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Revision 1.83 by root, Wed Dec 12 17:55:31 2007 UTC vs.
Revision 1.354 by root, Tue Jan 11 01:40:25 2011 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_run's to stop iterating
		32	ev_break (EV_A_ EVBREAK_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_run to stop iterating
		41	ev_break (EV_A_ EVBREAK_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
35	struct ev_loop *loop = ev_default_loop (0);	47	// use the default event loop unless you have special needs
		48	struct ev_loop *loop = EV_DEFAULT;
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_run (loop, 0);
47		62
		63	// 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.
…		…
225	}	299	}
226		300
227	...	301	...
228	ev_set_syserr_cb (fatal_error);	302	ev_set_syserr_cb (fatal_error);
229		303
		304	=item ev_feed_signal (int signum)
		305
		306	This function can be used to "simulate" a signal receive. It is completely
		307	safe to call this function at any time, from any context, including signal
		308	handlers or random threads.
		309
		310	Its main use is to customise signal handling in your process, especially
		311	in the presence of threads. For example, you could block signals
		312	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		313	creating any loops), and in one thread, use C<sigwait> or any other
		314	mechanism to wait for signals, then "deliver" them to libev by calling
		315	C<ev_feed_signal>.
		316
230	=back	317	=back
231		318
232	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	319	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
233		320
234	An event loop is described by a C<struct ev_loop *>. The library knows two	321	An event loop is described by a C<struct ev_loop *> (the C<struct> is
235	types of such loops, the I<default> loop, which supports signals and child	322	I<not> optional in this case unless libev 3 compatibility is disabled, as
236	events, and dynamically created loops which do not.	323	libev 3 had an C<ev_loop> function colliding with the struct name).
237		324
238	If you use threads, a common model is to run the default event loop	325	The library knows two types of such loops, the I<default> loop, which
239	in your main thread (or in a separate thread) and for each thread you	326	supports child process events, and dynamically created event loops which
240	create, you also create another event loop. Libev itself does no locking	327	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		328
245	=over 4	329	=over 4
246		330
247	=item struct ev_loop *ev_default_loop (unsigned int flags)	331	=item struct ev_loop *ev_default_loop (unsigned int flags)
248		332
249	This will initialise the default event loop if it hasn't been initialised	333	This returns the "default" event loop object, which is what you should
250	yet and return it. If the default loop could not be initialised, returns	334	normally use when you just need "the event loop". Event loop objects and
251	false. If it already was initialised it simply returns it (and ignores the	335	the C<flags> parameter are described in more detail in the entry for
252	flags. If that is troubling you, check C<ev_backend ()> afterwards).	336	C<ev_loop_new>.
		337
		338	If the default loop is already initialised then this function simply
		339	returns it (and ignores the flags. If that is troubling you, check
		340	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		341	flags, which should almost always be C<0>, unless the caller is also the
		342	one calling C<ev_run> or otherwise qualifies as "the main program".
253		343
254	If you don't know what event loop to use, use the one returned from this	344	If you don't know what event loop to use, use the one returned from this
255	function.	345	function (or via the C<EV_DEFAULT> macro).
		346
		347	Note that this function is I<not> thread-safe, so if you want to use it
		348	from multiple threads, you have to employ some kind of mutex (note also
		349	that this case is unlikely, as loops cannot be shared easily between
		350	threads anyway).
		351
		352	The default loop is the only loop that can handle C<ev_child> watchers,
		353	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		354	a problem for your application you can either create a dynamic loop with
		355	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		356	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
		357
		358	Example: This is the most typical usage.
		359
		360	if (!ev_default_loop (0))
		361	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		362
		363	Example: Restrict libev to the select and poll backends, and do not allow
		364	environment settings to be taken into account:
		365
		366	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		367
		368	=item struct ev_loop *ev_loop_new (unsigned int flags)
		369
		370	This will create and initialise a new event loop object. If the loop
		371	could not be initialised, returns false.
		372
		373	This function is thread-safe, and one common way to use libev with
		374	threads is indeed to create one loop per thread, and using the default
		375	loop in the "main" or "initial" thread.
256		376
257	The flags argument can be used to specify special behaviour or specific	377	The flags argument can be used to specify special behaviour or specific
258	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	378	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
259		379
260	The following flags are supported:	380	The following flags are supported:
…		…
266	The default flags value. Use this if you have no clue (it's the right	386	The default flags value. Use this if you have no clue (it's the right
267	thing, believe me).	387	thing, believe me).
268		388
269	=item C<EVFLAG_NOENV>	389	=item C<EVFLAG_NOENV>
270		390
271	If this flag bit is ored into the flag value (or the program runs setuid	391	If this flag bit is or'ed into the flag value (or the program runs setuid
272	or setgid) then libev will I<not> look at the environment variable	392	or setgid) then libev will I<not> look at the environment variable
273	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	393	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
274	override the flags completely if it is found in the environment. This is	394	override the flags completely if it is found in the environment. This is
275	useful to try out specific backends to test their performance, or to work	395	useful to try out specific backends to test their performance, or to work
276	around bugs.	396	around bugs.
277		397
278	=item C<EVFLAG_FORKCHECK>	398	=item C<EVFLAG_FORKCHECK>
279		399
280	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	400	Instead of calling C<ev_loop_fork> manually after a fork, you can also
281	a fork, you can also make libev check for a fork in each iteration by	401	make libev check for a fork in each iteration by enabling this flag.
282	enabling this flag.
283		402
284	This works by calling C<getpid ()> on every iteration of the loop,	403	This works by calling C<getpid ()> on every iteration of the loop,
285	and thus this might slow down your event loop if you do a lot of loop	404	and thus this might slow down your event loop if you do a lot of loop
286	iterations and little real work, but is usually not noticeable (on my	405	iterations and little real work, but is usually not noticeable (on my
287	Linux system for example, C<getpid> is actually a simple 5-insn sequence	406	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
288	without a syscall and thus I<very> fast, but my Linux system also has	407	without a system call and thus I<very> fast, but my GNU/Linux system also has
289	C<pthread_atfork> which is even faster).	408	C<pthread_atfork> which is even faster).
290		409
291	The big advantage of this flag is that you can forget about fork (and	410	The big advantage of this flag is that you can forget about fork (and
292	forget about forgetting to tell libev about forking) when you use this	411	forget about forgetting to tell libev about forking) when you use this
293	flag.	412	flag.
294		413
295	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	414	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
296	environment variable.	415	environment variable.
		416
		417	=item C<EVFLAG_NOINOTIFY>
		418
		419	When this flag is specified, then libev will not attempt to use the
		420	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		421	testing, this flag can be useful to conserve inotify file descriptors, as
		422	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		423
		424	=item C<EVFLAG_SIGNALFD>
		425
		426	When this flag is specified, then libev will attempt to use the
		427	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		428	delivers signals synchronously, which makes it both faster and might make
		429	it possible to get the queued signal data. It can also simplify signal
		430	handling with threads, as long as you properly block signals in your
		431	threads that are not interested in handling them.
		432
		433	Signalfd will not be used by default as this changes your signal mask, and
		434	there are a lot of shoddy libraries and programs (glib's threadpool for
		435	example) that can't properly initialise their signal masks.
		436
		437	=item C<EVFLAG_NOSIGMASK>
		438
		439	When this flag is specified, then libev will avoid to modify the signal
		440	mask. Specifically, this means you ahve to make sure signals are unblocked
		441	when you want to receive them.
		442
		443	This behaviour is useful when you want to do your own signal handling, or
		444	want to handle signals only in specific threads and want to avoid libev
		445	unblocking the signals.
		446
		447	This flag's behaviour will become the default in future versions of libev.
297		448
298	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
299		450
300	This is your standard select(2) backend. Not I<completely> standard, as	451	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,	452	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	453	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	454	using this backend. It doesn't scale too well (O(highest_fd)), but its
304	the fastest backend for a low number of fds.	455	usually the fastest backend for a low number of (low-numbered :) fds.
		456
		457	To get good performance out of this backend you need a high amount of
		458	parallelism (most of the file descriptors should be busy). If you are
		459	writing a server, you should C<accept ()> in a loop to accept as many
		460	connections as possible during one iteration. You might also want to have
		461	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		462	readiness notifications you get per iteration.
		463
		464	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		465	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		466	C<exceptfds> set on that platform).
305		467
306	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	468	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
307		469
308	And this is your standard poll(2) backend. It's more complicated than	470	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	471	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	472	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).	473	considerably with a lot of inactive fds). It scales similarly to select,
		474	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		475	performance tips.
		476
		477	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		478	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
312		479
313	=item C<EVBACKEND_EPOLL> (value 4, Linux)	480	=item C<EVBACKEND_EPOLL> (value 4, Linux)
314		481
		482	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		483	kernels).
		484
315	For few fds, this backend is a bit little slower than poll and select,	485	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	486	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	487	like O(total_fds) where n is the total number of fds (or the highest fd),
318	either O(1) or O(active_fds).	488	epoll scales either O(1) or O(active_fds).
319		489
		490	The epoll mechanism deserves honorable mention as the most misdesigned
		491	of the more advanced event mechanisms: mere annoyances include silently
		492	dropping file descriptors, requiring a system call per change per file
		493	descriptor (and unnecessary guessing of parameters), problems with dup,
		494	returning before the timeout value, resulting in additional iterations
		495	(and only giving 5ms accuracy while select on the same platform gives
		496	0.1ms) and so on. The biggest issue is fork races, however - if a program
		497	forks then I<both> parent and child process have to recreate the epoll
		498	set, which can take considerable time (one syscall per file descriptor)
		499	and is of course hard to detect.
		500
		501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		502	of course I<doesn't>, and epoll just loves to report events for totally
		503	I<different> file descriptors (even already closed ones, so one cannot
		504	even remove them from the set) than registered in the set (especially
		505	on SMP systems). Libev tries to counter these spurious notifications by
		506	employing an additional generation counter and comparing that against the
		507	events to filter out spurious ones, recreating the set when required. Last
		508	not least, it also refuses to work with some file descriptors which work
		509	perfectly fine with C<select> (files, many character devices...).
		510
		511	Epoll is truly the train wreck analog among event poll mechanisms,
		512	a frankenpoll, cobbled together in a hurry, no thought to design or
		513	interaction with others.
		514
320	While stopping and starting an I/O watcher in the same iteration will	515	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	516	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	517	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	518	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
324	well if you register events for both fds.	519	file descriptors might not work very well if you register events for both
		520	file descriptors.
325		521
326	Please note that epoll sometimes generates spurious notifications, so you	522	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	523	watchers for a file descriptor until it has been closed, if possible,
328	(or space) is available.	524	i.e. keep at least one watcher active per fd at all times. Stopping and
		525	starting a watcher (without re-setting it) also usually doesn't cause
		526	extra overhead. A fork can both result in spurious notifications as well
		527	as in libev having to destroy and recreate the epoll object, which can
		528	take considerable time and thus should be avoided.
		529
		530	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		531	faster than epoll for maybe up to a hundred file descriptors, depending on
		532	the usage. So sad.
		533
		534	While nominally embeddable in other event loops, this feature is broken in
		535	all kernel versions tested so far.
		536
		537	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		538	C<EVBACKEND_POLL>.
329		539
330	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	540	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
331		541
332	Kqueue deserves special mention, as at the time of this writing, it	542	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	543	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	544	with anything but sockets and pipes, except on Darwin, where of course
335	completely useless). For this reason its not being "autodetected"	545	it's completely useless). Unlike epoll, however, whose brokenness
		546	is by design, these kqueue bugs can (and eventually will) be fixed
		547	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	548	"auto-detected" unless you explicitly specify it in the flags (i.e. using
337	C<EVBACKEND_KQUEUE>).	549	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		550	system like NetBSD.
		551
		552	You still can embed kqueue into a normal poll or select backend and use it
		553	only for sockets (after having made sure that sockets work with kqueue on
		554	the target platform). See C<ev_embed> watchers for more info.
338		555
339	It scales in the same way as the epoll backend, but the interface to the	556	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	557	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	558	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	559	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
343	incident, so its best to avoid that.	560	two event changes per incident. Support for C<fork ()> is very bad (but
		561	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		562	cases
		563
		564	This backend usually performs well under most conditions.
		565
		566	While nominally embeddable in other event loops, this doesn't work
		567	everywhere, so you might need to test for this. And since it is broken
		568	almost everywhere, you should only use it when you have a lot of sockets
		569	(for which it usually works), by embedding it into another event loop
		570	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		571	also broken on OS X)) and, did I mention it, using it only for sockets.
		572
		573	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		574	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		575	C<NOTE_EOF>.
344		576
345	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	577	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
346		578
347	This is not implemented yet (and might never be).	579	This is not implemented yet (and might never be, unless you send me an
		580	implementation). According to reports, C</dev/poll> only supports sockets
		581	and is not embeddable, which would limit the usefulness of this backend
		582	immensely.
348		583
349	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	584	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
350		585
351	This uses the Solaris 10 port mechanism. As with everything on Solaris,	586	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)).	587	it's really slow, but it still scales very well (O(active_fds)).
353		588
354	Please note that solaris ports can result in a lot of spurious	589	While this backend scales well, it requires one system call per active
355	notifications, so you need to use non-blocking I/O or other means to avoid	590	file descriptor per loop iteration. For small and medium numbers of file
356	blocking when no data (or space) is available.	591	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		592	might perform better.
		593
		594	On the positive side, this backend actually performed fully to
		595	specification in all tests and is fully embeddable, which is a rare feat
		596	among the OS-specific backends (I vastly prefer correctness over speed
		597	hacks).
		598
		599	On the negative side, the interface is I<bizarre> - so bizarre that
		600	even sun itself gets it wrong in their code examples: The event polling
		601	function sometimes returning events to the caller even though an error
		602	occurred, but with no indication whether it has done so or not (yes, it's
		603	even documented that way) - deadly for edge-triggered interfaces where
		604	you absolutely have to know whether an event occurred or not because you
		605	have to re-arm the watcher.
		606
		607	Fortunately libev seems to be able to work around these idiocies.
		608
		609	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		610	C<EVBACKEND_POLL>.
357		611
358	=item C<EVBACKEND_ALL>	612	=item C<EVBACKEND_ALL>
359		613
360	Try all backends (even potentially broken ones that wouldn't be tried	614	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	615	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
362	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	616	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
363		617
		618	It is definitely not recommended to use this flag, use whatever
		619	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		620	at all.
		621
		622	=item C<EVBACKEND_MASK>
		623
		624	Not a backend at all, but a mask to select all backend bits from a
		625	C<flags> value, in case you want to mask out any backends from a flags
		626	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
		627
364	=back	628	=back
365		629
366	If one or more of these are ored into the flags value, then only these	630	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	631	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	632	here). If none are specified, all backends in C<ev_recommended_backends
369	order of their flag values :)	633	()> 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		634
394	Example: Try to create a event loop that uses epoll and nothing else.	635	Example: Try to create a event loop that uses epoll and nothing else.
395		636
396	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	637	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
397	if (!epoller)	638	if (!epoller)
398	fatal ("no epoll found here, maybe it hides under your chair");	639	fatal ("no epoll found here, maybe it hides under your chair");
399		640
		641	Example: Use whatever libev has to offer, but make sure that kqueue is
		642	used if available.
		643
		644	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		645
400	=item ev_default_destroy ()	646	=item ev_loop_destroy (loop)
401		647
402	Destroys the default loop again (frees all memory and kernel state	648	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	649	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	650	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>	651	responsibility to either stop all watchers cleanly yourself I<before>
406	calling this function, or cope with the fact afterwards (which is usually	652	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	653	the easiest thing, you can just ignore the watchers and/or C<free ()> them
408	for example).	654	for example).
409		655
		656	Note that certain global state, such as signal state (and installed signal
		657	handlers), will not be freed by this function, and related watchers (such
		658	as signal and child watchers) would need to be stopped manually.
		659
		660	This function is normally used on loop objects allocated by
		661	C<ev_loop_new>, but it can also be used on the default loop returned by
		662	C<ev_default_loop>, in which case it is not thread-safe.
		663
		664	Note that it is not advisable to call this function on the default loop
		665	except in the rare occasion where you really need to free its resources.
		666	If you need dynamically allocated loops it is better to use C<ev_loop_new>
		667	and C<ev_loop_destroy>.
		668
410	=item ev_loop_destroy (loop)	669	=item ev_loop_fork (loop)
411		670
412	Like C<ev_default_destroy>, but destroys an event loop created by an	671	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	672	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	673	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	674	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
420	again makes little sense).	675	child before resuming or calling C<ev_run>.
421		676
422	You I<must> call this function in the child process after forking if and	677	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	678	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.	679	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		680	during fork.
		681
		682	On the other hand, you only need to call this function in the child
		683	process if and only if you want to use the event loop in the child. If
		684	you just fork+exec or create a new loop in the child, you don't have to
		685	call it at all (in fact, C<epoll> is so badly broken that it makes a
		686	difference, but libev will usually detect this case on its own and do a
		687	costly reset of the backend).
425		688
426	The function itself is quite fast and it's usually not a problem to call	689	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	690	it just in case after a fork.
428	quite nicely into a call to C<pthread_atfork>:
429		691
		692	Example: Automate calling C<ev_loop_fork> on the default loop when
		693	using pthreads.
		694
		695	static void
		696	post_fork_child (void)
		697	{
		698	ev_loop_fork (EV_DEFAULT);
		699	}
		700
		701	...
430	pthread_atfork (0, 0, ev_default_fork);	702	pthread_atfork (0, 0, post_fork_child);
431		703
432	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	704	=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		705
436	=item ev_loop_fork (loop)	706	Returns true when the given loop is, in fact, the default loop, and false
		707	otherwise.
437		708
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)	709	=item unsigned int ev_iteration (loop)
443		710
444	Returns the count of loop iterations for the loop, which is identical to	711	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	712	to the number of times libev did poll for new events. It starts at C<0>
446	happily wraps around with enough iterations.	713	and happily wraps around with enough iterations.
447		714
448	This value can sometimes be useful as a generation counter of sorts (it	715	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	716	"ticks" the number of loop iterations), as it roughly corresponds with
450	C<ev_prepare> and C<ev_check> calls.	717	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		718	prepare and check phases.
		719
		720	=item unsigned int ev_depth (loop)
		721
		722	Returns the number of times C<ev_run> was entered minus the number of
		723	times C<ev_run> was exited normally, in other words, the recursion depth.
		724
		725	Outside C<ev_run>, this number is zero. In a callback, this number is
		726	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		727	in which case it is higher.
		728
		729	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		730	throwing an exception etc.), doesn't count as "exit" - consider this
		731	as a hint to avoid such ungentleman-like behaviour unless it's really
		732	convenient, in which case it is fully supported.
451		733
452	=item unsigned int ev_backend (loop)	734	=item unsigned int ev_backend (loop)
453		735
454	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	736	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
455	use.	737	use.
…		…
458		740
459	Returns the current "event loop time", which is the time the event loop	741	Returns the current "event loop time", which is the time the event loop
460	received events and started processing them. This timestamp does not	742	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	743	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	744	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).	745	event occurring (or more correctly, libev finding out about it).
464		746
		747	=item ev_now_update (loop)
		748
		749	Establishes the current time by querying the kernel, updating the time
		750	returned by C<ev_now ()> in the progress. This is a costly operation and
		751	is usually done automatically within C<ev_run ()>.
		752
		753	This function is rarely useful, but when some event callback runs for a
		754	very long time without entering the event loop, updating libev's idea of
		755	the current time is a good idea.
		756
		757	See also L<The special problem of time updates> in the C<ev_timer> section.
		758
		759	=item ev_suspend (loop)
		760
		761	=item ev_resume (loop)
		762
		763	These two functions suspend and resume an event loop, for use when the
		764	loop is not used for a while and timeouts should not be processed.
		765
		766	A typical use case would be an interactive program such as a game: When
		767	the user presses C<^Z> to suspend the game and resumes it an hour later it
		768	would be best to handle timeouts as if no time had actually passed while
		769	the program was suspended. This can be achieved by calling C<ev_suspend>
		770	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		771	C<ev_resume> directly afterwards to resume timer processing.
		772
		773	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		774	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		775	will be rescheduled (that is, they will lose any events that would have
		776	occurred while suspended).
		777
		778	After calling C<ev_suspend> you B<must not> call I<any> function on the
		779	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		780	without a previous call to C<ev_suspend>.
		781
		782	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		783	event loop time (see C<ev_now_update>).
		784
465	=item ev_loop (loop, int flags)	785	=item ev_run (loop, int flags)
466		786
467	Finally, this is it, the event handler. This function usually is called	787	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	788	after you have initialised all your watchers and you want to start
469	events.	789	handling events. It will ask the operating system for any new events, call
		790	the watcher callbacks, an then repeat the whole process indefinitely: This
		791	is why event loops are called I<loops>.
470		792
471	If the flags argument is specified as C<0>, it will not return until	793	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.	794	until either no event watchers are active anymore or C<ev_break> was
		795	called.
473		796
474	Please note that an explicit C<ev_unloop> is usually better than	797	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	798	relying on all watchers to be stopped when deciding when a program has
476	finished (especially in interactive programs), but having a program that	799	finished (especially in interactive programs), but having a program
477	automatically loops as long as it has to and no longer by virtue of	800	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.	801	of relying on its watchers stopping correctly, that is truly a thing of
		802	beauty.
479		803
		804	This function is also I<mostly> exception-safe - you can break out of
		805	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		806	exception and so on. This does not decrement the C<ev_depth> value, nor
		807	will it clear any outstanding C<EVBREAK_ONE> breaks.
		808
480	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	809	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	810	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.	811	block your process in case there are no events and will return after one
		812	iteration of the loop. This is sometimes useful to poll and handle new
		813	events while doing lengthy calculations, to keep the program responsive.
483		814
484	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	815	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	816	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	817	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	818	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	819	user-registered callback will be called), and will return after one
		820	iteration of the loop.
		821
		822	This is useful if you are waiting for some external event in conjunction
		823	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	824	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.	825	usually a better approach for this kind of thing.
491		826
492	Here are the gory details of what C<ev_loop> does:	827	Here are the gory details of what C<ev_run> does:
493		828
		829	- Increment loop depth.
		830	- Reset the ev_break status.
494	- Before the first iteration, call any pending watchers.	831	- Before the first iteration, call any pending watchers.
495	* If there are no active watchers (reference count is zero), return.	832	LOOP:
496	- Queue all prepare watchers and then call all outstanding watchers.	833	- If EVFLAG_FORKCHECK was used, check for a fork.
		834	- If a fork was detected (by any means), queue and call all fork watchers.
		835	- Queue and call all prepare watchers.
		836	- If ev_break was called, goto FINISH.
497	- If we have been forked, recreate the kernel state.	837	- If we have been forked, detach and recreate the kernel state
		838	as to not disturb the other process.
498	- Update the kernel state with all outstanding changes.	839	- Update the kernel state with all outstanding changes.
499	- Update the "event loop time".	840	- Update the "event loop time" (ev_now ()).
500	- Calculate for how long to block.	841	- Calculate for how long to sleep or block, if at all
		842	(active idle watchers, EVRUN_NOWAIT or not having
		843	any active watchers at all will result in not sleeping).
		844	- Sleep if the I/O and timer collect interval say so.
		845	- Increment loop iteration counter.
501	- Block the process, waiting for any events.	846	- Block the process, waiting for any events.
502	- Queue all outstanding I/O (fd) events.	847	- Queue all outstanding I/O (fd) events.
503	- Update the "event loop time" and do time jump handling.	848	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
504	- Queue all outstanding timers.	849	- Queue all expired timers.
505	- Queue all outstanding periodics.	850	- Queue all expired periodics.
506	- If no events are pending now, queue all idle watchers.	851	- Queue all idle watchers with priority higher than that of pending events.
507	- Queue all check watchers.	852	- Queue all check watchers.
508	- Call all queued watchers in reverse order (i.e. check watchers first).	853	- 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	854	Signals and child watchers are implemented as I/O watchers, and will
510	be handled here by queueing them when their watcher gets executed.	855	be handled here by queueing them when their watcher gets executed.
511	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	856	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
512	were used, return, otherwise continue with step *.	857	were used, or there are no active watchers, goto FINISH, otherwise
		858	continue with step LOOP.
		859	FINISH:
		860	- Reset the ev_break status iff it was EVBREAK_ONE.
		861	- Decrement the loop depth.
		862	- Return.
513		863
514	Example: Queue some jobs and then loop until no events are outsanding	864	Example: Queue some jobs and then loop until no events are outstanding
515	anymore.	865	anymore.
516		866
517	... queue jobs here, make sure they register event watchers as long	867	... 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..)	868	... as they still have work to do (even an idle watcher will do..)
519	ev_loop (my_loop, 0);	869	ev_run (my_loop, 0);
520	... jobs done. yeah!	870	... jobs done or somebody called unloop. yeah!
521		871
522	=item ev_unloop (loop, how)	872	=item ev_break (loop, how)
523		873
524	Can be used to make a call to C<ev_loop> return early (but only after it	874	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	875	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	876	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.	877	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		878
		879	This "break state" will be cleared on the next call to C<ev_run>.
		880
		881	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		882	which case it will have no effect.
528		883
529	=item ev_ref (loop)	884	=item ev_ref (loop)
530		885
531	=item ev_unref (loop)	886	=item ev_unref (loop)
532		887
533	Ref/unref can be used to add or remove a reference count on the event	888	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	889	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	890	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	891
537	returning, ev_unref() after starting, and ev_ref() before stopping it. For	892	This is useful when you have a watcher that you never intend to
		893	unregister, but that nevertheless should not keep C<ev_run> from
		894	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		895	before stopping it.
		896
538	example, libev itself uses this for its internal signal pipe: It is not	897	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	898	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	899	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	900	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>.	901	third-party libraries. Just remember to I<unref after start> and I<ref
		902	before stop> (but only if the watcher wasn't active before, or was active
		903	before, respectively. Note also that libev might stop watchers itself
		904	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		905	in the callback).
543		906
544	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	907	Example: Create a signal watcher, but keep it from keeping C<ev_run>
545	running when nothing else is active.	908	running when nothing else is active.
546		909
547	struct ev_signal exitsig;	910	ev_signal exitsig;
548	ev_signal_init (&exitsig, sig_cb, SIGINT);	911	ev_signal_init (&exitsig, sig_cb, SIGINT);
549	ev_signal_start (loop, &exitsig);	912	ev_signal_start (loop, &exitsig);
550	evf_unref (loop);	913	ev_unref (loop);
551		914
552	Example: For some weird reason, unregister the above signal handler again.	915	Example: For some weird reason, unregister the above signal handler again.
553		916
554	ev_ref (loop);	917	ev_ref (loop);
555	ev_signal_stop (loop, &exitsig);	918	ev_signal_stop (loop, &exitsig);
		919
		920	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		921
		922	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		923
		924	These advanced functions influence the time that libev will spend waiting
		925	for events. Both time intervals are by default C<0>, meaning that libev
		926	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		927	latency.
		928
		929	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		930	allows libev to delay invocation of I/O and timer/periodic callbacks
		931	to increase efficiency of loop iterations (or to increase power-saving
		932	opportunities).
		933
		934	The idea is that sometimes your program runs just fast enough to handle
		935	one (or very few) event(s) per loop iteration. While this makes the
		936	program responsive, it also wastes a lot of CPU time to poll for new
		937	events, especially with backends like C<select ()> which have a high
		938	overhead for the actual polling but can deliver many events at once.
		939
		940	By setting a higher I<io collect interval> you allow libev to spend more
		941	time collecting I/O events, so you can handle more events per iteration,
		942	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		943	C<ev_timer>) will be not affected. Setting this to a non-null value will
		944	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		945	sleep time ensures that libev will not poll for I/O events more often then
		946	once per this interval, on average.
		947
		948	Likewise, by setting a higher I<timeout collect interval> you allow libev
		949	to spend more time collecting timeouts, at the expense of increased
		950	latency/jitter/inexactness (the watcher callback will be called
		951	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		952	value will not introduce any overhead in libev.
		953
		954	Many (busy) programs can usually benefit by setting the I/O collect
		955	interval to a value near C<0.1> or so, which is often enough for
		956	interactive servers (of course not for games), likewise for timeouts. It
		957	usually doesn't make much sense to set it to a lower value than C<0.01>,
		958	as this approaches the timing granularity of most systems. Note that if
		959	you do transactions with the outside world and you can't increase the
		960	parallelity, then this setting will limit your transaction rate (if you
		961	need to poll once per transaction and the I/O collect interval is 0.01,
		962	then you can't do more than 100 transactions per second).
		963
		964	Setting the I<timeout collect interval> can improve the opportunity for
		965	saving power, as the program will "bundle" timer callback invocations that
		966	are "near" in time together, by delaying some, thus reducing the number of
		967	times the process sleeps and wakes up again. Another useful technique to
		968	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		969	they fire on, say, one-second boundaries only.
		970
		971	Example: we only need 0.1s timeout granularity, and we wish not to poll
		972	more often than 100 times per second:
		973
		974	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		975	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		976
		977	=item ev_invoke_pending (loop)
		978
		979	This call will simply invoke all pending watchers while resetting their
		980	pending state. Normally, C<ev_run> does this automatically when required,
		981	but when overriding the invoke callback this call comes handy. This
		982	function can be invoked from a watcher - this can be useful for example
		983	when you want to do some lengthy calculation and want to pass further
		984	event handling to another thread (you still have to make sure only one
		985	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		986
		987	=item int ev_pending_count (loop)
		988
		989	Returns the number of pending watchers - zero indicates that no watchers
		990	are pending.
		991
		992	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		993
		994	This overrides the invoke pending functionality of the loop: Instead of
		995	invoking all pending watchers when there are any, C<ev_run> will call
		996	this callback instead. This is useful, for example, when you want to
		997	invoke the actual watchers inside another context (another thread etc.).
		998
		999	If you want to reset the callback, use C<ev_invoke_pending> as new
		1000	callback.
		1001
		1002	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		1003
		1004	Sometimes you want to share the same loop between multiple threads. This
		1005	can be done relatively simply by putting mutex_lock/unlock calls around
		1006	each call to a libev function.
		1007
		1008	However, C<ev_run> can run an indefinite time, so it is not feasible
		1009	to wait for it to return. One way around this is to wake up the event
		1010	loop via C<ev_break> and C<av_async_send>, another way is to set these
		1011	I<release> and I<acquire> callbacks on the loop.
		1012
		1013	When set, then C<release> will be called just before the thread is
		1014	suspended waiting for new events, and C<acquire> is called just
		1015	afterwards.
		1016
		1017	Ideally, C<release> will just call your mutex_unlock function, and
		1018	C<acquire> will just call the mutex_lock function again.
		1019
		1020	While event loop modifications are allowed between invocations of
		1021	C<release> and C<acquire> (that's their only purpose after all), no
		1022	modifications done will affect the event loop, i.e. adding watchers will
		1023	have no effect on the set of file descriptors being watched, or the time
		1024	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1025	to take note of any changes you made.
		1026
		1027	In theory, threads executing C<ev_run> will be async-cancel safe between
		1028	invocations of C<release> and C<acquire>.
		1029
		1030	See also the locking example in the C<THREADS> section later in this
		1031	document.
		1032
		1033	=item ev_set_userdata (loop, void *data)
		1034
		1035	=item void *ev_userdata (loop)
		1036
		1037	Set and retrieve a single C<void *> associated with a loop. When
		1038	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1039	C<0>.
		1040
		1041	These two functions can be used to associate arbitrary data with a loop,
		1042	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1043	C<acquire> callbacks described above, but of course can be (ab-)used for
		1044	any other purpose as well.
		1045
		1046	=item ev_verify (loop)
		1047
		1048	This function only does something when C<EV_VERIFY> support has been
		1049	compiled in, which is the default for non-minimal builds. It tries to go
		1050	through all internal structures and checks them for validity. If anything
		1051	is found to be inconsistent, it will print an error message to standard
		1052	error and call C<abort ()>.
		1053
		1054	This can be used to catch bugs inside libev itself: under normal
		1055	circumstances, this function will never abort as of course libev keeps its
		1056	data structures consistent.
556		1057
557	=back	1058	=back
558		1059
559		1060
560	=head1 ANATOMY OF A WATCHER	1061	=head1 ANATOMY OF A WATCHER
561		1062
		1063	In the following description, uppercase C<TYPE> in names stands for the
		1064	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1065	watchers and C<ev_io_start> for I/O watchers.
		1066
562	A watcher is a structure that you create and register to record your	1067	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	1068	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:	1069	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1070	for that:
565		1071
566	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1072	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
567	{	1073	{
568	ev_io_stop (w);	1074	ev_io_stop (w);
569	ev_unloop (loop, EVUNLOOP_ALL);	1075	ev_break (loop, EVBREAK_ALL);
570	}	1076	}
571		1077
572	struct ev_loop *loop = ev_default_loop (0);	1078	struct ev_loop *loop = ev_default_loop (0);
		1079
573	struct ev_io stdin_watcher;	1080	ev_io stdin_watcher;
		1081
574	ev_init (&stdin_watcher, my_cb);	1082	ev_init (&stdin_watcher, my_cb);
575	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1083	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
576	ev_io_start (loop, &stdin_watcher);	1084	ev_io_start (loop, &stdin_watcher);
		1085
577	ev_loop (loop, 0);	1086	ev_run (loop, 0);
578		1087
579	As you can see, you are responsible for allocating the memory for your	1088	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,	1089	watcher structures (and it is I<usually> a bad idea to do this on the
581	although this can sometimes be quite valid).	1090	stack).
582		1091
		1092	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1093	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1094
583	Each watcher structure must be initialised by a call to C<ev_init	1095	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	1096	*, 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	1097	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	1098	time the event loop detects that the file descriptor given is readable
587	is readable and/or writable).	1099	and/or writable).
588		1100
589	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1101	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	1102	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	1103	is also a macro to combine initialisation and setting in one call: C<<
592	(watcher *, callback, ...) >>.	1104	ev_TYPE_init (watcher *, callback, ...) >>.
593		1105
594	To make the watcher actually watch out for events, you have to start it	1106	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	1107	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	1108	*) >>), and you can stop watching for events at any time by calling the
597	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1109	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
598		1110
599	As long as your watcher is active (has been started but not stopped) you	1111	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	1112	must not touch the values stored in it. Most specifically you must never
601	reinitialise it or call its C<set> macro.	1113	reinitialise it or call its C<ev_TYPE_set> macro.
602		1114
603	Each and every callback receives the event loop pointer as first, the	1115	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	1116	registered watcher structure as second, and a bitset of received events as
605	third argument.	1117	third argument.
606		1118
…		…
615	=item C<EV_WRITE>	1127	=item C<EV_WRITE>
616		1128
617	The file descriptor in the C<ev_io> watcher has become readable and/or	1129	The file descriptor in the C<ev_io> watcher has become readable and/or
618	writable.	1130	writable.
619		1131
620	=item C<EV_TIMEOUT>	1132	=item C<EV_TIMER>
621		1133
622	The C<ev_timer> watcher has timed out.	1134	The C<ev_timer> watcher has timed out.
623		1135
624	=item C<EV_PERIODIC>	1136	=item C<EV_PERIODIC>
625		1137
…		…
643		1155
644	=item C<EV_PREPARE>	1156	=item C<EV_PREPARE>
645		1157
646	=item C<EV_CHECK>	1158	=item C<EV_CHECK>
647		1159
648	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1160	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	1161	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	1162	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	1163	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	1164	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	1165	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
654	C<ev_loop> from blocking).	1166	C<ev_run> from blocking).
655		1167
656	=item C<EV_EMBED>	1168	=item C<EV_EMBED>
657		1169
658	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1170	The embedded event loop specified in the C<ev_embed> watcher needs attention.
659		1171
660	=item C<EV_FORK>	1172	=item C<EV_FORK>
661		1173
662	The event loop has been resumed in the child process after fork (see	1174	The event loop has been resumed in the child process after fork (see
663	C<ev_fork>).	1175	C<ev_fork>).
664		1176
		1177	=item C<EV_CLEANUP>
		1178
		1179	The event loop is about to be destroyed (see C<ev_cleanup>).
		1180
		1181	=item C<EV_ASYNC>
		1182
		1183	The given async watcher has been asynchronously notified (see C<ev_async>).
		1184
		1185	=item C<EV_CUSTOM>
		1186
		1187	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1188	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1189
665	=item C<EV_ERROR>	1190	=item C<EV_ERROR>
666		1191
667	An unspecified error has occured, the watcher has been stopped. This might	1192	An unspecified error has occurred, the watcher has been stopped. This might
668	happen because the watcher could not be properly started because libev	1193	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	1194	ran out of memory, a file descriptor was found to be closed or any other
		1195	problem. Libev considers these application bugs.
		1196
670	problem. You best act on it by reporting the problem and somehow coping	1197	You best act on it by reporting the problem and somehow coping with the
671	with the watcher being stopped.	1198	watcher being stopped. Note that well-written programs should not receive
		1199	an error ever, so when your watcher receives it, this usually indicates a
		1200	bug in your program.
672		1201
673	Libev will usually signal a few "dummy" events together with an error,	1202	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	1203	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	1204	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	1205	the error from read() or write(). This will not work in multi-threaded
677	programs, though, so beware.	1206	programs, though, as the fd could already be closed and reused for another
		1207	thing, so beware.
678		1208
679	=back	1209	=back
680		1210
681	=head2 GENERIC WATCHER FUNCTIONS	1211	=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		1212
686	=over 4	1213	=over 4
687		1214
688	=item C<ev_init> (ev_TYPE *watcher, callback)	1215	=item C<ev_init> (ev_TYPE *watcher, callback)
689		1216
…		…
695	which rolls both calls into one.	1222	which rolls both calls into one.
696		1223
697	You can reinitialise a watcher at any time as long as it has been stopped	1224	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.	1225	(or never started) and there are no pending events outstanding.
699		1226
700	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1227	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
701	int revents)>.	1228	int revents)>.
702		1229
		1230	Example: Initialise an C<ev_io> watcher in two steps.
		1231
		1232	ev_io w;
		1233	ev_init (&w, my_cb);
		1234	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1235
703	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1236	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
704		1237
705	This macro initialises the type-specific parts of a watcher. You need to	1238	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	1239	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	1240	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	1241	macro on a watcher that is active (it can be pending, however, which is a
709	difference to the C<ev_init> macro).	1242	difference to the C<ev_init> macro).
710		1243
711	Although some watcher types do not have type-specific arguments	1244	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.	1245	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
713		1246
		1247	See C<ev_init>, above, for an example.
		1248
714	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1249	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
715		1250
716	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1251	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	1252	calls into a single call. This is the most convenient method to initialise
718	a watcher. The same limitations apply, of course.	1253	a watcher. The same limitations apply, of course.
719		1254
		1255	Example: Initialise and set an C<ev_io> watcher in one step.
		1256
		1257	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1258
720	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1259	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
721		1260
722	Starts (activates) the given watcher. Only active watchers will receive	1261	Starts (activates) the given watcher. Only active watchers will receive
723	events. If the watcher is already active nothing will happen.	1262	events. If the watcher is already active nothing will happen.
724		1263
		1264	Example: Start the C<ev_io> watcher that is being abused as example in this
		1265	whole section.
		1266
		1267	ev_io_start (EV_DEFAULT_UC, &w);
		1268
725	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1269	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
726		1270
727	Stops the given watcher again (if active) and clears the pending	1271	Stops the given watcher if active, and clears the pending status (whether
		1272	the watcher was active or not).
		1273
728	status. It is possible that stopped watchers are pending (for example,	1274	It is possible that stopped watchers are pending - for example,
729	non-repeating timers are being stopped when they become pending), but	1275	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	1276	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	1277	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.	1278	therefore a good idea to always call its C<ev_TYPE_stop> function.
733		1279
734	=item bool ev_is_active (ev_TYPE *watcher)	1280	=item bool ev_is_active (ev_TYPE *watcher)
735		1281
736	Returns a true value iff the watcher is active (i.e. it has been started	1282	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	1283	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)	1299	=item ev_cb_set (ev_TYPE *watcher, callback)
754		1300
755	Change the callback. You can change the callback at virtually any time	1301	Change the callback. You can change the callback at virtually any time
756	(modulo threads).	1302	(modulo threads).
757		1303
758	=item ev_set_priority (ev_TYPE *watcher, priority)	1304	=item ev_set_priority (ev_TYPE *watcher, int priority)
759		1305
760	=item int ev_priority (ev_TYPE *watcher)	1306	=item int ev_priority (ev_TYPE *watcher)
761		1307
762	Set and query the priority of the watcher. The priority is a small	1308	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>	1309	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
764	(default: C<-2>). Pending watchers with higher priority will be invoked	1310	(default: C<-2>). Pending watchers with higher priority will be invoked
765	before watchers with lower priority, but priority will not keep watchers	1311	before watchers with lower priority, but priority will not keep watchers
766	from being executed (except for C<ev_idle> watchers).	1312	from being executed (except for C<ev_idle> watchers).
767		1313
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	1314	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.	1315	you need to look at C<ev_idle> watchers, which provide this functionality.
775		1316
776	You I<must not> change the priority of a watcher as long as it is active or	1317	You I<must not> change the priority of a watcher as long as it is active or
777	pending.	1318	pending.
778		1319
		1320	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1321	fine, as long as you do not mind that the priority value you query might
		1322	or might not have been clamped to the valid range.
		1323
779	The default priority used by watchers when no priority has been set is	1324	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 :).	1325	always C<0>, which is supposed to not be too high and not be too low :).
781		1326
782	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1327	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	1328	priorities.
784	or might not have been adjusted to be within valid range.
785		1329
786	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1330	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
787		1331
788	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1332	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	1333	C<loop> nor C<revents> need to be valid as long as the watcher callback
790	can deal with that fact.	1334	can deal with that fact, as both are simply passed through to the
		1335	callback.
791		1336
792	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1337	=item int ev_clear_pending (loop, ev_TYPE *watcher)
793		1338
794	If the watcher is pending, this function returns clears its pending status	1339	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	1340	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>.	1341	watcher isn't pending it does nothing and returns C<0>.
797		1342
		1343	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1344	callback to be invoked, which can be accomplished with this function.
		1345
		1346	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1347
		1348	Feeds the given event set into the event loop, as if the specified event
		1349	had happened for the specified watcher (which must be a pointer to an
		1350	initialised but not necessarily started event watcher). Obviously you must
		1351	not free the watcher as long as it has pending events.
		1352
		1353	Stopping the watcher, letting libev invoke it, or calling
		1354	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1355	not started in the first place.
		1356
		1357	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1358	functions that do not need a watcher.
		1359
798	=back	1360	=back
799		1361
800
801	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1362	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
802		1363
803	Each watcher has, by default, a member C<void *data> that you can change	1364	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	1365	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	1366	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	1367	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	1368	member, you can also "subclass" the watcher type and provide your own
808	data:	1369	data:
809		1370
810	struct my_io	1371	struct my_io
811	{	1372	{
812	struct ev_io io;	1373	ev_io io;
813	int otherfd;	1374	int otherfd;
814	void *somedata;	1375	void *somedata;
815	struct whatever *mostinteresting;	1376	struct whatever *mostinteresting;
816	}	1377	};
		1378
		1379	...
		1380	struct my_io w;
		1381	ev_io_init (&w.io, my_cb, fd, EV_READ);
817		1382
818	And since your callback will be called with a pointer to the watcher, you	1383	And since your callback will be called with a pointer to the watcher, you
819	can cast it back to your own type:	1384	can cast it back to your own type:
820		1385
821	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1386	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
822	{	1387	{
823	struct my_io *w = (struct my_io *)w_;	1388	struct my_io *w = (struct my_io *)w_;
824	...	1389	...
825	}	1390	}
826		1391
827	More interesting and less C-conformant ways of casting your callback type	1392	More interesting and less C-conformant ways of casting your callback type
828	instead have been omitted.	1393	instead have been omitted.
829		1394
830	Another common scenario is having some data structure with multiple	1395	Another common scenario is to use some data structure with multiple
831	watchers:	1396	embedded watchers:
832		1397
833	struct my_biggy	1398	struct my_biggy
834	{	1399	{
835	int some_data;	1400	int some_data;
836	ev_timer t1;	1401	ev_timer t1;
837	ev_timer t2;	1402	ev_timer t2;
838	}	1403	}
839		1404
840	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1405	In this case getting the pointer to C<my_biggy> is a bit more
841	you need to use C<offsetof>:	1406	complicated: Either you store the address of your C<my_biggy> struct
		1407	in the C<data> member of the watcher (for woozies), or you need to use
		1408	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1409	programmers):
842		1410
843	#include <stddef.h>	1411	#include <stddef.h>
844		1412
845	static void	1413	static void
846	t1_cb (EV_P_ struct ev_timer *w, int revents)	1414	t1_cb (EV_P_ ev_timer *w, int revents)
847	{	1415	{
848	struct my_biggy big = (struct my_biggy *	1416	struct my_biggy big = (struct my_biggy *)
849	(((char *)w) - offsetof (struct my_biggy, t1));	1417	(((char *)w) - offsetof (struct my_biggy, t1));
850	}	1418	}
851		1419
852	static void	1420	static void
853	t2_cb (EV_P_ struct ev_timer *w, int revents)	1421	t2_cb (EV_P_ ev_timer *w, int revents)
854	{	1422	{
855	struct my_biggy big = (struct my_biggy *	1423	struct my_biggy big = (struct my_biggy *)
856	(((char *)w) - offsetof (struct my_biggy, t2));	1424	(((char *)w) - offsetof (struct my_biggy, t2));
857	}	1425	}
		1426
		1427	=head2 WATCHER STATES
		1428
		1429	There are various watcher states mentioned throughout this manual -
		1430	active, pending and so on. In this section these states and the rules to
		1431	transition between them will be described in more detail - and while these
		1432	rules might look complicated, they usually do "the right thing".
		1433
		1434	=over 4
		1435
		1436	=item initialiased
		1437
		1438	Before a watcher can be registered with the event looop it has to be
		1439	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1440	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1441
		1442	In this state it is simply some block of memory that is suitable for use
		1443	in an event loop. It can be moved around, freed, reused etc. at will.
		1444
		1445	=item started/running/active
		1446
		1447	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1448	property of the event loop, and is actively waiting for events. While in
		1449	this state it cannot be accessed (except in a few documented ways), moved,
		1450	freed or anything else - the only legal thing is to keep a pointer to it,
		1451	and call libev functions on it that are documented to work on active watchers.
		1452
		1453	=item pending
		1454
		1455	If a watcher is active and libev determines that an event it is interested
		1456	in has occurred (such as a timer expiring), it will become pending. It will
		1457	stay in this pending state until either it is stopped or its callback is
		1458	about to be invoked, so it is not normally pending inside the watcher
		1459	callback.
		1460
		1461	The watcher might or might not be active while it is pending (for example,
		1462	an expired non-repeating timer can be pending but no longer active). If it
		1463	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1464	but it is still property of the event loop at this time, so cannot be
		1465	moved, freed or reused. And if it is active the rules described in the
		1466	previous item still apply.
		1467
		1468	It is also possible to feed an event on a watcher that is not active (e.g.
		1469	via C<ev_feed_event>), in which case it becomes pending without being
		1470	active.
		1471
		1472	=item stopped
		1473
		1474	A watcher can be stopped implicitly by libev (in which case it might still
		1475	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1476	latter will clear any pending state the watcher might be in, regardless
		1477	of whether it was active or not, so stopping a watcher explicitly before
		1478	freeing it is often a good idea.
		1479
		1480	While stopped (and not pending) the watcher is essentially in the
		1481	initialised state, that is it can be reused, moved, modified in any way
		1482	you wish.
		1483
		1484	=back
		1485
		1486	=head2 WATCHER PRIORITY MODELS
		1487
		1488	Many event loops support I<watcher priorities>, which are usually small
		1489	integers that influence the ordering of event callback invocation
		1490	between watchers in some way, all else being equal.
		1491
		1492	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1493	description for the more technical details such as the actual priority
		1494	range.
		1495
		1496	There are two common ways how these these priorities are being interpreted
		1497	by event loops:
		1498
		1499	In the more common lock-out model, higher priorities "lock out" invocation
		1500	of lower priority watchers, which means as long as higher priority
		1501	watchers receive events, lower priority watchers are not being invoked.
		1502
		1503	The less common only-for-ordering model uses priorities solely to order
		1504	callback invocation within a single event loop iteration: Higher priority
		1505	watchers are invoked before lower priority ones, but they all get invoked
		1506	before polling for new events.
		1507
		1508	Libev uses the second (only-for-ordering) model for all its watchers
		1509	except for idle watchers (which use the lock-out model).
		1510
		1511	The rationale behind this is that implementing the lock-out model for
		1512	watchers is not well supported by most kernel interfaces, and most event
		1513	libraries will just poll for the same events again and again as long as
		1514	their callbacks have not been executed, which is very inefficient in the
		1515	common case of one high-priority watcher locking out a mass of lower
		1516	priority ones.
		1517
		1518	Static (ordering) priorities are most useful when you have two or more
		1519	watchers handling the same resource: a typical usage example is having an
		1520	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1521	timeouts. Under load, data might be received while the program handles
		1522	other jobs, but since timers normally get invoked first, the timeout
		1523	handler will be executed before checking for data. In that case, giving
		1524	the timer a lower priority than the I/O watcher ensures that I/O will be
		1525	handled first even under adverse conditions (which is usually, but not
		1526	always, what you want).
		1527
		1528	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1529	will only be executed when no same or higher priority watchers have
		1530	received events, they can be used to implement the "lock-out" model when
		1531	required.
		1532
		1533	For example, to emulate how many other event libraries handle priorities,
		1534	you can associate an C<ev_idle> watcher to each such watcher, and in
		1535	the normal watcher callback, you just start the idle watcher. The real
		1536	processing is done in the idle watcher callback. This causes libev to
		1537	continuously poll and process kernel event data for the watcher, but when
		1538	the lock-out case is known to be rare (which in turn is rare :), this is
		1539	workable.
		1540
		1541	Usually, however, the lock-out model implemented that way will perform
		1542	miserably under the type of load it was designed to handle. In that case,
		1543	it might be preferable to stop the real watcher before starting the
		1544	idle watcher, so the kernel will not have to process the event in case
		1545	the actual processing will be delayed for considerable time.
		1546
		1547	Here is an example of an I/O watcher that should run at a strictly lower
		1548	priority than the default, and which should only process data when no
		1549	other events are pending:
		1550
		1551	ev_idle idle; // actual processing watcher
		1552	ev_io io; // actual event watcher
		1553
		1554	static void
		1555	io_cb (EV_P_ ev_io *w, int revents)
		1556	{
		1557	// stop the I/O watcher, we received the event, but
		1558	// are not yet ready to handle it.
		1559	ev_io_stop (EV_A_ w);
		1560
		1561	// start the idle watcher to handle the actual event.
		1562	// it will not be executed as long as other watchers
		1563	// with the default priority are receiving events.
		1564	ev_idle_start (EV_A_ &idle);
		1565	}
		1566
		1567	static void
		1568	idle_cb (EV_P_ ev_idle *w, int revents)
		1569	{
		1570	// actual processing
		1571	read (STDIN_FILENO, ...);
		1572
		1573	// have to start the I/O watcher again, as
		1574	// we have handled the event
		1575	ev_io_start (EV_P_ &io);
		1576	}
		1577
		1578	// initialisation
		1579	ev_idle_init (&idle, idle_cb);
		1580	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1581	ev_io_start (EV_DEFAULT_ &io);
		1582
		1583	In the "real" world, it might also be beneficial to start a timer, so that
		1584	low-priority connections can not be locked out forever under load. This
		1585	enables your program to keep a lower latency for important connections
		1586	during short periods of high load, while not completely locking out less
		1587	important ones.
858		1588
859		1589
860	=head1 WATCHER TYPES	1590	=head1 WATCHER TYPES
861		1591
862	This section describes each watcher in detail, but will not repeat	1592	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	1616	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	1617	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	1618	descriptors to non-blocking mode is also usually a good idea (but not
889	required if you know what you are doing).	1619	required if you know what you are doing).
890		1620
891	You have to be careful with dup'ed file descriptors, though. Some backends
892	(the linux epoll backend is a notable example) cannot handle dup'ed file
893	descriptors correctly if you register interest in two or more fds pointing
894	to the same underlying file/socket/etc. description (that is, they share
895	the same underlying "file open").
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
901	Another thing you have to watch out for is that it is quite easy to	1621	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	1622	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	1623	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	1624	because there is no data. It is very easy to get into this situation even
905	lot of those (for example solaris ports), it is very easy to get into	1625	with a relatively standard program structure. Thus it is best to always
906	this situation even with a relatively standard program structure. Thus	1626	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
907	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.	1627	preferable to a program hanging until some data arrives.
909		1628
910	If you cannot run the fd in non-blocking mode (for example you should not	1629	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	1630	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	1631	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	1632	interface such as poll (fortunately in the case of Xlib, it already does
914	its own, so its quite safe to use).	1633	this on its own, so its quite safe to use). Some people additionally
		1634	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1635	indefinitely.
		1636
		1637	But really, best use non-blocking mode.
915		1638
916	=head3 The special problem of disappearing file descriptors	1639	=head3 The special problem of disappearing file descriptors
917		1640
918	Some backends (e.g kqueue, epoll) need to be told about closing a file	1641	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,	1642	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	1643	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	1644	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	1645	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	1646	registered with libev, there is no efficient way to see that this is, in
924	fact, a different file descriptor.	1647	fact, a different file descriptor.
925		1648
…		…
932		1655
933	This is how one would do it normally anyway, the important point is that	1656	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	1657	the libev application should not optimise around libev but should leave
935	optimisations to libev.	1658	optimisations to libev.
936		1659
		1660	=head3 The special problem of dup'ed file descriptors
		1661
		1662	Some backends (e.g. epoll), cannot register events for file descriptors,
		1663	but only events for the underlying file descriptions. That means when you
		1664	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1665	events for them, only one file descriptor might actually receive events.
		1666
		1667	There is no workaround possible except not registering events
		1668	for potentially C<dup ()>'ed file descriptors, or to resort to
		1669	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1670
		1671	=head3 The special problem of files
		1672
		1673	Many people try to use C<select> (or libev) on file descriptors
		1674	representing files, and expect it to become ready when their program
		1675	doesn't block on disk accesses (which can take a long time on their own).
		1676
		1677	However, this cannot ever work in the "expected" way - you get a readiness
		1678	notification as soon as the kernel knows whether and how much data is
		1679	there, and in the case of open files, that's always the case, so you
		1680	always get a readiness notification instantly, and your read (or possibly
		1681	write) will still block on the disk I/O.
		1682
		1683	Another way to view it is that in the case of sockets, pipes, character
		1684	devices and so on, there is another party (the sender) that delivers data
		1685	on it's own, but in the case of files, there is no such thing: the disk
		1686	will not send data on it's own, simply because it doesn't know what you
		1687	wish to read - you would first have to request some data.
		1688
		1689	Since files are typically not-so-well supported by advanced notification
		1690	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1691	to files, even though you should not use it. The reason for this is
		1692	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1693	usually a tty, often a pipe, but also sometimes files or special devices
		1694	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1695	F</dev/urandom>), and even though the file might better be served with
		1696	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1697	it "just works" instead of freezing.
		1698
		1699	So avoid file descriptors pointing to files when you know it (e.g. use
		1700	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1701	when you rarely read from a file instead of from a socket, and want to
		1702	reuse the same code path.
		1703
		1704	=head3 The special problem of fork
		1705
		1706	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1707	useless behaviour. Libev fully supports fork, but needs to be told about
		1708	it in the child if you want to continue to use it in the child.
		1709
		1710	To support fork in your child processes, you have to call C<ev_loop_fork
		1711	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
		1712	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1713
		1714	=head3 The special problem of SIGPIPE
		1715
		1716	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1717	when writing to a pipe whose other end has been closed, your program gets
		1718	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1719	this is sensible behaviour, for daemons, this is usually undesirable.
		1720
		1721	So when you encounter spurious, unexplained daemon exits, make sure you
		1722	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1723	somewhere, as that would have given you a big clue).
		1724
		1725	=head3 The special problem of accept()ing when you can't
		1726
		1727	Many implementations of the POSIX C<accept> function (for example,
		1728	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1729	connection from the pending queue in all error cases.
		1730
		1731	For example, larger servers often run out of file descriptors (because
		1732	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1733	rejecting the connection, leading to libev signalling readiness on
		1734	the next iteration again (the connection still exists after all), and
		1735	typically causing the program to loop at 100% CPU usage.
		1736
		1737	Unfortunately, the set of errors that cause this issue differs between
		1738	operating systems, there is usually little the app can do to remedy the
		1739	situation, and no known thread-safe method of removing the connection to
		1740	cope with overload is known (to me).
		1741
		1742	One of the easiest ways to handle this situation is to just ignore it
		1743	- when the program encounters an overload, it will just loop until the
		1744	situation is over. While this is a form of busy waiting, no OS offers an
		1745	event-based way to handle this situation, so it's the best one can do.
		1746
		1747	A better way to handle the situation is to log any errors other than
		1748	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1749	messages, and continue as usual, which at least gives the user an idea of
		1750	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1751	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1752	usage.
		1753
		1754	If your program is single-threaded, then you could also keep a dummy file
		1755	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1756	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1757	close that fd, and create a new dummy fd. This will gracefully refuse
		1758	clients under typical overload conditions.
		1759
		1760	The last way to handle it is to simply log the error and C<exit>, as
		1761	is often done with C<malloc> failures, but this results in an easy
		1762	opportunity for a DoS attack.
937		1763
938	=head3 Watcher-Specific Functions	1764	=head3 Watcher-Specific Functions
939		1765
940	=over 4	1766	=over 4
941		1767
942	=item ev_io_init (ev_io *, callback, int fd, int events)	1768	=item ev_io_init (ev_io *, callback, int fd, int events)
943		1769
944	=item ev_io_set (ev_io *, int fd, int events)	1770	=item ev_io_set (ev_io *, int fd, int events)
945		1771
946	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1772	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	1773	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.	1774	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
949		1775
950	=item int fd [read-only]	1776	=item int fd [read-only]
951		1777
952	The file descriptor being watched.	1778	The file descriptor being watched.
953		1779
954	=item int events [read-only]	1780	=item int events [read-only]
955		1781
956	The events being watched.	1782	The events being watched.
957		1783
958	=back	1784	=back
		1785
		1786	=head3 Examples
959		1787
960	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1788	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	1789	readable, but only once. Since it is likely line-buffered, you could
962	attempt to read a whole line in the callback.	1790	attempt to read a whole line in the callback.
963		1791
964	static void	1792	static void
965	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1793	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
966	{	1794	{
967	ev_io_stop (loop, w);	1795	ev_io_stop (loop, w);
968	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1796	.. read from stdin here (or from w->fd) and handle any I/O errors
969	}	1797	}
970		1798
971	...	1799	...
972	struct ev_loop *loop = ev_default_init (0);	1800	struct ev_loop *loop = ev_default_init (0);
973	struct ev_io stdin_readable;	1801	ev_io stdin_readable;
974	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1802	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
975	ev_io_start (loop, &stdin_readable);	1803	ev_io_start (loop, &stdin_readable);
976	ev_loop (loop, 0);	1804	ev_run (loop, 0);
977		1805
978		1806
979	=head2 C<ev_timer> - relative and optionally repeating timeouts	1807	=head2 C<ev_timer> - relative and optionally repeating timeouts
980		1808
981	Timer watchers are simple relative timers that generate an event after a	1809	Timer watchers are simple relative timers that generate an event after a
982	given time, and optionally repeating in regular intervals after that.	1810	given time, and optionally repeating in regular intervals after that.
983		1811
984	The timers are based on real time, that is, if you register an event that	1812	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	1813	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	1814	year, it will still time out after (roughly) one hour. "Roughly" because
987	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1815	detecting time jumps is hard, and some inaccuracies are unavoidable (the
988	monotonic clock option helps a lot here).	1816	monotonic clock option helps a lot here).
		1817
		1818	The callback is guaranteed to be invoked only I<after> its timeout has
		1819	passed (not I<at>, so on systems with very low-resolution clocks this
		1820	might introduce a small delay). If multiple timers become ready during the
		1821	same loop iteration then the ones with earlier time-out values are invoked
		1822	before ones of the same priority with later time-out values (but this is
		1823	no longer true when a callback calls C<ev_run> recursively).
		1824
		1825	=head3 Be smart about timeouts
		1826
		1827	Many real-world problems involve some kind of timeout, usually for error
		1828	recovery. A typical example is an HTTP request - if the other side hangs,
		1829	you want to raise some error after a while.
		1830
		1831	What follows are some ways to handle this problem, from obvious and
		1832	inefficient to smart and efficient.
		1833
		1834	In the following, a 60 second activity timeout is assumed - a timeout that
		1835	gets reset to 60 seconds each time there is activity (e.g. each time some
		1836	data or other life sign was received).
		1837
		1838	=over 4
		1839
		1840	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1841
		1842	This is the most obvious, but not the most simple way: In the beginning,
		1843	start the watcher:
		1844
		1845	ev_timer_init (timer, callback, 60., 0.);
		1846	ev_timer_start (loop, timer);
		1847
		1848	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1849	and start it again:
		1850
		1851	ev_timer_stop (loop, timer);
		1852	ev_timer_set (timer, 60., 0.);
		1853	ev_timer_start (loop, timer);
		1854
		1855	This is relatively simple to implement, but means that each time there is
		1856	some activity, libev will first have to remove the timer from its internal
		1857	data structure and then add it again. Libev tries to be fast, but it's
		1858	still not a constant-time operation.
		1859
		1860	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1861
		1862	This is the easiest way, and involves using C<ev_timer_again> instead of
		1863	C<ev_timer_start>.
		1864
		1865	To implement this, configure an C<ev_timer> with a C<repeat> value
		1866	of C<60> and then call C<ev_timer_again> at start and each time you
		1867	successfully read or write some data. If you go into an idle state where
		1868	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1869	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1870
		1871	That means you can ignore both the C<ev_timer_start> function and the
		1872	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1873	member and C<ev_timer_again>.
		1874
		1875	At start:
		1876
		1877	ev_init (timer, callback);
		1878	timer->repeat = 60.;
		1879	ev_timer_again (loop, timer);
		1880
		1881	Each time there is some activity:
		1882
		1883	ev_timer_again (loop, timer);
		1884
		1885	It is even possible to change the time-out on the fly, regardless of
		1886	whether the watcher is active or not:
		1887
		1888	timer->repeat = 30.;
		1889	ev_timer_again (loop, timer);
		1890
		1891	This is slightly more efficient then stopping/starting the timer each time
		1892	you want to modify its timeout value, as libev does not have to completely
		1893	remove and re-insert the timer from/into its internal data structure.
		1894
		1895	It is, however, even simpler than the "obvious" way to do it.
		1896
		1897	=item 3. Let the timer time out, but then re-arm it as required.
		1898
		1899	This method is more tricky, but usually most efficient: Most timeouts are
		1900	relatively long compared to the intervals between other activity - in
		1901	our example, within 60 seconds, there are usually many I/O events with
		1902	associated activity resets.
		1903
		1904	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1905	but remember the time of last activity, and check for a real timeout only
		1906	within the callback:
		1907
		1908	ev_tstamp last_activity; // time of last activity
		1909
		1910	static void
		1911	callback (EV_P_ ev_timer *w, int revents)
		1912	{
		1913	ev_tstamp now = ev_now (EV_A);
		1914	ev_tstamp timeout = last_activity + 60.;
		1915
		1916	// if last_activity + 60. is older than now, we did time out
		1917	if (timeout < now)
		1918	{
		1919	// timeout occurred, take action
		1920	}
		1921	else
		1922	{
		1923	// callback was invoked, but there was some activity, re-arm
		1924	// the watcher to fire in last_activity + 60, which is
		1925	// guaranteed to be in the future, so "again" is positive:
		1926	w->repeat = timeout - now;
		1927	ev_timer_again (EV_A_ w);
		1928	}
		1929	}
		1930
		1931	To summarise the callback: first calculate the real timeout (defined
		1932	as "60 seconds after the last activity"), then check if that time has
		1933	been reached, which means something I<did>, in fact, time out. Otherwise
		1934	the callback was invoked too early (C<timeout> is in the future), so
		1935	re-schedule the timer to fire at that future time, to see if maybe we have
		1936	a timeout then.
		1937
		1938	Note how C<ev_timer_again> is used, taking advantage of the
		1939	C<ev_timer_again> optimisation when the timer is already running.
		1940
		1941	This scheme causes more callback invocations (about one every 60 seconds
		1942	minus half the average time between activity), but virtually no calls to
		1943	libev to change the timeout.
		1944
		1945	To start the timer, simply initialise the watcher and set C<last_activity>
		1946	to the current time (meaning we just have some activity :), then call the
		1947	callback, which will "do the right thing" and start the timer:
		1948
		1949	ev_init (timer, callback);
		1950	last_activity = ev_now (loop);
		1951	callback (loop, timer, EV_TIMER);
		1952
		1953	And when there is some activity, simply store the current time in
		1954	C<last_activity>, no libev calls at all:
		1955
		1956	last_activity = ev_now (loop);
		1957
		1958	This technique is slightly more complex, but in most cases where the
		1959	time-out is unlikely to be triggered, much more efficient.
		1960
		1961	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1962	callback :) - just change the timeout and invoke the callback, which will
		1963	fix things for you.
		1964
		1965	=item 4. Wee, just use a double-linked list for your timeouts.
		1966
		1967	If there is not one request, but many thousands (millions...), all
		1968	employing some kind of timeout with the same timeout value, then one can
		1969	do even better:
		1970
		1971	When starting the timeout, calculate the timeout value and put the timeout
		1972	at the I<end> of the list.
		1973
		1974	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1975	the list is expected to fire (for example, using the technique #3).
		1976
		1977	When there is some activity, remove the timer from the list, recalculate
		1978	the timeout, append it to the end of the list again, and make sure to
		1979	update the C<ev_timer> if it was taken from the beginning of the list.
		1980
		1981	This way, one can manage an unlimited number of timeouts in O(1) time for
		1982	starting, stopping and updating the timers, at the expense of a major
		1983	complication, and having to use a constant timeout. The constant timeout
		1984	ensures that the list stays sorted.
		1985
		1986	=back
		1987
		1988	So which method the best?
		1989
		1990	Method #2 is a simple no-brain-required solution that is adequate in most
		1991	situations. Method #3 requires a bit more thinking, but handles many cases
		1992	better, and isn't very complicated either. In most case, choosing either
		1993	one is fine, with #3 being better in typical situations.
		1994
		1995	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1996	rather complicated, but extremely efficient, something that really pays
		1997	off after the first million or so of active timers, i.e. it's usually
		1998	overkill :)
		1999
		2000	=head3 The special problem of time updates
		2001
		2002	Establishing the current time is a costly operation (it usually takes at
		2003	least two system calls): EV therefore updates its idea of the current
		2004	time only before and after C<ev_run> collects new events, which causes a
		2005	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2006	lots of events in one iteration.
989		2007
990	The relative timeouts are calculated relative to the C<ev_now ()>	2008	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	2009	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	2010	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	2011	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:	2012	timeout on the current time, use something like this to adjust for this:
995		2013
996	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2014	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
997		2015
998	The callback is guarenteed to be invoked only when its timeout has passed,	2016	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	2017	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1000	order of execution is undefined.	2018	()>.
		2019
		2020	=head3 The special problems of suspended animation
		2021
		2022	When you leave the server world it is quite customary to hit machines that
		2023	can suspend/hibernate - what happens to the clocks during such a suspend?
		2024
		2025	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2026	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2027	to run until the system is suspended, but they will not advance while the
		2028	system is suspended. That means, on resume, it will be as if the program
		2029	was frozen for a few seconds, but the suspend time will not be counted
		2030	towards C<ev_timer> when a monotonic clock source is used. The real time
		2031	clock advanced as expected, but if it is used as sole clocksource, then a
		2032	long suspend would be detected as a time jump by libev, and timers would
		2033	be adjusted accordingly.
		2034
		2035	I would not be surprised to see different behaviour in different between
		2036	operating systems, OS versions or even different hardware.
		2037
		2038	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2039	time jump in the monotonic clocks and the realtime clock. If the program
		2040	is suspended for a very long time, and monotonic clock sources are in use,
		2041	then you can expect C<ev_timer>s to expire as the full suspension time
		2042	will be counted towards the timers. When no monotonic clock source is in
		2043	use, then libev will again assume a timejump and adjust accordingly.
		2044
		2045	It might be beneficial for this latter case to call C<ev_suspend>
		2046	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2047	deterministic behaviour in this case (you can do nothing against
		2048	C<SIGSTOP>).
1001		2049
1002	=head3 Watcher-Specific Functions and Data Members	2050	=head3 Watcher-Specific Functions and Data Members
1003		2051
1004	=over 4	2052	=over 4
1005		2053
1006	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2054	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1007		2055
1008	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2056	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1009		2057
1010	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2058	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	2059	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	2060	reached. If it is positive, then the timer will automatically be
1013	later, again, and again, until stopped manually.	2061	configured to trigger again C<repeat> seconds later, again, and again,
		2062	until stopped manually.
1014		2063
1015	The timer itself will do a best-effort at avoiding drift, that is, if you	2064	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	2065	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	2066	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	2067	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.	2068	do stuff) the timer will not fire more than once per event loop iteration.
1020		2069
1021	=item ev_timer_again (loop)	2070	=item ev_timer_again (loop, ev_timer *)
1022		2071
1023	This will act as if the timer timed out and restart it again if it is	2072	This will act as if the timer timed out and restart it again if it is
1024	repeating. The exact semantics are:	2073	repeating. The exact semantics are:
1025		2074
1026	If the timer is pending, its pending status is cleared.	2075	If the timer is pending, its pending status is cleared.
1027		2076
1028	If the timer is started but nonrepeating, stop it (as if it timed out).	2077	If the timer is started but non-repeating, stop it (as if it timed out).
1029		2078
1030	If the timer is repeating, either start it if necessary (with the	2079	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.	2080	C<repeat> value), or reset the running timer to the C<repeat> value.
1032		2081
1033	This sounds a bit complicated, but here is a useful and typical	2082	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	2083	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		2084
1043	That means you can ignore the C<after> value and C<ev_timer_start>	2085	=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		2086
1046	ev_timer_init (timer, callback, 0., 5.);	2087	Returns the remaining time until a timer fires. If the timer is active,
1047	ev_timer_again (loop, timer);	2088	then this time is relative to the current event loop time, otherwise it's
1048	...	2089	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		2090
1055	This is more slightly efficient then stopping/starting the timer each time	2091	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1056	you want to modify its timeout value.	2092	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2093	will return C<4>. When the timer expires and is restarted, it will return
		2094	roughly C<7> (likely slightly less as callback invocation takes some time,
		2095	too), and so on.
1057		2096
1058	=item ev_tstamp repeat [read-write]	2097	=item ev_tstamp repeat [read-write]
1059		2098
1060	The current C<repeat> value. Will be used each time the watcher times out	2099	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),	2100	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.	2101	which is also when any modifications are taken into account.
1063		2102
1064	=back	2103	=back
1065		2104
		2105	=head3 Examples
		2106
1066	Example: Create a timer that fires after 60 seconds.	2107	Example: Create a timer that fires after 60 seconds.
1067		2108
1068	static void	2109	static void
1069	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2110	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1070	{	2111	{
1071	.. one minute over, w is actually stopped right here	2112	.. one minute over, w is actually stopped right here
1072	}	2113	}
1073		2114
1074	struct ev_timer mytimer;	2115	ev_timer mytimer;
1075	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2116	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1076	ev_timer_start (loop, &mytimer);	2117	ev_timer_start (loop, &mytimer);
1077		2118
1078	Example: Create a timeout timer that times out after 10 seconds of	2119	Example: Create a timeout timer that times out after 10 seconds of
1079	inactivity.	2120	inactivity.
1080		2121
1081	static void	2122	static void
1082	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2123	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1083	{	2124	{
1084	.. ten seconds without any activity	2125	.. ten seconds without any activity
1085	}	2126	}
1086		2127
1087	struct ev_timer mytimer;	2128	ev_timer mytimer;
1088	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2129	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1089	ev_timer_again (&mytimer); /* start timer */	2130	ev_timer_again (&mytimer); /* start timer */
1090	ev_loop (loop, 0);	2131	ev_run (loop, 0);
1091		2132
1092	// and in some piece of code that gets executed on any "activity":	2133	// and in some piece of code that gets executed on any "activity":
1093	// reset the timeout to start ticking again at 10 seconds	2134	// reset the timeout to start ticking again at 10 seconds
1094	ev_timer_again (&mytimer);	2135	ev_timer_again (&mytimer);
1095		2136
1096		2137
1097	=head2 C<ev_periodic> - to cron or not to cron?	2138	=head2 C<ev_periodic> - to cron or not to cron?
1098		2139
1099	Periodic watchers are also timers of a kind, but they are very versatile	2140	Periodic watchers are also timers of a kind, but they are very versatile
1100	(and unfortunately a bit complex).	2141	(and unfortunately a bit complex).
1101		2142
1102	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2143	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	2144	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	2145	(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 ()	2146	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	2147	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	2148	wrist-watch).
1108	roughly 10 seconds later).
1109		2149
1110	They can also be used to implement vastly more complex timers, such as	2150	You can tell a periodic watcher to trigger after some specific point
1111	triggering an event on each midnight, local time or other, complicated,	2151	in time: for example, if you tell a periodic watcher to trigger "in 10
1112	rules.	2152	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2153	not a delay) and then reset your system clock to January of the previous
		2154	year, then it will take a year or more to trigger the event (unlike an
		2155	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2156	it, as it uses a relative timeout).
1113		2157
		2158	C<ev_periodic> watchers can also be used to implement vastly more complex
		2159	timers, such as triggering an event on each "midnight, local time", or
		2160	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2161	those cannot react to time jumps.
		2162
1114	As with timers, the callback is guarenteed to be invoked only when the	2163	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	2164	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.	2165	timers become ready during the same loop iteration then the ones with
		2166	earlier time-out values are invoked before ones with later time-out values
		2167	(but this is no longer true when a callback calls C<ev_run> recursively).
1117		2168
1118	=head3 Watcher-Specific Functions and Data Members	2169	=head3 Watcher-Specific Functions and Data Members
1119		2170
1120	=over 4	2171	=over 4
1121		2172
1122	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2173	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1123		2174
1124	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2175	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1125		2176
1126	Lots of arguments, lets sort it out... There are basically three modes of	2177	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:	2178	operation, and we will explain them from simplest to most complex:
1128		2179
1129	=over 4	2180	=over 4
1130		2181
1131	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2182	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1132		2183
1133	In this configuration the watcher triggers an event at the wallclock time	2184	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,	2185	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	2186	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.	2187	will be stopped and invoked when the system clock reaches or surpasses
		2188	this point in time.
1137		2189
1138	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2190	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1139		2191
1140	In this mode the watcher will always be scheduled to time out at the next	2192	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)	2193	C<offset + N * interval> time (for some integer N, which can also be
1142	and then repeat, regardless of any time jumps.	2194	negative) and then repeat, regardless of any time jumps. The C<offset>
		2195	argument is merely an offset into the C<interval> periods.
1143		2196
1144	This can be used to create timers that do not drift with respect to system	2197	This can be used to create timers that do not drift with respect to the
1145	time:	2198	system clock, for example, here is an C<ev_periodic> that triggers each
		2199	hour, on the hour (with respect to UTC):
1146		2200
1147	ev_periodic_set (&periodic, 0., 3600., 0);	2201	ev_periodic_set (&periodic, 0., 3600., 0);
1148		2202
1149	This doesn't mean there will always be 3600 seconds in between triggers,	2203	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	2204	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	2205	full hour (UTC), or more correctly, when the system time is evenly divisible
1152	by 3600.	2206	by 3600.
1153		2207
1154	Another way to think about it (for the mathematically inclined) is that	2208	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	2209	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.	2210	time where C<time = offset (mod interval)>, regardless of any time jumps.
1157		2211
1158	For numerical stability it is preferable that the C<at> value is near	2212	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	2213	C<ev_now ()> (the current time), but there is no range requirement for
1160	this value.	2214	this value, and in fact is often specified as zero.
1161		2215
		2216	Note also that there is an upper limit to how often a timer can fire (CPU
		2217	speed for example), so if C<interval> is very small then timing stability
		2218	will of course deteriorate. Libev itself tries to be exact to be about one
		2219	millisecond (if the OS supports it and the machine is fast enough).
		2220
1162	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2221	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1163		2222
1164	In this mode the values for C<interval> and C<at> are both being	2223	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	2224	ignored. Instead, each time the periodic watcher gets scheduled, the
1166	reschedule callback will be called with the watcher as first, and the	2225	reschedule callback will be called with the watcher as first, and the
1167	current time as second argument.	2226	current time as second argument.
1168		2227
1169	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2228	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,	2229	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	2230	allowed by documentation here>.
1172	starting an C<ev_prepare> watcher, which is legal).
1173		2231
		2232	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2233	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2234	only event loop modification you are allowed to do).
		2235
1174	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2236	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1175	ev_tstamp now)>, e.g.:	2237	*w, ev_tstamp now)>, e.g.:
1176		2238
		2239	static ev_tstamp
1177	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2240	my_rescheduler (ev_periodic *w, ev_tstamp now)
1178	{	2241	{
1179	return now + 60.;	2242	return now + 60.;
1180	}	2243	}
1181		2244
1182	It must return the next time to trigger, based on the passed time value	2245	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	2246	(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	2247	will usually be called just before the callback will be triggered, but
1185	might be called at other times, too.	2248	might be called at other times, too.
1186		2249
1187	NOTE: I<< This callback must always return a time that is later than the	2250	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.	2251	equal to the passed C<now> value >>.
1189		2252
1190	This can be used to create very complex timers, such as a timer that	2253	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	2254	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	2255	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	2256	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).	2257	reason I omitted it as an example).
1195		2258
1196	=back	2259	=back
…		…
1200	Simply stops and restarts the periodic watcher again. This is only useful	2263	Simply stops and restarts the periodic watcher again. This is only useful
1201	when you changed some parameters or the reschedule callback would return	2264	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	2265	a different time than the last time it was called (e.g. in a crond like
1203	program when the crontabs have changed).	2266	program when the crontabs have changed).
1204		2267
		2268	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2269
		2270	When active, returns the absolute time that the watcher is supposed
		2271	to trigger next. This is not the same as the C<offset> argument to
		2272	C<ev_periodic_set>, but indeed works even in interval and manual
		2273	rescheduling modes.
		2274
1205	=item ev_tstamp offset [read-write]	2275	=item ev_tstamp offset [read-write]
1206		2276
1207	When repeating, this contains the offset value, otherwise this is the	2277	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>).	2278	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2279	although libev might modify this value for better numerical stability).
1209		2280
1210	Can be modified any time, but changes only take effect when the periodic	2281	Can be modified any time, but changes only take effect when the periodic
1211	timer fires or C<ev_periodic_again> is being called.	2282	timer fires or C<ev_periodic_again> is being called.
1212		2283
1213	=item ev_tstamp interval [read-write]	2284	=item ev_tstamp interval [read-write]
1214		2285
1215	The current interval value. Can be modified any time, but changes only	2286	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	2287	take effect when the periodic timer fires or C<ev_periodic_again> is being
1217	called.	2288	called.
1218		2289
1219	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2290	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1220		2291
1221	The current reschedule callback, or C<0>, if this functionality is	2292	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	2293	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.	2294	the periodic timer fires or C<ev_periodic_again> is being called.
1224		2295
1225	=back	2296	=back
1226		2297
		2298	=head3 Examples
		2299
1227	Example: Call a callback every hour, or, more precisely, whenever the	2300	Example: Call a callback every hour, or, more precisely, whenever the
1228	system clock is divisible by 3600. The callback invocation times have	2301	system time is divisible by 3600. The callback invocation times have
1229	potentially a lot of jittering, but good long-term stability.	2302	potentially a lot of jitter, but good long-term stability.
1230		2303
1231	static void	2304	static void
1232	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2305	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1233	{	2306	{
1234	... its now a full hour (UTC, or TAI or whatever your clock follows)	2307	... its now a full hour (UTC, or TAI or whatever your clock follows)
1235	}	2308	}
1236		2309
1237	struct ev_periodic hourly_tick;	2310	ev_periodic hourly_tick;
1238	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2311	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1239	ev_periodic_start (loop, &hourly_tick);	2312	ev_periodic_start (loop, &hourly_tick);
1240		2313
1241	Example: The same as above, but use a reschedule callback to do it:	2314	Example: The same as above, but use a reschedule callback to do it:
1242		2315
1243	#include <math.h>	2316	#include <math.h>
1244		2317
1245	static ev_tstamp	2318	static ev_tstamp
1246	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2319	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1247	{	2320	{
1248	return fmod (now, 3600.) + 3600.;	2321	return now + (3600. - fmod (now, 3600.));
1249	}	2322	}
1250		2323
1251	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2324	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1252		2325
1253	Example: Call a callback every hour, starting now:	2326	Example: Call a callback every hour, starting now:
1254		2327
1255	struct ev_periodic hourly_tick;	2328	ev_periodic hourly_tick;
1256	ev_periodic_init (&hourly_tick, clock_cb,	2329	ev_periodic_init (&hourly_tick, clock_cb,
1257	fmod (ev_now (loop), 3600.), 3600., 0);	2330	fmod (ev_now (loop), 3600.), 3600., 0);
1258	ev_periodic_start (loop, &hourly_tick);	2331	ev_periodic_start (loop, &hourly_tick);
1259		2332
1260		2333
1261	=head2 C<ev_signal> - signal me when a signal gets signalled!	2334	=head2 C<ev_signal> - signal me when a signal gets signalled!
1262		2335
1263	Signal watchers will trigger an event when the process receives a specific	2336	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	2337	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	2338	will try its best to deliver signals synchronously, i.e. as part of the
1266	normal event processing, like any other event.	2339	normal event processing, like any other event.
1267		2340
		2341	If you want signals to be delivered truly asynchronously, just use
		2342	C<sigaction> as you would do without libev and forget about sharing
		2343	the signal. You can even use C<ev_async> from a signal handler to
		2344	synchronously wake up an event loop.
		2345
1268	You can configure as many watchers as you like per signal. Only when the	2346	You can configure as many watchers as you like for the same signal, but
		2347	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2348	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2349	C<SIGINT> in both the default loop and another loop at the same time. At
		2350	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2351
1269	first watcher gets started will libev actually register a signal watcher	2352	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	2353	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	2354	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	2355
1273	SIG_DFL (regardless of what it was set to before).	2356	If possible and supported, libev will install its handlers with
		2357	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2358	not be unduly interrupted. If you have a problem with system calls getting
		2359	interrupted by signals you can block all signals in an C<ev_check> watcher
		2360	and unblock them in an C<ev_prepare> watcher.
		2361
		2362	=head3 The special problem of inheritance over fork/execve/pthread_create
		2363
		2364	Both the signal mask (C<sigprocmask>) and the signal disposition
		2365	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2366	stopping it again), that is, libev might or might not block the signal,
		2367	and might or might not set or restore the installed signal handler.
		2368
		2369	While this does not matter for the signal disposition (libev never
		2370	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2371	C<execve>), this matters for the signal mask: many programs do not expect
		2372	certain signals to be blocked.
		2373
		2374	This means that before calling C<exec> (from the child) you should reset
		2375	the signal mask to whatever "default" you expect (all clear is a good
		2376	choice usually).
		2377
		2378	The simplest way to ensure that the signal mask is reset in the child is
		2379	to install a fork handler with C<pthread_atfork> that resets it. That will
		2380	catch fork calls done by libraries (such as the libc) as well.
		2381
		2382	In current versions of libev, the signal will not be blocked indefinitely
		2383	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2384	the window of opportunity for problems, it will not go away, as libev
		2385	I<has> to modify the signal mask, at least temporarily.
		2386
		2387	So I can't stress this enough: I<If you do not reset your signal mask when
		2388	you expect it to be empty, you have a race condition in your code>. This
		2389	is not a libev-specific thing, this is true for most event libraries.
		2390
		2391	=head3 The special problem of threads signal handling
		2392
		2393	POSIX threads has problematic signal handling semantics, specifically,
		2394	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2395	threads in a process block signals, which is hard to achieve.
		2396
		2397	When you want to use sigwait (or mix libev signal handling with your own
		2398	for the same signals), you can tackle this problem by globally blocking
		2399	all signals before creating any threads (or creating them with a fully set
		2400	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2401	loops. Then designate one thread as "signal receiver thread" which handles
		2402	these signals. You can pass on any signals that libev might be interested
		2403	in by calling C<ev_feed_signal>.
1274		2404
1275	=head3 Watcher-Specific Functions and Data Members	2405	=head3 Watcher-Specific Functions and Data Members
1276		2406
1277	=over 4	2407	=over 4
1278		2408
…		…
1287		2417
1288	The signal the watcher watches out for.	2418	The signal the watcher watches out for.
1289		2419
1290	=back	2420	=back
1291		2421
		2422	=head3 Examples
		2423
		2424	Example: Try to exit cleanly on SIGINT.
		2425
		2426	static void
		2427	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2428	{
		2429	ev_break (loop, EVBREAK_ALL);
		2430	}
		2431
		2432	ev_signal signal_watcher;
		2433	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2434	ev_signal_start (loop, &signal_watcher);
		2435
1292		2436
1293	=head2 C<ev_child> - watch out for process status changes	2437	=head2 C<ev_child> - watch out for process status changes
1294		2438
1295	Child watchers trigger when your process receives a SIGCHLD in response to	2439	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).	2440	some child status changes (most typically when a child of yours dies or
		2441	exits). It is permissible to install a child watcher I<after> the child
		2442	has been forked (which implies it might have already exited), as long
		2443	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2444	forking and then immediately registering a watcher for the child is fine,
		2445	but forking and registering a watcher a few event loop iterations later or
		2446	in the next callback invocation is not.
		2447
		2448	Only the default event loop is capable of handling signals, and therefore
		2449	you can only register child watchers in the default event loop.
		2450
		2451	Due to some design glitches inside libev, child watchers will always be
		2452	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2453	libev)
		2454
		2455	=head3 Process Interaction
		2456
		2457	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2458	initialised. This is necessary to guarantee proper behaviour even if the
		2459	first child watcher is started after the child exits. The occurrence
		2460	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2461	synchronously as part of the event loop processing. Libev always reaps all
		2462	children, even ones not watched.
		2463
		2464	=head3 Overriding the Built-In Processing
		2465
		2466	Libev offers no special support for overriding the built-in child
		2467	processing, but if your application collides with libev's default child
		2468	handler, you can override it easily by installing your own handler for
		2469	C<SIGCHLD> after initialising the default loop, and making sure the
		2470	default loop never gets destroyed. You are encouraged, however, to use an
		2471	event-based approach to child reaping and thus use libev's support for
		2472	that, so other libev users can use C<ev_child> watchers freely.
		2473
		2474	=head3 Stopping the Child Watcher
		2475
		2476	Currently, the child watcher never gets stopped, even when the
		2477	child terminates, so normally one needs to stop the watcher in the
		2478	callback. Future versions of libev might stop the watcher automatically
		2479	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2480	problem).
1297		2481
1298	=head3 Watcher-Specific Functions and Data Members	2482	=head3 Watcher-Specific Functions and Data Members
1299		2483
1300	=over 4	2484	=over 4
1301		2485
1302	=item ev_child_init (ev_child *, callback, int pid)	2486	=item ev_child_init (ev_child *, callback, int pid, int trace)
1303		2487
1304	=item ev_child_set (ev_child *, int pid)	2488	=item ev_child_set (ev_child *, int pid, int trace)
1305		2489
1306	Configures the watcher to wait for status changes of process C<pid> (or	2490	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	2491	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	2492	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	2493	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	2494	C<waitpid> documentation). The C<rpid> member contains the pid of the
1311	process causing the status change.	2495	process causing the status change. C<trace> must be either C<0> (only
		2496	activate the watcher when the process terminates) or C<1> (additionally
		2497	activate the watcher when the process is stopped or continued).
1312		2498
1313	=item int pid [read-only]	2499	=item int pid [read-only]
1314		2500
1315	The process id this watcher watches out for, or C<0>, meaning any process id.	2501	The process id this watcher watches out for, or C<0>, meaning any process id.
1316		2502
…		…
1323	The process exit/trace status caused by C<rpid> (see your systems	2509	The process exit/trace status caused by C<rpid> (see your systems
1324	C<waitpid> and C<sys/wait.h> documentation for details).	2510	C<waitpid> and C<sys/wait.h> documentation for details).
1325		2511
1326	=back	2512	=back
1327		2513
1328	Example: Try to exit cleanly on SIGINT and SIGTERM.	2514	=head3 Examples
1329		2515
		2516	Example: C<fork()> a new process and install a child handler to wait for
		2517	its completion.
		2518
		2519	ev_child cw;
		2520
1330	static void	2521	static void
1331	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2522	child_cb (EV_P_ ev_child *w, int revents)
1332	{	2523	{
1333	ev_unloop (loop, EVUNLOOP_ALL);	2524	ev_child_stop (EV_A_ w);
		2525	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1334	}	2526	}
1335		2527
1336	struct ev_signal signal_watcher;	2528	pid_t pid = fork ();
1337	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2529
1338	ev_signal_start (loop, &sigint_cb);	2530	if (pid < 0)
		2531	// error
		2532	else if (pid == 0)
		2533	{
		2534	// the forked child executes here
		2535	exit (1);
		2536	}
		2537	else
		2538	{
		2539	ev_child_init (&cw, child_cb, pid, 0);
		2540	ev_child_start (EV_DEFAULT_ &cw);
		2541	}
1339		2542
1340		2543
1341	=head2 C<ev_stat> - did the file attributes just change?	2544	=head2 C<ev_stat> - did the file attributes just change?
1342		2545
1343	This watches a filesystem path for attribute changes. That is, it calls	2546	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	2547	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.	2548	and sees if it changed compared to the last time, invoking the callback if
		2549	it did.
1346		2550
1347	The path does not need to exist: changing from "path exists" to "path does	2551	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	2552	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	2553	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	2554	C<st_nlink> field being zero (which is otherwise always forced to be at
1351	the stat buffer having unspecified contents.	2555	least one) and all the other fields of the stat buffer having unspecified
		2556	contents.
1352		2557
1353	The path I<should> be absolute and I<must not> end in a slash. If it is	2558	The path I<must not> end in a slash or contain special components such as
		2559	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.	2560	your working directory changes, then the behaviour is undefined.
1355		2561
1356	Since there is no standard to do this, the portable implementation simply	2562	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	2563	portable implementation simply calls C<stat(2)> regularly on the path
1358	can specify a recommended polling interval for this case. If you specify	2564	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,	2565	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	2566	recommended!) then a I<suitable, unspecified default> value will be used
1361	five seconds, although this might change dynamically). Libev will also	2567	(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	2568	change dynamically). Libev will also impose a minimum interval which is
1363	usually overkill.	2569	currently around C<0.1>, but that's usually overkill.
1364		2570
1365	This watcher type is not meant for massive numbers of stat watchers,	2571	This watcher type is not meant for massive numbers of stat watchers,
1366	as even with OS-supported change notifications, this can be	2572	as even with OS-supported change notifications, this can be
1367	resource-intensive.	2573	resource-intensive.
1368		2574
1369	At the time of this writing, only the Linux inotify interface is	2575	At the time of this writing, the only OS-specific interface implemented
1370	implemented (implementing kqueue support is left as an exercise for the	2576	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	2577	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	2578	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	2579
1374	usually detected immediately, and if the file exists there will be no	2580	=head3 ABI Issues (Largefile Support)
1375	polling.	2581
		2582	Libev by default (unless the user overrides this) uses the default
		2583	compilation environment, which means that on systems with large file
		2584	support disabled by default, you get the 32 bit version of the stat
		2585	structure. When using the library from programs that change the ABI to
		2586	use 64 bit file offsets the programs will fail. In that case you have to
		2587	compile libev with the same flags to get binary compatibility. This is
		2588	obviously the case with any flags that change the ABI, but the problem is
		2589	most noticeably displayed with ev_stat and large file support.
		2590
		2591	The solution for this is to lobby your distribution maker to make large
		2592	file interfaces available by default (as e.g. FreeBSD does) and not
		2593	optional. Libev cannot simply switch on large file support because it has
		2594	to exchange stat structures with application programs compiled using the
		2595	default compilation environment.
		2596
		2597	=head3 Inotify and Kqueue
		2598
		2599	When C<inotify (7)> support has been compiled into libev and present at
		2600	runtime, it will be used to speed up change detection where possible. The
		2601	inotify descriptor will be created lazily when the first C<ev_stat>
		2602	watcher is being started.
		2603
		2604	Inotify presence does not change the semantics of C<ev_stat> watchers
		2605	except that changes might be detected earlier, and in some cases, to avoid
		2606	making regular C<stat> calls. Even in the presence of inotify support
		2607	there are many cases where libev has to resort to regular C<stat> polling,
		2608	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2609	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2610	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2611	xfs are fully working) libev usually gets away without polling.
		2612
		2613	There is no support for kqueue, as apparently it cannot be used to
		2614	implement this functionality, due to the requirement of having a file
		2615	descriptor open on the object at all times, and detecting renames, unlinks
		2616	etc. is difficult.
		2617
		2618	=head3 C<stat ()> is a synchronous operation
		2619
		2620	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2621	the process. The exception are C<ev_stat> watchers - those call C<stat
		2622	()>, which is a synchronous operation.
		2623
		2624	For local paths, this usually doesn't matter: unless the system is very
		2625	busy or the intervals between stat's are large, a stat call will be fast,
		2626	as the path data is usually in memory already (except when starting the
		2627	watcher).
		2628
		2629	For networked file systems, calling C<stat ()> can block an indefinite
		2630	time due to network issues, and even under good conditions, a stat call
		2631	often takes multiple milliseconds.
		2632
		2633	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2634	paths, although this is fully supported by libev.
		2635
		2636	=head3 The special problem of stat time resolution
		2637
		2638	The C<stat ()> system call only supports full-second resolution portably,
		2639	and even on systems where the resolution is higher, most file systems
		2640	still only support whole seconds.
		2641
		2642	That means that, if the time is the only thing that changes, you can
		2643	easily miss updates: on the first update, C<ev_stat> detects a change and
		2644	calls your callback, which does something. When there is another update
		2645	within the same second, C<ev_stat> will be unable to detect unless the
		2646	stat data does change in other ways (e.g. file size).
		2647
		2648	The solution to this is to delay acting on a change for slightly more
		2649	than a second (or till slightly after the next full second boundary), using
		2650	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2651	ev_timer_again (loop, w)>).
		2652
		2653	The C<.02> offset is added to work around small timing inconsistencies
		2654	of some operating systems (where the second counter of the current time
		2655	might be be delayed. One such system is the Linux kernel, where a call to
		2656	C<gettimeofday> might return a timestamp with a full second later than
		2657	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2658	update file times then there will be a small window where the kernel uses
		2659	the previous second to update file times but libev might already execute
		2660	the timer callback).
1376		2661
1377	=head3 Watcher-Specific Functions and Data Members	2662	=head3 Watcher-Specific Functions and Data Members
1378		2663
1379	=over 4	2664	=over 4
1380		2665
…		…
1386	C<path>. The C<interval> is a hint on how quickly a change is expected to	2671	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	2672	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	2673	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.	2674	path for as long as the watcher is active.
1390		2675
1391	The callback will be receive C<EV_STAT> when a change was detected,	2676	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	2677	relative to the attributes at the time the watcher was started (or the
1393	last change was detected).	2678	last change was detected).
1394		2679
1395	=item ev_stat_stat (ev_stat *)	2680	=item ev_stat_stat (loop, ev_stat *)
1396		2681
1397	Updates the stat buffer immediately with new values. If you change the	2682	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	2683	watched path in your callback, you could call this function to avoid
1399	detecting this change (while introducing a race condition). Can also be	2684	detecting this change (while introducing a race condition if you are not
1400	useful simply to find out the new values.	2685	the only one changing the path). Can also be useful simply to find out the
		2686	new values.
1401		2687
1402	=item ev_statdata attr [read-only]	2688	=item ev_statdata attr [read-only]
1403		2689
1404	The most-recently detected attributes of the file. Although the type is of	2690	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	2691	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	2692	suitable for your system, but you can only rely on the POSIX-standardised
		2693	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.	2694	some error while C<stat>ing the file.
1408		2695
1409	=item ev_statdata prev [read-only]	2696	=item ev_statdata prev [read-only]
1410		2697
1411	The previous attributes of the file. The callback gets invoked whenever	2698	The previous attributes of the file. The callback gets invoked whenever
1412	C<prev> != C<attr>.	2699	C<prev> != C<attr>, or, more precisely, one or more of these members
		2700	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2701	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1413		2702
1414	=item ev_tstamp interval [read-only]	2703	=item ev_tstamp interval [read-only]
1415		2704
1416	The specified interval.	2705	The specified interval.
1417		2706
1418	=item const char *path [read-only]	2707	=item const char *path [read-only]
1419		2708
1420	The filesystem path that is being watched.	2709	The file system path that is being watched.
1421		2710
1422	=back	2711	=back
1423		2712
		2713	=head3 Examples
		2714
1424	Example: Watch C</etc/passwd> for attribute changes.	2715	Example: Watch C</etc/passwd> for attribute changes.
1425		2716
1426	static void	2717	static void
1427	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2718	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1428	{	2719	{
1429	/* /etc/passwd changed in some way */	2720	/* /etc/passwd changed in some way */
1430	if (w->attr.st_nlink)	2721	if (w->attr.st_nlink)
1431	{	2722	{
1432	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2723	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1433	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2724	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1434	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2725	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1435	}	2726	}
1436	else	2727	else
1437	/* you shalt not abuse printf for puts */	2728	/* you shalt not abuse printf for puts */
1438	puts ("wow, /etc/passwd is not there, expect problems. "	2729	puts ("wow, /etc/passwd is not there, expect problems. "
1439	"if this is windows, they already arrived\n");	2730	"if this is windows, they already arrived\n");
1440	}	2731	}
1441		2732
1442	...	2733	...
1443	ev_stat passwd;	2734	ev_stat passwd;
1444		2735
1445	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2736	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1446	ev_stat_start (loop, &passwd);	2737	ev_stat_start (loop, &passwd);
		2738
		2739	Example: Like above, but additionally use a one-second delay so we do not
		2740	miss updates (however, frequent updates will delay processing, too, so
		2741	one might do the work both on C<ev_stat> callback invocation I<and> on
		2742	C<ev_timer> callback invocation).
		2743
		2744	static ev_stat passwd;
		2745	static ev_timer timer;
		2746
		2747	static void
		2748	timer_cb (EV_P_ ev_timer *w, int revents)
		2749	{
		2750	ev_timer_stop (EV_A_ w);
		2751
		2752	/* now it's one second after the most recent passwd change */
		2753	}
		2754
		2755	static void
		2756	stat_cb (EV_P_ ev_stat *w, int revents)
		2757	{
		2758	/* reset the one-second timer */
		2759	ev_timer_again (EV_A_ &timer);
		2760	}
		2761
		2762	...
		2763	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2764	ev_stat_start (loop, &passwd);
		2765	ev_timer_init (&timer, timer_cb, 0., 1.02);
1447		2766
1448		2767
1449	=head2 C<ev_idle> - when you've got nothing better to do...	2768	=head2 C<ev_idle> - when you've got nothing better to do...
1450		2769
1451	Idle watchers trigger events when no other events of the same or higher	2770	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	2771	priority are pending (prepare, check and other idle watchers do not count
1453	count).	2772	as receiving "events").
1454		2773
1455	That is, as long as your process is busy handling sockets or timeouts	2774	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	2775	(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	2776	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	2777	are pending), the idle watchers are being called once per event loop
…		…
1469		2788
1470	=head3 Watcher-Specific Functions and Data Members	2789	=head3 Watcher-Specific Functions and Data Members
1471		2790
1472	=over 4	2791	=over 4
1473		2792
1474	=item ev_idle_init (ev_signal *, callback)	2793	=item ev_idle_init (ev_idle *, callback)
1475		2794
1476	Initialises and configures the idle watcher - it has no parameters of any	2795	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,	2796	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1478	believe me.	2797	believe me.
1479		2798
1480	=back	2799	=back
1481		2800
		2801	=head3 Examples
		2802
1482	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2803	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1483	callback, free it. Also, use no error checking, as usual.	2804	callback, free it. Also, use no error checking, as usual.
1484		2805
1485	static void	2806	static void
1486	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2807	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1487	{	2808	{
1488	free (w);	2809	free (w);
1489	// now do something you wanted to do when the program has	2810	// now do something you wanted to do when the program has
1490	// no longer asnything immediate to do.	2811	// no longer anything immediate to do.
1491	}	2812	}
1492		2813
1493	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2814	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1494	ev_idle_init (idle_watcher, idle_cb);	2815	ev_idle_init (idle_watcher, idle_cb);
1495	ev_idle_start (loop, idle_cb);	2816	ev_idle_start (loop, idle_watcher);
1496		2817
1497		2818
1498	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2819	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1499		2820
1500	Prepare and check watchers are usually (but not always) used in tandem:	2821	Prepare and check watchers are usually (but not always) used in pairs:
1501	prepare watchers get invoked before the process blocks and check watchers	2822	prepare watchers get invoked before the process blocks and check watchers
1502	afterwards.	2823	afterwards.
1503		2824
1504	You I<must not> call C<ev_loop> or similar functions that enter	2825	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>	2826	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	2827	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	2828	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,	2829	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	2830	C<ev_check> so if you have one watcher of each kind they will always be
1510	called in pairs bracketing the blocking call.	2831	called in pairs bracketing the blocking call.
1511		2832
1512	Their main purpose is to integrate other event mechanisms into libev and	2833	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	2834	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	2835	variable changes, implement your own watchers, integrate net-snmp or a
1515	coroutine library and lots more. They are also occasionally useful if	2836	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,	2837	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>	2838	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1518	watcher).	2839	watcher).
1519		2840
1520	This is done by examining in each prepare call which file descriptors need	2841	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	2842	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	2843	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	2844	libraries provide exactly this functionality). Then, in the check watcher,
1524	any events that occured (by checking the pending status of all watchers	2845	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	2846	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,	2847	I/O and timer callbacks will never actually be called (but must be valid
1527	because you never know, you know?).	2848	nevertheless, because you never know, you know?).
1528		2849
1529	As another example, the Perl Coro module uses these hooks to integrate	2850	As another example, the Perl Coro module uses these hooks to integrate
1530	coroutines into libev programs, by yielding to other active coroutines	2851	coroutines into libev programs, by yielding to other active coroutines
1531	during each prepare and only letting the process block if no coroutines	2852	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	2853	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	2856	loop from blocking if lower-priority coroutines are active, thus mapping
1536	low-priority coroutines to idle/background tasks).	2857	low-priority coroutines to idle/background tasks).
1537		2858
1538	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2859	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	2860	priority, to ensure that they are being run before any other watchers
		2861	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2862
1540	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2863	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	2864	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	2865	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	2866	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	2867	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	2868	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1546	others).	2869	others).
1547		2870
1548	=head3 Watcher-Specific Functions and Data Members	2871	=head3 Watcher-Specific Functions and Data Members
…		…
1553		2876
1554	=item ev_check_init (ev_check *, callback)	2877	=item ev_check_init (ev_check *, callback)
1555		2878
1556	Initialises and configures the prepare or check watcher - they have no	2879	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>	2880	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.	2881	macros, but using them is utterly, utterly, utterly and completely
		2882	pointless.
1559		2883
1560	=back	2884	=back
		2885
		2886	=head3 Examples
1561		2887
1562	There are a number of principal ways to embed other event loops or modules	2888	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	2889	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	2890	(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>	2891	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	2892	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1567	into the Glib event loop).	2893	Glib event loop).
1568		2894
1569	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2895	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	2896	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	2897	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	2898	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.	2899	the callbacks for the IO/timeout watchers might not have been called yet.
1574		2900
1575	static ev_io iow [nfd];	2901	static ev_io iow [nfd];
1576	static ev_timer tw;	2902	static ev_timer tw;
1577		2903
1578	static void	2904	static void
1579	io_cb (ev_loop *loop, ev_io *w, int revents)	2905	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1580	{	2906	{
1581	}	2907	}
1582		2908
1583	// create io watchers for each fd and a timer before blocking	2909	// create io watchers for each fd and a timer before blocking
1584	static void	2910	static void
1585	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2911	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1586	{	2912	{
1587	int timeout = 3600000;	2913	int timeout = 3600000;
1588	struct pollfd fds [nfd];	2914	struct pollfd fds [nfd];
1589	// actual code will need to loop here and realloc etc.	2915	// actual code will need to loop here and realloc etc.
1590	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2916	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1591		2917
1592	/* the callback is illegal, but won't be called as we stop during check */	2918	/* the callback is illegal, but won't be called as we stop during check */
1593	ev_timer_init (&tw, 0, timeout * 1e-3);	2919	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1594	ev_timer_start (loop, &tw);	2920	ev_timer_start (loop, &tw);
1595		2921
1596	// create one ev_io per pollfd	2922	// create one ev_io per pollfd
1597	for (int i = 0; i < nfd; ++i)	2923	for (int i = 0; i < nfd; ++i)
1598	{	2924	{
1599	ev_io_init (iow + i, io_cb, fds [i].fd,	2925	ev_io_init (iow + i, io_cb, fds [i].fd,
1600	((fds [i].events & POLLIN ? EV_READ : 0)	2926	((fds [i].events & POLLIN ? EV_READ : 0)
1601	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2927	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1602		2928
1603	fds [i].revents = 0;	2929	fds [i].revents = 0;
1604	ev_io_start (loop, iow + i);	2930	ev_io_start (loop, iow + i);
1605	}	2931	}
1606	}	2932	}
1607		2933
1608	// stop all watchers after blocking	2934	// stop all watchers after blocking
1609	static void	2935	static void
1610	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2936	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1611	{	2937	{
1612	ev_timer_stop (loop, &tw);	2938	ev_timer_stop (loop, &tw);
1613		2939
1614	for (int i = 0; i < nfd; ++i)	2940	for (int i = 0; i < nfd; ++i)
1615	{	2941	{
1616	// set the relevant poll flags	2942	// set the relevant poll flags
1617	// could also call adns_processreadable etc. here	2943	// could also call adns_processreadable etc. here
1618	struct pollfd *fd = fds + i;	2944	struct pollfd *fd = fds + i;
1619	int revents = ev_clear_pending (iow + i);	2945	int revents = ev_clear_pending (iow + i);
1620	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2946	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1621	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2947	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1622		2948
1623	// now stop the watcher	2949	// now stop the watcher
1624	ev_io_stop (loop, iow + i);	2950	ev_io_stop (loop, iow + i);
1625	}	2951	}
1626		2952
1627	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2953	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1628	}	2954	}
1629		2955
1630	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2956	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.	2957	in the prepare watcher and would dispose of the check watcher.
1632		2958
1633	Method 3: If the module to be embedded supports explicit event	2959	Method 3: If the module to be embedded supports explicit event
1634	notification (adns does), you can also make use of the actual watcher	2960	notification (libadns does), you can also make use of the actual watcher
1635	callbacks, and only destroy/create the watchers in the prepare watcher.	2961	callbacks, and only destroy/create the watchers in the prepare watcher.
1636		2962
1637	static void	2963	static void
1638	timer_cb (EV_P_ ev_timer *w, int revents)	2964	timer_cb (EV_P_ ev_timer *w, int revents)
1639	{	2965	{
1640	adns_state ads = (adns_state)w->data;	2966	adns_state ads = (adns_state)w->data;
1641	update_now (EV_A);	2967	update_now (EV_A);
1642		2968
1643	adns_processtimeouts (ads, &tv_now);	2969	adns_processtimeouts (ads, &tv_now);
1644	}	2970	}
1645		2971
1646	static void	2972	static void
1647	io_cb (EV_P_ ev_io *w, int revents)	2973	io_cb (EV_P_ ev_io *w, int revents)
1648	{	2974	{
1649	adns_state ads = (adns_state)w->data;	2975	adns_state ads = (adns_state)w->data;
1650	update_now (EV_A);	2976	update_now (EV_A);
1651		2977
1652	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2978	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1653	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2979	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1654	}	2980	}
1655		2981
1656	// do not ever call adns_afterpoll	2982	// do not ever call adns_afterpoll
1657		2983
1658	Method 4: Do not use a prepare or check watcher because the module you	2984	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	2985	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	2986	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	2987	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1662	this.	2988	this approach, effectively embedding EV as a client into the horrible
		2989	libglib event loop.
1663		2990
1664	static gint	2991	static gint
1665	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2992	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1666	{	2993	{
1667	int got_events = 0;	2994	int got_events = 0;
1668		2995
1669	for (n = 0; n < nfds; ++n)	2996	for (n = 0; n < nfds; ++n)
1670	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2997	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1671		2998
1672	if (timeout >= 0)	2999	if (timeout >= 0)
1673	// create/start timer	3000	// create/start timer
1674		3001
1675	// poll	3002	// poll
1676	ev_loop (EV_A_ 0);	3003	ev_run (EV_A_ 0);
1677		3004
1678	// stop timer again	3005	// stop timer again
1679	if (timeout >= 0)	3006	if (timeout >= 0)
1680	ev_timer_stop (EV_A_ &to);	3007	ev_timer_stop (EV_A_ &to);
1681		3008
1682	// stop io watchers again - their callbacks should have set	3009	// stop io watchers again - their callbacks should have set
1683	for (n = 0; n < nfds; ++n)	3010	for (n = 0; n < nfds; ++n)
1684	ev_io_stop (EV_A_ iow [n]);	3011	ev_io_stop (EV_A_ iow [n]);
1685		3012
1686	return got_events;	3013	return got_events;
1687	}	3014	}
1688		3015
1689		3016
1690	=head2 C<ev_embed> - when one backend isn't enough...	3017	=head2 C<ev_embed> - when one backend isn't enough...
1691		3018
1692	This is a rather advanced watcher type that lets you embed one event loop	3019	This is a rather advanced watcher type that lets you embed one event loop
…		…
1698	prioritise I/O.	3025	prioritise I/O.
1699		3026
1700	As an example for a bug workaround, the kqueue backend might only support	3027	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	3028	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	3029	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	3030	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	3031	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	3032	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.	3033	C<kevent>, but at least you can use both mechanisms for what they are
		3034	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1707		3035
1708	As for prioritising I/O: rarely you have the case where some fds have	3036	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	3037	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	3038	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	3039	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.	3040	the rest in a second one, and embed the second one in the first.
1713		3041
1714	As long as the watcher is active, the callback will be invoked every time	3042	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	3043	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	3044	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	3045	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	3046	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	3047	to give the embedded loop strictly lower priority for example).
1720	embedded loop sweep.
1721		3048
1722	As long as the watcher is started it will automatically handle events. The	3049	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	3050	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		3051
1727	Also, there have not currently been made special provisions for forking:	3052	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,	3053	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	3054	embedding loop forks. In other cases, the user is responsible for calling
1730	yourself.	3055	C<ev_loop_fork> on the embedded loop.
1731		3056
1732	Unfortunately, not all backends are embeddable, only the ones returned by	3057	Unfortunately, not all backends are embeddable: only the ones returned by
1733	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3058	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1734	portable one.	3059	portable one.
1735		3060
1736	So when you want to use this feature you will always have to be prepared	3061	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	3062	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	3063	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:	3064	create it, and if that fails, use the normal loop for everything.
1740		3065
1741	struct ev_loop *loop_hi = ev_default_init (0);	3066	=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		3067
1751	// if we got one, then embed it, otherwise default to loop_hi	3068	While the C<ev_embed> watcher is running, forks in the embedding loop will
1752	if (loop_lo)	3069	automatically be applied to the embedded loop as well, so no special
1753	{	3070	fork handling is required in that case. When the watcher is not running,
1754	ev_embed_init (&embed, 0, loop_lo);	3071	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1755	ev_embed_start (loop_hi, &embed);	3072	as applicable.
1756	}
1757	else
1758	loop_lo = loop_hi;
1759		3073
1760	=head3 Watcher-Specific Functions and Data Members	3074	=head3 Watcher-Specific Functions and Data Members
1761		3075
1762	=over 4	3076	=over 4
1763		3077
…		…
1767		3081
1768	Configures the watcher to embed the given loop, which must be	3082	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	3083	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	3084	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,	3085	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).	3086	if you do not want that, you need to temporarily stop the embed watcher).
1773		3087
1774	=item ev_embed_sweep (loop, ev_embed *)	3088	=item ev_embed_sweep (loop, ev_embed *)
1775		3089
1776	Make a single, non-blocking sweep over the embedded loop. This works	3090	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	3091	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1778	apropriate way for embedded loops.	3092	appropriate way for embedded loops.
1779		3093
1780	=item struct ev_loop *loop [read-only]	3094	=item struct ev_loop *other [read-only]
1781		3095
1782	The embedded event loop.	3096	The embedded event loop.
1783		3097
1784	=back	3098	=back
		3099
		3100	=head3 Examples
		3101
		3102	Example: Try to get an embeddable event loop and embed it into the default
		3103	event loop. If that is not possible, use the default loop. The default
		3104	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3105	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3106	used).
		3107
		3108	struct ev_loop *loop_hi = ev_default_init (0);
		3109	struct ev_loop *loop_lo = 0;
		3110	ev_embed embed;
		3111
		3112	// see if there is a chance of getting one that works
		3113	// (remember that a flags value of 0 means autodetection)
		3114	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3115	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3116	: 0;
		3117
		3118	// if we got one, then embed it, otherwise default to loop_hi
		3119	if (loop_lo)
		3120	{
		3121	ev_embed_init (&embed, 0, loop_lo);
		3122	ev_embed_start (loop_hi, &embed);
		3123	}
		3124	else
		3125	loop_lo = loop_hi;
		3126
		3127	Example: Check if kqueue is available but not recommended and create
		3128	a kqueue backend for use with sockets (which usually work with any
		3129	kqueue implementation). Store the kqueue/socket-only event loop in
		3130	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3131
		3132	struct ev_loop *loop = ev_default_init (0);
		3133	struct ev_loop *loop_socket = 0;
		3134	ev_embed embed;
		3135
		3136	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3137	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3138	{
		3139	ev_embed_init (&embed, 0, loop_socket);
		3140	ev_embed_start (loop, &embed);
		3141	}
		3142
		3143	if (!loop_socket)
		3144	loop_socket = loop;
		3145
		3146	// now use loop_socket for all sockets, and loop for everything else
1785		3147
1786		3148
1787	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3149	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1788		3150
1789	Fork watchers are called when a C<fork ()> was detected (usually because	3151	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,	3154	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	3155	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	3156	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1795	handlers will be invoked, too, of course.	3157	handlers will be invoked, too, of course.
1796		3158
		3159	=head3 The special problem of life after fork - how is it possible?
		3160
		3161	Most uses of C<fork()> consist of forking, then some simple calls to set
		3162	up/change the process environment, followed by a call to C<exec()>. This
		3163	sequence should be handled by libev without any problems.
		3164
		3165	This changes when the application actually wants to do event handling
		3166	in the child, or both parent in child, in effect "continuing" after the
		3167	fork.
		3168
		3169	The default mode of operation (for libev, with application help to detect
		3170	forks) is to duplicate all the state in the child, as would be expected
		3171	when I<either> the parent I<or> the child process continues.
		3172
		3173	When both processes want to continue using libev, then this is usually the
		3174	wrong result. In that case, usually one process (typically the parent) is
		3175	supposed to continue with all watchers in place as before, while the other
		3176	process typically wants to start fresh, i.e. without any active watchers.
		3177
		3178	The cleanest and most efficient way to achieve that with libev is to
		3179	simply create a new event loop, which of course will be "empty", and
		3180	use that for new watchers. This has the advantage of not touching more
		3181	memory than necessary, and thus avoiding the copy-on-write, and the
		3182	disadvantage of having to use multiple event loops (which do not support
		3183	signal watchers).
		3184
		3185	When this is not possible, or you want to use the default loop for
		3186	other reasons, then in the process that wants to start "fresh", call
		3187	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3188	Destroying the default loop will "orphan" (not stop) all registered
		3189	watchers, so you have to be careful not to execute code that modifies
		3190	those watchers. Note also that in that case, you have to re-register any
		3191	signal watchers.
		3192
1797	=head3 Watcher-Specific Functions and Data Members	3193	=head3 Watcher-Specific Functions and Data Members
1798		3194
1799	=over 4	3195	=over 4
1800		3196
1801	=item ev_fork_init (ev_signal *, callback)	3197	=item ev_fork_init (ev_fork *, callback)
1802		3198
1803	Initialises and configures the fork watcher - it has no parameters of any	3199	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,	3200	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
1805	believe me.	3201	really.
1806		3202
1807	=back	3203	=back
1808		3204
1809		3205
		3206	=head2 C<ev_cleanup> - even the best things end
		3207
		3208	Cleanup watchers are called just before the event loop is being destroyed
		3209	by a call to C<ev_loop_destroy>.
		3210
		3211	While there is no guarantee that the event loop gets destroyed, cleanup
		3212	watchers provide a convenient method to install cleanup hooks for your
		3213	program, worker threads and so on - you just to make sure to destroy the
		3214	loop when you want them to be invoked.
		3215
		3216	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3217	all other watchers, they do not keep a reference to the event loop (which
		3218	makes a lot of sense if you think about it). Like all other watchers, you
		3219	can call libev functions in the callback, except C<ev_cleanup_start>.
		3220
		3221	=head3 Watcher-Specific Functions and Data Members
		3222
		3223	=over 4
		3224
		3225	=item ev_cleanup_init (ev_cleanup *, callback)
		3226
		3227	Initialises and configures the cleanup watcher - it has no parameters of
		3228	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3229	pointless, I assure you.
		3230
		3231	=back
		3232
		3233	Example: Register an atexit handler to destroy the default loop, so any
		3234	cleanup functions are called.
		3235
		3236	static void
		3237	program_exits (void)
		3238	{
		3239	ev_loop_destroy (EV_DEFAULT_UC);
		3240	}
		3241
		3242	...
		3243	atexit (program_exits);
		3244
		3245
		3246	=head2 C<ev_async> - how to wake up an event loop
		3247
		3248	In general, you cannot use an C<ev_run> from multiple threads or other
		3249	asynchronous sources such as signal handlers (as opposed to multiple event
		3250	loops - those are of course safe to use in different threads).
		3251
		3252	Sometimes, however, you need to wake up an event loop you do not control,
		3253	for example because it belongs to another thread. This is what C<ev_async>
		3254	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3255	it by calling C<ev_async_send>, which is thread- and signal safe.
		3256
		3257	This functionality is very similar to C<ev_signal> watchers, as signals,
		3258	too, are asynchronous in nature, and signals, too, will be compressed
		3259	(i.e. the number of callback invocations may be less than the number of
		3260	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3261	of "global async watchers" by using a watcher on an otherwise unused
		3262	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3263	even without knowing which loop owns the signal.
		3264
		3265	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3266	just the default loop.
		3267
		3268	=head3 Queueing
		3269
		3270	C<ev_async> does not support queueing of data in any way. The reason
		3271	is that the author does not know of a simple (or any) algorithm for a
		3272	multiple-writer-single-reader queue that works in all cases and doesn't
		3273	need elaborate support such as pthreads or unportable memory access
		3274	semantics.
		3275
		3276	That means that if you want to queue data, you have to provide your own
		3277	queue. But at least I can tell you how to implement locking around your
		3278	queue:
		3279
		3280	=over 4
		3281
		3282	=item queueing from a signal handler context
		3283
		3284	To implement race-free queueing, you simply add to the queue in the signal
		3285	handler but you block the signal handler in the watcher callback. Here is
		3286	an example that does that for some fictitious SIGUSR1 handler:
		3287
		3288	static ev_async mysig;
		3289
		3290	static void
		3291	sigusr1_handler (void)
		3292	{
		3293	sometype data;
		3294
		3295	// no locking etc.
		3296	queue_put (data);
		3297	ev_async_send (EV_DEFAULT_ &mysig);
		3298	}
		3299
		3300	static void
		3301	mysig_cb (EV_P_ ev_async *w, int revents)
		3302	{
		3303	sometype data;
		3304	sigset_t block, prev;
		3305
		3306	sigemptyset (&block);
		3307	sigaddset (&block, SIGUSR1);
		3308	sigprocmask (SIG_BLOCK, &block, &prev);
		3309
		3310	while (queue_get (&data))
		3311	process (data);
		3312
		3313	if (sigismember (&prev, SIGUSR1)
		3314	sigprocmask (SIG_UNBLOCK, &block, 0);
		3315	}
		3316
		3317	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3318	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3319	either...).
		3320
		3321	=item queueing from a thread context
		3322
		3323	The strategy for threads is different, as you cannot (easily) block
		3324	threads but you can easily preempt them, so to queue safely you need to
		3325	employ a traditional mutex lock, such as in this pthread example:
		3326
		3327	static ev_async mysig;
		3328	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3329
		3330	static void
		3331	otherthread (void)
		3332	{
		3333	// only need to lock the actual queueing operation
		3334	pthread_mutex_lock (&mymutex);
		3335	queue_put (data);
		3336	pthread_mutex_unlock (&mymutex);
		3337
		3338	ev_async_send (EV_DEFAULT_ &mysig);
		3339	}
		3340
		3341	static void
		3342	mysig_cb (EV_P_ ev_async *w, int revents)
		3343	{
		3344	pthread_mutex_lock (&mymutex);
		3345
		3346	while (queue_get (&data))
		3347	process (data);
		3348
		3349	pthread_mutex_unlock (&mymutex);
		3350	}
		3351
		3352	=back
		3353
		3354
		3355	=head3 Watcher-Specific Functions and Data Members
		3356
		3357	=over 4
		3358
		3359	=item ev_async_init (ev_async *, callback)
		3360
		3361	Initialises and configures the async watcher - it has no parameters of any
		3362	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3363	trust me.
		3364
		3365	=item ev_async_send (loop, ev_async *)
		3366
		3367	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3368	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3369	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3370	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3371	section below on what exactly this means).
		3372
		3373	Note that, as with other watchers in libev, multiple events might get
		3374	compressed into a single callback invocation (another way to look at this
		3375	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3376	reset when the event loop detects that).
		3377
		3378	This call incurs the overhead of a system call only once per event loop
		3379	iteration, so while the overhead might be noticeable, it doesn't apply to
		3380	repeated calls to C<ev_async_send> for the same event loop.
		3381
		3382	=item bool = ev_async_pending (ev_async *)
		3383
		3384	Returns a non-zero value when C<ev_async_send> has been called on the
		3385	watcher but the event has not yet been processed (or even noted) by the
		3386	event loop.
		3387
		3388	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3389	the loop iterates next and checks for the watcher to have become active,
		3390	it will reset the flag again. C<ev_async_pending> can be used to very
		3391	quickly check whether invoking the loop might be a good idea.
		3392
		3393	Not that this does I<not> check whether the watcher itself is pending,
		3394	only whether it has been requested to make this watcher pending: there
		3395	is a time window between the event loop checking and resetting the async
		3396	notification, and the callback being invoked.
		3397
		3398	=back
		3399
		3400
1810	=head1 OTHER FUNCTIONS	3401	=head1 OTHER FUNCTIONS
1811		3402
1812	There are some other functions of possible interest. Described. Here. Now.	3403	There are some other functions of possible interest. Described. Here. Now.
1813		3404
1814	=over 4	3405	=over 4
1815		3406
1816	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3407	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1817		3408
1818	This function combines a simple timer and an I/O watcher, calls your	3409	This function combines a simple timer and an I/O watcher, calls your
1819	callback on whichever event happens first and automatically stop both	3410	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	3411	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	3412	or timeout without having to allocate/configure/start/stop/free one or
1822	more watchers yourself.	3413	more watchers yourself.
1823		3414
1824	If C<fd> is less than 0, then no I/O watcher will be started and events	3415	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	3416	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1826	C<events> set will be craeted and started.	3417	the given C<fd> and C<events> set will be created and started.
1827		3418
1828	If C<timeout> is less than 0, then no timeout watcher will be	3419	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	3420	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	3421	repeat = 0) will be started. C<0> is a valid timeout.
1831	dubious value.
1832		3422
1833	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3423	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	3424	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>	3425	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1836	value passed to C<ev_once>:	3426	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3427	a timeout and an io event at the same time - you probably should give io
		3428	events precedence.
1837		3429
		3430	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3431
1838	static void stdin_ready (int revents, void *arg)	3432	static void stdin_ready (int revents, void *arg)
1839	{	3433	{
1840	if (revents & EV_TIMEOUT)
1841	/* doh, nothing entered */;
1842	else if (revents & EV_READ)	3434	if (revents & EV_READ)
1843	/* stdin might have data for us, joy! */;	3435	/* stdin might have data for us, joy! */;
		3436	else if (revents & EV_TIMER)
		3437	/* doh, nothing entered */;
1844	}	3438	}
1845		3439
1846	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3440	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1847		3441
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)	3442	=item ev_feed_fd_event (loop, int fd, int revents)
1855		3443
1856	Feed an event on the given fd, as if a file descriptor backend detected	3444	Feed an event on the given fd, as if a file descriptor backend detected
1857	the given events it.	3445	the given events it.
1858		3446
1859	=item ev_feed_signal_event (ev_loop *loop, int signum)	3447	=item ev_feed_signal_event (loop, int signum)
1860		3448
1861	Feed an event as if the given signal occured (C<loop> must be the default	3449	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
1862	loop!).	3450	which is async-safe.
		3451
		3452	=back
		3453
		3454
		3455	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3456
		3457	This section explains some common idioms that are not immediately
		3458	obvious. Note that examples are sprinkled over the whole manual, and this
		3459	section only contains stuff that wouldn't fit anywhere else.
		3460
		3461	=over 4
		3462
		3463	=item Model/nested event loop invocations and exit conditions.
		3464
		3465	Often (especially in GUI toolkits) there are places where you have
		3466	I<modal> interaction, which is most easily implemented by recursively
		3467	invoking C<ev_run>.
		3468
		3469	This brings the problem of exiting - a callback might want to finish the
		3470	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3471	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3472	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3473	other combination: In these cases, C<ev_break> will not work alone.
		3474
		3475	The solution is to maintain "break this loop" variable for each C<ev_run>
		3476	invocation, and use a loop around C<ev_run> until the condition is
		3477	triggered, using C<EVRUN_ONCE>:
		3478
		3479	// main loop
		3480	int exit_main_loop = 0;
		3481
		3482	while (!exit_main_loop)
		3483	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3484
		3485	// in a model watcher
		3486	int exit_nested_loop = 0;
		3487
		3488	while (!exit_nested_loop)
		3489	ev_run (EV_A_ EVRUN_ONCE);
		3490
		3491	To exit from any of these loops, just set the corresponding exit variable:
		3492
		3493	// exit modal loop
		3494	exit_nested_loop = 1;
		3495
		3496	// exit main program, after modal loop is finished
		3497	exit_main_loop = 1;
		3498
		3499	// exit both
		3500	exit_main_loop = exit_nested_loop = 1;
		3501
		3502	=item Thread locking example
		3503
		3504	Here is a fictitious example of how to run an event loop in a different
		3505	thread than where callbacks are being invoked and watchers are
		3506	created/added/removed.
		3507
		3508	For a real-world example, see the C<EV::Loop::Async> perl module,
		3509	which uses exactly this technique (which is suited for many high-level
		3510	languages).
		3511
		3512	The example uses a pthread mutex to protect the loop data, a condition
		3513	variable to wait for callback invocations, an async watcher to notify the
		3514	event loop thread and an unspecified mechanism to wake up the main thread.
		3515
		3516	First, you need to associate some data with the event loop:
		3517
		3518	typedef struct {
		3519	mutex_t lock; /* global loop lock */
		3520	ev_async async_w;
		3521	thread_t tid;
		3522	cond_t invoke_cv;
		3523	} userdata;
		3524
		3525	void prepare_loop (EV_P)
		3526	{
		3527	// for simplicity, we use a static userdata struct.
		3528	static userdata u;
		3529
		3530	ev_async_init (&u->async_w, async_cb);
		3531	ev_async_start (EV_A_ &u->async_w);
		3532
		3533	pthread_mutex_init (&u->lock, 0);
		3534	pthread_cond_init (&u->invoke_cv, 0);
		3535
		3536	// now associate this with the loop
		3537	ev_set_userdata (EV_A_ u);
		3538	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3539	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3540
		3541	// then create the thread running ev_loop
		3542	pthread_create (&u->tid, 0, l_run, EV_A);
		3543	}
		3544
		3545	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3546	solely to wake up the event loop so it takes notice of any new watchers
		3547	that might have been added:
		3548
		3549	static void
		3550	async_cb (EV_P_ ev_async *w, int revents)
		3551	{
		3552	// just used for the side effects
		3553	}
		3554
		3555	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3556	protecting the loop data, respectively.
		3557
		3558	static void
		3559	l_release (EV_P)
		3560	{
		3561	userdata *u = ev_userdata (EV_A);
		3562	pthread_mutex_unlock (&u->lock);
		3563	}
		3564
		3565	static void
		3566	l_acquire (EV_P)
		3567	{
		3568	userdata *u = ev_userdata (EV_A);
		3569	pthread_mutex_lock (&u->lock);
		3570	}
		3571
		3572	The event loop thread first acquires the mutex, and then jumps straight
		3573	into C<ev_run>:
		3574
		3575	void *
		3576	l_run (void *thr_arg)
		3577	{
		3578	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3579
		3580	l_acquire (EV_A);
		3581	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3582	ev_run (EV_A_ 0);
		3583	l_release (EV_A);
		3584
		3585	return 0;
		3586	}
		3587
		3588	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3589	signal the main thread via some unspecified mechanism (signals? pipe
		3590	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3591	have been called (in a while loop because a) spurious wakeups are possible
		3592	and b) skipping inter-thread-communication when there are no pending
		3593	watchers is very beneficial):
		3594
		3595	static void
		3596	l_invoke (EV_P)
		3597	{
		3598	userdata *u = ev_userdata (EV_A);
		3599
		3600	while (ev_pending_count (EV_A))
		3601	{
		3602	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3603	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3604	}
		3605	}
		3606
		3607	Now, whenever the main thread gets told to invoke pending watchers, it
		3608	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3609	thread to continue:
		3610
		3611	static void
		3612	real_invoke_pending (EV_P)
		3613	{
		3614	userdata *u = ev_userdata (EV_A);
		3615
		3616	pthread_mutex_lock (&u->lock);
		3617	ev_invoke_pending (EV_A);
		3618	pthread_cond_signal (&u->invoke_cv);
		3619	pthread_mutex_unlock (&u->lock);
		3620	}
		3621
		3622	Whenever you want to start/stop a watcher or do other modifications to an
		3623	event loop, you will now have to lock:
		3624
		3625	ev_timer timeout_watcher;
		3626	userdata *u = ev_userdata (EV_A);
		3627
		3628	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3629
		3630	pthread_mutex_lock (&u->lock);
		3631	ev_timer_start (EV_A_ &timeout_watcher);
		3632	ev_async_send (EV_A_ &u->async_w);
		3633	pthread_mutex_unlock (&u->lock);
		3634
		3635	Note that sending the C<ev_async> watcher is required because otherwise
		3636	an event loop currently blocking in the kernel will have no knowledge
		3637	about the newly added timer. By waking up the loop it will pick up any new
		3638	watchers in the next event loop iteration.
1863		3639
1864	=back	3640	=back
1865		3641
1866		3642
1867	=head1 LIBEVENT EMULATION	3643	=head1 LIBEVENT EMULATION
1868		3644
1869	Libev offers a compatibility emulation layer for libevent. It cannot	3645	Libev offers a compatibility emulation layer for libevent. It cannot
1870	emulate the internals of libevent, so here are some usage hints:	3646	emulate the internals of libevent, so here are some usage hints:
1871		3647
1872	=over 4	3648	=over 4
		3649
		3650	=item * Only the libevent-1.4.1-beta API is being emulated.
		3651
		3652	This was the newest libevent version available when libev was implemented,
		3653	and is still mostly unchanged in 2010.
1873		3654
1874	=item * Use it by including <event.h>, as usual.	3655	=item * Use it by including <event.h>, as usual.
1875		3656
1876	=item * The following members are fully supported: ev_base, ev_callback,	3657	=item * The following members are fully supported: ev_base, ev_callback,
1877	ev_arg, ev_fd, ev_res, ev_events.	3658	ev_arg, ev_fd, ev_res, ev_events.
…		…
1882		3663
1883	=item * Priorities are not currently supported. Initialising priorities	3664	=item * Priorities are not currently supported. Initialising priorities
1884	will fail and all watchers will have the same priority, even though there	3665	will fail and all watchers will have the same priority, even though there
1885	is an ev_pri field.	3666	is an ev_pri field.
1886		3667
		3668	=item * In libevent, the last base created gets the signals, in libev, the
		3669	base that registered the signal gets the signals.
		3670
1887	=item * Other members are not supported.	3671	=item * Other members are not supported.
1888		3672
1889	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3673	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1890	to use the libev header file and library.	3674	to use the libev header file and library.
1891		3675
1892	=back	3676	=back
1893		3677
1894	=head1 C++ SUPPORT	3678	=head1 C++ SUPPORT
1895		3679
1896	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3680	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	3681	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.	3682	the callback model to a model using method callbacks on objects.
1899		3683
1900	To use it,	3684	To use it,
1901		3685
1902	#include <ev++.h>	3686	#include <ev++.h>
1903		3687
1904	This automatically includes F<ev.h> and puts all of its definitions (many	3688	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	3689	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	3690	put into the C<ev> namespace. It should support all the same embedding
1907	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3691	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1909	Care has been taken to keep the overhead low. The only data member the C++	3693	Care has been taken to keep the overhead low. The only data member the C++
1910	classes add (compared to plain C-style watchers) is the event loop pointer	3694	classes add (compared to plain C-style watchers) is the event loop pointer
1911	that the watcher is associated with (or no additional members at all if	3695	that the watcher is associated with (or no additional members at all if
1912	you disable C<EV_MULTIPLICITY> when embedding libev).	3696	you disable C<EV_MULTIPLICITY> when embedding libev).
1913		3697
1914	Currently, functions, and static and non-static member functions can be	3698	Currently, functions, static and non-static member functions and classes
1915	used as callbacks. Other types should be easy to add as long as they only	3699	with C<operator ()> can be used as callbacks. Other types should be easy
1916	need one additional pointer for context. If you need support for other	3700	to add as long as they only need one additional pointer for context. If
1917	types of functors please contact the author (preferably after implementing	3701	you need support for other types of functors please contact the author
1918	it).	3702	(preferably after implementing it).
1919		3703
1920	Here is a list of things available in the C<ev> namespace:	3704	Here is a list of things available in the C<ev> namespace:
1921		3705
1922	=over 4	3706	=over 4
1923		3707
…		…
1941		3725
1942	=over 4	3726	=over 4
1943		3727
1944	=item ev::TYPE::TYPE ()	3728	=item ev::TYPE::TYPE ()
1945		3729
1946	=item ev::TYPE::TYPE (struct ev_loop *)	3730	=item ev::TYPE::TYPE (loop)
1947		3731
1948	=item ev::TYPE::~TYPE	3732	=item ev::TYPE::~TYPE
1949		3733
1950	The constructor (optionally) takes an event loop to associate the watcher	3734	The constructor (optionally) takes an event loop to associate the watcher
1951	with. If it is omitted, it will use C<EV_DEFAULT>.	3735	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	3758	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.	3759	thunking function, making it as fast as a direct C callback.
1976		3760
1977	Example: simple class declaration and watcher initialisation	3761	Example: simple class declaration and watcher initialisation
1978		3762
1979	struct myclass	3763	struct myclass
1980	{	3764	{
1981	void io_cb (ev::io &w, int revents) { }	3765	void io_cb (ev::io &w, int revents) { }
1982	}	3766	}
1983		3767
1984	myclass obj;	3768	myclass obj;
1985	ev::io iow;	3769	ev::io iow;
1986	iow.set <myclass, &myclass::io_cb> (&obj);	3770	iow.set <myclass, &myclass::io_cb> (&obj);
		3771
		3772	=item w->set (object *)
		3773
		3774	This is a variation of a method callback - leaving out the method to call
		3775	will default the method to C<operator ()>, which makes it possible to use
		3776	functor objects without having to manually specify the C<operator ()> all
		3777	the time. Incidentally, you can then also leave out the template argument
		3778	list.
		3779
		3780	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3781	int revents)>.
		3782
		3783	See the method-C<set> above for more details.
		3784
		3785	Example: use a functor object as callback.
		3786
		3787	struct myfunctor
		3788	{
		3789	void operator() (ev::io &w, int revents)
		3790	{
		3791	...
		3792	}
		3793	}
		3794
		3795	myfunctor f;
		3796
		3797	ev::io w;
		3798	w.set (&f);
1987		3799
1988	=item w->set<function> (void *data = 0)	3800	=item w->set<function> (void *data = 0)
1989		3801
1990	Also sets a callback, but uses a static method or plain function as	3802	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	3803	callback. The optional C<data> argument will be stored in the watcher's
…		…
1993		3805
1994	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3806	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
1995		3807
1996	See the method-C<set> above for more details.	3808	See the method-C<set> above for more details.
1997		3809
1998	Example:	3810	Example: Use a plain function as callback.
1999		3811
2000	static void io_cb (ev::io &w, int revents) { }	3812	static void io_cb (ev::io &w, int revents) { }
2001	iow.set <io_cb> ();	3813	iow.set <io_cb> ();
2002		3814
2003	=item w->set (struct ev_loop *)	3815	=item w->set (loop)
2004		3816
2005	Associates a different C<struct ev_loop> with this watcher. You can only	3817	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).	3818	do this when the watcher is inactive (and not pending either).
2007		3819
2008	=item w->set ([args])	3820	=item w->set ([arguments])
2009		3821
2010	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3822	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	3823	method or a suitable start method must be called at least once. Unlike the
2012	automatically stopped and restarted when reconfiguring it with this	3824	C counterpart, an active watcher gets automatically stopped and restarted
2013	method.	3825	when reconfiguring it with this method.
2014		3826
2015	=item w->start ()	3827	=item w->start ()
2016		3828
2017	Starts the watcher. Note that there is no C<loop> argument, as the	3829	Starts the watcher. Note that there is no C<loop> argument, as the
2018	constructor already stores the event loop.	3830	constructor already stores the event loop.
2019		3831
		3832	=item w->start ([arguments])
		3833
		3834	Instead of calling C<set> and C<start> methods separately, it is often
		3835	convenient to wrap them in one call. Uses the same type of arguments as
		3836	the configure C<set> method of the watcher.
		3837
2020	=item w->stop ()	3838	=item w->stop ()
2021		3839
2022	Stops the watcher if it is active. Again, no C<loop> argument.	3840	Stops the watcher if it is active. Again, no C<loop> argument.
2023		3841
2024	=item w->again () C<ev::timer>, C<ev::periodic> only	3842	=item w->again () (C<ev::timer>, C<ev::periodic> only)
2025		3843
2026	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3844	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
2027	C<ev_TYPE_again> function.	3845	C<ev_TYPE_again> function.
2028		3846
2029	=item w->sweep () C<ev::embed> only	3847	=item w->sweep () (C<ev::embed> only)
2030		3848
2031	Invokes C<ev_embed_sweep>.	3849	Invokes C<ev_embed_sweep>.
2032		3850
2033	=item w->update () C<ev::stat> only	3851	=item w->update () (C<ev::stat> only)
2034		3852
2035	Invokes C<ev_stat_stat>.	3853	Invokes C<ev_stat_stat>.
2036		3854
2037	=back	3855	=back
2038		3856
2039	=back	3857	=back
2040		3858
2041	Example: Define a class with an IO and idle watcher, start one of them in	3859	Example: Define a class with two I/O and idle watchers, start the I/O
2042	the constructor.	3860	watchers in the constructor.
2043		3861
2044	class myclass	3862	class myclass
2045	{	3863	{
2046	ev_io io; void io_cb (ev::io &w, int revents);	3864	ev::io io ; void io_cb (ev::io &w, int revents);
		3865	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
2047	ev_idle idle void idle_cb (ev::idle &w, int revents);	3866	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2048		3867
2049	myclass ();	3868	myclass (int fd)
2050	}	3869	{
2051
2052	myclass::myclass (int fd)
2053	{
2054	io .set <myclass, &myclass::io_cb > (this);	3870	io .set <myclass, &myclass::io_cb > (this);
		3871	io2 .set <myclass, &myclass::io2_cb > (this);
2055	idle.set <myclass, &myclass::idle_cb> (this);	3872	idle.set <myclass, &myclass::idle_cb> (this);
2056		3873
2057	io.start (fd, ev::READ);	3874	io.set (fd, ev::WRITE); // configure the watcher
		3875	io.start (); // start it whenever convenient
		3876
		3877	io2.start (fd, ev::READ); // set + start in one call
		3878	}
2058	}	3879	};
		3880
		3881
		3882	=head1 OTHER LANGUAGE BINDINGS
		3883
		3884	Libev does not offer other language bindings itself, but bindings for a
		3885	number of languages exist in the form of third-party packages. If you know
		3886	any interesting language binding in addition to the ones listed here, drop
		3887	me a note.
		3888
		3889	=over 4
		3890
		3891	=item Perl
		3892
		3893	The EV module implements the full libev API and is actually used to test
		3894	libev. EV is developed together with libev. Apart from the EV core module,
		3895	there are additional modules that implement libev-compatible interfaces
		3896	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3897	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3898	and C<EV::Glib>).
		3899
		3900	It can be found and installed via CPAN, its homepage is at
		3901	L<http://software.schmorp.de/pkg/EV>.
		3902
		3903	=item Python
		3904
		3905	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3906	seems to be quite complete and well-documented.
		3907
		3908	=item Ruby
		3909
		3910	Tony Arcieri has written a ruby extension that offers access to a subset
		3911	of the libev API and adds file handle abstractions, asynchronous DNS and
		3912	more on top of it. It can be found via gem servers. Its homepage is at
		3913	L<http://rev.rubyforge.org/>.
		3914
		3915	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3916	makes rev work even on mingw.
		3917
		3918	=item Haskell
		3919
		3920	A haskell binding to libev is available at
		3921	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3922
		3923	=item D
		3924
		3925	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3926	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3927
		3928	=item Ocaml
		3929
		3930	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3931	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3932
		3933	=item Lua
		3934
		3935	Brian Maher has written a partial interface to libev for lua (at the
		3936	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3937	L<http://github.com/brimworks/lua-ev>.
		3938
		3939	=back
2059		3940
2060		3941
2061	=head1 MACRO MAGIC	3942	=head1 MACRO MAGIC
2062		3943
2063	Libev can be compiled with a variety of options, the most fundemantal is	3944	Libev can be compiled with a variety of options, the most fundamental
2064	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	3945	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2065	callbacks have an initial C<struct ev_loop *> argument.	3946	functions and callbacks have an initial C<struct ev_loop *> argument.
2066		3947
2067	To make it easier to write programs that cope with either variant, the	3948	To make it easier to write programs that cope with either variant, the
2068	following macros are defined:	3949	following macros are defined:
2069		3950
2070	=over 4	3951	=over 4
…		…
2073		3954
2074	This provides the loop I<argument> for functions, if one is required ("ev	3955	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,	3956	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:	3957	C<EV_A_> is used when other arguments are following. Example:
2077		3958
2078	ev_unref (EV_A);	3959	ev_unref (EV_A);
2079	ev_timer_add (EV_A_ watcher);	3960	ev_timer_add (EV_A_ watcher);
2080	ev_loop (EV_A_ 0);	3961	ev_run (EV_A_ 0);
2081		3962
2082	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3963	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2083	which is often provided by the following macro.	3964	which is often provided by the following macro.
2084		3965
2085	=item C<EV_P>, C<EV_P_>	3966	=item C<EV_P>, C<EV_P_>
2086		3967
2087	This provides the loop I<parameter> for functions, if one is required ("ev	3968	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,	3969	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:	3970	C<EV_P_> is used when other parameters are following. Example:
2090		3971
2091	// this is how ev_unref is being declared	3972	// this is how ev_unref is being declared
2092	static void ev_unref (EV_P);	3973	static void ev_unref (EV_P);
2093		3974
2094	// this is how you can declare your typical callback	3975	// this is how you can declare your typical callback
2095	static void cb (EV_P_ ev_timer *w, int revents)	3976	static void cb (EV_P_ ev_timer *w, int revents)
2096		3977
2097	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3978	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2098	suitable for use with C<EV_A>.	3979	suitable for use with C<EV_A>.
2099		3980
2100	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3981	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2101		3982
2102	Similar to the other two macros, this gives you the value of the default	3983	Similar to the other two macros, this gives you the value of the default
2103	loop, if multiple loops are supported ("ev loop default").	3984	loop, if multiple loops are supported ("ev loop default").
		3985
		3986	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3987
		3988	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3989	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3990	is undefined when the default loop has not been initialised by a previous
		3991	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3992
		3993	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3994	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2104		3995
2105	=back	3996	=back
2106		3997
2107	Example: Declare and initialise a check watcher, utilising the above	3998	Example: Declare and initialise a check watcher, utilising the above
2108	macros so it will work regardless of whether multiple loops are supported	3999	macros so it will work regardless of whether multiple loops are supported
2109	or not.	4000	or not.
2110		4001
2111	static void	4002	static void
2112	check_cb (EV_P_ ev_timer *w, int revents)	4003	check_cb (EV_P_ ev_timer *w, int revents)
2113	{	4004	{
2114	ev_check_stop (EV_A_ w);	4005	ev_check_stop (EV_A_ w);
2115	}	4006	}
2116		4007
2117	ev_check check;	4008	ev_check check;
2118	ev_check_init (&check, check_cb);	4009	ev_check_init (&check, check_cb);
2119	ev_check_start (EV_DEFAULT_ &check);	4010	ev_check_start (EV_DEFAULT_ &check);
2120	ev_loop (EV_DEFAULT_ 0);	4011	ev_run (EV_DEFAULT_ 0);
2121		4012
2122	=head1 EMBEDDING	4013	=head1 EMBEDDING
2123		4014
2124	Libev can (and often is) directly embedded into host	4015	Libev can (and often is) directly embedded into host
2125	applications. Examples of applications that embed it include the Deliantra	4016	applications. Examples of applications that embed it include the Deliantra
2126	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	4017	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
2127	and rxvt-unicode.	4018	and rxvt-unicode.
2128		4019
2129	The goal is to enable you to just copy the neecssary files into your	4020	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	4021	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	4022	you can easily upgrade by simply copying (or having a checked-out copy of
2132	libev somewhere in your source tree).	4023	libev somewhere in your source tree).
2133		4024
2134	=head2 FILESETS	4025	=head2 FILESETS
2135		4026
2136	Depending on what features you need you need to include one or more sets of files	4027	Depending on what features you need you need to include one or more sets of files
2137	in your app.	4028	in your application.
2138		4029
2139	=head3 CORE EVENT LOOP	4030	=head3 CORE EVENT LOOP
2140		4031
2141	To include only the libev core (all the C<ev_*> functions), with manual	4032	To include only the libev core (all the C<ev_*> functions), with manual
2142	configuration (no autoconf):	4033	configuration (no autoconf):
2143		4034
2144	#define EV_STANDALONE 1	4035	#define EV_STANDALONE 1
2145	#include "ev.c"	4036	#include "ev.c"
2146		4037
2147	This will automatically include F<ev.h>, too, and should be done in a	4038	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	4039	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	4040	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	4041	done by writing a wrapper around F<ev.h> that you can include instead and
2151	where you can put other configuration options):	4042	where you can put other configuration options):
2152		4043
2153	#define EV_STANDALONE 1	4044	#define EV_STANDALONE 1
2154	#include "ev.h"	4045	#include "ev.h"
2155		4046
2156	Both header files and implementation files can be compiled with a C++	4047	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	4048	compiler (at least, that's a stated goal, and breakage will be treated
2158	as a bug).	4049	as a bug).
2159		4050
2160	You need the following files in your source tree, or in a directory	4051	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):	4052	in your include path (e.g. in libev/ when using -Ilibev):
2162		4053
2163	ev.h	4054	ev.h
2164	ev.c	4055	ev.c
2165	ev_vars.h	4056	ev_vars.h
2166	ev_wrap.h	4057	ev_wrap.h
2167		4058
2168	ev_win32.c required on win32 platforms only	4059	ev_win32.c required on win32 platforms only
2169		4060
2170	ev_select.c only when select backend is enabled (which is enabled by default)	4061	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)	4062	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)	4063	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)	4064	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)	4065	ev_port.c only when the solaris port backend is enabled (disabled by default)
2175		4066
2176	F<ev.c> includes the backend files directly when enabled, so you only need	4067	F<ev.c> includes the backend files directly when enabled, so you only need
2177	to compile this single file.	4068	to compile this single file.
2178		4069
2179	=head3 LIBEVENT COMPATIBILITY API	4070	=head3 LIBEVENT COMPATIBILITY API
2180		4071
2181	To include the libevent compatibility API, also include:	4072	To include the libevent compatibility API, also include:
2182		4073
2183	#include "event.c"	4074	#include "event.c"
2184		4075
2185	in the file including F<ev.c>, and:	4076	in the file including F<ev.c>, and:
2186		4077
2187	#include "event.h"	4078	#include "event.h"
2188		4079
2189	in the files that want to use the libevent API. This also includes F<ev.h>.	4080	in the files that want to use the libevent API. This also includes F<ev.h>.
2190		4081
2191	You need the following additional files for this:	4082	You need the following additional files for this:
2192		4083
2193	event.h	4084	event.h
2194	event.c	4085	event.c
2195		4086
2196	=head3 AUTOCONF SUPPORT	4087	=head3 AUTOCONF SUPPORT
2197		4088
2198	Instead of using C<EV_STANDALONE=1> and providing your config in	4089	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	4090	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	4091	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2201	include F<config.h> and configure itself accordingly.	4092	include F<config.h> and configure itself accordingly.
2202		4093
2203	For this of course you need the m4 file:	4094	For this of course you need the m4 file:
2204		4095
2205	libev.m4	4096	libev.m4
2206		4097
2207	=head2 PREPROCESSOR SYMBOLS/MACROS	4098	=head2 PREPROCESSOR SYMBOLS/MACROS
2208		4099
2209	Libev can be configured via a variety of preprocessor symbols you have to define	4100	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	4101	define before including (or compiling) any of its files. The default in
2211	and only include the select backend.	4102	the absence of autoconf is documented for every option.
		4103
		4104	Symbols marked with "(h)" do not change the ABI, and can have different
		4105	values when compiling libev vs. including F<ev.h>, so it is permissible
		4106	to redefine them before including F<ev.h> without breaking compatibility
		4107	to a compiled library. All other symbols change the ABI, which means all
		4108	users of libev and the libev code itself must be compiled with compatible
		4109	settings.
2212		4110
2213	=over 4	4111	=over 4
2214		4112
		4113	=item EV_COMPAT3 (h)
		4114
		4115	Backwards compatibility is a major concern for libev. This is why this
		4116	release of libev comes with wrappers for the functions and symbols that
		4117	have been renamed between libev version 3 and 4.
		4118
		4119	You can disable these wrappers (to test compatibility with future
		4120	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4121	sources. This has the additional advantage that you can drop the C<struct>
		4122	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4123	typedef in that case.
		4124
		4125	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4126	and in some even more future version the compatibility code will be
		4127	removed completely.
		4128
2215	=item EV_STANDALONE	4129	=item EV_STANDALONE (h)
2216		4130
2217	Must always be C<1> if you do not use autoconf configuration, which	4131	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	4132	keeps libev from including F<config.h>, and it also defines dummy
2219	implementations for some libevent functions (such as logging, which is not	4133	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	4134	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.	4135	F<event.h> that are not directly supported by the libev core alone.
2222		4136
		4137	In standalone mode, libev will still try to automatically deduce the
		4138	configuration, but has to be more conservative.
		4139
2223	=item EV_USE_MONOTONIC	4140	=item EV_USE_MONOTONIC
2224		4141
2225	If defined to be C<1>, libev will try to detect the availability of the	4142	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	4143	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	4144	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	4145	you usually have to link against librt or something similar. Enabling it
2229	the functionality isn't available is safe, though, althoguh you have	4146	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>	4147	to make sure you link against any libraries where the C<clock_gettime>
2231	function is hiding in (often F<-lrt>).	4148	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2232		4149
2233	=item EV_USE_REALTIME	4150	=item EV_USE_REALTIME
2234		4151
2235	If defined to be C<1>, libev will try to detect the availability of the	4152	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	4153	real-time clock option at compile time (and assume its availability
2237	runtime if successful). Otherwise no use of the realtime clock option will	4154	at runtime if successful). Otherwise no use of the real-time clock
2238	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4155	option will be attempted. This effectively replaces C<gettimeofday>
2239	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	4156	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2240	in the description of C<EV_USE_MONOTONIC>, though.	4157	correctness. See the note about libraries in the description of
		4158	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4159	C<EV_USE_CLOCK_SYSCALL>.
		4160
		4161	=item EV_USE_CLOCK_SYSCALL
		4162
		4163	If defined to be C<1>, libev will try to use a direct syscall instead
		4164	of calling the system-provided C<clock_gettime> function. This option
		4165	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4166	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4167	programs needlessly. Using a direct syscall is slightly slower (in
		4168	theory), because no optimised vdso implementation can be used, but avoids
		4169	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4170	higher, as it simplifies linking (no need for C<-lrt>).
		4171
		4172	=item EV_USE_NANOSLEEP
		4173
		4174	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		4175	and will use it for delays. Otherwise it will use C<select ()>.
		4176
		4177	=item EV_USE_EVENTFD
		4178
		4179	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4180	available and will probe for kernel support at runtime. This will improve
		4181	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4182	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4183	2.7 or newer, otherwise disabled.
2241		4184
2242	=item EV_USE_SELECT	4185	=item EV_USE_SELECT
2243		4186
2244	If undefined or defined to be C<1>, libev will compile in support for the	4187	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	4188	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	4189	other method takes over, select will be it. Otherwise the select backend
2247	will not be compiled in.	4190	will not be compiled in.
2248		4191
2249	=item EV_SELECT_USE_FD_SET	4192	=item EV_SELECT_USE_FD_SET
2250		4193
2251	If defined to C<1>, then the select backend will use the system C<fd_set>	4194	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	4195	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	4196	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	4197	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	4198	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	4199	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2257	influence the size of the C<fd_set> used.	4200	configures the maximum size of the C<fd_set>.
2258		4201
2259	=item EV_SELECT_IS_WINSOCKET	4202	=item EV_SELECT_IS_WINSOCKET
2260		4203
2261	When defined to C<1>, the select backend will assume that	4204	When defined to C<1>, the select backend will assume that
2262	select/socket/connect etc. don't understand file descriptors but	4205	select/socket/connect etc. don't understand file descriptors but
…		…
2264	be used is the winsock select). This means that it will call	4207	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,	4208	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	4209	it is assumed that all these functions actually work on fds, even
2267	on win32. Should not be defined on non-win32 platforms.	4210	on win32. Should not be defined on non-win32 platforms.
2268		4211
		4212	=item EV_FD_TO_WIN32_HANDLE(fd)
		4213
		4214	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4215	file descriptors to socket handles. When not defining this symbol (the
		4216	default), then libev will call C<_get_osfhandle>, which is usually
		4217	correct. In some cases, programs use their own file descriptor management,
		4218	in which case they can provide this function to map fds to socket handles.
		4219
		4220	=item EV_WIN32_HANDLE_TO_FD(handle)
		4221
		4222	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4223	using the standard C<_open_osfhandle> function. For programs implementing
		4224	their own fd to handle mapping, overwriting this function makes it easier
		4225	to do so. This can be done by defining this macro to an appropriate value.
		4226
		4227	=item EV_WIN32_CLOSE_FD(fd)
		4228
		4229	If programs implement their own fd to handle mapping on win32, then this
		4230	macro can be used to override the C<close> function, useful to unregister
		4231	file descriptors again. Note that the replacement function has to close
		4232	the underlying OS handle.
		4233
2269	=item EV_USE_POLL	4234	=item EV_USE_POLL
2270		4235
2271	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4236	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	4237	backend. Otherwise it will be enabled on non-win32 platforms. It
2273	takes precedence over select.	4238	takes precedence over select.
2274		4239
2275	=item EV_USE_EPOLL	4240	=item EV_USE_EPOLL
2276		4241
2277	If defined to be C<1>, libev will compile in support for the Linux	4242	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,	4243	C<epoll>(7) backend. Its availability will be detected at runtime,
2279	otherwise another method will be used as fallback. This is the	4244	otherwise another method will be used as fallback. This is the preferred
2280	preferred backend for GNU/Linux systems.	4245	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4246	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2281		4247
2282	=item EV_USE_KQUEUE	4248	=item EV_USE_KQUEUE
2283		4249
2284	If defined to be C<1>, libev will compile in support for the BSD style	4250	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,	4251	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	4264	otherwise another method will be used as fallback. This is the preferred
2299	backend for Solaris 10 systems.	4265	backend for Solaris 10 systems.
2300		4266
2301	=item EV_USE_DEVPOLL	4267	=item EV_USE_DEVPOLL
2302		4268
2303	reserved for future expansion, works like the USE symbols above.	4269	Reserved for future expansion, works like the USE symbols above.
2304		4270
2305	=item EV_USE_INOTIFY	4271	=item EV_USE_INOTIFY
2306		4272
2307	If defined to be C<1>, libev will compile in support for the Linux inotify	4273	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	4274	interface to speed up C<ev_stat> watchers. Its actual availability will
2309	be detected at runtime.	4275	be detected at runtime. If undefined, it will be enabled if the headers
		4276	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2310		4277
		4278	=item EV_ATOMIC_T
		4279
		4280	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4281	access is atomic with respect to other threads or signal contexts. No such
		4282	type is easily found in the C language, so you can provide your own type
		4283	that you know is safe for your purposes. It is used both for signal handler "locking"
		4284	as well as for signal and thread safety in C<ev_async> watchers.
		4285
		4286	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4287	(from F<signal.h>), which is usually good enough on most platforms.
		4288
2311	=item EV_H	4289	=item EV_H (h)
2312		4290
2313	The name of the F<ev.h> header file used to include it. The default if	4291	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	4292	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.	4293	used to virtually rename the F<ev.h> header file in case of conflicts.
2316		4294
2317	=item EV_CONFIG_H	4295	=item EV_CONFIG_H (h)
2318		4296
2319	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4297	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	4298	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2321	C<EV_H>, above.	4299	C<EV_H>, above.
2322		4300
2323	=item EV_EVENT_H	4301	=item EV_EVENT_H (h)
2324		4302
2325	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4303	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.	4304	of how the F<event.h> header can be found, the default is C<"event.h">.
2327		4305
2328	=item EV_PROTOTYPES	4306	=item EV_PROTOTYPES (h)
2329		4307
2330	If defined to be C<0>, then F<ev.h> will not define any function	4308	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	4309	prototypes, but still define all the structs and other symbols. This is
2332	occasionally useful if you want to provide your own wrapper functions	4310	occasionally useful if you want to provide your own wrapper functions
2333	around libev functions.	4311	around libev functions.
…		…
2352	When doing priority-based operations, libev usually has to linearly search	4330	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	4331	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	4332	and time, so using the defaults of five priorities (-2 .. +2) is usually
2355	fine.	4333	fine.
2356		4334
2357	If your embedding app does not need any priorities, defining these both to	4335	If your embedding application does not need any priorities, defining these
2358	C<0> will save some memory and cpu.	4336	both to C<0> will save some memory and CPU.
2359		4337
2360	=item EV_PERIODIC_ENABLE	4338	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4339	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4340	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2361		4341
2362	If undefined or defined to be C<1>, then periodic timers are supported. If	4342	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	4343	the respective watcher type is supported. If defined to be C<0>, then it
2364	code.	4344	is not. Disabling watcher types mainly saves code size.
2365		4345
2366	=item EV_IDLE_ENABLE	4346	=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		4347
2389	If you need to shave off some kilobytes of code at the expense of some	4348	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	4349	speed (but with the full API), you can define this symbol to request
2391	some inlining decisions, saves roughly 30% codesize of amd64.	4350	certain subsets of functionality. The default is to enable all features
		4351	that can be enabled on the platform.
		4352
		4353	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4354	with some broad features you want) and then selectively re-enable
		4355	additional parts you want, for example if you want everything minimal,
		4356	but multiple event loop support, async and child watchers and the poll
		4357	backend, use this:
		4358
		4359	#define EV_FEATURES 0
		4360	#define EV_MULTIPLICITY 1
		4361	#define EV_USE_POLL 1
		4362	#define EV_CHILD_ENABLE 1
		4363	#define EV_ASYNC_ENABLE 1
		4364
		4365	The actual value is a bitset, it can be a combination of the following
		4366	values:
		4367
		4368	=over 4
		4369
		4370	=item C<1> - faster/larger code
		4371
		4372	Use larger code to speed up some operations.
		4373
		4374	Currently this is used to override some inlining decisions (enlarging the
		4375	code size by roughly 30% on amd64).
		4376
		4377	When optimising for size, use of compiler flags such as C<-Os> with
		4378	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4379	assertions.
		4380
		4381	=item C<2> - faster/larger data structures
		4382
		4383	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4384	hash table sizes and so on. This will usually further increase code size
		4385	and can additionally have an effect on the size of data structures at
		4386	runtime.
		4387
		4388	=item C<4> - full API configuration
		4389
		4390	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4391	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4392
		4393	=item C<8> - full API
		4394
		4395	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4396	details on which parts of the API are still available without this
		4397	feature, and do not complain if this subset changes over time.
		4398
		4399	=item C<16> - enable all optional watcher types
		4400
		4401	Enables all optional watcher types. If you want to selectively enable
		4402	only some watcher types other than I/O and timers (e.g. prepare,
		4403	embed, async, child...) you can enable them manually by defining
		4404	C<EV_watchertype_ENABLE> to C<1> instead.
		4405
		4406	=item C<32> - enable all backends
		4407
		4408	This enables all backends - without this feature, you need to enable at
		4409	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4410
		4411	=item C<64> - enable OS-specific "helper" APIs
		4412
		4413	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4414	default.
		4415
		4416	=back
		4417
		4418	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4419	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4420	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4421	watchers, timers and monotonic clock support.
		4422
		4423	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4424	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4425	your program might be left out as well - a binary starting a timer and an
		4426	I/O watcher then might come out at only 5Kb.
		4427
		4428	=item EV_AVOID_STDIO
		4429
		4430	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4431	functions (printf, scanf, perror etc.). This will increase the code size
		4432	somewhat, but if your program doesn't otherwise depend on stdio and your
		4433	libc allows it, this avoids linking in the stdio library which is quite
		4434	big.
		4435
		4436	Note that error messages might become less precise when this option is
		4437	enabled.
		4438
		4439	=item EV_NSIG
		4440
		4441	The highest supported signal number, +1 (or, the number of
		4442	signals): Normally, libev tries to deduce the maximum number of signals
		4443	automatically, but sometimes this fails, in which case it can be
		4444	specified. Also, using a lower number than detected (C<32> should be
		4445	good for about any system in existence) can save some memory, as libev
		4446	statically allocates some 12-24 bytes per signal number.
2392		4447
2393	=item EV_PID_HASHSIZE	4448	=item EV_PID_HASHSIZE
2394		4449
2395	C<ev_child> watchers use a small hash table to distribute workload by	4450	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	4451	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	4452	usually more than enough. If you need to manage thousands of children you
2398	increase this value (I<must> be a power of two).	4453	might want to increase this value (I<must> be a power of two).
2399		4454
2400	=item EV_INOTIFY_HASHSIZE	4455	=item EV_INOTIFY_HASHSIZE
2401		4456
2402	C<ev_staz> watchers use a small hash table to distribute workload by	4457	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>),	4458	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>	4459	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	4460	C<ev_stat> watchers you might want to increase this value (I<must> be a
2406	two).	4461	power of two).
		4462
		4463	=item EV_USE_4HEAP
		4464
		4465	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4466	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4467	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4468	faster performance with many (thousands) of watchers.
		4469
		4470	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4471	will be C<0>.
		4472
		4473	=item EV_HEAP_CACHE_AT
		4474
		4475	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4476	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4477	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4478	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4479	but avoids random read accesses on heap changes. This improves performance
		4480	noticeably with many (hundreds) of watchers.
		4481
		4482	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4483	will be C<0>.
		4484
		4485	=item EV_VERIFY
		4486
		4487	Controls how much internal verification (see C<ev_verify ()>) will
		4488	be done: If set to C<0>, no internal verification code will be compiled
		4489	in. If set to C<1>, then verification code will be compiled in, but not
		4490	called. If set to C<2>, then the internal verification code will be
		4491	called once per loop, which can slow down libev. If set to C<3>, then the
		4492	verification code will be called very frequently, which will slow down
		4493	libev considerably.
		4494
		4495	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4496	will be C<0>.
2407		4497
2408	=item EV_COMMON	4498	=item EV_COMMON
2409		4499
2410	By default, all watchers have a C<void *data> member. By redefining	4500	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	4501	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,	4502	members. You have to define it each time you include one of the files,
2413	though, and it must be identical each time.	4503	though, and it must be identical each time.
2414		4504
2415	For example, the perl EV module uses something like this:	4505	For example, the perl EV module uses something like this:
2416		4506
2417	#define EV_COMMON \	4507	#define EV_COMMON \
2418	SV *self; /* contains this struct */ \	4508	SV *self; /* contains this struct */ \
2419	SV *cb_sv, *fh /* note no trailing ";" */	4509	SV *cb_sv, *fh /* note no trailing ";" */
2420		4510
2421	=item EV_CB_DECLARE (type)	4511	=item EV_CB_DECLARE (type)
2422		4512
2423	=item EV_CB_INVOKE (watcher, revents)	4513	=item EV_CB_INVOKE (watcher, revents)
2424		4514
2425	=item ev_set_cb (ev, cb)	4515	=item ev_set_cb (ev, cb)
2426		4516
2427	Can be used to change the callback member declaration in each watcher,	4517	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	4518	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	4519	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	4520	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	4521	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++.	4522	method calls instead of plain function calls in C++.
		4523
		4524	=back
		4525
		4526	=head2 EXPORTED API SYMBOLS
		4527
		4528	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4529	exported symbols, you can use the provided F<Symbol.*> files which list
		4530	all public symbols, one per line:
		4531
		4532	Symbols.ev for libev proper
		4533	Symbols.event for the libevent emulation
		4534
		4535	This can also be used to rename all public symbols to avoid clashes with
		4536	multiple versions of libev linked together (which is obviously bad in
		4537	itself, but sometimes it is inconvenient to avoid this).
		4538
		4539	A sed command like this will create wrapper C<#define>'s that you need to
		4540	include before including F<ev.h>:
		4541
		4542	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4543
		4544	This would create a file F<wrap.h> which essentially looks like this:
		4545
		4546	#define ev_backend myprefix_ev_backend
		4547	#define ev_check_start myprefix_ev_check_start
		4548	#define ev_check_stop myprefix_ev_check_stop
		4549	...
2433		4550
2434	=head2 EXAMPLES	4551	=head2 EXAMPLES
2435		4552
2436	For a real-world example of a program the includes libev	4553	For a real-world example of a program the includes libev
2437	verbatim, you can have a look at the EV perl module	4554	verbatim, you can have a look at the EV perl module
…		…
2442	file.	4559	file.
2443		4560
2444	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4561	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:	4562	that everybody includes and which overrides some configure choices:
2446		4563
2447	#define EV_MINIMAL 1	4564	#define EV_FEATURES 8
2448	#define EV_USE_POLL 0	4565	#define EV_USE_SELECT 1
2449	#define EV_MULTIPLICITY 0
2450	#define EV_PERIODIC_ENABLE 0	4566	#define EV_PREPARE_ENABLE 1
		4567	#define EV_IDLE_ENABLE 1
2451	#define EV_STAT_ENABLE 0	4568	#define EV_SIGNAL_ENABLE 1
2452	#define EV_FORK_ENABLE 0	4569	#define EV_CHILD_ENABLE 1
		4570	#define EV_USE_STDEXCEPT 0
2453	#define EV_CONFIG_H <config.h>	4571	#define EV_CONFIG_H <config.h>
2454	#define EV_MINPRI 0
2455	#define EV_MAXPRI 0
2456		4572
2457	#include "ev++.h"	4573	#include "ev++.h"
2458		4574
2459	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4575	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2460		4576
2461	#include "ev_cpp.h"	4577	#include "ev_cpp.h"
2462	#include "ev.c"	4578	#include "ev.c"
2463		4579
		4580	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2464		4581
		4582	=head2 THREADS AND COROUTINES
		4583
		4584	=head3 THREADS
		4585
		4586	All libev functions are reentrant and thread-safe unless explicitly
		4587	documented otherwise, but libev implements no locking itself. This means
		4588	that you can use as many loops as you want in parallel, as long as there
		4589	are no concurrent calls into any libev function with the same loop
		4590	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4591	of course): libev guarantees that different event loops share no data
		4592	structures that need any locking.
		4593
		4594	Or to put it differently: calls with different loop parameters can be done
		4595	concurrently from multiple threads, calls with the same loop parameter
		4596	must be done serially (but can be done from different threads, as long as
		4597	only one thread ever is inside a call at any point in time, e.g. by using
		4598	a mutex per loop).
		4599
		4600	Specifically to support threads (and signal handlers), libev implements
		4601	so-called C<ev_async> watchers, which allow some limited form of
		4602	concurrency on the same event loop, namely waking it up "from the
		4603	outside".
		4604
		4605	If you want to know which design (one loop, locking, or multiple loops
		4606	without or something else still) is best for your problem, then I cannot
		4607	help you, but here is some generic advice:
		4608
		4609	=over 4
		4610
		4611	=item * most applications have a main thread: use the default libev loop
		4612	in that thread, or create a separate thread running only the default loop.
		4613
		4614	This helps integrating other libraries or software modules that use libev
		4615	themselves and don't care/know about threading.
		4616
		4617	=item * one loop per thread is usually a good model.
		4618
		4619	Doing this is almost never wrong, sometimes a better-performance model
		4620	exists, but it is always a good start.
		4621
		4622	=item * other models exist, such as the leader/follower pattern, where one
		4623	loop is handed through multiple threads in a kind of round-robin fashion.
		4624
		4625	Choosing a model is hard - look around, learn, know that usually you can do
		4626	better than you currently do :-)
		4627
		4628	=item * often you need to talk to some other thread which blocks in the
		4629	event loop.
		4630
		4631	C<ev_async> watchers can be used to wake them up from other threads safely
		4632	(or from signal contexts...).
		4633
		4634	An example use would be to communicate signals or other events that only
		4635	work in the default loop by registering the signal watcher with the
		4636	default loop and triggering an C<ev_async> watcher from the default loop
		4637	watcher callback into the event loop interested in the signal.
		4638
		4639	=back
		4640
		4641	See also L<Thread locking example>.
		4642
		4643	=head3 COROUTINES
		4644
		4645	Libev is very accommodating to coroutines ("cooperative threads"):
		4646	libev fully supports nesting calls to its functions from different
		4647	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4648	different coroutines, and switch freely between both coroutines running
		4649	the loop, as long as you don't confuse yourself). The only exception is
		4650	that you must not do this from C<ev_periodic> reschedule callbacks.
		4651
		4652	Care has been taken to ensure that libev does not keep local state inside
		4653	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4654	they do not call any callbacks.
		4655
		4656	=head2 COMPILER WARNINGS
		4657
		4658	Depending on your compiler and compiler settings, you might get no or a
		4659	lot of warnings when compiling libev code. Some people are apparently
		4660	scared by this.
		4661
		4662	However, these are unavoidable for many reasons. For one, each compiler
		4663	has different warnings, and each user has different tastes regarding
		4664	warning options. "Warn-free" code therefore cannot be a goal except when
		4665	targeting a specific compiler and compiler-version.
		4666
		4667	Another reason is that some compiler warnings require elaborate
		4668	workarounds, or other changes to the code that make it less clear and less
		4669	maintainable.
		4670
		4671	And of course, some compiler warnings are just plain stupid, or simply
		4672	wrong (because they don't actually warn about the condition their message
		4673	seems to warn about). For example, certain older gcc versions had some
		4674	warnings that resulted in an extreme number of false positives. These have
		4675	been fixed, but some people still insist on making code warn-free with
		4676	such buggy versions.
		4677
		4678	While libev is written to generate as few warnings as possible,
		4679	"warn-free" code is not a goal, and it is recommended not to build libev
		4680	with any compiler warnings enabled unless you are prepared to cope with
		4681	them (e.g. by ignoring them). Remember that warnings are just that:
		4682	warnings, not errors, or proof of bugs.
		4683
		4684
		4685	=head2 VALGRIND
		4686
		4687	Valgrind has a special section here because it is a popular tool that is
		4688	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4689
		4690	If you think you found a bug (memory leak, uninitialised data access etc.)
		4691	in libev, then check twice: If valgrind reports something like:
		4692
		4693	==2274== definitely lost: 0 bytes in 0 blocks.
		4694	==2274== possibly lost: 0 bytes in 0 blocks.
		4695	==2274== still reachable: 256 bytes in 1 blocks.
		4696
		4697	Then there is no memory leak, just as memory accounted to global variables
		4698	is not a memleak - the memory is still being referenced, and didn't leak.
		4699
		4700	Similarly, under some circumstances, valgrind might report kernel bugs
		4701	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4702	although an acceptable workaround has been found here), or it might be
		4703	confused.
		4704
		4705	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4706	make it into some kind of religion.
		4707
		4708	If you are unsure about something, feel free to contact the mailing list
		4709	with the full valgrind report and an explanation on why you think this
		4710	is a bug in libev (best check the archives, too :). However, don't be
		4711	annoyed when you get a brisk "this is no bug" answer and take the chance
		4712	of learning how to interpret valgrind properly.
		4713
		4714	If you need, for some reason, empty reports from valgrind for your project
		4715	I suggest using suppression lists.
		4716
		4717
		4718	=head1 PORTABILITY NOTES
		4719
		4720	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4721
		4722	GNU/Linux is the only common platform that supports 64 bit file/large file
		4723	interfaces but I<disables> them by default.
		4724
		4725	That means that libev compiled in the default environment doesn't support
		4726	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4727
		4728	Unfortunately, many programs try to work around this GNU/Linux issue
		4729	by enabling the large file API, which makes them incompatible with the
		4730	standard libev compiled for their system.
		4731
		4732	Likewise, libev cannot enable the large file API itself as this would
		4733	suddenly make it incompatible to the default compile time environment,
		4734	i.e. all programs not using special compile switches.
		4735
		4736	=head2 OS/X AND DARWIN BUGS
		4737
		4738	The whole thing is a bug if you ask me - basically any system interface
		4739	you touch is broken, whether it is locales, poll, kqueue or even the
		4740	OpenGL drivers.
		4741
		4742	=head3 C<kqueue> is buggy
		4743
		4744	The kqueue syscall is broken in all known versions - most versions support
		4745	only sockets, many support pipes.
		4746
		4747	Libev tries to work around this by not using C<kqueue> by default on this
		4748	rotten platform, but of course you can still ask for it when creating a
		4749	loop - embedding a socket-only kqueue loop into a select-based one is
		4750	probably going to work well.
		4751
		4752	=head3 C<poll> is buggy
		4753
		4754	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4755	implementation by something calling C<kqueue> internally around the 10.5.6
		4756	release, so now C<kqueue> I<and> C<poll> are broken.
		4757
		4758	Libev tries to work around this by not using C<poll> by default on
		4759	this rotten platform, but of course you can still ask for it when creating
		4760	a loop.
		4761
		4762	=head3 C<select> is buggy
		4763
		4764	All that's left is C<select>, and of course Apple found a way to fuck this
		4765	one up as well: On OS/X, C<select> actively limits the number of file
		4766	descriptors you can pass in to 1024 - your program suddenly crashes when
		4767	you use more.
		4768
		4769	There is an undocumented "workaround" for this - defining
		4770	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4771	work on OS/X.
		4772
		4773	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4774
		4775	=head3 C<errno> reentrancy
		4776
		4777	The default compile environment on Solaris is unfortunately so
		4778	thread-unsafe that you can't even use components/libraries compiled
		4779	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4780	defined by default. A valid, if stupid, implementation choice.
		4781
		4782	If you want to use libev in threaded environments you have to make sure
		4783	it's compiled with C<_REENTRANT> defined.
		4784
		4785	=head3 Event port backend
		4786
		4787	The scalable event interface for Solaris is called "event
		4788	ports". Unfortunately, this mechanism is very buggy in all major
		4789	releases. If you run into high CPU usage, your program freezes or you get
		4790	a large number of spurious wakeups, make sure you have all the relevant
		4791	and latest kernel patches applied. No, I don't know which ones, but there
		4792	are multiple ones to apply, and afterwards, event ports actually work
		4793	great.
		4794
		4795	If you can't get it to work, you can try running the program by setting
		4796	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4797	C<select> backends.
		4798
		4799	=head2 AIX POLL BUG
		4800
		4801	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4802	this by trying to avoid the poll backend altogether (i.e. it's not even
		4803	compiled in), which normally isn't a big problem as C<select> works fine
		4804	with large bitsets on AIX, and AIX is dead anyway.
		4805
		4806	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4807
		4808	=head3 General issues
		4809
		4810	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4811	requires, and its I/O model is fundamentally incompatible with the POSIX
		4812	model. Libev still offers limited functionality on this platform in
		4813	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4814	descriptors. This only applies when using Win32 natively, not when using
		4815	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4816	as every compielr comes with a slightly differently broken/incompatible
		4817	environment.
		4818
		4819	Lifting these limitations would basically require the full
		4820	re-implementation of the I/O system. If you are into this kind of thing,
		4821	then note that glib does exactly that for you in a very portable way (note
		4822	also that glib is the slowest event library known to man).
		4823
		4824	There is no supported compilation method available on windows except
		4825	embedding it into other applications.
		4826
		4827	Sensible signal handling is officially unsupported by Microsoft - libev
		4828	tries its best, but under most conditions, signals will simply not work.
		4829
		4830	Not a libev limitation but worth mentioning: windows apparently doesn't
		4831	accept large writes: instead of resulting in a partial write, windows will
		4832	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4833	so make sure you only write small amounts into your sockets (less than a
		4834	megabyte seems safe, but this apparently depends on the amount of memory
		4835	available).
		4836
		4837	Due to the many, low, and arbitrary limits on the win32 platform and
		4838	the abysmal performance of winsockets, using a large number of sockets
		4839	is not recommended (and not reasonable). If your program needs to use
		4840	more than a hundred or so sockets, then likely it needs to use a totally
		4841	different implementation for windows, as libev offers the POSIX readiness
		4842	notification model, which cannot be implemented efficiently on windows
		4843	(due to Microsoft monopoly games).
		4844
		4845	A typical way to use libev under windows is to embed it (see the embedding
		4846	section for details) and use the following F<evwrap.h> header file instead
		4847	of F<ev.h>:
		4848
		4849	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4850	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4851
		4852	#include "ev.h"
		4853
		4854	And compile the following F<evwrap.c> file into your project (make sure
		4855	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4856
		4857	#include "evwrap.h"
		4858	#include "ev.c"
		4859
		4860	=head3 The winsocket C<select> function
		4861
		4862	The winsocket C<select> function doesn't follow POSIX in that it
		4863	requires socket I<handles> and not socket I<file descriptors> (it is
		4864	also extremely buggy). This makes select very inefficient, and also
		4865	requires a mapping from file descriptors to socket handles (the Microsoft
		4866	C runtime provides the function C<_open_osfhandle> for this). See the
		4867	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4868	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4869
		4870	The configuration for a "naked" win32 using the Microsoft runtime
		4871	libraries and raw winsocket select is:
		4872
		4873	#define EV_USE_SELECT 1
		4874	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4875
		4876	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4877	complexity in the O(n²) range when using win32.
		4878
		4879	=head3 Limited number of file descriptors
		4880
		4881	Windows has numerous arbitrary (and low) limits on things.
		4882
		4883	Early versions of winsocket's select only supported waiting for a maximum
		4884	of C<64> handles (probably owning to the fact that all windows kernels
		4885	can only wait for C<64> things at the same time internally; Microsoft
		4886	recommends spawning a chain of threads and wait for 63 handles and the
		4887	previous thread in each. Sounds great!).
		4888
		4889	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4890	to some high number (e.g. C<2048>) before compiling the winsocket select
		4891	call (which might be in libev or elsewhere, for example, perl and many
		4892	other interpreters do their own select emulation on windows).
		4893
		4894	Another limit is the number of file descriptors in the Microsoft runtime
		4895	libraries, which by default is C<64> (there must be a hidden I<64>
		4896	fetish or something like this inside Microsoft). You can increase this
		4897	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4898	(another arbitrary limit), but is broken in many versions of the Microsoft
		4899	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4900	(depending on windows version and/or the phase of the moon). To get more,
		4901	you need to wrap all I/O functions and provide your own fd management, but
		4902	the cost of calling select (O(n²)) will likely make this unworkable.
		4903
		4904	=head2 PORTABILITY REQUIREMENTS
		4905
		4906	In addition to a working ISO-C implementation and of course the
		4907	backend-specific APIs, libev relies on a few additional extensions:
		4908
		4909	=over 4
		4910
		4911	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4912	calling conventions regardless of C<ev_watcher_type *>.
		4913
		4914	Libev assumes not only that all watcher pointers have the same internal
		4915	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4916	assumes that the same (machine) code can be used to call any watcher
		4917	callback: The watcher callbacks have different type signatures, but libev
		4918	calls them using an C<ev_watcher *> internally.
		4919
		4920	=item pointer accesses must be thread-atomic
		4921
		4922	Accessing a pointer value must be atomic, it must both be readable and
		4923	writable in one piece - this is the case on all current architectures.
		4924
		4925	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4926
		4927	The type C<sig_atomic_t volatile> (or whatever is defined as
		4928	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4929	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4930	believed to be sufficiently portable.
		4931
		4932	=item C<sigprocmask> must work in a threaded environment
		4933
		4934	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4935	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4936	pthread implementations will either allow C<sigprocmask> in the "main
		4937	thread" or will block signals process-wide, both behaviours would
		4938	be compatible with libev. Interaction between C<sigprocmask> and
		4939	C<pthread_sigmask> could complicate things, however.
		4940
		4941	The most portable way to handle signals is to block signals in all threads
		4942	except the initial one, and run the default loop in the initial thread as
		4943	well.
		4944
		4945	=item C<long> must be large enough for common memory allocation sizes
		4946
		4947	To improve portability and simplify its API, libev uses C<long> internally
		4948	instead of C<size_t> when allocating its data structures. On non-POSIX
		4949	systems (Microsoft...) this might be unexpectedly low, but is still at
		4950	least 31 bits everywhere, which is enough for hundreds of millions of
		4951	watchers.
		4952
		4953	=item C<double> must hold a time value in seconds with enough accuracy
		4954
		4955	The type C<double> is used to represent timestamps. It is required to
		4956	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		4957	good enough for at least into the year 4000 with millisecond accuracy
		4958	(the design goal for libev). This requirement is overfulfilled by
		4959	implementations using IEEE 754, which is basically all existing ones. With
		4960	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
		4961
		4962	=back
		4963
		4964	If you know of other additional requirements drop me a note.
		4965
		4966
2465	=head1 COMPLEXITIES	4967	=head1 ALGORITHMIC COMPLEXITIES
2466		4968
2467	In this section the complexities of (many of) the algorithms used inside	4969	In this section the complexities of (many of) the algorithms used inside
2468	libev will be explained. For complexity discussions about backends see the	4970	libev will be documented. For complexity discussions about backends see
2469	documentation for C<ev_default_init>.	4971	the documentation for C<ev_default_init>.
2470		4972
2471	All of the following are about amortised time: If an array needs to be	4973	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	4974	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	4975	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	4976	mean that libev does a lengthy realloc operation in rare cases, but on
2475	it is much faster and asymptotically approaches constant time.	4977	average it is much faster and asymptotically approaches constant time.
2476		4978
2477	=over 4	4979	=over 4
2478		4980
2479	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4981	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2480		4982
2481	This means that, when you have a watcher that triggers in one hour and	4983	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	4984	there are 100 watchers that would trigger before that, then inserting will
2483	have to skip those 100 watchers.	4985	have to skip roughly seven (C<ld 100>) of these watchers.
2484		4986
2485	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4987	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2486		4988
2487	That means that for changing a timer costs less than removing/adding them	4989	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.	4990	as only the relative motion in the event queue has to be paid for.
2489		4991
2490	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4992	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2491		4993
2492	These just add the watcher into an array or at the head of a list.	4994	These just add the watcher into an array or at the head of a list.
		4995
2493	=item Stopping check/prepare/idle watchers: O(1)	4996	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2494		4997
2495	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4998	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2496		4999
2497	These watchers are stored in lists then need to be walked to find the	5000	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	5001	correct watcher to remove. The lists are usually short (you don't usually
2499	have many watchers waiting for the same fd or signal).	5002	have many watchers waiting for the same fd or signal: one is typical, two
		5003	is rare).
2500		5004
2501	=item Finding the next timer per loop iteration: O(1)	5005	=item Finding the next timer in each loop iteration: O(1)
		5006
		5007	By virtue of using a binary or 4-heap, the next timer is always found at a
		5008	fixed position in the storage array.
2502		5009
2503	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	5010	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2504		5011
2505	A change means an I/O watcher gets started or stopped, which requires	5012	A change means an I/O watcher gets started or stopped, which requires
2506	libev to recalculate its status (and possibly tell the kernel).	5013	libev to recalculate its status (and possibly tell the kernel, depending
		5014	on backend and whether C<ev_io_set> was used).
2507		5015
2508	=item Activating one watcher: O(1)	5016	=item Activating one watcher (putting it into the pending state): O(1)
2509		5017
2510	=item Priority handling: O(number_of_priorities)	5018	=item Priority handling: O(number_of_priorities)
2511		5019
2512	Priorities are implemented by allocating some space for each	5020	Priorities are implemented by allocating some space for each
2513	priority. When doing priority-based operations, libev usually has to	5021	priority. When doing priority-based operations, libev usually has to
2514	linearly search all the priorities.	5022	linearly search all the priorities, but starting/stopping and activating
		5023	watchers becomes O(1) with respect to priority handling.
		5024
		5025	=item Sending an ev_async: O(1)
		5026
		5027	=item Processing ev_async_send: O(number_of_async_watchers)
		5028
		5029	=item Processing signals: O(max_signal_number)
		5030
		5031	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5032	calls in the current loop iteration. Checking for async and signal events
		5033	involves iterating over all running async watchers or all signal numbers.
2515		5034
2516	=back	5035	=back
2517		5036
2518		5037
		5038	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5039
		5040	The major version 4 introduced some incompatible changes to the API.
		5041
		5042	At the moment, the C<ev.h> header file provides compatibility definitions
		5043	for all changes, so most programs should still compile. The compatibility
		5044	layer might be removed in later versions of libev, so better update to the
		5045	new API early than late.
		5046
		5047	=over 4
		5048
		5049	=item C<EV_COMPAT3> backwards compatibility mechanism
		5050
		5051	The backward compatibility mechanism can be controlled by
		5052	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5053	section.
		5054
		5055	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5056
		5057	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5058
		5059	ev_loop_destroy (EV_DEFAULT_UC);
		5060	ev_loop_fork (EV_DEFAULT);
		5061
		5062	=item function/symbol renames
		5063
		5064	A number of functions and symbols have been renamed:
		5065
		5066	ev_loop => ev_run
		5067	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5068	EVLOOP_ONESHOT => EVRUN_ONCE
		5069
		5070	ev_unloop => ev_break
		5071	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5072	EVUNLOOP_ONE => EVBREAK_ONE
		5073	EVUNLOOP_ALL => EVBREAK_ALL
		5074
		5075	EV_TIMEOUT => EV_TIMER
		5076
		5077	ev_loop_count => ev_iteration
		5078	ev_loop_depth => ev_depth
		5079	ev_loop_verify => ev_verify
		5080
		5081	Most functions working on C<struct ev_loop> objects don't have an
		5082	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5083	associated constants have been renamed to not collide with the C<struct
		5084	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5085	as all other watcher types. Note that C<ev_loop_fork> is still called
		5086	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5087	typedef.
		5088
		5089	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5090
		5091	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5092	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5093	and work, but the library code will of course be larger.
		5094
		5095	=back
		5096
		5097
		5098	=head1 GLOSSARY
		5099
		5100	=over 4
		5101
		5102	=item active
		5103
		5104	A watcher is active as long as it has been started and not yet stopped.
		5105	See L<WATCHER STATES> for details.
		5106
		5107	=item application
		5108
		5109	In this document, an application is whatever is using libev.
		5110
		5111	=item backend
		5112
		5113	The part of the code dealing with the operating system interfaces.
		5114
		5115	=item callback
		5116
		5117	The address of a function that is called when some event has been
		5118	detected. Callbacks are being passed the event loop, the watcher that
		5119	received the event, and the actual event bitset.
		5120
		5121	=item callback/watcher invocation
		5122
		5123	The act of calling the callback associated with a watcher.
		5124
		5125	=item event
		5126
		5127	A change of state of some external event, such as data now being available
		5128	for reading on a file descriptor, time having passed or simply not having
		5129	any other events happening anymore.
		5130
		5131	In libev, events are represented as single bits (such as C<EV_READ> or
		5132	C<EV_TIMER>).
		5133
		5134	=item event library
		5135
		5136	A software package implementing an event model and loop.
		5137
		5138	=item event loop
		5139
		5140	An entity that handles and processes external events and converts them
		5141	into callback invocations.
		5142
		5143	=item event model
		5144
		5145	The model used to describe how an event loop handles and processes
		5146	watchers and events.
		5147
		5148	=item pending
		5149
		5150	A watcher is pending as soon as the corresponding event has been
		5151	detected. See L<WATCHER STATES> for details.
		5152
		5153	=item real time
		5154
		5155	The physical time that is observed. It is apparently strictly monotonic :)
		5156
		5157	=item wall-clock time
		5158
		5159	The time and date as shown on clocks. Unlike real time, it can actually
		5160	be wrong and jump forwards and backwards, e.g. when the you adjust your
		5161	clock.
		5162
		5163	=item watcher
		5164
		5165	A data structure that describes interest in certain events. Watchers need
		5166	to be started (attached to an event loop) before they can receive events.
		5167
		5168	=back
		5169
2519	=head1 AUTHOR	5170	=head1 AUTHOR
2520		5171
2521	Marc Lehmann <libev@schmorp.de>.	5172	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5173	Magnusson and Emanuele Giaquinta.
2522		5174

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