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Revision 1.76 by root, Sat Dec 8 15:30:30 2007 UTC vs.
Revision 1.348 by sf-exg, Sat Jan 8 17:52:39 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
122	You can find out the major and minor version numbers of the library	191	You can find out the major and minor ABI version numbers of the library
123	you linked against by calling the functions C<ev_version_major> and	192	you linked against by calling the functions C<ev_version_major> and
124	C<ev_version_minor>. If you want, you can compare against the global	193	C<ev_version_minor>. If you want, you can compare against the global
125	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	194	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
126	version of the library your program was compiled against.	195	version of the library your program was compiled against.
127		196
		197	These version numbers refer to the ABI version of the library, not the
		198	release version.
		199
128	Usually, it's a good idea to terminate if the major versions mismatch,	200	Usually, it's a good idea to terminate if the major versions mismatch,
129	as this indicates an incompatible change. Minor versions are usually	201	as this indicates an incompatible change. Minor versions are usually
130	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
131	not a problem.	203	not a problem.
132		204
133	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
134	version.	206	version (note, however, that this will not detect other ABI mismatches,
		207	such as LFS or reentrancy).
135		208
136	assert (("libev version mismatch",	209	assert (("libev version mismatch",
137	ev_version_major () == EV_VERSION_MAJOR	210	ev_version_major () == EV_VERSION_MAJOR
138	&& ev_version_minor () >= EV_VERSION_MINOR));	211	&& ev_version_minor () >= EV_VERSION_MINOR));
139		212
140	=item unsigned int ev_supported_backends ()	213	=item unsigned int ev_supported_backends ()
141		214
142	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_*>
143	value) compiled into this binary of libev (independent of their	216	value) compiled into this binary of libev (independent of their
…		…
145	a description of the set values.	218	a description of the set values.
146		219
147	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
148	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
149		222
150	assert (("sorry, no epoll, no sex",	223	assert (("sorry, no epoll, no sex",
151	ev_supported_backends () & EVBACKEND_EPOLL));	224	ev_supported_backends () & EVBACKEND_EPOLL));
152		225
153	=item unsigned int ev_recommended_backends ()	226	=item unsigned int ev_recommended_backends ()
154		227
155	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
156	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
157	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
158	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
159	(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
160	libev will probe for if you specify no backends explicitly.	234	probe for if you specify no backends explicitly.
161		235
162	=item unsigned int ev_embeddable_backends ()	236	=item unsigned int ev_embeddable_backends ()
163		237
164	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
165	is the theoretical, all-platform, value. To find which backends	239	value is platform-specific but can include backends not available on the
166	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
167	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	241	the current system, you would need to look at C<ev_embeddable_backends ()
168	recommended ones.	242	& ev_supported_backends ()>, likewise for recommended ones.
169		243
170	See the description of C<ev_embed> watchers for more info.	244	See the description of C<ev_embed> watchers for more info.
171		245
172	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	246	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
173		247
174	Sets the allocation function to use (the prototype is similar - the	248	Sets the allocation function to use (the prototype is similar - the
175	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
176	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
177	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
178	potentially destructive action. The default is your system realloc	252	or take some potentially destructive action.
179	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.
180		257
181	You could override this function in high-availability programs to, say,	258	You could override this function in high-availability programs to, say,
182	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,
183	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.
184		261
185	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
186	retries).	263	retries (example requires a standards-compliant C<realloc>).
187		264
188	static void *	265	static void *
189	persistent_realloc (void *ptr, size_t size)	266	persistent_realloc (void *ptr, size_t size)
190	{	267	{
191	for (;;)	268	for (;;)
…		…
200	}	277	}
201		278
202	...	279	...
203	ev_set_allocator (persistent_realloc);	280	ev_set_allocator (persistent_realloc);
204		281
205	=item ev_set_syserr_cb (void (*cb)(const char *msg));	282	=item ev_set_syserr_cb (void (*cb)(const char *msg))
206		283
207	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
208	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
209	indicating the system call or subsystem causing the problem. If this	286	indicating the system call or subsystem causing the problem. If this
210	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
211	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
212	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
213	(such as abort).	290	(such as abort).
214		291
215	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.
…		…
224	...	301	...
225	ev_set_syserr_cb (fatal_error);	302	ev_set_syserr_cb (fatal_error);
226		303
227	=back	304	=back
228		305
229	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	306	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
230		307
231	An event loop is described by a C<struct ev_loop *>. The library knows two	308	An event loop is described by a C<struct ev_loop *> (the C<struct> is
232	types of such loops, the I<default> loop, which supports signals and child	309	I<not> optional in this case unless libev 3 compatibility is disabled, as
233	events, and dynamically created loops which do not.	310	libev 3 had an C<ev_loop> function colliding with the struct name).
234		311
235	If you use threads, a common model is to run the default event loop	312	The library knows two types of such loops, the I<default> loop, which
236	in your main thread (or in a separate thread) and for each thread you	313	supports child process events, and dynamically created event loops which
237	create, you also create another event loop. Libev itself does no locking	314	do not.
238	whatsoever, so if you mix calls to the same event loop in different
239	threads, make sure you lock (this is usually a bad idea, though, even if
240	done correctly, because it's hideous and inefficient).
241		315
242	=over 4	316	=over 4
243		317
244	=item struct ev_loop *ev_default_loop (unsigned int flags)	318	=item struct ev_loop *ev_default_loop (unsigned int flags)
245		319
246	This will initialise the default event loop if it hasn't been initialised	320	This returns the "default" event loop object, which is what you should
247	yet and return it. If the default loop could not be initialised, returns	321	normally use when you just need "the event loop". Event loop objects and
248	false. If it already was initialised it simply returns it (and ignores the	322	the C<flags> parameter are described in more detail in the entry for
249	flags. If that is troubling you, check C<ev_backend ()> afterwards).	323	C<ev_loop_new>.
		324
		325	If the default loop is already initialised then this function simply
		326	returns it (and ignores the flags. If that is troubling you, check
		327	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		328	flags, which should almost always be C<0>, unless the caller is also the
		329	one calling C<ev_run> or otherwise qualifies as "the main program".
250		330
251	If you don't know what event loop to use, use the one returned from this	331	If you don't know what event loop to use, use the one returned from this
252	function.	332	function (or via the C<EV_DEFAULT> macro).
		333
		334	Note that this function is I<not> thread-safe, so if you want to use it
		335	from multiple threads, you have to employ some kind of mutex (note also
		336	that this case is unlikely, as loops cannot be shared easily between
		337	threads anyway).
		338
		339	The default loop is the only loop that can handle C<ev_child> watchers,
		340	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		341	a problem for your application you can either create a dynamic loop with
		342	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		343	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
		344
		345	Example: This is the most typical usage.
		346
		347	if (!ev_default_loop (0))
		348	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		349
		350	Example: Restrict libev to the select and poll backends, and do not allow
		351	environment settings to be taken into account:
		352
		353	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		354
		355	=item struct ev_loop *ev_loop_new (unsigned int flags)
		356
		357	This will create and initialise a new event loop object. If the loop
		358	could not be initialised, returns false.
		359
		360	This function is thread-safe, and one common way to use libev with
		361	threads is indeed to create one loop per thread, and using the default
		362	loop in the "main" or "initial" thread.
253		363
254	The flags argument can be used to specify special behaviour or specific	364	The flags argument can be used to specify special behaviour or specific
255	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	365	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
256		366
257	The following flags are supported:	367	The following flags are supported:
…		…
263	The default flags value. Use this if you have no clue (it's the right	373	The default flags value. Use this if you have no clue (it's the right
264	thing, believe me).	374	thing, believe me).
265		375
266	=item C<EVFLAG_NOENV>	376	=item C<EVFLAG_NOENV>
267		377
268	If this flag bit is ored into the flag value (or the program runs setuid	378	If this flag bit is or'ed into the flag value (or the program runs setuid
269	or setgid) then libev will I<not> look at the environment variable	379	or setgid) then libev will I<not> look at the environment variable
270	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	380	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
271	override the flags completely if it is found in the environment. This is	381	override the flags completely if it is found in the environment. This is
272	useful to try out specific backends to test their performance, or to work	382	useful to try out specific backends to test their performance, or to work
273	around bugs.	383	around bugs.
274		384
275	=item C<EVFLAG_FORKCHECK>	385	=item C<EVFLAG_FORKCHECK>
276		386
277	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	387	Instead of calling C<ev_loop_fork> manually after a fork, you can also
278	a fork, you can also make libev check for a fork in each iteration by	388	make libev check for a fork in each iteration by enabling this flag.
279	enabling this flag.
280		389
281	This works by calling C<getpid ()> on every iteration of the loop,	390	This works by calling C<getpid ()> on every iteration of the loop,
282	and thus this might slow down your event loop if you do a lot of loop	391	and thus this might slow down your event loop if you do a lot of loop
283	iterations and little real work, but is usually not noticeable (on my	392	iterations and little real work, but is usually not noticeable (on my
284	Linux system for example, C<getpid> is actually a simple 5-insn sequence	393	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
285	without a syscall and thus I<very> fast, but my Linux system also has	394	without a system call and thus I<very> fast, but my GNU/Linux system also has
286	C<pthread_atfork> which is even faster).	395	C<pthread_atfork> which is even faster).
287		396
288	The big advantage of this flag is that you can forget about fork (and	397	The big advantage of this flag is that you can forget about fork (and
289	forget about forgetting to tell libev about forking) when you use this	398	forget about forgetting to tell libev about forking) when you use this
290	flag.	399	flag.
291		400
292	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	401	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
293	environment variable.	402	environment variable.
		403
		404	=item C<EVFLAG_NOINOTIFY>
		405
		406	When this flag is specified, then libev will not attempt to use the
		407	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		408	testing, this flag can be useful to conserve inotify file descriptors, as
		409	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		410
		411	=item C<EVFLAG_SIGNALFD>
		412
		413	When this flag is specified, then libev will attempt to use the
		414	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		415	delivers signals synchronously, which makes it both faster and might make
		416	it possible to get the queued signal data. It can also simplify signal
		417	handling with threads, as long as you properly block signals in your
		418	threads that are not interested in handling them.
		419
		420	Signalfd will not be used by default as this changes your signal mask, and
		421	there are a lot of shoddy libraries and programs (glib's threadpool for
		422	example) that can't properly initialise their signal masks.
294		423
295	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
296		425
297	This is your standard select(2) backend. Not I<completely> standard, as	426	This is your standard select(2) backend. Not I<completely> standard, as
298	libev tries to roll its own fd_set with no limits on the number of fds,	427	libev tries to roll its own fd_set with no limits on the number of fds,
299	but if that fails, expect a fairly low limit on the number of fds when	428	but if that fails, expect a fairly low limit on the number of fds when
300	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	429	using this backend. It doesn't scale too well (O(highest_fd)), but its
301	the fastest backend for a low number of fds.	430	usually the fastest backend for a low number of (low-numbered :) fds.
		431
		432	To get good performance out of this backend you need a high amount of
		433	parallelism (most of the file descriptors should be busy). If you are
		434	writing a server, you should C<accept ()> in a loop to accept as many
		435	connections as possible during one iteration. You might also want to have
		436	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		437	readiness notifications you get per iteration.
		438
		439	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		440	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		441	C<exceptfds> set on that platform).
302		442
303	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	443	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
304		444
305	And this is your standard poll(2) backend. It's more complicated than	445	And this is your standard poll(2) backend. It's more complicated
306	select, but handles sparse fds better and has no artificial limit on the	446	than select, but handles sparse fds better and has no artificial
307	number of fds you can use (except it will slow down considerably with a	447	limit on the number of fds you can use (except it will slow down
308	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	448	considerably with a lot of inactive fds). It scales similarly to select,
		449	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		450	performance tips.
		451
		452	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		453	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
309		454
310	=item C<EVBACKEND_EPOLL> (value 4, Linux)	455	=item C<EVBACKEND_EPOLL> (value 4, Linux)
311		456
		457	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		458	kernels).
		459
312	For few fds, this backend is a bit little slower than poll and select,	460	For few fds, this backend is a bit little slower than poll and select,
313	but it scales phenomenally better. While poll and select usually scale like	461	but it scales phenomenally better. While poll and select usually scale
314	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	462	like O(total_fds) where n is the total number of fds (or the highest fd),
315	either O(1) or O(active_fds).	463	epoll scales either O(1) or O(active_fds).
316		464
		465	The epoll mechanism deserves honorable mention as the most misdesigned
		466	of the more advanced event mechanisms: mere annoyances include silently
		467	dropping file descriptors, requiring a system call per change per file
		468	descriptor (and unnecessary guessing of parameters), problems with dup,
		469	returning before the timeout value, resulting in additional iterations
		470	(and only giving 5ms accuracy while select on the same platform gives
		471	0.1ms) and so on. The biggest issue is fork races, however - if a program
		472	forks then I<both> parent and child process have to recreate the epoll
		473	set, which can take considerable time (one syscall per file descriptor)
		474	and is of course hard to detect.
		475
		476	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		477	of course I<doesn't>, and epoll just loves to report events for totally
		478	I<different> file descriptors (even already closed ones, so one cannot
		479	even remove them from the set) than registered in the set (especially
		480	on SMP systems). Libev tries to counter these spurious notifications by
		481	employing an additional generation counter and comparing that against the
		482	events to filter out spurious ones, recreating the set when required. Last
		483	not least, it also refuses to work with some file descriptors which work
		484	perfectly fine with C<select> (files, many character devices...).
		485
		486	Epoll is truly the train wreck analog among event poll mechanisms.
		487
317	While stopping and starting an I/O watcher in the same iteration will	488	While stopping, setting and starting an I/O watcher in the same iteration
318	result in some caching, there is still a syscall per such incident	489	will result in some caching, there is still a system call per such
319	(because the fd could point to a different file description now), so its	490	incident (because the same I<file descriptor> could point to a different
320	best to avoid that. Also, dup()ed file descriptors might not work very	491	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
321	well if you register events for both fds.	492	file descriptors might not work very well if you register events for both
		493	file descriptors.
322		494
323	Please note that epoll sometimes generates spurious notifications, so you	495	Best performance from this backend is achieved by not unregistering all
324	need to use non-blocking I/O or other means to avoid blocking when no data	496	watchers for a file descriptor until it has been closed, if possible,
325	(or space) is available.	497	i.e. keep at least one watcher active per fd at all times. Stopping and
		498	starting a watcher (without re-setting it) also usually doesn't cause
		499	extra overhead. A fork can both result in spurious notifications as well
		500	as in libev having to destroy and recreate the epoll object, which can
		501	take considerable time and thus should be avoided.
		502
		503	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		504	faster than epoll for maybe up to a hundred file descriptors, depending on
		505	the usage. So sad.
		506
		507	While nominally embeddable in other event loops, this feature is broken in
		508	all kernel versions tested so far.
		509
		510	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		511	C<EVBACKEND_POLL>.
326		512
327	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	513	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
328		514
329	Kqueue deserves special mention, as at the time of this writing, it	515	Kqueue deserves special mention, as at the time of this writing, it
330	was broken on all BSDs except NetBSD (usually it doesn't work with	516	was broken on all BSDs except NetBSD (usually it doesn't work reliably
331	anything but sockets and pipes, except on Darwin, where of course its	517	with anything but sockets and pipes, except on Darwin, where of course
332	completely useless). For this reason its not being "autodetected"	518	it's completely useless). Unlike epoll, however, whose brokenness
		519	is by design, these kqueue bugs can (and eventually will) be fixed
		520	without API changes to existing programs. For this reason it's not being
333	unless you explicitly specify it explicitly in the flags (i.e. using	521	"auto-detected" unless you explicitly specify it in the flags (i.e. using
334	C<EVBACKEND_KQUEUE>).	522	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		523	system like NetBSD.
		524
		525	You still can embed kqueue into a normal poll or select backend and use it
		526	only for sockets (after having made sure that sockets work with kqueue on
		527	the target platform). See C<ev_embed> watchers for more info.
335		528
336	It scales in the same way as the epoll backend, but the interface to the	529	It scales in the same way as the epoll backend, but the interface to the
337	kernel is more efficient (which says nothing about its actual speed, of	530	kernel is more efficient (which says nothing about its actual speed, of
338	course). While starting and stopping an I/O watcher does not cause an	531	course). While stopping, setting and starting an I/O watcher does never
339	extra syscall as with epoll, it still adds up to four event changes per	532	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
340	incident, so its best to avoid that.	533	two event changes per incident. Support for C<fork ()> is very bad (but
		534	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		535	cases
		536
		537	This backend usually performs well under most conditions.
		538
		539	While nominally embeddable in other event loops, this doesn't work
		540	everywhere, so you might need to test for this. And since it is broken
		541	almost everywhere, you should only use it when you have a lot of sockets
		542	(for which it usually works), by embedding it into another event loop
		543	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		544	also broken on OS X)) and, did I mention it, using it only for sockets.
		545
		546	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		547	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		548	C<NOTE_EOF>.
341		549
342	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	550	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
343		551
344	This is not implemented yet (and might never be).	552	This is not implemented yet (and might never be, unless you send me an
		553	implementation). According to reports, C</dev/poll> only supports sockets
		554	and is not embeddable, which would limit the usefulness of this backend
		555	immensely.
345		556
346	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	557	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
347		558
348	This uses the Solaris 10 port mechanism. As with everything on Solaris,	559	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
349	it's really slow, but it still scales very well (O(active_fds)).	560	it's really slow, but it still scales very well (O(active_fds)).
350		561
351	Please note that solaris ports can result in a lot of spurious	562	Please note that Solaris event ports can deliver a lot of spurious
352	notifications, so you need to use non-blocking I/O or other means to avoid	563	notifications, so you need to use non-blocking I/O or other means to avoid
353	blocking when no data (or space) is available.	564	blocking when no data (or space) is available.
		565
		566	While this backend scales well, it requires one system call per active
		567	file descriptor per loop iteration. For small and medium numbers of file
		568	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		569	might perform better.
		570
		571	On the positive side, with the exception of the spurious readiness
		572	notifications, this backend actually performed fully to specification
		573	in all tests and is fully embeddable, which is a rare feat among the
		574	OS-specific backends (I vastly prefer correctness over speed hacks).
		575
		576	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		577	C<EVBACKEND_POLL>.
354		578
355	=item C<EVBACKEND_ALL>	579	=item C<EVBACKEND_ALL>
356		580
357	Try all backends (even potentially broken ones that wouldn't be tried	581	Try all backends (even potentially broken ones that wouldn't be tried
358	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	582	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
359	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	583	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
360		584
		585	It is definitely not recommended to use this flag.
		586
361	=back	587	=back
362		588
363	If one or more of these are ored into the flags value, then only these	589	If one or more of the backend flags are or'ed into the flags value,
364	backends will be tried (in the reverse order as given here). If none are	590	then only these backends will be tried (in the reverse order as listed
365	specified, most compiled-in backend will be tried, usually in reverse	591	here). If none are specified, all backends in C<ev_recommended_backends
366	order of their flag values :)	592	()> will be tried.
367
368	The most typical usage is like this:
369
370	if (!ev_default_loop (0))
371	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
372
373	Restrict libev to the select and poll backends, and do not allow
374	environment settings to be taken into account:
375
376	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
377
378	Use whatever libev has to offer, but make sure that kqueue is used if
379	available (warning, breaks stuff, best use only with your own private
380	event loop and only if you know the OS supports your types of fds):
381
382	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
383
384	=item struct ev_loop *ev_loop_new (unsigned int flags)
385
386	Similar to C<ev_default_loop>, but always creates a new event loop that is
387	always distinct from the default loop. Unlike the default loop, it cannot
388	handle signal and child watchers, and attempts to do so will be greeted by
389	undefined behaviour (or a failed assertion if assertions are enabled).
390		593
391	Example: Try to create a event loop that uses epoll and nothing else.	594	Example: Try to create a event loop that uses epoll and nothing else.
392		595
393	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	596	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
394	if (!epoller)	597	if (!epoller)
395	fatal ("no epoll found here, maybe it hides under your chair");	598	fatal ("no epoll found here, maybe it hides under your chair");
396		599
		600	Example: Use whatever libev has to offer, but make sure that kqueue is
		601	used if available.
		602
		603	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		604
397	=item ev_default_destroy ()	605	=item ev_loop_destroy (loop)
398		606
399	Destroys the default loop again (frees all memory and kernel state	607	Destroys an event loop object (frees all memory and kernel state
400	etc.). None of the active event watchers will be stopped in the normal	608	etc.). None of the active event watchers will be stopped in the normal
401	sense, so e.g. C<ev_is_active> might still return true. It is your	609	sense, so e.g. C<ev_is_active> might still return true. It is your
402	responsibility to either stop all watchers cleanly yoursef I<before>	610	responsibility to either stop all watchers cleanly yourself I<before>
403	calling this function, or cope with the fact afterwards (which is usually	611	calling this function, or cope with the fact afterwards (which is usually
404	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	612	the easiest thing, you can just ignore the watchers and/or C<free ()> them
405	for example).	613	for example).
406		614
		615	Note that certain global state, such as signal state (and installed signal
		616	handlers), will not be freed by this function, and related watchers (such
		617	as signal and child watchers) would need to be stopped manually.
		618
		619	This function is normally used on loop objects allocated by
		620	C<ev_loop_new>, but it can also be used on the default loop returned by
		621	C<ev_default_loop>, in which case it is not thread-safe.
		622
		623	Note that it is not advisable to call this function on the default loop
		624	except in the rare occasion where you really need to free its resources.
		625	If you need dynamically allocated loops it is better to use C<ev_loop_new>
		626	and C<ev_loop_destroy>.
		627
407	=item ev_loop_destroy (loop)	628	=item ev_loop_fork (loop)
408		629
409	Like C<ev_default_destroy>, but destroys an event loop created by an	630	This function sets a flag that causes subsequent C<ev_run> iterations to
410	earlier call to C<ev_loop_new>.
411
412	=item ev_default_fork ()
413
414	This function reinitialises the kernel state for backends that have	631	reinitialise the kernel state for backends that have one. Despite the
415	one. Despite the name, you can call it anytime, but it makes most sense	632	name, you can call it anytime, but it makes most sense after forking, in
416	after forking, in either the parent or child process (or both, but that	633	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
417	again makes little sense).	634	child before resuming or calling C<ev_run>.
418		635
419	You I<must> call this function in the child process after forking if and	636	Again, you I<have> to call it on I<any> loop that you want to re-use after
420	only if you want to use the event library in both processes. If you just	637	a fork, I<even if you do not plan to use the loop in the parent>. This is
421	fork+exec, you don't have to call it.	638	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		639	during fork.
		640
		641	On the other hand, you only need to call this function in the child
		642	process if and only if you want to use the event loop in the child. If
		643	you just fork+exec or create a new loop in the child, you don't have to
		644	call it at all (in fact, C<epoll> is so badly broken that it makes a
		645	difference, but libev will usually detect this case on its own and do a
		646	costly reset of the backend).
422		647
423	The function itself is quite fast and it's usually not a problem to call	648	The function itself is quite fast and it's usually not a problem to call
424	it just in case after a fork. To make this easy, the function will fit in	649	it just in case after a fork.
425	quite nicely into a call to C<pthread_atfork>:
426		650
		651	Example: Automate calling C<ev_loop_fork> on the default loop when
		652	using pthreads.
		653
		654	static void
		655	post_fork_child (void)
		656	{
		657	ev_loop_fork (EV_DEFAULT);
		658	}
		659
		660	...
427	pthread_atfork (0, 0, ev_default_fork);	661	pthread_atfork (0, 0, post_fork_child);
428		662
429	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	663	=item int ev_is_default_loop (loop)
430	without calling this function, so if you force one of those backends you
431	do not need to care.
432		664
433	=item ev_loop_fork (loop)	665	Returns true when the given loop is, in fact, the default loop, and false
		666	otherwise.
434		667
435	Like C<ev_default_fork>, but acts on an event loop created by
436	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
437	after fork, and how you do this is entirely your own problem.
438
439	=item unsigned int ev_loop_count (loop)	668	=item unsigned int ev_iteration (loop)
440		669
441	Returns the count of loop iterations for the loop, which is identical to	670	Returns the current iteration count for the event loop, which is identical
442	the number of times libev did poll for new events. It starts at C<0> and	671	to the number of times libev did poll for new events. It starts at C<0>
443	happily wraps around with enough iterations.	672	and happily wraps around with enough iterations.
444		673
445	This value can sometimes be useful as a generation counter of sorts (it	674	This value can sometimes be useful as a generation counter of sorts (it
446	"ticks" the number of loop iterations), as it roughly corresponds with	675	"ticks" the number of loop iterations), as it roughly corresponds with
447	C<ev_prepare> and C<ev_check> calls.	676	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		677	prepare and check phases.
		678
		679	=item unsigned int ev_depth (loop)
		680
		681	Returns the number of times C<ev_run> was entered minus the number of
		682	times C<ev_run> was exited normally, in other words, the recursion depth.
		683
		684	Outside C<ev_run>, this number is zero. In a callback, this number is
		685	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		686	in which case it is higher.
		687
		688	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		689	throwing an exception etc.), doesn't count as "exit" - consider this
		690	as a hint to avoid such ungentleman-like behaviour unless it's really
		691	convenient, in which case it is fully supported.
448		692
449	=item unsigned int ev_backend (loop)	693	=item unsigned int ev_backend (loop)
450		694
451	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	695	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
452	use.	696	use.
…		…
455		699
456	Returns the current "event loop time", which is the time the event loop	700	Returns the current "event loop time", which is the time the event loop
457	received events and started processing them. This timestamp does not	701	received events and started processing them. This timestamp does not
458	change as long as callbacks are being processed, and this is also the base	702	change as long as callbacks are being processed, and this is also the base
459	time used for relative timers. You can treat it as the timestamp of the	703	time used for relative timers. You can treat it as the timestamp of the
460	event occuring (or more correctly, libev finding out about it).	704	event occurring (or more correctly, libev finding out about it).
461		705
		706	=item ev_now_update (loop)
		707
		708	Establishes the current time by querying the kernel, updating the time
		709	returned by C<ev_now ()> in the progress. This is a costly operation and
		710	is usually done automatically within C<ev_run ()>.
		711
		712	This function is rarely useful, but when some event callback runs for a
		713	very long time without entering the event loop, updating libev's idea of
		714	the current time is a good idea.
		715
		716	See also L<The special problem of time updates> in the C<ev_timer> section.
		717
		718	=item ev_suspend (loop)
		719
		720	=item ev_resume (loop)
		721
		722	These two functions suspend and resume an event loop, for use when the
		723	loop is not used for a while and timeouts should not be processed.
		724
		725	A typical use case would be an interactive program such as a game: When
		726	the user presses C<^Z> to suspend the game and resumes it an hour later it
		727	would be best to handle timeouts as if no time had actually passed while
		728	the program was suspended. This can be achieved by calling C<ev_suspend>
		729	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		730	C<ev_resume> directly afterwards to resume timer processing.
		731
		732	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		733	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		734	will be rescheduled (that is, they will lose any events that would have
		735	occurred while suspended).
		736
		737	After calling C<ev_suspend> you B<must not> call I<any> function on the
		738	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		739	without a previous call to C<ev_suspend>.
		740
		741	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		742	event loop time (see C<ev_now_update>).
		743
462	=item ev_loop (loop, int flags)	744	=item ev_run (loop, int flags)
463		745
464	Finally, this is it, the event handler. This function usually is called	746	Finally, this is it, the event handler. This function usually is called
465	after you initialised all your watchers and you want to start handling	747	after you have initialised all your watchers and you want to start
466	events.	748	handling events. It will ask the operating system for any new events, call
		749	the watcher callbacks, an then repeat the whole process indefinitely: This
		750	is why event loops are called I<loops>.
467		751
468	If the flags argument is specified as C<0>, it will not return until	752	If the flags argument is specified as C<0>, it will keep handling events
469	either no event watchers are active anymore or C<ev_unloop> was called.	753	until either no event watchers are active anymore or C<ev_break> was
		754	called.
470		755
471	Please note that an explicit C<ev_unloop> is usually better than	756	Please note that an explicit C<ev_break> is usually better than
472	relying on all watchers to be stopped when deciding when a program has	757	relying on all watchers to be stopped when deciding when a program has
473	finished (especially in interactive programs), but having a program that	758	finished (especially in interactive programs), but having a program
474	automatically loops as long as it has to and no longer by virtue of	759	that automatically loops as long as it has to and no longer by virtue
475	relying on its watchers stopping correctly is a thing of beauty.	760	of relying on its watchers stopping correctly, that is truly a thing of
		761	beauty.
476		762
		763	This function is also I<mostly> exception-safe - you can break out of
		764	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		765	exception and so on. This does not decrement the C<ev_depth> value, nor
		766	will it clear any outstanding C<EVBREAK_ONE> breaks.
		767
477	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	768	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
478	those events and any outstanding ones, but will not block your process in	769	those events and any already outstanding ones, but will not wait and
479	case there are no events and will return after one iteration of the loop.	770	block your process in case there are no events and will return after one
		771	iteration of the loop. This is sometimes useful to poll and handle new
		772	events while doing lengthy calculations, to keep the program responsive.
480		773
481	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	774	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
482	neccessary) and will handle those and any outstanding ones. It will block	775	necessary) and will handle those and any already outstanding ones. It
483	your process until at least one new event arrives, and will return after	776	will block your process until at least one new event arrives (which could
484	one iteration of the loop. This is useful if you are waiting for some	777	be an event internal to libev itself, so there is no guarantee that a
485	external event in conjunction with something not expressible using other	778	user-registered callback will be called), and will return after one
		779	iteration of the loop.
		780
		781	This is useful if you are waiting for some external event in conjunction
		782	with something not expressible using other libev watchers (i.e. "roll your
486	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	783	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
487	usually a better approach for this kind of thing.	784	usually a better approach for this kind of thing.
488		785
489	Here are the gory details of what C<ev_loop> does:	786	Here are the gory details of what C<ev_run> does:
490		787
491	* If there are no active watchers (reference count is zero), return.	788	- Increment loop depth.
492	- Queue prepare watchers and then call all outstanding watchers.	789	- Reset the ev_break status.
		790	- Before the first iteration, call any pending watchers.
		791	LOOP:
		792	- If EVFLAG_FORKCHECK was used, check for a fork.
		793	- If a fork was detected (by any means), queue and call all fork watchers.
		794	- Queue and call all prepare watchers.
		795	- If ev_break was called, goto FINISH.
493	- If we have been forked, recreate the kernel state.	796	- If we have been forked, detach and recreate the kernel state
		797	as to not disturb the other process.
494	- Update the kernel state with all outstanding changes.	798	- Update the kernel state with all outstanding changes.
495	- Update the "event loop time".	799	- Update the "event loop time" (ev_now ()).
496	- Calculate for how long to block.	800	- Calculate for how long to sleep or block, if at all
		801	(active idle watchers, EVRUN_NOWAIT or not having
		802	any active watchers at all will result in not sleeping).
		803	- Sleep if the I/O and timer collect interval say so.
		804	- Increment loop iteration counter.
497	- Block the process, waiting for any events.	805	- Block the process, waiting for any events.
498	- Queue all outstanding I/O (fd) events.	806	- Queue all outstanding I/O (fd) events.
499	- Update the "event loop time" and do time jump handling.	807	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
500	- Queue all outstanding timers.	808	- Queue all expired timers.
501	- Queue all outstanding periodics.	809	- Queue all expired periodics.
502	- If no events are pending now, queue all idle watchers.	810	- Queue all idle watchers with priority higher than that of pending events.
503	- Queue all check watchers.	811	- Queue all check watchers.
504	- Call all queued watchers in reverse order (i.e. check watchers first).	812	- Call all queued watchers in reverse order (i.e. check watchers first).
505	Signals and child watchers are implemented as I/O watchers, and will	813	Signals and child watchers are implemented as I/O watchers, and will
506	be handled here by queueing them when their watcher gets executed.	814	be handled here by queueing them when their watcher gets executed.
507	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	815	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
508	were used, return, otherwise continue with step *.	816	were used, or there are no active watchers, goto FINISH, otherwise
		817	continue with step LOOP.
		818	FINISH:
		819	- Reset the ev_break status iff it was EVBREAK_ONE.
		820	- Decrement the loop depth.
		821	- Return.
509		822
510	Example: Queue some jobs and then loop until no events are outsanding	823	Example: Queue some jobs and then loop until no events are outstanding
511	anymore.	824	anymore.
512		825
513	... queue jobs here, make sure they register event watchers as long	826	... queue jobs here, make sure they register event watchers as long
514	... as they still have work to do (even an idle watcher will do..)	827	... as they still have work to do (even an idle watcher will do..)
515	ev_loop (my_loop, 0);	828	ev_run (my_loop, 0);
516	... jobs done. yeah!	829	... jobs done or somebody called unloop. yeah!
517		830
518	=item ev_unloop (loop, how)	831	=item ev_break (loop, how)
519		832
520	Can be used to make a call to C<ev_loop> return early (but only after it	833	Can be used to make a call to C<ev_run> return early (but only after it
521	has processed all outstanding events). The C<how> argument must be either	834	has processed all outstanding events). The C<how> argument must be either
522	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	835	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
523	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	836	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		837
		838	This "break state" will be cleared on the next call to C<ev_run>.
		839
		840	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		841	which case it will have no effect.
524		842
525	=item ev_ref (loop)	843	=item ev_ref (loop)
526		844
527	=item ev_unref (loop)	845	=item ev_unref (loop)
528		846
529	Ref/unref can be used to add or remove a reference count on the event	847	Ref/unref can be used to add or remove a reference count on the event
530	loop: Every watcher keeps one reference, and as long as the reference	848	loop: Every watcher keeps one reference, and as long as the reference
531	count is nonzero, C<ev_loop> will not return on its own. If you have	849	count is nonzero, C<ev_run> will not return on its own.
532	a watcher you never unregister that should not keep C<ev_loop> from	850
533	returning, ev_unref() after starting, and ev_ref() before stopping it. For	851	This is useful when you have a watcher that you never intend to
		852	unregister, but that nevertheless should not keep C<ev_run> from
		853	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		854	before stopping it.
		855
534	example, libev itself uses this for its internal signal pipe: It is not	856	As an example, libev itself uses this for its internal signal pipe: It
535	visible to the libev user and should not keep C<ev_loop> from exiting if	857	is not visible to the libev user and should not keep C<ev_run> from
536	no event watchers registered by it are active. It is also an excellent	858	exiting if no event watchers registered by it are active. It is also an
537	way to do this for generic recurring timers or from within third-party	859	excellent way to do this for generic recurring timers or from within
538	libraries. Just remember to I<unref after start> and I<ref before stop>.	860	third-party libraries. Just remember to I<unref after start> and I<ref
		861	before stop> (but only if the watcher wasn't active before, or was active
		862	before, respectively. Note also that libev might stop watchers itself
		863	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		864	in the callback).
539		865
540	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	866	Example: Create a signal watcher, but keep it from keeping C<ev_run>
541	running when nothing else is active.	867	running when nothing else is active.
542		868
543	struct ev_signal exitsig;	869	ev_signal exitsig;
544	ev_signal_init (&exitsig, sig_cb, SIGINT);	870	ev_signal_init (&exitsig, sig_cb, SIGINT);
545	ev_signal_start (loop, &exitsig);	871	ev_signal_start (loop, &exitsig);
546	evf_unref (loop);	872	ev_unref (loop);
547		873
548	Example: For some weird reason, unregister the above signal handler again.	874	Example: For some weird reason, unregister the above signal handler again.
549		875
550	ev_ref (loop);	876	ev_ref (loop);
551	ev_signal_stop (loop, &exitsig);	877	ev_signal_stop (loop, &exitsig);
		878
		879	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		880
		881	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		882
		883	These advanced functions influence the time that libev will spend waiting
		884	for events. Both time intervals are by default C<0>, meaning that libev
		885	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		886	latency.
		887
		888	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		889	allows libev to delay invocation of I/O and timer/periodic callbacks
		890	to increase efficiency of loop iterations (or to increase power-saving
		891	opportunities).
		892
		893	The idea is that sometimes your program runs just fast enough to handle
		894	one (or very few) event(s) per loop iteration. While this makes the
		895	program responsive, it also wastes a lot of CPU time to poll for new
		896	events, especially with backends like C<select ()> which have a high
		897	overhead for the actual polling but can deliver many events at once.
		898
		899	By setting a higher I<io collect interval> you allow libev to spend more
		900	time collecting I/O events, so you can handle more events per iteration,
		901	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		902	C<ev_timer>) will be not affected. Setting this to a non-null value will
		903	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		904	sleep time ensures that libev will not poll for I/O events more often then
		905	once per this interval, on average.
		906
		907	Likewise, by setting a higher I<timeout collect interval> you allow libev
		908	to spend more time collecting timeouts, at the expense of increased
		909	latency/jitter/inexactness (the watcher callback will be called
		910	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		911	value will not introduce any overhead in libev.
		912
		913	Many (busy) programs can usually benefit by setting the I/O collect
		914	interval to a value near C<0.1> or so, which is often enough for
		915	interactive servers (of course not for games), likewise for timeouts. It
		916	usually doesn't make much sense to set it to a lower value than C<0.01>,
		917	as this approaches the timing granularity of most systems. Note that if
		918	you do transactions with the outside world and you can't increase the
		919	parallelity, then this setting will limit your transaction rate (if you
		920	need to poll once per transaction and the I/O collect interval is 0.01,
		921	then you can't do more than 100 transactions per second).
		922
		923	Setting the I<timeout collect interval> can improve the opportunity for
		924	saving power, as the program will "bundle" timer callback invocations that
		925	are "near" in time together, by delaying some, thus reducing the number of
		926	times the process sleeps and wakes up again. Another useful technique to
		927	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		928	they fire on, say, one-second boundaries only.
		929
		930	Example: we only need 0.1s timeout granularity, and we wish not to poll
		931	more often than 100 times per second:
		932
		933	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		934	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		935
		936	=item ev_invoke_pending (loop)
		937
		938	This call will simply invoke all pending watchers while resetting their
		939	pending state. Normally, C<ev_run> does this automatically when required,
		940	but when overriding the invoke callback this call comes handy. This
		941	function can be invoked from a watcher - this can be useful for example
		942	when you want to do some lengthy calculation and want to pass further
		943	event handling to another thread (you still have to make sure only one
		944	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		945
		946	=item int ev_pending_count (loop)
		947
		948	Returns the number of pending watchers - zero indicates that no watchers
		949	are pending.
		950
		951	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		952
		953	This overrides the invoke pending functionality of the loop: Instead of
		954	invoking all pending watchers when there are any, C<ev_run> will call
		955	this callback instead. This is useful, for example, when you want to
		956	invoke the actual watchers inside another context (another thread etc.).
		957
		958	If you want to reset the callback, use C<ev_invoke_pending> as new
		959	callback.
		960
		961	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		962
		963	Sometimes you want to share the same loop between multiple threads. This
		964	can be done relatively simply by putting mutex_lock/unlock calls around
		965	each call to a libev function.
		966
		967	However, C<ev_run> can run an indefinite time, so it is not feasible
		968	to wait for it to return. One way around this is to wake up the event
		969	loop via C<ev_break> and C<av_async_send>, another way is to set these
		970	I<release> and I<acquire> callbacks on the loop.
		971
		972	When set, then C<release> will be called just before the thread is
		973	suspended waiting for new events, and C<acquire> is called just
		974	afterwards.
		975
		976	Ideally, C<release> will just call your mutex_unlock function, and
		977	C<acquire> will just call the mutex_lock function again.
		978
		979	While event loop modifications are allowed between invocations of
		980	C<release> and C<acquire> (that's their only purpose after all), no
		981	modifications done will affect the event loop, i.e. adding watchers will
		982	have no effect on the set of file descriptors being watched, or the time
		983	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		984	to take note of any changes you made.
		985
		986	In theory, threads executing C<ev_run> will be async-cancel safe between
		987	invocations of C<release> and C<acquire>.
		988
		989	See also the locking example in the C<THREADS> section later in this
		990	document.
		991
		992	=item ev_set_userdata (loop, void *data)
		993
		994	=item void *ev_userdata (loop)
		995
		996	Set and retrieve a single C<void *> associated with a loop. When
		997	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		998	C<0>.
		999
		1000	These two functions can be used to associate arbitrary data with a loop,
		1001	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1002	C<acquire> callbacks described above, but of course can be (ab-)used for
		1003	any other purpose as well.
		1004
		1005	=item ev_verify (loop)
		1006
		1007	This function only does something when C<EV_VERIFY> support has been
		1008	compiled in, which is the default for non-minimal builds. It tries to go
		1009	through all internal structures and checks them for validity. If anything
		1010	is found to be inconsistent, it will print an error message to standard
		1011	error and call C<abort ()>.
		1012
		1013	This can be used to catch bugs inside libev itself: under normal
		1014	circumstances, this function will never abort as of course libev keeps its
		1015	data structures consistent.
552		1016
553	=back	1017	=back
554		1018
555		1019
556	=head1 ANATOMY OF A WATCHER	1020	=head1 ANATOMY OF A WATCHER
557		1021
		1022	In the following description, uppercase C<TYPE> in names stands for the
		1023	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1024	watchers and C<ev_io_start> for I/O watchers.
		1025
558	A watcher is a structure that you create and register to record your	1026	A watcher is an opaque structure that you allocate and register to record
559	interest in some event. For instance, if you want to wait for STDIN to	1027	your interest in some event. To make a concrete example, imagine you want
560	become readable, you would create an C<ev_io> watcher for that:	1028	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1029	for that:
561		1030
562	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1031	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
563	{	1032	{
564	ev_io_stop (w);	1033	ev_io_stop (w);
565	ev_unloop (loop, EVUNLOOP_ALL);	1034	ev_break (loop, EVBREAK_ALL);
566	}	1035	}
567		1036
568	struct ev_loop *loop = ev_default_loop (0);	1037	struct ev_loop *loop = ev_default_loop (0);
		1038
569	struct ev_io stdin_watcher;	1039	ev_io stdin_watcher;
		1040
570	ev_init (&stdin_watcher, my_cb);	1041	ev_init (&stdin_watcher, my_cb);
571	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1042	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
572	ev_io_start (loop, &stdin_watcher);	1043	ev_io_start (loop, &stdin_watcher);
		1044
573	ev_loop (loop, 0);	1045	ev_run (loop, 0);
574		1046
575	As you can see, you are responsible for allocating the memory for your	1047	As you can see, you are responsible for allocating the memory for your
576	watcher structures (and it is usually a bad idea to do this on the stack,	1048	watcher structures (and it is I<usually> a bad idea to do this on the
577	although this can sometimes be quite valid).	1049	stack).
578		1050
		1051	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1052	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1053
579	Each watcher structure must be initialised by a call to C<ev_init	1054	Each watcher structure must be initialised by a call to C<ev_init (watcher
580	(watcher *, callback)>, which expects a callback to be provided. This	1055	*, callback)>, which expects a callback to be provided. This callback is
581	callback gets invoked each time the event occurs (or, in the case of io	1056	invoked each time the event occurs (or, in the case of I/O watchers, each
582	watchers, each time the event loop detects that the file descriptor given	1057	time the event loop detects that the file descriptor given is readable
583	is readable and/or writable).	1058	and/or writable).
584		1059
585	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1060	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
586	with arguments specific to this watcher type. There is also a macro	1061	macro to configure it, with arguments specific to the watcher type. There
587	to combine initialisation and setting in one call: C<< ev_<type>_init	1062	is also a macro to combine initialisation and setting in one call: C<<
588	(watcher *, callback, ...) >>.	1063	ev_TYPE_init (watcher *, callback, ...) >>.
589		1064
590	To make the watcher actually watch out for events, you have to start it	1065	To make the watcher actually watch out for events, you have to start it
591	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1066	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
592	*) >>), and you can stop watching for events at any time by calling the	1067	*) >>), and you can stop watching for events at any time by calling the
593	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1068	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
594		1069
595	As long as your watcher is active (has been started but not stopped) you	1070	As long as your watcher is active (has been started but not stopped) you
596	must not touch the values stored in it. Most specifically you must never	1071	must not touch the values stored in it. Most specifically you must never
597	reinitialise it or call its C<set> macro.	1072	reinitialise it or call its C<ev_TYPE_set> macro.
598		1073
599	Each and every callback receives the event loop pointer as first, the	1074	Each and every callback receives the event loop pointer as first, the
600	registered watcher structure as second, and a bitset of received events as	1075	registered watcher structure as second, and a bitset of received events as
601	third argument.	1076	third argument.
602		1077
…		…
611	=item C<EV_WRITE>	1086	=item C<EV_WRITE>
612		1087
613	The file descriptor in the C<ev_io> watcher has become readable and/or	1088	The file descriptor in the C<ev_io> watcher has become readable and/or
614	writable.	1089	writable.
615		1090
616	=item C<EV_TIMEOUT>	1091	=item C<EV_TIMER>
617		1092
618	The C<ev_timer> watcher has timed out.	1093	The C<ev_timer> watcher has timed out.
619		1094
620	=item C<EV_PERIODIC>	1095	=item C<EV_PERIODIC>
621		1096
…		…
639		1114
640	=item C<EV_PREPARE>	1115	=item C<EV_PREPARE>
641		1116
642	=item C<EV_CHECK>	1117	=item C<EV_CHECK>
643		1118
644	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1119	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
645	to gather new events, and all C<ev_check> watchers are invoked just after	1120	to gather new events, and all C<ev_check> watchers are invoked just after
646	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1121	C<ev_run> has gathered them, but before it invokes any callbacks for any
647	received events. Callbacks of both watcher types can start and stop as	1122	received events. Callbacks of both watcher types can start and stop as
648	many watchers as they want, and all of them will be taken into account	1123	many watchers as they want, and all of them will be taken into account
649	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1124	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
650	C<ev_loop> from blocking).	1125	C<ev_run> from blocking).
651		1126
652	=item C<EV_EMBED>	1127	=item C<EV_EMBED>
653		1128
654	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1129	The embedded event loop specified in the C<ev_embed> watcher needs attention.
655		1130
656	=item C<EV_FORK>	1131	=item C<EV_FORK>
657		1132
658	The event loop has been resumed in the child process after fork (see	1133	The event loop has been resumed in the child process after fork (see
659	C<ev_fork>).	1134	C<ev_fork>).
660		1135
		1136	=item C<EV_CLEANUP>
		1137
		1138	The event loop is about to be destroyed (see C<ev_cleanup>).
		1139
		1140	=item C<EV_ASYNC>
		1141
		1142	The given async watcher has been asynchronously notified (see C<ev_async>).
		1143
		1144	=item C<EV_CUSTOM>
		1145
		1146	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1147	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1148
661	=item C<EV_ERROR>	1149	=item C<EV_ERROR>
662		1150
663	An unspecified error has occured, the watcher has been stopped. This might	1151	An unspecified error has occurred, the watcher has been stopped. This might
664	happen because the watcher could not be properly started because libev	1152	happen because the watcher could not be properly started because libev
665	ran out of memory, a file descriptor was found to be closed or any other	1153	ran out of memory, a file descriptor was found to be closed or any other
		1154	problem. Libev considers these application bugs.
		1155
666	problem. You best act on it by reporting the problem and somehow coping	1156	You best act on it by reporting the problem and somehow coping with the
667	with the watcher being stopped.	1157	watcher being stopped. Note that well-written programs should not receive
		1158	an error ever, so when your watcher receives it, this usually indicates a
		1159	bug in your program.
668		1160
669	Libev will usually signal a few "dummy" events together with an error,	1161	Libev will usually signal a few "dummy" events together with an error, for
670	for example it might indicate that a fd is readable or writable, and if	1162	example it might indicate that a fd is readable or writable, and if your
671	your callbacks is well-written it can just attempt the operation and cope	1163	callbacks is well-written it can just attempt the operation and cope with
672	with the error from read() or write(). This will not work in multithreaded	1164	the error from read() or write(). This will not work in multi-threaded
673	programs, though, so beware.	1165	programs, though, as the fd could already be closed and reused for another
		1166	thing, so beware.
674		1167
675	=back	1168	=back
676		1169
677	=head2 GENERIC WATCHER FUNCTIONS	1170	=head2 GENERIC WATCHER FUNCTIONS
678
679	In the following description, C<TYPE> stands for the watcher type,
680	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
681		1171
682	=over 4	1172	=over 4
683		1173
684	=item C<ev_init> (ev_TYPE *watcher, callback)	1174	=item C<ev_init> (ev_TYPE *watcher, callback)
685		1175
…		…
691	which rolls both calls into one.	1181	which rolls both calls into one.
692		1182
693	You can reinitialise a watcher at any time as long as it has been stopped	1183	You can reinitialise a watcher at any time as long as it has been stopped
694	(or never started) and there are no pending events outstanding.	1184	(or never started) and there are no pending events outstanding.
695		1185
696	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1186	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
697	int revents)>.	1187	int revents)>.
698		1188
		1189	Example: Initialise an C<ev_io> watcher in two steps.
		1190
		1191	ev_io w;
		1192	ev_init (&w, my_cb);
		1193	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1194
699	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1195	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
700		1196
701	This macro initialises the type-specific parts of a watcher. You need to	1197	This macro initialises the type-specific parts of a watcher. You need to
702	call C<ev_init> at least once before you call this macro, but you can	1198	call C<ev_init> at least once before you call this macro, but you can
703	call C<ev_TYPE_set> any number of times. You must not, however, call this	1199	call C<ev_TYPE_set> any number of times. You must not, however, call this
704	macro on a watcher that is active (it can be pending, however, which is a	1200	macro on a watcher that is active (it can be pending, however, which is a
705	difference to the C<ev_init> macro).	1201	difference to the C<ev_init> macro).
706		1202
707	Although some watcher types do not have type-specific arguments	1203	Although some watcher types do not have type-specific arguments
708	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1204	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
709		1205
		1206	See C<ev_init>, above, for an example.
		1207
710	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1208	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
711		1209
712	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1210	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
713	calls into a single call. This is the most convinient method to initialise	1211	calls into a single call. This is the most convenient method to initialise
714	a watcher. The same limitations apply, of course.	1212	a watcher. The same limitations apply, of course.
715		1213
		1214	Example: Initialise and set an C<ev_io> watcher in one step.
		1215
		1216	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1217
716	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1218	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
717		1219
718	Starts (activates) the given watcher. Only active watchers will receive	1220	Starts (activates) the given watcher. Only active watchers will receive
719	events. If the watcher is already active nothing will happen.	1221	events. If the watcher is already active nothing will happen.
720		1222
		1223	Example: Start the C<ev_io> watcher that is being abused as example in this
		1224	whole section.
		1225
		1226	ev_io_start (EV_DEFAULT_UC, &w);
		1227
721	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1228	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
722		1229
723	Stops the given watcher again (if active) and clears the pending	1230	Stops the given watcher if active, and clears the pending status (whether
		1231	the watcher was active or not).
		1232
724	status. It is possible that stopped watchers are pending (for example,	1233	It is possible that stopped watchers are pending - for example,
725	non-repeating timers are being stopped when they become pending), but	1234	non-repeating timers are being stopped when they become pending - but
726	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1235	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
727	you want to free or reuse the memory used by the watcher it is therefore a	1236	pending. If you want to free or reuse the memory used by the watcher it is
728	good idea to always call its C<ev_TYPE_stop> function.	1237	therefore a good idea to always call its C<ev_TYPE_stop> function.
729		1238
730	=item bool ev_is_active (ev_TYPE *watcher)	1239	=item bool ev_is_active (ev_TYPE *watcher)
731		1240
732	Returns a true value iff the watcher is active (i.e. it has been started	1241	Returns a true value iff the watcher is active (i.e. it has been started
733	and not yet been stopped). As long as a watcher is active you must not modify	1242	and not yet been stopped). As long as a watcher is active you must not modify
…		…
749	=item ev_cb_set (ev_TYPE *watcher, callback)	1258	=item ev_cb_set (ev_TYPE *watcher, callback)
750		1259
751	Change the callback. You can change the callback at virtually any time	1260	Change the callback. You can change the callback at virtually any time
752	(modulo threads).	1261	(modulo threads).
753		1262
754	=item ev_set_priority (ev_TYPE *watcher, priority)	1263	=item ev_set_priority (ev_TYPE *watcher, int priority)
755		1264
756	=item int ev_priority (ev_TYPE *watcher)	1265	=item int ev_priority (ev_TYPE *watcher)
757		1266
758	Set and query the priority of the watcher. The priority is a small	1267	Set and query the priority of the watcher. The priority is a small
759	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1268	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
760	(default: C<-2>). Pending watchers with higher priority will be invoked	1269	(default: C<-2>). Pending watchers with higher priority will be invoked
761	before watchers with lower priority, but priority will not keep watchers	1270	before watchers with lower priority, but priority will not keep watchers
762	from being executed (except for C<ev_idle> watchers).	1271	from being executed (except for C<ev_idle> watchers).
763		1272
764	This means that priorities are I<only> used for ordering callback
765	invocation after new events have been received. This is useful, for
766	example, to reduce latency after idling, or more often, to bind two
767	watchers on the same event and make sure one is called first.
768
769	If you need to suppress invocation when higher priority events are pending	1273	If you need to suppress invocation when higher priority events are pending
770	you need to look at C<ev_idle> watchers, which provide this functionality.	1274	you need to look at C<ev_idle> watchers, which provide this functionality.
771		1275
772	You I<must not> change the priority of a watcher as long as it is active or	1276	You I<must not> change the priority of a watcher as long as it is active or
773	pending.	1277	pending.
774		1278
		1279	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1280	fine, as long as you do not mind that the priority value you query might
		1281	or might not have been clamped to the valid range.
		1282
775	The default priority used by watchers when no priority has been set is	1283	The default priority used by watchers when no priority has been set is
776	always C<0>, which is supposed to not be too high and not be too low :).	1284	always C<0>, which is supposed to not be too high and not be too low :).
777		1285
778	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1286	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
779	fine, as long as you do not mind that the priority value you query might	1287	priorities.
780	or might not have been adjusted to be within valid range.
781		1288
782	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1289	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
783		1290
784	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1291	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
785	C<loop> nor C<revents> need to be valid as long as the watcher callback	1292	C<loop> nor C<revents> need to be valid as long as the watcher callback
786	can deal with that fact.	1293	can deal with that fact, as both are simply passed through to the
		1294	callback.
787		1295
788	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1296	=item int ev_clear_pending (loop, ev_TYPE *watcher)
789		1297
790	If the watcher is pending, this function returns clears its pending status	1298	If the watcher is pending, this function clears its pending status and
791	and returns its C<revents> bitset (as if its callback was invoked). If the	1299	returns its C<revents> bitset (as if its callback was invoked). If the
792	watcher isn't pending it does nothing and returns C<0>.	1300	watcher isn't pending it does nothing and returns C<0>.
793		1301
		1302	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1303	callback to be invoked, which can be accomplished with this function.
		1304
		1305	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1306
		1307	Feeds the given event set into the event loop, as if the specified event
		1308	had happened for the specified watcher (which must be a pointer to an
		1309	initialised but not necessarily started event watcher). Obviously you must
		1310	not free the watcher as long as it has pending events.
		1311
		1312	Stopping the watcher, letting libev invoke it, or calling
		1313	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1314	not started in the first place.
		1315
		1316	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1317	functions that do not need a watcher.
		1318
794	=back	1319	=back
795		1320
796
797	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1321	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
798		1322
799	Each watcher has, by default, a member C<void *data> that you can change	1323	Each watcher has, by default, a member C<void *data> that you can change
800	and read at any time, libev will completely ignore it. This can be used	1324	and read at any time: libev will completely ignore it. This can be used
801	to associate arbitrary data with your watcher. If you need more data and	1325	to associate arbitrary data with your watcher. If you need more data and
802	don't want to allocate memory and store a pointer to it in that data	1326	don't want to allocate memory and store a pointer to it in that data
803	member, you can also "subclass" the watcher type and provide your own	1327	member, you can also "subclass" the watcher type and provide your own
804	data:	1328	data:
805		1329
806	struct my_io	1330	struct my_io
807	{	1331	{
808	struct ev_io io;	1332	ev_io io;
809	int otherfd;	1333	int otherfd;
810	void *somedata;	1334	void *somedata;
811	struct whatever *mostinteresting;	1335	struct whatever *mostinteresting;
812	}	1336	};
		1337
		1338	...
		1339	struct my_io w;
		1340	ev_io_init (&w.io, my_cb, fd, EV_READ);
813		1341
814	And since your callback will be called with a pointer to the watcher, you	1342	And since your callback will be called with a pointer to the watcher, you
815	can cast it back to your own type:	1343	can cast it back to your own type:
816		1344
817	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1345	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
818	{	1346	{
819	struct my_io *w = (struct my_io *)w_;	1347	struct my_io *w = (struct my_io *)w_;
820	...	1348	...
821	}	1349	}
822		1350
823	More interesting and less C-conformant ways of casting your callback type	1351	More interesting and less C-conformant ways of casting your callback type
824	instead have been omitted.	1352	instead have been omitted.
825		1353
826	Another common scenario is having some data structure with multiple	1354	Another common scenario is to use some data structure with multiple
827	watchers:	1355	embedded watchers:
828		1356
829	struct my_biggy	1357	struct my_biggy
830	{	1358	{
831	int some_data;	1359	int some_data;
832	ev_timer t1;	1360	ev_timer t1;
833	ev_timer t2;	1361	ev_timer t2;
834	}	1362	}
835		1363
836	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1364	In this case getting the pointer to C<my_biggy> is a bit more
837	you need to use C<offsetof>:	1365	complicated: Either you store the address of your C<my_biggy> struct
		1366	in the C<data> member of the watcher (for woozies), or you need to use
		1367	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1368	programmers):
838		1369
839	#include <stddef.h>	1370	#include <stddef.h>
840		1371
841	static void	1372	static void
842	t1_cb (EV_P_ struct ev_timer *w, int revents)	1373	t1_cb (EV_P_ ev_timer *w, int revents)
843	{	1374	{
844	struct my_biggy big = (struct my_biggy *	1375	struct my_biggy big = (struct my_biggy *)
845	(((char *)w) - offsetof (struct my_biggy, t1));	1376	(((char *)w) - offsetof (struct my_biggy, t1));
846	}	1377	}
847		1378
848	static void	1379	static void
849	t2_cb (EV_P_ struct ev_timer *w, int revents)	1380	t2_cb (EV_P_ ev_timer *w, int revents)
850	{	1381	{
851	struct my_biggy big = (struct my_biggy *	1382	struct my_biggy big = (struct my_biggy *)
852	(((char *)w) - offsetof (struct my_biggy, t2));	1383	(((char *)w) - offsetof (struct my_biggy, t2));
853	}	1384	}
		1385
		1386	=head2 WATCHER STATES
		1387
		1388	There are various watcher states mentioned throughout this manual -
		1389	active, pending and so on. In this section these states and the rules to
		1390	transition between them will be described in more detail - and while these
		1391	rules might look complicated, they usually do "the right thing".
		1392
		1393	=over 4
		1394
		1395	=item initialiased
		1396
		1397	Before a watcher can be registered with the event looop it has to be
		1398	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1399	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1400
		1401	In this state it is simply some block of memory that is suitable for use
		1402	in an event loop. It can be moved around, freed, reused etc. at will.
		1403
		1404	=item started/running/active
		1405
		1406	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1407	property of the event loop, and is actively waiting for events. While in
		1408	this state it cannot be accessed (except in a few documented ways), moved,
		1409	freed or anything else - the only legal thing is to keep a pointer to it,
		1410	and call libev functions on it that are documented to work on active watchers.
		1411
		1412	=item pending
		1413
		1414	If a watcher is active and libev determines that an event it is interested
		1415	in has occurred (such as a timer expiring), it will become pending. It will
		1416	stay in this pending state until either it is stopped or its callback is
		1417	about to be invoked, so it is not normally pending inside the watcher
		1418	callback.
		1419
		1420	The watcher might or might not be active while it is pending (for example,
		1421	an expired non-repeating timer can be pending but no longer active). If it
		1422	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1423	but it is still property of the event loop at this time, so cannot be
		1424	moved, freed or reused. And if it is active the rules described in the
		1425	previous item still apply.
		1426
		1427	It is also possible to feed an event on a watcher that is not active (e.g.
		1428	via C<ev_feed_event>), in which case it becomes pending without being
		1429	active.
		1430
		1431	=item stopped
		1432
		1433	A watcher can be stopped implicitly by libev (in which case it might still
		1434	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1435	latter will clear any pending state the watcher might be in, regardless
		1436	of whether it was active or not, so stopping a watcher explicitly before
		1437	freeing it is often a good idea.
		1438
		1439	While stopped (and not pending) the watcher is essentially in the
		1440	initialised state, that is it can be reused, moved, modified in any way
		1441	you wish.
		1442
		1443	=back
		1444
		1445	=head2 WATCHER PRIORITY MODELS
		1446
		1447	Many event loops support I<watcher priorities>, which are usually small
		1448	integers that influence the ordering of event callback invocation
		1449	between watchers in some way, all else being equal.
		1450
		1451	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1452	description for the more technical details such as the actual priority
		1453	range.
		1454
		1455	There are two common ways how these these priorities are being interpreted
		1456	by event loops:
		1457
		1458	In the more common lock-out model, higher priorities "lock out" invocation
		1459	of lower priority watchers, which means as long as higher priority
		1460	watchers receive events, lower priority watchers are not being invoked.
		1461
		1462	The less common only-for-ordering model uses priorities solely to order
		1463	callback invocation within a single event loop iteration: Higher priority
		1464	watchers are invoked before lower priority ones, but they all get invoked
		1465	before polling for new events.
		1466
		1467	Libev uses the second (only-for-ordering) model for all its watchers
		1468	except for idle watchers (which use the lock-out model).
		1469
		1470	The rationale behind this is that implementing the lock-out model for
		1471	watchers is not well supported by most kernel interfaces, and most event
		1472	libraries will just poll for the same events again and again as long as
		1473	their callbacks have not been executed, which is very inefficient in the
		1474	common case of one high-priority watcher locking out a mass of lower
		1475	priority ones.
		1476
		1477	Static (ordering) priorities are most useful when you have two or more
		1478	watchers handling the same resource: a typical usage example is having an
		1479	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1480	timeouts. Under load, data might be received while the program handles
		1481	other jobs, but since timers normally get invoked first, the timeout
		1482	handler will be executed before checking for data. In that case, giving
		1483	the timer a lower priority than the I/O watcher ensures that I/O will be
		1484	handled first even under adverse conditions (which is usually, but not
		1485	always, what you want).
		1486
		1487	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1488	will only be executed when no same or higher priority watchers have
		1489	received events, they can be used to implement the "lock-out" model when
		1490	required.
		1491
		1492	For example, to emulate how many other event libraries handle priorities,
		1493	you can associate an C<ev_idle> watcher to each such watcher, and in
		1494	the normal watcher callback, you just start the idle watcher. The real
		1495	processing is done in the idle watcher callback. This causes libev to
		1496	continuously poll and process kernel event data for the watcher, but when
		1497	the lock-out case is known to be rare (which in turn is rare :), this is
		1498	workable.
		1499
		1500	Usually, however, the lock-out model implemented that way will perform
		1501	miserably under the type of load it was designed to handle. In that case,
		1502	it might be preferable to stop the real watcher before starting the
		1503	idle watcher, so the kernel will not have to process the event in case
		1504	the actual processing will be delayed for considerable time.
		1505
		1506	Here is an example of an I/O watcher that should run at a strictly lower
		1507	priority than the default, and which should only process data when no
		1508	other events are pending:
		1509
		1510	ev_idle idle; // actual processing watcher
		1511	ev_io io; // actual event watcher
		1512
		1513	static void
		1514	io_cb (EV_P_ ev_io *w, int revents)
		1515	{
		1516	// stop the I/O watcher, we received the event, but
		1517	// are not yet ready to handle it.
		1518	ev_io_stop (EV_A_ w);
		1519
		1520	// start the idle watcher to handle the actual event.
		1521	// it will not be executed as long as other watchers
		1522	// with the default priority are receiving events.
		1523	ev_idle_start (EV_A_ &idle);
		1524	}
		1525
		1526	static void
		1527	idle_cb (EV_P_ ev_idle *w, int revents)
		1528	{
		1529	// actual processing
		1530	read (STDIN_FILENO, ...);
		1531
		1532	// have to start the I/O watcher again, as
		1533	// we have handled the event
		1534	ev_io_start (EV_P_ &io);
		1535	}
		1536
		1537	// initialisation
		1538	ev_idle_init (&idle, idle_cb);
		1539	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1540	ev_io_start (EV_DEFAULT_ &io);
		1541
		1542	In the "real" world, it might also be beneficial to start a timer, so that
		1543	low-priority connections can not be locked out forever under load. This
		1544	enables your program to keep a lower latency for important connections
		1545	during short periods of high load, while not completely locking out less
		1546	important ones.
854		1547
855		1548
856	=head1 WATCHER TYPES	1549	=head1 WATCHER TYPES
857		1550
858	This section describes each watcher in detail, but will not repeat	1551	This section describes each watcher in detail, but will not repeat
…		…
882	In general you can register as many read and/or write event watchers per	1575	In general you can register as many read and/or write event watchers per
883	fd as you want (as long as you don't confuse yourself). Setting all file	1576	fd as you want (as long as you don't confuse yourself). Setting all file
884	descriptors to non-blocking mode is also usually a good idea (but not	1577	descriptors to non-blocking mode is also usually a good idea (but not
885	required if you know what you are doing).	1578	required if you know what you are doing).
886		1579
887	You have to be careful with dup'ed file descriptors, though. Some backends	1580	If you cannot use non-blocking mode, then force the use of a
888	(the linux epoll backend is a notable example) cannot handle dup'ed file	1581	known-to-be-good backend (at the time of this writing, this includes only
889	descriptors correctly if you register interest in two or more fds pointing	1582	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
890	to the same underlying file/socket/etc. description (that is, they share	1583	descriptors for which non-blocking operation makes no sense (such as
891	the same underlying "file open").	1584	files) - libev doesn't guarantee any specific behaviour in that case.
892
893	If you must do this, then force the use of a known-to-be-good backend
894	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
895	C<EVBACKEND_POLL>).
896		1585
897	Another thing you have to watch out for is that it is quite easy to	1586	Another thing you have to watch out for is that it is quite easy to
898	receive "spurious" readyness notifications, that is your callback might	1587	receive "spurious" readiness notifications, that is your callback might
899	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1588	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
900	because there is no data. Not only are some backends known to create a	1589	because there is no data. Not only are some backends known to create a
901	lot of those (for example solaris ports), it is very easy to get into	1590	lot of those (for example Solaris ports), it is very easy to get into
902	this situation even with a relatively standard program structure. Thus	1591	this situation even with a relatively standard program structure. Thus
903	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1592	it is best to always use non-blocking I/O: An extra C<read>(2) returning
904	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1593	C<EAGAIN> is far preferable to a program hanging until some data arrives.
905		1594
906	If you cannot run the fd in non-blocking mode (for example you should not	1595	If you cannot run the fd in non-blocking mode (for example you should
907	play around with an Xlib connection), then you have to seperately re-test	1596	not play around with an Xlib connection), then you have to separately
908	whether a file descriptor is really ready with a known-to-be good interface	1597	re-test whether a file descriptor is really ready with a known-to-be good
909	such as poll (fortunately in our Xlib example, Xlib already does this on	1598	interface such as poll (fortunately in our Xlib example, Xlib already
910	its own, so its quite safe to use).	1599	does this on its own, so its quite safe to use). Some people additionally
		1600	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1601	indefinitely.
		1602
		1603	But really, best use non-blocking mode.
		1604
		1605	=head3 The special problem of disappearing file descriptors
		1606
		1607	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1608	descriptor (either due to calling C<close> explicitly or any other means,
		1609	such as C<dup2>). The reason is that you register interest in some file
		1610	descriptor, but when it goes away, the operating system will silently drop
		1611	this interest. If another file descriptor with the same number then is
		1612	registered with libev, there is no efficient way to see that this is, in
		1613	fact, a different file descriptor.
		1614
		1615	To avoid having to explicitly tell libev about such cases, libev follows
		1616	the following policy: Each time C<ev_io_set> is being called, libev
		1617	will assume that this is potentially a new file descriptor, otherwise
		1618	it is assumed that the file descriptor stays the same. That means that
		1619	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1620	descriptor even if the file descriptor number itself did not change.
		1621
		1622	This is how one would do it normally anyway, the important point is that
		1623	the libev application should not optimise around libev but should leave
		1624	optimisations to libev.
		1625
		1626	=head3 The special problem of dup'ed file descriptors
		1627
		1628	Some backends (e.g. epoll), cannot register events for file descriptors,
		1629	but only events for the underlying file descriptions. That means when you
		1630	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1631	events for them, only one file descriptor might actually receive events.
		1632
		1633	There is no workaround possible except not registering events
		1634	for potentially C<dup ()>'ed file descriptors, or to resort to
		1635	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1636
		1637	=head3 The special problem of fork
		1638
		1639	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1640	useless behaviour. Libev fully supports fork, but needs to be told about
		1641	it in the child.
		1642
		1643	To support fork in your programs, you either have to call
		1644	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1645	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1646	C<EVBACKEND_POLL>.
		1647
		1648	=head3 The special problem of SIGPIPE
		1649
		1650	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1651	when writing to a pipe whose other end has been closed, your program gets
		1652	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1653	this is sensible behaviour, for daemons, this is usually undesirable.
		1654
		1655	So when you encounter spurious, unexplained daemon exits, make sure you
		1656	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1657	somewhere, as that would have given you a big clue).
		1658
		1659	=head3 The special problem of accept()ing when you can't
		1660
		1661	Many implementations of the POSIX C<accept> function (for example,
		1662	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1663	connection from the pending queue in all error cases.
		1664
		1665	For example, larger servers often run out of file descriptors (because
		1666	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1667	rejecting the connection, leading to libev signalling readiness on
		1668	the next iteration again (the connection still exists after all), and
		1669	typically causing the program to loop at 100% CPU usage.
		1670
		1671	Unfortunately, the set of errors that cause this issue differs between
		1672	operating systems, there is usually little the app can do to remedy the
		1673	situation, and no known thread-safe method of removing the connection to
		1674	cope with overload is known (to me).
		1675
		1676	One of the easiest ways to handle this situation is to just ignore it
		1677	- when the program encounters an overload, it will just loop until the
		1678	situation is over. While this is a form of busy waiting, no OS offers an
		1679	event-based way to handle this situation, so it's the best one can do.
		1680
		1681	A better way to handle the situation is to log any errors other than
		1682	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1683	messages, and continue as usual, which at least gives the user an idea of
		1684	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1685	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1686	usage.
		1687
		1688	If your program is single-threaded, then you could also keep a dummy file
		1689	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1690	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1691	close that fd, and create a new dummy fd. This will gracefully refuse
		1692	clients under typical overload conditions.
		1693
		1694	The last way to handle it is to simply log the error and C<exit>, as
		1695	is often done with C<malloc> failures, but this results in an easy
		1696	opportunity for a DoS attack.
		1697
		1698	=head3 Watcher-Specific Functions
911		1699
912	=over 4	1700	=over 4
913		1701
914	=item ev_io_init (ev_io *, callback, int fd, int events)	1702	=item ev_io_init (ev_io *, callback, int fd, int events)
915		1703
916	=item ev_io_set (ev_io *, int fd, int events)	1704	=item ev_io_set (ev_io *, int fd, int events)
917		1705
918	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1706	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
919	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1707	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
920	C<EV_READ | EV_WRITE> to receive the given events.	1708	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
921		1709
922	=item int fd [read-only]	1710	=item int fd [read-only]
923		1711
924	The file descriptor being watched.	1712	The file descriptor being watched.
925		1713
926	=item int events [read-only]	1714	=item int events [read-only]
927		1715
928	The events being watched.	1716	The events being watched.
929		1717
930	=back	1718	=back
		1719
		1720	=head3 Examples
931		1721
932	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1722	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
933	readable, but only once. Since it is likely line-buffered, you could	1723	readable, but only once. Since it is likely line-buffered, you could
934	attempt to read a whole line in the callback.	1724	attempt to read a whole line in the callback.
935		1725
936	static void	1726	static void
937	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1727	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
938	{	1728	{
939	ev_io_stop (loop, w);	1729	ev_io_stop (loop, w);
940	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1730	.. read from stdin here (or from w->fd) and handle any I/O errors
941	}	1731	}
942		1732
943	...	1733	...
944	struct ev_loop *loop = ev_default_init (0);	1734	struct ev_loop *loop = ev_default_init (0);
945	struct ev_io stdin_readable;	1735	ev_io stdin_readable;
946	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1736	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
947	ev_io_start (loop, &stdin_readable);	1737	ev_io_start (loop, &stdin_readable);
948	ev_loop (loop, 0);	1738	ev_run (loop, 0);
949		1739
950		1740
951	=head2 C<ev_timer> - relative and optionally repeating timeouts	1741	=head2 C<ev_timer> - relative and optionally repeating timeouts
952		1742
953	Timer watchers are simple relative timers that generate an event after a	1743	Timer watchers are simple relative timers that generate an event after a
954	given time, and optionally repeating in regular intervals after that.	1744	given time, and optionally repeating in regular intervals after that.
955		1745
956	The timers are based on real time, that is, if you register an event that	1746	The timers are based on real time, that is, if you register an event that
957	times out after an hour and you reset your system clock to last years	1747	times out after an hour and you reset your system clock to January last
958	time, it will still time out after (roughly) and hour. "Roughly" because	1748	year, it will still time out after (roughly) one hour. "Roughly" because
959	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1749	detecting time jumps is hard, and some inaccuracies are unavoidable (the
960	monotonic clock option helps a lot here).	1750	monotonic clock option helps a lot here).
		1751
		1752	The callback is guaranteed to be invoked only I<after> its timeout has
		1753	passed (not I<at>, so on systems with very low-resolution clocks this
		1754	might introduce a small delay). If multiple timers become ready during the
		1755	same loop iteration then the ones with earlier time-out values are invoked
		1756	before ones of the same priority with later time-out values (but this is
		1757	no longer true when a callback calls C<ev_run> recursively).
		1758
		1759	=head3 Be smart about timeouts
		1760
		1761	Many real-world problems involve some kind of timeout, usually for error
		1762	recovery. A typical example is an HTTP request - if the other side hangs,
		1763	you want to raise some error after a while.
		1764
		1765	What follows are some ways to handle this problem, from obvious and
		1766	inefficient to smart and efficient.
		1767
		1768	In the following, a 60 second activity timeout is assumed - a timeout that
		1769	gets reset to 60 seconds each time there is activity (e.g. each time some
		1770	data or other life sign was received).
		1771
		1772	=over 4
		1773
		1774	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1775
		1776	This is the most obvious, but not the most simple way: In the beginning,
		1777	start the watcher:
		1778
		1779	ev_timer_init (timer, callback, 60., 0.);
		1780	ev_timer_start (loop, timer);
		1781
		1782	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1783	and start it again:
		1784
		1785	ev_timer_stop (loop, timer);
		1786	ev_timer_set (timer, 60., 0.);
		1787	ev_timer_start (loop, timer);
		1788
		1789	This is relatively simple to implement, but means that each time there is
		1790	some activity, libev will first have to remove the timer from its internal
		1791	data structure and then add it again. Libev tries to be fast, but it's
		1792	still not a constant-time operation.
		1793
		1794	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1795
		1796	This is the easiest way, and involves using C<ev_timer_again> instead of
		1797	C<ev_timer_start>.
		1798
		1799	To implement this, configure an C<ev_timer> with a C<repeat> value
		1800	of C<60> and then call C<ev_timer_again> at start and each time you
		1801	successfully read or write some data. If you go into an idle state where
		1802	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1803	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1804
		1805	That means you can ignore both the C<ev_timer_start> function and the
		1806	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1807	member and C<ev_timer_again>.
		1808
		1809	At start:
		1810
		1811	ev_init (timer, callback);
		1812	timer->repeat = 60.;
		1813	ev_timer_again (loop, timer);
		1814
		1815	Each time there is some activity:
		1816
		1817	ev_timer_again (loop, timer);
		1818
		1819	It is even possible to change the time-out on the fly, regardless of
		1820	whether the watcher is active or not:
		1821
		1822	timer->repeat = 30.;
		1823	ev_timer_again (loop, timer);
		1824
		1825	This is slightly more efficient then stopping/starting the timer each time
		1826	you want to modify its timeout value, as libev does not have to completely
		1827	remove and re-insert the timer from/into its internal data structure.
		1828
		1829	It is, however, even simpler than the "obvious" way to do it.
		1830
		1831	=item 3. Let the timer time out, but then re-arm it as required.
		1832
		1833	This method is more tricky, but usually most efficient: Most timeouts are
		1834	relatively long compared to the intervals between other activity - in
		1835	our example, within 60 seconds, there are usually many I/O events with
		1836	associated activity resets.
		1837
		1838	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1839	but remember the time of last activity, and check for a real timeout only
		1840	within the callback:
		1841
		1842	ev_tstamp last_activity; // time of last activity
		1843
		1844	static void
		1845	callback (EV_P_ ev_timer *w, int revents)
		1846	{
		1847	ev_tstamp now = ev_now (EV_A);
		1848	ev_tstamp timeout = last_activity + 60.;
		1849
		1850	// if last_activity + 60. is older than now, we did time out
		1851	if (timeout < now)
		1852	{
		1853	// timeout occurred, take action
		1854	}
		1855	else
		1856	{
		1857	// callback was invoked, but there was some activity, re-arm
		1858	// the watcher to fire in last_activity + 60, which is
		1859	// guaranteed to be in the future, so "again" is positive:
		1860	w->repeat = timeout - now;
		1861	ev_timer_again (EV_A_ w);
		1862	}
		1863	}
		1864
		1865	To summarise the callback: first calculate the real timeout (defined
		1866	as "60 seconds after the last activity"), then check if that time has
		1867	been reached, which means something I<did>, in fact, time out. Otherwise
		1868	the callback was invoked too early (C<timeout> is in the future), so
		1869	re-schedule the timer to fire at that future time, to see if maybe we have
		1870	a timeout then.
		1871
		1872	Note how C<ev_timer_again> is used, taking advantage of the
		1873	C<ev_timer_again> optimisation when the timer is already running.
		1874
		1875	This scheme causes more callback invocations (about one every 60 seconds
		1876	minus half the average time between activity), but virtually no calls to
		1877	libev to change the timeout.
		1878
		1879	To start the timer, simply initialise the watcher and set C<last_activity>
		1880	to the current time (meaning we just have some activity :), then call the
		1881	callback, which will "do the right thing" and start the timer:
		1882
		1883	ev_init (timer, callback);
		1884	last_activity = ev_now (loop);
		1885	callback (loop, timer, EV_TIMER);
		1886
		1887	And when there is some activity, simply store the current time in
		1888	C<last_activity>, no libev calls at all:
		1889
		1890	last_activity = ev_now (loop);
		1891
		1892	This technique is slightly more complex, but in most cases where the
		1893	time-out is unlikely to be triggered, much more efficient.
		1894
		1895	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1896	callback :) - just change the timeout and invoke the callback, which will
		1897	fix things for you.
		1898
		1899	=item 4. Wee, just use a double-linked list for your timeouts.
		1900
		1901	If there is not one request, but many thousands (millions...), all
		1902	employing some kind of timeout with the same timeout value, then one can
		1903	do even better:
		1904
		1905	When starting the timeout, calculate the timeout value and put the timeout
		1906	at the I<end> of the list.
		1907
		1908	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1909	the list is expected to fire (for example, using the technique #3).
		1910
		1911	When there is some activity, remove the timer from the list, recalculate
		1912	the timeout, append it to the end of the list again, and make sure to
		1913	update the C<ev_timer> if it was taken from the beginning of the list.
		1914
		1915	This way, one can manage an unlimited number of timeouts in O(1) time for
		1916	starting, stopping and updating the timers, at the expense of a major
		1917	complication, and having to use a constant timeout. The constant timeout
		1918	ensures that the list stays sorted.
		1919
		1920	=back
		1921
		1922	So which method the best?
		1923
		1924	Method #2 is a simple no-brain-required solution that is adequate in most
		1925	situations. Method #3 requires a bit more thinking, but handles many cases
		1926	better, and isn't very complicated either. In most case, choosing either
		1927	one is fine, with #3 being better in typical situations.
		1928
		1929	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1930	rather complicated, but extremely efficient, something that really pays
		1931	off after the first million or so of active timers, i.e. it's usually
		1932	overkill :)
		1933
		1934	=head3 The special problem of time updates
		1935
		1936	Establishing the current time is a costly operation (it usually takes at
		1937	least two system calls): EV therefore updates its idea of the current
		1938	time only before and after C<ev_run> collects new events, which causes a
		1939	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1940	lots of events in one iteration.
961		1941
962	The relative timeouts are calculated relative to the C<ev_now ()>	1942	The relative timeouts are calculated relative to the C<ev_now ()>
963	time. This is usually the right thing as this timestamp refers to the time	1943	time. This is usually the right thing as this timestamp refers to the time
964	of the event triggering whatever timeout you are modifying/starting. If	1944	of the event triggering whatever timeout you are modifying/starting. If
965	you suspect event processing to be delayed and you I<need> to base the timeout	1945	you suspect event processing to be delayed and you I<need> to base the
966	on the current time, use something like this to adjust for this:	1946	timeout on the current time, use something like this to adjust for this:
967		1947
968	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1948	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
969		1949
970	The callback is guarenteed to be invoked only when its timeout has passed,	1950	If the event loop is suspended for a long time, you can also force an
971	but if multiple timers become ready during the same loop iteration then	1951	update of the time returned by C<ev_now ()> by calling C<ev_now_update
972	order of execution is undefined.	1952	()>.
		1953
		1954	=head3 The special problems of suspended animation
		1955
		1956	When you leave the server world it is quite customary to hit machines that
		1957	can suspend/hibernate - what happens to the clocks during such a suspend?
		1958
		1959	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1960	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1961	to run until the system is suspended, but they will not advance while the
		1962	system is suspended. That means, on resume, it will be as if the program
		1963	was frozen for a few seconds, but the suspend time will not be counted
		1964	towards C<ev_timer> when a monotonic clock source is used. The real time
		1965	clock advanced as expected, but if it is used as sole clocksource, then a
		1966	long suspend would be detected as a time jump by libev, and timers would
		1967	be adjusted accordingly.
		1968
		1969	I would not be surprised to see different behaviour in different between
		1970	operating systems, OS versions or even different hardware.
		1971
		1972	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1973	time jump in the monotonic clocks and the realtime clock. If the program
		1974	is suspended for a very long time, and monotonic clock sources are in use,
		1975	then you can expect C<ev_timer>s to expire as the full suspension time
		1976	will be counted towards the timers. When no monotonic clock source is in
		1977	use, then libev will again assume a timejump and adjust accordingly.
		1978
		1979	It might be beneficial for this latter case to call C<ev_suspend>
		1980	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1981	deterministic behaviour in this case (you can do nothing against
		1982	C<SIGSTOP>).
		1983
		1984	=head3 Watcher-Specific Functions and Data Members
973		1985
974	=over 4	1986	=over 4
975		1987
976	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1988	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
977		1989
978	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1990	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
979		1991
980	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1992	Configure the timer to trigger after C<after> seconds. If C<repeat>
981	C<0.>, then it will automatically be stopped. If it is positive, then the	1993	is C<0.>, then it will automatically be stopped once the timeout is
982	timer will automatically be configured to trigger again C<repeat> seconds	1994	reached. If it is positive, then the timer will automatically be
983	later, again, and again, until stopped manually.	1995	configured to trigger again C<repeat> seconds later, again, and again,
		1996	until stopped manually.
984		1997
985	The timer itself will do a best-effort at avoiding drift, that is, if you	1998	The timer itself will do a best-effort at avoiding drift, that is, if
986	configure a timer to trigger every 10 seconds, then it will trigger at	1999	you configure a timer to trigger every 10 seconds, then it will normally
987	exactly 10 second intervals. If, however, your program cannot keep up with	2000	trigger at exactly 10 second intervals. If, however, your program cannot
988	the timer (because it takes longer than those 10 seconds to do stuff) the	2001	keep up with the timer (because it takes longer than those 10 seconds to
989	timer will not fire more than once per event loop iteration.	2002	do stuff) the timer will not fire more than once per event loop iteration.
990		2003
991	=item ev_timer_again (loop)	2004	=item ev_timer_again (loop, ev_timer *)
992		2005
993	This will act as if the timer timed out and restart it again if it is	2006	This will act as if the timer timed out and restart it again if it is
994	repeating. The exact semantics are:	2007	repeating. The exact semantics are:
995		2008
996	If the timer is pending, its pending status is cleared.	2009	If the timer is pending, its pending status is cleared.
997		2010
998	If the timer is started but nonrepeating, stop it (as if it timed out).	2011	If the timer is started but non-repeating, stop it (as if it timed out).
999		2012
1000	If the timer is repeating, either start it if necessary (with the	2013	If the timer is repeating, either start it if necessary (with the
1001	C<repeat> value), or reset the running timer to the C<repeat> value.	2014	C<repeat> value), or reset the running timer to the C<repeat> value.
1002		2015
1003	This sounds a bit complicated, but here is a useful and typical	2016	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1004	example: Imagine you have a tcp connection and you want a so-called idle	2017	usage example.
1005	timeout, that is, you want to be called when there have been, say, 60
1006	seconds of inactivity on the socket. The easiest way to do this is to
1007	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1008	C<ev_timer_again> each time you successfully read or write some data. If
1009	you go into an idle state where you do not expect data to travel on the
1010	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1011	automatically restart it if need be.
1012		2018
1013	That means you can ignore the C<after> value and C<ev_timer_start>	2019	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1014	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1015		2020
1016	ev_timer_init (timer, callback, 0., 5.);	2021	Returns the remaining time until a timer fires. If the timer is active,
1017	ev_timer_again (loop, timer);	2022	then this time is relative to the current event loop time, otherwise it's
1018	...	2023	the timeout value currently configured.
1019	timer->again = 17.;
1020	ev_timer_again (loop, timer);
1021	...
1022	timer->again = 10.;
1023	ev_timer_again (loop, timer);
1024		2024
1025	This is more slightly efficient then stopping/starting the timer each time	2025	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1026	you want to modify its timeout value.	2026	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2027	will return C<4>. When the timer expires and is restarted, it will return
		2028	roughly C<7> (likely slightly less as callback invocation takes some time,
		2029	too), and so on.
1027		2030
1028	=item ev_tstamp repeat [read-write]	2031	=item ev_tstamp repeat [read-write]
1029		2032
1030	The current C<repeat> value. Will be used each time the watcher times out	2033	The current C<repeat> value. Will be used each time the watcher times out
1031	or C<ev_timer_again> is called and determines the next timeout (if any),	2034	or C<ev_timer_again> is called, and determines the next timeout (if any),
1032	which is also when any modifications are taken into account.	2035	which is also when any modifications are taken into account.
1033		2036
1034	=back	2037	=back
1035		2038
		2039	=head3 Examples
		2040
1036	Example: Create a timer that fires after 60 seconds.	2041	Example: Create a timer that fires after 60 seconds.
1037		2042
1038	static void	2043	static void
1039	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2044	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1040	{	2045	{
1041	.. one minute over, w is actually stopped right here	2046	.. one minute over, w is actually stopped right here
1042	}	2047	}
1043		2048
1044	struct ev_timer mytimer;	2049	ev_timer mytimer;
1045	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2050	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1046	ev_timer_start (loop, &mytimer);	2051	ev_timer_start (loop, &mytimer);
1047		2052
1048	Example: Create a timeout timer that times out after 10 seconds of	2053	Example: Create a timeout timer that times out after 10 seconds of
1049	inactivity.	2054	inactivity.
1050		2055
1051	static void	2056	static void
1052	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2057	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1053	{	2058	{
1054	.. ten seconds without any activity	2059	.. ten seconds without any activity
1055	}	2060	}
1056		2061
1057	struct ev_timer mytimer;	2062	ev_timer mytimer;
1058	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2063	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1059	ev_timer_again (&mytimer); /* start timer */	2064	ev_timer_again (&mytimer); /* start timer */
1060	ev_loop (loop, 0);	2065	ev_run (loop, 0);
1061		2066
1062	// and in some piece of code that gets executed on any "activity":	2067	// and in some piece of code that gets executed on any "activity":
1063	// reset the timeout to start ticking again at 10 seconds	2068	// reset the timeout to start ticking again at 10 seconds
1064	ev_timer_again (&mytimer);	2069	ev_timer_again (&mytimer);
1065		2070
1066		2071
1067	=head2 C<ev_periodic> - to cron or not to cron?	2072	=head2 C<ev_periodic> - to cron or not to cron?
1068		2073
1069	Periodic watchers are also timers of a kind, but they are very versatile	2074	Periodic watchers are also timers of a kind, but they are very versatile
1070	(and unfortunately a bit complex).	2075	(and unfortunately a bit complex).
1071		2076
1072	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2077	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1073	but on wallclock time (absolute time). You can tell a periodic watcher	2078	relative time, the physical time that passes) but on wall clock time
1074	to trigger "at" some specific point in time. For example, if you tell a	2079	(absolute time, the thing you can read on your calender or clock). The
1075	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2080	difference is that wall clock time can run faster or slower than real
1076	+ 10.>) and then reset your system clock to the last year, then it will	2081	time, and time jumps are not uncommon (e.g. when you adjust your
1077	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2082	wrist-watch).
1078	roughly 10 seconds later and of course not if you reset your system time
1079	again).
1080		2083
1081	They can also be used to implement vastly more complex timers, such as	2084	You can tell a periodic watcher to trigger after some specific point
		2085	in time: for example, if you tell a periodic watcher to trigger "in 10
		2086	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2087	not a delay) and then reset your system clock to January of the previous
		2088	year, then it will take a year or more to trigger the event (unlike an
		2089	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2090	it, as it uses a relative timeout).
		2091
		2092	C<ev_periodic> watchers can also be used to implement vastly more complex
1082	triggering an event on eahc midnight, local time.	2093	timers, such as triggering an event on each "midnight, local time", or
		2094	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2095	those cannot react to time jumps.
1083		2096
1084	As with timers, the callback is guarenteed to be invoked only when the	2097	As with timers, the callback is guaranteed to be invoked only when the
1085	time (C<at>) has been passed, but if multiple periodic timers become ready	2098	point in time where it is supposed to trigger has passed. If multiple
1086	during the same loop iteration then order of execution is undefined.	2099	timers become ready during the same loop iteration then the ones with
		2100	earlier time-out values are invoked before ones with later time-out values
		2101	(but this is no longer true when a callback calls C<ev_run> recursively).
		2102
		2103	=head3 Watcher-Specific Functions and Data Members
1087		2104
1088	=over 4	2105	=over 4
1089		2106
1090	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2107	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1091		2108
1092	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2109	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1093		2110
1094	Lots of arguments, lets sort it out... There are basically three modes of	2111	Lots of arguments, let's sort it out... There are basically three modes of
1095	operation, and we will explain them from simplest to complex:	2112	operation, and we will explain them from simplest to most complex:
1096		2113
1097	=over 4	2114	=over 4
1098		2115
1099	=item * absolute timer (interval = reschedule_cb = 0)	2116	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1100		2117
1101	In this configuration the watcher triggers an event at the wallclock time	2118	In this configuration the watcher triggers an event after the wall clock
1102	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2119	time C<offset> has passed. It will not repeat and will not adjust when a
1103	that is, if it is to be run at January 1st 2011 then it will run when the	2120	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1104	system time reaches or surpasses this time.	2121	will be stopped and invoked when the system clock reaches or surpasses
		2122	this point in time.
1105		2123
1106	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2124	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1107		2125
1108	In this mode the watcher will always be scheduled to time out at the next	2126	In this mode the watcher will always be scheduled to time out at the next
1109	C<at + N * interval> time (for some integer N) and then repeat, regardless	2127	C<offset + N * interval> time (for some integer N, which can also be
1110	of any time jumps.	2128	negative) and then repeat, regardless of any time jumps. The C<offset>
		2129	argument is merely an offset into the C<interval> periods.
1111		2130
1112	This can be used to create timers that do not drift with respect to system	2131	This can be used to create timers that do not drift with respect to the
1113	time:	2132	system clock, for example, here is an C<ev_periodic> that triggers each
		2133	hour, on the hour (with respect to UTC):
1114		2134
1115	ev_periodic_set (&periodic, 0., 3600., 0);	2135	ev_periodic_set (&periodic, 0., 3600., 0);
1116		2136
1117	This doesn't mean there will always be 3600 seconds in between triggers,	2137	This doesn't mean there will always be 3600 seconds in between triggers,
1118	but only that the the callback will be called when the system time shows a	2138	but only that the callback will be called when the system time shows a
1119	full hour (UTC), or more correctly, when the system time is evenly divisible	2139	full hour (UTC), or more correctly, when the system time is evenly divisible
1120	by 3600.	2140	by 3600.
1121		2141
1122	Another way to think about it (for the mathematically inclined) is that	2142	Another way to think about it (for the mathematically inclined) is that
1123	C<ev_periodic> will try to run the callback in this mode at the next possible	2143	C<ev_periodic> will try to run the callback in this mode at the next possible
1124	time where C<time = at (mod interval)>, regardless of any time jumps.	2144	time where C<time = offset (mod interval)>, regardless of any time jumps.
1125		2145
		2146	For numerical stability it is preferable that the C<offset> value is near
		2147	C<ev_now ()> (the current time), but there is no range requirement for
		2148	this value, and in fact is often specified as zero.
		2149
		2150	Note also that there is an upper limit to how often a timer can fire (CPU
		2151	speed for example), so if C<interval> is very small then timing stability
		2152	will of course deteriorate. Libev itself tries to be exact to be about one
		2153	millisecond (if the OS supports it and the machine is fast enough).
		2154
1126	=item * manual reschedule mode (reschedule_cb = callback)	2155	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1127		2156
1128	In this mode the values for C<interval> and C<at> are both being	2157	In this mode the values for C<interval> and C<offset> are both being
1129	ignored. Instead, each time the periodic watcher gets scheduled, the	2158	ignored. Instead, each time the periodic watcher gets scheduled, the
1130	reschedule callback will be called with the watcher as first, and the	2159	reschedule callback will be called with the watcher as first, and the
1131	current time as second argument.	2160	current time as second argument.
1132		2161
1133	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2162	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1134	ever, or make any event loop modifications>. If you need to stop it,	2163	or make ANY other event loop modifications whatsoever, unless explicitly
1135	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2164	allowed by documentation here>.
1136	starting a prepare watcher).
1137		2165
		2166	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2167	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2168	only event loop modification you are allowed to do).
		2169
1138	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2170	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1139	ev_tstamp now)>, e.g.:	2171	*w, ev_tstamp now)>, e.g.:
1140		2172
		2173	static ev_tstamp
1141	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2174	my_rescheduler (ev_periodic *w, ev_tstamp now)
1142	{	2175	{
1143	return now + 60.;	2176	return now + 60.;
1144	}	2177	}
1145		2178
1146	It must return the next time to trigger, based on the passed time value	2179	It must return the next time to trigger, based on the passed time value
1147	(that is, the lowest time value larger than to the second argument). It	2180	(that is, the lowest time value larger than to the second argument). It
1148	will usually be called just before the callback will be triggered, but	2181	will usually be called just before the callback will be triggered, but
1149	might be called at other times, too.	2182	might be called at other times, too.
1150		2183
1151	NOTE: I<< This callback must always return a time that is later than the	2184	NOTE: I<< This callback must always return a time that is higher than or
1152	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2185	equal to the passed C<now> value >>.
1153		2186
1154	This can be used to create very complex timers, such as a timer that	2187	This can be used to create very complex timers, such as a timer that
1155	triggers on each midnight, local time. To do this, you would calculate the	2188	triggers on "next midnight, local time". To do this, you would calculate the
1156	next midnight after C<now> and return the timestamp value for this. How	2189	next midnight after C<now> and return the timestamp value for this. How
1157	you do this is, again, up to you (but it is not trivial, which is the main	2190	you do this is, again, up to you (but it is not trivial, which is the main
1158	reason I omitted it as an example).	2191	reason I omitted it as an example).
1159		2192
1160	=back	2193	=back
…		…
1164	Simply stops and restarts the periodic watcher again. This is only useful	2197	Simply stops and restarts the periodic watcher again. This is only useful
1165	when you changed some parameters or the reschedule callback would return	2198	when you changed some parameters or the reschedule callback would return
1166	a different time than the last time it was called (e.g. in a crond like	2199	a different time than the last time it was called (e.g. in a crond like
1167	program when the crontabs have changed).	2200	program when the crontabs have changed).
1168		2201
		2202	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2203
		2204	When active, returns the absolute time that the watcher is supposed
		2205	to trigger next. This is not the same as the C<offset> argument to
		2206	C<ev_periodic_set>, but indeed works even in interval and manual
		2207	rescheduling modes.
		2208
		2209	=item ev_tstamp offset [read-write]
		2210
		2211	When repeating, this contains the offset value, otherwise this is the
		2212	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2213	although libev might modify this value for better numerical stability).
		2214
		2215	Can be modified any time, but changes only take effect when the periodic
		2216	timer fires or C<ev_periodic_again> is being called.
		2217
1169	=item ev_tstamp interval [read-write]	2218	=item ev_tstamp interval [read-write]
1170		2219
1171	The current interval value. Can be modified any time, but changes only	2220	The current interval value. Can be modified any time, but changes only
1172	take effect when the periodic timer fires or C<ev_periodic_again> is being	2221	take effect when the periodic timer fires or C<ev_periodic_again> is being
1173	called.	2222	called.
1174		2223
1175	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2224	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1176		2225
1177	The current reschedule callback, or C<0>, if this functionality is	2226	The current reschedule callback, or C<0>, if this functionality is
1178	switched off. Can be changed any time, but changes only take effect when	2227	switched off. Can be changed any time, but changes only take effect when
1179	the periodic timer fires or C<ev_periodic_again> is being called.	2228	the periodic timer fires or C<ev_periodic_again> is being called.
1180		2229
1181	=back	2230	=back
1182		2231
		2232	=head3 Examples
		2233
1183	Example: Call a callback every hour, or, more precisely, whenever the	2234	Example: Call a callback every hour, or, more precisely, whenever the
1184	system clock is divisible by 3600. The callback invocation times have	2235	system time is divisible by 3600. The callback invocation times have
1185	potentially a lot of jittering, but good long-term stability.	2236	potentially a lot of jitter, but good long-term stability.
1186		2237
1187	static void	2238	static void
1188	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2239	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1189	{	2240	{
1190	... its now a full hour (UTC, or TAI or whatever your clock follows)	2241	... its now a full hour (UTC, or TAI or whatever your clock follows)
1191	}	2242	}
1192		2243
1193	struct ev_periodic hourly_tick;	2244	ev_periodic hourly_tick;
1194	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2245	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1195	ev_periodic_start (loop, &hourly_tick);	2246	ev_periodic_start (loop, &hourly_tick);
1196		2247
1197	Example: The same as above, but use a reschedule callback to do it:	2248	Example: The same as above, but use a reschedule callback to do it:
1198		2249
1199	#include <math.h>	2250	#include <math.h>
1200		2251
1201	static ev_tstamp	2252	static ev_tstamp
1202	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2253	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1203	{	2254	{
1204	return fmod (now, 3600.) + 3600.;	2255	return now + (3600. - fmod (now, 3600.));
1205	}	2256	}
1206		2257
1207	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2258	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1208		2259
1209	Example: Call a callback every hour, starting now:	2260	Example: Call a callback every hour, starting now:
1210		2261
1211	struct ev_periodic hourly_tick;	2262	ev_periodic hourly_tick;
1212	ev_periodic_init (&hourly_tick, clock_cb,	2263	ev_periodic_init (&hourly_tick, clock_cb,
1213	fmod (ev_now (loop), 3600.), 3600., 0);	2264	fmod (ev_now (loop), 3600.), 3600., 0);
1214	ev_periodic_start (loop, &hourly_tick);	2265	ev_periodic_start (loop, &hourly_tick);
1215		2266
1216		2267
1217	=head2 C<ev_signal> - signal me when a signal gets signalled!	2268	=head2 C<ev_signal> - signal me when a signal gets signalled!
1218		2269
1219	Signal watchers will trigger an event when the process receives a specific	2270	Signal watchers will trigger an event when the process receives a specific
1220	signal one or more times. Even though signals are very asynchronous, libev	2271	signal one or more times. Even though signals are very asynchronous, libev
1221	will try it's best to deliver signals synchronously, i.e. as part of the	2272	will try its best to deliver signals synchronously, i.e. as part of the
1222	normal event processing, like any other event.	2273	normal event processing, like any other event.
1223		2274
		2275	If you want signals to be delivered truly asynchronously, just use
		2276	C<sigaction> as you would do without libev and forget about sharing
		2277	the signal. You can even use C<ev_async> from a signal handler to
		2278	synchronously wake up an event loop.
		2279
1224	You can configure as many watchers as you like per signal. Only when the	2280	You can configure as many watchers as you like for the same signal, but
		2281	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2282	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2283	C<SIGINT> in both the default loop and another loop at the same time. At
		2284	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2285
1225	first watcher gets started will libev actually register a signal watcher	2286	When the first watcher gets started will libev actually register something
1226	with the kernel (thus it coexists with your own signal handlers as long	2287	with the kernel (thus it coexists with your own signal handlers as long as
1227	as you don't register any with libev). Similarly, when the last signal	2288	you don't register any with libev for the same signal).
1228	watcher for a signal is stopped libev will reset the signal handler to	2289
1229	SIG_DFL (regardless of what it was set to before).	2290	If possible and supported, libev will install its handlers with
		2291	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2292	not be unduly interrupted. If you have a problem with system calls getting
		2293	interrupted by signals you can block all signals in an C<ev_check> watcher
		2294	and unblock them in an C<ev_prepare> watcher.
		2295
		2296	=head3 The special problem of inheritance over fork/execve/pthread_create
		2297
		2298	Both the signal mask (C<sigprocmask>) and the signal disposition
		2299	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2300	stopping it again), that is, libev might or might not block the signal,
		2301	and might or might not set or restore the installed signal handler.
		2302
		2303	While this does not matter for the signal disposition (libev never
		2304	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2305	C<execve>), this matters for the signal mask: many programs do not expect
		2306	certain signals to be blocked.
		2307
		2308	This means that before calling C<exec> (from the child) you should reset
		2309	the signal mask to whatever "default" you expect (all clear is a good
		2310	choice usually).
		2311
		2312	The simplest way to ensure that the signal mask is reset in the child is
		2313	to install a fork handler with C<pthread_atfork> that resets it. That will
		2314	catch fork calls done by libraries (such as the libc) as well.
		2315
		2316	In current versions of libev, the signal will not be blocked indefinitely
		2317	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2318	the window of opportunity for problems, it will not go away, as libev
		2319	I<has> to modify the signal mask, at least temporarily.
		2320
		2321	So I can't stress this enough: I<If you do not reset your signal mask when
		2322	you expect it to be empty, you have a race condition in your code>. This
		2323	is not a libev-specific thing, this is true for most event libraries.
		2324
		2325	=head3 Watcher-Specific Functions and Data Members
1230		2326
1231	=over 4	2327	=over 4
1232		2328
1233	=item ev_signal_init (ev_signal *, callback, int signum)	2329	=item ev_signal_init (ev_signal *, callback, int signum)
1234		2330
…		…
1241		2337
1242	The signal the watcher watches out for.	2338	The signal the watcher watches out for.
1243		2339
1244	=back	2340	=back
1245		2341
		2342	=head3 Examples
		2343
		2344	Example: Try to exit cleanly on SIGINT.
		2345
		2346	static void
		2347	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2348	{
		2349	ev_break (loop, EVBREAK_ALL);
		2350	}
		2351
		2352	ev_signal signal_watcher;
		2353	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2354	ev_signal_start (loop, &signal_watcher);
		2355
1246		2356
1247	=head2 C<ev_child> - watch out for process status changes	2357	=head2 C<ev_child> - watch out for process status changes
1248		2358
1249	Child watchers trigger when your process receives a SIGCHLD in response to	2359	Child watchers trigger when your process receives a SIGCHLD in response to
1250	some child status changes (most typically when a child of yours dies).	2360	some child status changes (most typically when a child of yours dies or
		2361	exits). It is permissible to install a child watcher I<after> the child
		2362	has been forked (which implies it might have already exited), as long
		2363	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2364	forking and then immediately registering a watcher for the child is fine,
		2365	but forking and registering a watcher a few event loop iterations later or
		2366	in the next callback invocation is not.
		2367
		2368	Only the default event loop is capable of handling signals, and therefore
		2369	you can only register child watchers in the default event loop.
		2370
		2371	Due to some design glitches inside libev, child watchers will always be
		2372	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2373	libev)
		2374
		2375	=head3 Process Interaction
		2376
		2377	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2378	initialised. This is necessary to guarantee proper behaviour even if the
		2379	first child watcher is started after the child exits. The occurrence
		2380	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2381	synchronously as part of the event loop processing. Libev always reaps all
		2382	children, even ones not watched.
		2383
		2384	=head3 Overriding the Built-In Processing
		2385
		2386	Libev offers no special support for overriding the built-in child
		2387	processing, but if your application collides with libev's default child
		2388	handler, you can override it easily by installing your own handler for
		2389	C<SIGCHLD> after initialising the default loop, and making sure the
		2390	default loop never gets destroyed. You are encouraged, however, to use an
		2391	event-based approach to child reaping and thus use libev's support for
		2392	that, so other libev users can use C<ev_child> watchers freely.
		2393
		2394	=head3 Stopping the Child Watcher
		2395
		2396	Currently, the child watcher never gets stopped, even when the
		2397	child terminates, so normally one needs to stop the watcher in the
		2398	callback. Future versions of libev might stop the watcher automatically
		2399	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2400	problem).
		2401
		2402	=head3 Watcher-Specific Functions and Data Members
1251		2403
1252	=over 4	2404	=over 4
1253		2405
1254	=item ev_child_init (ev_child *, callback, int pid)	2406	=item ev_child_init (ev_child *, callback, int pid, int trace)
1255		2407
1256	=item ev_child_set (ev_child *, int pid)	2408	=item ev_child_set (ev_child *, int pid, int trace)
1257		2409
1258	Configures the watcher to wait for status changes of process C<pid> (or	2410	Configures the watcher to wait for status changes of process C<pid> (or
1259	I<any> process if C<pid> is specified as C<0>). The callback can look	2411	I<any> process if C<pid> is specified as C<0>). The callback can look
1260	at the C<rstatus> member of the C<ev_child> watcher structure to see	2412	at the C<rstatus> member of the C<ev_child> watcher structure to see
1261	the status word (use the macros from C<sys/wait.h> and see your systems	2413	the status word (use the macros from C<sys/wait.h> and see your systems
1262	C<waitpid> documentation). The C<rpid> member contains the pid of the	2414	C<waitpid> documentation). The C<rpid> member contains the pid of the
1263	process causing the status change.	2415	process causing the status change. C<trace> must be either C<0> (only
		2416	activate the watcher when the process terminates) or C<1> (additionally
		2417	activate the watcher when the process is stopped or continued).
1264		2418
1265	=item int pid [read-only]	2419	=item int pid [read-only]
1266		2420
1267	The process id this watcher watches out for, or C<0>, meaning any process id.	2421	The process id this watcher watches out for, or C<0>, meaning any process id.
1268		2422
…		…
1275	The process exit/trace status caused by C<rpid> (see your systems	2429	The process exit/trace status caused by C<rpid> (see your systems
1276	C<waitpid> and C<sys/wait.h> documentation for details).	2430	C<waitpid> and C<sys/wait.h> documentation for details).
1277		2431
1278	=back	2432	=back
1279		2433
1280	Example: Try to exit cleanly on SIGINT and SIGTERM.	2434	=head3 Examples
1281		2435
		2436	Example: C<fork()> a new process and install a child handler to wait for
		2437	its completion.
		2438
		2439	ev_child cw;
		2440
1282	static void	2441	static void
1283	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2442	child_cb (EV_P_ ev_child *w, int revents)
1284	{	2443	{
1285	ev_unloop (loop, EVUNLOOP_ALL);	2444	ev_child_stop (EV_A_ w);
		2445	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1286	}	2446	}
1287		2447
1288	struct ev_signal signal_watcher;	2448	pid_t pid = fork ();
1289	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2449
1290	ev_signal_start (loop, &sigint_cb);	2450	if (pid < 0)
		2451	// error
		2452	else if (pid == 0)
		2453	{
		2454	// the forked child executes here
		2455	exit (1);
		2456	}
		2457	else
		2458	{
		2459	ev_child_init (&cw, child_cb, pid, 0);
		2460	ev_child_start (EV_DEFAULT_ &cw);
		2461	}
1291		2462
1292		2463
1293	=head2 C<ev_stat> - did the file attributes just change?	2464	=head2 C<ev_stat> - did the file attributes just change?
1294		2465
1295	This watches a filesystem path for attribute changes. That is, it calls	2466	This watches a file system path for attribute changes. That is, it calls
1296	C<stat> regularly (or when the OS says it changed) and sees if it changed	2467	C<stat> on that path in regular intervals (or when the OS says it changed)
1297	compared to the last time, invoking the callback if it did.	2468	and sees if it changed compared to the last time, invoking the callback if
		2469	it did.
1298		2470
1299	The path does not need to exist: changing from "path exists" to "path does	2471	The path does not need to exist: changing from "path exists" to "path does
1300	not exist" is a status change like any other. The condition "path does	2472	not exist" is a status change like any other. The condition "path does not
1301	not exist" is signified by the C<st_nlink> field being zero (which is	2473	exist" (or more correctly "path cannot be stat'ed") is signified by the
1302	otherwise always forced to be at least one) and all the other fields of	2474	C<st_nlink> field being zero (which is otherwise always forced to be at
1303	the stat buffer having unspecified contents.	2475	least one) and all the other fields of the stat buffer having unspecified
		2476	contents.
1304		2477
1305	The path I<should> be absolute and I<must not> end in a slash. If it is	2478	The path I<must not> end in a slash or contain special components such as
		2479	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1306	relative and your working directory changes, the behaviour is undefined.	2480	your working directory changes, then the behaviour is undefined.
1307		2481
1308	Since there is no standard to do this, the portable implementation simply	2482	Since there is no portable change notification interface available, the
1309	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2483	portable implementation simply calls C<stat(2)> regularly on the path
1310	can specify a recommended polling interval for this case. If you specify	2484	to see if it changed somehow. You can specify a recommended polling
1311	a polling interval of C<0> (highly recommended!) then a I<suitable,	2485	interval for this case. If you specify a polling interval of C<0> (highly
1312	unspecified default> value will be used (which you can expect to be around	2486	recommended!) then a I<suitable, unspecified default> value will be used
1313	five seconds, although this might change dynamically). Libev will also	2487	(which you can expect to be around five seconds, although this might
1314	impose a minimum interval which is currently around C<0.1>, but thats	2488	change dynamically). Libev will also impose a minimum interval which is
1315	usually overkill.	2489	currently around C<0.1>, but that's usually overkill.
1316		2490
1317	This watcher type is not meant for massive numbers of stat watchers,	2491	This watcher type is not meant for massive numbers of stat watchers,
1318	as even with OS-supported change notifications, this can be	2492	as even with OS-supported change notifications, this can be
1319	resource-intensive.	2493	resource-intensive.
1320		2494
1321	At the time of this writing, only the Linux inotify interface is	2495	At the time of this writing, the only OS-specific interface implemented
1322	implemented (implementing kqueue support is left as an exercise for the	2496	is the Linux inotify interface (implementing kqueue support is left as an
1323	reader). Inotify will be used to give hints only and should not change the	2497	exercise for the reader. Note, however, that the author sees no way of
1324	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2498	implementing C<ev_stat> semantics with kqueue, except as a hint).
1325	to fall back to regular polling again even with inotify, but changes are	2499
1326	usually detected immediately, and if the file exists there will be no	2500	=head3 ABI Issues (Largefile Support)
1327	polling.	2501
		2502	Libev by default (unless the user overrides this) uses the default
		2503	compilation environment, which means that on systems with large file
		2504	support disabled by default, you get the 32 bit version of the stat
		2505	structure. When using the library from programs that change the ABI to
		2506	use 64 bit file offsets the programs will fail. In that case you have to
		2507	compile libev with the same flags to get binary compatibility. This is
		2508	obviously the case with any flags that change the ABI, but the problem is
		2509	most noticeably displayed with ev_stat and large file support.
		2510
		2511	The solution for this is to lobby your distribution maker to make large
		2512	file interfaces available by default (as e.g. FreeBSD does) and not
		2513	optional. Libev cannot simply switch on large file support because it has
		2514	to exchange stat structures with application programs compiled using the
		2515	default compilation environment.
		2516
		2517	=head3 Inotify and Kqueue
		2518
		2519	When C<inotify (7)> support has been compiled into libev and present at
		2520	runtime, it will be used to speed up change detection where possible. The
		2521	inotify descriptor will be created lazily when the first C<ev_stat>
		2522	watcher is being started.
		2523
		2524	Inotify presence does not change the semantics of C<ev_stat> watchers
		2525	except that changes might be detected earlier, and in some cases, to avoid
		2526	making regular C<stat> calls. Even in the presence of inotify support
		2527	there are many cases where libev has to resort to regular C<stat> polling,
		2528	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2529	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2530	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2531	xfs are fully working) libev usually gets away without polling.
		2532
		2533	There is no support for kqueue, as apparently it cannot be used to
		2534	implement this functionality, due to the requirement of having a file
		2535	descriptor open on the object at all times, and detecting renames, unlinks
		2536	etc. is difficult.
		2537
		2538	=head3 C<stat ()> is a synchronous operation
		2539
		2540	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2541	the process. The exception are C<ev_stat> watchers - those call C<stat
		2542	()>, which is a synchronous operation.
		2543
		2544	For local paths, this usually doesn't matter: unless the system is very
		2545	busy or the intervals between stat's are large, a stat call will be fast,
		2546	as the path data is usually in memory already (except when starting the
		2547	watcher).
		2548
		2549	For networked file systems, calling C<stat ()> can block an indefinite
		2550	time due to network issues, and even under good conditions, a stat call
		2551	often takes multiple milliseconds.
		2552
		2553	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2554	paths, although this is fully supported by libev.
		2555
		2556	=head3 The special problem of stat time resolution
		2557
		2558	The C<stat ()> system call only supports full-second resolution portably,
		2559	and even on systems where the resolution is higher, most file systems
		2560	still only support whole seconds.
		2561
		2562	That means that, if the time is the only thing that changes, you can
		2563	easily miss updates: on the first update, C<ev_stat> detects a change and
		2564	calls your callback, which does something. When there is another update
		2565	within the same second, C<ev_stat> will be unable to detect unless the
		2566	stat data does change in other ways (e.g. file size).
		2567
		2568	The solution to this is to delay acting on a change for slightly more
		2569	than a second (or till slightly after the next full second boundary), using
		2570	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2571	ev_timer_again (loop, w)>).
		2572
		2573	The C<.02> offset is added to work around small timing inconsistencies
		2574	of some operating systems (where the second counter of the current time
		2575	might be be delayed. One such system is the Linux kernel, where a call to
		2576	C<gettimeofday> might return a timestamp with a full second later than
		2577	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2578	update file times then there will be a small window where the kernel uses
		2579	the previous second to update file times but libev might already execute
		2580	the timer callback).
		2581
		2582	=head3 Watcher-Specific Functions and Data Members
1328		2583
1329	=over 4	2584	=over 4
1330		2585
1331	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2586	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1332		2587
…		…
1336	C<path>. The C<interval> is a hint on how quickly a change is expected to	2591	C<path>. The C<interval> is a hint on how quickly a change is expected to
1337	be detected and should normally be specified as C<0> to let libev choose	2592	be detected and should normally be specified as C<0> to let libev choose
1338	a suitable value. The memory pointed to by C<path> must point to the same	2593	a suitable value. The memory pointed to by C<path> must point to the same
1339	path for as long as the watcher is active.	2594	path for as long as the watcher is active.
1340		2595
1341	The callback will be receive C<EV_STAT> when a change was detected,	2596	The callback will receive an C<EV_STAT> event when a change was detected,
1342	relative to the attributes at the time the watcher was started (or the	2597	relative to the attributes at the time the watcher was started (or the
1343	last change was detected).	2598	last change was detected).
1344		2599
1345	=item ev_stat_stat (ev_stat *)	2600	=item ev_stat_stat (loop, ev_stat *)
1346		2601
1347	Updates the stat buffer immediately with new values. If you change the	2602	Updates the stat buffer immediately with new values. If you change the
1348	watched path in your callback, you could call this fucntion to avoid	2603	watched path in your callback, you could call this function to avoid
1349	detecting this change (while introducing a race condition). Can also be	2604	detecting this change (while introducing a race condition if you are not
1350	useful simply to find out the new values.	2605	the only one changing the path). Can also be useful simply to find out the
		2606	new values.
1351		2607
1352	=item ev_statdata attr [read-only]	2608	=item ev_statdata attr [read-only]
1353		2609
1354	The most-recently detected attributes of the file. Although the type is of	2610	The most-recently detected attributes of the file. Although the type is
1355	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2611	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1356	suitable for your system. If the C<st_nlink> member is C<0>, then there	2612	suitable for your system, but you can only rely on the POSIX-standardised
		2613	members to be present. If the C<st_nlink> member is C<0>, then there was
1357	was some error while C<stat>ing the file.	2614	some error while C<stat>ing the file.
1358		2615
1359	=item ev_statdata prev [read-only]	2616	=item ev_statdata prev [read-only]
1360		2617
1361	The previous attributes of the file. The callback gets invoked whenever	2618	The previous attributes of the file. The callback gets invoked whenever
1362	C<prev> != C<attr>.	2619	C<prev> != C<attr>, or, more precisely, one or more of these members
		2620	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2621	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1363		2622
1364	=item ev_tstamp interval [read-only]	2623	=item ev_tstamp interval [read-only]
1365		2624
1366	The specified interval.	2625	The specified interval.
1367		2626
1368	=item const char *path [read-only]	2627	=item const char *path [read-only]
1369		2628
1370	The filesystem path that is being watched.	2629	The file system path that is being watched.
1371		2630
1372	=back	2631	=back
1373		2632
		2633	=head3 Examples
		2634
1374	Example: Watch C</etc/passwd> for attribute changes.	2635	Example: Watch C</etc/passwd> for attribute changes.
1375		2636
1376	static void	2637	static void
1377	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2638	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1378	{	2639	{
1379	/* /etc/passwd changed in some way */	2640	/* /etc/passwd changed in some way */
1380	if (w->attr.st_nlink)	2641	if (w->attr.st_nlink)
1381	{	2642	{
1382	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2643	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1383	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2644	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1384	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2645	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1385	}	2646	}
1386	else	2647	else
1387	/* you shalt not abuse printf for puts */	2648	/* you shalt not abuse printf for puts */
1388	puts ("wow, /etc/passwd is not there, expect problems. "	2649	puts ("wow, /etc/passwd is not there, expect problems. "
1389	"if this is windows, they already arrived\n");	2650	"if this is windows, they already arrived\n");
1390	}	2651	}
1391		2652
1392	...	2653	...
1393	ev_stat passwd;	2654	ev_stat passwd;
1394		2655
1395	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2656	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1396	ev_stat_start (loop, &passwd);	2657	ev_stat_start (loop, &passwd);
		2658
		2659	Example: Like above, but additionally use a one-second delay so we do not
		2660	miss updates (however, frequent updates will delay processing, too, so
		2661	one might do the work both on C<ev_stat> callback invocation I<and> on
		2662	C<ev_timer> callback invocation).
		2663
		2664	static ev_stat passwd;
		2665	static ev_timer timer;
		2666
		2667	static void
		2668	timer_cb (EV_P_ ev_timer *w, int revents)
		2669	{
		2670	ev_timer_stop (EV_A_ w);
		2671
		2672	/* now it's one second after the most recent passwd change */
		2673	}
		2674
		2675	static void
		2676	stat_cb (EV_P_ ev_stat *w, int revents)
		2677	{
		2678	/* reset the one-second timer */
		2679	ev_timer_again (EV_A_ &timer);
		2680	}
		2681
		2682	...
		2683	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2684	ev_stat_start (loop, &passwd);
		2685	ev_timer_init (&timer, timer_cb, 0., 1.02);
1397		2686
1398		2687
1399	=head2 C<ev_idle> - when you've got nothing better to do...	2688	=head2 C<ev_idle> - when you've got nothing better to do...
1400		2689
1401	Idle watchers trigger events when no other events of the same or higher	2690	Idle watchers trigger events when no other events of the same or higher
1402	priority are pending (prepare, check and other idle watchers do not	2691	priority are pending (prepare, check and other idle watchers do not count
1403	count).	2692	as receiving "events").
1404		2693
1405	That is, as long as your process is busy handling sockets or timeouts	2694	That is, as long as your process is busy handling sockets or timeouts
1406	(or even signals, imagine) of the same or higher priority it will not be	2695	(or even signals, imagine) of the same or higher priority it will not be
1407	triggered. But when your process is idle (or only lower-priority watchers	2696	triggered. But when your process is idle (or only lower-priority watchers
1408	are pending), the idle watchers are being called once per event loop	2697	are pending), the idle watchers are being called once per event loop
…		…
1415	Apart from keeping your process non-blocking (which is a useful	2704	Apart from keeping your process non-blocking (which is a useful
1416	effect on its own sometimes), idle watchers are a good place to do	2705	effect on its own sometimes), idle watchers are a good place to do
1417	"pseudo-background processing", or delay processing stuff to after the	2706	"pseudo-background processing", or delay processing stuff to after the
1418	event loop has handled all outstanding events.	2707	event loop has handled all outstanding events.
1419		2708
		2709	=head3 Watcher-Specific Functions and Data Members
		2710
1420	=over 4	2711	=over 4
1421		2712
1422	=item ev_idle_init (ev_signal *, callback)	2713	=item ev_idle_init (ev_idle *, callback)
1423		2714
1424	Initialises and configures the idle watcher - it has no parameters of any	2715	Initialises and configures the idle watcher - it has no parameters of any
1425	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2716	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1426	believe me.	2717	believe me.
1427		2718
1428	=back	2719	=back
1429		2720
		2721	=head3 Examples
		2722
1430	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2723	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1431	callback, free it. Also, use no error checking, as usual.	2724	callback, free it. Also, use no error checking, as usual.
1432		2725
1433	static void	2726	static void
1434	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2727	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1435	{	2728	{
1436	free (w);	2729	free (w);
1437	// now do something you wanted to do when the program has	2730	// now do something you wanted to do when the program has
1438	// no longer asnything immediate to do.	2731	// no longer anything immediate to do.
1439	}	2732	}
1440		2733
1441	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2734	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1442	ev_idle_init (idle_watcher, idle_cb);	2735	ev_idle_init (idle_watcher, idle_cb);
1443	ev_idle_start (loop, idle_cb);	2736	ev_idle_start (loop, idle_watcher);
1444		2737
1445		2738
1446	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2739	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1447		2740
1448	Prepare and check watchers are usually (but not always) used in tandem:	2741	Prepare and check watchers are usually (but not always) used in pairs:
1449	prepare watchers get invoked before the process blocks and check watchers	2742	prepare watchers get invoked before the process blocks and check watchers
1450	afterwards.	2743	afterwards.
1451		2744
1452	You I<must not> call C<ev_loop> or similar functions that enter	2745	You I<must not> call C<ev_run> or similar functions that enter
1453	the current event loop from either C<ev_prepare> or C<ev_check>	2746	the current event loop from either C<ev_prepare> or C<ev_check>
1454	watchers. Other loops than the current one are fine, however. The	2747	watchers. Other loops than the current one are fine, however. The
1455	rationale behind this is that you do not need to check for recursion in	2748	rationale behind this is that you do not need to check for recursion in
1456	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2749	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1457	C<ev_check> so if you have one watcher of each kind they will always be	2750	C<ev_check> so if you have one watcher of each kind they will always be
1458	called in pairs bracketing the blocking call.	2751	called in pairs bracketing the blocking call.
1459		2752
1460	Their main purpose is to integrate other event mechanisms into libev and	2753	Their main purpose is to integrate other event mechanisms into libev and
1461	their use is somewhat advanced. This could be used, for example, to track	2754	their use is somewhat advanced. They could be used, for example, to track
1462	variable changes, implement your own watchers, integrate net-snmp or a	2755	variable changes, implement your own watchers, integrate net-snmp or a
1463	coroutine library and lots more. They are also occasionally useful if	2756	coroutine library and lots more. They are also occasionally useful if
1464	you cache some data and want to flush it before blocking (for example,	2757	you cache some data and want to flush it before blocking (for example,
1465	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2758	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1466	watcher).	2759	watcher).
1467		2760
1468	This is done by examining in each prepare call which file descriptors need	2761	This is done by examining in each prepare call which file descriptors
1469	to be watched by the other library, registering C<ev_io> watchers for	2762	need to be watched by the other library, registering C<ev_io> watchers
1470	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2763	for them and starting an C<ev_timer> watcher for any timeouts (many
1471	provide just this functionality). Then, in the check watcher you check for	2764	libraries provide exactly this functionality). Then, in the check watcher,
1472	any events that occured (by checking the pending status of all watchers	2765	you check for any events that occurred (by checking the pending status
1473	and stopping them) and call back into the library. The I/O and timer	2766	of all watchers and stopping them) and call back into the library. The
1474	callbacks will never actually be called (but must be valid nevertheless,	2767	I/O and timer callbacks will never actually be called (but must be valid
1475	because you never know, you know?).	2768	nevertheless, because you never know, you know?).
1476		2769
1477	As another example, the Perl Coro module uses these hooks to integrate	2770	As another example, the Perl Coro module uses these hooks to integrate
1478	coroutines into libev programs, by yielding to other active coroutines	2771	coroutines into libev programs, by yielding to other active coroutines
1479	during each prepare and only letting the process block if no coroutines	2772	during each prepare and only letting the process block if no coroutines
1480	are ready to run (it's actually more complicated: it only runs coroutines	2773	are ready to run (it's actually more complicated: it only runs coroutines
1481	with priority higher than or equal to the event loop and one coroutine	2774	with priority higher than or equal to the event loop and one coroutine
1482	of lower priority, but only once, using idle watchers to keep the event	2775	of lower priority, but only once, using idle watchers to keep the event
1483	loop from blocking if lower-priority coroutines are active, thus mapping	2776	loop from blocking if lower-priority coroutines are active, thus mapping
1484	low-priority coroutines to idle/background tasks).	2777	low-priority coroutines to idle/background tasks).
1485		2778
		2779	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2780	priority, to ensure that they are being run before any other watchers
		2781	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2782
		2783	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2784	activate ("feed") events into libev. While libev fully supports this, they
		2785	might get executed before other C<ev_check> watchers did their job. As
		2786	C<ev_check> watchers are often used to embed other (non-libev) event
		2787	loops those other event loops might be in an unusable state until their
		2788	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2789	others).
		2790
		2791	=head3 Watcher-Specific Functions and Data Members
		2792
1486	=over 4	2793	=over 4
1487		2794
1488	=item ev_prepare_init (ev_prepare *, callback)	2795	=item ev_prepare_init (ev_prepare *, callback)
1489		2796
1490	=item ev_check_init (ev_check *, callback)	2797	=item ev_check_init (ev_check *, callback)
1491		2798
1492	Initialises and configures the prepare or check watcher - they have no	2799	Initialises and configures the prepare or check watcher - they have no
1493	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2800	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1494	macros, but using them is utterly, utterly and completely pointless.	2801	macros, but using them is utterly, utterly, utterly and completely
		2802	pointless.
1495		2803
1496	=back	2804	=back
		2805
		2806	=head3 Examples
1497		2807
1498	There are a number of principal ways to embed other event loops or modules	2808	There are a number of principal ways to embed other event loops or modules
1499	into libev. Here are some ideas on how to include libadns into libev	2809	into libev. Here are some ideas on how to include libadns into libev
1500	(there is a Perl module named C<EV::ADNS> that does this, which you could	2810	(there is a Perl module named C<EV::ADNS> that does this, which you could
1501	use for an actually working example. Another Perl module named C<EV::Glib>	2811	use as a working example. Another Perl module named C<EV::Glib> embeds a
1502	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2812	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1503	into the Glib event loop).	2813	Glib event loop).
1504		2814
1505	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2815	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1506	and in a check watcher, destroy them and call into libadns. What follows	2816	and in a check watcher, destroy them and call into libadns. What follows
1507	is pseudo-code only of course. This requires you to either use a low	2817	is pseudo-code only of course. This requires you to either use a low
1508	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2818	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1509	the callbacks for the IO/timeout watchers might not have been called yet.	2819	the callbacks for the IO/timeout watchers might not have been called yet.
1510		2820
1511	static ev_io iow [nfd];	2821	static ev_io iow [nfd];
1512	static ev_timer tw;	2822	static ev_timer tw;
1513		2823
1514	static void	2824	static void
1515	io_cb (ev_loop *loop, ev_io *w, int revents)	2825	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1516	{	2826	{
1517	}	2827	}
1518		2828
1519	// create io watchers for each fd and a timer before blocking	2829	// create io watchers for each fd and a timer before blocking
1520	static void	2830	static void
1521	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2831	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1522	{	2832	{
1523	int timeout = 3600000;	2833	int timeout = 3600000;
1524	struct pollfd fds [nfd];	2834	struct pollfd fds [nfd];
1525	// actual code will need to loop here and realloc etc.	2835	// actual code will need to loop here and realloc etc.
1526	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2836	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1527		2837
1528	/* the callback is illegal, but won't be called as we stop during check */	2838	/* the callback is illegal, but won't be called as we stop during check */
1529	ev_timer_init (&tw, 0, timeout * 1e-3);	2839	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1530	ev_timer_start (loop, &tw);	2840	ev_timer_start (loop, &tw);
1531		2841
1532	// create one ev_io per pollfd	2842	// create one ev_io per pollfd
1533	for (int i = 0; i < nfd; ++i)	2843	for (int i = 0; i < nfd; ++i)
1534	{	2844	{
1535	ev_io_init (iow + i, io_cb, fds [i].fd,	2845	ev_io_init (iow + i, io_cb, fds [i].fd,
1536	((fds [i].events & POLLIN ? EV_READ : 0)	2846	((fds [i].events & POLLIN ? EV_READ : 0)
1537	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2847	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1538		2848
1539	fds [i].revents = 0;	2849	fds [i].revents = 0;
1540	ev_io_start (loop, iow + i);	2850	ev_io_start (loop, iow + i);
1541	}	2851	}
1542	}	2852	}
1543		2853
1544	// stop all watchers after blocking	2854	// stop all watchers after blocking
1545	static void	2855	static void
1546	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2856	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1547	{	2857	{
1548	ev_timer_stop (loop, &tw);	2858	ev_timer_stop (loop, &tw);
1549		2859
1550	for (int i = 0; i < nfd; ++i)	2860	for (int i = 0; i < nfd; ++i)
1551	{	2861	{
1552	// set the relevant poll flags	2862	// set the relevant poll flags
1553	// could also call adns_processreadable etc. here	2863	// could also call adns_processreadable etc. here
1554	struct pollfd *fd = fds + i;	2864	struct pollfd *fd = fds + i;
1555	int revents = ev_clear_pending (iow + i);	2865	int revents = ev_clear_pending (iow + i);
1556	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2866	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1557	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2867	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1558		2868
1559	// now stop the watcher	2869	// now stop the watcher
1560	ev_io_stop (loop, iow + i);	2870	ev_io_stop (loop, iow + i);
1561	}	2871	}
1562		2872
1563	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2873	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1564	}	2874	}
1565		2875
1566	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2876	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1567	in the prepare watcher and would dispose of the check watcher.	2877	in the prepare watcher and would dispose of the check watcher.
1568		2878
1569	Method 3: If the module to be embedded supports explicit event	2879	Method 3: If the module to be embedded supports explicit event
1570	notification (adns does), you can also make use of the actual watcher	2880	notification (libadns does), you can also make use of the actual watcher
1571	callbacks, and only destroy/create the watchers in the prepare watcher.	2881	callbacks, and only destroy/create the watchers in the prepare watcher.
1572		2882
1573	static void	2883	static void
1574	timer_cb (EV_P_ ev_timer *w, int revents)	2884	timer_cb (EV_P_ ev_timer *w, int revents)
1575	{	2885	{
1576	adns_state ads = (adns_state)w->data;	2886	adns_state ads = (adns_state)w->data;
1577	update_now (EV_A);	2887	update_now (EV_A);
1578		2888
1579	adns_processtimeouts (ads, &tv_now);	2889	adns_processtimeouts (ads, &tv_now);
1580	}	2890	}
1581		2891
1582	static void	2892	static void
1583	io_cb (EV_P_ ev_io *w, int revents)	2893	io_cb (EV_P_ ev_io *w, int revents)
1584	{	2894	{
1585	adns_state ads = (adns_state)w->data;	2895	adns_state ads = (adns_state)w->data;
1586	update_now (EV_A);	2896	update_now (EV_A);
1587		2897
1588	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2898	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1589	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2899	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1590	}	2900	}
1591		2901
1592	// do not ever call adns_afterpoll	2902	// do not ever call adns_afterpoll
1593		2903
1594	Method 4: Do not use a prepare or check watcher because the module you	2904	Method 4: Do not use a prepare or check watcher because the module you
1595	want to embed is too inflexible to support it. Instead, youc na override	2905	want to embed is not flexible enough to support it. Instead, you can
1596	their poll function. The drawback with this solution is that the main	2906	override their poll function. The drawback with this solution is that the
1597	loop is now no longer controllable by EV. The C<Glib::EV> module does	2907	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1598	this.	2908	this approach, effectively embedding EV as a client into the horrible
		2909	libglib event loop.
1599		2910
1600	static gint	2911	static gint
1601	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2912	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1602	{	2913	{
1603	int got_events = 0;	2914	int got_events = 0;
1604		2915
1605	for (n = 0; n < nfds; ++n)	2916	for (n = 0; n < nfds; ++n)
1606	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2917	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1607		2918
1608	if (timeout >= 0)	2919	if (timeout >= 0)
1609	// create/start timer	2920	// create/start timer
1610		2921
1611	// poll	2922	// poll
1612	ev_loop (EV_A_ 0);	2923	ev_run (EV_A_ 0);
1613		2924
1614	// stop timer again	2925	// stop timer again
1615	if (timeout >= 0)	2926	if (timeout >= 0)
1616	ev_timer_stop (EV_A_ &to);	2927	ev_timer_stop (EV_A_ &to);
1617		2928
1618	// stop io watchers again - their callbacks should have set	2929	// stop io watchers again - their callbacks should have set
1619	for (n = 0; n < nfds; ++n)	2930	for (n = 0; n < nfds; ++n)
1620	ev_io_stop (EV_A_ iow [n]);	2931	ev_io_stop (EV_A_ iow [n]);
1621		2932
1622	return got_events;	2933	return got_events;
1623	}	2934	}
1624		2935
1625		2936
1626	=head2 C<ev_embed> - when one backend isn't enough...	2937	=head2 C<ev_embed> - when one backend isn't enough...
1627		2938
1628	This is a rather advanced watcher type that lets you embed one event loop	2939	This is a rather advanced watcher type that lets you embed one event loop
…		…
1634	prioritise I/O.	2945	prioritise I/O.
1635		2946
1636	As an example for a bug workaround, the kqueue backend might only support	2947	As an example for a bug workaround, the kqueue backend might only support
1637	sockets on some platform, so it is unusable as generic backend, but you	2948	sockets on some platform, so it is unusable as generic backend, but you
1638	still want to make use of it because you have many sockets and it scales	2949	still want to make use of it because you have many sockets and it scales
1639	so nicely. In this case, you would create a kqueue-based loop and embed it	2950	so nicely. In this case, you would create a kqueue-based loop and embed
1640	into your default loop (which might use e.g. poll). Overall operation will	2951	it into your default loop (which might use e.g. poll). Overall operation
1641	be a bit slower because first libev has to poll and then call kevent, but	2952	will be a bit slower because first libev has to call C<poll> and then
1642	at least you can use both at what they are best.	2953	C<kevent>, but at least you can use both mechanisms for what they are
		2954	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1643		2955
1644	As for prioritising I/O: rarely you have the case where some fds have	2956	As for prioritising I/O: under rare circumstances you have the case where
1645	to be watched and handled very quickly (with low latency), and even	2957	some fds have to be watched and handled very quickly (with low latency),
1646	priorities and idle watchers might have too much overhead. In this case	2958	and even priorities and idle watchers might have too much overhead. In
1647	you would put all the high priority stuff in one loop and all the rest in	2959	this case you would put all the high priority stuff in one loop and all
1648	a second one, and embed the second one in the first.	2960	the rest in a second one, and embed the second one in the first.
1649		2961
1650	As long as the watcher is active, the callback will be invoked every time	2962	As long as the watcher is active, the callback will be invoked every
1651	there might be events pending in the embedded loop. The callback must then	2963	time there might be events pending in the embedded loop. The callback
1652	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2964	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1653	their callbacks (you could also start an idle watcher to give the embedded	2965	sweep and invoke their callbacks (the callback doesn't need to invoke the
1654	loop strictly lower priority for example). You can also set the callback	2966	C<ev_embed_sweep> function directly, it could also start an idle watcher
1655	to C<0>, in which case the embed watcher will automatically execute the	2967	to give the embedded loop strictly lower priority for example).
1656	embedded loop sweep.
1657		2968
1658	As long as the watcher is started it will automatically handle events. The	2969	You can also set the callback to C<0>, in which case the embed watcher
1659	callback will be invoked whenever some events have been handled. You can	2970	will automatically execute the embedded loop sweep whenever necessary.
1660	set the callback to C<0> to avoid having to specify one if you are not
1661	interested in that.
1662		2971
1663	Also, there have not currently been made special provisions for forking:	2972	Fork detection will be handled transparently while the C<ev_embed> watcher
1664	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2973	is active, i.e., the embedded loop will automatically be forked when the
1665	but you will also have to stop and restart any C<ev_embed> watchers	2974	embedding loop forks. In other cases, the user is responsible for calling
1666	yourself.	2975	C<ev_loop_fork> on the embedded loop.
1667		2976
1668	Unfortunately, not all backends are embeddable, only the ones returned by	2977	Unfortunately, not all backends are embeddable: only the ones returned by
1669	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2978	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1670	portable one.	2979	portable one.
1671		2980
1672	So when you want to use this feature you will always have to be prepared	2981	So when you want to use this feature you will always have to be prepared
1673	that you cannot get an embeddable loop. The recommended way to get around	2982	that you cannot get an embeddable loop. The recommended way to get around
1674	this is to have a separate variables for your embeddable loop, try to	2983	this is to have a separate variables for your embeddable loop, try to
1675	create it, and if that fails, use the normal loop for everything:	2984	create it, and if that fails, use the normal loop for everything.
1676		2985
1677	struct ev_loop *loop_hi = ev_default_init (0);	2986	=head3 C<ev_embed> and fork
1678	struct ev_loop *loop_lo = 0;
1679	struct ev_embed embed;
1680
1681	// see if there is a chance of getting one that works
1682	// (remember that a flags value of 0 means autodetection)
1683	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1684	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1685	: 0;
1686		2987
1687	// if we got one, then embed it, otherwise default to loop_hi	2988	While the C<ev_embed> watcher is running, forks in the embedding loop will
1688	if (loop_lo)	2989	automatically be applied to the embedded loop as well, so no special
1689	{	2990	fork handling is required in that case. When the watcher is not running,
1690	ev_embed_init (&embed, 0, loop_lo);	2991	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1691	ev_embed_start (loop_hi, &embed);	2992	as applicable.
1692	}	2993
1693	else	2994	=head3 Watcher-Specific Functions and Data Members
1694	loop_lo = loop_hi;
1695		2995
1696	=over 4	2996	=over 4
1697		2997
1698	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2998	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1699		2999
…		…
1701		3001
1702	Configures the watcher to embed the given loop, which must be	3002	Configures the watcher to embed the given loop, which must be
1703	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3003	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1704	invoked automatically, otherwise it is the responsibility of the callback	3004	invoked automatically, otherwise it is the responsibility of the callback
1705	to invoke it (it will continue to be called until the sweep has been done,	3005	to invoke it (it will continue to be called until the sweep has been done,
1706	if you do not want thta, you need to temporarily stop the embed watcher).	3006	if you do not want that, you need to temporarily stop the embed watcher).
1707		3007
1708	=item ev_embed_sweep (loop, ev_embed *)	3008	=item ev_embed_sweep (loop, ev_embed *)
1709		3009
1710	Make a single, non-blocking sweep over the embedded loop. This works	3010	Make a single, non-blocking sweep over the embedded loop. This works
1711	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3011	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1712	apropriate way for embedded loops.	3012	appropriate way for embedded loops.
1713		3013
1714	=item struct ev_loop *loop [read-only]	3014	=item struct ev_loop *other [read-only]
1715		3015
1716	The embedded event loop.	3016	The embedded event loop.
1717		3017
1718	=back	3018	=back
		3019
		3020	=head3 Examples
		3021
		3022	Example: Try to get an embeddable event loop and embed it into the default
		3023	event loop. If that is not possible, use the default loop. The default
		3024	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3025	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3026	used).
		3027
		3028	struct ev_loop *loop_hi = ev_default_init (0);
		3029	struct ev_loop *loop_lo = 0;
		3030	ev_embed embed;
		3031
		3032	// see if there is a chance of getting one that works
		3033	// (remember that a flags value of 0 means autodetection)
		3034	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3035	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3036	: 0;
		3037
		3038	// if we got one, then embed it, otherwise default to loop_hi
		3039	if (loop_lo)
		3040	{
		3041	ev_embed_init (&embed, 0, loop_lo);
		3042	ev_embed_start (loop_hi, &embed);
		3043	}
		3044	else
		3045	loop_lo = loop_hi;
		3046
		3047	Example: Check if kqueue is available but not recommended and create
		3048	a kqueue backend for use with sockets (which usually work with any
		3049	kqueue implementation). Store the kqueue/socket-only event loop in
		3050	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3051
		3052	struct ev_loop *loop = ev_default_init (0);
		3053	struct ev_loop *loop_socket = 0;
		3054	ev_embed embed;
		3055
		3056	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3057	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3058	{
		3059	ev_embed_init (&embed, 0, loop_socket);
		3060	ev_embed_start (loop, &embed);
		3061	}
		3062
		3063	if (!loop_socket)
		3064	loop_socket = loop;
		3065
		3066	// now use loop_socket for all sockets, and loop for everything else
1719		3067
1720		3068
1721	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3069	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1722		3070
1723	Fork watchers are called when a C<fork ()> was detected (usually because	3071	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1726	event loop blocks next and before C<ev_check> watchers are being called,	3074	event loop blocks next and before C<ev_check> watchers are being called,
1727	and only in the child after the fork. If whoever good citizen calling	3075	and only in the child after the fork. If whoever good citizen calling
1728	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3076	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1729	handlers will be invoked, too, of course.	3077	handlers will be invoked, too, of course.
1730		3078
		3079	=head3 The special problem of life after fork - how is it possible?
		3080
		3081	Most uses of C<fork()> consist of forking, then some simple calls to set
		3082	up/change the process environment, followed by a call to C<exec()>. This
		3083	sequence should be handled by libev without any problems.
		3084
		3085	This changes when the application actually wants to do event handling
		3086	in the child, or both parent in child, in effect "continuing" after the
		3087	fork.
		3088
		3089	The default mode of operation (for libev, with application help to detect
		3090	forks) is to duplicate all the state in the child, as would be expected
		3091	when I<either> the parent I<or> the child process continues.
		3092
		3093	When both processes want to continue using libev, then this is usually the
		3094	wrong result. In that case, usually one process (typically the parent) is
		3095	supposed to continue with all watchers in place as before, while the other
		3096	process typically wants to start fresh, i.e. without any active watchers.
		3097
		3098	The cleanest and most efficient way to achieve that with libev is to
		3099	simply create a new event loop, which of course will be "empty", and
		3100	use that for new watchers. This has the advantage of not touching more
		3101	memory than necessary, and thus avoiding the copy-on-write, and the
		3102	disadvantage of having to use multiple event loops (which do not support
		3103	signal watchers).
		3104
		3105	When this is not possible, or you want to use the default loop for
		3106	other reasons, then in the process that wants to start "fresh", call
		3107	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3108	Destroying the default loop will "orphan" (not stop) all registered
		3109	watchers, so you have to be careful not to execute code that modifies
		3110	those watchers. Note also that in that case, you have to re-register any
		3111	signal watchers.
		3112
		3113	=head3 Watcher-Specific Functions and Data Members
		3114
1731	=over 4	3115	=over 4
1732		3116
1733	=item ev_fork_init (ev_signal *, callback)	3117	=item ev_fork_init (ev_fork *, callback)
1734		3118
1735	Initialises and configures the fork watcher - it has no parameters of any	3119	Initialises and configures the fork watcher - it has no parameters of any
1736	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3120	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
1737	believe me.	3121	really.
1738		3122
1739	=back	3123	=back
1740		3124
1741		3125
		3126	=head2 C<ev_cleanup> - even the best things end
		3127
		3128	Cleanup watchers are called just before the event loop is being destroyed
		3129	by a call to C<ev_loop_destroy>.
		3130
		3131	While there is no guarantee that the event loop gets destroyed, cleanup
		3132	watchers provide a convenient method to install cleanup hooks for your
		3133	program, worker threads and so on - you just to make sure to destroy the
		3134	loop when you want them to be invoked.
		3135
		3136	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3137	all other watchers, they do not keep a reference to the event loop (which
		3138	makes a lot of sense if you think about it). Like all other watchers, you
		3139	can call libev functions in the callback, except C<ev_cleanup_start>.
		3140
		3141	=head3 Watcher-Specific Functions and Data Members
		3142
		3143	=over 4
		3144
		3145	=item ev_cleanup_init (ev_cleanup *, callback)
		3146
		3147	Initialises and configures the cleanup watcher - it has no parameters of
		3148	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3149	pointless, I assure you.
		3150
		3151	=back
		3152
		3153	Example: Register an atexit handler to destroy the default loop, so any
		3154	cleanup functions are called.
		3155
		3156	static void
		3157	program_exits (void)
		3158	{
		3159	ev_loop_destroy (EV_DEFAULT_UC);
		3160	}
		3161
		3162	...
		3163	atexit (program_exits);
		3164
		3165
		3166	=head2 C<ev_async> - how to wake up an event loop
		3167
		3168	In general, you cannot use an C<ev_run> from multiple threads or other
		3169	asynchronous sources such as signal handlers (as opposed to multiple event
		3170	loops - those are of course safe to use in different threads).
		3171
		3172	Sometimes, however, you need to wake up an event loop you do not control,
		3173	for example because it belongs to another thread. This is what C<ev_async>
		3174	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3175	it by calling C<ev_async_send>, which is thread- and signal safe.
		3176
		3177	This functionality is very similar to C<ev_signal> watchers, as signals,
		3178	too, are asynchronous in nature, and signals, too, will be compressed
		3179	(i.e. the number of callback invocations may be less than the number of
		3180	C<ev_async_sent> calls).
		3181
		3182	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3183	just the default loop.
		3184
		3185	=head3 Queueing
		3186
		3187	C<ev_async> does not support queueing of data in any way. The reason
		3188	is that the author does not know of a simple (or any) algorithm for a
		3189	multiple-writer-single-reader queue that works in all cases and doesn't
		3190	need elaborate support such as pthreads or unportable memory access
		3191	semantics.
		3192
		3193	That means that if you want to queue data, you have to provide your own
		3194	queue. But at least I can tell you how to implement locking around your
		3195	queue:
		3196
		3197	=over 4
		3198
		3199	=item queueing from a signal handler context
		3200
		3201	To implement race-free queueing, you simply add to the queue in the signal
		3202	handler but you block the signal handler in the watcher callback. Here is
		3203	an example that does that for some fictitious SIGUSR1 handler:
		3204
		3205	static ev_async mysig;
		3206
		3207	static void
		3208	sigusr1_handler (void)
		3209	{
		3210	sometype data;
		3211
		3212	// no locking etc.
		3213	queue_put (data);
		3214	ev_async_send (EV_DEFAULT_ &mysig);
		3215	}
		3216
		3217	static void
		3218	mysig_cb (EV_P_ ev_async *w, int revents)
		3219	{
		3220	sometype data;
		3221	sigset_t block, prev;
		3222
		3223	sigemptyset (&block);
		3224	sigaddset (&block, SIGUSR1);
		3225	sigprocmask (SIG_BLOCK, &block, &prev);
		3226
		3227	while (queue_get (&data))
		3228	process (data);
		3229
		3230	if (sigismember (&prev, SIGUSR1)
		3231	sigprocmask (SIG_UNBLOCK, &block, 0);
		3232	}
		3233
		3234	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3235	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3236	either...).
		3237
		3238	=item queueing from a thread context
		3239
		3240	The strategy for threads is different, as you cannot (easily) block
		3241	threads but you can easily preempt them, so to queue safely you need to
		3242	employ a traditional mutex lock, such as in this pthread example:
		3243
		3244	static ev_async mysig;
		3245	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3246
		3247	static void
		3248	otherthread (void)
		3249	{
		3250	// only need to lock the actual queueing operation
		3251	pthread_mutex_lock (&mymutex);
		3252	queue_put (data);
		3253	pthread_mutex_unlock (&mymutex);
		3254
		3255	ev_async_send (EV_DEFAULT_ &mysig);
		3256	}
		3257
		3258	static void
		3259	mysig_cb (EV_P_ ev_async *w, int revents)
		3260	{
		3261	pthread_mutex_lock (&mymutex);
		3262
		3263	while (queue_get (&data))
		3264	process (data);
		3265
		3266	pthread_mutex_unlock (&mymutex);
		3267	}
		3268
		3269	=back
		3270
		3271
		3272	=head3 Watcher-Specific Functions and Data Members
		3273
		3274	=over 4
		3275
		3276	=item ev_async_init (ev_async *, callback)
		3277
		3278	Initialises and configures the async watcher - it has no parameters of any
		3279	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3280	trust me.
		3281
		3282	=item ev_async_send (loop, ev_async *)
		3283
		3284	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3285	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3286	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3287	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3288	section below on what exactly this means).
		3289
		3290	Note that, as with other watchers in libev, multiple events might get
		3291	compressed into a single callback invocation (another way to look at this
		3292	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3293	reset when the event loop detects that).
		3294
		3295	This call incurs the overhead of a system call only once per event loop
		3296	iteration, so while the overhead might be noticeable, it doesn't apply to
		3297	repeated calls to C<ev_async_send> for the same event loop.
		3298
		3299	=item bool = ev_async_pending (ev_async *)
		3300
		3301	Returns a non-zero value when C<ev_async_send> has been called on the
		3302	watcher but the event has not yet been processed (or even noted) by the
		3303	event loop.
		3304
		3305	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3306	the loop iterates next and checks for the watcher to have become active,
		3307	it will reset the flag again. C<ev_async_pending> can be used to very
		3308	quickly check whether invoking the loop might be a good idea.
		3309
		3310	Not that this does I<not> check whether the watcher itself is pending,
		3311	only whether it has been requested to make this watcher pending: there
		3312	is a time window between the event loop checking and resetting the async
		3313	notification, and the callback being invoked.
		3314
		3315	=back
		3316
		3317
1742	=head1 OTHER FUNCTIONS	3318	=head1 OTHER FUNCTIONS
1743		3319
1744	There are some other functions of possible interest. Described. Here. Now.	3320	There are some other functions of possible interest. Described. Here. Now.
1745		3321
1746	=over 4	3322	=over 4
1747		3323
1748	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3324	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1749		3325
1750	This function combines a simple timer and an I/O watcher, calls your	3326	This function combines a simple timer and an I/O watcher, calls your
1751	callback on whichever event happens first and automatically stop both	3327	callback on whichever event happens first and automatically stops both
1752	watchers. This is useful if you want to wait for a single event on an fd	3328	watchers. This is useful if you want to wait for a single event on an fd
1753	or timeout without having to allocate/configure/start/stop/free one or	3329	or timeout without having to allocate/configure/start/stop/free one or
1754	more watchers yourself.	3330	more watchers yourself.
1755		3331
1756	If C<fd> is less than 0, then no I/O watcher will be started and events	3332	If C<fd> is less than 0, then no I/O watcher will be started and the
1757	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3333	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1758	C<events> set will be craeted and started.	3334	the given C<fd> and C<events> set will be created and started.
1759		3335
1760	If C<timeout> is less than 0, then no timeout watcher will be	3336	If C<timeout> is less than 0, then no timeout watcher will be
1761	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3337	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1762	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3338	repeat = 0) will be started. C<0> is a valid timeout.
1763	dubious value.
1764		3339
1765	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3340	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1766	passed an C<revents> set like normal event callbacks (a combination of	3341	passed an C<revents> set like normal event callbacks (a combination of
1767	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3342	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1768	value passed to C<ev_once>:	3343	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3344	a timeout and an io event at the same time - you probably should give io
		3345	events precedence.
1769		3346
		3347	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3348
1770	static void stdin_ready (int revents, void *arg)	3349	static void stdin_ready (int revents, void *arg)
1771	{	3350	{
1772	if (revents & EV_TIMEOUT)
1773	/* doh, nothing entered */;
1774	else if (revents & EV_READ)	3351	if (revents & EV_READ)
1775	/* stdin might have data for us, joy! */;	3352	/* stdin might have data for us, joy! */;
		3353	else if (revents & EV_TIMER)
		3354	/* doh, nothing entered */;
1776	}	3355	}
1777		3356
1778	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3357	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1779		3358
1780	=item ev_feed_event (ev_loop *, watcher *, int revents)
1781
1782	Feeds the given event set into the event loop, as if the specified event
1783	had happened for the specified watcher (which must be a pointer to an
1784	initialised but not necessarily started event watcher).
1785
1786	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3359	=item ev_feed_fd_event (loop, int fd, int revents)
1787		3360
1788	Feed an event on the given fd, as if a file descriptor backend detected	3361	Feed an event on the given fd, as if a file descriptor backend detected
1789	the given events it.	3362	the given events it.
1790		3363
1791	=item ev_feed_signal_event (ev_loop *loop, int signum)	3364	=item ev_feed_signal_event (loop, int signum)
1792		3365
1793	Feed an event as if the given signal occured (C<loop> must be the default	3366	Feed an event as if the given signal occurred (C<loop> must be the default
1794	loop!).	3367	loop!).
		3368
		3369	=back
		3370
		3371
		3372	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3373
		3374	This section explains some common idioms that are not immediately
		3375	obvious. Note that examples are sprinkled over the whole manual, and this
		3376	section only contains stuff that wouldn't fit anywhere else.
		3377
		3378	=over 4
		3379
		3380	=item Model/nested event loop invocations and exit conditions.
		3381
		3382	Often (especially in GUI toolkits) there are places where you have
		3383	I<modal> interaction, which is most easily implemented by recursively
		3384	invoking C<ev_run>.
		3385
		3386	This brings the problem of exiting - a callback might want to finish the
		3387	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3388	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3389	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3390	other combination: In these cases, C<ev_break> will not work alone.
		3391
		3392	The solution is to maintain "break this loop" variable for each C<ev_run>
		3393	invocation, and use a loop around C<ev_run> until the condition is
		3394	triggered, using C<EVRUN_ONCE>:
		3395
		3396	// main loop
		3397	int exit_main_loop = 0;
		3398
		3399	while (!exit_main_loop)
		3400	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3401
		3402	// in a model watcher
		3403	int exit_nested_loop = 0;
		3404
		3405	while (!exit_nested_loop)
		3406	ev_run (EV_A_ EVRUN_ONCE);
		3407
		3408	To exit from any of these loops, just set the corresponding exit variable:
		3409
		3410	// exit modal loop
		3411	exit_nested_loop = 1;
		3412
		3413	// exit main program, after modal loop is finished
		3414	exit_main_loop = 1;
		3415
		3416	// exit both
		3417	exit_main_loop = exit_nested_loop = 1;
1795		3418
1796	=back	3419	=back
1797		3420
1798		3421
1799	=head1 LIBEVENT EMULATION	3422	=head1 LIBEVENT EMULATION
1800		3423
1801	Libev offers a compatibility emulation layer for libevent. It cannot	3424	Libev offers a compatibility emulation layer for libevent. It cannot
1802	emulate the internals of libevent, so here are some usage hints:	3425	emulate the internals of libevent, so here are some usage hints:
1803		3426
1804	=over 4	3427	=over 4
		3428
		3429	=item * Only the libevent-1.4.1-beta API is being emulated.
		3430
		3431	This was the newest libevent version available when libev was implemented,
		3432	and is still mostly unchanged in 2010.
1805		3433
1806	=item * Use it by including <event.h>, as usual.	3434	=item * Use it by including <event.h>, as usual.
1807		3435
1808	=item * The following members are fully supported: ev_base, ev_callback,	3436	=item * The following members are fully supported: ev_base, ev_callback,
1809	ev_arg, ev_fd, ev_res, ev_events.	3437	ev_arg, ev_fd, ev_res, ev_events.
…		…
1814		3442
1815	=item * Priorities are not currently supported. Initialising priorities	3443	=item * Priorities are not currently supported. Initialising priorities
1816	will fail and all watchers will have the same priority, even though there	3444	will fail and all watchers will have the same priority, even though there
1817	is an ev_pri field.	3445	is an ev_pri field.
1818		3446
		3447	=item * In libevent, the last base created gets the signals, in libev, the
		3448	base that registered the signal gets the signals.
		3449
1819	=item * Other members are not supported.	3450	=item * Other members are not supported.
1820		3451
1821	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3452	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1822	to use the libev header file and library.	3453	to use the libev header file and library.
1823		3454
1824	=back	3455	=back
1825		3456
1826	=head1 C++ SUPPORT	3457	=head1 C++ SUPPORT
1827		3458
1828	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3459	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1829	you to use some convinience methods to start/stop watchers and also change	3460	you to use some convenience methods to start/stop watchers and also change
1830	the callback model to a model using method callbacks on objects.	3461	the callback model to a model using method callbacks on objects.
1831		3462
1832	To use it,	3463	To use it,
1833		3464
1834	#include <ev++.h>	3465	#include <ev++.h>
1835		3466
1836	This automatically includes F<ev.h> and puts all of its definitions (many	3467	This automatically includes F<ev.h> and puts all of its definitions (many
1837	of them macros) into the global namespace. All C++ specific things are	3468	of them macros) into the global namespace. All C++ specific things are
1838	put into the C<ev> namespace. It should support all the same embedding	3469	put into the C<ev> namespace. It should support all the same embedding
1839	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3470	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1841	Care has been taken to keep the overhead low. The only data member the C++	3472	Care has been taken to keep the overhead low. The only data member the C++
1842	classes add (compared to plain C-style watchers) is the event loop pointer	3473	classes add (compared to plain C-style watchers) is the event loop pointer
1843	that the watcher is associated with (or no additional members at all if	3474	that the watcher is associated with (or no additional members at all if
1844	you disable C<EV_MULTIPLICITY> when embedding libev).	3475	you disable C<EV_MULTIPLICITY> when embedding libev).
1845		3476
1846	Currently, functions, and static and non-static member functions can be	3477	Currently, functions, static and non-static member functions and classes
1847	used as callbacks. Other types should be easy to add as long as they only	3478	with C<operator ()> can be used as callbacks. Other types should be easy
1848	need one additional pointer for context. If you need support for other	3479	to add as long as they only need one additional pointer for context. If
1849	types of functors please contact the author (preferably after implementing	3480	you need support for other types of functors please contact the author
1850	it).	3481	(preferably after implementing it).
1851		3482
1852	Here is a list of things available in the C<ev> namespace:	3483	Here is a list of things available in the C<ev> namespace:
1853		3484
1854	=over 4	3485	=over 4
1855		3486
…		…
1873		3504
1874	=over 4	3505	=over 4
1875		3506
1876	=item ev::TYPE::TYPE ()	3507	=item ev::TYPE::TYPE ()
1877		3508
1878	=item ev::TYPE::TYPE (struct ev_loop *)	3509	=item ev::TYPE::TYPE (loop)
1879		3510
1880	=item ev::TYPE::~TYPE	3511	=item ev::TYPE::~TYPE
1881		3512
1882	The constructor (optionally) takes an event loop to associate the watcher	3513	The constructor (optionally) takes an event loop to associate the watcher
1883	with. If it is omitted, it will use C<EV_DEFAULT>.	3514	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
1906	your compiler is good :), then the method will be fully inlined into the	3537	your compiler is good :), then the method will be fully inlined into the
1907	thunking function, making it as fast as a direct C callback.	3538	thunking function, making it as fast as a direct C callback.
1908		3539
1909	Example: simple class declaration and watcher initialisation	3540	Example: simple class declaration and watcher initialisation
1910		3541
1911	struct myclass	3542	struct myclass
1912	{	3543	{
1913	void io_cb (ev::io &w, int revents) { }	3544	void io_cb (ev::io &w, int revents) { }
1914	}	3545	}
1915		3546
1916	myclass obj;	3547	myclass obj;
1917	ev::io iow;	3548	ev::io iow;
1918	iow.set <myclass, &myclass::io_cb> (&obj);	3549	iow.set <myclass, &myclass::io_cb> (&obj);
		3550
		3551	=item w->set (object *)
		3552
		3553	This is a variation of a method callback - leaving out the method to call
		3554	will default the method to C<operator ()>, which makes it possible to use
		3555	functor objects without having to manually specify the C<operator ()> all
		3556	the time. Incidentally, you can then also leave out the template argument
		3557	list.
		3558
		3559	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3560	int revents)>.
		3561
		3562	See the method-C<set> above for more details.
		3563
		3564	Example: use a functor object as callback.
		3565
		3566	struct myfunctor
		3567	{
		3568	void operator() (ev::io &w, int revents)
		3569	{
		3570	...
		3571	}
		3572	}
		3573
		3574	myfunctor f;
		3575
		3576	ev::io w;
		3577	w.set (&f);
1919		3578
1920	=item w->set<function> (void *data = 0)	3579	=item w->set<function> (void *data = 0)
1921		3580
1922	Also sets a callback, but uses a static method or plain function as	3581	Also sets a callback, but uses a static method or plain function as
1923	callback. The optional C<data> argument will be stored in the watcher's	3582	callback. The optional C<data> argument will be stored in the watcher's
…		…
1925		3584
1926	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3585	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
1927		3586
1928	See the method-C<set> above for more details.	3587	See the method-C<set> above for more details.
1929		3588
1930	Example:	3589	Example: Use a plain function as callback.
1931		3590
1932	static void io_cb (ev::io &w, int revents) { }	3591	static void io_cb (ev::io &w, int revents) { }
1933	iow.set <io_cb> ();	3592	iow.set <io_cb> ();
1934		3593
1935	=item w->set (struct ev_loop *)	3594	=item w->set (loop)
1936		3595
1937	Associates a different C<struct ev_loop> with this watcher. You can only	3596	Associates a different C<struct ev_loop> with this watcher. You can only
1938	do this when the watcher is inactive (and not pending either).	3597	do this when the watcher is inactive (and not pending either).
1939		3598
1940	=item w->set ([args])	3599	=item w->set ([arguments])
1941		3600
1942	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3601	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
1943	called at least once. Unlike the C counterpart, an active watcher gets	3602	method or a suitable start method must be called at least once. Unlike the
1944	automatically stopped and restarted when reconfiguring it with this	3603	C counterpart, an active watcher gets automatically stopped and restarted
1945	method.	3604	when reconfiguring it with this method.
1946		3605
1947	=item w->start ()	3606	=item w->start ()
1948		3607
1949	Starts the watcher. Note that there is no C<loop> argument, as the	3608	Starts the watcher. Note that there is no C<loop> argument, as the
1950	constructor already stores the event loop.	3609	constructor already stores the event loop.
1951		3610
		3611	=item w->start ([arguments])
		3612
		3613	Instead of calling C<set> and C<start> methods separately, it is often
		3614	convenient to wrap them in one call. Uses the same type of arguments as
		3615	the configure C<set> method of the watcher.
		3616
1952	=item w->stop ()	3617	=item w->stop ()
1953		3618
1954	Stops the watcher if it is active. Again, no C<loop> argument.	3619	Stops the watcher if it is active. Again, no C<loop> argument.
1955		3620
1956	=item w->again () C<ev::timer>, C<ev::periodic> only	3621	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1957		3622
1958	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3623	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1959	C<ev_TYPE_again> function.	3624	C<ev_TYPE_again> function.
1960		3625
1961	=item w->sweep () C<ev::embed> only	3626	=item w->sweep () (C<ev::embed> only)
1962		3627
1963	Invokes C<ev_embed_sweep>.	3628	Invokes C<ev_embed_sweep>.
1964		3629
1965	=item w->update () C<ev::stat> only	3630	=item w->update () (C<ev::stat> only)
1966		3631
1967	Invokes C<ev_stat_stat>.	3632	Invokes C<ev_stat_stat>.
1968		3633
1969	=back	3634	=back
1970		3635
1971	=back	3636	=back
1972		3637
1973	Example: Define a class with an IO and idle watcher, start one of them in	3638	Example: Define a class with two I/O and idle watchers, start the I/O
1974	the constructor.	3639	watchers in the constructor.
1975		3640
1976	class myclass	3641	class myclass
1977	{	3642	{
1978	ev_io io; void io_cb (ev::io &w, int revents);	3643	ev::io io ; void io_cb (ev::io &w, int revents);
		3644	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
1979	ev_idle idle void idle_cb (ev::idle &w, int revents);	3645	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1980		3646
1981	myclass ();	3647	myclass (int fd)
1982	}	3648	{
1983
1984	myclass::myclass (int fd)
1985	{
1986	io .set <myclass, &myclass::io_cb > (this);	3649	io .set <myclass, &myclass::io_cb > (this);
		3650	io2 .set <myclass, &myclass::io2_cb > (this);
1987	idle.set <myclass, &myclass::idle_cb> (this);	3651	idle.set <myclass, &myclass::idle_cb> (this);
1988		3652
1989	io.start (fd, ev::READ);	3653	io.set (fd, ev::WRITE); // configure the watcher
		3654	io.start (); // start it whenever convenient
		3655
		3656	io2.start (fd, ev::READ); // set + start in one call
		3657	}
1990	}	3658	};
		3659
		3660
		3661	=head1 OTHER LANGUAGE BINDINGS
		3662
		3663	Libev does not offer other language bindings itself, but bindings for a
		3664	number of languages exist in the form of third-party packages. If you know
		3665	any interesting language binding in addition to the ones listed here, drop
		3666	me a note.
		3667
		3668	=over 4
		3669
		3670	=item Perl
		3671
		3672	The EV module implements the full libev API and is actually used to test
		3673	libev. EV is developed together with libev. Apart from the EV core module,
		3674	there are additional modules that implement libev-compatible interfaces
		3675	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3676	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3677	and C<EV::Glib>).
		3678
		3679	It can be found and installed via CPAN, its homepage is at
		3680	L<http://software.schmorp.de/pkg/EV>.
		3681
		3682	=item Python
		3683
		3684	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3685	seems to be quite complete and well-documented.
		3686
		3687	=item Ruby
		3688
		3689	Tony Arcieri has written a ruby extension that offers access to a subset
		3690	of the libev API and adds file handle abstractions, asynchronous DNS and
		3691	more on top of it. It can be found via gem servers. Its homepage is at
		3692	L<http://rev.rubyforge.org/>.
		3693
		3694	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3695	makes rev work even on mingw.
		3696
		3697	=item Haskell
		3698
		3699	A haskell binding to libev is available at
		3700	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3701
		3702	=item D
		3703
		3704	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3705	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3706
		3707	=item Ocaml
		3708
		3709	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3710	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3711
		3712	=item Lua
		3713
		3714	Brian Maher has written a partial interface to libev for lua (at the
		3715	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3716	L<http://github.com/brimworks/lua-ev>.
		3717
		3718	=back
1991		3719
1992		3720
1993	=head1 MACRO MAGIC	3721	=head1 MACRO MAGIC
1994		3722
1995	Libev can be compiled with a variety of options, the most fundemantal is	3723	Libev can be compiled with a variety of options, the most fundamental
1996	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	3724	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1997	callbacks have an initial C<struct ev_loop *> argument.	3725	functions and callbacks have an initial C<struct ev_loop *> argument.
1998		3726
1999	To make it easier to write programs that cope with either variant, the	3727	To make it easier to write programs that cope with either variant, the
2000	following macros are defined:	3728	following macros are defined:
2001		3729
2002	=over 4	3730	=over 4
…		…
2005		3733
2006	This provides the loop I<argument> for functions, if one is required ("ev	3734	This provides the loop I<argument> for functions, if one is required ("ev
2007	loop argument"). The C<EV_A> form is used when this is the sole argument,	3735	loop argument"). The C<EV_A> form is used when this is the sole argument,
2008	C<EV_A_> is used when other arguments are following. Example:	3736	C<EV_A_> is used when other arguments are following. Example:
2009		3737
2010	ev_unref (EV_A);	3738	ev_unref (EV_A);
2011	ev_timer_add (EV_A_ watcher);	3739	ev_timer_add (EV_A_ watcher);
2012	ev_loop (EV_A_ 0);	3740	ev_run (EV_A_ 0);
2013		3741
2014	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3742	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2015	which is often provided by the following macro.	3743	which is often provided by the following macro.
2016		3744
2017	=item C<EV_P>, C<EV_P_>	3745	=item C<EV_P>, C<EV_P_>
2018		3746
2019	This provides the loop I<parameter> for functions, if one is required ("ev	3747	This provides the loop I<parameter> for functions, if one is required ("ev
2020	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3748	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2021	C<EV_P_> is used when other parameters are following. Example:	3749	C<EV_P_> is used when other parameters are following. Example:
2022		3750
2023	// this is how ev_unref is being declared	3751	// this is how ev_unref is being declared
2024	static void ev_unref (EV_P);	3752	static void ev_unref (EV_P);
2025		3753
2026	// this is how you can declare your typical callback	3754	// this is how you can declare your typical callback
2027	static void cb (EV_P_ ev_timer *w, int revents)	3755	static void cb (EV_P_ ev_timer *w, int revents)
2028		3756
2029	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3757	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2030	suitable for use with C<EV_A>.	3758	suitable for use with C<EV_A>.
2031		3759
2032	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3760	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2033		3761
2034	Similar to the other two macros, this gives you the value of the default	3762	Similar to the other two macros, this gives you the value of the default
2035	loop, if multiple loops are supported ("ev loop default").	3763	loop, if multiple loops are supported ("ev loop default").
		3764
		3765	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3766
		3767	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3768	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3769	is undefined when the default loop has not been initialised by a previous
		3770	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3771
		3772	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3773	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2036		3774
2037	=back	3775	=back
2038		3776
2039	Example: Declare and initialise a check watcher, utilising the above	3777	Example: Declare and initialise a check watcher, utilising the above
2040	macros so it will work regardless of whether multiple loops are supported	3778	macros so it will work regardless of whether multiple loops are supported
2041	or not.	3779	or not.
2042		3780
2043	static void	3781	static void
2044	check_cb (EV_P_ ev_timer *w, int revents)	3782	check_cb (EV_P_ ev_timer *w, int revents)
2045	{	3783	{
2046	ev_check_stop (EV_A_ w);	3784	ev_check_stop (EV_A_ w);
2047	}	3785	}
2048		3786
2049	ev_check check;	3787	ev_check check;
2050	ev_check_init (&check, check_cb);	3788	ev_check_init (&check, check_cb);
2051	ev_check_start (EV_DEFAULT_ &check);	3789	ev_check_start (EV_DEFAULT_ &check);
2052	ev_loop (EV_DEFAULT_ 0);	3790	ev_run (EV_DEFAULT_ 0);
2053		3791
2054	=head1 EMBEDDING	3792	=head1 EMBEDDING
2055		3793
2056	Libev can (and often is) directly embedded into host	3794	Libev can (and often is) directly embedded into host
2057	applications. Examples of applications that embed it include the Deliantra	3795	applications. Examples of applications that embed it include the Deliantra
2058	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3796	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
2059	and rxvt-unicode.	3797	and rxvt-unicode.
2060		3798
2061	The goal is to enable you to just copy the neecssary files into your	3799	The goal is to enable you to just copy the necessary files into your
2062	source directory without having to change even a single line in them, so	3800	source directory without having to change even a single line in them, so
2063	you can easily upgrade by simply copying (or having a checked-out copy of	3801	you can easily upgrade by simply copying (or having a checked-out copy of
2064	libev somewhere in your source tree).	3802	libev somewhere in your source tree).
2065		3803
2066	=head2 FILESETS	3804	=head2 FILESETS
2067		3805
2068	Depending on what features you need you need to include one or more sets of files	3806	Depending on what features you need you need to include one or more sets of files
2069	in your app.	3807	in your application.
2070		3808
2071	=head3 CORE EVENT LOOP	3809	=head3 CORE EVENT LOOP
2072		3810
2073	To include only the libev core (all the C<ev_*> functions), with manual	3811	To include only the libev core (all the C<ev_*> functions), with manual
2074	configuration (no autoconf):	3812	configuration (no autoconf):
2075		3813
2076	#define EV_STANDALONE 1	3814	#define EV_STANDALONE 1
2077	#include "ev.c"	3815	#include "ev.c"
2078		3816
2079	This will automatically include F<ev.h>, too, and should be done in a	3817	This will automatically include F<ev.h>, too, and should be done in a
2080	single C source file only to provide the function implementations. To use	3818	single C source file only to provide the function implementations. To use
2081	it, do the same for F<ev.h> in all files wishing to use this API (best	3819	it, do the same for F<ev.h> in all files wishing to use this API (best
2082	done by writing a wrapper around F<ev.h> that you can include instead and	3820	done by writing a wrapper around F<ev.h> that you can include instead and
2083	where you can put other configuration options):	3821	where you can put other configuration options):
2084		3822
2085	#define EV_STANDALONE 1	3823	#define EV_STANDALONE 1
2086	#include "ev.h"	3824	#include "ev.h"
2087		3825
2088	Both header files and implementation files can be compiled with a C++	3826	Both header files and implementation files can be compiled with a C++
2089	compiler (at least, thats a stated goal, and breakage will be treated	3827	compiler (at least, that's a stated goal, and breakage will be treated
2090	as a bug).	3828	as a bug).
2091		3829
2092	You need the following files in your source tree, or in a directory	3830	You need the following files in your source tree, or in a directory
2093	in your include path (e.g. in libev/ when using -Ilibev):	3831	in your include path (e.g. in libev/ when using -Ilibev):
2094		3832
2095	ev.h	3833	ev.h
2096	ev.c	3834	ev.c
2097	ev_vars.h	3835	ev_vars.h
2098	ev_wrap.h	3836	ev_wrap.h
2099		3837
2100	ev_win32.c required on win32 platforms only	3838	ev_win32.c required on win32 platforms only
2101		3839
2102	ev_select.c only when select backend is enabled (which is enabled by default)	3840	ev_select.c only when select backend is enabled (which is enabled by default)
2103	ev_poll.c only when poll backend is enabled (disabled by default)	3841	ev_poll.c only when poll backend is enabled (disabled by default)
2104	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3842	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2105	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3843	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2106	ev_port.c only when the solaris port backend is enabled (disabled by default)	3844	ev_port.c only when the solaris port backend is enabled (disabled by default)
2107		3845
2108	F<ev.c> includes the backend files directly when enabled, so you only need	3846	F<ev.c> includes the backend files directly when enabled, so you only need
2109	to compile this single file.	3847	to compile this single file.
2110		3848
2111	=head3 LIBEVENT COMPATIBILITY API	3849	=head3 LIBEVENT COMPATIBILITY API
2112		3850
2113	To include the libevent compatibility API, also include:	3851	To include the libevent compatibility API, also include:
2114		3852
2115	#include "event.c"	3853	#include "event.c"
2116		3854
2117	in the file including F<ev.c>, and:	3855	in the file including F<ev.c>, and:
2118		3856
2119	#include "event.h"	3857	#include "event.h"
2120		3858
2121	in the files that want to use the libevent API. This also includes F<ev.h>.	3859	in the files that want to use the libevent API. This also includes F<ev.h>.
2122		3860
2123	You need the following additional files for this:	3861	You need the following additional files for this:
2124		3862
2125	event.h	3863	event.h
2126	event.c	3864	event.c
2127		3865
2128	=head3 AUTOCONF SUPPORT	3866	=head3 AUTOCONF SUPPORT
2129		3867
2130	Instead of using C<EV_STANDALONE=1> and providing your config in	3868	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2131	whatever way you want, you can also C<m4_include([libev.m4])> in your	3869	whatever way you want, you can also C<m4_include([libev.m4])> in your
2132	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3870	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2133	include F<config.h> and configure itself accordingly.	3871	include F<config.h> and configure itself accordingly.
2134		3872
2135	For this of course you need the m4 file:	3873	For this of course you need the m4 file:
2136		3874
2137	libev.m4	3875	libev.m4
2138		3876
2139	=head2 PREPROCESSOR SYMBOLS/MACROS	3877	=head2 PREPROCESSOR SYMBOLS/MACROS
2140		3878
2141	Libev can be configured via a variety of preprocessor symbols you have to define	3879	Libev can be configured via a variety of preprocessor symbols you have to
2142	before including any of its files. The default is not to build for multiplicity	3880	define before including (or compiling) any of its files. The default in
2143	and only include the select backend.	3881	the absence of autoconf is documented for every option.
		3882
		3883	Symbols marked with "(h)" do not change the ABI, and can have different
		3884	values when compiling libev vs. including F<ev.h>, so it is permissible
		3885	to redefine them before including F<ev.h> without breaking compatibility
		3886	to a compiled library. All other symbols change the ABI, which means all
		3887	users of libev and the libev code itself must be compiled with compatible
		3888	settings.
2144		3889
2145	=over 4	3890	=over 4
2146		3891
		3892	=item EV_COMPAT3 (h)
		3893
		3894	Backwards compatibility is a major concern for libev. This is why this
		3895	release of libev comes with wrappers for the functions and symbols that
		3896	have been renamed between libev version 3 and 4.
		3897
		3898	You can disable these wrappers (to test compatibility with future
		3899	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		3900	sources. This has the additional advantage that you can drop the C<struct>
		3901	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		3902	typedef in that case.
		3903
		3904	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		3905	and in some even more future version the compatibility code will be
		3906	removed completely.
		3907
2147	=item EV_STANDALONE	3908	=item EV_STANDALONE (h)
2148		3909
2149	Must always be C<1> if you do not use autoconf configuration, which	3910	Must always be C<1> if you do not use autoconf configuration, which
2150	keeps libev from including F<config.h>, and it also defines dummy	3911	keeps libev from including F<config.h>, and it also defines dummy
2151	implementations for some libevent functions (such as logging, which is not	3912	implementations for some libevent functions (such as logging, which is not
2152	supported). It will also not define any of the structs usually found in	3913	supported). It will also not define any of the structs usually found in
2153	F<event.h> that are not directly supported by the libev core alone.	3914	F<event.h> that are not directly supported by the libev core alone.
2154		3915
		3916	In standalone mode, libev will still try to automatically deduce the
		3917	configuration, but has to be more conservative.
		3918
2155	=item EV_USE_MONOTONIC	3919	=item EV_USE_MONOTONIC
2156		3920
2157	If defined to be C<1>, libev will try to detect the availability of the	3921	If defined to be C<1>, libev will try to detect the availability of the
2158	monotonic clock option at both compiletime and runtime. Otherwise no use	3922	monotonic clock option at both compile time and runtime. Otherwise no
2159	of the monotonic clock option will be attempted. If you enable this, you	3923	use of the monotonic clock option will be attempted. If you enable this,
2160	usually have to link against librt or something similar. Enabling it when	3924	you usually have to link against librt or something similar. Enabling it
2161	the functionality isn't available is safe, though, althoguh you have	3925	when the functionality isn't available is safe, though, although you have
2162	to make sure you link against any libraries where the C<clock_gettime>	3926	to make sure you link against any libraries where the C<clock_gettime>
2163	function is hiding in (often F<-lrt>).	3927	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2164		3928
2165	=item EV_USE_REALTIME	3929	=item EV_USE_REALTIME
2166		3930
2167	If defined to be C<1>, libev will try to detect the availability of the	3931	If defined to be C<1>, libev will try to detect the availability of the
2168	realtime clock option at compiletime (and assume its availability at	3932	real-time clock option at compile time (and assume its availability
2169	runtime if successful). Otherwise no use of the realtime clock option will	3933	at runtime if successful). Otherwise no use of the real-time clock
2170	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3934	option will be attempted. This effectively replaces C<gettimeofday>
2171	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3935	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2172	in the description of C<EV_USE_MONOTONIC>, though.	3936	correctness. See the note about libraries in the description of
		3937	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3938	C<EV_USE_CLOCK_SYSCALL>.
		3939
		3940	=item EV_USE_CLOCK_SYSCALL
		3941
		3942	If defined to be C<1>, libev will try to use a direct syscall instead
		3943	of calling the system-provided C<clock_gettime> function. This option
		3944	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3945	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3946	programs needlessly. Using a direct syscall is slightly slower (in
		3947	theory), because no optimised vdso implementation can be used, but avoids
		3948	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3949	higher, as it simplifies linking (no need for C<-lrt>).
		3950
		3951	=item EV_USE_NANOSLEEP
		3952
		3953	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3954	and will use it for delays. Otherwise it will use C<select ()>.
		3955
		3956	=item EV_USE_EVENTFD
		3957
		3958	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3959	available and will probe for kernel support at runtime. This will improve
		3960	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3961	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3962	2.7 or newer, otherwise disabled.
2173		3963
2174	=item EV_USE_SELECT	3964	=item EV_USE_SELECT
2175		3965
2176	If undefined or defined to be C<1>, libev will compile in support for the	3966	If undefined or defined to be C<1>, libev will compile in support for the
2177	C<select>(2) backend. No attempt at autodetection will be done: if no	3967	C<select>(2) backend. No attempt at auto-detection will be done: if no
2178	other method takes over, select will be it. Otherwise the select backend	3968	other method takes over, select will be it. Otherwise the select backend
2179	will not be compiled in.	3969	will not be compiled in.
2180		3970
2181	=item EV_SELECT_USE_FD_SET	3971	=item EV_SELECT_USE_FD_SET
2182		3972
2183	If defined to C<1>, then the select backend will use the system C<fd_set>	3973	If defined to C<1>, then the select backend will use the system C<fd_set>
2184	structure. This is useful if libev doesn't compile due to a missing	3974	structure. This is useful if libev doesn't compile due to a missing
2185	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3975	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2186	exotic systems. This usually limits the range of file descriptors to some	3976	on exotic systems. This usually limits the range of file descriptors to
2187	low limit such as 1024 or might have other limitations (winsocket only	3977	some low limit such as 1024 or might have other limitations (winsocket
2188	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3978	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2189	influence the size of the C<fd_set> used.	3979	configures the maximum size of the C<fd_set>.
2190		3980
2191	=item EV_SELECT_IS_WINSOCKET	3981	=item EV_SELECT_IS_WINSOCKET
2192		3982
2193	When defined to C<1>, the select backend will assume that	3983	When defined to C<1>, the select backend will assume that
2194	select/socket/connect etc. don't understand file descriptors but	3984	select/socket/connect etc. don't understand file descriptors but
…		…
2196	be used is the winsock select). This means that it will call	3986	be used is the winsock select). This means that it will call
2197	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3987	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2198	it is assumed that all these functions actually work on fds, even	3988	it is assumed that all these functions actually work on fds, even
2199	on win32. Should not be defined on non-win32 platforms.	3989	on win32. Should not be defined on non-win32 platforms.
2200		3990
		3991	=item EV_FD_TO_WIN32_HANDLE(fd)
		3992
		3993	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3994	file descriptors to socket handles. When not defining this symbol (the
		3995	default), then libev will call C<_get_osfhandle>, which is usually
		3996	correct. In some cases, programs use their own file descriptor management,
		3997	in which case they can provide this function to map fds to socket handles.
		3998
		3999	=item EV_WIN32_HANDLE_TO_FD(handle)
		4000
		4001	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4002	using the standard C<_open_osfhandle> function. For programs implementing
		4003	their own fd to handle mapping, overwriting this function makes it easier
		4004	to do so. This can be done by defining this macro to an appropriate value.
		4005
		4006	=item EV_WIN32_CLOSE_FD(fd)
		4007
		4008	If programs implement their own fd to handle mapping on win32, then this
		4009	macro can be used to override the C<close> function, useful to unregister
		4010	file descriptors again. Note that the replacement function has to close
		4011	the underlying OS handle.
		4012
2201	=item EV_USE_POLL	4013	=item EV_USE_POLL
2202		4014
2203	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4015	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2204	backend. Otherwise it will be enabled on non-win32 platforms. It	4016	backend. Otherwise it will be enabled on non-win32 platforms. It
2205	takes precedence over select.	4017	takes precedence over select.
2206		4018
2207	=item EV_USE_EPOLL	4019	=item EV_USE_EPOLL
2208		4020
2209	If defined to be C<1>, libev will compile in support for the Linux	4021	If defined to be C<1>, libev will compile in support for the Linux
2210	C<epoll>(7) backend. Its availability will be detected at runtime,	4022	C<epoll>(7) backend. Its availability will be detected at runtime,
2211	otherwise another method will be used as fallback. This is the	4023	otherwise another method will be used as fallback. This is the preferred
2212	preferred backend for GNU/Linux systems.	4024	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4025	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2213		4026
2214	=item EV_USE_KQUEUE	4027	=item EV_USE_KQUEUE
2215		4028
2216	If defined to be C<1>, libev will compile in support for the BSD style	4029	If defined to be C<1>, libev will compile in support for the BSD style
2217	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4030	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2230	otherwise another method will be used as fallback. This is the preferred	4043	otherwise another method will be used as fallback. This is the preferred
2231	backend for Solaris 10 systems.	4044	backend for Solaris 10 systems.
2232		4045
2233	=item EV_USE_DEVPOLL	4046	=item EV_USE_DEVPOLL
2234		4047
2235	reserved for future expansion, works like the USE symbols above.	4048	Reserved for future expansion, works like the USE symbols above.
2236		4049
2237	=item EV_USE_INOTIFY	4050	=item EV_USE_INOTIFY
2238		4051
2239	If defined to be C<1>, libev will compile in support for the Linux inotify	4052	If defined to be C<1>, libev will compile in support for the Linux inotify
2240	interface to speed up C<ev_stat> watchers. Its actual availability will	4053	interface to speed up C<ev_stat> watchers. Its actual availability will
2241	be detected at runtime.	4054	be detected at runtime. If undefined, it will be enabled if the headers
		4055	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2242		4056
		4057	=item EV_ATOMIC_T
		4058
		4059	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4060	access is atomic with respect to other threads or signal contexts. No such
		4061	type is easily found in the C language, so you can provide your own type
		4062	that you know is safe for your purposes. It is used both for signal handler "locking"
		4063	as well as for signal and thread safety in C<ev_async> watchers.
		4064
		4065	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4066	(from F<signal.h>), which is usually good enough on most platforms.
		4067
2243	=item EV_H	4068	=item EV_H (h)
2244		4069
2245	The name of the F<ev.h> header file used to include it. The default if	4070	The name of the F<ev.h> header file used to include it. The default if
2246	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	4071	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2247	can be used to virtually rename the F<ev.h> header file in case of conflicts.	4072	used to virtually rename the F<ev.h> header file in case of conflicts.
2248		4073
2249	=item EV_CONFIG_H	4074	=item EV_CONFIG_H (h)
2250		4075
2251	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4076	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2252	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4077	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2253	C<EV_H>, above.	4078	C<EV_H>, above.
2254		4079
2255	=item EV_EVENT_H	4080	=item EV_EVENT_H (h)
2256		4081
2257	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4082	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2258	of how the F<event.h> header can be found.	4083	of how the F<event.h> header can be found, the default is C<"event.h">.
2259		4084
2260	=item EV_PROTOTYPES	4085	=item EV_PROTOTYPES (h)
2261		4086
2262	If defined to be C<0>, then F<ev.h> will not define any function	4087	If defined to be C<0>, then F<ev.h> will not define any function
2263	prototypes, but still define all the structs and other symbols. This is	4088	prototypes, but still define all the structs and other symbols. This is
2264	occasionally useful if you want to provide your own wrapper functions	4089	occasionally useful if you want to provide your own wrapper functions
2265	around libev functions.	4090	around libev functions.
…		…
2284	When doing priority-based operations, libev usually has to linearly search	4109	When doing priority-based operations, libev usually has to linearly search
2285	all the priorities, so having many of them (hundreds) uses a lot of space	4110	all the priorities, so having many of them (hundreds) uses a lot of space
2286	and time, so using the defaults of five priorities (-2 .. +2) is usually	4111	and time, so using the defaults of five priorities (-2 .. +2) is usually
2287	fine.	4112	fine.
2288		4113
2289	If your embedding app does not need any priorities, defining these both to	4114	If your embedding application does not need any priorities, defining these
2290	C<0> will save some memory and cpu.	4115	both to C<0> will save some memory and CPU.
2291		4116
2292	=item EV_PERIODIC_ENABLE	4117	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4118	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4119	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2293		4120
2294	If undefined or defined to be C<1>, then periodic timers are supported. If	4121	If undefined or defined to be C<1> (and the platform supports it), then
2295	defined to be C<0>, then they are not. Disabling them saves a few kB of	4122	the respective watcher type is supported. If defined to be C<0>, then it
2296	code.	4123	is not. Disabling watcher types mainly saves code size.
2297		4124
2298	=item EV_IDLE_ENABLE	4125	=item EV_FEATURES
2299
2300	If undefined or defined to be C<1>, then idle watchers are supported. If
2301	defined to be C<0>, then they are not. Disabling them saves a few kB of
2302	code.
2303
2304	=item EV_EMBED_ENABLE
2305
2306	If undefined or defined to be C<1>, then embed watchers are supported. If
2307	defined to be C<0>, then they are not.
2308
2309	=item EV_STAT_ENABLE
2310
2311	If undefined or defined to be C<1>, then stat watchers are supported. If
2312	defined to be C<0>, then they are not.
2313
2314	=item EV_FORK_ENABLE
2315
2316	If undefined or defined to be C<1>, then fork watchers are supported. If
2317	defined to be C<0>, then they are not.
2318
2319	=item EV_MINIMAL
2320		4126
2321	If you need to shave off some kilobytes of code at the expense of some	4127	If you need to shave off some kilobytes of code at the expense of some
2322	speed, define this symbol to C<1>. Currently only used for gcc to override	4128	speed (but with the full API), you can define this symbol to request
2323	some inlining decisions, saves roughly 30% codesize of amd64.	4129	certain subsets of functionality. The default is to enable all features
		4130	that can be enabled on the platform.
		4131
		4132	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4133	with some broad features you want) and then selectively re-enable
		4134	additional parts you want, for example if you want everything minimal,
		4135	but multiple event loop support, async and child watchers and the poll
		4136	backend, use this:
		4137
		4138	#define EV_FEATURES 0
		4139	#define EV_MULTIPLICITY 1
		4140	#define EV_USE_POLL 1
		4141	#define EV_CHILD_ENABLE 1
		4142	#define EV_ASYNC_ENABLE 1
		4143
		4144	The actual value is a bitset, it can be a combination of the following
		4145	values:
		4146
		4147	=over 4
		4148
		4149	=item C<1> - faster/larger code
		4150
		4151	Use larger code to speed up some operations.
		4152
		4153	Currently this is used to override some inlining decisions (enlarging the
		4154	code size by roughly 30% on amd64).
		4155
		4156	When optimising for size, use of compiler flags such as C<-Os> with
		4157	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4158	assertions.
		4159
		4160	=item C<2> - faster/larger data structures
		4161
		4162	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4163	hash table sizes and so on. This will usually further increase code size
		4164	and can additionally have an effect on the size of data structures at
		4165	runtime.
		4166
		4167	=item C<4> - full API configuration
		4168
		4169	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4170	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4171
		4172	=item C<8> - full API
		4173
		4174	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4175	details on which parts of the API are still available without this
		4176	feature, and do not complain if this subset changes over time.
		4177
		4178	=item C<16> - enable all optional watcher types
		4179
		4180	Enables all optional watcher types. If you want to selectively enable
		4181	only some watcher types other than I/O and timers (e.g. prepare,
		4182	embed, async, child...) you can enable them manually by defining
		4183	C<EV_watchertype_ENABLE> to C<1> instead.
		4184
		4185	=item C<32> - enable all backends
		4186
		4187	This enables all backends - without this feature, you need to enable at
		4188	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4189
		4190	=item C<64> - enable OS-specific "helper" APIs
		4191
		4192	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4193	default.
		4194
		4195	=back
		4196
		4197	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4198	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4199	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4200	watchers, timers and monotonic clock support.
		4201
		4202	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4203	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4204	your program might be left out as well - a binary starting a timer and an
		4205	I/O watcher then might come out at only 5Kb.
		4206
		4207	=item EV_AVOID_STDIO
		4208
		4209	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4210	functions (printf, scanf, perror etc.). This will increase the code size
		4211	somewhat, but if your program doesn't otherwise depend on stdio and your
		4212	libc allows it, this avoids linking in the stdio library which is quite
		4213	big.
		4214
		4215	Note that error messages might become less precise when this option is
		4216	enabled.
		4217
		4218	=item EV_NSIG
		4219
		4220	The highest supported signal number, +1 (or, the number of
		4221	signals): Normally, libev tries to deduce the maximum number of signals
		4222	automatically, but sometimes this fails, in which case it can be
		4223	specified. Also, using a lower number than detected (C<32> should be
		4224	good for about any system in existence) can save some memory, as libev
		4225	statically allocates some 12-24 bytes per signal number.
2324		4226
2325	=item EV_PID_HASHSIZE	4227	=item EV_PID_HASHSIZE
2326		4228
2327	C<ev_child> watchers use a small hash table to distribute workload by	4229	C<ev_child> watchers use a small hash table to distribute workload by
2328	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4230	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2329	than enough. If you need to manage thousands of children you might want to	4231	usually more than enough. If you need to manage thousands of children you
2330	increase this value (I<must> be a power of two).	4232	might want to increase this value (I<must> be a power of two).
2331		4233
2332	=item EV_INOTIFY_HASHSIZE	4234	=item EV_INOTIFY_HASHSIZE
2333		4235
2334	C<ev_staz> watchers use a small hash table to distribute workload by	4236	C<ev_stat> watchers use a small hash table to distribute workload by
2335	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4237	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2336	usually more than enough. If you need to manage thousands of C<ev_stat>	4238	disabled), usually more than enough. If you need to manage thousands of
2337	watchers you might want to increase this value (I<must> be a power of	4239	C<ev_stat> watchers you might want to increase this value (I<must> be a
2338	two).	4240	power of two).
		4241
		4242	=item EV_USE_4HEAP
		4243
		4244	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4245	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4246	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4247	faster performance with many (thousands) of watchers.
		4248
		4249	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4250	will be C<0>.
		4251
		4252	=item EV_HEAP_CACHE_AT
		4253
		4254	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4255	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4256	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4257	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4258	but avoids random read accesses on heap changes. This improves performance
		4259	noticeably with many (hundreds) of watchers.
		4260
		4261	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4262	will be C<0>.
		4263
		4264	=item EV_VERIFY
		4265
		4266	Controls how much internal verification (see C<ev_verify ()>) will
		4267	be done: If set to C<0>, no internal verification code will be compiled
		4268	in. If set to C<1>, then verification code will be compiled in, but not
		4269	called. If set to C<2>, then the internal verification code will be
		4270	called once per loop, which can slow down libev. If set to C<3>, then the
		4271	verification code will be called very frequently, which will slow down
		4272	libev considerably.
		4273
		4274	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4275	will be C<0>.
2339		4276
2340	=item EV_COMMON	4277	=item EV_COMMON
2341		4278
2342	By default, all watchers have a C<void *data> member. By redefining	4279	By default, all watchers have a C<void *data> member. By redefining
2343	this macro to a something else you can include more and other types of	4280	this macro to something else you can include more and other types of
2344	members. You have to define it each time you include one of the files,	4281	members. You have to define it each time you include one of the files,
2345	though, and it must be identical each time.	4282	though, and it must be identical each time.
2346		4283
2347	For example, the perl EV module uses something like this:	4284	For example, the perl EV module uses something like this:
2348		4285
2349	#define EV_COMMON \	4286	#define EV_COMMON \
2350	SV *self; /* contains this struct */ \	4287	SV *self; /* contains this struct */ \
2351	SV *cb_sv, *fh /* note no trailing ";" */	4288	SV *cb_sv, *fh /* note no trailing ";" */
2352		4289
2353	=item EV_CB_DECLARE (type)	4290	=item EV_CB_DECLARE (type)
2354		4291
2355	=item EV_CB_INVOKE (watcher, revents)	4292	=item EV_CB_INVOKE (watcher, revents)
2356		4293
2357	=item ev_set_cb (ev, cb)	4294	=item ev_set_cb (ev, cb)
2358		4295
2359	Can be used to change the callback member declaration in each watcher,	4296	Can be used to change the callback member declaration in each watcher,
2360	and the way callbacks are invoked and set. Must expand to a struct member	4297	and the way callbacks are invoked and set. Must expand to a struct member
2361	definition and a statement, respectively. See the F<ev.v> header file for	4298	definition and a statement, respectively. See the F<ev.h> header file for
2362	their default definitions. One possible use for overriding these is to	4299	their default definitions. One possible use for overriding these is to
2363	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4300	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2364	method calls instead of plain function calls in C++.	4301	method calls instead of plain function calls in C++.
		4302
		4303	=back
		4304
		4305	=head2 EXPORTED API SYMBOLS
		4306
		4307	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4308	exported symbols, you can use the provided F<Symbol.*> files which list
		4309	all public symbols, one per line:
		4310
		4311	Symbols.ev for libev proper
		4312	Symbols.event for the libevent emulation
		4313
		4314	This can also be used to rename all public symbols to avoid clashes with
		4315	multiple versions of libev linked together (which is obviously bad in
		4316	itself, but sometimes it is inconvenient to avoid this).
		4317
		4318	A sed command like this will create wrapper C<#define>'s that you need to
		4319	include before including F<ev.h>:
		4320
		4321	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4322
		4323	This would create a file F<wrap.h> which essentially looks like this:
		4324
		4325	#define ev_backend myprefix_ev_backend
		4326	#define ev_check_start myprefix_ev_check_start
		4327	#define ev_check_stop myprefix_ev_check_stop
		4328	...
2365		4329
2366	=head2 EXAMPLES	4330	=head2 EXAMPLES
2367		4331
2368	For a real-world example of a program the includes libev	4332	For a real-world example of a program the includes libev
2369	verbatim, you can have a look at the EV perl module	4333	verbatim, you can have a look at the EV perl module
…		…
2374	file.	4338	file.
2375		4339
2376	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4340	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2377	that everybody includes and which overrides some configure choices:	4341	that everybody includes and which overrides some configure choices:
2378		4342
2379	#define EV_MINIMAL 1	4343	#define EV_FEATURES 8
2380	#define EV_USE_POLL 0	4344	#define EV_USE_SELECT 1
2381	#define EV_MULTIPLICITY 0
2382	#define EV_PERIODIC_ENABLE 0	4345	#define EV_PREPARE_ENABLE 1
		4346	#define EV_IDLE_ENABLE 1
2383	#define EV_STAT_ENABLE 0	4347	#define EV_SIGNAL_ENABLE 1
2384	#define EV_FORK_ENABLE 0	4348	#define EV_CHILD_ENABLE 1
		4349	#define EV_USE_STDEXCEPT 0
2385	#define EV_CONFIG_H <config.h>	4350	#define EV_CONFIG_H <config.h>
2386	#define EV_MINPRI 0
2387	#define EV_MAXPRI 0
2388		4351
2389	#include "ev++.h"	4352	#include "ev++.h"
2390		4353
2391	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4354	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2392		4355
2393	#include "ev_cpp.h"	4356	#include "ev_cpp.h"
2394	#include "ev.c"	4357	#include "ev.c"
2395		4358
		4359	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2396		4360
		4361	=head2 THREADS AND COROUTINES
		4362
		4363	=head3 THREADS
		4364
		4365	All libev functions are reentrant and thread-safe unless explicitly
		4366	documented otherwise, but libev implements no locking itself. This means
		4367	that you can use as many loops as you want in parallel, as long as there
		4368	are no concurrent calls into any libev function with the same loop
		4369	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4370	of course): libev guarantees that different event loops share no data
		4371	structures that need any locking.
		4372
		4373	Or to put it differently: calls with different loop parameters can be done
		4374	concurrently from multiple threads, calls with the same loop parameter
		4375	must be done serially (but can be done from different threads, as long as
		4376	only one thread ever is inside a call at any point in time, e.g. by using
		4377	a mutex per loop).
		4378
		4379	Specifically to support threads (and signal handlers), libev implements
		4380	so-called C<ev_async> watchers, which allow some limited form of
		4381	concurrency on the same event loop, namely waking it up "from the
		4382	outside".
		4383
		4384	If you want to know which design (one loop, locking, or multiple loops
		4385	without or something else still) is best for your problem, then I cannot
		4386	help you, but here is some generic advice:
		4387
		4388	=over 4
		4389
		4390	=item * most applications have a main thread: use the default libev loop
		4391	in that thread, or create a separate thread running only the default loop.
		4392
		4393	This helps integrating other libraries or software modules that use libev
		4394	themselves and don't care/know about threading.
		4395
		4396	=item * one loop per thread is usually a good model.
		4397
		4398	Doing this is almost never wrong, sometimes a better-performance model
		4399	exists, but it is always a good start.
		4400
		4401	=item * other models exist, such as the leader/follower pattern, where one
		4402	loop is handed through multiple threads in a kind of round-robin fashion.
		4403
		4404	Choosing a model is hard - look around, learn, know that usually you can do
		4405	better than you currently do :-)
		4406
		4407	=item * often you need to talk to some other thread which blocks in the
		4408	event loop.
		4409
		4410	C<ev_async> watchers can be used to wake them up from other threads safely
		4411	(or from signal contexts...).
		4412
		4413	An example use would be to communicate signals or other events that only
		4414	work in the default loop by registering the signal watcher with the
		4415	default loop and triggering an C<ev_async> watcher from the default loop
		4416	watcher callback into the event loop interested in the signal.
		4417
		4418	=back
		4419
		4420	=head4 THREAD LOCKING EXAMPLE
		4421
		4422	Here is a fictitious example of how to run an event loop in a different
		4423	thread than where callbacks are being invoked and watchers are
		4424	created/added/removed.
		4425
		4426	For a real-world example, see the C<EV::Loop::Async> perl module,
		4427	which uses exactly this technique (which is suited for many high-level
		4428	languages).
		4429
		4430	The example uses a pthread mutex to protect the loop data, a condition
		4431	variable to wait for callback invocations, an async watcher to notify the
		4432	event loop thread and an unspecified mechanism to wake up the main thread.
		4433
		4434	First, you need to associate some data with the event loop:
		4435
		4436	typedef struct {
		4437	mutex_t lock; /* global loop lock */
		4438	ev_async async_w;
		4439	thread_t tid;
		4440	cond_t invoke_cv;
		4441	} userdata;
		4442
		4443	void prepare_loop (EV_P)
		4444	{
		4445	// for simplicity, we use a static userdata struct.
		4446	static userdata u;
		4447
		4448	ev_async_init (&u->async_w, async_cb);
		4449	ev_async_start (EV_A_ &u->async_w);
		4450
		4451	pthread_mutex_init (&u->lock, 0);
		4452	pthread_cond_init (&u->invoke_cv, 0);
		4453
		4454	// now associate this with the loop
		4455	ev_set_userdata (EV_A_ u);
		4456	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4457	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4458
		4459	// then create the thread running ev_loop
		4460	pthread_create (&u->tid, 0, l_run, EV_A);
		4461	}
		4462
		4463	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4464	solely to wake up the event loop so it takes notice of any new watchers
		4465	that might have been added:
		4466
		4467	static void
		4468	async_cb (EV_P_ ev_async *w, int revents)
		4469	{
		4470	// just used for the side effects
		4471	}
		4472
		4473	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4474	protecting the loop data, respectively.
		4475
		4476	static void
		4477	l_release (EV_P)
		4478	{
		4479	userdata *u = ev_userdata (EV_A);
		4480	pthread_mutex_unlock (&u->lock);
		4481	}
		4482
		4483	static void
		4484	l_acquire (EV_P)
		4485	{
		4486	userdata *u = ev_userdata (EV_A);
		4487	pthread_mutex_lock (&u->lock);
		4488	}
		4489
		4490	The event loop thread first acquires the mutex, and then jumps straight
		4491	into C<ev_run>:
		4492
		4493	void *
		4494	l_run (void *thr_arg)
		4495	{
		4496	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4497
		4498	l_acquire (EV_A);
		4499	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4500	ev_run (EV_A_ 0);
		4501	l_release (EV_A);
		4502
		4503	return 0;
		4504	}
		4505
		4506	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4507	signal the main thread via some unspecified mechanism (signals? pipe
		4508	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4509	have been called (in a while loop because a) spurious wakeups are possible
		4510	and b) skipping inter-thread-communication when there are no pending
		4511	watchers is very beneficial):
		4512
		4513	static void
		4514	l_invoke (EV_P)
		4515	{
		4516	userdata *u = ev_userdata (EV_A);
		4517
		4518	while (ev_pending_count (EV_A))
		4519	{
		4520	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4521	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4522	}
		4523	}
		4524
		4525	Now, whenever the main thread gets told to invoke pending watchers, it
		4526	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4527	thread to continue:
		4528
		4529	static void
		4530	real_invoke_pending (EV_P)
		4531	{
		4532	userdata *u = ev_userdata (EV_A);
		4533
		4534	pthread_mutex_lock (&u->lock);
		4535	ev_invoke_pending (EV_A);
		4536	pthread_cond_signal (&u->invoke_cv);
		4537	pthread_mutex_unlock (&u->lock);
		4538	}
		4539
		4540	Whenever you want to start/stop a watcher or do other modifications to an
		4541	event loop, you will now have to lock:
		4542
		4543	ev_timer timeout_watcher;
		4544	userdata *u = ev_userdata (EV_A);
		4545
		4546	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4547
		4548	pthread_mutex_lock (&u->lock);
		4549	ev_timer_start (EV_A_ &timeout_watcher);
		4550	ev_async_send (EV_A_ &u->async_w);
		4551	pthread_mutex_unlock (&u->lock);
		4552
		4553	Note that sending the C<ev_async> watcher is required because otherwise
		4554	an event loop currently blocking in the kernel will have no knowledge
		4555	about the newly added timer. By waking up the loop it will pick up any new
		4556	watchers in the next event loop iteration.
		4557
		4558	=head3 COROUTINES
		4559
		4560	Libev is very accommodating to coroutines ("cooperative threads"):
		4561	libev fully supports nesting calls to its functions from different
		4562	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4563	different coroutines, and switch freely between both coroutines running
		4564	the loop, as long as you don't confuse yourself). The only exception is
		4565	that you must not do this from C<ev_periodic> reschedule callbacks.
		4566
		4567	Care has been taken to ensure that libev does not keep local state inside
		4568	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4569	they do not call any callbacks.
		4570
		4571	=head2 COMPILER WARNINGS
		4572
		4573	Depending on your compiler and compiler settings, you might get no or a
		4574	lot of warnings when compiling libev code. Some people are apparently
		4575	scared by this.
		4576
		4577	However, these are unavoidable for many reasons. For one, each compiler
		4578	has different warnings, and each user has different tastes regarding
		4579	warning options. "Warn-free" code therefore cannot be a goal except when
		4580	targeting a specific compiler and compiler-version.
		4581
		4582	Another reason is that some compiler warnings require elaborate
		4583	workarounds, or other changes to the code that make it less clear and less
		4584	maintainable.
		4585
		4586	And of course, some compiler warnings are just plain stupid, or simply
		4587	wrong (because they don't actually warn about the condition their message
		4588	seems to warn about). For example, certain older gcc versions had some
		4589	warnings that resulted in an extreme number of false positives. These have
		4590	been fixed, but some people still insist on making code warn-free with
		4591	such buggy versions.
		4592
		4593	While libev is written to generate as few warnings as possible,
		4594	"warn-free" code is not a goal, and it is recommended not to build libev
		4595	with any compiler warnings enabled unless you are prepared to cope with
		4596	them (e.g. by ignoring them). Remember that warnings are just that:
		4597	warnings, not errors, or proof of bugs.
		4598
		4599
		4600	=head2 VALGRIND
		4601
		4602	Valgrind has a special section here because it is a popular tool that is
		4603	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4604
		4605	If you think you found a bug (memory leak, uninitialised data access etc.)
		4606	in libev, then check twice: If valgrind reports something like:
		4607
		4608	==2274== definitely lost: 0 bytes in 0 blocks.
		4609	==2274== possibly lost: 0 bytes in 0 blocks.
		4610	==2274== still reachable: 256 bytes in 1 blocks.
		4611
		4612	Then there is no memory leak, just as memory accounted to global variables
		4613	is not a memleak - the memory is still being referenced, and didn't leak.
		4614
		4615	Similarly, under some circumstances, valgrind might report kernel bugs
		4616	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4617	although an acceptable workaround has been found here), or it might be
		4618	confused.
		4619
		4620	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4621	make it into some kind of religion.
		4622
		4623	If you are unsure about something, feel free to contact the mailing list
		4624	with the full valgrind report and an explanation on why you think this
		4625	is a bug in libev (best check the archives, too :). However, don't be
		4626	annoyed when you get a brisk "this is no bug" answer and take the chance
		4627	of learning how to interpret valgrind properly.
		4628
		4629	If you need, for some reason, empty reports from valgrind for your project
		4630	I suggest using suppression lists.
		4631
		4632
		4633	=head1 PORTABILITY NOTES
		4634
		4635	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4636
		4637	GNU/Linux is the only common platform that supports 64 bit file/large file
		4638	interfaces but I<disables> them by default.
		4639
		4640	That means that libev compiled in the default environment doesn't support
		4641	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4642
		4643	Unfortunately, many programs try to work around this GNU/Linux issue
		4644	by enabling the large file API, which makes them incompatible with the
		4645	standard libev compiled for their system.
		4646
		4647	Likewise, libev cannot enable the large file API itself as this would
		4648	suddenly make it incompatible to the default compile time environment,
		4649	i.e. all programs not using special compile switches.
		4650
		4651	=head2 OS/X AND DARWIN BUGS
		4652
		4653	The whole thing is a bug if you ask me - basically any system interface
		4654	you touch is broken, whether it is locales, poll, kqueue or even the
		4655	OpenGL drivers.
		4656
		4657	=head3 C<kqueue> is buggy
		4658
		4659	The kqueue syscall is broken in all known versions - most versions support
		4660	only sockets, many support pipes.
		4661
		4662	Libev tries to work around this by not using C<kqueue> by default on this
		4663	rotten platform, but of course you can still ask for it when creating a
		4664	loop - embedding a socket-only kqueue loop into a select-based one is
		4665	probably going to work well.
		4666
		4667	=head3 C<poll> is buggy
		4668
		4669	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4670	implementation by something calling C<kqueue> internally around the 10.5.6
		4671	release, so now C<kqueue> I<and> C<poll> are broken.
		4672
		4673	Libev tries to work around this by not using C<poll> by default on
		4674	this rotten platform, but of course you can still ask for it when creating
		4675	a loop.
		4676
		4677	=head3 C<select> is buggy
		4678
		4679	All that's left is C<select>, and of course Apple found a way to fuck this
		4680	one up as well: On OS/X, C<select> actively limits the number of file
		4681	descriptors you can pass in to 1024 - your program suddenly crashes when
		4682	you use more.
		4683
		4684	There is an undocumented "workaround" for this - defining
		4685	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4686	work on OS/X.
		4687
		4688	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4689
		4690	=head3 C<errno> reentrancy
		4691
		4692	The default compile environment on Solaris is unfortunately so
		4693	thread-unsafe that you can't even use components/libraries compiled
		4694	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4695	defined by default. A valid, if stupid, implementation choice.
		4696
		4697	If you want to use libev in threaded environments you have to make sure
		4698	it's compiled with C<_REENTRANT> defined.
		4699
		4700	=head3 Event port backend
		4701
		4702	The scalable event interface for Solaris is called "event
		4703	ports". Unfortunately, this mechanism is very buggy in all major
		4704	releases. If you run into high CPU usage, your program freezes or you get
		4705	a large number of spurious wakeups, make sure you have all the relevant
		4706	and latest kernel patches applied. No, I don't know which ones, but there
		4707	are multiple ones to apply, and afterwards, event ports actually work
		4708	great.
		4709
		4710	If you can't get it to work, you can try running the program by setting
		4711	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4712	C<select> backends.
		4713
		4714	=head2 AIX POLL BUG
		4715
		4716	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4717	this by trying to avoid the poll backend altogether (i.e. it's not even
		4718	compiled in), which normally isn't a big problem as C<select> works fine
		4719	with large bitsets on AIX, and AIX is dead anyway.
		4720
		4721	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4722
		4723	=head3 General issues
		4724
		4725	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4726	requires, and its I/O model is fundamentally incompatible with the POSIX
		4727	model. Libev still offers limited functionality on this platform in
		4728	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4729	descriptors. This only applies when using Win32 natively, not when using
		4730	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4731	as every compielr comes with a slightly differently broken/incompatible
		4732	environment.
		4733
		4734	Lifting these limitations would basically require the full
		4735	re-implementation of the I/O system. If you are into this kind of thing,
		4736	then note that glib does exactly that for you in a very portable way (note
		4737	also that glib is the slowest event library known to man).
		4738
		4739	There is no supported compilation method available on windows except
		4740	embedding it into other applications.
		4741
		4742	Sensible signal handling is officially unsupported by Microsoft - libev
		4743	tries its best, but under most conditions, signals will simply not work.
		4744
		4745	Not a libev limitation but worth mentioning: windows apparently doesn't
		4746	accept large writes: instead of resulting in a partial write, windows will
		4747	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4748	so make sure you only write small amounts into your sockets (less than a
		4749	megabyte seems safe, but this apparently depends on the amount of memory
		4750	available).
		4751
		4752	Due to the many, low, and arbitrary limits on the win32 platform and
		4753	the abysmal performance of winsockets, using a large number of sockets
		4754	is not recommended (and not reasonable). If your program needs to use
		4755	more than a hundred or so sockets, then likely it needs to use a totally
		4756	different implementation for windows, as libev offers the POSIX readiness
		4757	notification model, which cannot be implemented efficiently on windows
		4758	(due to Microsoft monopoly games).
		4759
		4760	A typical way to use libev under windows is to embed it (see the embedding
		4761	section for details) and use the following F<evwrap.h> header file instead
		4762	of F<ev.h>:
		4763
		4764	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4765	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4766
		4767	#include "ev.h"
		4768
		4769	And compile the following F<evwrap.c> file into your project (make sure
		4770	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4771
		4772	#include "evwrap.h"
		4773	#include "ev.c"
		4774
		4775	=head3 The winsocket C<select> function
		4776
		4777	The winsocket C<select> function doesn't follow POSIX in that it
		4778	requires socket I<handles> and not socket I<file descriptors> (it is
		4779	also extremely buggy). This makes select very inefficient, and also
		4780	requires a mapping from file descriptors to socket handles (the Microsoft
		4781	C runtime provides the function C<_open_osfhandle> for this). See the
		4782	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4783	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4784
		4785	The configuration for a "naked" win32 using the Microsoft runtime
		4786	libraries and raw winsocket select is:
		4787
		4788	#define EV_USE_SELECT 1
		4789	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4790
		4791	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4792	complexity in the O(n²) range when using win32.
		4793
		4794	=head3 Limited number of file descriptors
		4795
		4796	Windows has numerous arbitrary (and low) limits on things.
		4797
		4798	Early versions of winsocket's select only supported waiting for a maximum
		4799	of C<64> handles (probably owning to the fact that all windows kernels
		4800	can only wait for C<64> things at the same time internally; Microsoft
		4801	recommends spawning a chain of threads and wait for 63 handles and the
		4802	previous thread in each. Sounds great!).
		4803
		4804	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4805	to some high number (e.g. C<2048>) before compiling the winsocket select
		4806	call (which might be in libev or elsewhere, for example, perl and many
		4807	other interpreters do their own select emulation on windows).
		4808
		4809	Another limit is the number of file descriptors in the Microsoft runtime
		4810	libraries, which by default is C<64> (there must be a hidden I<64>
		4811	fetish or something like this inside Microsoft). You can increase this
		4812	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4813	(another arbitrary limit), but is broken in many versions of the Microsoft
		4814	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4815	(depending on windows version and/or the phase of the moon). To get more,
		4816	you need to wrap all I/O functions and provide your own fd management, but
		4817	the cost of calling select (O(n²)) will likely make this unworkable.
		4818
		4819	=head2 PORTABILITY REQUIREMENTS
		4820
		4821	In addition to a working ISO-C implementation and of course the
		4822	backend-specific APIs, libev relies on a few additional extensions:
		4823
		4824	=over 4
		4825
		4826	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4827	calling conventions regardless of C<ev_watcher_type *>.
		4828
		4829	Libev assumes not only that all watcher pointers have the same internal
		4830	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4831	assumes that the same (machine) code can be used to call any watcher
		4832	callback: The watcher callbacks have different type signatures, but libev
		4833	calls them using an C<ev_watcher *> internally.
		4834
		4835	=item pointer accesses must be thread-atomic
		4836
		4837	Accessing a pointer value must be atomic, it must both be readable and
		4838	writable in one piece - this is the case on all current architectures.
		4839
		4840	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4841
		4842	The type C<sig_atomic_t volatile> (or whatever is defined as
		4843	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4844	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4845	believed to be sufficiently portable.
		4846
		4847	=item C<sigprocmask> must work in a threaded environment
		4848
		4849	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4850	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4851	pthread implementations will either allow C<sigprocmask> in the "main
		4852	thread" or will block signals process-wide, both behaviours would
		4853	be compatible with libev. Interaction between C<sigprocmask> and
		4854	C<pthread_sigmask> could complicate things, however.
		4855
		4856	The most portable way to handle signals is to block signals in all threads
		4857	except the initial one, and run the default loop in the initial thread as
		4858	well.
		4859
		4860	=item C<long> must be large enough for common memory allocation sizes
		4861
		4862	To improve portability and simplify its API, libev uses C<long> internally
		4863	instead of C<size_t> when allocating its data structures. On non-POSIX
		4864	systems (Microsoft...) this might be unexpectedly low, but is still at
		4865	least 31 bits everywhere, which is enough for hundreds of millions of
		4866	watchers.
		4867
		4868	=item C<double> must hold a time value in seconds with enough accuracy
		4869
		4870	The type C<double> is used to represent timestamps. It is required to
		4871	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		4872	good enough for at least into the year 4000 with millisecond accuracy
		4873	(the design goal for libev). This requirement is overfulfilled by
		4874	implementations using IEEE 754, which is basically all existing ones. With
		4875	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
		4876
		4877	=back
		4878
		4879	If you know of other additional requirements drop me a note.
		4880
		4881
2397	=head1 COMPLEXITIES	4882	=head1 ALGORITHMIC COMPLEXITIES
2398		4883
2399	In this section the complexities of (many of) the algorithms used inside	4884	In this section the complexities of (many of) the algorithms used inside
2400	libev will be explained. For complexity discussions about backends see the	4885	libev will be documented. For complexity discussions about backends see
2401	documentation for C<ev_default_init>.	4886	the documentation for C<ev_default_init>.
2402		4887
2403	All of the following are about amortised time: If an array needs to be	4888	All of the following are about amortised time: If an array needs to be
2404	extended, libev needs to realloc and move the whole array, but this	4889	extended, libev needs to realloc and move the whole array, but this
2405	happens asymptotically never with higher number of elements, so O(1) might	4890	happens asymptotically rarer with higher number of elements, so O(1) might
2406	mean it might do a lengthy realloc operation in rare cases, but on average	4891	mean that libev does a lengthy realloc operation in rare cases, but on
2407	it is much faster and asymptotically approaches constant time.	4892	average it is much faster and asymptotically approaches constant time.
2408		4893
2409	=over 4	4894	=over 4
2410		4895
2411	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4896	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2412		4897
2413	This means that, when you have a watcher that triggers in one hour and	4898	This means that, when you have a watcher that triggers in one hour and
2414	there are 100 watchers that would trigger before that then inserting will	4899	there are 100 watchers that would trigger before that, then inserting will
2415	have to skip those 100 watchers.	4900	have to skip roughly seven (C<ld 100>) of these watchers.
2416		4901
2417	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4902	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2418		4903
2419	That means that for changing a timer costs less than removing/adding them	4904	That means that changing a timer costs less than removing/adding them,
2420	as only the relative motion in the event queue has to be paid for.	4905	as only the relative motion in the event queue has to be paid for.
2421		4906
2422	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4907	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2423		4908
2424	These just add the watcher into an array or at the head of a list.	4909	These just add the watcher into an array or at the head of a list.
		4910
2425	=item Stopping check/prepare/idle watchers: O(1)	4911	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2426		4912
2427	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4913	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2428		4914
2429	These watchers are stored in lists then need to be walked to find the	4915	These watchers are stored in lists, so they need to be walked to find the
2430	correct watcher to remove. The lists are usually short (you don't usually	4916	correct watcher to remove. The lists are usually short (you don't usually
2431	have many watchers waiting for the same fd or signal).	4917	have many watchers waiting for the same fd or signal: one is typical, two
		4918	is rare).
2432		4919
2433	=item Finding the next timer per loop iteration: O(1)	4920	=item Finding the next timer in each loop iteration: O(1)
		4921
		4922	By virtue of using a binary or 4-heap, the next timer is always found at a
		4923	fixed position in the storage array.
2434		4924
2435	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4925	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2436		4926
2437	A change means an I/O watcher gets started or stopped, which requires	4927	A change means an I/O watcher gets started or stopped, which requires
2438	libev to recalculate its status (and possibly tell the kernel).	4928	libev to recalculate its status (and possibly tell the kernel, depending
		4929	on backend and whether C<ev_io_set> was used).
2439		4930
2440	=item Activating one watcher: O(1)	4931	=item Activating one watcher (putting it into the pending state): O(1)
2441		4932
2442	=item Priority handling: O(number_of_priorities)	4933	=item Priority handling: O(number_of_priorities)
2443		4934
2444	Priorities are implemented by allocating some space for each	4935	Priorities are implemented by allocating some space for each
2445	priority. When doing priority-based operations, libev usually has to	4936	priority. When doing priority-based operations, libev usually has to
2446	linearly search all the priorities.	4937	linearly search all the priorities, but starting/stopping and activating
		4938	watchers becomes O(1) with respect to priority handling.
		4939
		4940	=item Sending an ev_async: O(1)
		4941
		4942	=item Processing ev_async_send: O(number_of_async_watchers)
		4943
		4944	=item Processing signals: O(max_signal_number)
		4945
		4946	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4947	calls in the current loop iteration. Checking for async and signal events
		4948	involves iterating over all running async watchers or all signal numbers.
2447		4949
2448	=back	4950	=back
2449		4951
2450		4952
		4953	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4954
		4955	The major version 4 introduced some incompatible changes to the API.
		4956
		4957	At the moment, the C<ev.h> header file provides compatibility definitions
		4958	for all changes, so most programs should still compile. The compatibility
		4959	layer might be removed in later versions of libev, so better update to the
		4960	new API early than late.
		4961
		4962	=over 4
		4963
		4964	=item C<EV_COMPAT3> backwards compatibility mechanism
		4965
		4966	The backward compatibility mechanism can be controlled by
		4967	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		4968	section.
		4969
		4970	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		4971
		4972	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		4973
		4974	ev_loop_destroy (EV_DEFAULT_UC);
		4975	ev_loop_fork (EV_DEFAULT);
		4976
		4977	=item function/symbol renames
		4978
		4979	A number of functions and symbols have been renamed:
		4980
		4981	ev_loop => ev_run
		4982	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		4983	EVLOOP_ONESHOT => EVRUN_ONCE
		4984
		4985	ev_unloop => ev_break
		4986	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		4987	EVUNLOOP_ONE => EVBREAK_ONE
		4988	EVUNLOOP_ALL => EVBREAK_ALL
		4989
		4990	EV_TIMEOUT => EV_TIMER
		4991
		4992	ev_loop_count => ev_iteration
		4993	ev_loop_depth => ev_depth
		4994	ev_loop_verify => ev_verify
		4995
		4996	Most functions working on C<struct ev_loop> objects don't have an
		4997	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		4998	associated constants have been renamed to not collide with the C<struct
		4999	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5000	as all other watcher types. Note that C<ev_loop_fork> is still called
		5001	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5002	typedef.
		5003
		5004	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5005
		5006	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5007	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5008	and work, but the library code will of course be larger.
		5009
		5010	=back
		5011
		5012
		5013	=head1 GLOSSARY
		5014
		5015	=over 4
		5016
		5017	=item active
		5018
		5019	A watcher is active as long as it has been started and not yet stopped.
		5020	See L<WATCHER STATES> for details.
		5021
		5022	=item application
		5023
		5024	In this document, an application is whatever is using libev.
		5025
		5026	=item backend
		5027
		5028	The part of the code dealing with the operating system interfaces.
		5029
		5030	=item callback
		5031
		5032	The address of a function that is called when some event has been
		5033	detected. Callbacks are being passed the event loop, the watcher that
		5034	received the event, and the actual event bitset.
		5035
		5036	=item callback/watcher invocation
		5037
		5038	The act of calling the callback associated with a watcher.
		5039
		5040	=item event
		5041
		5042	A change of state of some external event, such as data now being available
		5043	for reading on a file descriptor, time having passed or simply not having
		5044	any other events happening anymore.
		5045
		5046	In libev, events are represented as single bits (such as C<EV_READ> or
		5047	C<EV_TIMER>).
		5048
		5049	=item event library
		5050
		5051	A software package implementing an event model and loop.
		5052
		5053	=item event loop
		5054
		5055	An entity that handles and processes external events and converts them
		5056	into callback invocations.
		5057
		5058	=item event model
		5059
		5060	The model used to describe how an event loop handles and processes
		5061	watchers and events.
		5062
		5063	=item pending
		5064
		5065	A watcher is pending as soon as the corresponding event has been
		5066	detected. See L<WATCHER STATES> for details.
		5067
		5068	=item real time
		5069
		5070	The physical time that is observed. It is apparently strictly monotonic :)
		5071
		5072	=item wall-clock time
		5073
		5074	The time and date as shown on clocks. Unlike real time, it can actually
		5075	be wrong and jump forwards and backwards, e.g. when the you adjust your
		5076	clock.
		5077
		5078	=item watcher
		5079
		5080	A data structure that describes interest in certain events. Watchers need
		5081	to be started (attached to an event loop) before they can receive events.
		5082
		5083	=back
		5084
2451	=head1 AUTHOR	5085	=head1 AUTHOR
2452		5086
2453	Marc Lehmann <libev@schmorp.de>.	5087	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5088	Magnusson and Emanuele Giaquinta.
2454		5089

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