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Revision 1.98 by root, Sat Dec 22 06:10:25 2007 UTC vs.
Revision 1.371 by root, Sat Jun 4 05:25:03 2011 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_run's to stop iterating
		32	ev_break (EV_A_ EVBREAK_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_run to stop iterating
		41	ev_break (EV_A_ EVBREAK_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
35	struct ev_loop *loop = ev_default_loop (0);	47	// use the default event loop unless you have special needs
		48	struct ev_loop *loop = EV_DEFAULT;
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_run (loop, 0);
47		62
		63	// break was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
52		68
		69	This document documents the libev software package.
		70
53	The newest version of this document is also available as a html-formatted	71	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	72	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familiarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 WHAT TO READ WHEN IN A HURRY
		84
		85	This manual tries to be very detailed, but unfortunately, this also makes
		86	it very long. If you just want to know the basics of libev, I suggest
		87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and
		88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and
		89	C<ev_timer> sections in L<WATCHER TYPES>.
		90
		91	=head1 ABOUT LIBEV
56		92
57	Libev is an event loop: you register interest in certain events (such as a	93	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occurring), and it will manage	94	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	95	these event sources and provide your program with events.
60		96
…		…
65	You register interest in certain events by registering so-called I<event	101	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	102	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	103	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	104	watcher.
69		105
70	=head1 FEATURES	106	=head2 FEATURES
71		107
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	108	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	109	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	110	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	111	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
76	with customised rescheduling (C<ev_periodic>), synchronous signals	112	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	113	timers (C<ev_timer>), absolute timers with customised rescheduling
78	watchers dealing with the event loop mechanism itself (C<ev_idle>,	114	(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	115	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	116	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
81	(C<ev_fork>).	117	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		118	limited support for fork events (C<ev_fork>).
82		119
83	It also is quite fast (see this	120	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	121	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	122	for example).
86		123
87	=head1 CONVENTIONS	124	=head2 CONVENTIONS
88		125
89	Libev is very configurable. In this manual the default configuration will	126	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	127	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	128	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	129	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>	130	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.	131	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		132	this argument.
95		133
96	=head1 TIME REPRESENTATION	134	=head2 TIME REPRESENTATION
97		135
98	Libev represents time as a single floating point number, representing the	136	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	137	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	138	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	139	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	140	too. It usually aliases to the C<double> type in C. When you need to do
103	it, you should treat it as some floatingpoint value. Unlike the name	141	any calculations on it, you should treat it as some floating point value.
		142
104	component C<stamp> might indicate, it is also used for time differences	143	Unlike the name component C<stamp> might indicate, it is also used for
105	throughout libev.	144	time differences (e.g. delays) throughout libev.
		145
		146	=head1 ERROR HANDLING
		147
		148	Libev knows three classes of errors: operating system errors, usage errors
		149	and internal errors (bugs).
		150
		151	When libev catches an operating system error it cannot handle (for example
		152	a system call indicating a condition libev cannot fix), it calls the callback
		153	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		154	abort. The default is to print a diagnostic message and to call C<abort
		155	()>.
		156
		157	When libev detects a usage error such as a negative timer interval, then
		158	it will print a diagnostic message and abort (via the C<assert> mechanism,
		159	so C<NDEBUG> will disable this checking): these are programming errors in
		160	the libev caller and need to be fixed there.
		161
		162	Libev also has a few internal error-checking C<assert>ions, and also has
		163	extensive consistency checking code. These do not trigger under normal
		164	circumstances, as they indicate either a bug in libev or worse.
		165
106		166
107	=head1 GLOBAL FUNCTIONS	167	=head1 GLOBAL FUNCTIONS
108		168
109	These functions can be called anytime, even before initialising the	169	These functions can be called anytime, even before initialising the
110	library in any way.	170	library in any way.
…		…
113		173
114	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
115		175
116	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
117	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
118	you actually want to know.	178	you actually want to know. Also interesting is the combination of
		179	C<ev_update_now> and C<ev_now>.
119		180
120	=item ev_sleep (ev_tstamp interval)	181	=item ev_sleep (ev_tstamp interval)
121		182
122	Sleep for the given interval: The current thread will be blocked until	183	Sleep for the given interval: The current thread will be blocked
123	either it is interrupted or the given time interval has passed. Basically	184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
124	this is a subsecond-resolution C<sleep ()>.	188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
125		192
126	=item int ev_version_major ()	193	=item int ev_version_major ()
127		194
128	=item int ev_version_minor ()	195	=item int ev_version_minor ()
129		196
…		…
140	as this indicates an incompatible change. Minor versions are usually	207	as this indicates an incompatible change. Minor versions are usually
141	compatible to older versions, so a larger minor version alone is usually	208	compatible to older versions, so a larger minor version alone is usually
142	not a problem.	209	not a problem.
143		210
144	Example: Make sure we haven't accidentally been linked against the wrong	211	Example: Make sure we haven't accidentally been linked against the wrong
145	version.	212	version (note, however, that this will not detect other ABI mismatches,
		213	such as LFS or reentrancy).
146		214
147	assert (("libev version mismatch",	215	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	216	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	217	&& ev_version_minor () >= EV_VERSION_MINOR));
150		218
151	=item unsigned int ev_supported_backends ()	219	=item unsigned int ev_supported_backends ()
152		220
153	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	221	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
154	value) compiled into this binary of libev (independent of their	222	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	224	a description of the set values.
157		225
158	Example: make sure we have the epoll method, because yeah this is cool and	226	Example: make sure we have the epoll method, because yeah this is cool and
159	a must have and can we have a torrent of it please!!!11	227	a must have and can we have a torrent of it please!!!11
160		228
161	assert (("sorry, no epoll, no sex",	229	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	230	ev_supported_backends () & EVBACKEND_EPOLL));
163		231
164	=item unsigned int ev_recommended_backends ()	232	=item unsigned int ev_recommended_backends ()
165		233
166	Return the set of all backends compiled into this binary of libev and also	234	Return the set of all backends compiled into this binary of libev and
167	recommended for this platform. This set is often smaller than the one	235	also recommended for this platform, meaning it will work for most file
		236	descriptor types. This set is often smaller than the one returned by
168	returned by C<ev_supported_backends>, as for example kqueue is broken on	237	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
169	most BSDs and will not be autodetected unless you explicitly request it	238	and will not be auto-detected unless you explicitly request it (assuming
170	(assuming you know what you are doing). This is the set of backends that	239	you know what you are doing). This is the set of backends that libev will
171	libev will probe for if you specify no backends explicitly.	240	probe for if you specify no backends explicitly.
172		241
173	=item unsigned int ev_embeddable_backends ()	242	=item unsigned int ev_embeddable_backends ()
174		243
175	Returns the set of backends that are embeddable in other event loops. This	244	Returns the set of backends that are embeddable in other event loops. This
176	is the theoretical, all-platform, value. To find which backends	245	value is platform-specific but can include backends not available on the
177	might be supported on the current system, you would need to look at	246	current system. To find which embeddable backends might be supported on
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	247	the current system, you would need to look at C<ev_embeddable_backends ()
179	recommended ones.	248	& ev_supported_backends ()>, likewise for recommended ones.
180		249
181	See the description of C<ev_embed> watchers for more info.	250	See the description of C<ev_embed> watchers for more info.
182		251
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	252	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
184		253
185	Sets the allocation function to use (the prototype is similar - the	254	Sets the allocation function to use (the prototype is similar - the
186	semantics is identical - to the realloc C function). It is used to	255	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
187	allocate and free memory (no surprises here). If it returns zero when	256	used to allocate and free memory (no surprises here). If it returns zero
188	memory needs to be allocated, the library might abort or take some	257	when memory needs to be allocated (C<size != 0>), the library might abort
189	potentially destructive action. The default is your system realloc	258	or take some potentially destructive action.
190	function.	259
		260	Since some systems (at least OpenBSD and Darwin) fail to implement
		261	correct C<realloc> semantics, libev will use a wrapper around the system
		262	C<realloc> and C<free> functions by default.
191		263
192	You could override this function in high-availability programs to, say,	264	You could override this function in high-availability programs to, say,
193	free some memory if it cannot allocate memory, to use a special allocator,	265	free some memory if it cannot allocate memory, to use a special allocator,
194	or even to sleep a while and retry until some memory is available.	266	or even to sleep a while and retry until some memory is available.
195		267
196	Example: Replace the libev allocator with one that waits a bit and then	268	Example: Replace the libev allocator with one that waits a bit and then
197	retries).	269	retries (example requires a standards-compliant C<realloc>).
198		270
199	static void *	271	static void *
200	persistent_realloc (void *ptr, size_t size)	272	persistent_realloc (void *ptr, size_t size)
201	{	273	{
202	for (;;)	274	for (;;)
…		…
211	}	283	}
212		284
213	...	285	...
214	ev_set_allocator (persistent_realloc);	286	ev_set_allocator (persistent_realloc);
215		287
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	288	=item ev_set_syserr_cb (void (*cb)(const char *msg))
217		289
218	Set the callback function to call on a retryable syscall error (such	290	Set the callback function to call on a retryable system call error (such
219	as failed select, poll, epoll_wait). The message is a printable string	291	as failed select, poll, epoll_wait). The message is a printable string
220	indicating the system call or subsystem causing the problem. If this	292	indicating the system call or subsystem causing the problem. If this
221	callback is set, then libev will expect it to remedy the sitution, no	293	callback is set, then libev will expect it to remedy the situation, no
222	matter what, when it returns. That is, libev will generally retry the	294	matter what, when it returns. That is, libev will generally retry the
223	requested operation, or, if the condition doesn't go away, do bad stuff	295	requested operation, or, if the condition doesn't go away, do bad stuff
224	(such as abort).	296	(such as abort).
225		297
226	Example: This is basically the same thing that libev does internally, too.	298	Example: This is basically the same thing that libev does internally, too.
…		…
233	}	305	}
234		306
235	...	307	...
236	ev_set_syserr_cb (fatal_error);	308	ev_set_syserr_cb (fatal_error);
237		309
		310	=item ev_feed_signal (int signum)
		311
		312	This function can be used to "simulate" a signal receive. It is completely
		313	safe to call this function at any time, from any context, including signal
		314	handlers or random threads.
		315
		316	Its main use is to customise signal handling in your process, especially
		317	in the presence of threads. For example, you could block signals
		318	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		319	creating any loops), and in one thread, use C<sigwait> or any other
		320	mechanism to wait for signals, then "deliver" them to libev by calling
		321	C<ev_feed_signal>.
		322
238	=back	323	=back
239		324
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	325	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
241		326
242	An event loop is described by a C<struct ev_loop *>. The library knows two	327	An event loop is described by a C<struct ev_loop *> (the C<struct> is
243	types of such loops, the I<default> loop, which supports signals and child	328	I<not> optional in this case unless libev 3 compatibility is disabled, as
244	events, and dynamically created loops which do not.	329	libev 3 had an C<ev_loop> function colliding with the struct name).
245		330
246	If you use threads, a common model is to run the default event loop	331	The library knows two types of such loops, the I<default> loop, which
247	in your main thread (or in a separate thread) and for each thread you	332	supports child process events, and dynamically created event loops which
248	create, you also create another event loop. Libev itself does no locking	333	do not.
249	whatsoever, so if you mix calls to the same event loop in different
250	threads, make sure you lock (this is usually a bad idea, though, even if
251	done correctly, because it's hideous and inefficient).
252		334
253	=over 4	335	=over 4
254		336
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	337	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		338
257	This will initialise the default event loop if it hasn't been initialised	339	This returns the "default" event loop object, which is what you should
258	yet and return it. If the default loop could not be initialised, returns	340	normally use when you just need "the event loop". Event loop objects and
259	false. If it already was initialised it simply returns it (and ignores the	341	the C<flags> parameter are described in more detail in the entry for
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	342	C<ev_loop_new>.
		343
		344	If the default loop is already initialised then this function simply
		345	returns it (and ignores the flags. If that is troubling you, check
		346	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		347	flags, which should almost always be C<0>, unless the caller is also the
		348	one calling C<ev_run> or otherwise qualifies as "the main program".
261		349
262	If you don't know what event loop to use, use the one returned from this	350	If you don't know what event loop to use, use the one returned from this
263	function.	351	function (or via the C<EV_DEFAULT> macro).
		352
		353	Note that this function is I<not> thread-safe, so if you want to use it
		354	from multiple threads, you have to employ some kind of mutex (note also
		355	that this case is unlikely, as loops cannot be shared easily between
		356	threads anyway).
		357
		358	The default loop is the only loop that can handle C<ev_child> watchers,
		359	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		360	a problem for your application you can either create a dynamic loop with
		361	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		362	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
		363
		364	Example: This is the most typical usage.
		365
		366	if (!ev_default_loop (0))
		367	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		368
		369	Example: Restrict libev to the select and poll backends, and do not allow
		370	environment settings to be taken into account:
		371
		372	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		373
		374	=item struct ev_loop *ev_loop_new (unsigned int flags)
		375
		376	This will create and initialise a new event loop object. If the loop
		377	could not be initialised, returns false.
		378
		379	This function is thread-safe, and one common way to use libev with
		380	threads is indeed to create one loop per thread, and using the default
		381	loop in the "main" or "initial" thread.
264		382
265	The flags argument can be used to specify special behaviour or specific	383	The flags argument can be used to specify special behaviour or specific
266	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	384	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
267		385
268	The following flags are supported:	386	The following flags are supported:
…		…
274	The default flags value. Use this if you have no clue (it's the right	392	The default flags value. Use this if you have no clue (it's the right
275	thing, believe me).	393	thing, believe me).
276		394
277	=item C<EVFLAG_NOENV>	395	=item C<EVFLAG_NOENV>
278		396
279	If this flag bit is ored into the flag value (or the program runs setuid	397	If this flag bit is or'ed into the flag value (or the program runs setuid
280	or setgid) then libev will I<not> look at the environment variable	398	or setgid) then libev will I<not> look at the environment variable
281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	399	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
282	override the flags completely if it is found in the environment. This is	400	override the flags completely if it is found in the environment. This is
283	useful to try out specific backends to test their performance, or to work	401	useful to try out specific backends to test their performance, or to work
284	around bugs.	402	around bugs.
285		403
286	=item C<EVFLAG_FORKCHECK>	404	=item C<EVFLAG_FORKCHECK>
287		405
288	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	406	Instead of calling C<ev_loop_fork> manually after a fork, you can also
289	a fork, you can also make libev check for a fork in each iteration by	407	make libev check for a fork in each iteration by enabling this flag.
290	enabling this flag.
291		408
292	This works by calling C<getpid ()> on every iteration of the loop,	409	This works by calling C<getpid ()> on every iteration of the loop,
293	and thus this might slow down your event loop if you do a lot of loop	410	and thus this might slow down your event loop if you do a lot of loop
294	iterations and little real work, but is usually not noticeable (on my	411	iterations and little real work, but is usually not noticeable (on my
295	Linux system for example, C<getpid> is actually a simple 5-insn sequence	412	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
296	without a syscall and thus I<very> fast, but my Linux system also has	413	without a system call and thus I<very> fast, but my GNU/Linux system also has
297	C<pthread_atfork> which is even faster).	414	C<pthread_atfork> which is even faster).
298		415
299	The big advantage of this flag is that you can forget about fork (and	416	The big advantage of this flag is that you can forget about fork (and
300	forget about forgetting to tell libev about forking) when you use this	417	forget about forgetting to tell libev about forking) when you use this
301	flag.	418	flag.
302		419
303	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	420	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
304	environment variable.	421	environment variable.
		422
		423	=item C<EVFLAG_NOINOTIFY>
		424
		425	When this flag is specified, then libev will not attempt to use the
		426	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		427	testing, this flag can be useful to conserve inotify file descriptors, as
		428	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		429
		430	=item C<EVFLAG_SIGNALFD>
		431
		432	When this flag is specified, then libev will attempt to use the
		433	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		434	delivers signals synchronously, which makes it both faster and might make
		435	it possible to get the queued signal data. It can also simplify signal
		436	handling with threads, as long as you properly block signals in your
		437	threads that are not interested in handling them.
		438
		439	Signalfd will not be used by default as this changes your signal mask, and
		440	there are a lot of shoddy libraries and programs (glib's threadpool for
		441	example) that can't properly initialise their signal masks.
		442
		443	=item C<EVFLAG_NOSIGMASK>
		444
		445	When this flag is specified, then libev will avoid to modify the signal
		446	mask. Specifically, this means you ahve to make sure signals are unblocked
		447	when you want to receive them.
		448
		449	This behaviour is useful when you want to do your own signal handling, or
		450	want to handle signals only in specific threads and want to avoid libev
		451	unblocking the signals.
		452
		453	It's also required by POSIX in a threaded program, as libev calls
		454	C<sigprocmask>, whose behaviour is officially unspecified.
		455
		456	This flag's behaviour will become the default in future versions of libev.
305		457
306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307		459
308	This is your standard select(2) backend. Not I<completely> standard, as	460	This is your standard select(2) backend. Not I<completely> standard, as
309	libev tries to roll its own fd_set with no limits on the number of fds,	461	libev tries to roll its own fd_set with no limits on the number of fds,
310	but if that fails, expect a fairly low limit on the number of fds when	462	but if that fails, expect a fairly low limit on the number of fds when
311	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	463	using this backend. It doesn't scale too well (O(highest_fd)), but its
312	the fastest backend for a low number of fds.	464	usually the fastest backend for a low number of (low-numbered :) fds.
		465
		466	To get good performance out of this backend you need a high amount of
		467	parallelism (most of the file descriptors should be busy). If you are
		468	writing a server, you should C<accept ()> in a loop to accept as many
		469	connections as possible during one iteration. You might also want to have
		470	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		471	readiness notifications you get per iteration.
		472
		473	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		474	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		475	C<exceptfds> set on that platform).
313		476
314	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	477	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
315		478
316	And this is your standard poll(2) backend. It's more complicated than	479	And this is your standard poll(2) backend. It's more complicated
317	select, but handles sparse fds better and has no artificial limit on the	480	than select, but handles sparse fds better and has no artificial
318	number of fds you can use (except it will slow down considerably with a	481	limit on the number of fds you can use (except it will slow down
319	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	482	considerably with a lot of inactive fds). It scales similarly to select,
		483	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		484	performance tips.
		485
		486	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		487	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
320		488
321	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
322		490
		491	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		492	kernels).
		493
323	For few fds, this backend is a bit little slower than poll and select,	494	For few fds, this backend is a bit little slower than poll and select, but
324	but it scales phenomenally better. While poll and select usually scale	495	it scales phenomenally better. While poll and select usually scale like
325	like O(total_fds) where n is the total number of fds (or the highest fd),	496	O(total_fds) where total_fds is the total number of fds (or the highest
326	epoll scales either O(1) or O(active_fds). The epoll design has a number	497	fd), epoll scales either O(1) or O(active_fds).
327	of shortcomings, such as silently dropping events in some hard-to-detect	498
328	cases and rewiring a syscall per fd change, no fork support and bad	499	The epoll mechanism deserves honorable mention as the most misdesigned
329	support for dup:	500	of the more advanced event mechanisms: mere annoyances include silently
		501	dropping file descriptors, requiring a system call per change per file
		502	descriptor (and unnecessary guessing of parameters), problems with dup,
		503	returning before the timeout value, resulting in additional iterations
		504	(and only giving 5ms accuracy while select on the same platform gives
		505	0.1ms) and so on. The biggest issue is fork races, however - if a program
		506	forks then I<both> parent and child process have to recreate the epoll
		507	set, which can take considerable time (one syscall per file descriptor)
		508	and is of course hard to detect.
		509
		510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		511	but of course I<doesn't>, and epoll just loves to report events for
		512	totally I<different> file descriptors (even already closed ones, so
		513	one cannot even remove them from the set) than registered in the set
		514	(especially on SMP systems). Libev tries to counter these spurious
		515	notifications by employing an additional generation counter and comparing
		516	that against the events to filter out spurious ones, recreating the set
		517	when required. Epoll also errornously rounds down timeouts, but gives you
		518	no way to know when and by how much, so sometimes you have to busy-wait
		519	because epoll returns immediately despite a nonzero timeout. And last
		520	not least, it also refuses to work with some file descriptors which work
		521	perfectly fine with C<select> (files, many character devices...).
		522
		523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
330		526
331	While stopping, setting and starting an I/O watcher in the same iteration	527	While stopping, setting and starting an I/O watcher in the same iteration
332	will result in some caching, there is still a syscall per such incident	528	will result in some caching, there is still a system call per such
333	(because the fd could point to a different file description now), so its	529	incident (because the same I<file descriptor> could point to a different
334	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	530	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
335	very well if you register events for both fds.	531	file descriptors might not work very well if you register events for both
		532	file descriptors.
336		533
337	Please note that epoll sometimes generates spurious notifications, so you	534	Best performance from this backend is achieved by not unregistering all
338	need to use non-blocking I/O or other means to avoid blocking when no data	535	watchers for a file descriptor until it has been closed, if possible,
339	(or space) is available.	536	i.e. keep at least one watcher active per fd at all times. Stopping and
		537	starting a watcher (without re-setting it) also usually doesn't cause
		538	extra overhead. A fork can both result in spurious notifications as well
		539	as in libev having to destroy and recreate the epoll object, which can
		540	take considerable time and thus should be avoided.
		541
		542	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		543	faster than epoll for maybe up to a hundred file descriptors, depending on
		544	the usage. So sad.
		545
		546	While nominally embeddable in other event loops, this feature is broken in
		547	all kernel versions tested so far.
		548
		549	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		550	C<EVBACKEND_POLL>.
340		551
341	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	552	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
342		553
343	Kqueue deserves special mention, as at the time of this writing, it	554	Kqueue deserves special mention, as at the time of this writing, it
344	was broken on I<all> BSDs (usually it doesn't work with anything but	555	was broken on all BSDs except NetBSD (usually it doesn't work reliably
345	sockets and pipes, except on Darwin, where of course it's completely	556	with anything but sockets and pipes, except on Darwin, where of course
346	useless. On NetBSD, it seems to work for all the FD types I tested, so it	557	it's completely useless). Unlike epoll, however, whose brokenness
347	is used by default there). For this reason it's not being "autodetected"	558	is by design, these kqueue bugs can (and eventually will) be fixed
		559	without API changes to existing programs. For this reason it's not being
348	unless you explicitly specify it explicitly in the flags (i.e. using	560	"auto-detected" unless you explicitly specify it in the flags (i.e. using
349	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	561	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
350	system like NetBSD.	562	system like NetBSD.
351		563
		564	You still can embed kqueue into a normal poll or select backend and use it
		565	only for sockets (after having made sure that sockets work with kqueue on
		566	the target platform). See C<ev_embed> watchers for more info.
		567
352	It scales in the same way as the epoll backend, but the interface to the	568	It scales in the same way as the epoll backend, but the interface to the
353	kernel is more efficient (which says nothing about its actual speed,	569	kernel is more efficient (which says nothing about its actual speed, of
354	of course). While stopping, setting and starting an I/O watcher does	570	course). While stopping, setting and starting an I/O watcher does never
355	never cause an extra syscall as with epoll, it still adds up to two event	571	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
356	changes per incident, support for C<fork ()> is very bad and it drops fds	572	two event changes per incident. Support for C<fork ()> is very bad (but
357	silently in similarly hard-to-detetc cases.	573	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		574	cases
		575
		576	This backend usually performs well under most conditions.
		577
		578	While nominally embeddable in other event loops, this doesn't work
		579	everywhere, so you might need to test for this. And since it is broken
		580	almost everywhere, you should only use it when you have a lot of sockets
		581	(for which it usually works), by embedding it into another event loop
		582	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		583	also broken on OS X)) and, did I mention it, using it only for sockets.
		584
		585	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		586	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		587	C<NOTE_EOF>.
358		588
359	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	589	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
360		590
361	This is not implemented yet (and might never be).	591	This is not implemented yet (and might never be, unless you send me an
		592	implementation). According to reports, C</dev/poll> only supports sockets
		593	and is not embeddable, which would limit the usefulness of this backend
		594	immensely.
362		595
363	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	596	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
364		597
365	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	598	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
366	it's really slow, but it still scales very well (O(active_fds)).	599	it's really slow, but it still scales very well (O(active_fds)).
367		600
368	Please note that solaris event ports can deliver a lot of spurious	601	While this backend scales well, it requires one system call per active
369	notifications, so you need to use non-blocking I/O or other means to avoid	602	file descriptor per loop iteration. For small and medium numbers of file
370	blocking when no data (or space) is available.	603	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		604	might perform better.
		605
		606	On the positive side, this backend actually performed fully to
		607	specification in all tests and is fully embeddable, which is a rare feat
		608	among the OS-specific backends (I vastly prefer correctness over speed
		609	hacks).
		610
		611	On the negative side, the interface is I<bizarre> - so bizarre that
		612	even sun itself gets it wrong in their code examples: The event polling
		613	function sometimes returning events to the caller even though an error
		614	occurred, but with no indication whether it has done so or not (yes, it's
		615	even documented that way) - deadly for edge-triggered interfaces where
		616	you absolutely have to know whether an event occurred or not because you
		617	have to re-arm the watcher.
		618
		619	Fortunately libev seems to be able to work around these idiocies.
		620
		621	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		622	C<EVBACKEND_POLL>.
371		623
372	=item C<EVBACKEND_ALL>	624	=item C<EVBACKEND_ALL>
373		625
374	Try all backends (even potentially broken ones that wouldn't be tried	626	Try all backends (even potentially broken ones that wouldn't be tried
375	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	627	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
376	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	628	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
377		629
		630	It is definitely not recommended to use this flag, use whatever
		631	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		632	at all.
		633
		634	=item C<EVBACKEND_MASK>
		635
		636	Not a backend at all, but a mask to select all backend bits from a
		637	C<flags> value, in case you want to mask out any backends from a flags
		638	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
		639
378	=back	640	=back
379		641
380	If one or more of these are ored into the flags value, then only these	642	If one or more of the backend flags are or'ed into the flags value,
381	backends will be tried (in the reverse order as given here). If none are	643	then only these backends will be tried (in the reverse order as listed
382	specified, most compiled-in backend will be tried, usually in reverse	644	here). If none are specified, all backends in C<ev_recommended_backends
383	order of their flag values :)	645	()> will be tried.
384
385	The most typical usage is like this:
386
387	if (!ev_default_loop (0))
388	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
389
390	Restrict libev to the select and poll backends, and do not allow
391	environment settings to be taken into account:
392
393	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
394
395	Use whatever libev has to offer, but make sure that kqueue is used if
396	available (warning, breaks stuff, best use only with your own private
397	event loop and only if you know the OS supports your types of fds):
398
399	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
400
401	=item struct ev_loop *ev_loop_new (unsigned int flags)
402
403	Similar to C<ev_default_loop>, but always creates a new event loop that is
404	always distinct from the default loop. Unlike the default loop, it cannot
405	handle signal and child watchers, and attempts to do so will be greeted by
406	undefined behaviour (or a failed assertion if assertions are enabled).
407		646
408	Example: Try to create a event loop that uses epoll and nothing else.	647	Example: Try to create a event loop that uses epoll and nothing else.
409		648
410	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	649	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
411	if (!epoller)	650	if (!epoller)
412	fatal ("no epoll found here, maybe it hides under your chair");	651	fatal ("no epoll found here, maybe it hides under your chair");
413		652
		653	Example: Use whatever libev has to offer, but make sure that kqueue is
		654	used if available.
		655
		656	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		657
414	=item ev_default_destroy ()	658	=item ev_loop_destroy (loop)
415		659
416	Destroys the default loop again (frees all memory and kernel state	660	Destroys an event loop object (frees all memory and kernel state
417	etc.). None of the active event watchers will be stopped in the normal	661	etc.). None of the active event watchers will be stopped in the normal
418	sense, so e.g. C<ev_is_active> might still return true. It is your	662	sense, so e.g. C<ev_is_active> might still return true. It is your
419	responsibility to either stop all watchers cleanly yoursef I<before>	663	responsibility to either stop all watchers cleanly yourself I<before>
420	calling this function, or cope with the fact afterwards (which is usually	664	calling this function, or cope with the fact afterwards (which is usually
421	the easiest thing, you can just ignore the watchers and/or C<free ()> them	665	the easiest thing, you can just ignore the watchers and/or C<free ()> them
422	for example).	666	for example).
423		667
424	Note that certain global state, such as signal state, will not be freed by	668	Note that certain global state, such as signal state (and installed signal
425	this function, and related watchers (such as signal and child watchers)	669	handlers), will not be freed by this function, and related watchers (such
426	would need to be stopped manually.	670	as signal and child watchers) would need to be stopped manually.
427		671
428	In general it is not advisable to call this function except in the	672	This function is normally used on loop objects allocated by
429	rare occasion where you really need to free e.g. the signal handling	673	C<ev_loop_new>, but it can also be used on the default loop returned by
		674	C<ev_default_loop>, in which case it is not thread-safe.
		675
		676	Note that it is not advisable to call this function on the default loop
		677	except in the rare occasion where you really need to free its resources.
430	pipe fds. If you need dynamically allocated loops it is better to use	678	If you need dynamically allocated loops it is better to use C<ev_loop_new>
431	C<ev_loop_new> and C<ev_loop_destroy>).	679	and C<ev_loop_destroy>.
432		680
433	=item ev_loop_destroy (loop)	681	=item ev_loop_fork (loop)
434		682
435	Like C<ev_default_destroy>, but destroys an event loop created by an	683	This function sets a flag that causes subsequent C<ev_run> iterations to
436	earlier call to C<ev_loop_new>.
437
438	=item ev_default_fork ()
439
440	This function reinitialises the kernel state for backends that have	684	reinitialise the kernel state for backends that have one. Despite the
441	one. Despite the name, you can call it anytime, but it makes most sense	685	name, you can call it anytime, but it makes most sense after forking, in
442	after forking, in either the parent or child process (or both, but that	686	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
443	again makes little sense).	687	child before resuming or calling C<ev_run>.
444		688
445	You I<must> call this function in the child process after forking if and	689	Again, you I<have> to call it on I<any> loop that you want to re-use after
446	only if you want to use the event library in both processes. If you just	690	a fork, I<even if you do not plan to use the loop in the parent>. This is
447	fork+exec, you don't have to call it.	691	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		692	during fork.
		693
		694	On the other hand, you only need to call this function in the child
		695	process if and only if you want to use the event loop in the child. If
		696	you just fork+exec or create a new loop in the child, you don't have to
		697	call it at all (in fact, C<epoll> is so badly broken that it makes a
		698	difference, but libev will usually detect this case on its own and do a
		699	costly reset of the backend).
448		700
449	The function itself is quite fast and it's usually not a problem to call	701	The function itself is quite fast and it's usually not a problem to call
450	it just in case after a fork. To make this easy, the function will fit in	702	it just in case after a fork.
451	quite nicely into a call to C<pthread_atfork>:
452		703
		704	Example: Automate calling C<ev_loop_fork> on the default loop when
		705	using pthreads.
		706
		707	static void
		708	post_fork_child (void)
		709	{
		710	ev_loop_fork (EV_DEFAULT);
		711	}
		712
		713	...
453	pthread_atfork (0, 0, ev_default_fork);	714	pthread_atfork (0, 0, post_fork_child);
454		715
455	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	716	=item int ev_is_default_loop (loop)
456	without calling this function, so if you force one of those backends you
457	do not need to care.
458		717
459	=item ev_loop_fork (loop)	718	Returns true when the given loop is, in fact, the default loop, and false
		719	otherwise.
460		720
461	Like C<ev_default_fork>, but acts on an event loop created by
462	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
463	after fork, and how you do this is entirely your own problem.
464
465	=item unsigned int ev_loop_count (loop)	721	=item unsigned int ev_iteration (loop)
466		722
467	Returns the count of loop iterations for the loop, which is identical to	723	Returns the current iteration count for the event loop, which is identical
468	the number of times libev did poll for new events. It starts at C<0> and	724	to the number of times libev did poll for new events. It starts at C<0>
469	happily wraps around with enough iterations.	725	and happily wraps around with enough iterations.
470		726
471	This value can sometimes be useful as a generation counter of sorts (it	727	This value can sometimes be useful as a generation counter of sorts (it
472	"ticks" the number of loop iterations), as it roughly corresponds with	728	"ticks" the number of loop iterations), as it roughly corresponds with
473	C<ev_prepare> and C<ev_check> calls.	729	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		730	prepare and check phases.
		731
		732	=item unsigned int ev_depth (loop)
		733
		734	Returns the number of times C<ev_run> was entered minus the number of
		735	times C<ev_run> was exited normally, in other words, the recursion depth.
		736
		737	Outside C<ev_run>, this number is zero. In a callback, this number is
		738	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		739	in which case it is higher.
		740
		741	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		742	throwing an exception etc.), doesn't count as "exit" - consider this
		743	as a hint to avoid such ungentleman-like behaviour unless it's really
		744	convenient, in which case it is fully supported.
474		745
475	=item unsigned int ev_backend (loop)	746	=item unsigned int ev_backend (loop)
476		747
477	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	748	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
478	use.	749	use.
…		…
483	received events and started processing them. This timestamp does not	754	received events and started processing them. This timestamp does not
484	change as long as callbacks are being processed, and this is also the base	755	change as long as callbacks are being processed, and this is also the base
485	time used for relative timers. You can treat it as the timestamp of the	756	time used for relative timers. You can treat it as the timestamp of the
486	event occurring (or more correctly, libev finding out about it).	757	event occurring (or more correctly, libev finding out about it).
487		758
		759	=item ev_now_update (loop)
		760
		761	Establishes the current time by querying the kernel, updating the time
		762	returned by C<ev_now ()> in the progress. This is a costly operation and
		763	is usually done automatically within C<ev_run ()>.
		764
		765	This function is rarely useful, but when some event callback runs for a
		766	very long time without entering the event loop, updating libev's idea of
		767	the current time is a good idea.
		768
		769	See also L<The special problem of time updates> in the C<ev_timer> section.
		770
		771	=item ev_suspend (loop)
		772
		773	=item ev_resume (loop)
		774
		775	These two functions suspend and resume an event loop, for use when the
		776	loop is not used for a while and timeouts should not be processed.
		777
		778	A typical use case would be an interactive program such as a game: When
		779	the user presses C<^Z> to suspend the game and resumes it an hour later it
		780	would be best to handle timeouts as if no time had actually passed while
		781	the program was suspended. This can be achieved by calling C<ev_suspend>
		782	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		783	C<ev_resume> directly afterwards to resume timer processing.
		784
		785	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		786	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		787	will be rescheduled (that is, they will lose any events that would have
		788	occurred while suspended).
		789
		790	After calling C<ev_suspend> you B<must not> call I<any> function on the
		791	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		792	without a previous call to C<ev_suspend>.
		793
		794	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		795	event loop time (see C<ev_now_update>).
		796
488	=item ev_loop (loop, int flags)	797	=item ev_run (loop, int flags)
489		798
490	Finally, this is it, the event handler. This function usually is called	799	Finally, this is it, the event handler. This function usually is called
491	after you initialised all your watchers and you want to start handling	800	after you have initialised all your watchers and you want to start
492	events.	801	handling events. It will ask the operating system for any new events, call
		802	the watcher callbacks, an then repeat the whole process indefinitely: This
		803	is why event loops are called I<loops>.
493		804
494	If the flags argument is specified as C<0>, it will not return until	805	If the flags argument is specified as C<0>, it will keep handling events
495	either no event watchers are active anymore or C<ev_unloop> was called.	806	until either no event watchers are active anymore or C<ev_break> was
		807	called.
496		808
497	Please note that an explicit C<ev_unloop> is usually better than	809	Please note that an explicit C<ev_break> is usually better than
498	relying on all watchers to be stopped when deciding when a program has	810	relying on all watchers to be stopped when deciding when a program has
499	finished (especially in interactive programs), but having a program that	811	finished (especially in interactive programs), but having a program
500	automatically loops as long as it has to and no longer by virtue of	812	that automatically loops as long as it has to and no longer by virtue
501	relying on its watchers stopping correctly is a thing of beauty.	813	of relying on its watchers stopping correctly, that is truly a thing of
		814	beauty.
502		815
		816	This function is also I<mostly> exception-safe - you can break out of
		817	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		818	exception and so on. This does not decrement the C<ev_depth> value, nor
		819	will it clear any outstanding C<EVBREAK_ONE> breaks.
		820
503	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	821	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
504	those events and any outstanding ones, but will not block your process in	822	those events and any already outstanding ones, but will not wait and
505	case there are no events and will return after one iteration of the loop.	823	block your process in case there are no events and will return after one
		824	iteration of the loop. This is sometimes useful to poll and handle new
		825	events while doing lengthy calculations, to keep the program responsive.
506		826
507	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	827	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
508	neccessary) and will handle those and any outstanding ones. It will block	828	necessary) and will handle those and any already outstanding ones. It
509	your process until at least one new event arrives, and will return after	829	will block your process until at least one new event arrives (which could
510	one iteration of the loop. This is useful if you are waiting for some	830	be an event internal to libev itself, so there is no guarantee that a
511	external event in conjunction with something not expressible using other	831	user-registered callback will be called), and will return after one
		832	iteration of the loop.
		833
		834	This is useful if you are waiting for some external event in conjunction
		835	with something not expressible using other libev watchers (i.e. "roll your
512	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	836	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
513	usually a better approach for this kind of thing.	837	usually a better approach for this kind of thing.
514		838
515	Here are the gory details of what C<ev_loop> does:	839	Here are the gory details of what C<ev_run> does (this is for your
		840	understanding, not a guarantee that things will work exactly like this in
		841	future versions):
516		842
		843	- Increment loop depth.
		844	- Reset the ev_break status.
517	- Before the first iteration, call any pending watchers.	845	- Before the first iteration, call any pending watchers.
518	* If there are no active watchers (reference count is zero), return.	846	LOOP:
519	- Queue all prepare watchers and then call all outstanding watchers.	847	- If EVFLAG_FORKCHECK was used, check for a fork.
		848	- If a fork was detected (by any means), queue and call all fork watchers.
		849	- Queue and call all prepare watchers.
		850	- If ev_break was called, goto FINISH.
520	- If we have been forked, recreate the kernel state.	851	- If we have been forked, detach and recreate the kernel state
		852	as to not disturb the other process.
521	- Update the kernel state with all outstanding changes.	853	- Update the kernel state with all outstanding changes.
522	- Update the "event loop time".	854	- Update the "event loop time" (ev_now ()).
523	- Calculate for how long to block.	855	- Calculate for how long to sleep or block, if at all
		856	(active idle watchers, EVRUN_NOWAIT or not having
		857	any active watchers at all will result in not sleeping).
		858	- Sleep if the I/O and timer collect interval say so.
		859	- Increment loop iteration counter.
524	- Block the process, waiting for any events.	860	- Block the process, waiting for any events.
525	- Queue all outstanding I/O (fd) events.	861	- Queue all outstanding I/O (fd) events.
526	- Update the "event loop time" and do time jump handling.	862	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
527	- Queue all outstanding timers.	863	- Queue all expired timers.
528	- Queue all outstanding periodics.	864	- Queue all expired periodics.
529	- If no events are pending now, queue all idle watchers.	865	- Queue all idle watchers with priority higher than that of pending events.
530	- Queue all check watchers.	866	- Queue all check watchers.
531	- Call all queued watchers in reverse order (i.e. check watchers first).	867	- Call all queued watchers in reverse order (i.e. check watchers first).
532	Signals and child watchers are implemented as I/O watchers, and will	868	Signals and child watchers are implemented as I/O watchers, and will
533	be handled here by queueing them when their watcher gets executed.	869	be handled here by queueing them when their watcher gets executed.
534	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	870	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
535	were used, return, otherwise continue with step *.	871	were used, or there are no active watchers, goto FINISH, otherwise
		872	continue with step LOOP.
		873	FINISH:
		874	- Reset the ev_break status iff it was EVBREAK_ONE.
		875	- Decrement the loop depth.
		876	- Return.
536		877
537	Example: Queue some jobs and then loop until no events are outsanding	878	Example: Queue some jobs and then loop until no events are outstanding
538	anymore.	879	anymore.
539		880
540	... queue jobs here, make sure they register event watchers as long	881	... queue jobs here, make sure they register event watchers as long
541	... as they still have work to do (even an idle watcher will do..)	882	... as they still have work to do (even an idle watcher will do..)
542	ev_loop (my_loop, 0);	883	ev_run (my_loop, 0);
543	... jobs done. yeah!	884	... jobs done or somebody called break. yeah!
544		885
545	=item ev_unloop (loop, how)	886	=item ev_break (loop, how)
546		887
547	Can be used to make a call to C<ev_loop> return early (but only after it	888	Can be used to make a call to C<ev_run> return early (but only after it
548	has processed all outstanding events). The C<how> argument must be either	889	has processed all outstanding events). The C<how> argument must be either
549	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	890	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
550	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	891	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		892
		893	This "break state" will be cleared on the next call to C<ev_run>.
		894
		895	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		896	which case it will have no effect.
551		897
552	=item ev_ref (loop)	898	=item ev_ref (loop)
553		899
554	=item ev_unref (loop)	900	=item ev_unref (loop)
555		901
556	Ref/unref can be used to add or remove a reference count on the event	902	Ref/unref can be used to add or remove a reference count on the event
557	loop: Every watcher keeps one reference, and as long as the reference	903	loop: Every watcher keeps one reference, and as long as the reference
558	count is nonzero, C<ev_loop> will not return on its own. If you have	904	count is nonzero, C<ev_run> will not return on its own.
559	a watcher you never unregister that should not keep C<ev_loop> from	905
560	returning, ev_unref() after starting, and ev_ref() before stopping it. For	906	This is useful when you have a watcher that you never intend to
		907	unregister, but that nevertheless should not keep C<ev_run> from
		908	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		909	before stopping it.
		910
561	example, libev itself uses this for its internal signal pipe: It is not	911	As an example, libev itself uses this for its internal signal pipe: It
562	visible to the libev user and should not keep C<ev_loop> from exiting if	912	is not visible to the libev user and should not keep C<ev_run> from
563	no event watchers registered by it are active. It is also an excellent	913	exiting if no event watchers registered by it are active. It is also an
564	way to do this for generic recurring timers or from within third-party	914	excellent way to do this for generic recurring timers or from within
565	libraries. Just remember to I<unref after start> and I<ref before stop>.	915	third-party libraries. Just remember to I<unref after start> and I<ref
		916	before stop> (but only if the watcher wasn't active before, or was active
		917	before, respectively. Note also that libev might stop watchers itself
		918	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		919	in the callback).
566		920
567	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	921	Example: Create a signal watcher, but keep it from keeping C<ev_run>
568	running when nothing else is active.	922	running when nothing else is active.
569		923
570	struct ev_signal exitsig;	924	ev_signal exitsig;
571	ev_signal_init (&exitsig, sig_cb, SIGINT);	925	ev_signal_init (&exitsig, sig_cb, SIGINT);
572	ev_signal_start (loop, &exitsig);	926	ev_signal_start (loop, &exitsig);
573	evf_unref (loop);	927	ev_unref (loop);
574		928
575	Example: For some weird reason, unregister the above signal handler again.	929	Example: For some weird reason, unregister the above signal handler again.
576		930
577	ev_ref (loop);	931	ev_ref (loop);
578	ev_signal_stop (loop, &exitsig);	932	ev_signal_stop (loop, &exitsig);
579		933
580	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	934	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
581		935
582	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	936	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
583		937
584	These advanced functions influence the time that libev will spend waiting	938	These advanced functions influence the time that libev will spend waiting
585	for events. Both are by default C<0>, meaning that libev will try to	939	for events. Both time intervals are by default C<0>, meaning that libev
586	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	940	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		941	latency.
587		942
588	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	943	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
589	allows libev to delay invocation of I/O and timer/periodic callbacks to	944	allows libev to delay invocation of I/O and timer/periodic callbacks
590	increase efficiency of loop iterations.	945	to increase efficiency of loop iterations (or to increase power-saving
		946	opportunities).
591		947
592	The background is that sometimes your program runs just fast enough to	948	The idea is that sometimes your program runs just fast enough to handle
593	handle one (or very few) event(s) per loop iteration. While this makes	949	one (or very few) event(s) per loop iteration. While this makes the
594	the program responsive, it also wastes a lot of CPU time to poll for new	950	program responsive, it also wastes a lot of CPU time to poll for new
595	events, especially with backends like C<select ()> which have a high	951	events, especially with backends like C<select ()> which have a high
596	overhead for the actual polling but can deliver many events at once.	952	overhead for the actual polling but can deliver many events at once.
597		953
598	By setting a higher I<io collect interval> you allow libev to spend more	954	By setting a higher I<io collect interval> you allow libev to spend more
599	time collecting I/O events, so you can handle more events per iteration,	955	time collecting I/O events, so you can handle more events per iteration,
600	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	956	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
601	C<ev_timer>) will be not affected.	957	C<ev_timer>) will be not affected. Setting this to a non-null value will
		958	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		959	sleep time ensures that libev will not poll for I/O events more often then
		960	once per this interval, on average.
602		961
603	Likewise, by setting a higher I<timeout collect interval> you allow libev	962	Likewise, by setting a higher I<timeout collect interval> you allow libev
604	to spend more time collecting timeouts, at the expense of increased	963	to spend more time collecting timeouts, at the expense of increased
605	latency (the watcher callback will be called later). C<ev_io> watchers	964	latency/jitter/inexactness (the watcher callback will be called
606	will not be affected.	965	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		966	value will not introduce any overhead in libev.
607		967
608	Many (busy) programs can usually benefit by setting the io collect	968	Many (busy) programs can usually benefit by setting the I/O collect
609	interval to a value near C<0.1> or so, which is often enough for	969	interval to a value near C<0.1> or so, which is often enough for
610	interactive servers (of course not for games), likewise for timeouts. It	970	interactive servers (of course not for games), likewise for timeouts. It
611	usually doesn't make much sense to set it to a lower value than C<0.01>,	971	usually doesn't make much sense to set it to a lower value than C<0.01>,
612	as this approsaches the timing granularity of most systems.	972	as this approaches the timing granularity of most systems. Note that if
		973	you do transactions with the outside world and you can't increase the
		974	parallelity, then this setting will limit your transaction rate (if you
		975	need to poll once per transaction and the I/O collect interval is 0.01,
		976	then you can't do more than 100 transactions per second).
		977
		978	Setting the I<timeout collect interval> can improve the opportunity for
		979	saving power, as the program will "bundle" timer callback invocations that
		980	are "near" in time together, by delaying some, thus reducing the number of
		981	times the process sleeps and wakes up again. Another useful technique to
		982	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		983	they fire on, say, one-second boundaries only.
		984
		985	Example: we only need 0.1s timeout granularity, and we wish not to poll
		986	more often than 100 times per second:
		987
		988	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		989	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		990
		991	=item ev_invoke_pending (loop)
		992
		993	This call will simply invoke all pending watchers while resetting their
		994	pending state. Normally, C<ev_run> does this automatically when required,
		995	but when overriding the invoke callback this call comes handy. This
		996	function can be invoked from a watcher - this can be useful for example
		997	when you want to do some lengthy calculation and want to pass further
		998	event handling to another thread (you still have to make sure only one
		999	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1000
		1001	=item int ev_pending_count (loop)
		1002
		1003	Returns the number of pending watchers - zero indicates that no watchers
		1004	are pending.
		1005
		1006	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1007
		1008	This overrides the invoke pending functionality of the loop: Instead of
		1009	invoking all pending watchers when there are any, C<ev_run> will call
		1010	this callback instead. This is useful, for example, when you want to
		1011	invoke the actual watchers inside another context (another thread etc.).
		1012
		1013	If you want to reset the callback, use C<ev_invoke_pending> as new
		1014	callback.
		1015
		1016	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		1017
		1018	Sometimes you want to share the same loop between multiple threads. This
		1019	can be done relatively simply by putting mutex_lock/unlock calls around
		1020	each call to a libev function.
		1021
		1022	However, C<ev_run> can run an indefinite time, so it is not feasible
		1023	to wait for it to return. One way around this is to wake up the event
		1024	loop via C<ev_break> and C<av_async_send>, another way is to set these
		1025	I<release> and I<acquire> callbacks on the loop.
		1026
		1027	When set, then C<release> will be called just before the thread is
		1028	suspended waiting for new events, and C<acquire> is called just
		1029	afterwards.
		1030
		1031	Ideally, C<release> will just call your mutex_unlock function, and
		1032	C<acquire> will just call the mutex_lock function again.
		1033
		1034	While event loop modifications are allowed between invocations of
		1035	C<release> and C<acquire> (that's their only purpose after all), no
		1036	modifications done will affect the event loop, i.e. adding watchers will
		1037	have no effect on the set of file descriptors being watched, or the time
		1038	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1039	to take note of any changes you made.
		1040
		1041	In theory, threads executing C<ev_run> will be async-cancel safe between
		1042	invocations of C<release> and C<acquire>.
		1043
		1044	See also the locking example in the C<THREADS> section later in this
		1045	document.
		1046
		1047	=item ev_set_userdata (loop, void *data)
		1048
		1049	=item void *ev_userdata (loop)
		1050
		1051	Set and retrieve a single C<void *> associated with a loop. When
		1052	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1053	C<0>.
		1054
		1055	These two functions can be used to associate arbitrary data with a loop,
		1056	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1057	C<acquire> callbacks described above, but of course can be (ab-)used for
		1058	any other purpose as well.
		1059
		1060	=item ev_verify (loop)
		1061
		1062	This function only does something when C<EV_VERIFY> support has been
		1063	compiled in, which is the default for non-minimal builds. It tries to go
		1064	through all internal structures and checks them for validity. If anything
		1065	is found to be inconsistent, it will print an error message to standard
		1066	error and call C<abort ()>.
		1067
		1068	This can be used to catch bugs inside libev itself: under normal
		1069	circumstances, this function will never abort as of course libev keeps its
		1070	data structures consistent.
613		1071
614	=back	1072	=back
615		1073
616		1074
617	=head1 ANATOMY OF A WATCHER	1075	=head1 ANATOMY OF A WATCHER
618		1076
		1077	In the following description, uppercase C<TYPE> in names stands for the
		1078	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1079	watchers and C<ev_io_start> for I/O watchers.
		1080
619	A watcher is a structure that you create and register to record your	1081	A watcher is an opaque structure that you allocate and register to record
620	interest in some event. For instance, if you want to wait for STDIN to	1082	your interest in some event. To make a concrete example, imagine you want
621	become readable, you would create an C<ev_io> watcher for that:	1083	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1084	for that:
622		1085
623	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1086	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
624	{	1087	{
625	ev_io_stop (w);	1088	ev_io_stop (w);
626	ev_unloop (loop, EVUNLOOP_ALL);	1089	ev_break (loop, EVBREAK_ALL);
627	}	1090	}
628		1091
629	struct ev_loop *loop = ev_default_loop (0);	1092	struct ev_loop *loop = ev_default_loop (0);
		1093
630	struct ev_io stdin_watcher;	1094	ev_io stdin_watcher;
		1095
631	ev_init (&stdin_watcher, my_cb);	1096	ev_init (&stdin_watcher, my_cb);
632	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1097	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
633	ev_io_start (loop, &stdin_watcher);	1098	ev_io_start (loop, &stdin_watcher);
		1099
634	ev_loop (loop, 0);	1100	ev_run (loop, 0);
635		1101
636	As you can see, you are responsible for allocating the memory for your	1102	As you can see, you are responsible for allocating the memory for your
637	watcher structures (and it is usually a bad idea to do this on the stack,	1103	watcher structures (and it is I<usually> a bad idea to do this on the
638	although this can sometimes be quite valid).	1104	stack).
639		1105
		1106	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1107	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1108
640	Each watcher structure must be initialised by a call to C<ev_init	1109	Each watcher structure must be initialised by a call to C<ev_init (watcher
641	(watcher *, callback)>, which expects a callback to be provided. This	1110	*, callback)>, which expects a callback to be provided. This callback is
642	callback gets invoked each time the event occurs (or, in the case of io	1111	invoked each time the event occurs (or, in the case of I/O watchers, each
643	watchers, each time the event loop detects that the file descriptor given	1112	time the event loop detects that the file descriptor given is readable
644	is readable and/or writable).	1113	and/or writable).
645		1114
646	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1115	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
647	with arguments specific to this watcher type. There is also a macro	1116	macro to configure it, with arguments specific to the watcher type. There
648	to combine initialisation and setting in one call: C<< ev_<type>_init	1117	is also a macro to combine initialisation and setting in one call: C<<
649	(watcher *, callback, ...) >>.	1118	ev_TYPE_init (watcher *, callback, ...) >>.
650		1119
651	To make the watcher actually watch out for events, you have to start it	1120	To make the watcher actually watch out for events, you have to start it
652	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1121	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
653	*) >>), and you can stop watching for events at any time by calling the	1122	*) >>), and you can stop watching for events at any time by calling the
654	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1123	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
655		1124
656	As long as your watcher is active (has been started but not stopped) you	1125	As long as your watcher is active (has been started but not stopped) you
657	must not touch the values stored in it. Most specifically you must never	1126	must not touch the values stored in it. Most specifically you must never
658	reinitialise it or call its C<set> macro.	1127	reinitialise it or call its C<ev_TYPE_set> macro.
659		1128
660	Each and every callback receives the event loop pointer as first, the	1129	Each and every callback receives the event loop pointer as first, the
661	registered watcher structure as second, and a bitset of received events as	1130	registered watcher structure as second, and a bitset of received events as
662	third argument.	1131	third argument.
663		1132
…		…
672	=item C<EV_WRITE>	1141	=item C<EV_WRITE>
673		1142
674	The file descriptor in the C<ev_io> watcher has become readable and/or	1143	The file descriptor in the C<ev_io> watcher has become readable and/or
675	writable.	1144	writable.
676		1145
677	=item C<EV_TIMEOUT>	1146	=item C<EV_TIMER>
678		1147
679	The C<ev_timer> watcher has timed out.	1148	The C<ev_timer> watcher has timed out.
680		1149
681	=item C<EV_PERIODIC>	1150	=item C<EV_PERIODIC>
682		1151
…		…
700		1169
701	=item C<EV_PREPARE>	1170	=item C<EV_PREPARE>
702		1171
703	=item C<EV_CHECK>	1172	=item C<EV_CHECK>
704		1173
705	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1174	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
706	to gather new events, and all C<ev_check> watchers are invoked just after	1175	to gather new events, and all C<ev_check> watchers are invoked just after
707	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1176	C<ev_run> has gathered them, but before it invokes any callbacks for any
708	received events. Callbacks of both watcher types can start and stop as	1177	received events. Callbacks of both watcher types can start and stop as
709	many watchers as they want, and all of them will be taken into account	1178	many watchers as they want, and all of them will be taken into account
710	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1179	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
711	C<ev_loop> from blocking).	1180	C<ev_run> from blocking).
712		1181
713	=item C<EV_EMBED>	1182	=item C<EV_EMBED>
714		1183
715	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1184	The embedded event loop specified in the C<ev_embed> watcher needs attention.
716		1185
717	=item C<EV_FORK>	1186	=item C<EV_FORK>
718		1187
719	The event loop has been resumed in the child process after fork (see	1188	The event loop has been resumed in the child process after fork (see
720	C<ev_fork>).	1189	C<ev_fork>).
721		1190
		1191	=item C<EV_CLEANUP>
		1192
		1193	The event loop is about to be destroyed (see C<ev_cleanup>).
		1194
		1195	=item C<EV_ASYNC>
		1196
		1197	The given async watcher has been asynchronously notified (see C<ev_async>).
		1198
		1199	=item C<EV_CUSTOM>
		1200
		1201	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1202	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1203
722	=item C<EV_ERROR>	1204	=item C<EV_ERROR>
723		1205
724	An unspecified error has occured, the watcher has been stopped. This might	1206	An unspecified error has occurred, the watcher has been stopped. This might
725	happen because the watcher could not be properly started because libev	1207	happen because the watcher could not be properly started because libev
726	ran out of memory, a file descriptor was found to be closed or any other	1208	ran out of memory, a file descriptor was found to be closed or any other
		1209	problem. Libev considers these application bugs.
		1210
727	problem. You best act on it by reporting the problem and somehow coping	1211	You best act on it by reporting the problem and somehow coping with the
728	with the watcher being stopped.	1212	watcher being stopped. Note that well-written programs should not receive
		1213	an error ever, so when your watcher receives it, this usually indicates a
		1214	bug in your program.
729		1215
730	Libev will usually signal a few "dummy" events together with an error,	1216	Libev will usually signal a few "dummy" events together with an error, for
731	for example it might indicate that a fd is readable or writable, and if	1217	example it might indicate that a fd is readable or writable, and if your
732	your callbacks is well-written it can just attempt the operation and cope	1218	callbacks is well-written it can just attempt the operation and cope with
733	with the error from read() or write(). This will not work in multithreaded	1219	the error from read() or write(). This will not work in multi-threaded
734	programs, though, so beware.	1220	programs, though, as the fd could already be closed and reused for another
		1221	thing, so beware.
735		1222
736	=back	1223	=back
737		1224
738	=head2 GENERIC WATCHER FUNCTIONS	1225	=head2 GENERIC WATCHER FUNCTIONS
739
740	In the following description, C<TYPE> stands for the watcher type,
741	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
742		1226
743	=over 4	1227	=over 4
744		1228
745	=item C<ev_init> (ev_TYPE *watcher, callback)	1229	=item C<ev_init> (ev_TYPE *watcher, callback)
746		1230
…		…
752	which rolls both calls into one.	1236	which rolls both calls into one.
753		1237
754	You can reinitialise a watcher at any time as long as it has been stopped	1238	You can reinitialise a watcher at any time as long as it has been stopped
755	(or never started) and there are no pending events outstanding.	1239	(or never started) and there are no pending events outstanding.
756		1240
757	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1241	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
758	int revents)>.	1242	int revents)>.
759		1243
		1244	Example: Initialise an C<ev_io> watcher in two steps.
		1245
		1246	ev_io w;
		1247	ev_init (&w, my_cb);
		1248	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1249
760	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1250	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
761		1251
762	This macro initialises the type-specific parts of a watcher. You need to	1252	This macro initialises the type-specific parts of a watcher. You need to
763	call C<ev_init> at least once before you call this macro, but you can	1253	call C<ev_init> at least once before you call this macro, but you can
764	call C<ev_TYPE_set> any number of times. You must not, however, call this	1254	call C<ev_TYPE_set> any number of times. You must not, however, call this
765	macro on a watcher that is active (it can be pending, however, which is a	1255	macro on a watcher that is active (it can be pending, however, which is a
766	difference to the C<ev_init> macro).	1256	difference to the C<ev_init> macro).
767		1257
768	Although some watcher types do not have type-specific arguments	1258	Although some watcher types do not have type-specific arguments
769	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1259	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
770		1260
		1261	See C<ev_init>, above, for an example.
		1262
771	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1263	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
772		1264
773	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1265	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
774	calls into a single call. This is the most convinient method to initialise	1266	calls into a single call. This is the most convenient method to initialise
775	a watcher. The same limitations apply, of course.	1267	a watcher. The same limitations apply, of course.
776		1268
		1269	Example: Initialise and set an C<ev_io> watcher in one step.
		1270
		1271	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1272
777	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1273	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
778		1274
779	Starts (activates) the given watcher. Only active watchers will receive	1275	Starts (activates) the given watcher. Only active watchers will receive
780	events. If the watcher is already active nothing will happen.	1276	events. If the watcher is already active nothing will happen.
781		1277
		1278	Example: Start the C<ev_io> watcher that is being abused as example in this
		1279	whole section.
		1280
		1281	ev_io_start (EV_DEFAULT_UC, &w);
		1282
782	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1283	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
783		1284
784	Stops the given watcher again (if active) and clears the pending	1285	Stops the given watcher if active, and clears the pending status (whether
		1286	the watcher was active or not).
		1287
785	status. It is possible that stopped watchers are pending (for example,	1288	It is possible that stopped watchers are pending - for example,
786	non-repeating timers are being stopped when they become pending), but	1289	non-repeating timers are being stopped when they become pending - but
787	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1290	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
788	you want to free or reuse the memory used by the watcher it is therefore a	1291	pending. If you want to free or reuse the memory used by the watcher it is
789	good idea to always call its C<ev_TYPE_stop> function.	1292	therefore a good idea to always call its C<ev_TYPE_stop> function.
790		1293
791	=item bool ev_is_active (ev_TYPE *watcher)	1294	=item bool ev_is_active (ev_TYPE *watcher)
792		1295
793	Returns a true value iff the watcher is active (i.e. it has been started	1296	Returns a true value iff the watcher is active (i.e. it has been started
794	and not yet been stopped). As long as a watcher is active you must not modify	1297	and not yet been stopped). As long as a watcher is active you must not modify
…		…
810	=item ev_cb_set (ev_TYPE *watcher, callback)	1313	=item ev_cb_set (ev_TYPE *watcher, callback)
811		1314
812	Change the callback. You can change the callback at virtually any time	1315	Change the callback. You can change the callback at virtually any time
813	(modulo threads).	1316	(modulo threads).
814		1317
815	=item ev_set_priority (ev_TYPE *watcher, priority)	1318	=item ev_set_priority (ev_TYPE *watcher, int priority)
816		1319
817	=item int ev_priority (ev_TYPE *watcher)	1320	=item int ev_priority (ev_TYPE *watcher)
818		1321
819	Set and query the priority of the watcher. The priority is a small	1322	Set and query the priority of the watcher. The priority is a small
820	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1323	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
821	(default: C<-2>). Pending watchers with higher priority will be invoked	1324	(default: C<-2>). Pending watchers with higher priority will be invoked
822	before watchers with lower priority, but priority will not keep watchers	1325	before watchers with lower priority, but priority will not keep watchers
823	from being executed (except for C<ev_idle> watchers).	1326	from being executed (except for C<ev_idle> watchers).
824		1327
825	This means that priorities are I<only> used for ordering callback
826	invocation after new events have been received. This is useful, for
827	example, to reduce latency after idling, or more often, to bind two
828	watchers on the same event and make sure one is called first.
829
830	If you need to suppress invocation when higher priority events are pending	1328	If you need to suppress invocation when higher priority events are pending
831	you need to look at C<ev_idle> watchers, which provide this functionality.	1329	you need to look at C<ev_idle> watchers, which provide this functionality.
832		1330
833	You I<must not> change the priority of a watcher as long as it is active or	1331	You I<must not> change the priority of a watcher as long as it is active or
834	pending.	1332	pending.
835		1333
		1334	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1335	fine, as long as you do not mind that the priority value you query might
		1336	or might not have been clamped to the valid range.
		1337
836	The default priority used by watchers when no priority has been set is	1338	The default priority used by watchers when no priority has been set is
837	always C<0>, which is supposed to not be too high and not be too low :).	1339	always C<0>, which is supposed to not be too high and not be too low :).
838		1340
839	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1341	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
840	fine, as long as you do not mind that the priority value you query might	1342	priorities.
841	or might not have been adjusted to be within valid range.
842		1343
843	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1344	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
844		1345
845	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1346	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
846	C<loop> nor C<revents> need to be valid as long as the watcher callback	1347	C<loop> nor C<revents> need to be valid as long as the watcher callback
847	can deal with that fact.	1348	can deal with that fact, as both are simply passed through to the
		1349	callback.
848		1350
849	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1351	=item int ev_clear_pending (loop, ev_TYPE *watcher)
850		1352
851	If the watcher is pending, this function returns clears its pending status	1353	If the watcher is pending, this function clears its pending status and
852	and returns its C<revents> bitset (as if its callback was invoked). If the	1354	returns its C<revents> bitset (as if its callback was invoked). If the
853	watcher isn't pending it does nothing and returns C<0>.	1355	watcher isn't pending it does nothing and returns C<0>.
854		1356
		1357	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1358	callback to be invoked, which can be accomplished with this function.
		1359
		1360	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1361
		1362	Feeds the given event set into the event loop, as if the specified event
		1363	had happened for the specified watcher (which must be a pointer to an
		1364	initialised but not necessarily started event watcher). Obviously you must
		1365	not free the watcher as long as it has pending events.
		1366
		1367	Stopping the watcher, letting libev invoke it, or calling
		1368	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1369	not started in the first place.
		1370
		1371	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1372	functions that do not need a watcher.
		1373
855	=back	1374	=back
856		1375
		1376	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
		1377	OWN COMPOSITE WATCHERS> idioms.
857		1378
858	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1379	=head2 WATCHER STATES
859		1380
860	Each watcher has, by default, a member C<void *data> that you can change	1381	There are various watcher states mentioned throughout this manual -
861	and read at any time, libev will completely ignore it. This can be used	1382	active, pending and so on. In this section these states and the rules to
862	to associate arbitrary data with your watcher. If you need more data and	1383	transition between them will be described in more detail - and while these
863	don't want to allocate memory and store a pointer to it in that data	1384	rules might look complicated, they usually do "the right thing".
864	member, you can also "subclass" the watcher type and provide your own
865	data:
866		1385
867	struct my_io	1386	=over 4
868	{
869	struct ev_io io;
870	int otherfd;
871	void *somedata;
872	struct whatever *mostinteresting;
873	}
874		1387
875	And since your callback will be called with a pointer to the watcher, you	1388	=item initialiased
876	can cast it back to your own type:
877		1389
878	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1390	Before a watcher can be registered with the event looop it has to be
879	{	1391	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
880	struct my_io *w = (struct my_io *)w_;	1392	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
881	...
882	}
883		1393
884	More interesting and less C-conformant ways of casting your callback type	1394	In this state it is simply some block of memory that is suitable for
885	instead have been omitted.	1395	use in an event loop. It can be moved around, freed, reused etc. at
		1396	will - as long as you either keep the memory contents intact, or call
		1397	C<ev_TYPE_init> again.
886		1398
887	Another common scenario is having some data structure with multiple	1399	=item started/running/active
888	watchers:
889		1400
890	struct my_biggy	1401	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
891	{	1402	property of the event loop, and is actively waiting for events. While in
892	int some_data;	1403	this state it cannot be accessed (except in a few documented ways), moved,
893	ev_timer t1;	1404	freed or anything else - the only legal thing is to keep a pointer to it,
894	ev_timer t2;	1405	and call libev functions on it that are documented to work on active watchers.
895	}
896		1406
897	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1407	=item pending
898	you need to use C<offsetof>:
899		1408
900	#include <stddef.h>	1409	If a watcher is active and libev determines that an event it is interested
		1410	in has occurred (such as a timer expiring), it will become pending. It will
		1411	stay in this pending state until either it is stopped or its callback is
		1412	about to be invoked, so it is not normally pending inside the watcher
		1413	callback.
901		1414
		1415	The watcher might or might not be active while it is pending (for example,
		1416	an expired non-repeating timer can be pending but no longer active). If it
		1417	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1418	but it is still property of the event loop at this time, so cannot be
		1419	moved, freed or reused. And if it is active the rules described in the
		1420	previous item still apply.
		1421
		1422	It is also possible to feed an event on a watcher that is not active (e.g.
		1423	via C<ev_feed_event>), in which case it becomes pending without being
		1424	active.
		1425
		1426	=item stopped
		1427
		1428	A watcher can be stopped implicitly by libev (in which case it might still
		1429	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1430	latter will clear any pending state the watcher might be in, regardless
		1431	of whether it was active or not, so stopping a watcher explicitly before
		1432	freeing it is often a good idea.
		1433
		1434	While stopped (and not pending) the watcher is essentially in the
		1435	initialised state, that is, it can be reused, moved, modified in any way
		1436	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1437	it again).
		1438
		1439	=back
		1440
		1441	=head2 WATCHER PRIORITY MODELS
		1442
		1443	Many event loops support I<watcher priorities>, which are usually small
		1444	integers that influence the ordering of event callback invocation
		1445	between watchers in some way, all else being equal.
		1446
		1447	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1448	description for the more technical details such as the actual priority
		1449	range.
		1450
		1451	There are two common ways how these these priorities are being interpreted
		1452	by event loops:
		1453
		1454	In the more common lock-out model, higher priorities "lock out" invocation
		1455	of lower priority watchers, which means as long as higher priority
		1456	watchers receive events, lower priority watchers are not being invoked.
		1457
		1458	The less common only-for-ordering model uses priorities solely to order
		1459	callback invocation within a single event loop iteration: Higher priority
		1460	watchers are invoked before lower priority ones, but they all get invoked
		1461	before polling for new events.
		1462
		1463	Libev uses the second (only-for-ordering) model for all its watchers
		1464	except for idle watchers (which use the lock-out model).
		1465
		1466	The rationale behind this is that implementing the lock-out model for
		1467	watchers is not well supported by most kernel interfaces, and most event
		1468	libraries will just poll for the same events again and again as long as
		1469	their callbacks have not been executed, which is very inefficient in the
		1470	common case of one high-priority watcher locking out a mass of lower
		1471	priority ones.
		1472
		1473	Static (ordering) priorities are most useful when you have two or more
		1474	watchers handling the same resource: a typical usage example is having an
		1475	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1476	timeouts. Under load, data might be received while the program handles
		1477	other jobs, but since timers normally get invoked first, the timeout
		1478	handler will be executed before checking for data. In that case, giving
		1479	the timer a lower priority than the I/O watcher ensures that I/O will be
		1480	handled first even under adverse conditions (which is usually, but not
		1481	always, what you want).
		1482
		1483	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1484	will only be executed when no same or higher priority watchers have
		1485	received events, they can be used to implement the "lock-out" model when
		1486	required.
		1487
		1488	For example, to emulate how many other event libraries handle priorities,
		1489	you can associate an C<ev_idle> watcher to each such watcher, and in
		1490	the normal watcher callback, you just start the idle watcher. The real
		1491	processing is done in the idle watcher callback. This causes libev to
		1492	continuously poll and process kernel event data for the watcher, but when
		1493	the lock-out case is known to be rare (which in turn is rare :), this is
		1494	workable.
		1495
		1496	Usually, however, the lock-out model implemented that way will perform
		1497	miserably under the type of load it was designed to handle. In that case,
		1498	it might be preferable to stop the real watcher before starting the
		1499	idle watcher, so the kernel will not have to process the event in case
		1500	the actual processing will be delayed for considerable time.
		1501
		1502	Here is an example of an I/O watcher that should run at a strictly lower
		1503	priority than the default, and which should only process data when no
		1504	other events are pending:
		1505
		1506	ev_idle idle; // actual processing watcher
		1507	ev_io io; // actual event watcher
		1508
902	static void	1509	static void
903	t1_cb (EV_P_ struct ev_timer *w, int revents)	1510	io_cb (EV_P_ ev_io *w, int revents)
904	{	1511	{
905	struct my_biggy big = (struct my_biggy *	1512	// stop the I/O watcher, we received the event, but
906	(((char *)w) - offsetof (struct my_biggy, t1));	1513	// are not yet ready to handle it.
		1514	ev_io_stop (EV_A_ w);
		1515
		1516	// start the idle watcher to handle the actual event.
		1517	// it will not be executed as long as other watchers
		1518	// with the default priority are receiving events.
		1519	ev_idle_start (EV_A_ &idle);
907	}	1520	}
908		1521
909	static void	1522	static void
910	t2_cb (EV_P_ struct ev_timer *w, int revents)	1523	idle_cb (EV_P_ ev_idle *w, int revents)
911	{	1524	{
912	struct my_biggy big = (struct my_biggy *	1525	// actual processing
913	(((char *)w) - offsetof (struct my_biggy, t2));	1526	read (STDIN_FILENO, ...);
		1527
		1528	// have to start the I/O watcher again, as
		1529	// we have handled the event
		1530	ev_io_start (EV_P_ &io);
914	}	1531	}
		1532
		1533	// initialisation
		1534	ev_idle_init (&idle, idle_cb);
		1535	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1536	ev_io_start (EV_DEFAULT_ &io);
		1537
		1538	In the "real" world, it might also be beneficial to start a timer, so that
		1539	low-priority connections can not be locked out forever under load. This
		1540	enables your program to keep a lower latency for important connections
		1541	during short periods of high load, while not completely locking out less
		1542	important ones.
915		1543
916		1544
917	=head1 WATCHER TYPES	1545	=head1 WATCHER TYPES
918		1546
919	This section describes each watcher in detail, but will not repeat	1547	This section describes each watcher in detail, but will not repeat
…		…
943	In general you can register as many read and/or write event watchers per	1571	In general you can register as many read and/or write event watchers per
944	fd as you want (as long as you don't confuse yourself). Setting all file	1572	fd as you want (as long as you don't confuse yourself). Setting all file
945	descriptors to non-blocking mode is also usually a good idea (but not	1573	descriptors to non-blocking mode is also usually a good idea (but not
946	required if you know what you are doing).	1574	required if you know what you are doing).
947		1575
948	You have to be careful with dup'ed file descriptors, though. Some backends
949	(the linux epoll backend is a notable example) cannot handle dup'ed file
950	descriptors correctly if you register interest in two or more fds pointing
951	to the same underlying file/socket/etc. description (that is, they share
952	the same underlying "file open").
953
954	If you must do this, then force the use of a known-to-be-good backend
955	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
956	C<EVBACKEND_POLL>).
957
958	Another thing you have to watch out for is that it is quite easy to	1576	Another thing you have to watch out for is that it is quite easy to
959	receive "spurious" readyness notifications, that is your callback might	1577	receive "spurious" readiness notifications, that is, your callback might
960	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1578	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
961	because there is no data. Not only are some backends known to create a	1579	because there is no data. It is very easy to get into this situation even
962	lot of those (for example solaris ports), it is very easy to get into	1580	with a relatively standard program structure. Thus it is best to always
963	this situation even with a relatively standard program structure. Thus	1581	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
964	it is best to always use non-blocking I/O: An extra C<read>(2) returning
965	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1582	preferable to a program hanging until some data arrives.
966		1583
967	If you cannot run the fd in non-blocking mode (for example you should not	1584	If you cannot run the fd in non-blocking mode (for example you should
968	play around with an Xlib connection), then you have to seperately re-test	1585	not play around with an Xlib connection), then you have to separately
969	whether a file descriptor is really ready with a known-to-be good interface	1586	re-test whether a file descriptor is really ready with a known-to-be good
970	such as poll (fortunately in our Xlib example, Xlib already does this on	1587	interface such as poll (fortunately in the case of Xlib, it already does
971	its own, so its quite safe to use).	1588	this on its own, so its quite safe to use). Some people additionally
		1589	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1590	indefinitely.
		1591
		1592	But really, best use non-blocking mode.
972		1593
973	=head3 The special problem of disappearing file descriptors	1594	=head3 The special problem of disappearing file descriptors
974		1595
975	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1596	Some backends (e.g. kqueue, epoll) need to be told about closing a file
976	descriptor (either by calling C<close> explicitly or by any other means,	1597	descriptor (either due to calling C<close> explicitly or any other means,
977	such as C<dup>). The reason is that you register interest in some file	1598	such as C<dup2>). The reason is that you register interest in some file
978	descriptor, but when it goes away, the operating system will silently drop	1599	descriptor, but when it goes away, the operating system will silently drop
979	this interest. If another file descriptor with the same number then is	1600	this interest. If another file descriptor with the same number then is
980	registered with libev, there is no efficient way to see that this is, in	1601	registered with libev, there is no efficient way to see that this is, in
981	fact, a different file descriptor.	1602	fact, a different file descriptor.
982		1603
…		…
992	optimisations to libev.	1613	optimisations to libev.
993		1614
994	=head3 The special problem of dup'ed file descriptors	1615	=head3 The special problem of dup'ed file descriptors
995		1616
996	Some backends (e.g. epoll), cannot register events for file descriptors,	1617	Some backends (e.g. epoll), cannot register events for file descriptors,
997	but only events for the underlying file descriptions. That menas when you	1618	but only events for the underlying file descriptions. That means when you
998	have C<dup ()>'ed file descriptors and register events for them, only one	1619	have C<dup ()>'ed file descriptors or weirder constellations, and register
999	file descriptor might actually receive events.	1620	events for them, only one file descriptor might actually receive events.
1000		1621
1001	There is no workaorund possible except not registering events	1622	There is no workaround possible except not registering events
1002	for potentially C<dup ()>'ed file descriptors or to resort to	1623	for potentially C<dup ()>'ed file descriptors, or to resort to
1003	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1624	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1625
		1626	=head3 The special problem of files
		1627
		1628	Many people try to use C<select> (or libev) on file descriptors
		1629	representing files, and expect it to become ready when their program
		1630	doesn't block on disk accesses (which can take a long time on their own).
		1631
		1632	However, this cannot ever work in the "expected" way - you get a readiness
		1633	notification as soon as the kernel knows whether and how much data is
		1634	there, and in the case of open files, that's always the case, so you
		1635	always get a readiness notification instantly, and your read (or possibly
		1636	write) will still block on the disk I/O.
		1637
		1638	Another way to view it is that in the case of sockets, pipes, character
		1639	devices and so on, there is another party (the sender) that delivers data
		1640	on its own, but in the case of files, there is no such thing: the disk
		1641	will not send data on its own, simply because it doesn't know what you
		1642	wish to read - you would first have to request some data.
		1643
		1644	Since files are typically not-so-well supported by advanced notification
		1645	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1646	to files, even though you should not use it. The reason for this is
		1647	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1648	usually a tty, often a pipe, but also sometimes files or special devices
		1649	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1650	F</dev/urandom>), and even though the file might better be served with
		1651	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1652	it "just works" instead of freezing.
		1653
		1654	So avoid file descriptors pointing to files when you know it (e.g. use
		1655	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1656	when you rarely read from a file instead of from a socket, and want to
		1657	reuse the same code path.
1004		1658
1005	=head3 The special problem of fork	1659	=head3 The special problem of fork
1006		1660
1007	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1661	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1008	useless behaviour. Libev fully supports fork, but needs to be told about	1662	useless behaviour. Libev fully supports fork, but needs to be told about
1009	it in the child.	1663	it in the child if you want to continue to use it in the child.
1010		1664
1011	To support fork in your programs, you either have to call	1665	To support fork in your child processes, you have to call C<ev_loop_fork
1012	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1666	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1013	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1667	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1014	C<EVBACKEND_POLL>.
1015		1668
		1669	=head3 The special problem of SIGPIPE
		1670
		1671	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1672	when writing to a pipe whose other end has been closed, your program gets
		1673	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1674	this is sensible behaviour, for daemons, this is usually undesirable.
		1675
		1676	So when you encounter spurious, unexplained daemon exits, make sure you
		1677	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1678	somewhere, as that would have given you a big clue).
		1679
		1680	=head3 The special problem of accept()ing when you can't
		1681
		1682	Many implementations of the POSIX C<accept> function (for example,
		1683	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1684	connection from the pending queue in all error cases.
		1685
		1686	For example, larger servers often run out of file descriptors (because
		1687	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1688	rejecting the connection, leading to libev signalling readiness on
		1689	the next iteration again (the connection still exists after all), and
		1690	typically causing the program to loop at 100% CPU usage.
		1691
		1692	Unfortunately, the set of errors that cause this issue differs between
		1693	operating systems, there is usually little the app can do to remedy the
		1694	situation, and no known thread-safe method of removing the connection to
		1695	cope with overload is known (to me).
		1696
		1697	One of the easiest ways to handle this situation is to just ignore it
		1698	- when the program encounters an overload, it will just loop until the
		1699	situation is over. While this is a form of busy waiting, no OS offers an
		1700	event-based way to handle this situation, so it's the best one can do.
		1701
		1702	A better way to handle the situation is to log any errors other than
		1703	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1704	messages, and continue as usual, which at least gives the user an idea of
		1705	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1706	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1707	usage.
		1708
		1709	If your program is single-threaded, then you could also keep a dummy file
		1710	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1711	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1712	close that fd, and create a new dummy fd. This will gracefully refuse
		1713	clients under typical overload conditions.
		1714
		1715	The last way to handle it is to simply log the error and C<exit>, as
		1716	is often done with C<malloc> failures, but this results in an easy
		1717	opportunity for a DoS attack.
1016		1718
1017	=head3 Watcher-Specific Functions	1719	=head3 Watcher-Specific Functions
1018		1720
1019	=over 4	1721	=over 4
1020		1722
1021	=item ev_io_init (ev_io *, callback, int fd, int events)	1723	=item ev_io_init (ev_io *, callback, int fd, int events)
1022		1724
1023	=item ev_io_set (ev_io *, int fd, int events)	1725	=item ev_io_set (ev_io *, int fd, int events)
1024		1726
1025	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1727	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1026	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1728	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1027	C<EV_READ | EV_WRITE> to receive the given events.	1729	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1028		1730
1029	=item int fd [read-only]	1731	=item int fd [read-only]
1030		1732
1031	The file descriptor being watched.	1733	The file descriptor being watched.
1032		1734
1033	=item int events [read-only]	1735	=item int events [read-only]
1034		1736
1035	The events being watched.	1737	The events being watched.
1036		1738
1037	=back	1739	=back
		1740
		1741	=head3 Examples
1038		1742
1039	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1743	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1040	readable, but only once. Since it is likely line-buffered, you could	1744	readable, but only once. Since it is likely line-buffered, you could
1041	attempt to read a whole line in the callback.	1745	attempt to read a whole line in the callback.
1042		1746
1043	static void	1747	static void
1044	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1748	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1045	{	1749	{
1046	ev_io_stop (loop, w);	1750	ev_io_stop (loop, w);
1047	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1751	.. read from stdin here (or from w->fd) and handle any I/O errors
1048	}	1752	}
1049		1753
1050	...	1754	...
1051	struct ev_loop *loop = ev_default_init (0);	1755	struct ev_loop *loop = ev_default_init (0);
1052	struct ev_io stdin_readable;	1756	ev_io stdin_readable;
1053	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1757	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1054	ev_io_start (loop, &stdin_readable);	1758	ev_io_start (loop, &stdin_readable);
1055	ev_loop (loop, 0);	1759	ev_run (loop, 0);
1056		1760
1057		1761
1058	=head2 C<ev_timer> - relative and optionally repeating timeouts	1762	=head2 C<ev_timer> - relative and optionally repeating timeouts
1059		1763
1060	Timer watchers are simple relative timers that generate an event after a	1764	Timer watchers are simple relative timers that generate an event after a
1061	given time, and optionally repeating in regular intervals after that.	1765	given time, and optionally repeating in regular intervals after that.
1062		1766
1063	The timers are based on real time, that is, if you register an event that	1767	The timers are based on real time, that is, if you register an event that
1064	times out after an hour and you reset your system clock to last years	1768	times out after an hour and you reset your system clock to January last
1065	time, it will still time out after (roughly) and hour. "Roughly" because	1769	year, it will still time out after (roughly) one hour. "Roughly" because
1066	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1770	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1067	monotonic clock option helps a lot here).	1771	monotonic clock option helps a lot here).
		1772
		1773	The callback is guaranteed to be invoked only I<after> its timeout has
		1774	passed (not I<at>, so on systems with very low-resolution clocks this
		1775	might introduce a small delay). If multiple timers become ready during the
		1776	same loop iteration then the ones with earlier time-out values are invoked
		1777	before ones of the same priority with later time-out values (but this is
		1778	no longer true when a callback calls C<ev_run> recursively).
		1779
		1780	=head3 Be smart about timeouts
		1781
		1782	Many real-world problems involve some kind of timeout, usually for error
		1783	recovery. A typical example is an HTTP request - if the other side hangs,
		1784	you want to raise some error after a while.
		1785
		1786	What follows are some ways to handle this problem, from obvious and
		1787	inefficient to smart and efficient.
		1788
		1789	In the following, a 60 second activity timeout is assumed - a timeout that
		1790	gets reset to 60 seconds each time there is activity (e.g. each time some
		1791	data or other life sign was received).
		1792
		1793	=over 4
		1794
		1795	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1796
		1797	This is the most obvious, but not the most simple way: In the beginning,
		1798	start the watcher:
		1799
		1800	ev_timer_init (timer, callback, 60., 0.);
		1801	ev_timer_start (loop, timer);
		1802
		1803	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1804	and start it again:
		1805
		1806	ev_timer_stop (loop, timer);
		1807	ev_timer_set (timer, 60., 0.);
		1808	ev_timer_start (loop, timer);
		1809
		1810	This is relatively simple to implement, but means that each time there is
		1811	some activity, libev will first have to remove the timer from its internal
		1812	data structure and then add it again. Libev tries to be fast, but it's
		1813	still not a constant-time operation.
		1814
		1815	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1816
		1817	This is the easiest way, and involves using C<ev_timer_again> instead of
		1818	C<ev_timer_start>.
		1819
		1820	To implement this, configure an C<ev_timer> with a C<repeat> value
		1821	of C<60> and then call C<ev_timer_again> at start and each time you
		1822	successfully read or write some data. If you go into an idle state where
		1823	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1824	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1825
		1826	That means you can ignore both the C<ev_timer_start> function and the
		1827	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1828	member and C<ev_timer_again>.
		1829
		1830	At start:
		1831
		1832	ev_init (timer, callback);
		1833	timer->repeat = 60.;
		1834	ev_timer_again (loop, timer);
		1835
		1836	Each time there is some activity:
		1837
		1838	ev_timer_again (loop, timer);
		1839
		1840	It is even possible to change the time-out on the fly, regardless of
		1841	whether the watcher is active or not:
		1842
		1843	timer->repeat = 30.;
		1844	ev_timer_again (loop, timer);
		1845
		1846	This is slightly more efficient then stopping/starting the timer each time
		1847	you want to modify its timeout value, as libev does not have to completely
		1848	remove and re-insert the timer from/into its internal data structure.
		1849
		1850	It is, however, even simpler than the "obvious" way to do it.
		1851
		1852	=item 3. Let the timer time out, but then re-arm it as required.
		1853
		1854	This method is more tricky, but usually most efficient: Most timeouts are
		1855	relatively long compared to the intervals between other activity - in
		1856	our example, within 60 seconds, there are usually many I/O events with
		1857	associated activity resets.
		1858
		1859	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1860	but remember the time of last activity, and check for a real timeout only
		1861	within the callback:
		1862
		1863	ev_tstamp last_activity; // time of last activity
		1864
		1865	static void
		1866	callback (EV_P_ ev_timer *w, int revents)
		1867	{
		1868	ev_tstamp now = ev_now (EV_A);
		1869	ev_tstamp timeout = last_activity + 60.;
		1870
		1871	// if last_activity + 60. is older than now, we did time out
		1872	if (timeout < now)
		1873	{
		1874	// timeout occurred, take action
		1875	}
		1876	else
		1877	{
		1878	// callback was invoked, but there was some activity, re-arm
		1879	// the watcher to fire in last_activity + 60, which is
		1880	// guaranteed to be in the future, so "again" is positive:
		1881	w->repeat = timeout - now;
		1882	ev_timer_again (EV_A_ w);
		1883	}
		1884	}
		1885
		1886	To summarise the callback: first calculate the real timeout (defined
		1887	as "60 seconds after the last activity"), then check if that time has
		1888	been reached, which means something I<did>, in fact, time out. Otherwise
		1889	the callback was invoked too early (C<timeout> is in the future), so
		1890	re-schedule the timer to fire at that future time, to see if maybe we have
		1891	a timeout then.
		1892
		1893	Note how C<ev_timer_again> is used, taking advantage of the
		1894	C<ev_timer_again> optimisation when the timer is already running.
		1895
		1896	This scheme causes more callback invocations (about one every 60 seconds
		1897	minus half the average time between activity), but virtually no calls to
		1898	libev to change the timeout.
		1899
		1900	To start the timer, simply initialise the watcher and set C<last_activity>
		1901	to the current time (meaning we just have some activity :), then call the
		1902	callback, which will "do the right thing" and start the timer:
		1903
		1904	ev_init (timer, callback);
		1905	last_activity = ev_now (loop);
		1906	callback (loop, timer, EV_TIMER);
		1907
		1908	And when there is some activity, simply store the current time in
		1909	C<last_activity>, no libev calls at all:
		1910
		1911	last_activity = ev_now (loop);
		1912
		1913	This technique is slightly more complex, but in most cases where the
		1914	time-out is unlikely to be triggered, much more efficient.
		1915
		1916	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1917	callback :) - just change the timeout and invoke the callback, which will
		1918	fix things for you.
		1919
		1920	=item 4. Wee, just use a double-linked list for your timeouts.
		1921
		1922	If there is not one request, but many thousands (millions...), all
		1923	employing some kind of timeout with the same timeout value, then one can
		1924	do even better:
		1925
		1926	When starting the timeout, calculate the timeout value and put the timeout
		1927	at the I<end> of the list.
		1928
		1929	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1930	the list is expected to fire (for example, using the technique #3).
		1931
		1932	When there is some activity, remove the timer from the list, recalculate
		1933	the timeout, append it to the end of the list again, and make sure to
		1934	update the C<ev_timer> if it was taken from the beginning of the list.
		1935
		1936	This way, one can manage an unlimited number of timeouts in O(1) time for
		1937	starting, stopping and updating the timers, at the expense of a major
		1938	complication, and having to use a constant timeout. The constant timeout
		1939	ensures that the list stays sorted.
		1940
		1941	=back
		1942
		1943	So which method the best?
		1944
		1945	Method #2 is a simple no-brain-required solution that is adequate in most
		1946	situations. Method #3 requires a bit more thinking, but handles many cases
		1947	better, and isn't very complicated either. In most case, choosing either
		1948	one is fine, with #3 being better in typical situations.
		1949
		1950	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1951	rather complicated, but extremely efficient, something that really pays
		1952	off after the first million or so of active timers, i.e. it's usually
		1953	overkill :)
		1954
		1955	=head3 The special problem of time updates
		1956
		1957	Establishing the current time is a costly operation (it usually takes at
		1958	least two system calls): EV therefore updates its idea of the current
		1959	time only before and after C<ev_run> collects new events, which causes a
		1960	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1961	lots of events in one iteration.
1068		1962
1069	The relative timeouts are calculated relative to the C<ev_now ()>	1963	The relative timeouts are calculated relative to the C<ev_now ()>
1070	time. This is usually the right thing as this timestamp refers to the time	1964	time. This is usually the right thing as this timestamp refers to the time
1071	of the event triggering whatever timeout you are modifying/starting. If	1965	of the event triggering whatever timeout you are modifying/starting. If
1072	you suspect event processing to be delayed and you I<need> to base the timeout	1966	you suspect event processing to be delayed and you I<need> to base the
1073	on the current time, use something like this to adjust for this:	1967	timeout on the current time, use something like this to adjust for this:
1074		1968
1075	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1969	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1076		1970
1077	The callback is guarenteed to be invoked only when its timeout has passed,	1971	If the event loop is suspended for a long time, you can also force an
1078	but if multiple timers become ready during the same loop iteration then	1972	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1079	order of execution is undefined.	1973	()>.
		1974
		1975	=head3 The special problems of suspended animation
		1976
		1977	When you leave the server world it is quite customary to hit machines that
		1978	can suspend/hibernate - what happens to the clocks during such a suspend?
		1979
		1980	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1981	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1982	to run until the system is suspended, but they will not advance while the
		1983	system is suspended. That means, on resume, it will be as if the program
		1984	was frozen for a few seconds, but the suspend time will not be counted
		1985	towards C<ev_timer> when a monotonic clock source is used. The real time
		1986	clock advanced as expected, but if it is used as sole clocksource, then a
		1987	long suspend would be detected as a time jump by libev, and timers would
		1988	be adjusted accordingly.
		1989
		1990	I would not be surprised to see different behaviour in different between
		1991	operating systems, OS versions or even different hardware.
		1992
		1993	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1994	time jump in the monotonic clocks and the realtime clock. If the program
		1995	is suspended for a very long time, and monotonic clock sources are in use,
		1996	then you can expect C<ev_timer>s to expire as the full suspension time
		1997	will be counted towards the timers. When no monotonic clock source is in
		1998	use, then libev will again assume a timejump and adjust accordingly.
		1999
		2000	It might be beneficial for this latter case to call C<ev_suspend>
		2001	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2002	deterministic behaviour in this case (you can do nothing against
		2003	C<SIGSTOP>).
1080		2004
1081	=head3 Watcher-Specific Functions and Data Members	2005	=head3 Watcher-Specific Functions and Data Members
1082		2006
1083	=over 4	2007	=over 4
1084		2008
1085	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2009	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1086		2010
1087	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2011	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1088		2012
1089	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2013	Configure the timer to trigger after C<after> seconds. If C<repeat>
1090	C<0.>, then it will automatically be stopped. If it is positive, then the	2014	is C<0.>, then it will automatically be stopped once the timeout is
1091	timer will automatically be configured to trigger again C<repeat> seconds	2015	reached. If it is positive, then the timer will automatically be
1092	later, again, and again, until stopped manually.	2016	configured to trigger again C<repeat> seconds later, again, and again,
		2017	until stopped manually.
1093		2018
1094	The timer itself will do a best-effort at avoiding drift, that is, if you	2019	The timer itself will do a best-effort at avoiding drift, that is, if
1095	configure a timer to trigger every 10 seconds, then it will trigger at	2020	you configure a timer to trigger every 10 seconds, then it will normally
1096	exactly 10 second intervals. If, however, your program cannot keep up with	2021	trigger at exactly 10 second intervals. If, however, your program cannot
1097	the timer (because it takes longer than those 10 seconds to do stuff) the	2022	keep up with the timer (because it takes longer than those 10 seconds to
1098	timer will not fire more than once per event loop iteration.	2023	do stuff) the timer will not fire more than once per event loop iteration.
1099		2024
1100	=item ev_timer_again (loop)	2025	=item ev_timer_again (loop, ev_timer *)
1101		2026
1102	This will act as if the timer timed out and restart it again if it is	2027	This will act as if the timer timed out and restart it again if it is
1103	repeating. The exact semantics are:	2028	repeating. The exact semantics are:
1104		2029
1105	If the timer is pending, its pending status is cleared.	2030	If the timer is pending, its pending status is cleared.
1106		2031
1107	If the timer is started but nonrepeating, stop it (as if it timed out).	2032	If the timer is started but non-repeating, stop it (as if it timed out).
1108		2033
1109	If the timer is repeating, either start it if necessary (with the	2034	If the timer is repeating, either start it if necessary (with the
1110	C<repeat> value), or reset the running timer to the C<repeat> value.	2035	C<repeat> value), or reset the running timer to the C<repeat> value.
1111		2036
1112	This sounds a bit complicated, but here is a useful and typical	2037	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1113	example: Imagine you have a tcp connection and you want a so-called idle	2038	usage example.
1114	timeout, that is, you want to be called when there have been, say, 60
1115	seconds of inactivity on the socket. The easiest way to do this is to
1116	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1117	C<ev_timer_again> each time you successfully read or write some data. If
1118	you go into an idle state where you do not expect data to travel on the
1119	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1120	automatically restart it if need be.
1121		2039
1122	That means you can ignore the C<after> value and C<ev_timer_start>	2040	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1123	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1124		2041
1125	ev_timer_init (timer, callback, 0., 5.);	2042	Returns the remaining time until a timer fires. If the timer is active,
1126	ev_timer_again (loop, timer);	2043	then this time is relative to the current event loop time, otherwise it's
1127	...	2044	the timeout value currently configured.
1128	timer->again = 17.;
1129	ev_timer_again (loop, timer);
1130	...
1131	timer->again = 10.;
1132	ev_timer_again (loop, timer);
1133		2045
1134	This is more slightly efficient then stopping/starting the timer each time	2046	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1135	you want to modify its timeout value.	2047	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2048	will return C<4>. When the timer expires and is restarted, it will return
		2049	roughly C<7> (likely slightly less as callback invocation takes some time,
		2050	too), and so on.
1136		2051
1137	=item ev_tstamp repeat [read-write]	2052	=item ev_tstamp repeat [read-write]
1138		2053
1139	The current C<repeat> value. Will be used each time the watcher times out	2054	The current C<repeat> value. Will be used each time the watcher times out
1140	or C<ev_timer_again> is called and determines the next timeout (if any),	2055	or C<ev_timer_again> is called, and determines the next timeout (if any),
1141	which is also when any modifications are taken into account.	2056	which is also when any modifications are taken into account.
1142		2057
1143	=back	2058	=back
1144		2059
		2060	=head3 Examples
		2061
1145	Example: Create a timer that fires after 60 seconds.	2062	Example: Create a timer that fires after 60 seconds.
1146		2063
1147	static void	2064	static void
1148	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2065	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1149	{	2066	{
1150	.. one minute over, w is actually stopped right here	2067	.. one minute over, w is actually stopped right here
1151	}	2068	}
1152		2069
1153	struct ev_timer mytimer;	2070	ev_timer mytimer;
1154	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2071	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1155	ev_timer_start (loop, &mytimer);	2072	ev_timer_start (loop, &mytimer);
1156		2073
1157	Example: Create a timeout timer that times out after 10 seconds of	2074	Example: Create a timeout timer that times out after 10 seconds of
1158	inactivity.	2075	inactivity.
1159		2076
1160	static void	2077	static void
1161	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2078	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1162	{	2079	{
1163	.. ten seconds without any activity	2080	.. ten seconds without any activity
1164	}	2081	}
1165		2082
1166	struct ev_timer mytimer;	2083	ev_timer mytimer;
1167	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2084	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1168	ev_timer_again (&mytimer); /* start timer */	2085	ev_timer_again (&mytimer); /* start timer */
1169	ev_loop (loop, 0);	2086	ev_run (loop, 0);
1170		2087
1171	// and in some piece of code that gets executed on any "activity":	2088	// and in some piece of code that gets executed on any "activity":
1172	// reset the timeout to start ticking again at 10 seconds	2089	// reset the timeout to start ticking again at 10 seconds
1173	ev_timer_again (&mytimer);	2090	ev_timer_again (&mytimer);
1174		2091
1175		2092
1176	=head2 C<ev_periodic> - to cron or not to cron?	2093	=head2 C<ev_periodic> - to cron or not to cron?
1177		2094
1178	Periodic watchers are also timers of a kind, but they are very versatile	2095	Periodic watchers are also timers of a kind, but they are very versatile
1179	(and unfortunately a bit complex).	2096	(and unfortunately a bit complex).
1180		2097
1181	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2098	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1182	but on wallclock time (absolute time). You can tell a periodic watcher	2099	relative time, the physical time that passes) but on wall clock time
1183	to trigger "at" some specific point in time. For example, if you tell a	2100	(absolute time, the thing you can read on your calender or clock). The
1184	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2101	difference is that wall clock time can run faster or slower than real
1185	+ 10.>) and then reset your system clock to the last year, then it will	2102	time, and time jumps are not uncommon (e.g. when you adjust your
1186	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2103	wrist-watch).
1187	roughly 10 seconds later).
1188		2104
1189	They can also be used to implement vastly more complex timers, such as	2105	You can tell a periodic watcher to trigger after some specific point
1190	triggering an event on each midnight, local time or other, complicated,	2106	in time: for example, if you tell a periodic watcher to trigger "in 10
1191	rules.	2107	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2108	not a delay) and then reset your system clock to January of the previous
		2109	year, then it will take a year or more to trigger the event (unlike an
		2110	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2111	it, as it uses a relative timeout).
1192		2112
		2113	C<ev_periodic> watchers can also be used to implement vastly more complex
		2114	timers, such as triggering an event on each "midnight, local time", or
		2115	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2116	those cannot react to time jumps.
		2117
1193	As with timers, the callback is guarenteed to be invoked only when the	2118	As with timers, the callback is guaranteed to be invoked only when the
1194	time (C<at>) has been passed, but if multiple periodic timers become ready	2119	point in time where it is supposed to trigger has passed. If multiple
1195	during the same loop iteration then order of execution is undefined.	2120	timers become ready during the same loop iteration then the ones with
		2121	earlier time-out values are invoked before ones with later time-out values
		2122	(but this is no longer true when a callback calls C<ev_run> recursively).
1196		2123
1197	=head3 Watcher-Specific Functions and Data Members	2124	=head3 Watcher-Specific Functions and Data Members
1198		2125
1199	=over 4	2126	=over 4
1200		2127
1201	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2128	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1202		2129
1203	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2130	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1204		2131
1205	Lots of arguments, lets sort it out... There are basically three modes of	2132	Lots of arguments, let's sort it out... There are basically three modes of
1206	operation, and we will explain them from simplest to complex:	2133	operation, and we will explain them from simplest to most complex:
1207		2134
1208	=over 4	2135	=over 4
1209		2136
1210	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2137	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1211		2138
1212	In this configuration the watcher triggers an event at the wallclock time	2139	In this configuration the watcher triggers an event after the wall clock
1213	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2140	time C<offset> has passed. It will not repeat and will not adjust when a
1214	that is, if it is to be run at January 1st 2011 then it will run when the	2141	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1215	system time reaches or surpasses this time.	2142	will be stopped and invoked when the system clock reaches or surpasses
		2143	this point in time.
1216		2144
1217	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2145	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1218		2146
1219	In this mode the watcher will always be scheduled to time out at the next	2147	In this mode the watcher will always be scheduled to time out at the next
1220	C<at + N * interval> time (for some integer N, which can also be negative)	2148	C<offset + N * interval> time (for some integer N, which can also be
1221	and then repeat, regardless of any time jumps.	2149	negative) and then repeat, regardless of any time jumps. The C<offset>
		2150	argument is merely an offset into the C<interval> periods.
1222		2151
1223	This can be used to create timers that do not drift with respect to system	2152	This can be used to create timers that do not drift with respect to the
1224	time:	2153	system clock, for example, here is an C<ev_periodic> that triggers each
		2154	hour, on the hour (with respect to UTC):
1225		2155
1226	ev_periodic_set (&periodic, 0., 3600., 0);	2156	ev_periodic_set (&periodic, 0., 3600., 0);
1227		2157
1228	This doesn't mean there will always be 3600 seconds in between triggers,	2158	This doesn't mean there will always be 3600 seconds in between triggers,
1229	but only that the the callback will be called when the system time shows a	2159	but only that the callback will be called when the system time shows a
1230	full hour (UTC), or more correctly, when the system time is evenly divisible	2160	full hour (UTC), or more correctly, when the system time is evenly divisible
1231	by 3600.	2161	by 3600.
1232		2162
1233	Another way to think about it (for the mathematically inclined) is that	2163	Another way to think about it (for the mathematically inclined) is that
1234	C<ev_periodic> will try to run the callback in this mode at the next possible	2164	C<ev_periodic> will try to run the callback in this mode at the next possible
1235	time where C<time = at (mod interval)>, regardless of any time jumps.	2165	time where C<time = offset (mod interval)>, regardless of any time jumps.
1236		2166
1237	For numerical stability it is preferable that the C<at> value is near	2167	The C<interval> I<MUST> be positive, and for numerical stability, the
1238	C<ev_now ()> (the current time), but there is no range requirement for	2168	interval value should be higher than C<1/8192> (which is around 100
1239	this value.	2169	microseconds) and C<offset> should be higher than C<0> and should have
		2170	at most a similar magnitude as the current time (say, within a factor of
		2171	ten). Typical values for offset are, in fact, C<0> or something between
		2172	C<0> and C<interval>, which is also the recommended range.
1240		2173
		2174	Note also that there is an upper limit to how often a timer can fire (CPU
		2175	speed for example), so if C<interval> is very small then timing stability
		2176	will of course deteriorate. Libev itself tries to be exact to be about one
		2177	millisecond (if the OS supports it and the machine is fast enough).
		2178
1241	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2179	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1242		2180
1243	In this mode the values for C<interval> and C<at> are both being	2181	In this mode the values for C<interval> and C<offset> are both being
1244	ignored. Instead, each time the periodic watcher gets scheduled, the	2182	ignored. Instead, each time the periodic watcher gets scheduled, the
1245	reschedule callback will be called with the watcher as first, and the	2183	reschedule callback will be called with the watcher as first, and the
1246	current time as second argument.	2184	current time as second argument.
1247		2185
1248	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2186	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1249	ever, or make any event loop modifications>. If you need to stop it,	2187	or make ANY other event loop modifications whatsoever, unless explicitly
1250	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2188	allowed by documentation here>.
1251	starting an C<ev_prepare> watcher, which is legal).
1252		2189
		2190	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2191	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2192	only event loop modification you are allowed to do).
		2193
1253	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2194	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1254	ev_tstamp now)>, e.g.:	2195	*w, ev_tstamp now)>, e.g.:
1255		2196
		2197	static ev_tstamp
1256	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2198	my_rescheduler (ev_periodic *w, ev_tstamp now)
1257	{	2199	{
1258	return now + 60.;	2200	return now + 60.;
1259	}	2201	}
1260		2202
1261	It must return the next time to trigger, based on the passed time value	2203	It must return the next time to trigger, based on the passed time value
1262	(that is, the lowest time value larger than to the second argument). It	2204	(that is, the lowest time value larger than to the second argument). It
1263	will usually be called just before the callback will be triggered, but	2205	will usually be called just before the callback will be triggered, but
1264	might be called at other times, too.	2206	might be called at other times, too.
1265		2207
1266	NOTE: I<< This callback must always return a time that is later than the	2208	NOTE: I<< This callback must always return a time that is higher than or
1267	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2209	equal to the passed C<now> value >>.
1268		2210
1269	This can be used to create very complex timers, such as a timer that	2211	This can be used to create very complex timers, such as a timer that
1270	triggers on each midnight, local time. To do this, you would calculate the	2212	triggers on "next midnight, local time". To do this, you would calculate the
1271	next midnight after C<now> and return the timestamp value for this. How	2213	next midnight after C<now> and return the timestamp value for this. How
1272	you do this is, again, up to you (but it is not trivial, which is the main	2214	you do this is, again, up to you (but it is not trivial, which is the main
1273	reason I omitted it as an example).	2215	reason I omitted it as an example).
1274		2216
1275	=back	2217	=back
…		…
1279	Simply stops and restarts the periodic watcher again. This is only useful	2221	Simply stops and restarts the periodic watcher again. This is only useful
1280	when you changed some parameters or the reschedule callback would return	2222	when you changed some parameters or the reschedule callback would return
1281	a different time than the last time it was called (e.g. in a crond like	2223	a different time than the last time it was called (e.g. in a crond like
1282	program when the crontabs have changed).	2224	program when the crontabs have changed).
1283		2225
		2226	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2227
		2228	When active, returns the absolute time that the watcher is supposed
		2229	to trigger next. This is not the same as the C<offset> argument to
		2230	C<ev_periodic_set>, but indeed works even in interval and manual
		2231	rescheduling modes.
		2232
1284	=item ev_tstamp offset [read-write]	2233	=item ev_tstamp offset [read-write]
1285		2234
1286	When repeating, this contains the offset value, otherwise this is the	2235	When repeating, this contains the offset value, otherwise this is the
1287	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2236	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2237	although libev might modify this value for better numerical stability).
1288		2238
1289	Can be modified any time, but changes only take effect when the periodic	2239	Can be modified any time, but changes only take effect when the periodic
1290	timer fires or C<ev_periodic_again> is being called.	2240	timer fires or C<ev_periodic_again> is being called.
1291		2241
1292	=item ev_tstamp interval [read-write]	2242	=item ev_tstamp interval [read-write]
1293		2243
1294	The current interval value. Can be modified any time, but changes only	2244	The current interval value. Can be modified any time, but changes only
1295	take effect when the periodic timer fires or C<ev_periodic_again> is being	2245	take effect when the periodic timer fires or C<ev_periodic_again> is being
1296	called.	2246	called.
1297		2247
1298	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2248	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1299		2249
1300	The current reschedule callback, or C<0>, if this functionality is	2250	The current reschedule callback, or C<0>, if this functionality is
1301	switched off. Can be changed any time, but changes only take effect when	2251	switched off. Can be changed any time, but changes only take effect when
1302	the periodic timer fires or C<ev_periodic_again> is being called.	2252	the periodic timer fires or C<ev_periodic_again> is being called.
1303		2253
1304	=item ev_tstamp at [read-only]
1305
1306	When active, contains the absolute time that the watcher is supposed to
1307	trigger next.
1308
1309	=back	2254	=back
1310		2255
		2256	=head3 Examples
		2257
1311	Example: Call a callback every hour, or, more precisely, whenever the	2258	Example: Call a callback every hour, or, more precisely, whenever the
1312	system clock is divisible by 3600. The callback invocation times have	2259	system time is divisible by 3600. The callback invocation times have
1313	potentially a lot of jittering, but good long-term stability.	2260	potentially a lot of jitter, but good long-term stability.
1314		2261
1315	static void	2262	static void
1316	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2263	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1317	{	2264	{
1318	... its now a full hour (UTC, or TAI or whatever your clock follows)	2265	... its now a full hour (UTC, or TAI or whatever your clock follows)
1319	}	2266	}
1320		2267
1321	struct ev_periodic hourly_tick;	2268	ev_periodic hourly_tick;
1322	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2269	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1323	ev_periodic_start (loop, &hourly_tick);	2270	ev_periodic_start (loop, &hourly_tick);
1324		2271
1325	Example: The same as above, but use a reschedule callback to do it:	2272	Example: The same as above, but use a reschedule callback to do it:
1326		2273
1327	#include <math.h>	2274	#include <math.h>
1328		2275
1329	static ev_tstamp	2276	static ev_tstamp
1330	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2277	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1331	{	2278	{
1332	return fmod (now, 3600.) + 3600.;	2279	return now + (3600. - fmod (now, 3600.));
1333	}	2280	}
1334		2281
1335	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2282	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1336		2283
1337	Example: Call a callback every hour, starting now:	2284	Example: Call a callback every hour, starting now:
1338		2285
1339	struct ev_periodic hourly_tick;	2286	ev_periodic hourly_tick;
1340	ev_periodic_init (&hourly_tick, clock_cb,	2287	ev_periodic_init (&hourly_tick, clock_cb,
1341	fmod (ev_now (loop), 3600.), 3600., 0);	2288	fmod (ev_now (loop), 3600.), 3600., 0);
1342	ev_periodic_start (loop, &hourly_tick);	2289	ev_periodic_start (loop, &hourly_tick);
1343		2290
1344		2291
1345	=head2 C<ev_signal> - signal me when a signal gets signalled!	2292	=head2 C<ev_signal> - signal me when a signal gets signalled!
1346		2293
1347	Signal watchers will trigger an event when the process receives a specific	2294	Signal watchers will trigger an event when the process receives a specific
1348	signal one or more times. Even though signals are very asynchronous, libev	2295	signal one or more times. Even though signals are very asynchronous, libev
1349	will try it's best to deliver signals synchronously, i.e. as part of the	2296	will try its best to deliver signals synchronously, i.e. as part of the
1350	normal event processing, like any other event.	2297	normal event processing, like any other event.
1351		2298
		2299	If you want signals to be delivered truly asynchronously, just use
		2300	C<sigaction> as you would do without libev and forget about sharing
		2301	the signal. You can even use C<ev_async> from a signal handler to
		2302	synchronously wake up an event loop.
		2303
1352	You can configure as many watchers as you like per signal. Only when the	2304	You can configure as many watchers as you like for the same signal, but
		2305	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2306	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2307	C<SIGINT> in both the default loop and another loop at the same time. At
		2308	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2309
1353	first watcher gets started will libev actually register a signal watcher	2310	When the first watcher gets started will libev actually register something
1354	with the kernel (thus it coexists with your own signal handlers as long	2311	with the kernel (thus it coexists with your own signal handlers as long as
1355	as you don't register any with libev). Similarly, when the last signal	2312	you don't register any with libev for the same signal).
1356	watcher for a signal is stopped libev will reset the signal handler to	2313
1357	SIG_DFL (regardless of what it was set to before).	2314	If possible and supported, libev will install its handlers with
		2315	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2316	not be unduly interrupted. If you have a problem with system calls getting
		2317	interrupted by signals you can block all signals in an C<ev_check> watcher
		2318	and unblock them in an C<ev_prepare> watcher.
		2319
		2320	=head3 The special problem of inheritance over fork/execve/pthread_create
		2321
		2322	Both the signal mask (C<sigprocmask>) and the signal disposition
		2323	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2324	stopping it again), that is, libev might or might not block the signal,
		2325	and might or might not set or restore the installed signal handler (but
		2326	see C<EVFLAG_NOSIGMASK>).
		2327
		2328	While this does not matter for the signal disposition (libev never
		2329	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2330	C<execve>), this matters for the signal mask: many programs do not expect
		2331	certain signals to be blocked.
		2332
		2333	This means that before calling C<exec> (from the child) you should reset
		2334	the signal mask to whatever "default" you expect (all clear is a good
		2335	choice usually).
		2336
		2337	The simplest way to ensure that the signal mask is reset in the child is
		2338	to install a fork handler with C<pthread_atfork> that resets it. That will
		2339	catch fork calls done by libraries (such as the libc) as well.
		2340
		2341	In current versions of libev, the signal will not be blocked indefinitely
		2342	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2343	the window of opportunity for problems, it will not go away, as libev
		2344	I<has> to modify the signal mask, at least temporarily.
		2345
		2346	So I can't stress this enough: I<If you do not reset your signal mask when
		2347	you expect it to be empty, you have a race condition in your code>. This
		2348	is not a libev-specific thing, this is true for most event libraries.
		2349
		2350	=head3 The special problem of threads signal handling
		2351
		2352	POSIX threads has problematic signal handling semantics, specifically,
		2353	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2354	threads in a process block signals, which is hard to achieve.
		2355
		2356	When you want to use sigwait (or mix libev signal handling with your own
		2357	for the same signals), you can tackle this problem by globally blocking
		2358	all signals before creating any threads (or creating them with a fully set
		2359	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2360	loops. Then designate one thread as "signal receiver thread" which handles
		2361	these signals. You can pass on any signals that libev might be interested
		2362	in by calling C<ev_feed_signal>.
1358		2363
1359	=head3 Watcher-Specific Functions and Data Members	2364	=head3 Watcher-Specific Functions and Data Members
1360		2365
1361	=over 4	2366	=over 4
1362		2367
…		…
1371		2376
1372	The signal the watcher watches out for.	2377	The signal the watcher watches out for.
1373		2378
1374	=back	2379	=back
1375		2380
		2381	=head3 Examples
		2382
		2383	Example: Try to exit cleanly on SIGINT.
		2384
		2385	static void
		2386	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2387	{
		2388	ev_break (loop, EVBREAK_ALL);
		2389	}
		2390
		2391	ev_signal signal_watcher;
		2392	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2393	ev_signal_start (loop, &signal_watcher);
		2394
1376		2395
1377	=head2 C<ev_child> - watch out for process status changes	2396	=head2 C<ev_child> - watch out for process status changes
1378		2397
1379	Child watchers trigger when your process receives a SIGCHLD in response to	2398	Child watchers trigger when your process receives a SIGCHLD in response to
1380	some child status changes (most typically when a child of yours dies).	2399	some child status changes (most typically when a child of yours dies or
		2400	exits). It is permissible to install a child watcher I<after> the child
		2401	has been forked (which implies it might have already exited), as long
		2402	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2403	forking and then immediately registering a watcher for the child is fine,
		2404	but forking and registering a watcher a few event loop iterations later or
		2405	in the next callback invocation is not.
		2406
		2407	Only the default event loop is capable of handling signals, and therefore
		2408	you can only register child watchers in the default event loop.
		2409
		2410	Due to some design glitches inside libev, child watchers will always be
		2411	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2412	libev)
		2413
		2414	=head3 Process Interaction
		2415
		2416	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2417	initialised. This is necessary to guarantee proper behaviour even if the
		2418	first child watcher is started after the child exits. The occurrence
		2419	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2420	synchronously as part of the event loop processing. Libev always reaps all
		2421	children, even ones not watched.
		2422
		2423	=head3 Overriding the Built-In Processing
		2424
		2425	Libev offers no special support for overriding the built-in child
		2426	processing, but if your application collides with libev's default child
		2427	handler, you can override it easily by installing your own handler for
		2428	C<SIGCHLD> after initialising the default loop, and making sure the
		2429	default loop never gets destroyed. You are encouraged, however, to use an
		2430	event-based approach to child reaping and thus use libev's support for
		2431	that, so other libev users can use C<ev_child> watchers freely.
		2432
		2433	=head3 Stopping the Child Watcher
		2434
		2435	Currently, the child watcher never gets stopped, even when the
		2436	child terminates, so normally one needs to stop the watcher in the
		2437	callback. Future versions of libev might stop the watcher automatically
		2438	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2439	problem).
1381		2440
1382	=head3 Watcher-Specific Functions and Data Members	2441	=head3 Watcher-Specific Functions and Data Members
1383		2442
1384	=over 4	2443	=over 4
1385		2444
1386	=item ev_child_init (ev_child *, callback, int pid)	2445	=item ev_child_init (ev_child *, callback, int pid, int trace)
1387		2446
1388	=item ev_child_set (ev_child *, int pid)	2447	=item ev_child_set (ev_child *, int pid, int trace)
1389		2448
1390	Configures the watcher to wait for status changes of process C<pid> (or	2449	Configures the watcher to wait for status changes of process C<pid> (or
1391	I<any> process if C<pid> is specified as C<0>). The callback can look	2450	I<any> process if C<pid> is specified as C<0>). The callback can look
1392	at the C<rstatus> member of the C<ev_child> watcher structure to see	2451	at the C<rstatus> member of the C<ev_child> watcher structure to see
1393	the status word (use the macros from C<sys/wait.h> and see your systems	2452	the status word (use the macros from C<sys/wait.h> and see your systems
1394	C<waitpid> documentation). The C<rpid> member contains the pid of the	2453	C<waitpid> documentation). The C<rpid> member contains the pid of the
1395	process causing the status change.	2454	process causing the status change. C<trace> must be either C<0> (only
		2455	activate the watcher when the process terminates) or C<1> (additionally
		2456	activate the watcher when the process is stopped or continued).
1396		2457
1397	=item int pid [read-only]	2458	=item int pid [read-only]
1398		2459
1399	The process id this watcher watches out for, or C<0>, meaning any process id.	2460	The process id this watcher watches out for, or C<0>, meaning any process id.
1400		2461
…		…
1407	The process exit/trace status caused by C<rpid> (see your systems	2468	The process exit/trace status caused by C<rpid> (see your systems
1408	C<waitpid> and C<sys/wait.h> documentation for details).	2469	C<waitpid> and C<sys/wait.h> documentation for details).
1409		2470
1410	=back	2471	=back
1411		2472
1412	Example: Try to exit cleanly on SIGINT and SIGTERM.	2473	=head3 Examples
1413		2474
		2475	Example: C<fork()> a new process and install a child handler to wait for
		2476	its completion.
		2477
		2478	ev_child cw;
		2479
1414	static void	2480	static void
1415	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2481	child_cb (EV_P_ ev_child *w, int revents)
1416	{	2482	{
1417	ev_unloop (loop, EVUNLOOP_ALL);	2483	ev_child_stop (EV_A_ w);
		2484	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1418	}	2485	}
1419		2486
1420	struct ev_signal signal_watcher;	2487	pid_t pid = fork ();
1421	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2488
1422	ev_signal_start (loop, &sigint_cb);	2489	if (pid < 0)
		2490	// error
		2491	else if (pid == 0)
		2492	{
		2493	// the forked child executes here
		2494	exit (1);
		2495	}
		2496	else
		2497	{
		2498	ev_child_init (&cw, child_cb, pid, 0);
		2499	ev_child_start (EV_DEFAULT_ &cw);
		2500	}
1423		2501
1424		2502
1425	=head2 C<ev_stat> - did the file attributes just change?	2503	=head2 C<ev_stat> - did the file attributes just change?
1426		2504
1427	This watches a filesystem path for attribute changes. That is, it calls	2505	This watches a file system path for attribute changes. That is, it calls
1428	C<stat> regularly (or when the OS says it changed) and sees if it changed	2506	C<stat> on that path in regular intervals (or when the OS says it changed)
1429	compared to the last time, invoking the callback if it did.	2507	and sees if it changed compared to the last time, invoking the callback if
		2508	it did.
1430		2509
1431	The path does not need to exist: changing from "path exists" to "path does	2510	The path does not need to exist: changing from "path exists" to "path does
1432	not exist" is a status change like any other. The condition "path does	2511	not exist" is a status change like any other. The condition "path does not
1433	not exist" is signified by the C<st_nlink> field being zero (which is	2512	exist" (or more correctly "path cannot be stat'ed") is signified by the
1434	otherwise always forced to be at least one) and all the other fields of	2513	C<st_nlink> field being zero (which is otherwise always forced to be at
1435	the stat buffer having unspecified contents.	2514	least one) and all the other fields of the stat buffer having unspecified
		2515	contents.
1436		2516
1437	The path I<should> be absolute and I<must not> end in a slash. If it is	2517	The path I<must not> end in a slash or contain special components such as
		2518	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1438	relative and your working directory changes, the behaviour is undefined.	2519	your working directory changes, then the behaviour is undefined.
1439		2520
1440	Since there is no standard to do this, the portable implementation simply	2521	Since there is no portable change notification interface available, the
1441	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2522	portable implementation simply calls C<stat(2)> regularly on the path
1442	can specify a recommended polling interval for this case. If you specify	2523	to see if it changed somehow. You can specify a recommended polling
1443	a polling interval of C<0> (highly recommended!) then a I<suitable,	2524	interval for this case. If you specify a polling interval of C<0> (highly
1444	unspecified default> value will be used (which you can expect to be around	2525	recommended!) then a I<suitable, unspecified default> value will be used
1445	five seconds, although this might change dynamically). Libev will also	2526	(which you can expect to be around five seconds, although this might
1446	impose a minimum interval which is currently around C<0.1>, but thats	2527	change dynamically). Libev will also impose a minimum interval which is
1447	usually overkill.	2528	currently around C<0.1>, but that's usually overkill.
1448		2529
1449	This watcher type is not meant for massive numbers of stat watchers,	2530	This watcher type is not meant for massive numbers of stat watchers,
1450	as even with OS-supported change notifications, this can be	2531	as even with OS-supported change notifications, this can be
1451	resource-intensive.	2532	resource-intensive.
1452		2533
1453	At the time of this writing, only the Linux inotify interface is	2534	At the time of this writing, the only OS-specific interface implemented
1454	implemented (implementing kqueue support is left as an exercise for the	2535	is the Linux inotify interface (implementing kqueue support is left as an
1455	reader). Inotify will be used to give hints only and should not change the	2536	exercise for the reader. Note, however, that the author sees no way of
1456	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2537	implementing C<ev_stat> semantics with kqueue, except as a hint).
1457	to fall back to regular polling again even with inotify, but changes are	2538
1458	usually detected immediately, and if the file exists there will be no	2539	=head3 ABI Issues (Largefile Support)
1459	polling.	2540
		2541	Libev by default (unless the user overrides this) uses the default
		2542	compilation environment, which means that on systems with large file
		2543	support disabled by default, you get the 32 bit version of the stat
		2544	structure. When using the library from programs that change the ABI to
		2545	use 64 bit file offsets the programs will fail. In that case you have to
		2546	compile libev with the same flags to get binary compatibility. This is
		2547	obviously the case with any flags that change the ABI, but the problem is
		2548	most noticeably displayed with ev_stat and large file support.
		2549
		2550	The solution for this is to lobby your distribution maker to make large
		2551	file interfaces available by default (as e.g. FreeBSD does) and not
		2552	optional. Libev cannot simply switch on large file support because it has
		2553	to exchange stat structures with application programs compiled using the
		2554	default compilation environment.
		2555
		2556	=head3 Inotify and Kqueue
		2557
		2558	When C<inotify (7)> support has been compiled into libev and present at
		2559	runtime, it will be used to speed up change detection where possible. The
		2560	inotify descriptor will be created lazily when the first C<ev_stat>
		2561	watcher is being started.
		2562
		2563	Inotify presence does not change the semantics of C<ev_stat> watchers
		2564	except that changes might be detected earlier, and in some cases, to avoid
		2565	making regular C<stat> calls. Even in the presence of inotify support
		2566	there are many cases where libev has to resort to regular C<stat> polling,
		2567	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2568	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2569	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2570	xfs are fully working) libev usually gets away without polling.
		2571
		2572	There is no support for kqueue, as apparently it cannot be used to
		2573	implement this functionality, due to the requirement of having a file
		2574	descriptor open on the object at all times, and detecting renames, unlinks
		2575	etc. is difficult.
		2576
		2577	=head3 C<stat ()> is a synchronous operation
		2578
		2579	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2580	the process. The exception are C<ev_stat> watchers - those call C<stat
		2581	()>, which is a synchronous operation.
		2582
		2583	For local paths, this usually doesn't matter: unless the system is very
		2584	busy or the intervals between stat's are large, a stat call will be fast,
		2585	as the path data is usually in memory already (except when starting the
		2586	watcher).
		2587
		2588	For networked file systems, calling C<stat ()> can block an indefinite
		2589	time due to network issues, and even under good conditions, a stat call
		2590	often takes multiple milliseconds.
		2591
		2592	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2593	paths, although this is fully supported by libev.
		2594
		2595	=head3 The special problem of stat time resolution
		2596
		2597	The C<stat ()> system call only supports full-second resolution portably,
		2598	and even on systems where the resolution is higher, most file systems
		2599	still only support whole seconds.
		2600
		2601	That means that, if the time is the only thing that changes, you can
		2602	easily miss updates: on the first update, C<ev_stat> detects a change and
		2603	calls your callback, which does something. When there is another update
		2604	within the same second, C<ev_stat> will be unable to detect unless the
		2605	stat data does change in other ways (e.g. file size).
		2606
		2607	The solution to this is to delay acting on a change for slightly more
		2608	than a second (or till slightly after the next full second boundary), using
		2609	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2610	ev_timer_again (loop, w)>).
		2611
		2612	The C<.02> offset is added to work around small timing inconsistencies
		2613	of some operating systems (where the second counter of the current time
		2614	might be be delayed. One such system is the Linux kernel, where a call to
		2615	C<gettimeofday> might return a timestamp with a full second later than
		2616	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2617	update file times then there will be a small window where the kernel uses
		2618	the previous second to update file times but libev might already execute
		2619	the timer callback).
1460		2620
1461	=head3 Watcher-Specific Functions and Data Members	2621	=head3 Watcher-Specific Functions and Data Members
1462		2622
1463	=over 4	2623	=over 4
1464		2624
…		…
1470	C<path>. The C<interval> is a hint on how quickly a change is expected to	2630	C<path>. The C<interval> is a hint on how quickly a change is expected to
1471	be detected and should normally be specified as C<0> to let libev choose	2631	be detected and should normally be specified as C<0> to let libev choose
1472	a suitable value. The memory pointed to by C<path> must point to the same	2632	a suitable value. The memory pointed to by C<path> must point to the same
1473	path for as long as the watcher is active.	2633	path for as long as the watcher is active.
1474		2634
1475	The callback will be receive C<EV_STAT> when a change was detected,	2635	The callback will receive an C<EV_STAT> event when a change was detected,
1476	relative to the attributes at the time the watcher was started (or the	2636	relative to the attributes at the time the watcher was started (or the
1477	last change was detected).	2637	last change was detected).
1478		2638
1479	=item ev_stat_stat (ev_stat *)	2639	=item ev_stat_stat (loop, ev_stat *)
1480		2640
1481	Updates the stat buffer immediately with new values. If you change the	2641	Updates the stat buffer immediately with new values. If you change the
1482	watched path in your callback, you could call this fucntion to avoid	2642	watched path in your callback, you could call this function to avoid
1483	detecting this change (while introducing a race condition). Can also be	2643	detecting this change (while introducing a race condition if you are not
1484	useful simply to find out the new values.	2644	the only one changing the path). Can also be useful simply to find out the
		2645	new values.
1485		2646
1486	=item ev_statdata attr [read-only]	2647	=item ev_statdata attr [read-only]
1487		2648
1488	The most-recently detected attributes of the file. Although the type is of	2649	The most-recently detected attributes of the file. Although the type is
1489	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2650	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1490	suitable for your system. If the C<st_nlink> member is C<0>, then there	2651	suitable for your system, but you can only rely on the POSIX-standardised
		2652	members to be present. If the C<st_nlink> member is C<0>, then there was
1491	was some error while C<stat>ing the file.	2653	some error while C<stat>ing the file.
1492		2654
1493	=item ev_statdata prev [read-only]	2655	=item ev_statdata prev [read-only]
1494		2656
1495	The previous attributes of the file. The callback gets invoked whenever	2657	The previous attributes of the file. The callback gets invoked whenever
1496	C<prev> != C<attr>.	2658	C<prev> != C<attr>, or, more precisely, one or more of these members
		2659	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2660	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1497		2661
1498	=item ev_tstamp interval [read-only]	2662	=item ev_tstamp interval [read-only]
1499		2663
1500	The specified interval.	2664	The specified interval.
1501		2665
1502	=item const char *path [read-only]	2666	=item const char *path [read-only]
1503		2667
1504	The filesystem path that is being watched.	2668	The file system path that is being watched.
1505		2669
1506	=back	2670	=back
1507		2671
		2672	=head3 Examples
		2673
1508	Example: Watch C</etc/passwd> for attribute changes.	2674	Example: Watch C</etc/passwd> for attribute changes.
1509		2675
1510	static void	2676	static void
1511	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2677	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1512	{	2678	{
1513	/* /etc/passwd changed in some way */	2679	/* /etc/passwd changed in some way */
1514	if (w->attr.st_nlink)	2680	if (w->attr.st_nlink)
1515	{	2681	{
1516	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2682	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1517	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2683	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1518	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2684	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1519	}	2685	}
1520	else	2686	else
1521	/* you shalt not abuse printf for puts */	2687	/* you shalt not abuse printf for puts */
1522	puts ("wow, /etc/passwd is not there, expect problems. "	2688	puts ("wow, /etc/passwd is not there, expect problems. "
1523	"if this is windows, they already arrived\n");	2689	"if this is windows, they already arrived\n");
1524	}	2690	}
1525		2691
1526	...	2692	...
1527	ev_stat passwd;	2693	ev_stat passwd;
1528		2694
1529	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2695	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1530	ev_stat_start (loop, &passwd);	2696	ev_stat_start (loop, &passwd);
		2697
		2698	Example: Like above, but additionally use a one-second delay so we do not
		2699	miss updates (however, frequent updates will delay processing, too, so
		2700	one might do the work both on C<ev_stat> callback invocation I<and> on
		2701	C<ev_timer> callback invocation).
		2702
		2703	static ev_stat passwd;
		2704	static ev_timer timer;
		2705
		2706	static void
		2707	timer_cb (EV_P_ ev_timer *w, int revents)
		2708	{
		2709	ev_timer_stop (EV_A_ w);
		2710
		2711	/* now it's one second after the most recent passwd change */
		2712	}
		2713
		2714	static void
		2715	stat_cb (EV_P_ ev_stat *w, int revents)
		2716	{
		2717	/* reset the one-second timer */
		2718	ev_timer_again (EV_A_ &timer);
		2719	}
		2720
		2721	...
		2722	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2723	ev_stat_start (loop, &passwd);
		2724	ev_timer_init (&timer, timer_cb, 0., 1.02);
1531		2725
1532		2726
1533	=head2 C<ev_idle> - when you've got nothing better to do...	2727	=head2 C<ev_idle> - when you've got nothing better to do...
1534		2728
1535	Idle watchers trigger events when no other events of the same or higher	2729	Idle watchers trigger events when no other events of the same or higher
1536	priority are pending (prepare, check and other idle watchers do not	2730	priority are pending (prepare, check and other idle watchers do not count
1537	count).	2731	as receiving "events").
1538		2732
1539	That is, as long as your process is busy handling sockets or timeouts	2733	That is, as long as your process is busy handling sockets or timeouts
1540	(or even signals, imagine) of the same or higher priority it will not be	2734	(or even signals, imagine) of the same or higher priority it will not be
1541	triggered. But when your process is idle (or only lower-priority watchers	2735	triggered. But when your process is idle (or only lower-priority watchers
1542	are pending), the idle watchers are being called once per event loop	2736	are pending), the idle watchers are being called once per event loop
…		…
1553		2747
1554	=head3 Watcher-Specific Functions and Data Members	2748	=head3 Watcher-Specific Functions and Data Members
1555		2749
1556	=over 4	2750	=over 4
1557		2751
1558	=item ev_idle_init (ev_signal *, callback)	2752	=item ev_idle_init (ev_idle *, callback)
1559		2753
1560	Initialises and configures the idle watcher - it has no parameters of any	2754	Initialises and configures the idle watcher - it has no parameters of any
1561	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2755	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1562	believe me.	2756	believe me.
1563		2757
1564	=back	2758	=back
1565		2759
		2760	=head3 Examples
		2761
1566	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2762	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1567	callback, free it. Also, use no error checking, as usual.	2763	callback, free it. Also, use no error checking, as usual.
1568		2764
1569	static void	2765	static void
1570	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2766	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1571	{	2767	{
1572	free (w);	2768	free (w);
1573	// now do something you wanted to do when the program has	2769	// now do something you wanted to do when the program has
1574	// no longer asnything immediate to do.	2770	// no longer anything immediate to do.
1575	}	2771	}
1576		2772
1577	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2773	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1578	ev_idle_init (idle_watcher, idle_cb);	2774	ev_idle_init (idle_watcher, idle_cb);
1579	ev_idle_start (loop, idle_cb);	2775	ev_idle_start (loop, idle_watcher);
1580		2776
1581		2777
1582	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2778	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1583		2779
1584	Prepare and check watchers are usually (but not always) used in tandem:	2780	Prepare and check watchers are usually (but not always) used in pairs:
1585	prepare watchers get invoked before the process blocks and check watchers	2781	prepare watchers get invoked before the process blocks and check watchers
1586	afterwards.	2782	afterwards.
1587		2783
1588	You I<must not> call C<ev_loop> or similar functions that enter	2784	You I<must not> call C<ev_run> or similar functions that enter
1589	the current event loop from either C<ev_prepare> or C<ev_check>	2785	the current event loop from either C<ev_prepare> or C<ev_check>
1590	watchers. Other loops than the current one are fine, however. The	2786	watchers. Other loops than the current one are fine, however. The
1591	rationale behind this is that you do not need to check for recursion in	2787	rationale behind this is that you do not need to check for recursion in
1592	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2788	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1593	C<ev_check> so if you have one watcher of each kind they will always be	2789	C<ev_check> so if you have one watcher of each kind they will always be
1594	called in pairs bracketing the blocking call.	2790	called in pairs bracketing the blocking call.
1595		2791
1596	Their main purpose is to integrate other event mechanisms into libev and	2792	Their main purpose is to integrate other event mechanisms into libev and
1597	their use is somewhat advanced. This could be used, for example, to track	2793	their use is somewhat advanced. They could be used, for example, to track
1598	variable changes, implement your own watchers, integrate net-snmp or a	2794	variable changes, implement your own watchers, integrate net-snmp or a
1599	coroutine library and lots more. They are also occasionally useful if	2795	coroutine library and lots more. They are also occasionally useful if
1600	you cache some data and want to flush it before blocking (for example,	2796	you cache some data and want to flush it before blocking (for example,
1601	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2797	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1602	watcher).	2798	watcher).
1603		2799
1604	This is done by examining in each prepare call which file descriptors need	2800	This is done by examining in each prepare call which file descriptors
1605	to be watched by the other library, registering C<ev_io> watchers for	2801	need to be watched by the other library, registering C<ev_io> watchers
1606	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2802	for them and starting an C<ev_timer> watcher for any timeouts (many
1607	provide just this functionality). Then, in the check watcher you check for	2803	libraries provide exactly this functionality). Then, in the check watcher,
1608	any events that occured (by checking the pending status of all watchers	2804	you check for any events that occurred (by checking the pending status
1609	and stopping them) and call back into the library. The I/O and timer	2805	of all watchers and stopping them) and call back into the library. The
1610	callbacks will never actually be called (but must be valid nevertheless,	2806	I/O and timer callbacks will never actually be called (but must be valid
1611	because you never know, you know?).	2807	nevertheless, because you never know, you know?).
1612		2808
1613	As another example, the Perl Coro module uses these hooks to integrate	2809	As another example, the Perl Coro module uses these hooks to integrate
1614	coroutines into libev programs, by yielding to other active coroutines	2810	coroutines into libev programs, by yielding to other active coroutines
1615	during each prepare and only letting the process block if no coroutines	2811	during each prepare and only letting the process block if no coroutines
1616	are ready to run (it's actually more complicated: it only runs coroutines	2812	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1619	loop from blocking if lower-priority coroutines are active, thus mapping	2815	loop from blocking if lower-priority coroutines are active, thus mapping
1620	low-priority coroutines to idle/background tasks).	2816	low-priority coroutines to idle/background tasks).
1621		2817
1622	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2818	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1623	priority, to ensure that they are being run before any other watchers	2819	priority, to ensure that they are being run before any other watchers
		2820	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2821
1624	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2822	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1625	too) should not activate ("feed") events into libev. While libev fully	2823	activate ("feed") events into libev. While libev fully supports this, they
1626	supports this, they will be called before other C<ev_check> watchers did	2824	might get executed before other C<ev_check> watchers did their job. As
1627	their job. As C<ev_check> watchers are often used to embed other event	2825	C<ev_check> watchers are often used to embed other (non-libev) event
1628	loops those other event loops might be in an unusable state until their	2826	loops those other event loops might be in an unusable state until their
1629	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2827	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1630	others).	2828	others).
1631		2829
1632	=head3 Watcher-Specific Functions and Data Members	2830	=head3 Watcher-Specific Functions and Data Members
…		…
1637		2835
1638	=item ev_check_init (ev_check *, callback)	2836	=item ev_check_init (ev_check *, callback)
1639		2837
1640	Initialises and configures the prepare or check watcher - they have no	2838	Initialises and configures the prepare or check watcher - they have no
1641	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2839	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1642	macros, but using them is utterly, utterly and completely pointless.	2840	macros, but using them is utterly, utterly, utterly and completely
		2841	pointless.
1643		2842
1644	=back	2843	=back
		2844
		2845	=head3 Examples
1645		2846
1646	There are a number of principal ways to embed other event loops or modules	2847	There are a number of principal ways to embed other event loops or modules
1647	into libev. Here are some ideas on how to include libadns into libev	2848	into libev. Here are some ideas on how to include libadns into libev
1648	(there is a Perl module named C<EV::ADNS> that does this, which you could	2849	(there is a Perl module named C<EV::ADNS> that does this, which you could
1649	use for an actually working example. Another Perl module named C<EV::Glib>	2850	use as a working example. Another Perl module named C<EV::Glib> embeds a
1650	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2851	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1651	into the Glib event loop).	2852	Glib event loop).
1652		2853
1653	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2854	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1654	and in a check watcher, destroy them and call into libadns. What follows	2855	and in a check watcher, destroy them and call into libadns. What follows
1655	is pseudo-code only of course. This requires you to either use a low	2856	is pseudo-code only of course. This requires you to either use a low
1656	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2857	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1657	the callbacks for the IO/timeout watchers might not have been called yet.	2858	the callbacks for the IO/timeout watchers might not have been called yet.
1658		2859
1659	static ev_io iow [nfd];	2860	static ev_io iow [nfd];
1660	static ev_timer tw;	2861	static ev_timer tw;
1661		2862
1662	static void	2863	static void
1663	io_cb (ev_loop *loop, ev_io *w, int revents)	2864	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1664	{	2865	{
1665	}	2866	}
1666		2867
1667	// create io watchers for each fd and a timer before blocking	2868	// create io watchers for each fd and a timer before blocking
1668	static void	2869	static void
1669	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2870	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1670	{	2871	{
1671	int timeout = 3600000;	2872	int timeout = 3600000;
1672	struct pollfd fds [nfd];	2873	struct pollfd fds [nfd];
1673	// actual code will need to loop here and realloc etc.	2874	// actual code will need to loop here and realloc etc.
1674	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2875	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1675		2876
1676	/* the callback is illegal, but won't be called as we stop during check */	2877	/* the callback is illegal, but won't be called as we stop during check */
1677	ev_timer_init (&tw, 0, timeout * 1e-3);	2878	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1678	ev_timer_start (loop, &tw);	2879	ev_timer_start (loop, &tw);
1679		2880
1680	// create one ev_io per pollfd	2881	// create one ev_io per pollfd
1681	for (int i = 0; i < nfd; ++i)	2882	for (int i = 0; i < nfd; ++i)
1682	{	2883	{
1683	ev_io_init (iow + i, io_cb, fds [i].fd,	2884	ev_io_init (iow + i, io_cb, fds [i].fd,
1684	((fds [i].events & POLLIN ? EV_READ : 0)	2885	((fds [i].events & POLLIN ? EV_READ : 0)
1685	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2886	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1686		2887
1687	fds [i].revents = 0;	2888	fds [i].revents = 0;
1688	ev_io_start (loop, iow + i);	2889	ev_io_start (loop, iow + i);
1689	}	2890	}
1690	}	2891	}
1691		2892
1692	// stop all watchers after blocking	2893	// stop all watchers after blocking
1693	static void	2894	static void
1694	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2895	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1695	{	2896	{
1696	ev_timer_stop (loop, &tw);	2897	ev_timer_stop (loop, &tw);
1697		2898
1698	for (int i = 0; i < nfd; ++i)	2899	for (int i = 0; i < nfd; ++i)
1699	{	2900	{
1700	// set the relevant poll flags	2901	// set the relevant poll flags
1701	// could also call adns_processreadable etc. here	2902	// could also call adns_processreadable etc. here
1702	struct pollfd *fd = fds + i;	2903	struct pollfd *fd = fds + i;
1703	int revents = ev_clear_pending (iow + i);	2904	int revents = ev_clear_pending (iow + i);
1704	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2905	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1705	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2906	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1706		2907
1707	// now stop the watcher	2908	// now stop the watcher
1708	ev_io_stop (loop, iow + i);	2909	ev_io_stop (loop, iow + i);
1709	}	2910	}
1710		2911
1711	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2912	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1712	}	2913	}
1713		2914
1714	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2915	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1715	in the prepare watcher and would dispose of the check watcher.	2916	in the prepare watcher and would dispose of the check watcher.
1716		2917
1717	Method 3: If the module to be embedded supports explicit event	2918	Method 3: If the module to be embedded supports explicit event
1718	notification (adns does), you can also make use of the actual watcher	2919	notification (libadns does), you can also make use of the actual watcher
1719	callbacks, and only destroy/create the watchers in the prepare watcher.	2920	callbacks, and only destroy/create the watchers in the prepare watcher.
1720		2921
1721	static void	2922	static void
1722	timer_cb (EV_P_ ev_timer *w, int revents)	2923	timer_cb (EV_P_ ev_timer *w, int revents)
1723	{	2924	{
1724	adns_state ads = (adns_state)w->data;	2925	adns_state ads = (adns_state)w->data;
1725	update_now (EV_A);	2926	update_now (EV_A);
1726		2927
1727	adns_processtimeouts (ads, &tv_now);	2928	adns_processtimeouts (ads, &tv_now);
1728	}	2929	}
1729		2930
1730	static void	2931	static void
1731	io_cb (EV_P_ ev_io *w, int revents)	2932	io_cb (EV_P_ ev_io *w, int revents)
1732	{	2933	{
1733	adns_state ads = (adns_state)w->data;	2934	adns_state ads = (adns_state)w->data;
1734	update_now (EV_A);	2935	update_now (EV_A);
1735		2936
1736	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2937	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1737	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2938	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1738	}	2939	}
1739		2940
1740	// do not ever call adns_afterpoll	2941	// do not ever call adns_afterpoll
1741		2942
1742	Method 4: Do not use a prepare or check watcher because the module you	2943	Method 4: Do not use a prepare or check watcher because the module you
1743	want to embed is too inflexible to support it. Instead, youc na override	2944	want to embed is not flexible enough to support it. Instead, you can
1744	their poll function. The drawback with this solution is that the main	2945	override their poll function. The drawback with this solution is that the
1745	loop is now no longer controllable by EV. The C<Glib::EV> module does	2946	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1746	this.	2947	this approach, effectively embedding EV as a client into the horrible
		2948	libglib event loop.
1747		2949
1748	static gint	2950	static gint
1749	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2951	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1750	{	2952	{
1751	int got_events = 0;	2953	int got_events = 0;
1752		2954
1753	for (n = 0; n < nfds; ++n)	2955	for (n = 0; n < nfds; ++n)
1754	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2956	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1755		2957
1756	if (timeout >= 0)	2958	if (timeout >= 0)
1757	// create/start timer	2959	// create/start timer
1758		2960
1759	// poll	2961	// poll
1760	ev_loop (EV_A_ 0);	2962	ev_run (EV_A_ 0);
1761		2963
1762	// stop timer again	2964	// stop timer again
1763	if (timeout >= 0)	2965	if (timeout >= 0)
1764	ev_timer_stop (EV_A_ &to);	2966	ev_timer_stop (EV_A_ &to);
1765		2967
1766	// stop io watchers again - their callbacks should have set	2968	// stop io watchers again - their callbacks should have set
1767	for (n = 0; n < nfds; ++n)	2969	for (n = 0; n < nfds; ++n)
1768	ev_io_stop (EV_A_ iow [n]);	2970	ev_io_stop (EV_A_ iow [n]);
1769		2971
1770	return got_events;	2972	return got_events;
1771	}	2973	}
1772		2974
1773		2975
1774	=head2 C<ev_embed> - when one backend isn't enough...	2976	=head2 C<ev_embed> - when one backend isn't enough...
1775		2977
1776	This is a rather advanced watcher type that lets you embed one event loop	2978	This is a rather advanced watcher type that lets you embed one event loop
1777	into another (currently only C<ev_io> events are supported in the embedded	2979	into another (currently only C<ev_io> events are supported in the embedded
1778	loop, other types of watchers might be handled in a delayed or incorrect	2980	loop, other types of watchers might be handled in a delayed or incorrect
1779	fashion and must not be used). (See portability notes, below).	2981	fashion and must not be used).
1780		2982
1781	There are primarily two reasons you would want that: work around bugs and	2983	There are primarily two reasons you would want that: work around bugs and
1782	prioritise I/O.	2984	prioritise I/O.
1783		2985
1784	As an example for a bug workaround, the kqueue backend might only support	2986	As an example for a bug workaround, the kqueue backend might only support
1785	sockets on some platform, so it is unusable as generic backend, but you	2987	sockets on some platform, so it is unusable as generic backend, but you
1786	still want to make use of it because you have many sockets and it scales	2988	still want to make use of it because you have many sockets and it scales
1787	so nicely. In this case, you would create a kqueue-based loop and embed it	2989	so nicely. In this case, you would create a kqueue-based loop and embed
1788	into your default loop (which might use e.g. poll). Overall operation will	2990	it into your default loop (which might use e.g. poll). Overall operation
1789	be a bit slower because first libev has to poll and then call kevent, but	2991	will be a bit slower because first libev has to call C<poll> and then
1790	at least you can use both at what they are best.	2992	C<kevent>, but at least you can use both mechanisms for what they are
		2993	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1791		2994
1792	As for prioritising I/O: rarely you have the case where some fds have	2995	As for prioritising I/O: under rare circumstances you have the case where
1793	to be watched and handled very quickly (with low latency), and even	2996	some fds have to be watched and handled very quickly (with low latency),
1794	priorities and idle watchers might have too much overhead. In this case	2997	and even priorities and idle watchers might have too much overhead. In
1795	you would put all the high priority stuff in one loop and all the rest in	2998	this case you would put all the high priority stuff in one loop and all
1796	a second one, and embed the second one in the first.	2999	the rest in a second one, and embed the second one in the first.
1797		3000
1798	As long as the watcher is active, the callback will be invoked every time	3001	As long as the watcher is active, the callback will be invoked every
1799	there might be events pending in the embedded loop. The callback must then	3002	time there might be events pending in the embedded loop. The callback
1800	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3003	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1801	their callbacks (you could also start an idle watcher to give the embedded	3004	sweep and invoke their callbacks (the callback doesn't need to invoke the
1802	loop strictly lower priority for example). You can also set the callback	3005	C<ev_embed_sweep> function directly, it could also start an idle watcher
1803	to C<0>, in which case the embed watcher will automatically execute the	3006	to give the embedded loop strictly lower priority for example).
1804	embedded loop sweep.
1805		3007
1806	As long as the watcher is started it will automatically handle events. The	3008	You can also set the callback to C<0>, in which case the embed watcher
1807	callback will be invoked whenever some events have been handled. You can	3009	will automatically execute the embedded loop sweep whenever necessary.
1808	set the callback to C<0> to avoid having to specify one if you are not
1809	interested in that.
1810		3010
1811	Also, there have not currently been made special provisions for forking:	3011	Fork detection will be handled transparently while the C<ev_embed> watcher
1812	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3012	is active, i.e., the embedded loop will automatically be forked when the
1813	but you will also have to stop and restart any C<ev_embed> watchers	3013	embedding loop forks. In other cases, the user is responsible for calling
1814	yourself.	3014	C<ev_loop_fork> on the embedded loop.
1815		3015
1816	Unfortunately, not all backends are embeddable, only the ones returned by	3016	Unfortunately, not all backends are embeddable: only the ones returned by
1817	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3017	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1818	portable one.	3018	portable one.
1819		3019
1820	So when you want to use this feature you will always have to be prepared	3020	So when you want to use this feature you will always have to be prepared
1821	that you cannot get an embeddable loop. The recommended way to get around	3021	that you cannot get an embeddable loop. The recommended way to get around
1822	this is to have a separate variables for your embeddable loop, try to	3022	this is to have a separate variables for your embeddable loop, try to
1823	create it, and if that fails, use the normal loop for everything:	3023	create it, and if that fails, use the normal loop for everything.
1824		3024
1825	struct ev_loop *loop_hi = ev_default_init (0);	3025	=head3 C<ev_embed> and fork
1826	struct ev_loop *loop_lo = 0;
1827	struct ev_embed embed;
1828
1829	// see if there is a chance of getting one that works
1830	// (remember that a flags value of 0 means autodetection)
1831	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1832	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1833	: 0;
1834		3026
1835	// if we got one, then embed it, otherwise default to loop_hi	3027	While the C<ev_embed> watcher is running, forks in the embedding loop will
1836	if (loop_lo)	3028	automatically be applied to the embedded loop as well, so no special
1837	{	3029	fork handling is required in that case. When the watcher is not running,
1838	ev_embed_init (&embed, 0, loop_lo);	3030	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1839	ev_embed_start (loop_hi, &embed);	3031	as applicable.
1840	}
1841	else
1842	loop_lo = loop_hi;
1843
1844	=head2 Portability notes
1845
1846	Kqueue is nominally embeddable, but this is broken on all BSDs that I
1847	tried, in various ways. Usually the embedded event loop will simply never
1848	receive events, sometimes it will only trigger a few times, sometimes in a
1849	loop. Epoll is also nominally embeddable, but many Linux kernel versions
1850	will always eport the epoll fd as ready, even when no events are pending.
1851
1852	While libev allows embedding these backends (they are contained in
1853	C<ev_embeddable_backends ()>), take extreme care that it will actually
1854	work.
1855
1856	When in doubt, create a dynamic event loop forced to use sockets (this
1857	usually works) and possibly another thread and a pipe or so to report to
1858	your main event loop.
1859		3032
1860	=head3 Watcher-Specific Functions and Data Members	3033	=head3 Watcher-Specific Functions and Data Members
1861		3034
1862	=over 4	3035	=over 4
1863		3036
…		…
1867		3040
1868	Configures the watcher to embed the given loop, which must be	3041	Configures the watcher to embed the given loop, which must be
1869	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3042	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1870	invoked automatically, otherwise it is the responsibility of the callback	3043	invoked automatically, otherwise it is the responsibility of the callback
1871	to invoke it (it will continue to be called until the sweep has been done,	3044	to invoke it (it will continue to be called until the sweep has been done,
1872	if you do not want thta, you need to temporarily stop the embed watcher).	3045	if you do not want that, you need to temporarily stop the embed watcher).
1873		3046
1874	=item ev_embed_sweep (loop, ev_embed *)	3047	=item ev_embed_sweep (loop, ev_embed *)
1875		3048
1876	Make a single, non-blocking sweep over the embedded loop. This works	3049	Make a single, non-blocking sweep over the embedded loop. This works
1877	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3050	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1878	apropriate way for embedded loops.	3051	appropriate way for embedded loops.
1879		3052
1880	=item struct ev_loop *other [read-only]	3053	=item struct ev_loop *other [read-only]
1881		3054
1882	The embedded event loop.	3055	The embedded event loop.
1883		3056
1884	=back	3057	=back
		3058
		3059	=head3 Examples
		3060
		3061	Example: Try to get an embeddable event loop and embed it into the default
		3062	event loop. If that is not possible, use the default loop. The default
		3063	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3064	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3065	used).
		3066
		3067	struct ev_loop *loop_hi = ev_default_init (0);
		3068	struct ev_loop *loop_lo = 0;
		3069	ev_embed embed;
		3070
		3071	// see if there is a chance of getting one that works
		3072	// (remember that a flags value of 0 means autodetection)
		3073	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3074	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3075	: 0;
		3076
		3077	// if we got one, then embed it, otherwise default to loop_hi
		3078	if (loop_lo)
		3079	{
		3080	ev_embed_init (&embed, 0, loop_lo);
		3081	ev_embed_start (loop_hi, &embed);
		3082	}
		3083	else
		3084	loop_lo = loop_hi;
		3085
		3086	Example: Check if kqueue is available but not recommended and create
		3087	a kqueue backend for use with sockets (which usually work with any
		3088	kqueue implementation). Store the kqueue/socket-only event loop in
		3089	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3090
		3091	struct ev_loop *loop = ev_default_init (0);
		3092	struct ev_loop *loop_socket = 0;
		3093	ev_embed embed;
		3094
		3095	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3096	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3097	{
		3098	ev_embed_init (&embed, 0, loop_socket);
		3099	ev_embed_start (loop, &embed);
		3100	}
		3101
		3102	if (!loop_socket)
		3103	loop_socket = loop;
		3104
		3105	// now use loop_socket for all sockets, and loop for everything else
1885		3106
1886		3107
1887	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3108	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1888		3109
1889	Fork watchers are called when a C<fork ()> was detected (usually because	3110	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1892	event loop blocks next and before C<ev_check> watchers are being called,	3113	event loop blocks next and before C<ev_check> watchers are being called,
1893	and only in the child after the fork. If whoever good citizen calling	3114	and only in the child after the fork. If whoever good citizen calling
1894	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3115	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1895	handlers will be invoked, too, of course.	3116	handlers will be invoked, too, of course.
1896		3117
		3118	=head3 The special problem of life after fork - how is it possible?
		3119
		3120	Most uses of C<fork()> consist of forking, then some simple calls to set
		3121	up/change the process environment, followed by a call to C<exec()>. This
		3122	sequence should be handled by libev without any problems.
		3123
		3124	This changes when the application actually wants to do event handling
		3125	in the child, or both parent in child, in effect "continuing" after the
		3126	fork.
		3127
		3128	The default mode of operation (for libev, with application help to detect
		3129	forks) is to duplicate all the state in the child, as would be expected
		3130	when I<either> the parent I<or> the child process continues.
		3131
		3132	When both processes want to continue using libev, then this is usually the
		3133	wrong result. In that case, usually one process (typically the parent) is
		3134	supposed to continue with all watchers in place as before, while the other
		3135	process typically wants to start fresh, i.e. without any active watchers.
		3136
		3137	The cleanest and most efficient way to achieve that with libev is to
		3138	simply create a new event loop, which of course will be "empty", and
		3139	use that for new watchers. This has the advantage of not touching more
		3140	memory than necessary, and thus avoiding the copy-on-write, and the
		3141	disadvantage of having to use multiple event loops (which do not support
		3142	signal watchers).
		3143
		3144	When this is not possible, or you want to use the default loop for
		3145	other reasons, then in the process that wants to start "fresh", call
		3146	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3147	Destroying the default loop will "orphan" (not stop) all registered
		3148	watchers, so you have to be careful not to execute code that modifies
		3149	those watchers. Note also that in that case, you have to re-register any
		3150	signal watchers.
		3151
1897	=head3 Watcher-Specific Functions and Data Members	3152	=head3 Watcher-Specific Functions and Data Members
1898		3153
1899	=over 4	3154	=over 4
1900		3155
1901	=item ev_fork_init (ev_signal *, callback)	3156	=item ev_fork_init (ev_fork *, callback)
1902		3157
1903	Initialises and configures the fork watcher - it has no parameters of any	3158	Initialises and configures the fork watcher - it has no parameters of any
1904	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3159	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
1905	believe me.	3160	really.
1906		3161
1907	=back	3162	=back
1908		3163
1909		3164
		3165	=head2 C<ev_cleanup> - even the best things end
		3166
		3167	Cleanup watchers are called just before the event loop is being destroyed
		3168	by a call to C<ev_loop_destroy>.
		3169
		3170	While there is no guarantee that the event loop gets destroyed, cleanup
		3171	watchers provide a convenient method to install cleanup hooks for your
		3172	program, worker threads and so on - you just to make sure to destroy the
		3173	loop when you want them to be invoked.
		3174
		3175	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3176	all other watchers, they do not keep a reference to the event loop (which
		3177	makes a lot of sense if you think about it). Like all other watchers, you
		3178	can call libev functions in the callback, except C<ev_cleanup_start>.
		3179
		3180	=head3 Watcher-Specific Functions and Data Members
		3181
		3182	=over 4
		3183
		3184	=item ev_cleanup_init (ev_cleanup *, callback)
		3185
		3186	Initialises and configures the cleanup watcher - it has no parameters of
		3187	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3188	pointless, I assure you.
		3189
		3190	=back
		3191
		3192	Example: Register an atexit handler to destroy the default loop, so any
		3193	cleanup functions are called.
		3194
		3195	static void
		3196	program_exits (void)
		3197	{
		3198	ev_loop_destroy (EV_DEFAULT_UC);
		3199	}
		3200
		3201	...
		3202	atexit (program_exits);
		3203
		3204
		3205	=head2 C<ev_async> - how to wake up an event loop
		3206
		3207	In general, you cannot use an C<ev_loop> from multiple threads or other
		3208	asynchronous sources such as signal handlers (as opposed to multiple event
		3209	loops - those are of course safe to use in different threads).
		3210
		3211	Sometimes, however, you need to wake up an event loop you do not control,
		3212	for example because it belongs to another thread. This is what C<ev_async>
		3213	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3214	it by calling C<ev_async_send>, which is thread- and signal safe.
		3215
		3216	This functionality is very similar to C<ev_signal> watchers, as signals,
		3217	too, are asynchronous in nature, and signals, too, will be compressed
		3218	(i.e. the number of callback invocations may be less than the number of
		3219	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3220	of "global async watchers" by using a watcher on an otherwise unused
		3221	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3222	even without knowing which loop owns the signal.
		3223
		3224	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3225	just the default loop.
		3226
		3227	=head3 Queueing
		3228
		3229	C<ev_async> does not support queueing of data in any way. The reason
		3230	is that the author does not know of a simple (or any) algorithm for a
		3231	multiple-writer-single-reader queue that works in all cases and doesn't
		3232	need elaborate support such as pthreads or unportable memory access
		3233	semantics.
		3234
		3235	That means that if you want to queue data, you have to provide your own
		3236	queue. But at least I can tell you how to implement locking around your
		3237	queue:
		3238
		3239	=over 4
		3240
		3241	=item queueing from a signal handler context
		3242
		3243	To implement race-free queueing, you simply add to the queue in the signal
		3244	handler but you block the signal handler in the watcher callback. Here is
		3245	an example that does that for some fictitious SIGUSR1 handler:
		3246
		3247	static ev_async mysig;
		3248
		3249	static void
		3250	sigusr1_handler (void)
		3251	{
		3252	sometype data;
		3253
		3254	// no locking etc.
		3255	queue_put (data);
		3256	ev_async_send (EV_DEFAULT_ &mysig);
		3257	}
		3258
		3259	static void
		3260	mysig_cb (EV_P_ ev_async *w, int revents)
		3261	{
		3262	sometype data;
		3263	sigset_t block, prev;
		3264
		3265	sigemptyset (&block);
		3266	sigaddset (&block, SIGUSR1);
		3267	sigprocmask (SIG_BLOCK, &block, &prev);
		3268
		3269	while (queue_get (&data))
		3270	process (data);
		3271
		3272	if (sigismember (&prev, SIGUSR1)
		3273	sigprocmask (SIG_UNBLOCK, &block, 0);
		3274	}
		3275
		3276	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3277	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3278	either...).
		3279
		3280	=item queueing from a thread context
		3281
		3282	The strategy for threads is different, as you cannot (easily) block
		3283	threads but you can easily preempt them, so to queue safely you need to
		3284	employ a traditional mutex lock, such as in this pthread example:
		3285
		3286	static ev_async mysig;
		3287	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3288
		3289	static void
		3290	otherthread (void)
		3291	{
		3292	// only need to lock the actual queueing operation
		3293	pthread_mutex_lock (&mymutex);
		3294	queue_put (data);
		3295	pthread_mutex_unlock (&mymutex);
		3296
		3297	ev_async_send (EV_DEFAULT_ &mysig);
		3298	}
		3299
		3300	static void
		3301	mysig_cb (EV_P_ ev_async *w, int revents)
		3302	{
		3303	pthread_mutex_lock (&mymutex);
		3304
		3305	while (queue_get (&data))
		3306	process (data);
		3307
		3308	pthread_mutex_unlock (&mymutex);
		3309	}
		3310
		3311	=back
		3312
		3313
		3314	=head3 Watcher-Specific Functions and Data Members
		3315
		3316	=over 4
		3317
		3318	=item ev_async_init (ev_async *, callback)
		3319
		3320	Initialises and configures the async watcher - it has no parameters of any
		3321	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3322	trust me.
		3323
		3324	=item ev_async_send (loop, ev_async *)
		3325
		3326	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3327	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3328	returns.
		3329
		3330	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3331	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3332	embedding section below on what exactly this means).
		3333
		3334	Note that, as with other watchers in libev, multiple events might get
		3335	compressed into a single callback invocation (another way to look at this
		3336	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3337	reset when the event loop detects that).
		3338
		3339	This call incurs the overhead of a system call only once per event loop
		3340	iteration, so while the overhead might be noticeable, it doesn't apply to
		3341	repeated calls to C<ev_async_send> for the same event loop.
		3342
		3343	=item bool = ev_async_pending (ev_async *)
		3344
		3345	Returns a non-zero value when C<ev_async_send> has been called on the
		3346	watcher but the event has not yet been processed (or even noted) by the
		3347	event loop.
		3348
		3349	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3350	the loop iterates next and checks for the watcher to have become active,
		3351	it will reset the flag again. C<ev_async_pending> can be used to very
		3352	quickly check whether invoking the loop might be a good idea.
		3353
		3354	Not that this does I<not> check whether the watcher itself is pending,
		3355	only whether it has been requested to make this watcher pending: there
		3356	is a time window between the event loop checking and resetting the async
		3357	notification, and the callback being invoked.
		3358
		3359	=back
		3360
		3361
1910	=head1 OTHER FUNCTIONS	3362	=head1 OTHER FUNCTIONS
1911		3363
1912	There are some other functions of possible interest. Described. Here. Now.	3364	There are some other functions of possible interest. Described. Here. Now.
1913		3365
1914	=over 4	3366	=over 4
1915		3367
1916	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3368	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1917		3369
1918	This function combines a simple timer and an I/O watcher, calls your	3370	This function combines a simple timer and an I/O watcher, calls your
1919	callback on whichever event happens first and automatically stop both	3371	callback on whichever event happens first and automatically stops both
1920	watchers. This is useful if you want to wait for a single event on an fd	3372	watchers. This is useful if you want to wait for a single event on an fd
1921	or timeout without having to allocate/configure/start/stop/free one or	3373	or timeout without having to allocate/configure/start/stop/free one or
1922	more watchers yourself.	3374	more watchers yourself.
1923		3375
1924	If C<fd> is less than 0, then no I/O watcher will be started and events	3376	If C<fd> is less than 0, then no I/O watcher will be started and the
1925	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3377	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1926	C<events> set will be craeted and started.	3378	the given C<fd> and C<events> set will be created and started.
1927		3379
1928	If C<timeout> is less than 0, then no timeout watcher will be	3380	If C<timeout> is less than 0, then no timeout watcher will be
1929	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3381	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1930	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3382	repeat = 0) will be started. C<0> is a valid timeout.
1931	dubious value.
1932		3383
1933	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3384	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1934	passed an C<revents> set like normal event callbacks (a combination of	3385	passed an C<revents> set like normal event callbacks (a combination of
1935	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3386	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1936	value passed to C<ev_once>:	3387	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3388	a timeout and an io event at the same time - you probably should give io
		3389	events precedence.
1937		3390
		3391	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3392
1938	static void stdin_ready (int revents, void *arg)	3393	static void stdin_ready (int revents, void *arg)
1939	{	3394	{
1940	if (revents & EV_TIMEOUT)
1941	/* doh, nothing entered */;
1942	else if (revents & EV_READ)	3395	if (revents & EV_READ)
1943	/* stdin might have data for us, joy! */;	3396	/* stdin might have data for us, joy! */;
		3397	else if (revents & EV_TIMER)
		3398	/* doh, nothing entered */;
1944	}	3399	}
1945		3400
1946	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3401	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1947		3402
1948	=item ev_feed_event (ev_loop *, watcher *, int revents)
1949
1950	Feeds the given event set into the event loop, as if the specified event
1951	had happened for the specified watcher (which must be a pointer to an
1952	initialised but not necessarily started event watcher).
1953
1954	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3403	=item ev_feed_fd_event (loop, int fd, int revents)
1955		3404
1956	Feed an event on the given fd, as if a file descriptor backend detected	3405	Feed an event on the given fd, as if a file descriptor backend detected
1957	the given events it.	3406	the given events it.
1958		3407
1959	=item ev_feed_signal_event (ev_loop *loop, int signum)	3408	=item ev_feed_signal_event (loop, int signum)
1960		3409
1961	Feed an event as if the given signal occured (C<loop> must be the default	3410	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
1962	loop!).	3411	which is async-safe.
1963		3412
1964	=back	3413	=back
		3414
		3415
		3416	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3417
		3418	This section explains some common idioms that are not immediately
		3419	obvious. Note that examples are sprinkled over the whole manual, and this
		3420	section only contains stuff that wouldn't fit anywhere else.
		3421
		3422	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3423
		3424	Each watcher has, by default, a C<void *data> member that you can read
		3425	or modify at any time: libev will completely ignore it. This can be used
		3426	to associate arbitrary data with your watcher. If you need more data and
		3427	don't want to allocate memory separately and store a pointer to it in that
		3428	data member, you can also "subclass" the watcher type and provide your own
		3429	data:
		3430
		3431	struct my_io
		3432	{
		3433	ev_io io;
		3434	int otherfd;
		3435	void *somedata;
		3436	struct whatever *mostinteresting;
		3437	};
		3438
		3439	...
		3440	struct my_io w;
		3441	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3442
		3443	And since your callback will be called with a pointer to the watcher, you
		3444	can cast it back to your own type:
		3445
		3446	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3447	{
		3448	struct my_io *w = (struct my_io *)w_;
		3449	...
		3450	}
		3451
		3452	More interesting and less C-conformant ways of casting your callback
		3453	function type instead have been omitted.
		3454
		3455	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3456
		3457	Another common scenario is to use some data structure with multiple
		3458	embedded watchers, in effect creating your own watcher that combines
		3459	multiple libev event sources into one "super-watcher":
		3460
		3461	struct my_biggy
		3462	{
		3463	int some_data;
		3464	ev_timer t1;
		3465	ev_timer t2;
		3466	}
		3467
		3468	In this case getting the pointer to C<my_biggy> is a bit more
		3469	complicated: Either you store the address of your C<my_biggy> struct in
		3470	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3471	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3472	real programmers):
		3473
		3474	#include <stddef.h>
		3475
		3476	static void
		3477	t1_cb (EV_P_ ev_timer *w, int revents)
		3478	{
		3479	struct my_biggy big = (struct my_biggy *)
		3480	(((char *)w) - offsetof (struct my_biggy, t1));
		3481	}
		3482
		3483	static void
		3484	t2_cb (EV_P_ ev_timer *w, int revents)
		3485	{
		3486	struct my_biggy big = (struct my_biggy *)
		3487	(((char *)w) - offsetof (struct my_biggy, t2));
		3488	}
		3489
		3490	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3491
		3492	Often (especially in GUI toolkits) there are places where you have
		3493	I<modal> interaction, which is most easily implemented by recursively
		3494	invoking C<ev_run>.
		3495
		3496	This brings the problem of exiting - a callback might want to finish the
		3497	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3498	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3499	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3500	other combination: In these cases, C<ev_break> will not work alone.
		3501
		3502	The solution is to maintain "break this loop" variable for each C<ev_run>
		3503	invocation, and use a loop around C<ev_run> until the condition is
		3504	triggered, using C<EVRUN_ONCE>:
		3505
		3506	// main loop
		3507	int exit_main_loop = 0;
		3508
		3509	while (!exit_main_loop)
		3510	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3511
		3512	// in a model watcher
		3513	int exit_nested_loop = 0;
		3514
		3515	while (!exit_nested_loop)
		3516	ev_run (EV_A_ EVRUN_ONCE);
		3517
		3518	To exit from any of these loops, just set the corresponding exit variable:
		3519
		3520	// exit modal loop
		3521	exit_nested_loop = 1;
		3522
		3523	// exit main program, after modal loop is finished
		3524	exit_main_loop = 1;
		3525
		3526	// exit both
		3527	exit_main_loop = exit_nested_loop = 1;
		3528
		3529	=head2 THREAD LOCKING EXAMPLE
		3530
		3531	Here is a fictitious example of how to run an event loop in a different
		3532	thread from where callbacks are being invoked and watchers are
		3533	created/added/removed.
		3534
		3535	For a real-world example, see the C<EV::Loop::Async> perl module,
		3536	which uses exactly this technique (which is suited for many high-level
		3537	languages).
		3538
		3539	The example uses a pthread mutex to protect the loop data, a condition
		3540	variable to wait for callback invocations, an async watcher to notify the
		3541	event loop thread and an unspecified mechanism to wake up the main thread.
		3542
		3543	First, you need to associate some data with the event loop:
		3544
		3545	typedef struct {
		3546	mutex_t lock; /* global loop lock */
		3547	ev_async async_w;
		3548	thread_t tid;
		3549	cond_t invoke_cv;
		3550	} userdata;
		3551
		3552	void prepare_loop (EV_P)
		3553	{
		3554	// for simplicity, we use a static userdata struct.
		3555	static userdata u;
		3556
		3557	ev_async_init (&u->async_w, async_cb);
		3558	ev_async_start (EV_A_ &u->async_w);
		3559
		3560	pthread_mutex_init (&u->lock, 0);
		3561	pthread_cond_init (&u->invoke_cv, 0);
		3562
		3563	// now associate this with the loop
		3564	ev_set_userdata (EV_A_ u);
		3565	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3566	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3567
		3568	// then create the thread running ev_run
		3569	pthread_create (&u->tid, 0, l_run, EV_A);
		3570	}
		3571
		3572	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3573	solely to wake up the event loop so it takes notice of any new watchers
		3574	that might have been added:
		3575
		3576	static void
		3577	async_cb (EV_P_ ev_async *w, int revents)
		3578	{
		3579	// just used for the side effects
		3580	}
		3581
		3582	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3583	protecting the loop data, respectively.
		3584
		3585	static void
		3586	l_release (EV_P)
		3587	{
		3588	userdata *u = ev_userdata (EV_A);
		3589	pthread_mutex_unlock (&u->lock);
		3590	}
		3591
		3592	static void
		3593	l_acquire (EV_P)
		3594	{
		3595	userdata *u = ev_userdata (EV_A);
		3596	pthread_mutex_lock (&u->lock);
		3597	}
		3598
		3599	The event loop thread first acquires the mutex, and then jumps straight
		3600	into C<ev_run>:
		3601
		3602	void *
		3603	l_run (void *thr_arg)
		3604	{
		3605	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3606
		3607	l_acquire (EV_A);
		3608	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3609	ev_run (EV_A_ 0);
		3610	l_release (EV_A);
		3611
		3612	return 0;
		3613	}
		3614
		3615	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3616	signal the main thread via some unspecified mechanism (signals? pipe
		3617	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3618	have been called (in a while loop because a) spurious wakeups are possible
		3619	and b) skipping inter-thread-communication when there are no pending
		3620	watchers is very beneficial):
		3621
		3622	static void
		3623	l_invoke (EV_P)
		3624	{
		3625	userdata *u = ev_userdata (EV_A);
		3626
		3627	while (ev_pending_count (EV_A))
		3628	{
		3629	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3630	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3631	}
		3632	}
		3633
		3634	Now, whenever the main thread gets told to invoke pending watchers, it
		3635	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3636	thread to continue:
		3637
		3638	static void
		3639	real_invoke_pending (EV_P)
		3640	{
		3641	userdata *u = ev_userdata (EV_A);
		3642
		3643	pthread_mutex_lock (&u->lock);
		3644	ev_invoke_pending (EV_A);
		3645	pthread_cond_signal (&u->invoke_cv);
		3646	pthread_mutex_unlock (&u->lock);
		3647	}
		3648
		3649	Whenever you want to start/stop a watcher or do other modifications to an
		3650	event loop, you will now have to lock:
		3651
		3652	ev_timer timeout_watcher;
		3653	userdata *u = ev_userdata (EV_A);
		3654
		3655	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3656
		3657	pthread_mutex_lock (&u->lock);
		3658	ev_timer_start (EV_A_ &timeout_watcher);
		3659	ev_async_send (EV_A_ &u->async_w);
		3660	pthread_mutex_unlock (&u->lock);
		3661
		3662	Note that sending the C<ev_async> watcher is required because otherwise
		3663	an event loop currently blocking in the kernel will have no knowledge
		3664	about the newly added timer. By waking up the loop it will pick up any new
		3665	watchers in the next event loop iteration.
		3666
		3667	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3668
		3669	While the overhead of a callback that e.g. schedules a thread is small, it
		3670	is still an overhead. If you embed libev, and your main usage is with some
		3671	kind of threads or coroutines, you might want to customise libev so that
		3672	doesn't need callbacks anymore.
		3673
		3674	Imagine you have coroutines that you can switch to using a function
		3675	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3676	and that due to some magic, the currently active coroutine is stored in a
		3677	global called C<current_coro>. Then you can build your own "wait for libev
		3678	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3679	the differing C<;> conventions):
		3680
		3681	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3682	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3683
		3684	That means instead of having a C callback function, you store the
		3685	coroutine to switch to in each watcher, and instead of having libev call
		3686	your callback, you instead have it switch to that coroutine.
		3687
		3688	A coroutine might now wait for an event with a function called
		3689	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3690	matter when, or whether the watcher is active or not when this function is
		3691	called):
		3692
		3693	void
		3694	wait_for_event (ev_watcher *w)
		3695	{
		3696	ev_cb_set (w) = current_coro;
		3697	switch_to (libev_coro);
		3698	}
		3699
		3700	That basically suspends the coroutine inside C<wait_for_event> and
		3701	continues the libev coroutine, which, when appropriate, switches back to
		3702	this or any other coroutine. I am sure if you sue this your own :)
		3703
		3704	You can do similar tricks if you have, say, threads with an event queue -
		3705	instead of storing a coroutine, you store the queue object and instead of
		3706	switching to a coroutine, you push the watcher onto the queue and notify
		3707	any waiters.
		3708
		3709	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3710	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3711
		3712	// my_ev.h
		3713	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3714	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3715	#include "../libev/ev.h"
		3716
		3717	// my_ev.c
		3718	#define EV_H "my_ev.h"
		3719	#include "../libev/ev.c"
		3720
		3721	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3722	F<my_ev.c> into your project. When properly specifying include paths, you
		3723	can even use F<ev.h> as header file name directly.
1965		3724
1966		3725
1967	=head1 LIBEVENT EMULATION	3726	=head1 LIBEVENT EMULATION
1968		3727
1969	Libev offers a compatibility emulation layer for libevent. It cannot	3728	Libev offers a compatibility emulation layer for libevent. It cannot
1970	emulate the internals of libevent, so here are some usage hints:	3729	emulate the internals of libevent, so here are some usage hints:
1971		3730
1972	=over 4	3731	=over 4
		3732
		3733	=item * Only the libevent-1.4.1-beta API is being emulated.
		3734
		3735	This was the newest libevent version available when libev was implemented,
		3736	and is still mostly unchanged in 2010.
1973		3737
1974	=item * Use it by including <event.h>, as usual.	3738	=item * Use it by including <event.h>, as usual.
1975		3739
1976	=item * The following members are fully supported: ev_base, ev_callback,	3740	=item * The following members are fully supported: ev_base, ev_callback,
1977	ev_arg, ev_fd, ev_res, ev_events.	3741	ev_arg, ev_fd, ev_res, ev_events.
…		…
1982		3746
1983	=item * Priorities are not currently supported. Initialising priorities	3747	=item * Priorities are not currently supported. Initialising priorities
1984	will fail and all watchers will have the same priority, even though there	3748	will fail and all watchers will have the same priority, even though there
1985	is an ev_pri field.	3749	is an ev_pri field.
1986		3750
		3751	=item * In libevent, the last base created gets the signals, in libev, the
		3752	base that registered the signal gets the signals.
		3753
1987	=item * Other members are not supported.	3754	=item * Other members are not supported.
1988		3755
1989	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3756	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1990	to use the libev header file and library.	3757	to use the libev header file and library.
1991		3758
1992	=back	3759	=back
1993		3760
1994	=head1 C++ SUPPORT	3761	=head1 C++ SUPPORT
1995		3762
1996	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3763	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1997	you to use some convinience methods to start/stop watchers and also change	3764	you to use some convenience methods to start/stop watchers and also change
1998	the callback model to a model using method callbacks on objects.	3765	the callback model to a model using method callbacks on objects.
1999		3766
2000	To use it,	3767	To use it,
2001		3768
2002	#include <ev++.h>	3769	#include <ev++.h>
2003		3770
2004	This automatically includes F<ev.h> and puts all of its definitions (many	3771	This automatically includes F<ev.h> and puts all of its definitions (many
2005	of them macros) into the global namespace. All C++ specific things are	3772	of them macros) into the global namespace. All C++ specific things are
2006	put into the C<ev> namespace. It should support all the same embedding	3773	put into the C<ev> namespace. It should support all the same embedding
2007	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3774	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2009	Care has been taken to keep the overhead low. The only data member the C++	3776	Care has been taken to keep the overhead low. The only data member the C++
2010	classes add (compared to plain C-style watchers) is the event loop pointer	3777	classes add (compared to plain C-style watchers) is the event loop pointer
2011	that the watcher is associated with (or no additional members at all if	3778	that the watcher is associated with (or no additional members at all if
2012	you disable C<EV_MULTIPLICITY> when embedding libev).	3779	you disable C<EV_MULTIPLICITY> when embedding libev).
2013		3780
2014	Currently, functions, and static and non-static member functions can be	3781	Currently, functions, static and non-static member functions and classes
2015	used as callbacks. Other types should be easy to add as long as they only	3782	with C<operator ()> can be used as callbacks. Other types should be easy
2016	need one additional pointer for context. If you need support for other	3783	to add as long as they only need one additional pointer for context. If
2017	types of functors please contact the author (preferably after implementing	3784	you need support for other types of functors please contact the author
2018	it).	3785	(preferably after implementing it).
2019		3786
2020	Here is a list of things available in the C<ev> namespace:	3787	Here is a list of things available in the C<ev> namespace:
2021		3788
2022	=over 4	3789	=over 4
2023		3790
…		…
2041		3808
2042	=over 4	3809	=over 4
2043		3810
2044	=item ev::TYPE::TYPE ()	3811	=item ev::TYPE::TYPE ()
2045		3812
2046	=item ev::TYPE::TYPE (struct ev_loop *)	3813	=item ev::TYPE::TYPE (loop)
2047		3814
2048	=item ev::TYPE::~TYPE	3815	=item ev::TYPE::~TYPE
2049		3816
2050	The constructor (optionally) takes an event loop to associate the watcher	3817	The constructor (optionally) takes an event loop to associate the watcher
2051	with. If it is omitted, it will use C<EV_DEFAULT>.	3818	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2074	your compiler is good :), then the method will be fully inlined into the	3841	your compiler is good :), then the method will be fully inlined into the
2075	thunking function, making it as fast as a direct C callback.	3842	thunking function, making it as fast as a direct C callback.
2076		3843
2077	Example: simple class declaration and watcher initialisation	3844	Example: simple class declaration and watcher initialisation
2078		3845
2079	struct myclass	3846	struct myclass
2080	{	3847	{
2081	void io_cb (ev::io &w, int revents) { }	3848	void io_cb (ev::io &w, int revents) { }
2082	}	3849	}
2083		3850
2084	myclass obj;	3851	myclass obj;
2085	ev::io iow;	3852	ev::io iow;
2086	iow.set <myclass, &myclass::io_cb> (&obj);	3853	iow.set <myclass, &myclass::io_cb> (&obj);
		3854
		3855	=item w->set (object *)
		3856
		3857	This is a variation of a method callback - leaving out the method to call
		3858	will default the method to C<operator ()>, which makes it possible to use
		3859	functor objects without having to manually specify the C<operator ()> all
		3860	the time. Incidentally, you can then also leave out the template argument
		3861	list.
		3862
		3863	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3864	int revents)>.
		3865
		3866	See the method-C<set> above for more details.
		3867
		3868	Example: use a functor object as callback.
		3869
		3870	struct myfunctor
		3871	{
		3872	void operator() (ev::io &w, int revents)
		3873	{
		3874	...
		3875	}
		3876	}
		3877
		3878	myfunctor f;
		3879
		3880	ev::io w;
		3881	w.set (&f);
2087		3882
2088	=item w->set<function> (void *data = 0)	3883	=item w->set<function> (void *data = 0)
2089		3884
2090	Also sets a callback, but uses a static method or plain function as	3885	Also sets a callback, but uses a static method or plain function as
2091	callback. The optional C<data> argument will be stored in the watcher's	3886	callback. The optional C<data> argument will be stored in the watcher's
…		…
2093		3888
2094	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3889	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2095		3890
2096	See the method-C<set> above for more details.	3891	See the method-C<set> above for more details.
2097		3892
2098	Example:	3893	Example: Use a plain function as callback.
2099		3894
2100	static void io_cb (ev::io &w, int revents) { }	3895	static void io_cb (ev::io &w, int revents) { }
2101	iow.set <io_cb> ();	3896	iow.set <io_cb> ();
2102		3897
2103	=item w->set (struct ev_loop *)	3898	=item w->set (loop)
2104		3899
2105	Associates a different C<struct ev_loop> with this watcher. You can only	3900	Associates a different C<struct ev_loop> with this watcher. You can only
2106	do this when the watcher is inactive (and not pending either).	3901	do this when the watcher is inactive (and not pending either).
2107		3902
2108	=item w->set ([args])	3903	=item w->set ([arguments])
2109		3904
2110	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3905	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2111	called at least once. Unlike the C counterpart, an active watcher gets	3906	method or a suitable start method must be called at least once. Unlike the
2112	automatically stopped and restarted when reconfiguring it with this	3907	C counterpart, an active watcher gets automatically stopped and restarted
2113	method.	3908	when reconfiguring it with this method.
2114		3909
2115	=item w->start ()	3910	=item w->start ()
2116		3911
2117	Starts the watcher. Note that there is no C<loop> argument, as the	3912	Starts the watcher. Note that there is no C<loop> argument, as the
2118	constructor already stores the event loop.	3913	constructor already stores the event loop.
2119		3914
		3915	=item w->start ([arguments])
		3916
		3917	Instead of calling C<set> and C<start> methods separately, it is often
		3918	convenient to wrap them in one call. Uses the same type of arguments as
		3919	the configure C<set> method of the watcher.
		3920
2120	=item w->stop ()	3921	=item w->stop ()
2121		3922
2122	Stops the watcher if it is active. Again, no C<loop> argument.	3923	Stops the watcher if it is active. Again, no C<loop> argument.
2123		3924
2124	=item w->again () (C<ev::timer>, C<ev::periodic> only)	3925	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2136		3937
2137	=back	3938	=back
2138		3939
2139	=back	3940	=back
2140		3941
2141	Example: Define a class with an IO and idle watcher, start one of them in	3942	Example: Define a class with two I/O and idle watchers, start the I/O
2142	the constructor.	3943	watchers in the constructor.
2143		3944
2144	class myclass	3945	class myclass
2145	{	3946	{
2146	ev_io io; void io_cb (ev::io &w, int revents);	3947	ev::io io ; void io_cb (ev::io &w, int revents);
		3948	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
2147	ev_idle idle void idle_cb (ev::idle &w, int revents);	3949	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2148		3950
2149	myclass ();	3951	myclass (int fd)
2150	}	3952	{
2151
2152	myclass::myclass (int fd)
2153	{
2154	io .set <myclass, &myclass::io_cb > (this);	3953	io .set <myclass, &myclass::io_cb > (this);
		3954	io2 .set <myclass, &myclass::io2_cb > (this);
2155	idle.set <myclass, &myclass::idle_cb> (this);	3955	idle.set <myclass, &myclass::idle_cb> (this);
2156		3956
2157	io.start (fd, ev::READ);	3957	io.set (fd, ev::WRITE); // configure the watcher
		3958	io.start (); // start it whenever convenient
		3959
		3960	io2.start (fd, ev::READ); // set + start in one call
		3961	}
2158	}	3962	};
		3963
		3964
		3965	=head1 OTHER LANGUAGE BINDINGS
		3966
		3967	Libev does not offer other language bindings itself, but bindings for a
		3968	number of languages exist in the form of third-party packages. If you know
		3969	any interesting language binding in addition to the ones listed here, drop
		3970	me a note.
		3971
		3972	=over 4
		3973
		3974	=item Perl
		3975
		3976	The EV module implements the full libev API and is actually used to test
		3977	libev. EV is developed together with libev. Apart from the EV core module,
		3978	there are additional modules that implement libev-compatible interfaces
		3979	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3980	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3981	and C<EV::Glib>).
		3982
		3983	It can be found and installed via CPAN, its homepage is at
		3984	L<http://software.schmorp.de/pkg/EV>.
		3985
		3986	=item Python
		3987
		3988	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3989	seems to be quite complete and well-documented.
		3990
		3991	=item Ruby
		3992
		3993	Tony Arcieri has written a ruby extension that offers access to a subset
		3994	of the libev API and adds file handle abstractions, asynchronous DNS and
		3995	more on top of it. It can be found via gem servers. Its homepage is at
		3996	L<http://rev.rubyforge.org/>.
		3997
		3998	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3999	makes rev work even on mingw.
		4000
		4001	=item Haskell
		4002
		4003	A haskell binding to libev is available at
		4004	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4005
		4006	=item D
		4007
		4008	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4009	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		4010
		4011	=item Ocaml
		4012
		4013	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4014	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4015
		4016	=item Lua
		4017
		4018	Brian Maher has written a partial interface to libev for lua (at the
		4019	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4020	L<http://github.com/brimworks/lua-ev>.
		4021
		4022	=back
2159		4023
2160		4024
2161	=head1 MACRO MAGIC	4025	=head1 MACRO MAGIC
2162		4026
2163	Libev can be compiled with a variety of options, the most fundamantal	4027	Libev can be compiled with a variety of options, the most fundamental
2164	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	4028	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2165	functions and callbacks have an initial C<struct ev_loop *> argument.	4029	functions and callbacks have an initial C<struct ev_loop *> argument.
2166		4030
2167	To make it easier to write programs that cope with either variant, the	4031	To make it easier to write programs that cope with either variant, the
2168	following macros are defined:	4032	following macros are defined:
…		…
2173		4037
2174	This provides the loop I<argument> for functions, if one is required ("ev	4038	This provides the loop I<argument> for functions, if one is required ("ev
2175	loop argument"). The C<EV_A> form is used when this is the sole argument,	4039	loop argument"). The C<EV_A> form is used when this is the sole argument,
2176	C<EV_A_> is used when other arguments are following. Example:	4040	C<EV_A_> is used when other arguments are following. Example:
2177		4041
2178	ev_unref (EV_A);	4042	ev_unref (EV_A);
2179	ev_timer_add (EV_A_ watcher);	4043	ev_timer_add (EV_A_ watcher);
2180	ev_loop (EV_A_ 0);	4044	ev_run (EV_A_ 0);
2181		4045
2182	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4046	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2183	which is often provided by the following macro.	4047	which is often provided by the following macro.
2184		4048
2185	=item C<EV_P>, C<EV_P_>	4049	=item C<EV_P>, C<EV_P_>
2186		4050
2187	This provides the loop I<parameter> for functions, if one is required ("ev	4051	This provides the loop I<parameter> for functions, if one is required ("ev
2188	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	4052	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2189	C<EV_P_> is used when other parameters are following. Example:	4053	C<EV_P_> is used when other parameters are following. Example:
2190		4054
2191	// this is how ev_unref is being declared	4055	// this is how ev_unref is being declared
2192	static void ev_unref (EV_P);	4056	static void ev_unref (EV_P);
2193		4057
2194	// this is how you can declare your typical callback	4058	// this is how you can declare your typical callback
2195	static void cb (EV_P_ ev_timer *w, int revents)	4059	static void cb (EV_P_ ev_timer *w, int revents)
2196		4060
2197	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	4061	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2198	suitable for use with C<EV_A>.	4062	suitable for use with C<EV_A>.
2199		4063
2200	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4064	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2201		4065
2202	Similar to the other two macros, this gives you the value of the default	4066	Similar to the other two macros, this gives you the value of the default
2203	loop, if multiple loops are supported ("ev loop default").	4067	loop, if multiple loops are supported ("ev loop default").
		4068
		4069	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4070
		4071	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4072	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4073	is undefined when the default loop has not been initialised by a previous
		4074	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4075
		4076	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4077	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2204		4078
2205	=back	4079	=back
2206		4080
2207	Example: Declare and initialise a check watcher, utilising the above	4081	Example: Declare and initialise a check watcher, utilising the above
2208	macros so it will work regardless of whether multiple loops are supported	4082	macros so it will work regardless of whether multiple loops are supported
2209	or not.	4083	or not.
2210		4084
2211	static void	4085	static void
2212	check_cb (EV_P_ ev_timer *w, int revents)	4086	check_cb (EV_P_ ev_timer *w, int revents)
2213	{	4087	{
2214	ev_check_stop (EV_A_ w);	4088	ev_check_stop (EV_A_ w);
2215	}	4089	}
2216		4090
2217	ev_check check;	4091	ev_check check;
2218	ev_check_init (&check, check_cb);	4092	ev_check_init (&check, check_cb);
2219	ev_check_start (EV_DEFAULT_ &check);	4093	ev_check_start (EV_DEFAULT_ &check);
2220	ev_loop (EV_DEFAULT_ 0);	4094	ev_run (EV_DEFAULT_ 0);
2221		4095
2222	=head1 EMBEDDING	4096	=head1 EMBEDDING
2223		4097
2224	Libev can (and often is) directly embedded into host	4098	Libev can (and often is) directly embedded into host
2225	applications. Examples of applications that embed it include the Deliantra	4099	applications. Examples of applications that embed it include the Deliantra
…		…
2232	libev somewhere in your source tree).	4106	libev somewhere in your source tree).
2233		4107
2234	=head2 FILESETS	4108	=head2 FILESETS
2235		4109
2236	Depending on what features you need you need to include one or more sets of files	4110	Depending on what features you need you need to include one or more sets of files
2237	in your app.	4111	in your application.
2238		4112
2239	=head3 CORE EVENT LOOP	4113	=head3 CORE EVENT LOOP
2240		4114
2241	To include only the libev core (all the C<ev_*> functions), with manual	4115	To include only the libev core (all the C<ev_*> functions), with manual
2242	configuration (no autoconf):	4116	configuration (no autoconf):
2243		4117
2244	#define EV_STANDALONE 1	4118	#define EV_STANDALONE 1
2245	#include "ev.c"	4119	#include "ev.c"
2246		4120
2247	This will automatically include F<ev.h>, too, and should be done in a	4121	This will automatically include F<ev.h>, too, and should be done in a
2248	single C source file only to provide the function implementations. To use	4122	single C source file only to provide the function implementations. To use
2249	it, do the same for F<ev.h> in all files wishing to use this API (best	4123	it, do the same for F<ev.h> in all files wishing to use this API (best
2250	done by writing a wrapper around F<ev.h> that you can include instead and	4124	done by writing a wrapper around F<ev.h> that you can include instead and
2251	where you can put other configuration options):	4125	where you can put other configuration options):
2252		4126
2253	#define EV_STANDALONE 1	4127	#define EV_STANDALONE 1
2254	#include "ev.h"	4128	#include "ev.h"
2255		4129
2256	Both header files and implementation files can be compiled with a C++	4130	Both header files and implementation files can be compiled with a C++
2257	compiler (at least, thats a stated goal, and breakage will be treated	4131	compiler (at least, that's a stated goal, and breakage will be treated
2258	as a bug).	4132	as a bug).
2259		4133
2260	You need the following files in your source tree, or in a directory	4134	You need the following files in your source tree, or in a directory
2261	in your include path (e.g. in libev/ when using -Ilibev):	4135	in your include path (e.g. in libev/ when using -Ilibev):
2262		4136
2263	ev.h	4137	ev.h
2264	ev.c	4138	ev.c
2265	ev_vars.h	4139	ev_vars.h
2266	ev_wrap.h	4140	ev_wrap.h
2267		4141
2268	ev_win32.c required on win32 platforms only	4142	ev_win32.c required on win32 platforms only
2269		4143
2270	ev_select.c only when select backend is enabled (which is enabled by default)	4144	ev_select.c only when select backend is enabled (which is enabled by default)
2271	ev_poll.c only when poll backend is enabled (disabled by default)	4145	ev_poll.c only when poll backend is enabled (disabled by default)
2272	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4146	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2273	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4147	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2274	ev_port.c only when the solaris port backend is enabled (disabled by default)	4148	ev_port.c only when the solaris port backend is enabled (disabled by default)
2275		4149
2276	F<ev.c> includes the backend files directly when enabled, so you only need	4150	F<ev.c> includes the backend files directly when enabled, so you only need
2277	to compile this single file.	4151	to compile this single file.
2278		4152
2279	=head3 LIBEVENT COMPATIBILITY API	4153	=head3 LIBEVENT COMPATIBILITY API
2280		4154
2281	To include the libevent compatibility API, also include:	4155	To include the libevent compatibility API, also include:
2282		4156
2283	#include "event.c"	4157	#include "event.c"
2284		4158
2285	in the file including F<ev.c>, and:	4159	in the file including F<ev.c>, and:
2286		4160
2287	#include "event.h"	4161	#include "event.h"
2288		4162
2289	in the files that want to use the libevent API. This also includes F<ev.h>.	4163	in the files that want to use the libevent API. This also includes F<ev.h>.
2290		4164
2291	You need the following additional files for this:	4165	You need the following additional files for this:
2292		4166
2293	event.h	4167	event.h
2294	event.c	4168	event.c
2295		4169
2296	=head3 AUTOCONF SUPPORT	4170	=head3 AUTOCONF SUPPORT
2297		4171
2298	Instead of using C<EV_STANDALONE=1> and providing your config in	4172	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2299	whatever way you want, you can also C<m4_include([libev.m4])> in your	4173	whatever way you want, you can also C<m4_include([libev.m4])> in your
2300	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4174	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2301	include F<config.h> and configure itself accordingly.	4175	include F<config.h> and configure itself accordingly.
2302		4176
2303	For this of course you need the m4 file:	4177	For this of course you need the m4 file:
2304		4178
2305	libev.m4	4179	libev.m4
2306		4180
2307	=head2 PREPROCESSOR SYMBOLS/MACROS	4181	=head2 PREPROCESSOR SYMBOLS/MACROS
2308		4182
2309	Libev can be configured via a variety of preprocessor symbols you have to define	4183	Libev can be configured via a variety of preprocessor symbols you have to
2310	before including any of its files. The default is not to build for multiplicity	4184	define before including (or compiling) any of its files. The default in
2311	and only include the select backend.	4185	the absence of autoconf is documented for every option.
		4186
		4187	Symbols marked with "(h)" do not change the ABI, and can have different
		4188	values when compiling libev vs. including F<ev.h>, so it is permissible
		4189	to redefine them before including F<ev.h> without breaking compatibility
		4190	to a compiled library. All other symbols change the ABI, which means all
		4191	users of libev and the libev code itself must be compiled with compatible
		4192	settings.
2312		4193
2313	=over 4	4194	=over 4
2314		4195
		4196	=item EV_COMPAT3 (h)
		4197
		4198	Backwards compatibility is a major concern for libev. This is why this
		4199	release of libev comes with wrappers for the functions and symbols that
		4200	have been renamed between libev version 3 and 4.
		4201
		4202	You can disable these wrappers (to test compatibility with future
		4203	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4204	sources. This has the additional advantage that you can drop the C<struct>
		4205	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4206	typedef in that case.
		4207
		4208	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4209	and in some even more future version the compatibility code will be
		4210	removed completely.
		4211
2315	=item EV_STANDALONE	4212	=item EV_STANDALONE (h)
2316		4213
2317	Must always be C<1> if you do not use autoconf configuration, which	4214	Must always be C<1> if you do not use autoconf configuration, which
2318	keeps libev from including F<config.h>, and it also defines dummy	4215	keeps libev from including F<config.h>, and it also defines dummy
2319	implementations for some libevent functions (such as logging, which is not	4216	implementations for some libevent functions (such as logging, which is not
2320	supported). It will also not define any of the structs usually found in	4217	supported). It will also not define any of the structs usually found in
2321	F<event.h> that are not directly supported by the libev core alone.	4218	F<event.h> that are not directly supported by the libev core alone.
2322		4219
		4220	In standalone mode, libev will still try to automatically deduce the
		4221	configuration, but has to be more conservative.
		4222
		4223	=item EV_USE_FLOOR
		4224
		4225	If defined to be C<1>, libev will use the C<floor ()> function for its
		4226	periodic reschedule calculations, otherwise libev will fall back on a
		4227	portable (slower) implementation. If you enable this, you usually have to
		4228	link against libm or something equivalent. Enabling this when the C<floor>
		4229	function is not available will fail, so the safe default is to not enable
		4230	this.
		4231
2323	=item EV_USE_MONOTONIC	4232	=item EV_USE_MONOTONIC
2324		4233
2325	If defined to be C<1>, libev will try to detect the availability of the	4234	If defined to be C<1>, libev will try to detect the availability of the
2326	monotonic clock option at both compiletime and runtime. Otherwise no use	4235	monotonic clock option at both compile time and runtime. Otherwise no
2327	of the monotonic clock option will be attempted. If you enable this, you	4236	use of the monotonic clock option will be attempted. If you enable this,
2328	usually have to link against librt or something similar. Enabling it when	4237	you usually have to link against librt or something similar. Enabling it
2329	the functionality isn't available is safe, though, although you have	4238	when the functionality isn't available is safe, though, although you have
2330	to make sure you link against any libraries where the C<clock_gettime>	4239	to make sure you link against any libraries where the C<clock_gettime>
2331	function is hiding in (often F<-lrt>).	4240	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2332		4241
2333	=item EV_USE_REALTIME	4242	=item EV_USE_REALTIME
2334		4243
2335	If defined to be C<1>, libev will try to detect the availability of the	4244	If defined to be C<1>, libev will try to detect the availability of the
2336	realtime clock option at compiletime (and assume its availability at	4245	real-time clock option at compile time (and assume its availability
2337	runtime if successful). Otherwise no use of the realtime clock option will	4246	at runtime if successful). Otherwise no use of the real-time clock
2338	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4247	option will be attempted. This effectively replaces C<gettimeofday>
2339	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4248	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2340	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4249	correctness. See the note about libraries in the description of
		4250	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4251	C<EV_USE_CLOCK_SYSCALL>.
		4252
		4253	=item EV_USE_CLOCK_SYSCALL
		4254
		4255	If defined to be C<1>, libev will try to use a direct syscall instead
		4256	of calling the system-provided C<clock_gettime> function. This option
		4257	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4258	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4259	programs needlessly. Using a direct syscall is slightly slower (in
		4260	theory), because no optimised vdso implementation can be used, but avoids
		4261	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4262	higher, as it simplifies linking (no need for C<-lrt>).
2341		4263
2342	=item EV_USE_NANOSLEEP	4264	=item EV_USE_NANOSLEEP
2343		4265
2344	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4266	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2345	and will use it for delays. Otherwise it will use C<select ()>.	4267	and will use it for delays. Otherwise it will use C<select ()>.
2346		4268
		4269	=item EV_USE_EVENTFD
		4270
		4271	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4272	available and will probe for kernel support at runtime. This will improve
		4273	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4274	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4275	2.7 or newer, otherwise disabled.
		4276
2347	=item EV_USE_SELECT	4277	=item EV_USE_SELECT
2348		4278
2349	If undefined or defined to be C<1>, libev will compile in support for the	4279	If undefined or defined to be C<1>, libev will compile in support for the
2350	C<select>(2) backend. No attempt at autodetection will be done: if no	4280	C<select>(2) backend. No attempt at auto-detection will be done: if no
2351	other method takes over, select will be it. Otherwise the select backend	4281	other method takes over, select will be it. Otherwise the select backend
2352	will not be compiled in.	4282	will not be compiled in.
2353		4283
2354	=item EV_SELECT_USE_FD_SET	4284	=item EV_SELECT_USE_FD_SET
2355		4285
2356	If defined to C<1>, then the select backend will use the system C<fd_set>	4286	If defined to C<1>, then the select backend will use the system C<fd_set>
2357	structure. This is useful if libev doesn't compile due to a missing	4287	structure. This is useful if libev doesn't compile due to a missing
2358	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4288	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2359	exotic systems. This usually limits the range of file descriptors to some	4289	on exotic systems. This usually limits the range of file descriptors to
2360	low limit such as 1024 or might have other limitations (winsocket only	4290	some low limit such as 1024 or might have other limitations (winsocket
2361	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4291	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2362	influence the size of the C<fd_set> used.	4292	configures the maximum size of the C<fd_set>.
2363		4293
2364	=item EV_SELECT_IS_WINSOCKET	4294	=item EV_SELECT_IS_WINSOCKET
2365		4295
2366	When defined to C<1>, the select backend will assume that	4296	When defined to C<1>, the select backend will assume that
2367	select/socket/connect etc. don't understand file descriptors but	4297	select/socket/connect etc. don't understand file descriptors but
…		…
2369	be used is the winsock select). This means that it will call	4299	be used is the winsock select). This means that it will call
2370	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4300	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2371	it is assumed that all these functions actually work on fds, even	4301	it is assumed that all these functions actually work on fds, even
2372	on win32. Should not be defined on non-win32 platforms.	4302	on win32. Should not be defined on non-win32 platforms.
2373		4303
		4304	=item EV_FD_TO_WIN32_HANDLE(fd)
		4305
		4306	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4307	file descriptors to socket handles. When not defining this symbol (the
		4308	default), then libev will call C<_get_osfhandle>, which is usually
		4309	correct. In some cases, programs use their own file descriptor management,
		4310	in which case they can provide this function to map fds to socket handles.
		4311
		4312	=item EV_WIN32_HANDLE_TO_FD(handle)
		4313
		4314	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4315	using the standard C<_open_osfhandle> function. For programs implementing
		4316	their own fd to handle mapping, overwriting this function makes it easier
		4317	to do so. This can be done by defining this macro to an appropriate value.
		4318
		4319	=item EV_WIN32_CLOSE_FD(fd)
		4320
		4321	If programs implement their own fd to handle mapping on win32, then this
		4322	macro can be used to override the C<close> function, useful to unregister
		4323	file descriptors again. Note that the replacement function has to close
		4324	the underlying OS handle.
		4325
2374	=item EV_USE_POLL	4326	=item EV_USE_POLL
2375		4327
2376	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4328	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2377	backend. Otherwise it will be enabled on non-win32 platforms. It	4329	backend. Otherwise it will be enabled on non-win32 platforms. It
2378	takes precedence over select.	4330	takes precedence over select.
2379		4331
2380	=item EV_USE_EPOLL	4332	=item EV_USE_EPOLL
2381		4333
2382	If defined to be C<1>, libev will compile in support for the Linux	4334	If defined to be C<1>, libev will compile in support for the Linux
2383	C<epoll>(7) backend. Its availability will be detected at runtime,	4335	C<epoll>(7) backend. Its availability will be detected at runtime,
2384	otherwise another method will be used as fallback. This is the	4336	otherwise another method will be used as fallback. This is the preferred
2385	preferred backend for GNU/Linux systems.	4337	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4338	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2386		4339
2387	=item EV_USE_KQUEUE	4340	=item EV_USE_KQUEUE
2388		4341
2389	If defined to be C<1>, libev will compile in support for the BSD style	4342	If defined to be C<1>, libev will compile in support for the BSD style
2390	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4343	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2403	otherwise another method will be used as fallback. This is the preferred	4356	otherwise another method will be used as fallback. This is the preferred
2404	backend for Solaris 10 systems.	4357	backend for Solaris 10 systems.
2405		4358
2406	=item EV_USE_DEVPOLL	4359	=item EV_USE_DEVPOLL
2407		4360
2408	reserved for future expansion, works like the USE symbols above.	4361	Reserved for future expansion, works like the USE symbols above.
2409		4362
2410	=item EV_USE_INOTIFY	4363	=item EV_USE_INOTIFY
2411		4364
2412	If defined to be C<1>, libev will compile in support for the Linux inotify	4365	If defined to be C<1>, libev will compile in support for the Linux inotify
2413	interface to speed up C<ev_stat> watchers. Its actual availability will	4366	interface to speed up C<ev_stat> watchers. Its actual availability will
2414	be detected at runtime.	4367	be detected at runtime. If undefined, it will be enabled if the headers
		4368	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2415		4369
		4370	=item EV_ATOMIC_T
		4371
		4372	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4373	access is atomic with respect to other threads or signal contexts. No such
		4374	type is easily found in the C language, so you can provide your own type
		4375	that you know is safe for your purposes. It is used both for signal handler "locking"
		4376	as well as for signal and thread safety in C<ev_async> watchers.
		4377
		4378	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4379	(from F<signal.h>), which is usually good enough on most platforms.
		4380
2416	=item EV_H	4381	=item EV_H (h)
2417		4382
2418	The name of the F<ev.h> header file used to include it. The default if	4383	The name of the F<ev.h> header file used to include it. The default if
2419	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	4384	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2420	can be used to virtually rename the F<ev.h> header file in case of conflicts.	4385	used to virtually rename the F<ev.h> header file in case of conflicts.
2421		4386
2422	=item EV_CONFIG_H	4387	=item EV_CONFIG_H (h)
2423		4388
2424	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4389	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2425	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4390	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2426	C<EV_H>, above.	4391	C<EV_H>, above.
2427		4392
2428	=item EV_EVENT_H	4393	=item EV_EVENT_H (h)
2429		4394
2430	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4395	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2431	of how the F<event.h> header can be found.	4396	of how the F<event.h> header can be found, the default is C<"event.h">.
2432		4397
2433	=item EV_PROTOTYPES	4398	=item EV_PROTOTYPES (h)
2434		4399
2435	If defined to be C<0>, then F<ev.h> will not define any function	4400	If defined to be C<0>, then F<ev.h> will not define any function
2436	prototypes, but still define all the structs and other symbols. This is	4401	prototypes, but still define all the structs and other symbols. This is
2437	occasionally useful if you want to provide your own wrapper functions	4402	occasionally useful if you want to provide your own wrapper functions
2438	around libev functions.	4403	around libev functions.
…		…
2457	When doing priority-based operations, libev usually has to linearly search	4422	When doing priority-based operations, libev usually has to linearly search
2458	all the priorities, so having many of them (hundreds) uses a lot of space	4423	all the priorities, so having many of them (hundreds) uses a lot of space
2459	and time, so using the defaults of five priorities (-2 .. +2) is usually	4424	and time, so using the defaults of five priorities (-2 .. +2) is usually
2460	fine.	4425	fine.
2461		4426
2462	If your embedding app does not need any priorities, defining these both to	4427	If your embedding application does not need any priorities, defining these
2463	C<0> will save some memory and cpu.	4428	both to C<0> will save some memory and CPU.
2464		4429
2465	=item EV_PERIODIC_ENABLE	4430	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4431	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4432	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2466		4433
2467	If undefined or defined to be C<1>, then periodic timers are supported. If	4434	If undefined or defined to be C<1> (and the platform supports it), then
2468	defined to be C<0>, then they are not. Disabling them saves a few kB of	4435	the respective watcher type is supported. If defined to be C<0>, then it
2469	code.	4436	is not. Disabling watcher types mainly saves code size.
2470		4437
2471	=item EV_IDLE_ENABLE	4438	=item EV_FEATURES
2472
2473	If undefined or defined to be C<1>, then idle watchers are supported. If
2474	defined to be C<0>, then they are not. Disabling them saves a few kB of
2475	code.
2476
2477	=item EV_EMBED_ENABLE
2478
2479	If undefined or defined to be C<1>, then embed watchers are supported. If
2480	defined to be C<0>, then they are not.
2481
2482	=item EV_STAT_ENABLE
2483
2484	If undefined or defined to be C<1>, then stat watchers are supported. If
2485	defined to be C<0>, then they are not.
2486
2487	=item EV_FORK_ENABLE
2488
2489	If undefined or defined to be C<1>, then fork watchers are supported. If
2490	defined to be C<0>, then they are not.
2491
2492	=item EV_MINIMAL
2493		4439
2494	If you need to shave off some kilobytes of code at the expense of some	4440	If you need to shave off some kilobytes of code at the expense of some
2495	speed, define this symbol to C<1>. Currently only used for gcc to override	4441	speed (but with the full API), you can define this symbol to request
2496	some inlining decisions, saves roughly 30% codesize of amd64.	4442	certain subsets of functionality. The default is to enable all features
		4443	that can be enabled on the platform.
		4444
		4445	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4446	with some broad features you want) and then selectively re-enable
		4447	additional parts you want, for example if you want everything minimal,
		4448	but multiple event loop support, async and child watchers and the poll
		4449	backend, use this:
		4450
		4451	#define EV_FEATURES 0
		4452	#define EV_MULTIPLICITY 1
		4453	#define EV_USE_POLL 1
		4454	#define EV_CHILD_ENABLE 1
		4455	#define EV_ASYNC_ENABLE 1
		4456
		4457	The actual value is a bitset, it can be a combination of the following
		4458	values:
		4459
		4460	=over 4
		4461
		4462	=item C<1> - faster/larger code
		4463
		4464	Use larger code to speed up some operations.
		4465
		4466	Currently this is used to override some inlining decisions (enlarging the
		4467	code size by roughly 30% on amd64).
		4468
		4469	When optimising for size, use of compiler flags such as C<-Os> with
		4470	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4471	assertions.
		4472
		4473	=item C<2> - faster/larger data structures
		4474
		4475	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4476	hash table sizes and so on. This will usually further increase code size
		4477	and can additionally have an effect on the size of data structures at
		4478	runtime.
		4479
		4480	=item C<4> - full API configuration
		4481
		4482	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4483	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4484
		4485	=item C<8> - full API
		4486
		4487	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4488	details on which parts of the API are still available without this
		4489	feature, and do not complain if this subset changes over time.
		4490
		4491	=item C<16> - enable all optional watcher types
		4492
		4493	Enables all optional watcher types. If you want to selectively enable
		4494	only some watcher types other than I/O and timers (e.g. prepare,
		4495	embed, async, child...) you can enable them manually by defining
		4496	C<EV_watchertype_ENABLE> to C<1> instead.
		4497
		4498	=item C<32> - enable all backends
		4499
		4500	This enables all backends - without this feature, you need to enable at
		4501	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4502
		4503	=item C<64> - enable OS-specific "helper" APIs
		4504
		4505	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4506	default.
		4507
		4508	=back
		4509
		4510	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4511	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4512	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4513	watchers, timers and monotonic clock support.
		4514
		4515	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4516	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4517	your program might be left out as well - a binary starting a timer and an
		4518	I/O watcher then might come out at only 5Kb.
		4519
		4520	=item EV_AVOID_STDIO
		4521
		4522	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4523	functions (printf, scanf, perror etc.). This will increase the code size
		4524	somewhat, but if your program doesn't otherwise depend on stdio and your
		4525	libc allows it, this avoids linking in the stdio library which is quite
		4526	big.
		4527
		4528	Note that error messages might become less precise when this option is
		4529	enabled.
		4530
		4531	=item EV_NSIG
		4532
		4533	The highest supported signal number, +1 (or, the number of
		4534	signals): Normally, libev tries to deduce the maximum number of signals
		4535	automatically, but sometimes this fails, in which case it can be
		4536	specified. Also, using a lower number than detected (C<32> should be
		4537	good for about any system in existence) can save some memory, as libev
		4538	statically allocates some 12-24 bytes per signal number.
2497		4539
2498	=item EV_PID_HASHSIZE	4540	=item EV_PID_HASHSIZE
2499		4541
2500	C<ev_child> watchers use a small hash table to distribute workload by	4542	C<ev_child> watchers use a small hash table to distribute workload by
2501	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4543	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2502	than enough. If you need to manage thousands of children you might want to	4544	usually more than enough. If you need to manage thousands of children you
2503	increase this value (I<must> be a power of two).	4545	might want to increase this value (I<must> be a power of two).
2504		4546
2505	=item EV_INOTIFY_HASHSIZE	4547	=item EV_INOTIFY_HASHSIZE
2506		4548
2507	C<ev_staz> watchers use a small hash table to distribute workload by	4549	C<ev_stat> watchers use a small hash table to distribute workload by
2508	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4550	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2509	usually more than enough. If you need to manage thousands of C<ev_stat>	4551	disabled), usually more than enough. If you need to manage thousands of
2510	watchers you might want to increase this value (I<must> be a power of	4552	C<ev_stat> watchers you might want to increase this value (I<must> be a
2511	two).	4553	power of two).
		4554
		4555	=item EV_USE_4HEAP
		4556
		4557	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4558	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4559	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4560	faster performance with many (thousands) of watchers.
		4561
		4562	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4563	will be C<0>.
		4564
		4565	=item EV_HEAP_CACHE_AT
		4566
		4567	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4568	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4569	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4570	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4571	but avoids random read accesses on heap changes. This improves performance
		4572	noticeably with many (hundreds) of watchers.
		4573
		4574	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4575	will be C<0>.
		4576
		4577	=item EV_VERIFY
		4578
		4579	Controls how much internal verification (see C<ev_verify ()>) will
		4580	be done: If set to C<0>, no internal verification code will be compiled
		4581	in. If set to C<1>, then verification code will be compiled in, but not
		4582	called. If set to C<2>, then the internal verification code will be
		4583	called once per loop, which can slow down libev. If set to C<3>, then the
		4584	verification code will be called very frequently, which will slow down
		4585	libev considerably.
		4586
		4587	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4588	will be C<0>.
2512		4589
2513	=item EV_COMMON	4590	=item EV_COMMON
2514		4591
2515	By default, all watchers have a C<void *data> member. By redefining	4592	By default, all watchers have a C<void *data> member. By redefining
2516	this macro to a something else you can include more and other types of	4593	this macro to something else you can include more and other types of
2517	members. You have to define it each time you include one of the files,	4594	members. You have to define it each time you include one of the files,
2518	though, and it must be identical each time.	4595	though, and it must be identical each time.
2519		4596
2520	For example, the perl EV module uses something like this:	4597	For example, the perl EV module uses something like this:
2521		4598
2522	#define EV_COMMON \	4599	#define EV_COMMON \
2523	SV *self; /* contains this struct */ \	4600	SV *self; /* contains this struct */ \
2524	SV *cb_sv, *fh /* note no trailing ";" */	4601	SV *cb_sv, *fh /* note no trailing ";" */
2525		4602
2526	=item EV_CB_DECLARE (type)	4603	=item EV_CB_DECLARE (type)
2527		4604
2528	=item EV_CB_INVOKE (watcher, revents)	4605	=item EV_CB_INVOKE (watcher, revents)
2529		4606
…		…
2534	definition and a statement, respectively. See the F<ev.h> header file for	4611	definition and a statement, respectively. See the F<ev.h> header file for
2535	their default definitions. One possible use for overriding these is to	4612	their default definitions. One possible use for overriding these is to
2536	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4613	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2537	method calls instead of plain function calls in C++.	4614	method calls instead of plain function calls in C++.
2538		4615
		4616	=back
		4617
2539	=head2 EXPORTED API SYMBOLS	4618	=head2 EXPORTED API SYMBOLS
2540		4619
2541	If you need to re-export the API (e.g. via a dll) and you need a list of	4620	If you need to re-export the API (e.g. via a DLL) and you need a list of
2542	exported symbols, you can use the provided F<Symbol.*> files which list	4621	exported symbols, you can use the provided F<Symbol.*> files which list
2543	all public symbols, one per line:	4622	all public symbols, one per line:
2544		4623
2545	Symbols.ev for libev proper	4624	Symbols.ev for libev proper
2546	Symbols.event for the libevent emulation	4625	Symbols.event for the libevent emulation
2547		4626
2548	This can also be used to rename all public symbols to avoid clashes with	4627	This can also be used to rename all public symbols to avoid clashes with
2549	multiple versions of libev linked together (which is obviously bad in	4628	multiple versions of libev linked together (which is obviously bad in
2550	itself, but sometimes it is inconvinient to avoid this).	4629	itself, but sometimes it is inconvenient to avoid this).
2551		4630
2552	A sed command like this will create wrapper C<#define>'s that you need to	4631	A sed command like this will create wrapper C<#define>'s that you need to
2553	include before including F<ev.h>:	4632	include before including F<ev.h>:
2554		4633
2555	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	4634	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2572	file.	4651	file.
2573		4652
2574	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4653	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2575	that everybody includes and which overrides some configure choices:	4654	that everybody includes and which overrides some configure choices:
2576		4655
2577	#define EV_MINIMAL 1	4656	#define EV_FEATURES 8
2578	#define EV_USE_POLL 0	4657	#define EV_USE_SELECT 1
2579	#define EV_MULTIPLICITY 0
2580	#define EV_PERIODIC_ENABLE 0	4658	#define EV_PREPARE_ENABLE 1
		4659	#define EV_IDLE_ENABLE 1
2581	#define EV_STAT_ENABLE 0	4660	#define EV_SIGNAL_ENABLE 1
2582	#define EV_FORK_ENABLE 0	4661	#define EV_CHILD_ENABLE 1
		4662	#define EV_USE_STDEXCEPT 0
2583	#define EV_CONFIG_H <config.h>	4663	#define EV_CONFIG_H <config.h>
2584	#define EV_MINPRI 0
2585	#define EV_MAXPRI 0
2586		4664
2587	#include "ev++.h"	4665	#include "ev++.h"
2588		4666
2589	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4667	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2590		4668
2591	#include "ev_cpp.h"	4669	#include "ev_cpp.h"
2592	#include "ev.c"	4670	#include "ev.c"
2593		4671
		4672	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
2594		4673
		4674	=head2 THREADS AND COROUTINES
		4675
		4676	=head3 THREADS
		4677
		4678	All libev functions are reentrant and thread-safe unless explicitly
		4679	documented otherwise, but libev implements no locking itself. This means
		4680	that you can use as many loops as you want in parallel, as long as there
		4681	are no concurrent calls into any libev function with the same loop
		4682	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4683	of course): libev guarantees that different event loops share no data
		4684	structures that need any locking.
		4685
		4686	Or to put it differently: calls with different loop parameters can be done
		4687	concurrently from multiple threads, calls with the same loop parameter
		4688	must be done serially (but can be done from different threads, as long as
		4689	only one thread ever is inside a call at any point in time, e.g. by using
		4690	a mutex per loop).
		4691
		4692	Specifically to support threads (and signal handlers), libev implements
		4693	so-called C<ev_async> watchers, which allow some limited form of
		4694	concurrency on the same event loop, namely waking it up "from the
		4695	outside".
		4696
		4697	If you want to know which design (one loop, locking, or multiple loops
		4698	without or something else still) is best for your problem, then I cannot
		4699	help you, but here is some generic advice:
		4700
		4701	=over 4
		4702
		4703	=item * most applications have a main thread: use the default libev loop
		4704	in that thread, or create a separate thread running only the default loop.
		4705
		4706	This helps integrating other libraries or software modules that use libev
		4707	themselves and don't care/know about threading.
		4708
		4709	=item * one loop per thread is usually a good model.
		4710
		4711	Doing this is almost never wrong, sometimes a better-performance model
		4712	exists, but it is always a good start.
		4713
		4714	=item * other models exist, such as the leader/follower pattern, where one
		4715	loop is handed through multiple threads in a kind of round-robin fashion.
		4716
		4717	Choosing a model is hard - look around, learn, know that usually you can do
		4718	better than you currently do :-)
		4719
		4720	=item * often you need to talk to some other thread which blocks in the
		4721	event loop.
		4722
		4723	C<ev_async> watchers can be used to wake them up from other threads safely
		4724	(or from signal contexts...).
		4725
		4726	An example use would be to communicate signals or other events that only
		4727	work in the default loop by registering the signal watcher with the
		4728	default loop and triggering an C<ev_async> watcher from the default loop
		4729	watcher callback into the event loop interested in the signal.
		4730
		4731	=back
		4732
		4733	See also L<THREAD LOCKING EXAMPLE>.
		4734
		4735	=head3 COROUTINES
		4736
		4737	Libev is very accommodating to coroutines ("cooperative threads"):
		4738	libev fully supports nesting calls to its functions from different
		4739	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4740	different coroutines, and switch freely between both coroutines running
		4741	the loop, as long as you don't confuse yourself). The only exception is
		4742	that you must not do this from C<ev_periodic> reschedule callbacks.
		4743
		4744	Care has been taken to ensure that libev does not keep local state inside
		4745	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4746	they do not call any callbacks.
		4747
		4748	=head2 COMPILER WARNINGS
		4749
		4750	Depending on your compiler and compiler settings, you might get no or a
		4751	lot of warnings when compiling libev code. Some people are apparently
		4752	scared by this.
		4753
		4754	However, these are unavoidable for many reasons. For one, each compiler
		4755	has different warnings, and each user has different tastes regarding
		4756	warning options. "Warn-free" code therefore cannot be a goal except when
		4757	targeting a specific compiler and compiler-version.
		4758
		4759	Another reason is that some compiler warnings require elaborate
		4760	workarounds, or other changes to the code that make it less clear and less
		4761	maintainable.
		4762
		4763	And of course, some compiler warnings are just plain stupid, or simply
		4764	wrong (because they don't actually warn about the condition their message
		4765	seems to warn about). For example, certain older gcc versions had some
		4766	warnings that resulted in an extreme number of false positives. These have
		4767	been fixed, but some people still insist on making code warn-free with
		4768	such buggy versions.
		4769
		4770	While libev is written to generate as few warnings as possible,
		4771	"warn-free" code is not a goal, and it is recommended not to build libev
		4772	with any compiler warnings enabled unless you are prepared to cope with
		4773	them (e.g. by ignoring them). Remember that warnings are just that:
		4774	warnings, not errors, or proof of bugs.
		4775
		4776
		4777	=head2 VALGRIND
		4778
		4779	Valgrind has a special section here because it is a popular tool that is
		4780	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4781
		4782	If you think you found a bug (memory leak, uninitialised data access etc.)
		4783	in libev, then check twice: If valgrind reports something like:
		4784
		4785	==2274== definitely lost: 0 bytes in 0 blocks.
		4786	==2274== possibly lost: 0 bytes in 0 blocks.
		4787	==2274== still reachable: 256 bytes in 1 blocks.
		4788
		4789	Then there is no memory leak, just as memory accounted to global variables
		4790	is not a memleak - the memory is still being referenced, and didn't leak.
		4791
		4792	Similarly, under some circumstances, valgrind might report kernel bugs
		4793	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4794	although an acceptable workaround has been found here), or it might be
		4795	confused.
		4796
		4797	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4798	make it into some kind of religion.
		4799
		4800	If you are unsure about something, feel free to contact the mailing list
		4801	with the full valgrind report and an explanation on why you think this
		4802	is a bug in libev (best check the archives, too :). However, don't be
		4803	annoyed when you get a brisk "this is no bug" answer and take the chance
		4804	of learning how to interpret valgrind properly.
		4805
		4806	If you need, for some reason, empty reports from valgrind for your project
		4807	I suggest using suppression lists.
		4808
		4809
		4810	=head1 PORTABILITY NOTES
		4811
		4812	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4813
		4814	GNU/Linux is the only common platform that supports 64 bit file/large file
		4815	interfaces but I<disables> them by default.
		4816
		4817	That means that libev compiled in the default environment doesn't support
		4818	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4819
		4820	Unfortunately, many programs try to work around this GNU/Linux issue
		4821	by enabling the large file API, which makes them incompatible with the
		4822	standard libev compiled for their system.
		4823
		4824	Likewise, libev cannot enable the large file API itself as this would
		4825	suddenly make it incompatible to the default compile time environment,
		4826	i.e. all programs not using special compile switches.
		4827
		4828	=head2 OS/X AND DARWIN BUGS
		4829
		4830	The whole thing is a bug if you ask me - basically any system interface
		4831	you touch is broken, whether it is locales, poll, kqueue or even the
		4832	OpenGL drivers.
		4833
		4834	=head3 C<kqueue> is buggy
		4835
		4836	The kqueue syscall is broken in all known versions - most versions support
		4837	only sockets, many support pipes.
		4838
		4839	Libev tries to work around this by not using C<kqueue> by default on this
		4840	rotten platform, but of course you can still ask for it when creating a
		4841	loop - embedding a socket-only kqueue loop into a select-based one is
		4842	probably going to work well.
		4843
		4844	=head3 C<poll> is buggy
		4845
		4846	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4847	implementation by something calling C<kqueue> internally around the 10.5.6
		4848	release, so now C<kqueue> I<and> C<poll> are broken.
		4849
		4850	Libev tries to work around this by not using C<poll> by default on
		4851	this rotten platform, but of course you can still ask for it when creating
		4852	a loop.
		4853
		4854	=head3 C<select> is buggy
		4855
		4856	All that's left is C<select>, and of course Apple found a way to fuck this
		4857	one up as well: On OS/X, C<select> actively limits the number of file
		4858	descriptors you can pass in to 1024 - your program suddenly crashes when
		4859	you use more.
		4860
		4861	There is an undocumented "workaround" for this - defining
		4862	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4863	work on OS/X.
		4864
		4865	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4866
		4867	=head3 C<errno> reentrancy
		4868
		4869	The default compile environment on Solaris is unfortunately so
		4870	thread-unsafe that you can't even use components/libraries compiled
		4871	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4872	defined by default. A valid, if stupid, implementation choice.
		4873
		4874	If you want to use libev in threaded environments you have to make sure
		4875	it's compiled with C<_REENTRANT> defined.
		4876
		4877	=head3 Event port backend
		4878
		4879	The scalable event interface for Solaris is called "event
		4880	ports". Unfortunately, this mechanism is very buggy in all major
		4881	releases. If you run into high CPU usage, your program freezes or you get
		4882	a large number of spurious wakeups, make sure you have all the relevant
		4883	and latest kernel patches applied. No, I don't know which ones, but there
		4884	are multiple ones to apply, and afterwards, event ports actually work
		4885	great.
		4886
		4887	If you can't get it to work, you can try running the program by setting
		4888	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4889	C<select> backends.
		4890
		4891	=head2 AIX POLL BUG
		4892
		4893	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4894	this by trying to avoid the poll backend altogether (i.e. it's not even
		4895	compiled in), which normally isn't a big problem as C<select> works fine
		4896	with large bitsets on AIX, and AIX is dead anyway.
		4897
		4898	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4899
		4900	=head3 General issues
		4901
		4902	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4903	requires, and its I/O model is fundamentally incompatible with the POSIX
		4904	model. Libev still offers limited functionality on this platform in
		4905	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4906	descriptors. This only applies when using Win32 natively, not when using
		4907	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4908	as every compielr comes with a slightly differently broken/incompatible
		4909	environment.
		4910
		4911	Lifting these limitations would basically require the full
		4912	re-implementation of the I/O system. If you are into this kind of thing,
		4913	then note that glib does exactly that for you in a very portable way (note
		4914	also that glib is the slowest event library known to man).
		4915
		4916	There is no supported compilation method available on windows except
		4917	embedding it into other applications.
		4918
		4919	Sensible signal handling is officially unsupported by Microsoft - libev
		4920	tries its best, but under most conditions, signals will simply not work.
		4921
		4922	Not a libev limitation but worth mentioning: windows apparently doesn't
		4923	accept large writes: instead of resulting in a partial write, windows will
		4924	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4925	so make sure you only write small amounts into your sockets (less than a
		4926	megabyte seems safe, but this apparently depends on the amount of memory
		4927	available).
		4928
		4929	Due to the many, low, and arbitrary limits on the win32 platform and
		4930	the abysmal performance of winsockets, using a large number of sockets
		4931	is not recommended (and not reasonable). If your program needs to use
		4932	more than a hundred or so sockets, then likely it needs to use a totally
		4933	different implementation for windows, as libev offers the POSIX readiness
		4934	notification model, which cannot be implemented efficiently on windows
		4935	(due to Microsoft monopoly games).
		4936
		4937	A typical way to use libev under windows is to embed it (see the embedding
		4938	section for details) and use the following F<evwrap.h> header file instead
		4939	of F<ev.h>:
		4940
		4941	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4942	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4943
		4944	#include "ev.h"
		4945
		4946	And compile the following F<evwrap.c> file into your project (make sure
		4947	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4948
		4949	#include "evwrap.h"
		4950	#include "ev.c"
		4951
		4952	=head3 The winsocket C<select> function
		4953
		4954	The winsocket C<select> function doesn't follow POSIX in that it
		4955	requires socket I<handles> and not socket I<file descriptors> (it is
		4956	also extremely buggy). This makes select very inefficient, and also
		4957	requires a mapping from file descriptors to socket handles (the Microsoft
		4958	C runtime provides the function C<_open_osfhandle> for this). See the
		4959	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4960	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4961
		4962	The configuration for a "naked" win32 using the Microsoft runtime
		4963	libraries and raw winsocket select is:
		4964
		4965	#define EV_USE_SELECT 1
		4966	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4967
		4968	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4969	complexity in the O(n²) range when using win32.
		4970
		4971	=head3 Limited number of file descriptors
		4972
		4973	Windows has numerous arbitrary (and low) limits on things.
		4974
		4975	Early versions of winsocket's select only supported waiting for a maximum
		4976	of C<64> handles (probably owning to the fact that all windows kernels
		4977	can only wait for C<64> things at the same time internally; Microsoft
		4978	recommends spawning a chain of threads and wait for 63 handles and the
		4979	previous thread in each. Sounds great!).
		4980
		4981	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4982	to some high number (e.g. C<2048>) before compiling the winsocket select
		4983	call (which might be in libev or elsewhere, for example, perl and many
		4984	other interpreters do their own select emulation on windows).
		4985
		4986	Another limit is the number of file descriptors in the Microsoft runtime
		4987	libraries, which by default is C<64> (there must be a hidden I<64>
		4988	fetish or something like this inside Microsoft). You can increase this
		4989	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4990	(another arbitrary limit), but is broken in many versions of the Microsoft
		4991	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4992	(depending on windows version and/or the phase of the moon). To get more,
		4993	you need to wrap all I/O functions and provide your own fd management, but
		4994	the cost of calling select (O(n²)) will likely make this unworkable.
		4995
		4996	=head2 PORTABILITY REQUIREMENTS
		4997
		4998	In addition to a working ISO-C implementation and of course the
		4999	backend-specific APIs, libev relies on a few additional extensions:
		5000
		5001	=over 4
		5002
		5003	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5004	calling conventions regardless of C<ev_watcher_type *>.
		5005
		5006	Libev assumes not only that all watcher pointers have the same internal
		5007	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5008	assumes that the same (machine) code can be used to call any watcher
		5009	callback: The watcher callbacks have different type signatures, but libev
		5010	calls them using an C<ev_watcher *> internally.
		5011
		5012	=item pointer accesses must be thread-atomic
		5013
		5014	Accessing a pointer value must be atomic, it must both be readable and
		5015	writable in one piece - this is the case on all current architectures.
		5016
		5017	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5018
		5019	The type C<sig_atomic_t volatile> (or whatever is defined as
		5020	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5021	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5022	believed to be sufficiently portable.
		5023
		5024	=item C<sigprocmask> must work in a threaded environment
		5025
		5026	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5027	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5028	pthread implementations will either allow C<sigprocmask> in the "main
		5029	thread" or will block signals process-wide, both behaviours would
		5030	be compatible with libev. Interaction between C<sigprocmask> and
		5031	C<pthread_sigmask> could complicate things, however.
		5032
		5033	The most portable way to handle signals is to block signals in all threads
		5034	except the initial one, and run the default loop in the initial thread as
		5035	well.
		5036
		5037	=item C<long> must be large enough for common memory allocation sizes
		5038
		5039	To improve portability and simplify its API, libev uses C<long> internally
		5040	instead of C<size_t> when allocating its data structures. On non-POSIX
		5041	systems (Microsoft...) this might be unexpectedly low, but is still at
		5042	least 31 bits everywhere, which is enough for hundreds of millions of
		5043	watchers.
		5044
		5045	=item C<double> must hold a time value in seconds with enough accuracy
		5046
		5047	The type C<double> is used to represent timestamps. It is required to
		5048	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5049	good enough for at least into the year 4000 with millisecond accuracy
		5050	(the design goal for libev). This requirement is overfulfilled by
		5051	implementations using IEEE 754, which is basically all existing ones. With
		5052	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
		5053
		5054	=back
		5055
		5056	If you know of other additional requirements drop me a note.
		5057
		5058
2595	=head1 COMPLEXITIES	5059	=head1 ALGORITHMIC COMPLEXITIES
2596		5060
2597	In this section the complexities of (many of) the algorithms used inside	5061	In this section the complexities of (many of) the algorithms used inside
2598	libev will be explained. For complexity discussions about backends see the	5062	libev will be documented. For complexity discussions about backends see
2599	documentation for C<ev_default_init>.	5063	the documentation for C<ev_default_init>.
2600		5064
2601	All of the following are about amortised time: If an array needs to be	5065	All of the following are about amortised time: If an array needs to be
2602	extended, libev needs to realloc and move the whole array, but this	5066	extended, libev needs to realloc and move the whole array, but this
2603	happens asymptotically never with higher number of elements, so O(1) might	5067	happens asymptotically rarer with higher number of elements, so O(1) might
2604	mean it might do a lengthy realloc operation in rare cases, but on average	5068	mean that libev does a lengthy realloc operation in rare cases, but on
2605	it is much faster and asymptotically approaches constant time.	5069	average it is much faster and asymptotically approaches constant time.
2606		5070
2607	=over 4	5071	=over 4
2608		5072
2609	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	5073	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2610		5074
2611	This means that, when you have a watcher that triggers in one hour and	5075	This means that, when you have a watcher that triggers in one hour and
2612	there are 100 watchers that would trigger before that then inserting will	5076	there are 100 watchers that would trigger before that, then inserting will
2613	have to skip those 100 watchers.	5077	have to skip roughly seven (C<ld 100>) of these watchers.
2614		5078
2615	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	5079	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2616		5080
2617	That means that for changing a timer costs less than removing/adding them	5081	That means that changing a timer costs less than removing/adding them,
2618	as only the relative motion in the event queue has to be paid for.	5082	as only the relative motion in the event queue has to be paid for.
2619		5083
2620	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	5084	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2621		5085
2622	These just add the watcher into an array or at the head of a list.	5086	These just add the watcher into an array or at the head of a list.
		5087
2623	=item Stopping check/prepare/idle watchers: O(1)	5088	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2624		5089
2625	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	5090	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2626		5091
2627	These watchers are stored in lists then need to be walked to find the	5092	These watchers are stored in lists, so they need to be walked to find the
2628	correct watcher to remove. The lists are usually short (you don't usually	5093	correct watcher to remove. The lists are usually short (you don't usually
2629	have many watchers waiting for the same fd or signal).	5094	have many watchers waiting for the same fd or signal: one is typical, two
		5095	is rare).
2630		5096
2631	=item Finding the next timer per loop iteration: O(1)	5097	=item Finding the next timer in each loop iteration: O(1)
		5098
		5099	By virtue of using a binary or 4-heap, the next timer is always found at a
		5100	fixed position in the storage array.
2632		5101
2633	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	5102	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2634		5103
2635	A change means an I/O watcher gets started or stopped, which requires	5104	A change means an I/O watcher gets started or stopped, which requires
2636	libev to recalculate its status (and possibly tell the kernel).	5105	libev to recalculate its status (and possibly tell the kernel, depending
		5106	on backend and whether C<ev_io_set> was used).
2637		5107
2638	=item Activating one watcher: O(1)	5108	=item Activating one watcher (putting it into the pending state): O(1)
2639		5109
2640	=item Priority handling: O(number_of_priorities)	5110	=item Priority handling: O(number_of_priorities)
2641		5111
2642	Priorities are implemented by allocating some space for each	5112	Priorities are implemented by allocating some space for each
2643	priority. When doing priority-based operations, libev usually has to	5113	priority. When doing priority-based operations, libev usually has to
2644	linearly search all the priorities.	5114	linearly search all the priorities, but starting/stopping and activating
		5115	watchers becomes O(1) with respect to priority handling.
		5116
		5117	=item Sending an ev_async: O(1)
		5118
		5119	=item Processing ev_async_send: O(number_of_async_watchers)
		5120
		5121	=item Processing signals: O(max_signal_number)
		5122
		5123	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5124	calls in the current loop iteration. Checking for async and signal events
		5125	involves iterating over all running async watchers or all signal numbers.
2645		5126
2646	=back	5127	=back
2647		5128
2648		5129
		5130	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5131
		5132	The major version 4 introduced some incompatible changes to the API.
		5133
		5134	At the moment, the C<ev.h> header file provides compatibility definitions
		5135	for all changes, so most programs should still compile. The compatibility
		5136	layer might be removed in later versions of libev, so better update to the
		5137	new API early than late.
		5138
		5139	=over 4
		5140
		5141	=item C<EV_COMPAT3> backwards compatibility mechanism
		5142
		5143	The backward compatibility mechanism can be controlled by
		5144	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5145	section.
		5146
		5147	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5148
		5149	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5150
		5151	ev_loop_destroy (EV_DEFAULT_UC);
		5152	ev_loop_fork (EV_DEFAULT);
		5153
		5154	=item function/symbol renames
		5155
		5156	A number of functions and symbols have been renamed:
		5157
		5158	ev_loop => ev_run
		5159	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5160	EVLOOP_ONESHOT => EVRUN_ONCE
		5161
		5162	ev_unloop => ev_break
		5163	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5164	EVUNLOOP_ONE => EVBREAK_ONE
		5165	EVUNLOOP_ALL => EVBREAK_ALL
		5166
		5167	EV_TIMEOUT => EV_TIMER
		5168
		5169	ev_loop_count => ev_iteration
		5170	ev_loop_depth => ev_depth
		5171	ev_loop_verify => ev_verify
		5172
		5173	Most functions working on C<struct ev_loop> objects don't have an
		5174	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5175	associated constants have been renamed to not collide with the C<struct
		5176	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5177	as all other watcher types. Note that C<ev_loop_fork> is still called
		5178	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5179	typedef.
		5180
		5181	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5182
		5183	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5184	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5185	and work, but the library code will of course be larger.
		5186
		5187	=back
		5188
		5189
		5190	=head1 GLOSSARY
		5191
		5192	=over 4
		5193
		5194	=item active
		5195
		5196	A watcher is active as long as it has been started and not yet stopped.
		5197	See L<WATCHER STATES> for details.
		5198
		5199	=item application
		5200
		5201	In this document, an application is whatever is using libev.
		5202
		5203	=item backend
		5204
		5205	The part of the code dealing with the operating system interfaces.
		5206
		5207	=item callback
		5208
		5209	The address of a function that is called when some event has been
		5210	detected. Callbacks are being passed the event loop, the watcher that
		5211	received the event, and the actual event bitset.
		5212
		5213	=item callback/watcher invocation
		5214
		5215	The act of calling the callback associated with a watcher.
		5216
		5217	=item event
		5218
		5219	A change of state of some external event, such as data now being available
		5220	for reading on a file descriptor, time having passed or simply not having
		5221	any other events happening anymore.
		5222
		5223	In libev, events are represented as single bits (such as C<EV_READ> or
		5224	C<EV_TIMER>).
		5225
		5226	=item event library
		5227
		5228	A software package implementing an event model and loop.
		5229
		5230	=item event loop
		5231
		5232	An entity that handles and processes external events and converts them
		5233	into callback invocations.
		5234
		5235	=item event model
		5236
		5237	The model used to describe how an event loop handles and processes
		5238	watchers and events.
		5239
		5240	=item pending
		5241
		5242	A watcher is pending as soon as the corresponding event has been
		5243	detected. See L<WATCHER STATES> for details.
		5244
		5245	=item real time
		5246
		5247	The physical time that is observed. It is apparently strictly monotonic :)
		5248
		5249	=item wall-clock time
		5250
		5251	The time and date as shown on clocks. Unlike real time, it can actually
		5252	be wrong and jump forwards and backwards, e.g. when you adjust your
		5253	clock.
		5254
		5255	=item watcher
		5256
		5257	A data structure that describes interest in certain events. Watchers need
		5258	to be started (attached to an event loop) before they can receive events.
		5259
		5260	=back
		5261
2649	=head1 AUTHOR	5262	=head1 AUTHOR
2650		5263
2651	Marc Lehmann <libev@schmorp.de>.	5264	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5265	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
2652		5266

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