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Revision 1.84 by root, Wed Dec 12 22:26:37 2007 UTC vs.
Revision 1.342 by root, Wed Nov 10 13:16:44 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	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_run's to stop iterating
		32	ev_break (EV_A_ EVBREAK_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_run to stop iterating
		41	ev_break (EV_A_ EVBREAK_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
35	struct ev_loop *loop = ev_default_loop (0);	47	// use the default event loop unless you have special needs
		48	struct ev_loop *loop = EV_DEFAULT;
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_run (loop, 0);
47		62
		63	// 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 occuring), 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
61	To do this, it must take more or less complete control over your process	97	To do this, it must take more or less complete control over your process
62	(or thread) by executing the I<event loop> handler, and will then	98	(or thread) by executing the I<event loop> handler, and will then
63	communicate events via a callback mechanism.	99	communicate events via a callback mechanism.
…		…
65	You register interest in certain events by registering so-called I<event	101	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	102	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	103	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	104	watcher.
69		105
70	=head1 FEATURES	106	=head2 FEATURES
71		107
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	108	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	109	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	110	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	111	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
76	with customised rescheduling (C<ev_periodic>), synchronous signals	112	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
77	(C<ev_signal>), process status change events (C<ev_child>), and event	113	timers (C<ev_timer>), absolute timers with customised rescheduling
78	watchers dealing with the event loop mechanism itself (C<ev_idle>,	114	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
79	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	115	change events (C<ev_child>), and event watchers dealing with the event
80	file watchers (C<ev_stat>) and even limited support for fork events	116	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
81	(C<ev_fork>).	117	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		118	limited support for fork events (C<ev_fork>).
82		119
83	It also is quite fast (see this	120	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	121	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	122	for example).
86		123
87	=head1 CONVENTIONS	124	=head2 CONVENTIONS
88		125
89	Libev is very configurable. In this manual the default configuration will	126	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	127	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	128	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	129	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	130	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	131	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		132	this argument.
95		133
96	=head1 TIME REPRESENTATION	134	=head2 TIME REPRESENTATION
97		135
98	Libev represents time as a single floating point number, representing the	136	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	137	the (fractional) number of seconds since the (POSIX) epoch (in practice
100	the beginning of 1970, details are complicated, don't ask). This type is	138	somewhere near the beginning of 1970, details are complicated, don't
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	139	ask). This type is called C<ev_tstamp>, which is what you should use
102	to the C<double> type in C, and when you need to do any calculations on	140	too. It usually aliases to the C<double> type in C. When you need to do
103	it, you should treat it as such.	141	any calculations on it, you should treat it as some floating point value.
		142
		143	Unlike the name component C<stamp> might indicate, it is also used for
		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
104		166
105	=head1 GLOBAL FUNCTIONS	167	=head1 GLOBAL FUNCTIONS
106		168
107	These functions can be called anytime, even before initialising the	169	These functions can be called anytime, even before initialising the
108	library in any way.	170	library in any way.
…		…
111		173
112	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
113		175
114	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
115	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
116	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>.
		180
		181	=item ev_sleep (ev_tstamp interval)
		182
		183	Sleep for the given interval: The current thread will be blocked until
		184	either it is interrupted or the given time interval has passed. Basically
		185	this is a sub-second-resolution C<sleep ()>.
117		186
118	=item int ev_version_major ()	187	=item int ev_version_major ()
119		188
120	=item int ev_version_minor ()	189	=item int ev_version_minor ()
121		190
…		…
132	as this indicates an incompatible change. Minor versions are usually	201	as this indicates an incompatible change. Minor versions are usually
133	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
134	not a problem.	203	not a problem.
135		204
136	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
137	version.	206	version (note, however, that this will not detect other ABI mismatches,
		207	such as LFS or reentrancy).
138		208
139	assert (("libev version mismatch",	209	assert (("libev version mismatch",
140	ev_version_major () == EV_VERSION_MAJOR	210	ev_version_major () == EV_VERSION_MAJOR
141	&& ev_version_minor () >= EV_VERSION_MINOR));	211	&& ev_version_minor () >= EV_VERSION_MINOR));
142		212
143	=item unsigned int ev_supported_backends ()	213	=item unsigned int ev_supported_backends ()
144		214
145	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_*>
146	value) compiled into this binary of libev (independent of their	216	value) compiled into this binary of libev (independent of their
…		…
148	a description of the set values.	218	a description of the set values.
149		219
150	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
151	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
152		222
153	assert (("sorry, no epoll, no sex",	223	assert (("sorry, no epoll, no sex",
154	ev_supported_backends () & EVBACKEND_EPOLL));	224	ev_supported_backends () & EVBACKEND_EPOLL));
155		225
156	=item unsigned int ev_recommended_backends ()	226	=item unsigned int ev_recommended_backends ()
157		227
158	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
159	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
160	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
161	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
162	(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
163	libev will probe for if you specify no backends explicitly.	234	probe for if you specify no backends explicitly.
164		235
165	=item unsigned int ev_embeddable_backends ()	236	=item unsigned int ev_embeddable_backends ()
166		237
167	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
168	is the theoretical, all-platform, value. To find which backends	239	value is platform-specific but can include backends not available on the
169	might be supported on the current system, you would need to look at	240	current system. To find which embeddable backends might be supported on
170	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	241	the current system, you would need to look at C<ev_embeddable_backends ()
171	recommended ones.	242	& ev_supported_backends ()>, likewise for recommended ones.
172		243
173	See the description of C<ev_embed> watchers for more info.	244	See the description of C<ev_embed> watchers for more info.
174		245
175	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	246	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
176		247
177	Sets the allocation function to use (the prototype is similar - the	248	Sets the allocation function to use (the prototype is similar - the
178	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
179	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
180	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
181	potentially destructive action. The default is your system realloc	252	or take some potentially destructive action.
182	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.
183		257
184	You could override this function in high-availability programs to, say,	258	You could override this function in high-availability programs to, say,
185	free some memory if it cannot allocate memory, to use a special allocator,	259	free some memory if it cannot allocate memory, to use a special allocator,
186	or even to sleep a while and retry until some memory is available.	260	or even to sleep a while and retry until some memory is available.
187		261
188	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
189	retries).	263	retries (example requires a standards-compliant C<realloc>).
190		264
191	static void *	265	static void *
192	persistent_realloc (void *ptr, size_t size)	266	persistent_realloc (void *ptr, size_t size)
193	{	267	{
194	for (;;)	268	for (;;)
…		…
203	}	277	}
204		278
205	...	279	...
206	ev_set_allocator (persistent_realloc);	280	ev_set_allocator (persistent_realloc);
207		281
208	=item ev_set_syserr_cb (void (*cb)(const char *msg));	282	=item ev_set_syserr_cb (void (*cb)(const char *msg))
209		283
210	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
211	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
212	indicating the system call or subsystem causing the problem. If this	286	indicating the system call or subsystem causing the problem. If this
213	callback is set, then libev will expect it to remedy the sitution, no	287	callback is set, then libev will expect it to remedy the situation, no
214	matter what, when it returns. That is, libev will generally retry the	288	matter what, when it returns. That is, libev will generally retry the
215	requested operation, or, if the condition doesn't go away, do bad stuff	289	requested operation, or, if the condition doesn't go away, do bad stuff
216	(such as abort).	290	(such as abort).
217		291
218	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.
…		…
227	...	301	...
228	ev_set_syserr_cb (fatal_error);	302	ev_set_syserr_cb (fatal_error);
229		303
230	=back	304	=back
231		305
232	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	306	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
233		307
234	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
235	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
236	events, and dynamically created loops which do not.	310	libev 3 had an C<ev_loop> function colliding with the struct name).
237		311
238	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
239	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
240	create, you also create another event loop. Libev itself does no locking	314	do not.
241	whatsoever, so if you mix calls to the same event loop in different
242	threads, make sure you lock (this is usually a bad idea, though, even if
243	done correctly, because it's hideous and inefficient).
244		315
245	=over 4	316	=over 4
246		317
247	=item struct ev_loop *ev_default_loop (unsigned int flags)	318	=item struct ev_loop *ev_default_loop (unsigned int flags)
248		319
249	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
250	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
251	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
252	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".
253		330
254	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
255	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.
256		363
257	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
258	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>).
259		366
260	The following flags are supported:	367	The following flags are supported:
…		…
266	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
267	thing, believe me).	374	thing, believe me).
268		375
269	=item C<EVFLAG_NOENV>	376	=item C<EVFLAG_NOENV>
270		377
271	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
272	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
273	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	380	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
274	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
275	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
276	around bugs.	383	around bugs.
277		384
278	=item C<EVFLAG_FORKCHECK>	385	=item C<EVFLAG_FORKCHECK>
279		386
280	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
281	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.
282	enabling this flag.
283		389
284	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,
285	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
286	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
287	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
288	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
289	C<pthread_atfork> which is even faster).	395	C<pthread_atfork> which is even faster).
290		396
291	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
292	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
293	flag.	399	flag.
294		400
295	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>
296	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 its 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 its 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.
297		423
298	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
299		425
300	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
301	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,
302	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
303	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	429	using this backend. It doesn't scale too well (O(highest_fd)), but its
304	the fastest backend for a low number of fds.	430	usually the fastest backend for a low number of (low-numbered :) fds.
		431
		432	To get good performance out of this backend you need a high amount of
		433	parallelism (most of the file descriptors should be busy). If you are
		434	writing a server, you should C<accept ()> in a loop to accept as many
		435	connections as possible during one iteration. You might also want to have
		436	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		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).
305		442
306	=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)
307		444
308	And this is your standard poll(2) backend. It's more complicated than	445	And this is your standard poll(2) backend. It's more complicated
309	select, but handles sparse fds better and has no artificial limit on the	446	than select, but handles sparse fds better and has no artificial
310	number of fds you can use (except it will slow down considerably with a	447	limit on the number of fds you can use (except it will slow down
311	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	448	considerably with a lot of inactive fds). It scales similarly to select,
		449	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		450	performance tips.
		451
		452	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		453	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
312		454
313	=item C<EVBACKEND_EPOLL> (value 4, Linux)	455	=item C<EVBACKEND_EPOLL> (value 4, Linux)
314		456
		457	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		458	kernels).
		459
315	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,
316	but it scales phenomenally better. While poll and select usually scale like	461	but it scales phenomenally better. While poll and select usually scale
317	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	462	like O(total_fds) where n is the total number of fds (or the highest fd),
318	either O(1) or O(active_fds).	463	epoll scales either O(1) or O(active_fds).
319		464
		465	The epoll mechanism deserves honorable mention as the most misdesigned
		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, resulting in additional iterations
		470	(and only giving 5ms accuracy while select on the same platform gives
		471	0.1ms) and so on. The biggest issue is fork races, however - if a program
		472	forks then I<both> parent and child process have to recreate the epoll
		473	set, which can take considerable time (one syscall per file descriptor)
		474	and is of course hard to detect.
		475
		476	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		477	of course I<doesn't>, and epoll just loves to report events for totally
		478	I<different> file descriptors (even already closed ones, so one cannot
		479	even remove them from the set) than registered in the set (especially
		480	on SMP systems). Libev tries to counter these spurious notifications by
		481	employing an additional generation counter and comparing that against the
		482	events to filter out spurious ones, recreating the set when required. Last
		483	not least, it also refuses to work with some file descriptors which work
		484	perfectly fine with C<select> (files, many character devices...).
		485
		486	Epoll is truly the train wreck analog among event poll mechanisms.
		487
320	While stopping and starting an I/O watcher in the same iteration will	488	While stopping, setting and starting an I/O watcher in the same iteration
321	result in some caching, there is still a syscall per such incident	489	will result in some caching, there is still a system call per such
322	(because the fd could point to a different file description now), so its	490	incident (because the same I<file descriptor> could point to a different
323	best to avoid that. Also, dup()ed file descriptors might not work very	491	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
324	well if you register events for both fds.	492	file descriptors might not work very well if you register events for both
		493	file descriptors.
325		494
326	Please note that epoll sometimes generates spurious notifications, so you	495	Best performance from this backend is achieved by not unregistering all
327	need to use non-blocking I/O or other means to avoid blocking when no data	496	watchers for a file descriptor until it has been closed, if possible,
328	(or space) is available.	497	i.e. keep at least one watcher active per fd at all times. Stopping and
		498	starting a watcher (without re-setting it) also usually doesn't cause
		499	extra overhead. A fork can both result in spurious notifications as well
		500	as in libev having to destroy and recreate the epoll object, which can
		501	take considerable time and thus should be avoided.
		502
		503	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		504	faster than epoll for maybe up to a hundred file descriptors, depending on
		505	the usage. So sad.
		506
		507	While nominally embeddable in other event loops, this feature is broken in
		508	all kernel versions tested so far.
		509
		510	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		511	C<EVBACKEND_POLL>.
329		512
330	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	513	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
331		514
332	Kqueue deserves special mention, as at the time of this writing, it	515	Kqueue deserves special mention, as at the time of this writing, it
333	was broken on all BSDs except NetBSD (usually it doesn't work with	516	was broken on all BSDs except NetBSD (usually it doesn't work reliably
334	anything but sockets and pipes, except on Darwin, where of course its	517	with anything but sockets and pipes, except on Darwin, where of course
335	completely useless). For this reason its not being "autodetected"	518	it's completely useless). Unlike epoll, however, whose brokenness
		519	is by design, these kqueue bugs can (and eventually will) be fixed
		520	without API changes to existing programs. For this reason it's not being
336	unless you explicitly specify it explicitly in the flags (i.e. using	521	"auto-detected" unless you explicitly specify it in the flags (i.e. using
337	C<EVBACKEND_KQUEUE>).	522	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		523	system like NetBSD.
		524
		525	You still can embed kqueue into a normal poll or select backend and use it
		526	only for sockets (after having made sure that sockets work with kqueue on
		527	the target platform). See C<ev_embed> watchers for more info.
338		528
339	It scales in the same way as the epoll backend, but the interface to the	529	It scales in the same way as the epoll backend, but the interface to the
340	kernel is more efficient (which says nothing about its actual speed, of	530	kernel is more efficient (which says nothing about its actual speed, of
341	course). While starting and stopping an I/O watcher does not cause an	531	course). While stopping, setting and starting an I/O watcher does never
342	extra syscall as with epoll, it still adds up to four event changes per	532	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
343	incident, so its best to avoid that.	533	two event changes per incident. Support for C<fork ()> is very bad (but
		534	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		535	cases
		536
		537	This backend usually performs well under most conditions.
		538
		539	While nominally embeddable in other event loops, this doesn't work
		540	everywhere, so you might need to test for this. And since it is broken
		541	almost everywhere, you should only use it when you have a lot of sockets
		542	(for which it usually works), by embedding it into another event loop
		543	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		544	also broken on OS X)) and, did I mention it, using it only for sockets.
		545
		546	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		547	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		548	C<NOTE_EOF>.
344		549
345	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	550	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
346		551
347	This is not implemented yet (and might never be).	552	This is not implemented yet (and might never be, unless you send me an
		553	implementation). According to reports, C</dev/poll> only supports sockets
		554	and is not embeddable, which would limit the usefulness of this backend
		555	immensely.
348		556
349	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	557	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
350		558
351	This uses the Solaris 10 port mechanism. As with everything on Solaris,	559	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
352	it's really slow, but it still scales very well (O(active_fds)).	560	it's really slow, but it still scales very well (O(active_fds)).
353		561
354	Please note that solaris ports can result in a lot of spurious	562	Please note that Solaris event ports can deliver a lot of spurious
355	notifications, so you need to use non-blocking I/O or other means to avoid	563	notifications, so you need to use non-blocking I/O or other means to avoid
356	blocking when no data (or space) is available.	564	blocking when no data (or space) is available.
		565
		566	While this backend scales well, it requires one system call per active
		567	file descriptor per loop iteration. For small and medium numbers of file
		568	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		569	might perform better.
		570
		571	On the positive side, with the exception of the spurious readiness
		572	notifications, this backend actually performed fully to specification
		573	in all tests and is fully embeddable, which is a rare feat among the
		574	OS-specific backends (I vastly prefer correctness over speed hacks).
		575
		576	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		577	C<EVBACKEND_POLL>.
357		578
358	=item C<EVBACKEND_ALL>	579	=item C<EVBACKEND_ALL>
359		580
360	Try all backends (even potentially broken ones that wouldn't be tried	581	Try all backends (even potentially broken ones that wouldn't be tried
361	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	582	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
362	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	583	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
363		584
		585	It is definitely not recommended to use this flag.
		586
364	=back	587	=back
365		588
366	If one or more of these are ored into the flags value, then only these	589	If one or more of the backend flags are or'ed into the flags value,
367	backends will be tried (in the reverse order as given here). If none are	590	then only these backends will be tried (in the reverse order as listed
368	specified, most compiled-in backend will be tried, usually in reverse	591	here). If none are specified, all backends in C<ev_recommended_backends
369	order of their flag values :)	592	()> will be tried.
370
371	The most typical usage is like this:
372
373	if (!ev_default_loop (0))
374	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
375
376	Restrict libev to the select and poll backends, and do not allow
377	environment settings to be taken into account:
378
379	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
380
381	Use whatever libev has to offer, but make sure that kqueue is used if
382	available (warning, breaks stuff, best use only with your own private
383	event loop and only if you know the OS supports your types of fds):
384
385	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
386
387	=item struct ev_loop *ev_loop_new (unsigned int flags)
388
389	Similar to C<ev_default_loop>, but always creates a new event loop that is
390	always distinct from the default loop. Unlike the default loop, it cannot
391	handle signal and child watchers, and attempts to do so will be greeted by
392	undefined behaviour (or a failed assertion if assertions are enabled).
393		593
394	Example: Try to create a event loop that uses epoll and nothing else.	594	Example: Try to create a event loop that uses epoll and nothing else.
395		595
396	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	596	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
397	if (!epoller)	597	if (!epoller)
398	fatal ("no epoll found here, maybe it hides under your chair");	598	fatal ("no epoll found here, maybe it hides under your chair");
399		599
		600	Example: Use whatever libev has to offer, but make sure that kqueue is
		601	used if available.
		602
		603	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		604
400	=item ev_default_destroy ()	605	=item ev_loop_destroy (loop)
401		606
402	Destroys the default loop again (frees all memory and kernel state	607	Destroys an event loop object (frees all memory and kernel state
403	etc.). None of the active event watchers will be stopped in the normal	608	etc.). None of the active event watchers will be stopped in the normal
404	sense, so e.g. C<ev_is_active> might still return true. It is your	609	sense, so e.g. C<ev_is_active> might still return true. It is your
405	responsibility to either stop all watchers cleanly yoursef I<before>	610	responsibility to either stop all watchers cleanly yourself I<before>
406	calling this function, or cope with the fact afterwards (which is usually	611	calling this function, or cope with the fact afterwards (which is usually
407	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	612	the easiest thing, you can just ignore the watchers and/or C<free ()> them
408	for example).	613	for example).
409		614
		615	Note that certain global state, such as signal state (and installed signal
		616	handlers), will not be freed by this function, and related watchers (such
		617	as signal and child watchers) would need to be stopped manually.
		618
		619	This function is normally used on loop objects allocated by
		620	C<ev_loop_new>, but it can also be used on the default loop returned by
		621	C<ev_default_loop>, in which case it is not thread-safe.
		622
		623	Note that it is not advisable to call this function on the default loop
		624	except in the rare occasion where you really need to free its resources.
		625	If you need dynamically allocated loops it is better to use C<ev_loop_new>
		626	and C<ev_loop_destroy>.
		627
410	=item ev_loop_destroy (loop)	628	=item ev_loop_fork (loop)
411		629
412	Like C<ev_default_destroy>, but destroys an event loop created by an	630	This function sets a flag that causes subsequent C<ev_run> iterations to
413	earlier call to C<ev_loop_new>.
414
415	=item ev_default_fork ()
416
417	This function reinitialises the kernel state for backends that have	631	reinitialise the kernel state for backends that have one. Despite the
418	one. Despite the name, you can call it anytime, but it makes most sense	632	name, you can call it anytime, but it makes most sense after forking, in
419	after forking, in either the parent or child process (or both, but that	633	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
420	again makes little sense).	634	child before resuming or calling C<ev_run>.
421		635
422	You I<must> call this function in the child process after forking if and	636	Again, you I<have> to call it on I<any> loop that you want to re-use after
423	only if you want to use the event library in both processes. If you just	637	a fork, I<even if you do not plan to use the loop in the parent>. This is
424	fork+exec, you don't have to call it.	638	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		639	during fork.
		640
		641	On the other hand, you only need to call this function in the child
		642	process if and only if you want to use the event loop in the child. If
		643	you just fork+exec or create a new loop in the child, you don't have to
		644	call it at all (in fact, C<epoll> is so badly broken that it makes a
		645	difference, but libev will usually detect this case on its own and do a
		646	costly reset of the backend).
425		647
426	The function itself is quite fast and it's usually not a problem to call	648	The function itself is quite fast and it's usually not a problem to call
427	it just in case after a fork. To make this easy, the function will fit in	649	it just in case after a fork.
428	quite nicely into a call to C<pthread_atfork>:
429		650
		651	Example: Automate calling C<ev_loop_fork> on the default loop when
		652	using pthreads.
		653
		654	static void
		655	post_fork_child (void)
		656	{
		657	ev_loop_fork (EV_DEFAULT);
		658	}
		659
		660	...
430	pthread_atfork (0, 0, ev_default_fork);	661	pthread_atfork (0, 0, post_fork_child);
431		662
432	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	663	=item int ev_is_default_loop (loop)
433	without calling this function, so if you force one of those backends you
434	do not need to care.
435		664
436	=item ev_loop_fork (loop)	665	Returns true when the given loop is, in fact, the default loop, and false
		666	otherwise.
437		667
438	Like C<ev_default_fork>, but acts on an event loop created by
439	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
440	after fork, and how you do this is entirely your own problem.
441
442	=item unsigned int ev_loop_count (loop)	668	=item unsigned int ev_iteration (loop)
443		669
444	Returns the count of loop iterations for the loop, which is identical to	670	Returns the current iteration count for the event loop, which is identical
445	the number of times libev did poll for new events. It starts at C<0> and	671	to the number of times libev did poll for new events. It starts at C<0>
446	happily wraps around with enough iterations.	672	and happily wraps around with enough iterations.
447		673
448	This value can sometimes be useful as a generation counter of sorts (it	674	This value can sometimes be useful as a generation counter of sorts (it
449	"ticks" the number of loop iterations), as it roughly corresponds with	675	"ticks" the number of loop iterations), as it roughly corresponds with
450	C<ev_prepare> and C<ev_check> calls.	676	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		677	prepare and check phases.
		678
		679	=item unsigned int ev_depth (loop)
		680
		681	Returns the number of times C<ev_run> was entered minus the number of
		682	times C<ev_run> was exited, in other words, the recursion depth.
		683
		684	Outside C<ev_run>, this number is zero. In a callback, this number is
		685	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		686	in which case it is higher.
		687
		688	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread
		689	etc.), doesn't count as "exit" - consider this as a hint to avoid such
		690	ungentleman-like behaviour unless it's really convenient.
451		691
452	=item unsigned int ev_backend (loop)	692	=item unsigned int ev_backend (loop)
453		693
454	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	694	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
455	use.	695	use.
…		…
458		698
459	Returns the current "event loop time", which is the time the event loop	699	Returns the current "event loop time", which is the time the event loop
460	received events and started processing them. This timestamp does not	700	received events and started processing them. This timestamp does not
461	change as long as callbacks are being processed, and this is also the base	701	change as long as callbacks are being processed, and this is also the base
462	time used for relative timers. You can treat it as the timestamp of the	702	time used for relative timers. You can treat it as the timestamp of the
463	event occuring (or more correctly, libev finding out about it).	703	event occurring (or more correctly, libev finding out about it).
464		704
		705	=item ev_now_update (loop)
		706
		707	Establishes the current time by querying the kernel, updating the time
		708	returned by C<ev_now ()> in the progress. This is a costly operation and
		709	is usually done automatically within C<ev_run ()>.
		710
		711	This function is rarely useful, but when some event callback runs for a
		712	very long time without entering the event loop, updating libev's idea of
		713	the current time is a good idea.
		714
		715	See also L<The special problem of time updates> in the C<ev_timer> section.
		716
		717	=item ev_suspend (loop)
		718
		719	=item ev_resume (loop)
		720
		721	These two functions suspend and resume an event loop, for use when the
		722	loop is not used for a while and timeouts should not be processed.
		723
		724	A typical use case would be an interactive program such as a game: When
		725	the user presses C<^Z> to suspend the game and resumes it an hour later it
		726	would be best to handle timeouts as if no time had actually passed while
		727	the program was suspended. This can be achieved by calling C<ev_suspend>
		728	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		729	C<ev_resume> directly afterwards to resume timer processing.
		730
		731	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		732	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		733	will be rescheduled (that is, they will lose any events that would have
		734	occurred while suspended).
		735
		736	After calling C<ev_suspend> you B<must not> call I<any> function on the
		737	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		738	without a previous call to C<ev_suspend>.
		739
		740	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		741	event loop time (see C<ev_now_update>).
		742
465	=item ev_loop (loop, int flags)	743	=item ev_run (loop, int flags)
466		744
467	Finally, this is it, the event handler. This function usually is called	745	Finally, this is it, the event handler. This function usually is called
468	after you initialised all your watchers and you want to start handling	746	after you have initialised all your watchers and you want to start
469	events.	747	handling events. It will ask the operating system for any new events, call
		748	the watcher callbacks, an then repeat the whole process indefinitely: This
		749	is why event loops are called I<loops>.
470		750
471	If the flags argument is specified as C<0>, it will not return until	751	If the flags argument is specified as C<0>, it will keep handling events
472	either no event watchers are active anymore or C<ev_unloop> was called.	752	until either no event watchers are active anymore or C<ev_break> was
		753	called.
473		754
474	Please note that an explicit C<ev_unloop> is usually better than	755	Please note that an explicit C<ev_break> is usually better than
475	relying on all watchers to be stopped when deciding when a program has	756	relying on all watchers to be stopped when deciding when a program has
476	finished (especially in interactive programs), but having a program that	757	finished (especially in interactive programs), but having a program
477	automatically loops as long as it has to and no longer by virtue of	758	that automatically loops as long as it has to and no longer by virtue
478	relying on its watchers stopping correctly is a thing of beauty.	759	of relying on its watchers stopping correctly, that is truly a thing of
		760	beauty.
479		761
480	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	762	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
481	those events and any outstanding ones, but will not block your process in	763	those events and any already outstanding ones, but will not wait and
482	case there are no events and will return after one iteration of the loop.	764	block your process in case there are no events and will return after one
		765	iteration of the loop. This is sometimes useful to poll and handle new
		766	events while doing lengthy calculations, to keep the program responsive.
483		767
484	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	768	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
485	neccessary) and will handle those and any outstanding ones. It will block	769	necessary) and will handle those and any already outstanding ones. It
486	your process until at least one new event arrives, and will return after	770	will block your process until at least one new event arrives (which could
487	one iteration of the loop. This is useful if you are waiting for some	771	be an event internal to libev itself, so there is no guarantee that a
488	external event in conjunction with something not expressible using other	772	user-registered callback will be called), and will return after one
		773	iteration of the loop.
		774
		775	This is useful if you are waiting for some external event in conjunction
		776	with something not expressible using other libev watchers (i.e. "roll your
489	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	777	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
490	usually a better approach for this kind of thing.	778	usually a better approach for this kind of thing.
491		779
492	Here are the gory details of what C<ev_loop> does:	780	Here are the gory details of what C<ev_run> does:
493		781
		782	- Increment loop depth.
		783	- Reset the ev_break status.
494	- Before the first iteration, call any pending watchers.	784	- Before the first iteration, call any pending watchers.
495	* If there are no active watchers (reference count is zero), return.	785	LOOP:
496	- Queue all prepare watchers and then call all outstanding watchers.	786	- If EVFLAG_FORKCHECK was used, check for a fork.
		787	- If a fork was detected (by any means), queue and call all fork watchers.
		788	- Queue and call all prepare watchers.
		789	- If ev_break was called, goto FINISH.
497	- If we have been forked, recreate the kernel state.	790	- If we have been forked, detach and recreate the kernel state
		791	as to not disturb the other process.
498	- Update the kernel state with all outstanding changes.	792	- Update the kernel state with all outstanding changes.
499	- Update the "event loop time".	793	- Update the "event loop time" (ev_now ()).
500	- Calculate for how long to block.	794	- Calculate for how long to sleep or block, if at all
		795	(active idle watchers, EVRUN_NOWAIT or not having
		796	any active watchers at all will result in not sleeping).
		797	- Sleep if the I/O and timer collect interval say so.
		798	- Increment loop iteration counter.
501	- Block the process, waiting for any events.	799	- Block the process, waiting for any events.
502	- Queue all outstanding I/O (fd) events.	800	- Queue all outstanding I/O (fd) events.
503	- Update the "event loop time" and do time jump handling.	801	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
504	- Queue all outstanding timers.	802	- Queue all expired timers.
505	- Queue all outstanding periodics.	803	- Queue all expired periodics.
506	- If no events are pending now, queue all idle watchers.	804	- Queue all idle watchers with priority higher than that of pending events.
507	- Queue all check watchers.	805	- Queue all check watchers.
508	- Call all queued watchers in reverse order (i.e. check watchers first).	806	- Call all queued watchers in reverse order (i.e. check watchers first).
509	Signals and child watchers are implemented as I/O watchers, and will	807	Signals and child watchers are implemented as I/O watchers, and will
510	be handled here by queueing them when their watcher gets executed.	808	be handled here by queueing them when their watcher gets executed.
511	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	809	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
512	were used, return, otherwise continue with step *.	810	were used, or there are no active watchers, goto FINISH, otherwise
		811	continue with step LOOP.
		812	FINISH:
		813	- Reset the ev_break status iff it was EVBREAK_ONE.
		814	- Decrement the loop depth.
		815	- Return.
513		816
514	Example: Queue some jobs and then loop until no events are outsanding	817	Example: Queue some jobs and then loop until no events are outstanding
515	anymore.	818	anymore.
516		819
517	... queue jobs here, make sure they register event watchers as long	820	... queue jobs here, make sure they register event watchers as long
518	... as they still have work to do (even an idle watcher will do..)	821	... as they still have work to do (even an idle watcher will do..)
519	ev_loop (my_loop, 0);	822	ev_run (my_loop, 0);
520	... jobs done. yeah!	823	... jobs done or somebody called unloop. yeah!
521		824
522	=item ev_unloop (loop, how)	825	=item ev_break (loop, how)
523		826
524	Can be used to make a call to C<ev_loop> return early (but only after it	827	Can be used to make a call to C<ev_run> return early (but only after it
525	has processed all outstanding events). The C<how> argument must be either	828	has processed all outstanding events). The C<how> argument must be either
526	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	829	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
527	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	830	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		831
		832	This "break state" will be cleared when entering C<ev_run> again.
		833
		834	It is safe to call C<ev_break> from outside any C<ev_run> calls, too.
528		835
529	=item ev_ref (loop)	836	=item ev_ref (loop)
530		837
531	=item ev_unref (loop)	838	=item ev_unref (loop)
532		839
533	Ref/unref can be used to add or remove a reference count on the event	840	Ref/unref can be used to add or remove a reference count on the event
534	loop: Every watcher keeps one reference, and as long as the reference	841	loop: Every watcher keeps one reference, and as long as the reference
535	count is nonzero, C<ev_loop> will not return on its own. If you have	842	count is nonzero, C<ev_run> will not return on its own.
536	a watcher you never unregister that should not keep C<ev_loop> from	843
537	returning, ev_unref() after starting, and ev_ref() before stopping it. For	844	This is useful when you have a watcher that you never intend to
		845	unregister, but that nevertheless should not keep C<ev_run> from
		846	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		847	before stopping it.
		848
538	example, libev itself uses this for its internal signal pipe: It is not	849	As an example, libev itself uses this for its internal signal pipe: It
539	visible to the libev user and should not keep C<ev_loop> from exiting if	850	is not visible to the libev user and should not keep C<ev_run> from
540	no event watchers registered by it are active. It is also an excellent	851	exiting if no event watchers registered by it are active. It is also an
541	way to do this for generic recurring timers or from within third-party	852	excellent way to do this for generic recurring timers or from within
542	libraries. Just remember to I<unref after start> and I<ref before stop>.	853	third-party libraries. Just remember to I<unref after start> and I<ref
		854	before stop> (but only if the watcher wasn't active before, or was active
		855	before, respectively. Note also that libev might stop watchers itself
		856	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		857	in the callback).
543		858
544	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	859	Example: Create a signal watcher, but keep it from keeping C<ev_run>
545	running when nothing else is active.	860	running when nothing else is active.
546		861
547	struct ev_signal exitsig;	862	ev_signal exitsig;
548	ev_signal_init (&exitsig, sig_cb, SIGINT);	863	ev_signal_init (&exitsig, sig_cb, SIGINT);
549	ev_signal_start (loop, &exitsig);	864	ev_signal_start (loop, &exitsig);
550	evf_unref (loop);	865	evf_unref (loop);
551		866
552	Example: For some weird reason, unregister the above signal handler again.	867	Example: For some weird reason, unregister the above signal handler again.
553		868
554	ev_ref (loop);	869	ev_ref (loop);
555	ev_signal_stop (loop, &exitsig);	870	ev_signal_stop (loop, &exitsig);
		871
		872	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		873
		874	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		875
		876	These advanced functions influence the time that libev will spend waiting
		877	for events. Both time intervals are by default C<0>, meaning that libev
		878	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		879	latency.
		880
		881	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		882	allows libev to delay invocation of I/O and timer/periodic callbacks
		883	to increase efficiency of loop iterations (or to increase power-saving
		884	opportunities).
		885
		886	The idea is that sometimes your program runs just fast enough to handle
		887	one (or very few) event(s) per loop iteration. While this makes the
		888	program responsive, it also wastes a lot of CPU time to poll for new
		889	events, especially with backends like C<select ()> which have a high
		890	overhead for the actual polling but can deliver many events at once.
		891
		892	By setting a higher I<io collect interval> you allow libev to spend more
		893	time collecting I/O events, so you can handle more events per iteration,
		894	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		895	C<ev_timer>) will be not affected. Setting this to a non-null value will
		896	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		897	sleep time ensures that libev will not poll for I/O events more often then
		898	once per this interval, on average.
		899
		900	Likewise, by setting a higher I<timeout collect interval> you allow libev
		901	to spend more time collecting timeouts, at the expense of increased
		902	latency/jitter/inexactness (the watcher callback will be called
		903	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		904	value will not introduce any overhead in libev.
		905
		906	Many (busy) programs can usually benefit by setting the I/O collect
		907	interval to a value near C<0.1> or so, which is often enough for
		908	interactive servers (of course not for games), likewise for timeouts. It
		909	usually doesn't make much sense to set it to a lower value than C<0.01>,
		910	as this approaches the timing granularity of most systems. Note that if
		911	you do transactions with the outside world and you can't increase the
		912	parallelity, then this setting will limit your transaction rate (if you
		913	need to poll once per transaction and the I/O collect interval is 0.01,
		914	then you can't do more than 100 transactions per second).
		915
		916	Setting the I<timeout collect interval> can improve the opportunity for
		917	saving power, as the program will "bundle" timer callback invocations that
		918	are "near" in time together, by delaying some, thus reducing the number of
		919	times the process sleeps and wakes up again. Another useful technique to
		920	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		921	they fire on, say, one-second boundaries only.
		922
		923	Example: we only need 0.1s timeout granularity, and we wish not to poll
		924	more often than 100 times per second:
		925
		926	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		927	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		928
		929	=item ev_invoke_pending (loop)
		930
		931	This call will simply invoke all pending watchers while resetting their
		932	pending state. Normally, C<ev_run> does this automatically when required,
		933	but when overriding the invoke callback this call comes handy. This
		934	function can be invoked from a watcher - this can be useful for example
		935	when you want to do some lengthy calculation and want to pass further
		936	event handling to another thread (you still have to make sure only one
		937	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		938
		939	=item int ev_pending_count (loop)
		940
		941	Returns the number of pending watchers - zero indicates that no watchers
		942	are pending.
		943
		944	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		945
		946	This overrides the invoke pending functionality of the loop: Instead of
		947	invoking all pending watchers when there are any, C<ev_run> will call
		948	this callback instead. This is useful, for example, when you want to
		949	invoke the actual watchers inside another context (another thread etc.).
		950
		951	If you want to reset the callback, use C<ev_invoke_pending> as new
		952	callback.
		953
		954	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		955
		956	Sometimes you want to share the same loop between multiple threads. This
		957	can be done relatively simply by putting mutex_lock/unlock calls around
		958	each call to a libev function.
		959
		960	However, C<ev_run> can run an indefinite time, so it is not feasible
		961	to wait for it to return. One way around this is to wake up the event
		962	loop via C<ev_break> and C<av_async_send>, another way is to set these
		963	I<release> and I<acquire> callbacks on the loop.
		964
		965	When set, then C<release> will be called just before the thread is
		966	suspended waiting for new events, and C<acquire> is called just
		967	afterwards.
		968
		969	Ideally, C<release> will just call your mutex_unlock function, and
		970	C<acquire> will just call the mutex_lock function again.
		971
		972	While event loop modifications are allowed between invocations of
		973	C<release> and C<acquire> (that's their only purpose after all), no
		974	modifications done will affect the event loop, i.e. adding watchers will
		975	have no effect on the set of file descriptors being watched, or the time
		976	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		977	to take note of any changes you made.
		978
		979	In theory, threads executing C<ev_run> will be async-cancel safe between
		980	invocations of C<release> and C<acquire>.
		981
		982	See also the locking example in the C<THREADS> section later in this
		983	document.
		984
		985	=item ev_set_userdata (loop, void *data)
		986
		987	=item ev_userdata (loop)
		988
		989	Set and retrieve a single C<void *> associated with a loop. When
		990	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		991	C<0>.
		992
		993	These two functions can be used to associate arbitrary data with a loop,
		994	and are intended solely for the C<invoke_pending_cb>, C<release> and
		995	C<acquire> callbacks described above, but of course can be (ab-)used for
		996	any other purpose as well.
		997
		998	=item ev_verify (loop)
		999
		1000	This function only does something when C<EV_VERIFY> support has been
		1001	compiled in, which is the default for non-minimal builds. It tries to go
		1002	through all internal structures and checks them for validity. If anything
		1003	is found to be inconsistent, it will print an error message to standard
		1004	error and call C<abort ()>.
		1005
		1006	This can be used to catch bugs inside libev itself: under normal
		1007	circumstances, this function will never abort as of course libev keeps its
		1008	data structures consistent.
556		1009
557	=back	1010	=back
558		1011
559		1012
560	=head1 ANATOMY OF A WATCHER	1013	=head1 ANATOMY OF A WATCHER
561		1014
		1015	In the following description, uppercase C<TYPE> in names stands for the
		1016	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1017	watchers and C<ev_io_start> for I/O watchers.
		1018
562	A watcher is a structure that you create and register to record your	1019	A watcher is an opaque structure that you allocate and register to record
563	interest in some event. For instance, if you want to wait for STDIN to	1020	your interest in some event. To make a concrete example, imagine you want
564	become readable, you would create an C<ev_io> watcher for that:	1021	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1022	for that:
565		1023
566	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1024	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
567	{	1025	{
568	ev_io_stop (w);	1026	ev_io_stop (w);
569	ev_unloop (loop, EVUNLOOP_ALL);	1027	ev_break (loop, EVBREAK_ALL);
570	}	1028	}
571		1029
572	struct ev_loop *loop = ev_default_loop (0);	1030	struct ev_loop *loop = ev_default_loop (0);
		1031
573	struct ev_io stdin_watcher;	1032	ev_io stdin_watcher;
		1033
574	ev_init (&stdin_watcher, my_cb);	1034	ev_init (&stdin_watcher, my_cb);
575	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1035	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
576	ev_io_start (loop, &stdin_watcher);	1036	ev_io_start (loop, &stdin_watcher);
		1037
577	ev_loop (loop, 0);	1038	ev_run (loop, 0);
578		1039
579	As you can see, you are responsible for allocating the memory for your	1040	As you can see, you are responsible for allocating the memory for your
580	watcher structures (and it is usually a bad idea to do this on the stack,	1041	watcher structures (and it is I<usually> a bad idea to do this on the
581	although this can sometimes be quite valid).	1042	stack).
582		1043
		1044	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1045	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1046
583	Each watcher structure must be initialised by a call to C<ev_init	1047	Each watcher structure must be initialised by a call to C<ev_init (watcher
584	(watcher *, callback)>, which expects a callback to be provided. This	1048	*, callback)>, which expects a callback to be provided. This callback is
585	callback gets invoked each time the event occurs (or, in the case of io	1049	invoked each time the event occurs (or, in the case of I/O watchers, each
586	watchers, each time the event loop detects that the file descriptor given	1050	time the event loop detects that the file descriptor given is readable
587	is readable and/or writable).	1051	and/or writable).
588		1052
589	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1053	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
590	with arguments specific to this watcher type. There is also a macro	1054	macro to configure it, with arguments specific to the watcher type. There
591	to combine initialisation and setting in one call: C<< ev_<type>_init	1055	is also a macro to combine initialisation and setting in one call: C<<
592	(watcher *, callback, ...) >>.	1056	ev_TYPE_init (watcher *, callback, ...) >>.
593		1057
594	To make the watcher actually watch out for events, you have to start it	1058	To make the watcher actually watch out for events, you have to start it
595	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1059	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
596	*) >>), and you can stop watching for events at any time by calling the	1060	*) >>), and you can stop watching for events at any time by calling the
597	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1061	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
598		1062
599	As long as your watcher is active (has been started but not stopped) you	1063	As long as your watcher is active (has been started but not stopped) you
600	must not touch the values stored in it. Most specifically you must never	1064	must not touch the values stored in it. Most specifically you must never
601	reinitialise it or call its C<set> macro.	1065	reinitialise it or call its C<ev_TYPE_set> macro.
602		1066
603	Each and every callback receives the event loop pointer as first, the	1067	Each and every callback receives the event loop pointer as first, the
604	registered watcher structure as second, and a bitset of received events as	1068	registered watcher structure as second, and a bitset of received events as
605	third argument.	1069	third argument.
606		1070
…		…
615	=item C<EV_WRITE>	1079	=item C<EV_WRITE>
616		1080
617	The file descriptor in the C<ev_io> watcher has become readable and/or	1081	The file descriptor in the C<ev_io> watcher has become readable and/or
618	writable.	1082	writable.
619		1083
620	=item C<EV_TIMEOUT>	1084	=item C<EV_TIMER>
621		1085
622	The C<ev_timer> watcher has timed out.	1086	The C<ev_timer> watcher has timed out.
623		1087
624	=item C<EV_PERIODIC>	1088	=item C<EV_PERIODIC>
625		1089
…		…
643		1107
644	=item C<EV_PREPARE>	1108	=item C<EV_PREPARE>
645		1109
646	=item C<EV_CHECK>	1110	=item C<EV_CHECK>
647		1111
648	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1112	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
649	to gather new events, and all C<ev_check> watchers are invoked just after	1113	to gather new events, and all C<ev_check> watchers are invoked just after
650	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1114	C<ev_run> has gathered them, but before it invokes any callbacks for any
651	received events. Callbacks of both watcher types can start and stop as	1115	received events. Callbacks of both watcher types can start and stop as
652	many watchers as they want, and all of them will be taken into account	1116	many watchers as they want, and all of them will be taken into account
653	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1117	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
654	C<ev_loop> from blocking).	1118	C<ev_run> from blocking).
655		1119
656	=item C<EV_EMBED>	1120	=item C<EV_EMBED>
657		1121
658	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1122	The embedded event loop specified in the C<ev_embed> watcher needs attention.
659		1123
660	=item C<EV_FORK>	1124	=item C<EV_FORK>
661		1125
662	The event loop has been resumed in the child process after fork (see	1126	The event loop has been resumed in the child process after fork (see
663	C<ev_fork>).	1127	C<ev_fork>).
664		1128
		1129	=item C<EV_CLEANUP>
		1130
		1131	The event loop is about to be destroyed (see C<ev_cleanup>).
		1132
		1133	=item C<EV_ASYNC>
		1134
		1135	The given async watcher has been asynchronously notified (see C<ev_async>).
		1136
		1137	=item C<EV_CUSTOM>
		1138
		1139	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1140	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1141
665	=item C<EV_ERROR>	1142	=item C<EV_ERROR>
666		1143
667	An unspecified error has occured, the watcher has been stopped. This might	1144	An unspecified error has occurred, the watcher has been stopped. This might
668	happen because the watcher could not be properly started because libev	1145	happen because the watcher could not be properly started because libev
669	ran out of memory, a file descriptor was found to be closed or any other	1146	ran out of memory, a file descriptor was found to be closed or any other
		1147	problem. Libev considers these application bugs.
		1148
670	problem. You best act on it by reporting the problem and somehow coping	1149	You best act on it by reporting the problem and somehow coping with the
671	with the watcher being stopped.	1150	watcher being stopped. Note that well-written programs should not receive
		1151	an error ever, so when your watcher receives it, this usually indicates a
		1152	bug in your program.
672		1153
673	Libev will usually signal a few "dummy" events together with an error,	1154	Libev will usually signal a few "dummy" events together with an error, for
674	for example it might indicate that a fd is readable or writable, and if	1155	example it might indicate that a fd is readable or writable, and if your
675	your callbacks is well-written it can just attempt the operation and cope	1156	callbacks is well-written it can just attempt the operation and cope with
676	with the error from read() or write(). This will not work in multithreaded	1157	the error from read() or write(). This will not work in multi-threaded
677	programs, though, so beware.	1158	programs, though, as the fd could already be closed and reused for another
		1159	thing, so beware.
678		1160
679	=back	1161	=back
680		1162
681	=head2 GENERIC WATCHER FUNCTIONS	1163	=head2 GENERIC WATCHER FUNCTIONS
682
683	In the following description, C<TYPE> stands for the watcher type,
684	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
685		1164
686	=over 4	1165	=over 4
687		1166
688	=item C<ev_init> (ev_TYPE *watcher, callback)	1167	=item C<ev_init> (ev_TYPE *watcher, callback)
689		1168
…		…
695	which rolls both calls into one.	1174	which rolls both calls into one.
696		1175
697	You can reinitialise a watcher at any time as long as it has been stopped	1176	You can reinitialise a watcher at any time as long as it has been stopped
698	(or never started) and there are no pending events outstanding.	1177	(or never started) and there are no pending events outstanding.
699		1178
700	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1179	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
701	int revents)>.	1180	int revents)>.
702		1181
		1182	Example: Initialise an C<ev_io> watcher in two steps.
		1183
		1184	ev_io w;
		1185	ev_init (&w, my_cb);
		1186	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1187
703	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1188	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
704		1189
705	This macro initialises the type-specific parts of a watcher. You need to	1190	This macro initialises the type-specific parts of a watcher. You need to
706	call C<ev_init> at least once before you call this macro, but you can	1191	call C<ev_init> at least once before you call this macro, but you can
707	call C<ev_TYPE_set> any number of times. You must not, however, call this	1192	call C<ev_TYPE_set> any number of times. You must not, however, call this
708	macro on a watcher that is active (it can be pending, however, which is a	1193	macro on a watcher that is active (it can be pending, however, which is a
709	difference to the C<ev_init> macro).	1194	difference to the C<ev_init> macro).
710		1195
711	Although some watcher types do not have type-specific arguments	1196	Although some watcher types do not have type-specific arguments
712	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1197	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
713		1198
		1199	See C<ev_init>, above, for an example.
		1200
714	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1201	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
715		1202
716	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1203	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
717	calls into a single call. This is the most convinient method to initialise	1204	calls into a single call. This is the most convenient method to initialise
718	a watcher. The same limitations apply, of course.	1205	a watcher. The same limitations apply, of course.
719		1206
		1207	Example: Initialise and set an C<ev_io> watcher in one step.
		1208
		1209	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1210
720	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1211	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
721		1212
722	Starts (activates) the given watcher. Only active watchers will receive	1213	Starts (activates) the given watcher. Only active watchers will receive
723	events. If the watcher is already active nothing will happen.	1214	events. If the watcher is already active nothing will happen.
724		1215
		1216	Example: Start the C<ev_io> watcher that is being abused as example in this
		1217	whole section.
		1218
		1219	ev_io_start (EV_DEFAULT_UC, &w);
		1220
725	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1221	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
726		1222
727	Stops the given watcher again (if active) and clears the pending	1223	Stops the given watcher if active, and clears the pending status (whether
		1224	the watcher was active or not).
		1225
728	status. It is possible that stopped watchers are pending (for example,	1226	It is possible that stopped watchers are pending - for example,
729	non-repeating timers are being stopped when they become pending), but	1227	non-repeating timers are being stopped when they become pending - but
730	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1228	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
731	you want to free or reuse the memory used by the watcher it is therefore a	1229	pending. If you want to free or reuse the memory used by the watcher it is
732	good idea to always call its C<ev_TYPE_stop> function.	1230	therefore a good idea to always call its C<ev_TYPE_stop> function.
733		1231
734	=item bool ev_is_active (ev_TYPE *watcher)	1232	=item bool ev_is_active (ev_TYPE *watcher)
735		1233
736	Returns a true value iff the watcher is active (i.e. it has been started	1234	Returns a true value iff the watcher is active (i.e. it has been started
737	and not yet been stopped). As long as a watcher is active you must not modify	1235	and not yet been stopped). As long as a watcher is active you must not modify
…		…
753	=item ev_cb_set (ev_TYPE *watcher, callback)	1251	=item ev_cb_set (ev_TYPE *watcher, callback)
754		1252
755	Change the callback. You can change the callback at virtually any time	1253	Change the callback. You can change the callback at virtually any time
756	(modulo threads).	1254	(modulo threads).
757		1255
758	=item ev_set_priority (ev_TYPE *watcher, priority)	1256	=item ev_set_priority (ev_TYPE *watcher, int priority)
759		1257
760	=item int ev_priority (ev_TYPE *watcher)	1258	=item int ev_priority (ev_TYPE *watcher)
761		1259
762	Set and query the priority of the watcher. The priority is a small	1260	Set and query the priority of the watcher. The priority is a small
763	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1261	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
764	(default: C<-2>). Pending watchers with higher priority will be invoked	1262	(default: C<-2>). Pending watchers with higher priority will be invoked
765	before watchers with lower priority, but priority will not keep watchers	1263	before watchers with lower priority, but priority will not keep watchers
766	from being executed (except for C<ev_idle> watchers).	1264	from being executed (except for C<ev_idle> watchers).
767		1265
768	This means that priorities are I<only> used for ordering callback
769	invocation after new events have been received. This is useful, for
770	example, to reduce latency after idling, or more often, to bind two
771	watchers on the same event and make sure one is called first.
772
773	If you need to suppress invocation when higher priority events are pending	1266	If you need to suppress invocation when higher priority events are pending
774	you need to look at C<ev_idle> watchers, which provide this functionality.	1267	you need to look at C<ev_idle> watchers, which provide this functionality.
775		1268
776	You I<must not> change the priority of a watcher as long as it is active or	1269	You I<must not> change the priority of a watcher as long as it is active or
777	pending.	1270	pending.
778		1271
		1272	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1273	fine, as long as you do not mind that the priority value you query might
		1274	or might not have been clamped to the valid range.
		1275
779	The default priority used by watchers when no priority has been set is	1276	The default priority used by watchers when no priority has been set is
780	always C<0>, which is supposed to not be too high and not be too low :).	1277	always C<0>, which is supposed to not be too high and not be too low :).
781		1278
782	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1279	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
783	fine, as long as you do not mind that the priority value you query might	1280	priorities.
784	or might not have been adjusted to be within valid range.
785		1281
786	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1282	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
787		1283
788	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1284	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
789	C<loop> nor C<revents> need to be valid as long as the watcher callback	1285	C<loop> nor C<revents> need to be valid as long as the watcher callback
790	can deal with that fact.	1286	can deal with that fact, as both are simply passed through to the
		1287	callback.
791		1288
792	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1289	=item int ev_clear_pending (loop, ev_TYPE *watcher)
793		1290
794	If the watcher is pending, this function returns clears its pending status	1291	If the watcher is pending, this function clears its pending status and
795	and returns its C<revents> bitset (as if its callback was invoked). If the	1292	returns its C<revents> bitset (as if its callback was invoked). If the
796	watcher isn't pending it does nothing and returns C<0>.	1293	watcher isn't pending it does nothing and returns C<0>.
797		1294
		1295	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1296	callback to be invoked, which can be accomplished with this function.
		1297
		1298	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1299
		1300	Feeds the given event set into the event loop, as if the specified event
		1301	had happened for the specified watcher (which must be a pointer to an
		1302	initialised but not necessarily started event watcher). Obviously you must
		1303	not free the watcher as long as it has pending events.
		1304
		1305	Stopping the watcher, letting libev invoke it, or calling
		1306	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1307	not started in the first place.
		1308
		1309	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1310	functions that do not need a watcher.
		1311
798	=back	1312	=back
799		1313
800
801	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1314	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
802		1315
803	Each watcher has, by default, a member C<void *data> that you can change	1316	Each watcher has, by default, a member C<void *data> that you can change
804	and read at any time, libev will completely ignore it. This can be used	1317	and read at any time: libev will completely ignore it. This can be used
805	to associate arbitrary data with your watcher. If you need more data and	1318	to associate arbitrary data with your watcher. If you need more data and
806	don't want to allocate memory and store a pointer to it in that data	1319	don't want to allocate memory and store a pointer to it in that data
807	member, you can also "subclass" the watcher type and provide your own	1320	member, you can also "subclass" the watcher type and provide your own
808	data:	1321	data:
809		1322
810	struct my_io	1323	struct my_io
811	{	1324	{
812	struct ev_io io;	1325	ev_io io;
813	int otherfd;	1326	int otherfd;
814	void *somedata;	1327	void *somedata;
815	struct whatever *mostinteresting;	1328	struct whatever *mostinteresting;
816	}	1329	};
		1330
		1331	...
		1332	struct my_io w;
		1333	ev_io_init (&w.io, my_cb, fd, EV_READ);
817		1334
818	And since your callback will be called with a pointer to the watcher, you	1335	And since your callback will be called with a pointer to the watcher, you
819	can cast it back to your own type:	1336	can cast it back to your own type:
820		1337
821	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1338	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
822	{	1339	{
823	struct my_io *w = (struct my_io *)w_;	1340	struct my_io *w = (struct my_io *)w_;
824	...	1341	...
825	}	1342	}
826		1343
827	More interesting and less C-conformant ways of casting your callback type	1344	More interesting and less C-conformant ways of casting your callback type
828	instead have been omitted.	1345	instead have been omitted.
829		1346
830	Another common scenario is having some data structure with multiple	1347	Another common scenario is to use some data structure with multiple
831	watchers:	1348	embedded watchers:
832		1349
833	struct my_biggy	1350	struct my_biggy
834	{	1351	{
835	int some_data;	1352	int some_data;
836	ev_timer t1;	1353	ev_timer t1;
837	ev_timer t2;	1354	ev_timer t2;
838	}	1355	}
839		1356
840	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1357	In this case getting the pointer to C<my_biggy> is a bit more
841	you need to use C<offsetof>:	1358	complicated: Either you store the address of your C<my_biggy> struct
		1359	in the C<data> member of the watcher (for woozies), or you need to use
		1360	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1361	programmers):
842		1362
843	#include <stddef.h>	1363	#include <stddef.h>
844		1364
845	static void	1365	static void
846	t1_cb (EV_P_ struct ev_timer *w, int revents)	1366	t1_cb (EV_P_ ev_timer *w, int revents)
847	{	1367	{
848	struct my_biggy big = (struct my_biggy *	1368	struct my_biggy big = (struct my_biggy *)
849	(((char *)w) - offsetof (struct my_biggy, t1));	1369	(((char *)w) - offsetof (struct my_biggy, t1));
850	}	1370	}
851		1371
852	static void	1372	static void
853	t2_cb (EV_P_ struct ev_timer *w, int revents)	1373	t2_cb (EV_P_ ev_timer *w, int revents)
854	{	1374	{
855	struct my_biggy big = (struct my_biggy *	1375	struct my_biggy big = (struct my_biggy *)
856	(((char *)w) - offsetof (struct my_biggy, t2));	1376	(((char *)w) - offsetof (struct my_biggy, t2));
857	}	1377	}
		1378
		1379	=head2 WATCHER STATES
		1380
		1381	There are various watcher states mentioned throughout this manual -
		1382	active, pending and so on. In this section these states and the rules to
		1383	transition between them will be described in more detail - and while these
		1384	rules might look complicated, they usually do "the right thing".
		1385
		1386	=over 4
		1387
		1388	=item initialiased
		1389
		1390	Before a watcher can be registered with the event looop it has to be
		1391	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1392	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1393
		1394	In this state it is simply some block of memory that is suitable for use
		1395	in an event loop. It can be moved around, freed, reused etc. at will.
		1396
		1397	=item started/running/active
		1398
		1399	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1400	property of the event loop, and is actively waiting for events. While in
		1401	this state it cannot be accessed (except in a few documented ways), moved,
		1402	freed or anything else - the only legal thing is to keep a pointer to it,
		1403	and call libev functions on it that are documented to work on active watchers.
		1404
		1405	=item pending
		1406
		1407	If a watcher is active and libev determines that an event it is interested
		1408	in has occurred (such as a timer expiring), it will become pending. It will
		1409	stay in this pending state until either it is stopped or its callback is
		1410	about to be invoked, so it is not normally pending inside the watcher
		1411	callback.
		1412
		1413	The watcher might or might not be active while it is pending (for example,
		1414	an expired non-repeating timer can be pending but no longer active). If it
		1415	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1416	but it is still property of the event loop at this time, so cannot be
		1417	moved, freed or reused. And if it is active the rules described in the
		1418	previous item still apply.
		1419
		1420	It is also possible to feed an event on a watcher that is not active (e.g.
		1421	via C<ev_feed_event>), in which case it becomes pending without being
		1422	active.
		1423
		1424	=item stopped
		1425
		1426	A watcher can be stopped implicitly by libev (in which case it might still
		1427	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1428	latter will clear any pending state the watcher might be in, regardless
		1429	of whether it was active or not, so stopping a watcher explicitly before
		1430	freeing it is often a good idea.
		1431
		1432	While stopped (and not pending) the watcher is essentially in the
		1433	initialised state, that is it can be reused, moved, modified in any way
		1434	you wish.
		1435
		1436	=back
		1437
		1438	=head2 WATCHER PRIORITY MODELS
		1439
		1440	Many event loops support I<watcher priorities>, which are usually small
		1441	integers that influence the ordering of event callback invocation
		1442	between watchers in some way, all else being equal.
		1443
		1444	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1445	description for the more technical details such as the actual priority
		1446	range.
		1447
		1448	There are two common ways how these these priorities are being interpreted
		1449	by event loops:
		1450
		1451	In the more common lock-out model, higher priorities "lock out" invocation
		1452	of lower priority watchers, which means as long as higher priority
		1453	watchers receive events, lower priority watchers are not being invoked.
		1454
		1455	The less common only-for-ordering model uses priorities solely to order
		1456	callback invocation within a single event loop iteration: Higher priority
		1457	watchers are invoked before lower priority ones, but they all get invoked
		1458	before polling for new events.
		1459
		1460	Libev uses the second (only-for-ordering) model for all its watchers
		1461	except for idle watchers (which use the lock-out model).
		1462
		1463	The rationale behind this is that implementing the lock-out model for
		1464	watchers is not well supported by most kernel interfaces, and most event
		1465	libraries will just poll for the same events again and again as long as
		1466	their callbacks have not been executed, which is very inefficient in the
		1467	common case of one high-priority watcher locking out a mass of lower
		1468	priority ones.
		1469
		1470	Static (ordering) priorities are most useful when you have two or more
		1471	watchers handling the same resource: a typical usage example is having an
		1472	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1473	timeouts. Under load, data might be received while the program handles
		1474	other jobs, but since timers normally get invoked first, the timeout
		1475	handler will be executed before checking for data. In that case, giving
		1476	the timer a lower priority than the I/O watcher ensures that I/O will be
		1477	handled first even under adverse conditions (which is usually, but not
		1478	always, what you want).
		1479
		1480	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1481	will only be executed when no same or higher priority watchers have
		1482	received events, they can be used to implement the "lock-out" model when
		1483	required.
		1484
		1485	For example, to emulate how many other event libraries handle priorities,
		1486	you can associate an C<ev_idle> watcher to each such watcher, and in
		1487	the normal watcher callback, you just start the idle watcher. The real
		1488	processing is done in the idle watcher callback. This causes libev to
		1489	continuously poll and process kernel event data for the watcher, but when
		1490	the lock-out case is known to be rare (which in turn is rare :), this is
		1491	workable.
		1492
		1493	Usually, however, the lock-out model implemented that way will perform
		1494	miserably under the type of load it was designed to handle. In that case,
		1495	it might be preferable to stop the real watcher before starting the
		1496	idle watcher, so the kernel will not have to process the event in case
		1497	the actual processing will be delayed for considerable time.
		1498
		1499	Here is an example of an I/O watcher that should run at a strictly lower
		1500	priority than the default, and which should only process data when no
		1501	other events are pending:
		1502
		1503	ev_idle idle; // actual processing watcher
		1504	ev_io io; // actual event watcher
		1505
		1506	static void
		1507	io_cb (EV_P_ ev_io *w, int revents)
		1508	{
		1509	// stop the I/O watcher, we received the event, but
		1510	// are not yet ready to handle it.
		1511	ev_io_stop (EV_A_ w);
		1512
		1513	// start the idle watcher to handle the actual event.
		1514	// it will not be executed as long as other watchers
		1515	// with the default priority are receiving events.
		1516	ev_idle_start (EV_A_ &idle);
		1517	}
		1518
		1519	static void
		1520	idle_cb (EV_P_ ev_idle *w, int revents)
		1521	{
		1522	// actual processing
		1523	read (STDIN_FILENO, ...);
		1524
		1525	// have to start the I/O watcher again, as
		1526	// we have handled the event
		1527	ev_io_start (EV_P_ &io);
		1528	}
		1529
		1530	// initialisation
		1531	ev_idle_init (&idle, idle_cb);
		1532	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1533	ev_io_start (EV_DEFAULT_ &io);
		1534
		1535	In the "real" world, it might also be beneficial to start a timer, so that
		1536	low-priority connections can not be locked out forever under load. This
		1537	enables your program to keep a lower latency for important connections
		1538	during short periods of high load, while not completely locking out less
		1539	important ones.
858		1540
859		1541
860	=head1 WATCHER TYPES	1542	=head1 WATCHER TYPES
861		1543
862	This section describes each watcher in detail, but will not repeat	1544	This section describes each watcher in detail, but will not repeat
…		…
886	In general you can register as many read and/or write event watchers per	1568	In general you can register as many read and/or write event watchers per
887	fd as you want (as long as you don't confuse yourself). Setting all file	1569	fd as you want (as long as you don't confuse yourself). Setting all file
888	descriptors to non-blocking mode is also usually a good idea (but not	1570	descriptors to non-blocking mode is also usually a good idea (but not
889	required if you know what you are doing).	1571	required if you know what you are doing).
890		1572
891	You have to be careful with dup'ed file descriptors, though. Some backends	1573	If you cannot use non-blocking mode, then force the use of a
892	(the linux epoll backend is a notable example) cannot handle dup'ed file	1574	known-to-be-good backend (at the time of this writing, this includes only
893	descriptors correctly if you register interest in two or more fds pointing	1575	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
894	to the same underlying file/socket/etc. description (that is, they share	1576	descriptors for which non-blocking operation makes no sense (such as
895	the same underlying "file open").	1577	files) - libev doesn't guarantee any specific behaviour in that case.
896
897	If you must do this, then force the use of a known-to-be-good backend
898	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
899	C<EVBACKEND_POLL>).
900		1578
901	Another thing you have to watch out for is that it is quite easy to	1579	Another thing you have to watch out for is that it is quite easy to
902	receive "spurious" readyness notifications, that is your callback might	1580	receive "spurious" readiness notifications, that is your callback might
903	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1581	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
904	because there is no data. Not only are some backends known to create a	1582	because there is no data. Not only are some backends known to create a
905	lot of those (for example solaris ports), it is very easy to get into	1583	lot of those (for example Solaris ports), it is very easy to get into
906	this situation even with a relatively standard program structure. Thus	1584	this situation even with a relatively standard program structure. Thus
907	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1585	it is best to always use non-blocking I/O: An extra C<read>(2) returning
908	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1586	C<EAGAIN> is far preferable to a program hanging until some data arrives.
909		1587
910	If you cannot run the fd in non-blocking mode (for example you should not	1588	If you cannot run the fd in non-blocking mode (for example you should
911	play around with an Xlib connection), then you have to seperately re-test	1589	not play around with an Xlib connection), then you have to separately
912	whether a file descriptor is really ready with a known-to-be good interface	1590	re-test whether a file descriptor is really ready with a known-to-be good
913	such as poll (fortunately in our Xlib example, Xlib already does this on	1591	interface such as poll (fortunately in our Xlib example, Xlib already
914	its own, so its quite safe to use).	1592	does this on its own, so its quite safe to use). Some people additionally
		1593	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1594	indefinitely.
		1595
		1596	But really, best use non-blocking mode.
915		1597
916	=head3 The special problem of disappearing file descriptors	1598	=head3 The special problem of disappearing file descriptors
917		1599
918	Some backends (e.g kqueue, epoll) need to be told about closing a file	1600	Some backends (e.g. kqueue, epoll) need to be told about closing a file
919	descriptor (either by calling C<close> explicitly or by any other means,	1601	descriptor (either due to calling C<close> explicitly or any other means,
920	such as C<dup>). The reason is that you register interest in some file	1602	such as C<dup2>). The reason is that you register interest in some file
921	descriptor, but when it goes away, the operating system will silently drop	1603	descriptor, but when it goes away, the operating system will silently drop
922	this interest. If another file descriptor with the same number then is	1604	this interest. If another file descriptor with the same number then is
923	registered with libev, there is no efficient way to see that this is, in	1605	registered with libev, there is no efficient way to see that this is, in
924	fact, a different file descriptor.	1606	fact, a different file descriptor.
925		1607
…		…
932		1614
933	This is how one would do it normally anyway, the important point is that	1615	This is how one would do it normally anyway, the important point is that
934	the libev application should not optimise around libev but should leave	1616	the libev application should not optimise around libev but should leave
935	optimisations to libev.	1617	optimisations to libev.
936		1618
		1619	=head3 The special problem of dup'ed file descriptors
		1620
		1621	Some backends (e.g. epoll), cannot register events for file descriptors,
		1622	but only events for the underlying file descriptions. That means when you
		1623	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1624	events for them, only one file descriptor might actually receive events.
		1625
		1626	There is no workaround possible except not registering events
		1627	for potentially C<dup ()>'ed file descriptors, or to resort to
		1628	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1629
		1630	=head3 The special problem of fork
		1631
		1632	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1633	useless behaviour. Libev fully supports fork, but needs to be told about
		1634	it in the child.
		1635
		1636	To support fork in your programs, you either have to call
		1637	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1638	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1639	C<EVBACKEND_POLL>.
		1640
		1641	=head3 The special problem of SIGPIPE
		1642
		1643	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1644	when writing to a pipe whose other end has been closed, your program gets
		1645	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1646	this is sensible behaviour, for daemons, this is usually undesirable.
		1647
		1648	So when you encounter spurious, unexplained daemon exits, make sure you
		1649	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1650	somewhere, as that would have given you a big clue).
		1651
		1652	=head3 The special problem of accept()ing when you can't
		1653
		1654	Many implementations of the POSIX C<accept> function (for example,
		1655	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1656	connection from the pending queue in all error cases.
		1657
		1658	For example, larger servers often run out of file descriptors (because
		1659	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1660	rejecting the connection, leading to libev signalling readiness on
		1661	the next iteration again (the connection still exists after all), and
		1662	typically causing the program to loop at 100% CPU usage.
		1663
		1664	Unfortunately, the set of errors that cause this issue differs between
		1665	operating systems, there is usually little the app can do to remedy the
		1666	situation, and no known thread-safe method of removing the connection to
		1667	cope with overload is known (to me).
		1668
		1669	One of the easiest ways to handle this situation is to just ignore it
		1670	- when the program encounters an overload, it will just loop until the
		1671	situation is over. While this is a form of busy waiting, no OS offers an
		1672	event-based way to handle this situation, so it's the best one can do.
		1673
		1674	A better way to handle the situation is to log any errors other than
		1675	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1676	messages, and continue as usual, which at least gives the user an idea of
		1677	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1678	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1679	usage.
		1680
		1681	If your program is single-threaded, then you could also keep a dummy file
		1682	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1683	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1684	close that fd, and create a new dummy fd. This will gracefully refuse
		1685	clients under typical overload conditions.
		1686
		1687	The last way to handle it is to simply log the error and C<exit>, as
		1688	is often done with C<malloc> failures, but this results in an easy
		1689	opportunity for a DoS attack.
937		1690
938	=head3 Watcher-Specific Functions	1691	=head3 Watcher-Specific Functions
939		1692
940	=over 4	1693	=over 4
941		1694
942	=item ev_io_init (ev_io *, callback, int fd, int events)	1695	=item ev_io_init (ev_io *, callback, int fd, int events)
943		1696
944	=item ev_io_set (ev_io *, int fd, int events)	1697	=item ev_io_set (ev_io *, int fd, int events)
945		1698
946	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1699	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
947	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1700	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
948	C<EV_READ | EV_WRITE> to receive the given events.	1701	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
949		1702
950	=item int fd [read-only]	1703	=item int fd [read-only]
951		1704
952	The file descriptor being watched.	1705	The file descriptor being watched.
953		1706
954	=item int events [read-only]	1707	=item int events [read-only]
955		1708
956	The events being watched.	1709	The events being watched.
957		1710
958	=back	1711	=back
		1712
		1713	=head3 Examples
959		1714
960	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1715	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
961	readable, but only once. Since it is likely line-buffered, you could	1716	readable, but only once. Since it is likely line-buffered, you could
962	attempt to read a whole line in the callback.	1717	attempt to read a whole line in the callback.
963		1718
964	static void	1719	static void
965	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1720	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
966	{	1721	{
967	ev_io_stop (loop, w);	1722	ev_io_stop (loop, w);
968	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1723	.. read from stdin here (or from w->fd) and handle any I/O errors
969	}	1724	}
970		1725
971	...	1726	...
972	struct ev_loop *loop = ev_default_init (0);	1727	struct ev_loop *loop = ev_default_init (0);
973	struct ev_io stdin_readable;	1728	ev_io stdin_readable;
974	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1729	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
975	ev_io_start (loop, &stdin_readable);	1730	ev_io_start (loop, &stdin_readable);
976	ev_loop (loop, 0);	1731	ev_run (loop, 0);
977		1732
978		1733
979	=head2 C<ev_timer> - relative and optionally repeating timeouts	1734	=head2 C<ev_timer> - relative and optionally repeating timeouts
980		1735
981	Timer watchers are simple relative timers that generate an event after a	1736	Timer watchers are simple relative timers that generate an event after a
982	given time, and optionally repeating in regular intervals after that.	1737	given time, and optionally repeating in regular intervals after that.
983		1738
984	The timers are based on real time, that is, if you register an event that	1739	The timers are based on real time, that is, if you register an event that
985	times out after an hour and you reset your system clock to last years	1740	times out after an hour and you reset your system clock to January last
986	time, it will still time out after (roughly) and hour. "Roughly" because	1741	year, it will still time out after (roughly) one hour. "Roughly" because
987	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1742	detecting time jumps is hard, and some inaccuracies are unavoidable (the
988	monotonic clock option helps a lot here).	1743	monotonic clock option helps a lot here).
		1744
		1745	The callback is guaranteed to be invoked only I<after> its timeout has
		1746	passed (not I<at>, so on systems with very low-resolution clocks this
		1747	might introduce a small delay). If multiple timers become ready during the
		1748	same loop iteration then the ones with earlier time-out values are invoked
		1749	before ones of the same priority with later time-out values (but this is
		1750	no longer true when a callback calls C<ev_run> recursively).
		1751
		1752	=head3 Be smart about timeouts
		1753
		1754	Many real-world problems involve some kind of timeout, usually for error
		1755	recovery. A typical example is an HTTP request - if the other side hangs,
		1756	you want to raise some error after a while.
		1757
		1758	What follows are some ways to handle this problem, from obvious and
		1759	inefficient to smart and efficient.
		1760
		1761	In the following, a 60 second activity timeout is assumed - a timeout that
		1762	gets reset to 60 seconds each time there is activity (e.g. each time some
		1763	data or other life sign was received).
		1764
		1765	=over 4
		1766
		1767	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1768
		1769	This is the most obvious, but not the most simple way: In the beginning,
		1770	start the watcher:
		1771
		1772	ev_timer_init (timer, callback, 60., 0.);
		1773	ev_timer_start (loop, timer);
		1774
		1775	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1776	and start it again:
		1777
		1778	ev_timer_stop (loop, timer);
		1779	ev_timer_set (timer, 60., 0.);
		1780	ev_timer_start (loop, timer);
		1781
		1782	This is relatively simple to implement, but means that each time there is
		1783	some activity, libev will first have to remove the timer from its internal
		1784	data structure and then add it again. Libev tries to be fast, but it's
		1785	still not a constant-time operation.
		1786
		1787	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1788
		1789	This is the easiest way, and involves using C<ev_timer_again> instead of
		1790	C<ev_timer_start>.
		1791
		1792	To implement this, configure an C<ev_timer> with a C<repeat> value
		1793	of C<60> and then call C<ev_timer_again> at start and each time you
		1794	successfully read or write some data. If you go into an idle state where
		1795	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1796	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1797
		1798	That means you can ignore both the C<ev_timer_start> function and the
		1799	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1800	member and C<ev_timer_again>.
		1801
		1802	At start:
		1803
		1804	ev_init (timer, callback);
		1805	timer->repeat = 60.;
		1806	ev_timer_again (loop, timer);
		1807
		1808	Each time there is some activity:
		1809
		1810	ev_timer_again (loop, timer);
		1811
		1812	It is even possible to change the time-out on the fly, regardless of
		1813	whether the watcher is active or not:
		1814
		1815	timer->repeat = 30.;
		1816	ev_timer_again (loop, timer);
		1817
		1818	This is slightly more efficient then stopping/starting the timer each time
		1819	you want to modify its timeout value, as libev does not have to completely
		1820	remove and re-insert the timer from/into its internal data structure.
		1821
		1822	It is, however, even simpler than the "obvious" way to do it.
		1823
		1824	=item 3. Let the timer time out, but then re-arm it as required.
		1825
		1826	This method is more tricky, but usually most efficient: Most timeouts are
		1827	relatively long compared to the intervals between other activity - in
		1828	our example, within 60 seconds, there are usually many I/O events with
		1829	associated activity resets.
		1830
		1831	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1832	but remember the time of last activity, and check for a real timeout only
		1833	within the callback:
		1834
		1835	ev_tstamp last_activity; // time of last activity
		1836
		1837	static void
		1838	callback (EV_P_ ev_timer *w, int revents)
		1839	{
		1840	ev_tstamp now = ev_now (EV_A);
		1841	ev_tstamp timeout = last_activity + 60.;
		1842
		1843	// if last_activity + 60. is older than now, we did time out
		1844	if (timeout < now)
		1845	{
		1846	// timeout occurred, take action
		1847	}
		1848	else
		1849	{
		1850	// callback was invoked, but there was some activity, re-arm
		1851	// the watcher to fire in last_activity + 60, which is
		1852	// guaranteed to be in the future, so "again" is positive:
		1853	w->repeat = timeout - now;
		1854	ev_timer_again (EV_A_ w);
		1855	}
		1856	}
		1857
		1858	To summarise the callback: first calculate the real timeout (defined
		1859	as "60 seconds after the last activity"), then check if that time has
		1860	been reached, which means something I<did>, in fact, time out. Otherwise
		1861	the callback was invoked too early (C<timeout> is in the future), so
		1862	re-schedule the timer to fire at that future time, to see if maybe we have
		1863	a timeout then.
		1864
		1865	Note how C<ev_timer_again> is used, taking advantage of the
		1866	C<ev_timer_again> optimisation when the timer is already running.
		1867
		1868	This scheme causes more callback invocations (about one every 60 seconds
		1869	minus half the average time between activity), but virtually no calls to
		1870	libev to change the timeout.
		1871
		1872	To start the timer, simply initialise the watcher and set C<last_activity>
		1873	to the current time (meaning we just have some activity :), then call the
		1874	callback, which will "do the right thing" and start the timer:
		1875
		1876	ev_init (timer, callback);
		1877	last_activity = ev_now (loop);
		1878	callback (loop, timer, EV_TIMER);
		1879
		1880	And when there is some activity, simply store the current time in
		1881	C<last_activity>, no libev calls at all:
		1882
		1883	last_activity = ev_now (loop);
		1884
		1885	This technique is slightly more complex, but in most cases where the
		1886	time-out is unlikely to be triggered, much more efficient.
		1887
		1888	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1889	callback :) - just change the timeout and invoke the callback, which will
		1890	fix things for you.
		1891
		1892	=item 4. Wee, just use a double-linked list for your timeouts.
		1893
		1894	If there is not one request, but many thousands (millions...), all
		1895	employing some kind of timeout with the same timeout value, then one can
		1896	do even better:
		1897
		1898	When starting the timeout, calculate the timeout value and put the timeout
		1899	at the I<end> of the list.
		1900
		1901	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1902	the list is expected to fire (for example, using the technique #3).
		1903
		1904	When there is some activity, remove the timer from the list, recalculate
		1905	the timeout, append it to the end of the list again, and make sure to
		1906	update the C<ev_timer> if it was taken from the beginning of the list.
		1907
		1908	This way, one can manage an unlimited number of timeouts in O(1) time for
		1909	starting, stopping and updating the timers, at the expense of a major
		1910	complication, and having to use a constant timeout. The constant timeout
		1911	ensures that the list stays sorted.
		1912
		1913	=back
		1914
		1915	So which method the best?
		1916
		1917	Method #2 is a simple no-brain-required solution that is adequate in most
		1918	situations. Method #3 requires a bit more thinking, but handles many cases
		1919	better, and isn't very complicated either. In most case, choosing either
		1920	one is fine, with #3 being better in typical situations.
		1921
		1922	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1923	rather complicated, but extremely efficient, something that really pays
		1924	off after the first million or so of active timers, i.e. it's usually
		1925	overkill :)
		1926
		1927	=head3 The special problem of time updates
		1928
		1929	Establishing the current time is a costly operation (it usually takes at
		1930	least two system calls): EV therefore updates its idea of the current
		1931	time only before and after C<ev_run> collects new events, which causes a
		1932	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1933	lots of events in one iteration.
989		1934
990	The relative timeouts are calculated relative to the C<ev_now ()>	1935	The relative timeouts are calculated relative to the C<ev_now ()>
991	time. This is usually the right thing as this timestamp refers to the time	1936	time. This is usually the right thing as this timestamp refers to the time
992	of the event triggering whatever timeout you are modifying/starting. If	1937	of the event triggering whatever timeout you are modifying/starting. If
993	you suspect event processing to be delayed and you I<need> to base the timeout	1938	you suspect event processing to be delayed and you I<need> to base the
994	on the current time, use something like this to adjust for this:	1939	timeout on the current time, use something like this to adjust for this:
995		1940
996	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1941	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
997		1942
998	The callback is guarenteed to be invoked only when its timeout has passed,	1943	If the event loop is suspended for a long time, you can also force an
999	but if multiple timers become ready during the same loop iteration then	1944	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1000	order of execution is undefined.	1945	()>.
		1946
		1947	=head3 The special problems of suspended animation
		1948
		1949	When you leave the server world it is quite customary to hit machines that
		1950	can suspend/hibernate - what happens to the clocks during such a suspend?
		1951
		1952	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1953	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1954	to run until the system is suspended, but they will not advance while the
		1955	system is suspended. That means, on resume, it will be as if the program
		1956	was frozen for a few seconds, but the suspend time will not be counted
		1957	towards C<ev_timer> when a monotonic clock source is used. The real time
		1958	clock advanced as expected, but if it is used as sole clocksource, then a
		1959	long suspend would be detected as a time jump by libev, and timers would
		1960	be adjusted accordingly.
		1961
		1962	I would not be surprised to see different behaviour in different between
		1963	operating systems, OS versions or even different hardware.
		1964
		1965	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1966	time jump in the monotonic clocks and the realtime clock. If the program
		1967	is suspended for a very long time, and monotonic clock sources are in use,
		1968	then you can expect C<ev_timer>s to expire as the full suspension time
		1969	will be counted towards the timers. When no monotonic clock source is in
		1970	use, then libev will again assume a timejump and adjust accordingly.
		1971
		1972	It might be beneficial for this latter case to call C<ev_suspend>
		1973	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1974	deterministic behaviour in this case (you can do nothing against
		1975	C<SIGSTOP>).
1001		1976
1002	=head3 Watcher-Specific Functions and Data Members	1977	=head3 Watcher-Specific Functions and Data Members
1003		1978
1004	=over 4	1979	=over 4
1005		1980
1006	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1981	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1007		1982
1008	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1983	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1009		1984
1010	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1985	Configure the timer to trigger after C<after> seconds. If C<repeat>
1011	C<0.>, then it will automatically be stopped. If it is positive, then the	1986	is C<0.>, then it will automatically be stopped once the timeout is
1012	timer will automatically be configured to trigger again C<repeat> seconds	1987	reached. If it is positive, then the timer will automatically be
1013	later, again, and again, until stopped manually.	1988	configured to trigger again C<repeat> seconds later, again, and again,
		1989	until stopped manually.
1014		1990
1015	The timer itself will do a best-effort at avoiding drift, that is, if you	1991	The timer itself will do a best-effort at avoiding drift, that is, if
1016	configure a timer to trigger every 10 seconds, then it will trigger at	1992	you configure a timer to trigger every 10 seconds, then it will normally
1017	exactly 10 second intervals. If, however, your program cannot keep up with	1993	trigger at exactly 10 second intervals. If, however, your program cannot
1018	the timer (because it takes longer than those 10 seconds to do stuff) the	1994	keep up with the timer (because it takes longer than those 10 seconds to
1019	timer will not fire more than once per event loop iteration.	1995	do stuff) the timer will not fire more than once per event loop iteration.
1020		1996
1021	=item ev_timer_again (loop)	1997	=item ev_timer_again (loop, ev_timer *)
1022		1998
1023	This will act as if the timer timed out and restart it again if it is	1999	This will act as if the timer timed out and restart it again if it is
1024	repeating. The exact semantics are:	2000	repeating. The exact semantics are:
1025		2001
1026	If the timer is pending, its pending status is cleared.	2002	If the timer is pending, its pending status is cleared.
1027		2003
1028	If the timer is started but nonrepeating, stop it (as if it timed out).	2004	If the timer is started but non-repeating, stop it (as if it timed out).
1029		2005
1030	If the timer is repeating, either start it if necessary (with the	2006	If the timer is repeating, either start it if necessary (with the
1031	C<repeat> value), or reset the running timer to the C<repeat> value.	2007	C<repeat> value), or reset the running timer to the C<repeat> value.
1032		2008
1033	This sounds a bit complicated, but here is a useful and typical	2009	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1034	example: Imagine you have a tcp connection and you want a so-called idle	2010	usage example.
1035	timeout, that is, you want to be called when there have been, say, 60
1036	seconds of inactivity on the socket. The easiest way to do this is to
1037	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1038	C<ev_timer_again> each time you successfully read or write some data. If
1039	you go into an idle state where you do not expect data to travel on the
1040	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1041	automatically restart it if need be.
1042		2011
1043	That means you can ignore the C<after> value and C<ev_timer_start>	2012	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1044	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1045		2013
1046	ev_timer_init (timer, callback, 0., 5.);	2014	Returns the remaining time until a timer fires. If the timer is active,
1047	ev_timer_again (loop, timer);	2015	then this time is relative to the current event loop time, otherwise it's
1048	...	2016	the timeout value currently configured.
1049	timer->again = 17.;
1050	ev_timer_again (loop, timer);
1051	...
1052	timer->again = 10.;
1053	ev_timer_again (loop, timer);
1054		2017
1055	This is more slightly efficient then stopping/starting the timer each time	2018	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1056	you want to modify its timeout value.	2019	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2020	will return C<4>. When the timer expires and is restarted, it will return
		2021	roughly C<7> (likely slightly less as callback invocation takes some time,
		2022	too), and so on.
1057		2023
1058	=item ev_tstamp repeat [read-write]	2024	=item ev_tstamp repeat [read-write]
1059		2025
1060	The current C<repeat> value. Will be used each time the watcher times out	2026	The current C<repeat> value. Will be used each time the watcher times out
1061	or C<ev_timer_again> is called and determines the next timeout (if any),	2027	or C<ev_timer_again> is called, and determines the next timeout (if any),
1062	which is also when any modifications are taken into account.	2028	which is also when any modifications are taken into account.
1063		2029
1064	=back	2030	=back
1065		2031
		2032	=head3 Examples
		2033
1066	Example: Create a timer that fires after 60 seconds.	2034	Example: Create a timer that fires after 60 seconds.
1067		2035
1068	static void	2036	static void
1069	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2037	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1070	{	2038	{
1071	.. one minute over, w is actually stopped right here	2039	.. one minute over, w is actually stopped right here
1072	}	2040	}
1073		2041
1074	struct ev_timer mytimer;	2042	ev_timer mytimer;
1075	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2043	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1076	ev_timer_start (loop, &mytimer);	2044	ev_timer_start (loop, &mytimer);
1077		2045
1078	Example: Create a timeout timer that times out after 10 seconds of	2046	Example: Create a timeout timer that times out after 10 seconds of
1079	inactivity.	2047	inactivity.
1080		2048
1081	static void	2049	static void
1082	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2050	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1083	{	2051	{
1084	.. ten seconds without any activity	2052	.. ten seconds without any activity
1085	}	2053	}
1086		2054
1087	struct ev_timer mytimer;	2055	ev_timer mytimer;
1088	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2056	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1089	ev_timer_again (&mytimer); /* start timer */	2057	ev_timer_again (&mytimer); /* start timer */
1090	ev_loop (loop, 0);	2058	ev_run (loop, 0);
1091		2059
1092	// and in some piece of code that gets executed on any "activity":	2060	// and in some piece of code that gets executed on any "activity":
1093	// reset the timeout to start ticking again at 10 seconds	2061	// reset the timeout to start ticking again at 10 seconds
1094	ev_timer_again (&mytimer);	2062	ev_timer_again (&mytimer);
1095		2063
1096		2064
1097	=head2 C<ev_periodic> - to cron or not to cron?	2065	=head2 C<ev_periodic> - to cron or not to cron?
1098		2066
1099	Periodic watchers are also timers of a kind, but they are very versatile	2067	Periodic watchers are also timers of a kind, but they are very versatile
1100	(and unfortunately a bit complex).	2068	(and unfortunately a bit complex).
1101		2069
1102	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2070	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1103	but on wallclock time (absolute time). You can tell a periodic watcher	2071	relative time, the physical time that passes) but on wall clock time
1104	to trigger "at" some specific point in time. For example, if you tell a	2072	(absolute time, the thing you can read on your calender or clock). The
1105	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2073	difference is that wall clock time can run faster or slower than real
1106	+ 10.>) and then reset your system clock to the last year, then it will	2074	time, and time jumps are not uncommon (e.g. when you adjust your
1107	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2075	wrist-watch).
1108	roughly 10 seconds later).
1109		2076
1110	They can also be used to implement vastly more complex timers, such as	2077	You can tell a periodic watcher to trigger after some specific point
1111	triggering an event on each midnight, local time or other, complicated,	2078	in time: for example, if you tell a periodic watcher to trigger "in 10
1112	rules.	2079	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2080	not a delay) and then reset your system clock to January of the previous
		2081	year, then it will take a year or more to trigger the event (unlike an
		2082	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2083	it, as it uses a relative timeout).
1113		2084
		2085	C<ev_periodic> watchers can also be used to implement vastly more complex
		2086	timers, such as triggering an event on each "midnight, local time", or
		2087	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2088	those cannot react to time jumps.
		2089
1114	As with timers, the callback is guarenteed to be invoked only when the	2090	As with timers, the callback is guaranteed to be invoked only when the
1115	time (C<at>) has been passed, but if multiple periodic timers become ready	2091	point in time where it is supposed to trigger has passed. If multiple
1116	during the same loop iteration then order of execution is undefined.	2092	timers become ready during the same loop iteration then the ones with
		2093	earlier time-out values are invoked before ones with later time-out values
		2094	(but this is no longer true when a callback calls C<ev_run> recursively).
1117		2095
1118	=head3 Watcher-Specific Functions and Data Members	2096	=head3 Watcher-Specific Functions and Data Members
1119		2097
1120	=over 4	2098	=over 4
1121		2099
1122	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2100	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1123		2101
1124	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2102	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1125		2103
1126	Lots of arguments, lets sort it out... There are basically three modes of	2104	Lots of arguments, let's sort it out... There are basically three modes of
1127	operation, and we will explain them from simplest to complex:	2105	operation, and we will explain them from simplest to most complex:
1128		2106
1129	=over 4	2107	=over 4
1130		2108
1131	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2109	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1132		2110
1133	In this configuration the watcher triggers an event at the wallclock time	2111	In this configuration the watcher triggers an event after the wall clock
1134	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2112	time C<offset> has passed. It will not repeat and will not adjust when a
1135	that is, if it is to be run at January 1st 2011 then it will run when the	2113	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1136	system time reaches or surpasses this time.	2114	will be stopped and invoked when the system clock reaches or surpasses
		2115	this point in time.
1137		2116
1138	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2117	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1139		2118
1140	In this mode the watcher will always be scheduled to time out at the next	2119	In this mode the watcher will always be scheduled to time out at the next
1141	C<at + N * interval> time (for some integer N, which can also be negative)	2120	C<offset + N * interval> time (for some integer N, which can also be
1142	and then repeat, regardless of any time jumps.	2121	negative) and then repeat, regardless of any time jumps. The C<offset>
		2122	argument is merely an offset into the C<interval> periods.
1143		2123
1144	This can be used to create timers that do not drift with respect to system	2124	This can be used to create timers that do not drift with respect to the
1145	time:	2125	system clock, for example, here is an C<ev_periodic> that triggers each
		2126	hour, on the hour (with respect to UTC):
1146		2127
1147	ev_periodic_set (&periodic, 0., 3600., 0);	2128	ev_periodic_set (&periodic, 0., 3600., 0);
1148		2129
1149	This doesn't mean there will always be 3600 seconds in between triggers,	2130	This doesn't mean there will always be 3600 seconds in between triggers,
1150	but only that the the callback will be called when the system time shows a	2131	but only that the callback will be called when the system time shows a
1151	full hour (UTC), or more correctly, when the system time is evenly divisible	2132	full hour (UTC), or more correctly, when the system time is evenly divisible
1152	by 3600.	2133	by 3600.
1153		2134
1154	Another way to think about it (for the mathematically inclined) is that	2135	Another way to think about it (for the mathematically inclined) is that
1155	C<ev_periodic> will try to run the callback in this mode at the next possible	2136	C<ev_periodic> will try to run the callback in this mode at the next possible
1156	time where C<time = at (mod interval)>, regardless of any time jumps.	2137	time where C<time = offset (mod interval)>, regardless of any time jumps.
1157		2138
1158	For numerical stability it is preferable that the C<at> value is near	2139	For numerical stability it is preferable that the C<offset> value is near
1159	C<ev_now ()> (the current time), but there is no range requirement for	2140	C<ev_now ()> (the current time), but there is no range requirement for
1160	this value.	2141	this value, and in fact is often specified as zero.
1161		2142
		2143	Note also that there is an upper limit to how often a timer can fire (CPU
		2144	speed for example), so if C<interval> is very small then timing stability
		2145	will of course deteriorate. Libev itself tries to be exact to be about one
		2146	millisecond (if the OS supports it and the machine is fast enough).
		2147
1162	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2148	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1163		2149
1164	In this mode the values for C<interval> and C<at> are both being	2150	In this mode the values for C<interval> and C<offset> are both being
1165	ignored. Instead, each time the periodic watcher gets scheduled, the	2151	ignored. Instead, each time the periodic watcher gets scheduled, the
1166	reschedule callback will be called with the watcher as first, and the	2152	reschedule callback will be called with the watcher as first, and the
1167	current time as second argument.	2153	current time as second argument.
1168		2154
1169	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2155	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1170	ever, or make any event loop modifications>. If you need to stop it,	2156	or make ANY other event loop modifications whatsoever, unless explicitly
1171	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2157	allowed by documentation here>.
1172	starting an C<ev_prepare> watcher, which is legal).
1173		2158
		2159	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2160	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2161	only event loop modification you are allowed to do).
		2162
1174	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2163	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1175	ev_tstamp now)>, e.g.:	2164	*w, ev_tstamp now)>, e.g.:
1176		2165
		2166	static ev_tstamp
1177	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2167	my_rescheduler (ev_periodic *w, ev_tstamp now)
1178	{	2168	{
1179	return now + 60.;	2169	return now + 60.;
1180	}	2170	}
1181		2171
1182	It must return the next time to trigger, based on the passed time value	2172	It must return the next time to trigger, based on the passed time value
1183	(that is, the lowest time value larger than to the second argument). It	2173	(that is, the lowest time value larger than to the second argument). It
1184	will usually be called just before the callback will be triggered, but	2174	will usually be called just before the callback will be triggered, but
1185	might be called at other times, too.	2175	might be called at other times, too.
1186		2176
1187	NOTE: I<< This callback must always return a time that is later than the	2177	NOTE: I<< This callback must always return a time that is higher than or
1188	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2178	equal to the passed C<now> value >>.
1189		2179
1190	This can be used to create very complex timers, such as a timer that	2180	This can be used to create very complex timers, such as a timer that
1191	triggers on each midnight, local time. To do this, you would calculate the	2181	triggers on "next midnight, local time". To do this, you would calculate the
1192	next midnight after C<now> and return the timestamp value for this. How	2182	next midnight after C<now> and return the timestamp value for this. How
1193	you do this is, again, up to you (but it is not trivial, which is the main	2183	you do this is, again, up to you (but it is not trivial, which is the main
1194	reason I omitted it as an example).	2184	reason I omitted it as an example).
1195		2185
1196	=back	2186	=back
…		…
1200	Simply stops and restarts the periodic watcher again. This is only useful	2190	Simply stops and restarts the periodic watcher again. This is only useful
1201	when you changed some parameters or the reschedule callback would return	2191	when you changed some parameters or the reschedule callback would return
1202	a different time than the last time it was called (e.g. in a crond like	2192	a different time than the last time it was called (e.g. in a crond like
1203	program when the crontabs have changed).	2193	program when the crontabs have changed).
1204		2194
		2195	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2196
		2197	When active, returns the absolute time that the watcher is supposed
		2198	to trigger next. This is not the same as the C<offset> argument to
		2199	C<ev_periodic_set>, but indeed works even in interval and manual
		2200	rescheduling modes.
		2201
1205	=item ev_tstamp offset [read-write]	2202	=item ev_tstamp offset [read-write]
1206		2203
1207	When repeating, this contains the offset value, otherwise this is the	2204	When repeating, this contains the offset value, otherwise this is the
1208	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2205	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2206	although libev might modify this value for better numerical stability).
1209		2207
1210	Can be modified any time, but changes only take effect when the periodic	2208	Can be modified any time, but changes only take effect when the periodic
1211	timer fires or C<ev_periodic_again> is being called.	2209	timer fires or C<ev_periodic_again> is being called.
1212		2210
1213	=item ev_tstamp interval [read-write]	2211	=item ev_tstamp interval [read-write]
1214		2212
1215	The current interval value. Can be modified any time, but changes only	2213	The current interval value. Can be modified any time, but changes only
1216	take effect when the periodic timer fires or C<ev_periodic_again> is being	2214	take effect when the periodic timer fires or C<ev_periodic_again> is being
1217	called.	2215	called.
1218		2216
1219	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2217	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1220		2218
1221	The current reschedule callback, or C<0>, if this functionality is	2219	The current reschedule callback, or C<0>, if this functionality is
1222	switched off. Can be changed any time, but changes only take effect when	2220	switched off. Can be changed any time, but changes only take effect when
1223	the periodic timer fires or C<ev_periodic_again> is being called.	2221	the periodic timer fires or C<ev_periodic_again> is being called.
1224		2222
1225	=back	2223	=back
1226		2224
		2225	=head3 Examples
		2226
1227	Example: Call a callback every hour, or, more precisely, whenever the	2227	Example: Call a callback every hour, or, more precisely, whenever the
1228	system clock is divisible by 3600. The callback invocation times have	2228	system time is divisible by 3600. The callback invocation times have
1229	potentially a lot of jittering, but good long-term stability.	2229	potentially a lot of jitter, but good long-term stability.
1230		2230
1231	static void	2231	static void
1232	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2232	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1233	{	2233	{
1234	... its now a full hour (UTC, or TAI or whatever your clock follows)	2234	... its now a full hour (UTC, or TAI or whatever your clock follows)
1235	}	2235	}
1236		2236
1237	struct ev_periodic hourly_tick;	2237	ev_periodic hourly_tick;
1238	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2238	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1239	ev_periodic_start (loop, &hourly_tick);	2239	ev_periodic_start (loop, &hourly_tick);
1240		2240
1241	Example: The same as above, but use a reschedule callback to do it:	2241	Example: The same as above, but use a reschedule callback to do it:
1242		2242
1243	#include <math.h>	2243	#include <math.h>
1244		2244
1245	static ev_tstamp	2245	static ev_tstamp
1246	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2246	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1247	{	2247	{
1248	return fmod (now, 3600.) + 3600.;	2248	return now + (3600. - fmod (now, 3600.));
1249	}	2249	}
1250		2250
1251	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2251	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1252		2252
1253	Example: Call a callback every hour, starting now:	2253	Example: Call a callback every hour, starting now:
1254		2254
1255	struct ev_periodic hourly_tick;	2255	ev_periodic hourly_tick;
1256	ev_periodic_init (&hourly_tick, clock_cb,	2256	ev_periodic_init (&hourly_tick, clock_cb,
1257	fmod (ev_now (loop), 3600.), 3600., 0);	2257	fmod (ev_now (loop), 3600.), 3600., 0);
1258	ev_periodic_start (loop, &hourly_tick);	2258	ev_periodic_start (loop, &hourly_tick);
1259		2259
1260		2260
1261	=head2 C<ev_signal> - signal me when a signal gets signalled!	2261	=head2 C<ev_signal> - signal me when a signal gets signalled!
1262		2262
1263	Signal watchers will trigger an event when the process receives a specific	2263	Signal watchers will trigger an event when the process receives a specific
1264	signal one or more times. Even though signals are very asynchronous, libev	2264	signal one or more times. Even though signals are very asynchronous, libev
1265	will try it's best to deliver signals synchronously, i.e. as part of the	2265	will try its best to deliver signals synchronously, i.e. as part of the
1266	normal event processing, like any other event.	2266	normal event processing, like any other event.
1267		2267
		2268	If you want signals to be delivered truly asynchronously, just use
		2269	C<sigaction> as you would do without libev and forget about sharing
		2270	the signal. You can even use C<ev_async> from a signal handler to
		2271	synchronously wake up an event loop.
		2272
1268	You can configure as many watchers as you like per signal. Only when the	2273	You can configure as many watchers as you like for the same signal, but
		2274	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2275	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2276	C<SIGINT> in both the default loop and another loop at the same time. At
		2277	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2278
1269	first watcher gets started will libev actually register a signal watcher	2279	When the first watcher gets started will libev actually register something
1270	with the kernel (thus it coexists with your own signal handlers as long	2280	with the kernel (thus it coexists with your own signal handlers as long as
1271	as you don't register any with libev). Similarly, when the last signal	2281	you don't register any with libev for the same signal).
1272	watcher for a signal is stopped libev will reset the signal handler to	2282
1273	SIG_DFL (regardless of what it was set to before).	2283	If possible and supported, libev will install its handlers with
		2284	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2285	not be unduly interrupted. If you have a problem with system calls getting
		2286	interrupted by signals you can block all signals in an C<ev_check> watcher
		2287	and unblock them in an C<ev_prepare> watcher.
		2288
		2289	=head3 The special problem of inheritance over fork/execve/pthread_create
		2290
		2291	Both the signal mask (C<sigprocmask>) and the signal disposition
		2292	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2293	stopping it again), that is, libev might or might not block the signal,
		2294	and might or might not set or restore the installed signal handler.
		2295
		2296	While this does not matter for the signal disposition (libev never
		2297	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2298	C<execve>), this matters for the signal mask: many programs do not expect
		2299	certain signals to be blocked.
		2300
		2301	This means that before calling C<exec> (from the child) you should reset
		2302	the signal mask to whatever "default" you expect (all clear is a good
		2303	choice usually).
		2304
		2305	The simplest way to ensure that the signal mask is reset in the child is
		2306	to install a fork handler with C<pthread_atfork> that resets it. That will
		2307	catch fork calls done by libraries (such as the libc) as well.
		2308
		2309	In current versions of libev, the signal will not be blocked indefinitely
		2310	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2311	the window of opportunity for problems, it will not go away, as libev
		2312	I<has> to modify the signal mask, at least temporarily.
		2313
		2314	So I can't stress this enough: I<If you do not reset your signal mask when
		2315	you expect it to be empty, you have a race condition in your code>. This
		2316	is not a libev-specific thing, this is true for most event libraries.
1274		2317
1275	=head3 Watcher-Specific Functions and Data Members	2318	=head3 Watcher-Specific Functions and Data Members
1276		2319
1277	=over 4	2320	=over 4
1278		2321
…		…
1287		2330
1288	The signal the watcher watches out for.	2331	The signal the watcher watches out for.
1289		2332
1290	=back	2333	=back
1291		2334
		2335	=head3 Examples
		2336
		2337	Example: Try to exit cleanly on SIGINT.
		2338
		2339	static void
		2340	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2341	{
		2342	ev_break (loop, EVBREAK_ALL);
		2343	}
		2344
		2345	ev_signal signal_watcher;
		2346	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2347	ev_signal_start (loop, &signal_watcher);
		2348
1292		2349
1293	=head2 C<ev_child> - watch out for process status changes	2350	=head2 C<ev_child> - watch out for process status changes
1294		2351
1295	Child watchers trigger when your process receives a SIGCHLD in response to	2352	Child watchers trigger when your process receives a SIGCHLD in response to
1296	some child status changes (most typically when a child of yours dies).	2353	some child status changes (most typically when a child of yours dies or
		2354	exits). It is permissible to install a child watcher I<after> the child
		2355	has been forked (which implies it might have already exited), as long
		2356	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2357	forking and then immediately registering a watcher for the child is fine,
		2358	but forking and registering a watcher a few event loop iterations later or
		2359	in the next callback invocation is not.
		2360
		2361	Only the default event loop is capable of handling signals, and therefore
		2362	you can only register child watchers in the default event loop.
		2363
		2364	Due to some design glitches inside libev, child watchers will always be
		2365	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2366	libev)
		2367
		2368	=head3 Process Interaction
		2369
		2370	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2371	initialised. This is necessary to guarantee proper behaviour even if the
		2372	first child watcher is started after the child exits. The occurrence
		2373	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2374	synchronously as part of the event loop processing. Libev always reaps all
		2375	children, even ones not watched.
		2376
		2377	=head3 Overriding the Built-In Processing
		2378
		2379	Libev offers no special support for overriding the built-in child
		2380	processing, but if your application collides with libev's default child
		2381	handler, you can override it easily by installing your own handler for
		2382	C<SIGCHLD> after initialising the default loop, and making sure the
		2383	default loop never gets destroyed. You are encouraged, however, to use an
		2384	event-based approach to child reaping and thus use libev's support for
		2385	that, so other libev users can use C<ev_child> watchers freely.
		2386
		2387	=head3 Stopping the Child Watcher
		2388
		2389	Currently, the child watcher never gets stopped, even when the
		2390	child terminates, so normally one needs to stop the watcher in the
		2391	callback. Future versions of libev might stop the watcher automatically
		2392	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2393	problem).
1297		2394
1298	=head3 Watcher-Specific Functions and Data Members	2395	=head3 Watcher-Specific Functions and Data Members
1299		2396
1300	=over 4	2397	=over 4
1301		2398
1302	=item ev_child_init (ev_child *, callback, int pid)	2399	=item ev_child_init (ev_child *, callback, int pid, int trace)
1303		2400
1304	=item ev_child_set (ev_child *, int pid)	2401	=item ev_child_set (ev_child *, int pid, int trace)
1305		2402
1306	Configures the watcher to wait for status changes of process C<pid> (or	2403	Configures the watcher to wait for status changes of process C<pid> (or
1307	I<any> process if C<pid> is specified as C<0>). The callback can look	2404	I<any> process if C<pid> is specified as C<0>). The callback can look
1308	at the C<rstatus> member of the C<ev_child> watcher structure to see	2405	at the C<rstatus> member of the C<ev_child> watcher structure to see
1309	the status word (use the macros from C<sys/wait.h> and see your systems	2406	the status word (use the macros from C<sys/wait.h> and see your systems
1310	C<waitpid> documentation). The C<rpid> member contains the pid of the	2407	C<waitpid> documentation). The C<rpid> member contains the pid of the
1311	process causing the status change.	2408	process causing the status change. C<trace> must be either C<0> (only
		2409	activate the watcher when the process terminates) or C<1> (additionally
		2410	activate the watcher when the process is stopped or continued).
1312		2411
1313	=item int pid [read-only]	2412	=item int pid [read-only]
1314		2413
1315	The process id this watcher watches out for, or C<0>, meaning any process id.	2414	The process id this watcher watches out for, or C<0>, meaning any process id.
1316		2415
…		…
1323	The process exit/trace status caused by C<rpid> (see your systems	2422	The process exit/trace status caused by C<rpid> (see your systems
1324	C<waitpid> and C<sys/wait.h> documentation for details).	2423	C<waitpid> and C<sys/wait.h> documentation for details).
1325		2424
1326	=back	2425	=back
1327		2426
1328	Example: Try to exit cleanly on SIGINT and SIGTERM.	2427	=head3 Examples
1329		2428
		2429	Example: C<fork()> a new process and install a child handler to wait for
		2430	its completion.
		2431
		2432	ev_child cw;
		2433
1330	static void	2434	static void
1331	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2435	child_cb (EV_P_ ev_child *w, int revents)
1332	{	2436	{
1333	ev_unloop (loop, EVUNLOOP_ALL);	2437	ev_child_stop (EV_A_ w);
		2438	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1334	}	2439	}
1335		2440
1336	struct ev_signal signal_watcher;	2441	pid_t pid = fork ();
1337	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2442
1338	ev_signal_start (loop, &sigint_cb);	2443	if (pid < 0)
		2444	// error
		2445	else if (pid == 0)
		2446	{
		2447	// the forked child executes here
		2448	exit (1);
		2449	}
		2450	else
		2451	{
		2452	ev_child_init (&cw, child_cb, pid, 0);
		2453	ev_child_start (EV_DEFAULT_ &cw);
		2454	}
1339		2455
1340		2456
1341	=head2 C<ev_stat> - did the file attributes just change?	2457	=head2 C<ev_stat> - did the file attributes just change?
1342		2458
1343	This watches a filesystem path for attribute changes. That is, it calls	2459	This watches a file system path for attribute changes. That is, it calls
1344	C<stat> regularly (or when the OS says it changed) and sees if it changed	2460	C<stat> on that path in regular intervals (or when the OS says it changed)
1345	compared to the last time, invoking the callback if it did.	2461	and sees if it changed compared to the last time, invoking the callback if
		2462	it did.
1346		2463
1347	The path does not need to exist: changing from "path exists" to "path does	2464	The path does not need to exist: changing from "path exists" to "path does
1348	not exist" is a status change like any other. The condition "path does	2465	not exist" is a status change like any other. The condition "path does not
1349	not exist" is signified by the C<st_nlink> field being zero (which is	2466	exist" (or more correctly "path cannot be stat'ed") is signified by the
1350	otherwise always forced to be at least one) and all the other fields of	2467	C<st_nlink> field being zero (which is otherwise always forced to be at
1351	the stat buffer having unspecified contents.	2468	least one) and all the other fields of the stat buffer having unspecified
		2469	contents.
1352		2470
1353	The path I<should> be absolute and I<must not> end in a slash. If it is	2471	The path I<must not> end in a slash or contain special components such as
		2472	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1354	relative and your working directory changes, the behaviour is undefined.	2473	your working directory changes, then the behaviour is undefined.
1355		2474
1356	Since there is no standard to do this, the portable implementation simply	2475	Since there is no portable change notification interface available, the
1357	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2476	portable implementation simply calls C<stat(2)> regularly on the path
1358	can specify a recommended polling interval for this case. If you specify	2477	to see if it changed somehow. You can specify a recommended polling
1359	a polling interval of C<0> (highly recommended!) then a I<suitable,	2478	interval for this case. If you specify a polling interval of C<0> (highly
1360	unspecified default> value will be used (which you can expect to be around	2479	recommended!) then a I<suitable, unspecified default> value will be used
1361	five seconds, although this might change dynamically). Libev will also	2480	(which you can expect to be around five seconds, although this might
1362	impose a minimum interval which is currently around C<0.1>, but thats	2481	change dynamically). Libev will also impose a minimum interval which is
1363	usually overkill.	2482	currently around C<0.1>, but that's usually overkill.
1364		2483
1365	This watcher type is not meant for massive numbers of stat watchers,	2484	This watcher type is not meant for massive numbers of stat watchers,
1366	as even with OS-supported change notifications, this can be	2485	as even with OS-supported change notifications, this can be
1367	resource-intensive.	2486	resource-intensive.
1368		2487
1369	At the time of this writing, only the Linux inotify interface is	2488	At the time of this writing, the only OS-specific interface implemented
1370	implemented (implementing kqueue support is left as an exercise for the	2489	is the Linux inotify interface (implementing kqueue support is left as an
1371	reader). Inotify will be used to give hints only and should not change the	2490	exercise for the reader. Note, however, that the author sees no way of
1372	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2491	implementing C<ev_stat> semantics with kqueue, except as a hint).
1373	to fall back to regular polling again even with inotify, but changes are	2492
1374	usually detected immediately, and if the file exists there will be no	2493	=head3 ABI Issues (Largefile Support)
1375	polling.	2494
		2495	Libev by default (unless the user overrides this) uses the default
		2496	compilation environment, which means that on systems with large file
		2497	support disabled by default, you get the 32 bit version of the stat
		2498	structure. When using the library from programs that change the ABI to
		2499	use 64 bit file offsets the programs will fail. In that case you have to
		2500	compile libev with the same flags to get binary compatibility. This is
		2501	obviously the case with any flags that change the ABI, but the problem is
		2502	most noticeably displayed with ev_stat and large file support.
		2503
		2504	The solution for this is to lobby your distribution maker to make large
		2505	file interfaces available by default (as e.g. FreeBSD does) and not
		2506	optional. Libev cannot simply switch on large file support because it has
		2507	to exchange stat structures with application programs compiled using the
		2508	default compilation environment.
		2509
		2510	=head3 Inotify and Kqueue
		2511
		2512	When C<inotify (7)> support has been compiled into libev and present at
		2513	runtime, it will be used to speed up change detection where possible. The
		2514	inotify descriptor will be created lazily when the first C<ev_stat>
		2515	watcher is being started.
		2516
		2517	Inotify presence does not change the semantics of C<ev_stat> watchers
		2518	except that changes might be detected earlier, and in some cases, to avoid
		2519	making regular C<stat> calls. Even in the presence of inotify support
		2520	there are many cases where libev has to resort to regular C<stat> polling,
		2521	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2522	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2523	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2524	xfs are fully working) libev usually gets away without polling.
		2525
		2526	There is no support for kqueue, as apparently it cannot be used to
		2527	implement this functionality, due to the requirement of having a file
		2528	descriptor open on the object at all times, and detecting renames, unlinks
		2529	etc. is difficult.
		2530
		2531	=head3 C<stat ()> is a synchronous operation
		2532
		2533	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2534	the process. The exception are C<ev_stat> watchers - those call C<stat
		2535	()>, which is a synchronous operation.
		2536
		2537	For local paths, this usually doesn't matter: unless the system is very
		2538	busy or the intervals between stat's are large, a stat call will be fast,
		2539	as the path data is usually in memory already (except when starting the
		2540	watcher).
		2541
		2542	For networked file systems, calling C<stat ()> can block an indefinite
		2543	time due to network issues, and even under good conditions, a stat call
		2544	often takes multiple milliseconds.
		2545
		2546	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2547	paths, although this is fully supported by libev.
		2548
		2549	=head3 The special problem of stat time resolution
		2550
		2551	The C<stat ()> system call only supports full-second resolution portably,
		2552	and even on systems where the resolution is higher, most file systems
		2553	still only support whole seconds.
		2554
		2555	That means that, if the time is the only thing that changes, you can
		2556	easily miss updates: on the first update, C<ev_stat> detects a change and
		2557	calls your callback, which does something. When there is another update
		2558	within the same second, C<ev_stat> will be unable to detect unless the
		2559	stat data does change in other ways (e.g. file size).
		2560
		2561	The solution to this is to delay acting on a change for slightly more
		2562	than a second (or till slightly after the next full second boundary), using
		2563	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2564	ev_timer_again (loop, w)>).
		2565
		2566	The C<.02> offset is added to work around small timing inconsistencies
		2567	of some operating systems (where the second counter of the current time
		2568	might be be delayed. One such system is the Linux kernel, where a call to
		2569	C<gettimeofday> might return a timestamp with a full second later than
		2570	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2571	update file times then there will be a small window where the kernel uses
		2572	the previous second to update file times but libev might already execute
		2573	the timer callback).
1376		2574
1377	=head3 Watcher-Specific Functions and Data Members	2575	=head3 Watcher-Specific Functions and Data Members
1378		2576
1379	=over 4	2577	=over 4
1380		2578
…		…
1386	C<path>. The C<interval> is a hint on how quickly a change is expected to	2584	C<path>. The C<interval> is a hint on how quickly a change is expected to
1387	be detected and should normally be specified as C<0> to let libev choose	2585	be detected and should normally be specified as C<0> to let libev choose
1388	a suitable value. The memory pointed to by C<path> must point to the same	2586	a suitable value. The memory pointed to by C<path> must point to the same
1389	path for as long as the watcher is active.	2587	path for as long as the watcher is active.
1390		2588
1391	The callback will be receive C<EV_STAT> when a change was detected,	2589	The callback will receive an C<EV_STAT> event when a change was detected,
1392	relative to the attributes at the time the watcher was started (or the	2590	relative to the attributes at the time the watcher was started (or the
1393	last change was detected).	2591	last change was detected).
1394		2592
1395	=item ev_stat_stat (ev_stat *)	2593	=item ev_stat_stat (loop, ev_stat *)
1396		2594
1397	Updates the stat buffer immediately with new values. If you change the	2595	Updates the stat buffer immediately with new values. If you change the
1398	watched path in your callback, you could call this fucntion to avoid	2596	watched path in your callback, you could call this function to avoid
1399	detecting this change (while introducing a race condition). Can also be	2597	detecting this change (while introducing a race condition if you are not
1400	useful simply to find out the new values.	2598	the only one changing the path). Can also be useful simply to find out the
		2599	new values.
1401		2600
1402	=item ev_statdata attr [read-only]	2601	=item ev_statdata attr [read-only]
1403		2602
1404	The most-recently detected attributes of the file. Although the type is of	2603	The most-recently detected attributes of the file. Although the type is
1405	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2604	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1406	suitable for your system. If the C<st_nlink> member is C<0>, then there	2605	suitable for your system, but you can only rely on the POSIX-standardised
		2606	members to be present. If the C<st_nlink> member is C<0>, then there was
1407	was some error while C<stat>ing the file.	2607	some error while C<stat>ing the file.
1408		2608
1409	=item ev_statdata prev [read-only]	2609	=item ev_statdata prev [read-only]
1410		2610
1411	The previous attributes of the file. The callback gets invoked whenever	2611	The previous attributes of the file. The callback gets invoked whenever
1412	C<prev> != C<attr>.	2612	C<prev> != C<attr>, or, more precisely, one or more of these members
		2613	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2614	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1413		2615
1414	=item ev_tstamp interval [read-only]	2616	=item ev_tstamp interval [read-only]
1415		2617
1416	The specified interval.	2618	The specified interval.
1417		2619
1418	=item const char *path [read-only]	2620	=item const char *path [read-only]
1419		2621
1420	The filesystem path that is being watched.	2622	The file system path that is being watched.
1421		2623
1422	=back	2624	=back
1423		2625
		2626	=head3 Examples
		2627
1424	Example: Watch C</etc/passwd> for attribute changes.	2628	Example: Watch C</etc/passwd> for attribute changes.
1425		2629
1426	static void	2630	static void
1427	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2631	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1428	{	2632	{
1429	/* /etc/passwd changed in some way */	2633	/* /etc/passwd changed in some way */
1430	if (w->attr.st_nlink)	2634	if (w->attr.st_nlink)
1431	{	2635	{
1432	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2636	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1433	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2637	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1434	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2638	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1435	}	2639	}
1436	else	2640	else
1437	/* you shalt not abuse printf for puts */	2641	/* you shalt not abuse printf for puts */
1438	puts ("wow, /etc/passwd is not there, expect problems. "	2642	puts ("wow, /etc/passwd is not there, expect problems. "
1439	"if this is windows, they already arrived\n");	2643	"if this is windows, they already arrived\n");
1440	}	2644	}
1441		2645
1442	...	2646	...
1443	ev_stat passwd;	2647	ev_stat passwd;
1444		2648
1445	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2649	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1446	ev_stat_start (loop, &passwd);	2650	ev_stat_start (loop, &passwd);
		2651
		2652	Example: Like above, but additionally use a one-second delay so we do not
		2653	miss updates (however, frequent updates will delay processing, too, so
		2654	one might do the work both on C<ev_stat> callback invocation I<and> on
		2655	C<ev_timer> callback invocation).
		2656
		2657	static ev_stat passwd;
		2658	static ev_timer timer;
		2659
		2660	static void
		2661	timer_cb (EV_P_ ev_timer *w, int revents)
		2662	{
		2663	ev_timer_stop (EV_A_ w);
		2664
		2665	/* now it's one second after the most recent passwd change */
		2666	}
		2667
		2668	static void
		2669	stat_cb (EV_P_ ev_stat *w, int revents)
		2670	{
		2671	/* reset the one-second timer */
		2672	ev_timer_again (EV_A_ &timer);
		2673	}
		2674
		2675	...
		2676	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2677	ev_stat_start (loop, &passwd);
		2678	ev_timer_init (&timer, timer_cb, 0., 1.02);
1447		2679
1448		2680
1449	=head2 C<ev_idle> - when you've got nothing better to do...	2681	=head2 C<ev_idle> - when you've got nothing better to do...
1450		2682
1451	Idle watchers trigger events when no other events of the same or higher	2683	Idle watchers trigger events when no other events of the same or higher
1452	priority are pending (prepare, check and other idle watchers do not	2684	priority are pending (prepare, check and other idle watchers do not count
1453	count).	2685	as receiving "events").
1454		2686
1455	That is, as long as your process is busy handling sockets or timeouts	2687	That is, as long as your process is busy handling sockets or timeouts
1456	(or even signals, imagine) of the same or higher priority it will not be	2688	(or even signals, imagine) of the same or higher priority it will not be
1457	triggered. But when your process is idle (or only lower-priority watchers	2689	triggered. But when your process is idle (or only lower-priority watchers
1458	are pending), the idle watchers are being called once per event loop	2690	are pending), the idle watchers are being called once per event loop
…		…
1469		2701
1470	=head3 Watcher-Specific Functions and Data Members	2702	=head3 Watcher-Specific Functions and Data Members
1471		2703
1472	=over 4	2704	=over 4
1473		2705
1474	=item ev_idle_init (ev_signal *, callback)	2706	=item ev_idle_init (ev_idle *, callback)
1475		2707
1476	Initialises and configures the idle watcher - it has no parameters of any	2708	Initialises and configures the idle watcher - it has no parameters of any
1477	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2709	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1478	believe me.	2710	believe me.
1479		2711
1480	=back	2712	=back
1481		2713
		2714	=head3 Examples
		2715
1482	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2716	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1483	callback, free it. Also, use no error checking, as usual.	2717	callback, free it. Also, use no error checking, as usual.
1484		2718
1485	static void	2719	static void
1486	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2720	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1487	{	2721	{
1488	free (w);	2722	free (w);
1489	// now do something you wanted to do when the program has	2723	// now do something you wanted to do when the program has
1490	// no longer asnything immediate to do.	2724	// no longer anything immediate to do.
1491	}	2725	}
1492		2726
1493	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2727	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1494	ev_idle_init (idle_watcher, idle_cb);	2728	ev_idle_init (idle_watcher, idle_cb);
1495	ev_idle_start (loop, idle_cb);	2729	ev_idle_start (loop, idle_watcher);
1496		2730
1497		2731
1498	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2732	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1499		2733
1500	Prepare and check watchers are usually (but not always) used in tandem:	2734	Prepare and check watchers are usually (but not always) used in pairs:
1501	prepare watchers get invoked before the process blocks and check watchers	2735	prepare watchers get invoked before the process blocks and check watchers
1502	afterwards.	2736	afterwards.
1503		2737
1504	You I<must not> call C<ev_loop> or similar functions that enter	2738	You I<must not> call C<ev_run> or similar functions that enter
1505	the current event loop from either C<ev_prepare> or C<ev_check>	2739	the current event loop from either C<ev_prepare> or C<ev_check>
1506	watchers. Other loops than the current one are fine, however. The	2740	watchers. Other loops than the current one are fine, however. The
1507	rationale behind this is that you do not need to check for recursion in	2741	rationale behind this is that you do not need to check for recursion in
1508	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2742	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1509	C<ev_check> so if you have one watcher of each kind they will always be	2743	C<ev_check> so if you have one watcher of each kind they will always be
1510	called in pairs bracketing the blocking call.	2744	called in pairs bracketing the blocking call.
1511		2745
1512	Their main purpose is to integrate other event mechanisms into libev and	2746	Their main purpose is to integrate other event mechanisms into libev and
1513	their use is somewhat advanced. This could be used, for example, to track	2747	their use is somewhat advanced. They could be used, for example, to track
1514	variable changes, implement your own watchers, integrate net-snmp or a	2748	variable changes, implement your own watchers, integrate net-snmp or a
1515	coroutine library and lots more. They are also occasionally useful if	2749	coroutine library and lots more. They are also occasionally useful if
1516	you cache some data and want to flush it before blocking (for example,	2750	you cache some data and want to flush it before blocking (for example,
1517	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2751	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1518	watcher).	2752	watcher).
1519		2753
1520	This is done by examining in each prepare call which file descriptors need	2754	This is done by examining in each prepare call which file descriptors
1521	to be watched by the other library, registering C<ev_io> watchers for	2755	need to be watched by the other library, registering C<ev_io> watchers
1522	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2756	for them and starting an C<ev_timer> watcher for any timeouts (many
1523	provide just this functionality). Then, in the check watcher you check for	2757	libraries provide exactly this functionality). Then, in the check watcher,
1524	any events that occured (by checking the pending status of all watchers	2758	you check for any events that occurred (by checking the pending status
1525	and stopping them) and call back into the library. The I/O and timer	2759	of all watchers and stopping them) and call back into the library. The
1526	callbacks will never actually be called (but must be valid nevertheless,	2760	I/O and timer callbacks will never actually be called (but must be valid
1527	because you never know, you know?).	2761	nevertheless, because you never know, you know?).
1528		2762
1529	As another example, the Perl Coro module uses these hooks to integrate	2763	As another example, the Perl Coro module uses these hooks to integrate
1530	coroutines into libev programs, by yielding to other active coroutines	2764	coroutines into libev programs, by yielding to other active coroutines
1531	during each prepare and only letting the process block if no coroutines	2765	during each prepare and only letting the process block if no coroutines
1532	are ready to run (it's actually more complicated: it only runs coroutines	2766	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1535	loop from blocking if lower-priority coroutines are active, thus mapping	2769	loop from blocking if lower-priority coroutines are active, thus mapping
1536	low-priority coroutines to idle/background tasks).	2770	low-priority coroutines to idle/background tasks).
1537		2771
1538	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2772	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1539	priority, to ensure that they are being run before any other watchers	2773	priority, to ensure that they are being run before any other watchers
		2774	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2775
1540	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2776	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1541	too) should not activate ("feed") events into libev. While libev fully	2777	activate ("feed") events into libev. While libev fully supports this, they
1542	supports this, they will be called before other C<ev_check> watchers did	2778	might get executed before other C<ev_check> watchers did their job. As
1543	their job. As C<ev_check> watchers are often used to embed other event	2779	C<ev_check> watchers are often used to embed other (non-libev) event
1544	loops those other event loops might be in an unusable state until their	2780	loops those other event loops might be in an unusable state until their
1545	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2781	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1546	others).	2782	others).
1547		2783
1548	=head3 Watcher-Specific Functions and Data Members	2784	=head3 Watcher-Specific Functions and Data Members
…		…
1553		2789
1554	=item ev_check_init (ev_check *, callback)	2790	=item ev_check_init (ev_check *, callback)
1555		2791
1556	Initialises and configures the prepare or check watcher - they have no	2792	Initialises and configures the prepare or check watcher - they have no
1557	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2793	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1558	macros, but using them is utterly, utterly and completely pointless.	2794	macros, but using them is utterly, utterly, utterly and completely
		2795	pointless.
1559		2796
1560	=back	2797	=back
		2798
		2799	=head3 Examples
1561		2800
1562	There are a number of principal ways to embed other event loops or modules	2801	There are a number of principal ways to embed other event loops or modules
1563	into libev. Here are some ideas on how to include libadns into libev	2802	into libev. Here are some ideas on how to include libadns into libev
1564	(there is a Perl module named C<EV::ADNS> that does this, which you could	2803	(there is a Perl module named C<EV::ADNS> that does this, which you could
1565	use for an actually working example. Another Perl module named C<EV::Glib>	2804	use as a working example. Another Perl module named C<EV::Glib> embeds a
1566	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2805	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1567	into the Glib event loop).	2806	Glib event loop).
1568		2807
1569	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2808	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1570	and in a check watcher, destroy them and call into libadns. What follows	2809	and in a check watcher, destroy them and call into libadns. What follows
1571	is pseudo-code only of course. This requires you to either use a low	2810	is pseudo-code only of course. This requires you to either use a low
1572	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2811	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1573	the callbacks for the IO/timeout watchers might not have been called yet.	2812	the callbacks for the IO/timeout watchers might not have been called yet.
1574		2813
1575	static ev_io iow [nfd];	2814	static ev_io iow [nfd];
1576	static ev_timer tw;	2815	static ev_timer tw;
1577		2816
1578	static void	2817	static void
1579	io_cb (ev_loop *loop, ev_io *w, int revents)	2818	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1580	{	2819	{
1581	}	2820	}
1582		2821
1583	// create io watchers for each fd and a timer before blocking	2822	// create io watchers for each fd and a timer before blocking
1584	static void	2823	static void
1585	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2824	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1586	{	2825	{
1587	int timeout = 3600000;	2826	int timeout = 3600000;
1588	struct pollfd fds [nfd];	2827	struct pollfd fds [nfd];
1589	// actual code will need to loop here and realloc etc.	2828	// actual code will need to loop here and realloc etc.
1590	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2829	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1591		2830
1592	/* the callback is illegal, but won't be called as we stop during check */	2831	/* the callback is illegal, but won't be called as we stop during check */
1593	ev_timer_init (&tw, 0, timeout * 1e-3);	2832	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1594	ev_timer_start (loop, &tw);	2833	ev_timer_start (loop, &tw);
1595		2834
1596	// create one ev_io per pollfd	2835	// create one ev_io per pollfd
1597	for (int i = 0; i < nfd; ++i)	2836	for (int i = 0; i < nfd; ++i)
1598	{	2837	{
1599	ev_io_init (iow + i, io_cb, fds [i].fd,	2838	ev_io_init (iow + i, io_cb, fds [i].fd,
1600	((fds [i].events & POLLIN ? EV_READ : 0)	2839	((fds [i].events & POLLIN ? EV_READ : 0)
1601	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2840	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1602		2841
1603	fds [i].revents = 0;	2842	fds [i].revents = 0;
1604	ev_io_start (loop, iow + i);	2843	ev_io_start (loop, iow + i);
1605	}	2844	}
1606	}	2845	}
1607		2846
1608	// stop all watchers after blocking	2847	// stop all watchers after blocking
1609	static void	2848	static void
1610	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2849	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1611	{	2850	{
1612	ev_timer_stop (loop, &tw);	2851	ev_timer_stop (loop, &tw);
1613		2852
1614	for (int i = 0; i < nfd; ++i)	2853	for (int i = 0; i < nfd; ++i)
1615	{	2854	{
1616	// set the relevant poll flags	2855	// set the relevant poll flags
1617	// could also call adns_processreadable etc. here	2856	// could also call adns_processreadable etc. here
1618	struct pollfd *fd = fds + i;	2857	struct pollfd *fd = fds + i;
1619	int revents = ev_clear_pending (iow + i);	2858	int revents = ev_clear_pending (iow + i);
1620	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2859	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1621	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2860	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1622		2861
1623	// now stop the watcher	2862	// now stop the watcher
1624	ev_io_stop (loop, iow + i);	2863	ev_io_stop (loop, iow + i);
1625	}	2864	}
1626		2865
1627	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2866	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1628	}	2867	}
1629		2868
1630	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2869	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1631	in the prepare watcher and would dispose of the check watcher.	2870	in the prepare watcher and would dispose of the check watcher.
1632		2871
1633	Method 3: If the module to be embedded supports explicit event	2872	Method 3: If the module to be embedded supports explicit event
1634	notification (adns does), you can also make use of the actual watcher	2873	notification (libadns does), you can also make use of the actual watcher
1635	callbacks, and only destroy/create the watchers in the prepare watcher.	2874	callbacks, and only destroy/create the watchers in the prepare watcher.
1636		2875
1637	static void	2876	static void
1638	timer_cb (EV_P_ ev_timer *w, int revents)	2877	timer_cb (EV_P_ ev_timer *w, int revents)
1639	{	2878	{
1640	adns_state ads = (adns_state)w->data;	2879	adns_state ads = (adns_state)w->data;
1641	update_now (EV_A);	2880	update_now (EV_A);
1642		2881
1643	adns_processtimeouts (ads, &tv_now);	2882	adns_processtimeouts (ads, &tv_now);
1644	}	2883	}
1645		2884
1646	static void	2885	static void
1647	io_cb (EV_P_ ev_io *w, int revents)	2886	io_cb (EV_P_ ev_io *w, int revents)
1648	{	2887	{
1649	adns_state ads = (adns_state)w->data;	2888	adns_state ads = (adns_state)w->data;
1650	update_now (EV_A);	2889	update_now (EV_A);
1651		2890
1652	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2891	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1653	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2892	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1654	}	2893	}
1655		2894
1656	// do not ever call adns_afterpoll	2895	// do not ever call adns_afterpoll
1657		2896
1658	Method 4: Do not use a prepare or check watcher because the module you	2897	Method 4: Do not use a prepare or check watcher because the module you
1659	want to embed is too inflexible to support it. Instead, youc na override	2898	want to embed is not flexible enough to support it. Instead, you can
1660	their poll function. The drawback with this solution is that the main	2899	override their poll function. The drawback with this solution is that the
1661	loop is now no longer controllable by EV. The C<Glib::EV> module does	2900	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1662	this.	2901	this approach, effectively embedding EV as a client into the horrible
		2902	libglib event loop.
1663		2903
1664	static gint	2904	static gint
1665	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2905	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1666	{	2906	{
1667	int got_events = 0;	2907	int got_events = 0;
1668		2908
1669	for (n = 0; n < nfds; ++n)	2909	for (n = 0; n < nfds; ++n)
1670	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2910	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1671		2911
1672	if (timeout >= 0)	2912	if (timeout >= 0)
1673	// create/start timer	2913	// create/start timer
1674		2914
1675	// poll	2915	// poll
1676	ev_loop (EV_A_ 0);	2916	ev_run (EV_A_ 0);
1677		2917
1678	// stop timer again	2918	// stop timer again
1679	if (timeout >= 0)	2919	if (timeout >= 0)
1680	ev_timer_stop (EV_A_ &to);	2920	ev_timer_stop (EV_A_ &to);
1681		2921
1682	// stop io watchers again - their callbacks should have set	2922	// stop io watchers again - their callbacks should have set
1683	for (n = 0; n < nfds; ++n)	2923	for (n = 0; n < nfds; ++n)
1684	ev_io_stop (EV_A_ iow [n]);	2924	ev_io_stop (EV_A_ iow [n]);
1685		2925
1686	return got_events;	2926	return got_events;
1687	}	2927	}
1688		2928
1689		2929
1690	=head2 C<ev_embed> - when one backend isn't enough...	2930	=head2 C<ev_embed> - when one backend isn't enough...
1691		2931
1692	This is a rather advanced watcher type that lets you embed one event loop	2932	This is a rather advanced watcher type that lets you embed one event loop
…		…
1698	prioritise I/O.	2938	prioritise I/O.
1699		2939
1700	As an example for a bug workaround, the kqueue backend might only support	2940	As an example for a bug workaround, the kqueue backend might only support
1701	sockets on some platform, so it is unusable as generic backend, but you	2941	sockets on some platform, so it is unusable as generic backend, but you
1702	still want to make use of it because you have many sockets and it scales	2942	still want to make use of it because you have many sockets and it scales
1703	so nicely. In this case, you would create a kqueue-based loop and embed it	2943	so nicely. In this case, you would create a kqueue-based loop and embed
1704	into your default loop (which might use e.g. poll). Overall operation will	2944	it into your default loop (which might use e.g. poll). Overall operation
1705	be a bit slower because first libev has to poll and then call kevent, but	2945	will be a bit slower because first libev has to call C<poll> and then
1706	at least you can use both at what they are best.	2946	C<kevent>, but at least you can use both mechanisms for what they are
		2947	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1707		2948
1708	As for prioritising I/O: rarely you have the case where some fds have	2949	As for prioritising I/O: under rare circumstances you have the case where
1709	to be watched and handled very quickly (with low latency), and even	2950	some fds have to be watched and handled very quickly (with low latency),
1710	priorities and idle watchers might have too much overhead. In this case	2951	and even priorities and idle watchers might have too much overhead. In
1711	you would put all the high priority stuff in one loop and all the rest in	2952	this case you would put all the high priority stuff in one loop and all
1712	a second one, and embed the second one in the first.	2953	the rest in a second one, and embed the second one in the first.
1713		2954
1714	As long as the watcher is active, the callback will be invoked every time	2955	As long as the watcher is active, the callback will be invoked every
1715	there might be events pending in the embedded loop. The callback must then	2956	time there might be events pending in the embedded loop. The callback
1716	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2957	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1717	their callbacks (you could also start an idle watcher to give the embedded	2958	sweep and invoke their callbacks (the callback doesn't need to invoke the
1718	loop strictly lower priority for example). You can also set the callback	2959	C<ev_embed_sweep> function directly, it could also start an idle watcher
1719	to C<0>, in which case the embed watcher will automatically execute the	2960	to give the embedded loop strictly lower priority for example).
1720	embedded loop sweep.
1721		2961
1722	As long as the watcher is started it will automatically handle events. The	2962	You can also set the callback to C<0>, in which case the embed watcher
1723	callback will be invoked whenever some events have been handled. You can	2963	will automatically execute the embedded loop sweep whenever necessary.
1724	set the callback to C<0> to avoid having to specify one if you are not
1725	interested in that.
1726		2964
1727	Also, there have not currently been made special provisions for forking:	2965	Fork detection will be handled transparently while the C<ev_embed> watcher
1728	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2966	is active, i.e., the embedded loop will automatically be forked when the
1729	but you will also have to stop and restart any C<ev_embed> watchers	2967	embedding loop forks. In other cases, the user is responsible for calling
1730	yourself.	2968	C<ev_loop_fork> on the embedded loop.
1731		2969
1732	Unfortunately, not all backends are embeddable, only the ones returned by	2970	Unfortunately, not all backends are embeddable: only the ones returned by
1733	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2971	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1734	portable one.	2972	portable one.
1735		2973
1736	So when you want to use this feature you will always have to be prepared	2974	So when you want to use this feature you will always have to be prepared
1737	that you cannot get an embeddable loop. The recommended way to get around	2975	that you cannot get an embeddable loop. The recommended way to get around
1738	this is to have a separate variables for your embeddable loop, try to	2976	this is to have a separate variables for your embeddable loop, try to
1739	create it, and if that fails, use the normal loop for everything:	2977	create it, and if that fails, use the normal loop for everything.
1740		2978
1741	struct ev_loop *loop_hi = ev_default_init (0);	2979	=head3 C<ev_embed> and fork
1742	struct ev_loop *loop_lo = 0;
1743	struct ev_embed embed;
1744
1745	// see if there is a chance of getting one that works
1746	// (remember that a flags value of 0 means autodetection)
1747	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1748	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1749	: 0;
1750		2980
1751	// if we got one, then embed it, otherwise default to loop_hi	2981	While the C<ev_embed> watcher is running, forks in the embedding loop will
1752	if (loop_lo)	2982	automatically be applied to the embedded loop as well, so no special
1753	{	2983	fork handling is required in that case. When the watcher is not running,
1754	ev_embed_init (&embed, 0, loop_lo);	2984	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1755	ev_embed_start (loop_hi, &embed);	2985	as applicable.
1756	}
1757	else
1758	loop_lo = loop_hi;
1759		2986
1760	=head3 Watcher-Specific Functions and Data Members	2987	=head3 Watcher-Specific Functions and Data Members
1761		2988
1762	=over 4	2989	=over 4
1763		2990
…		…
1767		2994
1768	Configures the watcher to embed the given loop, which must be	2995	Configures the watcher to embed the given loop, which must be
1769	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2996	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1770	invoked automatically, otherwise it is the responsibility of the callback	2997	invoked automatically, otherwise it is the responsibility of the callback
1771	to invoke it (it will continue to be called until the sweep has been done,	2998	to invoke it (it will continue to be called until the sweep has been done,
1772	if you do not want thta, you need to temporarily stop the embed watcher).	2999	if you do not want that, you need to temporarily stop the embed watcher).
1773		3000
1774	=item ev_embed_sweep (loop, ev_embed *)	3001	=item ev_embed_sweep (loop, ev_embed *)
1775		3002
1776	Make a single, non-blocking sweep over the embedded loop. This works	3003	Make a single, non-blocking sweep over the embedded loop. This works
1777	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3004	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1778	apropriate way for embedded loops.	3005	appropriate way for embedded loops.
1779		3006
1780	=item struct ev_loop *loop [read-only]	3007	=item struct ev_loop *other [read-only]
1781		3008
1782	The embedded event loop.	3009	The embedded event loop.
1783		3010
1784	=back	3011	=back
		3012
		3013	=head3 Examples
		3014
		3015	Example: Try to get an embeddable event loop and embed it into the default
		3016	event loop. If that is not possible, use the default loop. The default
		3017	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3018	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3019	used).
		3020
		3021	struct ev_loop *loop_hi = ev_default_init (0);
		3022	struct ev_loop *loop_lo = 0;
		3023	ev_embed embed;
		3024
		3025	// see if there is a chance of getting one that works
		3026	// (remember that a flags value of 0 means autodetection)
		3027	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3028	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3029	: 0;
		3030
		3031	// if we got one, then embed it, otherwise default to loop_hi
		3032	if (loop_lo)
		3033	{
		3034	ev_embed_init (&embed, 0, loop_lo);
		3035	ev_embed_start (loop_hi, &embed);
		3036	}
		3037	else
		3038	loop_lo = loop_hi;
		3039
		3040	Example: Check if kqueue is available but not recommended and create
		3041	a kqueue backend for use with sockets (which usually work with any
		3042	kqueue implementation). Store the kqueue/socket-only event loop in
		3043	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3044
		3045	struct ev_loop *loop = ev_default_init (0);
		3046	struct ev_loop *loop_socket = 0;
		3047	ev_embed embed;
		3048
		3049	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3050	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3051	{
		3052	ev_embed_init (&embed, 0, loop_socket);
		3053	ev_embed_start (loop, &embed);
		3054	}
		3055
		3056	if (!loop_socket)
		3057	loop_socket = loop;
		3058
		3059	// now use loop_socket for all sockets, and loop for everything else
1785		3060
1786		3061
1787	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3062	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1788		3063
1789	Fork watchers are called when a C<fork ()> was detected (usually because	3064	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1792	event loop blocks next and before C<ev_check> watchers are being called,	3067	event loop blocks next and before C<ev_check> watchers are being called,
1793	and only in the child after the fork. If whoever good citizen calling	3068	and only in the child after the fork. If whoever good citizen calling
1794	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3069	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1795	handlers will be invoked, too, of course.	3070	handlers will be invoked, too, of course.
1796		3071
		3072	=head3 The special problem of life after fork - how is it possible?
		3073
		3074	Most uses of C<fork()> consist of forking, then some simple calls to set
		3075	up/change the process environment, followed by a call to C<exec()>. This
		3076	sequence should be handled by libev without any problems.
		3077
		3078	This changes when the application actually wants to do event handling
		3079	in the child, or both parent in child, in effect "continuing" after the
		3080	fork.
		3081
		3082	The default mode of operation (for libev, with application help to detect
		3083	forks) is to duplicate all the state in the child, as would be expected
		3084	when I<either> the parent I<or> the child process continues.
		3085
		3086	When both processes want to continue using libev, then this is usually the
		3087	wrong result. In that case, usually one process (typically the parent) is
		3088	supposed to continue with all watchers in place as before, while the other
		3089	process typically wants to start fresh, i.e. without any active watchers.
		3090
		3091	The cleanest and most efficient way to achieve that with libev is to
		3092	simply create a new event loop, which of course will be "empty", and
		3093	use that for new watchers. This has the advantage of not touching more
		3094	memory than necessary, and thus avoiding the copy-on-write, and the
		3095	disadvantage of having to use multiple event loops (which do not support
		3096	signal watchers).
		3097
		3098	When this is not possible, or you want to use the default loop for
		3099	other reasons, then in the process that wants to start "fresh", call
		3100	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3101	Destroying the default loop will "orphan" (not stop) all registered
		3102	watchers, so you have to be careful not to execute code that modifies
		3103	those watchers. Note also that in that case, you have to re-register any
		3104	signal watchers.
		3105
1797	=head3 Watcher-Specific Functions and Data Members	3106	=head3 Watcher-Specific Functions and Data Members
1798		3107
1799	=over 4	3108	=over 4
1800		3109
1801	=item ev_fork_init (ev_signal *, callback)	3110	=item ev_fork_init (ev_fork *, callback)
1802		3111
1803	Initialises and configures the fork watcher - it has no parameters of any	3112	Initialises and configures the fork watcher - it has no parameters of any
1804	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3113	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
1805	believe me.	3114	really.
1806		3115
1807	=back	3116	=back
1808		3117
1809		3118
		3119	=head2 C<ev_cleanup> - even the best things end
		3120
		3121	Cleanup watchers are called just before the event loop is being destroyed
		3122	by a call to C<ev_loop_destroy>.
		3123
		3124	While there is no guarantee that the event loop gets destroyed, cleanup
		3125	watchers provide a convenient method to install cleanup hooks for your
		3126	program, worker threads and so on - you just to make sure to destroy the
		3127	loop when you want them to be invoked.
		3128
		3129	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3130	all other watchers, they do not keep a reference to the event loop (which
		3131	makes a lot of sense if you think about it). Like all other watchers, you
		3132	can call libev functions in the callback, except C<ev_cleanup_start>.
		3133
		3134	=head3 Watcher-Specific Functions and Data Members
		3135
		3136	=over 4
		3137
		3138	=item ev_cleanup_init (ev_cleanup *, callback)
		3139
		3140	Initialises and configures the cleanup watcher - it has no parameters of
		3141	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3142	pointless, I assure you.
		3143
		3144	=back
		3145
		3146	Example: Register an atexit handler to destroy the default loop, so any
		3147	cleanup functions are called.
		3148
		3149	static void
		3150	program_exits (void)
		3151	{
		3152	ev_loop_destroy (EV_DEFAULT_UC);
		3153	}
		3154
		3155	...
		3156	atexit (program_exits);
		3157
		3158
		3159	=head2 C<ev_async> - how to wake up an event loop
		3160
		3161	In general, you cannot use an C<ev_run> from multiple threads or other
		3162	asynchronous sources such as signal handlers (as opposed to multiple event
		3163	loops - those are of course safe to use in different threads).
		3164
		3165	Sometimes, however, you need to wake up an event loop you do not control,
		3166	for example because it belongs to another thread. This is what C<ev_async>
		3167	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3168	it by calling C<ev_async_send>, which is thread- and signal safe.
		3169
		3170	This functionality is very similar to C<ev_signal> watchers, as signals,
		3171	too, are asynchronous in nature, and signals, too, will be compressed
		3172	(i.e. the number of callback invocations may be less than the number of
		3173	C<ev_async_sent> calls).
		3174
		3175	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3176	just the default loop.
		3177
		3178	=head3 Queueing
		3179
		3180	C<ev_async> does not support queueing of data in any way. The reason
		3181	is that the author does not know of a simple (or any) algorithm for a
		3182	multiple-writer-single-reader queue that works in all cases and doesn't
		3183	need elaborate support such as pthreads or unportable memory access
		3184	semantics.
		3185
		3186	That means that if you want to queue data, you have to provide your own
		3187	queue. But at least I can tell you how to implement locking around your
		3188	queue:
		3189
		3190	=over 4
		3191
		3192	=item queueing from a signal handler context
		3193
		3194	To implement race-free queueing, you simply add to the queue in the signal
		3195	handler but you block the signal handler in the watcher callback. Here is
		3196	an example that does that for some fictitious SIGUSR1 handler:
		3197
		3198	static ev_async mysig;
		3199
		3200	static void
		3201	sigusr1_handler (void)
		3202	{
		3203	sometype data;
		3204
		3205	// no locking etc.
		3206	queue_put (data);
		3207	ev_async_send (EV_DEFAULT_ &mysig);
		3208	}
		3209
		3210	static void
		3211	mysig_cb (EV_P_ ev_async *w, int revents)
		3212	{
		3213	sometype data;
		3214	sigset_t block, prev;
		3215
		3216	sigemptyset (&block);
		3217	sigaddset (&block, SIGUSR1);
		3218	sigprocmask (SIG_BLOCK, &block, &prev);
		3219
		3220	while (queue_get (&data))
		3221	process (data);
		3222
		3223	if (sigismember (&prev, SIGUSR1)
		3224	sigprocmask (SIG_UNBLOCK, &block, 0);
		3225	}
		3226
		3227	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3228	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3229	either...).
		3230
		3231	=item queueing from a thread context
		3232
		3233	The strategy for threads is different, as you cannot (easily) block
		3234	threads but you can easily preempt them, so to queue safely you need to
		3235	employ a traditional mutex lock, such as in this pthread example:
		3236
		3237	static ev_async mysig;
		3238	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3239
		3240	static void
		3241	otherthread (void)
		3242	{
		3243	// only need to lock the actual queueing operation
		3244	pthread_mutex_lock (&mymutex);
		3245	queue_put (data);
		3246	pthread_mutex_unlock (&mymutex);
		3247
		3248	ev_async_send (EV_DEFAULT_ &mysig);
		3249	}
		3250
		3251	static void
		3252	mysig_cb (EV_P_ ev_async *w, int revents)
		3253	{
		3254	pthread_mutex_lock (&mymutex);
		3255
		3256	while (queue_get (&data))
		3257	process (data);
		3258
		3259	pthread_mutex_unlock (&mymutex);
		3260	}
		3261
		3262	=back
		3263
		3264
		3265	=head3 Watcher-Specific Functions and Data Members
		3266
		3267	=over 4
		3268
		3269	=item ev_async_init (ev_async *, callback)
		3270
		3271	Initialises and configures the async watcher - it has no parameters of any
		3272	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3273	trust me.
		3274
		3275	=item ev_async_send (loop, ev_async *)
		3276
		3277	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3278	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3279	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3280	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3281	section below on what exactly this means).
		3282
		3283	Note that, as with other watchers in libev, multiple events might get
		3284	compressed into a single callback invocation (another way to look at this
		3285	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3286	reset when the event loop detects that).
		3287
		3288	This call incurs the overhead of a system call only once per event loop
		3289	iteration, so while the overhead might be noticeable, it doesn't apply to
		3290	repeated calls to C<ev_async_send> for the same event loop.
		3291
		3292	=item bool = ev_async_pending (ev_async *)
		3293
		3294	Returns a non-zero value when C<ev_async_send> has been called on the
		3295	watcher but the event has not yet been processed (or even noted) by the
		3296	event loop.
		3297
		3298	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3299	the loop iterates next and checks for the watcher to have become active,
		3300	it will reset the flag again. C<ev_async_pending> can be used to very
		3301	quickly check whether invoking the loop might be a good idea.
		3302
		3303	Not that this does I<not> check whether the watcher itself is pending,
		3304	only whether it has been requested to make this watcher pending: there
		3305	is a time window between the event loop checking and resetting the async
		3306	notification, and the callback being invoked.
		3307
		3308	=back
		3309
		3310
1810	=head1 OTHER FUNCTIONS	3311	=head1 OTHER FUNCTIONS
1811		3312
1812	There are some other functions of possible interest. Described. Here. Now.	3313	There are some other functions of possible interest. Described. Here. Now.
1813		3314
1814	=over 4	3315	=over 4
1815		3316
1816	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3317	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1817		3318
1818	This function combines a simple timer and an I/O watcher, calls your	3319	This function combines a simple timer and an I/O watcher, calls your
1819	callback on whichever event happens first and automatically stop both	3320	callback on whichever event happens first and automatically stops both
1820	watchers. This is useful if you want to wait for a single event on an fd	3321	watchers. This is useful if you want to wait for a single event on an fd
1821	or timeout without having to allocate/configure/start/stop/free one or	3322	or timeout without having to allocate/configure/start/stop/free one or
1822	more watchers yourself.	3323	more watchers yourself.
1823		3324
1824	If C<fd> is less than 0, then no I/O watcher will be started and events	3325	If C<fd> is less than 0, then no I/O watcher will be started and the
1825	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3326	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1826	C<events> set will be craeted and started.	3327	the given C<fd> and C<events> set will be created and started.
1827		3328
1828	If C<timeout> is less than 0, then no timeout watcher will be	3329	If C<timeout> is less than 0, then no timeout watcher will be
1829	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3330	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1830	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3331	repeat = 0) will be started. C<0> is a valid timeout.
1831	dubious value.
1832		3332
1833	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3333	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1834	passed an C<revents> set like normal event callbacks (a combination of	3334	passed an C<revents> set like normal event callbacks (a combination of
1835	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3335	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1836	value passed to C<ev_once>:	3336	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3337	a timeout and an io event at the same time - you probably should give io
		3338	events precedence.
1837		3339
		3340	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3341
1838	static void stdin_ready (int revents, void *arg)	3342	static void stdin_ready (int revents, void *arg)
1839	{	3343	{
1840	if (revents & EV_TIMEOUT)
1841	/* doh, nothing entered */;
1842	else if (revents & EV_READ)	3344	if (revents & EV_READ)
1843	/* stdin might have data for us, joy! */;	3345	/* stdin might have data for us, joy! */;
		3346	else if (revents & EV_TIMER)
		3347	/* doh, nothing entered */;
1844	}	3348	}
1845		3349
1846	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3350	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1847		3351
1848	=item ev_feed_event (ev_loop *, watcher *, int revents)
1849
1850	Feeds the given event set into the event loop, as if the specified event
1851	had happened for the specified watcher (which must be a pointer to an
1852	initialised but not necessarily started event watcher).
1853
1854	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3352	=item ev_feed_fd_event (loop, int fd, int revents)
1855		3353
1856	Feed an event on the given fd, as if a file descriptor backend detected	3354	Feed an event on the given fd, as if a file descriptor backend detected
1857	the given events it.	3355	the given events it.
1858		3356
1859	=item ev_feed_signal_event (ev_loop *loop, int signum)	3357	=item ev_feed_signal_event (loop, int signum)
1860		3358
1861	Feed an event as if the given signal occured (C<loop> must be the default	3359	Feed an event as if the given signal occurred (C<loop> must be the default
1862	loop!).	3360	loop!).
1863		3361
1864	=back	3362	=back
1865		3363
1866		3364
…		…
1882		3380
1883	=item * Priorities are not currently supported. Initialising priorities	3381	=item * Priorities are not currently supported. Initialising priorities
1884	will fail and all watchers will have the same priority, even though there	3382	will fail and all watchers will have the same priority, even though there
1885	is an ev_pri field.	3383	is an ev_pri field.
1886		3384
		3385	=item * In libevent, the last base created gets the signals, in libev, the
		3386	base that registered the signal gets the signals.
		3387
1887	=item * Other members are not supported.	3388	=item * Other members are not supported.
1888		3389
1889	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3390	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1890	to use the libev header file and library.	3391	to use the libev header file and library.
1891		3392
1892	=back	3393	=back
1893		3394
1894	=head1 C++ SUPPORT	3395	=head1 C++ SUPPORT
1895		3396
1896	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3397	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1897	you to use some convinience methods to start/stop watchers and also change	3398	you to use some convenience methods to start/stop watchers and also change
1898	the callback model to a model using method callbacks on objects.	3399	the callback model to a model using method callbacks on objects.
1899		3400
1900	To use it,	3401	To use it,
1901		3402
1902	#include <ev++.h>	3403	#include <ev++.h>
1903		3404
1904	This automatically includes F<ev.h> and puts all of its definitions (many	3405	This automatically includes F<ev.h> and puts all of its definitions (many
1905	of them macros) into the global namespace. All C++ specific things are	3406	of them macros) into the global namespace. All C++ specific things are
1906	put into the C<ev> namespace. It should support all the same embedding	3407	put into the C<ev> namespace. It should support all the same embedding
1907	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3408	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1941		3442
1942	=over 4	3443	=over 4
1943		3444
1944	=item ev::TYPE::TYPE ()	3445	=item ev::TYPE::TYPE ()
1945		3446
1946	=item ev::TYPE::TYPE (struct ev_loop *)	3447	=item ev::TYPE::TYPE (loop)
1947		3448
1948	=item ev::TYPE::~TYPE	3449	=item ev::TYPE::~TYPE
1949		3450
1950	The constructor (optionally) takes an event loop to associate the watcher	3451	The constructor (optionally) takes an event loop to associate the watcher
1951	with. If it is omitted, it will use C<EV_DEFAULT>.	3452	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
1974	your compiler is good :), then the method will be fully inlined into the	3475	your compiler is good :), then the method will be fully inlined into the
1975	thunking function, making it as fast as a direct C callback.	3476	thunking function, making it as fast as a direct C callback.
1976		3477
1977	Example: simple class declaration and watcher initialisation	3478	Example: simple class declaration and watcher initialisation
1978		3479
1979	struct myclass	3480	struct myclass
1980	{	3481	{
1981	void io_cb (ev::io &w, int revents) { }	3482	void io_cb (ev::io &w, int revents) { }
1982	}	3483	}
1983		3484
1984	myclass obj;	3485	myclass obj;
1985	ev::io iow;	3486	ev::io iow;
1986	iow.set <myclass, &myclass::io_cb> (&obj);	3487	iow.set <myclass, &myclass::io_cb> (&obj);
		3488
		3489	=item w->set (object *)
		3490
		3491	This is a variation of a method callback - leaving out the method to call
		3492	will default the method to C<operator ()>, which makes it possible to use
		3493	functor objects without having to manually specify the C<operator ()> all
		3494	the time. Incidentally, you can then also leave out the template argument
		3495	list.
		3496
		3497	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3498	int revents)>.
		3499
		3500	See the method-C<set> above for more details.
		3501
		3502	Example: use a functor object as callback.
		3503
		3504	struct myfunctor
		3505	{
		3506	void operator() (ev::io &w, int revents)
		3507	{
		3508	...
		3509	}
		3510	}
		3511
		3512	myfunctor f;
		3513
		3514	ev::io w;
		3515	w.set (&f);
1987		3516
1988	=item w->set<function> (void *data = 0)	3517	=item w->set<function> (void *data = 0)
1989		3518
1990	Also sets a callback, but uses a static method or plain function as	3519	Also sets a callback, but uses a static method or plain function as
1991	callback. The optional C<data> argument will be stored in the watcher's	3520	callback. The optional C<data> argument will be stored in the watcher's
…		…
1993		3522
1994	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3523	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
1995		3524
1996	See the method-C<set> above for more details.	3525	See the method-C<set> above for more details.
1997		3526
1998	Example:	3527	Example: Use a plain function as callback.
1999		3528
2000	static void io_cb (ev::io &w, int revents) { }	3529	static void io_cb (ev::io &w, int revents) { }
2001	iow.set <io_cb> ();	3530	iow.set <io_cb> ();
2002		3531
2003	=item w->set (struct ev_loop *)	3532	=item w->set (loop)
2004		3533
2005	Associates a different C<struct ev_loop> with this watcher. You can only	3534	Associates a different C<struct ev_loop> with this watcher. You can only
2006	do this when the watcher is inactive (and not pending either).	3535	do this when the watcher is inactive (and not pending either).
2007		3536
2008	=item w->set ([args])	3537	=item w->set ([arguments])
2009		3538
2010	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3539	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2011	called at least once. Unlike the C counterpart, an active watcher gets	3540	method or a suitable start method must be called at least once. Unlike the
2012	automatically stopped and restarted when reconfiguring it with this	3541	C counterpart, an active watcher gets automatically stopped and restarted
2013	method.	3542	when reconfiguring it with this method.
2014		3543
2015	=item w->start ()	3544	=item w->start ()
2016		3545
2017	Starts the watcher. Note that there is no C<loop> argument, as the	3546	Starts the watcher. Note that there is no C<loop> argument, as the
2018	constructor already stores the event loop.	3547	constructor already stores the event loop.
2019		3548
		3549	=item w->start ([arguments])
		3550
		3551	Instead of calling C<set> and C<start> methods separately, it is often
		3552	convenient to wrap them in one call. Uses the same type of arguments as
		3553	the configure C<set> method of the watcher.
		3554
2020	=item w->stop ()	3555	=item w->stop ()
2021		3556
2022	Stops the watcher if it is active. Again, no C<loop> argument.	3557	Stops the watcher if it is active. Again, no C<loop> argument.
2023		3558
2024	=item w->again () (C<ev::timer>, C<ev::periodic> only)	3559	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2036		3571
2037	=back	3572	=back
2038		3573
2039	=back	3574	=back
2040		3575
2041	Example: Define a class with an IO and idle watcher, start one of them in	3576	Example: Define a class with two I/O and idle watchers, start the I/O
2042	the constructor.	3577	watchers in the constructor.
2043		3578
2044	class myclass	3579	class myclass
2045	{	3580	{
2046	ev_io io; void io_cb (ev::io &w, int revents);	3581	ev::io io ; void io_cb (ev::io &w, int revents);
		3582	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
2047	ev_idle idle void idle_cb (ev::idle &w, int revents);	3583	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2048		3584
2049	myclass ();	3585	myclass (int fd)
2050	}	3586	{
2051
2052	myclass::myclass (int fd)
2053	{
2054	io .set <myclass, &myclass::io_cb > (this);	3587	io .set <myclass, &myclass::io_cb > (this);
		3588	io2 .set <myclass, &myclass::io2_cb > (this);
2055	idle.set <myclass, &myclass::idle_cb> (this);	3589	idle.set <myclass, &myclass::idle_cb> (this);
2056		3590
2057	io.start (fd, ev::READ);	3591	io.set (fd, ev::WRITE); // configure the watcher
		3592	io.start (); // start it whenever convenient
		3593
		3594	io2.start (fd, ev::READ); // set + start in one call
		3595	}
2058	}	3596	};
		3597
		3598
		3599	=head1 OTHER LANGUAGE BINDINGS
		3600
		3601	Libev does not offer other language bindings itself, but bindings for a
		3602	number of languages exist in the form of third-party packages. If you know
		3603	any interesting language binding in addition to the ones listed here, drop
		3604	me a note.
		3605
		3606	=over 4
		3607
		3608	=item Perl
		3609
		3610	The EV module implements the full libev API and is actually used to test
		3611	libev. EV is developed together with libev. Apart from the EV core module,
		3612	there are additional modules that implement libev-compatible interfaces
		3613	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3614	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3615	and C<EV::Glib>).
		3616
		3617	It can be found and installed via CPAN, its homepage is at
		3618	L<http://software.schmorp.de/pkg/EV>.
		3619
		3620	=item Python
		3621
		3622	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3623	seems to be quite complete and well-documented.
		3624
		3625	=item Ruby
		3626
		3627	Tony Arcieri has written a ruby extension that offers access to a subset
		3628	of the libev API and adds file handle abstractions, asynchronous DNS and
		3629	more on top of it. It can be found via gem servers. Its homepage is at
		3630	L<http://rev.rubyforge.org/>.
		3631
		3632	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3633	makes rev work even on mingw.
		3634
		3635	=item Haskell
		3636
		3637	A haskell binding to libev is available at
		3638	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3639
		3640	=item D
		3641
		3642	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3643	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3644
		3645	=item Ocaml
		3646
		3647	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3648	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3649
		3650	=item Lua
		3651
		3652	Brian Maher has written a partial interface to libev for lua (at the
		3653	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3654	L<http://github.com/brimworks/lua-ev>.
		3655
		3656	=back
2059		3657
2060		3658
2061	=head1 MACRO MAGIC	3659	=head1 MACRO MAGIC
2062		3660
2063	Libev can be compiled with a variety of options, the most fundamantal	3661	Libev can be compiled with a variety of options, the most fundamental
2064	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3662	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2065	functions and callbacks have an initial C<struct ev_loop *> argument.	3663	functions and callbacks have an initial C<struct ev_loop *> argument.
2066		3664
2067	To make it easier to write programs that cope with either variant, the	3665	To make it easier to write programs that cope with either variant, the
2068	following macros are defined:	3666	following macros are defined:
…		…
2073		3671
2074	This provides the loop I<argument> for functions, if one is required ("ev	3672	This provides the loop I<argument> for functions, if one is required ("ev
2075	loop argument"). The C<EV_A> form is used when this is the sole argument,	3673	loop argument"). The C<EV_A> form is used when this is the sole argument,
2076	C<EV_A_> is used when other arguments are following. Example:	3674	C<EV_A_> is used when other arguments are following. Example:
2077		3675
2078	ev_unref (EV_A);	3676	ev_unref (EV_A);
2079	ev_timer_add (EV_A_ watcher);	3677	ev_timer_add (EV_A_ watcher);
2080	ev_loop (EV_A_ 0);	3678	ev_run (EV_A_ 0);
2081		3679
2082	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3680	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2083	which is often provided by the following macro.	3681	which is often provided by the following macro.
2084		3682
2085	=item C<EV_P>, C<EV_P_>	3683	=item C<EV_P>, C<EV_P_>
2086		3684
2087	This provides the loop I<parameter> for functions, if one is required ("ev	3685	This provides the loop I<parameter> for functions, if one is required ("ev
2088	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3686	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2089	C<EV_P_> is used when other parameters are following. Example:	3687	C<EV_P_> is used when other parameters are following. Example:
2090		3688
2091	// this is how ev_unref is being declared	3689	// this is how ev_unref is being declared
2092	static void ev_unref (EV_P);	3690	static void ev_unref (EV_P);
2093		3691
2094	// this is how you can declare your typical callback	3692	// this is how you can declare your typical callback
2095	static void cb (EV_P_ ev_timer *w, int revents)	3693	static void cb (EV_P_ ev_timer *w, int revents)
2096		3694
2097	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3695	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2098	suitable for use with C<EV_A>.	3696	suitable for use with C<EV_A>.
2099		3697
2100	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3698	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2101		3699
2102	Similar to the other two macros, this gives you the value of the default	3700	Similar to the other two macros, this gives you the value of the default
2103	loop, if multiple loops are supported ("ev loop default").	3701	loop, if multiple loops are supported ("ev loop default").
		3702
		3703	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3704
		3705	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3706	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3707	is undefined when the default loop has not been initialised by a previous
		3708	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3709
		3710	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3711	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2104		3712
2105	=back	3713	=back
2106		3714
2107	Example: Declare and initialise a check watcher, utilising the above	3715	Example: Declare and initialise a check watcher, utilising the above
2108	macros so it will work regardless of whether multiple loops are supported	3716	macros so it will work regardless of whether multiple loops are supported
2109	or not.	3717	or not.
2110		3718
2111	static void	3719	static void
2112	check_cb (EV_P_ ev_timer *w, int revents)	3720	check_cb (EV_P_ ev_timer *w, int revents)
2113	{	3721	{
2114	ev_check_stop (EV_A_ w);	3722	ev_check_stop (EV_A_ w);
2115	}	3723	}
2116		3724
2117	ev_check check;	3725	ev_check check;
2118	ev_check_init (&check, check_cb);	3726	ev_check_init (&check, check_cb);
2119	ev_check_start (EV_DEFAULT_ &check);	3727	ev_check_start (EV_DEFAULT_ &check);
2120	ev_loop (EV_DEFAULT_ 0);	3728	ev_run (EV_DEFAULT_ 0);
2121		3729
2122	=head1 EMBEDDING	3730	=head1 EMBEDDING
2123		3731
2124	Libev can (and often is) directly embedded into host	3732	Libev can (and often is) directly embedded into host
2125	applications. Examples of applications that embed it include the Deliantra	3733	applications. Examples of applications that embed it include the Deliantra
2126	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3734	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
2127	and rxvt-unicode.	3735	and rxvt-unicode.
2128		3736
2129	The goal is to enable you to just copy the neecssary files into your	3737	The goal is to enable you to just copy the necessary files into your
2130	source directory without having to change even a single line in them, so	3738	source directory without having to change even a single line in them, so
2131	you can easily upgrade by simply copying (or having a checked-out copy of	3739	you can easily upgrade by simply copying (or having a checked-out copy of
2132	libev somewhere in your source tree).	3740	libev somewhere in your source tree).
2133		3741
2134	=head2 FILESETS	3742	=head2 FILESETS
2135		3743
2136	Depending on what features you need you need to include one or more sets of files	3744	Depending on what features you need you need to include one or more sets of files
2137	in your app.	3745	in your application.
2138		3746
2139	=head3 CORE EVENT LOOP	3747	=head3 CORE EVENT LOOP
2140		3748
2141	To include only the libev core (all the C<ev_*> functions), with manual	3749	To include only the libev core (all the C<ev_*> functions), with manual
2142	configuration (no autoconf):	3750	configuration (no autoconf):
2143		3751
2144	#define EV_STANDALONE 1	3752	#define EV_STANDALONE 1
2145	#include "ev.c"	3753	#include "ev.c"
2146		3754
2147	This will automatically include F<ev.h>, too, and should be done in a	3755	This will automatically include F<ev.h>, too, and should be done in a
2148	single C source file only to provide the function implementations. To use	3756	single C source file only to provide the function implementations. To use
2149	it, do the same for F<ev.h> in all files wishing to use this API (best	3757	it, do the same for F<ev.h> in all files wishing to use this API (best
2150	done by writing a wrapper around F<ev.h> that you can include instead and	3758	done by writing a wrapper around F<ev.h> that you can include instead and
2151	where you can put other configuration options):	3759	where you can put other configuration options):
2152		3760
2153	#define EV_STANDALONE 1	3761	#define EV_STANDALONE 1
2154	#include "ev.h"	3762	#include "ev.h"
2155		3763
2156	Both header files and implementation files can be compiled with a C++	3764	Both header files and implementation files can be compiled with a C++
2157	compiler (at least, thats a stated goal, and breakage will be treated	3765	compiler (at least, that's a stated goal, and breakage will be treated
2158	as a bug).	3766	as a bug).
2159		3767
2160	You need the following files in your source tree, or in a directory	3768	You need the following files in your source tree, or in a directory
2161	in your include path (e.g. in libev/ when using -Ilibev):	3769	in your include path (e.g. in libev/ when using -Ilibev):
2162		3770
2163	ev.h	3771	ev.h
2164	ev.c	3772	ev.c
2165	ev_vars.h	3773	ev_vars.h
2166	ev_wrap.h	3774	ev_wrap.h
2167		3775
2168	ev_win32.c required on win32 platforms only	3776	ev_win32.c required on win32 platforms only
2169		3777
2170	ev_select.c only when select backend is enabled (which is enabled by default)	3778	ev_select.c only when select backend is enabled (which is enabled by default)
2171	ev_poll.c only when poll backend is enabled (disabled by default)	3779	ev_poll.c only when poll backend is enabled (disabled by default)
2172	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3780	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2173	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3781	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2174	ev_port.c only when the solaris port backend is enabled (disabled by default)	3782	ev_port.c only when the solaris port backend is enabled (disabled by default)
2175		3783
2176	F<ev.c> includes the backend files directly when enabled, so you only need	3784	F<ev.c> includes the backend files directly when enabled, so you only need
2177	to compile this single file.	3785	to compile this single file.
2178		3786
2179	=head3 LIBEVENT COMPATIBILITY API	3787	=head3 LIBEVENT COMPATIBILITY API
2180		3788
2181	To include the libevent compatibility API, also include:	3789	To include the libevent compatibility API, also include:
2182		3790
2183	#include "event.c"	3791	#include "event.c"
2184		3792
2185	in the file including F<ev.c>, and:	3793	in the file including F<ev.c>, and:
2186		3794
2187	#include "event.h"	3795	#include "event.h"
2188		3796
2189	in the files that want to use the libevent API. This also includes F<ev.h>.	3797	in the files that want to use the libevent API. This also includes F<ev.h>.
2190		3798
2191	You need the following additional files for this:	3799	You need the following additional files for this:
2192		3800
2193	event.h	3801	event.h
2194	event.c	3802	event.c
2195		3803
2196	=head3 AUTOCONF SUPPORT	3804	=head3 AUTOCONF SUPPORT
2197		3805
2198	Instead of using C<EV_STANDALONE=1> and providing your config in	3806	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2199	whatever way you want, you can also C<m4_include([libev.m4])> in your	3807	whatever way you want, you can also C<m4_include([libev.m4])> in your
2200	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3808	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2201	include F<config.h> and configure itself accordingly.	3809	include F<config.h> and configure itself accordingly.
2202		3810
2203	For this of course you need the m4 file:	3811	For this of course you need the m4 file:
2204		3812
2205	libev.m4	3813	libev.m4
2206		3814
2207	=head2 PREPROCESSOR SYMBOLS/MACROS	3815	=head2 PREPROCESSOR SYMBOLS/MACROS
2208		3816
2209	Libev can be configured via a variety of preprocessor symbols you have to define	3817	Libev can be configured via a variety of preprocessor symbols you have to
2210	before including any of its files. The default is not to build for multiplicity	3818	define before including (or compiling) any of its files. The default in
2211	and only include the select backend.	3819	the absence of autoconf is documented for every option.
		3820
		3821	Symbols marked with "(h)" do not change the ABI, and can have different
		3822	values when compiling libev vs. including F<ev.h>, so it is permissible
		3823	to redefine them before including F<ev.h> without breaking compatibility
		3824	to a compiled library. All other symbols change the ABI, which means all
		3825	users of libev and the libev code itself must be compiled with compatible
		3826	settings.
2212		3827
2213	=over 4	3828	=over 4
2214		3829
		3830	=item EV_COMPAT3 (h)
		3831
		3832	Backwards compatibility is a major concern for libev. This is why this
		3833	release of libev comes with wrappers for the functions and symbols that
		3834	have been renamed between libev version 3 and 4.
		3835
		3836	You can disable these wrappers (to test compatibility with future
		3837	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		3838	sources. This has the additional advantage that you can drop the C<struct>
		3839	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		3840	typedef in that case.
		3841
		3842	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		3843	and in some even more future version the compatibility code will be
		3844	removed completely.
		3845
2215	=item EV_STANDALONE	3846	=item EV_STANDALONE (h)
2216		3847
2217	Must always be C<1> if you do not use autoconf configuration, which	3848	Must always be C<1> if you do not use autoconf configuration, which
2218	keeps libev from including F<config.h>, and it also defines dummy	3849	keeps libev from including F<config.h>, and it also defines dummy
2219	implementations for some libevent functions (such as logging, which is not	3850	implementations for some libevent functions (such as logging, which is not
2220	supported). It will also not define any of the structs usually found in	3851	supported). It will also not define any of the structs usually found in
2221	F<event.h> that are not directly supported by the libev core alone.	3852	F<event.h> that are not directly supported by the libev core alone.
2222		3853
		3854	In standalone mode, libev will still try to automatically deduce the
		3855	configuration, but has to be more conservative.
		3856
2223	=item EV_USE_MONOTONIC	3857	=item EV_USE_MONOTONIC
2224		3858
2225	If defined to be C<1>, libev will try to detect the availability of the	3859	If defined to be C<1>, libev will try to detect the availability of the
2226	monotonic clock option at both compiletime and runtime. Otherwise no use	3860	monotonic clock option at both compile time and runtime. Otherwise no
2227	of the monotonic clock option will be attempted. If you enable this, you	3861	use of the monotonic clock option will be attempted. If you enable this,
2228	usually have to link against librt or something similar. Enabling it when	3862	you usually have to link against librt or something similar. Enabling it
2229	the functionality isn't available is safe, though, althoguh you have	3863	when the functionality isn't available is safe, though, although you have
2230	to make sure you link against any libraries where the C<clock_gettime>	3864	to make sure you link against any libraries where the C<clock_gettime>
2231	function is hiding in (often F<-lrt>).	3865	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2232		3866
2233	=item EV_USE_REALTIME	3867	=item EV_USE_REALTIME
2234		3868
2235	If defined to be C<1>, libev will try to detect the availability of the	3869	If defined to be C<1>, libev will try to detect the availability of the
2236	realtime clock option at compiletime (and assume its availability at	3870	real-time clock option at compile time (and assume its availability
2237	runtime if successful). Otherwise no use of the realtime clock option will	3871	at runtime if successful). Otherwise no use of the real-time clock
2238	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3872	option will be attempted. This effectively replaces C<gettimeofday>
2239	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3873	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2240	in the description of C<EV_USE_MONOTONIC>, though.	3874	correctness. See the note about libraries in the description of
		3875	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3876	C<EV_USE_CLOCK_SYSCALL>.
		3877
		3878	=item EV_USE_CLOCK_SYSCALL
		3879
		3880	If defined to be C<1>, libev will try to use a direct syscall instead
		3881	of calling the system-provided C<clock_gettime> function. This option
		3882	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3883	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3884	programs needlessly. Using a direct syscall is slightly slower (in
		3885	theory), because no optimised vdso implementation can be used, but avoids
		3886	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3887	higher, as it simplifies linking (no need for C<-lrt>).
		3888
		3889	=item EV_USE_NANOSLEEP
		3890
		3891	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3892	and will use it for delays. Otherwise it will use C<select ()>.
		3893
		3894	=item EV_USE_EVENTFD
		3895
		3896	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3897	available and will probe for kernel support at runtime. This will improve
		3898	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3899	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3900	2.7 or newer, otherwise disabled.
2241		3901
2242	=item EV_USE_SELECT	3902	=item EV_USE_SELECT
2243		3903
2244	If undefined or defined to be C<1>, libev will compile in support for the	3904	If undefined or defined to be C<1>, libev will compile in support for the
2245	C<select>(2) backend. No attempt at autodetection will be done: if no	3905	C<select>(2) backend. No attempt at auto-detection will be done: if no
2246	other method takes over, select will be it. Otherwise the select backend	3906	other method takes over, select will be it. Otherwise the select backend
2247	will not be compiled in.	3907	will not be compiled in.
2248		3908
2249	=item EV_SELECT_USE_FD_SET	3909	=item EV_SELECT_USE_FD_SET
2250		3910
2251	If defined to C<1>, then the select backend will use the system C<fd_set>	3911	If defined to C<1>, then the select backend will use the system C<fd_set>
2252	structure. This is useful if libev doesn't compile due to a missing	3912	structure. This is useful if libev doesn't compile due to a missing
2253	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3913	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2254	exotic systems. This usually limits the range of file descriptors to some	3914	on exotic systems. This usually limits the range of file descriptors to
2255	low limit such as 1024 or might have other limitations (winsocket only	3915	some low limit such as 1024 or might have other limitations (winsocket
2256	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3916	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2257	influence the size of the C<fd_set> used.	3917	configures the maximum size of the C<fd_set>.
2258		3918
2259	=item EV_SELECT_IS_WINSOCKET	3919	=item EV_SELECT_IS_WINSOCKET
2260		3920
2261	When defined to C<1>, the select backend will assume that	3921	When defined to C<1>, the select backend will assume that
2262	select/socket/connect etc. don't understand file descriptors but	3922	select/socket/connect etc. don't understand file descriptors but
…		…
2264	be used is the winsock select). This means that it will call	3924	be used is the winsock select). This means that it will call
2265	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3925	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2266	it is assumed that all these functions actually work on fds, even	3926	it is assumed that all these functions actually work on fds, even
2267	on win32. Should not be defined on non-win32 platforms.	3927	on win32. Should not be defined on non-win32 platforms.
2268		3928
		3929	=item EV_FD_TO_WIN32_HANDLE(fd)
		3930
		3931	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3932	file descriptors to socket handles. When not defining this symbol (the
		3933	default), then libev will call C<_get_osfhandle>, which is usually
		3934	correct. In some cases, programs use their own file descriptor management,
		3935	in which case they can provide this function to map fds to socket handles.
		3936
		3937	=item EV_WIN32_HANDLE_TO_FD(handle)
		3938
		3939	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3940	using the standard C<_open_osfhandle> function. For programs implementing
		3941	their own fd to handle mapping, overwriting this function makes it easier
		3942	to do so. This can be done by defining this macro to an appropriate value.
		3943
		3944	=item EV_WIN32_CLOSE_FD(fd)
		3945
		3946	If programs implement their own fd to handle mapping on win32, then this
		3947	macro can be used to override the C<close> function, useful to unregister
		3948	file descriptors again. Note that the replacement function has to close
		3949	the underlying OS handle.
		3950
2269	=item EV_USE_POLL	3951	=item EV_USE_POLL
2270		3952
2271	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3953	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2272	backend. Otherwise it will be enabled on non-win32 platforms. It	3954	backend. Otherwise it will be enabled on non-win32 platforms. It
2273	takes precedence over select.	3955	takes precedence over select.
2274		3956
2275	=item EV_USE_EPOLL	3957	=item EV_USE_EPOLL
2276		3958
2277	If defined to be C<1>, libev will compile in support for the Linux	3959	If defined to be C<1>, libev will compile in support for the Linux
2278	C<epoll>(7) backend. Its availability will be detected at runtime,	3960	C<epoll>(7) backend. Its availability will be detected at runtime,
2279	otherwise another method will be used as fallback. This is the	3961	otherwise another method will be used as fallback. This is the preferred
2280	preferred backend for GNU/Linux systems.	3962	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3963	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2281		3964
2282	=item EV_USE_KQUEUE	3965	=item EV_USE_KQUEUE
2283		3966
2284	If defined to be C<1>, libev will compile in support for the BSD style	3967	If defined to be C<1>, libev will compile in support for the BSD style
2285	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3968	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2298	otherwise another method will be used as fallback. This is the preferred	3981	otherwise another method will be used as fallback. This is the preferred
2299	backend for Solaris 10 systems.	3982	backend for Solaris 10 systems.
2300		3983
2301	=item EV_USE_DEVPOLL	3984	=item EV_USE_DEVPOLL
2302		3985
2303	reserved for future expansion, works like the USE symbols above.	3986	Reserved for future expansion, works like the USE symbols above.
2304		3987
2305	=item EV_USE_INOTIFY	3988	=item EV_USE_INOTIFY
2306		3989
2307	If defined to be C<1>, libev will compile in support for the Linux inotify	3990	If defined to be C<1>, libev will compile in support for the Linux inotify
2308	interface to speed up C<ev_stat> watchers. Its actual availability will	3991	interface to speed up C<ev_stat> watchers. Its actual availability will
2309	be detected at runtime.	3992	be detected at runtime. If undefined, it will be enabled if the headers
		3993	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2310		3994
		3995	=item EV_ATOMIC_T
		3996
		3997	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3998	access is atomic with respect to other threads or signal contexts. No such
		3999	type is easily found in the C language, so you can provide your own type
		4000	that you know is safe for your purposes. It is used both for signal handler "locking"
		4001	as well as for signal and thread safety in C<ev_async> watchers.
		4002
		4003	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4004	(from F<signal.h>), which is usually good enough on most platforms.
		4005
2311	=item EV_H	4006	=item EV_H (h)
2312		4007
2313	The name of the F<ev.h> header file used to include it. The default if	4008	The name of the F<ev.h> header file used to include it. The default if
2314	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	4009	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2315	can be used to virtually rename the F<ev.h> header file in case of conflicts.	4010	used to virtually rename the F<ev.h> header file in case of conflicts.
2316		4011
2317	=item EV_CONFIG_H	4012	=item EV_CONFIG_H (h)
2318		4013
2319	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4014	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2320	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4015	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2321	C<EV_H>, above.	4016	C<EV_H>, above.
2322		4017
2323	=item EV_EVENT_H	4018	=item EV_EVENT_H (h)
2324		4019
2325	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4020	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2326	of how the F<event.h> header can be found.	4021	of how the F<event.h> header can be found, the default is C<"event.h">.
2327		4022
2328	=item EV_PROTOTYPES	4023	=item EV_PROTOTYPES (h)
2329		4024
2330	If defined to be C<0>, then F<ev.h> will not define any function	4025	If defined to be C<0>, then F<ev.h> will not define any function
2331	prototypes, but still define all the structs and other symbols. This is	4026	prototypes, but still define all the structs and other symbols. This is
2332	occasionally useful if you want to provide your own wrapper functions	4027	occasionally useful if you want to provide your own wrapper functions
2333	around libev functions.	4028	around libev functions.
…		…
2352	When doing priority-based operations, libev usually has to linearly search	4047	When doing priority-based operations, libev usually has to linearly search
2353	all the priorities, so having many of them (hundreds) uses a lot of space	4048	all the priorities, so having many of them (hundreds) uses a lot of space
2354	and time, so using the defaults of five priorities (-2 .. +2) is usually	4049	and time, so using the defaults of five priorities (-2 .. +2) is usually
2355	fine.	4050	fine.
2356		4051
2357	If your embedding app does not need any priorities, defining these both to	4052	If your embedding application does not need any priorities, defining these
2358	C<0> will save some memory and cpu.	4053	both to C<0> will save some memory and CPU.
2359		4054
2360	=item EV_PERIODIC_ENABLE	4055	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4056	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4057	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2361		4058
2362	If undefined or defined to be C<1>, then periodic timers are supported. If	4059	If undefined or defined to be C<1> (and the platform supports it), then
2363	defined to be C<0>, then they are not. Disabling them saves a few kB of	4060	the respective watcher type is supported. If defined to be C<0>, then it
2364	code.	4061	is not. Disabling watcher types mainly saves code size.
2365		4062
2366	=item EV_IDLE_ENABLE	4063	=item EV_FEATURES
2367
2368	If undefined or defined to be C<1>, then idle watchers are supported. If
2369	defined to be C<0>, then they are not. Disabling them saves a few kB of
2370	code.
2371
2372	=item EV_EMBED_ENABLE
2373
2374	If undefined or defined to be C<1>, then embed watchers are supported. If
2375	defined to be C<0>, then they are not.
2376
2377	=item EV_STAT_ENABLE
2378
2379	If undefined or defined to be C<1>, then stat watchers are supported. If
2380	defined to be C<0>, then they are not.
2381
2382	=item EV_FORK_ENABLE
2383
2384	If undefined or defined to be C<1>, then fork watchers are supported. If
2385	defined to be C<0>, then they are not.
2386
2387	=item EV_MINIMAL
2388		4064
2389	If you need to shave off some kilobytes of code at the expense of some	4065	If you need to shave off some kilobytes of code at the expense of some
2390	speed, define this symbol to C<1>. Currently only used for gcc to override	4066	speed (but with the full API), you can define this symbol to request
2391	some inlining decisions, saves roughly 30% codesize of amd64.	4067	certain subsets of functionality. The default is to enable all features
		4068	that can be enabled on the platform.
		4069
		4070	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4071	with some broad features you want) and then selectively re-enable
		4072	additional parts you want, for example if you want everything minimal,
		4073	but multiple event loop support, async and child watchers and the poll
		4074	backend, use this:
		4075
		4076	#define EV_FEATURES 0
		4077	#define EV_MULTIPLICITY 1
		4078	#define EV_USE_POLL 1
		4079	#define EV_CHILD_ENABLE 1
		4080	#define EV_ASYNC_ENABLE 1
		4081
		4082	The actual value is a bitset, it can be a combination of the following
		4083	values:
		4084
		4085	=over 4
		4086
		4087	=item C<1> - faster/larger code
		4088
		4089	Use larger code to speed up some operations.
		4090
		4091	Currently this is used to override some inlining decisions (enlarging the
		4092	code size by roughly 30% on amd64).
		4093
		4094	When optimising for size, use of compiler flags such as C<-Os> with
		4095	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4096	assertions.
		4097
		4098	=item C<2> - faster/larger data structures
		4099
		4100	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4101	hash table sizes and so on. This will usually further increase code size
		4102	and can additionally have an effect on the size of data structures at
		4103	runtime.
		4104
		4105	=item C<4> - full API configuration
		4106
		4107	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4108	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4109
		4110	=item C<8> - full API
		4111
		4112	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4113	details on which parts of the API are still available without this
		4114	feature, and do not complain if this subset changes over time.
		4115
		4116	=item C<16> - enable all optional watcher types
		4117
		4118	Enables all optional watcher types. If you want to selectively enable
		4119	only some watcher types other than I/O and timers (e.g. prepare,
		4120	embed, async, child...) you can enable them manually by defining
		4121	C<EV_watchertype_ENABLE> to C<1> instead.
		4122
		4123	=item C<32> - enable all backends
		4124
		4125	This enables all backends - without this feature, you need to enable at
		4126	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4127
		4128	=item C<64> - enable OS-specific "helper" APIs
		4129
		4130	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4131	default.
		4132
		4133	=back
		4134
		4135	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4136	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4137	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4138	watchers, timers and monotonic clock support.
		4139
		4140	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4141	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4142	your program might be left out as well - a binary starting a timer and an
		4143	I/O watcher then might come out at only 5Kb.
		4144
		4145	=item EV_AVOID_STDIO
		4146
		4147	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4148	functions (printf, scanf, perror etc.). This will increase the code size
		4149	somewhat, but if your program doesn't otherwise depend on stdio and your
		4150	libc allows it, this avoids linking in the stdio library which is quite
		4151	big.
		4152
		4153	Note that error messages might become less precise when this option is
		4154	enabled.
		4155
		4156	=item EV_NSIG
		4157
		4158	The highest supported signal number, +1 (or, the number of
		4159	signals): Normally, libev tries to deduce the maximum number of signals
		4160	automatically, but sometimes this fails, in which case it can be
		4161	specified. Also, using a lower number than detected (C<32> should be
		4162	good for about any system in existence) can save some memory, as libev
		4163	statically allocates some 12-24 bytes per signal number.
2392		4164
2393	=item EV_PID_HASHSIZE	4165	=item EV_PID_HASHSIZE
2394		4166
2395	C<ev_child> watchers use a small hash table to distribute workload by	4167	C<ev_child> watchers use a small hash table to distribute workload by
2396	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4168	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2397	than enough. If you need to manage thousands of children you might want to	4169	usually more than enough. If you need to manage thousands of children you
2398	increase this value (I<must> be a power of two).	4170	might want to increase this value (I<must> be a power of two).
2399		4171
2400	=item EV_INOTIFY_HASHSIZE	4172	=item EV_INOTIFY_HASHSIZE
2401		4173
2402	C<ev_staz> watchers use a small hash table to distribute workload by	4174	C<ev_stat> watchers use a small hash table to distribute workload by
2403	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4175	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2404	usually more than enough. If you need to manage thousands of C<ev_stat>	4176	disabled), usually more than enough. If you need to manage thousands of
2405	watchers you might want to increase this value (I<must> be a power of	4177	C<ev_stat> watchers you might want to increase this value (I<must> be a
2406	two).	4178	power of two).
		4179
		4180	=item EV_USE_4HEAP
		4181
		4182	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4183	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4184	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4185	faster performance with many (thousands) of watchers.
		4186
		4187	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4188	will be C<0>.
		4189
		4190	=item EV_HEAP_CACHE_AT
		4191
		4192	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4193	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4194	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4195	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4196	but avoids random read accesses on heap changes. This improves performance
		4197	noticeably with many (hundreds) of watchers.
		4198
		4199	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4200	will be C<0>.
		4201
		4202	=item EV_VERIFY
		4203
		4204	Controls how much internal verification (see C<ev_verify ()>) will
		4205	be done: If set to C<0>, no internal verification code will be compiled
		4206	in. If set to C<1>, then verification code will be compiled in, but not
		4207	called. If set to C<2>, then the internal verification code will be
		4208	called once per loop, which can slow down libev. If set to C<3>, then the
		4209	verification code will be called very frequently, which will slow down
		4210	libev considerably.
		4211
		4212	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4213	will be C<0>.
2407		4214
2408	=item EV_COMMON	4215	=item EV_COMMON
2409		4216
2410	By default, all watchers have a C<void *data> member. By redefining	4217	By default, all watchers have a C<void *data> member. By redefining
2411	this macro to a something else you can include more and other types of	4218	this macro to something else you can include more and other types of
2412	members. You have to define it each time you include one of the files,	4219	members. You have to define it each time you include one of the files,
2413	though, and it must be identical each time.	4220	though, and it must be identical each time.
2414		4221
2415	For example, the perl EV module uses something like this:	4222	For example, the perl EV module uses something like this:
2416		4223
2417	#define EV_COMMON \	4224	#define EV_COMMON \
2418	SV *self; /* contains this struct */ \	4225	SV *self; /* contains this struct */ \
2419	SV *cb_sv, *fh /* note no trailing ";" */	4226	SV *cb_sv, *fh /* note no trailing ";" */
2420		4227
2421	=item EV_CB_DECLARE (type)	4228	=item EV_CB_DECLARE (type)
2422		4229
2423	=item EV_CB_INVOKE (watcher, revents)	4230	=item EV_CB_INVOKE (watcher, revents)
2424		4231
2425	=item ev_set_cb (ev, cb)	4232	=item ev_set_cb (ev, cb)
2426		4233
2427	Can be used to change the callback member declaration in each watcher,	4234	Can be used to change the callback member declaration in each watcher,
2428	and the way callbacks are invoked and set. Must expand to a struct member	4235	and the way callbacks are invoked and set. Must expand to a struct member
2429	definition and a statement, respectively. See the F<ev.v> header file for	4236	definition and a statement, respectively. See the F<ev.h> header file for
2430	their default definitions. One possible use for overriding these is to	4237	their default definitions. One possible use for overriding these is to
2431	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4238	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2432	method calls instead of plain function calls in C++.	4239	method calls instead of plain function calls in C++.
		4240
		4241	=back
		4242
		4243	=head2 EXPORTED API SYMBOLS
		4244
		4245	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4246	exported symbols, you can use the provided F<Symbol.*> files which list
		4247	all public symbols, one per line:
		4248
		4249	Symbols.ev for libev proper
		4250	Symbols.event for the libevent emulation
		4251
		4252	This can also be used to rename all public symbols to avoid clashes with
		4253	multiple versions of libev linked together (which is obviously bad in
		4254	itself, but sometimes it is inconvenient to avoid this).
		4255
		4256	A sed command like this will create wrapper C<#define>'s that you need to
		4257	include before including F<ev.h>:
		4258
		4259	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4260
		4261	This would create a file F<wrap.h> which essentially looks like this:
		4262
		4263	#define ev_backend myprefix_ev_backend
		4264	#define ev_check_start myprefix_ev_check_start
		4265	#define ev_check_stop myprefix_ev_check_stop
		4266	...
2433		4267
2434	=head2 EXAMPLES	4268	=head2 EXAMPLES
2435		4269
2436	For a real-world example of a program the includes libev	4270	For a real-world example of a program the includes libev
2437	verbatim, you can have a look at the EV perl module	4271	verbatim, you can have a look at the EV perl module
…		…
2442	file.	4276	file.
2443		4277
2444	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4278	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2445	that everybody includes and which overrides some configure choices:	4279	that everybody includes and which overrides some configure choices:
2446		4280
2447	#define EV_MINIMAL 1	4281	#define EV_FEATURES 8
2448	#define EV_USE_POLL 0	4282	#define EV_USE_SELECT 1
2449	#define EV_MULTIPLICITY 0
2450	#define EV_PERIODIC_ENABLE 0	4283	#define EV_PREPARE_ENABLE 1
		4284	#define EV_IDLE_ENABLE 1
2451	#define EV_STAT_ENABLE 0	4285	#define EV_SIGNAL_ENABLE 1
2452	#define EV_FORK_ENABLE 0	4286	#define EV_CHILD_ENABLE 1
		4287	#define EV_USE_STDEXCEPT 0
2453	#define EV_CONFIG_H <config.h>	4288	#define EV_CONFIG_H <config.h>
2454	#define EV_MINPRI 0
2455	#define EV_MAXPRI 0
2456		4289
2457	#include "ev++.h"	4290	#include "ev++.h"
2458		4291
2459	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4292	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2460		4293
2461	#include "ev_cpp.h"	4294	#include "ev_cpp.h"
2462	#include "ev.c"	4295	#include "ev.c"
2463		4296
		4297	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2464		4298
		4299	=head2 THREADS AND COROUTINES
		4300
		4301	=head3 THREADS
		4302
		4303	All libev functions are reentrant and thread-safe unless explicitly
		4304	documented otherwise, but libev implements no locking itself. This means
		4305	that you can use as many loops as you want in parallel, as long as there
		4306	are no concurrent calls into any libev function with the same loop
		4307	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4308	of course): libev guarantees that different event loops share no data
		4309	structures that need any locking.
		4310
		4311	Or to put it differently: calls with different loop parameters can be done
		4312	concurrently from multiple threads, calls with the same loop parameter
		4313	must be done serially (but can be done from different threads, as long as
		4314	only one thread ever is inside a call at any point in time, e.g. by using
		4315	a mutex per loop).
		4316
		4317	Specifically to support threads (and signal handlers), libev implements
		4318	so-called C<ev_async> watchers, which allow some limited form of
		4319	concurrency on the same event loop, namely waking it up "from the
		4320	outside".
		4321
		4322	If you want to know which design (one loop, locking, or multiple loops
		4323	without or something else still) is best for your problem, then I cannot
		4324	help you, but here is some generic advice:
		4325
		4326	=over 4
		4327
		4328	=item * most applications have a main thread: use the default libev loop
		4329	in that thread, or create a separate thread running only the default loop.
		4330
		4331	This helps integrating other libraries or software modules that use libev
		4332	themselves and don't care/know about threading.
		4333
		4334	=item * one loop per thread is usually a good model.
		4335
		4336	Doing this is almost never wrong, sometimes a better-performance model
		4337	exists, but it is always a good start.
		4338
		4339	=item * other models exist, such as the leader/follower pattern, where one
		4340	loop is handed through multiple threads in a kind of round-robin fashion.
		4341
		4342	Choosing a model is hard - look around, learn, know that usually you can do
		4343	better than you currently do :-)
		4344
		4345	=item * often you need to talk to some other thread which blocks in the
		4346	event loop.
		4347
		4348	C<ev_async> watchers can be used to wake them up from other threads safely
		4349	(or from signal contexts...).
		4350
		4351	An example use would be to communicate signals or other events that only
		4352	work in the default loop by registering the signal watcher with the
		4353	default loop and triggering an C<ev_async> watcher from the default loop
		4354	watcher callback into the event loop interested in the signal.
		4355
		4356	=back
		4357
		4358	=head4 THREAD LOCKING EXAMPLE
		4359
		4360	Here is a fictitious example of how to run an event loop in a different
		4361	thread than where callbacks are being invoked and watchers are
		4362	created/added/removed.
		4363
		4364	For a real-world example, see the C<EV::Loop::Async> perl module,
		4365	which uses exactly this technique (which is suited for many high-level
		4366	languages).
		4367
		4368	The example uses a pthread mutex to protect the loop data, a condition
		4369	variable to wait for callback invocations, an async watcher to notify the
		4370	event loop thread and an unspecified mechanism to wake up the main thread.
		4371
		4372	First, you need to associate some data with the event loop:
		4373
		4374	typedef struct {
		4375	mutex_t lock; /* global loop lock */
		4376	ev_async async_w;
		4377	thread_t tid;
		4378	cond_t invoke_cv;
		4379	} userdata;
		4380
		4381	void prepare_loop (EV_P)
		4382	{
		4383	// for simplicity, we use a static userdata struct.
		4384	static userdata u;
		4385
		4386	ev_async_init (&u->async_w, async_cb);
		4387	ev_async_start (EV_A_ &u->async_w);
		4388
		4389	pthread_mutex_init (&u->lock, 0);
		4390	pthread_cond_init (&u->invoke_cv, 0);
		4391
		4392	// now associate this with the loop
		4393	ev_set_userdata (EV_A_ u);
		4394	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4395	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4396
		4397	// then create the thread running ev_loop
		4398	pthread_create (&u->tid, 0, l_run, EV_A);
		4399	}
		4400
		4401	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4402	solely to wake up the event loop so it takes notice of any new watchers
		4403	that might have been added:
		4404
		4405	static void
		4406	async_cb (EV_P_ ev_async *w, int revents)
		4407	{
		4408	// just used for the side effects
		4409	}
		4410
		4411	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4412	protecting the loop data, respectively.
		4413
		4414	static void
		4415	l_release (EV_P)
		4416	{
		4417	userdata *u = ev_userdata (EV_A);
		4418	pthread_mutex_unlock (&u->lock);
		4419	}
		4420
		4421	static void
		4422	l_acquire (EV_P)
		4423	{
		4424	userdata *u = ev_userdata (EV_A);
		4425	pthread_mutex_lock (&u->lock);
		4426	}
		4427
		4428	The event loop thread first acquires the mutex, and then jumps straight
		4429	into C<ev_run>:
		4430
		4431	void *
		4432	l_run (void *thr_arg)
		4433	{
		4434	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4435
		4436	l_acquire (EV_A);
		4437	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4438	ev_run (EV_A_ 0);
		4439	l_release (EV_A);
		4440
		4441	return 0;
		4442	}
		4443
		4444	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4445	signal the main thread via some unspecified mechanism (signals? pipe
		4446	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4447	have been called (in a while loop because a) spurious wakeups are possible
		4448	and b) skipping inter-thread-communication when there are no pending
		4449	watchers is very beneficial):
		4450
		4451	static void
		4452	l_invoke (EV_P)
		4453	{
		4454	userdata *u = ev_userdata (EV_A);
		4455
		4456	while (ev_pending_count (EV_A))
		4457	{
		4458	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4459	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4460	}
		4461	}
		4462
		4463	Now, whenever the main thread gets told to invoke pending watchers, it
		4464	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4465	thread to continue:
		4466
		4467	static void
		4468	real_invoke_pending (EV_P)
		4469	{
		4470	userdata *u = ev_userdata (EV_A);
		4471
		4472	pthread_mutex_lock (&u->lock);
		4473	ev_invoke_pending (EV_A);
		4474	pthread_cond_signal (&u->invoke_cv);
		4475	pthread_mutex_unlock (&u->lock);
		4476	}
		4477
		4478	Whenever you want to start/stop a watcher or do other modifications to an
		4479	event loop, you will now have to lock:
		4480
		4481	ev_timer timeout_watcher;
		4482	userdata *u = ev_userdata (EV_A);
		4483
		4484	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4485
		4486	pthread_mutex_lock (&u->lock);
		4487	ev_timer_start (EV_A_ &timeout_watcher);
		4488	ev_async_send (EV_A_ &u->async_w);
		4489	pthread_mutex_unlock (&u->lock);
		4490
		4491	Note that sending the C<ev_async> watcher is required because otherwise
		4492	an event loop currently blocking in the kernel will have no knowledge
		4493	about the newly added timer. By waking up the loop it will pick up any new
		4494	watchers in the next event loop iteration.
		4495
		4496	=head3 COROUTINES
		4497
		4498	Libev is very accommodating to coroutines ("cooperative threads"):
		4499	libev fully supports nesting calls to its functions from different
		4500	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4501	different coroutines, and switch freely between both coroutines running
		4502	the loop, as long as you don't confuse yourself). The only exception is
		4503	that you must not do this from C<ev_periodic> reschedule callbacks.
		4504
		4505	Care has been taken to ensure that libev does not keep local state inside
		4506	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4507	they do not call any callbacks.
		4508
		4509	=head2 COMPILER WARNINGS
		4510
		4511	Depending on your compiler and compiler settings, you might get no or a
		4512	lot of warnings when compiling libev code. Some people are apparently
		4513	scared by this.
		4514
		4515	However, these are unavoidable for many reasons. For one, each compiler
		4516	has different warnings, and each user has different tastes regarding
		4517	warning options. "Warn-free" code therefore cannot be a goal except when
		4518	targeting a specific compiler and compiler-version.
		4519
		4520	Another reason is that some compiler warnings require elaborate
		4521	workarounds, or other changes to the code that make it less clear and less
		4522	maintainable.
		4523
		4524	And of course, some compiler warnings are just plain stupid, or simply
		4525	wrong (because they don't actually warn about the condition their message
		4526	seems to warn about). For example, certain older gcc versions had some
		4527	warnings that resulted in an extreme number of false positives. These have
		4528	been fixed, but some people still insist on making code warn-free with
		4529	such buggy versions.
		4530
		4531	While libev is written to generate as few warnings as possible,
		4532	"warn-free" code is not a goal, and it is recommended not to build libev
		4533	with any compiler warnings enabled unless you are prepared to cope with
		4534	them (e.g. by ignoring them). Remember that warnings are just that:
		4535	warnings, not errors, or proof of bugs.
		4536
		4537
		4538	=head2 VALGRIND
		4539
		4540	Valgrind has a special section here because it is a popular tool that is
		4541	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4542
		4543	If you think you found a bug (memory leak, uninitialised data access etc.)
		4544	in libev, then check twice: If valgrind reports something like:
		4545
		4546	==2274== definitely lost: 0 bytes in 0 blocks.
		4547	==2274== possibly lost: 0 bytes in 0 blocks.
		4548	==2274== still reachable: 256 bytes in 1 blocks.
		4549
		4550	Then there is no memory leak, just as memory accounted to global variables
		4551	is not a memleak - the memory is still being referenced, and didn't leak.
		4552
		4553	Similarly, under some circumstances, valgrind might report kernel bugs
		4554	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4555	although an acceptable workaround has been found here), or it might be
		4556	confused.
		4557
		4558	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4559	make it into some kind of religion.
		4560
		4561	If you are unsure about something, feel free to contact the mailing list
		4562	with the full valgrind report and an explanation on why you think this
		4563	is a bug in libev (best check the archives, too :). However, don't be
		4564	annoyed when you get a brisk "this is no bug" answer and take the chance
		4565	of learning how to interpret valgrind properly.
		4566
		4567	If you need, for some reason, empty reports from valgrind for your project
		4568	I suggest using suppression lists.
		4569
		4570
		4571	=head1 PORTABILITY NOTES
		4572
		4573	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4574
		4575	GNU/Linux is the only common platform that supports 64 bit file/large file
		4576	interfaces but I<disables> them by default.
		4577
		4578	That means that libev compiled in the default environment doesn't support
		4579	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4580
		4581	Unfortunately, many programs try to work around this GNU/Linux issue
		4582	by enabling the large file API, which makes them incompatible with the
		4583	standard libev compiled for their system.
		4584
		4585	Likewise, libev cannot enable the large file API itself as this would
		4586	suddenly make it incompatible to the default compile time environment,
		4587	i.e. all programs not using special compile switches.
		4588
		4589	=head2 OS/X AND DARWIN BUGS
		4590
		4591	The whole thing is a bug if you ask me - basically any system interface
		4592	you touch is broken, whether it is locales, poll, kqueue or even the
		4593	OpenGL drivers.
		4594
		4595	=head3 C<kqueue> is buggy
		4596
		4597	The kqueue syscall is broken in all known versions - most versions support
		4598	only sockets, many support pipes.
		4599
		4600	Libev tries to work around this by not using C<kqueue> by default on this
		4601	rotten platform, but of course you can still ask for it when creating a
		4602	loop - embedding a socket-only kqueue loop into a select-based one is
		4603	probably going to work well.
		4604
		4605	=head3 C<poll> is buggy
		4606
		4607	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4608	implementation by something calling C<kqueue> internally around the 10.5.6
		4609	release, so now C<kqueue> I<and> C<poll> are broken.
		4610
		4611	Libev tries to work around this by not using C<poll> by default on
		4612	this rotten platform, but of course you can still ask for it when creating
		4613	a loop.
		4614
		4615	=head3 C<select> is buggy
		4616
		4617	All that's left is C<select>, and of course Apple found a way to fuck this
		4618	one up as well: On OS/X, C<select> actively limits the number of file
		4619	descriptors you can pass in to 1024 - your program suddenly crashes when
		4620	you use more.
		4621
		4622	There is an undocumented "workaround" for this - defining
		4623	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4624	work on OS/X.
		4625
		4626	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4627
		4628	=head3 C<errno> reentrancy
		4629
		4630	The default compile environment on Solaris is unfortunately so
		4631	thread-unsafe that you can't even use components/libraries compiled
		4632	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4633	defined by default. A valid, if stupid, implementation choice.
		4634
		4635	If you want to use libev in threaded environments you have to make sure
		4636	it's compiled with C<_REENTRANT> defined.
		4637
		4638	=head3 Event port backend
		4639
		4640	The scalable event interface for Solaris is called "event
		4641	ports". Unfortunately, this mechanism is very buggy in all major
		4642	releases. If you run into high CPU usage, your program freezes or you get
		4643	a large number of spurious wakeups, make sure you have all the relevant
		4644	and latest kernel patches applied. No, I don't know which ones, but there
		4645	are multiple ones to apply, and afterwards, event ports actually work
		4646	great.
		4647
		4648	If you can't get it to work, you can try running the program by setting
		4649	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4650	C<select> backends.
		4651
		4652	=head2 AIX POLL BUG
		4653
		4654	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4655	this by trying to avoid the poll backend altogether (i.e. it's not even
		4656	compiled in), which normally isn't a big problem as C<select> works fine
		4657	with large bitsets on AIX, and AIX is dead anyway.
		4658
		4659	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4660
		4661	=head3 General issues
		4662
		4663	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4664	requires, and its I/O model is fundamentally incompatible with the POSIX
		4665	model. Libev still offers limited functionality on this platform in
		4666	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4667	descriptors. This only applies when using Win32 natively, not when using
		4668	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4669	as every compielr comes with a slightly differently broken/incompatible
		4670	environment.
		4671
		4672	Lifting these limitations would basically require the full
		4673	re-implementation of the I/O system. If you are into this kind of thing,
		4674	then note that glib does exactly that for you in a very portable way (note
		4675	also that glib is the slowest event library known to man).
		4676
		4677	There is no supported compilation method available on windows except
		4678	embedding it into other applications.
		4679
		4680	Sensible signal handling is officially unsupported by Microsoft - libev
		4681	tries its best, but under most conditions, signals will simply not work.
		4682
		4683	Not a libev limitation but worth mentioning: windows apparently doesn't
		4684	accept large writes: instead of resulting in a partial write, windows will
		4685	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4686	so make sure you only write small amounts into your sockets (less than a
		4687	megabyte seems safe, but this apparently depends on the amount of memory
		4688	available).
		4689
		4690	Due to the many, low, and arbitrary limits on the win32 platform and
		4691	the abysmal performance of winsockets, using a large number of sockets
		4692	is not recommended (and not reasonable). If your program needs to use
		4693	more than a hundred or so sockets, then likely it needs to use a totally
		4694	different implementation for windows, as libev offers the POSIX readiness
		4695	notification model, which cannot be implemented efficiently on windows
		4696	(due to Microsoft monopoly games).
		4697
		4698	A typical way to use libev under windows is to embed it (see the embedding
		4699	section for details) and use the following F<evwrap.h> header file instead
		4700	of F<ev.h>:
		4701
		4702	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4703	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4704
		4705	#include "ev.h"
		4706
		4707	And compile the following F<evwrap.c> file into your project (make sure
		4708	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4709
		4710	#include "evwrap.h"
		4711	#include "ev.c"
		4712
		4713	=head3 The winsocket C<select> function
		4714
		4715	The winsocket C<select> function doesn't follow POSIX in that it
		4716	requires socket I<handles> and not socket I<file descriptors> (it is
		4717	also extremely buggy). This makes select very inefficient, and also
		4718	requires a mapping from file descriptors to socket handles (the Microsoft
		4719	C runtime provides the function C<_open_osfhandle> for this). See the
		4720	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4721	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4722
		4723	The configuration for a "naked" win32 using the Microsoft runtime
		4724	libraries and raw winsocket select is:
		4725
		4726	#define EV_USE_SELECT 1
		4727	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4728
		4729	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4730	complexity in the O(n²) range when using win32.
		4731
		4732	=head3 Limited number of file descriptors
		4733
		4734	Windows has numerous arbitrary (and low) limits on things.
		4735
		4736	Early versions of winsocket's select only supported waiting for a maximum
		4737	of C<64> handles (probably owning to the fact that all windows kernels
		4738	can only wait for C<64> things at the same time internally; Microsoft
		4739	recommends spawning a chain of threads and wait for 63 handles and the
		4740	previous thread in each. Sounds great!).
		4741
		4742	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4743	to some high number (e.g. C<2048>) before compiling the winsocket select
		4744	call (which might be in libev or elsewhere, for example, perl and many
		4745	other interpreters do their own select emulation on windows).
		4746
		4747	Another limit is the number of file descriptors in the Microsoft runtime
		4748	libraries, which by default is C<64> (there must be a hidden I<64>
		4749	fetish or something like this inside Microsoft). You can increase this
		4750	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4751	(another arbitrary limit), but is broken in many versions of the Microsoft
		4752	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4753	(depending on windows version and/or the phase of the moon). To get more,
		4754	you need to wrap all I/O functions and provide your own fd management, but
		4755	the cost of calling select (O(n²)) will likely make this unworkable.
		4756
		4757	=head2 PORTABILITY REQUIREMENTS
		4758
		4759	In addition to a working ISO-C implementation and of course the
		4760	backend-specific APIs, libev relies on a few additional extensions:
		4761
		4762	=over 4
		4763
		4764	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4765	calling conventions regardless of C<ev_watcher_type *>.
		4766
		4767	Libev assumes not only that all watcher pointers have the same internal
		4768	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4769	assumes that the same (machine) code can be used to call any watcher
		4770	callback: The watcher callbacks have different type signatures, but libev
		4771	calls them using an C<ev_watcher *> internally.
		4772
		4773	=item pointer accesses must be thread-atomic
		4774
		4775	Accessing a pointer value must be atomic, it must both be readable and
		4776	writable in one piece - this is the case on all current architectures.
		4777
		4778	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4779
		4780	The type C<sig_atomic_t volatile> (or whatever is defined as
		4781	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4782	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4783	believed to be sufficiently portable.
		4784
		4785	=item C<sigprocmask> must work in a threaded environment
		4786
		4787	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4788	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4789	pthread implementations will either allow C<sigprocmask> in the "main
		4790	thread" or will block signals process-wide, both behaviours would
		4791	be compatible with libev. Interaction between C<sigprocmask> and
		4792	C<pthread_sigmask> could complicate things, however.
		4793
		4794	The most portable way to handle signals is to block signals in all threads
		4795	except the initial one, and run the default loop in the initial thread as
		4796	well.
		4797
		4798	=item C<long> must be large enough for common memory allocation sizes
		4799
		4800	To improve portability and simplify its API, libev uses C<long> internally
		4801	instead of C<size_t> when allocating its data structures. On non-POSIX
		4802	systems (Microsoft...) this might be unexpectedly low, but is still at
		4803	least 31 bits everywhere, which is enough for hundreds of millions of
		4804	watchers.
		4805
		4806	=item C<double> must hold a time value in seconds with enough accuracy
		4807
		4808	The type C<double> is used to represent timestamps. It is required to
		4809	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		4810	good enough for at least into the year 4000 with millisecond accuracy
		4811	(the design goal for libev). This requirement is overfulfilled by
		4812	implementations using IEEE 754, which is basically all existing ones. With
		4813	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
		4814
		4815	=back
		4816
		4817	If you know of other additional requirements drop me a note.
		4818
		4819
2465	=head1 COMPLEXITIES	4820	=head1 ALGORITHMIC COMPLEXITIES
2466		4821
2467	In this section the complexities of (many of) the algorithms used inside	4822	In this section the complexities of (many of) the algorithms used inside
2468	libev will be explained. For complexity discussions about backends see the	4823	libev will be documented. For complexity discussions about backends see
2469	documentation for C<ev_default_init>.	4824	the documentation for C<ev_default_init>.
2470		4825
2471	All of the following are about amortised time: If an array needs to be	4826	All of the following are about amortised time: If an array needs to be
2472	extended, libev needs to realloc and move the whole array, but this	4827	extended, libev needs to realloc and move the whole array, but this
2473	happens asymptotically never with higher number of elements, so O(1) might	4828	happens asymptotically rarer with higher number of elements, so O(1) might
2474	mean it might do a lengthy realloc operation in rare cases, but on average	4829	mean that libev does a lengthy realloc operation in rare cases, but on
2475	it is much faster and asymptotically approaches constant time.	4830	average it is much faster and asymptotically approaches constant time.
2476		4831
2477	=over 4	4832	=over 4
2478		4833
2479	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4834	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2480		4835
2481	This means that, when you have a watcher that triggers in one hour and	4836	This means that, when you have a watcher that triggers in one hour and
2482	there are 100 watchers that would trigger before that then inserting will	4837	there are 100 watchers that would trigger before that, then inserting will
2483	have to skip those 100 watchers.	4838	have to skip roughly seven (C<ld 100>) of these watchers.
2484		4839
2485	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4840	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2486		4841
2487	That means that for changing a timer costs less than removing/adding them	4842	That means that changing a timer costs less than removing/adding them,
2488	as only the relative motion in the event queue has to be paid for.	4843	as only the relative motion in the event queue has to be paid for.
2489		4844
2490	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4845	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2491		4846
2492	These just add the watcher into an array or at the head of a list.	4847	These just add the watcher into an array or at the head of a list.
		4848
2493	=item Stopping check/prepare/idle watchers: O(1)	4849	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2494		4850
2495	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4851	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2496		4852
2497	These watchers are stored in lists then need to be walked to find the	4853	These watchers are stored in lists, so they need to be walked to find the
2498	correct watcher to remove. The lists are usually short (you don't usually	4854	correct watcher to remove. The lists are usually short (you don't usually
2499	have many watchers waiting for the same fd or signal).	4855	have many watchers waiting for the same fd or signal: one is typical, two
		4856	is rare).
2500		4857
2501	=item Finding the next timer per loop iteration: O(1)	4858	=item Finding the next timer in each loop iteration: O(1)
		4859
		4860	By virtue of using a binary or 4-heap, the next timer is always found at a
		4861	fixed position in the storage array.
2502		4862
2503	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4863	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2504		4864
2505	A change means an I/O watcher gets started or stopped, which requires	4865	A change means an I/O watcher gets started or stopped, which requires
2506	libev to recalculate its status (and possibly tell the kernel).	4866	libev to recalculate its status (and possibly tell the kernel, depending
		4867	on backend and whether C<ev_io_set> was used).
2507		4868
2508	=item Activating one watcher: O(1)	4869	=item Activating one watcher (putting it into the pending state): O(1)
2509		4870
2510	=item Priority handling: O(number_of_priorities)	4871	=item Priority handling: O(number_of_priorities)
2511		4872
2512	Priorities are implemented by allocating some space for each	4873	Priorities are implemented by allocating some space for each
2513	priority. When doing priority-based operations, libev usually has to	4874	priority. When doing priority-based operations, libev usually has to
2514	linearly search all the priorities.	4875	linearly search all the priorities, but starting/stopping and activating
		4876	watchers becomes O(1) with respect to priority handling.
		4877
		4878	=item Sending an ev_async: O(1)
		4879
		4880	=item Processing ev_async_send: O(number_of_async_watchers)
		4881
		4882	=item Processing signals: O(max_signal_number)
		4883
		4884	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4885	calls in the current loop iteration. Checking for async and signal events
		4886	involves iterating over all running async watchers or all signal numbers.
2515		4887
2516	=back	4888	=back
2517		4889
2518		4890
		4891	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4892
		4893	The major version 4 introduced some incompatible changes to the API.
		4894
		4895	At the moment, the C<ev.h> header file provides compatibility definitions
		4896	for all changes, so most programs should still compile. The compatibility
		4897	layer might be removed in later versions of libev, so better update to the
		4898	new API early than late.
		4899
		4900	=over 4
		4901
		4902	=item C<EV_COMPAT3> backwards compatibility mechanism
		4903
		4904	The backward compatibility mechanism can be controlled by
		4905	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		4906	section.
		4907
		4908	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		4909
		4910	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		4911
		4912	ev_loop_destroy (EV_DEFAULT_UC);
		4913	ev_loop_fork (EV_DEFAULT);
		4914
		4915	=item function/symbol renames
		4916
		4917	A number of functions and symbols have been renamed:
		4918
		4919	ev_loop => ev_run
		4920	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		4921	EVLOOP_ONESHOT => EVRUN_ONCE
		4922
		4923	ev_unloop => ev_break
		4924	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		4925	EVUNLOOP_ONE => EVBREAK_ONE
		4926	EVUNLOOP_ALL => EVBREAK_ALL
		4927
		4928	EV_TIMEOUT => EV_TIMER
		4929
		4930	ev_loop_count => ev_iteration
		4931	ev_loop_depth => ev_depth
		4932	ev_loop_verify => ev_verify
		4933
		4934	Most functions working on C<struct ev_loop> objects don't have an
		4935	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		4936	associated constants have been renamed to not collide with the C<struct
		4937	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		4938	as all other watcher types. Note that C<ev_loop_fork> is still called
		4939	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		4940	typedef.
		4941
		4942	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4943
		4944	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4945	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4946	and work, but the library code will of course be larger.
		4947
		4948	=back
		4949
		4950
		4951	=head1 GLOSSARY
		4952
		4953	=over 4
		4954
		4955	=item active
		4956
		4957	A watcher is active as long as it has been started and not yet stopped.
		4958	See L<WATCHER STATES> for details.
		4959
		4960	=item application
		4961
		4962	In this document, an application is whatever is using libev.
		4963
		4964	=item backend
		4965
		4966	The part of the code dealing with the operating system interfaces.
		4967
		4968	=item callback
		4969
		4970	The address of a function that is called when some event has been
		4971	detected. Callbacks are being passed the event loop, the watcher that
		4972	received the event, and the actual event bitset.
		4973
		4974	=item callback/watcher invocation
		4975
		4976	The act of calling the callback associated with a watcher.
		4977
		4978	=item event
		4979
		4980	A change of state of some external event, such as data now being available
		4981	for reading on a file descriptor, time having passed or simply not having
		4982	any other events happening anymore.
		4983
		4984	In libev, events are represented as single bits (such as C<EV_READ> or
		4985	C<EV_TIMER>).
		4986
		4987	=item event library
		4988
		4989	A software package implementing an event model and loop.
		4990
		4991	=item event loop
		4992
		4993	An entity that handles and processes external events and converts them
		4994	into callback invocations.
		4995
		4996	=item event model
		4997
		4998	The model used to describe how an event loop handles and processes
		4999	watchers and events.
		5000
		5001	=item pending
		5002
		5003	A watcher is pending as soon as the corresponding event has been
		5004	detected. See L<WATCHER STATES> for details.
		5005
		5006	=item real time
		5007
		5008	The physical time that is observed. It is apparently strictly monotonic :)
		5009
		5010	=item wall-clock time
		5011
		5012	The time and date as shown on clocks. Unlike real time, it can actually
		5013	be wrong and jump forwards and backwards, e.g. when the you adjust your
		5014	clock.
		5015
		5016	=item watcher
		5017
		5018	A data structure that describes interest in certain events. Watchers need
		5019	to be started (attached to an event loop) before they can receive events.
		5020
		5021	=back
		5022
2519	=head1 AUTHOR	5023	=head1 AUTHOR
2520		5024
2521	Marc Lehmann <libev@schmorp.de>.	5025	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5026	Magnusson and Emanuele Giaquinta.
2522		5027

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