the watcher is inactive (and not pending either).
2007		4227
2008	=item w->set ([args])	4228	=item w->set ([arguments])
2009		4229
2010	Basically the same as C<ev_TYPE_set>, with the same args. Must be	4230	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4231	with the same arguments. Either this method or a suitable start method
2011	called at least once. Unlike the C counterpart, an active watcher gets	4232	must be called at least once. Unlike the C counterpart, an active watcher
2012	automatically stopped and restarted when reconfiguring it with this	4233	gets automatically stopped and restarted when reconfiguring it with this
2013	method.	4234	method.
		4235
		4236	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4237	clashing with the C<set (loop)> method.
2014		4238
2015	=item w->start ()	4239	=item w->start ()
2016		4240
2017	Starts the watcher. Note that there is no C<loop> argument, as the	4241	Starts the watcher. Note that there is no C<loop> argument, as the
2018	constructor already stores the event loop.	4242	constructor already stores the event loop.
2019		4243
		4244	=item w->start ([arguments])
		4245
		4246	Instead of calling C<set> and C<start> methods separately, it is often
		4247	convenient to wrap them in one call. Uses the same type of arguments as
		4248	the configure C<set> method of the watcher.
		4249
2020	=item w->stop ()	4250	=item w->stop ()
2021		4251
2022	Stops the watcher if it is active. Again, no C<loop> argument.	4252	Stops the watcher if it is active. Again, no C<loop> argument.
2023		4253
2024	=item w->again () C<ev::timer>, C<ev::periodic> only	4254	=item w->again () (C<ev::timer>, C<ev::periodic> only)
2025		4255
2026	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	4256	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
2027	C<ev_TYPE_again> function.	4257	C<ev_TYPE_again> function.
2028		4258
2029	=item w->sweep () C<ev::embed> only	4259	=item w->sweep () (C<ev::embed> only)
2030		4260
2031	Invokes C<ev_embed_sweep>.	4261	Invokes C<ev_embed_sweep>.
2032		4262
2033	=item w->update () C<ev::stat> only	4263	=item w->update () (C<ev::stat> only)
2034		4264
2035	Invokes C<ev_stat_stat>.	4265	Invokes C<ev_stat_stat>.
2036		4266
2037	=back	4267	=back
2038		4268
2039	=back	4269	=back
2040		4270
2041	Example: Define a class with an IO and idle watcher, start one of them in	4271	Example: Define a class with two I/O and idle watchers, start the I/O
2042	the constructor.	4272	watchers in the constructor.
2043		4273
2044	class myclass	4274	class myclass
2045	{	4275	{
2046	ev_io io; void io_cb (ev::io &w, int revents);	4276	ev::io io ; void io_cb (ev::io &w, int revents);
		4277	ev::io io2 ; void io2_cb (ev::io &w, int revents);
2047	ev_idle idle void idle_cb (ev::idle &w, int revents);	4278	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2048		4279
2049	myclass ();	4280	myclass (int fd)
2050	}	4281	{
2051
2052	myclass::myclass (int fd)
2053	{
2054	io .set <myclass, &myclass::io_cb > (this);	4282	io .set <myclass, &myclass::io_cb > (this);
		4283	io2 .set <myclass, &myclass::io2_cb > (this);
2055	idle.set <myclass, &myclass::idle_cb> (this);	4284	idle.set <myclass, &myclass::idle_cb> (this);
2056		4285
2057	io.start (fd, ev::READ);	4286	io.set (fd, ev::WRITE); // configure the watcher
		4287	io.start (); // start it whenever convenient
		4288
		4289	io2.start (fd, ev::READ); // set + start in one call
		4290	}
2058	}	4291	};
		4292
		4293
		4294	=head1 OTHER LANGUAGE BINDINGS
		4295
		4296	Libev does not offer other language bindings itself, but bindings for a
		4297	number of languages exist in the form of third-party packages. If you know
		4298	any interesting language binding in addition to the ones listed here, drop
		4299	me a note.
		4300
		4301	=over 4
		4302
		4303	=item Perl
		4304
		4305	The EV module implements the full libev API and is actually used to test
		4306	libev. EV is developed together with libev. Apart from the EV core module,
		4307	there are additional modules that implement libev-compatible interfaces
		4308	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		4309	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4310	and C<EV::Glib>).
		4311
		4312	It can be found and installed via CPAN, its homepage is at
		4313	L<http://software.schmorp.de/pkg/EV>.
		4314
		4315	=item Python
		4316
		4317	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4318	seems to be quite complete and well-documented.
		4319
		4320	=item Ruby
		4321
		4322	Tony Arcieri has written a ruby extension that offers access to a subset
		4323	of the libev API and adds file handle abstractions, asynchronous DNS and
		4324	more on top of it. It can be found via gem servers. Its homepage is at
		4325	L<http://rev.rubyforge.org/>.
		4326
		4327	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4328	makes rev work even on mingw.
		4329
		4330	=item Haskell
		4331
		4332	A haskell binding to libev is available at
		4333	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4334
		4335	=item D
		4336
		4337	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4338	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4339
		4340	=item Ocaml
		4341
		4342	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4343	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4344
		4345	=item Lua
		4346
		4347	Brian Maher has written a partial interface to libev for lua (at the
		4348	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4349	L<http://github.com/brimworks/lua-ev>.
		4350
		4351	=item Javascript
		4352
		4353	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4354
		4355	=item Others
		4356
		4357	There are others, and I stopped counting.
		4358
		4359	=back
2059		4360
2060		4361
2061	=head1 MACRO MAGIC	4362	=head1 MACRO MAGIC
2062		4363
2063	Libev can be compiled with a variety of options, the most fundemantal is	4364	Libev can be compiled with a variety of options, the most fundamental
2064	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	4365	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2065	callbacks have an initial C<struct ev_loop *> argument.	4366	functions and callbacks have an initial C<struct ev_loop *> argument.
2066		4367
2067	To make it easier to write programs that cope with either variant, the	4368	To make it easier to write programs that cope with either variant, the
2068	following macros are defined:	4369	following macros are defined:
2069		4370
2070	=over 4	4371	=over 4
…		…
2073		4374
2074	This provides the loop I<argument> for functions, if one is required ("ev	4375	This provides the loop I<argument> for functions, if one is required ("ev
2075	loop argument"). The C<EV_A> form is used when this is the sole argument,	4376	loop argument"). The C<EV_A> form is used when this is the sole argument,
2076	C<EV_A_> is used when other arguments are following. Example:	4377	C<EV_A_> is used when other arguments are following. Example:
2077		4378
2078	ev_unref (EV_A);	4379	ev_unref (EV_A);
2079	ev_timer_add (EV_A_ watcher);	4380	ev_timer_add (EV_A_ watcher);
2080	ev_loop (EV_A_ 0);	4381	ev_run (EV_A_ 0);
2081		4382
2082	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4383	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2083	which is often provided by the following macro.	4384	which is often provided by the following macro.
2084		4385
2085	=item C<EV_P>, C<EV_P_>	4386	=item C<EV_P>, C<EV_P_>
2086		4387
2087	This provides the loop I<parameter> for functions, if one is required ("ev	4388	This provides the loop I<parameter> for functions, if one is required ("ev
2088	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	4389	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2089	C<EV_P_> is used when other parameters are following. Example:	4390	C<EV_P_> is used when other parameters are following. Example:
2090		4391
2091	// this is how ev_unref is being declared	4392	// this is how ev_unref is being declared
2092	static void ev_unref (EV_P);	4393	static void ev_unref (EV_P);
2093		4394
2094	// this is how you can declare your typical callback	4395	// this is how you can declare your typical callback
2095	static void cb (EV_P_ ev_timer *w, int revents)	4396	static void cb (EV_P_ ev_timer *w, int revents)
2096		4397
2097	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	4398	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2098	suitable for use with C<EV_A>.	4399	suitable for use with C<EV_A>.
2099		4400
2100	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4401	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2101		4402
2102	Similar to the other two macros, this gives you the value of the default	4403	Similar to the other two macros, this gives you the value of the default
2103	loop, if multiple loops are supported ("ev loop default").	4404	loop, if multiple loops are supported ("ev loop default"). The default loop
		4405	will be initialised if it isn't already initialised.
		4406
		4407	For non-multiplicity builds, these macros do nothing, so you always have
		4408	to initialise the loop somewhere.
		4409
		4410	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4411
		4412	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4413	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4414	is undefined when the default loop has not been initialised by a previous
		4415	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4416
		4417	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4418	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2104		4419
2105	=back	4420	=back
2106		4421
2107	Example: Declare and initialise a check watcher, utilising the above	4422	Example: Declare and initialise a check watcher, utilising the above
2108	macros so it will work regardless of whether multiple loops are supported	4423	macros so it will work regardless of whether multiple loops are supported
2109	or not.	4424	or not.
2110		4425
2111	static void	4426	static void
2112	check_cb (EV_P_ ev_timer *w, int revents)	4427	check_cb (EV_P_ ev_timer *w, int revents)
2113	{	4428	{
2114	ev_check_stop (EV_A_ w);	4429	ev_check_stop (EV_A_ w);
2115	}	4430	}
2116		4431
2117	ev_check check;	4432	ev_check check;
2118	ev_check_init (&check, check_cb);	4433	ev_check_init (&check, check_cb);
2119	ev_check_start (EV_DEFAULT_ &check);	4434	ev_check_start (EV_DEFAULT_ &check);
2120	ev_loop (EV_DEFAULT_ 0);	4435	ev_run (EV_DEFAULT_ 0);
2121		4436
2122	=head1 EMBEDDING	4437	=head1 EMBEDDING
2123		4438
2124	Libev can (and often is) directly embedded into host	4439	Libev can (and often is) directly embedded into host
2125	applications. Examples of applications that embed it include the Deliantra	4440	applications. Examples of applications that embed it include the Deliantra
2126	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	4441	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
2127	and rxvt-unicode.	4442	and rxvt-unicode.
2128		4443
2129	The goal is to enable you to just copy the neecssary files into your	4444	The goal is to enable you to just copy the necessary files into your
2130	source directory without having to change even a single line in them, so	4445	source directory without having to change even a single line in them, so
2131	you can easily upgrade by simply copying (or having a checked-out copy of	4446	you can easily upgrade by simply copying (or having a checked-out copy of
2132	libev somewhere in your source tree).	4447	libev somewhere in your source tree).
2133		4448
2134	=head2 FILESETS	4449	=head2 FILESETS
2135		4450
2136	Depending on what features you need you need to include one or more sets of files	4451	Depending on what features you need you need to include one or more sets of files
2137	in your app.	4452	in your application.
2138		4453
2139	=head3 CORE EVENT LOOP	4454	=head3 CORE EVENT LOOP
2140		4455
2141	To include only the libev core (all the C<ev_*> functions), with manual	4456	To include only the libev core (all the C<ev_*> functions), with manual
2142	configuration (no autoconf):	4457	configuration (no autoconf):
2143		4458
2144	#define EV_STANDALONE 1	4459	#define EV_STANDALONE 1
2145	#include "ev.c"	4460	#include "ev.c"
2146		4461
2147	This will automatically include F<ev.h>, too, and should be done in a	4462	This will automatically include F<ev.h>, too, and should be done in a
2148	single C source file only to provide the function implementations. To use	4463	single C source file only to provide the function implementations. To use
2149	it, do the same for F<ev.h> in all files wishing to use this API (best	4464	it, do the same for F<ev.h> in all files wishing to use this API (best
2150	done by writing a wrapper around F<ev.h> that you can include instead and	4465	done by writing a wrapper around F<ev.h> that you can include instead and
2151	where you can put other configuration options):	4466	where you can put other configuration options):
2152		4467
2153	#define EV_STANDALONE 1	4468	#define EV_STANDALONE 1
2154	#include "ev.h"	4469	#include "ev.h"
2155		4470
2156	Both header files and implementation files can be compiled with a C++	4471	Both header files and implementation files can be compiled with a C++
2157	compiler (at least, thats a stated goal, and breakage will be treated	4472	compiler (at least, that's a stated goal, and breakage will be treated
2158	as a bug).	4473	as a bug).
2159		4474
2160	You need the following files in your source tree, or in a directory	4475	You need the following files in your source tree, or in a directory
2161	in your include path (e.g. in libev/ when using -Ilibev):	4476	in your include path (e.g. in libev/ when using -Ilibev):
2162		4477
2163	ev.h	4478	ev.h
2164	ev.c	4479	ev.c
2165	ev_vars.h	4480	ev_vars.h
2166	ev_wrap.h	4481	ev_wrap.h
2167		4482
2168	ev_win32.c required on win32 platforms only	4483	ev_win32.c required on win32 platforms only
2169		4484
2170	ev_select.c only when select backend is enabled (which is enabled by default)	4485	ev_select.c only when select backend is enabled
2171	ev_poll.c only when poll backend is enabled (disabled by default)	4486	ev_poll.c only when poll backend is enabled
2172	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4487	ev_epoll.c only when the epoll backend is enabled
		4488	ev_linuxaio.c only when the linux aio backend is enabled
		4489	ev_iouring.c only when the linux io_uring backend is enabled
2173	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4490	ev_kqueue.c only when the kqueue backend is enabled
2174	ev_port.c only when the solaris port backend is enabled (disabled by default)	4491	ev_port.c only when the solaris port backend is enabled
2175		4492
2176	F<ev.c> includes the backend files directly when enabled, so you only need	4493	F<ev.c> includes the backend files directly when enabled, so you only need
2177	to compile this single file.	4494	to compile this single file.
2178		4495
2179	=head3 LIBEVENT COMPATIBILITY API	4496	=head3 LIBEVENT COMPATIBILITY API
2180		4497
2181	To include the libevent compatibility API, also include:	4498	To include the libevent compatibility API, also include:
2182		4499
2183	#include "event.c"	4500	#include "event.c"
2184		4501
2185	in the file including F<ev.c>, and:	4502	in the file including F<ev.c>, and:
2186		4503
2187	#include "event.h"	4504	#include "event.h"
2188		4505
2189	in the files that want to use the libevent API. This also includes F<ev.h>.	4506	in the files that want to use the libevent API. This also includes F<ev.h>.
2190		4507
2191	You need the following additional files for this:	4508	You need the following additional files for this:
2192		4509
2193	event.h	4510	event.h
2194	event.c	4511	event.c
2195		4512
2196	=head3 AUTOCONF SUPPORT	4513	=head3 AUTOCONF SUPPORT
2197		4514
2198	Instead of using C<EV_STANDALONE=1> and providing your config in	4515	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2199	whatever way you want, you can also C<m4_include([libev.m4])> in your	4516	whatever way you want, you can also C<m4_include([libev.m4])> in your
2200	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4517	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2201	include F<config.h> and configure itself accordingly.	4518	include F<config.h> and configure itself accordingly.
2202		4519
2203	For this of course you need the m4 file:	4520	For this of course you need the m4 file:
2204		4521
2205	libev.m4	4522	libev.m4
2206		4523
2207	=head2 PREPROCESSOR SYMBOLS/MACROS	4524	=head2 PREPROCESSOR SYMBOLS/MACROS
2208		4525
2209	Libev can be configured via a variety of preprocessor symbols you have to define	4526	Libev can be configured via a variety of preprocessor symbols you have to
2210	before including any of its files. The default is not to build for multiplicity	4527	define before including (or compiling) any of its files. The default in
2211	and only include the select backend.	4528	the absence of autoconf is documented for every option.
		4529
		4530	Symbols marked with "(h)" do not change the ABI, and can have different
		4531	values when compiling libev vs. including F<ev.h>, so it is permissible
		4532	to redefine them before including F<ev.h> without breaking compatibility
		4533	to a compiled library. All other symbols change the ABI, which means all
		4534	users of libev and the libev code itself must be compiled with compatible
		4535	settings.
2212		4536
2213	=over 4	4537	=over 4
2214		4538
		4539	=item EV_COMPAT3 (h)
		4540
		4541	Backwards compatibility is a major concern for libev. This is why this
		4542	release of libev comes with wrappers for the functions and symbols that
		4543	have been renamed between libev version 3 and 4.
		4544
		4545	You can disable these wrappers (to test compatibility with future
		4546	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4547	sources. This has the additional advantage that you can drop the C<struct>
		4548	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4549	typedef in that case.
		4550
		4551	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4552	and in some even more future version the compatibility code will be
		4553	removed completely.
		4554
2215	=item EV_STANDALONE	4555	=item EV_STANDALONE (h)
2216		4556
2217	Must always be C<1> if you do not use autoconf configuration, which	4557	Must always be C<1> if you do not use autoconf configuration, which
2218	keeps libev from including F<config.h>, and it also defines dummy	4558	keeps libev from including F<config.h>, and it also defines dummy
2219	implementations for some libevent functions (such as logging, which is not	4559	implementations for some libevent functions (such as logging, which is not
2220	supported). It will also not define any of the structs usually found in	4560	supported). It will also not define any of the structs usually found in
2221	F<event.h> that are not directly supported by the libev core alone.	4561	F<event.h> that are not directly supported by the libev core alone.
2222		4562
		4563	In standalone mode, libev will still try to automatically deduce the
		4564	configuration, but has to be more conservative.
		4565
		4566	=item EV_USE_FLOOR
		4567
		4568	If defined to be C<1>, libev will use the C<floor ()> function for its
		4569	periodic reschedule calculations, otherwise libev will fall back on a
		4570	portable (slower) implementation. If you enable this, you usually have to
		4571	link against libm or something equivalent. Enabling this when the C<floor>
		4572	function is not available will fail, so the safe default is to not enable
		4573	this.
		4574
2223	=item EV_USE_MONOTONIC	4575	=item EV_USE_MONOTONIC
2224		4576
2225	If defined to be C<1>, libev will try to detect the availability of the	4577	If defined to be C<1>, libev will try to detect the availability of the
2226	monotonic clock option at both compiletime and runtime. Otherwise no use	4578	monotonic clock option at both compile time and runtime. Otherwise no
2227	of the monotonic clock option will be attempted. If you enable this, you	4579	use of the monotonic clock option will be attempted. If you enable this,
2228	usually have to link against librt or something similar. Enabling it when	4580	you usually have to link against librt or something similar. Enabling it
2229	the functionality isn't available is safe, though, althoguh you have	4581	when the functionality isn't available is safe, though, although you have
2230	to make sure you link against any libraries where the C<clock_gettime>	4582	to make sure you link against any libraries where the C<clock_gettime>
2231	function is hiding in (often F<-lrt>).	4583	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2232		4584
2233	=item EV_USE_REALTIME	4585	=item EV_USE_REALTIME
2234		4586
2235	If defined to be C<1>, libev will try to detect the availability of the	4587	If defined to be C<1>, libev will try to detect the availability of the
2236	realtime clock option at compiletime (and assume its availability at	4588	real-time clock option at compile time (and assume its availability
2237	runtime if successful). Otherwise no use of the realtime clock option will	4589	at runtime if successful). Otherwise no use of the real-time clock
2238	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4590	option will be attempted. This effectively replaces C<gettimeofday>
2239	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	4591	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2240	in the description of C<EV_USE_MONOTONIC>, though.	4592	correctness. See the note about libraries in the description of
		4593	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4594	C<EV_USE_CLOCK_SYSCALL>.
		4595
		4596	=item EV_USE_CLOCK_SYSCALL
		4597
		4598	If defined to be C<1>, libev will try to use a direct syscall instead
		4599	of calling the system-provided C<clock_gettime> function. This option
		4600	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4601	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4602	programs needlessly. Using a direct syscall is slightly slower (in
		4603	theory), because no optimised vdso implementation can be used, but avoids
		4604	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4605	higher, as it simplifies linking (no need for C<-lrt>).
		4606
		4607	=item EV_USE_NANOSLEEP
		4608
		4609	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		4610	and will use it for delays. Otherwise it will use C<select ()>.
		4611
		4612	=item EV_USE_EVENTFD
		4613
		4614	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4615	available and will probe for kernel support at runtime. This will improve
		4616	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4617	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4618	2.7 or newer, otherwise disabled.
2241		4619
2242	=item EV_USE_SELECT	4620	=item EV_USE_SELECT
2243		4621
2244	If undefined or defined to be C<1>, libev will compile in support for the	4622	If undefined or defined to be C<1>, libev will compile in support for the
2245	C<select>(2) backend. No attempt at autodetection will be done: if no	4623	C<select>(2) backend. No attempt at auto-detection will be done: if no
2246	other method takes over, select will be it. Otherwise the select backend	4624	other method takes over, select will be it. Otherwise the select backend
2247	will not be compiled in.	4625	will not be compiled in.
2248		4626
2249	=item EV_SELECT_USE_FD_SET	4627	=item EV_SELECT_USE_FD_SET
2250		4628
2251	If defined to C<1>, then the select backend will use the system C<fd_set>	4629	If defined to C<1>, then the select backend will use the system C<fd_set>
2252	structure. This is useful if libev doesn't compile due to a missing	4630	structure. This is useful if libev doesn't compile due to a missing
2253	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4631	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2254	exotic systems. This usually limits the range of file descriptors to some	4632	on exotic systems. This usually limits the range of file descriptors to
2255	low limit such as 1024 or might have other limitations (winsocket only	4633	some low limit such as 1024 or might have other limitations (winsocket
2256	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4634	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2257	influence the size of the C<fd_set> used.	4635	configures the maximum size of the C<fd_set>.
2258		4636
2259	=item EV_SELECT_IS_WINSOCKET	4637	=item EV_SELECT_IS_WINSOCKET
2260		4638
2261	When defined to C<1>, the select backend will assume that	4639	When defined to C<1>, the select backend will assume that
2262	select/socket/connect etc. don't understand file descriptors but	4640	select/socket/connect etc. don't understand file descriptors but
…		…
2264	be used is the winsock select). This means that it will call	4642	be used is the winsock select). This means that it will call
2265	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4643	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2266	it is assumed that all these functions actually work on fds, even	4644	it is assumed that all these functions actually work on fds, even
2267	on win32. Should not be defined on non-win32 platforms.	4645	on win32. Should not be defined on non-win32 platforms.
2268		4646
		4647	=item EV_FD_TO_WIN32_HANDLE(fd)
		4648
		4649	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4650	file descriptors to socket handles. When not defining this symbol (the
		4651	default), then libev will call C<_get_osfhandle>, which is usually
		4652	correct. In some cases, programs use their own file descriptor management,
		4653	in which case they can provide this function to map fds to socket handles.
		4654
		4655	=item EV_WIN32_HANDLE_TO_FD(handle)
		4656
		4657	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4658	using the standard C<_open_osfhandle> function. For programs implementing
		4659	their own fd to handle mapping, overwriting this function makes it easier
		4660	to do so. This can be done by defining this macro to an appropriate value.
		4661
		4662	=item EV_WIN32_CLOSE_FD(fd)
		4663
		4664	If programs implement their own fd to handle mapping on win32, then this
		4665	macro can be used to override the C<close> function, useful to unregister
		4666	file descriptors again. Note that the replacement function has to close
		4667	the underlying OS handle.
		4668
		4669	=item EV_USE_WSASOCKET
		4670
		4671	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4672	communication socket, which works better in some environments. Otherwise,
		4673	the normal C<socket> function will be used, which works better in other
		4674	environments.
		4675
2269	=item EV_USE_POLL	4676	=item EV_USE_POLL
2270		4677
2271	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4678	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2272	backend. Otherwise it will be enabled on non-win32 platforms. It	4679	backend. Otherwise it will be enabled on non-win32 platforms. It
2273	takes precedence over select.	4680	takes precedence over select.
2274		4681
2275	=item EV_USE_EPOLL	4682	=item EV_USE_EPOLL
2276		4683
2277	If defined to be C<1>, libev will compile in support for the Linux	4684	If defined to be C<1>, libev will compile in support for the Linux
2278	C<epoll>(7) backend. Its availability will be detected at runtime,	4685	C<epoll>(7) backend. Its availability will be detected at runtime,
2279	otherwise another method will be used as fallback. This is the	4686	otherwise another method will be used as fallback. This is the preferred
2280	preferred backend for GNU/Linux systems.	4687	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4688	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4689
		4690	=item EV_USE_LINUXAIO
		4691
		4692	If defined to be C<1>, libev will compile in support for the Linux aio
		4693	backend (C<EV_USE_EPOLL> must also be enabled). If undefined, it will be
		4694	enabled on linux, otherwise disabled.
		4695
		4696	=item EV_USE_IOURING
		4697
		4698	If defined to be C<1>, libev will compile in support for the Linux
		4699	io_uring backend (C<EV_USE_EPOLL> must also be enabled). Due to it's
		4700	current limitations it has to be requested explicitly. If undefined, it
		4701	will be enabled on linux, otherwise disabled.
2281		4702
2282	=item EV_USE_KQUEUE	4703	=item EV_USE_KQUEUE
2283		4704
2284	If defined to be C<1>, libev will compile in support for the BSD style	4705	If defined to be C<1>, libev will compile in support for the BSD style
2285	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4706	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2298	otherwise another method will be used as fallback. This is the preferred	4719	otherwise another method will be used as fallback. This is the preferred
2299	backend for Solaris 10 systems.	4720	backend for Solaris 10 systems.
2300		4721
2301	=item EV_USE_DEVPOLL	4722	=item EV_USE_DEVPOLL
2302		4723
2303	reserved for future expansion, works like the USE symbols above.	4724	Reserved for future expansion, works like the USE symbols above.
2304		4725
2305	=item EV_USE_INOTIFY	4726	=item EV_USE_INOTIFY
2306		4727
2307	If defined to be C<1>, libev will compile in support for the Linux inotify	4728	If defined to be C<1>, libev will compile in support for the Linux inotify
2308	interface to speed up C<ev_stat> watchers. Its actual availability will	4729	interface to speed up C<ev_stat> watchers. Its actual availability will
2309	be detected at runtime.	4730	be detected at runtime. If undefined, it will be enabled if the headers
		4731	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2310		4732
		4733	=item EV_NO_SMP
		4734
		4735	If defined to be C<1>, libev will assume that memory is always coherent
		4736	between threads, that is, threads can be used, but threads never run on
		4737	different cpus (or different cpu cores). This reduces dependencies
		4738	and makes libev faster.
		4739
		4740	=item EV_NO_THREADS
		4741
		4742	If defined to be C<1>, libev will assume that it will never be called from
		4743	different threads (that includes signal handlers), which is a stronger
		4744	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4745	libev faster.
		4746
		4747	=item EV_ATOMIC_T
		4748
		4749	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4750	access is atomic with respect to other threads or signal contexts. No
		4751	such type is easily found in the C language, so you can provide your own
		4752	type that you know is safe for your purposes. It is used both for signal
		4753	handler "locking" as well as for signal and thread safety in C<ev_async>
		4754	watchers.
		4755
		4756	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4757	(from F<signal.h>), which is usually good enough on most platforms.
		4758
2311	=item EV_H	4759	=item EV_H (h)
2312		4760
2313	The name of the F<ev.h> header file used to include it. The default if	4761	The name of the F<ev.h> header file used to include it. The default if
2314	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	4762	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2315	can be used to virtually rename the F<ev.h> header file in case of conflicts.	4763	used to virtually rename the F<ev.h> header file in case of conflicts.
2316		4764
2317	=item EV_CONFIG_H	4765	=item EV_CONFIG_H (h)
2318		4766
2319	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4767	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2320	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4768	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2321	C<EV_H>, above.	4769	C<EV_H>, above.
2322		4770
2323	=item EV_EVENT_H	4771	=item EV_EVENT_H (h)
2324		4772
2325	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4773	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2326	of how the F<event.h> header can be found.	4774	of how the F<event.h> header can be found, the default is C<"event.h">.
2327		4775
2328	=item EV_PROTOTYPES	4776	=item EV_PROTOTYPES (h)
2329		4777
2330	If defined to be C<0>, then F<ev.h> will not define any function	4778	If defined to be C<0>, then F<ev.h> will not define any function
2331	prototypes, but still define all the structs and other symbols. This is	4779	prototypes, but still define all the structs and other symbols. This is
2332	occasionally useful if you want to provide your own wrapper functions	4780	occasionally useful if you want to provide your own wrapper functions
2333	around libev functions.	4781	around libev functions.
…		…
2338	will have the C<struct ev_loop *> as first argument, and you can create	4786	will have the C<struct ev_loop *> as first argument, and you can create
2339	additional independent event loops. Otherwise there will be no support	4787	additional independent event loops. Otherwise there will be no support
2340	for multiple event loops and there is no first event loop pointer	4788	for multiple event loops and there is no first event loop pointer
2341	argument. Instead, all functions act on the single default loop.	4789	argument. Instead, all functions act on the single default loop.
2342		4790
		4791	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4792	default loop when multiplicity is switched off - you always have to
		4793	initialise the loop manually in this case.
		4794
2343	=item EV_MINPRI	4795	=item EV_MINPRI
2344		4796
2345	=item EV_MAXPRI	4797	=item EV_MAXPRI
2346		4798
2347	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4799	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
2352	When doing priority-based operations, libev usually has to linearly search	4804	When doing priority-based operations, libev usually has to linearly search
2353	all the priorities, so having many of them (hundreds) uses a lot of space	4805	all the priorities, so having many of them (hundreds) uses a lot of space
2354	and time, so using the defaults of five priorities (-2 .. +2) is usually	4806	and time, so using the defaults of five priorities (-2 .. +2) is usually
2355	fine.	4807	fine.
2356		4808
2357	If your embedding app does not need any priorities, defining these both to	4809	If your embedding application does not need any priorities, defining these
2358	C<0> will save some memory and cpu.	4810	both to C<0> will save some memory and CPU.
2359		4811
2360	=item EV_PERIODIC_ENABLE	4812	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4813	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4814	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2361		4815
2362	If undefined or defined to be C<1>, then periodic timers are supported. If	4816	If undefined or defined to be C<1> (and the platform supports it), then
2363	defined to be C<0>, then they are not. Disabling them saves a few kB of	4817	the respective watcher type is supported. If defined to be C<0>, then it
2364	code.	4818	is not. Disabling watcher types mainly saves code size.
2365		4819
2366	=item EV_IDLE_ENABLE	4820	=item EV_FEATURES
2367
2368	If undefined or defined to be C<1>, then idle watchers are supported. If
2369	defined to be C<0>, then they are not. Disabling them saves a few kB of
2370	code.
2371
2372	=item EV_EMBED_ENABLE
2373
2374	If undefined or defined to be C<1>, then embed watchers are supported. If
2375	defined to be C<0>, then they are not.
2376
2377	=item EV_STAT_ENABLE
2378
2379	If undefined or defined to be C<1>, then stat watchers are supported. If
2380	defined to be C<0>, then they are not.
2381
2382	=item EV_FORK_ENABLE
2383
2384	If undefined or defined to be C<1>, then fork watchers are supported. If
2385	defined to be C<0>, then they are not.
2386
2387	=item EV_MINIMAL
2388		4821
2389	If you need to shave off some kilobytes of code at the expense of some	4822	If you need to shave off some kilobytes of code at the expense of some
2390	speed, define this symbol to C<1>. Currently only used for gcc to override	4823	speed (but with the full API), you can define this symbol to request
2391	some inlining decisions, saves roughly 30% codesize of amd64.	4824	certain subsets of functionality. The default is to enable all features
		4825	that can be enabled on the platform.
		4826
		4827	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4828	with some broad features you want) and then selectively re-enable
		4829	additional parts you want, for example if you want everything minimal,
		4830	but multiple event loop support, async and child watchers and the poll
		4831	backend, use this:
		4832
		4833	#define EV_FEATURES 0
		4834	#define EV_MULTIPLICITY 1
		4835	#define EV_USE_POLL 1
		4836	#define EV_CHILD_ENABLE 1
		4837	#define EV_ASYNC_ENABLE 1
		4838
		4839	The actual value is a bitset, it can be a combination of the following
		4840	values (by default, all of these are enabled):
		4841
		4842	=over 4
		4843
		4844	=item C<1> - faster/larger code
		4845
		4846	Use larger code to speed up some operations.
		4847
		4848	Currently this is used to override some inlining decisions (enlarging the
		4849	code size by roughly 30% on amd64).
		4850
		4851	When optimising for size, use of compiler flags such as C<-Os> with
		4852	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4853	assertions.
		4854
		4855	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4856	(e.g. gcc with C<-Os>).
		4857
		4858	=item C<2> - faster/larger data structures
		4859
		4860	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4861	hash table sizes and so on. This will usually further increase code size
		4862	and can additionally have an effect on the size of data structures at
		4863	runtime.
		4864
		4865	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4866	(e.g. gcc with C<-Os>).
		4867
		4868	=item C<4> - full API configuration
		4869
		4870	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4871	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4872
		4873	=item C<8> - full API
		4874
		4875	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4876	details on which parts of the API are still available without this
		4877	feature, and do not complain if this subset changes over time.
		4878
		4879	=item C<16> - enable all optional watcher types
		4880
		4881	Enables all optional watcher types. If you want to selectively enable
		4882	only some watcher types other than I/O and timers (e.g. prepare,
		4883	embed, async, child...) you can enable them manually by defining
		4884	C<EV_watchertype_ENABLE> to C<1> instead.
		4885
		4886	=item C<32> - enable all backends
		4887
		4888	This enables all backends - without this feature, you need to enable at
		4889	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4890
		4891	=item C<64> - enable OS-specific "helper" APIs
		4892
		4893	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4894	default.
		4895
		4896	=back
		4897
		4898	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4899	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4900	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4901	watchers, timers and monotonic clock support.
		4902
		4903	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4904	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4905	your program might be left out as well - a binary starting a timer and an
		4906	I/O watcher then might come out at only 5Kb.
		4907
		4908	=item EV_API_STATIC
		4909
		4910	If this symbol is defined (by default it is not), then all identifiers
		4911	will have static linkage. This means that libev will not export any
		4912	identifiers, and you cannot link against libev anymore. This can be useful
		4913	when you embed libev, only want to use libev functions in a single file,
		4914	and do not want its identifiers to be visible.
		4915
		4916	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4917	wants to use libev.
		4918
		4919	This option only works when libev is compiled with a C compiler, as C++
		4920	doesn't support the required declaration syntax.
		4921
		4922	=item EV_AVOID_STDIO
		4923
		4924	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4925	functions (printf, scanf, perror etc.). This will increase the code size
		4926	somewhat, but if your program doesn't otherwise depend on stdio and your
		4927	libc allows it, this avoids linking in the stdio library which is quite
		4928	big.
		4929
		4930	Note that error messages might become less precise when this option is
		4931	enabled.
		4932
		4933	=item EV_NSIG
		4934
		4935	The highest supported signal number, +1 (or, the number of
		4936	signals): Normally, libev tries to deduce the maximum number of signals
		4937	automatically, but sometimes this fails, in which case it can be
		4938	specified. Also, using a lower number than detected (C<32> should be
		4939	good for about any system in existence) can save some memory, as libev
		4940	statically allocates some 12-24 bytes per signal number.
2392		4941
2393	=item EV_PID_HASHSIZE	4942	=item EV_PID_HASHSIZE
2394		4943
2395	C<ev_child> watchers use a small hash table to distribute workload by	4944	C<ev_child> watchers use a small hash table to distribute workload by
2396	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4945	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2397	than enough. If you need to manage thousands of children you might want to	4946	usually more than enough. If you need to manage thousands of children you
2398	increase this value (I<must> be a power of two).	4947	might want to increase this value (I<must> be a power of two).
2399		4948
2400	=item EV_INOTIFY_HASHSIZE	4949	=item EV_INOTIFY_HASHSIZE
2401		4950
2402	C<ev_staz> watchers use a small hash table to distribute workload by	4951	C<ev_stat> watchers use a small hash table to distribute workload by
2403	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4952	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2404	usually more than enough. If you need to manage thousands of C<ev_stat>	4953	disabled), usually more than enough. If you need to manage thousands of
2405	watchers you might want to increase this value (I<must> be a power of	4954	C<ev_stat> watchers you might want to increase this value (I<must> be a
2406	two).	4955	power of two).
		4956
		4957	=item EV_USE_4HEAP
		4958
		4959	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4960	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4961	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4962	faster performance with many (thousands) of watchers.
		4963
		4964	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4965	will be C<0>.
		4966
		4967	=item EV_HEAP_CACHE_AT
		4968
		4969	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4970	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4971	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4972	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4973	but avoids random read accesses on heap changes. This improves performance
		4974	noticeably with many (hundreds) of watchers.
		4975
		4976	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4977	will be C<0>.
		4978
		4979	=item EV_VERIFY
		4980
		4981	Controls how much internal verification (see C<ev_verify ()>) will
		4982	be done: If set to C<0>, no internal verification code will be compiled
		4983	in. If set to C<1>, then verification code will be compiled in, but not
		4984	called. If set to C<2>, then the internal verification code will be
		4985	called once per loop, which can slow down libev. If set to C<3>, then the
		4986	verification code will be called very frequently, which will slow down
		4987	libev considerably.
		4988
		4989	Verification errors are reported via C's C<assert> mechanism, so if you
		4990	disable that (e.g. by defining C<NDEBUG>) then no errors will be reported.
		4991
		4992	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4993	will be C<0>.
2407		4994
2408	=item EV_COMMON	4995	=item EV_COMMON
2409		4996
2410	By default, all watchers have a C<void *data> member. By redefining	4997	By default, all watchers have a C<void *data> member. By redefining
2411	this macro to a something else you can include more and other types of	4998	this macro to something else you can include more and other types of
2412	members. You have to define it each time you include one of the files,	4999	members. You have to define it each time you include one of the files,
2413	though, and it must be identical each time.	5000	though, and it must be identical each time.
2414		5001
2415	For example, the perl EV module uses something like this:	5002	For example, the perl EV module uses something like this:
2416		5003
2417	#define EV_COMMON \	5004	#define EV_COMMON \
2418	SV *self; /* contains this struct */ \	5005	SV *self; /* contains this struct */ \
2419	SV *cb_sv, *fh /* note no trailing ";" */	5006	SV *cb_sv, *fh /* note no trailing ";" */
2420		5007
2421	=item EV_CB_DECLARE (type)	5008	=item EV_CB_DECLARE (type)
2422		5009
2423	=item EV_CB_INVOKE (watcher, revents)	5010	=item EV_CB_INVOKE (watcher, revents)
2424		5011
2425	=item ev_set_cb (ev, cb)	5012	=item ev_set_cb (ev, cb)
2426		5013
2427	Can be used to change the callback member declaration in each watcher,	5014	Can be used to change the callback member declaration in each watcher,
2428	and the way callbacks are invoked and set. Must expand to a struct member	5015	and the way callbacks are invoked and set. Must expand to a struct member
2429	definition and a statement, respectively. See the F<ev.v> header file for	5016	definition and a statement, respectively. See the F<ev.h> header file for
2430	their default definitions. One possible use for overriding these is to	5017	their default definitions. One possible use for overriding these is to
2431	avoid the C<struct ev_loop *> as first argument in all cases, or to use	5018	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2432	method calls instead of plain function calls in C++.	5019	method calls instead of plain function calls in C++.
		5020
		5021	=back
		5022
		5023	=head2 EXPORTED API SYMBOLS
		5024
		5025	If you need to re-export the API (e.g. via a DLL) and you need a list of
		5026	exported symbols, you can use the provided F<Symbol.*> files which list
		5027	all public symbols, one per line:
		5028
		5029	Symbols.ev for libev proper
		5030	Symbols.event for the libevent emulation
		5031
		5032	This can also be used to rename all public symbols to avoid clashes with
		5033	multiple versions of libev linked together (which is obviously bad in
		5034	itself, but sometimes it is inconvenient to avoid this).
		5035
		5036	A sed command like this will create wrapper C<#define>'s that you need to
		5037	include before including F<ev.h>:
		5038
		5039	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		5040
		5041	This would create a file F<wrap.h> which essentially looks like this:
		5042
		5043	#define ev_backend myprefix_ev_backend
		5044	#define ev_check_start myprefix_ev_check_start
		5045	#define ev_check_stop myprefix_ev_check_stop
		5046	...
2433		5047
2434	=head2 EXAMPLES	5048	=head2 EXAMPLES
2435		5049
2436	For a real-world example of a program the includes libev	5050	For a real-world example of a program the includes libev
2437	verbatim, you can have a look at the EV perl module	5051	verbatim, you can have a look at the EV perl module
…		…
2442	file.	5056	file.
2443		5057
2444	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	5058	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2445	that everybody includes and which overrides some configure choices:	5059	that everybody includes and which overrides some configure choices:
2446		5060
2447	#define EV_MINIMAL 1	5061	#define EV_FEATURES 8
2448	#define EV_USE_POLL 0	5062	#define EV_USE_SELECT 1
2449	#define EV_MULTIPLICITY 0
2450	#define EV_PERIODIC_ENABLE 0	5063	#define EV_PREPARE_ENABLE 1
		5064	#define EV_IDLE_ENABLE 1
2451	#define EV_STAT_ENABLE 0	5065	#define EV_SIGNAL_ENABLE 1
2452	#define EV_FORK_ENABLE 0	5066	#define EV_CHILD_ENABLE 1
		5067	#define EV_USE_STDEXCEPT 0
2453	#define EV_CONFIG_H <config.h>	5068	#define EV_CONFIG_H <config.h>
2454	#define EV_MINPRI 0
2455	#define EV_MAXPRI 0
2456		5069
2457	#include "ev++.h"	5070	#include "ev++.h"
2458		5071
2459	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5072	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2460		5073
2461	#include "ev_cpp.h"	5074	#include "ev_cpp.h"
2462	#include "ev.c"	5075	#include "ev.c"
2463		5076
		5077	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
2464		5078
		5079	=head2 THREADS AND COROUTINES
		5080
		5081	=head3 THREADS
		5082
		5083	All libev functions are reentrant and thread-safe unless explicitly
		5084	documented otherwise, but libev implements no locking itself. This means
		5085	that you can use as many loops as you want in parallel, as long as there
		5086	are no concurrent calls into any libev function with the same loop
		5087	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		5088	of course): libev guarantees that different event loops share no data
		5089	structures that need any locking.
		5090
		5091	Or to put it differently: calls with different loop parameters can be done
		5092	concurrently from multiple threads, calls with the same loop parameter
		5093	must be done serially (but can be done from different threads, as long as
		5094	only one thread ever is inside a call at any point in time, e.g. by using
		5095	a mutex per loop).
		5096
		5097	Specifically to support threads (and signal handlers), libev implements
		5098	so-called C<ev_async> watchers, which allow some limited form of
		5099	concurrency on the same event loop, namely waking it up "from the
		5100	outside".
		5101
		5102	If you want to know which design (one loop, locking, or multiple loops
		5103	without or something else still) is best for your problem, then I cannot
		5104	help you, but here is some generic advice:
		5105
		5106	=over 4
		5107
		5108	=item * most applications have a main thread: use the default libev loop
		5109	in that thread, or create a separate thread running only the default loop.
		5110
		5111	This helps integrating other libraries or software modules that use libev
		5112	themselves and don't care/know about threading.
		5113
		5114	=item * one loop per thread is usually a good model.
		5115
		5116	Doing this is almost never wrong, sometimes a better-performance model
		5117	exists, but it is always a good start.
		5118
		5119	=item * other models exist, such as the leader/follower pattern, where one
		5120	loop is handed through multiple threads in a kind of round-robin fashion.
		5121
		5122	Choosing a model is hard - look around, learn, know that usually you can do
		5123	better than you currently do :-)
		5124
		5125	=item * often you need to talk to some other thread which blocks in the
		5126	event loop.
		5127
		5128	C<ev_async> watchers can be used to wake them up from other threads safely
		5129	(or from signal contexts...).
		5130
		5131	An example use would be to communicate signals or other events that only
		5132	work in the default loop by registering the signal watcher with the
		5133	default loop and triggering an C<ev_async> watcher from the default loop
		5134	watcher callback into the event loop interested in the signal.
		5135
		5136	=back
		5137
		5138	See also L</THREAD LOCKING EXAMPLE>.
		5139
		5140	=head3 COROUTINES
		5141
		5142	Libev is very accommodating to coroutines ("cooperative threads"):
		5143	libev fully supports nesting calls to its functions from different
		5144	coroutines (e.g. you can call C<ev_run> on the same loop from two
		5145	different coroutines, and switch freely between both coroutines running
		5146	the loop, as long as you don't confuse yourself). The only exception is
		5147	that you must not do this from C<ev_periodic> reschedule callbacks.
		5148
		5149	Care has been taken to ensure that libev does not keep local state inside
		5150	C<ev_run>, and other calls do not usually allow for coroutine switches as
		5151	they do not call any callbacks.
		5152
		5153	=head2 COMPILER WARNINGS
		5154
		5155	Depending on your compiler and compiler settings, you might get no or a
		5156	lot of warnings when compiling libev code. Some people are apparently
		5157	scared by this.
		5158
		5159	However, these are unavoidable for many reasons. For one, each compiler
		5160	has different warnings, and each user has different tastes regarding
		5161	warning options. "Warn-free" code therefore cannot be a goal except when
		5162	targeting a specific compiler and compiler-version.
		5163
		5164	Another reason is that some compiler warnings require elaborate
		5165	workarounds, or other changes to the code that make it less clear and less
		5166	maintainable.
		5167
		5168	And of course, some compiler warnings are just plain stupid, or simply
		5169	wrong (because they don't actually warn about the condition their message
		5170	seems to warn about). For example, certain older gcc versions had some
		5171	warnings that resulted in an extreme number of false positives. These have
		5172	been fixed, but some people still insist on making code warn-free with
		5173	such buggy versions.
		5174
		5175	While libev is written to generate as few warnings as possible,
		5176	"warn-free" code is not a goal, and it is recommended not to build libev
		5177	with any compiler warnings enabled unless you are prepared to cope with
		5178	them (e.g. by ignoring them). Remember that warnings are just that:
		5179	warnings, not errors, or proof of bugs.
		5180
		5181
		5182	=head2 VALGRIND
		5183
		5184	Valgrind has a special section here because it is a popular tool that is
		5185	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		5186
		5187	If you think you found a bug (memory leak, uninitialised data access etc.)
		5188	in libev, then check twice: If valgrind reports something like:
		5189
		5190	==2274== definitely lost: 0 bytes in 0 blocks.
		5191	==2274== possibly lost: 0 bytes in 0 blocks.
		5192	==2274== still reachable: 256 bytes in 1 blocks.
		5193
		5194	Then there is no memory leak, just as memory accounted to global variables
		5195	is not a memleak - the memory is still being referenced, and didn't leak.
		5196
		5197	Similarly, under some circumstances, valgrind might report kernel bugs
		5198	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5199	although an acceptable workaround has been found here), or it might be
		5200	confused.
		5201
		5202	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		5203	make it into some kind of religion.
		5204
		5205	If you are unsure about something, feel free to contact the mailing list
		5206	with the full valgrind report and an explanation on why you think this
		5207	is a bug in libev (best check the archives, too :). However, don't be
		5208	annoyed when you get a brisk "this is no bug" answer and take the chance
		5209	of learning how to interpret valgrind properly.
		5210
		5211	If you need, for some reason, empty reports from valgrind for your project
		5212	I suggest using suppression lists.
		5213
		5214
		5215	=head1 PORTABILITY NOTES
		5216
		5217	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5218
		5219	GNU/Linux is the only common platform that supports 64 bit file/large file
		5220	interfaces but I<disables> them by default.
		5221
		5222	That means that libev compiled in the default environment doesn't support
		5223	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5224
		5225	Unfortunately, many programs try to work around this GNU/Linux issue
		5226	by enabling the large file API, which makes them incompatible with the
		5227	standard libev compiled for their system.
		5228
		5229	Likewise, libev cannot enable the large file API itself as this would
		5230	suddenly make it incompatible to the default compile time environment,
		5231	i.e. all programs not using special compile switches.
		5232
		5233	=head2 OS/X AND DARWIN BUGS
		5234
		5235	The whole thing is a bug if you ask me - basically any system interface
		5236	you touch is broken, whether it is locales, poll, kqueue or even the
		5237	OpenGL drivers.
		5238
		5239	=head3 C<kqueue> is buggy
		5240
		5241	The kqueue syscall is broken in all known versions - most versions support
		5242	only sockets, many support pipes.
		5243
		5244	Libev tries to work around this by not using C<kqueue> by default on this
		5245	rotten platform, but of course you can still ask for it when creating a
		5246	loop - embedding a socket-only kqueue loop into a select-based one is
		5247	probably going to work well.
		5248
		5249	=head3 C<poll> is buggy
		5250
		5251	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5252	implementation by something calling C<kqueue> internally around the 10.5.6
		5253	release, so now C<kqueue> I<and> C<poll> are broken.
		5254
		5255	Libev tries to work around this by not using C<poll> by default on
		5256	this rotten platform, but of course you can still ask for it when creating
		5257	a loop.
		5258
		5259	=head3 C<select> is buggy
		5260
		5261	All that's left is C<select>, and of course Apple found a way to fuck this
		5262	one up as well: On OS/X, C<select> actively limits the number of file
		5263	descriptors you can pass in to 1024 - your program suddenly crashes when
		5264	you use more.
		5265
		5266	There is an undocumented "workaround" for this - defining
		5267	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5268	work on OS/X.
		5269
		5270	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5271
		5272	=head3 C<errno> reentrancy
		5273
		5274	The default compile environment on Solaris is unfortunately so
		5275	thread-unsafe that you can't even use components/libraries compiled
		5276	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5277	defined by default. A valid, if stupid, implementation choice.
		5278
		5279	If you want to use libev in threaded environments you have to make sure
		5280	it's compiled with C<_REENTRANT> defined.
		5281
		5282	=head3 Event port backend
		5283
		5284	The scalable event interface for Solaris is called "event
		5285	ports". Unfortunately, this mechanism is very buggy in all major
		5286	releases. If you run into high CPU usage, your program freezes or you get
		5287	a large number of spurious wakeups, make sure you have all the relevant
		5288	and latest kernel patches applied. No, I don't know which ones, but there
		5289	are multiple ones to apply, and afterwards, event ports actually work
		5290	great.
		5291
		5292	If you can't get it to work, you can try running the program by setting
		5293	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5294	C<select> backends.
		5295
		5296	=head2 AIX POLL BUG
		5297
		5298	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5299	this by trying to avoid the poll backend altogether (i.e. it's not even
		5300	compiled in), which normally isn't a big problem as C<select> works fine
		5301	with large bitsets on AIX, and AIX is dead anyway.
		5302
		5303	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5304
		5305	=head3 General issues
		5306
		5307	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		5308	requires, and its I/O model is fundamentally incompatible with the POSIX
		5309	model. Libev still offers limited functionality on this platform in
		5310	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		5311	descriptors. This only applies when using Win32 natively, not when using
		5312	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5313	as every compiler comes with a slightly differently broken/incompatible
		5314	environment.
		5315
		5316	Lifting these limitations would basically require the full
		5317	re-implementation of the I/O system. If you are into this kind of thing,
		5318	then note that glib does exactly that for you in a very portable way (note
		5319	also that glib is the slowest event library known to man).
		5320
		5321	There is no supported compilation method available on windows except
		5322	embedding it into other applications.
		5323
		5324	Sensible signal handling is officially unsupported by Microsoft - libev
		5325	tries its best, but under most conditions, signals will simply not work.
		5326
		5327	Not a libev limitation but worth mentioning: windows apparently doesn't
		5328	accept large writes: instead of resulting in a partial write, windows will
		5329	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5330	so make sure you only write small amounts into your sockets (less than a
		5331	megabyte seems safe, but this apparently depends on the amount of memory
		5332	available).
		5333
		5334	Due to the many, low, and arbitrary limits on the win32 platform and
		5335	the abysmal performance of winsockets, using a large number of sockets
		5336	is not recommended (and not reasonable). If your program needs to use
		5337	more than a hundred or so sockets, then likely it needs to use a totally
		5338	different implementation for windows, as libev offers the POSIX readiness
		5339	notification model, which cannot be implemented efficiently on windows
		5340	(due to Microsoft monopoly games).
		5341
		5342	A typical way to use libev under windows is to embed it (see the embedding
		5343	section for details) and use the following F<evwrap.h> header file instead
		5344	of F<ev.h>:
		5345
		5346	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5347	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5348
		5349	#include "ev.h"
		5350
		5351	And compile the following F<evwrap.c> file into your project (make sure
		5352	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5353
		5354	#include "evwrap.h"
		5355	#include "ev.c"
		5356
		5357	=head3 The winsocket C<select> function
		5358
		5359	The winsocket C<select> function doesn't follow POSIX in that it
		5360	requires socket I<handles> and not socket I<file descriptors> (it is
		5361	also extremely buggy). This makes select very inefficient, and also
		5362	requires a mapping from file descriptors to socket handles (the Microsoft
		5363	C runtime provides the function C<_open_osfhandle> for this). See the
		5364	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5365	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		5366
		5367	The configuration for a "naked" win32 using the Microsoft runtime
		5368	libraries and raw winsocket select is:
		5369
		5370	#define EV_USE_SELECT 1
		5371	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		5372
		5373	Note that winsockets handling of fd sets is O(n), so you can easily get a
		5374	complexity in the O(n²) range when using win32.
		5375
		5376	=head3 Limited number of file descriptors
		5377
		5378	Windows has numerous arbitrary (and low) limits on things.
		5379
		5380	Early versions of winsocket's select only supported waiting for a maximum
		5381	of C<64> handles (probably owning to the fact that all windows kernels
		5382	can only wait for C<64> things at the same time internally; Microsoft
		5383	recommends spawning a chain of threads and wait for 63 handles and the
		5384	previous thread in each. Sounds great!).
		5385
		5386	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		5387	to some high number (e.g. C<2048>) before compiling the winsocket select
		5388	call (which might be in libev or elsewhere, for example, perl and many
		5389	other interpreters do their own select emulation on windows).
		5390
		5391	Another limit is the number of file descriptors in the Microsoft runtime
		5392	libraries, which by default is C<64> (there must be a hidden I<64>
		5393	fetish or something like this inside Microsoft). You can increase this
		5394	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		5395	(another arbitrary limit), but is broken in many versions of the Microsoft
		5396	runtime libraries. This might get you to about C<512> or C<2048> sockets
		5397	(depending on windows version and/or the phase of the moon). To get more,
		5398	you need to wrap all I/O functions and provide your own fd management, but
		5399	the cost of calling select (O(n²)) will likely make this unworkable.
		5400
		5401	=head2 PORTABILITY REQUIREMENTS
		5402
		5403	In addition to a working ISO-C implementation and of course the
		5404	backend-specific APIs, libev relies on a few additional extensions:
		5405
		5406	=over 4
		5407
		5408	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5409	calling conventions regardless of C<ev_watcher_type *>.
		5410
		5411	Libev assumes not only that all watcher pointers have the same internal
		5412	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5413	assumes that the same (machine) code can be used to call any watcher
		5414	callback: The watcher callbacks have different type signatures, but libev
		5415	calls them using an C<ev_watcher *> internally.
		5416
		5417	=item null pointers and integer zero are represented by 0 bytes
		5418
		5419	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5420	relies on this setting pointers and integers to null.
		5421
		5422	=item pointer accesses must be thread-atomic
		5423
		5424	Accessing a pointer value must be atomic, it must both be readable and
		5425	writable in one piece - this is the case on all current architectures.
		5426
		5427	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5428
		5429	The type C<sig_atomic_t volatile> (or whatever is defined as
		5430	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5431	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5432	believed to be sufficiently portable.
		5433
		5434	=item C<sigprocmask> must work in a threaded environment
		5435
		5436	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5437	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5438	pthread implementations will either allow C<sigprocmask> in the "main
		5439	thread" or will block signals process-wide, both behaviours would
		5440	be compatible with libev. Interaction between C<sigprocmask> and
		5441	C<pthread_sigmask> could complicate things, however.
		5442
		5443	The most portable way to handle signals is to block signals in all threads
		5444	except the initial one, and run the signal handling loop in the initial
		5445	thread as well.
		5446
		5447	=item C<long> must be large enough for common memory allocation sizes
		5448
		5449	To improve portability and simplify its API, libev uses C<long> internally
		5450	instead of C<size_t> when allocating its data structures. On non-POSIX
		5451	systems (Microsoft...) this might be unexpectedly low, but is still at
		5452	least 31 bits everywhere, which is enough for hundreds of millions of
		5453	watchers.
		5454
		5455	=item C<double> must hold a time value in seconds with enough accuracy
		5456
		5457	The type C<double> is used to represent timestamps. It is required to
		5458	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5459	good enough for at least into the year 4000 with millisecond accuracy
		5460	(the design goal for libev). This requirement is overfulfilled by
		5461	implementations using IEEE 754, which is basically all existing ones.
		5462
		5463	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5464	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5465	is either obsolete or somebody patched it to use C<long double> or
		5466	something like that, just kidding).
		5467
		5468	=back
		5469
		5470	If you know of other additional requirements drop me a note.
		5471
		5472
2465	=head1 COMPLEXITIES	5473	=head1 ALGORITHMIC COMPLEXITIES
2466		5474
2467	In this section the complexities of (many of) the algorithms used inside	5475	In this section the complexities of (many of) the algorithms used inside
2468	libev will be explained. For complexity discussions about backends see the	5476	libev will be documented. For complexity discussions about backends see
2469	documentation for C<ev_default_init>.	5477	the documentation for C<ev_default_init>.
2470		5478
2471	All of the following are about amortised time: If an array needs to be	5479	All of the following are about amortised time: If an array needs to be
2472	extended, libev needs to realloc and move the whole array, but this	5480	extended, libev needs to realloc and move the whole array, but this
2473	happens asymptotically never with higher number of elements, so O(1) might	5481	happens asymptotically rarer with higher number of elements, so O(1) might
2474	mean it might do a lengthy realloc operation in rare cases, but on average	5482	mean that libev does a lengthy realloc operation in rare cases, but on
2475	it is much faster and asymptotically approaches constant time.	5483	average it is much faster and asymptotically approaches constant time.
2476		5484
2477	=over 4	5485	=over 4
2478		5486
2479	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	5487	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2480		5488
2481	This means that, when you have a watcher that triggers in one hour and	5489	This means that, when you have a watcher that triggers in one hour and
2482	there are 100 watchers that would trigger before that then inserting will	5490	there are 100 watchers that would trigger before that, then inserting will
2483	have to skip those 100 watchers.	5491	have to skip roughly seven (C<ld 100>) of these watchers.
2484		5492
2485	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	5493	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2486		5494
2487	That means that for changing a timer costs less than removing/adding them	5495	That means that changing a timer costs less than removing/adding them,
2488	as only the relative motion in the event queue has to be paid for.	5496	as only the relative motion in the event queue has to be paid for.
2489		5497
2490	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	5498	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2491		5499
2492	These just add the watcher into an array or at the head of a list.	5500	These just add the watcher into an array or at the head of a list.
		5501
2493	=item Stopping check/prepare/idle watchers: O(1)	5502	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2494		5503
2495	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	5504	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2496		5505
2497	These watchers are stored in lists then need to be walked to find the	5506	These watchers are stored in lists, so they need to be walked to find the
2498	correct watcher to remove. The lists are usually short (you don't usually	5507	correct watcher to remove. The lists are usually short (you don't usually
2499	have many watchers waiting for the same fd or signal).	5508	have many watchers waiting for the same fd or signal: one is typical, two
		5509	is rare).
2500		5510
2501	=item Finding the next timer per loop iteration: O(1)	5511	=item Finding the next timer in each loop iteration: O(1)
		5512
		5513	By virtue of using a binary or 4-heap, the next timer is always found at a
		5514	fixed position in the storage array.
2502		5515
2503	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	5516	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2504		5517
2505	A change means an I/O watcher gets started or stopped, which requires	5518	A change means an I/O watcher gets started or stopped, which requires
2506	libev to recalculate its status (and possibly tell the kernel).	5519	libev to recalculate its status (and possibly tell the kernel, depending
		5520	on backend and whether C<ev_io_set> was used).
2507		5521
2508	=item Activating one watcher: O(1)	5522	=item Activating one watcher (putting it into the pending state): O(1)
2509		5523
2510	=item Priority handling: O(number_of_priorities)	5524	=item Priority handling: O(number_of_priorities)
2511		5525
2512	Priorities are implemented by allocating some space for each	5526	Priorities are implemented by allocating some space for each
2513	priority. When doing priority-based operations, libev usually has to	5527	priority. When doing priority-based operations, libev usually has to
2514	linearly search all the priorities.	5528	linearly search all the priorities, but starting/stopping and activating
		5529	watchers becomes O(1) with respect to priority handling.
		5530
		5531	=item Sending an ev_async: O(1)
		5532
		5533	=item Processing ev_async_send: O(number_of_async_watchers)
		5534
		5535	=item Processing signals: O(max_signal_number)
		5536
		5537	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5538	calls in the current loop iteration and the loop is currently
		5539	blocked. Checking for async and signal events involves iterating over all
		5540	running async watchers or all signal numbers.
2515		5541
2516	=back	5542	=back
2517		5543
2518		5544
		5545	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5546
		5547	The major version 4 introduced some incompatible changes to the API.
		5548
		5549	At the moment, the C<ev.h> header file provides compatibility definitions
		5550	for all changes, so most programs should still compile. The compatibility
		5551	layer might be removed in later versions of libev, so better update to the
		5552	new API early than late.
		5553
		5554	=over 4
		5555
		5556	=item C<EV_COMPAT3> backwards compatibility mechanism
		5557
		5558	The backward compatibility mechanism can be controlled by
		5559	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5560	section.
		5561
		5562	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5563
		5564	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5565
		5566	ev_loop_destroy (EV_DEFAULT_UC);
		5567	ev_loop_fork (EV_DEFAULT);
		5568
		5569	=item function/symbol renames
		5570
		5571	A number of functions and symbols have been renamed:
		5572
		5573	ev_loop => ev_run
		5574	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5575	EVLOOP_ONESHOT => EVRUN_ONCE
		5576
		5577	ev_unloop => ev_break
		5578	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5579	EVUNLOOP_ONE => EVBREAK_ONE
		5580	EVUNLOOP_ALL => EVBREAK_ALL
		5581
		5582	EV_TIMEOUT => EV_TIMER
		5583
		5584	ev_loop_count => ev_iteration
		5585	ev_loop_depth => ev_depth
		5586	ev_loop_verify => ev_verify
		5587
		5588	Most functions working on C<struct ev_loop> objects don't have an
		5589	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5590	associated constants have been renamed to not collide with the C<struct
		5591	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5592	as all other watcher types. Note that C<ev_loop_fork> is still called
		5593	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5594	typedef.
		5595
		5596	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5597
		5598	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5599	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5600	and work, but the library code will of course be larger.
		5601
		5602	=back
		5603
		5604
		5605	=head1 GLOSSARY
		5606
		5607	=over 4
		5608
		5609	=item active
		5610
		5611	A watcher is active as long as it has been started and not yet stopped.
		5612	See L</WATCHER STATES> for details.
		5613
		5614	=item application
		5615
		5616	In this document, an application is whatever is using libev.
		5617
		5618	=item backend
		5619
		5620	The part of the code dealing with the operating system interfaces.
		5621
		5622	=item callback
		5623
		5624	The address of a function that is called when some event has been
		5625	detected. Callbacks are being passed the event loop, the watcher that
		5626	received the event, and the actual event bitset.
		5627
		5628	=item callback/watcher invocation
		5629
		5630	The act of calling the callback associated with a watcher.
		5631
		5632	=item event
		5633
		5634	A change of state of some external event, such as data now being available
		5635	for reading on a file descriptor, time having passed or simply not having
		5636	any other events happening anymore.
		5637
		5638	In libev, events are represented as single bits (such as C<EV_READ> or
		5639	C<EV_TIMER>).
		5640
		5641	=item event library
		5642
		5643	A software package implementing an event model and loop.
		5644
		5645	=item event loop
		5646
		5647	An entity that handles and processes external events and converts them
		5648	into callback invocations.
		5649
		5650	=item event model
		5651
		5652	The model used to describe how an event loop handles and processes
		5653	watchers and events.
		5654
		5655	=item pending
		5656
		5657	A watcher is pending as soon as the corresponding event has been
		5658	detected. See L</WATCHER STATES> for details.
		5659
		5660	=item real time
		5661
		5662	The physical time that is observed. It is apparently strictly monotonic :)
		5663
		5664	=item wall-clock time
		5665
		5666	The time and date as shown on clocks. Unlike real time, it can actually
		5667	be wrong and jump forwards and backwards, e.g. when you adjust your
		5668	clock.
		5669
		5670	=item watcher
		5671
		5672	A data structure that describes interest in certain events. Watchers need
		5673	to be started (attached to an event loop) before they can receive events.
		5674
		5675	=back
		5676
2519	=head1 AUTHOR	5677	=head1 AUTHOR
2520		5678
2521	Marc Lehmann <libev@schmorp.de>.	5679	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5680	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
2522		5681

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