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Revision 1.130 by root, Wed Feb 6 18:34:24 2008 UTC vs.
Revision 1.367 by root, Sun Feb 20 02:56:23 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	=head2 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
…		…
70	=head2 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	=head2 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	=head2 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 until
123	either it is interrupted or the given time interval has passed. Basically	184	either it is interrupted or the given time interval has passed. Basically
124	this is a subsecond-resolution C<sleep ()>.	185	this is a sub-second-resolution C<sleep ()>.
125		186
126	=item int ev_version_major ()	187	=item int ev_version_major ()
127		188
128	=item int ev_version_minor ()	189	=item int ev_version_minor ()
129		190
…		…
140	as this indicates an incompatible change. Minor versions are usually	201	as this indicates an incompatible change. Minor versions are usually
141	compatible to older versions, so a larger minor version alone is usually	202	compatible to older versions, so a larger minor version alone is usually
142	not a problem.	203	not a problem.
143		204
144	Example: Make sure we haven't accidentally been linked against the wrong	205	Example: Make sure we haven't accidentally been linked against the wrong
145	version.	206	version (note, however, that this will not detect other ABI mismatches,
		207	such as LFS or reentrancy).
146		208
147	assert (("libev version mismatch",	209	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	210	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	211	&& ev_version_minor () >= EV_VERSION_MINOR));
150		212
151	=item unsigned int ev_supported_backends ()	213	=item unsigned int ev_supported_backends ()
152		214
153	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	215	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
154	value) compiled into this binary of libev (independent of their	216	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	218	a description of the set values.
157		219
158	Example: make sure we have the epoll method, because yeah this is cool and	220	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	221	a must have and can we have a torrent of it please!!!11
160		222
161	assert (("sorry, no epoll, no sex",	223	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	224	ev_supported_backends () & EVBACKEND_EPOLL));
163		225
164	=item unsigned int ev_recommended_backends ()	226	=item unsigned int ev_recommended_backends ()
165		227
166	Return the set of all backends compiled into this binary of libev and also	228	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	229	also recommended for this platform, meaning it will work for most file
		230	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	231	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	232	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	233	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.	234	probe for if you specify no backends explicitly.
172		235
173	=item unsigned int ev_embeddable_backends ()	236	=item unsigned int ev_embeddable_backends ()
174		237
175	Returns the set of backends that are embeddable in other event loops. This	238	Returns the set of backends that are embeddable in other event loops. This
176	is the theoretical, all-platform, value. To find which backends	239	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	240	current system. To find which embeddable backends might be supported on
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	241	the current system, you would need to look at C<ev_embeddable_backends ()
179	recommended ones.	242	& ev_supported_backends ()>, likewise for recommended ones.
180		243
181	See the description of C<ev_embed> watchers for more info.	244	See the description of C<ev_embed> watchers for more info.
182		245
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	246	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
184		247
185	Sets the allocation function to use (the prototype is similar - the	248	Sets the allocation function to use (the prototype is similar - the
186	semantics is identical - to the realloc C function). It is used to	249	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	250	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	251	when memory needs to be allocated (C<size != 0>), the library might abort
189	potentially destructive action. The default is your system realloc	252	or take some potentially destructive action.
190	function.	253
		254	Since some systems (at least OpenBSD and Darwin) fail to implement
		255	correct C<realloc> semantics, libev will use a wrapper around the system
		256	C<realloc> and C<free> functions by default.
191		257
192	You could override this function in high-availability programs to, say,	258	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,	259	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.	260	or even to sleep a while and retry until some memory is available.
195		261
196	Example: Replace the libev allocator with one that waits a bit and then	262	Example: Replace the libev allocator with one that waits a bit and then
197	retries).	263	retries (example requires a standards-compliant C<realloc>).
198		264
199	static void *	265	static void *
200	persistent_realloc (void *ptr, size_t size)	266	persistent_realloc (void *ptr, size_t size)
201	{	267	{
202	for (;;)	268	for (;;)
…		…
211	}	277	}
212		278
213	...	279	...
214	ev_set_allocator (persistent_realloc);	280	ev_set_allocator (persistent_realloc);
215		281
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	282	=item ev_set_syserr_cb (void (*cb)(const char *msg))
217		283
218	Set the callback function to call on a retryable syscall error (such	284	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	285	as failed select, poll, epoll_wait). The message is a printable string
220	indicating the system call or subsystem causing the problem. If this	286	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	287	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	288	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	289	requested operation, or, if the condition doesn't go away, do bad stuff
224	(such as abort).	290	(such as abort).
225		291
226	Example: This is basically the same thing that libev does internally, too.	292	Example: This is basically the same thing that libev does internally, too.
…		…
233	}	299	}
234		300
235	...	301	...
236	ev_set_syserr_cb (fatal_error);	302	ev_set_syserr_cb (fatal_error);
237		303
		304	=item ev_feed_signal (int signum)
		305
		306	This function can be used to "simulate" a signal receive. It is completely
		307	safe to call this function at any time, from any context, including signal
		308	handlers or random threads.
		309
		310	Its main use is to customise signal handling in your process, especially
		311	in the presence of threads. For example, you could block signals
		312	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		313	creating any loops), and in one thread, use C<sigwait> or any other
		314	mechanism to wait for signals, then "deliver" them to libev by calling
		315	C<ev_feed_signal>.
		316
238	=back	317	=back
239		318
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	319	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
241		320
242	An event loop is described by a C<struct ev_loop *>. The library knows two	321	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	322	I<not> optional in this case unless libev 3 compatibility is disabled, as
244	events, and dynamically created loops which do not.	323	libev 3 had an C<ev_loop> function colliding with the struct name).
245		324
246	If you use threads, a common model is to run the default event loop	325	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	326	supports child process events, and dynamically created event loops which
248	create, you also create another event loop. Libev itself does no locking	327	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		328
253	=over 4	329	=over 4
254		330
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	331	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		332
257	This will initialise the default event loop if it hasn't been initialised	333	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	334	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	335	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).	336	C<ev_loop_new>.
		337
		338	If the default loop is already initialised then this function simply
		339	returns it (and ignores the flags. If that is troubling you, check
		340	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		341	flags, which should almost always be C<0>, unless the caller is also the
		342	one calling C<ev_run> or otherwise qualifies as "the main program".
261		343
262	If you don't know what event loop to use, use the one returned from this	344	If you don't know what event loop to use, use the one returned from this
263	function.	345	function (or via the C<EV_DEFAULT> macro).
264		346
		347	Note that this function is I<not> thread-safe, so if you want to use it
		348	from multiple threads, you have to employ some kind of mutex (note also
		349	that this case is unlikely, as loops cannot be shared easily between
		350	threads anyway).
		351
265	The default loop is the only loop that can handle C<ev_signal> and	352	The default loop is the only loop that can handle C<ev_child> watchers,
266	C<ev_child> watchers, and to do this, it always registers a handler	353	and to do this, it always registers a handler for C<SIGCHLD>. If this is
267	for C<SIGCHLD>. If this is a problem for your app you can either	354	a problem for your application you can either create a dynamic loop with
268	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	355	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
269	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	356	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
270	C<ev_default_init>.	357
		358	Example: This is the most typical usage.
		359
		360	if (!ev_default_loop (0))
		361	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		362
		363	Example: Restrict libev to the select and poll backends, and do not allow
		364	environment settings to be taken into account:
		365
		366	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		367
		368	=item struct ev_loop *ev_loop_new (unsigned int flags)
		369
		370	This will create and initialise a new event loop object. If the loop
		371	could not be initialised, returns false.
		372
		373	This function is thread-safe, and one common way to use libev with
		374	threads is indeed to create one loop per thread, and using the default
		375	loop in the "main" or "initial" thread.
271		376
272	The flags argument can be used to specify special behaviour or specific	377	The flags argument can be used to specify special behaviour or specific
273	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	378	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
274		379
275	The following flags are supported:	380	The following flags are supported:
…		…
281	The default flags value. Use this if you have no clue (it's the right	386	The default flags value. Use this if you have no clue (it's the right
282	thing, believe me).	387	thing, believe me).
283		388
284	=item C<EVFLAG_NOENV>	389	=item C<EVFLAG_NOENV>
285		390
286	If this flag bit is ored into the flag value (or the program runs setuid	391	If this flag bit is or'ed into the flag value (or the program runs setuid
287	or setgid) then libev will I<not> look at the environment variable	392	or setgid) then libev will I<not> look at the environment variable
288	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	393	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
289	override the flags completely if it is found in the environment. This is	394	override the flags completely if it is found in the environment. This is
290	useful to try out specific backends to test their performance, or to work	395	useful to try out specific backends to test their performance, or to work
291	around bugs.	396	around bugs.
292		397
293	=item C<EVFLAG_FORKCHECK>	398	=item C<EVFLAG_FORKCHECK>
294		399
295	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	400	Instead of calling C<ev_loop_fork> manually after a fork, you can also
296	a fork, you can also make libev check for a fork in each iteration by	401	make libev check for a fork in each iteration by enabling this flag.
297	enabling this flag.
298		402
299	This works by calling C<getpid ()> on every iteration of the loop,	403	This works by calling C<getpid ()> on every iteration of the loop,
300	and thus this might slow down your event loop if you do a lot of loop	404	and thus this might slow down your event loop if you do a lot of loop
301	iterations and little real work, but is usually not noticeable (on my	405	iterations and little real work, but is usually not noticeable (on my
302	Linux system for example, C<getpid> is actually a simple 5-insn sequence	406	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
303	without a syscall and thus I<very> fast, but my Linux system also has	407	without a system call and thus I<very> fast, but my GNU/Linux system also has
304	C<pthread_atfork> which is even faster).	408	C<pthread_atfork> which is even faster).
305		409
306	The big advantage of this flag is that you can forget about fork (and	410	The big advantage of this flag is that you can forget about fork (and
307	forget about forgetting to tell libev about forking) when you use this	411	forget about forgetting to tell libev about forking) when you use this
308	flag.	412	flag.
309		413
310	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	414	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
311	environment variable.	415	environment variable.
		416
		417	=item C<EVFLAG_NOINOTIFY>
		418
		419	When this flag is specified, then libev will not attempt to use the
		420	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		421	testing, this flag can be useful to conserve inotify file descriptors, as
		422	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		423
		424	=item C<EVFLAG_SIGNALFD>
		425
		426	When this flag is specified, then libev will attempt to use the
		427	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		428	delivers signals synchronously, which makes it both faster and might make
		429	it possible to get the queued signal data. It can also simplify signal
		430	handling with threads, as long as you properly block signals in your
		431	threads that are not interested in handling them.
		432
		433	Signalfd will not be used by default as this changes your signal mask, and
		434	there are a lot of shoddy libraries and programs (glib's threadpool for
		435	example) that can't properly initialise their signal masks.
		436
		437	=item C<EVFLAG_NOSIGMASK>
		438
		439	When this flag is specified, then libev will avoid to modify the signal
		440	mask. Specifically, this means you ahve to make sure signals are unblocked
		441	when you want to receive them.
		442
		443	This behaviour is useful when you want to do your own signal handling, or
		444	want to handle signals only in specific threads and want to avoid libev
		445	unblocking the signals.
		446
		447	It's also required by POSIX in a threaded program, as libev calls
		448	C<sigprocmask>, whose behaviour is officially unspecified.
		449
		450	This flag's behaviour will become the default in future versions of libev.
312		451
313	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	452	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
314		453
315	This is your standard select(2) backend. Not I<completely> standard, as	454	This is your standard select(2) backend. Not I<completely> standard, as
316	libev tries to roll its own fd_set with no limits on the number of fds,	455	libev tries to roll its own fd_set with no limits on the number of fds,
317	but if that fails, expect a fairly low limit on the number of fds when	456	but if that fails, expect a fairly low limit on the number of fds when
318	using this backend. It doesn't scale too well (O(highest_fd)), but its	457	using this backend. It doesn't scale too well (O(highest_fd)), but its
319	usually the fastest backend for a low number of (low-numbered :) fds.	458	usually the fastest backend for a low number of (low-numbered :) fds.
320		459
321	To get good performance out of this backend you need a high amount of	460	To get good performance out of this backend you need a high amount of
322	parallelity (most of the file descriptors should be busy). If you are	461	parallelism (most of the file descriptors should be busy). If you are
323	writing a server, you should C<accept ()> in a loop to accept as many	462	writing a server, you should C<accept ()> in a loop to accept as many
324	connections as possible during one iteration. You might also want to have	463	connections as possible during one iteration. You might also want to have
325	a look at C<ev_set_io_collect_interval ()> to increase the amount of	464	a look at C<ev_set_io_collect_interval ()> to increase the amount of
326	readyness notifications you get per iteration.	465	readiness notifications you get per iteration.
		466
		467	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		468	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		469	C<exceptfds> set on that platform).
327		470
328	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	471	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
329		472
330	And this is your standard poll(2) backend. It's more complicated	473	And this is your standard poll(2) backend. It's more complicated
331	than select, but handles sparse fds better and has no artificial	474	than select, but handles sparse fds better and has no artificial
332	limit on the number of fds you can use (except it will slow down	475	limit on the number of fds you can use (except it will slow down
333	considerably with a lot of inactive fds). It scales similarly to select,	476	considerably with a lot of inactive fds). It scales similarly to select,
334	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	477	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
335	performance tips.	478	performance tips.
336		479
		480	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		481	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		482
337	=item C<EVBACKEND_EPOLL> (value 4, Linux)	483	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		484
		485	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		486	kernels).
338		487
339	For few fds, this backend is a bit little slower than poll and select,	488	For few fds, this backend is a bit little slower than poll and select,
340	but it scales phenomenally better. While poll and select usually scale	489	but it scales phenomenally better. While poll and select usually scale
341	like O(total_fds) where n is the total number of fds (or the highest fd),	490	like O(total_fds) where n is the total number of fds (or the highest fd),
342	epoll scales either O(1) or O(active_fds). The epoll design has a number	491	epoll scales either O(1) or O(active_fds).
343	of shortcomings, such as silently dropping events in some hard-to-detect	492
344	cases and rewiring a syscall per fd change, no fork support and bad	493	The epoll mechanism deserves honorable mention as the most misdesigned
345	support for dup.	494	of the more advanced event mechanisms: mere annoyances include silently
		495	dropping file descriptors, requiring a system call per change per file
		496	descriptor (and unnecessary guessing of parameters), problems with dup,
		497	returning before the timeout value, resulting in additional iterations
		498	(and only giving 5ms accuracy while select on the same platform gives
		499	0.1ms) and so on. The biggest issue is fork races, however - if a program
		500	forks then I<both> parent and child process have to recreate the epoll
		501	set, which can take considerable time (one syscall per file descriptor)
		502	and is of course hard to detect.
		503
		504	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		505	of course I<doesn't>, and epoll just loves to report events for totally
		506	I<different> file descriptors (even already closed ones, so one cannot
		507	even remove them from the set) than registered in the set (especially
		508	on SMP systems). Libev tries to counter these spurious notifications by
		509	employing an additional generation counter and comparing that against the
		510	events to filter out spurious ones, recreating the set when required. Last
		511	not least, it also refuses to work with some file descriptors which work
		512	perfectly fine with C<select> (files, many character devices...).
		513
		514	Epoll is truly the train wreck analog among event poll mechanisms,
		515	a frankenpoll, cobbled together in a hurry, no thought to design or
		516	interaction with others.
346		517
347	While stopping, setting and starting an I/O watcher in the same iteration	518	While stopping, setting and starting an I/O watcher in the same iteration
348	will result in some caching, there is still a syscall per such incident	519	will result in some caching, there is still a system call per such
349	(because the fd could point to a different file description now), so its	520	incident (because the same I<file descriptor> could point to a different
350	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	521	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
351	very well if you register events for both fds.	522	file descriptors might not work very well if you register events for both
352		523	file descriptors.
353	Please note that epoll sometimes generates spurious notifications, so you
354	need to use non-blocking I/O or other means to avoid blocking when no data
355	(or space) is available.
356		524
357	Best performance from this backend is achieved by not unregistering all	525	Best performance from this backend is achieved by not unregistering all
358	watchers for a file descriptor until it has been closed, if possible, i.e.	526	watchers for a file descriptor until it has been closed, if possible,
359	keep at least one watcher active per fd at all times.	527	i.e. keep at least one watcher active per fd at all times. Stopping and
		528	starting a watcher (without re-setting it) also usually doesn't cause
		529	extra overhead. A fork can both result in spurious notifications as well
		530	as in libev having to destroy and recreate the epoll object, which can
		531	take considerable time and thus should be avoided.
360		532
		533	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		534	faster than epoll for maybe up to a hundred file descriptors, depending on
		535	the usage. So sad.
		536
361	While nominally embeddeble in other event loops, this feature is broken in	537	While nominally embeddable in other event loops, this feature is broken in
362	all kernel versions tested so far.	538	all kernel versions tested so far.
		539
		540	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		541	C<EVBACKEND_POLL>.
363		542
364	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	543	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
365		544
366	Kqueue deserves special mention, as at the time of this writing, it	545	Kqueue deserves special mention, as at the time of this writing, it
367	was broken on all BSDs except NetBSD (usually it doesn't work reliably	546	was broken on all BSDs except NetBSD (usually it doesn't work reliably
368	with anything but sockets and pipes, except on Darwin, where of course	547	with anything but sockets and pipes, except on Darwin, where of course
369	it's completely useless). For this reason it's not being "autodetected"	548	it's completely useless). Unlike epoll, however, whose brokenness
		549	is by design, these kqueue bugs can (and eventually will) be fixed
		550	without API changes to existing programs. For this reason it's not being
370	unless you explicitly specify it explicitly in the flags (i.e. using	551	"auto-detected" unless you explicitly specify it in the flags (i.e. using
371	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	552	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
372	system like NetBSD.	553	system like NetBSD.
373		554
374	You still can embed kqueue into a normal poll or select backend and use it	555	You still can embed kqueue into a normal poll or select backend and use it
375	only for sockets (after having made sure that sockets work with kqueue on	556	only for sockets (after having made sure that sockets work with kqueue on
376	the target platform). See C<ev_embed> watchers for more info.	557	the target platform). See C<ev_embed> watchers for more info.
377		558
378	It scales in the same way as the epoll backend, but the interface to the	559	It scales in the same way as the epoll backend, but the interface to the
379	kernel is more efficient (which says nothing about its actual speed, of	560	kernel is more efficient (which says nothing about its actual speed, of
380	course). While stopping, setting and starting an I/O watcher does never	561	course). While stopping, setting and starting an I/O watcher does never
381	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	562	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
382	two event changes per incident, support for C<fork ()> is very bad and it	563	two event changes per incident. Support for C<fork ()> is very bad (but
383	drops fds silently in similarly hard-to-detect cases.	564	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		565	cases
384		566
385	This backend usually performs well under most conditions.	567	This backend usually performs well under most conditions.
386		568
387	While nominally embeddable in other event loops, this doesn't work	569	While nominally embeddable in other event loops, this doesn't work
388	everywhere, so you might need to test for this. And since it is broken	570	everywhere, so you might need to test for this. And since it is broken
389	almost everywhere, you should only use it when you have a lot of sockets	571	almost everywhere, you should only use it when you have a lot of sockets
390	(for which it usually works), by embedding it into another event loop	572	(for which it usually works), by embedding it into another event loop
391	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	573	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
392	sockets.	574	also broken on OS X)) and, did I mention it, using it only for sockets.
		575
		576	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		577	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		578	C<NOTE_EOF>.
393		579
394	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	580	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
395		581
396	This is not implemented yet (and might never be, unless you send me an	582	This is not implemented yet (and might never be, unless you send me an
397	implementation). According to reports, C</dev/poll> only supports sockets	583	implementation). According to reports, C</dev/poll> only supports sockets
…		…
401	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	587	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
402		588
403	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	589	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
404	it's really slow, but it still scales very well (O(active_fds)).	590	it's really slow, but it still scales very well (O(active_fds)).
405		591
406	Please note that solaris event ports can deliver a lot of spurious
407	notifications, so you need to use non-blocking I/O or other means to avoid
408	blocking when no data (or space) is available.
409
410	While this backend scales well, it requires one system call per active	592	While this backend scales well, it requires one system call per active
411	file descriptor per loop iteration. For small and medium numbers of file	593	file descriptor per loop iteration. For small and medium numbers of file
412	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	594	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
413	might perform better.	595	might perform better.
414		596
415	On the positive side, ignoring the spurious readyness notifications, this	597	On the positive side, this backend actually performed fully to
416	backend actually performed to specification in all tests and is fully	598	specification in all tests and is fully embeddable, which is a rare feat
417	embeddable, which is a rare feat among the OS-specific backends.	599	among the OS-specific backends (I vastly prefer correctness over speed
		600	hacks).
		601
		602	On the negative side, the interface is I<bizarre> - so bizarre that
		603	even sun itself gets it wrong in their code examples: The event polling
		604	function sometimes returning events to the caller even though an error
		605	occurred, but with no indication whether it has done so or not (yes, it's
		606	even documented that way) - deadly for edge-triggered interfaces where
		607	you absolutely have to know whether an event occurred or not because you
		608	have to re-arm the watcher.
		609
		610	Fortunately libev seems to be able to work around these idiocies.
		611
		612	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		613	C<EVBACKEND_POLL>.
418		614
419	=item C<EVBACKEND_ALL>	615	=item C<EVBACKEND_ALL>
420		616
421	Try all backends (even potentially broken ones that wouldn't be tried	617	Try all backends (even potentially broken ones that wouldn't be tried
422	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	618	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
423	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	619	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
424		620
425	It is definitely not recommended to use this flag.	621	It is definitely not recommended to use this flag, use whatever
		622	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		623	at all.
		624
		625	=item C<EVBACKEND_MASK>
		626
		627	Not a backend at all, but a mask to select all backend bits from a
		628	C<flags> value, in case you want to mask out any backends from a flags
		629	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
426		630
427	=back	631	=back
428		632
429	If one or more of these are ored into the flags value, then only these	633	If one or more of the backend flags are or'ed into the flags value,
430	backends will be tried (in the reverse order as listed here). If none are	634	then only these backends will be tried (in the reverse order as listed
431	specified, all backends in C<ev_recommended_backends ()> will be tried.	635	here). If none are specified, all backends in C<ev_recommended_backends
432		636	()> will be tried.
433	The most typical usage is like this:
434
435	if (!ev_default_loop (0))
436	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
437
438	Restrict libev to the select and poll backends, and do not allow
439	environment settings to be taken into account:
440
441	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
442
443	Use whatever libev has to offer, but make sure that kqueue is used if
444	available (warning, breaks stuff, best use only with your own private
445	event loop and only if you know the OS supports your types of fds):
446
447	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
448
449	=item struct ev_loop *ev_loop_new (unsigned int flags)
450
451	Similar to C<ev_default_loop>, but always creates a new event loop that is
452	always distinct from the default loop. Unlike the default loop, it cannot
453	handle signal and child watchers, and attempts to do so will be greeted by
454	undefined behaviour (or a failed assertion if assertions are enabled).
455		637
456	Example: Try to create a event loop that uses epoll and nothing else.	638	Example: Try to create a event loop that uses epoll and nothing else.
457		639
458	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	640	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
459	if (!epoller)	641	if (!epoller)
460	fatal ("no epoll found here, maybe it hides under your chair");	642	fatal ("no epoll found here, maybe it hides under your chair");
461		643
		644	Example: Use whatever libev has to offer, but make sure that kqueue is
		645	used if available.
		646
		647	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		648
462	=item ev_default_destroy ()	649	=item ev_loop_destroy (loop)
463		650
464	Destroys the default loop again (frees all memory and kernel state	651	Destroys an event loop object (frees all memory and kernel state
465	etc.). None of the active event watchers will be stopped in the normal	652	etc.). None of the active event watchers will be stopped in the normal
466	sense, so e.g. C<ev_is_active> might still return true. It is your	653	sense, so e.g. C<ev_is_active> might still return true. It is your
467	responsibility to either stop all watchers cleanly yoursef I<before>	654	responsibility to either stop all watchers cleanly yourself I<before>
468	calling this function, or cope with the fact afterwards (which is usually	655	calling this function, or cope with the fact afterwards (which is usually
469	the easiest thing, you can just ignore the watchers and/or C<free ()> them	656	the easiest thing, you can just ignore the watchers and/or C<free ()> them
470	for example).	657	for example).
471		658
472	Note that certain global state, such as signal state, will not be freed by	659	Note that certain global state, such as signal state (and installed signal
473	this function, and related watchers (such as signal and child watchers)	660	handlers), will not be freed by this function, and related watchers (such
474	would need to be stopped manually.	661	as signal and child watchers) would need to be stopped manually.
475		662
476	In general it is not advisable to call this function except in the	663	This function is normally used on loop objects allocated by
477	rare occasion where you really need to free e.g. the signal handling	664	C<ev_loop_new>, but it can also be used on the default loop returned by
		665	C<ev_default_loop>, in which case it is not thread-safe.
		666
		667	Note that it is not advisable to call this function on the default loop
		668	except in the rare occasion where you really need to free its resources.
478	pipe fds. If you need dynamically allocated loops it is better to use	669	If you need dynamically allocated loops it is better to use C<ev_loop_new>
479	C<ev_loop_new> and C<ev_loop_destroy>).	670	and C<ev_loop_destroy>.
480		671
481	=item ev_loop_destroy (loop)	672	=item ev_loop_fork (loop)
482		673
483	Like C<ev_default_destroy>, but destroys an event loop created by an
484	earlier call to C<ev_loop_new>.
485
486	=item ev_default_fork ()
487
488	This function sets a flag that causes subsequent C<ev_loop> iterations	674	This function sets a flag that causes subsequent C<ev_run> iterations to
489	to reinitialise the kernel state for backends that have one. Despite the	675	reinitialise the kernel state for backends that have one. Despite the
490	name, you can call it anytime, but it makes most sense after forking, in	676	name, you can call it anytime, but it makes most sense after forking, in
491	the child process (or both child and parent, but that again makes little	677	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
492	sense). You I<must> call it in the child before using any of the libev	678	child before resuming or calling C<ev_run>.
493	functions, and it will only take effect at the next C<ev_loop> iteration.	679
		680	Again, you I<have> to call it on I<any> loop that you want to re-use after
		681	a fork, I<even if you do not plan to use the loop in the parent>. This is
		682	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		683	during fork.
494		684
495	On the other hand, you only need to call this function in the child	685	On the other hand, you only need to call this function in the child
496	process if and only if you want to use the event library in the child. If	686	process if and only if you want to use the event loop in the child. If
497	you just fork+exec, you don't have to call it at all.	687	you just fork+exec or create a new loop in the child, you don't have to
		688	call it at all (in fact, C<epoll> is so badly broken that it makes a
		689	difference, but libev will usually detect this case on its own and do a
		690	costly reset of the backend).
498		691
499	The function itself is quite fast and it's usually not a problem to call	692	The function itself is quite fast and it's usually not a problem to call
500	it just in case after a fork. To make this easy, the function will fit in	693	it just in case after a fork.
501	quite nicely into a call to C<pthread_atfork>:
502		694
		695	Example: Automate calling C<ev_loop_fork> on the default loop when
		696	using pthreads.
		697
		698	static void
		699	post_fork_child (void)
		700	{
		701	ev_loop_fork (EV_DEFAULT);
		702	}
		703
		704	...
503	pthread_atfork (0, 0, ev_default_fork);	705	pthread_atfork (0, 0, post_fork_child);
504		706
505	=item ev_loop_fork (loop)	707	=item int ev_is_default_loop (loop)
506		708
507	Like C<ev_default_fork>, but acts on an event loop created by	709	Returns true when the given loop is, in fact, the default loop, and false
508	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	710	otherwise.
509	after fork, and how you do this is entirely your own problem.
510		711
511	=item unsigned int ev_loop_count (loop)	712	=item unsigned int ev_iteration (loop)
512		713
513	Returns the count of loop iterations for the loop, which is identical to	714	Returns the current iteration count for the event loop, which is identical
514	the number of times libev did poll for new events. It starts at C<0> and	715	to the number of times libev did poll for new events. It starts at C<0>
515	happily wraps around with enough iterations.	716	and happily wraps around with enough iterations.
516		717
517	This value can sometimes be useful as a generation counter of sorts (it	718	This value can sometimes be useful as a generation counter of sorts (it
518	"ticks" the number of loop iterations), as it roughly corresponds with	719	"ticks" the number of loop iterations), as it roughly corresponds with
519	C<ev_prepare> and C<ev_check> calls.	720	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		721	prepare and check phases.
		722
		723	=item unsigned int ev_depth (loop)
		724
		725	Returns the number of times C<ev_run> was entered minus the number of
		726	times C<ev_run> was exited normally, in other words, the recursion depth.
		727
		728	Outside C<ev_run>, this number is zero. In a callback, this number is
		729	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		730	in which case it is higher.
		731
		732	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		733	throwing an exception etc.), doesn't count as "exit" - consider this
		734	as a hint to avoid such ungentleman-like behaviour unless it's really
		735	convenient, in which case it is fully supported.
520		736
521	=item unsigned int ev_backend (loop)	737	=item unsigned int ev_backend (loop)
522		738
523	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	739	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
524	use.	740	use.
…		…
529	received events and started processing them. This timestamp does not	745	received events and started processing them. This timestamp does not
530	change as long as callbacks are being processed, and this is also the base	746	change as long as callbacks are being processed, and this is also the base
531	time used for relative timers. You can treat it as the timestamp of the	747	time used for relative timers. You can treat it as the timestamp of the
532	event occurring (or more correctly, libev finding out about it).	748	event occurring (or more correctly, libev finding out about it).
533		749
		750	=item ev_now_update (loop)
		751
		752	Establishes the current time by querying the kernel, updating the time
		753	returned by C<ev_now ()> in the progress. This is a costly operation and
		754	is usually done automatically within C<ev_run ()>.
		755
		756	This function is rarely useful, but when some event callback runs for a
		757	very long time without entering the event loop, updating libev's idea of
		758	the current time is a good idea.
		759
		760	See also L<The special problem of time updates> in the C<ev_timer> section.
		761
		762	=item ev_suspend (loop)
		763
		764	=item ev_resume (loop)
		765
		766	These two functions suspend and resume an event loop, for use when the
		767	loop is not used for a while and timeouts should not be processed.
		768
		769	A typical use case would be an interactive program such as a game: When
		770	the user presses C<^Z> to suspend the game and resumes it an hour later it
		771	would be best to handle timeouts as if no time had actually passed while
		772	the program was suspended. This can be achieved by calling C<ev_suspend>
		773	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		774	C<ev_resume> directly afterwards to resume timer processing.
		775
		776	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		777	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		778	will be rescheduled (that is, they will lose any events that would have
		779	occurred while suspended).
		780
		781	After calling C<ev_suspend> you B<must not> call I<any> function on the
		782	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		783	without a previous call to C<ev_suspend>.
		784
		785	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		786	event loop time (see C<ev_now_update>).
		787
534	=item ev_loop (loop, int flags)	788	=item ev_run (loop, int flags)
535		789
536	Finally, this is it, the event handler. This function usually is called	790	Finally, this is it, the event handler. This function usually is called
537	after you initialised all your watchers and you want to start handling	791	after you have initialised all your watchers and you want to start
538	events.	792	handling events. It will ask the operating system for any new events, call
		793	the watcher callbacks, an then repeat the whole process indefinitely: This
		794	is why event loops are called I<loops>.
539		795
540	If the flags argument is specified as C<0>, it will not return until	796	If the flags argument is specified as C<0>, it will keep handling events
541	either no event watchers are active anymore or C<ev_unloop> was called.	797	until either no event watchers are active anymore or C<ev_break> was
		798	called.
542		799
543	Please note that an explicit C<ev_unloop> is usually better than	800	Please note that an explicit C<ev_break> is usually better than
544	relying on all watchers to be stopped when deciding when a program has	801	relying on all watchers to be stopped when deciding when a program has
545	finished (especially in interactive programs), but having a program that	802	finished (especially in interactive programs), but having a program
546	automatically loops as long as it has to and no longer by virtue of	803	that automatically loops as long as it has to and no longer by virtue
547	relying on its watchers stopping correctly is a thing of beauty.	804	of relying on its watchers stopping correctly, that is truly a thing of
		805	beauty.
548		806
		807	This function is also I<mostly> exception-safe - you can break out of
		808	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		809	exception and so on. This does not decrement the C<ev_depth> value, nor
		810	will it clear any outstanding C<EVBREAK_ONE> breaks.
		811
549	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	812	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
550	those events and any outstanding ones, but will not block your process in	813	those events and any already outstanding ones, but will not wait and
551	case there are no events and will return after one iteration of the loop.	814	block your process in case there are no events and will return after one
		815	iteration of the loop. This is sometimes useful to poll and handle new
		816	events while doing lengthy calculations, to keep the program responsive.
552		817
553	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	818	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
554	neccessary) and will handle those and any outstanding ones. It will block	819	necessary) and will handle those and any already outstanding ones. It
555	your process until at least one new event arrives, and will return after	820	will block your process until at least one new event arrives (which could
556	one iteration of the loop. This is useful if you are waiting for some	821	be an event internal to libev itself, so there is no guarantee that a
557	external event in conjunction with something not expressible using other	822	user-registered callback will be called), and will return after one
		823	iteration of the loop.
		824
		825	This is useful if you are waiting for some external event in conjunction
		826	with something not expressible using other libev watchers (i.e. "roll your
558	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	827	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
559	usually a better approach for this kind of thing.	828	usually a better approach for this kind of thing.
560		829
561	Here are the gory details of what C<ev_loop> does:	830	Here are the gory details of what C<ev_run> does:
562		831
		832	- Increment loop depth.
		833	- Reset the ev_break status.
563	- Before the first iteration, call any pending watchers.	834	- Before the first iteration, call any pending watchers.
		835	LOOP:
564	* If EVFLAG_FORKCHECK was used, check for a fork.	836	- If EVFLAG_FORKCHECK was used, check for a fork.
565	- If a fork was detected, queue and call all fork watchers.	837	- If a fork was detected (by any means), queue and call all fork watchers.
566	- Queue and call all prepare watchers.	838	- Queue and call all prepare watchers.
		839	- If ev_break was called, goto FINISH.
567	- If we have been forked, recreate the kernel state.	840	- If we have been forked, detach and recreate the kernel state
		841	as to not disturb the other process.
568	- Update the kernel state with all outstanding changes.	842	- Update the kernel state with all outstanding changes.
569	- Update the "event loop time".	843	- Update the "event loop time" (ev_now ()).
570	- Calculate for how long to sleep or block, if at all	844	- Calculate for how long to sleep or block, if at all
571	(active idle watchers, EVLOOP_NONBLOCK or not having	845	(active idle watchers, EVRUN_NOWAIT or not having
572	any active watchers at all will result in not sleeping).	846	any active watchers at all will result in not sleeping).
573	- Sleep if the I/O and timer collect interval say so.	847	- Sleep if the I/O and timer collect interval say so.
		848	- Increment loop iteration counter.
574	- Block the process, waiting for any events.	849	- Block the process, waiting for any events.
575	- Queue all outstanding I/O (fd) events.	850	- Queue all outstanding I/O (fd) events.
576	- Update the "event loop time" and do time jump handling.	851	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
577	- Queue all outstanding timers.	852	- Queue all expired timers.
578	- Queue all outstanding periodics.	853	- Queue all expired periodics.
579	- If no events are pending now, queue all idle watchers.	854	- Queue all idle watchers with priority higher than that of pending events.
580	- Queue all check watchers.	855	- Queue all check watchers.
581	- Call all queued watchers in reverse order (i.e. check watchers first).	856	- Call all queued watchers in reverse order (i.e. check watchers first).
582	Signals and child watchers are implemented as I/O watchers, and will	857	Signals and child watchers are implemented as I/O watchers, and will
583	be handled here by queueing them when their watcher gets executed.	858	be handled here by queueing them when their watcher gets executed.
584	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	859	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
585	were used, or there are no active watchers, return, otherwise	860	were used, or there are no active watchers, goto FINISH, otherwise
586	continue with step *.	861	continue with step LOOP.
		862	FINISH:
		863	- Reset the ev_break status iff it was EVBREAK_ONE.
		864	- Decrement the loop depth.
		865	- Return.
587		866
588	Example: Queue some jobs and then loop until no events are outstanding	867	Example: Queue some jobs and then loop until no events are outstanding
589	anymore.	868	anymore.
590		869
591	... queue jobs here, make sure they register event watchers as long	870	... queue jobs here, make sure they register event watchers as long
592	... as they still have work to do (even an idle watcher will do..)	871	... as they still have work to do (even an idle watcher will do..)
593	ev_loop (my_loop, 0);	872	ev_run (my_loop, 0);
594	... jobs done. yeah!	873	... jobs done or somebody called break. yeah!
595		874
596	=item ev_unloop (loop, how)	875	=item ev_break (loop, how)
597		876
598	Can be used to make a call to C<ev_loop> return early (but only after it	877	Can be used to make a call to C<ev_run> return early (but only after it
599	has processed all outstanding events). The C<how> argument must be either	878	has processed all outstanding events). The C<how> argument must be either
600	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	879	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
601	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	880	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
602		881
603	This "unloop state" will be cleared when entering C<ev_loop> again.	882	This "break state" will be cleared on the next call to C<ev_run>.
		883
		884	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		885	which case it will have no effect.
604		886
605	=item ev_ref (loop)	887	=item ev_ref (loop)
606		888
607	=item ev_unref (loop)	889	=item ev_unref (loop)
608		890
609	Ref/unref can be used to add or remove a reference count on the event	891	Ref/unref can be used to add or remove a reference count on the event
610	loop: Every watcher keeps one reference, and as long as the reference	892	loop: Every watcher keeps one reference, and as long as the reference
611	count is nonzero, C<ev_loop> will not return on its own. If you have	893	count is nonzero, C<ev_run> will not return on its own.
612	a watcher you never unregister that should not keep C<ev_loop> from	894
613	returning, ev_unref() after starting, and ev_ref() before stopping it. For	895	This is useful when you have a watcher that you never intend to
		896	unregister, but that nevertheless should not keep C<ev_run> from
		897	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		898	before stopping it.
		899
614	example, libev itself uses this for its internal signal pipe: It is not	900	As an example, libev itself uses this for its internal signal pipe: It
615	visible to the libev user and should not keep C<ev_loop> from exiting if	901	is not visible to the libev user and should not keep C<ev_run> from
616	no event watchers registered by it are active. It is also an excellent	902	exiting if no event watchers registered by it are active. It is also an
617	way to do this for generic recurring timers or from within third-party	903	excellent way to do this for generic recurring timers or from within
618	libraries. Just remember to I<unref after start> and I<ref before stop>	904	third-party libraries. Just remember to I<unref after start> and I<ref
619	(but only if the watcher wasn't active before, or was active before,	905	before stop> (but only if the watcher wasn't active before, or was active
620	respectively).	906	before, respectively. Note also that libev might stop watchers itself
		907	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		908	in the callback).
621		909
622	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	910	Example: Create a signal watcher, but keep it from keeping C<ev_run>
623	running when nothing else is active.	911	running when nothing else is active.
624		912
625	struct ev_signal exitsig;	913	ev_signal exitsig;
626	ev_signal_init (&exitsig, sig_cb, SIGINT);	914	ev_signal_init (&exitsig, sig_cb, SIGINT);
627	ev_signal_start (loop, &exitsig);	915	ev_signal_start (loop, &exitsig);
628	evf_unref (loop);	916	ev_unref (loop);
629		917
630	Example: For some weird reason, unregister the above signal handler again.	918	Example: For some weird reason, unregister the above signal handler again.
631		919
632	ev_ref (loop);	920	ev_ref (loop);
633	ev_signal_stop (loop, &exitsig);	921	ev_signal_stop (loop, &exitsig);
634		922
635	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	923	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
636		924
637	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	925	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
638		926
639	These advanced functions influence the time that libev will spend waiting	927	These advanced functions influence the time that libev will spend waiting
640	for events. Both are by default C<0>, meaning that libev will try to	928	for events. Both time intervals are by default C<0>, meaning that libev
641	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	929	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		930	latency.
642		931
643	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	932	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
644	allows libev to delay invocation of I/O and timer/periodic callbacks to	933	allows libev to delay invocation of I/O and timer/periodic callbacks
645	increase efficiency of loop iterations.	934	to increase efficiency of loop iterations (or to increase power-saving
		935	opportunities).
646		936
647	The background is that sometimes your program runs just fast enough to	937	The idea is that sometimes your program runs just fast enough to handle
648	handle one (or very few) event(s) per loop iteration. While this makes	938	one (or very few) event(s) per loop iteration. While this makes the
649	the program responsive, it also wastes a lot of CPU time to poll for new	939	program responsive, it also wastes a lot of CPU time to poll for new
650	events, especially with backends like C<select ()> which have a high	940	events, especially with backends like C<select ()> which have a high
651	overhead for the actual polling but can deliver many events at once.	941	overhead for the actual polling but can deliver many events at once.
652		942
653	By setting a higher I<io collect interval> you allow libev to spend more	943	By setting a higher I<io collect interval> you allow libev to spend more
654	time collecting I/O events, so you can handle more events per iteration,	944	time collecting I/O events, so you can handle more events per iteration,
655	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	945	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
656	C<ev_timer>) will be not affected. Setting this to a non-null value will	946	C<ev_timer>) will be not affected. Setting this to a non-null value will
657	introduce an additional C<ev_sleep ()> call into most loop iterations.	947	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		948	sleep time ensures that libev will not poll for I/O events more often then
		949	once per this interval, on average.
658		950
659	Likewise, by setting a higher I<timeout collect interval> you allow libev	951	Likewise, by setting a higher I<timeout collect interval> you allow libev
660	to spend more time collecting timeouts, at the expense of increased	952	to spend more time collecting timeouts, at the expense of increased
661	latency (the watcher callback will be called later). C<ev_io> watchers	953	latency/jitter/inexactness (the watcher callback will be called
662	will not be affected. Setting this to a non-null value will not introduce	954	later). C<ev_io> watchers will not be affected. Setting this to a non-null
663	any overhead in libev.	955	value will not introduce any overhead in libev.
664		956
665	Many (busy) programs can usually benefit by setting the io collect	957	Many (busy) programs can usually benefit by setting the I/O collect
666	interval to a value near C<0.1> or so, which is often enough for	958	interval to a value near C<0.1> or so, which is often enough for
667	interactive servers (of course not for games), likewise for timeouts. It	959	interactive servers (of course not for games), likewise for timeouts. It
668	usually doesn't make much sense to set it to a lower value than C<0.01>,	960	usually doesn't make much sense to set it to a lower value than C<0.01>,
669	as this approsaches the timing granularity of most systems.	961	as this approaches the timing granularity of most systems. Note that if
		962	you do transactions with the outside world and you can't increase the
		963	parallelity, then this setting will limit your transaction rate (if you
		964	need to poll once per transaction and the I/O collect interval is 0.01,
		965	then you can't do more than 100 transactions per second).
		966
		967	Setting the I<timeout collect interval> can improve the opportunity for
		968	saving power, as the program will "bundle" timer callback invocations that
		969	are "near" in time together, by delaying some, thus reducing the number of
		970	times the process sleeps and wakes up again. Another useful technique to
		971	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		972	they fire on, say, one-second boundaries only.
		973
		974	Example: we only need 0.1s timeout granularity, and we wish not to poll
		975	more often than 100 times per second:
		976
		977	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		978	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		979
		980	=item ev_invoke_pending (loop)
		981
		982	This call will simply invoke all pending watchers while resetting their
		983	pending state. Normally, C<ev_run> does this automatically when required,
		984	but when overriding the invoke callback this call comes handy. This
		985	function can be invoked from a watcher - this can be useful for example
		986	when you want to do some lengthy calculation and want to pass further
		987	event handling to another thread (you still have to make sure only one
		988	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		989
		990	=item int ev_pending_count (loop)
		991
		992	Returns the number of pending watchers - zero indicates that no watchers
		993	are pending.
		994
		995	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		996
		997	This overrides the invoke pending functionality of the loop: Instead of
		998	invoking all pending watchers when there are any, C<ev_run> will call
		999	this callback instead. This is useful, for example, when you want to
		1000	invoke the actual watchers inside another context (another thread etc.).
		1001
		1002	If you want to reset the callback, use C<ev_invoke_pending> as new
		1003	callback.
		1004
		1005	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		1006
		1007	Sometimes you want to share the same loop between multiple threads. This
		1008	can be done relatively simply by putting mutex_lock/unlock calls around
		1009	each call to a libev function.
		1010
		1011	However, C<ev_run> can run an indefinite time, so it is not feasible
		1012	to wait for it to return. One way around this is to wake up the event
		1013	loop via C<ev_break> and C<av_async_send>, another way is to set these
		1014	I<release> and I<acquire> callbacks on the loop.
		1015
		1016	When set, then C<release> will be called just before the thread is
		1017	suspended waiting for new events, and C<acquire> is called just
		1018	afterwards.
		1019
		1020	Ideally, C<release> will just call your mutex_unlock function, and
		1021	C<acquire> will just call the mutex_lock function again.
		1022
		1023	While event loop modifications are allowed between invocations of
		1024	C<release> and C<acquire> (that's their only purpose after all), no
		1025	modifications done will affect the event loop, i.e. adding watchers will
		1026	have no effect on the set of file descriptors being watched, or the time
		1027	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1028	to take note of any changes you made.
		1029
		1030	In theory, threads executing C<ev_run> will be async-cancel safe between
		1031	invocations of C<release> and C<acquire>.
		1032
		1033	See also the locking example in the C<THREADS> section later in this
		1034	document.
		1035
		1036	=item ev_set_userdata (loop, void *data)
		1037
		1038	=item void *ev_userdata (loop)
		1039
		1040	Set and retrieve a single C<void *> associated with a loop. When
		1041	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1042	C<0>.
		1043
		1044	These two functions can be used to associate arbitrary data with a loop,
		1045	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1046	C<acquire> callbacks described above, but of course can be (ab-)used for
		1047	any other purpose as well.
		1048
		1049	=item ev_verify (loop)
		1050
		1051	This function only does something when C<EV_VERIFY> support has been
		1052	compiled in, which is the default for non-minimal builds. It tries to go
		1053	through all internal structures and checks them for validity. If anything
		1054	is found to be inconsistent, it will print an error message to standard
		1055	error and call C<abort ()>.
		1056
		1057	This can be used to catch bugs inside libev itself: under normal
		1058	circumstances, this function will never abort as of course libev keeps its
		1059	data structures consistent.
670		1060
671	=back	1061	=back
672		1062
673		1063
674	=head1 ANATOMY OF A WATCHER	1064	=head1 ANATOMY OF A WATCHER
675		1065
		1066	In the following description, uppercase C<TYPE> in names stands for the
		1067	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1068	watchers and C<ev_io_start> for I/O watchers.
		1069
676	A watcher is a structure that you create and register to record your	1070	A watcher is an opaque structure that you allocate and register to record
677	interest in some event. For instance, if you want to wait for STDIN to	1071	your interest in some event. To make a concrete example, imagine you want
678	become readable, you would create an C<ev_io> watcher for that:	1072	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1073	for that:
679		1074
680	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1075	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
681	{	1076	{
682	ev_io_stop (w);	1077	ev_io_stop (w);
683	ev_unloop (loop, EVUNLOOP_ALL);	1078	ev_break (loop, EVBREAK_ALL);
684	}	1079	}
685		1080
686	struct ev_loop *loop = ev_default_loop (0);	1081	struct ev_loop *loop = ev_default_loop (0);
		1082
687	struct ev_io stdin_watcher;	1083	ev_io stdin_watcher;
		1084
688	ev_init (&stdin_watcher, my_cb);	1085	ev_init (&stdin_watcher, my_cb);
689	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1086	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
690	ev_io_start (loop, &stdin_watcher);	1087	ev_io_start (loop, &stdin_watcher);
		1088
691	ev_loop (loop, 0);	1089	ev_run (loop, 0);
692		1090
693	As you can see, you are responsible for allocating the memory for your	1091	As you can see, you are responsible for allocating the memory for your
694	watcher structures (and it is usually a bad idea to do this on the stack,	1092	watcher structures (and it is I<usually> a bad idea to do this on the
695	although this can sometimes be quite valid).	1093	stack).
696		1094
		1095	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1096	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1097
697	Each watcher structure must be initialised by a call to C<ev_init	1098	Each watcher structure must be initialised by a call to C<ev_init (watcher
698	(watcher *, callback)>, which expects a callback to be provided. This	1099	*, callback)>, which expects a callback to be provided. This callback is
699	callback gets invoked each time the event occurs (or, in the case of io	1100	invoked each time the event occurs (or, in the case of I/O watchers, each
700	watchers, each time the event loop detects that the file descriptor given	1101	time the event loop detects that the file descriptor given is readable
701	is readable and/or writable).	1102	and/or writable).
702		1103
703	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1104	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
704	with arguments specific to this watcher type. There is also a macro	1105	macro to configure it, with arguments specific to the watcher type. There
705	to combine initialisation and setting in one call: C<< ev_<type>_init	1106	is also a macro to combine initialisation and setting in one call: C<<
706	(watcher *, callback, ...) >>.	1107	ev_TYPE_init (watcher *, callback, ...) >>.
707		1108
708	To make the watcher actually watch out for events, you have to start it	1109	To make the watcher actually watch out for events, you have to start it
709	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1110	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
710	*) >>), and you can stop watching for events at any time by calling the	1111	*) >>), and you can stop watching for events at any time by calling the
711	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1112	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
712		1113
713	As long as your watcher is active (has been started but not stopped) you	1114	As long as your watcher is active (has been started but not stopped) you
714	must not touch the values stored in it. Most specifically you must never	1115	must not touch the values stored in it. Most specifically you must never
715	reinitialise it or call its C<set> macro.	1116	reinitialise it or call its C<ev_TYPE_set> macro.
716		1117
717	Each and every callback receives the event loop pointer as first, the	1118	Each and every callback receives the event loop pointer as first, the
718	registered watcher structure as second, and a bitset of received events as	1119	registered watcher structure as second, and a bitset of received events as
719	third argument.	1120	third argument.
720		1121
…		…
729	=item C<EV_WRITE>	1130	=item C<EV_WRITE>
730		1131
731	The file descriptor in the C<ev_io> watcher has become readable and/or	1132	The file descriptor in the C<ev_io> watcher has become readable and/or
732	writable.	1133	writable.
733		1134
734	=item C<EV_TIMEOUT>	1135	=item C<EV_TIMER>
735		1136
736	The C<ev_timer> watcher has timed out.	1137	The C<ev_timer> watcher has timed out.
737		1138
738	=item C<EV_PERIODIC>	1139	=item C<EV_PERIODIC>
739		1140
…		…
757		1158
758	=item C<EV_PREPARE>	1159	=item C<EV_PREPARE>
759		1160
760	=item C<EV_CHECK>	1161	=item C<EV_CHECK>
761		1162
762	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1163	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
763	to gather new events, and all C<ev_check> watchers are invoked just after	1164	to gather new events, and all C<ev_check> watchers are invoked just after
764	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1165	C<ev_run> has gathered them, but before it invokes any callbacks for any
765	received events. Callbacks of both watcher types can start and stop as	1166	received events. Callbacks of both watcher types can start and stop as
766	many watchers as they want, and all of them will be taken into account	1167	many watchers as they want, and all of them will be taken into account
767	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1168	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
768	C<ev_loop> from blocking).	1169	C<ev_run> from blocking).
769		1170
770	=item C<EV_EMBED>	1171	=item C<EV_EMBED>
771		1172
772	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1173	The embedded event loop specified in the C<ev_embed> watcher needs attention.
773		1174
774	=item C<EV_FORK>	1175	=item C<EV_FORK>
775		1176
776	The event loop has been resumed in the child process after fork (see	1177	The event loop has been resumed in the child process after fork (see
777	C<ev_fork>).	1178	C<ev_fork>).
778		1179
		1180	=item C<EV_CLEANUP>
		1181
		1182	The event loop is about to be destroyed (see C<ev_cleanup>).
		1183
779	=item C<EV_ASYNC>	1184	=item C<EV_ASYNC>
780		1185
781	The given async watcher has been asynchronously notified (see C<ev_async>).	1186	The given async watcher has been asynchronously notified (see C<ev_async>).
782		1187
		1188	=item C<EV_CUSTOM>
		1189
		1190	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1191	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1192
783	=item C<EV_ERROR>	1193	=item C<EV_ERROR>
784		1194
785	An unspecified error has occured, the watcher has been stopped. This might	1195	An unspecified error has occurred, the watcher has been stopped. This might
786	happen because the watcher could not be properly started because libev	1196	happen because the watcher could not be properly started because libev
787	ran out of memory, a file descriptor was found to be closed or any other	1197	ran out of memory, a file descriptor was found to be closed or any other
		1198	problem. Libev considers these application bugs.
		1199
788	problem. You best act on it by reporting the problem and somehow coping	1200	You best act on it by reporting the problem and somehow coping with the
789	with the watcher being stopped.	1201	watcher being stopped. Note that well-written programs should not receive
		1202	an error ever, so when your watcher receives it, this usually indicates a
		1203	bug in your program.
790		1204
791	Libev will usually signal a few "dummy" events together with an error,	1205	Libev will usually signal a few "dummy" events together with an error, for
792	for example it might indicate that a fd is readable or writable, and if	1206	example it might indicate that a fd is readable or writable, and if your
793	your callbacks is well-written it can just attempt the operation and cope	1207	callbacks is well-written it can just attempt the operation and cope with
794	with the error from read() or write(). This will not work in multithreaded	1208	the error from read() or write(). This will not work in multi-threaded
795	programs, though, so beware.	1209	programs, though, as the fd could already be closed and reused for another
		1210	thing, so beware.
796		1211
797	=back	1212	=back
798		1213
799	=head2 GENERIC WATCHER FUNCTIONS	1214	=head2 GENERIC WATCHER FUNCTIONS
800
801	In the following description, C<TYPE> stands for the watcher type,
802	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
803		1215
804	=over 4	1216	=over 4
805		1217
806	=item C<ev_init> (ev_TYPE *watcher, callback)	1218	=item C<ev_init> (ev_TYPE *watcher, callback)
807		1219
…		…
813	which rolls both calls into one.	1225	which rolls both calls into one.
814		1226
815	You can reinitialise a watcher at any time as long as it has been stopped	1227	You can reinitialise a watcher at any time as long as it has been stopped
816	(or never started) and there are no pending events outstanding.	1228	(or never started) and there are no pending events outstanding.
817		1229
818	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1230	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
819	int revents)>.	1231	int revents)>.
820		1232
		1233	Example: Initialise an C<ev_io> watcher in two steps.
		1234
		1235	ev_io w;
		1236	ev_init (&w, my_cb);
		1237	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1238
821	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1239	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
822		1240
823	This macro initialises the type-specific parts of a watcher. You need to	1241	This macro initialises the type-specific parts of a watcher. You need to
824	call C<ev_init> at least once before you call this macro, but you can	1242	call C<ev_init> at least once before you call this macro, but you can
825	call C<ev_TYPE_set> any number of times. You must not, however, call this	1243	call C<ev_TYPE_set> any number of times. You must not, however, call this
826	macro on a watcher that is active (it can be pending, however, which is a	1244	macro on a watcher that is active (it can be pending, however, which is a
827	difference to the C<ev_init> macro).	1245	difference to the C<ev_init> macro).
828		1246
829	Although some watcher types do not have type-specific arguments	1247	Although some watcher types do not have type-specific arguments
830	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1248	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
831		1249
		1250	See C<ev_init>, above, for an example.
		1251
832	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1252	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
833		1253
834	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1254	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
835	calls into a single call. This is the most convinient method to initialise	1255	calls into a single call. This is the most convenient method to initialise
836	a watcher. The same limitations apply, of course.	1256	a watcher. The same limitations apply, of course.
837		1257
		1258	Example: Initialise and set an C<ev_io> watcher in one step.
		1259
		1260	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1261
838	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1262	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
839		1263
840	Starts (activates) the given watcher. Only active watchers will receive	1264	Starts (activates) the given watcher. Only active watchers will receive
841	events. If the watcher is already active nothing will happen.	1265	events. If the watcher is already active nothing will happen.
842		1266
		1267	Example: Start the C<ev_io> watcher that is being abused as example in this
		1268	whole section.
		1269
		1270	ev_io_start (EV_DEFAULT_UC, &w);
		1271
843	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1272	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
844		1273
845	Stops the given watcher again (if active) and clears the pending	1274	Stops the given watcher if active, and clears the pending status (whether
		1275	the watcher was active or not).
		1276
846	status. It is possible that stopped watchers are pending (for example,	1277	It is possible that stopped watchers are pending - for example,
847	non-repeating timers are being stopped when they become pending), but	1278	non-repeating timers are being stopped when they become pending - but
848	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1279	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
849	you want to free or reuse the memory used by the watcher it is therefore a	1280	pending. If you want to free or reuse the memory used by the watcher it is
850	good idea to always call its C<ev_TYPE_stop> function.	1281	therefore a good idea to always call its C<ev_TYPE_stop> function.
851		1282
852	=item bool ev_is_active (ev_TYPE *watcher)	1283	=item bool ev_is_active (ev_TYPE *watcher)
853		1284
854	Returns a true value iff the watcher is active (i.e. it has been started	1285	Returns a true value iff the watcher is active (i.e. it has been started
855	and not yet been stopped). As long as a watcher is active you must not modify	1286	and not yet been stopped). As long as a watcher is active you must not modify
…		…
871	=item ev_cb_set (ev_TYPE *watcher, callback)	1302	=item ev_cb_set (ev_TYPE *watcher, callback)
872		1303
873	Change the callback. You can change the callback at virtually any time	1304	Change the callback. You can change the callback at virtually any time
874	(modulo threads).	1305	(modulo threads).
875		1306
876	=item ev_set_priority (ev_TYPE *watcher, priority)	1307	=item ev_set_priority (ev_TYPE *watcher, int priority)
877		1308
878	=item int ev_priority (ev_TYPE *watcher)	1309	=item int ev_priority (ev_TYPE *watcher)
879		1310
880	Set and query the priority of the watcher. The priority is a small	1311	Set and query the priority of the watcher. The priority is a small
881	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1312	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
882	(default: C<-2>). Pending watchers with higher priority will be invoked	1313	(default: C<-2>). Pending watchers with higher priority will be invoked
883	before watchers with lower priority, but priority will not keep watchers	1314	before watchers with lower priority, but priority will not keep watchers
884	from being executed (except for C<ev_idle> watchers).	1315	from being executed (except for C<ev_idle> watchers).
885		1316
886	This means that priorities are I<only> used for ordering callback
887	invocation after new events have been received. This is useful, for
888	example, to reduce latency after idling, or more often, to bind two
889	watchers on the same event and make sure one is called first.
890
891	If you need to suppress invocation when higher priority events are pending	1317	If you need to suppress invocation when higher priority events are pending
892	you need to look at C<ev_idle> watchers, which provide this functionality.	1318	you need to look at C<ev_idle> watchers, which provide this functionality.
893		1319
894	You I<must not> change the priority of a watcher as long as it is active or	1320	You I<must not> change the priority of a watcher as long as it is active or
895	pending.	1321	pending.
896		1322
		1323	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1324	fine, as long as you do not mind that the priority value you query might
		1325	or might not have been clamped to the valid range.
		1326
897	The default priority used by watchers when no priority has been set is	1327	The default priority used by watchers when no priority has been set is
898	always C<0>, which is supposed to not be too high and not be too low :).	1328	always C<0>, which is supposed to not be too high and not be too low :).
899		1329
900	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1330	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
901	fine, as long as you do not mind that the priority value you query might	1331	priorities.
902	or might not have been adjusted to be within valid range.
903		1332
904	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1333	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
905		1334
906	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1335	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
907	C<loop> nor C<revents> need to be valid as long as the watcher callback	1336	C<loop> nor C<revents> need to be valid as long as the watcher callback
908	can deal with that fact.	1337	can deal with that fact, as both are simply passed through to the
		1338	callback.
909		1339
910	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1340	=item int ev_clear_pending (loop, ev_TYPE *watcher)
911		1341
912	If the watcher is pending, this function returns clears its pending status	1342	If the watcher is pending, this function clears its pending status and
913	and returns its C<revents> bitset (as if its callback was invoked). If the	1343	returns its C<revents> bitset (as if its callback was invoked). If the
914	watcher isn't pending it does nothing and returns C<0>.	1344	watcher isn't pending it does nothing and returns C<0>.
915		1345
		1346	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1347	callback to be invoked, which can be accomplished with this function.
		1348
		1349	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1350
		1351	Feeds the given event set into the event loop, as if the specified event
		1352	had happened for the specified watcher (which must be a pointer to an
		1353	initialised but not necessarily started event watcher). Obviously you must
		1354	not free the watcher as long as it has pending events.
		1355
		1356	Stopping the watcher, letting libev invoke it, or calling
		1357	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1358	not started in the first place.
		1359
		1360	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1361	functions that do not need a watcher.
		1362
916	=back	1363	=back
917		1364
		1365	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
		1366	OWN COMPOSITE WATCHERS> idioms.
918		1367
919	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1368	=head2 WATCHER STATES
920		1369
921	Each watcher has, by default, a member C<void *data> that you can change	1370	There are various watcher states mentioned throughout this manual -
922	and read at any time, libev will completely ignore it. This can be used	1371	active, pending and so on. In this section these states and the rules to
923	to associate arbitrary data with your watcher. If you need more data and	1372	transition between them will be described in more detail - and while these
924	don't want to allocate memory and store a pointer to it in that data	1373	rules might look complicated, they usually do "the right thing".
925	member, you can also "subclass" the watcher type and provide your own
926	data:
927		1374
928	struct my_io	1375	=over 4
929	{
930	struct ev_io io;
931	int otherfd;
932	void *somedata;
933	struct whatever *mostinteresting;
934	}
935		1376
936	And since your callback will be called with a pointer to the watcher, you	1377	=item initialiased
937	can cast it back to your own type:
938		1378
939	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1379	Before a watcher can be registered with the event looop it has to be
940	{	1380	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
941	struct my_io *w = (struct my_io *)w_;	1381	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
942	...
943	}
944		1382
945	More interesting and less C-conformant ways of casting your callback type	1383	In this state it is simply some block of memory that is suitable for
946	instead have been omitted.	1384	use in an event loop. It can be moved around, freed, reused etc. at
		1385	will - as long as you either keep the memory contents intact, or call
		1386	C<ev_TYPE_init> again.
947		1387
948	Another common scenario is having some data structure with multiple	1388	=item started/running/active
949	watchers:
950		1389
951	struct my_biggy	1390	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
952	{	1391	property of the event loop, and is actively waiting for events. While in
953	int some_data;	1392	this state it cannot be accessed (except in a few documented ways), moved,
954	ev_timer t1;	1393	freed or anything else - the only legal thing is to keep a pointer to it,
955	ev_timer t2;	1394	and call libev functions on it that are documented to work on active watchers.
956	}
957		1395
958	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1396	=item pending
959	you need to use C<offsetof>:
960		1397
961	#include <stddef.h>	1398	If a watcher is active and libev determines that an event it is interested
		1399	in has occurred (such as a timer expiring), it will become pending. It will
		1400	stay in this pending state until either it is stopped or its callback is
		1401	about to be invoked, so it is not normally pending inside the watcher
		1402	callback.
962		1403
		1404	The watcher might or might not be active while it is pending (for example,
		1405	an expired non-repeating timer can be pending but no longer active). If it
		1406	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1407	but it is still property of the event loop at this time, so cannot be
		1408	moved, freed or reused. And if it is active the rules described in the
		1409	previous item still apply.
		1410
		1411	It is also possible to feed an event on a watcher that is not active (e.g.
		1412	via C<ev_feed_event>), in which case it becomes pending without being
		1413	active.
		1414
		1415	=item stopped
		1416
		1417	A watcher can be stopped implicitly by libev (in which case it might still
		1418	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1419	latter will clear any pending state the watcher might be in, regardless
		1420	of whether it was active or not, so stopping a watcher explicitly before
		1421	freeing it is often a good idea.
		1422
		1423	While stopped (and not pending) the watcher is essentially in the
		1424	initialised state, that is, it can be reused, moved, modified in any way
		1425	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1426	it again).
		1427
		1428	=back
		1429
		1430	=head2 WATCHER PRIORITY MODELS
		1431
		1432	Many event loops support I<watcher priorities>, which are usually small
		1433	integers that influence the ordering of event callback invocation
		1434	between watchers in some way, all else being equal.
		1435
		1436	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1437	description for the more technical details such as the actual priority
		1438	range.
		1439
		1440	There are two common ways how these these priorities are being interpreted
		1441	by event loops:
		1442
		1443	In the more common lock-out model, higher priorities "lock out" invocation
		1444	of lower priority watchers, which means as long as higher priority
		1445	watchers receive events, lower priority watchers are not being invoked.
		1446
		1447	The less common only-for-ordering model uses priorities solely to order
		1448	callback invocation within a single event loop iteration: Higher priority
		1449	watchers are invoked before lower priority ones, but they all get invoked
		1450	before polling for new events.
		1451
		1452	Libev uses the second (only-for-ordering) model for all its watchers
		1453	except for idle watchers (which use the lock-out model).
		1454
		1455	The rationale behind this is that implementing the lock-out model for
		1456	watchers is not well supported by most kernel interfaces, and most event
		1457	libraries will just poll for the same events again and again as long as
		1458	their callbacks have not been executed, which is very inefficient in the
		1459	common case of one high-priority watcher locking out a mass of lower
		1460	priority ones.
		1461
		1462	Static (ordering) priorities are most useful when you have two or more
		1463	watchers handling the same resource: a typical usage example is having an
		1464	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1465	timeouts. Under load, data might be received while the program handles
		1466	other jobs, but since timers normally get invoked first, the timeout
		1467	handler will be executed before checking for data. In that case, giving
		1468	the timer a lower priority than the I/O watcher ensures that I/O will be
		1469	handled first even under adverse conditions (which is usually, but not
		1470	always, what you want).
		1471
		1472	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1473	will only be executed when no same or higher priority watchers have
		1474	received events, they can be used to implement the "lock-out" model when
		1475	required.
		1476
		1477	For example, to emulate how many other event libraries handle priorities,
		1478	you can associate an C<ev_idle> watcher to each such watcher, and in
		1479	the normal watcher callback, you just start the idle watcher. The real
		1480	processing is done in the idle watcher callback. This causes libev to
		1481	continuously poll and process kernel event data for the watcher, but when
		1482	the lock-out case is known to be rare (which in turn is rare :), this is
		1483	workable.
		1484
		1485	Usually, however, the lock-out model implemented that way will perform
		1486	miserably under the type of load it was designed to handle. In that case,
		1487	it might be preferable to stop the real watcher before starting the
		1488	idle watcher, so the kernel will not have to process the event in case
		1489	the actual processing will be delayed for considerable time.
		1490
		1491	Here is an example of an I/O watcher that should run at a strictly lower
		1492	priority than the default, and which should only process data when no
		1493	other events are pending:
		1494
		1495	ev_idle idle; // actual processing watcher
		1496	ev_io io; // actual event watcher
		1497
963	static void	1498	static void
964	t1_cb (EV_P_ struct ev_timer *w, int revents)	1499	io_cb (EV_P_ ev_io *w, int revents)
965	{	1500	{
966	struct my_biggy big = (struct my_biggy *	1501	// stop the I/O watcher, we received the event, but
967	(((char *)w) - offsetof (struct my_biggy, t1));	1502	// are not yet ready to handle it.
		1503	ev_io_stop (EV_A_ w);
		1504
		1505	// start the idle watcher to handle the actual event.
		1506	// it will not be executed as long as other watchers
		1507	// with the default priority are receiving events.
		1508	ev_idle_start (EV_A_ &idle);
968	}	1509	}
969		1510
970	static void	1511	static void
971	t2_cb (EV_P_ struct ev_timer *w, int revents)	1512	idle_cb (EV_P_ ev_idle *w, int revents)
972	{	1513	{
973	struct my_biggy big = (struct my_biggy *	1514	// actual processing
974	(((char *)w) - offsetof (struct my_biggy, t2));	1515	read (STDIN_FILENO, ...);
		1516
		1517	// have to start the I/O watcher again, as
		1518	// we have handled the event
		1519	ev_io_start (EV_P_ &io);
975	}	1520	}
		1521
		1522	// initialisation
		1523	ev_idle_init (&idle, idle_cb);
		1524	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1525	ev_io_start (EV_DEFAULT_ &io);
		1526
		1527	In the "real" world, it might also be beneficial to start a timer, so that
		1528	low-priority connections can not be locked out forever under load. This
		1529	enables your program to keep a lower latency for important connections
		1530	during short periods of high load, while not completely locking out less
		1531	important ones.
976		1532
977		1533
978	=head1 WATCHER TYPES	1534	=head1 WATCHER TYPES
979		1535
980	This section describes each watcher in detail, but will not repeat	1536	This section describes each watcher in detail, but will not repeat
…		…
1004	In general you can register as many read and/or write event watchers per	1560	In general you can register as many read and/or write event watchers per
1005	fd as you want (as long as you don't confuse yourself). Setting all file	1561	fd as you want (as long as you don't confuse yourself). Setting all file
1006	descriptors to non-blocking mode is also usually a good idea (but not	1562	descriptors to non-blocking mode is also usually a good idea (but not
1007	required if you know what you are doing).	1563	required if you know what you are doing).
1008		1564
1009	If you must do this, then force the use of a known-to-be-good backend
1010	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1011	C<EVBACKEND_POLL>).
1012
1013	Another thing you have to watch out for is that it is quite easy to	1565	Another thing you have to watch out for is that it is quite easy to
1014	receive "spurious" readyness notifications, that is your callback might	1566	receive "spurious" readiness notifications, that is, your callback might
1015	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1567	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1016	because there is no data. Not only are some backends known to create a	1568	because there is no data. It is very easy to get into this situation even
1017	lot of those (for example solaris ports), it is very easy to get into	1569	with a relatively standard program structure. Thus it is best to always
1018	this situation even with a relatively standard program structure. Thus	1570	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1019	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1020	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1571	preferable to a program hanging until some data arrives.
1021		1572
1022	If you cannot run the fd in non-blocking mode (for example you should not	1573	If you cannot run the fd in non-blocking mode (for example you should
1023	play around with an Xlib connection), then you have to seperately re-test	1574	not play around with an Xlib connection), then you have to separately
1024	whether a file descriptor is really ready with a known-to-be good interface	1575	re-test whether a file descriptor is really ready with a known-to-be good
1025	such as poll (fortunately in our Xlib example, Xlib already does this on	1576	interface such as poll (fortunately in the case of Xlib, it already does
1026	its own, so its quite safe to use).	1577	this on its own, so its quite safe to use). Some people additionally
		1578	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1579	indefinitely.
		1580
		1581	But really, best use non-blocking mode.
1027		1582
1028	=head3 The special problem of disappearing file descriptors	1583	=head3 The special problem of disappearing file descriptors
1029		1584
1030	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1585	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1031	descriptor (either by calling C<close> explicitly or by any other means,	1586	descriptor (either due to calling C<close> explicitly or any other means,
1032	such as C<dup>). The reason is that you register interest in some file	1587	such as C<dup2>). The reason is that you register interest in some file
1033	descriptor, but when it goes away, the operating system will silently drop	1588	descriptor, but when it goes away, the operating system will silently drop
1034	this interest. If another file descriptor with the same number then is	1589	this interest. If another file descriptor with the same number then is
1035	registered with libev, there is no efficient way to see that this is, in	1590	registered with libev, there is no efficient way to see that this is, in
1036	fact, a different file descriptor.	1591	fact, a different file descriptor.
1037		1592
…		…
1055		1610
1056	There is no workaround possible except not registering events	1611	There is no workaround possible except not registering events
1057	for potentially C<dup ()>'ed file descriptors, or to resort to	1612	for potentially C<dup ()>'ed file descriptors, or to resort to
1058	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1613	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1059		1614
		1615	=head3 The special problem of files
		1616
		1617	Many people try to use C<select> (or libev) on file descriptors
		1618	representing files, and expect it to become ready when their program
		1619	doesn't block on disk accesses (which can take a long time on their own).
		1620
		1621	However, this cannot ever work in the "expected" way - you get a readiness
		1622	notification as soon as the kernel knows whether and how much data is
		1623	there, and in the case of open files, that's always the case, so you
		1624	always get a readiness notification instantly, and your read (or possibly
		1625	write) will still block on the disk I/O.
		1626
		1627	Another way to view it is that in the case of sockets, pipes, character
		1628	devices and so on, there is another party (the sender) that delivers data
		1629	on its own, but in the case of files, there is no such thing: the disk
		1630	will not send data on its own, simply because it doesn't know what you
		1631	wish to read - you would first have to request some data.
		1632
		1633	Since files are typically not-so-well supported by advanced notification
		1634	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1635	to files, even though you should not use it. The reason for this is
		1636	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1637	usually a tty, often a pipe, but also sometimes files or special devices
		1638	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1639	F</dev/urandom>), and even though the file might better be served with
		1640	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1641	it "just works" instead of freezing.
		1642
		1643	So avoid file descriptors pointing to files when you know it (e.g. use
		1644	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1645	when you rarely read from a file instead of from a socket, and want to
		1646	reuse the same code path.
		1647
1060	=head3 The special problem of fork	1648	=head3 The special problem of fork
1061		1649
1062	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1650	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1063	useless behaviour. Libev fully supports fork, but needs to be told about	1651	useless behaviour. Libev fully supports fork, but needs to be told about
1064	it in the child.	1652	it in the child if you want to continue to use it in the child.
1065		1653
1066	To support fork in your programs, you either have to call	1654	To support fork in your child processes, you have to call C<ev_loop_fork
1067	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1655	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1068	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1656	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1069	C<EVBACKEND_POLL>.
1070		1657
		1658	=head3 The special problem of SIGPIPE
		1659
		1660	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1661	when writing to a pipe whose other end has been closed, your program gets
		1662	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1663	this is sensible behaviour, for daemons, this is usually undesirable.
		1664
		1665	So when you encounter spurious, unexplained daemon exits, make sure you
		1666	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1667	somewhere, as that would have given you a big clue).
		1668
		1669	=head3 The special problem of accept()ing when you can't
		1670
		1671	Many implementations of the POSIX C<accept> function (for example,
		1672	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1673	connection from the pending queue in all error cases.
		1674
		1675	For example, larger servers often run out of file descriptors (because
		1676	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1677	rejecting the connection, leading to libev signalling readiness on
		1678	the next iteration again (the connection still exists after all), and
		1679	typically causing the program to loop at 100% CPU usage.
		1680
		1681	Unfortunately, the set of errors that cause this issue differs between
		1682	operating systems, there is usually little the app can do to remedy the
		1683	situation, and no known thread-safe method of removing the connection to
		1684	cope with overload is known (to me).
		1685
		1686	One of the easiest ways to handle this situation is to just ignore it
		1687	- when the program encounters an overload, it will just loop until the
		1688	situation is over. While this is a form of busy waiting, no OS offers an
		1689	event-based way to handle this situation, so it's the best one can do.
		1690
		1691	A better way to handle the situation is to log any errors other than
		1692	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1693	messages, and continue as usual, which at least gives the user an idea of
		1694	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1695	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1696	usage.
		1697
		1698	If your program is single-threaded, then you could also keep a dummy file
		1699	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1700	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1701	close that fd, and create a new dummy fd. This will gracefully refuse
		1702	clients under typical overload conditions.
		1703
		1704	The last way to handle it is to simply log the error and C<exit>, as
		1705	is often done with C<malloc> failures, but this results in an easy
		1706	opportunity for a DoS attack.
1071		1707
1072	=head3 Watcher-Specific Functions	1708	=head3 Watcher-Specific Functions
1073		1709
1074	=over 4	1710	=over 4
1075		1711
1076	=item ev_io_init (ev_io *, callback, int fd, int events)	1712	=item ev_io_init (ev_io *, callback, int fd, int events)
1077		1713
1078	=item ev_io_set (ev_io *, int fd, int events)	1714	=item ev_io_set (ev_io *, int fd, int events)
1079		1715
1080	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1716	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1081	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1717	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1082	C<EV_READ | EV_WRITE> to receive the given events.	1718	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1083		1719
1084	=item int fd [read-only]	1720	=item int fd [read-only]
1085		1721
1086	The file descriptor being watched.	1722	The file descriptor being watched.
1087		1723
…		…
1095		1731
1096	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1732	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1097	readable, but only once. Since it is likely line-buffered, you could	1733	readable, but only once. Since it is likely line-buffered, you could
1098	attempt to read a whole line in the callback.	1734	attempt to read a whole line in the callback.
1099		1735
1100	static void	1736	static void
1101	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1737	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1102	{	1738	{
1103	ev_io_stop (loop, w);	1739	ev_io_stop (loop, w);
1104	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1740	.. read from stdin here (or from w->fd) and handle any I/O errors
1105	}	1741	}
1106		1742
1107	...	1743	...
1108	struct ev_loop *loop = ev_default_init (0);	1744	struct ev_loop *loop = ev_default_init (0);
1109	struct ev_io stdin_readable;	1745	ev_io stdin_readable;
1110	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1746	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1111	ev_io_start (loop, &stdin_readable);	1747	ev_io_start (loop, &stdin_readable);
1112	ev_loop (loop, 0);	1748	ev_run (loop, 0);
1113		1749
1114		1750
1115	=head2 C<ev_timer> - relative and optionally repeating timeouts	1751	=head2 C<ev_timer> - relative and optionally repeating timeouts
1116		1752
1117	Timer watchers are simple relative timers that generate an event after a	1753	Timer watchers are simple relative timers that generate an event after a
1118	given time, and optionally repeating in regular intervals after that.	1754	given time, and optionally repeating in regular intervals after that.
1119		1755
1120	The timers are based on real time, that is, if you register an event that	1756	The timers are based on real time, that is, if you register an event that
1121	times out after an hour and you reset your system clock to last years	1757	times out after an hour and you reset your system clock to January last
1122	time, it will still time out after (roughly) and hour. "Roughly" because	1758	year, it will still time out after (roughly) one hour. "Roughly" because
1123	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1759	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1124	monotonic clock option helps a lot here).	1760	monotonic clock option helps a lot here).
		1761
		1762	The callback is guaranteed to be invoked only I<after> its timeout has
		1763	passed (not I<at>, so on systems with very low-resolution clocks this
		1764	might introduce a small delay). If multiple timers become ready during the
		1765	same loop iteration then the ones with earlier time-out values are invoked
		1766	before ones of the same priority with later time-out values (but this is
		1767	no longer true when a callback calls C<ev_run> recursively).
		1768
		1769	=head3 Be smart about timeouts
		1770
		1771	Many real-world problems involve some kind of timeout, usually for error
		1772	recovery. A typical example is an HTTP request - if the other side hangs,
		1773	you want to raise some error after a while.
		1774
		1775	What follows are some ways to handle this problem, from obvious and
		1776	inefficient to smart and efficient.
		1777
		1778	In the following, a 60 second activity timeout is assumed - a timeout that
		1779	gets reset to 60 seconds each time there is activity (e.g. each time some
		1780	data or other life sign was received).
		1781
		1782	=over 4
		1783
		1784	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1785
		1786	This is the most obvious, but not the most simple way: In the beginning,
		1787	start the watcher:
		1788
		1789	ev_timer_init (timer, callback, 60., 0.);
		1790	ev_timer_start (loop, timer);
		1791
		1792	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1793	and start it again:
		1794
		1795	ev_timer_stop (loop, timer);
		1796	ev_timer_set (timer, 60., 0.);
		1797	ev_timer_start (loop, timer);
		1798
		1799	This is relatively simple to implement, but means that each time there is
		1800	some activity, libev will first have to remove the timer from its internal
		1801	data structure and then add it again. Libev tries to be fast, but it's
		1802	still not a constant-time operation.
		1803
		1804	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1805
		1806	This is the easiest way, and involves using C<ev_timer_again> instead of
		1807	C<ev_timer_start>.
		1808
		1809	To implement this, configure an C<ev_timer> with a C<repeat> value
		1810	of C<60> and then call C<ev_timer_again> at start and each time you
		1811	successfully read or write some data. If you go into an idle state where
		1812	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1813	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1814
		1815	That means you can ignore both the C<ev_timer_start> function and the
		1816	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1817	member and C<ev_timer_again>.
		1818
		1819	At start:
		1820
		1821	ev_init (timer, callback);
		1822	timer->repeat = 60.;
		1823	ev_timer_again (loop, timer);
		1824
		1825	Each time there is some activity:
		1826
		1827	ev_timer_again (loop, timer);
		1828
		1829	It is even possible to change the time-out on the fly, regardless of
		1830	whether the watcher is active or not:
		1831
		1832	timer->repeat = 30.;
		1833	ev_timer_again (loop, timer);
		1834
		1835	This is slightly more efficient then stopping/starting the timer each time
		1836	you want to modify its timeout value, as libev does not have to completely
		1837	remove and re-insert the timer from/into its internal data structure.
		1838
		1839	It is, however, even simpler than the "obvious" way to do it.
		1840
		1841	=item 3. Let the timer time out, but then re-arm it as required.
		1842
		1843	This method is more tricky, but usually most efficient: Most timeouts are
		1844	relatively long compared to the intervals between other activity - in
		1845	our example, within 60 seconds, there are usually many I/O events with
		1846	associated activity resets.
		1847
		1848	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1849	but remember the time of last activity, and check for a real timeout only
		1850	within the callback:
		1851
		1852	ev_tstamp last_activity; // time of last activity
		1853
		1854	static void
		1855	callback (EV_P_ ev_timer *w, int revents)
		1856	{
		1857	ev_tstamp now = ev_now (EV_A);
		1858	ev_tstamp timeout = last_activity + 60.;
		1859
		1860	// if last_activity + 60. is older than now, we did time out
		1861	if (timeout < now)
		1862	{
		1863	// timeout occurred, take action
		1864	}
		1865	else
		1866	{
		1867	// callback was invoked, but there was some activity, re-arm
		1868	// the watcher to fire in last_activity + 60, which is
		1869	// guaranteed to be in the future, so "again" is positive:
		1870	w->repeat = timeout - now;
		1871	ev_timer_again (EV_A_ w);
		1872	}
		1873	}
		1874
		1875	To summarise the callback: first calculate the real timeout (defined
		1876	as "60 seconds after the last activity"), then check if that time has
		1877	been reached, which means something I<did>, in fact, time out. Otherwise
		1878	the callback was invoked too early (C<timeout> is in the future), so
		1879	re-schedule the timer to fire at that future time, to see if maybe we have
		1880	a timeout then.
		1881
		1882	Note how C<ev_timer_again> is used, taking advantage of the
		1883	C<ev_timer_again> optimisation when the timer is already running.
		1884
		1885	This scheme causes more callback invocations (about one every 60 seconds
		1886	minus half the average time between activity), but virtually no calls to
		1887	libev to change the timeout.
		1888
		1889	To start the timer, simply initialise the watcher and set C<last_activity>
		1890	to the current time (meaning we just have some activity :), then call the
		1891	callback, which will "do the right thing" and start the timer:
		1892
		1893	ev_init (timer, callback);
		1894	last_activity = ev_now (loop);
		1895	callback (loop, timer, EV_TIMER);
		1896
		1897	And when there is some activity, simply store the current time in
		1898	C<last_activity>, no libev calls at all:
		1899
		1900	last_activity = ev_now (loop);
		1901
		1902	This technique is slightly more complex, but in most cases where the
		1903	time-out is unlikely to be triggered, much more efficient.
		1904
		1905	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1906	callback :) - just change the timeout and invoke the callback, which will
		1907	fix things for you.
		1908
		1909	=item 4. Wee, just use a double-linked list for your timeouts.
		1910
		1911	If there is not one request, but many thousands (millions...), all
		1912	employing some kind of timeout with the same timeout value, then one can
		1913	do even better:
		1914
		1915	When starting the timeout, calculate the timeout value and put the timeout
		1916	at the I<end> of the list.
		1917
		1918	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1919	the list is expected to fire (for example, using the technique #3).
		1920
		1921	When there is some activity, remove the timer from the list, recalculate
		1922	the timeout, append it to the end of the list again, and make sure to
		1923	update the C<ev_timer> if it was taken from the beginning of the list.
		1924
		1925	This way, one can manage an unlimited number of timeouts in O(1) time for
		1926	starting, stopping and updating the timers, at the expense of a major
		1927	complication, and having to use a constant timeout. The constant timeout
		1928	ensures that the list stays sorted.
		1929
		1930	=back
		1931
		1932	So which method the best?
		1933
		1934	Method #2 is a simple no-brain-required solution that is adequate in most
		1935	situations. Method #3 requires a bit more thinking, but handles many cases
		1936	better, and isn't very complicated either. In most case, choosing either
		1937	one is fine, with #3 being better in typical situations.
		1938
		1939	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1940	rather complicated, but extremely efficient, something that really pays
		1941	off after the first million or so of active timers, i.e. it's usually
		1942	overkill :)
		1943
		1944	=head3 The special problem of time updates
		1945
		1946	Establishing the current time is a costly operation (it usually takes at
		1947	least two system calls): EV therefore updates its idea of the current
		1948	time only before and after C<ev_run> collects new events, which causes a
		1949	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1950	lots of events in one iteration.
1125		1951
1126	The relative timeouts are calculated relative to the C<ev_now ()>	1952	The relative timeouts are calculated relative to the C<ev_now ()>
1127	time. This is usually the right thing as this timestamp refers to the time	1953	time. This is usually the right thing as this timestamp refers to the time
1128	of the event triggering whatever timeout you are modifying/starting. If	1954	of the event triggering whatever timeout you are modifying/starting. If
1129	you suspect event processing to be delayed and you I<need> to base the timeout	1955	you suspect event processing to be delayed and you I<need> to base the
1130	on the current time, use something like this to adjust for this:	1956	timeout on the current time, use something like this to adjust for this:
1131		1957
1132	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1958	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1133		1959
1134	The callback is guarenteed to be invoked only when its timeout has passed,	1960	If the event loop is suspended for a long time, you can also force an
1135	but if multiple timers become ready during the same loop iteration then	1961	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1136	order of execution is undefined.	1962	()>.
		1963
		1964	=head3 The special problems of suspended animation
		1965
		1966	When you leave the server world it is quite customary to hit machines that
		1967	can suspend/hibernate - what happens to the clocks during such a suspend?
		1968
		1969	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1970	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1971	to run until the system is suspended, but they will not advance while the
		1972	system is suspended. That means, on resume, it will be as if the program
		1973	was frozen for a few seconds, but the suspend time will not be counted
		1974	towards C<ev_timer> when a monotonic clock source is used. The real time
		1975	clock advanced as expected, but if it is used as sole clocksource, then a
		1976	long suspend would be detected as a time jump by libev, and timers would
		1977	be adjusted accordingly.
		1978
		1979	I would not be surprised to see different behaviour in different between
		1980	operating systems, OS versions or even different hardware.
		1981
		1982	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1983	time jump in the monotonic clocks and the realtime clock. If the program
		1984	is suspended for a very long time, and monotonic clock sources are in use,
		1985	then you can expect C<ev_timer>s to expire as the full suspension time
		1986	will be counted towards the timers. When no monotonic clock source is in
		1987	use, then libev will again assume a timejump and adjust accordingly.
		1988
		1989	It might be beneficial for this latter case to call C<ev_suspend>
		1990	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1991	deterministic behaviour in this case (you can do nothing against
		1992	C<SIGSTOP>).
1137		1993
1138	=head3 Watcher-Specific Functions and Data Members	1994	=head3 Watcher-Specific Functions and Data Members
1139		1995
1140	=over 4	1996	=over 4
1141		1997
1142	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1998	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1143		1999
1144	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2000	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1145		2001
1146	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2002	Configure the timer to trigger after C<after> seconds. If C<repeat>
1147	C<0.>, then it will automatically be stopped. If it is positive, then the	2003	is C<0.>, then it will automatically be stopped once the timeout is
1148	timer will automatically be configured to trigger again C<repeat> seconds	2004	reached. If it is positive, then the timer will automatically be
1149	later, again, and again, until stopped manually.	2005	configured to trigger again C<repeat> seconds later, again, and again,
		2006	until stopped manually.
1150		2007
1151	The timer itself will do a best-effort at avoiding drift, that is, if you	2008	The timer itself will do a best-effort at avoiding drift, that is, if
1152	configure a timer to trigger every 10 seconds, then it will trigger at	2009	you configure a timer to trigger every 10 seconds, then it will normally
1153	exactly 10 second intervals. If, however, your program cannot keep up with	2010	trigger at exactly 10 second intervals. If, however, your program cannot
1154	the timer (because it takes longer than those 10 seconds to do stuff) the	2011	keep up with the timer (because it takes longer than those 10 seconds to
1155	timer will not fire more than once per event loop iteration.	2012	do stuff) the timer will not fire more than once per event loop iteration.
1156		2013
1157	=item ev_timer_again (loop)	2014	=item ev_timer_again (loop, ev_timer *)
1158		2015
1159	This will act as if the timer timed out and restart it again if it is	2016	This will act as if the timer timed out and restart it again if it is
1160	repeating. The exact semantics are:	2017	repeating. The exact semantics are:
1161		2018
1162	If the timer is pending, its pending status is cleared.	2019	If the timer is pending, its pending status is cleared.
1163		2020
1164	If the timer is started but nonrepeating, stop it (as if it timed out).	2021	If the timer is started but non-repeating, stop it (as if it timed out).
1165		2022
1166	If the timer is repeating, either start it if necessary (with the	2023	If the timer is repeating, either start it if necessary (with the
1167	C<repeat> value), or reset the running timer to the C<repeat> value.	2024	C<repeat> value), or reset the running timer to the C<repeat> value.
1168		2025
1169	This sounds a bit complicated, but here is a useful and typical	2026	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1170	example: Imagine you have a tcp connection and you want a so-called idle	2027	usage example.
1171	timeout, that is, you want to be called when there have been, say, 60
1172	seconds of inactivity on the socket. The easiest way to do this is to
1173	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1174	C<ev_timer_again> each time you successfully read or write some data. If
1175	you go into an idle state where you do not expect data to travel on the
1176	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1177	automatically restart it if need be.
1178		2028
1179	That means you can ignore the C<after> value and C<ev_timer_start>	2029	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1180	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1181		2030
1182	ev_timer_init (timer, callback, 0., 5.);	2031	Returns the remaining time until a timer fires. If the timer is active,
1183	ev_timer_again (loop, timer);	2032	then this time is relative to the current event loop time, otherwise it's
1184	...	2033	the timeout value currently configured.
1185	timer->again = 17.;
1186	ev_timer_again (loop, timer);
1187	...
1188	timer->again = 10.;
1189	ev_timer_again (loop, timer);
1190		2034
1191	This is more slightly efficient then stopping/starting the timer each time	2035	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1192	you want to modify its timeout value.	2036	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2037	will return C<4>. When the timer expires and is restarted, it will return
		2038	roughly C<7> (likely slightly less as callback invocation takes some time,
		2039	too), and so on.
1193		2040
1194	=item ev_tstamp repeat [read-write]	2041	=item ev_tstamp repeat [read-write]
1195		2042
1196	The current C<repeat> value. Will be used each time the watcher times out	2043	The current C<repeat> value. Will be used each time the watcher times out
1197	or C<ev_timer_again> is called and determines the next timeout (if any),	2044	or C<ev_timer_again> is called, and determines the next timeout (if any),
1198	which is also when any modifications are taken into account.	2045	which is also when any modifications are taken into account.
1199		2046
1200	=back	2047	=back
1201		2048
1202	=head3 Examples	2049	=head3 Examples
1203		2050
1204	Example: Create a timer that fires after 60 seconds.	2051	Example: Create a timer that fires after 60 seconds.
1205		2052
1206	static void	2053	static void
1207	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2054	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1208	{	2055	{
1209	.. one minute over, w is actually stopped right here	2056	.. one minute over, w is actually stopped right here
1210	}	2057	}
1211		2058
1212	struct ev_timer mytimer;	2059	ev_timer mytimer;
1213	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2060	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1214	ev_timer_start (loop, &mytimer);	2061	ev_timer_start (loop, &mytimer);
1215		2062
1216	Example: Create a timeout timer that times out after 10 seconds of	2063	Example: Create a timeout timer that times out after 10 seconds of
1217	inactivity.	2064	inactivity.
1218		2065
1219	static void	2066	static void
1220	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2067	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1221	{	2068	{
1222	.. ten seconds without any activity	2069	.. ten seconds without any activity
1223	}	2070	}
1224		2071
1225	struct ev_timer mytimer;	2072	ev_timer mytimer;
1226	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2073	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1227	ev_timer_again (&mytimer); /* start timer */	2074	ev_timer_again (&mytimer); /* start timer */
1228	ev_loop (loop, 0);	2075	ev_run (loop, 0);
1229		2076
1230	// and in some piece of code that gets executed on any "activity":	2077	// and in some piece of code that gets executed on any "activity":
1231	// reset the timeout to start ticking again at 10 seconds	2078	// reset the timeout to start ticking again at 10 seconds
1232	ev_timer_again (&mytimer);	2079	ev_timer_again (&mytimer);
1233		2080
1234		2081
1235	=head2 C<ev_periodic> - to cron or not to cron?	2082	=head2 C<ev_periodic> - to cron or not to cron?
1236		2083
1237	Periodic watchers are also timers of a kind, but they are very versatile	2084	Periodic watchers are also timers of a kind, but they are very versatile
1238	(and unfortunately a bit complex).	2085	(and unfortunately a bit complex).
1239		2086
1240	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2087	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1241	but on wallclock time (absolute time). You can tell a periodic watcher	2088	relative time, the physical time that passes) but on wall clock time
1242	to trigger "at" some specific point in time. For example, if you tell a	2089	(absolute time, the thing you can read on your calender or clock). The
1243	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2090	difference is that wall clock time can run faster or slower than real
1244	+ 10.>) and then reset your system clock to the last year, then it will	2091	time, and time jumps are not uncommon (e.g. when you adjust your
1245	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2092	wrist-watch).
1246	roughly 10 seconds later).
1247		2093
1248	They can also be used to implement vastly more complex timers, such as	2094	You can tell a periodic watcher to trigger after some specific point
1249	triggering an event on each midnight, local time or other, complicated,	2095	in time: for example, if you tell a periodic watcher to trigger "in 10
1250	rules.	2096	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2097	not a delay) and then reset your system clock to January of the previous
		2098	year, then it will take a year or more to trigger the event (unlike an
		2099	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2100	it, as it uses a relative timeout).
1251		2101
		2102	C<ev_periodic> watchers can also be used to implement vastly more complex
		2103	timers, such as triggering an event on each "midnight, local time", or
		2104	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2105	those cannot react to time jumps.
		2106
1252	As with timers, the callback is guarenteed to be invoked only when the	2107	As with timers, the callback is guaranteed to be invoked only when the
1253	time (C<at>) has been passed, but if multiple periodic timers become ready	2108	point in time where it is supposed to trigger has passed. If multiple
1254	during the same loop iteration then order of execution is undefined.	2109	timers become ready during the same loop iteration then the ones with
		2110	earlier time-out values are invoked before ones with later time-out values
		2111	(but this is no longer true when a callback calls C<ev_run> recursively).
1255		2112
1256	=head3 Watcher-Specific Functions and Data Members	2113	=head3 Watcher-Specific Functions and Data Members
1257		2114
1258	=over 4	2115	=over 4
1259		2116
1260	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2117	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1261		2118
1262	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2119	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1263		2120
1264	Lots of arguments, lets sort it out... There are basically three modes of	2121	Lots of arguments, let's sort it out... There are basically three modes of
1265	operation, and we will explain them from simplest to complex:	2122	operation, and we will explain them from simplest to most complex:
1266		2123
1267	=over 4	2124	=over 4
1268		2125
1269	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2126	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1270		2127
1271	In this configuration the watcher triggers an event at the wallclock time	2128	In this configuration the watcher triggers an event after the wall clock
1272	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2129	time C<offset> has passed. It will not repeat and will not adjust when a
1273	that is, if it is to be run at January 1st 2011 then it will run when the	2130	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1274	system time reaches or surpasses this time.	2131	will be stopped and invoked when the system clock reaches or surpasses
		2132	this point in time.
1275		2133
1276	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2134	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1277		2135
1278	In this mode the watcher will always be scheduled to time out at the next	2136	In this mode the watcher will always be scheduled to time out at the next
1279	C<at + N * interval> time (for some integer N, which can also be negative)	2137	C<offset + N * interval> time (for some integer N, which can also be
1280	and then repeat, regardless of any time jumps.	2138	negative) and then repeat, regardless of any time jumps. The C<offset>
		2139	argument is merely an offset into the C<interval> periods.
1281		2140
1282	This can be used to create timers that do not drift with respect to system	2141	This can be used to create timers that do not drift with respect to the
1283	time:	2142	system clock, for example, here is an C<ev_periodic> that triggers each
		2143	hour, on the hour (with respect to UTC):
1284		2144
1285	ev_periodic_set (&periodic, 0., 3600., 0);	2145	ev_periodic_set (&periodic, 0., 3600., 0);
1286		2146
1287	This doesn't mean there will always be 3600 seconds in between triggers,	2147	This doesn't mean there will always be 3600 seconds in between triggers,
1288	but only that the the callback will be called when the system time shows a	2148	but only that the callback will be called when the system time shows a
1289	full hour (UTC), or more correctly, when the system time is evenly divisible	2149	full hour (UTC), or more correctly, when the system time is evenly divisible
1290	by 3600.	2150	by 3600.
1291		2151
1292	Another way to think about it (for the mathematically inclined) is that	2152	Another way to think about it (for the mathematically inclined) is that
1293	C<ev_periodic> will try to run the callback in this mode at the next possible	2153	C<ev_periodic> will try to run the callback in this mode at the next possible
1294	time where C<time = at (mod interval)>, regardless of any time jumps.	2154	time where C<time = offset (mod interval)>, regardless of any time jumps.
1295		2155
1296	For numerical stability it is preferable that the C<at> value is near	2156	The C<interval> I<MUST> be positive, and for numerical stability, the
1297	C<ev_now ()> (the current time), but there is no range requirement for	2157	interval value should be higher than C<1/8192> (which is around 100
1298	this value.	2158	microseconds) and C<offset> should be higher than C<0> and should have
		2159	at most a similar magnitude as the current time (say, within a factor of
		2160	ten). Typical values for offset are, in fact, C<0> or something between
		2161	C<0> and C<interval>, which is also the recommended range.
1299		2162
		2163	Note also that there is an upper limit to how often a timer can fire (CPU
		2164	speed for example), so if C<interval> is very small then timing stability
		2165	will of course deteriorate. Libev itself tries to be exact to be about one
		2166	millisecond (if the OS supports it and the machine is fast enough).
		2167
1300	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2168	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1301		2169
1302	In this mode the values for C<interval> and C<at> are both being	2170	In this mode the values for C<interval> and C<offset> are both being
1303	ignored. Instead, each time the periodic watcher gets scheduled, the	2171	ignored. Instead, each time the periodic watcher gets scheduled, the
1304	reschedule callback will be called with the watcher as first, and the	2172	reschedule callback will be called with the watcher as first, and the
1305	current time as second argument.	2173	current time as second argument.
1306		2174
1307	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2175	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1308	ever, or make any event loop modifications>. If you need to stop it,	2176	or make ANY other event loop modifications whatsoever, unless explicitly
1309	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2177	allowed by documentation here>.
1310	starting an C<ev_prepare> watcher, which is legal).
1311		2178
		2179	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2180	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2181	only event loop modification you are allowed to do).
		2182
1312	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2183	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1313	ev_tstamp now)>, e.g.:	2184	*w, ev_tstamp now)>, e.g.:
1314		2185
		2186	static ev_tstamp
1315	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2187	my_rescheduler (ev_periodic *w, ev_tstamp now)
1316	{	2188	{
1317	return now + 60.;	2189	return now + 60.;
1318	}	2190	}
1319		2191
1320	It must return the next time to trigger, based on the passed time value	2192	It must return the next time to trigger, based on the passed time value
1321	(that is, the lowest time value larger than to the second argument). It	2193	(that is, the lowest time value larger than to the second argument). It
1322	will usually be called just before the callback will be triggered, but	2194	will usually be called just before the callback will be triggered, but
1323	might be called at other times, too.	2195	might be called at other times, too.
1324		2196
1325	NOTE: I<< This callback must always return a time that is later than the	2197	NOTE: I<< This callback must always return a time that is higher than or
1326	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2198	equal to the passed C<now> value >>.
1327		2199
1328	This can be used to create very complex timers, such as a timer that	2200	This can be used to create very complex timers, such as a timer that
1329	triggers on each midnight, local time. To do this, you would calculate the	2201	triggers on "next midnight, local time". To do this, you would calculate the
1330	next midnight after C<now> and return the timestamp value for this. How	2202	next midnight after C<now> and return the timestamp value for this. How
1331	you do this is, again, up to you (but it is not trivial, which is the main	2203	you do this is, again, up to you (but it is not trivial, which is the main
1332	reason I omitted it as an example).	2204	reason I omitted it as an example).
1333		2205
1334	=back	2206	=back
…		…
1338	Simply stops and restarts the periodic watcher again. This is only useful	2210	Simply stops and restarts the periodic watcher again. This is only useful
1339	when you changed some parameters or the reschedule callback would return	2211	when you changed some parameters or the reschedule callback would return
1340	a different time than the last time it was called (e.g. in a crond like	2212	a different time than the last time it was called (e.g. in a crond like
1341	program when the crontabs have changed).	2213	program when the crontabs have changed).
1342		2214
		2215	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2216
		2217	When active, returns the absolute time that the watcher is supposed
		2218	to trigger next. This is not the same as the C<offset> argument to
		2219	C<ev_periodic_set>, but indeed works even in interval and manual
		2220	rescheduling modes.
		2221
1343	=item ev_tstamp offset [read-write]	2222	=item ev_tstamp offset [read-write]
1344		2223
1345	When repeating, this contains the offset value, otherwise this is the	2224	When repeating, this contains the offset value, otherwise this is the
1346	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2225	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2226	although libev might modify this value for better numerical stability).
1347		2227
1348	Can be modified any time, but changes only take effect when the periodic	2228	Can be modified any time, but changes only take effect when the periodic
1349	timer fires or C<ev_periodic_again> is being called.	2229	timer fires or C<ev_periodic_again> is being called.
1350		2230
1351	=item ev_tstamp interval [read-write]	2231	=item ev_tstamp interval [read-write]
1352		2232
1353	The current interval value. Can be modified any time, but changes only	2233	The current interval value. Can be modified any time, but changes only
1354	take effect when the periodic timer fires or C<ev_periodic_again> is being	2234	take effect when the periodic timer fires or C<ev_periodic_again> is being
1355	called.	2235	called.
1356		2236
1357	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2237	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1358		2238
1359	The current reschedule callback, or C<0>, if this functionality is	2239	The current reschedule callback, or C<0>, if this functionality is
1360	switched off. Can be changed any time, but changes only take effect when	2240	switched off. Can be changed any time, but changes only take effect when
1361	the periodic timer fires or C<ev_periodic_again> is being called.	2241	the periodic timer fires or C<ev_periodic_again> is being called.
1362		2242
1363	=item ev_tstamp at [read-only]
1364
1365	When active, contains the absolute time that the watcher is supposed to
1366	trigger next.
1367
1368	=back	2243	=back
1369		2244
1370	=head3 Examples	2245	=head3 Examples
1371		2246
1372	Example: Call a callback every hour, or, more precisely, whenever the	2247	Example: Call a callback every hour, or, more precisely, whenever the
1373	system clock is divisible by 3600. The callback invocation times have	2248	system time is divisible by 3600. The callback invocation times have
1374	potentially a lot of jittering, but good long-term stability.	2249	potentially a lot of jitter, but good long-term stability.
1375		2250
1376	static void	2251	static void
1377	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2252	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1378	{	2253	{
1379	... its now a full hour (UTC, or TAI or whatever your clock follows)	2254	... its now a full hour (UTC, or TAI or whatever your clock follows)
1380	}	2255	}
1381		2256
1382	struct ev_periodic hourly_tick;	2257	ev_periodic hourly_tick;
1383	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2258	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1384	ev_periodic_start (loop, &hourly_tick);	2259	ev_periodic_start (loop, &hourly_tick);
1385		2260
1386	Example: The same as above, but use a reschedule callback to do it:	2261	Example: The same as above, but use a reschedule callback to do it:
1387		2262
1388	#include <math.h>	2263	#include <math.h>
1389		2264
1390	static ev_tstamp	2265	static ev_tstamp
1391	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2266	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1392	{	2267	{
1393	return fmod (now, 3600.) + 3600.;	2268	return now + (3600. - fmod (now, 3600.));
1394	}	2269	}
1395		2270
1396	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2271	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1397		2272
1398	Example: Call a callback every hour, starting now:	2273	Example: Call a callback every hour, starting now:
1399		2274
1400	struct ev_periodic hourly_tick;	2275	ev_periodic hourly_tick;
1401	ev_periodic_init (&hourly_tick, clock_cb,	2276	ev_periodic_init (&hourly_tick, clock_cb,
1402	fmod (ev_now (loop), 3600.), 3600., 0);	2277	fmod (ev_now (loop), 3600.), 3600., 0);
1403	ev_periodic_start (loop, &hourly_tick);	2278	ev_periodic_start (loop, &hourly_tick);
1404		2279
1405		2280
1406	=head2 C<ev_signal> - signal me when a signal gets signalled!	2281	=head2 C<ev_signal> - signal me when a signal gets signalled!
1407		2282
1408	Signal watchers will trigger an event when the process receives a specific	2283	Signal watchers will trigger an event when the process receives a specific
1409	signal one or more times. Even though signals are very asynchronous, libev	2284	signal one or more times. Even though signals are very asynchronous, libev
1410	will try it's best to deliver signals synchronously, i.e. as part of the	2285	will try its best to deliver signals synchronously, i.e. as part of the
1411	normal event processing, like any other event.	2286	normal event processing, like any other event.
1412		2287
		2288	If you want signals to be delivered truly asynchronously, just use
		2289	C<sigaction> as you would do without libev and forget about sharing
		2290	the signal. You can even use C<ev_async> from a signal handler to
		2291	synchronously wake up an event loop.
		2292
1413	You can configure as many watchers as you like per signal. Only when the	2293	You can configure as many watchers as you like for the same signal, but
		2294	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2295	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2296	C<SIGINT> in both the default loop and another loop at the same time. At
		2297	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2298
1414	first watcher gets started will libev actually register a signal watcher	2299	When the first watcher gets started will libev actually register something
1415	with the kernel (thus it coexists with your own signal handlers as long	2300	with the kernel (thus it coexists with your own signal handlers as long as
1416	as you don't register any with libev). Similarly, when the last signal	2301	you don't register any with libev for the same signal).
1417	watcher for a signal is stopped libev will reset the signal handler to	2302
1418	SIG_DFL (regardless of what it was set to before).	2303	If possible and supported, libev will install its handlers with
		2304	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2305	not be unduly interrupted. If you have a problem with system calls getting
		2306	interrupted by signals you can block all signals in an C<ev_check> watcher
		2307	and unblock them in an C<ev_prepare> watcher.
		2308
		2309	=head3 The special problem of inheritance over fork/execve/pthread_create
		2310
		2311	Both the signal mask (C<sigprocmask>) and the signal disposition
		2312	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2313	stopping it again), that is, libev might or might not block the signal,
		2314	and might or might not set or restore the installed signal handler (but
		2315	see C<EVFLAG_NOSIGMASK>).
		2316
		2317	While this does not matter for the signal disposition (libev never
		2318	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2319	C<execve>), this matters for the signal mask: many programs do not expect
		2320	certain signals to be blocked.
		2321
		2322	This means that before calling C<exec> (from the child) you should reset
		2323	the signal mask to whatever "default" you expect (all clear is a good
		2324	choice usually).
		2325
		2326	The simplest way to ensure that the signal mask is reset in the child is
		2327	to install a fork handler with C<pthread_atfork> that resets it. That will
		2328	catch fork calls done by libraries (such as the libc) as well.
		2329
		2330	In current versions of libev, the signal will not be blocked indefinitely
		2331	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2332	the window of opportunity for problems, it will not go away, as libev
		2333	I<has> to modify the signal mask, at least temporarily.
		2334
		2335	So I can't stress this enough: I<If you do not reset your signal mask when
		2336	you expect it to be empty, you have a race condition in your code>. This
		2337	is not a libev-specific thing, this is true for most event libraries.
		2338
		2339	=head3 The special problem of threads signal handling
		2340
		2341	POSIX threads has problematic signal handling semantics, specifically,
		2342	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2343	threads in a process block signals, which is hard to achieve.
		2344
		2345	When you want to use sigwait (or mix libev signal handling with your own
		2346	for the same signals), you can tackle this problem by globally blocking
		2347	all signals before creating any threads (or creating them with a fully set
		2348	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2349	loops. Then designate one thread as "signal receiver thread" which handles
		2350	these signals. You can pass on any signals that libev might be interested
		2351	in by calling C<ev_feed_signal>.
1419		2352
1420	=head3 Watcher-Specific Functions and Data Members	2353	=head3 Watcher-Specific Functions and Data Members
1421		2354
1422	=over 4	2355	=over 4
1423		2356
…		…
1432		2365
1433	The signal the watcher watches out for.	2366	The signal the watcher watches out for.
1434		2367
1435	=back	2368	=back
1436		2369
		2370	=head3 Examples
		2371
		2372	Example: Try to exit cleanly on SIGINT.
		2373
		2374	static void
		2375	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2376	{
		2377	ev_break (loop, EVBREAK_ALL);
		2378	}
		2379
		2380	ev_signal signal_watcher;
		2381	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2382	ev_signal_start (loop, &signal_watcher);
		2383
1437		2384
1438	=head2 C<ev_child> - watch out for process status changes	2385	=head2 C<ev_child> - watch out for process status changes
1439		2386
1440	Child watchers trigger when your process receives a SIGCHLD in response to	2387	Child watchers trigger when your process receives a SIGCHLD in response to
1441	some child status changes (most typically when a child of yours dies).	2388	some child status changes (most typically when a child of yours dies or
		2389	exits). It is permissible to install a child watcher I<after> the child
		2390	has been forked (which implies it might have already exited), as long
		2391	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2392	forking and then immediately registering a watcher for the child is fine,
		2393	but forking and registering a watcher a few event loop iterations later or
		2394	in the next callback invocation is not.
		2395
		2396	Only the default event loop is capable of handling signals, and therefore
		2397	you can only register child watchers in the default event loop.
		2398
		2399	Due to some design glitches inside libev, child watchers will always be
		2400	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2401	libev)
		2402
		2403	=head3 Process Interaction
		2404
		2405	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2406	initialised. This is necessary to guarantee proper behaviour even if the
		2407	first child watcher is started after the child exits. The occurrence
		2408	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2409	synchronously as part of the event loop processing. Libev always reaps all
		2410	children, even ones not watched.
		2411
		2412	=head3 Overriding the Built-In Processing
		2413
		2414	Libev offers no special support for overriding the built-in child
		2415	processing, but if your application collides with libev's default child
		2416	handler, you can override it easily by installing your own handler for
		2417	C<SIGCHLD> after initialising the default loop, and making sure the
		2418	default loop never gets destroyed. You are encouraged, however, to use an
		2419	event-based approach to child reaping and thus use libev's support for
		2420	that, so other libev users can use C<ev_child> watchers freely.
		2421
		2422	=head3 Stopping the Child Watcher
		2423
		2424	Currently, the child watcher never gets stopped, even when the
		2425	child terminates, so normally one needs to stop the watcher in the
		2426	callback. Future versions of libev might stop the watcher automatically
		2427	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2428	problem).
1442		2429
1443	=head3 Watcher-Specific Functions and Data Members	2430	=head3 Watcher-Specific Functions and Data Members
1444		2431
1445	=over 4	2432	=over 4
1446		2433
…		…
1472		2459
1473	=back	2460	=back
1474		2461
1475	=head3 Examples	2462	=head3 Examples
1476		2463
1477	Example: Try to exit cleanly on SIGINT and SIGTERM.	2464	Example: C<fork()> a new process and install a child handler to wait for
		2465	its completion.
1478		2466
		2467	ev_child cw;
		2468
1479	static void	2469	static void
1480	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2470	child_cb (EV_P_ ev_child *w, int revents)
1481	{	2471	{
1482	ev_unloop (loop, EVUNLOOP_ALL);	2472	ev_child_stop (EV_A_ w);
		2473	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1483	}	2474	}
1484		2475
1485	struct ev_signal signal_watcher;	2476	pid_t pid = fork ();
1486	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2477
1487	ev_signal_start (loop, &sigint_cb);	2478	if (pid < 0)
		2479	// error
		2480	else if (pid == 0)
		2481	{
		2482	// the forked child executes here
		2483	exit (1);
		2484	}
		2485	else
		2486	{
		2487	ev_child_init (&cw, child_cb, pid, 0);
		2488	ev_child_start (EV_DEFAULT_ &cw);
		2489	}
1488		2490
1489		2491
1490	=head2 C<ev_stat> - did the file attributes just change?	2492	=head2 C<ev_stat> - did the file attributes just change?
1491		2493
1492	This watches a filesystem path for attribute changes. That is, it calls	2494	This watches a file system path for attribute changes. That is, it calls
1493	C<stat> regularly (or when the OS says it changed) and sees if it changed	2495	C<stat> on that path in regular intervals (or when the OS says it changed)
1494	compared to the last time, invoking the callback if it did.	2496	and sees if it changed compared to the last time, invoking the callback if
		2497	it did.
1495		2498
1496	The path does not need to exist: changing from "path exists" to "path does	2499	The path does not need to exist: changing from "path exists" to "path does
1497	not exist" is a status change like any other. The condition "path does	2500	not exist" is a status change like any other. The condition "path does not
1498	not exist" is signified by the C<st_nlink> field being zero (which is	2501	exist" (or more correctly "path cannot be stat'ed") is signified by the
1499	otherwise always forced to be at least one) and all the other fields of	2502	C<st_nlink> field being zero (which is otherwise always forced to be at
1500	the stat buffer having unspecified contents.	2503	least one) and all the other fields of the stat buffer having unspecified
		2504	contents.
1501		2505
1502	The path I<should> be absolute and I<must not> end in a slash. If it is	2506	The path I<must not> end in a slash or contain special components such as
		2507	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1503	relative and your working directory changes, the behaviour is undefined.	2508	your working directory changes, then the behaviour is undefined.
1504		2509
1505	Since there is no standard to do this, the portable implementation simply	2510	Since there is no portable change notification interface available, the
1506	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2511	portable implementation simply calls C<stat(2)> regularly on the path
1507	can specify a recommended polling interval for this case. If you specify	2512	to see if it changed somehow. You can specify a recommended polling
1508	a polling interval of C<0> (highly recommended!) then a I<suitable,	2513	interval for this case. If you specify a polling interval of C<0> (highly
1509	unspecified default> value will be used (which you can expect to be around	2514	recommended!) then a I<suitable, unspecified default> value will be used
1510	five seconds, although this might change dynamically). Libev will also	2515	(which you can expect to be around five seconds, although this might
1511	impose a minimum interval which is currently around C<0.1>, but thats	2516	change dynamically). Libev will also impose a minimum interval which is
1512	usually overkill.	2517	currently around C<0.1>, but that's usually overkill.
1513		2518
1514	This watcher type is not meant for massive numbers of stat watchers,	2519	This watcher type is not meant for massive numbers of stat watchers,
1515	as even with OS-supported change notifications, this can be	2520	as even with OS-supported change notifications, this can be
1516	resource-intensive.	2521	resource-intensive.
1517		2522
1518	At the time of this writing, only the Linux inotify interface is	2523	At the time of this writing, the only OS-specific interface implemented
1519	implemented (implementing kqueue support is left as an exercise for the	2524	is the Linux inotify interface (implementing kqueue support is left as an
1520	reader). Inotify will be used to give hints only and should not change the	2525	exercise for the reader. Note, however, that the author sees no way of
1521	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2526	implementing C<ev_stat> semantics with kqueue, except as a hint).
1522	to fall back to regular polling again even with inotify, but changes are
1523	usually detected immediately, and if the file exists there will be no
1524	polling.
1525		2527
1526	=head3 Inotify	2528	=head3 ABI Issues (Largefile Support)
1527		2529
		2530	Libev by default (unless the user overrides this) uses the default
		2531	compilation environment, which means that on systems with large file
		2532	support disabled by default, you get the 32 bit version of the stat
		2533	structure. When using the library from programs that change the ABI to
		2534	use 64 bit file offsets the programs will fail. In that case you have to
		2535	compile libev with the same flags to get binary compatibility. This is
		2536	obviously the case with any flags that change the ABI, but the problem is
		2537	most noticeably displayed with ev_stat and large file support.
		2538
		2539	The solution for this is to lobby your distribution maker to make large
		2540	file interfaces available by default (as e.g. FreeBSD does) and not
		2541	optional. Libev cannot simply switch on large file support because it has
		2542	to exchange stat structures with application programs compiled using the
		2543	default compilation environment.
		2544
		2545	=head3 Inotify and Kqueue
		2546
1528	When C<inotify (7)> support has been compiled into libev (generally only	2547	When C<inotify (7)> support has been compiled into libev and present at
1529	available on Linux) and present at runtime, it will be used to speed up	2548	runtime, it will be used to speed up change detection where possible. The
1530	change detection where possible. The inotify descriptor will be created lazily	2549	inotify descriptor will be created lazily when the first C<ev_stat>
1531	when the first C<ev_stat> watcher is being started.	2550	watcher is being started.
1532		2551
1533	Inotify presense does not change the semantics of C<ev_stat> watchers	2552	Inotify presence does not change the semantics of C<ev_stat> watchers
1534	except that changes might be detected earlier, and in some cases, to avoid	2553	except that changes might be detected earlier, and in some cases, to avoid
1535	making regular C<stat> calls. Even in the presense of inotify support	2554	making regular C<stat> calls. Even in the presence of inotify support
1536	there are many cases where libev has to resort to regular C<stat> polling.	2555	there are many cases where libev has to resort to regular C<stat> polling,
		2556	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2557	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2558	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2559	xfs are fully working) libev usually gets away without polling.
1537		2560
1538	(There is no support for kqueue, as apparently it cannot be used to	2561	There is no support for kqueue, as apparently it cannot be used to
1539	implement this functionality, due to the requirement of having a file	2562	implement this functionality, due to the requirement of having a file
1540	descriptor open on the object at all times).	2563	descriptor open on the object at all times, and detecting renames, unlinks
		2564	etc. is difficult.
		2565
		2566	=head3 C<stat ()> is a synchronous operation
		2567
		2568	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2569	the process. The exception are C<ev_stat> watchers - those call C<stat
		2570	()>, which is a synchronous operation.
		2571
		2572	For local paths, this usually doesn't matter: unless the system is very
		2573	busy or the intervals between stat's are large, a stat call will be fast,
		2574	as the path data is usually in memory already (except when starting the
		2575	watcher).
		2576
		2577	For networked file systems, calling C<stat ()> can block an indefinite
		2578	time due to network issues, and even under good conditions, a stat call
		2579	often takes multiple milliseconds.
		2580
		2581	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2582	paths, although this is fully supported by libev.
1541		2583
1542	=head3 The special problem of stat time resolution	2584	=head3 The special problem of stat time resolution
1543		2585
1544	The C<stat ()> syscall only supports full-second resolution portably, and	2586	The C<stat ()> system call only supports full-second resolution portably,
1545	even on systems where the resolution is higher, many filesystems still	2587	and even on systems where the resolution is higher, most file systems
1546	only support whole seconds.	2588	still only support whole seconds.
1547		2589
1548	That means that, if the time is the only thing that changes, you might	2590	That means that, if the time is the only thing that changes, you can
1549	miss updates: on the first update, C<ev_stat> detects a change and calls	2591	easily miss updates: on the first update, C<ev_stat> detects a change and
1550	your callback, which does something. When there is another update within	2592	calls your callback, which does something. When there is another update
1551	the same second, C<ev_stat> will be unable to detect it.	2593	within the same second, C<ev_stat> will be unable to detect unless the
		2594	stat data does change in other ways (e.g. file size).
1552		2595
1553	The solution to this is to delay acting on a change for a second (or till	2596	The solution to this is to delay acting on a change for slightly more
1554	the next second boundary), using a roughly one-second delay C<ev_timer>	2597	than a second (or till slightly after the next full second boundary), using
1555	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2598	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1556	is added to work around small timing inconsistencies of some operating	2599	ev_timer_again (loop, w)>).
1557	systems.	2600
		2601	The C<.02> offset is added to work around small timing inconsistencies
		2602	of some operating systems (where the second counter of the current time
		2603	might be be delayed. One such system is the Linux kernel, where a call to
		2604	C<gettimeofday> might return a timestamp with a full second later than
		2605	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2606	update file times then there will be a small window where the kernel uses
		2607	the previous second to update file times but libev might already execute
		2608	the timer callback).
1558		2609
1559	=head3 Watcher-Specific Functions and Data Members	2610	=head3 Watcher-Specific Functions and Data Members
1560		2611
1561	=over 4	2612	=over 4
1562		2613
…		…
1568	C<path>. The C<interval> is a hint on how quickly a change is expected to	2619	C<path>. The C<interval> is a hint on how quickly a change is expected to
1569	be detected and should normally be specified as C<0> to let libev choose	2620	be detected and should normally be specified as C<0> to let libev choose
1570	a suitable value. The memory pointed to by C<path> must point to the same	2621	a suitable value. The memory pointed to by C<path> must point to the same
1571	path for as long as the watcher is active.	2622	path for as long as the watcher is active.
1572		2623
1573	The callback will be receive C<EV_STAT> when a change was detected,	2624	The callback will receive an C<EV_STAT> event when a change was detected,
1574	relative to the attributes at the time the watcher was started (or the	2625	relative to the attributes at the time the watcher was started (or the
1575	last change was detected).	2626	last change was detected).
1576		2627
1577	=item ev_stat_stat (ev_stat *)	2628	=item ev_stat_stat (loop, ev_stat *)
1578		2629
1579	Updates the stat buffer immediately with new values. If you change the	2630	Updates the stat buffer immediately with new values. If you change the
1580	watched path in your callback, you could call this fucntion to avoid	2631	watched path in your callback, you could call this function to avoid
1581	detecting this change (while introducing a race condition). Can also be	2632	detecting this change (while introducing a race condition if you are not
1582	useful simply to find out the new values.	2633	the only one changing the path). Can also be useful simply to find out the
		2634	new values.
1583		2635
1584	=item ev_statdata attr [read-only]	2636	=item ev_statdata attr [read-only]
1585		2637
1586	The most-recently detected attributes of the file. Although the type is of	2638	The most-recently detected attributes of the file. Although the type is
1587	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2639	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1588	suitable for your system. If the C<st_nlink> member is C<0>, then there	2640	suitable for your system, but you can only rely on the POSIX-standardised
		2641	members to be present. If the C<st_nlink> member is C<0>, then there was
1589	was some error while C<stat>ing the file.	2642	some error while C<stat>ing the file.
1590		2643
1591	=item ev_statdata prev [read-only]	2644	=item ev_statdata prev [read-only]
1592		2645
1593	The previous attributes of the file. The callback gets invoked whenever	2646	The previous attributes of the file. The callback gets invoked whenever
1594	C<prev> != C<attr>.	2647	C<prev> != C<attr>, or, more precisely, one or more of these members
		2648	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2649	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1595		2650
1596	=item ev_tstamp interval [read-only]	2651	=item ev_tstamp interval [read-only]
1597		2652
1598	The specified interval.	2653	The specified interval.
1599		2654
1600	=item const char *path [read-only]	2655	=item const char *path [read-only]
1601		2656
1602	The filesystem path that is being watched.	2657	The file system path that is being watched.
1603		2658
1604	=back	2659	=back
1605		2660
1606	=head3 Examples	2661	=head3 Examples
1607		2662
1608	Example: Watch C</etc/passwd> for attribute changes.	2663	Example: Watch C</etc/passwd> for attribute changes.
1609		2664
1610	static void	2665	static void
1611	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2666	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1612	{	2667	{
1613	/* /etc/passwd changed in some way */	2668	/* /etc/passwd changed in some way */
1614	if (w->attr.st_nlink)	2669	if (w->attr.st_nlink)
1615	{	2670	{
1616	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2671	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1617	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2672	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1618	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2673	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1619	}	2674	}
1620	else	2675	else
1621	/* you shalt not abuse printf for puts */	2676	/* you shalt not abuse printf for puts */
1622	puts ("wow, /etc/passwd is not there, expect problems. "	2677	puts ("wow, /etc/passwd is not there, expect problems. "
1623	"if this is windows, they already arrived\n");	2678	"if this is windows, they already arrived\n");
1624	}	2679	}
1625		2680
1626	...	2681	...
1627	ev_stat passwd;	2682	ev_stat passwd;
1628		2683
1629	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2684	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1630	ev_stat_start (loop, &passwd);	2685	ev_stat_start (loop, &passwd);
1631		2686
1632	Example: Like above, but additionally use a one-second delay so we do not	2687	Example: Like above, but additionally use a one-second delay so we do not
1633	miss updates (however, frequent updates will delay processing, too, so	2688	miss updates (however, frequent updates will delay processing, too, so
1634	one might do the work both on C<ev_stat> callback invocation I<and> on	2689	one might do the work both on C<ev_stat> callback invocation I<and> on
1635	C<ev_timer> callback invocation).	2690	C<ev_timer> callback invocation).
1636		2691
1637	static ev_stat passwd;	2692	static ev_stat passwd;
1638	static ev_timer timer;	2693	static ev_timer timer;
1639		2694
1640	static void	2695	static void
1641	timer_cb (EV_P_ ev_timer *w, int revents)	2696	timer_cb (EV_P_ ev_timer *w, int revents)
1642	{	2697	{
1643	ev_timer_stop (EV_A_ w);	2698	ev_timer_stop (EV_A_ w);
1644		2699
1645	/* now it's one second after the most recent passwd change */	2700	/* now it's one second after the most recent passwd change */
1646	}	2701	}
1647		2702
1648	static void	2703	static void
1649	stat_cb (EV_P_ ev_stat *w, int revents)	2704	stat_cb (EV_P_ ev_stat *w, int revents)
1650	{	2705	{
1651	/* reset the one-second timer */	2706	/* reset the one-second timer */
1652	ev_timer_again (EV_A_ &timer);	2707	ev_timer_again (EV_A_ &timer);
1653	}	2708	}
1654		2709
1655	...	2710	...
1656	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2711	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1657	ev_stat_start (loop, &passwd);	2712	ev_stat_start (loop, &passwd);
1658	ev_timer_init (&timer, timer_cb, 0., 1.01);	2713	ev_timer_init (&timer, timer_cb, 0., 1.02);
1659		2714
1660		2715
1661	=head2 C<ev_idle> - when you've got nothing better to do...	2716	=head2 C<ev_idle> - when you've got nothing better to do...
1662		2717
1663	Idle watchers trigger events when no other events of the same or higher	2718	Idle watchers trigger events when no other events of the same or higher
1664	priority are pending (prepare, check and other idle watchers do not	2719	priority are pending (prepare, check and other idle watchers do not count
1665	count).	2720	as receiving "events").
1666		2721
1667	That is, as long as your process is busy handling sockets or timeouts	2722	That is, as long as your process is busy handling sockets or timeouts
1668	(or even signals, imagine) of the same or higher priority it will not be	2723	(or even signals, imagine) of the same or higher priority it will not be
1669	triggered. But when your process is idle (or only lower-priority watchers	2724	triggered. But when your process is idle (or only lower-priority watchers
1670	are pending), the idle watchers are being called once per event loop	2725	are pending), the idle watchers are being called once per event loop
…		…
1681		2736
1682	=head3 Watcher-Specific Functions and Data Members	2737	=head3 Watcher-Specific Functions and Data Members
1683		2738
1684	=over 4	2739	=over 4
1685		2740
1686	=item ev_idle_init (ev_signal *, callback)	2741	=item ev_idle_init (ev_idle *, callback)
1687		2742
1688	Initialises and configures the idle watcher - it has no parameters of any	2743	Initialises and configures the idle watcher - it has no parameters of any
1689	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2744	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1690	believe me.	2745	believe me.
1691		2746
…		…
1694	=head3 Examples	2749	=head3 Examples
1695		2750
1696	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2751	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1697	callback, free it. Also, use no error checking, as usual.	2752	callback, free it. Also, use no error checking, as usual.
1698		2753
1699	static void	2754	static void
1700	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2755	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1701	{	2756	{
1702	free (w);	2757	free (w);
1703	// now do something you wanted to do when the program has	2758	// now do something you wanted to do when the program has
1704	// no longer anything immediate to do.	2759	// no longer anything immediate to do.
1705	}	2760	}
1706		2761
1707	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2762	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1708	ev_idle_init (idle_watcher, idle_cb);	2763	ev_idle_init (idle_watcher, idle_cb);
1709	ev_idle_start (loop, idle_cb);	2764	ev_idle_start (loop, idle_watcher);
1710		2765
1711		2766
1712	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2767	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1713		2768
1714	Prepare and check watchers are usually (but not always) used in tandem:	2769	Prepare and check watchers are usually (but not always) used in pairs:
1715	prepare watchers get invoked before the process blocks and check watchers	2770	prepare watchers get invoked before the process blocks and check watchers
1716	afterwards.	2771	afterwards.
1717		2772
1718	You I<must not> call C<ev_loop> or similar functions that enter	2773	You I<must not> call C<ev_run> or similar functions that enter
1719	the current event loop from either C<ev_prepare> or C<ev_check>	2774	the current event loop from either C<ev_prepare> or C<ev_check>
1720	watchers. Other loops than the current one are fine, however. The	2775	watchers. Other loops than the current one are fine, however. The
1721	rationale behind this is that you do not need to check for recursion in	2776	rationale behind this is that you do not need to check for recursion in
1722	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2777	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1723	C<ev_check> so if you have one watcher of each kind they will always be	2778	C<ev_check> so if you have one watcher of each kind they will always be
1724	called in pairs bracketing the blocking call.	2779	called in pairs bracketing the blocking call.
1725		2780
1726	Their main purpose is to integrate other event mechanisms into libev and	2781	Their main purpose is to integrate other event mechanisms into libev and
1727	their use is somewhat advanced. This could be used, for example, to track	2782	their use is somewhat advanced. They could be used, for example, to track
1728	variable changes, implement your own watchers, integrate net-snmp or a	2783	variable changes, implement your own watchers, integrate net-snmp or a
1729	coroutine library and lots more. They are also occasionally useful if	2784	coroutine library and lots more. They are also occasionally useful if
1730	you cache some data and want to flush it before blocking (for example,	2785	you cache some data and want to flush it before blocking (for example,
1731	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2786	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1732	watcher).	2787	watcher).
1733		2788
1734	This is done by examining in each prepare call which file descriptors need	2789	This is done by examining in each prepare call which file descriptors
1735	to be watched by the other library, registering C<ev_io> watchers for	2790	need to be watched by the other library, registering C<ev_io> watchers
1736	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2791	for them and starting an C<ev_timer> watcher for any timeouts (many
1737	provide just this functionality). Then, in the check watcher you check for	2792	libraries provide exactly this functionality). Then, in the check watcher,
1738	any events that occured (by checking the pending status of all watchers	2793	you check for any events that occurred (by checking the pending status
1739	and stopping them) and call back into the library. The I/O and timer	2794	of all watchers and stopping them) and call back into the library. The
1740	callbacks will never actually be called (but must be valid nevertheless,	2795	I/O and timer callbacks will never actually be called (but must be valid
1741	because you never know, you know?).	2796	nevertheless, because you never know, you know?).
1742		2797
1743	As another example, the Perl Coro module uses these hooks to integrate	2798	As another example, the Perl Coro module uses these hooks to integrate
1744	coroutines into libev programs, by yielding to other active coroutines	2799	coroutines into libev programs, by yielding to other active coroutines
1745	during each prepare and only letting the process block if no coroutines	2800	during each prepare and only letting the process block if no coroutines
1746	are ready to run (it's actually more complicated: it only runs coroutines	2801	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1749	loop from blocking if lower-priority coroutines are active, thus mapping	2804	loop from blocking if lower-priority coroutines are active, thus mapping
1750	low-priority coroutines to idle/background tasks).	2805	low-priority coroutines to idle/background tasks).
1751		2806
1752	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2807	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1753	priority, to ensure that they are being run before any other watchers	2808	priority, to ensure that they are being run before any other watchers
		2809	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2810
1754	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2811	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1755	too) should not activate ("feed") events into libev. While libev fully	2812	activate ("feed") events into libev. While libev fully supports this, they
1756	supports this, they will be called before other C<ev_check> watchers	2813	might get executed before other C<ev_check> watchers did their job. As
1757	did their job. As C<ev_check> watchers are often used to embed other	2814	C<ev_check> watchers are often used to embed other (non-libev) event
1758	(non-libev) event loops those other event loops might be in an unusable	2815	loops those other event loops might be in an unusable state until their
1759	state until their C<ev_check> watcher ran (always remind yourself to	2816	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1760	coexist peacefully with others).	2817	others).
1761		2818
1762	=head3 Watcher-Specific Functions and Data Members	2819	=head3 Watcher-Specific Functions and Data Members
1763		2820
1764	=over 4	2821	=over 4
1765		2822
…		…
1767		2824
1768	=item ev_check_init (ev_check *, callback)	2825	=item ev_check_init (ev_check *, callback)
1769		2826
1770	Initialises and configures the prepare or check watcher - they have no	2827	Initialises and configures the prepare or check watcher - they have no
1771	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2828	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1772	macros, but using them is utterly, utterly and completely pointless.	2829	macros, but using them is utterly, utterly, utterly and completely
		2830	pointless.
1773		2831
1774	=back	2832	=back
1775		2833
1776	=head3 Examples	2834	=head3 Examples
1777		2835
1778	There are a number of principal ways to embed other event loops or modules	2836	There are a number of principal ways to embed other event loops or modules
1779	into libev. Here are some ideas on how to include libadns into libev	2837	into libev. Here are some ideas on how to include libadns into libev
1780	(there is a Perl module named C<EV::ADNS> that does this, which you could	2838	(there is a Perl module named C<EV::ADNS> that does this, which you could
1781	use for an actually working example. Another Perl module named C<EV::Glib>	2839	use as a working example. Another Perl module named C<EV::Glib> embeds a
1782	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2840	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1783	into the Glib event loop).	2841	Glib event loop).
1784		2842
1785	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2843	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1786	and in a check watcher, destroy them and call into libadns. What follows	2844	and in a check watcher, destroy them and call into libadns. What follows
1787	is pseudo-code only of course. This requires you to either use a low	2845	is pseudo-code only of course. This requires you to either use a low
1788	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2846	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1789	the callbacks for the IO/timeout watchers might not have been called yet.	2847	the callbacks for the IO/timeout watchers might not have been called yet.
1790		2848
1791	static ev_io iow [nfd];	2849	static ev_io iow [nfd];
1792	static ev_timer tw;	2850	static ev_timer tw;
1793		2851
1794	static void	2852	static void
1795	io_cb (ev_loop *loop, ev_io *w, int revents)	2853	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1796	{	2854	{
1797	}	2855	}
1798		2856
1799	// create io watchers for each fd and a timer before blocking	2857	// create io watchers for each fd and a timer before blocking
1800	static void	2858	static void
1801	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2859	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1802	{	2860	{
1803	int timeout = 3600000;	2861	int timeout = 3600000;
1804	struct pollfd fds [nfd];	2862	struct pollfd fds [nfd];
1805	// actual code will need to loop here and realloc etc.	2863	// actual code will need to loop here and realloc etc.
1806	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2864	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1807		2865
1808	/* the callback is illegal, but won't be called as we stop during check */	2866	/* the callback is illegal, but won't be called as we stop during check */
1809	ev_timer_init (&tw, 0, timeout * 1e-3);	2867	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1810	ev_timer_start (loop, &tw);	2868	ev_timer_start (loop, &tw);
1811		2869
1812	// create one ev_io per pollfd	2870	// create one ev_io per pollfd
1813	for (int i = 0; i < nfd; ++i)	2871	for (int i = 0; i < nfd; ++i)
1814	{	2872	{
1815	ev_io_init (iow + i, io_cb, fds [i].fd,	2873	ev_io_init (iow + i, io_cb, fds [i].fd,
1816	((fds [i].events & POLLIN ? EV_READ : 0)	2874	((fds [i].events & POLLIN ? EV_READ : 0)
1817	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2875	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1818		2876
1819	fds [i].revents = 0;	2877	fds [i].revents = 0;
1820	ev_io_start (loop, iow + i);	2878	ev_io_start (loop, iow + i);
1821	}	2879	}
1822	}	2880	}
1823		2881
1824	// stop all watchers after blocking	2882	// stop all watchers after blocking
1825	static void	2883	static void
1826	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2884	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1827	{	2885	{
1828	ev_timer_stop (loop, &tw);	2886	ev_timer_stop (loop, &tw);
1829		2887
1830	for (int i = 0; i < nfd; ++i)	2888	for (int i = 0; i < nfd; ++i)
1831	{	2889	{
1832	// set the relevant poll flags	2890	// set the relevant poll flags
1833	// could also call adns_processreadable etc. here	2891	// could also call adns_processreadable etc. here
1834	struct pollfd *fd = fds + i;	2892	struct pollfd *fd = fds + i;
1835	int revents = ev_clear_pending (iow + i);	2893	int revents = ev_clear_pending (iow + i);
1836	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2894	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1837	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2895	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1838		2896
1839	// now stop the watcher	2897	// now stop the watcher
1840	ev_io_stop (loop, iow + i);	2898	ev_io_stop (loop, iow + i);
1841	}	2899	}
1842		2900
1843	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2901	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1844	}	2902	}
1845		2903
1846	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2904	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1847	in the prepare watcher and would dispose of the check watcher.	2905	in the prepare watcher and would dispose of the check watcher.
1848		2906
1849	Method 3: If the module to be embedded supports explicit event	2907	Method 3: If the module to be embedded supports explicit event
1850	notification (adns does), you can also make use of the actual watcher	2908	notification (libadns does), you can also make use of the actual watcher
1851	callbacks, and only destroy/create the watchers in the prepare watcher.	2909	callbacks, and only destroy/create the watchers in the prepare watcher.
1852		2910
1853	static void	2911	static void
1854	timer_cb (EV_P_ ev_timer *w, int revents)	2912	timer_cb (EV_P_ ev_timer *w, int revents)
1855	{	2913	{
1856	adns_state ads = (adns_state)w->data;	2914	adns_state ads = (adns_state)w->data;
1857	update_now (EV_A);	2915	update_now (EV_A);
1858		2916
1859	adns_processtimeouts (ads, &tv_now);	2917	adns_processtimeouts (ads, &tv_now);
1860	}	2918	}
1861		2919
1862	static void	2920	static void
1863	io_cb (EV_P_ ev_io *w, int revents)	2921	io_cb (EV_P_ ev_io *w, int revents)
1864	{	2922	{
1865	adns_state ads = (adns_state)w->data;	2923	adns_state ads = (adns_state)w->data;
1866	update_now (EV_A);	2924	update_now (EV_A);
1867		2925
1868	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2926	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1869	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2927	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1870	}	2928	}
1871		2929
1872	// do not ever call adns_afterpoll	2930	// do not ever call adns_afterpoll
1873		2931
1874	Method 4: Do not use a prepare or check watcher because the module you	2932	Method 4: Do not use a prepare or check watcher because the module you
1875	want to embed is too inflexible to support it. Instead, youc na override	2933	want to embed is not flexible enough to support it. Instead, you can
1876	their poll function. The drawback with this solution is that the main	2934	override their poll function. The drawback with this solution is that the
1877	loop is now no longer controllable by EV. The C<Glib::EV> module does	2935	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1878	this.	2936	this approach, effectively embedding EV as a client into the horrible
		2937	libglib event loop.
1879		2938
1880	static gint	2939	static gint
1881	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2940	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1882	{	2941	{
1883	int got_events = 0;	2942	int got_events = 0;
1884		2943
1885	for (n = 0; n < nfds; ++n)	2944	for (n = 0; n < nfds; ++n)
1886	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2945	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1887		2946
1888	if (timeout >= 0)	2947	if (timeout >= 0)
1889	// create/start timer	2948	// create/start timer
1890		2949
1891	// poll	2950	// poll
1892	ev_loop (EV_A_ 0);	2951	ev_run (EV_A_ 0);
1893		2952
1894	// stop timer again	2953	// stop timer again
1895	if (timeout >= 0)	2954	if (timeout >= 0)
1896	ev_timer_stop (EV_A_ &to);	2955	ev_timer_stop (EV_A_ &to);
1897		2956
1898	// stop io watchers again - their callbacks should have set	2957	// stop io watchers again - their callbacks should have set
1899	for (n = 0; n < nfds; ++n)	2958	for (n = 0; n < nfds; ++n)
1900	ev_io_stop (EV_A_ iow [n]);	2959	ev_io_stop (EV_A_ iow [n]);
1901		2960
1902	return got_events;	2961	return got_events;
1903	}	2962	}
1904		2963
1905		2964
1906	=head2 C<ev_embed> - when one backend isn't enough...	2965	=head2 C<ev_embed> - when one backend isn't enough...
1907		2966
1908	This is a rather advanced watcher type that lets you embed one event loop	2967	This is a rather advanced watcher type that lets you embed one event loop
…		…
1914	prioritise I/O.	2973	prioritise I/O.
1915		2974
1916	As an example for a bug workaround, the kqueue backend might only support	2975	As an example for a bug workaround, the kqueue backend might only support
1917	sockets on some platform, so it is unusable as generic backend, but you	2976	sockets on some platform, so it is unusable as generic backend, but you
1918	still want to make use of it because you have many sockets and it scales	2977	still want to make use of it because you have many sockets and it scales
1919	so nicely. In this case, you would create a kqueue-based loop and embed it	2978	so nicely. In this case, you would create a kqueue-based loop and embed
1920	into your default loop (which might use e.g. poll). Overall operation will	2979	it into your default loop (which might use e.g. poll). Overall operation
1921	be a bit slower because first libev has to poll and then call kevent, but	2980	will be a bit slower because first libev has to call C<poll> and then
1922	at least you can use both at what they are best.	2981	C<kevent>, but at least you can use both mechanisms for what they are
		2982	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1923		2983
1924	As for prioritising I/O: rarely you have the case where some fds have	2984	As for prioritising I/O: under rare circumstances you have the case where
1925	to be watched and handled very quickly (with low latency), and even	2985	some fds have to be watched and handled very quickly (with low latency),
1926	priorities and idle watchers might have too much overhead. In this case	2986	and even priorities and idle watchers might have too much overhead. In
1927	you would put all the high priority stuff in one loop and all the rest in	2987	this case you would put all the high priority stuff in one loop and all
1928	a second one, and embed the second one in the first.	2988	the rest in a second one, and embed the second one in the first.
1929		2989
1930	As long as the watcher is active, the callback will be invoked every time	2990	As long as the watcher is active, the callback will be invoked every
1931	there might be events pending in the embedded loop. The callback must then	2991	time there might be events pending in the embedded loop. The callback
1932	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2992	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1933	their callbacks (you could also start an idle watcher to give the embedded	2993	sweep and invoke their callbacks (the callback doesn't need to invoke the
1934	loop strictly lower priority for example). You can also set the callback	2994	C<ev_embed_sweep> function directly, it could also start an idle watcher
1935	to C<0>, in which case the embed watcher will automatically execute the	2995	to give the embedded loop strictly lower priority for example).
1936	embedded loop sweep.
1937		2996
1938	As long as the watcher is started it will automatically handle events. The	2997	You can also set the callback to C<0>, in which case the embed watcher
1939	callback will be invoked whenever some events have been handled. You can	2998	will automatically execute the embedded loop sweep whenever necessary.
1940	set the callback to C<0> to avoid having to specify one if you are not
1941	interested in that.
1942		2999
1943	Also, there have not currently been made special provisions for forking:	3000	Fork detection will be handled transparently while the C<ev_embed> watcher
1944	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3001	is active, i.e., the embedded loop will automatically be forked when the
1945	but you will also have to stop and restart any C<ev_embed> watchers	3002	embedding loop forks. In other cases, the user is responsible for calling
1946	yourself.	3003	C<ev_loop_fork> on the embedded loop.
1947		3004
1948	Unfortunately, not all backends are embeddable, only the ones returned by	3005	Unfortunately, not all backends are embeddable: only the ones returned by
1949	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3006	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1950	portable one.	3007	portable one.
1951		3008
1952	So when you want to use this feature you will always have to be prepared	3009	So when you want to use this feature you will always have to be prepared
1953	that you cannot get an embeddable loop. The recommended way to get around	3010	that you cannot get an embeddable loop. The recommended way to get around
1954	this is to have a separate variables for your embeddable loop, try to	3011	this is to have a separate variables for your embeddable loop, try to
1955	create it, and if that fails, use the normal loop for everything.	3012	create it, and if that fails, use the normal loop for everything.
1956		3013
		3014	=head3 C<ev_embed> and fork
		3015
		3016	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3017	automatically be applied to the embedded loop as well, so no special
		3018	fork handling is required in that case. When the watcher is not running,
		3019	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3020	as applicable.
		3021
1957	=head3 Watcher-Specific Functions and Data Members	3022	=head3 Watcher-Specific Functions and Data Members
1958		3023
1959	=over 4	3024	=over 4
1960		3025
1961	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3026	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
1964		3029
1965	Configures the watcher to embed the given loop, which must be	3030	Configures the watcher to embed the given loop, which must be
1966	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3031	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1967	invoked automatically, otherwise it is the responsibility of the callback	3032	invoked automatically, otherwise it is the responsibility of the callback
1968	to invoke it (it will continue to be called until the sweep has been done,	3033	to invoke it (it will continue to be called until the sweep has been done,
1969	if you do not want thta, you need to temporarily stop the embed watcher).	3034	if you do not want that, you need to temporarily stop the embed watcher).
1970		3035
1971	=item ev_embed_sweep (loop, ev_embed *)	3036	=item ev_embed_sweep (loop, ev_embed *)
1972		3037
1973	Make a single, non-blocking sweep over the embedded loop. This works	3038	Make a single, non-blocking sweep over the embedded loop. This works
1974	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3039	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1975	apropriate way for embedded loops.	3040	appropriate way for embedded loops.
1976		3041
1977	=item struct ev_loop *other [read-only]	3042	=item struct ev_loop *other [read-only]
1978		3043
1979	The embedded event loop.	3044	The embedded event loop.
1980		3045
…		…
1982		3047
1983	=head3 Examples	3048	=head3 Examples
1984		3049
1985	Example: Try to get an embeddable event loop and embed it into the default	3050	Example: Try to get an embeddable event loop and embed it into the default
1986	event loop. If that is not possible, use the default loop. The default	3051	event loop. If that is not possible, use the default loop. The default
1987	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	3052	loop is stored in C<loop_hi>, while the embeddable loop is stored in
1988	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	3053	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
1989	used).	3054	used).
1990		3055
1991	struct ev_loop *loop_hi = ev_default_init (0);	3056	struct ev_loop *loop_hi = ev_default_init (0);
1992	struct ev_loop *loop_lo = 0;	3057	struct ev_loop *loop_lo = 0;
1993	struct ev_embed embed;	3058	ev_embed embed;
1994		3059
1995	// see if there is a chance of getting one that works	3060	// see if there is a chance of getting one that works
1996	// (remember that a flags value of 0 means autodetection)	3061	// (remember that a flags value of 0 means autodetection)
1997	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3062	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1998	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3063	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1999	: 0;	3064	: 0;
2000		3065
2001	// if we got one, then embed it, otherwise default to loop_hi	3066	// if we got one, then embed it, otherwise default to loop_hi
2002	if (loop_lo)	3067	if (loop_lo)
2003	{	3068	{
2004	ev_embed_init (&embed, 0, loop_lo);	3069	ev_embed_init (&embed, 0, loop_lo);
2005	ev_embed_start (loop_hi, &embed);	3070	ev_embed_start (loop_hi, &embed);
2006	}	3071	}
2007	else	3072	else
2008	loop_lo = loop_hi;	3073	loop_lo = loop_hi;
2009		3074
2010	Example: Check if kqueue is available but not recommended and create	3075	Example: Check if kqueue is available but not recommended and create
2011	a kqueue backend for use with sockets (which usually work with any	3076	a kqueue backend for use with sockets (which usually work with any
2012	kqueue implementation). Store the kqueue/socket-only event loop in	3077	kqueue implementation). Store the kqueue/socket-only event loop in
2013	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3078	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2014		3079
2015	struct ev_loop *loop = ev_default_init (0);	3080	struct ev_loop *loop = ev_default_init (0);
2016	struct ev_loop *loop_socket = 0;	3081	struct ev_loop *loop_socket = 0;
2017	struct ev_embed embed;	3082	ev_embed embed;
2018		3083
2019	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3084	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2020	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3085	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2021	{	3086	{
2022	ev_embed_init (&embed, 0, loop_socket);	3087	ev_embed_init (&embed, 0, loop_socket);
2023	ev_embed_start (loop, &embed);	3088	ev_embed_start (loop, &embed);
2024	}	3089	}
2025		3090
2026	if (!loop_socket)	3091	if (!loop_socket)
2027	loop_socket = loop;	3092	loop_socket = loop;
2028		3093
2029	// now use loop_socket for all sockets, and loop for everything else	3094	// now use loop_socket for all sockets, and loop for everything else
2030		3095
2031		3096
2032	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3097	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2033		3098
2034	Fork watchers are called when a C<fork ()> was detected (usually because	3099	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
2037	event loop blocks next and before C<ev_check> watchers are being called,	3102	event loop blocks next and before C<ev_check> watchers are being called,
2038	and only in the child after the fork. If whoever good citizen calling	3103	and only in the child after the fork. If whoever good citizen calling
2039	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3104	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2040	handlers will be invoked, too, of course.	3105	handlers will be invoked, too, of course.
2041		3106
		3107	=head3 The special problem of life after fork - how is it possible?
		3108
		3109	Most uses of C<fork()> consist of forking, then some simple calls to set
		3110	up/change the process environment, followed by a call to C<exec()>. This
		3111	sequence should be handled by libev without any problems.
		3112
		3113	This changes when the application actually wants to do event handling
		3114	in the child, or both parent in child, in effect "continuing" after the
		3115	fork.
		3116
		3117	The default mode of operation (for libev, with application help to detect
		3118	forks) is to duplicate all the state in the child, as would be expected
		3119	when I<either> the parent I<or> the child process continues.
		3120
		3121	When both processes want to continue using libev, then this is usually the
		3122	wrong result. In that case, usually one process (typically the parent) is
		3123	supposed to continue with all watchers in place as before, while the other
		3124	process typically wants to start fresh, i.e. without any active watchers.
		3125
		3126	The cleanest and most efficient way to achieve that with libev is to
		3127	simply create a new event loop, which of course will be "empty", and
		3128	use that for new watchers. This has the advantage of not touching more
		3129	memory than necessary, and thus avoiding the copy-on-write, and the
		3130	disadvantage of having to use multiple event loops (which do not support
		3131	signal watchers).
		3132
		3133	When this is not possible, or you want to use the default loop for
		3134	other reasons, then in the process that wants to start "fresh", call
		3135	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3136	Destroying the default loop will "orphan" (not stop) all registered
		3137	watchers, so you have to be careful not to execute code that modifies
		3138	those watchers. Note also that in that case, you have to re-register any
		3139	signal watchers.
		3140
2042	=head3 Watcher-Specific Functions and Data Members	3141	=head3 Watcher-Specific Functions and Data Members
2043		3142
2044	=over 4	3143	=over 4
2045		3144
2046	=item ev_fork_init (ev_signal *, callback)	3145	=item ev_fork_init (ev_fork *, callback)
2047		3146
2048	Initialises and configures the fork watcher - it has no parameters of any	3147	Initialises and configures the fork watcher - it has no parameters of any
2049	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3148	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2050	believe me.	3149	really.
2051		3150
2052	=back	3151	=back
2053		3152
2054		3153
		3154	=head2 C<ev_cleanup> - even the best things end
		3155
		3156	Cleanup watchers are called just before the event loop is being destroyed
		3157	by a call to C<ev_loop_destroy>.
		3158
		3159	While there is no guarantee that the event loop gets destroyed, cleanup
		3160	watchers provide a convenient method to install cleanup hooks for your
		3161	program, worker threads and so on - you just to make sure to destroy the
		3162	loop when you want them to be invoked.
		3163
		3164	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3165	all other watchers, they do not keep a reference to the event loop (which
		3166	makes a lot of sense if you think about it). Like all other watchers, you
		3167	can call libev functions in the callback, except C<ev_cleanup_start>.
		3168
		3169	=head3 Watcher-Specific Functions and Data Members
		3170
		3171	=over 4
		3172
		3173	=item ev_cleanup_init (ev_cleanup *, callback)
		3174
		3175	Initialises and configures the cleanup watcher - it has no parameters of
		3176	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3177	pointless, I assure you.
		3178
		3179	=back
		3180
		3181	Example: Register an atexit handler to destroy the default loop, so any
		3182	cleanup functions are called.
		3183
		3184	static void
		3185	program_exits (void)
		3186	{
		3187	ev_loop_destroy (EV_DEFAULT_UC);
		3188	}
		3189
		3190	...
		3191	atexit (program_exits);
		3192
		3193
2055	=head2 C<ev_async> - how to wake up another event loop	3194	=head2 C<ev_async> - how to wake up an event loop
2056		3195
2057	In general, you cannot use an C<ev_loop> from multiple threads or other	3196	In general, you cannot use an C<ev_loop> from multiple threads or other
2058	asynchronous sources such as signal handlers (as opposed to multiple event	3197	asynchronous sources such as signal handlers (as opposed to multiple event
2059	loops - those are of course safe to use in different threads).	3198	loops - those are of course safe to use in different threads).
2060		3199
2061	Sometimes, however, you need to wake up another event loop you do not	3200	Sometimes, however, you need to wake up an event loop you do not control,
2062	control, for example because it belongs to another thread. This is what	3201	for example because it belongs to another thread. This is what C<ev_async>
2063	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3202	watchers do: as long as the C<ev_async> watcher is active, you can signal
2064	can signal it by calling C<ev_async_send>, which is thread- and signal	3203	it by calling C<ev_async_send>, which is thread- and signal safe.
2065	safe.
2066		3204
2067	This functionality is very similar to C<ev_signal> watchers, as signals,	3205	This functionality is very similar to C<ev_signal> watchers, as signals,
2068	too, are asynchronous in nature, and signals, too, will be compressed	3206	too, are asynchronous in nature, and signals, too, will be compressed
2069	(i.e. the number of callback invocations may be less than the number of	3207	(i.e. the number of callback invocations may be less than the number of
2070	C<ev_async_sent> calls).	3208	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3209	of "global async watchers" by using a watcher on an otherwise unused
		3210	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3211	even without knowing which loop owns the signal.
2071		3212
2072	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3213	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
2073	just the default loop.	3214	just the default loop.
2074		3215
2075	=head3 Queueing	3216	=head3 Queueing
2076		3217
2077	C<ev_async> does not support queueing of data in any way. The reason	3218	C<ev_async> does not support queueing of data in any way. The reason
2078	is that the author does not know of a simple (or any) algorithm for a	3219	is that the author does not know of a simple (or any) algorithm for a
2079	multiple-writer-single-reader queue that works in all cases and doesn't	3220	multiple-writer-single-reader queue that works in all cases and doesn't
2080	need elaborate support such as pthreads.	3221	need elaborate support such as pthreads or unportable memory access
		3222	semantics.
2081		3223
2082	That means that if you want to queue data, you have to provide your own	3224	That means that if you want to queue data, you have to provide your own
2083	queue. But at least I can tell you would implement locking around your	3225	queue. But at least I can tell you how to implement locking around your
2084	queue:	3226	queue:
2085		3227
2086	=over 4	3228	=over 4
2087		3229
2088	=item queueing from a signal handler context	3230	=item queueing from a signal handler context
2089		3231
2090	To implement race-free queueing, you simply add to the queue in the signal	3232	To implement race-free queueing, you simply add to the queue in the signal
2091	handler but you block the signal handler in the watcher callback. Here is an example that does that for	3233	handler but you block the signal handler in the watcher callback. Here is
2092	some fictitiuous SIGUSR1 handler:	3234	an example that does that for some fictitious SIGUSR1 handler:
2093		3235
2094	static ev_async mysig;	3236	static ev_async mysig;
2095		3237
2096	static void	3238	static void
2097	sigusr1_handler (void)	3239	sigusr1_handler (void)
2098	{	3240	{
2099	sometype data;	3241	sometype data;
2100		3242
2101	// no locking etc.	3243	// no locking etc.
2102	queue_put (data);	3244	queue_put (data);
2103	ev_async_send (DEFAULT_ &mysig);	3245	ev_async_send (EV_DEFAULT_ &mysig);
2104	}	3246	}
2105		3247
2106	static void	3248	static void
2107	mysig_cb (EV_P_ ev_async *w, int revents)	3249	mysig_cb (EV_P_ ev_async *w, int revents)
2108	{	3250	{
…		…
2139	// only need to lock the actual queueing operation	3281	// only need to lock the actual queueing operation
2140	pthread_mutex_lock (&mymutex);	3282	pthread_mutex_lock (&mymutex);
2141	queue_put (data);	3283	queue_put (data);
2142	pthread_mutex_unlock (&mymutex);	3284	pthread_mutex_unlock (&mymutex);
2143		3285
2144	ev_async_send (DEFAULT_ &mysig);	3286	ev_async_send (EV_DEFAULT_ &mysig);
2145	}	3287	}
2146		3288
2147	static void	3289	static void
2148	mysig_cb (EV_P_ ev_async *w, int revents)	3290	mysig_cb (EV_P_ ev_async *w, int revents)
2149	{	3291	{
…		…
2163	=over 4	3305	=over 4
2164		3306
2165	=item ev_async_init (ev_async *, callback)	3307	=item ev_async_init (ev_async *, callback)
2166		3308
2167	Initialises and configures the async watcher - it has no parameters of any	3309	Initialises and configures the async watcher - it has no parameters of any
2168	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3310	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2169	believe me.	3311	trust me.
2170		3312
2171	=item ev_async_send (loop, ev_async *)	3313	=item ev_async_send (loop, ev_async *)
2172		3314
2173	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3315	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2174	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3316	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3317	returns.
		3318
2175	C<ev_feed_event>, this call is safe to do in other threads, signal or	3319	Unlike C<ev_feed_event>, this call is safe to do from other threads,
2176	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding	3320	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
2177	section below on what exactly this means).	3321	embedding section below on what exactly this means).
2178		3322
		3323	Note that, as with other watchers in libev, multiple events might get
		3324	compressed into a single callback invocation (another way to look at this
		3325	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3326	reset when the event loop detects that).
		3327
2179	This call incurs the overhead of a syscall only once per loop iteration,	3328	This call incurs the overhead of a system call only once per event loop
2180	so while the overhead might be noticable, it doesn't apply to repeated	3329	iteration, so while the overhead might be noticeable, it doesn't apply to
2181	calls to C<ev_async_send>.	3330	repeated calls to C<ev_async_send> for the same event loop.
		3331
		3332	=item bool = ev_async_pending (ev_async *)
		3333
		3334	Returns a non-zero value when C<ev_async_send> has been called on the
		3335	watcher but the event has not yet been processed (or even noted) by the
		3336	event loop.
		3337
		3338	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3339	the loop iterates next and checks for the watcher to have become active,
		3340	it will reset the flag again. C<ev_async_pending> can be used to very
		3341	quickly check whether invoking the loop might be a good idea.
		3342
		3343	Not that this does I<not> check whether the watcher itself is pending,
		3344	only whether it has been requested to make this watcher pending: there
		3345	is a time window between the event loop checking and resetting the async
		3346	notification, and the callback being invoked.
2182		3347
2183	=back	3348	=back
2184		3349
2185		3350
2186	=head1 OTHER FUNCTIONS	3351	=head1 OTHER FUNCTIONS
…		…
2190	=over 4	3355	=over 4
2191		3356
2192	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3357	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2193		3358
2194	This function combines a simple timer and an I/O watcher, calls your	3359	This function combines a simple timer and an I/O watcher, calls your
2195	callback on whichever event happens first and automatically stop both	3360	callback on whichever event happens first and automatically stops both
2196	watchers. This is useful if you want to wait for a single event on an fd	3361	watchers. This is useful if you want to wait for a single event on an fd
2197	or timeout without having to allocate/configure/start/stop/free one or	3362	or timeout without having to allocate/configure/start/stop/free one or
2198	more watchers yourself.	3363	more watchers yourself.
2199		3364
2200	If C<fd> is less than 0, then no I/O watcher will be started and events	3365	If C<fd> is less than 0, then no I/O watcher will be started and the
2201	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3366	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2202	C<events> set will be craeted and started.	3367	the given C<fd> and C<events> set will be created and started.
2203		3368
2204	If C<timeout> is less than 0, then no timeout watcher will be	3369	If C<timeout> is less than 0, then no timeout watcher will be
2205	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3370	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2206	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3371	repeat = 0) will be started. C<0> is a valid timeout.
2207	dubious value.
2208		3372
2209	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3373	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2210	passed an C<revents> set like normal event callbacks (a combination of	3374	passed an C<revents> set like normal event callbacks (a combination of
2211	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3375	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2212	value passed to C<ev_once>:	3376	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3377	a timeout and an io event at the same time - you probably should give io
		3378	events precedence.
2213		3379
		3380	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3381
2214	static void stdin_ready (int revents, void *arg)	3382	static void stdin_ready (int revents, void *arg)
2215	{	3383	{
2216	if (revents & EV_TIMEOUT)
2217	/* doh, nothing entered */;
2218	else if (revents & EV_READ)	3384	if (revents & EV_READ)
2219	/* stdin might have data for us, joy! */;	3385	/* stdin might have data for us, joy! */;
		3386	else if (revents & EV_TIMER)
		3387	/* doh, nothing entered */;
2220	}	3388	}
2221		3389
2222	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3390	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2223		3391
2224	=item ev_feed_event (ev_loop *, watcher *, int revents)
2225
2226	Feeds the given event set into the event loop, as if the specified event
2227	had happened for the specified watcher (which must be a pointer to an
2228	initialised but not necessarily started event watcher).
2229
2230	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3392	=item ev_feed_fd_event (loop, int fd, int revents)
2231		3393
2232	Feed an event on the given fd, as if a file descriptor backend detected	3394	Feed an event on the given fd, as if a file descriptor backend detected
2233	the given events it.	3395	the given events it.
2234		3396
2235	=item ev_feed_signal_event (ev_loop *loop, int signum)	3397	=item ev_feed_signal_event (loop, int signum)
2236		3398
2237	Feed an event as if the given signal occured (C<loop> must be the default	3399	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
2238	loop!).	3400	which is async-safe.
2239		3401
2240	=back	3402	=back
		3403
		3404
		3405	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3406
		3407	This section explains some common idioms that are not immediately
		3408	obvious. Note that examples are sprinkled over the whole manual, and this
		3409	section only contains stuff that wouldn't fit anywhere else.
		3410
		3411	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3412
		3413	Each watcher has, by default, a C<void *data> member that you can read
		3414	or modify at any time: libev will completely ignore it. This can be used
		3415	to associate arbitrary data with your watcher. If you need more data and
		3416	don't want to allocate memory separately and store a pointer to it in that
		3417	data member, you can also "subclass" the watcher type and provide your own
		3418	data:
		3419
		3420	struct my_io
		3421	{
		3422	ev_io io;
		3423	int otherfd;
		3424	void *somedata;
		3425	struct whatever *mostinteresting;
		3426	};
		3427
		3428	...
		3429	struct my_io w;
		3430	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3431
		3432	And since your callback will be called with a pointer to the watcher, you
		3433	can cast it back to your own type:
		3434
		3435	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3436	{
		3437	struct my_io *w = (struct my_io *)w_;
		3438	...
		3439	}
		3440
		3441	More interesting and less C-conformant ways of casting your callback
		3442	function type instead have been omitted.
		3443
		3444	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3445
		3446	Another common scenario is to use some data structure with multiple
		3447	embedded watchers, in effect creating your own watcher that combines
		3448	multiple libev event sources into one "super-watcher":
		3449
		3450	struct my_biggy
		3451	{
		3452	int some_data;
		3453	ev_timer t1;
		3454	ev_timer t2;
		3455	}
		3456
		3457	In this case getting the pointer to C<my_biggy> is a bit more
		3458	complicated: Either you store the address of your C<my_biggy> struct in
		3459	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3460	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3461	real programmers):
		3462
		3463	#include <stddef.h>
		3464
		3465	static void
		3466	t1_cb (EV_P_ ev_timer *w, int revents)
		3467	{
		3468	struct my_biggy big = (struct my_biggy *)
		3469	(((char *)w) - offsetof (struct my_biggy, t1));
		3470	}
		3471
		3472	static void
		3473	t2_cb (EV_P_ ev_timer *w, int revents)
		3474	{
		3475	struct my_biggy big = (struct my_biggy *)
		3476	(((char *)w) - offsetof (struct my_biggy, t2));
		3477	}
		3478
		3479	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3480
		3481	Often (especially in GUI toolkits) there are places where you have
		3482	I<modal> interaction, which is most easily implemented by recursively
		3483	invoking C<ev_run>.
		3484
		3485	This brings the problem of exiting - a callback might want to finish the
		3486	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3487	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3488	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3489	other combination: In these cases, C<ev_break> will not work alone.
		3490
		3491	The solution is to maintain "break this loop" variable for each C<ev_run>
		3492	invocation, and use a loop around C<ev_run> until the condition is
		3493	triggered, using C<EVRUN_ONCE>:
		3494
		3495	// main loop
		3496	int exit_main_loop = 0;
		3497
		3498	while (!exit_main_loop)
		3499	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3500
		3501	// in a model watcher
		3502	int exit_nested_loop = 0;
		3503
		3504	while (!exit_nested_loop)
		3505	ev_run (EV_A_ EVRUN_ONCE);
		3506
		3507	To exit from any of these loops, just set the corresponding exit variable:
		3508
		3509	// exit modal loop
		3510	exit_nested_loop = 1;
		3511
		3512	// exit main program, after modal loop is finished
		3513	exit_main_loop = 1;
		3514
		3515	// exit both
		3516	exit_main_loop = exit_nested_loop = 1;
		3517
		3518	=head2 THREAD LOCKING EXAMPLE
		3519
		3520	Here is a fictitious example of how to run an event loop in a different
		3521	thread from where callbacks are being invoked and watchers are
		3522	created/added/removed.
		3523
		3524	For a real-world example, see the C<EV::Loop::Async> perl module,
		3525	which uses exactly this technique (which is suited for many high-level
		3526	languages).
		3527
		3528	The example uses a pthread mutex to protect the loop data, a condition
		3529	variable to wait for callback invocations, an async watcher to notify the
		3530	event loop thread and an unspecified mechanism to wake up the main thread.
		3531
		3532	First, you need to associate some data with the event loop:
		3533
		3534	typedef struct {
		3535	mutex_t lock; /* global loop lock */
		3536	ev_async async_w;
		3537	thread_t tid;
		3538	cond_t invoke_cv;
		3539	} userdata;
		3540
		3541	void prepare_loop (EV_P)
		3542	{
		3543	// for simplicity, we use a static userdata struct.
		3544	static userdata u;
		3545
		3546	ev_async_init (&u->async_w, async_cb);
		3547	ev_async_start (EV_A_ &u->async_w);
		3548
		3549	pthread_mutex_init (&u->lock, 0);
		3550	pthread_cond_init (&u->invoke_cv, 0);
		3551
		3552	// now associate this with the loop
		3553	ev_set_userdata (EV_A_ u);
		3554	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3555	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3556
		3557	// then create the thread running ev_run
		3558	pthread_create (&u->tid, 0, l_run, EV_A);
		3559	}
		3560
		3561	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3562	solely to wake up the event loop so it takes notice of any new watchers
		3563	that might have been added:
		3564
		3565	static void
		3566	async_cb (EV_P_ ev_async *w, int revents)
		3567	{
		3568	// just used for the side effects
		3569	}
		3570
		3571	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3572	protecting the loop data, respectively.
		3573
		3574	static void
		3575	l_release (EV_P)
		3576	{
		3577	userdata *u = ev_userdata (EV_A);
		3578	pthread_mutex_unlock (&u->lock);
		3579	}
		3580
		3581	static void
		3582	l_acquire (EV_P)
		3583	{
		3584	userdata *u = ev_userdata (EV_A);
		3585	pthread_mutex_lock (&u->lock);
		3586	}
		3587
		3588	The event loop thread first acquires the mutex, and then jumps straight
		3589	into C<ev_run>:
		3590
		3591	void *
		3592	l_run (void *thr_arg)
		3593	{
		3594	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3595
		3596	l_acquire (EV_A);
		3597	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3598	ev_run (EV_A_ 0);
		3599	l_release (EV_A);
		3600
		3601	return 0;
		3602	}
		3603
		3604	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3605	signal the main thread via some unspecified mechanism (signals? pipe
		3606	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3607	have been called (in a while loop because a) spurious wakeups are possible
		3608	and b) skipping inter-thread-communication when there are no pending
		3609	watchers is very beneficial):
		3610
		3611	static void
		3612	l_invoke (EV_P)
		3613	{
		3614	userdata *u = ev_userdata (EV_A);
		3615
		3616	while (ev_pending_count (EV_A))
		3617	{
		3618	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3619	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3620	}
		3621	}
		3622
		3623	Now, whenever the main thread gets told to invoke pending watchers, it
		3624	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3625	thread to continue:
		3626
		3627	static void
		3628	real_invoke_pending (EV_P)
		3629	{
		3630	userdata *u = ev_userdata (EV_A);
		3631
		3632	pthread_mutex_lock (&u->lock);
		3633	ev_invoke_pending (EV_A);
		3634	pthread_cond_signal (&u->invoke_cv);
		3635	pthread_mutex_unlock (&u->lock);
		3636	}
		3637
		3638	Whenever you want to start/stop a watcher or do other modifications to an
		3639	event loop, you will now have to lock:
		3640
		3641	ev_timer timeout_watcher;
		3642	userdata *u = ev_userdata (EV_A);
		3643
		3644	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3645
		3646	pthread_mutex_lock (&u->lock);
		3647	ev_timer_start (EV_A_ &timeout_watcher);
		3648	ev_async_send (EV_A_ &u->async_w);
		3649	pthread_mutex_unlock (&u->lock);
		3650
		3651	Note that sending the C<ev_async> watcher is required because otherwise
		3652	an event loop currently blocking in the kernel will have no knowledge
		3653	about the newly added timer. By waking up the loop it will pick up any new
		3654	watchers in the next event loop iteration.
		3655
		3656	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3657
		3658	While the overhead of a callback that e.g. schedules a thread is small, it
		3659	is still an overhead. If you embed libev, and your main usage is with some
		3660	kind of threads or coroutines, you might want to customise libev so that
		3661	doesn't need callbacks anymore.
		3662
		3663	Imagine you have coroutines that you can switch to using a function
		3664	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3665	and that due to some magic, the currently active coroutine is stored in a
		3666	global called C<current_coro>. Then you can build your own "wait for libev
		3667	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3668	the differing C<;> conventions):
		3669
		3670	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3671	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3672
		3673	That means instead of having a C callback function, you store the
		3674	coroutine to switch to in each watcher, and instead of having libev call
		3675	your callback, you instead have it switch to that coroutine.
		3676
		3677	A coroutine might now wait for an event with a function called
		3678	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3679	matter when, or whether the watcher is active or not when this function is
		3680	called):
		3681
		3682	void
		3683	wait_for_event (ev_watcher *w)
		3684	{
		3685	ev_cb_set (w) = current_coro;
		3686	switch_to (libev_coro);
		3687	}
		3688
		3689	That basically suspends the coroutine inside C<wait_for_event> and
		3690	continues the libev coroutine, which, when appropriate, switches back to
		3691	this or any other coroutine. I am sure if you sue this your own :)
		3692
		3693	You can do similar tricks if you have, say, threads with an event queue -
		3694	instead of storing a coroutine, you store the queue object and instead of
		3695	switching to a coroutine, you push the watcher onto the queue and notify
		3696	any waiters.
		3697
		3698	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3699	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3700
		3701	// my_ev.h
		3702	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3703	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3704	#include "../libev/ev.h"
		3705
		3706	// my_ev.c
		3707	#define EV_H "my_ev.h"
		3708	#include "../libev/ev.c"
		3709
		3710	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3711	F<my_ev.c> into your project. When properly specifying include paths, you
		3712	can even use F<ev.h> as header file name directly.
2241		3713
2242		3714
2243	=head1 LIBEVENT EMULATION	3715	=head1 LIBEVENT EMULATION
2244		3716
2245	Libev offers a compatibility emulation layer for libevent. It cannot	3717	Libev offers a compatibility emulation layer for libevent. It cannot
2246	emulate the internals of libevent, so here are some usage hints:	3718	emulate the internals of libevent, so here are some usage hints:
2247		3719
2248	=over 4	3720	=over 4
		3721
		3722	=item * Only the libevent-1.4.1-beta API is being emulated.
		3723
		3724	This was the newest libevent version available when libev was implemented,
		3725	and is still mostly unchanged in 2010.
2249		3726
2250	=item * Use it by including <event.h>, as usual.	3727	=item * Use it by including <event.h>, as usual.
2251		3728
2252	=item * The following members are fully supported: ev_base, ev_callback,	3729	=item * The following members are fully supported: ev_base, ev_callback,
2253	ev_arg, ev_fd, ev_res, ev_events.	3730	ev_arg, ev_fd, ev_res, ev_events.
…		…
2258		3735
2259	=item * Priorities are not currently supported. Initialising priorities	3736	=item * Priorities are not currently supported. Initialising priorities
2260	will fail and all watchers will have the same priority, even though there	3737	will fail and all watchers will have the same priority, even though there
2261	is an ev_pri field.	3738	is an ev_pri field.
2262		3739
		3740	=item * In libevent, the last base created gets the signals, in libev, the
		3741	base that registered the signal gets the signals.
		3742
2263	=item * Other members are not supported.	3743	=item * Other members are not supported.
2264		3744
2265	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3745	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2266	to use the libev header file and library.	3746	to use the libev header file and library.
2267		3747
2268	=back	3748	=back
2269		3749
2270	=head1 C++ SUPPORT	3750	=head1 C++ SUPPORT
2271		3751
2272	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3752	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2273	you to use some convinience methods to start/stop watchers and also change	3753	you to use some convenience methods to start/stop watchers and also change
2274	the callback model to a model using method callbacks on objects.	3754	the callback model to a model using method callbacks on objects.
2275		3755
2276	To use it,	3756	To use it,
2277		3757
2278	#include <ev++.h>	3758	#include <ev++.h>
2279		3759
2280	This automatically includes F<ev.h> and puts all of its definitions (many	3760	This automatically includes F<ev.h> and puts all of its definitions (many
2281	of them macros) into the global namespace. All C++ specific things are	3761	of them macros) into the global namespace. All C++ specific things are
2282	put into the C<ev> namespace. It should support all the same embedding	3762	put into the C<ev> namespace. It should support all the same embedding
2283	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3763	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2285	Care has been taken to keep the overhead low. The only data member the C++	3765	Care has been taken to keep the overhead low. The only data member the C++
2286	classes add (compared to plain C-style watchers) is the event loop pointer	3766	classes add (compared to plain C-style watchers) is the event loop pointer
2287	that the watcher is associated with (or no additional members at all if	3767	that the watcher is associated with (or no additional members at all if
2288	you disable C<EV_MULTIPLICITY> when embedding libev).	3768	you disable C<EV_MULTIPLICITY> when embedding libev).
2289		3769
2290	Currently, functions, and static and non-static member functions can be	3770	Currently, functions, static and non-static member functions and classes
2291	used as callbacks. Other types should be easy to add as long as they only	3771	with C<operator ()> can be used as callbacks. Other types should be easy
2292	need one additional pointer for context. If you need support for other	3772	to add as long as they only need one additional pointer for context. If
2293	types of functors please contact the author (preferably after implementing	3773	you need support for other types of functors please contact the author
2294	it).	3774	(preferably after implementing it).
2295		3775
2296	Here is a list of things available in the C<ev> namespace:	3776	Here is a list of things available in the C<ev> namespace:
2297		3777
2298	=over 4	3778	=over 4
2299		3779
…		…
2317		3797
2318	=over 4	3798	=over 4
2319		3799
2320	=item ev::TYPE::TYPE ()	3800	=item ev::TYPE::TYPE ()
2321		3801
2322	=item ev::TYPE::TYPE (struct ev_loop *)	3802	=item ev::TYPE::TYPE (loop)
2323		3803
2324	=item ev::TYPE::~TYPE	3804	=item ev::TYPE::~TYPE
2325		3805
2326	The constructor (optionally) takes an event loop to associate the watcher	3806	The constructor (optionally) takes an event loop to associate the watcher
2327	with. If it is omitted, it will use C<EV_DEFAULT>.	3807	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2350	your compiler is good :), then the method will be fully inlined into the	3830	your compiler is good :), then the method will be fully inlined into the
2351	thunking function, making it as fast as a direct C callback.	3831	thunking function, making it as fast as a direct C callback.
2352		3832
2353	Example: simple class declaration and watcher initialisation	3833	Example: simple class declaration and watcher initialisation
2354		3834
2355	struct myclass	3835	struct myclass
2356	{	3836	{
2357	void io_cb (ev::io &w, int revents) { }	3837	void io_cb (ev::io &w, int revents) { }
2358	}	3838	}
2359		3839
2360	myclass obj;	3840	myclass obj;
2361	ev::io iow;	3841	ev::io iow;
2362	iow.set <myclass, &myclass::io_cb> (&obj);	3842	iow.set <myclass, &myclass::io_cb> (&obj);
		3843
		3844	=item w->set (object *)
		3845
		3846	This is a variation of a method callback - leaving out the method to call
		3847	will default the method to C<operator ()>, which makes it possible to use
		3848	functor objects without having to manually specify the C<operator ()> all
		3849	the time. Incidentally, you can then also leave out the template argument
		3850	list.
		3851
		3852	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3853	int revents)>.
		3854
		3855	See the method-C<set> above for more details.
		3856
		3857	Example: use a functor object as callback.
		3858
		3859	struct myfunctor
		3860	{
		3861	void operator() (ev::io &w, int revents)
		3862	{
		3863	...
		3864	}
		3865	}
		3866
		3867	myfunctor f;
		3868
		3869	ev::io w;
		3870	w.set (&f);
2363		3871
2364	=item w->set<function> (void *data = 0)	3872	=item w->set<function> (void *data = 0)
2365		3873
2366	Also sets a callback, but uses a static method or plain function as	3874	Also sets a callback, but uses a static method or plain function as
2367	callback. The optional C<data> argument will be stored in the watcher's	3875	callback. The optional C<data> argument will be stored in the watcher's
…		…
2369		3877
2370	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3878	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2371		3879
2372	See the method-C<set> above for more details.	3880	See the method-C<set> above for more details.
2373		3881
2374	Example:	3882	Example: Use a plain function as callback.
2375		3883
2376	static void io_cb (ev::io &w, int revents) { }	3884	static void io_cb (ev::io &w, int revents) { }
2377	iow.set <io_cb> ();	3885	iow.set <io_cb> ();
2378		3886
2379	=item w->set (struct ev_loop *)	3887	=item w->set (loop)
2380		3888
2381	Associates a different C<struct ev_loop> with this watcher. You can only	3889	Associates a different C<struct ev_loop> with this watcher. You can only
2382	do this when the watcher is inactive (and not pending either).	3890	do this when the watcher is inactive (and not pending either).
2383		3891
2384	=item w->set ([args])	3892	=item w->set ([arguments])
2385		3893
2386	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3894	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2387	called at least once. Unlike the C counterpart, an active watcher gets	3895	method or a suitable start method must be called at least once. Unlike the
2388	automatically stopped and restarted when reconfiguring it with this	3896	C counterpart, an active watcher gets automatically stopped and restarted
2389	method.	3897	when reconfiguring it with this method.
2390		3898
2391	=item w->start ()	3899	=item w->start ()
2392		3900
2393	Starts the watcher. Note that there is no C<loop> argument, as the	3901	Starts the watcher. Note that there is no C<loop> argument, as the
2394	constructor already stores the event loop.	3902	constructor already stores the event loop.
2395		3903
		3904	=item w->start ([arguments])
		3905
		3906	Instead of calling C<set> and C<start> methods separately, it is often
		3907	convenient to wrap them in one call. Uses the same type of arguments as
		3908	the configure C<set> method of the watcher.
		3909
2396	=item w->stop ()	3910	=item w->stop ()
2397		3911
2398	Stops the watcher if it is active. Again, no C<loop> argument.	3912	Stops the watcher if it is active. Again, no C<loop> argument.
2399		3913
2400	=item w->again () (C<ev::timer>, C<ev::periodic> only)	3914	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2412		3926
2413	=back	3927	=back
2414		3928
2415	=back	3929	=back
2416		3930
2417	Example: Define a class with an IO and idle watcher, start one of them in	3931	Example: Define a class with two I/O and idle watchers, start the I/O
2418	the constructor.	3932	watchers in the constructor.
2419		3933
2420	class myclass	3934	class myclass
2421	{	3935	{
2422	ev::io io; void io_cb (ev::io &w, int revents);	3936	ev::io io ; void io_cb (ev::io &w, int revents);
		3937	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
2423	ev:idle idle void idle_cb (ev::idle &w, int revents);	3938	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2424		3939
2425	myclass (int fd)	3940	myclass (int fd)
2426	{	3941	{
2427	io .set <myclass, &myclass::io_cb > (this);	3942	io .set <myclass, &myclass::io_cb > (this);
		3943	io2 .set <myclass, &myclass::io2_cb > (this);
2428	idle.set <myclass, &myclass::idle_cb> (this);	3944	idle.set <myclass, &myclass::idle_cb> (this);
2429		3945
2430	io.start (fd, ev::READ);	3946	io.set (fd, ev::WRITE); // configure the watcher
		3947	io.start (); // start it whenever convenient
		3948
		3949	io2.start (fd, ev::READ); // set + start in one call
2431	}	3950	}
2432	};	3951	};
		3952
		3953
		3954	=head1 OTHER LANGUAGE BINDINGS
		3955
		3956	Libev does not offer other language bindings itself, but bindings for a
		3957	number of languages exist in the form of third-party packages. If you know
		3958	any interesting language binding in addition to the ones listed here, drop
		3959	me a note.
		3960
		3961	=over 4
		3962
		3963	=item Perl
		3964
		3965	The EV module implements the full libev API and is actually used to test
		3966	libev. EV is developed together with libev. Apart from the EV core module,
		3967	there are additional modules that implement libev-compatible interfaces
		3968	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3969	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3970	and C<EV::Glib>).
		3971
		3972	It can be found and installed via CPAN, its homepage is at
		3973	L<http://software.schmorp.de/pkg/EV>.
		3974
		3975	=item Python
		3976
		3977	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3978	seems to be quite complete and well-documented.
		3979
		3980	=item Ruby
		3981
		3982	Tony Arcieri has written a ruby extension that offers access to a subset
		3983	of the libev API and adds file handle abstractions, asynchronous DNS and
		3984	more on top of it. It can be found via gem servers. Its homepage is at
		3985	L<http://rev.rubyforge.org/>.
		3986
		3987	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3988	makes rev work even on mingw.
		3989
		3990	=item Haskell
		3991
		3992	A haskell binding to libev is available at
		3993	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3994
		3995	=item D
		3996
		3997	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3998	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3999
		4000	=item Ocaml
		4001
		4002	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4003	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4004
		4005	=item Lua
		4006
		4007	Brian Maher has written a partial interface to libev for lua (at the
		4008	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4009	L<http://github.com/brimworks/lua-ev>.
		4010
		4011	=back
2433		4012
2434		4013
2435	=head1 MACRO MAGIC	4014	=head1 MACRO MAGIC
2436		4015
2437	Libev can be compiled with a variety of options, the most fundamantal	4016	Libev can be compiled with a variety of options, the most fundamental
2438	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	4017	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2439	functions and callbacks have an initial C<struct ev_loop *> argument.	4018	functions and callbacks have an initial C<struct ev_loop *> argument.
2440		4019
2441	To make it easier to write programs that cope with either variant, the	4020	To make it easier to write programs that cope with either variant, the
2442	following macros are defined:	4021	following macros are defined:
…		…
2447		4026
2448	This provides the loop I<argument> for functions, if one is required ("ev	4027	This provides the loop I<argument> for functions, if one is required ("ev
2449	loop argument"). The C<EV_A> form is used when this is the sole argument,	4028	loop argument"). The C<EV_A> form is used when this is the sole argument,
2450	C<EV_A_> is used when other arguments are following. Example:	4029	C<EV_A_> is used when other arguments are following. Example:
2451		4030
2452	ev_unref (EV_A);	4031	ev_unref (EV_A);
2453	ev_timer_add (EV_A_ watcher);	4032	ev_timer_add (EV_A_ watcher);
2454	ev_loop (EV_A_ 0);	4033	ev_run (EV_A_ 0);
2455		4034
2456	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4035	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2457	which is often provided by the following macro.	4036	which is often provided by the following macro.
2458		4037
2459	=item C<EV_P>, C<EV_P_>	4038	=item C<EV_P>, C<EV_P_>
2460		4039
2461	This provides the loop I<parameter> for functions, if one is required ("ev	4040	This provides the loop I<parameter> for functions, if one is required ("ev
2462	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	4041	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2463	C<EV_P_> is used when other parameters are following. Example:	4042	C<EV_P_> is used when other parameters are following. Example:
2464		4043
2465	// this is how ev_unref is being declared	4044	// this is how ev_unref is being declared
2466	static void ev_unref (EV_P);	4045	static void ev_unref (EV_P);
2467		4046
2468	// this is how you can declare your typical callback	4047	// this is how you can declare your typical callback
2469	static void cb (EV_P_ ev_timer *w, int revents)	4048	static void cb (EV_P_ ev_timer *w, int revents)
2470		4049
2471	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	4050	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2472	suitable for use with C<EV_A>.	4051	suitable for use with C<EV_A>.
2473		4052
2474	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4053	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2475		4054
2476	Similar to the other two macros, this gives you the value of the default	4055	Similar to the other two macros, this gives you the value of the default
2477	loop, if multiple loops are supported ("ev loop default").	4056	loop, if multiple loops are supported ("ev loop default").
		4057
		4058	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4059
		4060	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4061	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4062	is undefined when the default loop has not been initialised by a previous
		4063	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4064
		4065	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4066	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2478		4067
2479	=back	4068	=back
2480		4069
2481	Example: Declare and initialise a check watcher, utilising the above	4070	Example: Declare and initialise a check watcher, utilising the above
2482	macros so it will work regardless of whether multiple loops are supported	4071	macros so it will work regardless of whether multiple loops are supported
2483	or not.	4072	or not.
2484		4073
2485	static void	4074	static void
2486	check_cb (EV_P_ ev_timer *w, int revents)	4075	check_cb (EV_P_ ev_timer *w, int revents)
2487	{	4076	{
2488	ev_check_stop (EV_A_ w);	4077	ev_check_stop (EV_A_ w);
2489	}	4078	}
2490		4079
2491	ev_check check;	4080	ev_check check;
2492	ev_check_init (&check, check_cb);	4081	ev_check_init (&check, check_cb);
2493	ev_check_start (EV_DEFAULT_ &check);	4082	ev_check_start (EV_DEFAULT_ &check);
2494	ev_loop (EV_DEFAULT_ 0);	4083	ev_run (EV_DEFAULT_ 0);
2495		4084
2496	=head1 EMBEDDING	4085	=head1 EMBEDDING
2497		4086
2498	Libev can (and often is) directly embedded into host	4087	Libev can (and often is) directly embedded into host
2499	applications. Examples of applications that embed it include the Deliantra	4088	applications. Examples of applications that embed it include the Deliantra
…		…
2506	libev somewhere in your source tree).	4095	libev somewhere in your source tree).
2507		4096
2508	=head2 FILESETS	4097	=head2 FILESETS
2509		4098
2510	Depending on what features you need you need to include one or more sets of files	4099	Depending on what features you need you need to include one or more sets of files
2511	in your app.	4100	in your application.
2512		4101
2513	=head3 CORE EVENT LOOP	4102	=head3 CORE EVENT LOOP
2514		4103
2515	To include only the libev core (all the C<ev_*> functions), with manual	4104	To include only the libev core (all the C<ev_*> functions), with manual
2516	configuration (no autoconf):	4105	configuration (no autoconf):
2517		4106
2518	#define EV_STANDALONE 1	4107	#define EV_STANDALONE 1
2519	#include "ev.c"	4108	#include "ev.c"
2520		4109
2521	This will automatically include F<ev.h>, too, and should be done in a	4110	This will automatically include F<ev.h>, too, and should be done in a
2522	single C source file only to provide the function implementations. To use	4111	single C source file only to provide the function implementations. To use
2523	it, do the same for F<ev.h> in all files wishing to use this API (best	4112	it, do the same for F<ev.h> in all files wishing to use this API (best
2524	done by writing a wrapper around F<ev.h> that you can include instead and	4113	done by writing a wrapper around F<ev.h> that you can include instead and
2525	where you can put other configuration options):	4114	where you can put other configuration options):
2526		4115
2527	#define EV_STANDALONE 1	4116	#define EV_STANDALONE 1
2528	#include "ev.h"	4117	#include "ev.h"
2529		4118
2530	Both header files and implementation files can be compiled with a C++	4119	Both header files and implementation files can be compiled with a C++
2531	compiler (at least, thats a stated goal, and breakage will be treated	4120	compiler (at least, that's a stated goal, and breakage will be treated
2532	as a bug).	4121	as a bug).
2533		4122
2534	You need the following files in your source tree, or in a directory	4123	You need the following files in your source tree, or in a directory
2535	in your include path (e.g. in libev/ when using -Ilibev):	4124	in your include path (e.g. in libev/ when using -Ilibev):
2536		4125
2537	ev.h	4126	ev.h
2538	ev.c	4127	ev.c
2539	ev_vars.h	4128	ev_vars.h
2540	ev_wrap.h	4129	ev_wrap.h
2541		4130
2542	ev_win32.c required on win32 platforms only	4131	ev_win32.c required on win32 platforms only
2543		4132
2544	ev_select.c only when select backend is enabled (which is enabled by default)	4133	ev_select.c only when select backend is enabled (which is enabled by default)
2545	ev_poll.c only when poll backend is enabled (disabled by default)	4134	ev_poll.c only when poll backend is enabled (disabled by default)
2546	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4135	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2547	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4136	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2548	ev_port.c only when the solaris port backend is enabled (disabled by default)	4137	ev_port.c only when the solaris port backend is enabled (disabled by default)
2549		4138
2550	F<ev.c> includes the backend files directly when enabled, so you only need	4139	F<ev.c> includes the backend files directly when enabled, so you only need
2551	to compile this single file.	4140	to compile this single file.
2552		4141
2553	=head3 LIBEVENT COMPATIBILITY API	4142	=head3 LIBEVENT COMPATIBILITY API
2554		4143
2555	To include the libevent compatibility API, also include:	4144	To include the libevent compatibility API, also include:
2556		4145
2557	#include "event.c"	4146	#include "event.c"
2558		4147
2559	in the file including F<ev.c>, and:	4148	in the file including F<ev.c>, and:
2560		4149
2561	#include "event.h"	4150	#include "event.h"
2562		4151
2563	in the files that want to use the libevent API. This also includes F<ev.h>.	4152	in the files that want to use the libevent API. This also includes F<ev.h>.
2564		4153
2565	You need the following additional files for this:	4154	You need the following additional files for this:
2566		4155
2567	event.h	4156	event.h
2568	event.c	4157	event.c
2569		4158
2570	=head3 AUTOCONF SUPPORT	4159	=head3 AUTOCONF SUPPORT
2571		4160
2572	Instead of using C<EV_STANDALONE=1> and providing your config in	4161	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2573	whatever way you want, you can also C<m4_include([libev.m4])> in your	4162	whatever way you want, you can also C<m4_include([libev.m4])> in your
2574	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4163	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2575	include F<config.h> and configure itself accordingly.	4164	include F<config.h> and configure itself accordingly.
2576		4165
2577	For this of course you need the m4 file:	4166	For this of course you need the m4 file:
2578		4167
2579	libev.m4	4168	libev.m4
2580		4169
2581	=head2 PREPROCESSOR SYMBOLS/MACROS	4170	=head2 PREPROCESSOR SYMBOLS/MACROS
2582		4171
2583	Libev can be configured via a variety of preprocessor symbols you have to define	4172	Libev can be configured via a variety of preprocessor symbols you have to
2584	before including any of its files. The default is not to build for multiplicity	4173	define before including (or compiling) any of its files. The default in
2585	and only include the select backend.	4174	the absence of autoconf is documented for every option.
		4175
		4176	Symbols marked with "(h)" do not change the ABI, and can have different
		4177	values when compiling libev vs. including F<ev.h>, so it is permissible
		4178	to redefine them before including F<ev.h> without breaking compatibility
		4179	to a compiled library. All other symbols change the ABI, which means all
		4180	users of libev and the libev code itself must be compiled with compatible
		4181	settings.
2586		4182
2587	=over 4	4183	=over 4
2588		4184
		4185	=item EV_COMPAT3 (h)
		4186
		4187	Backwards compatibility is a major concern for libev. This is why this
		4188	release of libev comes with wrappers for the functions and symbols that
		4189	have been renamed between libev version 3 and 4.
		4190
		4191	You can disable these wrappers (to test compatibility with future
		4192	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4193	sources. This has the additional advantage that you can drop the C<struct>
		4194	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4195	typedef in that case.
		4196
		4197	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4198	and in some even more future version the compatibility code will be
		4199	removed completely.
		4200
2589	=item EV_STANDALONE	4201	=item EV_STANDALONE (h)
2590		4202
2591	Must always be C<1> if you do not use autoconf configuration, which	4203	Must always be C<1> if you do not use autoconf configuration, which
2592	keeps libev from including F<config.h>, and it also defines dummy	4204	keeps libev from including F<config.h>, and it also defines dummy
2593	implementations for some libevent functions (such as logging, which is not	4205	implementations for some libevent functions (such as logging, which is not
2594	supported). It will also not define any of the structs usually found in	4206	supported). It will also not define any of the structs usually found in
2595	F<event.h> that are not directly supported by the libev core alone.	4207	F<event.h> that are not directly supported by the libev core alone.
2596		4208
		4209	In standalone mode, libev will still try to automatically deduce the
		4210	configuration, but has to be more conservative.
		4211
		4212	=item EV_USE_FLOOR
		4213
		4214	If defined to be C<1>, libev will use the C<floor ()> function for its
		4215	periodic reschedule calculations, otherwise libev will fall back on a
		4216	portable (slower) implementation. If you enable this, you usually have to
		4217	link against libm or something equivalent. Enabling this when the C<floor>
		4218	function is not available will fail, so the safe default is to not enable
		4219	this.
		4220
2597	=item EV_USE_MONOTONIC	4221	=item EV_USE_MONOTONIC
2598		4222
2599	If defined to be C<1>, libev will try to detect the availability of the	4223	If defined to be C<1>, libev will try to detect the availability of the
2600	monotonic clock option at both compiletime and runtime. Otherwise no use	4224	monotonic clock option at both compile time and runtime. Otherwise no
2601	of the monotonic clock option will be attempted. If you enable this, you	4225	use of the monotonic clock option will be attempted. If you enable this,
2602	usually have to link against librt or something similar. Enabling it when	4226	you usually have to link against librt or something similar. Enabling it
2603	the functionality isn't available is safe, though, although you have	4227	when the functionality isn't available is safe, though, although you have
2604	to make sure you link against any libraries where the C<clock_gettime>	4228	to make sure you link against any libraries where the C<clock_gettime>
2605	function is hiding in (often F<-lrt>).	4229	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2606		4230
2607	=item EV_USE_REALTIME	4231	=item EV_USE_REALTIME
2608		4232
2609	If defined to be C<1>, libev will try to detect the availability of the	4233	If defined to be C<1>, libev will try to detect the availability of the
2610	realtime clock option at compiletime (and assume its availability at	4234	real-time clock option at compile time (and assume its availability
2611	runtime if successful). Otherwise no use of the realtime clock option will	4235	at runtime if successful). Otherwise no use of the real-time clock
2612	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4236	option will be attempted. This effectively replaces C<gettimeofday>
2613	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4237	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2614	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4238	correctness. See the note about libraries in the description of
		4239	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4240	C<EV_USE_CLOCK_SYSCALL>.
		4241
		4242	=item EV_USE_CLOCK_SYSCALL
		4243
		4244	If defined to be C<1>, libev will try to use a direct syscall instead
		4245	of calling the system-provided C<clock_gettime> function. This option
		4246	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4247	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4248	programs needlessly. Using a direct syscall is slightly slower (in
		4249	theory), because no optimised vdso implementation can be used, but avoids
		4250	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4251	higher, as it simplifies linking (no need for C<-lrt>).
2615		4252
2616	=item EV_USE_NANOSLEEP	4253	=item EV_USE_NANOSLEEP
2617		4254
2618	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4255	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2619	and will use it for delays. Otherwise it will use C<select ()>.	4256	and will use it for delays. Otherwise it will use C<select ()>.
2620		4257
		4258	=item EV_USE_EVENTFD
		4259
		4260	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4261	available and will probe for kernel support at runtime. This will improve
		4262	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4263	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4264	2.7 or newer, otherwise disabled.
		4265
2621	=item EV_USE_SELECT	4266	=item EV_USE_SELECT
2622		4267
2623	If undefined or defined to be C<1>, libev will compile in support for the	4268	If undefined or defined to be C<1>, libev will compile in support for the
2624	C<select>(2) backend. No attempt at autodetection will be done: if no	4269	C<select>(2) backend. No attempt at auto-detection will be done: if no
2625	other method takes over, select will be it. Otherwise the select backend	4270	other method takes over, select will be it. Otherwise the select backend
2626	will not be compiled in.	4271	will not be compiled in.
2627		4272
2628	=item EV_SELECT_USE_FD_SET	4273	=item EV_SELECT_USE_FD_SET
2629		4274
2630	If defined to C<1>, then the select backend will use the system C<fd_set>	4275	If defined to C<1>, then the select backend will use the system C<fd_set>
2631	structure. This is useful if libev doesn't compile due to a missing	4276	structure. This is useful if libev doesn't compile due to a missing
2632	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4277	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2633	exotic systems. This usually limits the range of file descriptors to some	4278	on exotic systems. This usually limits the range of file descriptors to
2634	low limit such as 1024 or might have other limitations (winsocket only	4279	some low limit such as 1024 or might have other limitations (winsocket
2635	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4280	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2636	influence the size of the C<fd_set> used.	4281	configures the maximum size of the C<fd_set>.
2637		4282
2638	=item EV_SELECT_IS_WINSOCKET	4283	=item EV_SELECT_IS_WINSOCKET
2639		4284
2640	When defined to C<1>, the select backend will assume that	4285	When defined to C<1>, the select backend will assume that
2641	select/socket/connect etc. don't understand file descriptors but	4286	select/socket/connect etc. don't understand file descriptors but
…		…
2643	be used is the winsock select). This means that it will call	4288	be used is the winsock select). This means that it will call
2644	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4289	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2645	it is assumed that all these functions actually work on fds, even	4290	it is assumed that all these functions actually work on fds, even
2646	on win32. Should not be defined on non-win32 platforms.	4291	on win32. Should not be defined on non-win32 platforms.
2647		4292
2648	=item EV_FD_TO_WIN32_HANDLE	4293	=item EV_FD_TO_WIN32_HANDLE(fd)
2649		4294
2650	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4295	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2651	file descriptors to socket handles. When not defining this symbol (the	4296	file descriptors to socket handles. When not defining this symbol (the
2652	default), then libev will call C<_get_osfhandle>, which is usually	4297	default), then libev will call C<_get_osfhandle>, which is usually
2653	correct. In some cases, programs use their own file descriptor management,	4298	correct. In some cases, programs use their own file descriptor management,
2654	in which case they can provide this function to map fds to socket handles.	4299	in which case they can provide this function to map fds to socket handles.
2655		4300
		4301	=item EV_WIN32_HANDLE_TO_FD(handle)
		4302
		4303	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4304	using the standard C<_open_osfhandle> function. For programs implementing
		4305	their own fd to handle mapping, overwriting this function makes it easier
		4306	to do so. This can be done by defining this macro to an appropriate value.
		4307
		4308	=item EV_WIN32_CLOSE_FD(fd)
		4309
		4310	If programs implement their own fd to handle mapping on win32, then this
		4311	macro can be used to override the C<close> function, useful to unregister
		4312	file descriptors again. Note that the replacement function has to close
		4313	the underlying OS handle.
		4314
2656	=item EV_USE_POLL	4315	=item EV_USE_POLL
2657		4316
2658	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4317	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2659	backend. Otherwise it will be enabled on non-win32 platforms. It	4318	backend. Otherwise it will be enabled on non-win32 platforms. It
2660	takes precedence over select.	4319	takes precedence over select.
2661		4320
2662	=item EV_USE_EPOLL	4321	=item EV_USE_EPOLL
2663		4322
2664	If defined to be C<1>, libev will compile in support for the Linux	4323	If defined to be C<1>, libev will compile in support for the Linux
2665	C<epoll>(7) backend. Its availability will be detected at runtime,	4324	C<epoll>(7) backend. Its availability will be detected at runtime,
2666	otherwise another method will be used as fallback. This is the	4325	otherwise another method will be used as fallback. This is the preferred
2667	preferred backend for GNU/Linux systems.	4326	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4327	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2668		4328
2669	=item EV_USE_KQUEUE	4329	=item EV_USE_KQUEUE
2670		4330
2671	If defined to be C<1>, libev will compile in support for the BSD style	4331	If defined to be C<1>, libev will compile in support for the BSD style
2672	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4332	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2685	otherwise another method will be used as fallback. This is the preferred	4345	otherwise another method will be used as fallback. This is the preferred
2686	backend for Solaris 10 systems.	4346	backend for Solaris 10 systems.
2687		4347
2688	=item EV_USE_DEVPOLL	4348	=item EV_USE_DEVPOLL
2689		4349
2690	reserved for future expansion, works like the USE symbols above.	4350	Reserved for future expansion, works like the USE symbols above.
2691		4351
2692	=item EV_USE_INOTIFY	4352	=item EV_USE_INOTIFY
2693		4353
2694	If defined to be C<1>, libev will compile in support for the Linux inotify	4354	If defined to be C<1>, libev will compile in support for the Linux inotify
2695	interface to speed up C<ev_stat> watchers. Its actual availability will	4355	interface to speed up C<ev_stat> watchers. Its actual availability will
2696	be detected at runtime.	4356	be detected at runtime. If undefined, it will be enabled if the headers
		4357	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2697		4358
2698	=item EV_ATOMIC_T	4359	=item EV_ATOMIC_T
2699		4360
2700	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4361	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2701	access is atomic with respect to other threads or signal contexts. No such	4362	access is atomic with respect to other threads or signal contexts. No such
2702	type is easily found in the C language, so you can provide your own type	4363	type is easily found in the C language, so you can provide your own type
2703	that you know is safe for your purposes. It is used both for signal handler "locking"	4364	that you know is safe for your purposes. It is used both for signal handler "locking"
2704	as well as for signal and thread safety in C<ev_async> watchers.	4365	as well as for signal and thread safety in C<ev_async> watchers.
2705		4366
2706	In the absense of this define, libev will use C<sig_atomic_t volatile>	4367	In the absence of this define, libev will use C<sig_atomic_t volatile>
2707	(from F<signal.h>), which is usually good enough on most platforms.	4368	(from F<signal.h>), which is usually good enough on most platforms.
2708		4369
2709	=item EV_H	4370	=item EV_H (h)
2710		4371
2711	The name of the F<ev.h> header file used to include it. The default if	4372	The name of the F<ev.h> header file used to include it. The default if
2712	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4373	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2713	used to virtually rename the F<ev.h> header file in case of conflicts.	4374	used to virtually rename the F<ev.h> header file in case of conflicts.
2714		4375
2715	=item EV_CONFIG_H	4376	=item EV_CONFIG_H (h)
2716		4377
2717	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4378	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2718	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4379	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2719	C<EV_H>, above.	4380	C<EV_H>, above.
2720		4381
2721	=item EV_EVENT_H	4382	=item EV_EVENT_H (h)
2722		4383
2723	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4384	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2724	of how the F<event.h> header can be found, the default is C<"event.h">.	4385	of how the F<event.h> header can be found, the default is C<"event.h">.
2725		4386
2726	=item EV_PROTOTYPES	4387	=item EV_PROTOTYPES (h)
2727		4388
2728	If defined to be C<0>, then F<ev.h> will not define any function	4389	If defined to be C<0>, then F<ev.h> will not define any function
2729	prototypes, but still define all the structs and other symbols. This is	4390	prototypes, but still define all the structs and other symbols. This is
2730	occasionally useful if you want to provide your own wrapper functions	4391	occasionally useful if you want to provide your own wrapper functions
2731	around libev functions.	4392	around libev functions.
…		…
2750	When doing priority-based operations, libev usually has to linearly search	4411	When doing priority-based operations, libev usually has to linearly search
2751	all the priorities, so having many of them (hundreds) uses a lot of space	4412	all the priorities, so having many of them (hundreds) uses a lot of space
2752	and time, so using the defaults of five priorities (-2 .. +2) is usually	4413	and time, so using the defaults of five priorities (-2 .. +2) is usually
2753	fine.	4414	fine.
2754		4415
2755	If your embedding app does not need any priorities, defining these both to	4416	If your embedding application does not need any priorities, defining these
2756	C<0> will save some memory and cpu.	4417	both to C<0> will save some memory and CPU.
2757		4418
2758	=item EV_PERIODIC_ENABLE	4419	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4420	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4421	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2759		4422
2760	If undefined or defined to be C<1>, then periodic timers are supported. If	4423	If undefined or defined to be C<1> (and the platform supports it), then
2761	defined to be C<0>, then they are not. Disabling them saves a few kB of	4424	the respective watcher type is supported. If defined to be C<0>, then it
2762	code.	4425	is not. Disabling watcher types mainly saves code size.
2763		4426
2764	=item EV_IDLE_ENABLE	4427	=item EV_FEATURES
2765
2766	If undefined or defined to be C<1>, then idle watchers are supported. If
2767	defined to be C<0>, then they are not. Disabling them saves a few kB of
2768	code.
2769
2770	=item EV_EMBED_ENABLE
2771
2772	If undefined or defined to be C<1>, then embed watchers are supported. If
2773	defined to be C<0>, then they are not.
2774
2775	=item EV_STAT_ENABLE
2776
2777	If undefined or defined to be C<1>, then stat watchers are supported. If
2778	defined to be C<0>, then they are not.
2779
2780	=item EV_FORK_ENABLE
2781
2782	If undefined or defined to be C<1>, then fork watchers are supported. If
2783	defined to be C<0>, then they are not.
2784
2785	=item EV_ASYNC_ENABLE
2786
2787	If undefined or defined to be C<1>, then async watchers are supported. If
2788	defined to be C<0>, then they are not.
2789
2790	=item EV_MINIMAL
2791		4428
2792	If you need to shave off some kilobytes of code at the expense of some	4429	If you need to shave off some kilobytes of code at the expense of some
2793	speed, define this symbol to C<1>. Currently only used for gcc to override	4430	speed (but with the full API), you can define this symbol to request
2794	some inlining decisions, saves roughly 30% codesize of amd64.	4431	certain subsets of functionality. The default is to enable all features
		4432	that can be enabled on the platform.
		4433
		4434	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4435	with some broad features you want) and then selectively re-enable
		4436	additional parts you want, for example if you want everything minimal,
		4437	but multiple event loop support, async and child watchers and the poll
		4438	backend, use this:
		4439
		4440	#define EV_FEATURES 0
		4441	#define EV_MULTIPLICITY 1
		4442	#define EV_USE_POLL 1
		4443	#define EV_CHILD_ENABLE 1
		4444	#define EV_ASYNC_ENABLE 1
		4445
		4446	The actual value is a bitset, it can be a combination of the following
		4447	values:
		4448
		4449	=over 4
		4450
		4451	=item C<1> - faster/larger code
		4452
		4453	Use larger code to speed up some operations.
		4454
		4455	Currently this is used to override some inlining decisions (enlarging the
		4456	code size by roughly 30% on amd64).
		4457
		4458	When optimising for size, use of compiler flags such as C<-Os> with
		4459	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4460	assertions.
		4461
		4462	=item C<2> - faster/larger data structures
		4463
		4464	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4465	hash table sizes and so on. This will usually further increase code size
		4466	and can additionally have an effect on the size of data structures at
		4467	runtime.
		4468
		4469	=item C<4> - full API configuration
		4470
		4471	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4472	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4473
		4474	=item C<8> - full API
		4475
		4476	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4477	details on which parts of the API are still available without this
		4478	feature, and do not complain if this subset changes over time.
		4479
		4480	=item C<16> - enable all optional watcher types
		4481
		4482	Enables all optional watcher types. If you want to selectively enable
		4483	only some watcher types other than I/O and timers (e.g. prepare,
		4484	embed, async, child...) you can enable them manually by defining
		4485	C<EV_watchertype_ENABLE> to C<1> instead.
		4486
		4487	=item C<32> - enable all backends
		4488
		4489	This enables all backends - without this feature, you need to enable at
		4490	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4491
		4492	=item C<64> - enable OS-specific "helper" APIs
		4493
		4494	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4495	default.
		4496
		4497	=back
		4498
		4499	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4500	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4501	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4502	watchers, timers and monotonic clock support.
		4503
		4504	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4505	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4506	your program might be left out as well - a binary starting a timer and an
		4507	I/O watcher then might come out at only 5Kb.
		4508
		4509	=item EV_AVOID_STDIO
		4510
		4511	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4512	functions (printf, scanf, perror etc.). This will increase the code size
		4513	somewhat, but if your program doesn't otherwise depend on stdio and your
		4514	libc allows it, this avoids linking in the stdio library which is quite
		4515	big.
		4516
		4517	Note that error messages might become less precise when this option is
		4518	enabled.
		4519
		4520	=item EV_NSIG
		4521
		4522	The highest supported signal number, +1 (or, the number of
		4523	signals): Normally, libev tries to deduce the maximum number of signals
		4524	automatically, but sometimes this fails, in which case it can be
		4525	specified. Also, using a lower number than detected (C<32> should be
		4526	good for about any system in existence) can save some memory, as libev
		4527	statically allocates some 12-24 bytes per signal number.
2795		4528
2796	=item EV_PID_HASHSIZE	4529	=item EV_PID_HASHSIZE
2797		4530
2798	C<ev_child> watchers use a small hash table to distribute workload by	4531	C<ev_child> watchers use a small hash table to distribute workload by
2799	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4532	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2800	than enough. If you need to manage thousands of children you might want to	4533	usually more than enough. If you need to manage thousands of children you
2801	increase this value (I<must> be a power of two).	4534	might want to increase this value (I<must> be a power of two).
2802		4535
2803	=item EV_INOTIFY_HASHSIZE	4536	=item EV_INOTIFY_HASHSIZE
2804		4537
2805	C<ev_stat> watchers use a small hash table to distribute workload by	4538	C<ev_stat> watchers use a small hash table to distribute workload by
2806	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4539	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2807	usually more than enough. If you need to manage thousands of C<ev_stat>	4540	disabled), usually more than enough. If you need to manage thousands of
2808	watchers you might want to increase this value (I<must> be a power of	4541	C<ev_stat> watchers you might want to increase this value (I<must> be a
2809	two).	4542	power of two).
		4543
		4544	=item EV_USE_4HEAP
		4545
		4546	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4547	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4548	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4549	faster performance with many (thousands) of watchers.
		4550
		4551	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4552	will be C<0>.
		4553
		4554	=item EV_HEAP_CACHE_AT
		4555
		4556	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4557	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4558	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4559	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4560	but avoids random read accesses on heap changes. This improves performance
		4561	noticeably with many (hundreds) of watchers.
		4562
		4563	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4564	will be C<0>.
		4565
		4566	=item EV_VERIFY
		4567
		4568	Controls how much internal verification (see C<ev_verify ()>) will
		4569	be done: If set to C<0>, no internal verification code will be compiled
		4570	in. If set to C<1>, then verification code will be compiled in, but not
		4571	called. If set to C<2>, then the internal verification code will be
		4572	called once per loop, which can slow down libev. If set to C<3>, then the
		4573	verification code will be called very frequently, which will slow down
		4574	libev considerably.
		4575
		4576	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4577	will be C<0>.
2810		4578
2811	=item EV_COMMON	4579	=item EV_COMMON
2812		4580
2813	By default, all watchers have a C<void *data> member. By redefining	4581	By default, all watchers have a C<void *data> member. By redefining
2814	this macro to a something else you can include more and other types of	4582	this macro to something else you can include more and other types of
2815	members. You have to define it each time you include one of the files,	4583	members. You have to define it each time you include one of the files,
2816	though, and it must be identical each time.	4584	though, and it must be identical each time.
2817		4585
2818	For example, the perl EV module uses something like this:	4586	For example, the perl EV module uses something like this:
2819		4587
2820	#define EV_COMMON \	4588	#define EV_COMMON \
2821	SV *self; /* contains this struct */ \	4589	SV *self; /* contains this struct */ \
2822	SV *cb_sv, *fh /* note no trailing ";" */	4590	SV *cb_sv, *fh /* note no trailing ";" */
2823		4591
2824	=item EV_CB_DECLARE (type)	4592	=item EV_CB_DECLARE (type)
2825		4593
2826	=item EV_CB_INVOKE (watcher, revents)	4594	=item EV_CB_INVOKE (watcher, revents)
2827		4595
…		…
2832	definition and a statement, respectively. See the F<ev.h> header file for	4600	definition and a statement, respectively. See the F<ev.h> header file for
2833	their default definitions. One possible use for overriding these is to	4601	their default definitions. One possible use for overriding these is to
2834	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4602	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2835	method calls instead of plain function calls in C++.	4603	method calls instead of plain function calls in C++.
2836		4604
		4605	=back
		4606
2837	=head2 EXPORTED API SYMBOLS	4607	=head2 EXPORTED API SYMBOLS
2838		4608
2839	If you need to re-export the API (e.g. via a dll) and you need a list of	4609	If you need to re-export the API (e.g. via a DLL) and you need a list of
2840	exported symbols, you can use the provided F<Symbol.*> files which list	4610	exported symbols, you can use the provided F<Symbol.*> files which list
2841	all public symbols, one per line:	4611	all public symbols, one per line:
2842		4612
2843	Symbols.ev for libev proper	4613	Symbols.ev for libev proper
2844	Symbols.event for the libevent emulation	4614	Symbols.event for the libevent emulation
2845		4615
2846	This can also be used to rename all public symbols to avoid clashes with	4616	This can also be used to rename all public symbols to avoid clashes with
2847	multiple versions of libev linked together (which is obviously bad in	4617	multiple versions of libev linked together (which is obviously bad in
2848	itself, but sometimes it is inconvinient to avoid this).	4618	itself, but sometimes it is inconvenient to avoid this).
2849		4619
2850	A sed command like this will create wrapper C<#define>'s that you need to	4620	A sed command like this will create wrapper C<#define>'s that you need to
2851	include before including F<ev.h>:	4621	include before including F<ev.h>:
2852		4622
2853	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	4623	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2870	file.	4640	file.
2871		4641
2872	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4642	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2873	that everybody includes and which overrides some configure choices:	4643	that everybody includes and which overrides some configure choices:
2874		4644
2875	#define EV_MINIMAL 1	4645	#define EV_FEATURES 8
2876	#define EV_USE_POLL 0	4646	#define EV_USE_SELECT 1
2877	#define EV_MULTIPLICITY 0
2878	#define EV_PERIODIC_ENABLE 0	4647	#define EV_PREPARE_ENABLE 1
		4648	#define EV_IDLE_ENABLE 1
2879	#define EV_STAT_ENABLE 0	4649	#define EV_SIGNAL_ENABLE 1
2880	#define EV_FORK_ENABLE 0	4650	#define EV_CHILD_ENABLE 1
		4651	#define EV_USE_STDEXCEPT 0
2881	#define EV_CONFIG_H <config.h>	4652	#define EV_CONFIG_H <config.h>
2882	#define EV_MINPRI 0
2883	#define EV_MAXPRI 0
2884		4653
2885	#include "ev++.h"	4654	#include "ev++.h"
2886		4655
2887	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4656	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2888		4657
2889	#include "ev_cpp.h"	4658	#include "ev_cpp.h"
2890	#include "ev.c"	4659	#include "ev.c"
2891		4660
		4661	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
2892		4662
2893	=head1 COMPLEXITIES	4663	=head2 THREADS AND COROUTINES
2894		4664
2895	In this section the complexities of (many of) the algorithms used inside	4665	=head3 THREADS
2896	libev will be explained. For complexity discussions about backends see the
2897	documentation for C<ev_default_init>.
2898		4666
2899	All of the following are about amortised time: If an array needs to be	4667	All libev functions are reentrant and thread-safe unless explicitly
2900	extended, libev needs to realloc and move the whole array, but this	4668	documented otherwise, but libev implements no locking itself. This means
2901	happens asymptotically never with higher number of elements, so O(1) might	4669	that you can use as many loops as you want in parallel, as long as there
2902	mean it might do a lengthy realloc operation in rare cases, but on average	4670	are no concurrent calls into any libev function with the same loop
2903	it is much faster and asymptotically approaches constant time.	4671	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4672	of course): libev guarantees that different event loops share no data
		4673	structures that need any locking.
		4674
		4675	Or to put it differently: calls with different loop parameters can be done
		4676	concurrently from multiple threads, calls with the same loop parameter
		4677	must be done serially (but can be done from different threads, as long as
		4678	only one thread ever is inside a call at any point in time, e.g. by using
		4679	a mutex per loop).
		4680
		4681	Specifically to support threads (and signal handlers), libev implements
		4682	so-called C<ev_async> watchers, which allow some limited form of
		4683	concurrency on the same event loop, namely waking it up "from the
		4684	outside".
		4685
		4686	If you want to know which design (one loop, locking, or multiple loops
		4687	without or something else still) is best for your problem, then I cannot
		4688	help you, but here is some generic advice:
2904		4689
2905	=over 4	4690	=over 4
2906		4691
2907	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4692	=item * most applications have a main thread: use the default libev loop
		4693	in that thread, or create a separate thread running only the default loop.
2908		4694
2909	This means that, when you have a watcher that triggers in one hour and	4695	This helps integrating other libraries or software modules that use libev
2910	there are 100 watchers that would trigger before that then inserting will	4696	themselves and don't care/know about threading.
2911	have to skip roughly seven (C<ld 100>) of these watchers.
2912		4697
2913	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4698	=item * one loop per thread is usually a good model.
2914		4699
2915	That means that changing a timer costs less than removing/adding them	4700	Doing this is almost never wrong, sometimes a better-performance model
2916	as only the relative motion in the event queue has to be paid for.	4701	exists, but it is always a good start.
2917		4702
2918	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4703	=item * other models exist, such as the leader/follower pattern, where one
		4704	loop is handed through multiple threads in a kind of round-robin fashion.
2919		4705
2920	These just add the watcher into an array or at the head of a list.	4706	Choosing a model is hard - look around, learn, know that usually you can do
		4707	better than you currently do :-)
2921		4708
2922	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4709	=item * often you need to talk to some other thread which blocks in the
		4710	event loop.
2923		4711
2924	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4712	C<ev_async> watchers can be used to wake them up from other threads safely
		4713	(or from signal contexts...).
2925		4714
2926	These watchers are stored in lists then need to be walked to find the	4715	An example use would be to communicate signals or other events that only
2927	correct watcher to remove. The lists are usually short (you don't usually	4716	work in the default loop by registering the signal watcher with the
2928	have many watchers waiting for the same fd or signal).	4717	default loop and triggering an C<ev_async> watcher from the default loop
2929		4718	watcher callback into the event loop interested in the signal.
2930	=item Finding the next timer in each loop iteration: O(1)
2931
2932	By virtue of using a binary heap, the next timer is always found at the
2933	beginning of the storage array.
2934
2935	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2936
2937	A change means an I/O watcher gets started or stopped, which requires
2938	libev to recalculate its status (and possibly tell the kernel, depending
2939	on backend and wether C<ev_io_set> was used).
2940
2941	=item Activating one watcher (putting it into the pending state): O(1)
2942
2943	=item Priority handling: O(number_of_priorities)
2944
2945	Priorities are implemented by allocating some space for each
2946	priority. When doing priority-based operations, libev usually has to
2947	linearly search all the priorities, but starting/stopping and activating
2948	watchers becomes O(1) w.r.t. priority handling.
2949
2950	=item Sending an ev_async: O(1)
2951
2952	=item Processing ev_async_send: O(number_of_async_watchers)
2953
2954	=item Processing signals: O(max_signal_number)
2955
2956	Sending involves a syscall I<iff> there were no other C<ev_async_send>
2957	calls in the current loop iteration. Checking for async and signal events
2958	involves iterating over all running async watchers or all signal numbers.
2959		4719
2960	=back	4720	=back
2961		4721
		4722	See also L<THREAD LOCKING EXAMPLE>.
2962		4723
2963	=head1 Win32 platform limitations and workarounds	4724	=head3 COROUTINES
		4725
		4726	Libev is very accommodating to coroutines ("cooperative threads"):
		4727	libev fully supports nesting calls to its functions from different
		4728	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4729	different coroutines, and switch freely between both coroutines running
		4730	the loop, as long as you don't confuse yourself). The only exception is
		4731	that you must not do this from C<ev_periodic> reschedule callbacks.
		4732
		4733	Care has been taken to ensure that libev does not keep local state inside
		4734	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4735	they do not call any callbacks.
		4736
		4737	=head2 COMPILER WARNINGS
		4738
		4739	Depending on your compiler and compiler settings, you might get no or a
		4740	lot of warnings when compiling libev code. Some people are apparently
		4741	scared by this.
		4742
		4743	However, these are unavoidable for many reasons. For one, each compiler
		4744	has different warnings, and each user has different tastes regarding
		4745	warning options. "Warn-free" code therefore cannot be a goal except when
		4746	targeting a specific compiler and compiler-version.
		4747
		4748	Another reason is that some compiler warnings require elaborate
		4749	workarounds, or other changes to the code that make it less clear and less
		4750	maintainable.
		4751
		4752	And of course, some compiler warnings are just plain stupid, or simply
		4753	wrong (because they don't actually warn about the condition their message
		4754	seems to warn about). For example, certain older gcc versions had some
		4755	warnings that resulted in an extreme number of false positives. These have
		4756	been fixed, but some people still insist on making code warn-free with
		4757	such buggy versions.
		4758
		4759	While libev is written to generate as few warnings as possible,
		4760	"warn-free" code is not a goal, and it is recommended not to build libev
		4761	with any compiler warnings enabled unless you are prepared to cope with
		4762	them (e.g. by ignoring them). Remember that warnings are just that:
		4763	warnings, not errors, or proof of bugs.
		4764
		4765
		4766	=head2 VALGRIND
		4767
		4768	Valgrind has a special section here because it is a popular tool that is
		4769	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4770
		4771	If you think you found a bug (memory leak, uninitialised data access etc.)
		4772	in libev, then check twice: If valgrind reports something like:
		4773
		4774	==2274== definitely lost: 0 bytes in 0 blocks.
		4775	==2274== possibly lost: 0 bytes in 0 blocks.
		4776	==2274== still reachable: 256 bytes in 1 blocks.
		4777
		4778	Then there is no memory leak, just as memory accounted to global variables
		4779	is not a memleak - the memory is still being referenced, and didn't leak.
		4780
		4781	Similarly, under some circumstances, valgrind might report kernel bugs
		4782	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4783	although an acceptable workaround has been found here), or it might be
		4784	confused.
		4785
		4786	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4787	make it into some kind of religion.
		4788
		4789	If you are unsure about something, feel free to contact the mailing list
		4790	with the full valgrind report and an explanation on why you think this
		4791	is a bug in libev (best check the archives, too :). However, don't be
		4792	annoyed when you get a brisk "this is no bug" answer and take the chance
		4793	of learning how to interpret valgrind properly.
		4794
		4795	If you need, for some reason, empty reports from valgrind for your project
		4796	I suggest using suppression lists.
		4797
		4798
		4799	=head1 PORTABILITY NOTES
		4800
		4801	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4802
		4803	GNU/Linux is the only common platform that supports 64 bit file/large file
		4804	interfaces but I<disables> them by default.
		4805
		4806	That means that libev compiled in the default environment doesn't support
		4807	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4808
		4809	Unfortunately, many programs try to work around this GNU/Linux issue
		4810	by enabling the large file API, which makes them incompatible with the
		4811	standard libev compiled for their system.
		4812
		4813	Likewise, libev cannot enable the large file API itself as this would
		4814	suddenly make it incompatible to the default compile time environment,
		4815	i.e. all programs not using special compile switches.
		4816
		4817	=head2 OS/X AND DARWIN BUGS
		4818
		4819	The whole thing is a bug if you ask me - basically any system interface
		4820	you touch is broken, whether it is locales, poll, kqueue or even the
		4821	OpenGL drivers.
		4822
		4823	=head3 C<kqueue> is buggy
		4824
		4825	The kqueue syscall is broken in all known versions - most versions support
		4826	only sockets, many support pipes.
		4827
		4828	Libev tries to work around this by not using C<kqueue> by default on this
		4829	rotten platform, but of course you can still ask for it when creating a
		4830	loop - embedding a socket-only kqueue loop into a select-based one is
		4831	probably going to work well.
		4832
		4833	=head3 C<poll> is buggy
		4834
		4835	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4836	implementation by something calling C<kqueue> internally around the 10.5.6
		4837	release, so now C<kqueue> I<and> C<poll> are broken.
		4838
		4839	Libev tries to work around this by not using C<poll> by default on
		4840	this rotten platform, but of course you can still ask for it when creating
		4841	a loop.
		4842
		4843	=head3 C<select> is buggy
		4844
		4845	All that's left is C<select>, and of course Apple found a way to fuck this
		4846	one up as well: On OS/X, C<select> actively limits the number of file
		4847	descriptors you can pass in to 1024 - your program suddenly crashes when
		4848	you use more.
		4849
		4850	There is an undocumented "workaround" for this - defining
		4851	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4852	work on OS/X.
		4853
		4854	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4855
		4856	=head3 C<errno> reentrancy
		4857
		4858	The default compile environment on Solaris is unfortunately so
		4859	thread-unsafe that you can't even use components/libraries compiled
		4860	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4861	defined by default. A valid, if stupid, implementation choice.
		4862
		4863	If you want to use libev in threaded environments you have to make sure
		4864	it's compiled with C<_REENTRANT> defined.
		4865
		4866	=head3 Event port backend
		4867
		4868	The scalable event interface for Solaris is called "event
		4869	ports". Unfortunately, this mechanism is very buggy in all major
		4870	releases. If you run into high CPU usage, your program freezes or you get
		4871	a large number of spurious wakeups, make sure you have all the relevant
		4872	and latest kernel patches applied. No, I don't know which ones, but there
		4873	are multiple ones to apply, and afterwards, event ports actually work
		4874	great.
		4875
		4876	If you can't get it to work, you can try running the program by setting
		4877	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4878	C<select> backends.
		4879
		4880	=head2 AIX POLL BUG
		4881
		4882	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4883	this by trying to avoid the poll backend altogether (i.e. it's not even
		4884	compiled in), which normally isn't a big problem as C<select> works fine
		4885	with large bitsets on AIX, and AIX is dead anyway.
		4886
		4887	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4888
		4889	=head3 General issues
2964		4890
2965	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4891	Win32 doesn't support any of the standards (e.g. POSIX) that libev
2966	requires, and its I/O model is fundamentally incompatible with the POSIX	4892	requires, and its I/O model is fundamentally incompatible with the POSIX
2967	model. Libev still offers limited functionality on this platform in	4893	model. Libev still offers limited functionality on this platform in
2968	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4894	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
2969	descriptors. This only applies when using Win32 natively, not when using	4895	descriptors. This only applies when using Win32 natively, not when using
2970	e.g. cygwin.	4896	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4897	as every compielr comes with a slightly differently broken/incompatible
		4898	environment.
		4899
		4900	Lifting these limitations would basically require the full
		4901	re-implementation of the I/O system. If you are into this kind of thing,
		4902	then note that glib does exactly that for you in a very portable way (note
		4903	also that glib is the slowest event library known to man).
2971		4904
2972	There is no supported compilation method available on windows except	4905	There is no supported compilation method available on windows except
2973	embedding it into other applications.	4906	embedding it into other applications.
2974		4907
		4908	Sensible signal handling is officially unsupported by Microsoft - libev
		4909	tries its best, but under most conditions, signals will simply not work.
		4910
		4911	Not a libev limitation but worth mentioning: windows apparently doesn't
		4912	accept large writes: instead of resulting in a partial write, windows will
		4913	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4914	so make sure you only write small amounts into your sockets (less than a
		4915	megabyte seems safe, but this apparently depends on the amount of memory
		4916	available).
		4917
2975	Due to the many, low, and arbitrary limits on the win32 platform and the	4918	Due to the many, low, and arbitrary limits on the win32 platform and
2976	abysmal performance of winsockets, using a large number of sockets is not	4919	the abysmal performance of winsockets, using a large number of sockets
2977	recommended (and not reasonable). If your program needs to use more than	4920	is not recommended (and not reasonable). If your program needs to use
2978	a hundred or so sockets, then likely it needs to use a totally different	4921	more than a hundred or so sockets, then likely it needs to use a totally
2979	implementation for windows, as libev offers the POSIX model, which cannot	4922	different implementation for windows, as libev offers the POSIX readiness
2980	be implemented efficiently on windows (microsoft monopoly games).	4923	notification model, which cannot be implemented efficiently on windows
		4924	(due to Microsoft monopoly games).
2981		4925
2982	=over 4	4926	A typical way to use libev under windows is to embed it (see the embedding
		4927	section for details) and use the following F<evwrap.h> header file instead
		4928	of F<ev.h>:
2983		4929
		4930	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4931	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4932
		4933	#include "ev.h"
		4934
		4935	And compile the following F<evwrap.c> file into your project (make sure
		4936	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4937
		4938	#include "evwrap.h"
		4939	#include "ev.c"
		4940
2984	=item The winsocket select function	4941	=head3 The winsocket C<select> function
2985		4942
2986	The winsocket C<select> function doesn't follow POSIX in that it requires	4943	The winsocket C<select> function doesn't follow POSIX in that it
2987	socket I<handles> and not socket I<file descriptors>. This makes select	4944	requires socket I<handles> and not socket I<file descriptors> (it is
2988	very inefficient, and also requires a mapping from file descriptors	4945	also extremely buggy). This makes select very inefficient, and also
2989	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	4946	requires a mapping from file descriptors to socket handles (the Microsoft
2990	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	4947	C runtime provides the function C<_open_osfhandle> for this). See the
2991	symbols for more info.	4948	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4949	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
2992		4950
2993	The configuration for a "naked" win32 using the microsoft runtime	4951	The configuration for a "naked" win32 using the Microsoft runtime
2994	libraries and raw winsocket select is:	4952	libraries and raw winsocket select is:
2995		4953
2996	#define EV_USE_SELECT 1	4954	#define EV_USE_SELECT 1
2997	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4955	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
2998		4956
2999	Note that winsockets handling of fd sets is O(n), so you can easily get a	4957	Note that winsockets handling of fd sets is O(n), so you can easily get a
3000	complexity in the O(n²) range when using win32.	4958	complexity in the O(n²) range when using win32.
3001		4959
3002	=item Limited number of file descriptors	4960	=head3 Limited number of file descriptors
3003		4961
3004	Windows has numerous arbitrary (and low) limits on things. Early versions	4962	Windows has numerous arbitrary (and low) limits on things.
3005	of winsocket's select only supported waiting for a max. of C<64> handles	4963
		4964	Early versions of winsocket's select only supported waiting for a maximum
3006	(probably owning to the fact that all windows kernels can only wait for	4965	of C<64> handles (probably owning to the fact that all windows kernels
3007	C<64> things at the same time internally; microsoft recommends spawning a	4966	can only wait for C<64> things at the same time internally; Microsoft
3008	chain of threads and wait for 63 handles and the previous thread in each).	4967	recommends spawning a chain of threads and wait for 63 handles and the
		4968	previous thread in each. Sounds great!).
3009		4969
3010	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4970	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3011	to some high number (e.g. C<2048>) before compiling the winsocket select	4971	to some high number (e.g. C<2048>) before compiling the winsocket select
3012	call (which might be in libev or elsewhere, for example, perl does its own	4972	call (which might be in libev or elsewhere, for example, perl and many
3013	select emulation on windows).	4973	other interpreters do their own select emulation on windows).
3014		4974
3015	Another limit is the number of file descriptors in the microsoft runtime	4975	Another limit is the number of file descriptors in the Microsoft runtime
3016	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4976	libraries, which by default is C<64> (there must be a hidden I<64>
3017	or something like this inside microsoft). You can increase this by calling	4977	fetish or something like this inside Microsoft). You can increase this
3018	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4978	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3019	arbitrary limit), but is broken in many versions of the microsoft runtime	4979	(another arbitrary limit), but is broken in many versions of the Microsoft
3020	libraries.
3021
3022	This might get you to about C<512> or C<2048> sockets (depending on	4980	runtime libraries. This might get you to about C<512> or C<2048> sockets
3023	windows version and/or the phase of the moon). To get more, you need to	4981	(depending on windows version and/or the phase of the moon). To get more,
3024	wrap all I/O functions and provide your own fd management, but the cost of	4982	you need to wrap all I/O functions and provide your own fd management, but
3025	calling select (O(n²)) will likely make this unworkable.	4983	the cost of calling select (O(n²)) will likely make this unworkable.
		4984
		4985	=head2 PORTABILITY REQUIREMENTS
		4986
		4987	In addition to a working ISO-C implementation and of course the
		4988	backend-specific APIs, libev relies on a few additional extensions:
		4989
		4990	=over 4
		4991
		4992	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4993	calling conventions regardless of C<ev_watcher_type *>.
		4994
		4995	Libev assumes not only that all watcher pointers have the same internal
		4996	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4997	assumes that the same (machine) code can be used to call any watcher
		4998	callback: The watcher callbacks have different type signatures, but libev
		4999	calls them using an C<ev_watcher *> internally.
		5000
		5001	=item pointer accesses must be thread-atomic
		5002
		5003	Accessing a pointer value must be atomic, it must both be readable and
		5004	writable in one piece - this is the case on all current architectures.
		5005
		5006	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5007
		5008	The type C<sig_atomic_t volatile> (or whatever is defined as
		5009	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5010	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5011	believed to be sufficiently portable.
		5012
		5013	=item C<sigprocmask> must work in a threaded environment
		5014
		5015	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5016	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5017	pthread implementations will either allow C<sigprocmask> in the "main
		5018	thread" or will block signals process-wide, both behaviours would
		5019	be compatible with libev. Interaction between C<sigprocmask> and
		5020	C<pthread_sigmask> could complicate things, however.
		5021
		5022	The most portable way to handle signals is to block signals in all threads
		5023	except the initial one, and run the default loop in the initial thread as
		5024	well.
		5025
		5026	=item C<long> must be large enough for common memory allocation sizes
		5027
		5028	To improve portability and simplify its API, libev uses C<long> internally
		5029	instead of C<size_t> when allocating its data structures. On non-POSIX
		5030	systems (Microsoft...) this might be unexpectedly low, but is still at
		5031	least 31 bits everywhere, which is enough for hundreds of millions of
		5032	watchers.
		5033
		5034	=item C<double> must hold a time value in seconds with enough accuracy
		5035
		5036	The type C<double> is used to represent timestamps. It is required to
		5037	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5038	good enough for at least into the year 4000 with millisecond accuracy
		5039	(the design goal for libev). This requirement is overfulfilled by
		5040	implementations using IEEE 754, which is basically all existing ones. With
		5041	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
3026		5042
3027	=back	5043	=back
3028		5044
		5045	If you know of other additional requirements drop me a note.
		5046
		5047
		5048	=head1 ALGORITHMIC COMPLEXITIES
		5049
		5050	In this section the complexities of (many of) the algorithms used inside
		5051	libev will be documented. For complexity discussions about backends see
		5052	the documentation for C<ev_default_init>.
		5053
		5054	All of the following are about amortised time: If an array needs to be
		5055	extended, libev needs to realloc and move the whole array, but this
		5056	happens asymptotically rarer with higher number of elements, so O(1) might
		5057	mean that libev does a lengthy realloc operation in rare cases, but on
		5058	average it is much faster and asymptotically approaches constant time.
		5059
		5060	=over 4
		5061
		5062	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		5063
		5064	This means that, when you have a watcher that triggers in one hour and
		5065	there are 100 watchers that would trigger before that, then inserting will
		5066	have to skip roughly seven (C<ld 100>) of these watchers.
		5067
		5068	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		5069
		5070	That means that changing a timer costs less than removing/adding them,
		5071	as only the relative motion in the event queue has to be paid for.
		5072
		5073	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		5074
		5075	These just add the watcher into an array or at the head of a list.
		5076
		5077	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		5078
		5079	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		5080
		5081	These watchers are stored in lists, so they need to be walked to find the
		5082	correct watcher to remove. The lists are usually short (you don't usually
		5083	have many watchers waiting for the same fd or signal: one is typical, two
		5084	is rare).
		5085
		5086	=item Finding the next timer in each loop iteration: O(1)
		5087
		5088	By virtue of using a binary or 4-heap, the next timer is always found at a
		5089	fixed position in the storage array.
		5090
		5091	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5092
		5093	A change means an I/O watcher gets started or stopped, which requires
		5094	libev to recalculate its status (and possibly tell the kernel, depending
		5095	on backend and whether C<ev_io_set> was used).
		5096
		5097	=item Activating one watcher (putting it into the pending state): O(1)
		5098
		5099	=item Priority handling: O(number_of_priorities)
		5100
		5101	Priorities are implemented by allocating some space for each
		5102	priority. When doing priority-based operations, libev usually has to
		5103	linearly search all the priorities, but starting/stopping and activating
		5104	watchers becomes O(1) with respect to priority handling.
		5105
		5106	=item Sending an ev_async: O(1)
		5107
		5108	=item Processing ev_async_send: O(number_of_async_watchers)
		5109
		5110	=item Processing signals: O(max_signal_number)
		5111
		5112	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5113	calls in the current loop iteration. Checking for async and signal events
		5114	involves iterating over all running async watchers or all signal numbers.
		5115
		5116	=back
		5117
		5118
		5119	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5120
		5121	The major version 4 introduced some incompatible changes to the API.
		5122
		5123	At the moment, the C<ev.h> header file provides compatibility definitions
		5124	for all changes, so most programs should still compile. The compatibility
		5125	layer might be removed in later versions of libev, so better update to the
		5126	new API early than late.
		5127
		5128	=over 4
		5129
		5130	=item C<EV_COMPAT3> backwards compatibility mechanism
		5131
		5132	The backward compatibility mechanism can be controlled by
		5133	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5134	section.
		5135
		5136	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5137
		5138	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5139
		5140	ev_loop_destroy (EV_DEFAULT_UC);
		5141	ev_loop_fork (EV_DEFAULT);
		5142
		5143	=item function/symbol renames
		5144
		5145	A number of functions and symbols have been renamed:
		5146
		5147	ev_loop => ev_run
		5148	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5149	EVLOOP_ONESHOT => EVRUN_ONCE
		5150
		5151	ev_unloop => ev_break
		5152	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5153	EVUNLOOP_ONE => EVBREAK_ONE
		5154	EVUNLOOP_ALL => EVBREAK_ALL
		5155
		5156	EV_TIMEOUT => EV_TIMER
		5157
		5158	ev_loop_count => ev_iteration
		5159	ev_loop_depth => ev_depth
		5160	ev_loop_verify => ev_verify
		5161
		5162	Most functions working on C<struct ev_loop> objects don't have an
		5163	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5164	associated constants have been renamed to not collide with the C<struct
		5165	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5166	as all other watcher types. Note that C<ev_loop_fork> is still called
		5167	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5168	typedef.
		5169
		5170	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5171
		5172	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5173	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5174	and work, but the library code will of course be larger.
		5175
		5176	=back
		5177
		5178
		5179	=head1 GLOSSARY
		5180
		5181	=over 4
		5182
		5183	=item active
		5184
		5185	A watcher is active as long as it has been started and not yet stopped.
		5186	See L<WATCHER STATES> for details.
		5187
		5188	=item application
		5189
		5190	In this document, an application is whatever is using libev.
		5191
		5192	=item backend
		5193
		5194	The part of the code dealing with the operating system interfaces.
		5195
		5196	=item callback
		5197
		5198	The address of a function that is called when some event has been
		5199	detected. Callbacks are being passed the event loop, the watcher that
		5200	received the event, and the actual event bitset.
		5201
		5202	=item callback/watcher invocation
		5203
		5204	The act of calling the callback associated with a watcher.
		5205
		5206	=item event
		5207
		5208	A change of state of some external event, such as data now being available
		5209	for reading on a file descriptor, time having passed or simply not having
		5210	any other events happening anymore.
		5211
		5212	In libev, events are represented as single bits (such as C<EV_READ> or
		5213	C<EV_TIMER>).
		5214
		5215	=item event library
		5216
		5217	A software package implementing an event model and loop.
		5218
		5219	=item event loop
		5220
		5221	An entity that handles and processes external events and converts them
		5222	into callback invocations.
		5223
		5224	=item event model
		5225
		5226	The model used to describe how an event loop handles and processes
		5227	watchers and events.
		5228
		5229	=item pending
		5230
		5231	A watcher is pending as soon as the corresponding event has been
		5232	detected. See L<WATCHER STATES> for details.
		5233
		5234	=item real time
		5235
		5236	The physical time that is observed. It is apparently strictly monotonic :)
		5237
		5238	=item wall-clock time
		5239
		5240	The time and date as shown on clocks. Unlike real time, it can actually
		5241	be wrong and jump forwards and backwards, e.g. when you adjust your
		5242	clock.
		5243
		5244	=item watcher
		5245
		5246	A data structure that describes interest in certain events. Watchers need
		5247	to be started (attached to an event loop) before they can receive events.
		5248
		5249	=back
3029		5250
3030	=head1 AUTHOR	5251	=head1 AUTHOR
3031		5252
3032	Marc Lehmann <libev@schmorp.de>.	5253	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5254	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
3033		5255

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