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Revision 1.121 by root, Mon Jan 28 12:13:54 2008 UTC vs.
Revision 1.361 by root, Sun Jan 23 18:53:06 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	// unloop 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 unloop. 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
		1184	=item C<EV_ASYNC>
		1185
		1186	The given async watcher has been asynchronously notified (see C<ev_async>).
		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
779	=item C<EV_ERROR>	1193	=item C<EV_ERROR>
780		1194
781	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
782	happen because the watcher could not be properly started because libev	1196	happen because the watcher could not be properly started because libev
783	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
784	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
785	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.
786		1204
787	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
788	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
789	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
790	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
791	programs, though, so beware.	1209	programs, though, as the fd could already be closed and reused for another
		1210	thing, so beware.
792		1211
793	=back	1212	=back
794		1213
795	=head2 GENERIC WATCHER FUNCTIONS	1214	=head2 GENERIC WATCHER FUNCTIONS
796
797	In the following description, C<TYPE> stands for the watcher type,
798	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
799		1215
800	=over 4	1216	=over 4
801		1217
802	=item C<ev_init> (ev_TYPE *watcher, callback)	1218	=item C<ev_init> (ev_TYPE *watcher, callback)
803		1219
…		…
809	which rolls both calls into one.	1225	which rolls both calls into one.
810		1226
811	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
812	(or never started) and there are no pending events outstanding.	1228	(or never started) and there are no pending events outstanding.
813		1229
814	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,
815	int revents)>.	1231	int revents)>.
816		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
817	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1239	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
818		1240
819	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
820	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
821	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
822	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
823	difference to the C<ev_init> macro).	1245	difference to the C<ev_init> macro).
824		1246
825	Although some watcher types do not have type-specific arguments	1247	Although some watcher types do not have type-specific arguments
826	(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.
827		1249
		1250	See C<ev_init>, above, for an example.
		1251
828	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1252	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
829		1253
830	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
831	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
832	a watcher. The same limitations apply, of course.	1256	a watcher. The same limitations apply, of course.
833		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
834	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1262	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
835		1263
836	Starts (activates) the given watcher. Only active watchers will receive	1264	Starts (activates) the given watcher. Only active watchers will receive
837	events. If the watcher is already active nothing will happen.	1265	events. If the watcher is already active nothing will happen.
838		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
839	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1272	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
840		1273
841	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
842	status. It is possible that stopped watchers are pending (for example,	1277	It is possible that stopped watchers are pending - for example,
843	non-repeating timers are being stopped when they become pending), but	1278	non-repeating timers are being stopped when they become pending - but
844	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
845	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
846	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.
847		1282
848	=item bool ev_is_active (ev_TYPE *watcher)	1283	=item bool ev_is_active (ev_TYPE *watcher)
849		1284
850	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
851	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
…		…
867	=item ev_cb_set (ev_TYPE *watcher, callback)	1302	=item ev_cb_set (ev_TYPE *watcher, callback)
868		1303
869	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
870	(modulo threads).	1305	(modulo threads).
871		1306
872	=item ev_set_priority (ev_TYPE *watcher, priority)	1307	=item ev_set_priority (ev_TYPE *watcher, int priority)
873		1308
874	=item int ev_priority (ev_TYPE *watcher)	1309	=item int ev_priority (ev_TYPE *watcher)
875		1310
876	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
877	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>
878	(default: C<-2>). Pending watchers with higher priority will be invoked	1313	(default: C<-2>). Pending watchers with higher priority will be invoked
879	before watchers with lower priority, but priority will not keep watchers	1314	before watchers with lower priority, but priority will not keep watchers
880	from being executed (except for C<ev_idle> watchers).	1315	from being executed (except for C<ev_idle> watchers).
881		1316
882	This means that priorities are I<only> used for ordering callback
883	invocation after new events have been received. This is useful, for
884	example, to reduce latency after idling, or more often, to bind two
885	watchers on the same event and make sure one is called first.
886
887	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
888	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.
889		1319
890	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
891	pending.	1321	pending.
892		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
893	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
894	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 :).
895		1329
896	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
897	fine, as long as you do not mind that the priority value you query might	1331	priorities.
898	or might not have been adjusted to be within valid range.
899		1332
900	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1333	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
901		1334
902	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
903	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
904	can deal with that fact.	1337	can deal with that fact, as both are simply passed through to the
		1338	callback.
905		1339
906	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1340	=item int ev_clear_pending (loop, ev_TYPE *watcher)
907		1341
908	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
909	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
910	watcher isn't pending it does nothing and returns C<0>.	1344	watcher isn't pending it does nothing and returns C<0>.
911		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
912	=back	1363	=back
913		1364
		1365	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
		1366	OWN COMPOSITE WATCHERS> idioms.
914		1367
915	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1368	=head2 WATCHER STATES
916		1369
917	Each watcher has, by default, a member C<void *data> that you can change	1370	There are various watcher states mentioned throughout this manual -
918	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
919	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
920	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".
921	member, you can also "subclass" the watcher type and provide your own
922	data:
923		1374
924	struct my_io	1375	=over 4
925	{
926	struct ev_io io;
927	int otherfd;
928	void *somedata;
929	struct whatever *mostinteresting;
930	}
931		1376
932	And since your callback will be called with a pointer to the watcher, you	1377	=item initialiased
933	can cast it back to your own type:
934		1378
935	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
936	{	1380	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
937	struct my_io *w = (struct my_io *)w_;	1381	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
938	...
939	}
940		1382
941	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
942	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.
943		1387
944	Another common scenario is having some data structure with multiple	1388	=item started/running/active
945	watchers:
946		1389
947	struct my_biggy	1390	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
948	{	1391	property of the event loop, and is actively waiting for events. While in
949	int some_data;	1392	this state it cannot be accessed (except in a few documented ways), moved,
950	ev_timer t1;	1393	freed or anything else - the only legal thing is to keep a pointer to it,
951	ev_timer t2;	1394	and call libev functions on it that are documented to work on active watchers.
952	}
953		1395
954	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1396	=item pending
955	you need to use C<offsetof>:
956		1397
957	#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.
958		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
959	static void	1498	static void
960	t1_cb (EV_P_ struct ev_timer *w, int revents)	1499	io_cb (EV_P_ ev_io *w, int revents)
961	{	1500	{
962	struct my_biggy big = (struct my_biggy *	1501	// stop the I/O watcher, we received the event, but
963	(((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);
964	}	1509	}
965		1510
966	static void	1511	static void
967	t2_cb (EV_P_ struct ev_timer *w, int revents)	1512	idle_cb (EV_P_ ev_idle *w, int revents)
968	{	1513	{
969	struct my_biggy big = (struct my_biggy *	1514	// actual processing
970	(((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);
971	}	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.
972		1532
973		1533
974	=head1 WATCHER TYPES	1534	=head1 WATCHER TYPES
975		1535
976	This section describes each watcher in detail, but will not repeat	1536	This section describes each watcher in detail, but will not repeat
…		…
1000	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
1001	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
1002	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
1003	required if you know what you are doing).	1563	required if you know what you are doing).
1004		1564
1005	If you must do this, then force the use of a known-to-be-good backend
1006	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1007	C<EVBACKEND_POLL>).
1008
1009	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
1010	receive "spurious" readyness notifications, that is your callback might	1566	receive "spurious" readiness notifications, that is, your callback might
1011	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
1012	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
1013	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
1014	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
1015	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1016	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1571	preferable to a program hanging until some data arrives.
1017		1572
1018	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
1019	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
1020	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
1021	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
1022	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.
1023		1582
1024	=head3 The special problem of disappearing file descriptors	1583	=head3 The special problem of disappearing file descriptors
1025		1584
1026	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
1027	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,
1028	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
1029	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
1030	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
1031	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
1032	fact, a different file descriptor.	1591	fact, a different file descriptor.
1033		1592
…		…
1051		1610
1052	There is no workaround possible except not registering events	1611	There is no workaround possible except not registering events
1053	for potentially C<dup ()>'ed file descriptors, or to resort to	1612	for potentially C<dup ()>'ed file descriptors, or to resort to
1054	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1613	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1055		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
1056	=head3 The special problem of fork	1648	=head3 The special problem of fork
1057		1649
1058	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
1059	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
1060	it in the child.	1652	it in the child if you want to continue to use it in the child.
1061		1653
1062	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
1063	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
1064	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1656	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1065	C<EVBACKEND_POLL>.
1066		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.
1067		1707
1068	=head3 Watcher-Specific Functions	1708	=head3 Watcher-Specific Functions
1069		1709
1070	=over 4	1710	=over 4
1071		1711
1072	=item ev_io_init (ev_io *, callback, int fd, int events)	1712	=item ev_io_init (ev_io *, callback, int fd, int events)
1073		1713
1074	=item ev_io_set (ev_io *, int fd, int events)	1714	=item ev_io_set (ev_io *, int fd, int events)
1075		1715
1076	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
1077	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
1078	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.
1079		1719
1080	=item int fd [read-only]	1720	=item int fd [read-only]
1081		1721
1082	The file descriptor being watched.	1722	The file descriptor being watched.
1083		1723
…		…
1091		1731
1092	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
1093	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
1094	attempt to read a whole line in the callback.	1734	attempt to read a whole line in the callback.
1095		1735
1096	static void	1736	static void
1097	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)
1098	{	1738	{
1099	ev_io_stop (loop, w);	1739	ev_io_stop (loop, w);
1100	.. 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
1101	}	1741	}
1102		1742
1103	...	1743	...
1104	struct ev_loop *loop = ev_default_init (0);	1744	struct ev_loop *loop = ev_default_init (0);
1105	struct ev_io stdin_readable;	1745	ev_io stdin_readable;
1106	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);
1107	ev_io_start (loop, &stdin_readable);	1747	ev_io_start (loop, &stdin_readable);
1108	ev_loop (loop, 0);	1748	ev_run (loop, 0);
1109		1749
1110		1750
1111	=head2 C<ev_timer> - relative and optionally repeating timeouts	1751	=head2 C<ev_timer> - relative and optionally repeating timeouts
1112		1752
1113	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
1114	given time, and optionally repeating in regular intervals after that.	1754	given time, and optionally repeating in regular intervals after that.
1115		1755
1116	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
1117	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
1118	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
1119	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1759	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1120	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.
1121		1951
1122	The relative timeouts are calculated relative to the C<ev_now ()>	1952	The relative timeouts are calculated relative to the C<ev_now ()>
1123	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
1124	of the event triggering whatever timeout you are modifying/starting. If	1954	of the event triggering whatever timeout you are modifying/starting. If
1125	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
1126	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:
1127		1957
1128	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1958	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1129		1959
1130	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
1131	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
1132	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>).
1133		1993
1134	=head3 Watcher-Specific Functions and Data Members	1994	=head3 Watcher-Specific Functions and Data Members
1135		1995
1136	=over 4	1996	=over 4
1137		1997
1138	=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)
1139		1999
1140	=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)
1141		2001
1142	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>
1143	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
1144	timer will automatically be configured to trigger again C<repeat> seconds	2004	reached. If it is positive, then the timer will automatically be
1145	later, again, and again, until stopped manually.	2005	configured to trigger again C<repeat> seconds later, again, and again,
		2006	until stopped manually.
1146		2007
1147	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
1148	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
1149	exactly 10 second intervals. If, however, your program cannot keep up with	2010	trigger at exactly 10 second intervals. If, however, your program cannot
1150	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
1151	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.
1152		2013
1153	=item ev_timer_again (loop)	2014	=item ev_timer_again (loop, ev_timer *)
1154		2015
1155	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
1156	repeating. The exact semantics are:	2017	repeating. The exact semantics are:
1157		2018
1158	If the timer is pending, its pending status is cleared.	2019	If the timer is pending, its pending status is cleared.
1159		2020
1160	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).
1161		2022
1162	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
1163	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.
1164		2025
1165	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
1166	example: Imagine you have a tcp connection and you want a so-called idle	2027	usage example.
1167	timeout, that is, you want to be called when there have been, say, 60
1168	seconds of inactivity on the socket. The easiest way to do this is to
1169	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1170	C<ev_timer_again> each time you successfully read or write some data. If
1171	you go into an idle state where you do not expect data to travel on the
1172	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1173	automatically restart it if need be.
1174		2028
1175	That means you can ignore the C<after> value and C<ev_timer_start>	2029	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1176	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1177		2030
1178	ev_timer_init (timer, callback, 0., 5.);	2031	Returns the remaining time until a timer fires. If the timer is active,
1179	ev_timer_again (loop, timer);	2032	then this time is relative to the current event loop time, otherwise it's
1180	...	2033	the timeout value currently configured.
1181	timer->again = 17.;
1182	ev_timer_again (loop, timer);
1183	...
1184	timer->again = 10.;
1185	ev_timer_again (loop, timer);
1186		2034
1187	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
1188	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.
1189		2040
1190	=item ev_tstamp repeat [read-write]	2041	=item ev_tstamp repeat [read-write]
1191		2042
1192	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
1193	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),
1194	which is also when any modifications are taken into account.	2045	which is also when any modifications are taken into account.
1195		2046
1196	=back	2047	=back
1197		2048
1198	=head3 Examples	2049	=head3 Examples
1199		2050
1200	Example: Create a timer that fires after 60 seconds.	2051	Example: Create a timer that fires after 60 seconds.
1201		2052
1202	static void	2053	static void
1203	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)
1204	{	2055	{
1205	.. one minute over, w is actually stopped right here	2056	.. one minute over, w is actually stopped right here
1206	}	2057	}
1207		2058
1208	struct ev_timer mytimer;	2059	ev_timer mytimer;
1209	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2060	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1210	ev_timer_start (loop, &mytimer);	2061	ev_timer_start (loop, &mytimer);
1211		2062
1212	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
1213	inactivity.	2064	inactivity.
1214		2065
1215	static void	2066	static void
1216	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2067	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1217	{	2068	{
1218	.. ten seconds without any activity	2069	.. ten seconds without any activity
1219	}	2070	}
1220		2071
1221	struct ev_timer mytimer;	2072	ev_timer mytimer;
1222	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 */
1223	ev_timer_again (&mytimer); /* start timer */	2074	ev_timer_again (&mytimer); /* start timer */
1224	ev_loop (loop, 0);	2075	ev_run (loop, 0);
1225		2076
1226	// 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":
1227	// reset the timeout to start ticking again at 10 seconds	2078	// reset the timeout to start ticking again at 10 seconds
1228	ev_timer_again (&mytimer);	2079	ev_timer_again (&mytimer);
1229		2080
1230		2081
1231	=head2 C<ev_periodic> - to cron or not to cron?	2082	=head2 C<ev_periodic> - to cron or not to cron?
1232		2083
1233	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
1234	(and unfortunately a bit complex).	2085	(and unfortunately a bit complex).
1235		2086
1236	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
1237	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
1238	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
1239	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
1240	+ 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
1241	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2092	wrist-watch).
1242	roughly 10 seconds later).
1243		2093
1244	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
1245	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
1246	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).
1247		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
1248	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
1249	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
1250	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).
1251		2112
1252	=head3 Watcher-Specific Functions and Data Members	2113	=head3 Watcher-Specific Functions and Data Members
1253		2114
1254	=over 4	2115	=over 4
1255		2116
1256	=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)
1257		2118
1258	=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)
1259		2120
1260	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
1261	operation, and we will explain them from simplest to complex:	2122	operation, and we will explain them from simplest to most complex:
1262		2123
1263	=over 4	2124	=over 4
1264		2125
1265	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2126	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1266		2127
1267	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
1268	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
1269	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
1270	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.
1271		2133
1272	=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)
1273		2135
1274	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
1275	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
1276	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.
1277		2140
1278	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
1279	time:	2142	system clock, for example, here is an C<ev_periodic> that triggers each
		2143	hour, on the hour (with respect to UTC):
1280		2144
1281	ev_periodic_set (&periodic, 0., 3600., 0);	2145	ev_periodic_set (&periodic, 0., 3600., 0);
1282		2146
1283	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,
1284	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
1285	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
1286	by 3600.	2150	by 3600.
1287		2151
1288	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
1289	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
1290	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.
1291		2155
1292	For numerical stability it is preferable that the C<at> value is near	2156	For numerical stability it is preferable that the C<offset> value is near
1293	C<ev_now ()> (the current time), but there is no range requirement for	2157	C<ev_now ()> (the current time), but there is no range requirement for
1294	this value.	2158	this value, and in fact is often specified as zero.
1295		2159
		2160	Note also that there is an upper limit to how often a timer can fire (CPU
		2161	speed for example), so if C<interval> is very small then timing stability
		2162	will of course deteriorate. Libev itself tries to be exact to be about one
		2163	millisecond (if the OS supports it and the machine is fast enough).
		2164
1296	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2165	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1297		2166
1298	In this mode the values for C<interval> and C<at> are both being	2167	In this mode the values for C<interval> and C<offset> are both being
1299	ignored. Instead, each time the periodic watcher gets scheduled, the	2168	ignored. Instead, each time the periodic watcher gets scheduled, the
1300	reschedule callback will be called with the watcher as first, and the	2169	reschedule callback will be called with the watcher as first, and the
1301	current time as second argument.	2170	current time as second argument.
1302		2171
1303	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2172	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1304	ever, or make any event loop modifications>. If you need to stop it,	2173	or make ANY other event loop modifications whatsoever, unless explicitly
1305	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2174	allowed by documentation here>.
1306	starting an C<ev_prepare> watcher, which is legal).
1307		2175
		2176	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2177	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2178	only event loop modification you are allowed to do).
		2179
1308	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2180	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1309	ev_tstamp now)>, e.g.:	2181	*w, ev_tstamp now)>, e.g.:
1310		2182
		2183	static ev_tstamp
1311	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2184	my_rescheduler (ev_periodic *w, ev_tstamp now)
1312	{	2185	{
1313	return now + 60.;	2186	return now + 60.;
1314	}	2187	}
1315		2188
1316	It must return the next time to trigger, based on the passed time value	2189	It must return the next time to trigger, based on the passed time value
1317	(that is, the lowest time value larger than to the second argument). It	2190	(that is, the lowest time value larger than to the second argument). It
1318	will usually be called just before the callback will be triggered, but	2191	will usually be called just before the callback will be triggered, but
1319	might be called at other times, too.	2192	might be called at other times, too.
1320		2193
1321	NOTE: I<< This callback must always return a time that is later than the	2194	NOTE: I<< This callback must always return a time that is higher than or
1322	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2195	equal to the passed C<now> value >>.
1323		2196
1324	This can be used to create very complex timers, such as a timer that	2197	This can be used to create very complex timers, such as a timer that
1325	triggers on each midnight, local time. To do this, you would calculate the	2198	triggers on "next midnight, local time". To do this, you would calculate the
1326	next midnight after C<now> and return the timestamp value for this. How	2199	next midnight after C<now> and return the timestamp value for this. How
1327	you do this is, again, up to you (but it is not trivial, which is the main	2200	you do this is, again, up to you (but it is not trivial, which is the main
1328	reason I omitted it as an example).	2201	reason I omitted it as an example).
1329		2202
1330	=back	2203	=back
…		…
1334	Simply stops and restarts the periodic watcher again. This is only useful	2207	Simply stops and restarts the periodic watcher again. This is only useful
1335	when you changed some parameters or the reschedule callback would return	2208	when you changed some parameters or the reschedule callback would return
1336	a different time than the last time it was called (e.g. in a crond like	2209	a different time than the last time it was called (e.g. in a crond like
1337	program when the crontabs have changed).	2210	program when the crontabs have changed).
1338		2211
		2212	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2213
		2214	When active, returns the absolute time that the watcher is supposed
		2215	to trigger next. This is not the same as the C<offset> argument to
		2216	C<ev_periodic_set>, but indeed works even in interval and manual
		2217	rescheduling modes.
		2218
1339	=item ev_tstamp offset [read-write]	2219	=item ev_tstamp offset [read-write]
1340		2220
1341	When repeating, this contains the offset value, otherwise this is the	2221	When repeating, this contains the offset value, otherwise this is the
1342	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2222	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2223	although libev might modify this value for better numerical stability).
1343		2224
1344	Can be modified any time, but changes only take effect when the periodic	2225	Can be modified any time, but changes only take effect when the periodic
1345	timer fires or C<ev_periodic_again> is being called.	2226	timer fires or C<ev_periodic_again> is being called.
1346		2227
1347	=item ev_tstamp interval [read-write]	2228	=item ev_tstamp interval [read-write]
1348		2229
1349	The current interval value. Can be modified any time, but changes only	2230	The current interval value. Can be modified any time, but changes only
1350	take effect when the periodic timer fires or C<ev_periodic_again> is being	2231	take effect when the periodic timer fires or C<ev_periodic_again> is being
1351	called.	2232	called.
1352		2233
1353	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2234	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1354		2235
1355	The current reschedule callback, or C<0>, if this functionality is	2236	The current reschedule callback, or C<0>, if this functionality is
1356	switched off. Can be changed any time, but changes only take effect when	2237	switched off. Can be changed any time, but changes only take effect when
1357	the periodic timer fires or C<ev_periodic_again> is being called.	2238	the periodic timer fires or C<ev_periodic_again> is being called.
1358		2239
1359	=item ev_tstamp at [read-only]
1360
1361	When active, contains the absolute time that the watcher is supposed to
1362	trigger next.
1363
1364	=back	2240	=back
1365		2241
1366	=head3 Examples	2242	=head3 Examples
1367		2243
1368	Example: Call a callback every hour, or, more precisely, whenever the	2244	Example: Call a callback every hour, or, more precisely, whenever the
1369	system clock is divisible by 3600. The callback invocation times have	2245	system time is divisible by 3600. The callback invocation times have
1370	potentially a lot of jittering, but good long-term stability.	2246	potentially a lot of jitter, but good long-term stability.
1371		2247
1372	static void	2248	static void
1373	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2249	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1374	{	2250	{
1375	... its now a full hour (UTC, or TAI or whatever your clock follows)	2251	... its now a full hour (UTC, or TAI or whatever your clock follows)
1376	}	2252	}
1377		2253
1378	struct ev_periodic hourly_tick;	2254	ev_periodic hourly_tick;
1379	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2255	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1380	ev_periodic_start (loop, &hourly_tick);	2256	ev_periodic_start (loop, &hourly_tick);
1381		2257
1382	Example: The same as above, but use a reschedule callback to do it:	2258	Example: The same as above, but use a reschedule callback to do it:
1383		2259
1384	#include <math.h>	2260	#include <math.h>
1385		2261
1386	static ev_tstamp	2262	static ev_tstamp
1387	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2263	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1388	{	2264	{
1389	return fmod (now, 3600.) + 3600.;	2265	return now + (3600. - fmod (now, 3600.));
1390	}	2266	}
1391		2267
1392	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2268	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1393		2269
1394	Example: Call a callback every hour, starting now:	2270	Example: Call a callback every hour, starting now:
1395		2271
1396	struct ev_periodic hourly_tick;	2272	ev_periodic hourly_tick;
1397	ev_periodic_init (&hourly_tick, clock_cb,	2273	ev_periodic_init (&hourly_tick, clock_cb,
1398	fmod (ev_now (loop), 3600.), 3600., 0);	2274	fmod (ev_now (loop), 3600.), 3600., 0);
1399	ev_periodic_start (loop, &hourly_tick);	2275	ev_periodic_start (loop, &hourly_tick);
1400		2276
1401		2277
1402	=head2 C<ev_signal> - signal me when a signal gets signalled!	2278	=head2 C<ev_signal> - signal me when a signal gets signalled!
1403		2279
1404	Signal watchers will trigger an event when the process receives a specific	2280	Signal watchers will trigger an event when the process receives a specific
1405	signal one or more times. Even though signals are very asynchronous, libev	2281	signal one or more times. Even though signals are very asynchronous, libev
1406	will try it's best to deliver signals synchronously, i.e. as part of the	2282	will try its best to deliver signals synchronously, i.e. as part of the
1407	normal event processing, like any other event.	2283	normal event processing, like any other event.
1408		2284
		2285	If you want signals to be delivered truly asynchronously, just use
		2286	C<sigaction> as you would do without libev and forget about sharing
		2287	the signal. You can even use C<ev_async> from a signal handler to
		2288	synchronously wake up an event loop.
		2289
1409	You can configure as many watchers as you like per signal. Only when the	2290	You can configure as many watchers as you like for the same signal, but
		2291	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2292	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2293	C<SIGINT> in both the default loop and another loop at the same time. At
		2294	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2295
1410	first watcher gets started will libev actually register a signal watcher	2296	When the first watcher gets started will libev actually register something
1411	with the kernel (thus it coexists with your own signal handlers as long	2297	with the kernel (thus it coexists with your own signal handlers as long as
1412	as you don't register any with libev). Similarly, when the last signal	2298	you don't register any with libev for the same signal).
1413	watcher for a signal is stopped libev will reset the signal handler to	2299
1414	SIG_DFL (regardless of what it was set to before).	2300	If possible and supported, libev will install its handlers with
		2301	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2302	not be unduly interrupted. If you have a problem with system calls getting
		2303	interrupted by signals you can block all signals in an C<ev_check> watcher
		2304	and unblock them in an C<ev_prepare> watcher.
		2305
		2306	=head3 The special problem of inheritance over fork/execve/pthread_create
		2307
		2308	Both the signal mask (C<sigprocmask>) and the signal disposition
		2309	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2310	stopping it again), that is, libev might or might not block the signal,
		2311	and might or might not set or restore the installed signal handler (but
		2312	see C<EVFLAG_NOSIGMASK>).
		2313
		2314	While this does not matter for the signal disposition (libev never
		2315	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2316	C<execve>), this matters for the signal mask: many programs do not expect
		2317	certain signals to be blocked.
		2318
		2319	This means that before calling C<exec> (from the child) you should reset
		2320	the signal mask to whatever "default" you expect (all clear is a good
		2321	choice usually).
		2322
		2323	The simplest way to ensure that the signal mask is reset in the child is
		2324	to install a fork handler with C<pthread_atfork> that resets it. That will
		2325	catch fork calls done by libraries (such as the libc) as well.
		2326
		2327	In current versions of libev, the signal will not be blocked indefinitely
		2328	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2329	the window of opportunity for problems, it will not go away, as libev
		2330	I<has> to modify the signal mask, at least temporarily.
		2331
		2332	So I can't stress this enough: I<If you do not reset your signal mask when
		2333	you expect it to be empty, you have a race condition in your code>. This
		2334	is not a libev-specific thing, this is true for most event libraries.
		2335
		2336	=head3 The special problem of threads signal handling
		2337
		2338	POSIX threads has problematic signal handling semantics, specifically,
		2339	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2340	threads in a process block signals, which is hard to achieve.
		2341
		2342	When you want to use sigwait (or mix libev signal handling with your own
		2343	for the same signals), you can tackle this problem by globally blocking
		2344	all signals before creating any threads (or creating them with a fully set
		2345	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2346	loops. Then designate one thread as "signal receiver thread" which handles
		2347	these signals. You can pass on any signals that libev might be interested
		2348	in by calling C<ev_feed_signal>.
1415		2349
1416	=head3 Watcher-Specific Functions and Data Members	2350	=head3 Watcher-Specific Functions and Data Members
1417		2351
1418	=over 4	2352	=over 4
1419		2353
…		…
1428		2362
1429	The signal the watcher watches out for.	2363	The signal the watcher watches out for.
1430		2364
1431	=back	2365	=back
1432		2366
		2367	=head3 Examples
		2368
		2369	Example: Try to exit cleanly on SIGINT.
		2370
		2371	static void
		2372	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2373	{
		2374	ev_break (loop, EVBREAK_ALL);
		2375	}
		2376
		2377	ev_signal signal_watcher;
		2378	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2379	ev_signal_start (loop, &signal_watcher);
		2380
1433		2381
1434	=head2 C<ev_child> - watch out for process status changes	2382	=head2 C<ev_child> - watch out for process status changes
1435		2383
1436	Child watchers trigger when your process receives a SIGCHLD in response to	2384	Child watchers trigger when your process receives a SIGCHLD in response to
1437	some child status changes (most typically when a child of yours dies).	2385	some child status changes (most typically when a child of yours dies or
		2386	exits). It is permissible to install a child watcher I<after> the child
		2387	has been forked (which implies it might have already exited), as long
		2388	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2389	forking and then immediately registering a watcher for the child is fine,
		2390	but forking and registering a watcher a few event loop iterations later or
		2391	in the next callback invocation is not.
		2392
		2393	Only the default event loop is capable of handling signals, and therefore
		2394	you can only register child watchers in the default event loop.
		2395
		2396	Due to some design glitches inside libev, child watchers will always be
		2397	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2398	libev)
		2399
		2400	=head3 Process Interaction
		2401
		2402	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2403	initialised. This is necessary to guarantee proper behaviour even if the
		2404	first child watcher is started after the child exits. The occurrence
		2405	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2406	synchronously as part of the event loop processing. Libev always reaps all
		2407	children, even ones not watched.
		2408
		2409	=head3 Overriding the Built-In Processing
		2410
		2411	Libev offers no special support for overriding the built-in child
		2412	processing, but if your application collides with libev's default child
		2413	handler, you can override it easily by installing your own handler for
		2414	C<SIGCHLD> after initialising the default loop, and making sure the
		2415	default loop never gets destroyed. You are encouraged, however, to use an
		2416	event-based approach to child reaping and thus use libev's support for
		2417	that, so other libev users can use C<ev_child> watchers freely.
		2418
		2419	=head3 Stopping the Child Watcher
		2420
		2421	Currently, the child watcher never gets stopped, even when the
		2422	child terminates, so normally one needs to stop the watcher in the
		2423	callback. Future versions of libev might stop the watcher automatically
		2424	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2425	problem).
1438		2426
1439	=head3 Watcher-Specific Functions and Data Members	2427	=head3 Watcher-Specific Functions and Data Members
1440		2428
1441	=over 4	2429	=over 4
1442		2430
…		…
1468		2456
1469	=back	2457	=back
1470		2458
1471	=head3 Examples	2459	=head3 Examples
1472		2460
1473	Example: Try to exit cleanly on SIGINT and SIGTERM.	2461	Example: C<fork()> a new process and install a child handler to wait for
		2462	its completion.
1474		2463
		2464	ev_child cw;
		2465
1475	static void	2466	static void
1476	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2467	child_cb (EV_P_ ev_child *w, int revents)
1477	{	2468	{
1478	ev_unloop (loop, EVUNLOOP_ALL);	2469	ev_child_stop (EV_A_ w);
		2470	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1479	}	2471	}
1480		2472
1481	struct ev_signal signal_watcher;	2473	pid_t pid = fork ();
1482	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2474
1483	ev_signal_start (loop, &sigint_cb);	2475	if (pid < 0)
		2476	// error
		2477	else if (pid == 0)
		2478	{
		2479	// the forked child executes here
		2480	exit (1);
		2481	}
		2482	else
		2483	{
		2484	ev_child_init (&cw, child_cb, pid, 0);
		2485	ev_child_start (EV_DEFAULT_ &cw);
		2486	}
1484		2487
1485		2488
1486	=head2 C<ev_stat> - did the file attributes just change?	2489	=head2 C<ev_stat> - did the file attributes just change?
1487		2490
1488	This watches a filesystem path for attribute changes. That is, it calls	2491	This watches a file system path for attribute changes. That is, it calls
1489	C<stat> regularly (or when the OS says it changed) and sees if it changed	2492	C<stat> on that path in regular intervals (or when the OS says it changed)
1490	compared to the last time, invoking the callback if it did.	2493	and sees if it changed compared to the last time, invoking the callback if
		2494	it did.
1491		2495
1492	The path does not need to exist: changing from "path exists" to "path does	2496	The path does not need to exist: changing from "path exists" to "path does
1493	not exist" is a status change like any other. The condition "path does	2497	not exist" is a status change like any other. The condition "path does not
1494	not exist" is signified by the C<st_nlink> field being zero (which is	2498	exist" (or more correctly "path cannot be stat'ed") is signified by the
1495	otherwise always forced to be at least one) and all the other fields of	2499	C<st_nlink> field being zero (which is otherwise always forced to be at
1496	the stat buffer having unspecified contents.	2500	least one) and all the other fields of the stat buffer having unspecified
		2501	contents.
1497		2502
1498	The path I<should> be absolute and I<must not> end in a slash. If it is	2503	The path I<must not> end in a slash or contain special components such as
		2504	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1499	relative and your working directory changes, the behaviour is undefined.	2505	your working directory changes, then the behaviour is undefined.
1500		2506
1501	Since there is no standard to do this, the portable implementation simply	2507	Since there is no portable change notification interface available, the
1502	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2508	portable implementation simply calls C<stat(2)> regularly on the path
1503	can specify a recommended polling interval for this case. If you specify	2509	to see if it changed somehow. You can specify a recommended polling
1504	a polling interval of C<0> (highly recommended!) then a I<suitable,	2510	interval for this case. If you specify a polling interval of C<0> (highly
1505	unspecified default> value will be used (which you can expect to be around	2511	recommended!) then a I<suitable, unspecified default> value will be used
1506	five seconds, although this might change dynamically). Libev will also	2512	(which you can expect to be around five seconds, although this might
1507	impose a minimum interval which is currently around C<0.1>, but thats	2513	change dynamically). Libev will also impose a minimum interval which is
1508	usually overkill.	2514	currently around C<0.1>, but that's usually overkill.
1509		2515
1510	This watcher type is not meant for massive numbers of stat watchers,	2516	This watcher type is not meant for massive numbers of stat watchers,
1511	as even with OS-supported change notifications, this can be	2517	as even with OS-supported change notifications, this can be
1512	resource-intensive.	2518	resource-intensive.
1513		2519
1514	At the time of this writing, only the Linux inotify interface is	2520	At the time of this writing, the only OS-specific interface implemented
1515	implemented (implementing kqueue support is left as an exercise for the	2521	is the Linux inotify interface (implementing kqueue support is left as an
1516	reader). Inotify will be used to give hints only and should not change the	2522	exercise for the reader. Note, however, that the author sees no way of
1517	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2523	implementing C<ev_stat> semantics with kqueue, except as a hint).
1518	to fall back to regular polling again even with inotify, but changes are
1519	usually detected immediately, and if the file exists there will be no
1520	polling.
1521		2524
1522	=head3 Inotify	2525	=head3 ABI Issues (Largefile Support)
1523		2526
		2527	Libev by default (unless the user overrides this) uses the default
		2528	compilation environment, which means that on systems with large file
		2529	support disabled by default, you get the 32 bit version of the stat
		2530	structure. When using the library from programs that change the ABI to
		2531	use 64 bit file offsets the programs will fail. In that case you have to
		2532	compile libev with the same flags to get binary compatibility. This is
		2533	obviously the case with any flags that change the ABI, but the problem is
		2534	most noticeably displayed with ev_stat and large file support.
		2535
		2536	The solution for this is to lobby your distribution maker to make large
		2537	file interfaces available by default (as e.g. FreeBSD does) and not
		2538	optional. Libev cannot simply switch on large file support because it has
		2539	to exchange stat structures with application programs compiled using the
		2540	default compilation environment.
		2541
		2542	=head3 Inotify and Kqueue
		2543
1524	When C<inotify (7)> support has been compiled into libev (generally only	2544	When C<inotify (7)> support has been compiled into libev and present at
1525	available on Linux) and present at runtime, it will be used to speed up	2545	runtime, it will be used to speed up change detection where possible. The
1526	change detection where possible. The inotify descriptor will be created lazily	2546	inotify descriptor will be created lazily when the first C<ev_stat>
1527	when the first C<ev_stat> watcher is being started.	2547	watcher is being started.
1528		2548
1529	Inotify presense does not change the semantics of C<ev_stat> watchers	2549	Inotify presence does not change the semantics of C<ev_stat> watchers
1530	except that changes might be detected earlier, and in some cases, to avoid	2550	except that changes might be detected earlier, and in some cases, to avoid
1531	making regular C<stat> calls. Even in the presense of inotify support	2551	making regular C<stat> calls. Even in the presence of inotify support
1532	there are many cases where libev has to resort to regular C<stat> polling.	2552	there are many cases where libev has to resort to regular C<stat> polling,
		2553	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2554	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2555	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2556	xfs are fully working) libev usually gets away without polling.
1533		2557
1534	(There is no support for kqueue, as apparently it cannot be used to	2558	There is no support for kqueue, as apparently it cannot be used to
1535	implement this functionality, due to the requirement of having a file	2559	implement this functionality, due to the requirement of having a file
1536	descriptor open on the object at all times).	2560	descriptor open on the object at all times, and detecting renames, unlinks
		2561	etc. is difficult.
		2562
		2563	=head3 C<stat ()> is a synchronous operation
		2564
		2565	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2566	the process. The exception are C<ev_stat> watchers - those call C<stat
		2567	()>, which is a synchronous operation.
		2568
		2569	For local paths, this usually doesn't matter: unless the system is very
		2570	busy or the intervals between stat's are large, a stat call will be fast,
		2571	as the path data is usually in memory already (except when starting the
		2572	watcher).
		2573
		2574	For networked file systems, calling C<stat ()> can block an indefinite
		2575	time due to network issues, and even under good conditions, a stat call
		2576	often takes multiple milliseconds.
		2577
		2578	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2579	paths, although this is fully supported by libev.
1537		2580
1538	=head3 The special problem of stat time resolution	2581	=head3 The special problem of stat time resolution
1539		2582
1540	The C<stat ()> syscall only supports full-second resolution portably, and	2583	The C<stat ()> system call only supports full-second resolution portably,
1541	even on systems where the resolution is higher, many filesystems still	2584	and even on systems where the resolution is higher, most file systems
1542	only support whole seconds.	2585	still only support whole seconds.
1543		2586
1544	That means that, if the time is the only thing that changes, you might	2587	That means that, if the time is the only thing that changes, you can
1545	miss updates: on the first update, C<ev_stat> detects a change and calls	2588	easily miss updates: on the first update, C<ev_stat> detects a change and
1546	your callback, which does something. When there is another update within	2589	calls your callback, which does something. When there is another update
1547	the same second, C<ev_stat> will be unable to detect it.	2590	within the same second, C<ev_stat> will be unable to detect unless the
		2591	stat data does change in other ways (e.g. file size).
1548		2592
1549	The solution to this is to delay acting on a change for a second (or till	2593	The solution to this is to delay acting on a change for slightly more
1550	the next second boundary), using a roughly one-second delay C<ev_timer>	2594	than a second (or till slightly after the next full second boundary), using
1551	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2595	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1552	is added to work around small timing inconsistencies of some operating	2596	ev_timer_again (loop, w)>).
1553	systems.	2597
		2598	The C<.02> offset is added to work around small timing inconsistencies
		2599	of some operating systems (where the second counter of the current time
		2600	might be be delayed. One such system is the Linux kernel, where a call to
		2601	C<gettimeofday> might return a timestamp with a full second later than
		2602	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2603	update file times then there will be a small window where the kernel uses
		2604	the previous second to update file times but libev might already execute
		2605	the timer callback).
1554		2606
1555	=head3 Watcher-Specific Functions and Data Members	2607	=head3 Watcher-Specific Functions and Data Members
1556		2608
1557	=over 4	2609	=over 4
1558		2610
…		…
1564	C<path>. The C<interval> is a hint on how quickly a change is expected to	2616	C<path>. The C<interval> is a hint on how quickly a change is expected to
1565	be detected and should normally be specified as C<0> to let libev choose	2617	be detected and should normally be specified as C<0> to let libev choose
1566	a suitable value. The memory pointed to by C<path> must point to the same	2618	a suitable value. The memory pointed to by C<path> must point to the same
1567	path for as long as the watcher is active.	2619	path for as long as the watcher is active.
1568		2620
1569	The callback will be receive C<EV_STAT> when a change was detected,	2621	The callback will receive an C<EV_STAT> event when a change was detected,
1570	relative to the attributes at the time the watcher was started (or the	2622	relative to the attributes at the time the watcher was started (or the
1571	last change was detected).	2623	last change was detected).
1572		2624
1573	=item ev_stat_stat (ev_stat *)	2625	=item ev_stat_stat (loop, ev_stat *)
1574		2626
1575	Updates the stat buffer immediately with new values. If you change the	2627	Updates the stat buffer immediately with new values. If you change the
1576	watched path in your callback, you could call this fucntion to avoid	2628	watched path in your callback, you could call this function to avoid
1577	detecting this change (while introducing a race condition). Can also be	2629	detecting this change (while introducing a race condition if you are not
1578	useful simply to find out the new values.	2630	the only one changing the path). Can also be useful simply to find out the
		2631	new values.
1579		2632
1580	=item ev_statdata attr [read-only]	2633	=item ev_statdata attr [read-only]
1581		2634
1582	The most-recently detected attributes of the file. Although the type is of	2635	The most-recently detected attributes of the file. Although the type is
1583	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2636	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1584	suitable for your system. If the C<st_nlink> member is C<0>, then there	2637	suitable for your system, but you can only rely on the POSIX-standardised
		2638	members to be present. If the C<st_nlink> member is C<0>, then there was
1585	was some error while C<stat>ing the file.	2639	some error while C<stat>ing the file.
1586		2640
1587	=item ev_statdata prev [read-only]	2641	=item ev_statdata prev [read-only]
1588		2642
1589	The previous attributes of the file. The callback gets invoked whenever	2643	The previous attributes of the file. The callback gets invoked whenever
1590	C<prev> != C<attr>.	2644	C<prev> != C<attr>, or, more precisely, one or more of these members
		2645	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2646	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1591		2647
1592	=item ev_tstamp interval [read-only]	2648	=item ev_tstamp interval [read-only]
1593		2649
1594	The specified interval.	2650	The specified interval.
1595		2651
1596	=item const char *path [read-only]	2652	=item const char *path [read-only]
1597		2653
1598	The filesystem path that is being watched.	2654	The file system path that is being watched.
1599		2655
1600	=back	2656	=back
1601		2657
1602	=head3 Examples	2658	=head3 Examples
1603		2659
1604	Example: Watch C</etc/passwd> for attribute changes.	2660	Example: Watch C</etc/passwd> for attribute changes.
1605		2661
1606	static void	2662	static void
1607	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2663	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1608	{	2664	{
1609	/* /etc/passwd changed in some way */	2665	/* /etc/passwd changed in some way */
1610	if (w->attr.st_nlink)	2666	if (w->attr.st_nlink)
1611	{	2667	{
1612	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2668	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1613	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2669	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1614	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2670	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1615	}	2671	}
1616	else	2672	else
1617	/* you shalt not abuse printf for puts */	2673	/* you shalt not abuse printf for puts */
1618	puts ("wow, /etc/passwd is not there, expect problems. "	2674	puts ("wow, /etc/passwd is not there, expect problems. "
1619	"if this is windows, they already arrived\n");	2675	"if this is windows, they already arrived\n");
1620	}	2676	}
1621		2677
1622	...	2678	...
1623	ev_stat passwd;	2679	ev_stat passwd;
1624		2680
1625	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2681	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1626	ev_stat_start (loop, &passwd);	2682	ev_stat_start (loop, &passwd);
1627		2683
1628	Example: Like above, but additionally use a one-second delay so we do not	2684	Example: Like above, but additionally use a one-second delay so we do not
1629	miss updates (however, frequent updates will delay processing, too, so	2685	miss updates (however, frequent updates will delay processing, too, so
1630	one might do the work both on C<ev_stat> callback invocation I<and> on	2686	one might do the work both on C<ev_stat> callback invocation I<and> on
1631	C<ev_timer> callback invocation).	2687	C<ev_timer> callback invocation).
1632		2688
1633	static ev_stat passwd;	2689	static ev_stat passwd;
1634	static ev_timer timer;	2690	static ev_timer timer;
1635		2691
1636	static void	2692	static void
1637	timer_cb (EV_P_ ev_timer *w, int revents)	2693	timer_cb (EV_P_ ev_timer *w, int revents)
1638	{	2694	{
1639	ev_timer_stop (EV_A_ w);	2695	ev_timer_stop (EV_A_ w);
1640		2696
1641	/* now it's one second after the most recent passwd change */	2697	/* now it's one second after the most recent passwd change */
1642	}	2698	}
1643		2699
1644	static void	2700	static void
1645	stat_cb (EV_P_ ev_stat *w, int revents)	2701	stat_cb (EV_P_ ev_stat *w, int revents)
1646	{	2702	{
1647	/* reset the one-second timer */	2703	/* reset the one-second timer */
1648	ev_timer_again (EV_A_ &timer);	2704	ev_timer_again (EV_A_ &timer);
1649	}	2705	}
1650		2706
1651	...	2707	...
1652	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2708	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1653	ev_stat_start (loop, &passwd);	2709	ev_stat_start (loop, &passwd);
1654	ev_timer_init (&timer, timer_cb, 0., 1.01);	2710	ev_timer_init (&timer, timer_cb, 0., 1.02);
1655		2711
1656		2712
1657	=head2 C<ev_idle> - when you've got nothing better to do...	2713	=head2 C<ev_idle> - when you've got nothing better to do...
1658		2714
1659	Idle watchers trigger events when no other events of the same or higher	2715	Idle watchers trigger events when no other events of the same or higher
1660	priority are pending (prepare, check and other idle watchers do not	2716	priority are pending (prepare, check and other idle watchers do not count
1661	count).	2717	as receiving "events").
1662		2718
1663	That is, as long as your process is busy handling sockets or timeouts	2719	That is, as long as your process is busy handling sockets or timeouts
1664	(or even signals, imagine) of the same or higher priority it will not be	2720	(or even signals, imagine) of the same or higher priority it will not be
1665	triggered. But when your process is idle (or only lower-priority watchers	2721	triggered. But when your process is idle (or only lower-priority watchers
1666	are pending), the idle watchers are being called once per event loop	2722	are pending), the idle watchers are being called once per event loop
…		…
1677		2733
1678	=head3 Watcher-Specific Functions and Data Members	2734	=head3 Watcher-Specific Functions and Data Members
1679		2735
1680	=over 4	2736	=over 4
1681		2737
1682	=item ev_idle_init (ev_signal *, callback)	2738	=item ev_idle_init (ev_idle *, callback)
1683		2739
1684	Initialises and configures the idle watcher - it has no parameters of any	2740	Initialises and configures the idle watcher - it has no parameters of any
1685	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2741	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1686	believe me.	2742	believe me.
1687		2743
…		…
1690	=head3 Examples	2746	=head3 Examples
1691		2747
1692	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2748	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1693	callback, free it. Also, use no error checking, as usual.	2749	callback, free it. Also, use no error checking, as usual.
1694		2750
1695	static void	2751	static void
1696	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2752	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1697	{	2753	{
1698	free (w);	2754	free (w);
1699	// now do something you wanted to do when the program has	2755	// now do something you wanted to do when the program has
1700	// no longer anything immediate to do.	2756	// no longer anything immediate to do.
1701	}	2757	}
1702		2758
1703	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2759	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1704	ev_idle_init (idle_watcher, idle_cb);	2760	ev_idle_init (idle_watcher, idle_cb);
1705	ev_idle_start (loop, idle_cb);	2761	ev_idle_start (loop, idle_watcher);
1706		2762
1707		2763
1708	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2764	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1709		2765
1710	Prepare and check watchers are usually (but not always) used in tandem:	2766	Prepare and check watchers are usually (but not always) used in pairs:
1711	prepare watchers get invoked before the process blocks and check watchers	2767	prepare watchers get invoked before the process blocks and check watchers
1712	afterwards.	2768	afterwards.
1713		2769
1714	You I<must not> call C<ev_loop> or similar functions that enter	2770	You I<must not> call C<ev_run> or similar functions that enter
1715	the current event loop from either C<ev_prepare> or C<ev_check>	2771	the current event loop from either C<ev_prepare> or C<ev_check>
1716	watchers. Other loops than the current one are fine, however. The	2772	watchers. Other loops than the current one are fine, however. The
1717	rationale behind this is that you do not need to check for recursion in	2773	rationale behind this is that you do not need to check for recursion in
1718	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2774	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1719	C<ev_check> so if you have one watcher of each kind they will always be	2775	C<ev_check> so if you have one watcher of each kind they will always be
1720	called in pairs bracketing the blocking call.	2776	called in pairs bracketing the blocking call.
1721		2777
1722	Their main purpose is to integrate other event mechanisms into libev and	2778	Their main purpose is to integrate other event mechanisms into libev and
1723	their use is somewhat advanced. This could be used, for example, to track	2779	their use is somewhat advanced. They could be used, for example, to track
1724	variable changes, implement your own watchers, integrate net-snmp or a	2780	variable changes, implement your own watchers, integrate net-snmp or a
1725	coroutine library and lots more. They are also occasionally useful if	2781	coroutine library and lots more. They are also occasionally useful if
1726	you cache some data and want to flush it before blocking (for example,	2782	you cache some data and want to flush it before blocking (for example,
1727	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2783	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1728	watcher).	2784	watcher).
1729		2785
1730	This is done by examining in each prepare call which file descriptors need	2786	This is done by examining in each prepare call which file descriptors
1731	to be watched by the other library, registering C<ev_io> watchers for	2787	need to be watched by the other library, registering C<ev_io> watchers
1732	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2788	for them and starting an C<ev_timer> watcher for any timeouts (many
1733	provide just this functionality). Then, in the check watcher you check for	2789	libraries provide exactly this functionality). Then, in the check watcher,
1734	any events that occured (by checking the pending status of all watchers	2790	you check for any events that occurred (by checking the pending status
1735	and stopping them) and call back into the library. The I/O and timer	2791	of all watchers and stopping them) and call back into the library. The
1736	callbacks will never actually be called (but must be valid nevertheless,	2792	I/O and timer callbacks will never actually be called (but must be valid
1737	because you never know, you know?).	2793	nevertheless, because you never know, you know?).
1738		2794
1739	As another example, the Perl Coro module uses these hooks to integrate	2795	As another example, the Perl Coro module uses these hooks to integrate
1740	coroutines into libev programs, by yielding to other active coroutines	2796	coroutines into libev programs, by yielding to other active coroutines
1741	during each prepare and only letting the process block if no coroutines	2797	during each prepare and only letting the process block if no coroutines
1742	are ready to run (it's actually more complicated: it only runs coroutines	2798	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1745	loop from blocking if lower-priority coroutines are active, thus mapping	2801	loop from blocking if lower-priority coroutines are active, thus mapping
1746	low-priority coroutines to idle/background tasks).	2802	low-priority coroutines to idle/background tasks).
1747		2803
1748	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2804	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1749	priority, to ensure that they are being run before any other watchers	2805	priority, to ensure that they are being run before any other watchers
		2806	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2807
1750	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2808	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1751	too) should not activate ("feed") events into libev. While libev fully	2809	activate ("feed") events into libev. While libev fully supports this, they
1752	supports this, they will be called before other C<ev_check> watchers	2810	might get executed before other C<ev_check> watchers did their job. As
1753	did their job. As C<ev_check> watchers are often used to embed other	2811	C<ev_check> watchers are often used to embed other (non-libev) event
1754	(non-libev) event loops those other event loops might be in an unusable	2812	loops those other event loops might be in an unusable state until their
1755	state until their C<ev_check> watcher ran (always remind yourself to	2813	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1756	coexist peacefully with others).	2814	others).
1757		2815
1758	=head3 Watcher-Specific Functions and Data Members	2816	=head3 Watcher-Specific Functions and Data Members
1759		2817
1760	=over 4	2818	=over 4
1761		2819
…		…
1763		2821
1764	=item ev_check_init (ev_check *, callback)	2822	=item ev_check_init (ev_check *, callback)
1765		2823
1766	Initialises and configures the prepare or check watcher - they have no	2824	Initialises and configures the prepare or check watcher - they have no
1767	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2825	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1768	macros, but using them is utterly, utterly and completely pointless.	2826	macros, but using them is utterly, utterly, utterly and completely
		2827	pointless.
1769		2828
1770	=back	2829	=back
1771		2830
1772	=head3 Examples	2831	=head3 Examples
1773		2832
1774	There are a number of principal ways to embed other event loops or modules	2833	There are a number of principal ways to embed other event loops or modules
1775	into libev. Here are some ideas on how to include libadns into libev	2834	into libev. Here are some ideas on how to include libadns into libev
1776	(there is a Perl module named C<EV::ADNS> that does this, which you could	2835	(there is a Perl module named C<EV::ADNS> that does this, which you could
1777	use for an actually working example. Another Perl module named C<EV::Glib>	2836	use as a working example. Another Perl module named C<EV::Glib> embeds a
1778	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2837	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1779	into the Glib event loop).	2838	Glib event loop).
1780		2839
1781	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2840	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1782	and in a check watcher, destroy them and call into libadns. What follows	2841	and in a check watcher, destroy them and call into libadns. What follows
1783	is pseudo-code only of course. This requires you to either use a low	2842	is pseudo-code only of course. This requires you to either use a low
1784	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2843	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1785	the callbacks for the IO/timeout watchers might not have been called yet.	2844	the callbacks for the IO/timeout watchers might not have been called yet.
1786		2845
1787	static ev_io iow [nfd];	2846	static ev_io iow [nfd];
1788	static ev_timer tw;	2847	static ev_timer tw;
1789		2848
1790	static void	2849	static void
1791	io_cb (ev_loop *loop, ev_io *w, int revents)	2850	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1792	{	2851	{
1793	}	2852	}
1794		2853
1795	// create io watchers for each fd and a timer before blocking	2854	// create io watchers for each fd and a timer before blocking
1796	static void	2855	static void
1797	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2856	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1798	{	2857	{
1799	int timeout = 3600000;	2858	int timeout = 3600000;
1800	struct pollfd fds [nfd];	2859	struct pollfd fds [nfd];
1801	// actual code will need to loop here and realloc etc.	2860	// actual code will need to loop here and realloc etc.
1802	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2861	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1803		2862
1804	/* the callback is illegal, but won't be called as we stop during check */	2863	/* the callback is illegal, but won't be called as we stop during check */
1805	ev_timer_init (&tw, 0, timeout * 1e-3);	2864	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1806	ev_timer_start (loop, &tw);	2865	ev_timer_start (loop, &tw);
1807		2866
1808	// create one ev_io per pollfd	2867	// create one ev_io per pollfd
1809	for (int i = 0; i < nfd; ++i)	2868	for (int i = 0; i < nfd; ++i)
1810	{	2869	{
1811	ev_io_init (iow + i, io_cb, fds [i].fd,	2870	ev_io_init (iow + i, io_cb, fds [i].fd,
1812	((fds [i].events & POLLIN ? EV_READ : 0)	2871	((fds [i].events & POLLIN ? EV_READ : 0)
1813	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2872	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1814		2873
1815	fds [i].revents = 0;	2874	fds [i].revents = 0;
1816	ev_io_start (loop, iow + i);	2875	ev_io_start (loop, iow + i);
1817	}	2876	}
1818	}	2877	}
1819		2878
1820	// stop all watchers after blocking	2879	// stop all watchers after blocking
1821	static void	2880	static void
1822	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2881	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1823	{	2882	{
1824	ev_timer_stop (loop, &tw);	2883	ev_timer_stop (loop, &tw);
1825		2884
1826	for (int i = 0; i < nfd; ++i)	2885	for (int i = 0; i < nfd; ++i)
1827	{	2886	{
1828	// set the relevant poll flags	2887	// set the relevant poll flags
1829	// could also call adns_processreadable etc. here	2888	// could also call adns_processreadable etc. here
1830	struct pollfd *fd = fds + i;	2889	struct pollfd *fd = fds + i;
1831	int revents = ev_clear_pending (iow + i);	2890	int revents = ev_clear_pending (iow + i);
1832	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2891	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1833	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2892	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1834		2893
1835	// now stop the watcher	2894	// now stop the watcher
1836	ev_io_stop (loop, iow + i);	2895	ev_io_stop (loop, iow + i);
1837	}	2896	}
1838		2897
1839	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2898	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1840	}	2899	}
1841		2900
1842	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2901	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1843	in the prepare watcher and would dispose of the check watcher.	2902	in the prepare watcher and would dispose of the check watcher.
1844		2903
1845	Method 3: If the module to be embedded supports explicit event	2904	Method 3: If the module to be embedded supports explicit event
1846	notification (adns does), you can also make use of the actual watcher	2905	notification (libadns does), you can also make use of the actual watcher
1847	callbacks, and only destroy/create the watchers in the prepare watcher.	2906	callbacks, and only destroy/create the watchers in the prepare watcher.
1848		2907
1849	static void	2908	static void
1850	timer_cb (EV_P_ ev_timer *w, int revents)	2909	timer_cb (EV_P_ ev_timer *w, int revents)
1851	{	2910	{
1852	adns_state ads = (adns_state)w->data;	2911	adns_state ads = (adns_state)w->data;
1853	update_now (EV_A);	2912	update_now (EV_A);
1854		2913
1855	adns_processtimeouts (ads, &tv_now);	2914	adns_processtimeouts (ads, &tv_now);
1856	}	2915	}
1857		2916
1858	static void	2917	static void
1859	io_cb (EV_P_ ev_io *w, int revents)	2918	io_cb (EV_P_ ev_io *w, int revents)
1860	{	2919	{
1861	adns_state ads = (adns_state)w->data;	2920	adns_state ads = (adns_state)w->data;
1862	update_now (EV_A);	2921	update_now (EV_A);
1863		2922
1864	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2923	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1865	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2924	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1866	}	2925	}
1867		2926
1868	// do not ever call adns_afterpoll	2927	// do not ever call adns_afterpoll
1869		2928
1870	Method 4: Do not use a prepare or check watcher because the module you	2929	Method 4: Do not use a prepare or check watcher because the module you
1871	want to embed is too inflexible to support it. Instead, youc na override	2930	want to embed is not flexible enough to support it. Instead, you can
1872	their poll function. The drawback with this solution is that the main	2931	override their poll function. The drawback with this solution is that the
1873	loop is now no longer controllable by EV. The C<Glib::EV> module does	2932	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1874	this.	2933	this approach, effectively embedding EV as a client into the horrible
		2934	libglib event loop.
1875		2935
1876	static gint	2936	static gint
1877	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2937	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1878	{	2938	{
1879	int got_events = 0;	2939	int got_events = 0;
1880		2940
1881	for (n = 0; n < nfds; ++n)	2941	for (n = 0; n < nfds; ++n)
1882	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2942	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1883		2943
1884	if (timeout >= 0)	2944	if (timeout >= 0)
1885	// create/start timer	2945	// create/start timer
1886		2946
1887	// poll	2947	// poll
1888	ev_loop (EV_A_ 0);	2948	ev_run (EV_A_ 0);
1889		2949
1890	// stop timer again	2950	// stop timer again
1891	if (timeout >= 0)	2951	if (timeout >= 0)
1892	ev_timer_stop (EV_A_ &to);	2952	ev_timer_stop (EV_A_ &to);
1893		2953
1894	// stop io watchers again - their callbacks should have set	2954	// stop io watchers again - their callbacks should have set
1895	for (n = 0; n < nfds; ++n)	2955	for (n = 0; n < nfds; ++n)
1896	ev_io_stop (EV_A_ iow [n]);	2956	ev_io_stop (EV_A_ iow [n]);
1897		2957
1898	return got_events;	2958	return got_events;
1899	}	2959	}
1900		2960
1901		2961
1902	=head2 C<ev_embed> - when one backend isn't enough...	2962	=head2 C<ev_embed> - when one backend isn't enough...
1903		2963
1904	This is a rather advanced watcher type that lets you embed one event loop	2964	This is a rather advanced watcher type that lets you embed one event loop
…		…
1910	prioritise I/O.	2970	prioritise I/O.
1911		2971
1912	As an example for a bug workaround, the kqueue backend might only support	2972	As an example for a bug workaround, the kqueue backend might only support
1913	sockets on some platform, so it is unusable as generic backend, but you	2973	sockets on some platform, so it is unusable as generic backend, but you
1914	still want to make use of it because you have many sockets and it scales	2974	still want to make use of it because you have many sockets and it scales
1915	so nicely. In this case, you would create a kqueue-based loop and embed it	2975	so nicely. In this case, you would create a kqueue-based loop and embed
1916	into your default loop (which might use e.g. poll). Overall operation will	2976	it into your default loop (which might use e.g. poll). Overall operation
1917	be a bit slower because first libev has to poll and then call kevent, but	2977	will be a bit slower because first libev has to call C<poll> and then
1918	at least you can use both at what they are best.	2978	C<kevent>, but at least you can use both mechanisms for what they are
		2979	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1919		2980
1920	As for prioritising I/O: rarely you have the case where some fds have	2981	As for prioritising I/O: under rare circumstances you have the case where
1921	to be watched and handled very quickly (with low latency), and even	2982	some fds have to be watched and handled very quickly (with low latency),
1922	priorities and idle watchers might have too much overhead. In this case	2983	and even priorities and idle watchers might have too much overhead. In
1923	you would put all the high priority stuff in one loop and all the rest in	2984	this case you would put all the high priority stuff in one loop and all
1924	a second one, and embed the second one in the first.	2985	the rest in a second one, and embed the second one in the first.
1925		2986
1926	As long as the watcher is active, the callback will be invoked every time	2987	As long as the watcher is active, the callback will be invoked every
1927	there might be events pending in the embedded loop. The callback must then	2988	time there might be events pending in the embedded loop. The callback
1928	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2989	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1929	their callbacks (you could also start an idle watcher to give the embedded	2990	sweep and invoke their callbacks (the callback doesn't need to invoke the
1930	loop strictly lower priority for example). You can also set the callback	2991	C<ev_embed_sweep> function directly, it could also start an idle watcher
1931	to C<0>, in which case the embed watcher will automatically execute the	2992	to give the embedded loop strictly lower priority for example).
1932	embedded loop sweep.
1933		2993
1934	As long as the watcher is started it will automatically handle events. The	2994	You can also set the callback to C<0>, in which case the embed watcher
1935	callback will be invoked whenever some events have been handled. You can	2995	will automatically execute the embedded loop sweep whenever necessary.
1936	set the callback to C<0> to avoid having to specify one if you are not
1937	interested in that.
1938		2996
1939	Also, there have not currently been made special provisions for forking:	2997	Fork detection will be handled transparently while the C<ev_embed> watcher
1940	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2998	is active, i.e., the embedded loop will automatically be forked when the
1941	but you will also have to stop and restart any C<ev_embed> watchers	2999	embedding loop forks. In other cases, the user is responsible for calling
1942	yourself.	3000	C<ev_loop_fork> on the embedded loop.
1943		3001
1944	Unfortunately, not all backends are embeddable, only the ones returned by	3002	Unfortunately, not all backends are embeddable: only the ones returned by
1945	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3003	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1946	portable one.	3004	portable one.
1947		3005
1948	So when you want to use this feature you will always have to be prepared	3006	So when you want to use this feature you will always have to be prepared
1949	that you cannot get an embeddable loop. The recommended way to get around	3007	that you cannot get an embeddable loop. The recommended way to get around
1950	this is to have a separate variables for your embeddable loop, try to	3008	this is to have a separate variables for your embeddable loop, try to
1951	create it, and if that fails, use the normal loop for everything.	3009	create it, and if that fails, use the normal loop for everything.
1952		3010
		3011	=head3 C<ev_embed> and fork
		3012
		3013	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3014	automatically be applied to the embedded loop as well, so no special
		3015	fork handling is required in that case. When the watcher is not running,
		3016	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3017	as applicable.
		3018
1953	=head3 Watcher-Specific Functions and Data Members	3019	=head3 Watcher-Specific Functions and Data Members
1954		3020
1955	=over 4	3021	=over 4
1956		3022
1957	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3023	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
1960		3026
1961	Configures the watcher to embed the given loop, which must be	3027	Configures the watcher to embed the given loop, which must be
1962	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3028	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1963	invoked automatically, otherwise it is the responsibility of the callback	3029	invoked automatically, otherwise it is the responsibility of the callback
1964	to invoke it (it will continue to be called until the sweep has been done,	3030	to invoke it (it will continue to be called until the sweep has been done,
1965	if you do not want thta, you need to temporarily stop the embed watcher).	3031	if you do not want that, you need to temporarily stop the embed watcher).
1966		3032
1967	=item ev_embed_sweep (loop, ev_embed *)	3033	=item ev_embed_sweep (loop, ev_embed *)
1968		3034
1969	Make a single, non-blocking sweep over the embedded loop. This works	3035	Make a single, non-blocking sweep over the embedded loop. This works
1970	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3036	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1971	apropriate way for embedded loops.	3037	appropriate way for embedded loops.
1972		3038
1973	=item struct ev_loop *other [read-only]	3039	=item struct ev_loop *other [read-only]
1974		3040
1975	The embedded event loop.	3041	The embedded event loop.
1976		3042
…		…
1978		3044
1979	=head3 Examples	3045	=head3 Examples
1980		3046
1981	Example: Try to get an embeddable event loop and embed it into the default	3047	Example: Try to get an embeddable event loop and embed it into the default
1982	event loop. If that is not possible, use the default loop. The default	3048	event loop. If that is not possible, use the default loop. The default
1983	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	3049	loop is stored in C<loop_hi>, while the embeddable loop is stored in
1984	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	3050	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
1985	used).	3051	used).
1986		3052
1987	struct ev_loop *loop_hi = ev_default_init (0);	3053	struct ev_loop *loop_hi = ev_default_init (0);
1988	struct ev_loop *loop_lo = 0;	3054	struct ev_loop *loop_lo = 0;
1989	struct ev_embed embed;	3055	ev_embed embed;
1990		3056
1991	// see if there is a chance of getting one that works	3057	// see if there is a chance of getting one that works
1992	// (remember that a flags value of 0 means autodetection)	3058	// (remember that a flags value of 0 means autodetection)
1993	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3059	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1994	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3060	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1995	: 0;	3061	: 0;
1996		3062
1997	// if we got one, then embed it, otherwise default to loop_hi	3063	// if we got one, then embed it, otherwise default to loop_hi
1998	if (loop_lo)	3064	if (loop_lo)
1999	{	3065	{
2000	ev_embed_init (&embed, 0, loop_lo);	3066	ev_embed_init (&embed, 0, loop_lo);
2001	ev_embed_start (loop_hi, &embed);	3067	ev_embed_start (loop_hi, &embed);
2002	}	3068	}
2003	else	3069	else
2004	loop_lo = loop_hi;	3070	loop_lo = loop_hi;
2005		3071
2006	Example: Check if kqueue is available but not recommended and create	3072	Example: Check if kqueue is available but not recommended and create
2007	a kqueue backend for use with sockets (which usually work with any	3073	a kqueue backend for use with sockets (which usually work with any
2008	kqueue implementation). Store the kqueue/socket-only event loop in	3074	kqueue implementation). Store the kqueue/socket-only event loop in
2009	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3075	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2010		3076
2011	struct ev_loop *loop = ev_default_init (0);	3077	struct ev_loop *loop = ev_default_init (0);
2012	struct ev_loop *loop_socket = 0;	3078	struct ev_loop *loop_socket = 0;
2013	struct ev_embed embed;	3079	ev_embed embed;
2014		3080
2015	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3081	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2016	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3082	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2017	{	3083	{
2018	ev_embed_init (&embed, 0, loop_socket);	3084	ev_embed_init (&embed, 0, loop_socket);
2019	ev_embed_start (loop, &embed);	3085	ev_embed_start (loop, &embed);
2020	}	3086	}
2021		3087
2022	if (!loop_socket)	3088	if (!loop_socket)
2023	loop_socket = loop;	3089	loop_socket = loop;
2024		3090
2025	// now use loop_socket for all sockets, and loop for everything else	3091	// now use loop_socket for all sockets, and loop for everything else
2026		3092
2027		3093
2028	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3094	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2029		3095
2030	Fork watchers are called when a C<fork ()> was detected (usually because	3096	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
2033	event loop blocks next and before C<ev_check> watchers are being called,	3099	event loop blocks next and before C<ev_check> watchers are being called,
2034	and only in the child after the fork. If whoever good citizen calling	3100	and only in the child after the fork. If whoever good citizen calling
2035	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3101	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2036	handlers will be invoked, too, of course.	3102	handlers will be invoked, too, of course.
2037		3103
		3104	=head3 The special problem of life after fork - how is it possible?
		3105
		3106	Most uses of C<fork()> consist of forking, then some simple calls to set
		3107	up/change the process environment, followed by a call to C<exec()>. This
		3108	sequence should be handled by libev without any problems.
		3109
		3110	This changes when the application actually wants to do event handling
		3111	in the child, or both parent in child, in effect "continuing" after the
		3112	fork.
		3113
		3114	The default mode of operation (for libev, with application help to detect
		3115	forks) is to duplicate all the state in the child, as would be expected
		3116	when I<either> the parent I<or> the child process continues.
		3117
		3118	When both processes want to continue using libev, then this is usually the
		3119	wrong result. In that case, usually one process (typically the parent) is
		3120	supposed to continue with all watchers in place as before, while the other
		3121	process typically wants to start fresh, i.e. without any active watchers.
		3122
		3123	The cleanest and most efficient way to achieve that with libev is to
		3124	simply create a new event loop, which of course will be "empty", and
		3125	use that for new watchers. This has the advantage of not touching more
		3126	memory than necessary, and thus avoiding the copy-on-write, and the
		3127	disadvantage of having to use multiple event loops (which do not support
		3128	signal watchers).
		3129
		3130	When this is not possible, or you want to use the default loop for
		3131	other reasons, then in the process that wants to start "fresh", call
		3132	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3133	Destroying the default loop will "orphan" (not stop) all registered
		3134	watchers, so you have to be careful not to execute code that modifies
		3135	those watchers. Note also that in that case, you have to re-register any
		3136	signal watchers.
		3137
2038	=head3 Watcher-Specific Functions and Data Members	3138	=head3 Watcher-Specific Functions and Data Members
2039		3139
2040	=over 4	3140	=over 4
2041		3141
2042	=item ev_fork_init (ev_signal *, callback)	3142	=item ev_fork_init (ev_fork *, callback)
2043		3143
2044	Initialises and configures the fork watcher - it has no parameters of any	3144	Initialises and configures the fork watcher - it has no parameters of any
2045	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3145	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2046	believe me.	3146	really.
2047		3147
2048	=back	3148	=back
2049		3149
2050		3150
		3151	=head2 C<ev_cleanup> - even the best things end
		3152
		3153	Cleanup watchers are called just before the event loop is being destroyed
		3154	by a call to C<ev_loop_destroy>.
		3155
		3156	While there is no guarantee that the event loop gets destroyed, cleanup
		3157	watchers provide a convenient method to install cleanup hooks for your
		3158	program, worker threads and so on - you just to make sure to destroy the
		3159	loop when you want them to be invoked.
		3160
		3161	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3162	all other watchers, they do not keep a reference to the event loop (which
		3163	makes a lot of sense if you think about it). Like all other watchers, you
		3164	can call libev functions in the callback, except C<ev_cleanup_start>.
		3165
		3166	=head3 Watcher-Specific Functions and Data Members
		3167
		3168	=over 4
		3169
		3170	=item ev_cleanup_init (ev_cleanup *, callback)
		3171
		3172	Initialises and configures the cleanup watcher - it has no parameters of
		3173	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3174	pointless, I assure you.
		3175
		3176	=back
		3177
		3178	Example: Register an atexit handler to destroy the default loop, so any
		3179	cleanup functions are called.
		3180
		3181	static void
		3182	program_exits (void)
		3183	{
		3184	ev_loop_destroy (EV_DEFAULT_UC);
		3185	}
		3186
		3187	...
		3188	atexit (program_exits);
		3189
		3190
		3191	=head2 C<ev_async> - how to wake up an event loop
		3192
		3193	In general, you cannot use an C<ev_run> from multiple threads or other
		3194	asynchronous sources such as signal handlers (as opposed to multiple event
		3195	loops - those are of course safe to use in different threads).
		3196
		3197	Sometimes, however, you need to wake up an event loop you do not control,
		3198	for example because it belongs to another thread. This is what C<ev_async>
		3199	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3200	it by calling C<ev_async_send>, which is thread- and signal safe.
		3201
		3202	This functionality is very similar to C<ev_signal> watchers, as signals,
		3203	too, are asynchronous in nature, and signals, too, will be compressed
		3204	(i.e. the number of callback invocations may be less than the number of
		3205	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3206	of "global async watchers" by using a watcher on an otherwise unused
		3207	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3208	even without knowing which loop owns the signal.
		3209
		3210	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3211	just the default loop.
		3212
		3213	=head3 Queueing
		3214
		3215	C<ev_async> does not support queueing of data in any way. The reason
		3216	is that the author does not know of a simple (or any) algorithm for a
		3217	multiple-writer-single-reader queue that works in all cases and doesn't
		3218	need elaborate support such as pthreads or unportable memory access
		3219	semantics.
		3220
		3221	That means that if you want to queue data, you have to provide your own
		3222	queue. But at least I can tell you how to implement locking around your
		3223	queue:
		3224
		3225	=over 4
		3226
		3227	=item queueing from a signal handler context
		3228
		3229	To implement race-free queueing, you simply add to the queue in the signal
		3230	handler but you block the signal handler in the watcher callback. Here is
		3231	an example that does that for some fictitious SIGUSR1 handler:
		3232
		3233	static ev_async mysig;
		3234
		3235	static void
		3236	sigusr1_handler (void)
		3237	{
		3238	sometype data;
		3239
		3240	// no locking etc.
		3241	queue_put (data);
		3242	ev_async_send (EV_DEFAULT_ &mysig);
		3243	}
		3244
		3245	static void
		3246	mysig_cb (EV_P_ ev_async *w, int revents)
		3247	{
		3248	sometype data;
		3249	sigset_t block, prev;
		3250
		3251	sigemptyset (&block);
		3252	sigaddset (&block, SIGUSR1);
		3253	sigprocmask (SIG_BLOCK, &block, &prev);
		3254
		3255	while (queue_get (&data))
		3256	process (data);
		3257
		3258	if (sigismember (&prev, SIGUSR1)
		3259	sigprocmask (SIG_UNBLOCK, &block, 0);
		3260	}
		3261
		3262	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3263	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3264	either...).
		3265
		3266	=item queueing from a thread context
		3267
		3268	The strategy for threads is different, as you cannot (easily) block
		3269	threads but you can easily preempt them, so to queue safely you need to
		3270	employ a traditional mutex lock, such as in this pthread example:
		3271
		3272	static ev_async mysig;
		3273	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3274
		3275	static void
		3276	otherthread (void)
		3277	{
		3278	// only need to lock the actual queueing operation
		3279	pthread_mutex_lock (&mymutex);
		3280	queue_put (data);
		3281	pthread_mutex_unlock (&mymutex);
		3282
		3283	ev_async_send (EV_DEFAULT_ &mysig);
		3284	}
		3285
		3286	static void
		3287	mysig_cb (EV_P_ ev_async *w, int revents)
		3288	{
		3289	pthread_mutex_lock (&mymutex);
		3290
		3291	while (queue_get (&data))
		3292	process (data);
		3293
		3294	pthread_mutex_unlock (&mymutex);
		3295	}
		3296
		3297	=back
		3298
		3299
		3300	=head3 Watcher-Specific Functions and Data Members
		3301
		3302	=over 4
		3303
		3304	=item ev_async_init (ev_async *, callback)
		3305
		3306	Initialises and configures the async watcher - it has no parameters of any
		3307	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3308	trust me.
		3309
		3310	=item ev_async_send (loop, ev_async *)
		3311
		3312	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3313	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3314	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3315	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3316	section below on what exactly this means).
		3317
		3318	Note that, as with other watchers in libev, multiple events might get
		3319	compressed into a single callback invocation (another way to look at this
		3320	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3321	reset when the event loop detects that).
		3322
		3323	This call incurs the overhead of a system call only once per event loop
		3324	iteration, so while the overhead might be noticeable, it doesn't apply to
		3325	repeated calls to C<ev_async_send> for the same event loop.
		3326
		3327	=item bool = ev_async_pending (ev_async *)
		3328
		3329	Returns a non-zero value when C<ev_async_send> has been called on the
		3330	watcher but the event has not yet been processed (or even noted) by the
		3331	event loop.
		3332
		3333	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3334	the loop iterates next and checks for the watcher to have become active,
		3335	it will reset the flag again. C<ev_async_pending> can be used to very
		3336	quickly check whether invoking the loop might be a good idea.
		3337
		3338	Not that this does I<not> check whether the watcher itself is pending,
		3339	only whether it has been requested to make this watcher pending: there
		3340	is a time window between the event loop checking and resetting the async
		3341	notification, and the callback being invoked.
		3342
		3343	=back
		3344
		3345
2051	=head1 OTHER FUNCTIONS	3346	=head1 OTHER FUNCTIONS
2052		3347
2053	There are some other functions of possible interest. Described. Here. Now.	3348	There are some other functions of possible interest. Described. Here. Now.
2054		3349
2055	=over 4	3350	=over 4
2056		3351
2057	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3352	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2058		3353
2059	This function combines a simple timer and an I/O watcher, calls your	3354	This function combines a simple timer and an I/O watcher, calls your
2060	callback on whichever event happens first and automatically stop both	3355	callback on whichever event happens first and automatically stops both
2061	watchers. This is useful if you want to wait for a single event on an fd	3356	watchers. This is useful if you want to wait for a single event on an fd
2062	or timeout without having to allocate/configure/start/stop/free one or	3357	or timeout without having to allocate/configure/start/stop/free one or
2063	more watchers yourself.	3358	more watchers yourself.
2064		3359
2065	If C<fd> is less than 0, then no I/O watcher will be started and events	3360	If C<fd> is less than 0, then no I/O watcher will be started and the
2066	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3361	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2067	C<events> set will be craeted and started.	3362	the given C<fd> and C<events> set will be created and started.
2068		3363
2069	If C<timeout> is less than 0, then no timeout watcher will be	3364	If C<timeout> is less than 0, then no timeout watcher will be
2070	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3365	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2071	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3366	repeat = 0) will be started. C<0> is a valid timeout.
2072	dubious value.
2073		3367
2074	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3368	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2075	passed an C<revents> set like normal event callbacks (a combination of	3369	passed an C<revents> set like normal event callbacks (a combination of
2076	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3370	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2077	value passed to C<ev_once>:	3371	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3372	a timeout and an io event at the same time - you probably should give io
		3373	events precedence.
2078		3374
		3375	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3376
2079	static void stdin_ready (int revents, void *arg)	3377	static void stdin_ready (int revents, void *arg)
2080	{	3378	{
2081	if (revents & EV_TIMEOUT)
2082	/* doh, nothing entered */;
2083	else if (revents & EV_READ)	3379	if (revents & EV_READ)
2084	/* stdin might have data for us, joy! */;	3380	/* stdin might have data for us, joy! */;
		3381	else if (revents & EV_TIMER)
		3382	/* doh, nothing entered */;
2085	}	3383	}
2086		3384
2087	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3385	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2088		3386
2089	=item ev_feed_event (ev_loop *, watcher *, int revents)
2090
2091	Feeds the given event set into the event loop, as if the specified event
2092	had happened for the specified watcher (which must be a pointer to an
2093	initialised but not necessarily started event watcher).
2094
2095	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3387	=item ev_feed_fd_event (loop, int fd, int revents)
2096		3388
2097	Feed an event on the given fd, as if a file descriptor backend detected	3389	Feed an event on the given fd, as if a file descriptor backend detected
2098	the given events it.	3390	the given events it.
2099		3391
2100	=item ev_feed_signal_event (ev_loop *loop, int signum)	3392	=item ev_feed_signal_event (loop, int signum)
2101		3393
2102	Feed an event as if the given signal occured (C<loop> must be the default	3394	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
2103	loop!).	3395	which is async-safe.
2104		3396
2105	=back	3397	=back
		3398
		3399
		3400	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3401
		3402	This section explains some common idioms that are not immediately
		3403	obvious. Note that examples are sprinkled over the whole manual, and this
		3404	section only contains stuff that wouldn't fit anywhere else.
		3405
		3406	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3407
		3408	Each watcher has, by default, a C<void *data> member that you can read
		3409	or modify at any time: libev will completely ignore it. This can be used
		3410	to associate arbitrary data with your watcher. If you need more data and
		3411	don't want to allocate memory separately and store a pointer to it in that
		3412	data member, you can also "subclass" the watcher type and provide your own
		3413	data:
		3414
		3415	struct my_io
		3416	{
		3417	ev_io io;
		3418	int otherfd;
		3419	void *somedata;
		3420	struct whatever *mostinteresting;
		3421	};
		3422
		3423	...
		3424	struct my_io w;
		3425	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3426
		3427	And since your callback will be called with a pointer to the watcher, you
		3428	can cast it back to your own type:
		3429
		3430	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3431	{
		3432	struct my_io *w = (struct my_io *)w_;
		3433	...
		3434	}
		3435
		3436	More interesting and less C-conformant ways of casting your callback
		3437	function type instead have been omitted.
		3438
		3439	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3440
		3441	Another common scenario is to use some data structure with multiple
		3442	embedded watchers, in effect creating your own watcher that combines
		3443	multiple libev event sources into one "super-watcher":
		3444
		3445	struct my_biggy
		3446	{
		3447	int some_data;
		3448	ev_timer t1;
		3449	ev_timer t2;
		3450	}
		3451
		3452	In this case getting the pointer to C<my_biggy> is a bit more
		3453	complicated: Either you store the address of your C<my_biggy> struct in
		3454	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3455	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3456	real programmers):
		3457
		3458	#include <stddef.h>
		3459
		3460	static void
		3461	t1_cb (EV_P_ ev_timer *w, int revents)
		3462	{
		3463	struct my_biggy big = (struct my_biggy *)
		3464	(((char *)w) - offsetof (struct my_biggy, t1));
		3465	}
		3466
		3467	static void
		3468	t2_cb (EV_P_ ev_timer *w, int revents)
		3469	{
		3470	struct my_biggy big = (struct my_biggy *)
		3471	(((char *)w) - offsetof (struct my_biggy, t2));
		3472	}
		3473
		3474	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3475
		3476	Often (especially in GUI toolkits) there are places where you have
		3477	I<modal> interaction, which is most easily implemented by recursively
		3478	invoking C<ev_run>.
		3479
		3480	This brings the problem of exiting - a callback might want to finish the
		3481	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3482	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3483	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3484	other combination: In these cases, C<ev_break> will not work alone.
		3485
		3486	The solution is to maintain "break this loop" variable for each C<ev_run>
		3487	invocation, and use a loop around C<ev_run> until the condition is
		3488	triggered, using C<EVRUN_ONCE>:
		3489
		3490	// main loop
		3491	int exit_main_loop = 0;
		3492
		3493	while (!exit_main_loop)
		3494	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3495
		3496	// in a model watcher
		3497	int exit_nested_loop = 0;
		3498
		3499	while (!exit_nested_loop)
		3500	ev_run (EV_A_ EVRUN_ONCE);
		3501
		3502	To exit from any of these loops, just set the corresponding exit variable:
		3503
		3504	// exit modal loop
		3505	exit_nested_loop = 1;
		3506
		3507	// exit main program, after modal loop is finished
		3508	exit_main_loop = 1;
		3509
		3510	// exit both
		3511	exit_main_loop = exit_nested_loop = 1;
		3512
		3513	=head2 THREAD LOCKING EXAMPLE
		3514
		3515	Here is a fictitious example of how to run an event loop in a different
		3516	thread from where callbacks are being invoked and watchers are
		3517	created/added/removed.
		3518
		3519	For a real-world example, see the C<EV::Loop::Async> perl module,
		3520	which uses exactly this technique (which is suited for many high-level
		3521	languages).
		3522
		3523	The example uses a pthread mutex to protect the loop data, a condition
		3524	variable to wait for callback invocations, an async watcher to notify the
		3525	event loop thread and an unspecified mechanism to wake up the main thread.
		3526
		3527	First, you need to associate some data with the event loop:
		3528
		3529	typedef struct {
		3530	mutex_t lock; /* global loop lock */
		3531	ev_async async_w;
		3532	thread_t tid;
		3533	cond_t invoke_cv;
		3534	} userdata;
		3535
		3536	void prepare_loop (EV_P)
		3537	{
		3538	// for simplicity, we use a static userdata struct.
		3539	static userdata u;
		3540
		3541	ev_async_init (&u->async_w, async_cb);
		3542	ev_async_start (EV_A_ &u->async_w);
		3543
		3544	pthread_mutex_init (&u->lock, 0);
		3545	pthread_cond_init (&u->invoke_cv, 0);
		3546
		3547	// now associate this with the loop
		3548	ev_set_userdata (EV_A_ u);
		3549	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3550	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3551
		3552	// then create the thread running ev_loop
		3553	pthread_create (&u->tid, 0, l_run, EV_A);
		3554	}
		3555
		3556	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3557	solely to wake up the event loop so it takes notice of any new watchers
		3558	that might have been added:
		3559
		3560	static void
		3561	async_cb (EV_P_ ev_async *w, int revents)
		3562	{
		3563	// just used for the side effects
		3564	}
		3565
		3566	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3567	protecting the loop data, respectively.
		3568
		3569	static void
		3570	l_release (EV_P)
		3571	{
		3572	userdata *u = ev_userdata (EV_A);
		3573	pthread_mutex_unlock (&u->lock);
		3574	}
		3575
		3576	static void
		3577	l_acquire (EV_P)
		3578	{
		3579	userdata *u = ev_userdata (EV_A);
		3580	pthread_mutex_lock (&u->lock);
		3581	}
		3582
		3583	The event loop thread first acquires the mutex, and then jumps straight
		3584	into C<ev_run>:
		3585
		3586	void *
		3587	l_run (void *thr_arg)
		3588	{
		3589	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3590
		3591	l_acquire (EV_A);
		3592	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3593	ev_run (EV_A_ 0);
		3594	l_release (EV_A);
		3595
		3596	return 0;
		3597	}
		3598
		3599	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3600	signal the main thread via some unspecified mechanism (signals? pipe
		3601	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3602	have been called (in a while loop because a) spurious wakeups are possible
		3603	and b) skipping inter-thread-communication when there are no pending
		3604	watchers is very beneficial):
		3605
		3606	static void
		3607	l_invoke (EV_P)
		3608	{
		3609	userdata *u = ev_userdata (EV_A);
		3610
		3611	while (ev_pending_count (EV_A))
		3612	{
		3613	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3614	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3615	}
		3616	}
		3617
		3618	Now, whenever the main thread gets told to invoke pending watchers, it
		3619	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3620	thread to continue:
		3621
		3622	static void
		3623	real_invoke_pending (EV_P)
		3624	{
		3625	userdata *u = ev_userdata (EV_A);
		3626
		3627	pthread_mutex_lock (&u->lock);
		3628	ev_invoke_pending (EV_A);
		3629	pthread_cond_signal (&u->invoke_cv);
		3630	pthread_mutex_unlock (&u->lock);
		3631	}
		3632
		3633	Whenever you want to start/stop a watcher or do other modifications to an
		3634	event loop, you will now have to lock:
		3635
		3636	ev_timer timeout_watcher;
		3637	userdata *u = ev_userdata (EV_A);
		3638
		3639	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3640
		3641	pthread_mutex_lock (&u->lock);
		3642	ev_timer_start (EV_A_ &timeout_watcher);
		3643	ev_async_send (EV_A_ &u->async_w);
		3644	pthread_mutex_unlock (&u->lock);
		3645
		3646	Note that sending the C<ev_async> watcher is required because otherwise
		3647	an event loop currently blocking in the kernel will have no knowledge
		3648	about the newly added timer. By waking up the loop it will pick up any new
		3649	watchers in the next event loop iteration.
		3650
		3651	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3652
		3653	While the overhead of a callback that e.g. schedules a thread is small, it
		3654	is still an overhead. If you embed libev, and your main usage is with some
		3655	kind of threads or coroutines, you might want to customise libev so that
		3656	doesn't need callbacks anymore.
		3657
		3658	Imagine you have coroutines that you can switch to using a function
		3659	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3660	and that due to some magic, the currently active coroutine is stored in a
		3661	global called C<current_coro>. Then you can build your own "wait for libev
		3662	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3663	the differing C<;> conventions):
		3664
		3665	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3666	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3667
		3668	That means instead of having a C callback function, you store the
		3669	coroutine to switch to in each watcher, and instead of having libev call
		3670	your callback, you instead have it switch to that coroutine.
		3671
		3672	A coroutine might now wait for an event with a function called
		3673	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3674	matter when, or whether the watcher is active or not when this function is
		3675	called):
		3676
		3677	void
		3678	wait_for_event (ev_watcher *w)
		3679	{
		3680	ev_cb_set (w) = current_coro;
		3681	switch_to (libev_coro);
		3682	}
		3683
		3684	That basically suspends the coroutine inside C<wait_for_event> and
		3685	continues the libev coroutine, which, when appropriate, switches back to
		3686	this or any other coroutine. I am sure if you sue this your own :)
		3687
		3688	You can do similar tricks if you have, say, threads with an event queue -
		3689	instead of storing a coroutine, you store the queue object and instead of
		3690	switching to a coroutine, you push the watcher onto the queue and notify
		3691	any waiters.
		3692
		3693	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3694	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3695
		3696	// my_ev.h
		3697	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3698	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3699	#include "../libev/ev.h"
		3700
		3701	// my_ev.c
		3702	#define EV_H "my_ev.h"
		3703	#include "../libev/ev.c"
		3704
		3705	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3706	F<my_ev.c> into your project. When properly specifying include paths, you
		3707	can even use F<ev.h> as header file name directly.
2106		3708
2107		3709
2108	=head1 LIBEVENT EMULATION	3710	=head1 LIBEVENT EMULATION
2109		3711
2110	Libev offers a compatibility emulation layer for libevent. It cannot	3712	Libev offers a compatibility emulation layer for libevent. It cannot
2111	emulate the internals of libevent, so here are some usage hints:	3713	emulate the internals of libevent, so here are some usage hints:
2112		3714
2113	=over 4	3715	=over 4
		3716
		3717	=item * Only the libevent-1.4.1-beta API is being emulated.
		3718
		3719	This was the newest libevent version available when libev was implemented,
		3720	and is still mostly unchanged in 2010.
2114		3721
2115	=item * Use it by including <event.h>, as usual.	3722	=item * Use it by including <event.h>, as usual.
2116		3723
2117	=item * The following members are fully supported: ev_base, ev_callback,	3724	=item * The following members are fully supported: ev_base, ev_callback,
2118	ev_arg, ev_fd, ev_res, ev_events.	3725	ev_arg, ev_fd, ev_res, ev_events.
…		…
2123		3730
2124	=item * Priorities are not currently supported. Initialising priorities	3731	=item * Priorities are not currently supported. Initialising priorities
2125	will fail and all watchers will have the same priority, even though there	3732	will fail and all watchers will have the same priority, even though there
2126	is an ev_pri field.	3733	is an ev_pri field.
2127		3734
		3735	=item * In libevent, the last base created gets the signals, in libev, the
		3736	base that registered the signal gets the signals.
		3737
2128	=item * Other members are not supported.	3738	=item * Other members are not supported.
2129		3739
2130	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3740	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2131	to use the libev header file and library.	3741	to use the libev header file and library.
2132		3742
2133	=back	3743	=back
2134		3744
2135	=head1 C++ SUPPORT	3745	=head1 C++ SUPPORT
2136		3746
2137	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3747	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2138	you to use some convinience methods to start/stop watchers and also change	3748	you to use some convenience methods to start/stop watchers and also change
2139	the callback model to a model using method callbacks on objects.	3749	the callback model to a model using method callbacks on objects.
2140		3750
2141	To use it,	3751	To use it,
2142		3752
2143	#include <ev++.h>	3753	#include <ev++.h>
2144		3754
2145	This automatically includes F<ev.h> and puts all of its definitions (many	3755	This automatically includes F<ev.h> and puts all of its definitions (many
2146	of them macros) into the global namespace. All C++ specific things are	3756	of them macros) into the global namespace. All C++ specific things are
2147	put into the C<ev> namespace. It should support all the same embedding	3757	put into the C<ev> namespace. It should support all the same embedding
2148	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3758	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2150	Care has been taken to keep the overhead low. The only data member the C++	3760	Care has been taken to keep the overhead low. The only data member the C++
2151	classes add (compared to plain C-style watchers) is the event loop pointer	3761	classes add (compared to plain C-style watchers) is the event loop pointer
2152	that the watcher is associated with (or no additional members at all if	3762	that the watcher is associated with (or no additional members at all if
2153	you disable C<EV_MULTIPLICITY> when embedding libev).	3763	you disable C<EV_MULTIPLICITY> when embedding libev).
2154		3764
2155	Currently, functions, and static and non-static member functions can be	3765	Currently, functions, static and non-static member functions and classes
2156	used as callbacks. Other types should be easy to add as long as they only	3766	with C<operator ()> can be used as callbacks. Other types should be easy
2157	need one additional pointer for context. If you need support for other	3767	to add as long as they only need one additional pointer for context. If
2158	types of functors please contact the author (preferably after implementing	3768	you need support for other types of functors please contact the author
2159	it).	3769	(preferably after implementing it).
2160		3770
2161	Here is a list of things available in the C<ev> namespace:	3771	Here is a list of things available in the C<ev> namespace:
2162		3772
2163	=over 4	3773	=over 4
2164		3774
…		…
2182		3792
2183	=over 4	3793	=over 4
2184		3794
2185	=item ev::TYPE::TYPE ()	3795	=item ev::TYPE::TYPE ()
2186		3796
2187	=item ev::TYPE::TYPE (struct ev_loop *)	3797	=item ev::TYPE::TYPE (loop)
2188		3798
2189	=item ev::TYPE::~TYPE	3799	=item ev::TYPE::~TYPE
2190		3800
2191	The constructor (optionally) takes an event loop to associate the watcher	3801	The constructor (optionally) takes an event loop to associate the watcher
2192	with. If it is omitted, it will use C<EV_DEFAULT>.	3802	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2215	your compiler is good :), then the method will be fully inlined into the	3825	your compiler is good :), then the method will be fully inlined into the
2216	thunking function, making it as fast as a direct C callback.	3826	thunking function, making it as fast as a direct C callback.
2217		3827
2218	Example: simple class declaration and watcher initialisation	3828	Example: simple class declaration and watcher initialisation
2219		3829
2220	struct myclass	3830	struct myclass
2221	{	3831	{
2222	void io_cb (ev::io &w, int revents) { }	3832	void io_cb (ev::io &w, int revents) { }
2223	}	3833	}
2224		3834
2225	myclass obj;	3835	myclass obj;
2226	ev::io iow;	3836	ev::io iow;
2227	iow.set <myclass, &myclass::io_cb> (&obj);	3837	iow.set <myclass, &myclass::io_cb> (&obj);
		3838
		3839	=item w->set (object *)
		3840
		3841	This is a variation of a method callback - leaving out the method to call
		3842	will default the method to C<operator ()>, which makes it possible to use
		3843	functor objects without having to manually specify the C<operator ()> all
		3844	the time. Incidentally, you can then also leave out the template argument
		3845	list.
		3846
		3847	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3848	int revents)>.
		3849
		3850	See the method-C<set> above for more details.
		3851
		3852	Example: use a functor object as callback.
		3853
		3854	struct myfunctor
		3855	{
		3856	void operator() (ev::io &w, int revents)
		3857	{
		3858	...
		3859	}
		3860	}
		3861
		3862	myfunctor f;
		3863
		3864	ev::io w;
		3865	w.set (&f);
2228		3866
2229	=item w->set<function> (void *data = 0)	3867	=item w->set<function> (void *data = 0)
2230		3868
2231	Also sets a callback, but uses a static method or plain function as	3869	Also sets a callback, but uses a static method or plain function as
2232	callback. The optional C<data> argument will be stored in the watcher's	3870	callback. The optional C<data> argument will be stored in the watcher's
…		…
2234		3872
2235	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3873	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2236		3874
2237	See the method-C<set> above for more details.	3875	See the method-C<set> above for more details.
2238		3876
2239	Example:	3877	Example: Use a plain function as callback.
2240		3878
2241	static void io_cb (ev::io &w, int revents) { }	3879	static void io_cb (ev::io &w, int revents) { }
2242	iow.set <io_cb> ();	3880	iow.set <io_cb> ();
2243		3881
2244	=item w->set (struct ev_loop *)	3882	=item w->set (loop)
2245		3883
2246	Associates a different C<struct ev_loop> with this watcher. You can only	3884	Associates a different C<struct ev_loop> with this watcher. You can only
2247	do this when the watcher is inactive (and not pending either).	3885	do this when the watcher is inactive (and not pending either).
2248		3886
2249	=item w->set ([args])	3887	=item w->set ([arguments])
2250		3888
2251	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3889	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2252	called at least once. Unlike the C counterpart, an active watcher gets	3890	method or a suitable start method must be called at least once. Unlike the
2253	automatically stopped and restarted when reconfiguring it with this	3891	C counterpart, an active watcher gets automatically stopped and restarted
2254	method.	3892	when reconfiguring it with this method.
2255		3893
2256	=item w->start ()	3894	=item w->start ()
2257		3895
2258	Starts the watcher. Note that there is no C<loop> argument, as the	3896	Starts the watcher. Note that there is no C<loop> argument, as the
2259	constructor already stores the event loop.	3897	constructor already stores the event loop.
2260		3898
		3899	=item w->start ([arguments])
		3900
		3901	Instead of calling C<set> and C<start> methods separately, it is often
		3902	convenient to wrap them in one call. Uses the same type of arguments as
		3903	the configure C<set> method of the watcher.
		3904
2261	=item w->stop ()	3905	=item w->stop ()
2262		3906
2263	Stops the watcher if it is active. Again, no C<loop> argument.	3907	Stops the watcher if it is active. Again, no C<loop> argument.
2264		3908
2265	=item w->again () (C<ev::timer>, C<ev::periodic> only)	3909	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2277		3921
2278	=back	3922	=back
2279		3923
2280	=back	3924	=back
2281		3925
2282	Example: Define a class with an IO and idle watcher, start one of them in	3926	Example: Define a class with two I/O and idle watchers, start the I/O
2283	the constructor.	3927	watchers in the constructor.
2284		3928
2285	class myclass	3929	class myclass
2286	{	3930	{
2287	ev::io io; void io_cb (ev::io &w, int revents);	3931	ev::io io ; void io_cb (ev::io &w, int revents);
		3932	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
2288	ev:idle idle void idle_cb (ev::idle &w, int revents);	3933	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2289		3934
2290	myclass (int fd)	3935	myclass (int fd)
2291	{	3936	{
2292	io .set <myclass, &myclass::io_cb > (this);	3937	io .set <myclass, &myclass::io_cb > (this);
		3938	io2 .set <myclass, &myclass::io2_cb > (this);
2293	idle.set <myclass, &myclass::idle_cb> (this);	3939	idle.set <myclass, &myclass::idle_cb> (this);
2294		3940
2295	io.start (fd, ev::READ);	3941	io.set (fd, ev::WRITE); // configure the watcher
		3942	io.start (); // start it whenever convenient
		3943
		3944	io2.start (fd, ev::READ); // set + start in one call
2296	}	3945	}
2297	};	3946	};
		3947
		3948
		3949	=head1 OTHER LANGUAGE BINDINGS
		3950
		3951	Libev does not offer other language bindings itself, but bindings for a
		3952	number of languages exist in the form of third-party packages. If you know
		3953	any interesting language binding in addition to the ones listed here, drop
		3954	me a note.
		3955
		3956	=over 4
		3957
		3958	=item Perl
		3959
		3960	The EV module implements the full libev API and is actually used to test
		3961	libev. EV is developed together with libev. Apart from the EV core module,
		3962	there are additional modules that implement libev-compatible interfaces
		3963	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3964	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3965	and C<EV::Glib>).
		3966
		3967	It can be found and installed via CPAN, its homepage is at
		3968	L<http://software.schmorp.de/pkg/EV>.
		3969
		3970	=item Python
		3971
		3972	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3973	seems to be quite complete and well-documented.
		3974
		3975	=item Ruby
		3976
		3977	Tony Arcieri has written a ruby extension that offers access to a subset
		3978	of the libev API and adds file handle abstractions, asynchronous DNS and
		3979	more on top of it. It can be found via gem servers. Its homepage is at
		3980	L<http://rev.rubyforge.org/>.
		3981
		3982	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3983	makes rev work even on mingw.
		3984
		3985	=item Haskell
		3986
		3987	A haskell binding to libev is available at
		3988	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3989
		3990	=item D
		3991
		3992	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3993	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3994
		3995	=item Ocaml
		3996
		3997	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3998	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3999
		4000	=item Lua
		4001
		4002	Brian Maher has written a partial interface to libev for lua (at the
		4003	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4004	L<http://github.com/brimworks/lua-ev>.
		4005
		4006	=back
2298		4007
2299		4008
2300	=head1 MACRO MAGIC	4009	=head1 MACRO MAGIC
2301		4010
2302	Libev can be compiled with a variety of options, the most fundamantal	4011	Libev can be compiled with a variety of options, the most fundamental
2303	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	4012	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2304	functions and callbacks have an initial C<struct ev_loop *> argument.	4013	functions and callbacks have an initial C<struct ev_loop *> argument.
2305		4014
2306	To make it easier to write programs that cope with either variant, the	4015	To make it easier to write programs that cope with either variant, the
2307	following macros are defined:	4016	following macros are defined:
…		…
2312		4021
2313	This provides the loop I<argument> for functions, if one is required ("ev	4022	This provides the loop I<argument> for functions, if one is required ("ev
2314	loop argument"). The C<EV_A> form is used when this is the sole argument,	4023	loop argument"). The C<EV_A> form is used when this is the sole argument,
2315	C<EV_A_> is used when other arguments are following. Example:	4024	C<EV_A_> is used when other arguments are following. Example:
2316		4025
2317	ev_unref (EV_A);	4026	ev_unref (EV_A);
2318	ev_timer_add (EV_A_ watcher);	4027	ev_timer_add (EV_A_ watcher);
2319	ev_loop (EV_A_ 0);	4028	ev_run (EV_A_ 0);
2320		4029
2321	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4030	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2322	which is often provided by the following macro.	4031	which is often provided by the following macro.
2323		4032
2324	=item C<EV_P>, C<EV_P_>	4033	=item C<EV_P>, C<EV_P_>
2325		4034
2326	This provides the loop I<parameter> for functions, if one is required ("ev	4035	This provides the loop I<parameter> for functions, if one is required ("ev
2327	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	4036	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2328	C<EV_P_> is used when other parameters are following. Example:	4037	C<EV_P_> is used when other parameters are following. Example:
2329		4038
2330	// this is how ev_unref is being declared	4039	// this is how ev_unref is being declared
2331	static void ev_unref (EV_P);	4040	static void ev_unref (EV_P);
2332		4041
2333	// this is how you can declare your typical callback	4042	// this is how you can declare your typical callback
2334	static void cb (EV_P_ ev_timer *w, int revents)	4043	static void cb (EV_P_ ev_timer *w, int revents)
2335		4044
2336	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	4045	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2337	suitable for use with C<EV_A>.	4046	suitable for use with C<EV_A>.
2338		4047
2339	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4048	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2340		4049
2341	Similar to the other two macros, this gives you the value of the default	4050	Similar to the other two macros, this gives you the value of the default
2342	loop, if multiple loops are supported ("ev loop default").	4051	loop, if multiple loops are supported ("ev loop default").
		4052
		4053	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4054
		4055	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4056	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4057	is undefined when the default loop has not been initialised by a previous
		4058	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4059
		4060	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4061	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2343		4062
2344	=back	4063	=back
2345		4064
2346	Example: Declare and initialise a check watcher, utilising the above	4065	Example: Declare and initialise a check watcher, utilising the above
2347	macros so it will work regardless of whether multiple loops are supported	4066	macros so it will work regardless of whether multiple loops are supported
2348	or not.	4067	or not.
2349		4068
2350	static void	4069	static void
2351	check_cb (EV_P_ ev_timer *w, int revents)	4070	check_cb (EV_P_ ev_timer *w, int revents)
2352	{	4071	{
2353	ev_check_stop (EV_A_ w);	4072	ev_check_stop (EV_A_ w);
2354	}	4073	}
2355		4074
2356	ev_check check;	4075	ev_check check;
2357	ev_check_init (&check, check_cb);	4076	ev_check_init (&check, check_cb);
2358	ev_check_start (EV_DEFAULT_ &check);	4077	ev_check_start (EV_DEFAULT_ &check);
2359	ev_loop (EV_DEFAULT_ 0);	4078	ev_run (EV_DEFAULT_ 0);
2360		4079
2361	=head1 EMBEDDING	4080	=head1 EMBEDDING
2362		4081
2363	Libev can (and often is) directly embedded into host	4082	Libev can (and often is) directly embedded into host
2364	applications. Examples of applications that embed it include the Deliantra	4083	applications. Examples of applications that embed it include the Deliantra
…		…
2371	libev somewhere in your source tree).	4090	libev somewhere in your source tree).
2372		4091
2373	=head2 FILESETS	4092	=head2 FILESETS
2374		4093
2375	Depending on what features you need you need to include one or more sets of files	4094	Depending on what features you need you need to include one or more sets of files
2376	in your app.	4095	in your application.
2377		4096
2378	=head3 CORE EVENT LOOP	4097	=head3 CORE EVENT LOOP
2379		4098
2380	To include only the libev core (all the C<ev_*> functions), with manual	4099	To include only the libev core (all the C<ev_*> functions), with manual
2381	configuration (no autoconf):	4100	configuration (no autoconf):
2382		4101
2383	#define EV_STANDALONE 1	4102	#define EV_STANDALONE 1
2384	#include "ev.c"	4103	#include "ev.c"
2385		4104
2386	This will automatically include F<ev.h>, too, and should be done in a	4105	This will automatically include F<ev.h>, too, and should be done in a
2387	single C source file only to provide the function implementations. To use	4106	single C source file only to provide the function implementations. To use
2388	it, do the same for F<ev.h> in all files wishing to use this API (best	4107	it, do the same for F<ev.h> in all files wishing to use this API (best
2389	done by writing a wrapper around F<ev.h> that you can include instead and	4108	done by writing a wrapper around F<ev.h> that you can include instead and
2390	where you can put other configuration options):	4109	where you can put other configuration options):
2391		4110
2392	#define EV_STANDALONE 1	4111	#define EV_STANDALONE 1
2393	#include "ev.h"	4112	#include "ev.h"
2394		4113
2395	Both header files and implementation files can be compiled with a C++	4114	Both header files and implementation files can be compiled with a C++
2396	compiler (at least, thats a stated goal, and breakage will be treated	4115	compiler (at least, that's a stated goal, and breakage will be treated
2397	as a bug).	4116	as a bug).
2398		4117
2399	You need the following files in your source tree, or in a directory	4118	You need the following files in your source tree, or in a directory
2400	in your include path (e.g. in libev/ when using -Ilibev):	4119	in your include path (e.g. in libev/ when using -Ilibev):
2401		4120
2402	ev.h	4121	ev.h
2403	ev.c	4122	ev.c
2404	ev_vars.h	4123	ev_vars.h
2405	ev_wrap.h	4124	ev_wrap.h
2406		4125
2407	ev_win32.c required on win32 platforms only	4126	ev_win32.c required on win32 platforms only
2408		4127
2409	ev_select.c only when select backend is enabled (which is enabled by default)	4128	ev_select.c only when select backend is enabled (which is enabled by default)
2410	ev_poll.c only when poll backend is enabled (disabled by default)	4129	ev_poll.c only when poll backend is enabled (disabled by default)
2411	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4130	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2412	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4131	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2413	ev_port.c only when the solaris port backend is enabled (disabled by default)	4132	ev_port.c only when the solaris port backend is enabled (disabled by default)
2414		4133
2415	F<ev.c> includes the backend files directly when enabled, so you only need	4134	F<ev.c> includes the backend files directly when enabled, so you only need
2416	to compile this single file.	4135	to compile this single file.
2417		4136
2418	=head3 LIBEVENT COMPATIBILITY API	4137	=head3 LIBEVENT COMPATIBILITY API
2419		4138
2420	To include the libevent compatibility API, also include:	4139	To include the libevent compatibility API, also include:
2421		4140
2422	#include "event.c"	4141	#include "event.c"
2423		4142
2424	in the file including F<ev.c>, and:	4143	in the file including F<ev.c>, and:
2425		4144
2426	#include "event.h"	4145	#include "event.h"
2427		4146
2428	in the files that want to use the libevent API. This also includes F<ev.h>.	4147	in the files that want to use the libevent API. This also includes F<ev.h>.
2429		4148
2430	You need the following additional files for this:	4149	You need the following additional files for this:
2431		4150
2432	event.h	4151	event.h
2433	event.c	4152	event.c
2434		4153
2435	=head3 AUTOCONF SUPPORT	4154	=head3 AUTOCONF SUPPORT
2436		4155
2437	Instead of using C<EV_STANDALONE=1> and providing your config in	4156	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2438	whatever way you want, you can also C<m4_include([libev.m4])> in your	4157	whatever way you want, you can also C<m4_include([libev.m4])> in your
2439	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4158	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2440	include F<config.h> and configure itself accordingly.	4159	include F<config.h> and configure itself accordingly.
2441		4160
2442	For this of course you need the m4 file:	4161	For this of course you need the m4 file:
2443		4162
2444	libev.m4	4163	libev.m4
2445		4164
2446	=head2 PREPROCESSOR SYMBOLS/MACROS	4165	=head2 PREPROCESSOR SYMBOLS/MACROS
2447		4166
2448	Libev can be configured via a variety of preprocessor symbols you have to define	4167	Libev can be configured via a variety of preprocessor symbols you have to
2449	before including any of its files. The default is not to build for multiplicity	4168	define before including (or compiling) any of its files. The default in
2450	and only include the select backend.	4169	the absence of autoconf is documented for every option.
		4170
		4171	Symbols marked with "(h)" do not change the ABI, and can have different
		4172	values when compiling libev vs. including F<ev.h>, so it is permissible
		4173	to redefine them before including F<ev.h> without breaking compatibility
		4174	to a compiled library. All other symbols change the ABI, which means all
		4175	users of libev and the libev code itself must be compiled with compatible
		4176	settings.
2451		4177
2452	=over 4	4178	=over 4
2453		4179
		4180	=item EV_COMPAT3 (h)
		4181
		4182	Backwards compatibility is a major concern for libev. This is why this
		4183	release of libev comes with wrappers for the functions and symbols that
		4184	have been renamed between libev version 3 and 4.
		4185
		4186	You can disable these wrappers (to test compatibility with future
		4187	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4188	sources. This has the additional advantage that you can drop the C<struct>
		4189	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4190	typedef in that case.
		4191
		4192	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4193	and in some even more future version the compatibility code will be
		4194	removed completely.
		4195
2454	=item EV_STANDALONE	4196	=item EV_STANDALONE (h)
2455		4197
2456	Must always be C<1> if you do not use autoconf configuration, which	4198	Must always be C<1> if you do not use autoconf configuration, which
2457	keeps libev from including F<config.h>, and it also defines dummy	4199	keeps libev from including F<config.h>, and it also defines dummy
2458	implementations for some libevent functions (such as logging, which is not	4200	implementations for some libevent functions (such as logging, which is not
2459	supported). It will also not define any of the structs usually found in	4201	supported). It will also not define any of the structs usually found in
2460	F<event.h> that are not directly supported by the libev core alone.	4202	F<event.h> that are not directly supported by the libev core alone.
2461		4203
		4204	In standalone mode, libev will still try to automatically deduce the
		4205	configuration, but has to be more conservative.
		4206
2462	=item EV_USE_MONOTONIC	4207	=item EV_USE_MONOTONIC
2463		4208
2464	If defined to be C<1>, libev will try to detect the availability of the	4209	If defined to be C<1>, libev will try to detect the availability of the
2465	monotonic clock option at both compiletime and runtime. Otherwise no use	4210	monotonic clock option at both compile time and runtime. Otherwise no
2466	of the monotonic clock option will be attempted. If you enable this, you	4211	use of the monotonic clock option will be attempted. If you enable this,
2467	usually have to link against librt or something similar. Enabling it when	4212	you usually have to link against librt or something similar. Enabling it
2468	the functionality isn't available is safe, though, although you have	4213	when the functionality isn't available is safe, though, although you have
2469	to make sure you link against any libraries where the C<clock_gettime>	4214	to make sure you link against any libraries where the C<clock_gettime>
2470	function is hiding in (often F<-lrt>).	4215	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2471		4216
2472	=item EV_USE_REALTIME	4217	=item EV_USE_REALTIME
2473		4218
2474	If defined to be C<1>, libev will try to detect the availability of the	4219	If defined to be C<1>, libev will try to detect the availability of the
2475	realtime clock option at compiletime (and assume its availability at	4220	real-time clock option at compile time (and assume its availability
2476	runtime if successful). Otherwise no use of the realtime clock option will	4221	at runtime if successful). Otherwise no use of the real-time clock
2477	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4222	option will be attempted. This effectively replaces C<gettimeofday>
2478	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4223	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2479	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4224	correctness. See the note about libraries in the description of
		4225	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4226	C<EV_USE_CLOCK_SYSCALL>.
		4227
		4228	=item EV_USE_CLOCK_SYSCALL
		4229
		4230	If defined to be C<1>, libev will try to use a direct syscall instead
		4231	of calling the system-provided C<clock_gettime> function. This option
		4232	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4233	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4234	programs needlessly. Using a direct syscall is slightly slower (in
		4235	theory), because no optimised vdso implementation can be used, but avoids
		4236	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4237	higher, as it simplifies linking (no need for C<-lrt>).
2480		4238
2481	=item EV_USE_NANOSLEEP	4239	=item EV_USE_NANOSLEEP
2482		4240
2483	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4241	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2484	and will use it for delays. Otherwise it will use C<select ()>.	4242	and will use it for delays. Otherwise it will use C<select ()>.
2485		4243
		4244	=item EV_USE_EVENTFD
		4245
		4246	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4247	available and will probe for kernel support at runtime. This will improve
		4248	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4249	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4250	2.7 or newer, otherwise disabled.
		4251
2486	=item EV_USE_SELECT	4252	=item EV_USE_SELECT
2487		4253
2488	If undefined or defined to be C<1>, libev will compile in support for the	4254	If undefined or defined to be C<1>, libev will compile in support for the
2489	C<select>(2) backend. No attempt at autodetection will be done: if no	4255	C<select>(2) backend. No attempt at auto-detection will be done: if no
2490	other method takes over, select will be it. Otherwise the select backend	4256	other method takes over, select will be it. Otherwise the select backend
2491	will not be compiled in.	4257	will not be compiled in.
2492		4258
2493	=item EV_SELECT_USE_FD_SET	4259	=item EV_SELECT_USE_FD_SET
2494		4260
2495	If defined to C<1>, then the select backend will use the system C<fd_set>	4261	If defined to C<1>, then the select backend will use the system C<fd_set>
2496	structure. This is useful if libev doesn't compile due to a missing	4262	structure. This is useful if libev doesn't compile due to a missing
2497	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4263	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2498	exotic systems. This usually limits the range of file descriptors to some	4264	on exotic systems. This usually limits the range of file descriptors to
2499	low limit such as 1024 or might have other limitations (winsocket only	4265	some low limit such as 1024 or might have other limitations (winsocket
2500	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4266	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2501	influence the size of the C<fd_set> used.	4267	configures the maximum size of the C<fd_set>.
2502		4268
2503	=item EV_SELECT_IS_WINSOCKET	4269	=item EV_SELECT_IS_WINSOCKET
2504		4270
2505	When defined to C<1>, the select backend will assume that	4271	When defined to C<1>, the select backend will assume that
2506	select/socket/connect etc. don't understand file descriptors but	4272	select/socket/connect etc. don't understand file descriptors but
…		…
2508	be used is the winsock select). This means that it will call	4274	be used is the winsock select). This means that it will call
2509	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4275	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2510	it is assumed that all these functions actually work on fds, even	4276	it is assumed that all these functions actually work on fds, even
2511	on win32. Should not be defined on non-win32 platforms.	4277	on win32. Should not be defined on non-win32 platforms.
2512		4278
2513	=item EV_FD_TO_WIN32_HANDLE	4279	=item EV_FD_TO_WIN32_HANDLE(fd)
2514		4280
2515	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4281	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2516	file descriptors to socket handles. When not defining this symbol (the	4282	file descriptors to socket handles. When not defining this symbol (the
2517	default), then libev will call C<_get_osfhandle>, which is usually	4283	default), then libev will call C<_get_osfhandle>, which is usually
2518	correct. In some cases, programs use their own file descriptor management,	4284	correct. In some cases, programs use their own file descriptor management,
2519	in which case they can provide this function to map fds to socket handles.	4285	in which case they can provide this function to map fds to socket handles.
2520		4286
		4287	=item EV_WIN32_HANDLE_TO_FD(handle)
		4288
		4289	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4290	using the standard C<_open_osfhandle> function. For programs implementing
		4291	their own fd to handle mapping, overwriting this function makes it easier
		4292	to do so. This can be done by defining this macro to an appropriate value.
		4293
		4294	=item EV_WIN32_CLOSE_FD(fd)
		4295
		4296	If programs implement their own fd to handle mapping on win32, then this
		4297	macro can be used to override the C<close> function, useful to unregister
		4298	file descriptors again. Note that the replacement function has to close
		4299	the underlying OS handle.
		4300
2521	=item EV_USE_POLL	4301	=item EV_USE_POLL
2522		4302
2523	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4303	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2524	backend. Otherwise it will be enabled on non-win32 platforms. It	4304	backend. Otherwise it will be enabled on non-win32 platforms. It
2525	takes precedence over select.	4305	takes precedence over select.
2526		4306
2527	=item EV_USE_EPOLL	4307	=item EV_USE_EPOLL
2528		4308
2529	If defined to be C<1>, libev will compile in support for the Linux	4309	If defined to be C<1>, libev will compile in support for the Linux
2530	C<epoll>(7) backend. Its availability will be detected at runtime,	4310	C<epoll>(7) backend. Its availability will be detected at runtime,
2531	otherwise another method will be used as fallback. This is the	4311	otherwise another method will be used as fallback. This is the preferred
2532	preferred backend for GNU/Linux systems.	4312	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4313	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2533		4314
2534	=item EV_USE_KQUEUE	4315	=item EV_USE_KQUEUE
2535		4316
2536	If defined to be C<1>, libev will compile in support for the BSD style	4317	If defined to be C<1>, libev will compile in support for the BSD style
2537	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4318	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2550	otherwise another method will be used as fallback. This is the preferred	4331	otherwise another method will be used as fallback. This is the preferred
2551	backend for Solaris 10 systems.	4332	backend for Solaris 10 systems.
2552		4333
2553	=item EV_USE_DEVPOLL	4334	=item EV_USE_DEVPOLL
2554		4335
2555	reserved for future expansion, works like the USE symbols above.	4336	Reserved for future expansion, works like the USE symbols above.
2556		4337
2557	=item EV_USE_INOTIFY	4338	=item EV_USE_INOTIFY
2558		4339
2559	If defined to be C<1>, libev will compile in support for the Linux inotify	4340	If defined to be C<1>, libev will compile in support for the Linux inotify
2560	interface to speed up C<ev_stat> watchers. Its actual availability will	4341	interface to speed up C<ev_stat> watchers. Its actual availability will
2561	be detected at runtime.	4342	be detected at runtime. If undefined, it will be enabled if the headers
		4343	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2562		4344
		4345	=item EV_ATOMIC_T
		4346
		4347	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4348	access is atomic with respect to other threads or signal contexts. No such
		4349	type is easily found in the C language, so you can provide your own type
		4350	that you know is safe for your purposes. It is used both for signal handler "locking"
		4351	as well as for signal and thread safety in C<ev_async> watchers.
		4352
		4353	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4354	(from F<signal.h>), which is usually good enough on most platforms.
		4355
2563	=item EV_H	4356	=item EV_H (h)
2564		4357
2565	The name of the F<ev.h> header file used to include it. The default if	4358	The name of the F<ev.h> header file used to include it. The default if
2566	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4359	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2567	used to virtually rename the F<ev.h> header file in case of conflicts.	4360	used to virtually rename the F<ev.h> header file in case of conflicts.
2568		4361
2569	=item EV_CONFIG_H	4362	=item EV_CONFIG_H (h)
2570		4363
2571	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4364	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2572	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4365	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2573	C<EV_H>, above.	4366	C<EV_H>, above.
2574		4367
2575	=item EV_EVENT_H	4368	=item EV_EVENT_H (h)
2576		4369
2577	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4370	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2578	of how the F<event.h> header can be found, the default is C<"event.h">.	4371	of how the F<event.h> header can be found, the default is C<"event.h">.
2579		4372
2580	=item EV_PROTOTYPES	4373	=item EV_PROTOTYPES (h)
2581		4374
2582	If defined to be C<0>, then F<ev.h> will not define any function	4375	If defined to be C<0>, then F<ev.h> will not define any function
2583	prototypes, but still define all the structs and other symbols. This is	4376	prototypes, but still define all the structs and other symbols. This is
2584	occasionally useful if you want to provide your own wrapper functions	4377	occasionally useful if you want to provide your own wrapper functions
2585	around libev functions.	4378	around libev functions.
…		…
2604	When doing priority-based operations, libev usually has to linearly search	4397	When doing priority-based operations, libev usually has to linearly search
2605	all the priorities, so having many of them (hundreds) uses a lot of space	4398	all the priorities, so having many of them (hundreds) uses a lot of space
2606	and time, so using the defaults of five priorities (-2 .. +2) is usually	4399	and time, so using the defaults of five priorities (-2 .. +2) is usually
2607	fine.	4400	fine.
2608		4401
2609	If your embedding app does not need any priorities, defining these both to	4402	If your embedding application does not need any priorities, defining these
2610	C<0> will save some memory and cpu.	4403	both to C<0> will save some memory and CPU.
2611		4404
2612	=item EV_PERIODIC_ENABLE	4405	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4406	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4407	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2613		4408
2614	If undefined or defined to be C<1>, then periodic timers are supported. If	4409	If undefined or defined to be C<1> (and the platform supports it), then
2615	defined to be C<0>, then they are not. Disabling them saves a few kB of	4410	the respective watcher type is supported. If defined to be C<0>, then it
2616	code.	4411	is not. Disabling watcher types mainly saves code size.
2617		4412
2618	=item EV_IDLE_ENABLE	4413	=item EV_FEATURES
2619
2620	If undefined or defined to be C<1>, then idle watchers are supported. If
2621	defined to be C<0>, then they are not. Disabling them saves a few kB of
2622	code.
2623
2624	=item EV_EMBED_ENABLE
2625
2626	If undefined or defined to be C<1>, then embed watchers are supported. If
2627	defined to be C<0>, then they are not.
2628
2629	=item EV_STAT_ENABLE
2630
2631	If undefined or defined to be C<1>, then stat watchers are supported. If
2632	defined to be C<0>, then they are not.
2633
2634	=item EV_FORK_ENABLE
2635
2636	If undefined or defined to be C<1>, then fork watchers are supported. If
2637	defined to be C<0>, then they are not.
2638
2639	=item EV_MINIMAL
2640		4414
2641	If you need to shave off some kilobytes of code at the expense of some	4415	If you need to shave off some kilobytes of code at the expense of some
2642	speed, define this symbol to C<1>. Currently only used for gcc to override	4416	speed (but with the full API), you can define this symbol to request
2643	some inlining decisions, saves roughly 30% codesize of amd64.	4417	certain subsets of functionality. The default is to enable all features
		4418	that can be enabled on the platform.
		4419
		4420	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4421	with some broad features you want) and then selectively re-enable
		4422	additional parts you want, for example if you want everything minimal,
		4423	but multiple event loop support, async and child watchers and the poll
		4424	backend, use this:
		4425
		4426	#define EV_FEATURES 0
		4427	#define EV_MULTIPLICITY 1
		4428	#define EV_USE_POLL 1
		4429	#define EV_CHILD_ENABLE 1
		4430	#define EV_ASYNC_ENABLE 1
		4431
		4432	The actual value is a bitset, it can be a combination of the following
		4433	values:
		4434
		4435	=over 4
		4436
		4437	=item C<1> - faster/larger code
		4438
		4439	Use larger code to speed up some operations.
		4440
		4441	Currently this is used to override some inlining decisions (enlarging the
		4442	code size by roughly 30% on amd64).
		4443
		4444	When optimising for size, use of compiler flags such as C<-Os> with
		4445	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4446	assertions.
		4447
		4448	=item C<2> - faster/larger data structures
		4449
		4450	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4451	hash table sizes and so on. This will usually further increase code size
		4452	and can additionally have an effect on the size of data structures at
		4453	runtime.
		4454
		4455	=item C<4> - full API configuration
		4456
		4457	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4458	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4459
		4460	=item C<8> - full API
		4461
		4462	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4463	details on which parts of the API are still available without this
		4464	feature, and do not complain if this subset changes over time.
		4465
		4466	=item C<16> - enable all optional watcher types
		4467
		4468	Enables all optional watcher types. If you want to selectively enable
		4469	only some watcher types other than I/O and timers (e.g. prepare,
		4470	embed, async, child...) you can enable them manually by defining
		4471	C<EV_watchertype_ENABLE> to C<1> instead.
		4472
		4473	=item C<32> - enable all backends
		4474
		4475	This enables all backends - without this feature, you need to enable at
		4476	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4477
		4478	=item C<64> - enable OS-specific "helper" APIs
		4479
		4480	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4481	default.
		4482
		4483	=back
		4484
		4485	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4486	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4487	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4488	watchers, timers and monotonic clock support.
		4489
		4490	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4491	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4492	your program might be left out as well - a binary starting a timer and an
		4493	I/O watcher then might come out at only 5Kb.
		4494
		4495	=item EV_AVOID_STDIO
		4496
		4497	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4498	functions (printf, scanf, perror etc.). This will increase the code size
		4499	somewhat, but if your program doesn't otherwise depend on stdio and your
		4500	libc allows it, this avoids linking in the stdio library which is quite
		4501	big.
		4502
		4503	Note that error messages might become less precise when this option is
		4504	enabled.
		4505
		4506	=item EV_NSIG
		4507
		4508	The highest supported signal number, +1 (or, the number of
		4509	signals): Normally, libev tries to deduce the maximum number of signals
		4510	automatically, but sometimes this fails, in which case it can be
		4511	specified. Also, using a lower number than detected (C<32> should be
		4512	good for about any system in existence) can save some memory, as libev
		4513	statically allocates some 12-24 bytes per signal number.
2644		4514
2645	=item EV_PID_HASHSIZE	4515	=item EV_PID_HASHSIZE
2646		4516
2647	C<ev_child> watchers use a small hash table to distribute workload by	4517	C<ev_child> watchers use a small hash table to distribute workload by
2648	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4518	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2649	than enough. If you need to manage thousands of children you might want to	4519	usually more than enough. If you need to manage thousands of children you
2650	increase this value (I<must> be a power of two).	4520	might want to increase this value (I<must> be a power of two).
2651		4521
2652	=item EV_INOTIFY_HASHSIZE	4522	=item EV_INOTIFY_HASHSIZE
2653		4523
2654	C<ev_stat> watchers use a small hash table to distribute workload by	4524	C<ev_stat> watchers use a small hash table to distribute workload by
2655	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4525	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2656	usually more than enough. If you need to manage thousands of C<ev_stat>	4526	disabled), usually more than enough. If you need to manage thousands of
2657	watchers you might want to increase this value (I<must> be a power of	4527	C<ev_stat> watchers you might want to increase this value (I<must> be a
2658	two).	4528	power of two).
		4529
		4530	=item EV_USE_4HEAP
		4531
		4532	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4533	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4534	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4535	faster performance with many (thousands) of watchers.
		4536
		4537	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4538	will be C<0>.
		4539
		4540	=item EV_HEAP_CACHE_AT
		4541
		4542	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4543	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4544	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4545	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4546	but avoids random read accesses on heap changes. This improves performance
		4547	noticeably with many (hundreds) of watchers.
		4548
		4549	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4550	will be C<0>.
		4551
		4552	=item EV_VERIFY
		4553
		4554	Controls how much internal verification (see C<ev_verify ()>) will
		4555	be done: If set to C<0>, no internal verification code will be compiled
		4556	in. If set to C<1>, then verification code will be compiled in, but not
		4557	called. If set to C<2>, then the internal verification code will be
		4558	called once per loop, which can slow down libev. If set to C<3>, then the
		4559	verification code will be called very frequently, which will slow down
		4560	libev considerably.
		4561
		4562	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4563	will be C<0>.
2659		4564
2660	=item EV_COMMON	4565	=item EV_COMMON
2661		4566
2662	By default, all watchers have a C<void *data> member. By redefining	4567	By default, all watchers have a C<void *data> member. By redefining
2663	this macro to a something else you can include more and other types of	4568	this macro to something else you can include more and other types of
2664	members. You have to define it each time you include one of the files,	4569	members. You have to define it each time you include one of the files,
2665	though, and it must be identical each time.	4570	though, and it must be identical each time.
2666		4571
2667	For example, the perl EV module uses something like this:	4572	For example, the perl EV module uses something like this:
2668		4573
2669	#define EV_COMMON \	4574	#define EV_COMMON \
2670	SV *self; /* contains this struct */ \	4575	SV *self; /* contains this struct */ \
2671	SV *cb_sv, *fh /* note no trailing ";" */	4576	SV *cb_sv, *fh /* note no trailing ";" */
2672		4577
2673	=item EV_CB_DECLARE (type)	4578	=item EV_CB_DECLARE (type)
2674		4579
2675	=item EV_CB_INVOKE (watcher, revents)	4580	=item EV_CB_INVOKE (watcher, revents)
2676		4581
…		…
2681	definition and a statement, respectively. See the F<ev.h> header file for	4586	definition and a statement, respectively. See the F<ev.h> header file for
2682	their default definitions. One possible use for overriding these is to	4587	their default definitions. One possible use for overriding these is to
2683	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4588	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2684	method calls instead of plain function calls in C++.	4589	method calls instead of plain function calls in C++.
2685		4590
		4591	=back
		4592
2686	=head2 EXPORTED API SYMBOLS	4593	=head2 EXPORTED API SYMBOLS
2687		4594
2688	If you need to re-export the API (e.g. via a dll) and you need a list of	4595	If you need to re-export the API (e.g. via a DLL) and you need a list of
2689	exported symbols, you can use the provided F<Symbol.*> files which list	4596	exported symbols, you can use the provided F<Symbol.*> files which list
2690	all public symbols, one per line:	4597	all public symbols, one per line:
2691		4598
2692	Symbols.ev for libev proper	4599	Symbols.ev for libev proper
2693	Symbols.event for the libevent emulation	4600	Symbols.event for the libevent emulation
2694		4601
2695	This can also be used to rename all public symbols to avoid clashes with	4602	This can also be used to rename all public symbols to avoid clashes with
2696	multiple versions of libev linked together (which is obviously bad in	4603	multiple versions of libev linked together (which is obviously bad in
2697	itself, but sometimes it is inconvinient to avoid this).	4604	itself, but sometimes it is inconvenient to avoid this).
2698		4605
2699	A sed command like this will create wrapper C<#define>'s that you need to	4606	A sed command like this will create wrapper C<#define>'s that you need to
2700	include before including F<ev.h>:	4607	include before including F<ev.h>:
2701		4608
2702	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	4609	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2719	file.	4626	file.
2720		4627
2721	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4628	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2722	that everybody includes and which overrides some configure choices:	4629	that everybody includes and which overrides some configure choices:
2723		4630
2724	#define EV_MINIMAL 1	4631	#define EV_FEATURES 8
2725	#define EV_USE_POLL 0	4632	#define EV_USE_SELECT 1
2726	#define EV_MULTIPLICITY 0
2727	#define EV_PERIODIC_ENABLE 0	4633	#define EV_PREPARE_ENABLE 1
		4634	#define EV_IDLE_ENABLE 1
2728	#define EV_STAT_ENABLE 0	4635	#define EV_SIGNAL_ENABLE 1
2729	#define EV_FORK_ENABLE 0	4636	#define EV_CHILD_ENABLE 1
		4637	#define EV_USE_STDEXCEPT 0
2730	#define EV_CONFIG_H <config.h>	4638	#define EV_CONFIG_H <config.h>
2731	#define EV_MINPRI 0
2732	#define EV_MAXPRI 0
2733		4639
2734	#include "ev++.h"	4640	#include "ev++.h"
2735		4641
2736	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4642	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2737		4643
2738	#include "ev_cpp.h"	4644	#include "ev_cpp.h"
2739	#include "ev.c"	4645	#include "ev.c"
2740		4646
		4647	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
2741		4648
2742	=head1 COMPLEXITIES	4649	=head2 THREADS AND COROUTINES
2743		4650
2744	In this section the complexities of (many of) the algorithms used inside	4651	=head3 THREADS
2745	libev will be explained. For complexity discussions about backends see the
2746	documentation for C<ev_default_init>.
2747		4652
2748	All of the following are about amortised time: If an array needs to be	4653	All libev functions are reentrant and thread-safe unless explicitly
2749	extended, libev needs to realloc and move the whole array, but this	4654	documented otherwise, but libev implements no locking itself. This means
2750	happens asymptotically never with higher number of elements, so O(1) might	4655	that you can use as many loops as you want in parallel, as long as there
2751	mean it might do a lengthy realloc operation in rare cases, but on average	4656	are no concurrent calls into any libev function with the same loop
2752	it is much faster and asymptotically approaches constant time.	4657	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4658	of course): libev guarantees that different event loops share no data
		4659	structures that need any locking.
		4660
		4661	Or to put it differently: calls with different loop parameters can be done
		4662	concurrently from multiple threads, calls with the same loop parameter
		4663	must be done serially (but can be done from different threads, as long as
		4664	only one thread ever is inside a call at any point in time, e.g. by using
		4665	a mutex per loop).
		4666
		4667	Specifically to support threads (and signal handlers), libev implements
		4668	so-called C<ev_async> watchers, which allow some limited form of
		4669	concurrency on the same event loop, namely waking it up "from the
		4670	outside".
		4671
		4672	If you want to know which design (one loop, locking, or multiple loops
		4673	without or something else still) is best for your problem, then I cannot
		4674	help you, but here is some generic advice:
2753		4675
2754	=over 4	4676	=over 4
2755		4677
2756	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4678	=item * most applications have a main thread: use the default libev loop
		4679	in that thread, or create a separate thread running only the default loop.
2757		4680
2758	This means that, when you have a watcher that triggers in one hour and	4681	This helps integrating other libraries or software modules that use libev
2759	there are 100 watchers that would trigger before that then inserting will	4682	themselves and don't care/know about threading.
2760	have to skip roughly seven (C<ld 100>) of these watchers.
2761		4683
2762	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4684	=item * one loop per thread is usually a good model.
2763		4685
2764	That means that changing a timer costs less than removing/adding them	4686	Doing this is almost never wrong, sometimes a better-performance model
2765	as only the relative motion in the event queue has to be paid for.	4687	exists, but it is always a good start.
2766		4688
2767	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4689	=item * other models exist, such as the leader/follower pattern, where one
		4690	loop is handed through multiple threads in a kind of round-robin fashion.
2768		4691
2769	These just add the watcher into an array or at the head of a list.	4692	Choosing a model is hard - look around, learn, know that usually you can do
		4693	better than you currently do :-)
2770		4694
2771	=item Stopping check/prepare/idle watchers: O(1)	4695	=item * often you need to talk to some other thread which blocks in the
		4696	event loop.
2772		4697
2773	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4698	C<ev_async> watchers can be used to wake them up from other threads safely
		4699	(or from signal contexts...).
2774		4700
2775	These watchers are stored in lists then need to be walked to find the	4701	An example use would be to communicate signals or other events that only
2776	correct watcher to remove. The lists are usually short (you don't usually	4702	work in the default loop by registering the signal watcher with the
2777	have many watchers waiting for the same fd or signal).	4703	default loop and triggering an C<ev_async> watcher from the default loop
2778		4704	watcher callback into the event loop interested in the signal.
2779	=item Finding the next timer in each loop iteration: O(1)
2780
2781	By virtue of using a binary heap, the next timer is always found at the
2782	beginning of the storage array.
2783
2784	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2785
2786	A change means an I/O watcher gets started or stopped, which requires
2787	libev to recalculate its status (and possibly tell the kernel, depending
2788	on backend and wether C<ev_io_set> was used).
2789
2790	=item Activating one watcher (putting it into the pending state): O(1)
2791
2792	=item Priority handling: O(number_of_priorities)
2793
2794	Priorities are implemented by allocating some space for each
2795	priority. When doing priority-based operations, libev usually has to
2796	linearly search all the priorities, but starting/stopping and activating
2797	watchers becomes O(1) w.r.t. prioritiy handling.
2798		4705
2799	=back	4706	=back
2800		4707
		4708	See also L<THREAD LOCKING EXAMPLE>.
2801		4709
2802	=head1 Win32 platform limitations and workarounds	4710	=head3 COROUTINES
		4711
		4712	Libev is very accommodating to coroutines ("cooperative threads"):
		4713	libev fully supports nesting calls to its functions from different
		4714	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4715	different coroutines, and switch freely between both coroutines running
		4716	the loop, as long as you don't confuse yourself). The only exception is
		4717	that you must not do this from C<ev_periodic> reschedule callbacks.
		4718
		4719	Care has been taken to ensure that libev does not keep local state inside
		4720	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4721	they do not call any callbacks.
		4722
		4723	=head2 COMPILER WARNINGS
		4724
		4725	Depending on your compiler and compiler settings, you might get no or a
		4726	lot of warnings when compiling libev code. Some people are apparently
		4727	scared by this.
		4728
		4729	However, these are unavoidable for many reasons. For one, each compiler
		4730	has different warnings, and each user has different tastes regarding
		4731	warning options. "Warn-free" code therefore cannot be a goal except when
		4732	targeting a specific compiler and compiler-version.
		4733
		4734	Another reason is that some compiler warnings require elaborate
		4735	workarounds, or other changes to the code that make it less clear and less
		4736	maintainable.
		4737
		4738	And of course, some compiler warnings are just plain stupid, or simply
		4739	wrong (because they don't actually warn about the condition their message
		4740	seems to warn about). For example, certain older gcc versions had some
		4741	warnings that resulted in an extreme number of false positives. These have
		4742	been fixed, but some people still insist on making code warn-free with
		4743	such buggy versions.
		4744
		4745	While libev is written to generate as few warnings as possible,
		4746	"warn-free" code is not a goal, and it is recommended not to build libev
		4747	with any compiler warnings enabled unless you are prepared to cope with
		4748	them (e.g. by ignoring them). Remember that warnings are just that:
		4749	warnings, not errors, or proof of bugs.
		4750
		4751
		4752	=head2 VALGRIND
		4753
		4754	Valgrind has a special section here because it is a popular tool that is
		4755	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4756
		4757	If you think you found a bug (memory leak, uninitialised data access etc.)
		4758	in libev, then check twice: If valgrind reports something like:
		4759
		4760	==2274== definitely lost: 0 bytes in 0 blocks.
		4761	==2274== possibly lost: 0 bytes in 0 blocks.
		4762	==2274== still reachable: 256 bytes in 1 blocks.
		4763
		4764	Then there is no memory leak, just as memory accounted to global variables
		4765	is not a memleak - the memory is still being referenced, and didn't leak.
		4766
		4767	Similarly, under some circumstances, valgrind might report kernel bugs
		4768	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4769	although an acceptable workaround has been found here), or it might be
		4770	confused.
		4771
		4772	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4773	make it into some kind of religion.
		4774
		4775	If you are unsure about something, feel free to contact the mailing list
		4776	with the full valgrind report and an explanation on why you think this
		4777	is a bug in libev (best check the archives, too :). However, don't be
		4778	annoyed when you get a brisk "this is no bug" answer and take the chance
		4779	of learning how to interpret valgrind properly.
		4780
		4781	If you need, for some reason, empty reports from valgrind for your project
		4782	I suggest using suppression lists.
		4783
		4784
		4785	=head1 PORTABILITY NOTES
		4786
		4787	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4788
		4789	GNU/Linux is the only common platform that supports 64 bit file/large file
		4790	interfaces but I<disables> them by default.
		4791
		4792	That means that libev compiled in the default environment doesn't support
		4793	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4794
		4795	Unfortunately, many programs try to work around this GNU/Linux issue
		4796	by enabling the large file API, which makes them incompatible with the
		4797	standard libev compiled for their system.
		4798
		4799	Likewise, libev cannot enable the large file API itself as this would
		4800	suddenly make it incompatible to the default compile time environment,
		4801	i.e. all programs not using special compile switches.
		4802
		4803	=head2 OS/X AND DARWIN BUGS
		4804
		4805	The whole thing is a bug if you ask me - basically any system interface
		4806	you touch is broken, whether it is locales, poll, kqueue or even the
		4807	OpenGL drivers.
		4808
		4809	=head3 C<kqueue> is buggy
		4810
		4811	The kqueue syscall is broken in all known versions - most versions support
		4812	only sockets, many support pipes.
		4813
		4814	Libev tries to work around this by not using C<kqueue> by default on this
		4815	rotten platform, but of course you can still ask for it when creating a
		4816	loop - embedding a socket-only kqueue loop into a select-based one is
		4817	probably going to work well.
		4818
		4819	=head3 C<poll> is buggy
		4820
		4821	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4822	implementation by something calling C<kqueue> internally around the 10.5.6
		4823	release, so now C<kqueue> I<and> C<poll> are broken.
		4824
		4825	Libev tries to work around this by not using C<poll> by default on
		4826	this rotten platform, but of course you can still ask for it when creating
		4827	a loop.
		4828
		4829	=head3 C<select> is buggy
		4830
		4831	All that's left is C<select>, and of course Apple found a way to fuck this
		4832	one up as well: On OS/X, C<select> actively limits the number of file
		4833	descriptors you can pass in to 1024 - your program suddenly crashes when
		4834	you use more.
		4835
		4836	There is an undocumented "workaround" for this - defining
		4837	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4838	work on OS/X.
		4839
		4840	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4841
		4842	=head3 C<errno> reentrancy
		4843
		4844	The default compile environment on Solaris is unfortunately so
		4845	thread-unsafe that you can't even use components/libraries compiled
		4846	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4847	defined by default. A valid, if stupid, implementation choice.
		4848
		4849	If you want to use libev in threaded environments you have to make sure
		4850	it's compiled with C<_REENTRANT> defined.
		4851
		4852	=head3 Event port backend
		4853
		4854	The scalable event interface for Solaris is called "event
		4855	ports". Unfortunately, this mechanism is very buggy in all major
		4856	releases. If you run into high CPU usage, your program freezes or you get
		4857	a large number of spurious wakeups, make sure you have all the relevant
		4858	and latest kernel patches applied. No, I don't know which ones, but there
		4859	are multiple ones to apply, and afterwards, event ports actually work
		4860	great.
		4861
		4862	If you can't get it to work, you can try running the program by setting
		4863	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4864	C<select> backends.
		4865
		4866	=head2 AIX POLL BUG
		4867
		4868	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4869	this by trying to avoid the poll backend altogether (i.e. it's not even
		4870	compiled in), which normally isn't a big problem as C<select> works fine
		4871	with large bitsets on AIX, and AIX is dead anyway.
		4872
		4873	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4874
		4875	=head3 General issues
2803		4876
2804	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4877	Win32 doesn't support any of the standards (e.g. POSIX) that libev
2805	requires, and its I/O model is fundamentally incompatible with the POSIX	4878	requires, and its I/O model is fundamentally incompatible with the POSIX
2806	model. Libev still offers limited functionality on this platform in	4879	model. Libev still offers limited functionality on this platform in
2807	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4880	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
2808	descriptors. This only applies when using Win32 natively, not when using	4881	descriptors. This only applies when using Win32 natively, not when using
2809	e.g. cygwin.	4882	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4883	as every compielr comes with a slightly differently broken/incompatible
		4884	environment.
		4885
		4886	Lifting these limitations would basically require the full
		4887	re-implementation of the I/O system. If you are into this kind of thing,
		4888	then note that glib does exactly that for you in a very portable way (note
		4889	also that glib is the slowest event library known to man).
2810		4890
2811	There is no supported compilation method available on windows except	4891	There is no supported compilation method available on windows except
2812	embedding it into other applications.	4892	embedding it into other applications.
2813		4893
		4894	Sensible signal handling is officially unsupported by Microsoft - libev
		4895	tries its best, but under most conditions, signals will simply not work.
		4896
		4897	Not a libev limitation but worth mentioning: windows apparently doesn't
		4898	accept large writes: instead of resulting in a partial write, windows will
		4899	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4900	so make sure you only write small amounts into your sockets (less than a
		4901	megabyte seems safe, but this apparently depends on the amount of memory
		4902	available).
		4903
2814	Due to the many, low, and arbitrary limits on the win32 platform and the	4904	Due to the many, low, and arbitrary limits on the win32 platform and
2815	abysmal performance of winsockets, using a large number of sockets is not	4905	the abysmal performance of winsockets, using a large number of sockets
2816	recommended (and not reasonable). If your program needs to use more than	4906	is not recommended (and not reasonable). If your program needs to use
2817	a hundred or so sockets, then likely it needs to use a totally different	4907	more than a hundred or so sockets, then likely it needs to use a totally
2818	implementation for windows, as libev offers the POSIX model, which cannot	4908	different implementation for windows, as libev offers the POSIX readiness
2819	be implemented efficiently on windows (microsoft monopoly games).	4909	notification model, which cannot be implemented efficiently on windows
		4910	(due to Microsoft monopoly games).
2820		4911
2821	=over 4	4912	A typical way to use libev under windows is to embed it (see the embedding
		4913	section for details) and use the following F<evwrap.h> header file instead
		4914	of F<ev.h>:
2822		4915
		4916	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4917	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4918
		4919	#include "ev.h"
		4920
		4921	And compile the following F<evwrap.c> file into your project (make sure
		4922	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4923
		4924	#include "evwrap.h"
		4925	#include "ev.c"
		4926
2823	=item The winsocket select function	4927	=head3 The winsocket C<select> function
2824		4928
2825	The winsocket C<select> function doesn't follow POSIX in that it requires	4929	The winsocket C<select> function doesn't follow POSIX in that it
2826	socket I<handles> and not socket I<file descriptors>. This makes select	4930	requires socket I<handles> and not socket I<file descriptors> (it is
2827	very inefficient, and also requires a mapping from file descriptors	4931	also extremely buggy). This makes select very inefficient, and also
2828	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	4932	requires a mapping from file descriptors to socket handles (the Microsoft
2829	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	4933	C runtime provides the function C<_open_osfhandle> for this). See the
2830	symbols for more info.	4934	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4935	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
2831		4936
2832	The configuration for a "naked" win32 using the microsoft runtime	4937	The configuration for a "naked" win32 using the Microsoft runtime
2833	libraries and raw winsocket select is:	4938	libraries and raw winsocket select is:
2834		4939
2835	#define EV_USE_SELECT 1	4940	#define EV_USE_SELECT 1
2836	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4941	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
2837		4942
2838	Note that winsockets handling of fd sets is O(n), so you can easily get a	4943	Note that winsockets handling of fd sets is O(n), so you can easily get a
2839	complexity in the O(n²) range when using win32.	4944	complexity in the O(n²) range when using win32.
2840		4945
2841	=item Limited number of file descriptors	4946	=head3 Limited number of file descriptors
2842		4947
2843	Windows has numerous arbitrary (and low) limits on things. Early versions	4948	Windows has numerous arbitrary (and low) limits on things.
2844	of winsocket's select only supported waiting for a max. of C<64> handles	4949
		4950	Early versions of winsocket's select only supported waiting for a maximum
2845	(probably owning to the fact that all windows kernels can only wait for	4951	of C<64> handles (probably owning to the fact that all windows kernels
2846	C<64> things at the same time internally; microsoft recommends spawning a	4952	can only wait for C<64> things at the same time internally; Microsoft
2847	chain of threads and wait for 63 handles and the previous thread in each).	4953	recommends spawning a chain of threads and wait for 63 handles and the
		4954	previous thread in each. Sounds great!).
2848		4955
2849	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4956	Newer versions support more handles, but you need to define C<FD_SETSIZE>
2850	to some high number (e.g. C<2048>) before compiling the winsocket select	4957	to some high number (e.g. C<2048>) before compiling the winsocket select
2851	call (which might be in libev or elsewhere, for example, perl does its own	4958	call (which might be in libev or elsewhere, for example, perl and many
2852	select emulation on windows).	4959	other interpreters do their own select emulation on windows).
2853		4960
2854	Another limit is the number of file descriptors in the microsoft runtime	4961	Another limit is the number of file descriptors in the Microsoft runtime
2855	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4962	libraries, which by default is C<64> (there must be a hidden I<64>
2856	or something like this inside microsoft). You can increase this by calling	4963	fetish or something like this inside Microsoft). You can increase this
2857	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4964	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
2858	arbitrary limit), but is broken in many versions of the microsoft runtime	4965	(another arbitrary limit), but is broken in many versions of the Microsoft
2859	libraries.
2860
2861	This might get you to about C<512> or C<2048> sockets (depending on	4966	runtime libraries. This might get you to about C<512> or C<2048> sockets
2862	windows version and/or the phase of the moon). To get more, you need to	4967	(depending on windows version and/or the phase of the moon). To get more,
2863	wrap all I/O functions and provide your own fd management, but the cost of	4968	you need to wrap all I/O functions and provide your own fd management, but
2864	calling select (O(n²)) will likely make this unworkable.	4969	the cost of calling select (O(n²)) will likely make this unworkable.
		4970
		4971	=head2 PORTABILITY REQUIREMENTS
		4972
		4973	In addition to a working ISO-C implementation and of course the
		4974	backend-specific APIs, libev relies on a few additional extensions:
		4975
		4976	=over 4
		4977
		4978	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4979	calling conventions regardless of C<ev_watcher_type *>.
		4980
		4981	Libev assumes not only that all watcher pointers have the same internal
		4982	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4983	assumes that the same (machine) code can be used to call any watcher
		4984	callback: The watcher callbacks have different type signatures, but libev
		4985	calls them using an C<ev_watcher *> internally.
		4986
		4987	=item pointer accesses must be thread-atomic
		4988
		4989	Accessing a pointer value must be atomic, it must both be readable and
		4990	writable in one piece - this is the case on all current architectures.
		4991
		4992	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4993
		4994	The type C<sig_atomic_t volatile> (or whatever is defined as
		4995	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4996	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4997	believed to be sufficiently portable.
		4998
		4999	=item C<sigprocmask> must work in a threaded environment
		5000
		5001	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5002	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5003	pthread implementations will either allow C<sigprocmask> in the "main
		5004	thread" or will block signals process-wide, both behaviours would
		5005	be compatible with libev. Interaction between C<sigprocmask> and
		5006	C<pthread_sigmask> could complicate things, however.
		5007
		5008	The most portable way to handle signals is to block signals in all threads
		5009	except the initial one, and run the default loop in the initial thread as
		5010	well.
		5011
		5012	=item C<long> must be large enough for common memory allocation sizes
		5013
		5014	To improve portability and simplify its API, libev uses C<long> internally
		5015	instead of C<size_t> when allocating its data structures. On non-POSIX
		5016	systems (Microsoft...) this might be unexpectedly low, but is still at
		5017	least 31 bits everywhere, which is enough for hundreds of millions of
		5018	watchers.
		5019
		5020	=item C<double> must hold a time value in seconds with enough accuracy
		5021
		5022	The type C<double> is used to represent timestamps. It is required to
		5023	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5024	good enough for at least into the year 4000 with millisecond accuracy
		5025	(the design goal for libev). This requirement is overfulfilled by
		5026	implementations using IEEE 754, which is basically all existing ones. With
		5027	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
2865		5028
2866	=back	5029	=back
2867		5030
		5031	If you know of other additional requirements drop me a note.
		5032
		5033
		5034	=head1 ALGORITHMIC COMPLEXITIES
		5035
		5036	In this section the complexities of (many of) the algorithms used inside
		5037	libev will be documented. For complexity discussions about backends see
		5038	the documentation for C<ev_default_init>.
		5039
		5040	All of the following are about amortised time: If an array needs to be
		5041	extended, libev needs to realloc and move the whole array, but this
		5042	happens asymptotically rarer with higher number of elements, so O(1) might
		5043	mean that libev does a lengthy realloc operation in rare cases, but on
		5044	average it is much faster and asymptotically approaches constant time.
		5045
		5046	=over 4
		5047
		5048	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		5049
		5050	This means that, when you have a watcher that triggers in one hour and
		5051	there are 100 watchers that would trigger before that, then inserting will
		5052	have to skip roughly seven (C<ld 100>) of these watchers.
		5053
		5054	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		5055
		5056	That means that changing a timer costs less than removing/adding them,
		5057	as only the relative motion in the event queue has to be paid for.
		5058
		5059	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		5060
		5061	These just add the watcher into an array or at the head of a list.
		5062
		5063	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		5064
		5065	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		5066
		5067	These watchers are stored in lists, so they need to be walked to find the
		5068	correct watcher to remove. The lists are usually short (you don't usually
		5069	have many watchers waiting for the same fd or signal: one is typical, two
		5070	is rare).
		5071
		5072	=item Finding the next timer in each loop iteration: O(1)
		5073
		5074	By virtue of using a binary or 4-heap, the next timer is always found at a
		5075	fixed position in the storage array.
		5076
		5077	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5078
		5079	A change means an I/O watcher gets started or stopped, which requires
		5080	libev to recalculate its status (and possibly tell the kernel, depending
		5081	on backend and whether C<ev_io_set> was used).
		5082
		5083	=item Activating one watcher (putting it into the pending state): O(1)
		5084
		5085	=item Priority handling: O(number_of_priorities)
		5086
		5087	Priorities are implemented by allocating some space for each
		5088	priority. When doing priority-based operations, libev usually has to
		5089	linearly search all the priorities, but starting/stopping and activating
		5090	watchers becomes O(1) with respect to priority handling.
		5091
		5092	=item Sending an ev_async: O(1)
		5093
		5094	=item Processing ev_async_send: O(number_of_async_watchers)
		5095
		5096	=item Processing signals: O(max_signal_number)
		5097
		5098	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5099	calls in the current loop iteration. Checking for async and signal events
		5100	involves iterating over all running async watchers or all signal numbers.
		5101
		5102	=back
		5103
		5104
		5105	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5106
		5107	The major version 4 introduced some incompatible changes to the API.
		5108
		5109	At the moment, the C<ev.h> header file provides compatibility definitions
		5110	for all changes, so most programs should still compile. The compatibility
		5111	layer might be removed in later versions of libev, so better update to the
		5112	new API early than late.
		5113
		5114	=over 4
		5115
		5116	=item C<EV_COMPAT3> backwards compatibility mechanism
		5117
		5118	The backward compatibility mechanism can be controlled by
		5119	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5120	section.
		5121
		5122	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5123
		5124	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5125
		5126	ev_loop_destroy (EV_DEFAULT_UC);
		5127	ev_loop_fork (EV_DEFAULT);
		5128
		5129	=item function/symbol renames
		5130
		5131	A number of functions and symbols have been renamed:
		5132
		5133	ev_loop => ev_run
		5134	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5135	EVLOOP_ONESHOT => EVRUN_ONCE
		5136
		5137	ev_unloop => ev_break
		5138	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5139	EVUNLOOP_ONE => EVBREAK_ONE
		5140	EVUNLOOP_ALL => EVBREAK_ALL
		5141
		5142	EV_TIMEOUT => EV_TIMER
		5143
		5144	ev_loop_count => ev_iteration
		5145	ev_loop_depth => ev_depth
		5146	ev_loop_verify => ev_verify
		5147
		5148	Most functions working on C<struct ev_loop> objects don't have an
		5149	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5150	associated constants have been renamed to not collide with the C<struct
		5151	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5152	as all other watcher types. Note that C<ev_loop_fork> is still called
		5153	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5154	typedef.
		5155
		5156	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5157
		5158	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5159	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5160	and work, but the library code will of course be larger.
		5161
		5162	=back
		5163
		5164
		5165	=head1 GLOSSARY
		5166
		5167	=over 4
		5168
		5169	=item active
		5170
		5171	A watcher is active as long as it has been started and not yet stopped.
		5172	See L<WATCHER STATES> for details.
		5173
		5174	=item application
		5175
		5176	In this document, an application is whatever is using libev.
		5177
		5178	=item backend
		5179
		5180	The part of the code dealing with the operating system interfaces.
		5181
		5182	=item callback
		5183
		5184	The address of a function that is called when some event has been
		5185	detected. Callbacks are being passed the event loop, the watcher that
		5186	received the event, and the actual event bitset.
		5187
		5188	=item callback/watcher invocation
		5189
		5190	The act of calling the callback associated with a watcher.
		5191
		5192	=item event
		5193
		5194	A change of state of some external event, such as data now being available
		5195	for reading on a file descriptor, time having passed or simply not having
		5196	any other events happening anymore.
		5197
		5198	In libev, events are represented as single bits (such as C<EV_READ> or
		5199	C<EV_TIMER>).
		5200
		5201	=item event library
		5202
		5203	A software package implementing an event model and loop.
		5204
		5205	=item event loop
		5206
		5207	An entity that handles and processes external events and converts them
		5208	into callback invocations.
		5209
		5210	=item event model
		5211
		5212	The model used to describe how an event loop handles and processes
		5213	watchers and events.
		5214
		5215	=item pending
		5216
		5217	A watcher is pending as soon as the corresponding event has been
		5218	detected. See L<WATCHER STATES> for details.
		5219
		5220	=item real time
		5221
		5222	The physical time that is observed. It is apparently strictly monotonic :)
		5223
		5224	=item wall-clock time
		5225
		5226	The time and date as shown on clocks. Unlike real time, it can actually
		5227	be wrong and jump forwards and backwards, e.g. when the you adjust your
		5228	clock.
		5229
		5230	=item watcher
		5231
		5232	A data structure that describes interest in certain events. Watchers need
		5233	to be started (attached to an event loop) before they can receive events.
		5234
		5235	=back
2868		5236
2869	=head1 AUTHOR	5237	=head1 AUTHOR
2870		5238
2871	Marc Lehmann <libev@schmorp.de>.	5239	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5240	Magnusson and Emanuele Giaquinta.
2872		5241

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