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Revision 1.109 by root, Mon Dec 24 13:19:12 2007 UTC vs.
Revision 1.337 by root, Sun Oct 31 20:20:20 2010 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)) [NOT REENTRANT]
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)); [NOT REENTRANT]
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.
…		…
235	...	301	...
236	ev_set_syserr_cb (fatal_error);	302	ev_set_syserr_cb (fatal_error);
237		303
238	=back	304	=back
239		305
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	306	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
241		307
242	An event loop is described by a C<struct ev_loop *>. The library knows two	308	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	309	I<not> optional in this case unless libev 3 compatibility is disabled, as
244	events, and dynamically created loops which do not.	310	libev 3 had an C<ev_loop> function colliding with the struct name).
245		311
246	If you use threads, a common model is to run the default event loop	312	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	313	supports child process events, and dynamically created event loops which
248	create, you also create another event loop. Libev itself does no locking	314	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		315
253	=over 4	316	=over 4
254		317
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	318	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		319
257	This will initialise the default event loop if it hasn't been initialised	320	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	321	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	322	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).	323	C<ev_loop_new>.
		324
		325	If the default loop is already initialised then this function simply
		326	returns it (and ignores the flags. If that is troubling you, check
		327	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		328	flags, which should almost always be C<0>, unless the caller is also the
		329	one calling C<ev_run> or otherwise qualifies as "the main program".
261		330
262	If you don't know what event loop to use, use the one returned from this	331	If you don't know what event loop to use, use the one returned from this
263	function.	332	function (or via the C<EV_DEFAULT> macro).
		333
		334	Note that this function is I<not> thread-safe, so if you want to use it
		335	from multiple threads, you have to employ some kind of mutex (note also
		336	that this case is unlikely, as loops cannot be shared easily between
		337	threads anyway).
		338
		339	The default loop is the only loop that can handle C<ev_child> watchers,
		340	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		341	a problem for your application you can either create a dynamic loop with
		342	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		343	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
		344
		345	Example: This is the most typical usage.
		346
		347	if (!ev_default_loop (0))
		348	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		349
		350	Example: Restrict libev to the select and poll backends, and do not allow
		351	environment settings to be taken into account:
		352
		353	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		354
		355	=item struct ev_loop *ev_loop_new (unsigned int flags)
		356
		357	This will create and initialise a new event loop object. If the loop
		358	could not be initialised, returns false.
		359
		360	Note that this function I<is> thread-safe, and one common way to use
		361	libev with threads is indeed to create one loop per thread, and using the
		362	default loop in the "main" or "initial" thread.
264		363
265	The flags argument can be used to specify special behaviour or specific	364	The flags argument can be used to specify special behaviour or specific
266	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	365	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
267		366
268	The following flags are supported:	367	The following flags are supported:
…		…
274	The default flags value. Use this if you have no clue (it's the right	373	The default flags value. Use this if you have no clue (it's the right
275	thing, believe me).	374	thing, believe me).
276		375
277	=item C<EVFLAG_NOENV>	376	=item C<EVFLAG_NOENV>
278		377
279	If this flag bit is ored into the flag value (or the program runs setuid	378	If this flag bit is or'ed into the flag value (or the program runs setuid
280	or setgid) then libev will I<not> look at the environment variable	379	or setgid) then libev will I<not> look at the environment variable
281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	380	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
282	override the flags completely if it is found in the environment. This is	381	override the flags completely if it is found in the environment. This is
283	useful to try out specific backends to test their performance, or to work	382	useful to try out specific backends to test their performance, or to work
284	around bugs.	383	around bugs.
285		384
286	=item C<EVFLAG_FORKCHECK>	385	=item C<EVFLAG_FORKCHECK>
287		386
288	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	387	Instead of calling C<ev_loop_fork> manually after a fork, you can also
289	a fork, you can also make libev check for a fork in each iteration by	388	make libev check for a fork in each iteration by enabling this flag.
290	enabling this flag.
291		389
292	This works by calling C<getpid ()> on every iteration of the loop,	390	This works by calling C<getpid ()> on every iteration of the loop,
293	and thus this might slow down your event loop if you do a lot of loop	391	and thus this might slow down your event loop if you do a lot of loop
294	iterations and little real work, but is usually not noticeable (on my	392	iterations and little real work, but is usually not noticeable (on my
295	Linux system for example, C<getpid> is actually a simple 5-insn sequence	393	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
296	without a syscall and thus I<very> fast, but my Linux system also has	394	without a system call and thus I<very> fast, but my GNU/Linux system also has
297	C<pthread_atfork> which is even faster).	395	C<pthread_atfork> which is even faster).
298		396
299	The big advantage of this flag is that you can forget about fork (and	397	The big advantage of this flag is that you can forget about fork (and
300	forget about forgetting to tell libev about forking) when you use this	398	forget about forgetting to tell libev about forking) when you use this
301	flag.	399	flag.
302		400
303	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	401	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
304	environment variable.	402	environment variable.
		403
		404	=item C<EVFLAG_NOINOTIFY>
		405
		406	When this flag is specified, then libev will not attempt to use the
		407	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		408	testing, this flag can be useful to conserve inotify file descriptors, as
		409	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		410
		411	=item C<EVFLAG_SIGNALFD>
		412
		413	When this flag is specified, then libev will attempt to use the
		414	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		415	delivers signals synchronously, which makes it both faster and might make
		416	it possible to get the queued signal data. It can also simplify signal
		417	handling with threads, as long as you properly block signals in your
		418	threads that are not interested in handling them.
		419
		420	Signalfd will not be used by default as this changes your signal mask, and
		421	there are a lot of shoddy libraries and programs (glib's threadpool for
		422	example) that can't properly initialise their signal masks.
305		423
306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307		425
308	This is your standard select(2) backend. Not I<completely> standard, as	426	This is your standard select(2) backend. Not I<completely> standard, as
309	libev tries to roll its own fd_set with no limits on the number of fds,	427	libev tries to roll its own fd_set with no limits on the number of fds,
310	but if that fails, expect a fairly low limit on the number of fds when	428	but if that fails, expect a fairly low limit on the number of fds when
311	using this backend. It doesn't scale too well (O(highest_fd)), but its	429	using this backend. It doesn't scale too well (O(highest_fd)), but its
312	usually the fastest backend for a low number of (low-numbered :) fds.	430	usually the fastest backend for a low number of (low-numbered :) fds.
313		431
314	To get good performance out of this backend you need a high amount of	432	To get good performance out of this backend you need a high amount of
315	parallelity (most of the file descriptors should be busy). If you are	433	parallelism (most of the file descriptors should be busy). If you are
316	writing a server, you should C<accept ()> in a loop to accept as many	434	writing a server, you should C<accept ()> in a loop to accept as many
317	connections as possible during one iteration. You might also want to have	435	connections as possible during one iteration. You might also want to have
318	a look at C<ev_set_io_collect_interval ()> to increase the amount of	436	a look at C<ev_set_io_collect_interval ()> to increase the amount of
319	readyness notifications you get per iteration.	437	readiness notifications you get per iteration.
		438
		439	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		440	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		441	C<exceptfds> set on that platform).
320		442
321	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	443	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
322		444
323	And this is your standard poll(2) backend. It's more complicated	445	And this is your standard poll(2) backend. It's more complicated
324	than select, but handles sparse fds better and has no artificial	446	than select, but handles sparse fds better and has no artificial
325	limit on the number of fds you can use (except it will slow down	447	limit on the number of fds you can use (except it will slow down
326	considerably with a lot of inactive fds). It scales similarly to select,	448	considerably with a lot of inactive fds). It scales similarly to select,
327	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	449	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
328	performance tips.	450	performance tips.
329		451
		452	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		453	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		454
330	=item C<EVBACKEND_EPOLL> (value 4, Linux)	455	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		456
		457	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		458	kernels).
331		459
332	For few fds, this backend is a bit little slower than poll and select,	460	For few fds, this backend is a bit little slower than poll and select,
333	but it scales phenomenally better. While poll and select usually scale	461	but it scales phenomenally better. While poll and select usually scale
334	like O(total_fds) where n is the total number of fds (or the highest fd),	462	like O(total_fds) where n is the total number of fds (or the highest fd),
335	epoll scales either O(1) or O(active_fds). The epoll design has a number	463	epoll scales either O(1) or O(active_fds).
336	of shortcomings, such as silently dropping events in some hard-to-detect	464
337	cases and rewiring a syscall per fd change, no fork support and bad	465	The epoll mechanism deserves honorable mention as the most misdesigned
338	support for dup.	466	of the more advanced event mechanisms: mere annoyances include silently
		467	dropping file descriptors, requiring a system call per change per file
		468	descriptor (and unnecessary guessing of parameters), problems with dup,
		469	returning before the timeout value requiring additional iterations and so
		470	on. The biggest issue is fork races, however - if a program forks then
		471	I<both> parent and child process have to recreate the epoll set, which can
		472	take considerable time (one syscall per file descriptor) and is of course
		473	hard to detect.
		474
		475	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		476	of course I<doesn't>, and epoll just loves to report events for totally
		477	I<different> file descriptors (even already closed ones, so one cannot
		478	even remove them from the set) than registered in the set (especially
		479	on SMP systems). Libev tries to counter these spurious notifications by
		480	employing an additional generation counter and comparing that against the
		481	events to filter out spurious ones, recreating the set when required. Last
		482	not least, it also refuses to work with some file descriptors which work
		483	perfectly fine with C<select> (files, many character devices...).
339		484
340	While stopping, setting and starting an I/O watcher in the same iteration	485	While stopping, setting and starting an I/O watcher in the same iteration
341	will result in some caching, there is still a syscall per such incident	486	will result in some caching, there is still a system call per such
342	(because the fd could point to a different file description now), so its	487	incident (because the same I<file descriptor> could point to a different
343	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	488	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
344	very well if you register events for both fds.	489	file descriptors might not work very well if you register events for both
345		490	file descriptors.
346	Please note that epoll sometimes generates spurious notifications, so you
347	need to use non-blocking I/O or other means to avoid blocking when no data
348	(or space) is available.
349		491
350	Best performance from this backend is achieved by not unregistering all	492	Best performance from this backend is achieved by not unregistering all
351	watchers for a file descriptor until it has been closed, if possible, i.e.	493	watchers for a file descriptor until it has been closed, if possible,
352	keep at least one watcher active per fd at all times.	494	i.e. keep at least one watcher active per fd at all times. Stopping and
		495	starting a watcher (without re-setting it) also usually doesn't cause
		496	extra overhead. A fork can both result in spurious notifications as well
		497	as in libev having to destroy and recreate the epoll object, which can
		498	take considerable time and thus should be avoided.
353		499
		500	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		501	faster than epoll for maybe up to a hundred file descriptors, depending on
		502	the usage. So sad.
		503
354	While nominally embeddeble in other event loops, this feature is broken in	504	While nominally embeddable in other event loops, this feature is broken in
355	all kernel versions tested so far.	505	all kernel versions tested so far.
		506
		507	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		508	C<EVBACKEND_POLL>.
356		509
357	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	510	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
358		511
359	Kqueue deserves special mention, as at the time of this writing, it	512	Kqueue deserves special mention, as at the time of this writing, it
360	was broken on all BSDs except NetBSD (usually it doesn't work reliably	513	was broken on all BSDs except NetBSD (usually it doesn't work reliably
361	with anything but sockets and pipes, except on Darwin, where of course	514	with anything but sockets and pipes, except on Darwin, where of course
362	it's completely useless). For this reason it's not being "autodetected"	515	it's completely useless). Unlike epoll, however, whose brokenness
		516	is by design, these kqueue bugs can (and eventually will) be fixed
		517	without API changes to existing programs. For this reason it's not being
363	unless you explicitly specify it explicitly in the flags (i.e. using	518	"auto-detected" unless you explicitly specify it in the flags (i.e. using
364	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	519	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
365	system like NetBSD.	520	system like NetBSD.
366		521
367	You still can embed kqueue into a normal poll or select backend and use it	522	You still can embed kqueue into a normal poll or select backend and use it
368	only for sockets (after having made sure that sockets work with kqueue on	523	only for sockets (after having made sure that sockets work with kqueue on
369	the target platform). See C<ev_embed> watchers for more info.	524	the target platform). See C<ev_embed> watchers for more info.
370		525
371	It scales in the same way as the epoll backend, but the interface to the	526	It scales in the same way as the epoll backend, but the interface to the
372	kernel is more efficient (which says nothing about its actual speed, of	527	kernel is more efficient (which says nothing about its actual speed, of
373	course). While stopping, setting and starting an I/O watcher does never	528	course). While stopping, setting and starting an I/O watcher does never
374	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	529	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
375	two event changes per incident, support for C<fork ()> is very bad and it	530	two event changes per incident. Support for C<fork ()> is very bad (but
376	drops fds silently in similarly hard-to-detect cases.	531	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		532	cases
377		533
378	This backend usually performs well under most conditions.	534	This backend usually performs well under most conditions.
379		535
380	While nominally embeddable in other event loops, this doesn't work	536	While nominally embeddable in other event loops, this doesn't work
381	everywhere, so you might need to test for this. And since it is broken	537	everywhere, so you might need to test for this. And since it is broken
382	almost everywhere, you should only use it when you have a lot of sockets	538	almost everywhere, you should only use it when you have a lot of sockets
383	(for which it usually works), by embedding it into another event loop	539	(for which it usually works), by embedding it into another event loop
384	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	540	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
385	sockets.	541	also broken on OS X)) and, did I mention it, using it only for sockets.
		542
		543	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		544	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		545	C<NOTE_EOF>.
386		546
387	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	547	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
388		548
389	This is not implemented yet (and might never be, unless you send me an	549	This is not implemented yet (and might never be, unless you send me an
390	implementation). According to reports, C</dev/poll> only supports sockets	550	implementation). According to reports, C</dev/poll> only supports sockets
…		…
394	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	554	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
395		555
396	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	556	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
397	it's really slow, but it still scales very well (O(active_fds)).	557	it's really slow, but it still scales very well (O(active_fds)).
398		558
399	Please note that solaris event ports can deliver a lot of spurious	559	Please note that Solaris event ports can deliver a lot of spurious
400	notifications, so you need to use non-blocking I/O or other means to avoid	560	notifications, so you need to use non-blocking I/O or other means to avoid
401	blocking when no data (or space) is available.	561	blocking when no data (or space) is available.
402		562
403	While this backend scales well, it requires one system call per active	563	While this backend scales well, it requires one system call per active
404	file descriptor per loop iteration. For small and medium numbers of file	564	file descriptor per loop iteration. For small and medium numbers of file
405	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	565	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
406	might perform better.	566	might perform better.
407		567
		568	On the positive side, with the exception of the spurious readiness
		569	notifications, this backend actually performed fully to specification
		570	in all tests and is fully embeddable, which is a rare feat among the
		571	OS-specific backends (I vastly prefer correctness over speed hacks).
		572
		573	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		574	C<EVBACKEND_POLL>.
		575
408	=item C<EVBACKEND_ALL>	576	=item C<EVBACKEND_ALL>
409		577
410	Try all backends (even potentially broken ones that wouldn't be tried	578	Try all backends (even potentially broken ones that wouldn't be tried
411	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	579	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
412	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	580	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
413		581
414	It is definitely not recommended to use this flag.	582	It is definitely not recommended to use this flag.
415		583
416	=back	584	=back
417		585
418	If one or more of these are ored into the flags value, then only these	586	If one or more of the backend flags are or'ed into the flags value,
419	backends will be tried (in the reverse order as given here). If none are	587	then only these backends will be tried (in the reverse order as listed
420	specified, most compiled-in backend will be tried, usually in reverse	588	here). If none are specified, all backends in C<ev_recommended_backends
421	order of their flag values :)	589	()> will be tried.
422
423	The most typical usage is like this:
424
425	if (!ev_default_loop (0))
426	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
427
428	Restrict libev to the select and poll backends, and do not allow
429	environment settings to be taken into account:
430
431	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
432
433	Use whatever libev has to offer, but make sure that kqueue is used if
434	available (warning, breaks stuff, best use only with your own private
435	event loop and only if you know the OS supports your types of fds):
436
437	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
438
439	=item struct ev_loop *ev_loop_new (unsigned int flags)
440
441	Similar to C<ev_default_loop>, but always creates a new event loop that is
442	always distinct from the default loop. Unlike the default loop, it cannot
443	handle signal and child watchers, and attempts to do so will be greeted by
444	undefined behaviour (or a failed assertion if assertions are enabled).
445		590
446	Example: Try to create a event loop that uses epoll and nothing else.	591	Example: Try to create a event loop that uses epoll and nothing else.
447		592
448	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	593	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
449	if (!epoller)	594	if (!epoller)
450	fatal ("no epoll found here, maybe it hides under your chair");	595	fatal ("no epoll found here, maybe it hides under your chair");
451		596
		597	Example: Use whatever libev has to offer, but make sure that kqueue is
		598	used if available.
		599
		600	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		601
452	=item ev_default_destroy ()	602	=item ev_loop_destroy (loop)
453		603
454	Destroys the default loop again (frees all memory and kernel state	604	Destroys an event loop object (frees all memory and kernel state
455	etc.). None of the active event watchers will be stopped in the normal	605	etc.). None of the active event watchers will be stopped in the normal
456	sense, so e.g. C<ev_is_active> might still return true. It is your	606	sense, so e.g. C<ev_is_active> might still return true. It is your
457	responsibility to either stop all watchers cleanly yoursef I<before>	607	responsibility to either stop all watchers cleanly yourself I<before>
458	calling this function, or cope with the fact afterwards (which is usually	608	calling this function, or cope with the fact afterwards (which is usually
459	the easiest thing, you can just ignore the watchers and/or C<free ()> them	609	the easiest thing, you can just ignore the watchers and/or C<free ()> them
460	for example).	610	for example).
461		611
462	Note that certain global state, such as signal state, will not be freed by	612	Note that certain global state, such as signal state (and installed signal
463	this function, and related watchers (such as signal and child watchers)	613	handlers), will not be freed by this function, and related watchers (such
464	would need to be stopped manually.	614	as signal and child watchers) would need to be stopped manually.
465		615
466	In general it is not advisable to call this function except in the	616	This function is normally used on loop objects allocated by
467	rare occasion where you really need to free e.g. the signal handling	617	C<ev_loop_new>, but it can also be used on the default loop returned by
		618	C<ev_default_loop>, in which case it is not thread-safe.
		619
		620	Note that it is not advisable to call this function on the default loop
		621	except in the rare occasion where you really need to free it's resources.
468	pipe fds. If you need dynamically allocated loops it is better to use	622	If you need dynamically allocated loops it is better to use C<ev_loop_new>
469	C<ev_loop_new> and C<ev_loop_destroy>).	623	and C<ev_loop_destroy>.
470		624
471	=item ev_loop_destroy (loop)	625	=item ev_loop_fork (loop)
472		626
473	Like C<ev_default_destroy>, but destroys an event loop created by an	627	This function sets a flag that causes subsequent C<ev_run> iterations to
474	earlier call to C<ev_loop_new>.
475
476	=item ev_default_fork ()
477
478	This function reinitialises the kernel state for backends that have	628	reinitialise the kernel state for backends that have one. Despite the
479	one. Despite the name, you can call it anytime, but it makes most sense	629	name, you can call it anytime, but it makes most sense after forking, in
480	after forking, in either the parent or child process (or both, but that	630	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
481	again makes little sense).	631	child before resuming or calling C<ev_run>.
482		632
483	You I<must> call this function in the child process after forking if and	633	Again, you I<have> to call it on I<any> loop that you want to re-use after
484	only if you want to use the event library in both processes. If you just	634	a fork, I<even if you do not plan to use the loop in the parent>. This is
485	fork+exec, you don't have to call it.	635	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		636	during fork.
		637
		638	On the other hand, you only need to call this function in the child
		639	process if and only if you want to use the event loop in the child. If
		640	you just fork+exec or create a new loop in the child, you don't have to
		641	call it at all (in fact, C<epoll> is so badly broken that it makes a
		642	difference, but libev will usually detect this case on its own and do a
		643	costly reset of the backend).
486		644
487	The function itself is quite fast and it's usually not a problem to call	645	The function itself is quite fast and it's usually not a problem to call
488	it just in case after a fork. To make this easy, the function will fit in	646	it just in case after a fork.
489	quite nicely into a call to C<pthread_atfork>:
490		647
		648	Example: Automate calling C<ev_loop_fork> on the default loop when
		649	using pthreads.
		650
		651	static void
		652	post_fork_child (void)
		653	{
		654	ev_loop_fork (EV_DEFAULT);
		655	}
		656
		657	...
491	pthread_atfork (0, 0, ev_default_fork);	658	pthread_atfork (0, 0, post_fork_child);
492		659
493	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	660	=item int ev_is_default_loop (loop)
494	without calling this function, so if you force one of those backends you
495	do not need to care.
496		661
497	=item ev_loop_fork (loop)	662	Returns true when the given loop is, in fact, the default loop, and false
		663	otherwise.
498		664
499	Like C<ev_default_fork>, but acts on an event loop created by
500	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
501	after fork, and how you do this is entirely your own problem.
502
503	=item unsigned int ev_loop_count (loop)	665	=item unsigned int ev_iteration (loop)
504		666
505	Returns the count of loop iterations for the loop, which is identical to	667	Returns the current iteration count for the event loop, which is identical
506	the number of times libev did poll for new events. It starts at C<0> and	668	to the number of times libev did poll for new events. It starts at C<0>
507	happily wraps around with enough iterations.	669	and happily wraps around with enough iterations.
508		670
509	This value can sometimes be useful as a generation counter of sorts (it	671	This value can sometimes be useful as a generation counter of sorts (it
510	"ticks" the number of loop iterations), as it roughly corresponds with	672	"ticks" the number of loop iterations), as it roughly corresponds with
511	C<ev_prepare> and C<ev_check> calls.	673	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		674	prepare and check phases.
		675
		676	=item unsigned int ev_depth (loop)
		677
		678	Returns the number of times C<ev_run> was entered minus the number of
		679	times C<ev_run> was exited, in other words, the recursion depth.
		680
		681	Outside C<ev_run>, this number is zero. In a callback, this number is
		682	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		683	in which case it is higher.
		684
		685	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread
		686	etc.), doesn't count as "exit" - consider this as a hint to avoid such
		687	ungentleman-like behaviour unless it's really convenient.
512		688
513	=item unsigned int ev_backend (loop)	689	=item unsigned int ev_backend (loop)
514		690
515	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	691	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
516	use.	692	use.
…		…
521	received events and started processing them. This timestamp does not	697	received events and started processing them. This timestamp does not
522	change as long as callbacks are being processed, and this is also the base	698	change as long as callbacks are being processed, and this is also the base
523	time used for relative timers. You can treat it as the timestamp of the	699	time used for relative timers. You can treat it as the timestamp of the
524	event occurring (or more correctly, libev finding out about it).	700	event occurring (or more correctly, libev finding out about it).
525		701
		702	=item ev_now_update (loop)
		703
		704	Establishes the current time by querying the kernel, updating the time
		705	returned by C<ev_now ()> in the progress. This is a costly operation and
		706	is usually done automatically within C<ev_run ()>.
		707
		708	This function is rarely useful, but when some event callback runs for a
		709	very long time without entering the event loop, updating libev's idea of
		710	the current time is a good idea.
		711
		712	See also L<The special problem of time updates> in the C<ev_timer> section.
		713
		714	=item ev_suspend (loop)
		715
		716	=item ev_resume (loop)
		717
		718	These two functions suspend and resume an event loop, for use when the
		719	loop is not used for a while and timeouts should not be processed.
		720
		721	A typical use case would be an interactive program such as a game: When
		722	the user presses C<^Z> to suspend the game and resumes it an hour later it
		723	would be best to handle timeouts as if no time had actually passed while
		724	the program was suspended. This can be achieved by calling C<ev_suspend>
		725	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		726	C<ev_resume> directly afterwards to resume timer processing.
		727
		728	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		729	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		730	will be rescheduled (that is, they will lose any events that would have
		731	occurred while suspended).
		732
		733	After calling C<ev_suspend> you B<must not> call I<any> function on the
		734	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		735	without a previous call to C<ev_suspend>.
		736
		737	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		738	event loop time (see C<ev_now_update>).
		739
526	=item ev_loop (loop, int flags)	740	=item ev_run (loop, int flags)
527		741
528	Finally, this is it, the event handler. This function usually is called	742	Finally, this is it, the event handler. This function usually is called
529	after you initialised all your watchers and you want to start handling	743	after you have initialised all your watchers and you want to start
530	events.	744	handling events. It will ask the operating system for any new events, call
		745	the watcher callbacks, an then repeat the whole process indefinitely: This
		746	is why event loops are called I<loops>.
531		747
532	If the flags argument is specified as C<0>, it will not return until	748	If the flags argument is specified as C<0>, it will keep handling events
533	either no event watchers are active anymore or C<ev_unloop> was called.	749	until either no event watchers are active anymore or C<ev_break> was
		750	called.
534		751
535	Please note that an explicit C<ev_unloop> is usually better than	752	Please note that an explicit C<ev_break> is usually better than
536	relying on all watchers to be stopped when deciding when a program has	753	relying on all watchers to be stopped when deciding when a program has
537	finished (especially in interactive programs), but having a program that	754	finished (especially in interactive programs), but having a program
538	automatically loops as long as it has to and no longer by virtue of	755	that automatically loops as long as it has to and no longer by virtue
539	relying on its watchers stopping correctly is a thing of beauty.	756	of relying on its watchers stopping correctly, that is truly a thing of
		757	beauty.
540		758
541	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	759	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
542	those events and any outstanding ones, but will not block your process in	760	those events and any already outstanding ones, but will not wait and
543	case there are no events and will return after one iteration of the loop.	761	block your process in case there are no events and will return after one
		762	iteration of the loop. This is sometimes useful to poll and handle new
		763	events while doing lengthy calculations, to keep the program responsive.
544		764
545	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	765	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
546	neccessary) and will handle those and any outstanding ones. It will block	766	necessary) and will handle those and any already outstanding ones. It
547	your process until at least one new event arrives, and will return after	767	will block your process until at least one new event arrives (which could
548	one iteration of the loop. This is useful if you are waiting for some	768	be an event internal to libev itself, so there is no guarantee that a
549	external event in conjunction with something not expressible using other	769	user-registered callback will be called), and will return after one
		770	iteration of the loop.
		771
		772	This is useful if you are waiting for some external event in conjunction
		773	with something not expressible using other libev watchers (i.e. "roll your
550	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	774	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
551	usually a better approach for this kind of thing.	775	usually a better approach for this kind of thing.
552		776
553	Here are the gory details of what C<ev_loop> does:	777	Here are the gory details of what C<ev_run> does:
554		778
		779	- Increment loop depth.
		780	- Reset the ev_break status.
555	- Before the first iteration, call any pending watchers.	781	- Before the first iteration, call any pending watchers.
556	* If there are no active watchers (reference count is zero), return.	782	LOOP:
557	- Queue all prepare watchers and then call all outstanding watchers.	783	- If EVFLAG_FORKCHECK was used, check for a fork.
		784	- If a fork was detected (by any means), queue and call all fork watchers.
		785	- Queue and call all prepare watchers.
		786	- If ev_break was called, goto FINISH.
558	- If we have been forked, recreate the kernel state.	787	- If we have been forked, detach and recreate the kernel state
		788	as to not disturb the other process.
559	- Update the kernel state with all outstanding changes.	789	- Update the kernel state with all outstanding changes.
560	- Update the "event loop time".	790	- Update the "event loop time" (ev_now ()).
561	- Calculate for how long to block.	791	- Calculate for how long to sleep or block, if at all
		792	(active idle watchers, EVRUN_NOWAIT or not having
		793	any active watchers at all will result in not sleeping).
		794	- Sleep if the I/O and timer collect interval say so.
		795	- Increment loop iteration counter.
562	- Block the process, waiting for any events.	796	- Block the process, waiting for any events.
563	- Queue all outstanding I/O (fd) events.	797	- Queue all outstanding I/O (fd) events.
564	- Update the "event loop time" and do time jump handling.	798	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
565	- Queue all outstanding timers.	799	- Queue all expired timers.
566	- Queue all outstanding periodics.	800	- Queue all expired periodics.
567	- If no events are pending now, queue all idle watchers.	801	- Queue all idle watchers with priority higher than that of pending events.
568	- Queue all check watchers.	802	- Queue all check watchers.
569	- Call all queued watchers in reverse order (i.e. check watchers first).	803	- Call all queued watchers in reverse order (i.e. check watchers first).
570	Signals and child watchers are implemented as I/O watchers, and will	804	Signals and child watchers are implemented as I/O watchers, and will
571	be handled here by queueing them when their watcher gets executed.	805	be handled here by queueing them when their watcher gets executed.
572	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	806	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
573	were used, return, otherwise continue with step *.	807	were used, or there are no active watchers, goto FINISH, otherwise
		808	continue with step LOOP.
		809	FINISH:
		810	- Reset the ev_break status iff it was EVBREAK_ONE.
		811	- Decrement the loop depth.
		812	- Return.
574		813
575	Example: Queue some jobs and then loop until no events are outsanding	814	Example: Queue some jobs and then loop until no events are outstanding
576	anymore.	815	anymore.
577		816
578	... queue jobs here, make sure they register event watchers as long	817	... queue jobs here, make sure they register event watchers as long
579	... as they still have work to do (even an idle watcher will do..)	818	... as they still have work to do (even an idle watcher will do..)
580	ev_loop (my_loop, 0);	819	ev_run (my_loop, 0);
581	... jobs done. yeah!	820	... jobs done or somebody called unloop. yeah!
582		821
583	=item ev_unloop (loop, how)	822	=item ev_break (loop, how)
584		823
585	Can be used to make a call to C<ev_loop> return early (but only after it	824	Can be used to make a call to C<ev_run> return early (but only after it
586	has processed all outstanding events). The C<how> argument must be either	825	has processed all outstanding events). The C<how> argument must be either
587	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	826	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
588	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	827	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		828
		829	This "break state" will be cleared when entering C<ev_run> again.
		830
		831	It is safe to call C<ev_break> from outside any C<ev_run> calls, too.
589		832
590	=item ev_ref (loop)	833	=item ev_ref (loop)
591		834
592	=item ev_unref (loop)	835	=item ev_unref (loop)
593		836
594	Ref/unref can be used to add or remove a reference count on the event	837	Ref/unref can be used to add or remove a reference count on the event
595	loop: Every watcher keeps one reference, and as long as the reference	838	loop: Every watcher keeps one reference, and as long as the reference
596	count is nonzero, C<ev_loop> will not return on its own. If you have	839	count is nonzero, C<ev_run> will not return on its own.
597	a watcher you never unregister that should not keep C<ev_loop> from	840
598	returning, ev_unref() after starting, and ev_ref() before stopping it. For	841	This is useful when you have a watcher that you never intend to
		842	unregister, but that nevertheless should not keep C<ev_run> from
		843	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		844	before stopping it.
		845
599	example, libev itself uses this for its internal signal pipe: It is not	846	As an example, libev itself uses this for its internal signal pipe: It
600	visible to the libev user and should not keep C<ev_loop> from exiting if	847	is not visible to the libev user and should not keep C<ev_run> from
601	no event watchers registered by it are active. It is also an excellent	848	exiting if no event watchers registered by it are active. It is also an
602	way to do this for generic recurring timers or from within third-party	849	excellent way to do this for generic recurring timers or from within
603	libraries. Just remember to I<unref after start> and I<ref before stop>.	850	third-party libraries. Just remember to I<unref after start> and I<ref
		851	before stop> (but only if the watcher wasn't active before, or was active
		852	before, respectively. Note also that libev might stop watchers itself
		853	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		854	in the callback).
604		855
605	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	856	Example: Create a signal watcher, but keep it from keeping C<ev_run>
606	running when nothing else is active.	857	running when nothing else is active.
607		858
608	struct ev_signal exitsig;	859	ev_signal exitsig;
609	ev_signal_init (&exitsig, sig_cb, SIGINT);	860	ev_signal_init (&exitsig, sig_cb, SIGINT);
610	ev_signal_start (loop, &exitsig);	861	ev_signal_start (loop, &exitsig);
611	evf_unref (loop);	862	evf_unref (loop);
612		863
613	Example: For some weird reason, unregister the above signal handler again.	864	Example: For some weird reason, unregister the above signal handler again.
614		865
615	ev_ref (loop);	866	ev_ref (loop);
616	ev_signal_stop (loop, &exitsig);	867	ev_signal_stop (loop, &exitsig);
617		868
618	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	869	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
619		870
620	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	871	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
621		872
622	These advanced functions influence the time that libev will spend waiting	873	These advanced functions influence the time that libev will spend waiting
623	for events. Both are by default C<0>, meaning that libev will try to	874	for events. Both time intervals are by default C<0>, meaning that libev
624	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	875	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		876	latency.
625		877
626	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	878	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
627	allows libev to delay invocation of I/O and timer/periodic callbacks to	879	allows libev to delay invocation of I/O and timer/periodic callbacks
628	increase efficiency of loop iterations.	880	to increase efficiency of loop iterations (or to increase power-saving
		881	opportunities).
629		882
630	The background is that sometimes your program runs just fast enough to	883	The idea is that sometimes your program runs just fast enough to handle
631	handle one (or very few) event(s) per loop iteration. While this makes	884	one (or very few) event(s) per loop iteration. While this makes the
632	the program responsive, it also wastes a lot of CPU time to poll for new	885	program responsive, it also wastes a lot of CPU time to poll for new
633	events, especially with backends like C<select ()> which have a high	886	events, especially with backends like C<select ()> which have a high
634	overhead for the actual polling but can deliver many events at once.	887	overhead for the actual polling but can deliver many events at once.
635		888
636	By setting a higher I<io collect interval> you allow libev to spend more	889	By setting a higher I<io collect interval> you allow libev to spend more
637	time collecting I/O events, so you can handle more events per iteration,	890	time collecting I/O events, so you can handle more events per iteration,
638	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	891	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
639	C<ev_timer>) will be not affected. Setting this to a non-null value will	892	C<ev_timer>) will be not affected. Setting this to a non-null value will
640	introduce an additional C<ev_sleep ()> call into most loop iterations.	893	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		894	sleep time ensures that libev will not poll for I/O events more often then
		895	once per this interval, on average.
641		896
642	Likewise, by setting a higher I<timeout collect interval> you allow libev	897	Likewise, by setting a higher I<timeout collect interval> you allow libev
643	to spend more time collecting timeouts, at the expense of increased	898	to spend more time collecting timeouts, at the expense of increased
644	latency (the watcher callback will be called later). C<ev_io> watchers	899	latency/jitter/inexactness (the watcher callback will be called
645	will not be affected. Setting this to a non-null value will not introduce	900	later). C<ev_io> watchers will not be affected. Setting this to a non-null
646	any overhead in libev.	901	value will not introduce any overhead in libev.
647		902
648	Many (busy) programs can usually benefit by setting the io collect	903	Many (busy) programs can usually benefit by setting the I/O collect
649	interval to a value near C<0.1> or so, which is often enough for	904	interval to a value near C<0.1> or so, which is often enough for
650	interactive servers (of course not for games), likewise for timeouts. It	905	interactive servers (of course not for games), likewise for timeouts. It
651	usually doesn't make much sense to set it to a lower value than C<0.01>,	906	usually doesn't make much sense to set it to a lower value than C<0.01>,
652	as this approsaches the timing granularity of most systems.	907	as this approaches the timing granularity of most systems. Note that if
		908	you do transactions with the outside world and you can't increase the
		909	parallelity, then this setting will limit your transaction rate (if you
		910	need to poll once per transaction and the I/O collect interval is 0.01,
		911	then you can't do more than 100 transactions per second).
		912
		913	Setting the I<timeout collect interval> can improve the opportunity for
		914	saving power, as the program will "bundle" timer callback invocations that
		915	are "near" in time together, by delaying some, thus reducing the number of
		916	times the process sleeps and wakes up again. Another useful technique to
		917	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		918	they fire on, say, one-second boundaries only.
		919
		920	Example: we only need 0.1s timeout granularity, and we wish not to poll
		921	more often than 100 times per second:
		922
		923	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		924	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		925
		926	=item ev_invoke_pending (loop)
		927
		928	This call will simply invoke all pending watchers while resetting their
		929	pending state. Normally, C<ev_run> does this automatically when required,
		930	but when overriding the invoke callback this call comes handy. This
		931	function can be invoked from a watcher - this can be useful for example
		932	when you want to do some lengthy calculation and want to pass further
		933	event handling to another thread (you still have to make sure only one
		934	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		935
		936	=item int ev_pending_count (loop)
		937
		938	Returns the number of pending watchers - zero indicates that no watchers
		939	are pending.
		940
		941	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		942
		943	This overrides the invoke pending functionality of the loop: Instead of
		944	invoking all pending watchers when there are any, C<ev_run> will call
		945	this callback instead. This is useful, for example, when you want to
		946	invoke the actual watchers inside another context (another thread etc.).
		947
		948	If you want to reset the callback, use C<ev_invoke_pending> as new
		949	callback.
		950
		951	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		952
		953	Sometimes you want to share the same loop between multiple threads. This
		954	can be done relatively simply by putting mutex_lock/unlock calls around
		955	each call to a libev function.
		956
		957	However, C<ev_run> can run an indefinite time, so it is not feasible
		958	to wait for it to return. One way around this is to wake up the event
		959	loop via C<ev_break> and C<av_async_send>, another way is to set these
		960	I<release> and I<acquire> callbacks on the loop.
		961
		962	When set, then C<release> will be called just before the thread is
		963	suspended waiting for new events, and C<acquire> is called just
		964	afterwards.
		965
		966	Ideally, C<release> will just call your mutex_unlock function, and
		967	C<acquire> will just call the mutex_lock function again.
		968
		969	While event loop modifications are allowed between invocations of
		970	C<release> and C<acquire> (that's their only purpose after all), no
		971	modifications done will affect the event loop, i.e. adding watchers will
		972	have no effect on the set of file descriptors being watched, or the time
		973	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		974	to take note of any changes you made.
		975
		976	In theory, threads executing C<ev_run> will be async-cancel safe between
		977	invocations of C<release> and C<acquire>.
		978
		979	See also the locking example in the C<THREADS> section later in this
		980	document.
		981
		982	=item ev_set_userdata (loop, void *data)
		983
		984	=item ev_userdata (loop)
		985
		986	Set and retrieve a single C<void *> associated with a loop. When
		987	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		988	C<0.>
		989
		990	These two functions can be used to associate arbitrary data with a loop,
		991	and are intended solely for the C<invoke_pending_cb>, C<release> and
		992	C<acquire> callbacks described above, but of course can be (ab-)used for
		993	any other purpose as well.
		994
		995	=item ev_verify (loop)
		996
		997	This function only does something when C<EV_VERIFY> support has been
		998	compiled in, which is the default for non-minimal builds. It tries to go
		999	through all internal structures and checks them for validity. If anything
		1000	is found to be inconsistent, it will print an error message to standard
		1001	error and call C<abort ()>.
		1002
		1003	This can be used to catch bugs inside libev itself: under normal
		1004	circumstances, this function will never abort as of course libev keeps its
		1005	data structures consistent.
653		1006
654	=back	1007	=back
655		1008
656		1009
657	=head1 ANATOMY OF A WATCHER	1010	=head1 ANATOMY OF A WATCHER
658		1011
		1012	In the following description, uppercase C<TYPE> in names stands for the
		1013	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1014	watchers and C<ev_io_start> for I/O watchers.
		1015
659	A watcher is a structure that you create and register to record your	1016	A watcher is an opaque structure that you allocate and register to record
660	interest in some event. For instance, if you want to wait for STDIN to	1017	your interest in some event. To make a concrete example, imagine you want
661	become readable, you would create an C<ev_io> watcher for that:	1018	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1019	for that:
662		1020
663	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1021	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
664	{	1022	{
665	ev_io_stop (w);	1023	ev_io_stop (w);
666	ev_unloop (loop, EVUNLOOP_ALL);	1024	ev_break (loop, EVBREAK_ALL);
667	}	1025	}
668		1026
669	struct ev_loop *loop = ev_default_loop (0);	1027	struct ev_loop *loop = ev_default_loop (0);
		1028
670	struct ev_io stdin_watcher;	1029	ev_io stdin_watcher;
		1030
671	ev_init (&stdin_watcher, my_cb);	1031	ev_init (&stdin_watcher, my_cb);
672	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1032	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
673	ev_io_start (loop, &stdin_watcher);	1033	ev_io_start (loop, &stdin_watcher);
		1034
674	ev_loop (loop, 0);	1035	ev_run (loop, 0);
675		1036
676	As you can see, you are responsible for allocating the memory for your	1037	As you can see, you are responsible for allocating the memory for your
677	watcher structures (and it is usually a bad idea to do this on the stack,	1038	watcher structures (and it is I<usually> a bad idea to do this on the
678	although this can sometimes be quite valid).	1039	stack).
679		1040
		1041	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1042	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1043
680	Each watcher structure must be initialised by a call to C<ev_init	1044	Each watcher structure must be initialised by a call to C<ev_init (watcher
681	(watcher *, callback)>, which expects a callback to be provided. This	1045	*, callback)>, which expects a callback to be provided. This callback is
682	callback gets invoked each time the event occurs (or, in the case of io	1046	invoked each time the event occurs (or, in the case of I/O watchers, each
683	watchers, each time the event loop detects that the file descriptor given	1047	time the event loop detects that the file descriptor given is readable
684	is readable and/or writable).	1048	and/or writable).
685		1049
686	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1050	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
687	with arguments specific to this watcher type. There is also a macro	1051	macro to configure it, with arguments specific to the watcher type. There
688	to combine initialisation and setting in one call: C<< ev_<type>_init	1052	is also a macro to combine initialisation and setting in one call: C<<
689	(watcher *, callback, ...) >>.	1053	ev_TYPE_init (watcher *, callback, ...) >>.
690		1054
691	To make the watcher actually watch out for events, you have to start it	1055	To make the watcher actually watch out for events, you have to start it
692	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1056	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
693	*) >>), and you can stop watching for events at any time by calling the	1057	*) >>), and you can stop watching for events at any time by calling the
694	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1058	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
695		1059
696	As long as your watcher is active (has been started but not stopped) you	1060	As long as your watcher is active (has been started but not stopped) you
697	must not touch the values stored in it. Most specifically you must never	1061	must not touch the values stored in it. Most specifically you must never
698	reinitialise it or call its C<set> macro.	1062	reinitialise it or call its C<ev_TYPE_set> macro.
699		1063
700	Each and every callback receives the event loop pointer as first, the	1064	Each and every callback receives the event loop pointer as first, the
701	registered watcher structure as second, and a bitset of received events as	1065	registered watcher structure as second, and a bitset of received events as
702	third argument.	1066	third argument.
703		1067
…		…
712	=item C<EV_WRITE>	1076	=item C<EV_WRITE>
713		1077
714	The file descriptor in the C<ev_io> watcher has become readable and/or	1078	The file descriptor in the C<ev_io> watcher has become readable and/or
715	writable.	1079	writable.
716		1080
717	=item C<EV_TIMEOUT>	1081	=item C<EV_TIMER>
718		1082
719	The C<ev_timer> watcher has timed out.	1083	The C<ev_timer> watcher has timed out.
720		1084
721	=item C<EV_PERIODIC>	1085	=item C<EV_PERIODIC>
722		1086
…		…
740		1104
741	=item C<EV_PREPARE>	1105	=item C<EV_PREPARE>
742		1106
743	=item C<EV_CHECK>	1107	=item C<EV_CHECK>
744		1108
745	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1109	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
746	to gather new events, and all C<ev_check> watchers are invoked just after	1110	to gather new events, and all C<ev_check> watchers are invoked just after
747	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1111	C<ev_run> has gathered them, but before it invokes any callbacks for any
748	received events. Callbacks of both watcher types can start and stop as	1112	received events. Callbacks of both watcher types can start and stop as
749	many watchers as they want, and all of them will be taken into account	1113	many watchers as they want, and all of them will be taken into account
750	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1114	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
751	C<ev_loop> from blocking).	1115	C<ev_run> from blocking).
752		1116
753	=item C<EV_EMBED>	1117	=item C<EV_EMBED>
754		1118
755	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1119	The embedded event loop specified in the C<ev_embed> watcher needs attention.
756		1120
757	=item C<EV_FORK>	1121	=item C<EV_FORK>
758		1122
759	The event loop has been resumed in the child process after fork (see	1123	The event loop has been resumed in the child process after fork (see
760	C<ev_fork>).	1124	C<ev_fork>).
761		1125
		1126	=item C<EV_CLEANUP>
		1127
		1128	The event loop is about to be destroyed (see C<ev_cleanup>).
		1129
		1130	=item C<EV_ASYNC>
		1131
		1132	The given async watcher has been asynchronously notified (see C<ev_async>).
		1133
		1134	=item C<EV_CUSTOM>
		1135
		1136	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1137	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1138
762	=item C<EV_ERROR>	1139	=item C<EV_ERROR>
763		1140
764	An unspecified error has occured, the watcher has been stopped. This might	1141	An unspecified error has occurred, the watcher has been stopped. This might
765	happen because the watcher could not be properly started because libev	1142	happen because the watcher could not be properly started because libev
766	ran out of memory, a file descriptor was found to be closed or any other	1143	ran out of memory, a file descriptor was found to be closed or any other
		1144	problem. Libev considers these application bugs.
		1145
767	problem. You best act on it by reporting the problem and somehow coping	1146	You best act on it by reporting the problem and somehow coping with the
768	with the watcher being stopped.	1147	watcher being stopped. Note that well-written programs should not receive
		1148	an error ever, so when your watcher receives it, this usually indicates a
		1149	bug in your program.
769		1150
770	Libev will usually signal a few "dummy" events together with an error,	1151	Libev will usually signal a few "dummy" events together with an error, for
771	for example it might indicate that a fd is readable or writable, and if	1152	example it might indicate that a fd is readable or writable, and if your
772	your callbacks is well-written it can just attempt the operation and cope	1153	callbacks is well-written it can just attempt the operation and cope with
773	with the error from read() or write(). This will not work in multithreaded	1154	the error from read() or write(). This will not work in multi-threaded
774	programs, though, so beware.	1155	programs, though, as the fd could already be closed and reused for another
		1156	thing, so beware.
775		1157
776	=back	1158	=back
777		1159
778	=head2 GENERIC WATCHER FUNCTIONS	1160	=head2 GENERIC WATCHER FUNCTIONS
779
780	In the following description, C<TYPE> stands for the watcher type,
781	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
782		1161
783	=over 4	1162	=over 4
784		1163
785	=item C<ev_init> (ev_TYPE *watcher, callback)	1164	=item C<ev_init> (ev_TYPE *watcher, callback)
786		1165
…		…
792	which rolls both calls into one.	1171	which rolls both calls into one.
793		1172
794	You can reinitialise a watcher at any time as long as it has been stopped	1173	You can reinitialise a watcher at any time as long as it has been stopped
795	(or never started) and there are no pending events outstanding.	1174	(or never started) and there are no pending events outstanding.
796		1175
797	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1176	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
798	int revents)>.	1177	int revents)>.
799		1178
		1179	Example: Initialise an C<ev_io> watcher in two steps.
		1180
		1181	ev_io w;
		1182	ev_init (&w, my_cb);
		1183	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1184
800	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1185	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
801		1186
802	This macro initialises the type-specific parts of a watcher. You need to	1187	This macro initialises the type-specific parts of a watcher. You need to
803	call C<ev_init> at least once before you call this macro, but you can	1188	call C<ev_init> at least once before you call this macro, but you can
804	call C<ev_TYPE_set> any number of times. You must not, however, call this	1189	call C<ev_TYPE_set> any number of times. You must not, however, call this
805	macro on a watcher that is active (it can be pending, however, which is a	1190	macro on a watcher that is active (it can be pending, however, which is a
806	difference to the C<ev_init> macro).	1191	difference to the C<ev_init> macro).
807		1192
808	Although some watcher types do not have type-specific arguments	1193	Although some watcher types do not have type-specific arguments
809	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1194	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
810		1195
		1196	See C<ev_init>, above, for an example.
		1197
811	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1198	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
812		1199
813	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1200	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
814	calls into a single call. This is the most convinient method to initialise	1201	calls into a single call. This is the most convenient method to initialise
815	a watcher. The same limitations apply, of course.	1202	a watcher. The same limitations apply, of course.
816		1203
		1204	Example: Initialise and set an C<ev_io> watcher in one step.
		1205
		1206	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1207
817	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1208	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
818		1209
819	Starts (activates) the given watcher. Only active watchers will receive	1210	Starts (activates) the given watcher. Only active watchers will receive
820	events. If the watcher is already active nothing will happen.	1211	events. If the watcher is already active nothing will happen.
821		1212
		1213	Example: Start the C<ev_io> watcher that is being abused as example in this
		1214	whole section.
		1215
		1216	ev_io_start (EV_DEFAULT_UC, &w);
		1217
822	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1218	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
823		1219
824	Stops the given watcher again (if active) and clears the pending	1220	Stops the given watcher if active, and clears the pending status (whether
		1221	the watcher was active or not).
		1222
825	status. It is possible that stopped watchers are pending (for example,	1223	It is possible that stopped watchers are pending - for example,
826	non-repeating timers are being stopped when they become pending), but	1224	non-repeating timers are being stopped when they become pending - but
827	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1225	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
828	you want to free or reuse the memory used by the watcher it is therefore a	1226	pending. If you want to free or reuse the memory used by the watcher it is
829	good idea to always call its C<ev_TYPE_stop> function.	1227	therefore a good idea to always call its C<ev_TYPE_stop> function.
830		1228
831	=item bool ev_is_active (ev_TYPE *watcher)	1229	=item bool ev_is_active (ev_TYPE *watcher)
832		1230
833	Returns a true value iff the watcher is active (i.e. it has been started	1231	Returns a true value iff the watcher is active (i.e. it has been started
834	and not yet been stopped). As long as a watcher is active you must not modify	1232	and not yet been stopped). As long as a watcher is active you must not modify
…		…
850	=item ev_cb_set (ev_TYPE *watcher, callback)	1248	=item ev_cb_set (ev_TYPE *watcher, callback)
851		1249
852	Change the callback. You can change the callback at virtually any time	1250	Change the callback. You can change the callback at virtually any time
853	(modulo threads).	1251	(modulo threads).
854		1252
855	=item ev_set_priority (ev_TYPE *watcher, priority)	1253	=item ev_set_priority (ev_TYPE *watcher, int priority)
856		1254
857	=item int ev_priority (ev_TYPE *watcher)	1255	=item int ev_priority (ev_TYPE *watcher)
858		1256
859	Set and query the priority of the watcher. The priority is a small	1257	Set and query the priority of the watcher. The priority is a small
860	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1258	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
861	(default: C<-2>). Pending watchers with higher priority will be invoked	1259	(default: C<-2>). Pending watchers with higher priority will be invoked
862	before watchers with lower priority, but priority will not keep watchers	1260	before watchers with lower priority, but priority will not keep watchers
863	from being executed (except for C<ev_idle> watchers).	1261	from being executed (except for C<ev_idle> watchers).
864		1262
865	This means that priorities are I<only> used for ordering callback
866	invocation after new events have been received. This is useful, for
867	example, to reduce latency after idling, or more often, to bind two
868	watchers on the same event and make sure one is called first.
869
870	If you need to suppress invocation when higher priority events are pending	1263	If you need to suppress invocation when higher priority events are pending
871	you need to look at C<ev_idle> watchers, which provide this functionality.	1264	you need to look at C<ev_idle> watchers, which provide this functionality.
872		1265
873	You I<must not> change the priority of a watcher as long as it is active or	1266	You I<must not> change the priority of a watcher as long as it is active or
874	pending.	1267	pending.
875		1268
		1269	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1270	fine, as long as you do not mind that the priority value you query might
		1271	or might not have been clamped to the valid range.
		1272
876	The default priority used by watchers when no priority has been set is	1273	The default priority used by watchers when no priority has been set is
877	always C<0>, which is supposed to not be too high and not be too low :).	1274	always C<0>, which is supposed to not be too high and not be too low :).
878		1275
879	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1276	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
880	fine, as long as you do not mind that the priority value you query might	1277	priorities.
881	or might not have been adjusted to be within valid range.
882		1278
883	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1279	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
884		1280
885	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1281	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
886	C<loop> nor C<revents> need to be valid as long as the watcher callback	1282	C<loop> nor C<revents> need to be valid as long as the watcher callback
887	can deal with that fact.	1283	can deal with that fact, as both are simply passed through to the
		1284	callback.
888		1285
889	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1286	=item int ev_clear_pending (loop, ev_TYPE *watcher)
890		1287
891	If the watcher is pending, this function returns clears its pending status	1288	If the watcher is pending, this function clears its pending status and
892	and returns its C<revents> bitset (as if its callback was invoked). If the	1289	returns its C<revents> bitset (as if its callback was invoked). If the
893	watcher isn't pending it does nothing and returns C<0>.	1290	watcher isn't pending it does nothing and returns C<0>.
894		1291
		1292	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1293	callback to be invoked, which can be accomplished with this function.
		1294
		1295	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1296
		1297	Feeds the given event set into the event loop, as if the specified event
		1298	had happened for the specified watcher (which must be a pointer to an
		1299	initialised but not necessarily started event watcher). Obviously you must
		1300	not free the watcher as long as it has pending events.
		1301
		1302	Stopping the watcher, letting libev invoke it, or calling
		1303	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1304	not started in the first place.
		1305
		1306	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1307	functions that do not need a watcher.
		1308
895	=back	1309	=back
896		1310
897
898	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1311	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
899		1312
900	Each watcher has, by default, a member C<void *data> that you can change	1313	Each watcher has, by default, a member C<void *data> that you can change
901	and read at any time, libev will completely ignore it. This can be used	1314	and read at any time: libev will completely ignore it. This can be used
902	to associate arbitrary data with your watcher. If you need more data and	1315	to associate arbitrary data with your watcher. If you need more data and
903	don't want to allocate memory and store a pointer to it in that data	1316	don't want to allocate memory and store a pointer to it in that data
904	member, you can also "subclass" the watcher type and provide your own	1317	member, you can also "subclass" the watcher type and provide your own
905	data:	1318	data:
906		1319
907	struct my_io	1320	struct my_io
908	{	1321	{
909	struct ev_io io;	1322	ev_io io;
910	int otherfd;	1323	int otherfd;
911	void *somedata;	1324	void *somedata;
912	struct whatever *mostinteresting;	1325	struct whatever *mostinteresting;
913	}	1326	};
		1327
		1328	...
		1329	struct my_io w;
		1330	ev_io_init (&w.io, my_cb, fd, EV_READ);
914		1331
915	And since your callback will be called with a pointer to the watcher, you	1332	And since your callback will be called with a pointer to the watcher, you
916	can cast it back to your own type:	1333	can cast it back to your own type:
917		1334
918	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1335	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
919	{	1336	{
920	struct my_io *w = (struct my_io *)w_;	1337	struct my_io *w = (struct my_io *)w_;
921	...	1338	...
922	}	1339	}
923		1340
924	More interesting and less C-conformant ways of casting your callback type	1341	More interesting and less C-conformant ways of casting your callback type
925	instead have been omitted.	1342	instead have been omitted.
926		1343
927	Another common scenario is having some data structure with multiple	1344	Another common scenario is to use some data structure with multiple
928	watchers:	1345	embedded watchers:
929		1346
930	struct my_biggy	1347	struct my_biggy
931	{	1348	{
932	int some_data;	1349	int some_data;
933	ev_timer t1;	1350	ev_timer t1;
934	ev_timer t2;	1351	ev_timer t2;
935	}	1352	}
936		1353
937	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1354	In this case getting the pointer to C<my_biggy> is a bit more
938	you need to use C<offsetof>:	1355	complicated: Either you store the address of your C<my_biggy> struct
		1356	in the C<data> member of the watcher (for woozies), or you need to use
		1357	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1358	programmers):
939		1359
940	#include <stddef.h>	1360	#include <stddef.h>
941		1361
942	static void	1362	static void
943	t1_cb (EV_P_ struct ev_timer *w, int revents)	1363	t1_cb (EV_P_ ev_timer *w, int revents)
944	{	1364	{
945	struct my_biggy big = (struct my_biggy *	1365	struct my_biggy big = (struct my_biggy *)
946	(((char *)w) - offsetof (struct my_biggy, t1));	1366	(((char *)w) - offsetof (struct my_biggy, t1));
947	}	1367	}
948		1368
949	static void	1369	static void
950	t2_cb (EV_P_ struct ev_timer *w, int revents)	1370	t2_cb (EV_P_ ev_timer *w, int revents)
951	{	1371	{
952	struct my_biggy big = (struct my_biggy *	1372	struct my_biggy big = (struct my_biggy *)
953	(((char *)w) - offsetof (struct my_biggy, t2));	1373	(((char *)w) - offsetof (struct my_biggy, t2));
954	}	1374	}
		1375
		1376	=head2 WATCHER STATES
		1377
		1378	There are various watcher states mentioned throughout this manual -
		1379	active, pending and so on. In this section these states and the rules to
		1380	transition between them will be described in more detail - and while these
		1381	rules might look complicated, they usually do "the right thing".
		1382
		1383	=over 4
		1384
		1385	=item initialiased
		1386
		1387	Before a watcher can be registered with the event looop it has to be
		1388	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1389	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1390
		1391	In this state it is simply some block of memory that is suitable for use
		1392	in an event loop. It can be moved around, freed, reused etc. at will.
		1393
		1394	=item started/running/active
		1395
		1396	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1397	property of the event loop, and is actively waiting for events. While in
		1398	this state it cannot be accessed (except in a few documented ways), moved,
		1399	freed or anything else - the only legal thing is to keep a pointer to it,
		1400	and call libev functions on it that are documented to work on active watchers.
		1401
		1402	=item pending
		1403
		1404	If a watcher is active and libev determines that an event it is interested
		1405	in has occurred (such as a timer expiring), it will become pending. It will
		1406	stay in this pending state until either it is stopped or its callback is
		1407	about to be invoked, so it is not normally pending inside the watcher
		1408	callback.
		1409
		1410	The watcher might or might not be active while it is pending (for example,
		1411	an expired non-repeating timer can be pending but no longer active). If it
		1412	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1413	but it is still property of the event loop at this time, so cannot be
		1414	moved, freed or reused. And if it is active the rules described in the
		1415	previous item still apply.
		1416
		1417	It is also possible to feed an event on a watcher that is not active (e.g.
		1418	via C<ev_feed_event>), in which case it becomes pending without being
		1419	active.
		1420
		1421	=item stopped
		1422
		1423	A watcher can be stopped implicitly by libev (in which case it might still
		1424	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1425	latter will clear any pending state the watcher might be in, regardless
		1426	of whether it was active or not, so stopping a watcher explicitly before
		1427	freeing it is often a good idea.
		1428
		1429	While stopped (and not pending) the watcher is essentially in the
		1430	initialised state, that is it can be reused, moved, modified in any way
		1431	you wish.
		1432
		1433	=back
		1434
		1435	=head2 WATCHER PRIORITY MODELS
		1436
		1437	Many event loops support I<watcher priorities>, which are usually small
		1438	integers that influence the ordering of event callback invocation
		1439	between watchers in some way, all else being equal.
		1440
		1441	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1442	description for the more technical details such as the actual priority
		1443	range.
		1444
		1445	There are two common ways how these these priorities are being interpreted
		1446	by event loops:
		1447
		1448	In the more common lock-out model, higher priorities "lock out" invocation
		1449	of lower priority watchers, which means as long as higher priority
		1450	watchers receive events, lower priority watchers are not being invoked.
		1451
		1452	The less common only-for-ordering model uses priorities solely to order
		1453	callback invocation within a single event loop iteration: Higher priority
		1454	watchers are invoked before lower priority ones, but they all get invoked
		1455	before polling for new events.
		1456
		1457	Libev uses the second (only-for-ordering) model for all its watchers
		1458	except for idle watchers (which use the lock-out model).
		1459
		1460	The rationale behind this is that implementing the lock-out model for
		1461	watchers is not well supported by most kernel interfaces, and most event
		1462	libraries will just poll for the same events again and again as long as
		1463	their callbacks have not been executed, which is very inefficient in the
		1464	common case of one high-priority watcher locking out a mass of lower
		1465	priority ones.
		1466
		1467	Static (ordering) priorities are most useful when you have two or more
		1468	watchers handling the same resource: a typical usage example is having an
		1469	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1470	timeouts. Under load, data might be received while the program handles
		1471	other jobs, but since timers normally get invoked first, the timeout
		1472	handler will be executed before checking for data. In that case, giving
		1473	the timer a lower priority than the I/O watcher ensures that I/O will be
		1474	handled first even under adverse conditions (which is usually, but not
		1475	always, what you want).
		1476
		1477	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1478	will only be executed when no same or higher priority watchers have
		1479	received events, they can be used to implement the "lock-out" model when
		1480	required.
		1481
		1482	For example, to emulate how many other event libraries handle priorities,
		1483	you can associate an C<ev_idle> watcher to each such watcher, and in
		1484	the normal watcher callback, you just start the idle watcher. The real
		1485	processing is done in the idle watcher callback. This causes libev to
		1486	continuously poll and process kernel event data for the watcher, but when
		1487	the lock-out case is known to be rare (which in turn is rare :), this is
		1488	workable.
		1489
		1490	Usually, however, the lock-out model implemented that way will perform
		1491	miserably under the type of load it was designed to handle. In that case,
		1492	it might be preferable to stop the real watcher before starting the
		1493	idle watcher, so the kernel will not have to process the event in case
		1494	the actual processing will be delayed for considerable time.
		1495
		1496	Here is an example of an I/O watcher that should run at a strictly lower
		1497	priority than the default, and which should only process data when no
		1498	other events are pending:
		1499
		1500	ev_idle idle; // actual processing watcher
		1501	ev_io io; // actual event watcher
		1502
		1503	static void
		1504	io_cb (EV_P_ ev_io *w, int revents)
		1505	{
		1506	// stop the I/O watcher, we received the event, but
		1507	// are not yet ready to handle it.
		1508	ev_io_stop (EV_A_ w);
		1509
		1510	// start the idle watcher to handle the actual event.
		1511	// it will not be executed as long as other watchers
		1512	// with the default priority are receiving events.
		1513	ev_idle_start (EV_A_ &idle);
		1514	}
		1515
		1516	static void
		1517	idle_cb (EV_P_ ev_idle *w, int revents)
		1518	{
		1519	// actual processing
		1520	read (STDIN_FILENO, ...);
		1521
		1522	// have to start the I/O watcher again, as
		1523	// we have handled the event
		1524	ev_io_start (EV_P_ &io);
		1525	}
		1526
		1527	// initialisation
		1528	ev_idle_init (&idle, idle_cb);
		1529	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1530	ev_io_start (EV_DEFAULT_ &io);
		1531
		1532	In the "real" world, it might also be beneficial to start a timer, so that
		1533	low-priority connections can not be locked out forever under load. This
		1534	enables your program to keep a lower latency for important connections
		1535	during short periods of high load, while not completely locking out less
		1536	important ones.
955		1537
956		1538
957	=head1 WATCHER TYPES	1539	=head1 WATCHER TYPES
958		1540
959	This section describes each watcher in detail, but will not repeat	1541	This section describes each watcher in detail, but will not repeat
…		…
983	In general you can register as many read and/or write event watchers per	1565	In general you can register as many read and/or write event watchers per
984	fd as you want (as long as you don't confuse yourself). Setting all file	1566	fd as you want (as long as you don't confuse yourself). Setting all file
985	descriptors to non-blocking mode is also usually a good idea (but not	1567	descriptors to non-blocking mode is also usually a good idea (but not
986	required if you know what you are doing).	1568	required if you know what you are doing).
987		1569
988	If you must do this, then force the use of a known-to-be-good backend	1570	If you cannot use non-blocking mode, then force the use of a
989	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1571	known-to-be-good backend (at the time of this writing, this includes only
990	C<EVBACKEND_POLL>).	1572	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1573	descriptors for which non-blocking operation makes no sense (such as
		1574	files) - libev doesn't guarantee any specific behaviour in that case.
991		1575
992	Another thing you have to watch out for is that it is quite easy to	1576	Another thing you have to watch out for is that it is quite easy to
993	receive "spurious" readyness notifications, that is your callback might	1577	receive "spurious" readiness notifications, that is your callback might
994	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1578	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
995	because there is no data. Not only are some backends known to create a	1579	because there is no data. Not only are some backends known to create a
996	lot of those (for example solaris ports), it is very easy to get into	1580	lot of those (for example Solaris ports), it is very easy to get into
997	this situation even with a relatively standard program structure. Thus	1581	this situation even with a relatively standard program structure. Thus
998	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1582	it is best to always use non-blocking I/O: An extra C<read>(2) returning
999	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1583	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1000		1584
1001	If you cannot run the fd in non-blocking mode (for example you should not	1585	If you cannot run the fd in non-blocking mode (for example you should
1002	play around with an Xlib connection), then you have to seperately re-test	1586	not play around with an Xlib connection), then you have to separately
1003	whether a file descriptor is really ready with a known-to-be good interface	1587	re-test whether a file descriptor is really ready with a known-to-be good
1004	such as poll (fortunately in our Xlib example, Xlib already does this on	1588	interface such as poll (fortunately in our Xlib example, Xlib already
1005	its own, so its quite safe to use).	1589	does this on its own, so its quite safe to use). Some people additionally
		1590	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1591	indefinitely.
		1592
		1593	But really, best use non-blocking mode.
1006		1594
1007	=head3 The special problem of disappearing file descriptors	1595	=head3 The special problem of disappearing file descriptors
1008		1596
1009	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1597	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1010	descriptor (either by calling C<close> explicitly or by any other means,	1598	descriptor (either due to calling C<close> explicitly or any other means,
1011	such as C<dup>). The reason is that you register interest in some file	1599	such as C<dup2>). The reason is that you register interest in some file
1012	descriptor, but when it goes away, the operating system will silently drop	1600	descriptor, but when it goes away, the operating system will silently drop
1013	this interest. If another file descriptor with the same number then is	1601	this interest. If another file descriptor with the same number then is
1014	registered with libev, there is no efficient way to see that this is, in	1602	registered with libev, there is no efficient way to see that this is, in
1015	fact, a different file descriptor.	1603	fact, a different file descriptor.
1016		1604
…		…
1045	To support fork in your programs, you either have to call	1633	To support fork in your programs, you either have to call
1046	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1634	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1047	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1635	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1048	C<EVBACKEND_POLL>.	1636	C<EVBACKEND_POLL>.
1049		1637
		1638	=head3 The special problem of SIGPIPE
		1639
		1640	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1641	when writing to a pipe whose other end has been closed, your program gets
		1642	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1643	this is sensible behaviour, for daemons, this is usually undesirable.
		1644
		1645	So when you encounter spurious, unexplained daemon exits, make sure you
		1646	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1647	somewhere, as that would have given you a big clue).
		1648
		1649	=head3 The special problem of accept()ing when you can't
		1650
		1651	Many implementations of the POSIX C<accept> function (for example,
		1652	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1653	connection from the pending queue in all error cases.
		1654
		1655	For example, larger servers often run out of file descriptors (because
		1656	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1657	rejecting the connection, leading to libev signalling readiness on
		1658	the next iteration again (the connection still exists after all), and
		1659	typically causing the program to loop at 100% CPU usage.
		1660
		1661	Unfortunately, the set of errors that cause this issue differs between
		1662	operating systems, there is usually little the app can do to remedy the
		1663	situation, and no known thread-safe method of removing the connection to
		1664	cope with overload is known (to me).
		1665
		1666	One of the easiest ways to handle this situation is to just ignore it
		1667	- when the program encounters an overload, it will just loop until the
		1668	situation is over. While this is a form of busy waiting, no OS offers an
		1669	event-based way to handle this situation, so it's the best one can do.
		1670
		1671	A better way to handle the situation is to log any errors other than
		1672	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1673	messages, and continue as usual, which at least gives the user an idea of
		1674	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1675	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1676	usage.
		1677
		1678	If your program is single-threaded, then you could also keep a dummy file
		1679	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1680	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1681	close that fd, and create a new dummy fd. This will gracefully refuse
		1682	clients under typical overload conditions.
		1683
		1684	The last way to handle it is to simply log the error and C<exit>, as
		1685	is often done with C<malloc> failures, but this results in an easy
		1686	opportunity for a DoS attack.
1050		1687
1051	=head3 Watcher-Specific Functions	1688	=head3 Watcher-Specific Functions
1052		1689
1053	=over 4	1690	=over 4
1054		1691
1055	=item ev_io_init (ev_io *, callback, int fd, int events)	1692	=item ev_io_init (ev_io *, callback, int fd, int events)
1056		1693
1057	=item ev_io_set (ev_io *, int fd, int events)	1694	=item ev_io_set (ev_io *, int fd, int events)
1058		1695
1059	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1696	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1060	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1697	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1061	C<EV_READ | EV_WRITE> to receive the given events.	1698	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1062		1699
1063	=item int fd [read-only]	1700	=item int fd [read-only]
1064		1701
1065	The file descriptor being watched.	1702	The file descriptor being watched.
1066		1703
1067	=item int events [read-only]	1704	=item int events [read-only]
1068		1705
1069	The events being watched.	1706	The events being watched.
1070		1707
1071	=back	1708	=back
		1709
		1710	=head3 Examples
1072		1711
1073	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1712	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1074	readable, but only once. Since it is likely line-buffered, you could	1713	readable, but only once. Since it is likely line-buffered, you could
1075	attempt to read a whole line in the callback.	1714	attempt to read a whole line in the callback.
1076		1715
1077	static void	1716	static void
1078	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1717	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1079	{	1718	{
1080	ev_io_stop (loop, w);	1719	ev_io_stop (loop, w);
1081	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1720	.. read from stdin here (or from w->fd) and handle any I/O errors
1082	}	1721	}
1083		1722
1084	...	1723	...
1085	struct ev_loop *loop = ev_default_init (0);	1724	struct ev_loop *loop = ev_default_init (0);
1086	struct ev_io stdin_readable;	1725	ev_io stdin_readable;
1087	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1726	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1088	ev_io_start (loop, &stdin_readable);	1727	ev_io_start (loop, &stdin_readable);
1089	ev_loop (loop, 0);	1728	ev_run (loop, 0);
1090		1729
1091		1730
1092	=head2 C<ev_timer> - relative and optionally repeating timeouts	1731	=head2 C<ev_timer> - relative and optionally repeating timeouts
1093		1732
1094	Timer watchers are simple relative timers that generate an event after a	1733	Timer watchers are simple relative timers that generate an event after a
1095	given time, and optionally repeating in regular intervals after that.	1734	given time, and optionally repeating in regular intervals after that.
1096		1735
1097	The timers are based on real time, that is, if you register an event that	1736	The timers are based on real time, that is, if you register an event that
1098	times out after an hour and you reset your system clock to last years	1737	times out after an hour and you reset your system clock to January last
1099	time, it will still time out after (roughly) and hour. "Roughly" because	1738	year, it will still time out after (roughly) one hour. "Roughly" because
1100	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1739	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1101	monotonic clock option helps a lot here).	1740	monotonic clock option helps a lot here).
		1741
		1742	The callback is guaranteed to be invoked only I<after> its timeout has
		1743	passed (not I<at>, so on systems with very low-resolution clocks this
		1744	might introduce a small delay). If multiple timers become ready during the
		1745	same loop iteration then the ones with earlier time-out values are invoked
		1746	before ones of the same priority with later time-out values (but this is
		1747	no longer true when a callback calls C<ev_run> recursively).
		1748
		1749	=head3 Be smart about timeouts
		1750
		1751	Many real-world problems involve some kind of timeout, usually for error
		1752	recovery. A typical example is an HTTP request - if the other side hangs,
		1753	you want to raise some error after a while.
		1754
		1755	What follows are some ways to handle this problem, from obvious and
		1756	inefficient to smart and efficient.
		1757
		1758	In the following, a 60 second activity timeout is assumed - a timeout that
		1759	gets reset to 60 seconds each time there is activity (e.g. each time some
		1760	data or other life sign was received).
		1761
		1762	=over 4
		1763
		1764	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1765
		1766	This is the most obvious, but not the most simple way: In the beginning,
		1767	start the watcher:
		1768
		1769	ev_timer_init (timer, callback, 60., 0.);
		1770	ev_timer_start (loop, timer);
		1771
		1772	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1773	and start it again:
		1774
		1775	ev_timer_stop (loop, timer);
		1776	ev_timer_set (timer, 60., 0.);
		1777	ev_timer_start (loop, timer);
		1778
		1779	This is relatively simple to implement, but means that each time there is
		1780	some activity, libev will first have to remove the timer from its internal
		1781	data structure and then add it again. Libev tries to be fast, but it's
		1782	still not a constant-time operation.
		1783
		1784	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1785
		1786	This is the easiest way, and involves using C<ev_timer_again> instead of
		1787	C<ev_timer_start>.
		1788
		1789	To implement this, configure an C<ev_timer> with a C<repeat> value
		1790	of C<60> and then call C<ev_timer_again> at start and each time you
		1791	successfully read or write some data. If you go into an idle state where
		1792	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1793	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1794
		1795	That means you can ignore both the C<ev_timer_start> function and the
		1796	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1797	member and C<ev_timer_again>.
		1798
		1799	At start:
		1800
		1801	ev_init (timer, callback);
		1802	timer->repeat = 60.;
		1803	ev_timer_again (loop, timer);
		1804
		1805	Each time there is some activity:
		1806
		1807	ev_timer_again (loop, timer);
		1808
		1809	It is even possible to change the time-out on the fly, regardless of
		1810	whether the watcher is active or not:
		1811
		1812	timer->repeat = 30.;
		1813	ev_timer_again (loop, timer);
		1814
		1815	This is slightly more efficient then stopping/starting the timer each time
		1816	you want to modify its timeout value, as libev does not have to completely
		1817	remove and re-insert the timer from/into its internal data structure.
		1818
		1819	It is, however, even simpler than the "obvious" way to do it.
		1820
		1821	=item 3. Let the timer time out, but then re-arm it as required.
		1822
		1823	This method is more tricky, but usually most efficient: Most timeouts are
		1824	relatively long compared to the intervals between other activity - in
		1825	our example, within 60 seconds, there are usually many I/O events with
		1826	associated activity resets.
		1827
		1828	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1829	but remember the time of last activity, and check for a real timeout only
		1830	within the callback:
		1831
		1832	ev_tstamp last_activity; // time of last activity
		1833
		1834	static void
		1835	callback (EV_P_ ev_timer *w, int revents)
		1836	{
		1837	ev_tstamp now = ev_now (EV_A);
		1838	ev_tstamp timeout = last_activity + 60.;
		1839
		1840	// if last_activity + 60. is older than now, we did time out
		1841	if (timeout < now)
		1842	{
		1843	// timeout occurred, take action
		1844	}
		1845	else
		1846	{
		1847	// callback was invoked, but there was some activity, re-arm
		1848	// the watcher to fire in last_activity + 60, which is
		1849	// guaranteed to be in the future, so "again" is positive:
		1850	w->repeat = timeout - now;
		1851	ev_timer_again (EV_A_ w);
		1852	}
		1853	}
		1854
		1855	To summarise the callback: first calculate the real timeout (defined
		1856	as "60 seconds after the last activity"), then check if that time has
		1857	been reached, which means something I<did>, in fact, time out. Otherwise
		1858	the callback was invoked too early (C<timeout> is in the future), so
		1859	re-schedule the timer to fire at that future time, to see if maybe we have
		1860	a timeout then.
		1861
		1862	Note how C<ev_timer_again> is used, taking advantage of the
		1863	C<ev_timer_again> optimisation when the timer is already running.
		1864
		1865	This scheme causes more callback invocations (about one every 60 seconds
		1866	minus half the average time between activity), but virtually no calls to
		1867	libev to change the timeout.
		1868
		1869	To start the timer, simply initialise the watcher and set C<last_activity>
		1870	to the current time (meaning we just have some activity :), then call the
		1871	callback, which will "do the right thing" and start the timer:
		1872
		1873	ev_init (timer, callback);
		1874	last_activity = ev_now (loop);
		1875	callback (loop, timer, EV_TIMER);
		1876
		1877	And when there is some activity, simply store the current time in
		1878	C<last_activity>, no libev calls at all:
		1879
		1880	last_activity = ev_now (loop);
		1881
		1882	This technique is slightly more complex, but in most cases where the
		1883	time-out is unlikely to be triggered, much more efficient.
		1884
		1885	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1886	callback :) - just change the timeout and invoke the callback, which will
		1887	fix things for you.
		1888
		1889	=item 4. Wee, just use a double-linked list for your timeouts.
		1890
		1891	If there is not one request, but many thousands (millions...), all
		1892	employing some kind of timeout with the same timeout value, then one can
		1893	do even better:
		1894
		1895	When starting the timeout, calculate the timeout value and put the timeout
		1896	at the I<end> of the list.
		1897
		1898	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1899	the list is expected to fire (for example, using the technique #3).
		1900
		1901	When there is some activity, remove the timer from the list, recalculate
		1902	the timeout, append it to the end of the list again, and make sure to
		1903	update the C<ev_timer> if it was taken from the beginning of the list.
		1904
		1905	This way, one can manage an unlimited number of timeouts in O(1) time for
		1906	starting, stopping and updating the timers, at the expense of a major
		1907	complication, and having to use a constant timeout. The constant timeout
		1908	ensures that the list stays sorted.
		1909
		1910	=back
		1911
		1912	So which method the best?
		1913
		1914	Method #2 is a simple no-brain-required solution that is adequate in most
		1915	situations. Method #3 requires a bit more thinking, but handles many cases
		1916	better, and isn't very complicated either. In most case, choosing either
		1917	one is fine, with #3 being better in typical situations.
		1918
		1919	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1920	rather complicated, but extremely efficient, something that really pays
		1921	off after the first million or so of active timers, i.e. it's usually
		1922	overkill :)
		1923
		1924	=head3 The special problem of time updates
		1925
		1926	Establishing the current time is a costly operation (it usually takes at
		1927	least two system calls): EV therefore updates its idea of the current
		1928	time only before and after C<ev_run> collects new events, which causes a
		1929	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1930	lots of events in one iteration.
1102		1931
1103	The relative timeouts are calculated relative to the C<ev_now ()>	1932	The relative timeouts are calculated relative to the C<ev_now ()>
1104	time. This is usually the right thing as this timestamp refers to the time	1933	time. This is usually the right thing as this timestamp refers to the time
1105	of the event triggering whatever timeout you are modifying/starting. If	1934	of the event triggering whatever timeout you are modifying/starting. If
1106	you suspect event processing to be delayed and you I<need> to base the timeout	1935	you suspect event processing to be delayed and you I<need> to base the
1107	on the current time, use something like this to adjust for this:	1936	timeout on the current time, use something like this to adjust for this:
1108		1937
1109	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1938	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1110		1939
1111	The callback is guarenteed to be invoked only when its timeout has passed,	1940	If the event loop is suspended for a long time, you can also force an
1112	but if multiple timers become ready during the same loop iteration then	1941	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1113	order of execution is undefined.	1942	()>.
		1943
		1944	=head3 The special problems of suspended animation
		1945
		1946	When you leave the server world it is quite customary to hit machines that
		1947	can suspend/hibernate - what happens to the clocks during such a suspend?
		1948
		1949	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1950	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1951	to run until the system is suspended, but they will not advance while the
		1952	system is suspended. That means, on resume, it will be as if the program
		1953	was frozen for a few seconds, but the suspend time will not be counted
		1954	towards C<ev_timer> when a monotonic clock source is used. The real time
		1955	clock advanced as expected, but if it is used as sole clocksource, then a
		1956	long suspend would be detected as a time jump by libev, and timers would
		1957	be adjusted accordingly.
		1958
		1959	I would not be surprised to see different behaviour in different between
		1960	operating systems, OS versions or even different hardware.
		1961
		1962	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1963	time jump in the monotonic clocks and the realtime clock. If the program
		1964	is suspended for a very long time, and monotonic clock sources are in use,
		1965	then you can expect C<ev_timer>s to expire as the full suspension time
		1966	will be counted towards the timers. When no monotonic clock source is in
		1967	use, then libev will again assume a timejump and adjust accordingly.
		1968
		1969	It might be beneficial for this latter case to call C<ev_suspend>
		1970	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1971	deterministic behaviour in this case (you can do nothing against
		1972	C<SIGSTOP>).
1114		1973
1115	=head3 Watcher-Specific Functions and Data Members	1974	=head3 Watcher-Specific Functions and Data Members
1116		1975
1117	=over 4	1976	=over 4
1118		1977
1119	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1978	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1120		1979
1121	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1980	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1122		1981
1123	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1982	Configure the timer to trigger after C<after> seconds. If C<repeat>
1124	C<0.>, then it will automatically be stopped. If it is positive, then the	1983	is C<0.>, then it will automatically be stopped once the timeout is
1125	timer will automatically be configured to trigger again C<repeat> seconds	1984	reached. If it is positive, then the timer will automatically be
1126	later, again, and again, until stopped manually.	1985	configured to trigger again C<repeat> seconds later, again, and again,
		1986	until stopped manually.
1127		1987
1128	The timer itself will do a best-effort at avoiding drift, that is, if you	1988	The timer itself will do a best-effort at avoiding drift, that is, if
1129	configure a timer to trigger every 10 seconds, then it will trigger at	1989	you configure a timer to trigger every 10 seconds, then it will normally
1130	exactly 10 second intervals. If, however, your program cannot keep up with	1990	trigger at exactly 10 second intervals. If, however, your program cannot
1131	the timer (because it takes longer than those 10 seconds to do stuff) the	1991	keep up with the timer (because it takes longer than those 10 seconds to
1132	timer will not fire more than once per event loop iteration.	1992	do stuff) the timer will not fire more than once per event loop iteration.
1133		1993
1134	=item ev_timer_again (loop)	1994	=item ev_timer_again (loop, ev_timer *)
1135		1995
1136	This will act as if the timer timed out and restart it again if it is	1996	This will act as if the timer timed out and restart it again if it is
1137	repeating. The exact semantics are:	1997	repeating. The exact semantics are:
1138		1998
1139	If the timer is pending, its pending status is cleared.	1999	If the timer is pending, its pending status is cleared.
1140		2000
1141	If the timer is started but nonrepeating, stop it (as if it timed out).	2001	If the timer is started but non-repeating, stop it (as if it timed out).
1142		2002
1143	If the timer is repeating, either start it if necessary (with the	2003	If the timer is repeating, either start it if necessary (with the
1144	C<repeat> value), or reset the running timer to the C<repeat> value.	2004	C<repeat> value), or reset the running timer to the C<repeat> value.
1145		2005
1146	This sounds a bit complicated, but here is a useful and typical	2006	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1147	example: Imagine you have a tcp connection and you want a so-called idle	2007	usage example.
1148	timeout, that is, you want to be called when there have been, say, 60
1149	seconds of inactivity on the socket. The easiest way to do this is to
1150	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1151	C<ev_timer_again> each time you successfully read or write some data. If
1152	you go into an idle state where you do not expect data to travel on the
1153	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1154	automatically restart it if need be.
1155		2008
1156	That means you can ignore the C<after> value and C<ev_timer_start>	2009	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1157	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1158		2010
1159	ev_timer_init (timer, callback, 0., 5.);	2011	Returns the remaining time until a timer fires. If the timer is active,
1160	ev_timer_again (loop, timer);	2012	then this time is relative to the current event loop time, otherwise it's
1161	...	2013	the timeout value currently configured.
1162	timer->again = 17.;
1163	ev_timer_again (loop, timer);
1164	...
1165	timer->again = 10.;
1166	ev_timer_again (loop, timer);
1167		2014
1168	This is more slightly efficient then stopping/starting the timer each time	2015	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1169	you want to modify its timeout value.	2016	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2017	will return C<4>. When the timer expires and is restarted, it will return
		2018	roughly C<7> (likely slightly less as callback invocation takes some time,
		2019	too), and so on.
1170		2020
1171	=item ev_tstamp repeat [read-write]	2021	=item ev_tstamp repeat [read-write]
1172		2022
1173	The current C<repeat> value. Will be used each time the watcher times out	2023	The current C<repeat> value. Will be used each time the watcher times out
1174	or C<ev_timer_again> is called and determines the next timeout (if any),	2024	or C<ev_timer_again> is called, and determines the next timeout (if any),
1175	which is also when any modifications are taken into account.	2025	which is also when any modifications are taken into account.
1176		2026
1177	=back	2027	=back
1178		2028
		2029	=head3 Examples
		2030
1179	Example: Create a timer that fires after 60 seconds.	2031	Example: Create a timer that fires after 60 seconds.
1180		2032
1181	static void	2033	static void
1182	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2034	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1183	{	2035	{
1184	.. one minute over, w is actually stopped right here	2036	.. one minute over, w is actually stopped right here
1185	}	2037	}
1186		2038
1187	struct ev_timer mytimer;	2039	ev_timer mytimer;
1188	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2040	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1189	ev_timer_start (loop, &mytimer);	2041	ev_timer_start (loop, &mytimer);
1190		2042
1191	Example: Create a timeout timer that times out after 10 seconds of	2043	Example: Create a timeout timer that times out after 10 seconds of
1192	inactivity.	2044	inactivity.
1193		2045
1194	static void	2046	static void
1195	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2047	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1196	{	2048	{
1197	.. ten seconds without any activity	2049	.. ten seconds without any activity
1198	}	2050	}
1199		2051
1200	struct ev_timer mytimer;	2052	ev_timer mytimer;
1201	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2053	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1202	ev_timer_again (&mytimer); /* start timer */	2054	ev_timer_again (&mytimer); /* start timer */
1203	ev_loop (loop, 0);	2055	ev_run (loop, 0);
1204		2056
1205	// and in some piece of code that gets executed on any "activity":	2057	// and in some piece of code that gets executed on any "activity":
1206	// reset the timeout to start ticking again at 10 seconds	2058	// reset the timeout to start ticking again at 10 seconds
1207	ev_timer_again (&mytimer);	2059	ev_timer_again (&mytimer);
1208		2060
1209		2061
1210	=head2 C<ev_periodic> - to cron or not to cron?	2062	=head2 C<ev_periodic> - to cron or not to cron?
1211		2063
1212	Periodic watchers are also timers of a kind, but they are very versatile	2064	Periodic watchers are also timers of a kind, but they are very versatile
1213	(and unfortunately a bit complex).	2065	(and unfortunately a bit complex).
1214		2066
1215	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2067	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1216	but on wallclock time (absolute time). You can tell a periodic watcher	2068	relative time, the physical time that passes) but on wall clock time
1217	to trigger "at" some specific point in time. For example, if you tell a	2069	(absolute time, the thing you can read on your calender or clock). The
1218	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2070	difference is that wall clock time can run faster or slower than real
1219	+ 10.>) and then reset your system clock to the last year, then it will	2071	time, and time jumps are not uncommon (e.g. when you adjust your
1220	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2072	wrist-watch).
1221	roughly 10 seconds later).
1222		2073
1223	They can also be used to implement vastly more complex timers, such as	2074	You can tell a periodic watcher to trigger after some specific point
1224	triggering an event on each midnight, local time or other, complicated,	2075	in time: for example, if you tell a periodic watcher to trigger "in 10
1225	rules.	2076	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2077	not a delay) and then reset your system clock to January of the previous
		2078	year, then it will take a year or more to trigger the event (unlike an
		2079	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2080	it, as it uses a relative timeout).
1226		2081
		2082	C<ev_periodic> watchers can also be used to implement vastly more complex
		2083	timers, such as triggering an event on each "midnight, local time", or
		2084	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2085	those cannot react to time jumps.
		2086
1227	As with timers, the callback is guarenteed to be invoked only when the	2087	As with timers, the callback is guaranteed to be invoked only when the
1228	time (C<at>) has been passed, but if multiple periodic timers become ready	2088	point in time where it is supposed to trigger has passed. If multiple
1229	during the same loop iteration then order of execution is undefined.	2089	timers become ready during the same loop iteration then the ones with
		2090	earlier time-out values are invoked before ones with later time-out values
		2091	(but this is no longer true when a callback calls C<ev_run> recursively).
1230		2092
1231	=head3 Watcher-Specific Functions and Data Members	2093	=head3 Watcher-Specific Functions and Data Members
1232		2094
1233	=over 4	2095	=over 4
1234		2096
1235	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2097	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1236		2098
1237	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2099	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1238		2100
1239	Lots of arguments, lets sort it out... There are basically three modes of	2101	Lots of arguments, let's sort it out... There are basically three modes of
1240	operation, and we will explain them from simplest to complex:	2102	operation, and we will explain them from simplest to most complex:
1241		2103
1242	=over 4	2104	=over 4
1243		2105
1244	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2106	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1245		2107
1246	In this configuration the watcher triggers an event at the wallclock time	2108	In this configuration the watcher triggers an event after the wall clock
1247	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2109	time C<offset> has passed. It will not repeat and will not adjust when a
1248	that is, if it is to be run at January 1st 2011 then it will run when the	2110	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1249	system time reaches or surpasses this time.	2111	will be stopped and invoked when the system clock reaches or surpasses
		2112	this point in time.
1250		2113
1251	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2114	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1252		2115
1253	In this mode the watcher will always be scheduled to time out at the next	2116	In this mode the watcher will always be scheduled to time out at the next
1254	C<at + N * interval> time (for some integer N, which can also be negative)	2117	C<offset + N * interval> time (for some integer N, which can also be
1255	and then repeat, regardless of any time jumps.	2118	negative) and then repeat, regardless of any time jumps. The C<offset>
		2119	argument is merely an offset into the C<interval> periods.
1256		2120
1257	This can be used to create timers that do not drift with respect to system	2121	This can be used to create timers that do not drift with respect to the
1258	time:	2122	system clock, for example, here is an C<ev_periodic> that triggers each
		2123	hour, on the hour (with respect to UTC):
1259		2124
1260	ev_periodic_set (&periodic, 0., 3600., 0);	2125	ev_periodic_set (&periodic, 0., 3600., 0);
1261		2126
1262	This doesn't mean there will always be 3600 seconds in between triggers,	2127	This doesn't mean there will always be 3600 seconds in between triggers,
1263	but only that the the callback will be called when the system time shows a	2128	but only that the callback will be called when the system time shows a
1264	full hour (UTC), or more correctly, when the system time is evenly divisible	2129	full hour (UTC), or more correctly, when the system time is evenly divisible
1265	by 3600.	2130	by 3600.
1266		2131
1267	Another way to think about it (for the mathematically inclined) is that	2132	Another way to think about it (for the mathematically inclined) is that
1268	C<ev_periodic> will try to run the callback in this mode at the next possible	2133	C<ev_periodic> will try to run the callback in this mode at the next possible
1269	time where C<time = at (mod interval)>, regardless of any time jumps.	2134	time where C<time = offset (mod interval)>, regardless of any time jumps.
1270		2135
1271	For numerical stability it is preferable that the C<at> value is near	2136	For numerical stability it is preferable that the C<offset> value is near
1272	C<ev_now ()> (the current time), but there is no range requirement for	2137	C<ev_now ()> (the current time), but there is no range requirement for
1273	this value.	2138	this value, and in fact is often specified as zero.
1274		2139
		2140	Note also that there is an upper limit to how often a timer can fire (CPU
		2141	speed for example), so if C<interval> is very small then timing stability
		2142	will of course deteriorate. Libev itself tries to be exact to be about one
		2143	millisecond (if the OS supports it and the machine is fast enough).
		2144
1275	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2145	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1276		2146
1277	In this mode the values for C<interval> and C<at> are both being	2147	In this mode the values for C<interval> and C<offset> are both being
1278	ignored. Instead, each time the periodic watcher gets scheduled, the	2148	ignored. Instead, each time the periodic watcher gets scheduled, the
1279	reschedule callback will be called with the watcher as first, and the	2149	reschedule callback will be called with the watcher as first, and the
1280	current time as second argument.	2150	current time as second argument.
1281		2151
1282	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2152	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1283	ever, or make any event loop modifications>. If you need to stop it,	2153	or make ANY other event loop modifications whatsoever, unless explicitly
1284	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2154	allowed by documentation here>.
1285	starting an C<ev_prepare> watcher, which is legal).
1286		2155
		2156	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2157	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2158	only event loop modification you are allowed to do).
		2159
1287	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2160	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1288	ev_tstamp now)>, e.g.:	2161	*w, ev_tstamp now)>, e.g.:
1289		2162
		2163	static ev_tstamp
1290	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2164	my_rescheduler (ev_periodic *w, ev_tstamp now)
1291	{	2165	{
1292	return now + 60.;	2166	return now + 60.;
1293	}	2167	}
1294		2168
1295	It must return the next time to trigger, based on the passed time value	2169	It must return the next time to trigger, based on the passed time value
1296	(that is, the lowest time value larger than to the second argument). It	2170	(that is, the lowest time value larger than to the second argument). It
1297	will usually be called just before the callback will be triggered, but	2171	will usually be called just before the callback will be triggered, but
1298	might be called at other times, too.	2172	might be called at other times, too.
1299		2173
1300	NOTE: I<< This callback must always return a time that is later than the	2174	NOTE: I<< This callback must always return a time that is higher than or
1301	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2175	equal to the passed C<now> value >>.
1302		2176
1303	This can be used to create very complex timers, such as a timer that	2177	This can be used to create very complex timers, such as a timer that
1304	triggers on each midnight, local time. To do this, you would calculate the	2178	triggers on "next midnight, local time". To do this, you would calculate the
1305	next midnight after C<now> and return the timestamp value for this. How	2179	next midnight after C<now> and return the timestamp value for this. How
1306	you do this is, again, up to you (but it is not trivial, which is the main	2180	you do this is, again, up to you (but it is not trivial, which is the main
1307	reason I omitted it as an example).	2181	reason I omitted it as an example).
1308		2182
1309	=back	2183	=back
…		…
1313	Simply stops and restarts the periodic watcher again. This is only useful	2187	Simply stops and restarts the periodic watcher again. This is only useful
1314	when you changed some parameters or the reschedule callback would return	2188	when you changed some parameters or the reschedule callback would return
1315	a different time than the last time it was called (e.g. in a crond like	2189	a different time than the last time it was called (e.g. in a crond like
1316	program when the crontabs have changed).	2190	program when the crontabs have changed).
1317		2191
		2192	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2193
		2194	When active, returns the absolute time that the watcher is supposed
		2195	to trigger next. This is not the same as the C<offset> argument to
		2196	C<ev_periodic_set>, but indeed works even in interval and manual
		2197	rescheduling modes.
		2198
1318	=item ev_tstamp offset [read-write]	2199	=item ev_tstamp offset [read-write]
1319		2200
1320	When repeating, this contains the offset value, otherwise this is the	2201	When repeating, this contains the offset value, otherwise this is the
1321	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2202	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2203	although libev might modify this value for better numerical stability).
1322		2204
1323	Can be modified any time, but changes only take effect when the periodic	2205	Can be modified any time, but changes only take effect when the periodic
1324	timer fires or C<ev_periodic_again> is being called.	2206	timer fires or C<ev_periodic_again> is being called.
1325		2207
1326	=item ev_tstamp interval [read-write]	2208	=item ev_tstamp interval [read-write]
1327		2209
1328	The current interval value. Can be modified any time, but changes only	2210	The current interval value. Can be modified any time, but changes only
1329	take effect when the periodic timer fires or C<ev_periodic_again> is being	2211	take effect when the periodic timer fires or C<ev_periodic_again> is being
1330	called.	2212	called.
1331		2213
1332	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2214	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1333		2215
1334	The current reschedule callback, or C<0>, if this functionality is	2216	The current reschedule callback, or C<0>, if this functionality is
1335	switched off. Can be changed any time, but changes only take effect when	2217	switched off. Can be changed any time, but changes only take effect when
1336	the periodic timer fires or C<ev_periodic_again> is being called.	2218	the periodic timer fires or C<ev_periodic_again> is being called.
1337		2219
1338	=item ev_tstamp at [read-only]
1339
1340	When active, contains the absolute time that the watcher is supposed to
1341	trigger next.
1342
1343	=back	2220	=back
1344		2221
		2222	=head3 Examples
		2223
1345	Example: Call a callback every hour, or, more precisely, whenever the	2224	Example: Call a callback every hour, or, more precisely, whenever the
1346	system clock is divisible by 3600. The callback invocation times have	2225	system time is divisible by 3600. The callback invocation times have
1347	potentially a lot of jittering, but good long-term stability.	2226	potentially a lot of jitter, but good long-term stability.
1348		2227
1349	static void	2228	static void
1350	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2229	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1351	{	2230	{
1352	... its now a full hour (UTC, or TAI or whatever your clock follows)	2231	... its now a full hour (UTC, or TAI or whatever your clock follows)
1353	}	2232	}
1354		2233
1355	struct ev_periodic hourly_tick;	2234	ev_periodic hourly_tick;
1356	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2235	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1357	ev_periodic_start (loop, &hourly_tick);	2236	ev_periodic_start (loop, &hourly_tick);
1358		2237
1359	Example: The same as above, but use a reschedule callback to do it:	2238	Example: The same as above, but use a reschedule callback to do it:
1360		2239
1361	#include <math.h>	2240	#include <math.h>
1362		2241
1363	static ev_tstamp	2242	static ev_tstamp
1364	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2243	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1365	{	2244	{
1366	return fmod (now, 3600.) + 3600.;	2245	return now + (3600. - fmod (now, 3600.));
1367	}	2246	}
1368		2247
1369	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2248	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1370		2249
1371	Example: Call a callback every hour, starting now:	2250	Example: Call a callback every hour, starting now:
1372		2251
1373	struct ev_periodic hourly_tick;	2252	ev_periodic hourly_tick;
1374	ev_periodic_init (&hourly_tick, clock_cb,	2253	ev_periodic_init (&hourly_tick, clock_cb,
1375	fmod (ev_now (loop), 3600.), 3600., 0);	2254	fmod (ev_now (loop), 3600.), 3600., 0);
1376	ev_periodic_start (loop, &hourly_tick);	2255	ev_periodic_start (loop, &hourly_tick);
1377		2256
1378		2257
1379	=head2 C<ev_signal> - signal me when a signal gets signalled!	2258	=head2 C<ev_signal> - signal me when a signal gets signalled!
1380		2259
1381	Signal watchers will trigger an event when the process receives a specific	2260	Signal watchers will trigger an event when the process receives a specific
1382	signal one or more times. Even though signals are very asynchronous, libev	2261	signal one or more times. Even though signals are very asynchronous, libev
1383	will try it's best to deliver signals synchronously, i.e. as part of the	2262	will try it's best to deliver signals synchronously, i.e. as part of the
1384	normal event processing, like any other event.	2263	normal event processing, like any other event.
1385		2264
		2265	If you want signals to be delivered truly asynchronously, just use
		2266	C<sigaction> as you would do without libev and forget about sharing
		2267	the signal. You can even use C<ev_async> from a signal handler to
		2268	synchronously wake up an event loop.
		2269
1386	You can configure as many watchers as you like per signal. Only when the	2270	You can configure as many watchers as you like for the same signal, but
		2271	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2272	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2273	C<SIGINT> in both the default loop and another loop at the same time. At
		2274	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2275
1387	first watcher gets started will libev actually register a signal watcher	2276	When the first watcher gets started will libev actually register something
1388	with the kernel (thus it coexists with your own signal handlers as long	2277	with the kernel (thus it coexists with your own signal handlers as long as
1389	as you don't register any with libev). Similarly, when the last signal	2278	you don't register any with libev for the same signal).
1390	watcher for a signal is stopped libev will reset the signal handler to	2279
1391	SIG_DFL (regardless of what it was set to before).	2280	If possible and supported, libev will install its handlers with
		2281	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2282	not be unduly interrupted. If you have a problem with system calls getting
		2283	interrupted by signals you can block all signals in an C<ev_check> watcher
		2284	and unblock them in an C<ev_prepare> watcher.
		2285
		2286	=head3 The special problem of inheritance over fork/execve/pthread_create
		2287
		2288	Both the signal mask (C<sigprocmask>) and the signal disposition
		2289	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2290	stopping it again), that is, libev might or might not block the signal,
		2291	and might or might not set or restore the installed signal handler.
		2292
		2293	While this does not matter for the signal disposition (libev never
		2294	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2295	C<execve>), this matters for the signal mask: many programs do not expect
		2296	certain signals to be blocked.
		2297
		2298	This means that before calling C<exec> (from the child) you should reset
		2299	the signal mask to whatever "default" you expect (all clear is a good
		2300	choice usually).
		2301
		2302	The simplest way to ensure that the signal mask is reset in the child is
		2303	to install a fork handler with C<pthread_atfork> that resets it. That will
		2304	catch fork calls done by libraries (such as the libc) as well.
		2305
		2306	In current versions of libev, the signal will not be blocked indefinitely
		2307	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2308	the window of opportunity for problems, it will not go away, as libev
		2309	I<has> to modify the signal mask, at least temporarily.
		2310
		2311	So I can't stress this enough: I<If you do not reset your signal mask when
		2312	you expect it to be empty, you have a race condition in your code>. This
		2313	is not a libev-specific thing, this is true for most event libraries.
1392		2314
1393	=head3 Watcher-Specific Functions and Data Members	2315	=head3 Watcher-Specific Functions and Data Members
1394		2316
1395	=over 4	2317	=over 4
1396		2318
…		…
1405		2327
1406	The signal the watcher watches out for.	2328	The signal the watcher watches out for.
1407		2329
1408	=back	2330	=back
1409		2331
		2332	=head3 Examples
		2333
		2334	Example: Try to exit cleanly on SIGINT.
		2335
		2336	static void
		2337	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2338	{
		2339	ev_break (loop, EVBREAK_ALL);
		2340	}
		2341
		2342	ev_signal signal_watcher;
		2343	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2344	ev_signal_start (loop, &signal_watcher);
		2345
1410		2346
1411	=head2 C<ev_child> - watch out for process status changes	2347	=head2 C<ev_child> - watch out for process status changes
1412		2348
1413	Child watchers trigger when your process receives a SIGCHLD in response to	2349	Child watchers trigger when your process receives a SIGCHLD in response to
1414	some child status changes (most typically when a child of yours dies).	2350	some child status changes (most typically when a child of yours dies or
		2351	exits). It is permissible to install a child watcher I<after> the child
		2352	has been forked (which implies it might have already exited), as long
		2353	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2354	forking and then immediately registering a watcher for the child is fine,
		2355	but forking and registering a watcher a few event loop iterations later or
		2356	in the next callback invocation is not.
		2357
		2358	Only the default event loop is capable of handling signals, and therefore
		2359	you can only register child watchers in the default event loop.
		2360
		2361	Due to some design glitches inside libev, child watchers will always be
		2362	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2363	libev)
		2364
		2365	=head3 Process Interaction
		2366
		2367	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2368	initialised. This is necessary to guarantee proper behaviour even if the
		2369	first child watcher is started after the child exits. The occurrence
		2370	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2371	synchronously as part of the event loop processing. Libev always reaps all
		2372	children, even ones not watched.
		2373
		2374	=head3 Overriding the Built-In Processing
		2375
		2376	Libev offers no special support for overriding the built-in child
		2377	processing, but if your application collides with libev's default child
		2378	handler, you can override it easily by installing your own handler for
		2379	C<SIGCHLD> after initialising the default loop, and making sure the
		2380	default loop never gets destroyed. You are encouraged, however, to use an
		2381	event-based approach to child reaping and thus use libev's support for
		2382	that, so other libev users can use C<ev_child> watchers freely.
		2383
		2384	=head3 Stopping the Child Watcher
		2385
		2386	Currently, the child watcher never gets stopped, even when the
		2387	child terminates, so normally one needs to stop the watcher in the
		2388	callback. Future versions of libev might stop the watcher automatically
		2389	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2390	problem).
1415		2391
1416	=head3 Watcher-Specific Functions and Data Members	2392	=head3 Watcher-Specific Functions and Data Members
1417		2393
1418	=over 4	2394	=over 4
1419		2395
1420	=item ev_child_init (ev_child *, callback, int pid)	2396	=item ev_child_init (ev_child *, callback, int pid, int trace)
1421		2397
1422	=item ev_child_set (ev_child *, int pid)	2398	=item ev_child_set (ev_child *, int pid, int trace)
1423		2399
1424	Configures the watcher to wait for status changes of process C<pid> (or	2400	Configures the watcher to wait for status changes of process C<pid> (or
1425	I<any> process if C<pid> is specified as C<0>). The callback can look	2401	I<any> process if C<pid> is specified as C<0>). The callback can look
1426	at the C<rstatus> member of the C<ev_child> watcher structure to see	2402	at the C<rstatus> member of the C<ev_child> watcher structure to see
1427	the status word (use the macros from C<sys/wait.h> and see your systems	2403	the status word (use the macros from C<sys/wait.h> and see your systems
1428	C<waitpid> documentation). The C<rpid> member contains the pid of the	2404	C<waitpid> documentation). The C<rpid> member contains the pid of the
1429	process causing the status change.	2405	process causing the status change. C<trace> must be either C<0> (only
		2406	activate the watcher when the process terminates) or C<1> (additionally
		2407	activate the watcher when the process is stopped or continued).
1430		2408
1431	=item int pid [read-only]	2409	=item int pid [read-only]
1432		2410
1433	The process id this watcher watches out for, or C<0>, meaning any process id.	2411	The process id this watcher watches out for, or C<0>, meaning any process id.
1434		2412
…		…
1441	The process exit/trace status caused by C<rpid> (see your systems	2419	The process exit/trace status caused by C<rpid> (see your systems
1442	C<waitpid> and C<sys/wait.h> documentation for details).	2420	C<waitpid> and C<sys/wait.h> documentation for details).
1443		2421
1444	=back	2422	=back
1445		2423
1446	Example: Try to exit cleanly on SIGINT and SIGTERM.	2424	=head3 Examples
1447		2425
		2426	Example: C<fork()> a new process and install a child handler to wait for
		2427	its completion.
		2428
		2429	ev_child cw;
		2430
1448	static void	2431	static void
1449	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2432	child_cb (EV_P_ ev_child *w, int revents)
1450	{	2433	{
1451	ev_unloop (loop, EVUNLOOP_ALL);	2434	ev_child_stop (EV_A_ w);
		2435	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1452	}	2436	}
1453		2437
1454	struct ev_signal signal_watcher;	2438	pid_t pid = fork ();
1455	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2439
1456	ev_signal_start (loop, &sigint_cb);	2440	if (pid < 0)
		2441	// error
		2442	else if (pid == 0)
		2443	{
		2444	// the forked child executes here
		2445	exit (1);
		2446	}
		2447	else
		2448	{
		2449	ev_child_init (&cw, child_cb, pid, 0);
		2450	ev_child_start (EV_DEFAULT_ &cw);
		2451	}
1457		2452
1458		2453
1459	=head2 C<ev_stat> - did the file attributes just change?	2454	=head2 C<ev_stat> - did the file attributes just change?
1460		2455
1461	This watches a filesystem path for attribute changes. That is, it calls	2456	This watches a file system path for attribute changes. That is, it calls
1462	C<stat> regularly (or when the OS says it changed) and sees if it changed	2457	C<stat> on that path in regular intervals (or when the OS says it changed)
1463	compared to the last time, invoking the callback if it did.	2458	and sees if it changed compared to the last time, invoking the callback if
		2459	it did.
1464		2460
1465	The path does not need to exist: changing from "path exists" to "path does	2461	The path does not need to exist: changing from "path exists" to "path does
1466	not exist" is a status change like any other. The condition "path does	2462	not exist" is a status change like any other. The condition "path does not
1467	not exist" is signified by the C<st_nlink> field being zero (which is	2463	exist" (or more correctly "path cannot be stat'ed") is signified by the
1468	otherwise always forced to be at least one) and all the other fields of	2464	C<st_nlink> field being zero (which is otherwise always forced to be at
1469	the stat buffer having unspecified contents.	2465	least one) and all the other fields of the stat buffer having unspecified
		2466	contents.
1470		2467
1471	The path I<should> be absolute and I<must not> end in a slash. If it is	2468	The path I<must not> end in a slash or contain special components such as
		2469	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1472	relative and your working directory changes, the behaviour is undefined.	2470	your working directory changes, then the behaviour is undefined.
1473		2471
1474	Since there is no standard to do this, the portable implementation simply	2472	Since there is no portable change notification interface available, the
1475	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2473	portable implementation simply calls C<stat(2)> regularly on the path
1476	can specify a recommended polling interval for this case. If you specify	2474	to see if it changed somehow. You can specify a recommended polling
1477	a polling interval of C<0> (highly recommended!) then a I<suitable,	2475	interval for this case. If you specify a polling interval of C<0> (highly
1478	unspecified default> value will be used (which you can expect to be around	2476	recommended!) then a I<suitable, unspecified default> value will be used
1479	five seconds, although this might change dynamically). Libev will also	2477	(which you can expect to be around five seconds, although this might
1480	impose a minimum interval which is currently around C<0.1>, but thats	2478	change dynamically). Libev will also impose a minimum interval which is
1481	usually overkill.	2479	currently around C<0.1>, but that's usually overkill.
1482		2480
1483	This watcher type is not meant for massive numbers of stat watchers,	2481	This watcher type is not meant for massive numbers of stat watchers,
1484	as even with OS-supported change notifications, this can be	2482	as even with OS-supported change notifications, this can be
1485	resource-intensive.	2483	resource-intensive.
1486		2484
1487	At the time of this writing, only the Linux inotify interface is	2485	At the time of this writing, the only OS-specific interface implemented
1488	implemented (implementing kqueue support is left as an exercise for the	2486	is the Linux inotify interface (implementing kqueue support is left as an
1489	reader). Inotify will be used to give hints only and should not change the	2487	exercise for the reader. Note, however, that the author sees no way of
1490	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2488	implementing C<ev_stat> semantics with kqueue, except as a hint).
1491	to fall back to regular polling again even with inotify, but changes are
1492	usually detected immediately, and if the file exists there will be no
1493	polling.
1494		2489
1495	=head3 Inotify	2490	=head3 ABI Issues (Largefile Support)
1496		2491
		2492	Libev by default (unless the user overrides this) uses the default
		2493	compilation environment, which means that on systems with large file
		2494	support disabled by default, you get the 32 bit version of the stat
		2495	structure. When using the library from programs that change the ABI to
		2496	use 64 bit file offsets the programs will fail. In that case you have to
		2497	compile libev with the same flags to get binary compatibility. This is
		2498	obviously the case with any flags that change the ABI, but the problem is
		2499	most noticeably displayed with ev_stat and large file support.
		2500
		2501	The solution for this is to lobby your distribution maker to make large
		2502	file interfaces available by default (as e.g. FreeBSD does) and not
		2503	optional. Libev cannot simply switch on large file support because it has
		2504	to exchange stat structures with application programs compiled using the
		2505	default compilation environment.
		2506
		2507	=head3 Inotify and Kqueue
		2508
1497	When C<inotify (7)> support has been compiled into libev (generally only	2509	When C<inotify (7)> support has been compiled into libev and present at
1498	available on Linux) and present at runtime, it will be used to speed up	2510	runtime, it will be used to speed up change detection where possible. The
1499	change detection where possible. The inotify descriptor will be created lazily	2511	inotify descriptor will be created lazily when the first C<ev_stat>
1500	when the first C<ev_stat> watcher is being started.	2512	watcher is being started.
1501		2513
1502	Inotify presense does not change the semantics of C<ev_stat> watchers	2514	Inotify presence does not change the semantics of C<ev_stat> watchers
1503	except that changes might be detected earlier, and in some cases, to avoid	2515	except that changes might be detected earlier, and in some cases, to avoid
1504	making regular C<stat> calls. Even in the presense of inotify support	2516	making regular C<stat> calls. Even in the presence of inotify support
1505	there are many cases where libev has to resort to regular C<stat> polling.	2517	there are many cases where libev has to resort to regular C<stat> polling,
		2518	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2519	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2520	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2521	xfs are fully working) libev usually gets away without polling.
1506		2522
1507	(There is no support for kqueue, as apparently it cannot be used to	2523	There is no support for kqueue, as apparently it cannot be used to
1508	implement this functionality, due to the requirement of having a file	2524	implement this functionality, due to the requirement of having a file
1509	descriptor open on the object at all times).	2525	descriptor open on the object at all times, and detecting renames, unlinks
		2526	etc. is difficult.
		2527
		2528	=head3 C<stat ()> is a synchronous operation
		2529
		2530	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2531	the process. The exception are C<ev_stat> watchers - those call C<stat
		2532	()>, which is a synchronous operation.
		2533
		2534	For local paths, this usually doesn't matter: unless the system is very
		2535	busy or the intervals between stat's are large, a stat call will be fast,
		2536	as the path data is usually in memory already (except when starting the
		2537	watcher).
		2538
		2539	For networked file systems, calling C<stat ()> can block an indefinite
		2540	time due to network issues, and even under good conditions, a stat call
		2541	often takes multiple milliseconds.
		2542
		2543	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2544	paths, although this is fully supported by libev.
1510		2545
1511	=head3 The special problem of stat time resolution	2546	=head3 The special problem of stat time resolution
1512		2547
1513	The C<stat ()> syscall only supports full-second resolution portably, and	2548	The C<stat ()> system call only supports full-second resolution portably,
1514	even on systems where the resolution is higher, many filesystems still	2549	and even on systems where the resolution is higher, most file systems
1515	only support whole seconds.	2550	still only support whole seconds.
1516		2551
1517	That means that, if the time is the only thing that changes, you might	2552	That means that, if the time is the only thing that changes, you can
1518	miss updates: on the first update, C<ev_stat> detects a change and calls	2553	easily miss updates: on the first update, C<ev_stat> detects a change and
1519	your callback, which does something. When there is another update within	2554	calls your callback, which does something. When there is another update
1520	the same second, C<ev_stat> will be unable to detect it.	2555	within the same second, C<ev_stat> will be unable to detect unless the
		2556	stat data does change in other ways (e.g. file size).
1521		2557
1522	The solution to this is to delay acting on a change for a second (or till	2558	The solution to this is to delay acting on a change for slightly more
1523	the next second boundary), using a roughly one-second delay C<ev_timer>	2559	than a second (or till slightly after the next full second boundary), using
1524	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2560	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1525	is added to work around small timing inconsistencies of some operating	2561	ev_timer_again (loop, w)>).
1526	systems.	2562
		2563	The C<.02> offset is added to work around small timing inconsistencies
		2564	of some operating systems (where the second counter of the current time
		2565	might be be delayed. One such system is the Linux kernel, where a call to
		2566	C<gettimeofday> might return a timestamp with a full second later than
		2567	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2568	update file times then there will be a small window where the kernel uses
		2569	the previous second to update file times but libev might already execute
		2570	the timer callback).
1527		2571
1528	=head3 Watcher-Specific Functions and Data Members	2572	=head3 Watcher-Specific Functions and Data Members
1529		2573
1530	=over 4	2574	=over 4
1531		2575
…		…
1537	C<path>. The C<interval> is a hint on how quickly a change is expected to	2581	C<path>. The C<interval> is a hint on how quickly a change is expected to
1538	be detected and should normally be specified as C<0> to let libev choose	2582	be detected and should normally be specified as C<0> to let libev choose
1539	a suitable value. The memory pointed to by C<path> must point to the same	2583	a suitable value. The memory pointed to by C<path> must point to the same
1540	path for as long as the watcher is active.	2584	path for as long as the watcher is active.
1541		2585
1542	The callback will be receive C<EV_STAT> when a change was detected,	2586	The callback will receive an C<EV_STAT> event when a change was detected,
1543	relative to the attributes at the time the watcher was started (or the	2587	relative to the attributes at the time the watcher was started (or the
1544	last change was detected).	2588	last change was detected).
1545		2589
1546	=item ev_stat_stat (ev_stat *)	2590	=item ev_stat_stat (loop, ev_stat *)
1547		2591
1548	Updates the stat buffer immediately with new values. If you change the	2592	Updates the stat buffer immediately with new values. If you change the
1549	watched path in your callback, you could call this fucntion to avoid	2593	watched path in your callback, you could call this function to avoid
1550	detecting this change (while introducing a race condition). Can also be	2594	detecting this change (while introducing a race condition if you are not
1551	useful simply to find out the new values.	2595	the only one changing the path). Can also be useful simply to find out the
		2596	new values.
1552		2597
1553	=item ev_statdata attr [read-only]	2598	=item ev_statdata attr [read-only]
1554		2599
1555	The most-recently detected attributes of the file. Although the type is of	2600	The most-recently detected attributes of the file. Although the type is
1556	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2601	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1557	suitable for your system. If the C<st_nlink> member is C<0>, then there	2602	suitable for your system, but you can only rely on the POSIX-standardised
		2603	members to be present. If the C<st_nlink> member is C<0>, then there was
1558	was some error while C<stat>ing the file.	2604	some error while C<stat>ing the file.
1559		2605
1560	=item ev_statdata prev [read-only]	2606	=item ev_statdata prev [read-only]
1561		2607
1562	The previous attributes of the file. The callback gets invoked whenever	2608	The previous attributes of the file. The callback gets invoked whenever
1563	C<prev> != C<attr>.	2609	C<prev> != C<attr>, or, more precisely, one or more of these members
		2610	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2611	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1564		2612
1565	=item ev_tstamp interval [read-only]	2613	=item ev_tstamp interval [read-only]
1566		2614
1567	The specified interval.	2615	The specified interval.
1568		2616
1569	=item const char *path [read-only]	2617	=item const char *path [read-only]
1570		2618
1571	The filesystem path that is being watched.	2619	The file system path that is being watched.
1572		2620
1573	=back	2621	=back
1574		2622
1575	=head3 Examples	2623	=head3 Examples
1576		2624
1577	Example: Watch C</etc/passwd> for attribute changes.	2625	Example: Watch C</etc/passwd> for attribute changes.
1578		2626
1579	static void	2627	static void
1580	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2628	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1581	{	2629	{
1582	/* /etc/passwd changed in some way */	2630	/* /etc/passwd changed in some way */
1583	if (w->attr.st_nlink)	2631	if (w->attr.st_nlink)
1584	{	2632	{
1585	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2633	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1586	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2634	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1587	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2635	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1588	}	2636	}
1589	else	2637	else
1590	/* you shalt not abuse printf for puts */	2638	/* you shalt not abuse printf for puts */
1591	puts ("wow, /etc/passwd is not there, expect problems. "	2639	puts ("wow, /etc/passwd is not there, expect problems. "
1592	"if this is windows, they already arrived\n");	2640	"if this is windows, they already arrived\n");
1593	}	2641	}
1594		2642
1595	...	2643	...
1596	ev_stat passwd;	2644	ev_stat passwd;
1597		2645
1598	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2646	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1599	ev_stat_start (loop, &passwd);	2647	ev_stat_start (loop, &passwd);
1600		2648
1601	Example: Like above, but additionally use a one-second delay so we do not	2649	Example: Like above, but additionally use a one-second delay so we do not
1602	miss updates (however, frequent updates will delay processing, too, so	2650	miss updates (however, frequent updates will delay processing, too, so
1603	one might do the work both on C<ev_stat> callback invocation I<and> on	2651	one might do the work both on C<ev_stat> callback invocation I<and> on
1604	C<ev_timer> callback invocation).	2652	C<ev_timer> callback invocation).
1605		2653
1606	static ev_stat passwd;	2654	static ev_stat passwd;
1607	static ev_timer timer;	2655	static ev_timer timer;
1608		2656
1609	static void	2657	static void
1610	timer_cb (EV_P_ ev_timer *w, int revents)	2658	timer_cb (EV_P_ ev_timer *w, int revents)
1611	{	2659	{
1612	ev_timer_stop (EV_A_ w);	2660	ev_timer_stop (EV_A_ w);
1613		2661
1614	/* now it's one second after the most recent passwd change */	2662	/* now it's one second after the most recent passwd change */
1615	}	2663	}
1616		2664
1617	static void	2665	static void
1618	stat_cb (EV_P_ ev_stat *w, int revents)	2666	stat_cb (EV_P_ ev_stat *w, int revents)
1619	{	2667	{
1620	/* reset the one-second timer */	2668	/* reset the one-second timer */
1621	ev_timer_again (EV_A_ &timer);	2669	ev_timer_again (EV_A_ &timer);
1622	}	2670	}
1623		2671
1624	...	2672	...
1625	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2673	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1626	ev_stat_start (loop, &passwd);	2674	ev_stat_start (loop, &passwd);
1627	ev_timer_init (&timer, timer_cb, 0., 1.01);	2675	ev_timer_init (&timer, timer_cb, 0., 1.02);
1628		2676
1629		2677
1630	=head2 C<ev_idle> - when you've got nothing better to do...	2678	=head2 C<ev_idle> - when you've got nothing better to do...
1631		2679
1632	Idle watchers trigger events when no other events of the same or higher	2680	Idle watchers trigger events when no other events of the same or higher
1633	priority are pending (prepare, check and other idle watchers do not	2681	priority are pending (prepare, check and other idle watchers do not count
1634	count).	2682	as receiving "events").
1635		2683
1636	That is, as long as your process is busy handling sockets or timeouts	2684	That is, as long as your process is busy handling sockets or timeouts
1637	(or even signals, imagine) of the same or higher priority it will not be	2685	(or even signals, imagine) of the same or higher priority it will not be
1638	triggered. But when your process is idle (or only lower-priority watchers	2686	triggered. But when your process is idle (or only lower-priority watchers
1639	are pending), the idle watchers are being called once per event loop	2687	are pending), the idle watchers are being called once per event loop
…		…
1650		2698
1651	=head3 Watcher-Specific Functions and Data Members	2699	=head3 Watcher-Specific Functions and Data Members
1652		2700
1653	=over 4	2701	=over 4
1654		2702
1655	=item ev_idle_init (ev_signal *, callback)	2703	=item ev_idle_init (ev_idle *, callback)
1656		2704
1657	Initialises and configures the idle watcher - it has no parameters of any	2705	Initialises and configures the idle watcher - it has no parameters of any
1658	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2706	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1659	believe me.	2707	believe me.
1660		2708
1661	=back	2709	=back
1662		2710
		2711	=head3 Examples
		2712
1663	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2713	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1664	callback, free it. Also, use no error checking, as usual.	2714	callback, free it. Also, use no error checking, as usual.
1665		2715
1666	static void	2716	static void
1667	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2717	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1668	{	2718	{
1669	free (w);	2719	free (w);
1670	// now do something you wanted to do when the program has	2720	// now do something you wanted to do when the program has
1671	// no longer asnything immediate to do.	2721	// no longer anything immediate to do.
1672	}	2722	}
1673		2723
1674	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2724	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1675	ev_idle_init (idle_watcher, idle_cb);	2725	ev_idle_init (idle_watcher, idle_cb);
1676	ev_idle_start (loop, idle_cb);	2726	ev_idle_start (loop, idle_watcher);
1677		2727
1678		2728
1679	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2729	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1680		2730
1681	Prepare and check watchers are usually (but not always) used in tandem:	2731	Prepare and check watchers are usually (but not always) used in pairs:
1682	prepare watchers get invoked before the process blocks and check watchers	2732	prepare watchers get invoked before the process blocks and check watchers
1683	afterwards.	2733	afterwards.
1684		2734
1685	You I<must not> call C<ev_loop> or similar functions that enter	2735	You I<must not> call C<ev_run> or similar functions that enter
1686	the current event loop from either C<ev_prepare> or C<ev_check>	2736	the current event loop from either C<ev_prepare> or C<ev_check>
1687	watchers. Other loops than the current one are fine, however. The	2737	watchers. Other loops than the current one are fine, however. The
1688	rationale behind this is that you do not need to check for recursion in	2738	rationale behind this is that you do not need to check for recursion in
1689	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2739	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1690	C<ev_check> so if you have one watcher of each kind they will always be	2740	C<ev_check> so if you have one watcher of each kind they will always be
1691	called in pairs bracketing the blocking call.	2741	called in pairs bracketing the blocking call.
1692		2742
1693	Their main purpose is to integrate other event mechanisms into libev and	2743	Their main purpose is to integrate other event mechanisms into libev and
1694	their use is somewhat advanced. This could be used, for example, to track	2744	their use is somewhat advanced. They could be used, for example, to track
1695	variable changes, implement your own watchers, integrate net-snmp or a	2745	variable changes, implement your own watchers, integrate net-snmp or a
1696	coroutine library and lots more. They are also occasionally useful if	2746	coroutine library and lots more. They are also occasionally useful if
1697	you cache some data and want to flush it before blocking (for example,	2747	you cache some data and want to flush it before blocking (for example,
1698	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2748	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1699	watcher).	2749	watcher).
1700		2750
1701	This is done by examining in each prepare call which file descriptors need	2751	This is done by examining in each prepare call which file descriptors
1702	to be watched by the other library, registering C<ev_io> watchers for	2752	need to be watched by the other library, registering C<ev_io> watchers
1703	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2753	for them and starting an C<ev_timer> watcher for any timeouts (many
1704	provide just this functionality). Then, in the check watcher you check for	2754	libraries provide exactly this functionality). Then, in the check watcher,
1705	any events that occured (by checking the pending status of all watchers	2755	you check for any events that occurred (by checking the pending status
1706	and stopping them) and call back into the library. The I/O and timer	2756	of all watchers and stopping them) and call back into the library. The
1707	callbacks will never actually be called (but must be valid nevertheless,	2757	I/O and timer callbacks will never actually be called (but must be valid
1708	because you never know, you know?).	2758	nevertheless, because you never know, you know?).
1709		2759
1710	As another example, the Perl Coro module uses these hooks to integrate	2760	As another example, the Perl Coro module uses these hooks to integrate
1711	coroutines into libev programs, by yielding to other active coroutines	2761	coroutines into libev programs, by yielding to other active coroutines
1712	during each prepare and only letting the process block if no coroutines	2762	during each prepare and only letting the process block if no coroutines
1713	are ready to run (it's actually more complicated: it only runs coroutines	2763	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1716	loop from blocking if lower-priority coroutines are active, thus mapping	2766	loop from blocking if lower-priority coroutines are active, thus mapping
1717	low-priority coroutines to idle/background tasks).	2767	low-priority coroutines to idle/background tasks).
1718		2768
1719	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2769	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1720	priority, to ensure that they are being run before any other watchers	2770	priority, to ensure that they are being run before any other watchers
		2771	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2772
1721	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2773	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1722	too) should not activate ("feed") events into libev. While libev fully	2774	activate ("feed") events into libev. While libev fully supports this, they
1723	supports this, they will be called before other C<ev_check> watchers	2775	might get executed before other C<ev_check> watchers did their job. As
1724	did their job. As C<ev_check> watchers are often used to embed other	2776	C<ev_check> watchers are often used to embed other (non-libev) event
1725	(non-libev) event loops those other event loops might be in an unusable	2777	loops those other event loops might be in an unusable state until their
1726	state until their C<ev_check> watcher ran (always remind yourself to	2778	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1727	coexist peacefully with others).	2779	others).
1728		2780
1729	=head3 Watcher-Specific Functions and Data Members	2781	=head3 Watcher-Specific Functions and Data Members
1730		2782
1731	=over 4	2783	=over 4
1732		2784
…		…
1734		2786
1735	=item ev_check_init (ev_check *, callback)	2787	=item ev_check_init (ev_check *, callback)
1736		2788
1737	Initialises and configures the prepare or check watcher - they have no	2789	Initialises and configures the prepare or check watcher - they have no
1738	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2790	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1739	macros, but using them is utterly, utterly and completely pointless.	2791	macros, but using them is utterly, utterly, utterly and completely
		2792	pointless.
1740		2793
1741	=back	2794	=back
		2795
		2796	=head3 Examples
1742		2797
1743	There are a number of principal ways to embed other event loops or modules	2798	There are a number of principal ways to embed other event loops or modules
1744	into libev. Here are some ideas on how to include libadns into libev	2799	into libev. Here are some ideas on how to include libadns into libev
1745	(there is a Perl module named C<EV::ADNS> that does this, which you could	2800	(there is a Perl module named C<EV::ADNS> that does this, which you could
1746	use for an actually working example. Another Perl module named C<EV::Glib>	2801	use as a working example. Another Perl module named C<EV::Glib> embeds a
1747	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2802	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1748	into the Glib event loop).	2803	Glib event loop).
1749		2804
1750	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2805	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1751	and in a check watcher, destroy them and call into libadns. What follows	2806	and in a check watcher, destroy them and call into libadns. What follows
1752	is pseudo-code only of course. This requires you to either use a low	2807	is pseudo-code only of course. This requires you to either use a low
1753	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2808	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1754	the callbacks for the IO/timeout watchers might not have been called yet.	2809	the callbacks for the IO/timeout watchers might not have been called yet.
1755		2810
1756	static ev_io iow [nfd];	2811	static ev_io iow [nfd];
1757	static ev_timer tw;	2812	static ev_timer tw;
1758		2813
1759	static void	2814	static void
1760	io_cb (ev_loop *loop, ev_io *w, int revents)	2815	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1761	{	2816	{
1762	}	2817	}
1763		2818
1764	// create io watchers for each fd and a timer before blocking	2819	// create io watchers for each fd and a timer before blocking
1765	static void	2820	static void
1766	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2821	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1767	{	2822	{
1768	int timeout = 3600000;	2823	int timeout = 3600000;
1769	struct pollfd fds [nfd];	2824	struct pollfd fds [nfd];
1770	// actual code will need to loop here and realloc etc.	2825	// actual code will need to loop here and realloc etc.
1771	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2826	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1772		2827
1773	/* the callback is illegal, but won't be called as we stop during check */	2828	/* the callback is illegal, but won't be called as we stop during check */
1774	ev_timer_init (&tw, 0, timeout * 1e-3);	2829	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1775	ev_timer_start (loop, &tw);	2830	ev_timer_start (loop, &tw);
1776		2831
1777	// create one ev_io per pollfd	2832	// create one ev_io per pollfd
1778	for (int i = 0; i < nfd; ++i)	2833	for (int i = 0; i < nfd; ++i)
1779	{	2834	{
1780	ev_io_init (iow + i, io_cb, fds [i].fd,	2835	ev_io_init (iow + i, io_cb, fds [i].fd,
1781	((fds [i].events & POLLIN ? EV_READ : 0)	2836	((fds [i].events & POLLIN ? EV_READ : 0)
1782	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2837	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1783		2838
1784	fds [i].revents = 0;	2839	fds [i].revents = 0;
1785	ev_io_start (loop, iow + i);	2840	ev_io_start (loop, iow + i);
1786	}	2841	}
1787	}	2842	}
1788		2843
1789	// stop all watchers after blocking	2844	// stop all watchers after blocking
1790	static void	2845	static void
1791	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2846	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1792	{	2847	{
1793	ev_timer_stop (loop, &tw);	2848	ev_timer_stop (loop, &tw);
1794		2849
1795	for (int i = 0; i < nfd; ++i)	2850	for (int i = 0; i < nfd; ++i)
1796	{	2851	{
1797	// set the relevant poll flags	2852	// set the relevant poll flags
1798	// could also call adns_processreadable etc. here	2853	// could also call adns_processreadable etc. here
1799	struct pollfd *fd = fds + i;	2854	struct pollfd *fd = fds + i;
1800	int revents = ev_clear_pending (iow + i);	2855	int revents = ev_clear_pending (iow + i);
1801	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2856	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1802	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2857	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1803		2858
1804	// now stop the watcher	2859	// now stop the watcher
1805	ev_io_stop (loop, iow + i);	2860	ev_io_stop (loop, iow + i);
1806	}	2861	}
1807		2862
1808	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2863	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1809	}	2864	}
1810		2865
1811	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2866	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1812	in the prepare watcher and would dispose of the check watcher.	2867	in the prepare watcher and would dispose of the check watcher.
1813		2868
1814	Method 3: If the module to be embedded supports explicit event	2869	Method 3: If the module to be embedded supports explicit event
1815	notification (adns does), you can also make use of the actual watcher	2870	notification (libadns does), you can also make use of the actual watcher
1816	callbacks, and only destroy/create the watchers in the prepare watcher.	2871	callbacks, and only destroy/create the watchers in the prepare watcher.
1817		2872
1818	static void	2873	static void
1819	timer_cb (EV_P_ ev_timer *w, int revents)	2874	timer_cb (EV_P_ ev_timer *w, int revents)
1820	{	2875	{
1821	adns_state ads = (adns_state)w->data;	2876	adns_state ads = (adns_state)w->data;
1822	update_now (EV_A);	2877	update_now (EV_A);
1823		2878
1824	adns_processtimeouts (ads, &tv_now);	2879	adns_processtimeouts (ads, &tv_now);
1825	}	2880	}
1826		2881
1827	static void	2882	static void
1828	io_cb (EV_P_ ev_io *w, int revents)	2883	io_cb (EV_P_ ev_io *w, int revents)
1829	{	2884	{
1830	adns_state ads = (adns_state)w->data;	2885	adns_state ads = (adns_state)w->data;
1831	update_now (EV_A);	2886	update_now (EV_A);
1832		2887
1833	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2888	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1834	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2889	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1835	}	2890	}
1836		2891
1837	// do not ever call adns_afterpoll	2892	// do not ever call adns_afterpoll
1838		2893
1839	Method 4: Do not use a prepare or check watcher because the module you	2894	Method 4: Do not use a prepare or check watcher because the module you
1840	want to embed is too inflexible to support it. Instead, youc na override	2895	want to embed is not flexible enough to support it. Instead, you can
1841	their poll function. The drawback with this solution is that the main	2896	override their poll function. The drawback with this solution is that the
1842	loop is now no longer controllable by EV. The C<Glib::EV> module does	2897	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1843	this.	2898	this approach, effectively embedding EV as a client into the horrible
		2899	libglib event loop.
1844		2900
1845	static gint	2901	static gint
1846	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2902	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1847	{	2903	{
1848	int got_events = 0;	2904	int got_events = 0;
1849		2905
1850	for (n = 0; n < nfds; ++n)	2906	for (n = 0; n < nfds; ++n)
1851	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2907	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1852		2908
1853	if (timeout >= 0)	2909	if (timeout >= 0)
1854	// create/start timer	2910	// create/start timer
1855		2911
1856	// poll	2912	// poll
1857	ev_loop (EV_A_ 0);	2913	ev_run (EV_A_ 0);
1858		2914
1859	// stop timer again	2915	// stop timer again
1860	if (timeout >= 0)	2916	if (timeout >= 0)
1861	ev_timer_stop (EV_A_ &to);	2917	ev_timer_stop (EV_A_ &to);
1862		2918
1863	// stop io watchers again - their callbacks should have set	2919	// stop io watchers again - their callbacks should have set
1864	for (n = 0; n < nfds; ++n)	2920	for (n = 0; n < nfds; ++n)
1865	ev_io_stop (EV_A_ iow [n]);	2921	ev_io_stop (EV_A_ iow [n]);
1866		2922
1867	return got_events;	2923	return got_events;
1868	}	2924	}
1869		2925
1870		2926
1871	=head2 C<ev_embed> - when one backend isn't enough...	2927	=head2 C<ev_embed> - when one backend isn't enough...
1872		2928
1873	This is a rather advanced watcher type that lets you embed one event loop	2929	This is a rather advanced watcher type that lets you embed one event loop
…		…
1879	prioritise I/O.	2935	prioritise I/O.
1880		2936
1881	As an example for a bug workaround, the kqueue backend might only support	2937	As an example for a bug workaround, the kqueue backend might only support
1882	sockets on some platform, so it is unusable as generic backend, but you	2938	sockets on some platform, so it is unusable as generic backend, but you
1883	still want to make use of it because you have many sockets and it scales	2939	still want to make use of it because you have many sockets and it scales
1884	so nicely. In this case, you would create a kqueue-based loop and embed it	2940	so nicely. In this case, you would create a kqueue-based loop and embed
1885	into your default loop (which might use e.g. poll). Overall operation will	2941	it into your default loop (which might use e.g. poll). Overall operation
1886	be a bit slower because first libev has to poll and then call kevent, but	2942	will be a bit slower because first libev has to call C<poll> and then
1887	at least you can use both at what they are best.	2943	C<kevent>, but at least you can use both mechanisms for what they are
		2944	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1888		2945
1889	As for prioritising I/O: rarely you have the case where some fds have	2946	As for prioritising I/O: under rare circumstances you have the case where
1890	to be watched and handled very quickly (with low latency), and even	2947	some fds have to be watched and handled very quickly (with low latency),
1891	priorities and idle watchers might have too much overhead. In this case	2948	and even priorities and idle watchers might have too much overhead. In
1892	you would put all the high priority stuff in one loop and all the rest in	2949	this case you would put all the high priority stuff in one loop and all
1893	a second one, and embed the second one in the first.	2950	the rest in a second one, and embed the second one in the first.
1894		2951
1895	As long as the watcher is active, the callback will be invoked every time	2952	As long as the watcher is active, the callback will be invoked every
1896	there might be events pending in the embedded loop. The callback must then	2953	time there might be events pending in the embedded loop. The callback
1897	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2954	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1898	their callbacks (you could also start an idle watcher to give the embedded	2955	sweep and invoke their callbacks (the callback doesn't need to invoke the
1899	loop strictly lower priority for example). You can also set the callback	2956	C<ev_embed_sweep> function directly, it could also start an idle watcher
1900	to C<0>, in which case the embed watcher will automatically execute the	2957	to give the embedded loop strictly lower priority for example).
1901	embedded loop sweep.
1902		2958
1903	As long as the watcher is started it will automatically handle events. The	2959	You can also set the callback to C<0>, in which case the embed watcher
1904	callback will be invoked whenever some events have been handled. You can	2960	will automatically execute the embedded loop sweep whenever necessary.
1905	set the callback to C<0> to avoid having to specify one if you are not
1906	interested in that.
1907		2961
1908	Also, there have not currently been made special provisions for forking:	2962	Fork detection will be handled transparently while the C<ev_embed> watcher
1909	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2963	is active, i.e., the embedded loop will automatically be forked when the
1910	but you will also have to stop and restart any C<ev_embed> watchers	2964	embedding loop forks. In other cases, the user is responsible for calling
1911	yourself.	2965	C<ev_loop_fork> on the embedded loop.
1912		2966
1913	Unfortunately, not all backends are embeddable, only the ones returned by	2967	Unfortunately, not all backends are embeddable: only the ones returned by
1914	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2968	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1915	portable one.	2969	portable one.
1916		2970
1917	So when you want to use this feature you will always have to be prepared	2971	So when you want to use this feature you will always have to be prepared
1918	that you cannot get an embeddable loop. The recommended way to get around	2972	that you cannot get an embeddable loop. The recommended way to get around
1919	this is to have a separate variables for your embeddable loop, try to	2973	this is to have a separate variables for your embeddable loop, try to
1920	create it, and if that fails, use the normal loop for everything:	2974	create it, and if that fails, use the normal loop for everything.
1921		2975
1922	struct ev_loop *loop_hi = ev_default_init (0);	2976	=head3 C<ev_embed> and fork
1923	struct ev_loop *loop_lo = 0;
1924	struct ev_embed embed;
1925
1926	// see if there is a chance of getting one that works
1927	// (remember that a flags value of 0 means autodetection)
1928	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1929	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1930	: 0;
1931		2977
1932	// if we got one, then embed it, otherwise default to loop_hi	2978	While the C<ev_embed> watcher is running, forks in the embedding loop will
1933	if (loop_lo)	2979	automatically be applied to the embedded loop as well, so no special
1934	{	2980	fork handling is required in that case. When the watcher is not running,
1935	ev_embed_init (&embed, 0, loop_lo);	2981	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1936	ev_embed_start (loop_hi, &embed);	2982	as applicable.
1937	}
1938	else
1939	loop_lo = loop_hi;
1940		2983
1941	=head3 Watcher-Specific Functions and Data Members	2984	=head3 Watcher-Specific Functions and Data Members
1942		2985
1943	=over 4	2986	=over 4
1944		2987
…		…
1948		2991
1949	Configures the watcher to embed the given loop, which must be	2992	Configures the watcher to embed the given loop, which must be
1950	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2993	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1951	invoked automatically, otherwise it is the responsibility of the callback	2994	invoked automatically, otherwise it is the responsibility of the callback
1952	to invoke it (it will continue to be called until the sweep has been done,	2995	to invoke it (it will continue to be called until the sweep has been done,
1953	if you do not want thta, you need to temporarily stop the embed watcher).	2996	if you do not want that, you need to temporarily stop the embed watcher).
1954		2997
1955	=item ev_embed_sweep (loop, ev_embed *)	2998	=item ev_embed_sweep (loop, ev_embed *)
1956		2999
1957	Make a single, non-blocking sweep over the embedded loop. This works	3000	Make a single, non-blocking sweep over the embedded loop. This works
1958	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3001	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1959	apropriate way for embedded loops.	3002	appropriate way for embedded loops.
1960		3003
1961	=item struct ev_loop *other [read-only]	3004	=item struct ev_loop *other [read-only]
1962		3005
1963	The embedded event loop.	3006	The embedded event loop.
1964		3007
1965	=back	3008	=back
		3009
		3010	=head3 Examples
		3011
		3012	Example: Try to get an embeddable event loop and embed it into the default
		3013	event loop. If that is not possible, use the default loop. The default
		3014	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3015	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3016	used).
		3017
		3018	struct ev_loop *loop_hi = ev_default_init (0);
		3019	struct ev_loop *loop_lo = 0;
		3020	ev_embed embed;
		3021
		3022	// see if there is a chance of getting one that works
		3023	// (remember that a flags value of 0 means autodetection)
		3024	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3025	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3026	: 0;
		3027
		3028	// if we got one, then embed it, otherwise default to loop_hi
		3029	if (loop_lo)
		3030	{
		3031	ev_embed_init (&embed, 0, loop_lo);
		3032	ev_embed_start (loop_hi, &embed);
		3033	}
		3034	else
		3035	loop_lo = loop_hi;
		3036
		3037	Example: Check if kqueue is available but not recommended and create
		3038	a kqueue backend for use with sockets (which usually work with any
		3039	kqueue implementation). Store the kqueue/socket-only event loop in
		3040	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3041
		3042	struct ev_loop *loop = ev_default_init (0);
		3043	struct ev_loop *loop_socket = 0;
		3044	ev_embed embed;
		3045
		3046	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3047	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3048	{
		3049	ev_embed_init (&embed, 0, loop_socket);
		3050	ev_embed_start (loop, &embed);
		3051	}
		3052
		3053	if (!loop_socket)
		3054	loop_socket = loop;
		3055
		3056	// now use loop_socket for all sockets, and loop for everything else
1966		3057
1967		3058
1968	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3059	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1969		3060
1970	Fork watchers are called when a C<fork ()> was detected (usually because	3061	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1973	event loop blocks next and before C<ev_check> watchers are being called,	3064	event loop blocks next and before C<ev_check> watchers are being called,
1974	and only in the child after the fork. If whoever good citizen calling	3065	and only in the child after the fork. If whoever good citizen calling
1975	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3066	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1976	handlers will be invoked, too, of course.	3067	handlers will be invoked, too, of course.
1977		3068
		3069	=head3 The special problem of life after fork - how is it possible?
		3070
		3071	Most uses of C<fork()> consist of forking, then some simple calls to set
		3072	up/change the process environment, followed by a call to C<exec()>. This
		3073	sequence should be handled by libev without any problems.
		3074
		3075	This changes when the application actually wants to do event handling
		3076	in the child, or both parent in child, in effect "continuing" after the
		3077	fork.
		3078
		3079	The default mode of operation (for libev, with application help to detect
		3080	forks) is to duplicate all the state in the child, as would be expected
		3081	when I<either> the parent I<or> the child process continues.
		3082
		3083	When both processes want to continue using libev, then this is usually the
		3084	wrong result. In that case, usually one process (typically the parent) is
		3085	supposed to continue with all watchers in place as before, while the other
		3086	process typically wants to start fresh, i.e. without any active watchers.
		3087
		3088	The cleanest and most efficient way to achieve that with libev is to
		3089	simply create a new event loop, which of course will be "empty", and
		3090	use that for new watchers. This has the advantage of not touching more
		3091	memory than necessary, and thus avoiding the copy-on-write, and the
		3092	disadvantage of having to use multiple event loops (which do not support
		3093	signal watchers).
		3094
		3095	When this is not possible, or you want to use the default loop for
		3096	other reasons, then in the process that wants to start "fresh", call
		3097	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3098	Destroying the default loop will "orphan" (not stop) all registered
		3099	watchers, so you have to be careful not to execute code that modifies
		3100	those watchers. Note also that in that case, you have to re-register any
		3101	signal watchers.
		3102
1978	=head3 Watcher-Specific Functions and Data Members	3103	=head3 Watcher-Specific Functions and Data Members
1979		3104
1980	=over 4	3105	=over 4
1981		3106
1982	=item ev_fork_init (ev_signal *, callback)	3107	=item ev_fork_init (ev_fork *, callback)
1983		3108
1984	Initialises and configures the fork watcher - it has no parameters of any	3109	Initialises and configures the fork watcher - it has no parameters of any
1985	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3110	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
1986	believe me.	3111	really.
1987		3112
1988	=back	3113	=back
1989		3114
1990		3115
		3116	=head2 C<ev_cleanup> - even the best things end
		3117
		3118	Cleanup watchers are called just before the event loop is being destroyed
		3119	by a call to C<ev_loop_destroy>.
		3120
		3121	While there is no guarantee that the event loop gets destroyed, cleanup
		3122	watchers provide a convenient method to install cleanup hooks for your
		3123	program, worker threads and so on - you just to make sure to destroy the
		3124	loop when you want them to be invoked.
		3125
		3126	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3127	all other watchers, they do not keep a reference to the event loop (which
		3128	makes a lot of sense if you think about it). Like all other watchers, you
		3129	can call libev functions in the callback, except C<ev_cleanup_start>.
		3130
		3131	=head3 Watcher-Specific Functions and Data Members
		3132
		3133	=over 4
		3134
		3135	=item ev_cleanup_init (ev_cleanup *, callback)
		3136
		3137	Initialises and configures the cleanup watcher - it has no parameters of
		3138	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3139	pointless, I assure you.
		3140
		3141	=back
		3142
		3143	Example: Register an atexit handler to destroy the default loop, so any
		3144	cleanup functions are called.
		3145
		3146	static void
		3147	program_exits (void)
		3148	{
		3149	ev_loop_destroy (EV_DEFAULT_UC);
		3150	}
		3151
		3152	...
		3153	atexit (program_exits);
		3154
		3155
		3156	=head2 C<ev_async> - how to wake up an event loop
		3157
		3158	In general, you cannot use an C<ev_run> from multiple threads or other
		3159	asynchronous sources such as signal handlers (as opposed to multiple event
		3160	loops - those are of course safe to use in different threads).
		3161
		3162	Sometimes, however, you need to wake up an event loop you do not control,
		3163	for example because it belongs to another thread. This is what C<ev_async>
		3164	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3165	it by calling C<ev_async_send>, which is thread- and signal safe.
		3166
		3167	This functionality is very similar to C<ev_signal> watchers, as signals,
		3168	too, are asynchronous in nature, and signals, too, will be compressed
		3169	(i.e. the number of callback invocations may be less than the number of
		3170	C<ev_async_sent> calls).
		3171
		3172	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3173	just the default loop.
		3174
		3175	=head3 Queueing
		3176
		3177	C<ev_async> does not support queueing of data in any way. The reason
		3178	is that the author does not know of a simple (or any) algorithm for a
		3179	multiple-writer-single-reader queue that works in all cases and doesn't
		3180	need elaborate support such as pthreads or unportable memory access
		3181	semantics.
		3182
		3183	That means that if you want to queue data, you have to provide your own
		3184	queue. But at least I can tell you how to implement locking around your
		3185	queue:
		3186
		3187	=over 4
		3188
		3189	=item queueing from a signal handler context
		3190
		3191	To implement race-free queueing, you simply add to the queue in the signal
		3192	handler but you block the signal handler in the watcher callback. Here is
		3193	an example that does that for some fictitious SIGUSR1 handler:
		3194
		3195	static ev_async mysig;
		3196
		3197	static void
		3198	sigusr1_handler (void)
		3199	{
		3200	sometype data;
		3201
		3202	// no locking etc.
		3203	queue_put (data);
		3204	ev_async_send (EV_DEFAULT_ &mysig);
		3205	}
		3206
		3207	static void
		3208	mysig_cb (EV_P_ ev_async *w, int revents)
		3209	{
		3210	sometype data;
		3211	sigset_t block, prev;
		3212
		3213	sigemptyset (&block);
		3214	sigaddset (&block, SIGUSR1);
		3215	sigprocmask (SIG_BLOCK, &block, &prev);
		3216
		3217	while (queue_get (&data))
		3218	process (data);
		3219
		3220	if (sigismember (&prev, SIGUSR1)
		3221	sigprocmask (SIG_UNBLOCK, &block, 0);
		3222	}
		3223
		3224	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3225	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3226	either...).
		3227
		3228	=item queueing from a thread context
		3229
		3230	The strategy for threads is different, as you cannot (easily) block
		3231	threads but you can easily preempt them, so to queue safely you need to
		3232	employ a traditional mutex lock, such as in this pthread example:
		3233
		3234	static ev_async mysig;
		3235	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3236
		3237	static void
		3238	otherthread (void)
		3239	{
		3240	// only need to lock the actual queueing operation
		3241	pthread_mutex_lock (&mymutex);
		3242	queue_put (data);
		3243	pthread_mutex_unlock (&mymutex);
		3244
		3245	ev_async_send (EV_DEFAULT_ &mysig);
		3246	}
		3247
		3248	static void
		3249	mysig_cb (EV_P_ ev_async *w, int revents)
		3250	{
		3251	pthread_mutex_lock (&mymutex);
		3252
		3253	while (queue_get (&data))
		3254	process (data);
		3255
		3256	pthread_mutex_unlock (&mymutex);
		3257	}
		3258
		3259	=back
		3260
		3261
		3262	=head3 Watcher-Specific Functions and Data Members
		3263
		3264	=over 4
		3265
		3266	=item ev_async_init (ev_async *, callback)
		3267
		3268	Initialises and configures the async watcher - it has no parameters of any
		3269	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3270	trust me.
		3271
		3272	=item ev_async_send (loop, ev_async *)
		3273
		3274	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3275	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3276	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3277	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3278	section below on what exactly this means).
		3279
		3280	Note that, as with other watchers in libev, multiple events might get
		3281	compressed into a single callback invocation (another way to look at this
		3282	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3283	reset when the event loop detects that).
		3284
		3285	This call incurs the overhead of a system call only once per event loop
		3286	iteration, so while the overhead might be noticeable, it doesn't apply to
		3287	repeated calls to C<ev_async_send> for the same event loop.
		3288
		3289	=item bool = ev_async_pending (ev_async *)
		3290
		3291	Returns a non-zero value when C<ev_async_send> has been called on the
		3292	watcher but the event has not yet been processed (or even noted) by the
		3293	event loop.
		3294
		3295	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3296	the loop iterates next and checks for the watcher to have become active,
		3297	it will reset the flag again. C<ev_async_pending> can be used to very
		3298	quickly check whether invoking the loop might be a good idea.
		3299
		3300	Not that this does I<not> check whether the watcher itself is pending,
		3301	only whether it has been requested to make this watcher pending: there
		3302	is a time window between the event loop checking and resetting the async
		3303	notification, and the callback being invoked.
		3304
		3305	=back
		3306
		3307
1991	=head1 OTHER FUNCTIONS	3308	=head1 OTHER FUNCTIONS
1992		3309
1993	There are some other functions of possible interest. Described. Here. Now.	3310	There are some other functions of possible interest. Described. Here. Now.
1994		3311
1995	=over 4	3312	=over 4
1996		3313
1997	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3314	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1998		3315
1999	This function combines a simple timer and an I/O watcher, calls your	3316	This function combines a simple timer and an I/O watcher, calls your
2000	callback on whichever event happens first and automatically stop both	3317	callback on whichever event happens first and automatically stops both
2001	watchers. This is useful if you want to wait for a single event on an fd	3318	watchers. This is useful if you want to wait for a single event on an fd
2002	or timeout without having to allocate/configure/start/stop/free one or	3319	or timeout without having to allocate/configure/start/stop/free one or
2003	more watchers yourself.	3320	more watchers yourself.
2004		3321
2005	If C<fd> is less than 0, then no I/O watcher will be started and events	3322	If C<fd> is less than 0, then no I/O watcher will be started and the
2006	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3323	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2007	C<events> set will be craeted and started.	3324	the given C<fd> and C<events> set will be created and started.
2008		3325
2009	If C<timeout> is less than 0, then no timeout watcher will be	3326	If C<timeout> is less than 0, then no timeout watcher will be
2010	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3327	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2011	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3328	repeat = 0) will be started. C<0> is a valid timeout.
2012	dubious value.
2013		3329
2014	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3330	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2015	passed an C<revents> set like normal event callbacks (a combination of	3331	passed an C<revents> set like normal event callbacks (a combination of
2016	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3332	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2017	value passed to C<ev_once>:	3333	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3334	a timeout and an io event at the same time - you probably should give io
		3335	events precedence.
2018		3336
		3337	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3338
2019	static void stdin_ready (int revents, void *arg)	3339	static void stdin_ready (int revents, void *arg)
2020	{	3340	{
2021	if (revents & EV_TIMEOUT)
2022	/* doh, nothing entered */;
2023	else if (revents & EV_READ)	3341	if (revents & EV_READ)
2024	/* stdin might have data for us, joy! */;	3342	/* stdin might have data for us, joy! */;
		3343	else if (revents & EV_TIMER)
		3344	/* doh, nothing entered */;
2025	}	3345	}
2026		3346
2027	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3347	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2028		3348
2029	=item ev_feed_event (ev_loop *, watcher *, int revents)
2030
2031	Feeds the given event set into the event loop, as if the specified event
2032	had happened for the specified watcher (which must be a pointer to an
2033	initialised but not necessarily started event watcher).
2034
2035	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3349	=item ev_feed_fd_event (loop, int fd, int revents)
2036		3350
2037	Feed an event on the given fd, as if a file descriptor backend detected	3351	Feed an event on the given fd, as if a file descriptor backend detected
2038	the given events it.	3352	the given events it.
2039		3353
2040	=item ev_feed_signal_event (ev_loop *loop, int signum)	3354	=item ev_feed_signal_event (loop, int signum)
2041		3355
2042	Feed an event as if the given signal occured (C<loop> must be the default	3356	Feed an event as if the given signal occurred (C<loop> must be the default
2043	loop!).	3357	loop!).
2044		3358
2045	=back	3359	=back
2046		3360
2047		3361
…		…
2063		3377
2064	=item * Priorities are not currently supported. Initialising priorities	3378	=item * Priorities are not currently supported. Initialising priorities
2065	will fail and all watchers will have the same priority, even though there	3379	will fail and all watchers will have the same priority, even though there
2066	is an ev_pri field.	3380	is an ev_pri field.
2067		3381
		3382	=item * In libevent, the last base created gets the signals, in libev, the
		3383	first base created (== the default loop) gets the signals.
		3384
2068	=item * Other members are not supported.	3385	=item * Other members are not supported.
2069		3386
2070	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3387	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2071	to use the libev header file and library.	3388	to use the libev header file and library.
2072		3389
2073	=back	3390	=back
2074		3391
2075	=head1 C++ SUPPORT	3392	=head1 C++ SUPPORT
2076		3393
2077	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3394	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2078	you to use some convinience methods to start/stop watchers and also change	3395	you to use some convenience methods to start/stop watchers and also change
2079	the callback model to a model using method callbacks on objects.	3396	the callback model to a model using method callbacks on objects.
2080		3397
2081	To use it,	3398	To use it,
2082		3399
2083	#include <ev++.h>	3400	#include <ev++.h>
2084		3401
2085	This automatically includes F<ev.h> and puts all of its definitions (many	3402	This automatically includes F<ev.h> and puts all of its definitions (many
2086	of them macros) into the global namespace. All C++ specific things are	3403	of them macros) into the global namespace. All C++ specific things are
2087	put into the C<ev> namespace. It should support all the same embedding	3404	put into the C<ev> namespace. It should support all the same embedding
2088	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3405	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2122		3439
2123	=over 4	3440	=over 4
2124		3441
2125	=item ev::TYPE::TYPE ()	3442	=item ev::TYPE::TYPE ()
2126		3443
2127	=item ev::TYPE::TYPE (struct ev_loop *)	3444	=item ev::TYPE::TYPE (loop)
2128		3445
2129	=item ev::TYPE::~TYPE	3446	=item ev::TYPE::~TYPE
2130		3447
2131	The constructor (optionally) takes an event loop to associate the watcher	3448	The constructor (optionally) takes an event loop to associate the watcher
2132	with. If it is omitted, it will use C<EV_DEFAULT>.	3449	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2155	your compiler is good :), then the method will be fully inlined into the	3472	your compiler is good :), then the method will be fully inlined into the
2156	thunking function, making it as fast as a direct C callback.	3473	thunking function, making it as fast as a direct C callback.
2157		3474
2158	Example: simple class declaration and watcher initialisation	3475	Example: simple class declaration and watcher initialisation
2159		3476
2160	struct myclass	3477	struct myclass
2161	{	3478	{
2162	void io_cb (ev::io &w, int revents) { }	3479	void io_cb (ev::io &w, int revents) { }
2163	}	3480	}
2164		3481
2165	myclass obj;	3482	myclass obj;
2166	ev::io iow;	3483	ev::io iow;
2167	iow.set <myclass, &myclass::io_cb> (&obj);	3484	iow.set <myclass, &myclass::io_cb> (&obj);
		3485
		3486	=item w->set (object *)
		3487
		3488	This is a variation of a method callback - leaving out the method to call
		3489	will default the method to C<operator ()>, which makes it possible to use
		3490	functor objects without having to manually specify the C<operator ()> all
		3491	the time. Incidentally, you can then also leave out the template argument
		3492	list.
		3493
		3494	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3495	int revents)>.
		3496
		3497	See the method-C<set> above for more details.
		3498
		3499	Example: use a functor object as callback.
		3500
		3501	struct myfunctor
		3502	{
		3503	void operator() (ev::io &w, int revents)
		3504	{
		3505	...
		3506	}
		3507	}
		3508
		3509	myfunctor f;
		3510
		3511	ev::io w;
		3512	w.set (&f);
2168		3513
2169	=item w->set<function> (void *data = 0)	3514	=item w->set<function> (void *data = 0)
2170		3515
2171	Also sets a callback, but uses a static method or plain function as	3516	Also sets a callback, but uses a static method or plain function as
2172	callback. The optional C<data> argument will be stored in the watcher's	3517	callback. The optional C<data> argument will be stored in the watcher's
…		…
2174		3519
2175	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3520	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2176		3521
2177	See the method-C<set> above for more details.	3522	See the method-C<set> above for more details.
2178		3523
2179	Example:	3524	Example: Use a plain function as callback.
2180		3525
2181	static void io_cb (ev::io &w, int revents) { }	3526	static void io_cb (ev::io &w, int revents) { }
2182	iow.set <io_cb> ();	3527	iow.set <io_cb> ();
2183		3528
2184	=item w->set (struct ev_loop *)	3529	=item w->set (loop)
2185		3530
2186	Associates a different C<struct ev_loop> with this watcher. You can only	3531	Associates a different C<struct ev_loop> with this watcher. You can only
2187	do this when the watcher is inactive (and not pending either).	3532	do this when the watcher is inactive (and not pending either).
2188		3533
2189	=item w->set ([args])	3534	=item w->set ([arguments])
2190		3535
2191	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3536	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2192	called at least once. Unlike the C counterpart, an active watcher gets	3537	method or a suitable start method must be called at least once. Unlike the
2193	automatically stopped and restarted when reconfiguring it with this	3538	C counterpart, an active watcher gets automatically stopped and restarted
2194	method.	3539	when reconfiguring it with this method.
2195		3540
2196	=item w->start ()	3541	=item w->start ()
2197		3542
2198	Starts the watcher. Note that there is no C<loop> argument, as the	3543	Starts the watcher. Note that there is no C<loop> argument, as the
2199	constructor already stores the event loop.	3544	constructor already stores the event loop.
2200		3545
		3546	=item w->start ([arguments])
		3547
		3548	Instead of calling C<set> and C<start> methods separately, it is often
		3549	convenient to wrap them in one call. Uses the same type of arguments as
		3550	the configure C<set> method of the watcher.
		3551
2201	=item w->stop ()	3552	=item w->stop ()
2202		3553
2203	Stops the watcher if it is active. Again, no C<loop> argument.	3554	Stops the watcher if it is active. Again, no C<loop> argument.
2204		3555
2205	=item w->again () (C<ev::timer>, C<ev::periodic> only)	3556	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2217		3568
2218	=back	3569	=back
2219		3570
2220	=back	3571	=back
2221		3572
2222	Example: Define a class with an IO and idle watcher, start one of them in	3573	Example: Define a class with two I/O and idle watchers, start the I/O
2223	the constructor.	3574	watchers in the constructor.
2224		3575
2225	class myclass	3576	class myclass
2226	{	3577	{
2227	ev_io io; void io_cb (ev::io &w, int revents);	3578	ev::io io ; void io_cb (ev::io &w, int revents);
		3579	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
2228	ev_idle idle void idle_cb (ev::idle &w, int revents);	3580	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2229		3581
2230	myclass ();	3582	myclass (int fd)
2231	}	3583	{
2232
2233	myclass::myclass (int fd)
2234	{
2235	io .set <myclass, &myclass::io_cb > (this);	3584	io .set <myclass, &myclass::io_cb > (this);
		3585	io2 .set <myclass, &myclass::io2_cb > (this);
2236	idle.set <myclass, &myclass::idle_cb> (this);	3586	idle.set <myclass, &myclass::idle_cb> (this);
2237		3587
2238	io.start (fd, ev::READ);	3588	io.set (fd, ev::WRITE); // configure the watcher
		3589	io.start (); // start it whenever convenient
		3590
		3591	io2.start (fd, ev::READ); // set + start in one call
		3592	}
2239	}	3593	};
		3594
		3595
		3596	=head1 OTHER LANGUAGE BINDINGS
		3597
		3598	Libev does not offer other language bindings itself, but bindings for a
		3599	number of languages exist in the form of third-party packages. If you know
		3600	any interesting language binding in addition to the ones listed here, drop
		3601	me a note.
		3602
		3603	=over 4
		3604
		3605	=item Perl
		3606
		3607	The EV module implements the full libev API and is actually used to test
		3608	libev. EV is developed together with libev. Apart from the EV core module,
		3609	there are additional modules that implement libev-compatible interfaces
		3610	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3611	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3612	and C<EV::Glib>).
		3613
		3614	It can be found and installed via CPAN, its homepage is at
		3615	L<http://software.schmorp.de/pkg/EV>.
		3616
		3617	=item Python
		3618
		3619	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3620	seems to be quite complete and well-documented.
		3621
		3622	=item Ruby
		3623
		3624	Tony Arcieri has written a ruby extension that offers access to a subset
		3625	of the libev API and adds file handle abstractions, asynchronous DNS and
		3626	more on top of it. It can be found via gem servers. Its homepage is at
		3627	L<http://rev.rubyforge.org/>.
		3628
		3629	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3630	makes rev work even on mingw.
		3631
		3632	=item Haskell
		3633
		3634	A haskell binding to libev is available at
		3635	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3636
		3637	=item D
		3638
		3639	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3640	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3641
		3642	=item Ocaml
		3643
		3644	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3645	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3646
		3647	=item Lua
		3648
		3649	Brian Maher has written a partial interface to libev for lua (at the
		3650	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3651	L<http://github.com/brimworks/lua-ev>.
		3652
		3653	=back
2240		3654
2241		3655
2242	=head1 MACRO MAGIC	3656	=head1 MACRO MAGIC
2243		3657
2244	Libev can be compiled with a variety of options, the most fundamantal	3658	Libev can be compiled with a variety of options, the most fundamental
2245	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3659	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2246	functions and callbacks have an initial C<struct ev_loop *> argument.	3660	functions and callbacks have an initial C<struct ev_loop *> argument.
2247		3661
2248	To make it easier to write programs that cope with either variant, the	3662	To make it easier to write programs that cope with either variant, the
2249	following macros are defined:	3663	following macros are defined:
…		…
2254		3668
2255	This provides the loop I<argument> for functions, if one is required ("ev	3669	This provides the loop I<argument> for functions, if one is required ("ev
2256	loop argument"). The C<EV_A> form is used when this is the sole argument,	3670	loop argument"). The C<EV_A> form is used when this is the sole argument,
2257	C<EV_A_> is used when other arguments are following. Example:	3671	C<EV_A_> is used when other arguments are following. Example:
2258		3672
2259	ev_unref (EV_A);	3673	ev_unref (EV_A);
2260	ev_timer_add (EV_A_ watcher);	3674	ev_timer_add (EV_A_ watcher);
2261	ev_loop (EV_A_ 0);	3675	ev_run (EV_A_ 0);
2262		3676
2263	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3677	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2264	which is often provided by the following macro.	3678	which is often provided by the following macro.
2265		3679
2266	=item C<EV_P>, C<EV_P_>	3680	=item C<EV_P>, C<EV_P_>
2267		3681
2268	This provides the loop I<parameter> for functions, if one is required ("ev	3682	This provides the loop I<parameter> for functions, if one is required ("ev
2269	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3683	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2270	C<EV_P_> is used when other parameters are following. Example:	3684	C<EV_P_> is used when other parameters are following. Example:
2271		3685
2272	// this is how ev_unref is being declared	3686	// this is how ev_unref is being declared
2273	static void ev_unref (EV_P);	3687	static void ev_unref (EV_P);
2274		3688
2275	// this is how you can declare your typical callback	3689	// this is how you can declare your typical callback
2276	static void cb (EV_P_ ev_timer *w, int revents)	3690	static void cb (EV_P_ ev_timer *w, int revents)
2277		3691
2278	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3692	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2279	suitable for use with C<EV_A>.	3693	suitable for use with C<EV_A>.
2280		3694
2281	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3695	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2282		3696
2283	Similar to the other two macros, this gives you the value of the default	3697	Similar to the other two macros, this gives you the value of the default
2284	loop, if multiple loops are supported ("ev loop default").	3698	loop, if multiple loops are supported ("ev loop default").
		3699
		3700	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3701
		3702	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3703	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3704	is undefined when the default loop has not been initialised by a previous
		3705	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3706
		3707	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3708	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2285		3709
2286	=back	3710	=back
2287		3711
2288	Example: Declare and initialise a check watcher, utilising the above	3712	Example: Declare and initialise a check watcher, utilising the above
2289	macros so it will work regardless of whether multiple loops are supported	3713	macros so it will work regardless of whether multiple loops are supported
2290	or not.	3714	or not.
2291		3715
2292	static void	3716	static void
2293	check_cb (EV_P_ ev_timer *w, int revents)	3717	check_cb (EV_P_ ev_timer *w, int revents)
2294	{	3718	{
2295	ev_check_stop (EV_A_ w);	3719	ev_check_stop (EV_A_ w);
2296	}	3720	}
2297		3721
2298	ev_check check;	3722	ev_check check;
2299	ev_check_init (&check, check_cb);	3723	ev_check_init (&check, check_cb);
2300	ev_check_start (EV_DEFAULT_ &check);	3724	ev_check_start (EV_DEFAULT_ &check);
2301	ev_loop (EV_DEFAULT_ 0);	3725	ev_run (EV_DEFAULT_ 0);
2302		3726
2303	=head1 EMBEDDING	3727	=head1 EMBEDDING
2304		3728
2305	Libev can (and often is) directly embedded into host	3729	Libev can (and often is) directly embedded into host
2306	applications. Examples of applications that embed it include the Deliantra	3730	applications. Examples of applications that embed it include the Deliantra
…		…
2313	libev somewhere in your source tree).	3737	libev somewhere in your source tree).
2314		3738
2315	=head2 FILESETS	3739	=head2 FILESETS
2316		3740
2317	Depending on what features you need you need to include one or more sets of files	3741	Depending on what features you need you need to include one or more sets of files
2318	in your app.	3742	in your application.
2319		3743
2320	=head3 CORE EVENT LOOP	3744	=head3 CORE EVENT LOOP
2321		3745
2322	To include only the libev core (all the C<ev_*> functions), with manual	3746	To include only the libev core (all the C<ev_*> functions), with manual
2323	configuration (no autoconf):	3747	configuration (no autoconf):
2324		3748
2325	#define EV_STANDALONE 1	3749	#define EV_STANDALONE 1
2326	#include "ev.c"	3750	#include "ev.c"
2327		3751
2328	This will automatically include F<ev.h>, too, and should be done in a	3752	This will automatically include F<ev.h>, too, and should be done in a
2329	single C source file only to provide the function implementations. To use	3753	single C source file only to provide the function implementations. To use
2330	it, do the same for F<ev.h> in all files wishing to use this API (best	3754	it, do the same for F<ev.h> in all files wishing to use this API (best
2331	done by writing a wrapper around F<ev.h> that you can include instead and	3755	done by writing a wrapper around F<ev.h> that you can include instead and
2332	where you can put other configuration options):	3756	where you can put other configuration options):
2333		3757
2334	#define EV_STANDALONE 1	3758	#define EV_STANDALONE 1
2335	#include "ev.h"	3759	#include "ev.h"
2336		3760
2337	Both header files and implementation files can be compiled with a C++	3761	Both header files and implementation files can be compiled with a C++
2338	compiler (at least, thats a stated goal, and breakage will be treated	3762	compiler (at least, that's a stated goal, and breakage will be treated
2339	as a bug).	3763	as a bug).
2340		3764
2341	You need the following files in your source tree, or in a directory	3765	You need the following files in your source tree, or in a directory
2342	in your include path (e.g. in libev/ when using -Ilibev):	3766	in your include path (e.g. in libev/ when using -Ilibev):
2343		3767
2344	ev.h	3768	ev.h
2345	ev.c	3769	ev.c
2346	ev_vars.h	3770	ev_vars.h
2347	ev_wrap.h	3771	ev_wrap.h
2348		3772
2349	ev_win32.c required on win32 platforms only	3773	ev_win32.c required on win32 platforms only
2350		3774
2351	ev_select.c only when select backend is enabled (which is enabled by default)	3775	ev_select.c only when select backend is enabled (which is enabled by default)
2352	ev_poll.c only when poll backend is enabled (disabled by default)	3776	ev_poll.c only when poll backend is enabled (disabled by default)
2353	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3777	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2354	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3778	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2355	ev_port.c only when the solaris port backend is enabled (disabled by default)	3779	ev_port.c only when the solaris port backend is enabled (disabled by default)
2356		3780
2357	F<ev.c> includes the backend files directly when enabled, so you only need	3781	F<ev.c> includes the backend files directly when enabled, so you only need
2358	to compile this single file.	3782	to compile this single file.
2359		3783
2360	=head3 LIBEVENT COMPATIBILITY API	3784	=head3 LIBEVENT COMPATIBILITY API
2361		3785
2362	To include the libevent compatibility API, also include:	3786	To include the libevent compatibility API, also include:
2363		3787
2364	#include "event.c"	3788	#include "event.c"
2365		3789
2366	in the file including F<ev.c>, and:	3790	in the file including F<ev.c>, and:
2367		3791
2368	#include "event.h"	3792	#include "event.h"
2369		3793
2370	in the files that want to use the libevent API. This also includes F<ev.h>.	3794	in the files that want to use the libevent API. This also includes F<ev.h>.
2371		3795
2372	You need the following additional files for this:	3796	You need the following additional files for this:
2373		3797
2374	event.h	3798	event.h
2375	event.c	3799	event.c
2376		3800
2377	=head3 AUTOCONF SUPPORT	3801	=head3 AUTOCONF SUPPORT
2378		3802
2379	Instead of using C<EV_STANDALONE=1> and providing your config in	3803	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2380	whatever way you want, you can also C<m4_include([libev.m4])> in your	3804	whatever way you want, you can also C<m4_include([libev.m4])> in your
2381	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3805	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2382	include F<config.h> and configure itself accordingly.	3806	include F<config.h> and configure itself accordingly.
2383		3807
2384	For this of course you need the m4 file:	3808	For this of course you need the m4 file:
2385		3809
2386	libev.m4	3810	libev.m4
2387		3811
2388	=head2 PREPROCESSOR SYMBOLS/MACROS	3812	=head2 PREPROCESSOR SYMBOLS/MACROS
2389		3813
2390	Libev can be configured via a variety of preprocessor symbols you have to define	3814	Libev can be configured via a variety of preprocessor symbols you have to
2391	before including any of its files. The default is not to build for multiplicity	3815	define before including (or compiling) any of its files. The default in
2392	and only include the select backend.	3816	the absence of autoconf is documented for every option.
		3817
		3818	Symbols marked with "(h)" do not change the ABI, and can have different
		3819	values when compiling libev vs. including F<ev.h>, so it is permissible
		3820	to redefine them before including F<ev.h> without breaking compatibility
		3821	to a compiled library. All other symbols change the ABI, which means all
		3822	users of libev and the libev code itself must be compiled with compatible
		3823	settings.
2393		3824
2394	=over 4	3825	=over 4
2395		3826
		3827	=item EV_COMPAT3 (h)
		3828
		3829	Backwards compatibility is a major concern for libev. This is why this
		3830	release of libev comes with wrappers for the functions and symbols that
		3831	have been renamed between libev version 3 and 4.
		3832
		3833	You can disable these wrappers (to test compatibility with future
		3834	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		3835	sources. This has the additional advantage that you can drop the C<struct>
		3836	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		3837	typedef in that case.
		3838
		3839	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		3840	and in some even more future version the compatibility code will be
		3841	removed completely.
		3842
2396	=item EV_STANDALONE	3843	=item EV_STANDALONE (h)
2397		3844
2398	Must always be C<1> if you do not use autoconf configuration, which	3845	Must always be C<1> if you do not use autoconf configuration, which
2399	keeps libev from including F<config.h>, and it also defines dummy	3846	keeps libev from including F<config.h>, and it also defines dummy
2400	implementations for some libevent functions (such as logging, which is not	3847	implementations for some libevent functions (such as logging, which is not
2401	supported). It will also not define any of the structs usually found in	3848	supported). It will also not define any of the structs usually found in
2402	F<event.h> that are not directly supported by the libev core alone.	3849	F<event.h> that are not directly supported by the libev core alone.
2403		3850
		3851	In standalone mode, libev will still try to automatically deduce the
		3852	configuration, but has to be more conservative.
		3853
2404	=item EV_USE_MONOTONIC	3854	=item EV_USE_MONOTONIC
2405		3855
2406	If defined to be C<1>, libev will try to detect the availability of the	3856	If defined to be C<1>, libev will try to detect the availability of the
2407	monotonic clock option at both compiletime and runtime. Otherwise no use	3857	monotonic clock option at both compile time and runtime. Otherwise no
2408	of the monotonic clock option will be attempted. If you enable this, you	3858	use of the monotonic clock option will be attempted. If you enable this,
2409	usually have to link against librt or something similar. Enabling it when	3859	you usually have to link against librt or something similar. Enabling it
2410	the functionality isn't available is safe, though, although you have	3860	when the functionality isn't available is safe, though, although you have
2411	to make sure you link against any libraries where the C<clock_gettime>	3861	to make sure you link against any libraries where the C<clock_gettime>
2412	function is hiding in (often F<-lrt>).	3862	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2413		3863
2414	=item EV_USE_REALTIME	3864	=item EV_USE_REALTIME
2415		3865
2416	If defined to be C<1>, libev will try to detect the availability of the	3866	If defined to be C<1>, libev will try to detect the availability of the
2417	realtime clock option at compiletime (and assume its availability at	3867	real-time clock option at compile time (and assume its availability
2418	runtime if successful). Otherwise no use of the realtime clock option will	3868	at runtime if successful). Otherwise no use of the real-time clock
2419	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3869	option will be attempted. This effectively replaces C<gettimeofday>
2420	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3870	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2421	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3871	correctness. See the note about libraries in the description of
		3872	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3873	C<EV_USE_CLOCK_SYSCALL>.
		3874
		3875	=item EV_USE_CLOCK_SYSCALL
		3876
		3877	If defined to be C<1>, libev will try to use a direct syscall instead
		3878	of calling the system-provided C<clock_gettime> function. This option
		3879	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3880	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3881	programs needlessly. Using a direct syscall is slightly slower (in
		3882	theory), because no optimised vdso implementation can be used, but avoids
		3883	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3884	higher, as it simplifies linking (no need for C<-lrt>).
2422		3885
2423	=item EV_USE_NANOSLEEP	3886	=item EV_USE_NANOSLEEP
2424		3887
2425	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3888	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2426	and will use it for delays. Otherwise it will use C<select ()>.	3889	and will use it for delays. Otherwise it will use C<select ()>.
2427		3890
		3891	=item EV_USE_EVENTFD
		3892
		3893	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3894	available and will probe for kernel support at runtime. This will improve
		3895	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3896	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3897	2.7 or newer, otherwise disabled.
		3898
2428	=item EV_USE_SELECT	3899	=item EV_USE_SELECT
2429		3900
2430	If undefined or defined to be C<1>, libev will compile in support for the	3901	If undefined or defined to be C<1>, libev will compile in support for the
2431	C<select>(2) backend. No attempt at autodetection will be done: if no	3902	C<select>(2) backend. No attempt at auto-detection will be done: if no
2432	other method takes over, select will be it. Otherwise the select backend	3903	other method takes over, select will be it. Otherwise the select backend
2433	will not be compiled in.	3904	will not be compiled in.
2434		3905
2435	=item EV_SELECT_USE_FD_SET	3906	=item EV_SELECT_USE_FD_SET
2436		3907
2437	If defined to C<1>, then the select backend will use the system C<fd_set>	3908	If defined to C<1>, then the select backend will use the system C<fd_set>
2438	structure. This is useful if libev doesn't compile due to a missing	3909	structure. This is useful if libev doesn't compile due to a missing
2439	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3910	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2440	exotic systems. This usually limits the range of file descriptors to some	3911	on exotic systems. This usually limits the range of file descriptors to
2441	low limit such as 1024 or might have other limitations (winsocket only	3912	some low limit such as 1024 or might have other limitations (winsocket
2442	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3913	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2443	influence the size of the C<fd_set> used.	3914	configures the maximum size of the C<fd_set>.
2444		3915
2445	=item EV_SELECT_IS_WINSOCKET	3916	=item EV_SELECT_IS_WINSOCKET
2446		3917
2447	When defined to C<1>, the select backend will assume that	3918	When defined to C<1>, the select backend will assume that
2448	select/socket/connect etc. don't understand file descriptors but	3919	select/socket/connect etc. don't understand file descriptors but
…		…
2450	be used is the winsock select). This means that it will call	3921	be used is the winsock select). This means that it will call
2451	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3922	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2452	it is assumed that all these functions actually work on fds, even	3923	it is assumed that all these functions actually work on fds, even
2453	on win32. Should not be defined on non-win32 platforms.	3924	on win32. Should not be defined on non-win32 platforms.
2454		3925
		3926	=item EV_FD_TO_WIN32_HANDLE(fd)
		3927
		3928	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3929	file descriptors to socket handles. When not defining this symbol (the
		3930	default), then libev will call C<_get_osfhandle>, which is usually
		3931	correct. In some cases, programs use their own file descriptor management,
		3932	in which case they can provide this function to map fds to socket handles.
		3933
		3934	=item EV_WIN32_HANDLE_TO_FD(handle)
		3935
		3936	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3937	using the standard C<_open_osfhandle> function. For programs implementing
		3938	their own fd to handle mapping, overwriting this function makes it easier
		3939	to do so. This can be done by defining this macro to an appropriate value.
		3940
		3941	=item EV_WIN32_CLOSE_FD(fd)
		3942
		3943	If programs implement their own fd to handle mapping on win32, then this
		3944	macro can be used to override the C<close> function, useful to unregister
		3945	file descriptors again. Note that the replacement function has to close
		3946	the underlying OS handle.
		3947
2455	=item EV_USE_POLL	3948	=item EV_USE_POLL
2456		3949
2457	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3950	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2458	backend. Otherwise it will be enabled on non-win32 platforms. It	3951	backend. Otherwise it will be enabled on non-win32 platforms. It
2459	takes precedence over select.	3952	takes precedence over select.
2460		3953
2461	=item EV_USE_EPOLL	3954	=item EV_USE_EPOLL
2462		3955
2463	If defined to be C<1>, libev will compile in support for the Linux	3956	If defined to be C<1>, libev will compile in support for the Linux
2464	C<epoll>(7) backend. Its availability will be detected at runtime,	3957	C<epoll>(7) backend. Its availability will be detected at runtime,
2465	otherwise another method will be used as fallback. This is the	3958	otherwise another method will be used as fallback. This is the preferred
2466	preferred backend for GNU/Linux systems.	3959	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3960	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2467		3961
2468	=item EV_USE_KQUEUE	3962	=item EV_USE_KQUEUE
2469		3963
2470	If defined to be C<1>, libev will compile in support for the BSD style	3964	If defined to be C<1>, libev will compile in support for the BSD style
2471	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3965	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2484	otherwise another method will be used as fallback. This is the preferred	3978	otherwise another method will be used as fallback. This is the preferred
2485	backend for Solaris 10 systems.	3979	backend for Solaris 10 systems.
2486		3980
2487	=item EV_USE_DEVPOLL	3981	=item EV_USE_DEVPOLL
2488		3982
2489	reserved for future expansion, works like the USE symbols above.	3983	Reserved for future expansion, works like the USE symbols above.
2490		3984
2491	=item EV_USE_INOTIFY	3985	=item EV_USE_INOTIFY
2492		3986
2493	If defined to be C<1>, libev will compile in support for the Linux inotify	3987	If defined to be C<1>, libev will compile in support for the Linux inotify
2494	interface to speed up C<ev_stat> watchers. Its actual availability will	3988	interface to speed up C<ev_stat> watchers. Its actual availability will
2495	be detected at runtime.	3989	be detected at runtime. If undefined, it will be enabled if the headers
		3990	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2496		3991
		3992	=item EV_ATOMIC_T
		3993
		3994	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3995	access is atomic with respect to other threads or signal contexts. No such
		3996	type is easily found in the C language, so you can provide your own type
		3997	that you know is safe for your purposes. It is used both for signal handler "locking"
		3998	as well as for signal and thread safety in C<ev_async> watchers.
		3999
		4000	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4001	(from F<signal.h>), which is usually good enough on most platforms.
		4002
2497	=item EV_H	4003	=item EV_H (h)
2498		4004
2499	The name of the F<ev.h> header file used to include it. The default if	4005	The name of the F<ev.h> header file used to include it. The default if
2500	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	4006	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2501	can be used to virtually rename the F<ev.h> header file in case of conflicts.	4007	used to virtually rename the F<ev.h> header file in case of conflicts.
2502		4008
2503	=item EV_CONFIG_H	4009	=item EV_CONFIG_H (h)
2504		4010
2505	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4011	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2506	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4012	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2507	C<EV_H>, above.	4013	C<EV_H>, above.
2508		4014
2509	=item EV_EVENT_H	4015	=item EV_EVENT_H (h)
2510		4016
2511	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4017	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2512	of how the F<event.h> header can be found.	4018	of how the F<event.h> header can be found, the default is C<"event.h">.
2513		4019
2514	=item EV_PROTOTYPES	4020	=item EV_PROTOTYPES (h)
2515		4021
2516	If defined to be C<0>, then F<ev.h> will not define any function	4022	If defined to be C<0>, then F<ev.h> will not define any function
2517	prototypes, but still define all the structs and other symbols. This is	4023	prototypes, but still define all the structs and other symbols. This is
2518	occasionally useful if you want to provide your own wrapper functions	4024	occasionally useful if you want to provide your own wrapper functions
2519	around libev functions.	4025	around libev functions.
…		…
2538	When doing priority-based operations, libev usually has to linearly search	4044	When doing priority-based operations, libev usually has to linearly search
2539	all the priorities, so having many of them (hundreds) uses a lot of space	4045	all the priorities, so having many of them (hundreds) uses a lot of space
2540	and time, so using the defaults of five priorities (-2 .. +2) is usually	4046	and time, so using the defaults of five priorities (-2 .. +2) is usually
2541	fine.	4047	fine.
2542		4048
2543	If your embedding app does not need any priorities, defining these both to	4049	If your embedding application does not need any priorities, defining these
2544	C<0> will save some memory and cpu.	4050	both to C<0> will save some memory and CPU.
2545		4051
2546	=item EV_PERIODIC_ENABLE	4052	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4053	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4054	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2547		4055
2548	If undefined or defined to be C<1>, then periodic timers are supported. If	4056	If undefined or defined to be C<1> (and the platform supports it), then
2549	defined to be C<0>, then they are not. Disabling them saves a few kB of	4057	the respective watcher type is supported. If defined to be C<0>, then it
2550	code.	4058	is not. Disabling watcher types mainly saves code size.
2551		4059
2552	=item EV_IDLE_ENABLE	4060	=item EV_FEATURES
2553
2554	If undefined or defined to be C<1>, then idle watchers are supported. If
2555	defined to be C<0>, then they are not. Disabling them saves a few kB of
2556	code.
2557
2558	=item EV_EMBED_ENABLE
2559
2560	If undefined or defined to be C<1>, then embed watchers are supported. If
2561	defined to be C<0>, then they are not.
2562
2563	=item EV_STAT_ENABLE
2564
2565	If undefined or defined to be C<1>, then stat watchers are supported. If
2566	defined to be C<0>, then they are not.
2567
2568	=item EV_FORK_ENABLE
2569
2570	If undefined or defined to be C<1>, then fork watchers are supported. If
2571	defined to be C<0>, then they are not.
2572
2573	=item EV_MINIMAL
2574		4061
2575	If you need to shave off some kilobytes of code at the expense of some	4062	If you need to shave off some kilobytes of code at the expense of some
2576	speed, define this symbol to C<1>. Currently only used for gcc to override	4063	speed (but with the full API), you can define this symbol to request
2577	some inlining decisions, saves roughly 30% codesize of amd64.	4064	certain subsets of functionality. The default is to enable all features
		4065	that can be enabled on the platform.
		4066
		4067	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4068	with some broad features you want) and then selectively re-enable
		4069	additional parts you want, for example if you want everything minimal,
		4070	but multiple event loop support, async and child watchers and the poll
		4071	backend, use this:
		4072
		4073	#define EV_FEATURES 0
		4074	#define EV_MULTIPLICITY 1
		4075	#define EV_USE_POLL 1
		4076	#define EV_CHILD_ENABLE 1
		4077	#define EV_ASYNC_ENABLE 1
		4078
		4079	The actual value is a bitset, it can be a combination of the following
		4080	values:
		4081
		4082	=over 4
		4083
		4084	=item C<1> - faster/larger code
		4085
		4086	Use larger code to speed up some operations.
		4087
		4088	Currently this is used to override some inlining decisions (enlarging the
		4089	code size by roughly 30% on amd64).
		4090
		4091	When optimising for size, use of compiler flags such as C<-Os> with
		4092	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4093	assertions.
		4094
		4095	=item C<2> - faster/larger data structures
		4096
		4097	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4098	hash table sizes and so on. This will usually further increase code size
		4099	and can additionally have an effect on the size of data structures at
		4100	runtime.
		4101
		4102	=item C<4> - full API configuration
		4103
		4104	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4105	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4106
		4107	=item C<8> - full API
		4108
		4109	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4110	details on which parts of the API are still available without this
		4111	feature, and do not complain if this subset changes over time.
		4112
		4113	=item C<16> - enable all optional watcher types
		4114
		4115	Enables all optional watcher types. If you want to selectively enable
		4116	only some watcher types other than I/O and timers (e.g. prepare,
		4117	embed, async, child...) you can enable them manually by defining
		4118	C<EV_watchertype_ENABLE> to C<1> instead.
		4119
		4120	=item C<32> - enable all backends
		4121
		4122	This enables all backends - without this feature, you need to enable at
		4123	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4124
		4125	=item C<64> - enable OS-specific "helper" APIs
		4126
		4127	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4128	default.
		4129
		4130	=back
		4131
		4132	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4133	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4134	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4135	watchers, timers and monotonic clock support.
		4136
		4137	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4138	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4139	your program might be left out as well - a binary starting a timer and an
		4140	I/O watcher then might come out at only 5Kb.
		4141
		4142	=item EV_AVOID_STDIO
		4143
		4144	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4145	functions (printf, scanf, perror etc.). This will increase the code size
		4146	somewhat, but if your program doesn't otherwise depend on stdio and your
		4147	libc allows it, this avoids linking in the stdio library which is quite
		4148	big.
		4149
		4150	Note that error messages might become less precise when this option is
		4151	enabled.
		4152
		4153	=item EV_NSIG
		4154
		4155	The highest supported signal number, +1 (or, the number of
		4156	signals): Normally, libev tries to deduce the maximum number of signals
		4157	automatically, but sometimes this fails, in which case it can be
		4158	specified. Also, using a lower number than detected (C<32> should be
		4159	good for about any system in existence) can save some memory, as libev
		4160	statically allocates some 12-24 bytes per signal number.
2578		4161
2579	=item EV_PID_HASHSIZE	4162	=item EV_PID_HASHSIZE
2580		4163
2581	C<ev_child> watchers use a small hash table to distribute workload by	4164	C<ev_child> watchers use a small hash table to distribute workload by
2582	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4165	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2583	than enough. If you need to manage thousands of children you might want to	4166	usually more than enough. If you need to manage thousands of children you
2584	increase this value (I<must> be a power of two).	4167	might want to increase this value (I<must> be a power of two).
2585		4168
2586	=item EV_INOTIFY_HASHSIZE	4169	=item EV_INOTIFY_HASHSIZE
2587		4170
2588	C<ev_stat> watchers use a small hash table to distribute workload by	4171	C<ev_stat> watchers use a small hash table to distribute workload by
2589	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4172	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2590	usually more than enough. If you need to manage thousands of C<ev_stat>	4173	disabled), usually more than enough. If you need to manage thousands of
2591	watchers you might want to increase this value (I<must> be a power of	4174	C<ev_stat> watchers you might want to increase this value (I<must> be a
2592	two).	4175	power of two).
		4176
		4177	=item EV_USE_4HEAP
		4178
		4179	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4180	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4181	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4182	faster performance with many (thousands) of watchers.
		4183
		4184	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4185	will be C<0>.
		4186
		4187	=item EV_HEAP_CACHE_AT
		4188
		4189	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4190	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4191	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4192	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4193	but avoids random read accesses on heap changes. This improves performance
		4194	noticeably with many (hundreds) of watchers.
		4195
		4196	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4197	will be C<0>.
		4198
		4199	=item EV_VERIFY
		4200
		4201	Controls how much internal verification (see C<ev_verify ()>) will
		4202	be done: If set to C<0>, no internal verification code will be compiled
		4203	in. If set to C<1>, then verification code will be compiled in, but not
		4204	called. If set to C<2>, then the internal verification code will be
		4205	called once per loop, which can slow down libev. If set to C<3>, then the
		4206	verification code will be called very frequently, which will slow down
		4207	libev considerably.
		4208
		4209	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4210	will be C<0>.
2593		4211
2594	=item EV_COMMON	4212	=item EV_COMMON
2595		4213
2596	By default, all watchers have a C<void *data> member. By redefining	4214	By default, all watchers have a C<void *data> member. By redefining
2597	this macro to a something else you can include more and other types of	4215	this macro to something else you can include more and other types of
2598	members. You have to define it each time you include one of the files,	4216	members. You have to define it each time you include one of the files,
2599	though, and it must be identical each time.	4217	though, and it must be identical each time.
2600		4218
2601	For example, the perl EV module uses something like this:	4219	For example, the perl EV module uses something like this:
2602		4220
2603	#define EV_COMMON \	4221	#define EV_COMMON \
2604	SV *self; /* contains this struct */ \	4222	SV *self; /* contains this struct */ \
2605	SV *cb_sv, *fh /* note no trailing ";" */	4223	SV *cb_sv, *fh /* note no trailing ";" */
2606		4224
2607	=item EV_CB_DECLARE (type)	4225	=item EV_CB_DECLARE (type)
2608		4226
2609	=item EV_CB_INVOKE (watcher, revents)	4227	=item EV_CB_INVOKE (watcher, revents)
2610		4228
…		…
2615	definition and a statement, respectively. See the F<ev.h> header file for	4233	definition and a statement, respectively. See the F<ev.h> header file for
2616	their default definitions. One possible use for overriding these is to	4234	their default definitions. One possible use for overriding these is to
2617	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4235	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2618	method calls instead of plain function calls in C++.	4236	method calls instead of plain function calls in C++.
2619		4237
		4238	=back
		4239
2620	=head2 EXPORTED API SYMBOLS	4240	=head2 EXPORTED API SYMBOLS
2621		4241
2622	If you need to re-export the API (e.g. via a dll) and you need a list of	4242	If you need to re-export the API (e.g. via a DLL) and you need a list of
2623	exported symbols, you can use the provided F<Symbol.*> files which list	4243	exported symbols, you can use the provided F<Symbol.*> files which list
2624	all public symbols, one per line:	4244	all public symbols, one per line:
2625		4245
2626	Symbols.ev for libev proper	4246	Symbols.ev for libev proper
2627	Symbols.event for the libevent emulation	4247	Symbols.event for the libevent emulation
2628		4248
2629	This can also be used to rename all public symbols to avoid clashes with	4249	This can also be used to rename all public symbols to avoid clashes with
2630	multiple versions of libev linked together (which is obviously bad in	4250	multiple versions of libev linked together (which is obviously bad in
2631	itself, but sometimes it is inconvinient to avoid this).	4251	itself, but sometimes it is inconvenient to avoid this).
2632		4252
2633	A sed command like this will create wrapper C<#define>'s that you need to	4253	A sed command like this will create wrapper C<#define>'s that you need to
2634	include before including F<ev.h>:	4254	include before including F<ev.h>:
2635		4255
2636	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	4256	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2653	file.	4273	file.
2654		4274
2655	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4275	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2656	that everybody includes and which overrides some configure choices:	4276	that everybody includes and which overrides some configure choices:
2657		4277
2658	#define EV_MINIMAL 1	4278	#define EV_FEATURES 8
2659	#define EV_USE_POLL 0	4279	#define EV_USE_SELECT 1
2660	#define EV_MULTIPLICITY 0
2661	#define EV_PERIODIC_ENABLE 0	4280	#define EV_PREPARE_ENABLE 1
		4281	#define EV_IDLE_ENABLE 1
2662	#define EV_STAT_ENABLE 0	4282	#define EV_SIGNAL_ENABLE 1
2663	#define EV_FORK_ENABLE 0	4283	#define EV_CHILD_ENABLE 1
		4284	#define EV_USE_STDEXCEPT 0
2664	#define EV_CONFIG_H <config.h>	4285	#define EV_CONFIG_H <config.h>
2665	#define EV_MINPRI 0
2666	#define EV_MAXPRI 0
2667		4286
2668	#include "ev++.h"	4287	#include "ev++.h"
2669		4288
2670	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4289	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2671		4290
2672	#include "ev_cpp.h"	4291	#include "ev_cpp.h"
2673	#include "ev.c"	4292	#include "ev.c"
2674		4293
		4294	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2675		4295
		4296	=head2 THREADS AND COROUTINES
		4297
		4298	=head3 THREADS
		4299
		4300	All libev functions are reentrant and thread-safe unless explicitly
		4301	documented otherwise, but libev implements no locking itself. This means
		4302	that you can use as many loops as you want in parallel, as long as there
		4303	are no concurrent calls into any libev function with the same loop
		4304	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4305	of course): libev guarantees that different event loops share no data
		4306	structures that need any locking.
		4307
		4308	Or to put it differently: calls with different loop parameters can be done
		4309	concurrently from multiple threads, calls with the same loop parameter
		4310	must be done serially (but can be done from different threads, as long as
		4311	only one thread ever is inside a call at any point in time, e.g. by using
		4312	a mutex per loop).
		4313
		4314	Specifically to support threads (and signal handlers), libev implements
		4315	so-called C<ev_async> watchers, which allow some limited form of
		4316	concurrency on the same event loop, namely waking it up "from the
		4317	outside".
		4318
		4319	If you want to know which design (one loop, locking, or multiple loops
		4320	without or something else still) is best for your problem, then I cannot
		4321	help you, but here is some generic advice:
		4322
		4323	=over 4
		4324
		4325	=item * most applications have a main thread: use the default libev loop
		4326	in that thread, or create a separate thread running only the default loop.
		4327
		4328	This helps integrating other libraries or software modules that use libev
		4329	themselves and don't care/know about threading.
		4330
		4331	=item * one loop per thread is usually a good model.
		4332
		4333	Doing this is almost never wrong, sometimes a better-performance model
		4334	exists, but it is always a good start.
		4335
		4336	=item * other models exist, such as the leader/follower pattern, where one
		4337	loop is handed through multiple threads in a kind of round-robin fashion.
		4338
		4339	Choosing a model is hard - look around, learn, know that usually you can do
		4340	better than you currently do :-)
		4341
		4342	=item * often you need to talk to some other thread which blocks in the
		4343	event loop.
		4344
		4345	C<ev_async> watchers can be used to wake them up from other threads safely
		4346	(or from signal contexts...).
		4347
		4348	An example use would be to communicate signals or other events that only
		4349	work in the default loop by registering the signal watcher with the
		4350	default loop and triggering an C<ev_async> watcher from the default loop
		4351	watcher callback into the event loop interested in the signal.
		4352
		4353	=back
		4354
		4355	=head4 THREAD LOCKING EXAMPLE
		4356
		4357	Here is a fictitious example of how to run an event loop in a different
		4358	thread than where callbacks are being invoked and watchers are
		4359	created/added/removed.
		4360
		4361	For a real-world example, see the C<EV::Loop::Async> perl module,
		4362	which uses exactly this technique (which is suited for many high-level
		4363	languages).
		4364
		4365	The example uses a pthread mutex to protect the loop data, a condition
		4366	variable to wait for callback invocations, an async watcher to notify the
		4367	event loop thread and an unspecified mechanism to wake up the main thread.
		4368
		4369	First, you need to associate some data with the event loop:
		4370
		4371	typedef struct {
		4372	mutex_t lock; /* global loop lock */
		4373	ev_async async_w;
		4374	thread_t tid;
		4375	cond_t invoke_cv;
		4376	} userdata;
		4377
		4378	void prepare_loop (EV_P)
		4379	{
		4380	// for simplicity, we use a static userdata struct.
		4381	static userdata u;
		4382
		4383	ev_async_init (&u->async_w, async_cb);
		4384	ev_async_start (EV_A_ &u->async_w);
		4385
		4386	pthread_mutex_init (&u->lock, 0);
		4387	pthread_cond_init (&u->invoke_cv, 0);
		4388
		4389	// now associate this with the loop
		4390	ev_set_userdata (EV_A_ u);
		4391	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4392	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4393
		4394	// then create the thread running ev_loop
		4395	pthread_create (&u->tid, 0, l_run, EV_A);
		4396	}
		4397
		4398	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4399	solely to wake up the event loop so it takes notice of any new watchers
		4400	that might have been added:
		4401
		4402	static void
		4403	async_cb (EV_P_ ev_async *w, int revents)
		4404	{
		4405	// just used for the side effects
		4406	}
		4407
		4408	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4409	protecting the loop data, respectively.
		4410
		4411	static void
		4412	l_release (EV_P)
		4413	{
		4414	userdata *u = ev_userdata (EV_A);
		4415	pthread_mutex_unlock (&u->lock);
		4416	}
		4417
		4418	static void
		4419	l_acquire (EV_P)
		4420	{
		4421	userdata *u = ev_userdata (EV_A);
		4422	pthread_mutex_lock (&u->lock);
		4423	}
		4424
		4425	The event loop thread first acquires the mutex, and then jumps straight
		4426	into C<ev_run>:
		4427
		4428	void *
		4429	l_run (void *thr_arg)
		4430	{
		4431	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4432
		4433	l_acquire (EV_A);
		4434	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4435	ev_run (EV_A_ 0);
		4436	l_release (EV_A);
		4437
		4438	return 0;
		4439	}
		4440
		4441	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4442	signal the main thread via some unspecified mechanism (signals? pipe
		4443	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4444	have been called (in a while loop because a) spurious wakeups are possible
		4445	and b) skipping inter-thread-communication when there are no pending
		4446	watchers is very beneficial):
		4447
		4448	static void
		4449	l_invoke (EV_P)
		4450	{
		4451	userdata *u = ev_userdata (EV_A);
		4452
		4453	while (ev_pending_count (EV_A))
		4454	{
		4455	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4456	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4457	}
		4458	}
		4459
		4460	Now, whenever the main thread gets told to invoke pending watchers, it
		4461	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4462	thread to continue:
		4463
		4464	static void
		4465	real_invoke_pending (EV_P)
		4466	{
		4467	userdata *u = ev_userdata (EV_A);
		4468
		4469	pthread_mutex_lock (&u->lock);
		4470	ev_invoke_pending (EV_A);
		4471	pthread_cond_signal (&u->invoke_cv);
		4472	pthread_mutex_unlock (&u->lock);
		4473	}
		4474
		4475	Whenever you want to start/stop a watcher or do other modifications to an
		4476	event loop, you will now have to lock:
		4477
		4478	ev_timer timeout_watcher;
		4479	userdata *u = ev_userdata (EV_A);
		4480
		4481	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4482
		4483	pthread_mutex_lock (&u->lock);
		4484	ev_timer_start (EV_A_ &timeout_watcher);
		4485	ev_async_send (EV_A_ &u->async_w);
		4486	pthread_mutex_unlock (&u->lock);
		4487
		4488	Note that sending the C<ev_async> watcher is required because otherwise
		4489	an event loop currently blocking in the kernel will have no knowledge
		4490	about the newly added timer. By waking up the loop it will pick up any new
		4491	watchers in the next event loop iteration.
		4492
		4493	=head3 COROUTINES
		4494
		4495	Libev is very accommodating to coroutines ("cooperative threads"):
		4496	libev fully supports nesting calls to its functions from different
		4497	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4498	different coroutines, and switch freely between both coroutines running
		4499	the loop, as long as you don't confuse yourself). The only exception is
		4500	that you must not do this from C<ev_periodic> reschedule callbacks.
		4501
		4502	Care has been taken to ensure that libev does not keep local state inside
		4503	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4504	they do not call any callbacks.
		4505
		4506	=head2 COMPILER WARNINGS
		4507
		4508	Depending on your compiler and compiler settings, you might get no or a
		4509	lot of warnings when compiling libev code. Some people are apparently
		4510	scared by this.
		4511
		4512	However, these are unavoidable for many reasons. For one, each compiler
		4513	has different warnings, and each user has different tastes regarding
		4514	warning options. "Warn-free" code therefore cannot be a goal except when
		4515	targeting a specific compiler and compiler-version.
		4516
		4517	Another reason is that some compiler warnings require elaborate
		4518	workarounds, or other changes to the code that make it less clear and less
		4519	maintainable.
		4520
		4521	And of course, some compiler warnings are just plain stupid, or simply
		4522	wrong (because they don't actually warn about the condition their message
		4523	seems to warn about). For example, certain older gcc versions had some
		4524	warnings that resulted in an extreme number of false positives. These have
		4525	been fixed, but some people still insist on making code warn-free with
		4526	such buggy versions.
		4527
		4528	While libev is written to generate as few warnings as possible,
		4529	"warn-free" code is not a goal, and it is recommended not to build libev
		4530	with any compiler warnings enabled unless you are prepared to cope with
		4531	them (e.g. by ignoring them). Remember that warnings are just that:
		4532	warnings, not errors, or proof of bugs.
		4533
		4534
		4535	=head2 VALGRIND
		4536
		4537	Valgrind has a special section here because it is a popular tool that is
		4538	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4539
		4540	If you think you found a bug (memory leak, uninitialised data access etc.)
		4541	in libev, then check twice: If valgrind reports something like:
		4542
		4543	==2274== definitely lost: 0 bytes in 0 blocks.
		4544	==2274== possibly lost: 0 bytes in 0 blocks.
		4545	==2274== still reachable: 256 bytes in 1 blocks.
		4546
		4547	Then there is no memory leak, just as memory accounted to global variables
		4548	is not a memleak - the memory is still being referenced, and didn't leak.
		4549
		4550	Similarly, under some circumstances, valgrind might report kernel bugs
		4551	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4552	although an acceptable workaround has been found here), or it might be
		4553	confused.
		4554
		4555	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4556	make it into some kind of religion.
		4557
		4558	If you are unsure about something, feel free to contact the mailing list
		4559	with the full valgrind report and an explanation on why you think this
		4560	is a bug in libev (best check the archives, too :). However, don't be
		4561	annoyed when you get a brisk "this is no bug" answer and take the chance
		4562	of learning how to interpret valgrind properly.
		4563
		4564	If you need, for some reason, empty reports from valgrind for your project
		4565	I suggest using suppression lists.
		4566
		4567
		4568	=head1 PORTABILITY NOTES
		4569
		4570	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4571
		4572	GNU/Linux is the only common platform that supports 64 bit file/large file
		4573	interfaces but I<disables> them by default.
		4574
		4575	That means that libev compiled in the default environment doesn't support
		4576	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4577
		4578	Unfortunately, many programs try to work around this GNU/Linux issue
		4579	by enabling the large file API, which makes them incompatible with the
		4580	standard libev compiled for their system.
		4581
		4582	Likewise, libev cannot enable the large file API itself as this would
		4583	suddenly make it incompatible to the default compile time environment,
		4584	i.e. all programs not using special compile switches.
		4585
		4586	=head2 OS/X AND DARWIN BUGS
		4587
		4588	The whole thing is a bug if you ask me - basically any system interface
		4589	you touch is broken, whether it is locales, poll, kqueue or even the
		4590	OpenGL drivers.
		4591
		4592	=head3 C<kqueue> is buggy
		4593
		4594	The kqueue syscall is broken in all known versions - most versions support
		4595	only sockets, many support pipes.
		4596
		4597	Libev tries to work around this by not using C<kqueue> by default on this
		4598	rotten platform, but of course you can still ask for it when creating a
		4599	loop - embedding a socket-only kqueue loop into a select-based one is
		4600	probably going to work well.
		4601
		4602	=head3 C<poll> is buggy
		4603
		4604	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4605	implementation by something calling C<kqueue> internally around the 10.5.6
		4606	release, so now C<kqueue> I<and> C<poll> are broken.
		4607
		4608	Libev tries to work around this by not using C<poll> by default on
		4609	this rotten platform, but of course you can still ask for it when creating
		4610	a loop.
		4611
		4612	=head3 C<select> is buggy
		4613
		4614	All that's left is C<select>, and of course Apple found a way to fuck this
		4615	one up as well: On OS/X, C<select> actively limits the number of file
		4616	descriptors you can pass in to 1024 - your program suddenly crashes when
		4617	you use more.
		4618
		4619	There is an undocumented "workaround" for this - defining
		4620	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4621	work on OS/X.
		4622
		4623	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4624
		4625	=head3 C<errno> reentrancy
		4626
		4627	The default compile environment on Solaris is unfortunately so
		4628	thread-unsafe that you can't even use components/libraries compiled
		4629	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4630	defined by default. A valid, if stupid, implementation choice.
		4631
		4632	If you want to use libev in threaded environments you have to make sure
		4633	it's compiled with C<_REENTRANT> defined.
		4634
		4635	=head3 Event port backend
		4636
		4637	The scalable event interface for Solaris is called "event
		4638	ports". Unfortunately, this mechanism is very buggy in all major
		4639	releases. If you run into high CPU usage, your program freezes or you get
		4640	a large number of spurious wakeups, make sure you have all the relevant
		4641	and latest kernel patches applied. No, I don't know which ones, but there
		4642	are multiple ones to apply, and afterwards, event ports actually work
		4643	great.
		4644
		4645	If you can't get it to work, you can try running the program by setting
		4646	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4647	C<select> backends.
		4648
		4649	=head2 AIX POLL BUG
		4650
		4651	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4652	this by trying to avoid the poll backend altogether (i.e. it's not even
		4653	compiled in), which normally isn't a big problem as C<select> works fine
		4654	with large bitsets on AIX, and AIX is dead anyway.
		4655
		4656	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4657
		4658	=head3 General issues
		4659
		4660	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4661	requires, and its I/O model is fundamentally incompatible with the POSIX
		4662	model. Libev still offers limited functionality on this platform in
		4663	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4664	descriptors. This only applies when using Win32 natively, not when using
		4665	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4666	as every compielr comes with a slightly differently broken/incompatible
		4667	environment.
		4668
		4669	Lifting these limitations would basically require the full
		4670	re-implementation of the I/O system. If you are into this kind of thing,
		4671	then note that glib does exactly that for you in a very portable way (note
		4672	also that glib is the slowest event library known to man).
		4673
		4674	There is no supported compilation method available on windows except
		4675	embedding it into other applications.
		4676
		4677	Sensible signal handling is officially unsupported by Microsoft - libev
		4678	tries its best, but under most conditions, signals will simply not work.
		4679
		4680	Not a libev limitation but worth mentioning: windows apparently doesn't
		4681	accept large writes: instead of resulting in a partial write, windows will
		4682	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4683	so make sure you only write small amounts into your sockets (less than a
		4684	megabyte seems safe, but this apparently depends on the amount of memory
		4685	available).
		4686
		4687	Due to the many, low, and arbitrary limits on the win32 platform and
		4688	the abysmal performance of winsockets, using a large number of sockets
		4689	is not recommended (and not reasonable). If your program needs to use
		4690	more than a hundred or so sockets, then likely it needs to use a totally
		4691	different implementation for windows, as libev offers the POSIX readiness
		4692	notification model, which cannot be implemented efficiently on windows
		4693	(due to Microsoft monopoly games).
		4694
		4695	A typical way to use libev under windows is to embed it (see the embedding
		4696	section for details) and use the following F<evwrap.h> header file instead
		4697	of F<ev.h>:
		4698
		4699	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4700	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4701
		4702	#include "ev.h"
		4703
		4704	And compile the following F<evwrap.c> file into your project (make sure
		4705	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4706
		4707	#include "evwrap.h"
		4708	#include "ev.c"
		4709
		4710	=head3 The winsocket C<select> function
		4711
		4712	The winsocket C<select> function doesn't follow POSIX in that it
		4713	requires socket I<handles> and not socket I<file descriptors> (it is
		4714	also extremely buggy). This makes select very inefficient, and also
		4715	requires a mapping from file descriptors to socket handles (the Microsoft
		4716	C runtime provides the function C<_open_osfhandle> for this). See the
		4717	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4718	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4719
		4720	The configuration for a "naked" win32 using the Microsoft runtime
		4721	libraries and raw winsocket select is:
		4722
		4723	#define EV_USE_SELECT 1
		4724	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4725
		4726	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4727	complexity in the O(n²) range when using win32.
		4728
		4729	=head3 Limited number of file descriptors
		4730
		4731	Windows has numerous arbitrary (and low) limits on things.
		4732
		4733	Early versions of winsocket's select only supported waiting for a maximum
		4734	of C<64> handles (probably owning to the fact that all windows kernels
		4735	can only wait for C<64> things at the same time internally; Microsoft
		4736	recommends spawning a chain of threads and wait for 63 handles and the
		4737	previous thread in each. Sounds great!).
		4738
		4739	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4740	to some high number (e.g. C<2048>) before compiling the winsocket select
		4741	call (which might be in libev or elsewhere, for example, perl and many
		4742	other interpreters do their own select emulation on windows).
		4743
		4744	Another limit is the number of file descriptors in the Microsoft runtime
		4745	libraries, which by default is C<64> (there must be a hidden I<64>
		4746	fetish or something like this inside Microsoft). You can increase this
		4747	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4748	(another arbitrary limit), but is broken in many versions of the Microsoft
		4749	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4750	(depending on windows version and/or the phase of the moon). To get more,
		4751	you need to wrap all I/O functions and provide your own fd management, but
		4752	the cost of calling select (O(n²)) will likely make this unworkable.
		4753
		4754	=head2 PORTABILITY REQUIREMENTS
		4755
		4756	In addition to a working ISO-C implementation and of course the
		4757	backend-specific APIs, libev relies on a few additional extensions:
		4758
		4759	=over 4
		4760
		4761	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4762	calling conventions regardless of C<ev_watcher_type *>.
		4763
		4764	Libev assumes not only that all watcher pointers have the same internal
		4765	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4766	assumes that the same (machine) code can be used to call any watcher
		4767	callback: The watcher callbacks have different type signatures, but libev
		4768	calls them using an C<ev_watcher *> internally.
		4769
		4770	=item pointer accesses must be thread-atomic
		4771
		4772	Accessing a pointer value must be atomic, it must both be readable and
		4773	writable in one piece - this is the case on all current architectures.
		4774
		4775	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4776
		4777	The type C<sig_atomic_t volatile> (or whatever is defined as
		4778	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4779	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4780	believed to be sufficiently portable.
		4781
		4782	=item C<sigprocmask> must work in a threaded environment
		4783
		4784	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4785	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4786	pthread implementations will either allow C<sigprocmask> in the "main
		4787	thread" or will block signals process-wide, both behaviours would
		4788	be compatible with libev. Interaction between C<sigprocmask> and
		4789	C<pthread_sigmask> could complicate things, however.
		4790
		4791	The most portable way to handle signals is to block signals in all threads
		4792	except the initial one, and run the default loop in the initial thread as
		4793	well.
		4794
		4795	=item C<long> must be large enough for common memory allocation sizes
		4796
		4797	To improve portability and simplify its API, libev uses C<long> internally
		4798	instead of C<size_t> when allocating its data structures. On non-POSIX
		4799	systems (Microsoft...) this might be unexpectedly low, but is still at
		4800	least 31 bits everywhere, which is enough for hundreds of millions of
		4801	watchers.
		4802
		4803	=item C<double> must hold a time value in seconds with enough accuracy
		4804
		4805	The type C<double> is used to represent timestamps. It is required to
		4806	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		4807	good enough for at least into the year 4000 with millisecond accuracy
		4808	(the design goal for libev). This requirement is overfulfilled by
		4809	implementations using IEEE 754, which is basically all existing ones. With
		4810	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
		4811
		4812	=back
		4813
		4814	If you know of other additional requirements drop me a note.
		4815
		4816
2676	=head1 COMPLEXITIES	4817	=head1 ALGORITHMIC COMPLEXITIES
2677		4818
2678	In this section the complexities of (many of) the algorithms used inside	4819	In this section the complexities of (many of) the algorithms used inside
2679	libev will be explained. For complexity discussions about backends see the	4820	libev will be documented. For complexity discussions about backends see
2680	documentation for C<ev_default_init>.	4821	the documentation for C<ev_default_init>.
2681		4822
2682	All of the following are about amortised time: If an array needs to be	4823	All of the following are about amortised time: If an array needs to be
2683	extended, libev needs to realloc and move the whole array, but this	4824	extended, libev needs to realloc and move the whole array, but this
2684	happens asymptotically never with higher number of elements, so O(1) might	4825	happens asymptotically rarer with higher number of elements, so O(1) might
2685	mean it might do a lengthy realloc operation in rare cases, but on average	4826	mean that libev does a lengthy realloc operation in rare cases, but on
2686	it is much faster and asymptotically approaches constant time.	4827	average it is much faster and asymptotically approaches constant time.
2687		4828
2688	=over 4	4829	=over 4
2689		4830
2690	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4831	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2691		4832
2692	This means that, when you have a watcher that triggers in one hour and	4833	This means that, when you have a watcher that triggers in one hour and
2693	there are 100 watchers that would trigger before that then inserting will	4834	there are 100 watchers that would trigger before that, then inserting will
2694	have to skip roughly seven (C<ld 100>) of these watchers.	4835	have to skip roughly seven (C<ld 100>) of these watchers.
2695		4836
2696	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4837	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2697		4838
2698	That means that changing a timer costs less than removing/adding them	4839	That means that changing a timer costs less than removing/adding them,
2699	as only the relative motion in the event queue has to be paid for.	4840	as only the relative motion in the event queue has to be paid for.
2700		4841
2701	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4842	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2702		4843
2703	These just add the watcher into an array or at the head of a list.	4844	These just add the watcher into an array or at the head of a list.
2704		4845
2705	=item Stopping check/prepare/idle watchers: O(1)	4846	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2706		4847
2707	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4848	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2708		4849
2709	These watchers are stored in lists then need to be walked to find the	4850	These watchers are stored in lists, so they need to be walked to find the
2710	correct watcher to remove. The lists are usually short (you don't usually	4851	correct watcher to remove. The lists are usually short (you don't usually
2711	have many watchers waiting for the same fd or signal).	4852	have many watchers waiting for the same fd or signal: one is typical, two
		4853	is rare).
2712		4854
2713	=item Finding the next timer in each loop iteration: O(1)	4855	=item Finding the next timer in each loop iteration: O(1)
2714		4856
2715	By virtue of using a binary heap, the next timer is always found at the	4857	By virtue of using a binary or 4-heap, the next timer is always found at a
2716	beginning of the storage array.	4858	fixed position in the storage array.
2717		4859
2718	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4860	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2719		4861
2720	A change means an I/O watcher gets started or stopped, which requires	4862	A change means an I/O watcher gets started or stopped, which requires
2721	libev to recalculate its status (and possibly tell the kernel, depending	4863	libev to recalculate its status (and possibly tell the kernel, depending
2722	on backend and wether C<ev_io_set> was used).	4864	on backend and whether C<ev_io_set> was used).
2723		4865
2724	=item Activating one watcher (putting it into the pending state): O(1)	4866	=item Activating one watcher (putting it into the pending state): O(1)
2725		4867
2726	=item Priority handling: O(number_of_priorities)	4868	=item Priority handling: O(number_of_priorities)
2727		4869
2728	Priorities are implemented by allocating some space for each	4870	Priorities are implemented by allocating some space for each
2729	priority. When doing priority-based operations, libev usually has to	4871	priority. When doing priority-based operations, libev usually has to
2730	linearly search all the priorities, but starting/stopping and activating	4872	linearly search all the priorities, but starting/stopping and activating
2731	watchers becomes O(1) w.r.t. prioritiy handling.	4873	watchers becomes O(1) with respect to priority handling.
		4874
		4875	=item Sending an ev_async: O(1)
		4876
		4877	=item Processing ev_async_send: O(number_of_async_watchers)
		4878
		4879	=item Processing signals: O(max_signal_number)
		4880
		4881	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4882	calls in the current loop iteration. Checking for async and signal events
		4883	involves iterating over all running async watchers or all signal numbers.
2732		4884
2733	=back	4885	=back
2734		4886
2735		4887
		4888	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4889
		4890	The major version 4 introduced some incompatible changes to the API.
		4891
		4892	At the moment, the C<ev.h> header file provides compatibility definitions
		4893	for all changes, so most programs should still compile. The compatibility
		4894	layer might be removed in later versions of libev, so better update to the
		4895	new API early than late.
		4896
		4897	=over 4
		4898
		4899	=item C<EV_COMPAT3> backwards compatibility mechanism
		4900
		4901	The backward compatibility mechanism can be controlled by
		4902	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		4903	section.
		4904
		4905	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		4906
		4907	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		4908
		4909	ev_loop_destroy (EV_DEFAULT_UC);
		4910	ev_loop_fork (EV_DEFAULT);
		4911
		4912	=item function/symbol renames
		4913
		4914	A number of functions and symbols have been renamed:
		4915
		4916	ev_loop => ev_run
		4917	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		4918	EVLOOP_ONESHOT => EVRUN_ONCE
		4919
		4920	ev_unloop => ev_break
		4921	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		4922	EVUNLOOP_ONE => EVBREAK_ONE
		4923	EVUNLOOP_ALL => EVBREAK_ALL
		4924
		4925	EV_TIMEOUT => EV_TIMER
		4926
		4927	ev_loop_count => ev_iteration
		4928	ev_loop_depth => ev_depth
		4929	ev_loop_verify => ev_verify
		4930
		4931	Most functions working on C<struct ev_loop> objects don't have an
		4932	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		4933	associated constants have been renamed to not collide with the C<struct
		4934	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		4935	as all other watcher types. Note that C<ev_loop_fork> is still called
		4936	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		4937	typedef.
		4938
		4939	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4940
		4941	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4942	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4943	and work, but the library code will of course be larger.
		4944
		4945	=back
		4946
		4947
		4948	=head1 GLOSSARY
		4949
		4950	=over 4
		4951
		4952	=item active
		4953
		4954	A watcher is active as long as it has been started and not yet stopped.
		4955	See L<WATCHER STATES> for details.
		4956
		4957	=item application
		4958
		4959	In this document, an application is whatever is using libev.
		4960
		4961	=item backend
		4962
		4963	The part of the code dealing with the operating system interfaces.
		4964
		4965	=item callback
		4966
		4967	The address of a function that is called when some event has been
		4968	detected. Callbacks are being passed the event loop, the watcher that
		4969	received the event, and the actual event bitset.
		4970
		4971	=item callback/watcher invocation
		4972
		4973	The act of calling the callback associated with a watcher.
		4974
		4975	=item event
		4976
		4977	A change of state of some external event, such as data now being available
		4978	for reading on a file descriptor, time having passed or simply not having
		4979	any other events happening anymore.
		4980
		4981	In libev, events are represented as single bits (such as C<EV_READ> or
		4982	C<EV_TIMER>).
		4983
		4984	=item event library
		4985
		4986	A software package implementing an event model and loop.
		4987
		4988	=item event loop
		4989
		4990	An entity that handles and processes external events and converts them
		4991	into callback invocations.
		4992
		4993	=item event model
		4994
		4995	The model used to describe how an event loop handles and processes
		4996	watchers and events.
		4997
		4998	=item pending
		4999
		5000	A watcher is pending as soon as the corresponding event has been
		5001	detected. See L<WATCHER STATES> for details.
		5002
		5003	=item real time
		5004
		5005	The physical time that is observed. It is apparently strictly monotonic :)
		5006
		5007	=item wall-clock time
		5008
		5009	The time and date as shown on clocks. Unlike real time, it can actually
		5010	be wrong and jump forwards and backwards, e.g. when the you adjust your
		5011	clock.
		5012
		5013	=item watcher
		5014
		5015	A data structure that describes interest in certain events. Watchers need
		5016	to be started (attached to an event loop) before they can receive events.
		5017
		5018	=back
		5019
2736	=head1 AUTHOR	5020	=head1 AUTHOR
2737		5021
2738	Marc Lehmann <libev@schmorp.de>.	5022	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5023	Magnusson and Emanuele Giaquinta.
2739		5024

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